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Latest research in football - week 33 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Validity and reliability of speed tests used in soccer: A systematic review
Reference: PLoS One. 2019 Aug 14;14(8):e0220982. doi: 10.1371/journal.pone.0220982. eCollection 2019.
Authors: Altmann S, Ringhof S, Neumann R, Woll A, Rumpf MC
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Summary: Speed is an important prerequisite in soccer. Therefore, a large number of tests have been developed aiming to investigate several speed skills relevant to soccer. This systematic review aimed to examine the validity and reliability of speed tests used in adult soccer players. A systematic search was performed according to the PRISMA guidelines. Studies were included if they investigated speed tests in adult soccer players and reported validity (construct and criterion) or reliability (intraday and interday) data. The tests were categorized into linear-sprint, repeated-sprint, change-of-direction sprint, agility, and tests incorporating combinations of these skills. In total, 90 studies covering 167 tests were included. Linear-sprint (n = 67) and change-of-direction sprint (n = 60) were studied most often, followed by combinations of the aforementioned (n = 21) and repeated-sprint tests (n = 15). Agility tests were examined fewest (n = 4). Mainly based on construct validity studies, acceptable validity was reported for the majority of the tests in all categories, except for agility tests, where no validity study was identified. Regarding intraday and interday reliability, ICCs>0.75 and CVs<3.0% were evident for most of the tests in all categories. These results applied for total and average times. In contrast, measures representing fatigue such as percent decrement scores indicated inconsistent validity findings. Regarding reliability, ICCs were 0.11-0.49 and CVs were 16.8-51.0%. Except for agility tests, several tests for all categories with acceptable levels of validity and high levels of reliability for adult soccer players are available. Caution should be given when interpreting fatigue measures, e.g., percent decrement scores. Given the lack of accepted gold-standard tests for each category, researchers and practitioners may base their test selection on the broad database provided in this systematic review. Future research should pay attention to the criterion validity examining the relationship between test results and match parameters as well as to the development and evaluation of soccer-specific agility tests.

#2 Correlation of Fiber-Type Composition and Sprint Performance in Youth Soccer Players
Reference: J Strength Cond Res. 2019 Aug 8. doi: 10.1519/JSC.0000000000003320. [Epub ahead of print]
Authors: Metaxas T, Mandroukas A, Michailidis Y, Koutlianos N, Christoulas K, Ekblom B
Summary: The aim of this study was to examine the correlation between muscle fiber type and sprint performance in elite young soccer players of different age groups of the same team. Twenty-eight young players participated in this study (group U15, n = 8; group U13, n = 9; and group U11, n = 11). Anthropometric assessments, acceleration (10 m), and Bangsbo modified sprint test (30 m) were performed. Muscle biopsies were obtained from the vastus lateralis, and after that, fiber-type composition was determined by immunohistochemistry. No significant correlations were found between the sprint test and muscle fiber distribution for the groups U13 and U11 (p > 0.05). Also, no correlations were found between cross-sectional areas in the types of fibers with the sprint test in all groups (p > 0.05). A positive correlation was found between type I fibers and the performance in the acceleration test (10 m) (r = 0.77, p < 0.05) was found only in group U15 and a negative correlation between type IIA fibers and the performance in the acceleration test (10 m) (r = -0.89, p < 0.05). The correlations were observed only in group U15, which may indicate that the duration and the intensity of the soccer systematic training can affect the plasticity of the muscle fibers. Specific soccer training in youth is one of the factors that can affect fiber-type plasticity. The specific training programs and status of U15 are more intensive, and the exercises are oriented more to improve physical fitness.

#3 Biomarker Response to a Competitive Season in Division I Female Soccer Players
Reference: J Strength Cond Res. 2019 Aug 8. doi: 10.1519/JSC.0000000000003264. [Epub ahead of print]
Authors: Walker AJ, McFadden BA, Sanders DJ, Rabideau MM, Hofacker ML, Arent SM
Summary: The purpose of this study was to evaluate effects of training load (TL) on performance and biomarkers of health, performance, and recovery in Division I female soccer players throughout a competitive season. Participants (N = 25, Mage = 20 ± 1.1 years) were monitored before the start of preseason and every 4-weeks thereafter (T1-T5). A battery of performance tests was administered before the start of preseason (P1) and end-of-season (P2), including body composition (percent body fat [%BF], fat free mass [FFM], and fat mass), vertical jump (VJ), and V[Combining Dot Above]O2max. Blood draws were conducted at every time point (T1-T5) to assess free and total cortisol (CORTF and CORTT), prolactin (PRL), T3, IL-6, creatine kinase (CK), sex-hormone binding globulin, omega-3 (n-3FA), vitamin-D (Vit-D), iron (Fe), hematocrit (HcT), ferritin (Fer), percent saturation (%Sat), and total iron-binding capacity (TIBC). Daily exercise energy expenditure (EEE) and TL were determined. There were significant declines in V[Combining Dot Above]O2max, VJ, weight, and %BF from P1-P2 (p < 0.05) with no significant differences in FFM. Training load and EEE significantly decreased from T1-T3 (p < 0.05). Significant increases were seen in CORTT, CORTF, PRL, T3, IL-6, CK, and TIBC throughout the season (p < 0.05). Significant decreases were seen in n-3FA, Fe, Fer, %Sat, and Hct throughout the season (p < 0.05). Female athletes experience significant physiological changes following high TL and EEE associated with preseason and appear to be further exacerbated by the cumulative effects of the season. Unique insights provided by biomarkers enable athletes and coaches to be cognizant of the physiological changes that are occurring throughout the season.

#4 Where to go: Computational and visual what-if analyses in soccer
Reference: J Sports Sci. 2019 Aug 11:1-9. doi: 10.1080/02640414.2019.1652541. [Epub ahead of print]
Authors: Stein M, Seebacher D, Marcelino R, Schreck T, Grossniklaus M, Keim DA, Janetzko H
Summary: To prepare their teams for upcoming matches, analysts in professional soccer watch and manually annotate up to three matches a day. When annotating matches, domain experts try to identify and improve suboptimal movements based on intuition and professional experience. The high amount of matches needing to be analysed manually result in a tedious and time-consuming process, and results may be subjective. We propose an automatic approach for the realisation of effective region-based what-if analyses in soccer. Our system covers the automatic detection of region-based faulty movement behaviour, as well as the automatic suggestion of possible improved alternative movements. As we show, our approach effectively supports analysts and coaches investigating matches by speeding up previously time-consuming work. We enable domain experts to include their domain knowledge in the analysis process by allowing to interactively adjust suggested improved movement, as well as its implications on region control. We demonstrate the usefulness of our proposed approach via an expert study with three invited domain experts, one being head coach from the first Austrian soccer league. As our results show that experts most often agree with the suggested player movement (83%), our proposed approach enhances the analytical capabilities in soccer and supports a more efficient analysis.

#4 Relative Age Effect in the Sport Environment. Role of Physical Fitness and Cognitive Function in Youth Soccer Players
Reference: Int J Environ Res Public Health. 2019 Aug 8;16(16). pii: E2837. doi: 10.3390/ijerph16162837.
Authors: Huertas F, Ballester R, Gines HJ, Hamidi AK, Moratal C, Lupiáñez J
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Summary: The need to achieve short-term competitive outcomes in sports may influence the emergence of talent selection strategies, which could bias individuals' opportunities. The present study aimed to further explore the relative age effect (RAE), a phenomenon that strongly influences youth sport development. The RAE refers to a disproportionately high percentage in sport teams of athletes born early in the selection year. Our primary focus was to explore whether the RAE is supported by behavioral evidence in favor of better fitness-and especially cognitive-attentional functioning-of early as compared to late-born players. A cross-sectional study was conducted on 105 young athletes (u10, n = 52; 9.8 ± 0.3 years old, and u12, n = 53; 11.8 ± 0.2 years old) attending two youth elite soccer academies. Attentional functioning, anthropometrics, physical fitness, and game intelligence were compared across two Age Groups (u10 vs. u12) and four Birth Quarters (BQ1-BQ4). The RAE was statistically significant (p < 0.001), showing that about 50% of participants were born in the first quarter and 75% were born in the first half of the year. More importantly, U12 players outperformed u10 players in measures that were related to sustained attention (with faster and less variable responses; p < 0.001 and p < 0.05, respectively), and in all anthropometric measures (p < 0.001), physical-fitness capacities (p < 0.05). Crucially, neither the attentional measures, game intelligence, anthropometrics, nor physical fitness were affected by BQ (all ps > 0.1 and BF10 between 0.08 and 0.6, showing strong evidence for the null hypothesis). The present findings suggest that the early selection process that occurs during scouting in youth soccer academies offsets the age-related differences that could be anticipated in cognitive skills, anthropometrics, and physical abilities, due to growth and maturation. These birth asymmetries could lead teams to disregard later maturation athletes and athletes born later in the year inducing a larger dropout of those players with the consequent reduction in the talent pool.

#5 Similar risk of ACL graft revision for alpine skiers, football and handball players: the graft revision rate is influenced by age and graft choice
Reference: Br J Sports Med. 2019 Aug 9. pii: bjsports-2018-100020. doi: 10.1136/bjsports-2018-100020. [Epub ahead of print]
Authors: Ekeland A, Engebretsen L, Fenstad AM, Heir S
Summary: The risk of graft revision following ACL reconstruction may depend on the sport type the individuals are engaged in. The purpose of this study was to report the ACL graft revision rate in alpine skiers, football and handball players. Primary ACL reconstructions and graft revision data from 2004 to December 2016 were obtained from the Norwegian Cruciate Ligament Registry. The graft survival rates were calculated for individuals in each of the three sport types, for bone patellar tendon bone (BPTB) and hamstring tendons (HT) grafts separately, and related to age at primary operation and sex. A total of 711 grafts in 14 201 primary ACL reconstructions were revised (5.0%) after median 6 years, 3.8% in alpine skiers, 5.0% in soccer and 6.1% in handball players (p<0.001). Adjusted Cox regression showed similar ACL graft survival rates in the three groups. The HR for graft revision was 5 times higher for individuals aged ≤18 years than for those aged ≥35 years (p<0.001). The corresponding HR for graft type was 1.8 times higher for HT than for BPTB grafts (p<0.001), but 2.8 times higher for individuals aged ≤18 years (p<0.001). The 12 years survival of BPTB grafts was 96% compared with 93% for HT grafts (p <0.001). The revision rate for ACL grafts was similar among alpine skiers, football and handball players, and the results support the use of BPTB grafts in young athletes with closed growth zones in the knee.

#6 Functional Deficits in the Wrist and Finger Joints of Goalkeepers After 20 Years of Playing Recreational Football
Reference: Sportverletz Sportschaden. 2019 Aug;33(3):142-148. doi: 10.1055/a-0884-3334. Epub 2019 Aug 16.
Authors: Hilber F, Wiesenberg A, Kerschbaum M, Ernstberger A, Worlicek M, Nerlich M, Prantl L, Koch M, Krutsch V, Krutsch W
Summary: Long-term damage in the hip, knee and ankle joints of football players has been thoroughly discussed in the literature. Compared with outfield players, however, goalkeepers sustain injuries to the upper extremities five times more often. There is a lack of studies on long-term functional damage to the wrist and finger joints of football goalkeepers. The hypothesis was that repetitive micro-traumas and injuries lead to degenerative diseases in goalkeepers after 20 years of playing recreational soccer.  The personal histories, injury histories and clinical examination findings of the wrist and finger joints of 27 goalkeepers were compared with the findings obtained in a control group of outfield players. Goalkeepers were significantly more restricted in finger movement (p < 0.05) and experienced more pain and swelling (p < 0.05) as well as higher levels of instability (p < 0.05) in the wrist and finger joints than outfield players. Medical history and clinical findings indicate deficits in the hands of soccer goalkeepers and a high prevalence of joint and ligament injuries sustained to the fingers over the course of their sports activity. This necessitates specific strategies in the future to prevent injuries and long-term posttraumatic deficits.

#7 Editorial: Fatigue and Recovery in Football
Reference: Sports (Basel). 2019 Aug 13;7(8). pii: E192. doi: 10.3390/sports7080192.
Authors: Clarke N, Noon M
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#8 Play-by-Play Network Analysis in Football
Reference: Front Psychol. 2019 Jul 25;10:1738. doi: 10.3389/fpsyg.2019.01738. eCollection 2019.
Authors: Korte F, Link D, Groll J, Lames M
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Summary: This study identifies dominant and intermediary players in football by applying a play-by-play social network analysis (SNA) on 70 professional matches from the 1. and 2. German Bundesliga during the 2017/2018 season. SNA provides a quantification of the complex interaction patterns between players in team sports. So far, the individual contributions and roles of players in football have only been studied at match-level considering the overall passing of a team. In order to consider the real structure of football, a play-by-play network analysis is needed that reflects actual interplay. Moreover, a distinction between plays of certain characteristics is important to qualify different interaction phases. As it is often impossible to calculate well known network metrics such as betweenness on play-level, new adequate metrics are required. Therefore, flow betweenness is introduced as a new playmaker indicator on play-level and computed alongside flow centrality. The data on passing and the position of players was provided by the Deutsche Fußball Liga (DFL) and gathered through a semi-automatic multiple-camera tracking system. Central defenders are identified as dominant and intermediary players, however, mostly in unsuccessful plays. Offensive midfielders are most involved and defensive midfielders are the main intermediary players in successful plays. Forward are frequently involved in successful plays but show negligible playmaker status. Play-by-play network analysis facilitates a better understanding of the role of players in football interaction.

#9 A comparative study of core musculature endurance and strength between soccer players with and without lower extremity sprain and strain injury
Reference: Int J Sports Phys Ther. 2019 Jul;14(4):525-536.
Authors: Abdallah AA, Mohamed NA, Hegazy MA
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Summary: Lower extremity sprain and strain injury constitutes a large percentage of lower extremity injuries experienced by soccer players. Yet, very limited data exists on the association between core strength and endurance and this injury. The purpose of this study was to compare core muscle endurance and hip muscle strength between soccer players who experienced non-contact lower extremity sprain and/or strain injury during their season and those who did not. Additionally, the frequency of injury was correlated with core muscle endurance and hip strength, and endurance was used for predicting the risk for injury. Twenty-one (35.59%) athletes experienced non-contact lower extremity sprain and/or strain injury during the season. Fifty-nine male athletes (mean age 20.92 ± 4.08 years, mass 77.34 ± 12.02 kg and height 1.79 ± 0.06m) were tested. Prior to the start of the season, prone-bridge, side-bridge, trunk flexion and horizontal back extension hold times were recorded for endurance assessment and peak hip abductor and external rotator isokinetic torques for strength assessment. Prone-bridge and side-bridge hold times were significantly longer in the non-injured players when compared with the times of the injured players (p=0.043 & 0.008 for the prone-bridge and side-bridge, respectively). There were significant negative correlations between the frequency of injury and both prone-bridge (r=-0.324, p=0.007) and side-bridge (r=-0.385, p=0.003) hold times. Logistic regression analysis revealed that side-bridge hold time was a significant predictor of injury (OR=0.956, CI=0.925-0.989). Soccer players with non-contact lower extremity sprain and/or strain have less core endurance than non-injured players. Reduced core endurance is associated with increased incidence of injury. Improving side-bridge hold time, specifically, may reduce the risk for injury.

#10 High Risk of Further ACL Injury in a 10-Year Follow-up Study of ACL-Reconstructed Soccer Players in the Swedish National Knee Ligament Registry
Reference: Arthroscopy. 2019 Aug 19. pii: S0749-8063(19)30500-6. doi: 10.1016/j.arthro.2019.05.052. [Epub ahead of print]
Authors: Sandon A, Engström B, Forssblad M
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Summary: To follow up on soccer players 10 years after a primary anterior cruciate ligament (ACL) reconstruction to find out how many players returned to play soccer, what influenced their decision, and if there are any differences in additional ACL injuries (graft failure and/or contralateral ACL injury) between those who returned to play and those who did not. The study cohort consists of 1661 soccer players from the Swedish National Knee Ligament Registry. A questionnaire was sent to each player regarding their return to play and additional knee injuries that may have occurred 10 years after their primary ACL. The results are based on the 684 responders. Data such as age, sex, surgical procedural data, associated injuries, patient-reported outcome measures, and additional knee surgeries were collected from the registry. In this study, 51% returned to play soccer. For those who did not return to play, the primary reason was knee related (65.4% of the cases). The most common knee-related reasons for not returning were pain and/or instability (50%; n = 109), followed by fear of reinjury (32%; n = 69). Players who return to soccer have a significantly higher risk of additional ACL injury. Of the players who returned to play soccer, 28.7% (odds ratio [OR] 2.3, P < .001) had additional ACL injury, 9.7% (OR 2.9, P < .001) had a graft failure and 20.6% (OR 2.1, P < .001) had a contralateral ACL injury. Players that return to soccer have a significantly higher risk of sustaining further ACL injury. Only half of the soccer players return to play after ACL reconstruction, and in two-thirds of those who did not return, the reason was knee related. The high risk of sustaining additional knee injury is of serious concern to the player's future knee health and should be considered when deciding on a return to play.

#11 Phase Angle is Moderately Associated with Short-term Maximal Intensity Efforts in Soccer Players
Reference: Int J Sports Med. 2019 Aug 22. doi: 10.1055/a-0969-2003. [Epub ahead of print]
Authors: Nabuco HCG, Silva AM, Sardinha LB, Rodrigues FB, Tomeleri CM, Ravagnani FCP, Cyrino ES, Ravagnani CFC
Summary: This study examined the relationship between PhA and short-term maximal intensity efforts in soccer players, and was conducted in 99 male soccer players, ages 19-36 years. Bioelectrical impedance was used to assess body fat, fat free mass (FFM) and PhA (phase angle). Running Anaerobic Sprint Test (RAST) was used to evaluate physical performance. Food consumption was assessed through the 24-hour dietary recall method. Pearson correlation and multiple regressions were used for statistical analysis. Phase angle exhibited a positive relationship with maximum power (β=0.66; P<0.001), even after adjustment for the co-variables FFM and body fat (β=0.52; P=0.02). Phase angle was inversely related with fatigue index (β=- 0.61; P=0.04), even after adjusting for FFM (β=- 0.70; P=0.020). Our results indicated that independently of FFM and body fat, PhA was inversely associated with fatigue index and positively related with maximum power, revealing the PhA appeared as a valid predictor of fatigue.





Latest research in football - week 32 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Effects of Neuromuscular Training on Agility Performance in Elite Soccer Players
Reference: Front Physiol. 2019 Jul 23;10:947. doi: 10.3389/fphys.2019.00947. eCollection 2019.
Authors: Zouhal H, Abderrahman AB, Dupont G, Truptin P, Le Bris R, Le Postec E, Sghaeir Z, Brughelli M, Granacher U, Bideau B
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Summary: Agility in general and change-of-direction speed (CoD) in particular represent important performance determinants in elite soccer. The objectives of this study were to determine the effects of a 6-week neuromuscular training program on agility performance, and to determine differences in movement times between the slower and faster turning directions in elite soccer players. Twenty male elite soccer players from the Stade Rennais Football Club (Ligue 1, France) participated in this study. The players were randomly assigned to a neuromuscular training group (NTG, n = 10) or an active control (CG, n = 10) according to their playing position. NTG participated in a 6-week, twice per week neuromuscular training program that included CoD, plyometric and dynamic stability exercises. Neuromuscular training replaced the regular warm-up program. Each training session lasted 30 min. CG continued their regular training program. Training volume was similar between groups. Before and after the intervention, the two groups performed a reactive agility test that included 180° left and right body rotations followed by a 5-m linear sprint. The weak side was defined as the left/right turning direction that produced slower overall movement times (MT). Reaction time (RT) was assessed and defined as the time from the first appearance of a visual stimulus until the athlete's first movement. MT corresponded to the time from the first movement until the athlete reached the arrival gate (5 m distance). No significant between-group baseline differences were observed for RT or MT. Significant group x time interactions were found for MT (p = 0.012, effect size = 0.332, small) for the slower and faster directions (p = 0.011, effect size = 0.627, moderate). Significant pre-to post improvements in MT were observed for NTG but not CG (p = 0.011, effect size = 0.877, moderate). For NTG, post hoc analyses revealed significant MT improvements for the slower (p = 0.012, effect size = 0.897, moderate) and faster directions (p = 0.017, effect size = 0.968, moderate). Our results illustrate that 6 weeks of neuromuscular training with two sessions per week included in the warm-up program, significantly enhanced agility performance in elite soccer players. Moreover, improvements were found on both sides during body rotations. Thus, practitioners are advised to focus their training programs on both turning directions.

#2 A Meta-Analysis of Meta-Analyses of the Effectiveness of FIFA Injury Prevention Programmes in Soccer
Reference: Scand J Med Sci Sports. 2019 Aug 8. doi: 10.1111/sms.13535. [Epub ahead of print]
Authors: Al Attar WSA, Alshehri MA
Summary: FIFA has a Medical and Research Centre (F-MARC) which has designed a comprehensive programme targeting muscle strength, kinaesthetic awareness, and neuromuscular control during static and dynamic movements to decrease injury risk for soccer players. A number of meta-analyses now exist on how effective FIFA's programmes to prevent and reduce injury actually are, with various degrees of injury reduction reported. This research aimed to carry out a systematic review and to meta analyse the existing meta-analyses so that a conclusion can be drawn on how effective the injury programmes are. Relevant studies were identified by searching five databases for the period January 1990 till 1 July 2018. Results of each meta-analysis were combined together using risk ratios (RR) in a summary meta-analysis. QUOROM checklist and AMSTAR 2 assessment were used to assess the quality of reporting and methodology in the meta-analyses. Four meta-analyses met the inclusion criteria covering fifteen primary studies. All four meta-analyses scored quite highly on QUOROM, but two were rated by AMSTAR 2 as moderate quality and two were found to be of critically low quality. An overall risk reduction of 34% [RR= 0.66 (0.60 - 0.73)] for all injuries and a reduction of 29% [RR= 0.71 (0.63 - 0.81)] for injuries to the lower limbs were revealed by this meta-analysis of meta-analyses. Combining every previous meta-analysis into a single source in this paper produced decisive evidence that the risk of injuries while playing soccer is reduced as a result of FIFA's injury prevention programmes.

#3 A comparison of a GPS device and a multi-camera video technology during official soccer matches: Agreement between systems
Reference: PLoS One. 2019 Aug 8;14(8):e0220729. doi: 10.1371/journal.pone.0220729. eCollection 2019.
Authors: Pons E, García-Calvo T, Resta R, Blanco H, López Del Campo R, Díaz García J, Pulido JJ
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Summary: The aim of this study was to compare the agreement of the movement demands data during a soccer match (total distance, distance per minute, average speed, maximum speed and distance covered in different speed sectors) between an optical tracking system (Mediacoach System) and a GPS device (Wimu Pro). Participants were twenty-six male professional soccer players (age: 21.65 ± 2.03 years; height: 180.00 ± 7.47 cm; weight: 73.81 ± 5.65 kg) from FC Barcelona B, of whom were recorded a total of 759 measurements during 38 official matches in the Spanish second division. The Mediacoach System and the Wimu Pro were compared using the standardized mean bias, standard error of estimate, intraclass correlation coefficients (ICC), coefficient of variation (%), and the regression equation to estimate data for each variable. In terms of agreement between systems, the magnitude of the ICC was almost perfect (> 0.90-1.00) for all variables analyzed. The coefficient of the variations between devices was close to zero (< 5%) for total distance, distance per minute, average speed, maximum speed, and walking and jogging, and between 9% and 15% for running, intense running, and sprinting at low and at high intensities. It can be observed that, compared to Wimu Pro the Mediacoach System slightly overestimated all the variables analyzed except for average speed, maximum speed, and walking variables. In conclusion, both systems can be used, and the information they provide in the analyzed variables can be interchanged, with the benefits implied for practitioners and researchers.

#4 Genomic analysis reveals association of specific SNPs with athletic performance and susceptibility to injuries in professional soccer players
Reference: J Cell Physiol. 2019 Aug 7. doi: 10.1002/jcp.29118. [Epub ahead of print]
Authors: La Montagna R, Canonico R, Alfano L, Bucci E, Boffo S, Staiano L, Fulco B, D'Andrea E, De Nicola A, Maiorano P, D'Angelo C, Chirico A, De Nicola A, Giordano A
Summary: The development of specific and individualized training programs is a possible way to improve athletic performance and minimize injuries in professional athletes. The information regarding the sport's physical demands and the athletes' physical profile have been, so far, considered as exhaustive for the design of effective training programs. However, it is currently emerging that the genetic profile has to be also taken into consideration. By merging medical and genetic data, it is thus possible to identify the athlete's specific attitude to respond to training, diet, and physical stress. In this context, we performed a study in which 30 professional soccer players, subjected to standard sport medical evaluation and practices, were also screened for genetic polymorphism in five key genes (ACTN3, COL5A1, MCT1, VEGF, and HFE). This genetic analysis represents the central point of a multidisciplinary method that can be adopted by elite soccer teams to obtain an improvement in athletic performance and a concomitant reduction of injuries by tailoring training and nutritional programs. The genetic fingerprinting of single athletes led to the identification of two performance-enhancing polymorphisms (ACTN3 18705C>T, VEGF-634C>G) significantly enriched. Moreover, we derived a genetic model based on the gene set analyzed, which was tentatively used to reduce athletes' predisposition to injuries, by dictating a personalized nutrition and training program. The potential usefulness of this approach is concordant with data showing that this team has been classified as the healthiest and least injured team in Europe while covering the highest distance/match with the highest number of high-intensity actions/match.

#5 Ten-Year Epidemiology of Ankle Injuries in Men's and Women's Collegiate Soccer Players
Reference: J Athl Train. 2019 Aug 7. doi: 10.4085/1062-6050-144-18. [Epub ahead of print]
Authors: Gulbrandsen M, Hartigan DE, Patel K, Makovicka J, Tummala S, Chhabra A
Summary: Data from the National Collegiate Athletic Association (NCAA) Injury Surveillance Program (ISP) has indicated that ankle injuries are the most common injuries among NCAA soccer players. The objective was to review 10 years of NCAA-ISP data for soccer players' ankle injuries to understand how the time period (2004-2005 through 2008-2009 versus 2009-2010 through 2013-2014), anatomical structure injured, and sex of the athlete affected the injury rate, mechanism, and prognoses. The NCAA-ISP was queried for men's and women's soccer ankle data from 2004 to 2014. Ankle injury rates were calculated on the basis of injuries per 1000 athlete-exposures. Rate ratios (RRs) were used to compare injury rates. Injury proportion ratios (IPRs) were used to compare injury characteristics. When compared with the 2004-2005 through 2008-2009 seasons, the 2009-2010 through 2013-2014 seasons showed a similar rate of injuries (RR = 0.94, 95% confidence interval [CI] = 0.85, 1.04) but fewer days missed (P < .001) and fewer recurrent injuries (IPR = 0.55, 95% CI = 0.41, 0.74). The 4 most common ankle injuries, which accounted for 95% of ankle injuries, were lateral ligament complex tears (65.67%), tibiofibular ligament (high ankle) sprains (10.3%), contusions (10.1%), and medial (deltoid) ligament tears (9.77%). Of these injuries, high ankle sprains were most likely to cause athletes to miss ≥30+ days (IPR = 1.9, 95% CI = 1.24, 2.90). Men and women had similar injury rates (RR = 1.02, 95% CI = 0.94, 1.11). Men had more contact injuries (IPR = 1.28, 95% CI = 1.16, 1.41) and contusion injuries (IPR = 1.34, CI = 1.03, 1.73) but fewer noncontact injuries (IPR = 0.86, 95% CI = 0.78, 0.95) and lateral ligamentous complex injuries (IPR = 0.92, 95% CI = 0.86, 0.98). Although the rate of ankle injuries did not change between the 2004-2005 through 2008-2009 seasons and the 2009-2010 through 2013-2014 seasons, the prognoses improved. Among the 4 most common ankle injuries, high ankle sprains resulted in the worst prognosis. Overall, male and female NCAA soccer players injured their ankles at similar rates; however, men were more likely to sustain contact injuries.

#6 Power training in elite young soccer players: Effects of using loads above or below the optimum power zone
Reference: J Sports Sci. 2019 Aug 7:1-7. doi: 10.1080/02640414.2019.1651614. [Epub ahead of print]
Authors: Loturco I, Pereira LA, Reis VP, Bishop C, Zanetti V, Alcaraz PE, Freitas TT, Mcguigan MR
Summary: This study aimed to examine the effects of two jump squat (JS) training programs involving different loading ranges in under-20 soccer players during a preseason period. Twenty-three elite young soccer players performed sprint speed (at 5-, 10-, and 20-m), change-of-direction (COD) speed, JS peak-power (PP), and countermovement jump (CMJ) tests pre and post four weeks of training. Athletes were pair-matched in two groups according to their optimum power loads (OPL) as follows: lower than OPL (LOPL; athletes who trained at a load 20% lower than the OPL) and higher than OPL (HOPL; athletes who trained at a load 20% higher than the OPL). Magnitude-based inferences were used to compare pre- and post-training measures. Meaningful increases in the PP JS were observed for both groups. Likely and possible improvements were observed in the 5- and 10-m sprint velocity in the LOPL group. Meanwhile, possible and likely improvements were observed in the CMJ, 5- and 10-m sprint velocity, and COD speed in the HOPL group. Overall, both training schemes induced positive changes in athletic performance. Soccer coaches and sport scientists can implement the JS OPL-based training schemes presented here, either separately or combined, to improve the physical performance of youth soccer players

#7 Coaches' Emotional Intelligence and Reactive Behaviors in Soccer Matches: Mediating Effects of Coach Efficacy Beliefs
Reference: Front Psychol. 2019 Jul 10;10:1629. doi: 10.3389/fpsyg.2019.01629. eCollection 2019.
Authors: Teques P, Duarte D, Viana J
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Summary: In the last 10 years, emotional intelligence (EI) has become a current issue of research in psychology, and there are indicators to consider that EI should be analyzed to help the coach to behave effectively during competitions. According to Boardley's (2018) revised model of coaching efficacy, coaches' EI is predictive of their efficacy beliefs, which, in turn, is predictive of coaching behavior. However, little is known about the mediating effects of coaching efficacy dimensions on the relationships between coach's EI and reactive behaviors in competitive settings. Thus, the purpose of this study is to examine mediating effects of coaching efficacy dimensions on the relationship between EI and coaches' reactive behaviors during a game using a multimethod approach. Participants were 258 coaches of youth football players aged 9 to 17 years old. Observations in situ using Coaching Behavior Assessment System (CBAS) were carried on 258 football games during two seasons. At the end of each game, coaches completed the Wong and Law Emotional Intelligence Scale (WLEIS) and the Coaching Efficacy Scale (CES). Structural equation modeling (SEM) analyses revealed that motivation efficacy and character building mediated the relationship between regulation of emotion and positive and negative coaches' reactions during game. Specifically, motivation efficacy mediated the association between regulation of emotion and positive coaches' reactions, and the relationship between regulation of emotion and negative coaches' reactions were mediated by motivation efficacy and character building. In addition, coaching level moderated the relationships between EI, self-efficacy and coaches' reactive behaviors. Findings of the present study showed that coaching efficacy dimensions (i.e., motivation efficacy and character building) that have the capacity to influence their confidence in ability to affect the psychological mood and positive attitude of athletes, transfer the effects of EI (i.e., regulation of emotion) on coaches' verbal reactions during a youth soccer game. Specifically, a coach who feels competent to regulate their own emotions would perceive high beliefs of efficacy to motivate and to build character of their athletes, and this insight has an impact on their positive verbal reactions in response to athletes' performances.

#8 Ratings of perceived recovery and exertion in elite youth soccer players: Interchangeability of 10-point and 100-point scales
Reference: Physiol Behav. 2019 Aug 1;210:112641. doi: 10.1016/j.physbeh.2019.112641. [Epub ahead of print]
Authors: Clemente FM, Rabbani A, Araújo JP
Summary: The purpose of this study was to examine the interchangeability of a new perceived recovery status scale (PRS) of 100 points through a comparison to the original 10-point version. This study also aimed to test the interchangeability of CR100 scale (Borg's rate of perceived exertion scale) in comparison to the CR10. Twenty-five male elite youth soccer players (age: 18.0 ± 0.5 years old; body mass: 70.1 ± 6.7 kg; height: 177.8 ± 6.5 cm; experience: 11.7 ± 1.2 years) from the same team competing in the first national under-19 competition participated in this study. During two consecutive weeks, the players completed PRS (both 10- and 100-points) and CR10 and CR100 scales. Nearly perfect relationships were observed between 0-to-10 and 0-to-100 scales, both for recovery status (r = 0.96, confidence interval [0.95;0.97]) and ratings of perceived exertion (RPE) (r = 0.97 [0.97;0.98]). Moreover, almost 95% of individuals showed nearly-perfect-to-perfect associations between 0-to-10 and 0-to100 in terms of RPE and recovery scales. Both a PRS of 100 points and CR100 can be used interchangeably with a PRS of 10 points and CR10, respectively.

#9 Inter-rater Reliability in Assessing Exercise Fidelity for the Injury Prevention Exercise Programme Knee Control in Youth Football Players
Reference: Sports Med Open. 2019 Aug 7;5(1):35. doi: 10.1186/s40798-019-0209-9.
Authors: Ljunggren G, Perera NKP, Hägglund M
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Summary: To receive maximum benefits from injury prevention exercise programmes (IPEP) such as Knee Control, players need to perform the exercises as prescribed. But, exercise fidelity in IPEPs is seldom evaluated. We developed a checklist to assess exercise fidelity in the Knee Control IPEP, and the primary aim was to evaluate its inter-rater reliability. The secondary aim was to study Knee Control exercise fidelity in youth football players and compare sex differences. This observational study included 11 teams with male and female youth players (11-18 years). On average, the players trained with the Knee Control IPEP for 7 weeks (SD 1.4, range 6-10 weeks). After the training period, two physiotherapists attended a team training session to observe players executing exercises and individually assessed their performance of these exercises as correct or incorrect based on standardised criteria set in the fidelity checklist. Agreement between observers was assessed using Cohen's kappa coefficient. The observers agreed on 144 out of 160 (90%) observations (Kappa = 0.80, substantial agreement). Both observers agreed on correct exercise performance for 69 out of 144 observations (exercise fidelity 48%). Exercise fidelity was higher in females (56%) than males (40%), but the difference was not statistically significant (p = 0.18). The Knee Control exercise fidelity checklist had high inter-rater reliability with substantial agreement. The exercise fidelity was low, which could hamper the preventive effects of an IPEP. Understanding the reasons for low exercise fidelity is important and more effort should focus on increasing exercise fidelity alongside the implementation of IPEPs.

#10 Effects of Linear Versus Changes of Direction Repeated Sprints on Intermittent High Intensity Running Performance in High-level Junior Football Players over an Entire Season: A Randomized Trial
Reference: Sports (Basel). 2019 Aug 6;7(8). pii: E189. doi: 10.3390/sports7080189.
Authors: Sagelv EH, Selnæs I, Pedersen S, Pettersen SA, Randers MB, Welde B
Summary: Changes of direction (COD) repeated sprints (RSs) might have greater relevance to football than linear RSs. We aimed to compare the effects of linear and COD RSs on intermittent high intensity running (HIR) over an entire season. In total, 19 high-level male football players (16-19 years) randomly performed linear RSs or COD RSs twice a week during their competitive season over 22 weeks. Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2), and 10- and 20-m sprint was assessed pre-, mid- (11 weeks), and post-intervention (22 weeks). Maximal oxygen uptake (VO2max) was assessed pre- and post-intervention. There was no interaction effect (time x group) in Yo-Yo IR2 (p = 0.36, pη2 = 0.06) or sprint tests (10 m: p = 0.55, pη2 = 0.04, 20 m: p = 0.28 pη2 = 0.08), and no change differences between groups. There was a main effect of time for Yo-Yo IR2 (p = 0.002, pη2 = 0.31) but not in sprints or VO2max. Linear and COD RS exercise twice a week over 22 weeks equally improves intermittent HIR performance but does not improve sprint time or aerobic power in high-level junior football players. However, due to our two-armed intervention, we cannot exclude possible effects from other exercise components in the players' exercise program.

#11 Rescheduling Part 2 of the 11+ reduces injury burden and increases compliance in semi-professional football
Reference: Scand J Med Sci Sports. 2019 Aug 3. doi: 10.1111/sms.13532. [Epub ahead of print]
Authors: Whalan M, Lovell R, Steele JR, Sampson JA
Summary: Although the 11+ programme has been shown to reduce injuries in sub-elite football, programme compliance is typically poor, suggesting that strategies to optimize delivery are necessary. This study investigated the effect of rescheduling Part 2 of the three-part 11+ programme on programme effectiveness. Twenty-five semi-professional football clubs were randomly allocated to either a Standard-11+ (n=398 players) or P2post group (n=408 players). Both groups performed the 11+ programme at least twice a week throughout the 2017 football season. The Standard-11+ group performed the entire 11+ programme before training activities commenced, whereas the P2post group performed Parts 1 and 3 of the 11+ programme before and Part 2 after training. Injuries, exposure and individual player 11+ dose were monitored throughout the season. No significant between group difference in injury incidence rate (P2post vs Standard-11+ = 11.8 vs 12.3 injuries/1000 h) was observed. Severe time loss injuries >28 days (33 vs 58 injuries; p<0.002) and total days lost to injury (4303 vs 5815 days; p<0.001) were lower in the P2post group. A higher 11+ programme dose was observed in the P2post (29.1 doses; 95% CI 27.9-30.1) versus Standard-11+ group (18.9 doses; 95% CI 17.6 -20.2; p<0.001). In semi-professional football, rescheduling Part 2 of the 11+ programme to the end of training maintained the effectiveness of the original 11+ programme to reduce injury incidence. Importantly, rescheduling Part 2 improved player compliance and reduced the number of severe injuries and total injury burden thereby enhancing effectiveness of the 11+ programm

#12 Performance Activities and Match Outcomes of Professional Soccer Teams during the 2016/2017 Serie A Season
Reference: Medicina (Kaunas). 2019 Aug 12;55(8). pii: E469. doi: 10.3390/medicina55080469.
Authors: Longo UG, Sofi F, Candela V, Dinu M, Cimmino M, Massaroni C, Schena E, Denaro V
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Summary: Soccer is the most popular sport in the world. To describe athletic performance, match statistics, and their relationships with the probability of achieving the first positions of the final ranking in the Italian football league "Serie A", season 2016/2017. Analyses comprised all the matches played by the 20 teams of the "Serie A" championship during the season 2016-2017. Indicators of athletic performance (total distance covered in km, jogging, running and sprint activities, and average speed) and match statistics (total shots, shots on target, goal attempts, assists, turnovers, and steals) were obtained from the Italian football league. Analyses of performance activities according to the final ranking showed no significant differences for the total distance covered and speed, while a statistically significant difference (p < 0.05) among teams was observed for jogging, running and sprint activities. In regard to match statistics, all the parameters investigated were significantly different among the teams. By grouping teams into four subgroups (those who qualified for the Champions League, those who qualified for the Europe League, those who ranked intermediate positions and those who relegated from the "Serie A" league), the percentage of jogging, running and sprint activities, as well as match statistics were significantly different among groups, with a downward trend for total shots, shots on target, goal attempts, assists, and turnovers. The logistic regression analysis revealed that sprint activities as well as total shots, shots on target, goal attempts, and assists higher than the 3rd tertile of their distribution were associated with a higher probability of reaching the first three positions of the final ranking. An increased probability to achieve the first positions of the final ranking in the Italian football league "Serie A" seemed to be mainly related to sprint activity, goal attempts, total shots, shots on target and assists.





Latest research in football - week 31 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Field Methods to Estimate Fat-free Mass in International Soccer Players
Reference: Int J Sports Med. 2019 Jul 31. doi: 10.1055/a-0969-8591. [Epub ahead of print]
Authors: Nuñez FJ, Munguia-Izquierdo D, Petri C, Suarez-Arrones L
Summary: Based on the high financial and logistical costs associated with the assessment of body composition with dual-energy X-ray absorptiometry (DXA), this study determined which field method has the best correlation with DXA data, and developed an equation to estimate fat-free mass (FFM) using the field anthropometric data in international soccer players. A total of 17 international soccer players participated in this study. DXA values provided a criterion measure of FFM. Correlation coefficients, biases, limits of agreement, and differences were used as validity measures, and regression analyses were used to develop the prediction equation. All field methods used to obtain FFM data showed positive correlations (r from 0.90-0.96) with DXA. Only the equation developed by Deurenberg et al. [6] showed no differences from DXA with a low bias. The main strength of this study was providing a valid and accurate equation to estimate FFM specifically in international soccer players.

#2 Prospective Evaluation of Injuries occurred during the Brazilian Soccer Championship in 2016
Reference: Rev Bras Ortop (Sao Paulo). 2019 May;54(3):329-334. doi: 10.1055/s-0039-1692429. Epub 2019 Jun 27.
Authors: Netto DC, Arliani GG, Thiele ES, Cat MNL, Cohen M, Pagura JR
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Summary: The purpose was to identify the incidence, the prevalence, the characteristics, and the possible risk factors for injuries occurring during the matches of the Brazilian Soccer Championship. A prospective study was carried out to collect data on the injuries that occurred during the 2016 Brazilian Soccer Championship. Lesions were recorded by the physician responsible for each team through an online software. Among the 864 athletes included in the study, 231 (26.7%) of the players presented some injury during the tournament. In total, 312 injuries were recorded during the Brazilian Soccer Championship, with an average of 0.82 injuries per game. The incidence of injuries was 24.9 injuries per 1,000 match hours. Midfielders and forwards presented, respectively, an injury risk 3.6 and 2.4 times higher than goalkeepers. The prevalence and incidence of lesions were, respectively, 26.7% and 24.9 injuries per 1,000 match hours. The most frequently affected body segment was the lower limbs (76.3%), and the athletes acting in midfield and forward positions were the most affected. Moreover, the greater prevalence of injuries occurred in the first part of the championship.

#3 Imaging Assessment of the Pubis in Soccer Players
Reference: Rev Bras Ortop (Sao Paulo). 2019 Apr;54(2):118-127. doi: 10.1016/j.rbo.2017.12.012. Epub 2019 May 10.
Authors: Todeschini K, Daruge P, Bordalo-Rodrigues M, Pedrinelli A, Busetto AM
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Summary: The purpose was to compare the accuracy of ultrasound (US) with that of magnetic resonance imaging (MRI) in the detection of aponeurosis lesions of the rectus abdominis/adductor longus muscles, to study the characteristics of the athletes and imaging findings associated with pubalgia, and to demonstrate the importance of each method in evaluating this condition. The present study was conducted from 2011 to 2016 with 39 professional soccer players: 15 with pubalgia and 24 without pubalgia. Age, field position, body mass index (BMI), weekly training load, career length, and history of thigh/knee injury and lower back pain were recorded. The following tests were performed: radiographs (anteroposterior view of the pelvis in standing and flamingo positions) to evaluate hip impingement, sacroiliac joint, and pubic symphysis instability; US to analyze the common aponeurosis of the rectus abdominis/adductor longus muscles and inguinal hernias; and MRI for pubic bone degenerative alterations and edema, and lesions in the adductor and rectus abdominis muscles and their aponeurosis. There was an association between pubalgia, high BMI ( p  = 0.032) and muscle alterations ( p  < 0.001). Two patients with pubalgia had inguinal hernias and one patient with pubalgia and two controls had sports hernias. Pubic degenerative changes were frequent in both groups. Aponeurosis lesions were more frequent in patients with pain. The US detection had 44.4% sensitivity and 100% specificity. The evaluation of athletic pubalgia should be performed with radiography, US, and MRI. High BMI, muscle injuries, geodes, and osteophytes are findings associated with pubalgia; US has low sensitivity to detect injuries of the common aponeurosis of the rectus abdominis/adductor longus muscles.

#4 Eighty-two per cent of male professional football (soccer) players return to play at the previous level two seasons after Achilles tendon rupture treated with surgical repair
Reference: Br J Sports Med. 2019 Jul 30. pii: bjsports-2019-100556. doi: 10.1136/bjsports-2019-100556. [Epub ahead of print]
Authors: Grassi A, Rossi G, D'Hooghe P, Aujla R, Mosca M, Samuelsson K, Zaffagnini S
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Summary: The purpose was to evaluate the time to return to playing following acute Achilles tendon rupture (ATR) and surgical repair in professional male football (soccer) players. Professional male football (soccer) players who sustained an ATR and underwent surgical repair were identified through internet-based injury reports from January 2008 to August 2018. Only League 1 and 2 players with injuries who had at least 1 year of follow-up from the search date were included. Injury history and time to return to play were retrieved from the public platform For athletes who competed for at least two seasons after returning to play, re-ruptures and number of matches played were reported. 118 athletes (mean age 27.2±7.2 years) were included. 113 (96%) returned to unrestricted practice after a mean of 199±53 days, with faster recovery in players involved in national teams. Return to competition was after a mean of 274±114 days. In the 76 athletes with at least two seasons of follow-up, 14 (18%) did not compete at the pre-injury level during the two seasons following the index injury. Six players (8%) sustained a re-rupture within the first two seasons after return to play; four re-ruptures were in footballers who returned to play <180 days after injury. Age >30 years and re-ruptures had higher odds ratios of not returning to the same level of play. 96% of professional male football players who underwent surgery to repair an ATR returned to unrestricted practice and then competition after an average time of 7 and 9 months, respectively. However, 18% did not return to the same level of play within the two seasons following their return, with a higher risk in those experiencing a re-rupture.

#5 Test-Retest Reliability of Skill Tests in the F-MARC Battery for Youth Soccer Players
Reference: Percept Mot Skills. 2019 Jul 30:31512519866038. doi: 10.1177/0031512519866038. [Epub ahead of print]
Authors: Padrón-Cabo A, Rey E, Pérez-Ferreirós A, Kalén A
Summary: This study aimed to evaluate the test-retest reliability of soccer skill tests belonging to the F-MARC test battery. To avoid bias during talent identification and development, coaches and scouts should be using reliable tests for assessing soccer-specific skills in young male players. Fifty-two U-14 outfield male soccer players performed F-MARC soccer skill tests on two occasions, separated by 7 days. After familiarization, we administered two trial sessions of five skill tests: speed dribbling, juggling, shooting, passing, and heading. We assessed absolute reliability by expressing the standard error of measurement as a coefficient of variation with 95% limits of agreement, and we assessed relative reliability with the intraclass correlation coefficient and with Pearson's correlation (r). The results demonstrated satisfactory relative and absolute reliability for speed dribbling, right foot juggling, short passing, shooting a dead ball right, shooting from a pass, heading in front, and heading right. However, reliability values for left foot juggling, chest-head-foot juggling, head-left-foot-right foot-chest-head juggling, long pass, and shooting a dead ball left tests were not strong enough to suggest their usage by coaches in training or sport scientists in research.

#6 Range of Motion and Injury Occurrence in Elite Spanish Soccer Academies. Not Only a Hamstring Shortening-Related Problem
Reference: J Strength Cond Res. 2019 Jul 29. doi: 10.1519/JSC.0000000000003302. [Epub ahead of print]
Authors: Sanz A, Pablos C, Ballester R, Sánchez-Alarcos JV, Huertas F
Summary: Age-related development of range of motion (ROM) during an active hip flexion (active straight leg raise) and its relationship with hamstring injury occurrence were examined in 1657 young male soccer players (9-18 years of age). Age-related differences in ROM showed a significant decrease from U9 to U11 (p = 0.001), from U11 to U13 (p < 0.005), and from U9 to U13 (p < 0.001), whereas ROM increased from U13 to U15 and from U13 to U18 (both p's < 0.001). Interestingly, younger and older players reached similar ROM values (U9-U18, p = 0.87). Higher ROM was found in dominant than nondominant leg in all age groups (all ps < 0.001). No differences related to playing position were found on ROM (all ps > 0.478). During the follow-up period (11 months) 97 hamstring injuries were reported showing higher rates in the older age groups (p < 0.001) and outfield players (p < 0.001). Remarkably, no differences in ROM average were found between injured players and noninjured players (p = 0.152). Our results suggest that ROM during hip flexion does not only depend on the hamstrings shortening but also on the variables related to joint stability, motor control, and hip flexor muscle weakness. Sport scientists in youth sport soccer academies should develop age-specific screening and action plans to develop strength, motor control, and flexibility to optimize ROM and reduce injuries from the grassroots stages.

#7 Comparing the magnitude and direction of asymmetry during the squat, countermovement and drop jump tests in elite youth female soccer players
Reference: J Sports Sci. 2019 Jul 29:1-8. doi: 10.1080/02640414.2019.1649525. [Epub ahead of print]
Authors: Bishop C, Pereira LA, Reis VP, Read P, Turner AN, Loturco I
Summary: The aims of the present study were to provide an in-depth comparison of inter-limb asymmetry and determine how consistently asymmetry favours the same limb during different vertical jump tests. Eighteen elite female under-17 soccer players conducted unilateral squat jumps (SJ), countermovement jumps (CMJ) and drop jumps (DJ) on a portable force platform, with jump height, peak force, concentric impulse and peak power as common metrics across tests. For the magnitude of asymmetry, concentric impulse was significantly greater during the SJ test compared to CMJ (p = 0.019) and DJ (p = 0.003). No other significant differences in magnitude were present. For the direction of asymmetry, Kappa coefficients revealed fair to substantial levels of agreement between the SJ and CMJ (Kappa = 0.35 to 0.61) tests, but only slight to fair levels of agreement between the SJ and DJ (Kappa = -0.26 to 0.18) and CMJ and DJ (Kappa = -0.13 to 0.26) tests. These results highlight that the mean asymmetry value may be a poor indicator of true variability of between-limb differences in healthy athletes. The direction of asymmetry may provide a useful monitoring tool for practitioners in healthy athletes, when no obvious between-limb deficit exists.

#8 Relative age and maturation selection biases in academy football
Reference: J Sports Sci. 2019 Jul 31:1-9. doi: 10.1080/02640414.2019.1649524. [Epub ahead of print]
Authors: Hill M, Scott S, Malina RM, McGee D, Cumming SP
Summary: This study examined the simultaneous effects of relative age and biological maturity status upon player selection in an English professional soccer academy. A total of 202 players from the U9 to U16 age groups, over an eight-year period (total of 566 observations), had their relative age (birth quarter) and biological maturity (categorised as late, on-time or early maturing based upon the Khamis-Roche method of percentage of predicted adult height at time of observation) recorded. Players born in the first birth quarter of the year (54.8%) were over-represented across all age groups. A selection bias towards players advanced in maturity status for chronological age emerged in U12 players and increased with age; 0% of players in the U15 and U16 age group were categorised as late maturing. A clear maturity selection bias for early maturing players was, however, only apparent when the least conservative criterion for estimating maturity status was applied (53.8% early and 1.9% late maturing in the U16 age group). Professional football academies need to recognise relative age and maturation as independent constructs that exist and operate independently. Thus, separate strategies should perhaps be designed to address the respective selection biases, to better identify, retain and develop players.

#9 High return to competition rate following ACL injury - A 10-year media-based epidemiological injury study in men`s professional football
Reference: Eur J Sport Sci. 2019 Jul 29:1-15. doi: 10.1080/17461391.2019.1648557. [Epub ahead of print]
Authors: Werner K, Clemens M, Volker K, Peter A, Tobias T, Karen AF, Tim M
Summary: Ruptures of the anterior cruciate ligament (ACL) typically occur in professional football and epidemiological data about longitudinal injury development is needed. The purpose was to This practice-driven investigation of media-derived ACL data provides information about professional football over 10 years. Injury registration was based on "kicker" sports magazine information that have been recorded over one decade in a standardized manner. Only ACL ruptures in the first German football league were included when they could be verified by a second reliable source. Fifty-seven primary ACL ruptures were verified in the first German football league during the seasons 2007/08 to 2016/17. Among them, 6 re-injuries were found. Mean age at the time of injury was 24.8 years (SD 3.8). 31% (n = 20) of ACL ruptures occurred at the beginning of the season in August or September (p = 0.02). Mean time of RTC after primary ACL ruptures was 226.7 days (SD: 93.5) and 245.6 days (SD: 45.4) after re-injury. Although 62 (98%) players returned to football after injury and only one player immediately finished his career, 54.9% of the affected individuals played 3 years after the ACL rupture in the same league. ACL ruptures lead to longer absence than 7 months from football but does not give reason for immediate career-ending. The decrease in playing level after 3 years illustrate the serious consequences of ACL ruptures in football. Media-based injury reports may provide interesting information.

#10 Gender-dependent evaluation of football as medicine for prediabetes
Reference: Eur J Appl Physiol. 2019 Sep;119(9):2011-2024. doi: 10.1007/s00421-019-04188-5. Epub 2019 Jul 26
Authors: Mohr M, Skoradal MB, Andersen TR, Krustrup P
Summary: Training intensity and health effects of football were investigated gender specifically in individuals with prediabetes. Participants with prediabetes (age 60 ± 6 years) were randomised into a football and dietary advice group (FD-men n = 13 and FD-women n = 14) or a dietary advice only group (D-men n = 12 and D-women n = 11). FD performed football training (twice/week for 16 weeks), while both groups received dietary advice. Body composition, bone variables, blood pressure, blood lipid profile and peak oxygen uptake (VO2peak) were determined pre- and post-intervention. Mean heart rate during football training was 79 ± 2 and 80 ± 3% HRmax for FD-men and FD-women, respectively, with peak heart rate values of 96 ± 1 and 97 ± 2% HRmax, with no gender differences. VO2peak increased more (P < 0.05) in FD-men and FD-women than in D-men and D-women. However, relative delta change in VO2peak was 21 ± 14% in FD-women, which was greater (P < 0.05) than in FD-men (11 ± 12%). Reduction in SBP and DBP, respectively, was similar in FD-men (- 10.8 ± 13.0 and - 7.3 ± 11.8 mmHg) and FD-women (- 11.3 ± 11.0 and - 7.1 ± 6.2 mmHg), with within-gender differences for men. Total plasma cholesterol and LDL cholesterol decreased (P < 0.05) by - 0.7 ± 1.1 and - 0.5 ± 0.9 mmol L-1, respectively, in FD-women and - 0.2 ± 0.4 and - 0.2 ± 0.3 mmol L-1 in FD-men, with no significant gender differences (P = 0.08). Body fat content was lowered (P < 0.05) by 3 and 4%-points in FD-men and FD-women, respectively. Gender-mixed football training combined with dietary advice causes broad-spectrum health effects for men and women with prediabetes, with minor gender-specific differences. Thus, the intensity and training-induced effects of football training are also high for elderly women with prediabetes.

#11 Characteristics of plantar pressure distribution in elite male soccer players with or without history of proximal fifth metatarsal fracture: a case-control study
Reference: J Phys Ther Sci. 2019 Jul;31(7):530-535. doi: 10.1589/jpts.31.530. Epub 2019 Jul 2.
Authors: Kuzuyama M, Perrier J, Kusaki Y, Sato K, Yamaura I, Tsuchiya A
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Summary: Studies have demonstrated a relationship between plantar pressure distribution and proximal fifth metatarsal fracture. We aimed to investigate the plantar pressure patterns of soccer players with or without a history of proximal fifth metatarsal fracture. Fifty-one male soccer players (31 professional, 20 high-school) participated in this study (mean age, weight, and height ± SD: 21.1 ± 4.7 years, 68.8 ± 5.8 kg, and 175.4 ± 5.9 cm, respectively). Seven of them had a history of proximal fifth metatarsal fracture before this study (the fracture group) and 44 had no history of fracture (the control group). A Win-Pod (Medicapteurs) platform was used to measure foot pressure forces. The center of plantar pressure was measured during double and single-limb stances for 25 seconds. Fifth metatarsal pressure and the center of plantar pressure angle was calculated from the walking footprint. The calculated data were compared between the fracture group and the control group. [Results] Comparisons between the fracture and control groups in terms of morphology and the center of plantar pressure length showed no significant differences. However, the fifth metatarsal pressure and the center of plantar pressure angle were significantly higher in the fracture group. [Conclusion] The results of this study revealed that players with excessive loading in the lateral areas of the foot while walking have a risk of developing proximal fifth metatarsal fracture.

#12 Effects of Bio-Banding upon Physical and Technical Performance during Soccer Competition: A Preliminary Analysis
Reference: Sports (Basel). 2019 Aug 14;7(8). pii: E193. doi: 10.3390/sports7080193.
Authors: Abbott W, Williams S, Brickley G, Smeeton NJ
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Summary: Bio-banded competition has been introduced to address the variation in physical maturity within soccer. To date, no research has investigated the effect of bio-banded competition relative to chronological competition. The current study investigated the effect of bio-banding upon physical and technical performance in elite youth soccer athletes. Twenty-five male soccer athletes (11-15 years) from an English Premier League soccer academy participated in bio-banded and chronological competition, with physical and technical performance data collected for each athlete. Athletes were between 85-90% of predicted adult stature, and sub-divided into early, on-time and late developers. For early developers, significantly more short passes, significantly less dribbles and a higher rating of perceived exertion (RPE) were evident during bio-banded competition compared to chronological competition (p < 0.05). Significantly more short passes and dribbles, and significantly fewer long passes were seen for on-time developers during bio-banded competition (p < 0.05). For late developers, significantly more tackles, and significantly fewer long passes were evident during bio-banded competition (p < 0.05). No significant differences in physical performance were identified between competition formats. Results demonstrated that bio-banded competition changed the technical demand placed upon athletes compared to chronological competition, without reducing the physical demands. Bio-banded competition can be prescribed to athletes of differing maturation groups dependent upon their specific developmental needs.





Latest research in football - week 30 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Are acceleration and cardiovascular capacities related to perceived load in professional soccer players?
Reference: Res Sports Med. 2019 Jul 21:1-15. doi: 10.1080/15438627.2019.1644642. [Epub ahead of print]
Authors: Azcárate U, Los Arcos A, Jiménez-Reyes P, Yanci J
Summary: This study aims at assessing physical fitness performance and its relationship with the differential ratings of perceived exertion of training load (dRPE TL) and match load (dRPE ML) in a Spanish professional soccer team at the beginning of several in-season periods: 1-4 weeks, 5-8 weeks and 1-8 weeks. Performance and mechanical variables over the acceleration phase, as well as cardiovascular performance variables were evaluated in 20 male professional soccer players of a team competing in the Spanish Second Division League. Moreover, dRPE TL and dRPE ML were quantified. The dRPE TL showed negative and large associations between both maximal aerobic speed (MAS) and maximal oxygen consumption (VO2max) (from r = -0.53; ± 0.06 to r = -0.53; ± 0.05 95% CL, p = 0.035 to 0.036) and RPEres TL values throughout the 5-8 and 1-8 week periods. Furthermore, dRPE ML positive and large associations were found between players initial MAS or VO2max (from r = 0.50; ± 0.17 to r = 0.56; ± 0.11 95% CL, p = 0.026 to 0.049) and RPEmus ML in 1-4 and 1-8 week periods. The current study suggests that a better cardiovascular capacity could be connected with a lower RPEres TL and higher RPEmus ML.

#2 Injury burden differs considerably between single teams from German professional male football (soccer): surveillance of three consecutive seasons
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Jul 19. doi: 10.1007/s00167-019-05623-y. [Epub ahead of print]
Authors: Klein C, Luig P, Henke T, Platen P
Summary: The purpose of this study was to analyse unique injury data of the national statutory accident insurance for the two highest divisions in German male football (Bundesliga and 2. Bundesliga) over three consecutive seasons regarding inter-season, inter-division and inter-team differences. This was a prospective observational open cohort study over the seasons 2014/2015, 2015/2016 and 2016/2017. Every acute injury that was registered by clubs or physicians with the German statutory accident insurance for professional athletes (VBG) as part of occupational accident reporting and that led to time loss and/or to medical attention, was included. The complete sample consisted of 1449 players. The study covered 2663.5 player seasons with an observed match exposure of 69,058 h and a projected training exposure of 529,136 h. In total, 7493 injuries were included. The overall incidence rate was 12.5 (± 0.28) injuries per 1000 exposure hours, which translated into match and training rates of 47.0 (± 1.62) and 8.02 (± 0.24) injuries per 1000 h, respectively. Findings of 2.7 injuries per player and season underline the need of effective preventive approaches. Higher injury incidences in seasons after international tournaments suggest an increasing risk of injury with increasing number of matches. However, large differences between the single teams from the same division indicate that a reduction in the injury burden is generally possible. Continuing the presented injury surveillance might be helpful to identify injury trends in the future and to evaluate the effectiveness of preventive approaches under real-life conditions.

#3 An Approach to the Fatigue in Young Soccer Players Resulting from Sided Games
Reference: Sports (Basel). 2019 Jul 18;7(7). pii: E174. doi: 10.3390/sports7070174.
Authors: Castillo D, Yanci J, Sánchez-Díaz S, Raya-González J
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Summary: It is crucial to understand the fatigue associated with sided games (SGs) of soccer in the training context, in order to establish the appropriate intervals between training sessions. Thus, the aim of this study was to investigate the effects of different SGs on internal load, measured by the session rating of perceived exertion (sRPE), and on sprint performance. Ten outfield players (age: 14.5 ± 0.5 years, height: 169 ± 6 cm, body mass: 59.7 ± 6.4 kg) belonging to U15 age category participated in this study. The participants played four SG formats with modifications in the pitch size and in the bout duration, but with the same total duration for the SGs (SG1, SG2, SG3, and SG4). All the players performed a 10 and a 30 m sprint test before and after the SGs. The internal load was measured by the sRPE. The results showed no significant differences (p > 0.05) in the sRPE registered by the soccer players for the different SGs, but worse sprint performances over the 10 m (p < 0.05; ES: 0.74-1.38, large) and 30 m (p < 0.05; ES: 0.70-2.10, moderate to large) distances after completion of the SGs, except the 10 m sprint after SG2 and SG3 (p > 0.05; ES: 0.43-0.55, moderate). In addition, no correlation (p > 0.05) was reported between the sprint performances for the 10 and 30 m distances and the sRPE registered during the SGs. These results could be useful for technical staff wishing to design the playing area and bout duration of their training tasks effectively.

#4 A Genome-Wide Association Study of Sprint Performance in Elite Youth Football Players
Reference: J Strength Cond Res. 2019 Jul 22. doi: 10.1519/JSC.0000000000003259. [Epub ahead of print]
Authors: Pickering C, Suraci B, Semenova EA, Boulygina EA, Kostryukova ES, Kulemin NA, Borisov OV, Khabibova SA, Larin AK, Pavlenko AV, Lyubaeva EV, Popov DV, Lysenko EA, `Vepkhvadze TF, Lednev EM, Leońska-Duniec A, Pająk B, Chycki J, Moska W, Lulińska-Kuklik E, Dornowski M, Maszczyk A, Bradley B, Kana-Ah A, Cięszczyk P, Generozov EV, Ahmetov II
Summary: Sprint speed is an important component of football performance, with teams often placing a high value on sprint and acceleration ability. The aim of this study was to undertake the first genome-wide association study to identify genetic variants associated with sprint test performance in elite youth football players and to further validate the obtained results in additional studies. Using micro-array data (600 K-1.14 M single nucleotide polymorphisms [SNPs]) of 1,206 subjects, we identified 12 SNPs with suggestive significance after passing replication criteria. The polymorphism rs55743914 located in the PTPRK gene was found as the most significant for 5-m sprint test (p = 7.7 × 10). Seven of the discovered SNPs were also associated with sprint test performance in a cohort of 126 Polish women, and 4 were associated with power athlete status in a cohort of 399 elite Russian athletes. Six SNPs were associated with muscle fiber type in a cohort of 96 Russian subjects. We also examined genotype distributions and possible associations for 16 SNPs previously linked with sprint performance. Four SNPs (AGT rs699, HSD17B14 rs7247312, IGF2 rs680, and IL6 rs1800795) were associated with sprint test performance in this cohort. In addition, the G alleles of 2 SNPs in ADRB2 (rs1042713 & rs1042714) were significantly over-represented in these players compared with British and European controls. These results suggest that there is a genetic influence on sprint test performance in footballers, and identifies some of the genetic variants that help explain this influence.

#5 Kinematic Profile of Visually Impaired Football Players During Specific Sports Actions
Reference: Sci Rep. 2019 Jul 23;9(1):10660. doi: 10.1038/s41598-019-47162-z.
Authors: Finocchietti S, Gori M, Souza Oliveira A
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Summary: Blind football, or Football 5-a-side, is a very popular sport amongst visually impaired individuals (VI) worldwide. However, little is known regarding the movement patterns these players perform in sports actions. Therefore, the aim of this study was to determine whether visually impaired players present changes in their movement patterns in specific functional tasks compared with sighted amateur football players. Six VI and eight sighted amateur football players performed two functional tasks: (1) 5 m shuttle test and (2) 60 s ball passing against a wall. The sighted players performed the tests while fully sighted (SIG) as well as blindfolded (BFO). During both tasks, full-body kinematics was recorded using an inertial motion capture system. The maximal center-of-mass speed and turning center-of-mass speed were computed during the 5 m shuttle test. Foot resultant speed, bilateral arm speed, and trunk flexion were measured during the 60 s ball passing test. The results showed that VI players achieved lower maximal and turning speed compared to SIG players (p < 0.05), but BFO were slower than the VI players. The VI players presented similar foot contact speed during passes when compared to SIG, but they presented greater arm movement speed (p < 0.05) compared to both SIG and BFO. In addition, VI players presented greater trunk flexion angles while passing when compared to both SIG and BFO (p < 0.05). It is concluded that VI players present slower speed while running and turning, and they adopt specific adaptations from arm movements and trunk flexion to perform passes.

#6 Interpersonal Dynamics in 2-vs-1 Contexts of Football: The Effects of Field Location and Player Roles
Reference: Front Psychol. 2019 Jul 3;10:1407. doi: 10.3389/fpsyg.2019.01407. eCollection 2019.
Authors: Laakso T, Davids K, Liukkonen J, Travassos B
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Summary: This study analyzed the spatial-temporal interactions that sustained 2-vs-1 contexts in football at different field locations near the goal. Fifteen male players (under 15 years, age 13.2 ± 1.03 years, years of practice 4.2 ± 1.10 years), 5 defenders, 7 midfielders, and 3 attackers, participated in the study. Each participant performed a game to simulate a 2-vs-1 sub-phase as a ball carrier, second attacker, and defender at three different field locations, resulting in a total number of 142 trials. The movements of participants in each trial were recorded and digitized with TACTO software. Values of interpersonal distance between the ball carrier and defender and interpersonal angles between players and between the goal target, defender, and ball carrier were calculated. The results revealed a general main effect of field location. Generally, the middle zone revealed the lowest values of interpersonal distance and angle between players and the right zone and the highest values of interpersonal distance between players and interpersonal angle between players and the goal. Related with participants' roles, defenders revealed subtle differences as attackers on interpersonal distances and relative angles compared with midfielders and attackers. Findings supported that field location is a key constraint of players' performance and that players' role constraint performance effectiveness in football.

#7 Characteristics of potential concussive events in three elite football tournaments
Reference: Inj Prev. 2019 Jul 22. pii: injuryprev-2019-043242. doi: 10.1136/injuryprev-2019-043242. [Epub ahead of print]
Authors: Armstrong N, Rotundo M, Aubrey J, Tarzi C, Cusimano MD
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Summary: Identify patterns in the nature and characteristics of potential concussive events (PCEs) in football. This study analysed the incidence and characteristics of PCEs that occurred during the 2014 and 2018 Fédération Internationale de Football Association World Cups, and the 2016 UEFA Euro Cup. PCEs were defined as direct head collision incidents resulting in the athlete being unable to immediately resume play for at least 5 sec following impact. A total of 218 incidents were identified in 179 matches (1.22 per match, 36.91 per 1000 hours of exposure). The most common mechanism of PCE was elbow-to-head (28.7%, n=68). The frontal region was the most frequently affected location of impact with 22.8% (n=54). Our study defined the identification, prevalence and nature of PCEs in professional international soccer tournaments. Our findings indicate the different contexts and mechanisms of head contact and contact to different regions of the head can be associated with varying signs of concussion. The results highlight targets for future injury prevention strategies.

#8 Neuromuscular changes in football players with previous hamstring injury
Reference: Clin Biomech (Bristol, Avon). 2019 Jul 13;69:115-119. doi: 10.1016/j.clinbiomech.2019.07.010. [Epub ahead of print]
Authors: Areia C, Barreira P, Montanha T, Oliveira J, Ribeiro F
Summary: Impact of prior injury on myoelectrical activity of the hamstrings during isokinetic eccentric contractions has received increased literature attention. This cross-sectional study aimed to assess neuromuscular adaptations, namely proprioception, core stability, muscle strength, extensibility and activity, in football players with history of hamstring strain injury. Seventeen players, 10 with history of hamstring injury and 7 without prior injury underwent isokinetic strength testing, eccentric knee extension at 30 and 120°/s. Myoelectrical activity of bicep femoris and medial hamstrings was calculated at 30, 50 and 100 ms after onset of contraction. Functional tests included core stability, muscle strength, and knee proprioception tests. Differences were observed between Hamstring Group injured and uninjured and Control Group dominant limbs in the bicep femoris activity at almost all times in both velocities (p < 0.05). Joint position sense error was higher in the injured side compared to uninjured and control dominant limb; additionally there were also differences between injured and uninjured limb in the triple-hop test. Previously injured side showed deficits in bicep femoris myoelectrical activity after onset of contraction during eccentric testing, proprioceptive deficits, and functional asymmetry.

#9 Effects of Different Training Interventions on the Recovery of Physical and Neuromuscular Performance After a Soccer Match
Reference: J Strength Cond Res. 2019 Jul 31. doi: 10.1519/JSC.0000000000003269. [Epub ahead of print]
Authors: Trecroci A, Porcelli S, Perri E, Pedrali M, Rasica L, Alberti G, Longo S, Iaia FM
Summary:  In competitive soccer, players are frequently required to play in periods with congested fixtures in which they have limited time to recover between matches (3-4 days). Thus, finding the most appropriate intervention strategy to limit players' neuromuscular (muscle function of lower limbs) and physical (running performance) impairments in this short period becomes crucial. The aim of the study was to examine how muscle function of knee extensors and flexors and sprint performance recovered +72 hours after match in relation to different field-based training sessions. Using a crossover design, 9 subelite players (age 17.6 ± 0.5 years, height 1.77 ± 0.02 m, body mass 66.4 ± 5.8 kg) underwent a soccer-specific training (SST) session or an active recovery regime (AR) on the second day after a match. Immediately after (0 hour) and +72 hours after match, 30-m sprint and repeated sprint ability (RSA) were assessed. Maximum isometric voluntary force (MVF) of knee extensors and flexors was determined at 120° and 90° (with 180° being full extension), respectively. SST and AR promoted similar effects on the recovery kinetics of sprint, RSA, and MVF of knee extensors (p > 0.05). However, compared with SST, AR promoted a significantly better restoration of MVF of knee flexors (p < 0.05) after +72 hours from the match. Because muscle fatigue has been related with increased hamstring injury risk, a training based on AR can be a valid intervention to promote the recovery of muscle force production of knee flexors and reduce hamstring injury risk in the postmatch period.

#10 Anterior Cruciate Ligament Repair in a Professional Soccer Player Using Internal Brace Ligament Augmentation: A Case Report Focusing on Rehabilitation
Reference: Surg Technol Int. 2019 Aug 1;35. pii: sti35/1162. [Epub ahead of print]
Authors: McIntyre V, Hopper GP, Mackay GM
Summary: Anterior cruciate ligament (ACL) reconstruction with hamstring or patellar tendon autograft has been the gold standard for the operative treatment of an ACL rupture for many years. Repair with Internal Brace Ligament Augmentation (IBLA) is a new technique that uses ultra-high strength tape (FiberTape, Arthrex, Naples, FL, USA) to bridge the ligament. This technique reinforces the ligament as a secondary stabiliser, encouraging natural healing of the ligament by protecting it during the healing phase and supporting early mobilisation. This retrospective case report focuses on the rehabilitation of a 21-year-old male professional soccer player who ruptured his ACL in a contact injury whilst playing a competitive game. He underwent ACL repair with IBLA two weeks following injury. The six-month rehabilitation programme consisted of gradual progressions for mobility, proprioception, strengthening, cardiovascular maintenance and running in conjunction with physiotherapy to assist with the maintenance of soft tissue quality, pain management and control of oedema. After completing the rehabilitation programme, the patient returned to unrestricted sporting activity within six months. At 18-month follow-up, the patient continues to play at the same competitive level without any issues. This rehabilitation programme after ACL repair with IBLA successfully enabled a professional soccer player to return to his pre-injury playing level.

#11 Posture correctness of young female soccer players
Reference: Sci Rep. 2019 Aug 1;9(1):11179. doi: 10.1038/s41598-019-47619-1.
Authors: Żuk B, Sutkowski M, Paśko S, Grudniewski T
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Summary: The objectives of the study were to evaluate the correctness of the body posture of female soccer players in the frontal plane from the back based on selected body points in two static positions (habitual and actively corrected) using a non-contact optical measurement method. Forty-two young women (aged 16-20) playing soccer in a sports club in Poland were examined and compared with controls. The spatial coordinates (x, y, z) of the selected body points were determined. Four points (OcL, OcR, PvL and PvR) were extracted and used to calculate vectors [Formula: see text] and [Formula: see text] for analysis. The results show that median of the pelvic line angle was positive (PvR was lower than PvL) in both groups. For the habitual posture, the absolute value of the difference between the 25th and 75th percentiles in the pelvic line was almost three times greater among the soccer players than the controls (ratio between soccer players and controls: 2.93). Static postural imbalances in female soccer players require diagnosis of the sacroiliac joints with analysis of lumbar-pelvic system support and inhibition in the context of myofascial connection integration. Exercises can be implemented to stabilize the lumbar-pelvis complex as prophylaxis for spinal overload during the training cycle.

#12 Comparison of Complex Versus Contrast Training on Steroid Hormones and Sports Performance in Male Soccer Players
Reference: J Chiropr Med. 2019 Jun;18(2):131-138. doi: 10.1016/j.jcm.2018.12.001. Epub 2019 Jun 26.
Authors: Ali K, Verma S, Ahmad I, Singla D, Saleem M, Hussain ME
Summary: The purpose of this study was to compare the effects of a complex versus a contrast training regimen with steroid hormones and the performance of soccer players. Thirty-six professional male soccer players were randomly divided into 3 equal groups: complex training (n = 12; body mass index [BMI], 22.95 ± 1.76 kg/m2), contrast training (n = 12; BMI, 22.05 ± 2.03 kg/m2), and control (n = 12; BMI, 22.27 ± 1.44 kg/m2). Players from the complex and contrast groups were trained for 6 weeks (3 d/wk). The complex group performed 4 different exercises, each composed of strength (80% of 1 repetition maximum [RM]) and power components alternately. The contrast group performed the same strengthening exercises alternately at different intensities (40% and 80% of 1 RM). All players were tested for free testosterone, cortisol, vertical jump, 20-m sprint, and agility T-test at the baseline and after 6 weeks of training. A 3 × 2 mixed analysis of variance revealed a significant difference in time effect (P ≤ .05), whereas a nonsignificant difference was found in the group effect for all outcome variables. group × time interaction was significant in all the variables (P < .01) except cortisol (P = .28). Complex training showed greater improvement in physical performance and free testosterone concentration compared with contrast training, whereas both types of training decreased cortisol concentration in a similar fashion.





Latest research in football - week 29 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 A new approach to study the relative age effect with the use of additive logistic regression models: A case of study of FIFA football tournaments (1908-2012)
Reference: PLoS One. 2019 Jul 16;14(7):e0219757. doi: 10.1371/journal.pone.0219757. eCollection 2019.
Authors: Saavedra-García M, Matabuena M, Montero-Seoane A, Fernández-Romero JJ
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Summary: The relative age effect plays an important role in the pursuit of excellence, providing advantage to athletes born at the beginning of the year or near the cut-off date. This phenomenon has been observed in areas such as sports, education or business. Traditionally, the chi-square test has been used to analyze whether there are statistically significant differences in the distribution of births in each of the four quarters of the year. However, this approach is limited, focusing only on the analysis of the response variable, without taking into account the effect of a set of predictive variables. In this paper a new approach is proposed to study the relative age effect with the use of a logistic regression additive model. The new method has been evaluated with a sample of 21,639 players involved in football tournaments organized by the Fédération Internationale de Football Association (FIFA) between 1908 and 2012. New conclusions have been established that the relative age effect exists regarding player age and the year of the competition in male FIFA competitions and its effect is dynamic and complex.

#2 Effect of a New Rule Limiting Full Contact Practice on the Incidence of Sport-Related Concussion in High School Football Players
Reference: Am J Sports Med. 2019 Jul 15:363546519860120. doi: 10.1177/0363546519860120. [Epub ahead of print]
Authors: Pfaller AY, Brooks MA, Hetzel S, McGuine TA
Summary: Sport-related concussion (SRC) has been associated with cognitive impairment, depression, and chronic traumatic encephalopathy. American football is the most popular sport among males in the United States and has one of the highest concussion rates among high school sports. Measured head impacts and concussions are approximately 4 times more common in contact practices compared with noncontact practices. The Wisconsin Interscholastic Athletic Association passed new rules defining and limiting contact during practice before the 2014 football season. The purpose was to determine if the SRC rate is lower after a rule change that limited the amount and duration of full-contact activities during high school football practice sessions. A total of 2081 high school football athletes enrolled and participated in the study in 2012-2013 (before the rule change), and 945 players participated in the study in 2014 (after the rule change). Players self-reported previous concussion and demographic information. Athletic trainers recorded athlete exposures (AEs), concussion incidence, and days lost for each SRC. Chi-square tests were used to compare the incidence of SRC in prerule 2012-2013 seasons with the incidence in the postrule 2014 season. Wilcoxon rank sum tests were used to determine differences in days lost because of SRC. A total of 67 players (7.1%) sustained 70 SRCs in 2014. The overall rate of SRC per 1000 AEs was 1.28 in 2014 as compared with 1.58 in 2012-2013 (P = .139). The rate of SRC sustained overall in practice was significantly lower (P = .003) after the rule change in 2014 (15 SRCs, 0.33 per 1000 AEs) as compared with prerule 2012-2013 (86 SRCs, 0.76 per 1000 AEs). There was no difference (P = .999) in the rate of SRC sustained in games before (5.81 per 1000 AEs) and after (5.74 per 1000 AEs) the rule change. There was no difference (P = .967) in days lost from SRC before (13 days lost [interquartile range, 10-18]) and after (14 days lost [interquartile range, 10-16]) the rule change. The rate of SRC sustained in high school football practice decreased by 57% after a rule change limiting the amount and duration of full-contact activities, with no change in competition concussion rate. Limitations on contact during high school football practice may be one effective measure to reduce the incidence of SRC.

#3 Influence of pitch size and age category on the physical and physiological responses of young football players during small-sided games using GPS devices
Reference: Res Sports Med. 2019 Jul 15:1-11. doi: 10.1080/15438627.2019.1643349. [Epub ahead of print]
Authors: Lemes JC, Luchesi M, Diniz LBF, Bredt SDGT, Chagas MH, Praça GM
Summary: This study aimed to compare the physical and physiological responses of young football players of different categories during small-sided games (SSGs) played on different pitch sizes. Forty-eight (24 U-13 and 24 U-14) athletes played a 3 vs. 3 + 1 SSG in two experimental conditions: regular (36 × 27 m) and large pitch sizes (40 × 29 m). The total distance covered, the distances covered at different speed zones (0 to 6.9 km/h, 6.9 to 14.3, and 14.3 to 21.4), maximum heart rate, and mean heart rate were recorded. The results showed that older athletes covered larger distances during SSGs (p = 0.001; d = 0.937; large effect) and lower distances at the lowest (0-6.9 km/h) speed zone (p = 0.001; d = 0.657; moderate-to-large effect). Neither the physical nor physiological variables (except for distance covered between 14.3 and 21.4 km/h) differed between pitch sizes. This result indicates that pitch size may not impact the physical or physiological responses of U-13 and U-14 players during SSGs, but differences between categories were found. In conclusion, the development of tactical skills may be desirable to better explore the available space in the same age categories.

#4 Comparative study on skill and health related physical fitness characteristics between national basketball and football players in Sri Lanka
Reference: BMC Res Notes. 2019 Jul 12;12(1):397. doi: 10.1186/s13104-019-4434-6.
Authors: Kariyawasam A, Ariyasinghe A, Rajaratnam A, Subasinghe P
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Summary: The purpose was to compare health and skill related physical fitness profiles between healthy, male, basketball and football players of Sri Lankan national teams. Thirty basketball players (mean age 24 ± 4.5 years) and 30 football players (mean age 23 ± 4.3 years) were evaluated for health related fitness characteristics (body fat percentage, cardio-respiratory fitness, isometric hand grip strength, lower body and upper body muscular strength, abdominal and upper body muscular endurance, and flexibility) and skill related fitness characteristics (agility, speed, explosive throwing power, jumping power, reaction time, coordination, static balance). Fat percentage, upper body endurance, grip strength, running speed, explosive power, jumping power, balance and coordination were significantly higher in basketball players than in footballers. Football players had better upper body strength, flexibility, reaction time and agility than those of basketball players. The latter two were statistically significant. Basketball players had better mean lower body strength, although not significant. Fitness characteristics were different between basketball and football players. The results have implications in tailoring training activities to improve relevant fitness characteristics.

#5 Effects of a six-week period of congested match play on plasma volume variations, hematological parameters, training workload and physical fitness in elite soccer players
Reference: PLoS One. 2019 Jul 25;14(7):e0219692. doi: 10.1371/journal.pone.0219692. eCollection 2019.
Authors: Saidi K, Zouhal H, Rhibi F, Tijani JM, Boullosa D, Chebbi A, Hackney AC, Granacher U, Bideau B, Ben Abderrahman A
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Summary: The aims of this study were to investigate the effects of a six-week in-season period of soccer training and games (congested period) on plasma volume variations (PV), hematological parameters, and physical fitness in elite players. In addition, we analyzed relationships between training load, hematological parameters and players' physical fitness. Eighteen elite players were evaluated before (T1) and after (T2) a six-week in-season period interspersed with 10 soccer matches. At T1 and T2, players performed the Yo-Yo intermittent recovery test level 1 (YYIR1), the repeated shuttle sprint ability test (RSSA), the countermovement jump test (CMJ), and the squat jump test (SJ). In addition, PV and hematological parameters (erythrocytes [M/mm3], hematocrit [%], hemoglobin [g/dl], mean corpuscular volume [fl], mean corpuscular hemoglobin content [pg], and mean hemoglobin concentration [%]) were assessed. Daily ratings of perceived exertion (RPE) were monitored in order to quantify the internal training load. From T1 to T2, significant performance declines were found for the YYIR1 (p<0.001, effect size [ES] = 0.5), RSSA (p<0.01, ES = 0.6) and SJ tests (p< 0.046, ES = 0.7). However, no significant changes were found for the CMJ (p = 0.86, ES = 0.1). Post-exercise, RSSA blood lactate (p<0.012, ES = 0.2) and PV (p<0.01, ES = 0.7) increased significantly from T1 to T2. A significant decrease was found from T1 to T2 for the erythrocyte value (p<0.002, ES = 0.5) and the hemoglobin concentration (p<0.018, ES = 0.8). The hematocrit percentage rate was also significantly lower (p<0.001, ES = 0.6) at T2. The mean corpuscular volume, mean corpuscular hemoglobin content and the mean hemoglobin content values were not statistically different from T1 to T2. No significant relationships were detected between training load parameters and percentage changes of hematological parameters. However, a significant relationship was observed between training load and changes in RSSA performance (r = -0.60; p<0.003). An intensive period of "congested match play" over 6 weeks significantly compromised players' physical fitness. These changes were not related to hematological parameters, even though significant alterations were detected for selected measures.

#6 Effects of an 8-Week Pre-seasonal Training on the Aerobic Fitness of Professional Soccer Players
Reference: J Strength Cond Res. 2019 Jul 19. doi: 10.1519/JSC.0000000000003209. [Epub ahead of print]
Authors: Michaelides MA, Parpa KM, Zacharia AI.
Summary: Pre-season in soccer training develops the physical requisites for competition and usually consists of a high volume of aerobic and anaerobic conditioning training including friendly games. The purpose of the study was to determine the effects of pre-season training on the aerobic fitness of professional soccer players. Nineteen professional male soccer players (age = 27.37 ± 3.67 years, height = 179.61 ± 5.17 cm, and body fat percentage = 11.3 ± 3.19%) participated in this study performed an incremental cardiopulmonary exercise testing on a treadmill before and after the 8 weeks of pre-season preparation. The results were analyzed using paired t tests, revealing significant differences on several indices. The subjects improved significantly on maximal aerobic capacity (V[Combining Dot Above]O2max) and lasted significantly longer on the treadmill (p < 0.05). The V[Combining Dot Above]O2 at ventilatory threshold (VT) and respiratory compensation point (RCP) increased significantly (p < 0.05). The running velocity at ventilatory thresholds (vVT and vRCP) and at V[Combining Dot Above]O2 max (vVO2max) also increased significantly (p < 0.05). In conclusion, the results of this study, as expected, demonstrated that the proposed 8 weeks of pre-season training program was sufficient to cause significant improvements on the aerobic performance indices of professional soccer players. The study confirms the beneficial changes in the process of adaptations that occur with this type of training and can assist coaches and trainers in planning a successful pre-season training program.

#7 In-season in-field variable resistance training: effects on strength, power, and anthropometry of junior soccer players
Reference: J Sports Med Phys Fitness. 2019 Jul 24. doi: 10.23736/S0022-4707.19.09937-7. [Epub ahead of print]
Authors: Izadi M, Arazi H, Ramirez-Campillo R, Mirzaei M, Saidei P
Summary: Soccer players' leg muscular strength and power have been shown to be significant due to their association with soccer-specific performance including jumps, sprints, tackles and kicks. The aim of this study, therefore, was to examine the effects of an in-season in- field variable resistance training (VRT) program on strength, power, and anthropometry of junior soccer players. A team of male soccer players were randomly divided into Experimental (n=10) and Control groups (n=10). The Control group performed 8 weeks of soccer training alone. The Experimental group performed squat VRT using chains in addition to soccer training. Measures before and after training included one repetition maximum (1RM) of squat, countermovement jump (CMJ), and anthropometric estimation of thigh muscle cross sectional area (CSA). The VRT induced large improvements in absolute (34.45%; p=0.001; Cohen's d=1.78) and relative strength to thigh muscle CSA (21.53%; p=0.002; Cohen's d=1.04). Similarly, there were large (18.07%, p=0.007; Cohen's d=1.5) increases in jump height and medium gains in absolute peak power output (16.13%; p=0.009; Cohen's d=0.34) and relative peak power output to thigh muscle CSA (9.6%; p=0.002; Cohen's d=0.31). Further, there was a medium increase (5.9%, p=0.03; Cohen's d=0.36) in thigh muscle CSA. No significant changes were observed in the Control group. In-season in-field biweekly squat VRT enhanced strength and power measures in junior soccer players.

#8 Selection and promotion processes are not associated by the relative age effect in an elite Spanish soccer academy
Reference: PLoS One. 2019 Jul 24;14(7):e0219945. doi: 10.1371/journal.pone.0219945. eCollection 2019.
Auhors: Castillo D, Pérez-González B, Raya-González J, Fernández-Luna Á, Burillo P, Lago-Rodríguez Á
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Summary: The aim of this study was to analyze the influence of the relative age effect (RAE) on the selection and promotion processes in an elite soccer academy. One hundred and eleven elite youth players who belonged to an elite soccer club from the Spanish "La Liga" participated in this study. Players were classified into three age-categories: under 14 years (U14), under 16 years (U16) and under 18 years (U18); and they were also classified in quartiles based on their date of birth (i.e., January-March, Q1; April-June, Q2; July-September, Q3; October-December, Q4). In addition, two further classification criteria were established based on the selection (i.e., selected and non-selected players) and promotion (i.e., promoted and non-promoted players) processes. The main results showed that in U14 and U16 age-categories, players born early in the year were over-represented compared to players born late in the year, although birth-distribution was not associated with the likelihood of a player to be selected or promoted. In addition, less fat in sum skinfolds, less percentage of fat, higher percentage of muscle and lower endomorphy and mesomorphy components were showed in U14 selected players, in comparison with non-selected players. Likewise, better sprint performance was found in U16 selected players versus non-selected ones. However, no significant differences on anthropometry, body composition, somatotype and physical performance were found between promoted and non-promoted players. Therefore, our results suggest there is need for coaches to reorient their talent identification programs in order to make sure that players selected to continue playing in the club have the potential to promote to the excellence in soccer.

#9 Changing Rules and Configurations During Soccer Small-Sided and Conditioned Games. How Does It Impact Teams' Tactical Behavior?
Reference: Front Psychol. 2019 Jul 9;10:1554. doi: 10.3389/fpsyg.2019.01554. eCollection 2019.
Authors: Machado JC, Ribeiro J, Palheta CE, Alcântara C, Barreira D, Guilherme J, Garganta J, Scaglia AJ
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Summary: The present study aimed to investigate how team's tactical behavior varies within and between age categories in different Small-Sided and Conditioned Games' configurations and conditions. Twenty non-elite youth male soccer players (U15, n = 10, mean age = 13.5 ± 1.2 years; U17, n = 10, mean age = 16.3 ± 0.5 years) were selected. Thirty-six Small-Sided and Conditioned Games (SSCG) were played in both categories, namely three Representative SSCG (R-SSCG), three Maintaining Ball Possession Games (MBPG) and three Progression to Target Games (PTG) performed for each configuration (Gk+3vs3+Gk and Gk+4vs4+Gk). Teams' tactical behavior was analyzed based on simple and composite performance indicators, as well as through Lag Sequential Analysis. Rules manipulation and SSCG configurations influenced teams' tactical behavior on both categories, but in different ways. Teams composed by younger players presented greater difficulties in MBPG played in smaller games configuration, while Gk+4vs4+Gk configuration can be used to enhance teams' tactical performance of younger players in R-SSCG and MBPG conditions. Moreover, increasing rules manipulations appeared to negatively impact on teams' exploratory behavior. Therefore, practitioners should carefully manipulate key constraints to adapt task demands to players' age category and training session's goals in order to enhance tactical performance.

#10 Differences in Player Position Running Velocity at Lactate Thresholds Among Male Professional German Soccer Players
Reference: Front Physiol. 2019 Jul 9;10:886. doi: 10.3389/fphys.2019.00886. eCollection 2019.
Authors: Schwesig R, Schulze S, Reinhardt L, Laudner KG, Delank KS, Hermassi S
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Summary: This study investigated the differences in running velocities at specific lactate thresholds among male German soccer players. One hundred fifty-two professional (3rd league: n = 78; 4th league: n = 74) male soccer players (mean ± SD; age: 24.7 ± 4.37 years, body mass: 80.8 ± 7.33 kg, body height: 1.83 ± 0.06 m) volunteered for the investigation. Players were categorized as goalkeepers, central defenders, central midfielders, wings and forward. Players completed a treadmill test, at incremental speeds, to determine running velocity at different blood lactate concentrations (v2 = 2 mmol/l; v4 = 4 mmol/l; and v6 = 6 mmol/l). In addition, the largest difference between positions for running velocity was found at the lactate threshold v2 (p = 0.005). The running data revealed that only goalkeepers had significantly lower velocities at the lactate thresholds compared to outfield players. The central midfielders showed the highest average performance level at the lactate thresholds (v2: 12.5 ± 1.20 km/h; v4: 15.2 ± 1.14 km/h; and v6: 16.6 ± 1.14 km/h). In conclusion, this study provides soccer and position-specific reference data for the running performance of male professional German soccer players to evaluate the endurance performance in a standardized way. In this context, future research should extend the database for the first and second leagues. Further research assessing running performance during competition matches over the entire season is required to validate the endurance test performance data.

#11 Salivary Metabolome and Soccer Match: Challenges for Understanding Exercise induced Changes
Reference: Metabolites. 2019 Jul 11;9(7). pii: E141. doi: 10.3390/metabo9070141.
Authors: Pitti E, Petrella G, Di Marino S, Summa V, Perrone M, D'Ottavio S, Bernardini A, Cicero DO
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Summary: Saliva samples of seventeen soccer players were analyzed by nuclear magnetic resonance before and after an official match. Two different ways of normalizing data are discussed, using total proteins and total metabolite concentrations. Changes in markers related to energy, hydration status, amino acids and other compounds were found. The limits and advantages of using saliva to define the systemic responses to exercise are examined, both in terms of data normalization and interpretation, and the time that the effect lasts in this biofluid, which is shorter to that commonly observed in blood. The heterogeneous nature and different timing of the exercise developed by players also plays an important role in the metabolic changes that can be measured. Our work focuses mainly on three different aspects: The effect that time sampling has on the observed effect, the type of normalization that is necessary to perform in order to cope with changes in water content, and the metabolic response that can be observed using saliva.

#12 The Importance of Fundamental Motor Skills in Identifying Differences in Performance Levels of U10 Soccer Players
Reference: Sports (Basel). 2019 Jul 22;7(7). pii: E178. doi: 10.3390/sports7070178.
Authors: Jukic I, Prnjak K, Zoellner A, Tufano JJ, Sekulic D, Salaj S
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Summary: This study examined the differences in fundamental motor skills (FMSs) and specific conditioning capacities (SCCs) between a coach's classification of first team (FT) and second team (ST) U10 soccer players and examined the most important qualities based on how the coach differentiates them. The FT (n = 12; Mage = 9.72 ± 0.41) and ST (n = 11; Mage = 9.57 ± 0.41) soccer players were assessed using the Test of Gross Motor Development-2, standing long jump, sit and reach, diverse sprints, and the 20 m multistage fitness test (MSFT). The coach's subjective evaluation of players was obtained using a questionnaire. No significant differences existed between the FT and ST in any variables (p > 0.05). However, large and moderate effect sizes were present in favour of the FT group in locomotor skills (d = 0.82 (0.08, 1.51)), gross motor quotient (d = 0.73 (0.00, 1.41)), height (d = 0.61 (-0.12, 1.29)), MSFT (d = 0.58 (-0.14, 1.25)), and maximum oxygen uptake (VO2max) (d = 0.55 (-0.17, 1.22)). Furthermore, the coach perceived the FT group as having greater technical and tactical qualities relative to ST players. This suggests that it might be more relevant for players of this age to develop good FMS connected to technical skills, before focusing on SCC. Therefore, it might be beneficial for soccer coaches to emphasize the development of FMSs due to their potential to identify talented young soccer players and because they underpin the technical soccer skills that are required for future soccer success.





Latest research in football - week 28 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Biomarkers of insulin action during single soccer sessions before and after a 12-week training period in type 2 diabetes patients on a caloric-restricted diet
Reference: Physiol Behav. 2019 Jul 16:112618. doi: 10.1016/j.physbeh.2019.112618. [Epub ahead of print]
Authors: de Sousa MV, Fukui R, Dagogo-Jack S, Krustrup P, Zouhal H, da Silva MER
Summary: We investigated the biomarkers of insulin action as well as changes in free fatty acids and lactate concentration after an acute soccer session pre and post training with caloric-restricted diet versus diet alone in type 2 diabetes (T2D) patients. Fifty-one middle-aged (61.1 ± 6.4 years) T2D patients were randomly allocated to the soccer+diet group (SDG) or the diet group (DG). The control group comprised T2D patients observing a caloric-restricted diet who did not receive soccer training. Over 12 weeks, SDG performed 3 × 40 min per week of soccer training. The first soccer session for SDG induced acute increases in blood lactate (1.4 ± 0.1-6.0 ± 0.7 mmol/L, P < 0.05) and glucagon levels (112.1 ± 6.2-142.9 ± 8.0 pg/mL, P < 0.05), whereas glucose and insulin levels remained unchanged. Moreover, this session showed suppressed insulin levels as well as higher free fatty acids, lactate levels and glucagon/insulin ratio compared to DG (p < 0.05). After 12 weeks, a baseline decrease was observed in glucagon, leptin and lactate levels in SDG and DG (p < 0.05), whereas HOMA-IR, Adipo-IR and glucose levels were lower only in SDG (p < 0.05). At the last soccer training session, the blood lactate response was significantly lower than for the first session (4.0 ± 0.4 vs 6.0 ± 0.7 mmol/L). At 48 h pre intervention, a decrease was observed in leptin levels (p < 0.05), which remained lower post intervention. The positive correlation between leptin and insulin, and the lower levels after training, could be attributed to the improved insulin sensitivity along with the weight loss observed in both groups (~3.4 kg for DG and 3.7 kg for SDG). Acute soccer sessions markedly improved insulin action markers in T2D patients, while the cumulative effects enhanced insulin sensitivity and decreased risk factors associated with cardiovascular disease after 12 weeks of intervention better than caloric-restricted diet.

#2 "REOFUT" as an Observation Tool for Tactical Analysis on Offensive Performance in Soccer: Mixed Method Perspective
Reference: Front Psychol. 2019 Jun 28;10:1476. doi: 10.3389/fpsyg.2019.01476. eCollection 2019.
Authors: Aranda R, González-Ródenas J, López-Bondia I, Aranda-Malavés R, Tudela-Desantes A, Anguera MT
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Summary: Performance analysis in complex sports like soccer requires the study of the influence of the interaction between both teams during the game on final performance. The mixed methods approach involves the collection, analysis, and interpretation of qualitative and quantitative data for the same purpose and within the framework of the same study. To build certain observation tools, mixed methods are necessary in order to take advantage of integration between qualitative and quantitative elements. The aim of this study was to develop a new no standard observation tool to analyze soccer offensive performance considering not only the observed team but also some aspects of the opponent behavior, as well as to test its reliability. The process consisted in expert meetings and exploratory observations. Experts carried out several design and re-design steps of the observation tool to its final form which includes two macro-criteria and 31 dimensions. The basic unit of analysis was the "team possession" and the main aims of study were: (a) technical, tactical and spatial characteristics of the start, the development and the end of the team possession and its offensive performance, (b) the behavior of the observed team just after losing the ball possession and its defensive performance. Inter-observer and intra-observer analysis were carried out and kappa coefficient was calculated to test the observation tool reliability and improve the quality of data. Results indicate that optimal inter and intra-reliability levels obtained in this work are high enough as for suggesting that the observation tool for offensive performance in soccer (REOFUT) could be an adequate tool for analyzing offensive play actions and their performance in soccer.

#3 Self-Control in Aiming Supports Coping With Psychological Pressure in Soccer Penalty Kicks
Reference: Front Psychol. 2019 Jun 27;10:1438. doi: 10.3389/fpsyg.2019.01438. eCollection 2019.
Authors: Navia JA, van der Kamp J, Avilés C, Aceituno J
Summary: This study addressed the question whether coaches better allow athletes to self-control their decisions when under pressure or whether to impose a decision upon them. To this end, an experiment was conducted that manipulated the soccer kickers' degree of control in decision-making. Two groups of elite under-19 soccer players (n = 18) took penalty kicks in a self-controlled (i.e., kickers themselves decided to which side to direct the ball) and an externally controlled condition (i.e., the decision to which side to direct the ball was imposed upon the kickers). One group performed the penalty kick under psychological pressure (i.e., the present coaching staff assessed their performance), while the second group performed without pressure. Just before and after performing the kicks, CSAI-2 was used to measure cognitive and somatic anxiety and self-confidence. Further, the number of goals scored, ball placement and speed, and the duration of preparatory and performatory behaviors were determined. The results verified increased levels of cognitive and somatic anxiety after performing the kicks in the pressured group compared to the no-pressure group. In addition, degree of self-control affected the participants' performance, particularly in the pressured group. They scored more goals and placed the kicks higher in the self-controlled than in the externally-controlled condition. Participants also took more time preparing and performing the run-up in the self-controlled condition. Findings indicate that increased self-control helps coping with the debilitating effects of pressure and can counter performance deteriorations. The findings are discussed within the framework of self-control theories, and recommendations for practitioners and athletes are made.

#4 Variation of aerobic performance indices of professional elite soccer players during the annual macrocycle
Reference: J Sports Med Phys Fitness. 2019 Jul 15. doi: 10.23736/S0022-4707.19.09800-1. [Epub ahead of print]
Authors: Bekris E, Mylonis E, Gissis I, Katis A, Metaxas T, Komsis S, Kombotieta N
Summary: The purpose of the present study was to examine the variation of aerobic performance parameters of elite Greek soccer players. In the study participated twenty-four (24) male professional soccer players (age: 24.3±4.3 years, height: 180.3±3.8 cm and mass: 77.4±6.1 kg), who competed at the top level of the Greek National Championship. Four measurements regarding aerobic parameters were conducted during the annual training cycle (preseason, start of the season, end of the first championship round and end of the season). The ANOVA analysis showed that maximum oxygen uptake (VO2max) was significantly increased after the completion of the preseason and continued to increase until the end of the first round of the Championship. In contrast, a decline was observed towards the end of the season. The velocity to maximum oxygen uptake (vVO2max) and the velocity parameter in respiratory threshold were significantly increased at the end of the preseason and the end of the first round, while the parameters were differentiated at the end of the season. The lactate concentration showed no significant changes during the four measurements. A systematic observation of players' performance, especially recording parameters such as VO2max, during the annual training cycle, could provide the necessary feedback for both trainers and players in order to increase team performance.

#5 Knee isokinetic muscle strength and balance ratio in female soccer players of different age groups: a cross-sectional study
Reference: Phys Sportsmed. 2019 Jul 16. doi: 10.1080/00913847.2019.1642808. [Epub ahead of print]
Authors: Vargas VZ, Motta C, Peres B, Vancini RL, Andre Barbosa de Lira C, Andrade MS
Summary: As a consequence of years of soccer training and sexual maturation, there is an increase in lower body muscle mass and strength especially in the knee extensors and flexors muscles. In this context, the lack of knee joint stability, resulting from strength imbalance between knee extensor and flexors muscles, has been associated with knee injuries. The aim of this study was to compare the knee flexor and extensor muscle peak torque, average power, contralateral deficit, conventional and functional balance ratios of female soccer players from different age groups.  Sixty-six female soccer players were divided into four groups: under 13 (U13), under 15 (U15), under 17 (U17) years old and professional (PRO). Flexor and extensor knee muscle strength in concentric and eccentric actions of both limbs were assessed using isokinetic dynamometer. For the dominant limb, the knee concentric extensor muscles peak torques, assessed at 60 and at 240 deg/sec, and average power of U15 group were significantly higher than U13 group. Extensor muscles average power of PRO group was higher than U17. Dominant knee flexor average power of U15 was significant higher than U13 group. Peak torque at 60 deg/sec and 240 deg/sec and average power of PRO group were higher than U17 group. No differences were found regarding the eccentric action for flexor and extensor muscles. Conventional and functional balance ratios were similar among all age group, except for U13, which presented higher values than U15 group for dominant limb. The greatest increases in muscular performance occur when the athlete starts practicing soccer (after U13) and when they become professional (after U17) and the balance ratios, and muscle balance ratios remain stable in all age groups, although they are below the recommended level in the literature, which may increase the risk for lower limb injury

#6 The influence of youth soccer players' sprint performance on the different sided games' external load using GPS devices
Reference: Res Sports Med. 2019 Jul 15:1-12. doi: 10.1080/15438627.2019.1643726. [Epub ahead of print]
Authors: Castillo D, Raya-González J, Manuel Clemente F, Yanci J
Summary: The aims of this study are 1) to compare sided games' (SGs) external responses encountered by players according to pitch size and to 2) examine the relationships between sprint performance and SGs' external physical responses. Twenty soccer players under 15 years of age (U-15) participated in this study. Each player performed a sprinting test (10 m and 30 m sprints) and played a SG on two different pitch sizes (small at 100 [SSG] and large at 200 [LSG] m2 per player). Higher external responses (p < 0.01, ES = -6.41-1.22) were found in LSG in comparison to SSG, except to distance accelerating and decelerating (p > 0.05, ES = -0.26-0.27). Players who were faster over 10 and 30 m covered higher distances cruising and sprinting (r = -0.47/-0.66; ± 0.23/± 0.30, respectively, p < 0.05), performed a greater number of sprints, achieved higher maximum velocity (Velmax) during LSG and covered a greater distance at high-intensity accelerating (r = -0.50/-0.70; ±0.21/±0.29, respectively, p < 0.05) during both SG. LSG demanded a higher external load in comparison with SSG. In addition, the improved sprint capacity could allow players to perform greater running activities and short-term actions at high-intensities during SG.

#7 Injury Surveillance in Major League Soccer: A 4-Year Comparison of Injury on Natural Grass Versus Artificial Turf Field
Reference: Am J Sports Med. 2019 Jul 15:363546519860522. doi: 10.1177/0363546519860522. [Epub ahead of print]
Authors: Calloway SP, Hardin DM, Crawford MD, Hardin JM, Lemak LJ, Giza E, Forsythe B, Lu Y, Patel BH, Osbahr DC, Gerhardt MB, Mandelbaum BR, Baldwin WW
Summary: Artificial playing surfaces are becoming more common due to decreased cost of maintenance and increased field usability across different environmental conditions. The Fédération Internationale de Football Association (FIFA) has approved newer generation artificial turf for soccer competition at the elite level, but many elite-level athletes prefer to play on natural grass surfaces due to a perceived increase in injury rate, discomfort, and fatigability on artificial turf. Injury rates and rates of individually categorized types of injury experienced on artificial turf are noninferior to rates of injury on the standard comparator, natural grass, in elite-level Major League Soccer athletes. Over the course of 4 Major League Soccer seasons (2013-2016), athlete injury data were recorded electronically. Injury data recorded in matches between 2 Major League Soccer teams were then analyzed. Playing surface was known for each venue, and all artificial turf surfaces were rated as 2-star according to FIFA criteria. Incidence rate ratios (Artificial Turf ÷ Natural Grass) were calculated with a 95% CI (α = .05) for both overall injury incidence and individual injury subgroups. A noninferiority margin (δ) of 0.15 was used to determine noninferiority of injury incidence rates. A total of 2174 in-game injuries were recorded during the study period, with 1.54 injuries per game on artificial turf and 1.49 injuries per game on natural grass (incidence rate ratio, 1.033; 95% CI, 0.937-1.139). Within injury subgroups, overall ankle injury, Achilles injury, and ankle fracture were found to have a statistically higher incidence on artificial turf. Artificial turf was found to be noninferior to natural grass for overall foot injury and forefoot injury. No statistically significant differences were found in knee injuries between the 2 surfaces. The overall rate of injury on artificial turf was noninferior to that on natural grass. Within individual injury categories, a higher rate of ankle injury was found on artificial turf. No other injury subgroup demonstrated statistically significant differences between surfaces. FIFA 2-star rated artificial turf is a viable alternative to natural grass in elite-level soccer competition. Innovative research methods for comparing artificial turf versus natural grass may elucidate relative advantages with respect to player safety.

#8 Orthopedic injuries in a formation of a soccer club
Reference: Rev Bras Ortop. 2013 Jun 11;48(1):41-45. doi: 10.1016/j.rboe.2011.12.001. eCollection 2013 Jan-Feb.
Authors: Carvalho DA
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Summary: Football is one of the most popular sports in the world with approximately 400 million practitioners. All physical activity generates an overload somewhere in the locomotor system, above all, in young athletes. The purpose was to conduct the epidemiological survey of orthopedic injuries in a medical department of the categories of junior soccer a football club in Curitiba. Epidemiological survey of injuries in 310 different athletes during the 2009 and 2010 seasons were analysed. The number of recorded visits was 3.64 per athlete orthopedic complaints in two years. Furthermore, we find 2.88 injuries/1,000 hours of play, and the junior (under 20 and under 18) with the highest rate (3.05). The most frequent injury was contusion (32.15%), lower limbs, especially the thigh (3.94%). The higher incidence of injuries occurred in the Middle - campers (30.65%), being the training responsible for 88.31% of the complaints. The epidemiological survey of medical care is a medical department is an important tool for analysis of the main complaints, as well as the primary means of prevention and maintaining the health of athletes.

#9 Concussion in American Versus European Professional Soccer: A Decade-Long Comparative Analysis of Incidence, Return to Play, Performance, and Longevity
Reference: Am J Sports Med. 2019 Jul 15:363546519859542. doi: 10.1177/0363546519859542. [Epub ahead of print]
Authors: Ramkumar PN, Navarro SM, Haeberle HS, Luu BC, Jang A, Frangiamore SJ, Farrow LD, Schickendantz MS, Williams RJ 3rd
Summary: The incidence and effect of sports-related concussions (SRCs) within the global sport of professional soccer is poorly described. The purpose was to comparatively examine the effects of SRC on athletes in Major League Soccer (MLS) and the English Premier League (EPL) in terms of incidence, return to play (RTP), performance, and career longevity. Contracts, transactions, injury reports, and performance statistics from 2008 to 2017 were obtained and cross-referenced across 6 publicly available websites detailing MLS and EPL data, including official league publications. For each league, players who sustained a concussion were compared with the 2008-2017 uninjured player pool. RTP and games missed were analyzed and compared. Career length was analyzed with Kaplan-Meier survival curves. Player performance changes were evaluated before and after concussion. Of the 1784 eligible MLS and 2001 eligible EPL players evaluated over the 10-year period, the incidence of publicly reported concussions per 1000 athlete-exposures was 20.22 and 18.68, respectively (P = .53). The incidence of reported concussions steadily increased in both leagues. MLS players missed a mean 7.3 games after concussion (37.0 days missed); EPL players missed a mean 0.6 games after concussion (10.9 days missed) (P < .0001, P < .0001). Statistical performance in terms of games started, assists, shots on goal, and total shots after concussion was significantly reduced at all nongoalie positions for players in the EPL; however, MLS nongoalie positions with concussion had no significant decreases in these categories. Goalies in both leagues had no significant change in performance or games started. The probability of playing a full season after concussion was not significantly decreased when compared with the uninjured pool in both leagues. This study established the SRC incidence among elite soccer players in 2 international professional leagues and identified major RTP and performance differences between EPL and MLS players. While career longevity was unaffected, the approach to managing concussion as in MLS may better promote player safety and preserve on-field performance.

#10 How does the modern football goalkeeper train? - An exploration of expert goalkeeper coaches' skill training approaches
Reference: J Sports Sci. 2019 Jul 16:1-9. doi: 10.1080/02640414.2019.1643202. [Epub ahead of print]
Authors: Otte FW, Millar SK, Hüttermann S
Summary: The football goalkeeper position arguably represents a unique role within the team sport. Despite its highly complex skill demands, research on football goalkeeping has only sporadically examined the position within isolated and limited parameters. In particular, there is limited literature on "modern" skill acquisition training methods and approaches within the field of goalkeeper training. In a cross-cultural study with fifteen expert goalkeeper coaches, researchers here examined the overarching research question of "how does the modern football goalkeeper train?". Semi-structured interviews explored expert coaches' views on critical skills for performance in goalkeeping and the training approaches used to develop these critical skills. Results indicate that four skill sets are considered essential by goalkeeper coaches, these are: decision-making skills, athleticism, mentality, and technical skills. In terms of developing these skills in goalkeeper-specific training, the majority of expert coaches apply a similar microstructure to training sessions. This structure involves a steady progression from simple to complex training tasks, where for large parts, isolated technical training appears to be prioritised over a holistic training approach that integrates technical skills and perceptual-cognitive components (e.g., decision making). Scientific and practical recommendations for researchers and practitioners in the field of football goalkeeper coaching are provided.

#11 A Decision-Analytic Approach to Addressing the Evidence About Football and Chronic Traumatic Encephalopathy
Reference: Semin Neurol. 2019 Jul 16. doi: 10.1055/s-0039-1688484. [Epub ahead of print]
Authors: Brand KP, Finkel AM
Summary: Doubts can be raised about almost any assertion that a particular exposure can lead to an increase in a given adverse health effect. Even some of the most well-accepted causal associations in public health, such as that linking cigarette smoking to increased lung cancer risk, have intriguing research questions remaining to be answered. The inquiry whether an exposure causes a disease is never wholly a yes/no question but ought to follow from an appraisal of the weight of evidence supporting the positive conclusion in light of any coherent theories casting doubt on this evidence and the data supporting these. More importantly, such an appraisal cannot be made sensibly without considering the relative consequences to public health and economic welfare of specific actions based on unwarranted credulity (false positives) versus unwarranted skepticism (false negatives). Here we appraise the weight of evidence for the premise that repeated head impacts (RHIs) in professional football can increase the incidence of chronic traumatic encephalopathy (CTE) and, in turn, cause a variety of cognitive and behavioral symptoms. We first dismiss four logical fallacies that should not affect the appraisal of the weight of evidence. We then examine four alternative hypotheses in which RHI is not associated with CTE or symptoms (or both), and we conclude that the chances are small that the RHI→ CTE→ symptoms link is coincidental or artifactual. In particular, we observe that there are many specific interventions for which, even under a skeptical appraisal of the weight of evidence, the costs of a false positive are smaller than the false negative costs of refusing to intervene.





Latest research in football - week 27 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 The complex and bidirectional interaction between sex hormones and exercise performance in team sports with emphasis on soccer
Reference: Hormones (Athens). 2019 Jun 29. doi: 10.1007/s42000-019-00115-7. [Epub ahead of print]
Authors: Koundourakis NE, Margioris AN
Summary: A constant topic reported in the lay press is the effect of sex hormones on athletic performance and their abuse by athletes in their effort to enhance their performance or to either boost or sidestep their hard, protracted, and demanding training regimens. However, an issue that it is almost never mentioned is that the athletic training itself affects the endogenous production of androgens and estrogens, while also being affected by them. Among sports, soccer is a particularly demanding activity, soccer players needing to possess high levels of endurance, strength, and both aerobic and anaerobic capacity, with the very great physiological, metabolic, physical, and psychological exertion required of the players being both influenced by sex steroids and, reciprocally, affecting sex steroid levels. This review focuses on the currently available knowledge regarding the complex relationship between athletic training and competition and sex steroid hormone adaptation to the demands of the exercise effort. In the first part of the review, we will examine the effects of endogenous testosterone, estrogen, and adrenal androgens on athletic performance both during training and in competition. In the second part, we will explore the reciprocal effects of exercise on the endogenous sex hormones while briefly discussing the recent data on anabolic androgenic steroid abuse

#2 Isokinetic strength differences between elite senior and youth female soccer players identifies training requirements
Reference: Phys Ther Sport. 2019 Jun 21;39:45-51. doi: 10.1016/j.ptsp.2019.06.008. [Epub ahead of print]
Authors: Eustace SJ, Page RM, Greig M
Summary: The aim was to compare traditional and angle-specific isokinetic strength of eccentric knee flexors and concentric knee extensors in female senior professional and youth soccer players. A total of 34 players (17 seniors [age 25.31 ± 4.51 years; height 167.89 ± 7.04 cm; mass 63.12 ± 7.79 kg] and 17 youths [16.91 ± 1.16 years; height 165.92 ± 4.42 cm; mass 60.07 ± 4.48 kg]) from the Women's Super League 1 completed strength assessments at 180, 270 and 60°∙s-1 participated in this study.  Peak torque (PT), dynamic control ratio (DCR), angle of peak torque (APT), functional range (FR), angle-specific torque (AST) and angle-specific DCR (DCRAST) were compared between age groups. The PT (P = 0.016) AST (P = 0.041) were significantly higher in seniors compared to youths; however APT (P = 0.141), DCR (P = 0.524) FR (P = 0.821) and DCRAST (P = 0.053) were not significant between playing age. The use of absolute and angle-specific strength measures were able to distinguish between female playing ages, whereas DCR and DCRAST was unable to identify differences. The PT and AST metrics may be the most useful metrics to help identify and inform training needs, particularly in youths.

#3 Offensive Transitions in High-Performance Football: Differences Between UEFA Euro 2008 and UEFA Euro 2016
Reference: Front Psychol. 2019 Jun 18;10:1230. doi: 10.3389/fpsyg.2019.01230. eCollection 2019.
Authors: Maneiro R, Casal CA, Álvarez I, Moral JE, López S, Ardá A, Losada JL
Summary: Coaches, footballers and researchers agree that offensive transitions are one of the most important moments in football today. In a sport where defense over attack dominates, with low scores on the scoreboard, the importance of these actions from the offensive point of view becomes very important. Despite this, scientific literature is still very limited on this topic. Therefore, the objectives set out in the present investigation have been two: first, by means of a proportion analysis and the application of a chi-square test, it was intended to describe the possible differences between the offensive transitions made in the UEFA Euro 2008 and UEFA Euro 2016; then, through different multivariate analyzes based on logistic regression models, it was intended to know the possible differences among the proposed models. Using observational methodology as a methodological filter, 1,533 offensive transitions corresponding to the observation of the quarter final, semifinal, and final quarter of UEFA Euro 2008 and UEFA Euro 2016 have been analyzed. The results obtained have shown that offensive transitions between both championships have changed throughout both UEFA Euro, as well as some of the variables or behaviors associated with them (p < 0.05). The predictive models considered, although they have been developed from the same predictor variables, have also yielded different results for both championships, evidencing predictive differences among themselves. These results allow to corroborate that the offensive phase in high level football, specifically in what refers to moments of transition defense-attack, have evolved over these 8 years. At the applied level, the results of this research allow coaches to have current and contemporary information on these actions, potentially allowing them to improve their offensive performance during competition.

#4 Association Between Match Activity, Endurance Levels and Maturity in Youth Football Players
Reference: Int J Sports Med. 2019 Jul 4. doi: 10.1055/a-0938-5431. [Epub ahead of print]
Authors: Francini L, Rampinini E, Bosio A, Connolly D, Carlomagno D, Castagna C
Summary: The aim of the study was to examine the associations between maximal and submaximal field tests with match physical activity and biological maturation in youth football players. Sixty-eight youth football players (U14, U15, U16, U17) performed maximal and submaximal field endurance tests. Biological maturity was estimated calculating the distance from peak height velocity (Y-PHV). Physical match activities were tracked using GPS units and players' post-match rate of perceived exertion (RPE) was recorded. Mainly moderate associations were found between field tests and match activities. Large correlations were found between Yo-Yo Intermittent Recovery test level 1, distance covered at high and very high-speed running, the quantity of very high and maximal metabolic power running. Small to moderate associations between match activities and Y-PHV were observed. The magnitude of correlation between match activities and field tests increased from moderate to large when matches with an RPE>5 were considered. The results provide further evidence of the association between young football players' aerobic performance and match work rate. Submaximal field tests demonstrate ecological validity and may constitute a practical alternative to performing maximal tests. Maturation was found to have a moderate effect on youth players' match work rate.

#5 Postprandial lipaemia 10 and 34 hours after playing football: Does playing frequency affect the response?
Reference: PLoS One. 2019 Jul 2;14(7):e0218043. doi: 10.1371/journal.pone.0218043. eCollection 2019.
Authors: Paul DJ, Nassis GP, Kerouani AC, Bangsbo J
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Summary: Elevated postprandial triglyceride (TG) is associated with increased risk of cardiovascular disease. The time window for the last bout beneficial effect on postprandial lipaemia after football play is unknown. The aim of the present study was to examine whether playing affects postprandial TG during 1.5 day of reduced activity. Eighteen males were randomly allocated to perform either 1 (1FOOT; n = 9; age = 33.0 ± 5.0 yrs; body mass index = 24.2 ± 3.6 kg/m2) or 3 (3FOOT) consecutive days of 60-min 5 vs 5 football (n = 9; age = 32.8 ± 5.2 yrs; body mass index = 26.2 ± 4.1 kg/m2) matches across a 5-day study period. They arrived to the laboratory 10 hrs and 34 hrs after the final football session and blood samples were collected at fasted (0 min) and 45, 90, 240 and 360 min post a high fat load meal. There were non significant increase for postprandial TG AUC (9.1%; p = 0.17; 95%CI = -0.43 to 2.0; ES = -0.23) and iAUC (14.2%; p = 0.43; 95%CI = -0.92 to 1.9; ES = -0.24) between 10 and 34 hrs after the 1FOOT. For the 3FOOT, there was a non significant decrease in postprandial TG AUC (-2.7%; p = 0.73; 95%CI = -2.0 to 1.5; ES = 0.05) and iAUC (-17.5%; p = 0.41; 95%ci = -2.5 to 1.1; ES = 0.31) from 10 to 34 hrs, respectively. Performing three consecutive days of football exercise may offer no greater protective effect for postprandial TG before a period of reduced activity, compared to a single session.

#6 The role of a trauma-sensitive football group in the recovery of survivors of torture
Reference: Torture. 2019;29(1):97-109. doi: 10.7146/torture.v29i1.106613.
Authors: Horn R, Ewart-Biggs R, Hudson F, Berilgen S, Ironside J, Prodromou A
Summary: Whilst there is some preliminary evidence for the benefits of sports-related interventions for survivors of torture, how sport and exercise can contribute to the rehabilitation of torture survivors needs to be better understood. Specifically, this paper aims to: 1) explore the ways in which a football group contributed to the wellbeing of participants and; 2) suggest characteristics of the football group which could potentially contribute to its effectiveness. An exploratory mixed methods study was undertaken with participants and trainers of a joint programme delivered by Arsenal Football Club and Freedom from Torture in London. Individual discussions, group discussions and participatory ranking activities were used which led to the development of an initial programme model. This model was, subsequently, further developed through a variety of data collection methods. Six potential outcomes of involvement in the football group were identified: relationships, a sense of belonging, hope for the future, emotion management, enjoyment, and improved physical health. In addition, the process highlighted factors contributing to the effectiveness of the football group: a sense of safety, therapeutic aims, similar participants, a partnership approach, staff characteristics, other opportunities, and consistency in terms of approach, session content and staff. This exploratory study outlines the potential benefits of the football programme that would require further validation through a case-control study and participant follow-up. A model is put forward as well as a number of recommendations that serve as a starting point for similar programmes and guides academic research in the area.

#7 On-field Rehabilitation Part 2: A 5-Stage Program for the Soccer Player Focused on Linear Movements, Multidirectional Movements, Soccer-Specific Skills, Soccer-Specific Movements, and Modified Practice
Reference: J Orthop Sports Phys Ther. 2019 Jul 10:1-6. doi: 10.2519/jospt.2019.8952. [Epub ahead of print]
Authors: Buckthorpe M, Della Villa F, Della Villa S, Roi GS
Summary: This paper is part 2 of a 2-part series aimed at discussing the key elements of on-field rehabilitation training. In part 1, we described 4 pillars underpinning high-quality on-field rehabilitation: (1) restoring movement quality, (2) physical conditioning, (3) restoring sport-specific skills, and (4) progressively developing chronic training load. In part 2, we describe how the pillars contribute to a 5-stage on-field rehabilitation program to help injured players transition to team practice and match play. We use the example of a soccer player with ambitions to return to sport after anterior cruciate ligament reconstruction. The program moves through 5 field-based training stages: (1) linear movement, (2) multidirectional movement, (3) soccer-specific technical skills, (4) soccer-specific movement, and (5) practice simulation. The staged program is research based and facilitates communication, planning, control, and safety in return to sport following long-term injury.

#8 Anthropometric Profile of Soccer Players as a Determinant of Position Specificity and Methodological Issues of Body Composition Estimation
Reference: Int J Environ Res Public Health. 2019 Jul 5;16(13). pii: E2386. doi: 10.3390/ijerph16132386.
Authors: Leão C, Camões M, Clemente FM, Nikolaidis PT, Lima R, Bezerra P, Rosemann T, Knechtle B
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Summary: The aim of the present study was (a) to describe the anthropometric profile of a large group of soccer players based on different age groups and their playing positions on the field, and (b) to examine the variations of body composition among adult soccer players using diverse equations based on skinfold thickness. A total of 618 Greek soccer players who were grouped by age (i.e., 12-14, 14-16, 16-18, and 18-37 years) and playing position (i.e., goalkeeper, defender, midfielder, and forward) were evaluated for weight, height, and skinfolds. The Pařízková formula was used to estimate the percentage of body fat. Furthermore, for players who were 18 years or older the Reilly and Evans formulas was used to estimate the percentage of body fat. Independent of the age, in this large sample, goalkeepers presented higher values for weight, height and the percentage of body fat estimation as compared with other field positions. An anthropometric pattern was observed in each tactical position, namely, across a specific age of increasing maturation process (14-16 years). With the Pařízková formula, we found a mean (SD) range of variation in the percentage of body fat estimation between 4.87 ± 1.46 and 5.51 ± 1.46 as compared with the Evans formula. The same pattern of differences was found when the Reilly equation was considered. In conclusion, we observed a position specificity of anthropometric characteristics across different age categories. Additionally, the same data supported different validated equations which resulted in large differences in the final outcome estimations.

#9 Effect of a mindfulness programme training to prevent the sport injury and improve the performance of semi-professional soccer players
Reference: Australas Psychiatry. 2019 Jul 8:1039856219859288. doi: 10.1177/1039856219859288. [Epub ahead of print]
Authors: Zadeh MM, Ajilchi B, Salman Z, Kisely S
Summary: Mindfulness improves psychological outcomes. We examined whether greater mindfulness scores were associated with reduced injury rates in soccer players, as well as improved performance at both the individual and team level. This was a parallel-group, pre- and post-test, randomised controlled pilot trial. Forty-five male amateur soccer players from Tehran, Iran, were randomly assigned into experimental (n=23) and control groups (n=22). Outcomes were scores on the mindfulness sport inventory, as well as injury rates and recovery as assessed by a physiotherapist using standardised criteria. Expert observers assessed the effect on individual and team performance. Data were analysed using mixed analysis of variance and, where indicated, its non-parametric alternative, the Friedman test. Significantly greater mindfulness scores in the intervention group were associated with both reduced injury and improved performance. Mindfulness training shows promise in preventing injury and improving performance. The intervention could be applied to other sports and be helpful in clinical settings given the importance of exercise in promoting psychological well-being.

#10 Accuracy of the 2017 international recommendations for clinicians who interpret adolescent athletes' ECGs: a cohort study of 11 168 British white and black soccer players
Reference: Br J Sports Med. 2019 Jul 5. pii: bjsports-2017-098528. doi: 10.1136/bjsports-2017-098528. [Epub ahead of print]
Authors: Malhotra A, Dhutia H, Yeo TJ, Finocchiaro G, Gati S, Bulleros P, Fanton Z, Papatheodorou E, Miles C, Keteepe-Arachi T, Basu J, Parry-Williams G, Prakash K, Gray B, D'Silva A, Ensam B, Behr E, Tome M, Papadakis M, Sharma S.
Summary: The aim was to investigate the accuracy of the recently published international recommendations for ECG interpretation in young athletes in a large cohort of white and black adolescent soccer players. 11 168 soccer players (mean age 16.4±1.2 years) were evaluated with a health questionnaire, ECG and echocardiogram; 10 581 (95%) of the players were male and 10 163 (91%) were white. ECGs were retrospectively analysed according to (1) the 2010 European Society of Cardiology (ESC) recommendations, (2) Seattle criteria, (3) refined criteria and (4) the international recommendations for ECG interpretation in young athletes. The ESC recommendations resulted in a higher number of abnormal ECGs compared with the Seattle, refined and international criteria (13.2%, 4.3%, 2.9% and 1.8%, respectively). All four criteria were associated with a higher prevalence of abnormal ECGs in black athletes compared with white athletes (ESC: 16.2% vs 12.9%; Seattle: 5.9% vs 4.2%; refined: 3.8% vs 2.8%; international 3.6% vs 1.6%; p<0.001 each). Compared with ESC recommendations, the Seattle, refined and international criteria identified a lower number of abnormal ECGs-by 67%, 78% and 86%, respectively. All four criteria identified 36 (86%) of 42 athletes with serious cardiac pathology. Compared with ESC recommendations, the Seattle criteria improved specificity from 87% to 96% in white athletes and 84% to 94% in black athletes. The international recommendations demonstrated the highest specificity for white (99%) and black (97%) athletes and a sensitivity of 86%. The 2017 international recommendations for ECG interpretation in young athletes can be applied to adolescent athletes to detect serious cardiac disease. These recommendations perform more effectively than previous ECG criteria in both white and black adolescent soccer players.

#11 Classification of Soccer and Basketball Players' Jumping Performance Characteristics: A Logistic Regression Approach
Reference: Sports (Basel). 2019 Jul 4;7(7). pii: E163. doi: 10.3390/sports7070163.
Authors: Chalitsios C, Nikodelis T, Panoutsakopoulos V, Chassanidis C, Kollias I
Summary: This study aimed to examine countermovement jump (CMJ) kinetic data using logistic regression, in order to distinguish sports-related mechanical profiles. Eighty-one professional basketball and soccer athletes participated, each performing three CMJs on a force platform. Inferential parametric and nonparametric statistics were performed to explore group differences. Binary logistic regression was used to model the response variable (soccer or not soccer). Statistical significance (p < 0.05) was reached for differences between groups in maximum braking rate of force development (RFDDmax, U79 = 1035), mean braking rate of force development (RFDDavg, U79 = 1038), propulsive impulse (IMPU, t79 = 2.375), minimum value of vertical displacement for center of mass (SBCMmin, t79 = 3.135), and time difference (% of impulse time; ΔΤ) between the peak value of maximum force value (FUmax) and SBCMmin (U79 = 1188). Logistic regression showed that RFDDavg, impulse during the downward phase (IMPD), IMPU, and ΔΤ were all significant predictors. The model showed that soccer group membership could be strongly related to IMPU, with the odds ratio being 6.48 times higher from the basketball group, whereas RFDDavg, IMPD, and ΔΤ were related to basketball group. The results imply that soccer players execute CMJ differently compared to basketball players, exhibiting increased countermovement depth and impulse generation during the propulsive phase.

#12 Bio-banding in Academy Football: Player's Perceptions of a Maturity Matched Tournament
Reference: Ann Hum Biol. 2019 Jul 10:1-28. doi: 10.1080/03014460.2019.1640284. [Epub ahead of print]
Authors: Bradley B, Johnson D, Hill M, McGee D, Kana-Ah A, Sharpin C, Sharp P, Kelly A, Cumming SP, Malina RM
Summary: Individual differences in biological maturation impact player selection and development in youth football. The aim was to evaluate players perceptions of competing in a football tournament where they were matched by maturity rather than chronological age. Participants included male junior footballers from three professional academies (N = 115). The study employed multiple methods of analysis, including one sample means t-tests, equivalence tests, ANOVAs, and thematic analysis of qualitative data derived from open-ended questions. Player's perceived the bio-banding format as providing two main benefits. Early maturing players perceived greater physical and technical challenge, and in turn new opportunities and challenges. Late maturing players perceived less physical and technical challenge, yet greater opportunity to demonstrate technical and tactical abilities. The players reported that they enjoyed and understood the purpose of the bio-banded format, and perceived less risk for injury. Players in all three maturity groups reported more opportunity to engage in leadership behaviours, influence game-play, and express themselves on the ball in the bio-banded format. Bio-banding may facilitate development for both early and late maturing academy players by presenting new learning environments and challenges.

#13 The association between the isokinetic muscle strength and lower extremity injuries in young male football players
Reference: Phys Ther Sport. 2019 Jun 29;39:76-81. doi: 10.1016/j.ptsp.2019.06.013. [Epub ahead of print]
Authors: Namazi P, Zarei M, Hovanloo F, Abbasi H
Summary: Validating any screening test to predict and prevent football injuries is in need of identifying related risk factors through prospective designs. In spite of the extensive use of strength testing in football players, there are limited studies investigating the relationship between isokinetic muscle strength and injury risk in young football players. The present study aimed to evaluate the relationship between isokinetic strength and the risk of lower extremity injury among Iranian young football players. Seventy three U-21 football players participated in this study. Isokinetic strength of hip, knee and ankle muscles were measured using the Isokinetic system pro 4. Injuries and exposure in training and matches were registered prospectively by club medical staff for one season. Significant relationships were revealed between the isokinetic strength of hip abductor and adductor muscles, and isokinetic strength ratio of hip abductor/adductor muscles at an angular speed of 30°/sec, the isokinetic strength of hip abductor muscles at 90°/sec, and isokinetic strength of knee flexor and extensor muscles at 60°/sec and knee flexor/extensor strength ratio at angular velocities of 60°/sec with the injury occurrence among football players. Lower extremity isokinetic strength indices are associated with injuries in young male football players.

#14 A Lethal Blow to the Chest as an Underdiagnosed Cause of Sudden Death in United Kingdom Sports (Football, Cricket, Rugby)
Reference: Am J Cardiol. 2019 Jun 7. pii: S0002-9149(19)30629-0. doi: 10.1016/j.amjcard.2019.05.050. [Epub ahead of print]
Authors: Cooper S, Woodford NW, Maron BJ, Harris KM, Sheppard MN
Summary: Nonpenetrating blunt force trauma to the front of the chest can lead to commotio cordis, a cardiac rhythm disturbance, which can result in cardiac arrest and death. The condition is particularly noted during sport. No series of such cases has been published in the UK. This study is a retrospective analysis of a database of 6000 cases of sudden cardiac death examining commotio cordis in the setting of collapse and death shortly following a blow to the precordium where no structural heart disease was identified at autopsy. Of the 17 cases, 16 were male, and 11 were 18 years old or younger. Eleven occurred whilst playing sport while 6 involved physical interaction including assault. The most common circumstance of death involved a youth being struck in the chest by a ball during sporting activity. In conclusion, this study demonstrates that cases of commotio cordis in the UK follow a similar circumstantial and age profile to those reported in the United States, and indicates that ball sports such as football, cricket, and rugby expose young participants to a similar risk. There is currently no nation-wide registry of deaths occurring during sporting activity in the UK, and although the true incidence of this condition is not currently known, it is most probably under-recognised and underdiagnosed.





Latest research in football - week 26 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Changes in Lactate Kinetics Underpin Soccer Performance Adaptations to Cycling-Based Sprint Interval Training
Reference: Eur J Sport Sci. 2019 Jun 24:1-24. doi: 10.1080/17461391.2019.1635650. [Epub ahead of print]
Authors: Thom G, Kavaliauskas M, Babraj J
Summary: In adolescent soccer, 23% of the distance covers happens at speeds above onset of blood lactate accumulation which suggests that lactate kinetics may be important for soccer performance. We sought to determine the effectiveness of sprint interval training (SIT) on changing performance and lactate kinetics in adolescent soccer players. Thirteen elite soccer academy players (age 15 ± 0.5y) underwent baseline testing (0-10m and 10-20m sprint performance, Wingate anaerobic Test (WaNT) with blood lactate measurements and incremental VO2 peak test) before being allocated to control or SIT group. The control group maintained training whilst the HIT group carried out twice-weekly all-out effort cycle sprints consisting of 6 x 10sec sprint with 80sec recovery. There were significant time x group interactions for 10- 20m sprint time (Control pre: 1.32 ± 0.07s post: 1.35 ± 0.08s; SIT pre: 1.29 ± 0.04s post: 1.25 ± 0.04s; p=0.01), Peak Power (Control pre: 13.1 ± post: 13.2 ± 1.47; SIT pre: 12.4 ± 1.3 post: 15.3 ±; p=0.01) and time to exhaustion (Control pre: 596 ± 62s post: 562 ± 85s; SIT pre: 655 ± 54s post: 688 ± 55s; p=0.001). The changes in performance were significantly correlated to changes in lactate kinetics (power: r=0.55; 10-20m speed: r=-0.54; time to exhaustion: r=0.55). Therefore, cycle based SIT is an effective training paradigm for elite adolescent soccer players and the improvements in performance are associated with changes in lactate kinetics.

#2 The Validity and Reliability of Live Football Match Statistics From Champdas Master Match Analysis System
Reference: Front Psychol. 2019 Jun 11;10:1339. doi: 10.3389/fpsyg.2019.01339. eCollection 2019.
Authors: Gong B, Cui Y, Gai Y, Yi Q, Gómez MÁ
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Summary: The aim of the present study was to investigate the validity of match variables and the reliability of Champdas Master System used by trained operators in live association football match. Twenty professional football coaches voluntarily participated in the validation of match variables used in the System. Four well-trained operators divided into two groups that independently analyzed a match of Spanish La Liga. The Aiken's V averaged at 0.84 ± 0.03 and 0.85 ± 0.03 for the validation of indicators. The high Kappa values (Operator 1: 0.92, 0.90; Operator 2: 0.91, 0.88), high intra-class correlation coefficients (varied from 0.93 to 1.00), and low typical errors (varied from 0.01 to 0.34) between the first and second data collection represented a high level of intra-operator reliability. The Kappa values for the inter-operator reliability of were 0.97 and 0.89. The intra-class correlation coefficients and typical errors ranged from 0.90 to 1.00 and ranged from 0.01 to 0.24 for two independent operators within two data collections. The results suggest that the Champdas Master system can be used validly and reliably to gather live football match statistics by well-trained operators. Therefore, the data obtained by the company can be used by coaches, managers, researchers and performance analysts as valid match statistics from players and teams during their professional tasks and investigations.

#3 Coach Turnover in Top Professional Brazilian Football Championship: A Multilevel Survival Analysis
Reference: Front Psychol. 2019 Jun 6;10:1246. doi: 10.3389/fpsyg.2019.01246. eCollection 2019.
Authors: Tozetto AB, Carvalho HM, Rosa RS, Mendes FG, Silva WR, Nascimento JV, Milistetd M
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Summary: In this study, we examined the probability of coaches' survival in the top Brazilian professional football championship considering variation across the competitive seasons between 2012 and 2017, considering a multilevel framework. We also considered whether previous coaching experience in the top Brazilian professional football championship would change the probability of coaches' survival across the season. The data considered 4,560 games from the top professional Brazilian football league (Campeonato Brasileiro Série A) between the 2012 and 2017 seasons. At the start of each season, the coach from each team was followed, being recorded at the time the event occurred, i.e., the coach being sacked. A total survival of 120 coaches was considered between the seasons of 2012 and 2017, i.e., 20 coaches at the beginning of each season. Coaches were assigned as novice (no previous experience as head coach in the top Brazilian championship) or experienced (with at least some previous experience as head coach in the top Brazilian championship). Data were available and extracted from the official website of the Brazilian Football Confederation. On average and considering un-pooled observations, the median life of a coach was about 16.5 rounds. Considering variation between 2012 and 2017 seasons, only about 26.3% (95% CI: 18.2-36.1) of the coaches ended a season without being sacked. By mid-season, at round 19, the probability of coaches' survival was 0.42 (95% CI: 0.32-0.53). Variation between season on survival estimates per round was substantial (between-season standard deviation = 0.48, 95% credible intervals: 0.25-0.95; corresponding to an inverse logit = 0.62, 95% CI: 0.56-0.72). There was no substantial variation between novice and experienced coaches' survival probability. The present results expose the vulnerability of the coaching context in Brazilian football, potentially highlighting an excessive emphasis on short-term results to mediate club management decisions.

#4 Incidence and Prevalence of Borrelia burgdorferi Antibodies in Male Professional Football Players
Reference: Clin J Sport Med. 2019 May 30. doi: 10.1097/JSM.0000000000000758. [Epub ahead of print]
Authors: Breitbart P, Meister S, Meyer T, Gärtner BC
Summary: Infections with Borrelia burgdorferi can cause Lyme disease with multiorganic involvement such as (myo)carditis or joint manifestations. Musculoskeletal complaints possibly mimicking some of these symptoms are common among elite athletes. This study aimed to determine seroprevalence and incidence of B. burgdorferi antibodies in professional football players. Five hundred thirty-five men in the first and second German league participated in this study. Two screening assays were used to examine immunoglobulin M (IgM) and immunoglobulin G (IgG) against B. burgdorferi: an enzyme immunoassay (EIA) and a chemiluminescence assay (CLIA). In case of a positive or equivocal result, an immunoblot including in vivo antigens was performed. Course of IgM and IgG against B. burgdorferi in overall 1529 blood samples were used as outcome measures.  A total of 96.4% of all results were concordant between EIA and CLIA. Considering only samples with identical results in both assays, prevalence was 1.6%. A positive IgM was detected in 2.3%. No player showed any symptoms of Lyme disease. A seroconversion to IgG was not found. Three players developed a positive IgM corresponding to an incidence of 1032/100 000 person-years. Depending on the assay, 49% to 75% of positive or equivocal screening results could not be confirmed by immunoblot. Seroprevalence and incidence of B. burgdorferi among healthy male professional football players are low. Therefore, infections with B. burgdorferi have to be regarded a rare differential diagnosis in professional football in Central Europe. The low confirmation rate of positive screening assays points to an unspecific immune activation.

#5 Use of viscosupplementation for the recovery of active football players complaining of knee pain
Reference: Open Access J Sports Med. 2019 Jun 6;10:87. doi: 10.2147/OAJSM.S212442. eCollection 2019.
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#6 External Load Variables Affect Recovery Markers up to 72 h After Semiprofessional Football Matches
Reference: Front Physiol. 2019 Jun 4;10:689. doi: 10.3389/fphys.2019.00689. eCollection 2019.
Authors: Wiig H, Raastad T, Luteberget LS, Ims I, Spencer M
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Summary: Player tracking devices are commonly used to monitor external load from training and matches in team sports. Yet, how the derived external load variables relate to fatigue and recovery post-training or post-match is scarcely researched. The objective was, therefore, to investigate how external load variables affect recovery markers up to 72 h post-match. Semiprofessional players from six teams wore tracking devices during three experimental football matches. External load variables including individual playing duration, total distance, PlayerLoad™, high-intensity running, and high-intensity events were derived from the tracking devices, and blood samples and performance tests from 24-59 players were undertaken post-match. The effect of the external load variables on creatine kinase, myoglobin, and countermovement jump at 1, 24, 48, and 72 h, and 30-m sprint and Yo-Yo intermittent recovery tests level 1 at 72 h post-match, were modeled. Effects were gauged as two standard deviations of the external load and interpreted as the difference between a typical high-load and a typical low-load match. The effects were evaluated with 90% confidence intervals and magnitude-based inferences. High-intensity running had very likely substantial effects on creatine kinase and myoglobin (moderate factor increases of 1.5-2.0 and 1.3-1.6 respectively), while duration, total distance, and HIE showed small, likely substantial effects. PlayerLoad™ and total distance had likely substantial effects on 30-m sprint time (small increases of 2.1-2.6%). Effects on countermovement jump performance were generally non-substantial. Despite these relationships, the uncertainty was too large to predict the recovery of individual players from the external load variables. This study provides evidence that external load variables have an effect on recovery markers up to 72 h post-match. Hence, tracking external load in matches may be helpful for practitioners when managing training load and recovery strategies post-match. However, it is recommended that several different external load variables are monitored. Future research should continue to address the problem of predicting recovery from external load variables.

#7 Effect of biological maturation on strength-related adaptations in young soccer players
Reference: PLoS One. 2019 Jul 5;14(7):e0219355. doi: 10.1371/journal.pone.0219355. eCollection 2019.
Authors: Peña-González I, Fernández-Fernández J, Cervelló E, Moya-Ramón M
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Summary: Strength training is crucial for soccer players' long-term development at early ages and the biological maturation may influence specific strength-training adaptations. The aim of this study was to propose a strength-training programme for the strength development of pre-pubertal players and to analyse the adaptations to this training programme in players with different maturity status. One hundred and thirty young male soccer players participated in an 8-week strength-training programme consisting of two sessions per week (20-minutes of a combination of plyometric and resistance exercises) which was conducted prior to their normal soccer training. Three maturity groups were defined according to the years from/to their peak height velocity (PHV) as Pre-, Mid- and Post-PHV. Initial differences between the maturity groups were found in anthropometrical (weight and height) and physical performance variables (One Repetition Maximum (RM), Peak Power output (PP), 30-m sprint and T-test). The strength-training programme was beneficial for the three maturity groups (p< 0.05) with general greater improvements for the Pre- and Mid-PHV groups, with large effects in RM, PP and T-test, than for the Post-PHV group (moderate effects). The strength-training programme proposed in the present study seems to be positive for the strength-related development in young soccer players especially for Pre- and Mid-PHV players. The differences in the training adaptations for players with different maturity status suggest the individualization of the training stimulus for the correct long-term development of the players.

#8 Gender but not diabetes, hypertension or smoking affects infarct evolution in ST-elevation myocardial infarction patients - data from the CHILL-MI, MITOCARE

Reference: BMC Cardiovasc Disord. 2019 Jul 3;19(1):161. doi: 10.1186/s12872-019-1139-7.
and SOCCER trials.
Authors: Nordlund D, Engblom H, Bonnet JL, Hansen HS, Atar D, Erlinge D, Ekelund U, Heiberg E, Carlsson M, Arheden H
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Summary: Infarct evolution rate and response to acute reperfusion therapy may differ between patients, which is important to consider for accurate management and treatment of patients with ST-elevation myocardial infarction (STEMI). The aim of this study was therefore to investigate the association of infarct size and myocardial salvage with gender, smoking status, presence of diabetes or history of hypertension in a cohort of STEMI-patients. Patients (n = 301) with first-time STEMI from the three recent multi-center trials (CHILL-MI, MITOCARE and SOCCER) underwent cardiac magnetic resonance (CMR) imaging to determine myocardium at risk (MaR) and infarct size (IS). Myocardial salvage index (MSI) was calculated as MSI = 1-IS/MaR. Pain to balloon time, culprit vessel, trial treatments, age, TIMI grade flow and collateral flow by Rentrop grading were included as explanatory variables in the statistical model. Women (n = 66) had significantly smaller MaR (mean difference: 5.0 ± 1.5% of left ventricle (LV), p < 0.01), smaller IS (mean difference: 5.1 ± 1.4% of LV, p = 0.03), and larger MSI (mean difference: 9.6 ± 2.8% of LV, p < 0.01) compared to men (n = 238). These differences remained significant when adjusting for other explanatory variables. There were no significant effects on MaR, IS or MSI for diabetes, hypertension or smoking. Female gender is associated with higher myocardial salvage and smaller infarct size suggesting a pathophysiological difference in infarct evolution between men and women.

#9 Effects of Age on Physical Match Performance in Professional Soccer Players
Reference: J Strength Cond Res. 2019 Jul 1. doi: 10.1519/JSC.0000000000003244. [Epub ahead of print]
Authors: Rey E, Costa PB, Corredoira FJ, Sal de Rellán Guerra A
Summary: This study aimed to evaluate the effects of age using a large-scale analysis of match physical performance in professional soccer players. A total of 10,739 individual match observations were undertaken on outfield players competing in the first and second divisions of the Spanish soccer professional leagues during the 2017-2018 season, using a computerized tracking system (TRACAB, Chyronhego, New York, USA). The players were classified into five positions and into 5 age groups (<20 years, 20-24.9 years, 25-29.9 years, 30-34.9 years, and ≥35 years). The results showed that (a) professional soccer players aged ≥30 years exhibit a significant decrease (p < 0.01) in the total distance covered, medium-speed running distance, high-speed running (HSR) distance, very HSR (VHSR) distance, sprint distance, and maximum running speed compared with younger players (<30 years); (b) professional soccer players aged ≥35 years exhibit a significant decrease (p < 0.01) in the number of HSR, number of VHSR, and number of sprints compared with younger players (<35 years); and (c) all playing positions reduced their physical performance; however, external midfielders were less affected by age effects. In conclusion, this study demonstrates players' physical match performance reduces with increasing age. Such findings may help coaches and managers to better understand the effects of age on match-related physical performance and may have the potential to assist in decisions regarding recruitment and player list management within professional soccer clubs.

#10 Biomechanical Associates of Performance and Knee Joint Loads During A 70-90° Cutting Maneuver in Subelite Soccer Players
Reference: J Strength Cond Res. 2019 Jul 1. doi: 10.1519/JSC.0000000000003252. [Epub ahead of print]
Authors: McBurnie AJ, DosʼSantos T, Jones PA
Summary: The aim of this study was to explore the "performance-injury risk" conflict during cutting, by examining whole-body joint kinematics and kinetics that are responsible for faster change-of-direction (COD) performance of a cutting task in soccer players, and to determine whether these factors relate to peak external multiplanar knee moments. 34 male soccer players (age: 20 ± 3.2 years; body mass: 73.5 ± 9.2 kg; height: 1.77 ± 0.06 m) were recruited to investigate the relationships between COD kinetics and kinematics with performance and multiplanar knee joint moments during cutting. Three-dimensional motion data using 10 Qualisys Oqus 7 infrared cameras (240 Hz) and ground reaction force data from 2 AMTI force platforms (1,200 Hz) were collected to analyze the penultimate foot contact and final foot contact (FFC). Pearson's or Spearman's correlations coefficients revealed performance time (PT), peak external knee abduction moment (KAM), and peak external knee rotation moment (KRM) were all significantly related (p < 0.05) to horizontal approach velocity (PT: ρ = -0.579; peak KAM: ρ = 0.414; peak KRM: R = -0.568) and FFC peak hip flexor moment (PT: ρ = 0.418; peak KAM: ρ = -0.624; peak KRM: ρ = 0.517). Performance time was also significantly (p < 0.01) associated with horizontal exit velocity (ρ = -0.451) and, notably, multiplanar knee joint loading (peak KAM: ρ = -0.590; peak KRM: ρ = 0.525; peak KFM: ρ = -0.509). Cohen's d effect sizes (d) revealed that faster performers demonstrated significantly greater (p < 0.05; d = 1.1-1.7) multiplanar knee joint loading, as well as significantly greater (p < 0.05; d = 0.9-1.2) FFC peak hip flexor moments, PFC average horizontal GRFs, and peak knee adduction angles. To conclude, mechanics associated with faster cutting performance seem to be "at odds" with lower multiplanar knee joint loads. This highlights the potential performance-injury conflict present during cutting.

#11 A retrospective study of mechanisms of anterior cruciate ligament injuries in high school basketball, handball, judo, soccer, and volleyball
Reference: Medicine (Baltimore). 2019 Jun;98(26):e16030. doi: 10.1097/MD.0000000000016030.
Authors: Takahashi S, Nagano Y, Ito W, Kido Y, Okuwaki T
Summary: The purpose of this study was to analyze the mechanism of anterior cruciate ligament (ACL) injuries among male and female high school students across several different sports to understand ACL injury trends.A total of 1000 cases involving high school students who suffered ACL injuries during school activities (soccer, basketball, volleyball, handball, and judo) and who received insurance benefits through the Injury and Accident Mutual Aid Benefit System, were included to clarify the various mechanisms of ACL injuries. The mechanism of ACL injury was divided into contact and non-contact injuries. Contact injuries were further divided into direct and indirect contact injuries. Non-contact ACL injuries were also further divided into landing injuries, which involved jump-landing movements, and cutting and stopping injuries, which involved movement with a change of direction and deceleration.Overall, 99.0% of judo ACL injuries were categorized as contact ACL injuries. With regards to ball sports, the number of non-contact ACL injuries among basketball, volleyball, and handball players was significantly higher than the number of contact injuries (67.0%, 86.5%, and 68.5% respectively). With regards to female soccer and basketball players, the number of indirect ACL injuries was higher than direct injuries (72.2% and 76.7%, respectively).Volleyball was associated with a higher rate of non-contact injuries. Soccer, basketball, and handball were associated with more or similar rates of indirect and non-contact injuries than direct injuries. Judo was associated with a higher rate of contact injuries.

#12 Self-reported head injury symptoms exacerbated in those with previous concussions following an acute bout of purposeful soccer heading
Reference: Res Sports Med. 2019 Jun 30:1-14. doi: 10.1080/15438627.2019.1635130. [Epub ahead of print]
Authors: Kaminski TW, Thompson A, Wahlquist VE, Glutting J
Summary: Rates of concussion in soccer are high, especially in female players. The primary aim of this study was to examine differences in self-reported concussion-related symptoms (CRS), balance (BESS), and neurocognitive performance (ImPACT) following an acute bout of soccer heading in a group of female collegiate players with and without a history of concussion. Eighty-seven players with 0 to 3+ previous concussions participated. The measurement variables were assessed before and after heading sessions; including one linear and one rotational bout. Players with concussion histories reported more CRS than their non-concussed teammates both before and after the heading sessions. Balance and neurocognitive scores were generally unaffected. This finding should heighten our awareness to carefully monitor soccer players who have experienced concussions and be aware that they may develop concussion-like symptoms, especially after acute bouts of heading either during practice or in matches. The long-term implications of this finding remain unknown.





Latest research in football - week 25 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Correction: Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football
Reference: PLoS One. 2019 Jun 19;14(6):e0218865. doi: 10.1371/journal.pone.0218865. eCollection 2019.
Authors: Thomson A, Whiteley R, Wilson M, Bleakley C.
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#2 Growing Pains: Maturity Associated Variation in Injury Risk in Academy Football
Reference: Eur J Sport Sci. 2019 Jun 19:1-21. doi: 10.1080/17461391.2019.1633416. [Epub ahead of print]
Authors: Johnson DM, Williams S, Bradley B, Sayer S, Murray Fisher J, Cumming S
Summary: Reducing injuries to youth players is of primary importance to academies, as injuries can result in a significant loss in both training and match time, as well as negatively affecting player development. In total, 76 talented young football players were analysed over two full competitive seasons. The injury incidence and burden for all non-contact and overuse injuries were recorded. Exposure was calculated as the total number of competitive matches hours played. Somatic maturation was estimated by expressing the current height of each player as a percentage of their predicted adult height (Roche, Tyleshevski, & Rogers, 1983). The period of circa-peak height velocity (PHV) (24.5 injuries per 1000 h) was associated with a significantly higher injury incidence rate and burden compared to pre-PHV (11.5 injuries per 1000 h; RR:2.15, 95%CI:1.37-3.38, P < .001). No significant differences in injury risk between maturity timing groups were observed. The interaction effect between maturity status and maturity timing confirmed there is a risk period circa-PHV, but this was not dependent on maturity timing. The main practical application of this study is that football academies should regularly assess the maturity status of young footballers to identify those players with increased susceptibility to injury. Moreover, academies should individualise training and injury prevention strategies based on maturation.

#3 Epidemiological Study on Professional Football Injuries During the 2011 Copa America, Argentina
Reference: Rev Bras Ortop. 2013 Jun 20;48(2):131-136. doi: 10.1016/j.rboe.2012.09.003. eCollection 2013 Mar-Apr.
Authors: Pedrinelli A, Filho GARDC, Thiele ES, Kullak OP
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Summary: Develop an epidemiological study of injuries occurred among male professional football players during the Copa America 2011, held in Argentina. We conducted a retrospective study of injuries sustained during the 43rd edition of the Copa America football in Argentina, in 2011. The lesions were evaluated by the medical department of the selections and reported to the CONMEBOL. The data were compiled and reported in accordance with rules established by the FIFA Medical Assessment and Research Centre (F-MARC) in 2005. There was a higher prevalence of lesions in the lower limbs. Thighs and knees were the most affected segments. The most frequent diagnoses were muscle injuries. The injuries were mostly minor degrees of severity and there was little difference in the prevalence of lesions according to the stages of the match, with slight predominance in the final 15 minutes. The incidence of lesions per 1,000 game hours was similar to the average found in the literature. The results obtained allowed us to outline a profile of the prevalence, distribution per body segment, minute in which occurred and severity of injuries in professional football players of participating teams in the Copa America 2011 in Argentina. The extreme rigor of referees may be partly attributed to the highly competitive nature of international tournaments. However, this results cannot be considered definitive because of the need to be compared to other epidemiological studies with same design using similar concepts and criteria.

#4 Every second retired elite female football player has MRI evidence of knee osteoarthritis before age 50 years: a cross-sectional study of clinical and MRI outcomes
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Jun 17. doi: 10.1007/s00167-019-05560-w. [Epub ahead of print]
Authors: Prien A, Boudabous S, Junge A, Verhagen E, Delattre BMA, Tscholl PM
Summary: The purpose was to assess knee health in retired female football players, using magnetic resonance imaging (MRI) and self-report. The focus of analysis were degenerative changes of the tibiofemoral joint, and their relationship to osteoarthritis symptoms and previous knee injury. Forty-nine retired elite, female football players (98 knees) aged 37 years on average participated. Tibiofemoral cartilage and meniscus status of both knees were evaluated using MRI and graded according to modified Outerbridge and Stoller classifications, respectively. Symptoms were assessed through a standardised questionnaire (Knee Osteoarthritis Outcome Score: KOOS). Knee injury history was recorded via a semi-structured interview. To investigate how injury variables relate to outcomes, binary logistic regression models were used and reported with odds ratios (OR). Fifty-one per cent of players (n = 25) fulfilled the MRI criterion for knee osteoarthritis, 69.4% (n = 34) had substantial meniscal loss and 59.6% (n = 28) reported substantial clinical symptoms. Chondral- and meniscal loss were associated with significantly lower scores on three of five KOOS subscales (p < .05). Both chondral and meniscal loss were significantly predicted by previous traumatic knee injury (OR = 4.6, OR = 2.6), the injury affecting the non-striking leg (OR = 8.6, OR = 10.6) and type of injury; participants with combined ACL/meniscus injuries had the highest risk for substantial chondral and meniscal loss (OR = 14.8, OR = 9.5). Chondral loss was significantly predicted by isolated meniscus injury treated with partial meniscectomy (OR = 5.4), but not by isolated reconstructed ACL injury. Clinical symptoms were only significantly predicted by previous traumatic knee injury (OR = 5.1). Serious degenerative changes were found in a high number of retired female football players' knees 10 years after their career. Meniscal integrity is key for knee osteoarthritis outcomes in young adults, and thus, its preservation should be a priority.

#5 Quantifying the physical loading of five weeks of pre-season training in professional soccer teams from Dutch and Portuguese leagues
Reference: Physiol Behav. 2019 Jun 24;209:112588. doi: 10.1016/j.physbeh.2019.112588. [Epub ahead of print]
Authors: Clemente FM, Seerden G, van der Linden CMI
Summary: The purpose of this study was to quantify the physical loads of programmed pre-season training in four different professional Dutch and Portuguese soccer teams. Eighty-nine professional players were monitored daily during a five-week period. We monitored the physical loading of training by measuring the external load measures of total distance covered, walking distance, jogging distance, running distance, sprinting distance, high-intensity sprint distance, player's load and number of sprints using a 10 Hz GPS technology. Weekly external load and intra-week external load variations were tested. Repeated measures did not show significant differences between weeks in terms of weekly loads based on total distance and sprinting distance. Significant differences were found between training days considering the duration (p = .011), walking distance (p = .017), running distance (p = .004), player's load (p = .040) and number of sprints (p = .006). Variations between weeks were small, however intra-week variations were observed namely considering the measures associated with great volume and lower intensity.

#6 Technical and tactical performance indicators discriminating winning and losing team in elite Asian beach soccer tournament
Reference: PLoS One. 2019 Jun 27;14(6):e0219138. doi: 10.1371/journal.pone.0219138. eCollection 2019.
Authors: Muazu Musa R, P P Abdul Majeed A, Abdullah MR, Ab Nasir AF, Arif Hassan MH, Mohd Razman MA
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Summary: The present study aims to identify the essential technical and tactical performance indicators that could differentiate winning and losing performance in the Asian elite beach soccer competition. A set of 20 technical and tactical performance indicators namely; shot back-third, shot mid-third, shot front-third, pass back-third, pass mid-third, pass front-third, shot in box, shot outbox, chances created, interception, turnover, goals scored 1st period, goals scored 2nd period, goals scored 3rd period, goals scored extra time, tackling, fouls committed, complete save, incomplete save and passing error were observed during the beach soccer Asian Football Confederation tournament 2017 held in Malaysia. A total of 23 matches from 12 teams were notated using StatWatch application in real-time. Discriminant analysis (DA) of standard, backward as well stepwise modes were used to develop a model for the winning (WT) and losing team (LT) whilst Mann-Whitney U test was utilized to ascertain the differences between the WT and LT with respect to the performance indicators evaluated. The standard backward, forward and stepwise discriminates the WT and the LT with an excellent accuracy of 95.65%, 91.30% and 89.13%, respectively. The standard DA model discriminated the teams from seven performance indicators whilst both the backward and forward stepwise identified two performance indicators. The Mann-Whitney U test analysis indicated that the WT is statistically significant from the LT based on the performance indicators determined from the standard mode model of the DA. It was demonstrated that seven performance indicators namely; shot front-third, pass front-third, chances created, goals scores at the 1st period, goals scored at the 2nd period, goals scored at 3rd period were directly linked to a successful performance whilst the incomplete save by the keeper attribute towards the poor performance of the team. The present finding could serve useful to the coaches as well as performance analysts as a measure of profiling successful performance and enables team improvement with respect to the associated performance indicators.

#7 Post-activation Potentiation: Effects of Different Conditioning Intensities on Measures of Physical Fitness in Male Young Professional Soccer Players
Reference: Front Psychol. 2019 Jun 6;10:1167. doi: 10.3389/fpsyg.2019.01167. eCollection 2019.
Authors: Petisco C, Ramirez-Campillo R, Hernández D, Gonzalo-Skok O, Nakamura FY, Sanchez-Sanchez J
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Summary: The aim of this study was to compare the effects of different warm-up conditioning intensities on the physical fitness (i.e., post-activation potentiation -PAP), of professional male field soccer players. Athletes (n = 10; age: 21.6 ± 3.2 years) completed a control warm-up and warm-ups aimed to induce PAP, in random and counterbalanced order. After control and experimental warm-up sessions participants completed a triple hop test with the dominant (H3Jd) and a non-dominant (H3Jnd) leg, a squat jump (SJ), a countermovement jump (CMJ), a change of direction ability (COD) test, a repeated sprint with a COD (RSCOD) test and a linear 30-m sprint test (S-30). The control warm-up (WU) protocol was designed according to athlete's regular warm-up practice. The experimental warm-ups included the same exercises as the WU, with addition of one set of half-back squats for 10 repetitions at 60%, 5 repetitions at 80%, and 1 repetition at 100% of 1RM (60%-1RM, 80%-1RM and 100%-1RM, respectively.) Threshold values for Cohen's effect sizes (ES) were calculated and used for group's comparison. Likely to most likely improvements were shown in H3Jd (ES = 0.52), H3Jnd (ES = 0.51), COD (ES = 0.38), fasted sprint (RSCODb) (ES = 0.58) and the total time of all sprints (RSCODt) (ES = 0.99) only after the 80%-1RM protocol in comparison to the WU. Conversely, 100%-1RM and 60%-1RM protocols, compared to WU, induced possibly to most likely poorer performance in all jumps, COD and RSCODb (ES = -0.07 to -1.03 and ES = -0.48 to -0.91, respectively). Possibly to most likely improvements were shown in all jumps, COD, RSCODb and RSCODt after the 80%-1RM warm-up protocol in comparison to the 100%-1RM and 60%-1RM warm-up protocols (ES = 0.35 to 2.15 and ES = 0.61 to 1.46, respectively). A moderate warm-up intensity (i.e., 80%-1RM back squat) may induce greater PAP, including improvements in jumping, repeated and non-repeated change of direction speed in male soccer players.

#8 The Effect of Phase Change Material on Recovery of Neuromuscular Function Following Competitive Soccer Match-Play
Reference: Front Physiol. 2019 Jun 6;10:647. doi: 10.3389/fphys.2019.00647. eCollection 2019.
Authors: Brownstein CG, Ansdell P, Škarabot J, McHugh MP, Howatson G, Goodall S, Thomas K
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Summary: Cryotherapy is commonly implemented following soccer match-play in an attempt to accelerate the natural time-course of recovery, but the effect of this intervention on neuromuscular function is unknown. The aim of the present study was to examine the effect of donning lower-body garments fitted with cooled phase change material (PCM) on recovery of neuromuscular function following competitive soccer match-play. Using a randomized, crossover design, 11 male semi-professional soccer players wore PCM cooled to 15°C (PCMcold) or left at ambient temperature (PCMamb; sham control) for 3 h following soccer match-play. Pre-, and 24, 48, and 72 h post-match, participants completed a battery of neuromuscular, physical, and perceptual tests. Maximal voluntary contraction force (MVC) and twitch responses to electrical (femoral nerve) and magnetic (motor cortex) stimulation (TMS) during isometric knee-extension and at rest were measured to assess central nervous system (CNS) (voluntary activation, VA) and muscle contractile (quadriceps potentiated twitch force, Qtw,pot) function. Fatigue and perceptions of muscle soreness were assessed via visual analog scales, and physical function was assessed through measures of jump [countermovement jump (CMJ) height and reactive strength index (RSI)] performance. A belief questionnaire was completed pre- and post-intervention to determine the perceived effectiveness of each garment. Competitive soccer match-play elicited persistent decrements in MVC, VA measured with femoral nerve stimulation, Qtw,pot, as well as reactive strength, fatigue and muscle soreness (P < 0.05). Both MVC and VA were higher at 48 h post-match after wearing PCMcold compared with PCMamb (P < 0.05). However, there was no effect of PCM on the magnitude or time-course of recovery for any other neuromuscular, physical function, or perceptual indices studied (P > 0.05). The belief questionnaire revealed that players perceived that both PCMcold and PCMamb were moderately effective in improving recovery, with no difference between the two interventions (P = 0.56).: Although wearing cooled PCM garments improved MVC and VA 48 h following match-play, the lack of effect on measures of physical function or perceptual responses to match-play suggest that PCM offers a limited benefit to the recovery process. The lack of effect could have been due to the relatively small magnitude of change in most of the outcome measures studied.

#9 What Frequency of Technical Activity Is Needed to Improve Results? New Approach to Analysis of Match Status in Professional Soccer
Reference: Int J Environ Res Public Health. 2019 Jun 25;16(12). pii: E2233. doi: 10.3390/ijerph16122233.
Authors: Konefał M, Chmura P, Rybka K, Chmura J, Huzarski M, Andrzejewski M
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Summary: The aim of the research detailed here has been to assess the frequency with which football players engage in technical activity of various different types, in relation to seven phases of a game associated with changes in match status. To this end, 2016-2017 domestic-season matches in Germany's Bundesliga were analyzed, the relevant data being retrieved using an Opta Sportsdata Company system. Technical activity taken into consideration included shots, passes, ball possession, dribbles, and tackles. It was found that there was a large impact of frequency of shots on target (H = 466.999(6); p = 0.001) in relation to the different match-status phases. Furthermore, moderate effect sizes were then obtained for frequency of shots (H = 187.073(6); p = 0.001), frequency of passes (H = 133.547(6); p = 0.001), and percentage of ball possession (H = 123.401(6); p = 0.001). The implication would be that a team trying to change the match score of a game experienced at a given moment in a more favorable direction will need to raise the frequency and accuracy of passes, the percentage of ball possession, and the percentage of tackles ending in success. The maintenance of a winning match status requires a high frequency of occurrence of shots and shots on target as well as greater frequency and effectiveness of dribbling. The main finding from our work is that consideration of the consequences of a game presented in relation to seven potential phases to match status can point to a novel approach to analysis.

#10 Relationships Among Circuit Training, Small-Sided and Mini Goal Games, and Competition in Professional Soccer Players: A Comparison of On-Field Integrated Training Routines
Reference: J Strength Cond Res. 2019 Jul;33(7):1887-1896. doi: 10.1519/JSC.0000000000002804.
Authors: Giménez JV, Gomez MA
Summary: The aim of this study was to investigate and compare different physical variables and load indicators of 2 small-sided game (SSG) formats and ball circuit training (CT). Fourteen professional players participated in 3 training routines using a similar occupied area per player (90 m). The CT, SSGs, and mini goal games (MGs) consisted of 8 repetitions of 4-minute game play, interspersed by 2 minutes of active recovery, and data were compared with the first 32 minutes of 2 competitive match simulations (MS). All movement patterns from walking to sprinting were recorded using 10-Hz global positioning system devices, whereas player perception of exertion was recorded after trial using a visual analogue scale. Practical differences among the 3 drills and MS were analyzed using magnitude-based inferences. The results suggested that the training routines did not exactly replicate the movement patterns of a competitive match. Furthermore, this study provides evidence that if high-intensity play is preferred, then SSGs should be emphasized (because they provide more total accelerations compared with the other drills; most likely effects). Moreover, the CT showed lower load and distance covered (m) than the MGs and SSGs. In conclusion, these drills may be useful for competition and impact microcycles (i.e., intermittent efforts with accelerations, decelerations, and walking actions) to achieve the specific adaptations of high-intensity efforts.

#11 Are two different speed endurance training protocols able to affect the concentration of serum cortisol in response to a shuttle run test in soccer players?
Reference: Res Sports Med. 2019 Jun 25:1-9. doi: 10.1080/15438627.2019.1635131. [Epub ahead of print]
Authors: Vitale JA, Povìa V, Belli E, Lombardi G, Banfi G, La Torre A
Summary: Soccer involves multiple high-intensity physical, technical and tactical actions; as result of this, soccer training must include high-intensity exercises, which can act as a stimulus to the hypothalamus pituitary-adrenal axis, resulting in a significant increase in circulating cortisol levels. This study examined the effect of 4 weeks of Speed Endurance Maintenance (SEM) and Speed Endurance Production (SEP) on the serum cortisol concentration in response to a 5-meter multiple shuttle run test (5-m MST) in young elite soccer players. Fifteen soccer players were divided to SEM (n = 7) or SEP (n = 8) training group. Blood drawings were performed four times: before and after the 5-m MST at baseline (T1a, T1b) and at follow-up (T2a, T2b). Both training regimes determined a cortisol secretion following the 5-m MST at both baseline and follow-up. Data on delta values highlighted that SEP had greater values than SEM at baseline and registered a significant decrease at the follow-up. This difference is probably due to the lack of specific speed endurance training for players of SEP group prior to the beginning of the protocol. The physiological mechanisms behind the observed biological differences should be deeply investigated.

#12 Design and evaluation of sound-based electronic football soccer training system for visually impaired athletes
Reference: Biomed Eng Online. 2019 Jun 24;18(1):76. doi: 10.1186/s12938-019-0695-5.
Authors: Yandun F, Auat Cheein FA, Lorca D, Acevedo O, Auat Cheein C
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Summary: Several countries encourage the practice of football for rehabilitation and social inclusion purposes. For visually impaired people, football is purely sound-based, where the ball and the players are constantly emitting sounds for localization purposes in the field. However, the task of shooting the ball requires of a non-visually impaired extra person, behind the goal (known as caller), whom is punching the four corner of such goal to help the athletes. The presence of the caller restricts the self-sufficiency of the players. This work addresses such problem, by presenting a goal for visually impaired players with the aim of enhancing their self-sufficiency. The electronic goal is designed with four functionalities for training purposes, by returning sound-based feedback of its position and the places where the ball has impacted. The system is validated with seven volunteers from Chilean Football Soccer National Team. A questionnaire was answered by the players before and after the tests to statically validate the proposed device. The presented system is portable and designed following a modular criterion suitable for visually impaired people self-assembling. From a test of 350 shootings, the electronic goal showed to enhance the shooting assertiveness from 82 to 92%, and the accuracy from 20 to 56% compared to the traditional caller. The electronic goal showed to enhance the self-sufficiency of athletes, by improving their assertiveness in shooting training. Nevertheless, and according to the responses to the questionnaires, the system needs improvements in its portability and handling.






Latest research in football - week 24 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Assessment of a Nutrition Intervention on the Nutrition Knowledge, of Adolescent Soccer Academy Players
Reference: Curr Dev Nutr. 2019 Jun 13;3(Suppl 1). pii: nzz050.P16-044-19. doi: 10.1093/cdn/nzz050.P16-044-19. eCollection 2019 Jun.
Authors: Ray S, Mounce CD, Gonzalez-Rodenas J, Prieto MS, Brannan R
Summary: National surveys found that adolescents in America often fail to meet dietary recommendations probably due to lack of nutrition knowledge, giving rise to chronic diseases such as obesity, coronary heart diseases and type 2 diabetes. Knowledge about sports nutrition is considered essential for adolescent athletes to have healthy eating habits. It would help maximize their performance. The aim of the study was to assess the nutrition knowledge of adolescent soccer players pre and post a nutrition education intervention. A study was conducted on the youth academy level soccer players (n = 21) from three age groups (U19, U17, U15), to determine their nutrition knowledge using a validated Nutrition Knowledge Questionnaire. From the completed questionnaire, on factors like energy refueling, hydration, supplements and protein, a knowledge score was calculated for each athlete ranging from 0 (0%) to 16 (100%). The players participated in a nutrition education intervention for 5 months, consisting of monthly nutritional education newsletters, electronic handouts and one-hour nutrition lesson in the form of jeopardy game and nutrition education workshop for the players and their parents. Following the intervention, they filled out the same questionnaire again. From their responses, pre- and post-intervention, we found that at baseline, nutrition knowledge was highest in the U19 team as 44% of the responses were correct, lesser for the U17 team (25%) and least for the U15 team (6%). However, the intervention only produced a 6% increase in nutrition knowledge in the U19 while the intervention produced a 19% increase in the U17 team and a 44% increase in the U15 team. There was significant improvement in the category under supplements which asked whether it was better to get vitamins and minerals from supplements than from foods (P = 0.002). There was no significant difference in improvement of protein knowledge after the intervention in any group. The study shows that the nutrition education intervention was most effective for the younger players. Overall, more nutrition education, especially in the area of proteins, would be required for these players to increase their nutrition knowledge so that they know the type of food they should select and understand the importance of healthy eating.

#2 Evolution of technical activity in various playing positions, in relation to match outcomes in professional soccer
Reference: Biol Sport. 2019 Jun;36(2):181-189. doi: 10.5114/biolsport.2019.83958. Epub 2019 Apr 25.
Authors: Konefał M, Chmura P, Zając T, Chmura J, Kowalczuk E, Andrzejewski M
Summary: The study presented below aimed to examine the position-specific evolution of technical activity among soccer players and how it is related to match outcomes over three consecutive domestic seasons in Germany's Bundesliga. The research was based on a sample of 13,032 individual match observations of 556 soccer players during the 2014/2015, 2015/2016 and 2016/2017 seasons. These players were classified into five positional roles: central defenders (CD), full-backs (FB), central midfielders (CM), wide midfielders (WM) and forwards (F). The activity of the players was analysed using the Impire AG motion analysis system. Our study indicates that over the course of the three seasons: 1) the total numbers of shots by CMs decreased in the case of won or drawn matches; 2) the number of passes by CD players increased in matches won, and by CM and WM players in matches won, drawn and lost, whereas percentage pass accuracy increased at the CM position in won and drawn matches; 3) players at each position engaged in a substantially smaller number of duels, no matter what the match outcome, while the percentage of encounters won in subsequent seasons decreased among CD, and increased among WM in matches won and at F positions in both won and drawn matches. This research clearly shows that the evolution of technique among professional soccer players is heading in the direction of increased accuracy, with a simultaneous stabilisation of, or even a decline in, the number of activities engaged in.

#3 Influence of warm-up duration on perceived exertion and subsequent physical performance of soccer players
Reference: Biol Sport. 2019 Jun;36(2):125-131. doi: 10.5114/biolsport.2019.81114. Epub 2019 Jan 11.
Authors: Yanci J, Iturri J, Castillo D, Pardeiro M, Nakamura FY
Summary: The aim of this study was to analyse the effects of three warm-up protocols with different durations in semiprofessional soccer players. Fifteen semi-professional soccer players performed three warm-up protocols (Wup25min: 25 min, Wup15min: 15 min and Wup8min: 8 min duration) on three different days. Before (pre-test) and after (post-test) each warm-up protocol, the players' physical performance (sprint, vertical jump and change of direction) was evaluated and all the players were asked to respond to the subjective scale of readiness to play a match. Also, after completing each warm-up protocol, all players responded to the rating of perceived exertion (RPE) scale. Although all protocols significantly improved the feeling of players being prepared to play the game (p<0.05 or p<0.01), after performing the Wup25min protocol the players performed worse in the 10 m sprint (p<0.01) and in the 20 m sprint (p<0.05). However, the Wup8min protocol significantly improved performance in both the 10 m sprint (p<0.05) and the 20 m sprint (p<0.05). In addition, with the Wup25min protocol players stated a higher perceived exertion (RPE) (p < 0.05) than in the Wup15min and Wup8min protocols. The Wup8min protocol was the only one that improved the acceleration ability of the soccer players in this study.

#4 Sprint force-velocity profiles in soccer players: impact of sex and playing level
Reference: Sports Biomech. 2019 Jun 21:1-11. doi: 10.1080/14763141.2019.1618900. [Epub ahead of print]
Authors: Devismes M, Aeles J, Philips J, Vanwanseele B
Summary: This study aimed to assess potential differences in force-velocity (Fv) profiles in both male and female soccer players of different playing levels. One hundred sixty three soccer players (63 women and 100 men) competing from the Regional to the National Belgian league were recruited. The participants performed two maximal 60-m sprints monitored via a 312 Hz laser. For each participant, the theoretical maximal force (F0) and velocity (v0), maximal power (Pmax), maximal ratio of force (RF) and the slope of the Fv profile (Sfv) were computed. Male players in the highest competition level showed higher values for all the Fv variables compared to lower level groups (Effect size range: 1.01-1.97). Higher Pmax and v0 were observed in the female players of highest competition level compared to all other groups (ES range: 1.09-1.48). Female players showed more negative Sfv than male players (ES = 1.11), which suggests that male players' Fv profile is more velocity-oriented compared to female players. This study shows that the determinants of sprint performance increase with soccer playing level in both men and women, but that the contribution of each variable varies with sex.

#5 Vague Posterior Knee Discomfort in a Soccer Player: A Case Report
Reference: Am J Phys Med Rehabil. 2019 Jun 17. doi: 10.1097/PHM.0000000000001248. [Epub ahead of print]
Authors: Schroeder A, Onishi K
Summary: A 24-year-old male soccer player presented with a 7-year history of left posterior knee "looseness." Evaluation 7 years ago, at the time of initial injury, revealed atraumatic ACL and PCL sprains. On re-presentation, the patient described the pain as a constant, dull ache, 3/10, but his biggest complaint was this feeling of "instability" and "looseness" where his knee would "buckle" 3-4 times a week. Physical exam was positive for grade 1 posterior drawer and grade 1 posterior sag signs. Reverse KT-1000 testing showed a 3 mm side-to-side difference. Sonographic evaluation confirmed MRI findings of PCL laxity and buckling and a small cystic lesion abutting the posteromedial margin of the distal 1/3 of the PCL. After a trial of physical therapy, the patient elected to undergo experimental injection of dextrose hyperosmolar solution. This resulted in resolution of the cyst and reverse KT-1000 measurements improved to a side-to-side difference of 1 mm. The patient's subjective feeling of "looseness" and "instability" resolved by 7 weeks.

#6 Physical performance metrics in elite soccer: do power and acceleration metrics provide insight into positional demands and match-related fatigue in the 4-3-3 system?
Reference: J Sports Med Phys Fitness. 2019 Jun 19. doi: 10.23736/S0022-4707.19.09772-X. [Epub ahead of print]
Authors: Filetti C, Ruscello B, Ascenzi G, Di Mascio M, D'ottavio S
Summary: The aim of this study was to quantify power and acceleration metrics in elite soccer matches to gain an insight into positional demands and match-related fatigue patterns. Elite players (n = 212, observations = 522) were analysed during 50 matches of the Italian Serie A using a semi-automatic tracking system (K-Sport, Montelabbate, PU, Italy - Stats, Leeds, UK) during the 2015/16 season. A principal component analysis (PCA) was performed to find the latent variables that better explain the huge amount of data collected; an ANOVA was performed to find differences among positional roles and a mixed factorial analysis of mixed data (FAMD) was carried out to investigate the patterns of fatigue over time. Power and Acceleration were defined as the latent variables out of the 19 investigated that provided most of the variance (90.39%); significant differences among roles were found (p<0.05; Effect Size (ES) as ω2>0.14) and significant patterns of fatigue (p<0.05) with a moderate to large ES were observed over time in some of the key performance indicators. The data demonstrate that there are implications for developing power and acceleration in training sessions and assessing these components during a game. With the introduction of 'live streaming' of GPS data, the movement patterns could be observed in real time, and interchanges could be made before the onset of fatigue and before evident reductions in performance might be observed.

#7 The Effect of a Four-Month Training Program on Body Fat and Pulmonary Parameters of Young Soccer Players
Reference: Iran J Public Health. 2019 Feb;48(2):353-354.
Authors: Sermaxhaj S
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#8 Relation of injuries and psychological symptoms in amateur soccer players
Reference: BMJ Open Sport Exerc Med. 2019 Apr 24;5(1):e000522. doi: 10.1136/bmjsem-2019-000522. eCollection 2019.
Authors: Jansen P, Lehmann J, Fellner B, Huppertz G, Loose O, Achenbach L, Krutsch W
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Summary: The first main goal of this study was to investigate the prevalence of depression and anxiety as well as self-compassion in a heterogeneous sample of male amateur soccer players. The second main goal of this study was the examination of the relationship between injuries and psychological factors in amateur soccer players. Players were recruited from German amateur soccer clubs of the fourth to seventh league. 419 soccer players with the mean age of 22.88 years participated in the psychological and the injury assessment at the beginning of the season and at the end, 9 months later. For the psychological assessment, depression and anxiety rate as well as self-compassion was analysed. Furthermore, the frequencies of injuries were registered. The results showed that players of the highest amateur league, the fourth league in German soccer, showed significantly higher anxiety values than players from a lower league (p=0.013). There were no differences in depression values dependent on the league. Furthermore, players who suffered from an injury before the start of the season demonstrated higher anxiety values (p=0.027). This result was independent of the respective league. The results of this study demonstrate that even in higher amateur soccer the anxiety level of the players varies between soccer players of different leagues. Because an injury before the start of the season influenced the anxiety level, a psychological treatment during injury should be considered.

#9 Professional soccer player with an in-game ankle injury
Reference: Skeletal Radiol. 2019 Jun 16. doi: 10.1007/s00256-019-03253-6. [Epub ahead of print]
Authors: Iqbal A, McLoughlin E, Botchu R, James SL
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#10 Comparison of knee sonography and pressure pain threshold after anterior cruciate ligament reconstruction with quadriceps tendon versus hamstring tendon autografts in soccer players
Reference: Acta Orthop Traumatol Turc. 2019 Jun 12. pii: S1017-995X(18)30300-6. doi: 10.1016/j.aott.2019.04.012. [Epub ahead of print]
Authors: Martin-Alguacil JL, Arroyo-Morales M, Martin-Gómez JL, Lozano-Lozano M, Galiano-Castillo N, Cantarero-Villanueva I
Summary: The aim of this study was to compare the pressure pain threshold and muscle architecture after an anatomic single bundle reconstruction with quadriceps tendon and hamstring tendon autografts of the anterior cruciate ligament in competitive soccer players. We hypothesized that both procedures will obtain similar outcomes. Fifty-one participants were enrolled in this secondary analysis of a randomized controlled trial and were categorised into two groups: quadriceps tendon (QT) group (23 men and 3 women; mean age 18.7 ± 3.6; BMI 23.0 ± 2.2) or hamstring tendon (HT) group (16 men and 9 women; mean age 19.2 ± 3.6 BMI 23.5 ± 3.5). Both groups followed the same rehabilitation staged protocol. Pressure pain threshold (PPT), as a measure of perceived pain, was obtained in several points of quadriceps and hamstring muscles. Ultrasound imaging measurements were obtained in quadriceps tendon and knee cartilage thickness. Four measurements were taken in this study: baseline, 1, 3, 6, and 12 months after the anterior cruciate ligament (ACL) reconstruction. The analysis of PPT did not find significant differences in both groups × interaction time in the points evaluated: epicondyle (QT = 421.1 ± 184.1 vs HT = 384.7 ± 154.1 kPa), vastus lateralis (QT = 576.2 ± 221.3 vs HT = 560.1 ± 167.7 kPa), vastus medialis (QT = 544.7 ± 198.8 vs HT = 541.1.1 ± 181.77 kPa), patellar tendon (QT = 626.3 ± 221.1 vs HT = 665.0 ± 205.5 kPa), QT (QT = 651.1 ± 276.9 vs HT = 660.0 ± 195.2 kPa). (QT = 667.8 ± 284.7 vs HT = 648.2 ± 193.4 kPa) injured knee (all P > 0.05). The results of ultrasound imaging did not show significant differences in both groups × interaction time in the thickness of the QT (QT = 9.9 ± 2.4 vs HT = 9.4 ± 1.7 kPa) and patellar cartilage (QT = 3.2 ± 0.6 vs HT = 3.2 ± 0.4 kPa) (P > 0.05). A QT autograft produces similar results to a HT autograft in ACL reconstructions in terms of pressure pain threshold and ultrasound muscle architecture during the 1-year follow-up.

#11 Positional demands for various-sided games with goalkeepers according to the most demanding passages of match play in football
Reference: Biol Sport. 2019 Jun;36(2):171-180. doi: 10.5114/biolsport.2019.83507. Epub 2019 Mar 14.
Authors: Martin-Garcia A, Castellano J, Diaz AG, Cos F, Casamichana D
Summary: The main aim was to determine the differences between four training games and competitive matches (CM) according to position and compared to the most demanding passages (MDP) of competitive match play. Global Positioning System data were obtained from 21 football players belonging to the reserve squad of a Spanish La Liga club during the 2015/16 season. The training games were small-sided games (SSGs) with 5 and 6 and large-sided games with 9 and 10 outfield players per team. The players were categorized based on positional groups: full back (FB), central defender (CD), midfielder (MF), offensive midfielder (OMF), and forward (FW). The variables recorded were the distance covered (DIS), DIS at high speed (HSR; >19.8 km·h-1), DIS at sprint (SPR; >25.2 km·h-1), high metabolic load distance (HMLD; >25.5 W·kg-1) all in m·min-1, average metabolic power (AMP; W·kg-1) and number of high-intensity accelerations (ACC; >3 m·s-2) and decelerations (DEC; <-3 m·s-2), both in n·min-1. The MDP was analysed using a rolling average method for AMP as a criterion variable, where maximal values were calculated for time windows of 5 and 10 minutes of CM and after that compared with the training game formats. As the SSG format increases, all the rest of the variables increase and the number of cases with significant interposition differences also increases (effect size [ES]: DIS: 0.7-2.2; HSR: 0.7-2.1; SPR: 0.8-1.4; HMLD: 0.9-2.0; AMP: 0.8-1.9; ACC: 0.8-1.7; DEC: 0.5-1.7). The large-sided game 10v10 + 2 goalkeepers over-stimulates sprint values relative to MDP (all: 121.0% of MDP, ES=0.5-1.8). This study provides useful information for coaching staff on the heightened impact of different training game formats on physical load, considering positional differences in relation to the MDP of competitive match play.

#12 Relative pitch area plays an important role in movement pattern and intensity in recreational male football
Reference: Biol Sport. 2019 Jun;36(2):119-124. doi: 10.5114/biolsport.2019.81113. Epub 2019 Jan 11.
Authors: Pantelić S, Rađa A, Erceg M, Milanović Z, Trajković N, Stojanović E, Krustrup P, Randers MB
Summary: Recreational football has been shown to be an effective health-promoting activity, but it is still unclear how changes in game formats affect external and internal load. The aim of this study was therefore to evaluate the effect of area per player in recreational small-sided football games. Ten recreational active male football participants (mean±standard deviation, age: 20.1±1.1 years; height: 182.2±7.4 cm; body mass: 75.9±9.8 kg) completed two sessions comprising 2x20 min of 5v5 football with 80 and 60 m2 per player, during which heart rate (HR) and movement pattern were measured. In 80 m2, mean HR (167±9 vs. 160±10 b.p.m., P<0.001, ES=0.70) and peak HR (192±8 vs. 188±9 b.p.m., P=0.041, ES=0.50) were significantly higher than in 60 m2. Percentage playing time with HR >90%HRpeak was higher in 80 m2 than 60 m2 (45±14 vs. 29±16%, P=0.004, ES=1.07). Moreover, a higher number of sprints (8.0±4.8 vs. 3.0±1.3, P=0.014, ES=1.41) and a greater distance in the highest speed zones (>13, >16 and >20 km·h1) were covered in 80 m2 than 60 m2. Peak running speed was also higher in 80 m2 (24.3±1.7 vs. 22.3±1.4 km·h-1, P=0.011, ES=1.27), whereas no statistically significant differences were found in total distance covered, player load, or the acceleration-deceleration profiles. In conclusion, the internal and external loading was higher for recreationally active male football players when playing on a pitch with 80 m2 area per player compared to 60 m2.





Latest research in football - week 23 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Fundamental Motor Skills Mediate the Relationship Between Physical Fitness and Soccer-Specific Motor Skills in Young Soccer Players
Reference: Front Physiol. 2019 May 28;10:596. doi: 10.3389/fphys.2019.00596. eCollection 2019.
Authors: Kokstejn J, Musalek M, Wolanski P, Murawska-Cialowicz E, Stastny P
Summary: Fundamental motor skills (FMS) are the basic elements of more complex sport-specific skills and should be mastered at the end of early childhood; however, the relationship between FMS and sport-specific skills has not yet been verified in prepubertal soccer players. Therefore, the aim of this study was to determine the role of FMS in the process of acquiring soccer-specific motor skills (measured using speed dribbling) with regard to physical fitness and biological maturation. Forty male soccer players (11.5 ± 0.3 years of age) at the highest performance level participated in the study. The test of Gross Motor Development - second edition and Unifittest 6-60 were used to assess FMS and physical fitness, respectively. The role of FMS in a complex theoretical model with the relationships between physical fitness, biological maturation and speed dribbling was analyzed by multiple regression path analyses (MRPA). Moderate to strong correlations were found between FMS, physical fitness, and speed dribbling (r = 0.56-0.66). Biological maturation did not appear to be a significant predictor of physical fitness or speed dribbling. The MRPA model using FMS as mediator variable between physical fitness and speed dribbling showed a significant indirect effect (standard estimation = -0.31, p = 0.001; R 2 = 0.25). However, the direct correlation between physical fitness and speed dribbling was non-significant. Our results showed that FMS significantly strengthened the influence of physical fitness on the performance of speed dribbling, a soccer-specific motor skill, and thus play an important role in the process of acquiring sport-specific motor skills in prepubertal soccer players. When considering the long-term training process, especially during childhood and before puberty, a wide range of FMS activities should be applied for better and possibly faster acquisition of soccer-specific motor skills.

#2 Tart Cherry Juice: No Effect on Muscle Function Loss or Muscle Soreness in Professional Soccer Players After a Match
Reference: Int J Sports Physiol Perform. 2019 Jun 12:1-21. doi: 10.1123/ijspp.2019-0221. [Epub ahead of print]
Authors: Abbott W, Brashill C, Brett A, Clifford T
Summary: The purpose was to investigate the effects of tart cherry juice (TCJ) on recovery from a soccer match in professional players. In a double-blind, placebo-controlled, crossover design, 10 male professional soccer players from the reserve team of an English Premier League Club (age 19 ± 1 y, height 1.8 ± 0.6 m, body mass 77.3 ± 6.4 kg) consumed 2 × 30-mL servings of TCJ or an isocaloric cherry-flavored control drink (CON) before and after a 90-min match, and 12 and 36 h after the match. Muscle function (countermovement jump-height [CMJ], reactive strength index [RSI]), subjective well-being, and subjective muscle soreness (MS) were measured before and 12, 36, and 60 h after each match. CMJ height was similarly reduced in the days after the match after TCJ and CON supplementation, with the greatest loss occurring at 12 h postmatch (-5.9% ± 3.1% vs -5.4% ± 2.9% of baseline values, respectively; P = .966, ηp2 = .010). Decrements in RSI were also greatest at 12 h postmatch (TCJ -9.4% ± 8.4% vs CON -13.9% ± 4.8% of baseline values), but no group differences were observed at any time point (P = .097, ηp2 = .205). MS increased 12-60 h postmatch in both groups, peaking at 12 h postmatch (TCJ 122 ± 27 mm vs CON 119 ± 22 mm), but no group differences were observed (P = .808, ηp2 = .024). No interaction effects were observed for subjective well-being (P = .874, ηp2 = .025). Tart cherry juice did not hasten recovery after a soccer match in professional players. These findings bring into question the use of TCJ as a recovery aid in professional soccer players.

#3 Macronutrient Intake in Soccer Players-A Meta-Analysis
Reference: Nutrients. 2019 Jun 9;11(6). pii: E1305. doi: 10.3390/nu11061305.
Authors: Steffl M, Kinkorova I, Kokstejn J, Petr M
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Summary: The nutrition of soccer players is an important topic and its knowledge may help to increase the quality of this popular game and prevent possible health problems and injuries in players. This meta-analysis aims to estimate the current dietary trends of three basic macronutrients in junior and senior soccer players during the first two decades of the 21st century. We analyzed data from 647 junior players (mean age 10.0-19.3) from 27 groups, and 277 senior (mean age 20.7-27.1) players from 8 groups from altogether 21 papers in this meta-analysis. Weighted averages were calculated for each macronutrients. Protein intake is higher than recommended in both juniors, 1.9 95% confidence interval (CI) 1.8-2.0 g/kg/day, and seniors 1.8 95% CI 1.6-2.0 g/kg/day. However, carbohydrate intake is still below the recommended values in both groups (5.7 95% CI 5.5-5.9 g/kg/day in junior and 4.7 95% CI 4.3-5.0 g/kg/day in senior players). The proportion of fat as total energy intake is in concordance with the recommendations (31.5 95% CI 32.0-35.9% in junior and 33.1 95% CI 29.9-36.2% in senior players). In particular, due to possible health complications, the small carbohydrate intake should be alarming for coaches, nutritional experts, and parents.

#4 How anterior pelvic tilt affects the lower extremity kinematics during the late swing phase in soccer players while running: A time series analysis
Reference: Hum Mov Sci. 2019 Jun 5;66:459-466. doi: 10.1016/j.humov.2019.06.001. [Epub ahead of print]
Authors: Alizadeh S, Mattes K
Summary: Anterior pelvic tilt has been proposed to predispose the hamstring in soccer players to injury at the late swing phase during a sprint, however the mechanism on how the changes in the alignment would affect the kinematics are still unclear. Thirty-four male amateur soccer players were recruited for this study. Pelvic tilt was measured using the DIERS Formetric 4D. Lower extremity angles were recorded using an 8-camera Vicon motion capture system at 200 Hz while the athlete performed a high speed run on a motorised treadmill. Late swing phase was extracted from 5 running cycle which were later analysed using statistical parametric mapping (SPM). The results show that the increase of anterior pelvic tilt angle was significantly correlated with hip (r = -0.421 to -0.462, p = 0.015) and knee flexion (r = -0.424 to -0.472, p = 0.026) values. No other correlation was found between the anterior pelvic tilt and the angles at the coronal plane. By using time series analysis it was shown that the anterior pelvic tilt measured in a standing position would affect the adjacent segments' kinematics while running as suggested in the kinetic chain theory; which would potentially predispose the soccer athletes to hamstring injury by maintaining knee extension.

#5 Gaining or Losing Team Ball Possession: The Dynamics of Momentum Perception and Strategic Choice in Football Coaches
Reference: Front Psychol. 2019 May 28;10:1019. doi: 10.3389/fpsyg.2019.01019. eCollection 2019.
Authors: Briki W, Zoudji B
Summary: Grounded in the dynamical systems approach, the present research examined the influence of team ball possession (TBP) in soccer on coaches' perceived psychological momentum (PM) and strategic choice (i.e., game-based "stick" vs. "switch" choices) during a simulated match. Experienced soccer coaches imagined being the coach of the team involved in a highly important match that was displayed on a wall in a lecture hall. The match scenario was manipulated so that the coach was exposed to either a positive momentum sequence (i.e., ascending scenario of TBP) or a negative momentum sequence (i.e., descending scenario of TBP). Results revealed that positive (or negative) momentum sequence increased (or decreased) perceived PM and increased stick (or switch) choices. Perceived PM globally evolved linearly, while strategic choice displayed a dynamical pattern of "critical boundary" (thus showing a nonlinear change). Nonetheless, both variables displayed asymmetrical effects, in the sense that: (1) the strength of positive PM appeared to be easier to decrease than to increase; and (2) the greater the positive PM (or the negative PM), the lesser (or the greater) the coaches' tendency to make a change in the organization of their teams. This investigation evidences that TBP can powerfully influence coaches' perceptions and strategic decisions, and that coaches are more likely to be sensitive to negative events than to equivalent positive events.

#6 Time before return to play for the most common injuries in professional football: a 16-year follow-up of the UEFA Elite Club Injury Study
Reference: Br J Sports Med. 2019 Jun 10. pii: bjsports-2019-100666. doi: 10.1136/bjsports-2019-100666. [Epub ahead of print]
Authors: Ekstrand J, Krutsch W, Spreco A, van Zoest W, Roberts C, Meyer T, Bengtsson H
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Summary: The objective was to describe the typical duration of absence following the most common injury diagnoses in professional football. Injuries were registered by medical staff members of football clubs participating in the Union of European Football Association Elite Club Injury Study. Duration of absence due to an injury was defined by the number of days that passed between the date of the injury occurrence and the date when the medical team allowed the player to return to full participation. In total, 22 942 injuries registered during 494 team-seasons were included in the study. The 31 most common injury diagnoses constituted a total of 78 % of all reported injuries. Most of these injuries were either mild (leading to a median absence of 7 days or less, 6440 cases = 42%) or moderate (median absence: 7-28 days, 56% = 8518 cases) while only few (2% = 311 cases) were severe (median absence of >28 days). The mean duration of absence from training and competition was significantly different (p < 0.05) between index injuries and re-injuries for six diagnoses (Achilles tendon pain, calf muscle injury, groin adductor pain, hamstring muscle injuries and quadriceps muscle injury) with longer absence following re-injuries for all six diagnoses. The majority of all time loss due to injuries in professional football stems from injuries with an individual absence of up to 4 weeks. This article can provide guidelines for expected time away from training and competition for the most common injury types as well as for its realistic range.

#7 Keep Your Head Up-Correlation between Visual Exploration Frequency, Passing Percentage and Turnover Rate in Elite Football Midfielders
Reference: Sports (Basel). 2019 Jun 6;7(6). pii: E139. doi: 10.3390/sports7060139.
Authors: Phatak A, Gruber M
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Summary: Statistical analysis of real in-game situations plays an increasing role in talent identification and player recruitment across team sports. Recently, visual exploration frequency (VEF) in football has been discussed as being one of the important performance-determining parameters. However, until now, VEF has been studied almost exclusively in laboratory settings. Moreover, the VEF of individuals has not been correlated with performance parameters in a statistically significant number of top-level players. Thus, the objective of the present study was to examine the relationship between VEF and individual performance parameters in elite football midfielders. Thirty-five midfielders participating in the Euro 2016 championship were analyzed using game video. Their VEF was categorized into scans, transition scans, and total scans. Linear regression analysis was used to correlate the three different VEF parameters with the passing percentage and the turnover rate for individual players. The linear regression showed significant positive correlations between scan rate (p = 0.033, R 2 = 3.0%) and total scan rate (p = 0.015, R 2 = 4.0%) and passing percentage but not between transition scan rate and passing percentage (p = 0.074). There was a significant negative correlation between transition scan rate and turnover rate (p = 0.023, R 2 = 3.5%) but not between total scan rate (p = 0.857) or scan rate (p = 0.817) and turnover rate. In conclusion, the present study shows that players with a higher VEF may complete more passes and cause fewer turnovers. VEF explains up to 4% of variance in pass completion and turnover rate and thus should be considered as one of the factors that can help to evaluate players and identify talents as well as to tailor training interventions to the needs of midfielders up to the highest level of professional football.

#8 Tackling Similarity Search for Soccer Match Analysis: Multimodal Distance Measure and Interactive Query Definition
Reference: IEEE Comput Graph Appl. 2019 Jun 12. doi: 10.1109/MCG.2019.2922224. [Epub ahead of print]
Authors: Stein M, Janetzko H, Keim DA, Schreck T.
Summary: Analysts and coaches in soccer sports need to investigate large sets of past matches of opposing teams in short time to prepare their teams for upcoming matches. Thus, they need appropriate methods and systems supporting them in searching for soccer moves for comparison and explanation. For the search of similar soccer moves, established distance and similarity measures typically only take spatio-temporal features like shape and speed of movement into account. However, movement in invasive team sports such as soccer, includes much more than just a sequence of spatial locations. We propose an enhanced similarity measure integrating spatial, player, event as well as high level context such as pressure into the process of similarity search. We present a visual search system supporting analysts in interactively identifying similar contextual enhanced soccer moves in a dataset containing more than 60 soccer matches. Our approach is evaluated by several expert studies. The results of the evaluation reveal the large potential of enhanced similarity measures in the future.

#9 Inter-relationship between sleep quality, insomnia and sleep disorders in professional soccer players
Reference: BMJ Open Sport Exerc Med. 2019 Apr 24;5(1):e000498. doi: 10.1136/bmjsem-2018-000498. eCollection 2019.
Authors: Khalladi K, Farooq A, Souissi S, Herrera CP, Chamari K, Taylor L, El Massioui F
Summary: Insufficient sleep duration and quality has negative effects on athletic performance, injury susceptibility and athlete development. This study aimed to assess the sleep characteristics of professional Qatar Stars League (QSL) soccer players. In a cross-sectional study, QSL players (n=111; 23.7±4.8 years) completed three questionnaires to screen sleep disorders: (1) Pittsburgh Sleep Quality Index (PSQI), (2) Insomnia Severity Index (ISI) and (3) Epworth Sleepiness Scale (ESS). Poor sleep quality was defined as PSQI≥5, excessive daytime sleepiness was defined by ESS>8 and insomnia was defined as ISI≥11. The prevalence of poor sleep quality (PSQI≥5) was 68.5%, with subthreshold insomnia (ISI≥11) 27.0% and daytime sleepiness 22.5% (ESS>8). Sleep quality was positively associated with insomnia (r=0.42, p<0.001) and daytime sleepiness (r=0.23, p=0.018). Age, anthropometry, body composition and ethnicity were not associated with any of the reported sleep quality parameters. The prevalence of poor sleep quality (68.5%) reported should concern practitioners. Increasing awareness of the importance of sleep relative to athletic performance, recovery, injury and illness appears prudent. Further, regular qualitative/quantitative sleep monitoring may help target subsequent evidence-informed interventions to improve sleep in those demonstrating undesirable sleep traits.

#10 Competitive Psychological Disposition and Perception of Performance in Young Female Soccer Players
Reference: Front Psychol. 2019 May 22;10:1168. doi: 10.3389/fpsyg.2019.01168. eCollection 2019.
Authors: Olmedilla A, Ruiz-Barquín R, Ponseti FJ, Robles-Palazón FJ, García-Mas A
Summary: The athletes' psychological disposition is a factor that is increasingly considered by researchers as a key to sports performance, even as a mediator between the physical, technical and tactical abilities of the athlete and their competitive performance, thus acquiring great relevance in training and in sports performance. The purpose of this study is to analyze the psychological characteristics of young soccer players and their relation to their performance perception, made both by the player herself and by their coaches. The sample is composed of 108 women (M age = 15.53, SD age = 1.05), with ages between 13 and 17 years (13 years, n = 1, 14 years, n = 18, 15 years, n = 36, 16 years, n = 29, 17 years, n = 24), and with a sport practice experience of 7.27 years on average (SD = 2.64). For to address this aim, we used the Psychological Characteristics related to the Sport Performance Questionnaire (CPRD) and the Psychological Skills Inventory for Sports (PSIS). In addition, regarding the evaluation of performance perception, an ad hoc short questionnaire was created, composed by one question addressed to the player and one directed to the coach. The results indicate that the group of players of the under-16 category obtained higher scores in all the psychological dimensions than the U-18 players, showing significant differences in Team Cohesion (p < 0.048). Regarding the degree of congruence between the player's psychological features, and the player's and coach's performance perceptions, the results show statistically significant and negative correlations between the Team Cohesion factor and the athlete's own outcome perception for the match #1 (rxy = -0.479; p < 0.001), and match #2 (rxy = -0.402; p < 0.01). The results of this study may contribute to establish the differences between different constellations of psychological characteristics according to the categories of competition and their relationship with the perception of performance. This knowledge can be used by sports professionals: coaches, psychologists, physical educators, etc., in order to help athletes to reach their maximum performance.





Latest research in football - week 22 -2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 The Benefits of a Challenge Approach on Match Day: Investigating Cardiovascular Reactivity in Professional Academy Soccer Players
Reference: Eur J Sport Sci. 2019 Jun 6:1-32. doi: 10.1080/17461391.2019.1629179. [Epub ahead of print]
Authors: Dixon JG, Jones MV, Turner MJ
Summary: This study assessed physiological (cardiovascular) and psychological (confidence, control, and approach focus) data in professional academy soccer players prior to performance in competitive matches. A challenge state is characterised by an increase in cardiac output (CO), and a decrease in total peripheral vascular resistance (TPR). Data were collected from 37 participants, with 19 of these providing data on two separate occasions. Performance was measured using coach and player self-ratings. Challenge reactivity was positively, and significantly, associated with performance. Participants who demonstrated blunted cardiovascular (CV) responses performed significantly worse than participants who displayed either challenge or threat reactivity. There was mixed consistency in CV reactivity for those participants whose data were collected on more than one occasion, suggesting that some participants responded differently across the competitive matches. The association between self-report data and CV responses was weak. This study supports previous research demonstrating that challenge reactivity is associated with superior performance.

#2 First-Stance Phase Force Contributions to Acceleration Sprint Performance in Semi-Professional Soccer Players
Reference: Eur J Sport Sci. 2019 Jun 6:1-23. doi: 10.1080/17461391.2019.1629178. [Epub ahead of print]
Authors: Wdowski MM, Gittoes MJR
Summary: Sprint running is a key determinant of player performance in soccer that is typically assessed and monitored using temporal methods. The aim of this study was to examine the relationship between ground reaction force kinetics at the first step and sprint running performance in soccer players in order to enhance the development of training and assessment methods. Nineteen semi-professional soccer players participated (mean ± s: age 21.1 ± 1.9 years, body mass 79.4 ± 7.3 kg and stature 1.79 ± 0.06 m). The participants completed 20 m acceleration sprint runs as timing gates recorded split times between 0-5 m, 5-10 m, 10-15 m, 15-20 m and 0-20 m. A force plate captured vertical, anteroposterior and mediolateral ground reaction force data (1000 Hz) of the first right foot strike stance phase. Ground reaction force metrics, including peak anteroposterior propulsive force (r = 0.66 to 0.751; P = 0.000 to 0.002), peak vertical ground reaction force (r = 0.456 to 0.464; P = 0.045 to 0.05), average medial-lateral/anteroposterior orientation angle (r =-0.463; P = 0.023), and average anteroposterior/vertical orientation angle (r =-0.44; P = 0.03) were correlated with one or all split times between 0-5 m, 5-10 m, 10-15 m, 15-20 m and 0-20 m. Acceleration sprint running in soccer requires minimised mediolateral and increased anteroposterior loading in the stance phase. Multi-component ground reaction force measures of the first step in acceleration sprint runs are important for developing performance assessments, and understanding force application techniques employed by soccer players.

#3 Body composition, strength static and isokinetic, and bone health: comparative study between active adults and amateur soccer players
Reference: Einstein (Sao Paulo). 2019 May 30;17(3):eAO4419. doi: 10.31744/einstein_journal/2019AO4419. [Article in English, Portuguese]
Authors: Tavares ÓM, Duarte JP, Werneck AO, Costa DC, Sousa-E-Silva P, Martinho D, Luz LGO, Morouço P, Valente-Dos-Santos J, Soles-Gonçalves R, Conde J, Casanova JM, Coelho-E-Silva MJ
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Summary: The purpose was to compare tissue composition, total and regional bone mineral content and bone mineral density, static hand grip and knee joint isokinetic strength between amateur soccer players and Control Group. Cross-sectional study. Air displacement plethysmography was used to estimate body volume and, in turn, density. Body composition, bone mineral content and bone mineral density were assessed for the whole body and at standardized regions using dual energy X-ray absorptiometry. Static grip strength was assessed with an adjustable dynamometer, and peak torque derived from isokinetic strength dynamometer (concentric muscular knee actions at 60°/s). Magnitude of the differences between groups was examined using d-Cohen. Compared to healthy active adults, soccer players showed larger values of whole body bone mineral content (+651g; d=1.60; p<0.01). In addition, differences between groups were large for whole body bone mineral density (d=1.20 to 1.90; p<0.01): lumbar spine, i.e. L1-L4 (+19.4%), upper limbs (+8.6%) and lower limbs (+16.8%). Soccer players attained larger mean values in strength test given by static hand grip protocol (+5.6kg, d=0.99; p<0.01). Soccer adequately regulates body composition and is associated better bone health parameters (bone mineral content and density at whole-body and at particular sites exposed to mechanical loadings).

#4 Exploring simulated driving performance among varsity male soccer players
Reference: Traffic Inj Prev. 2019 Jun 5:1-6. doi: 10.1080/15389588.2019.1601715. [Epub ahead of print]
Authors: Tremblay M, Lavallière M, Albert WJ, Boudreau SR, Johnson MJ
Summary: It is documented that male athletes display riskier behaviors while driving (as well as in life in general) than female athletes and nonathletes. However, the literature has reported that athletes show better driving ability than nonathletes. This paradox between behaviors and abilities motivated the present study to further understand the collision risk of varsity athletes. The current study estimates the performance differences between varsity male soccer players and male undergraduate nonathletes on (1) a driving task and (2) three perceptual-cognitive tasks (associated with collision risk prediction; i.e., Useful Field of View [UFOV] test). Thirty-five male undergraduate students (15 varsity soccer players, 20 undergraduate nonathletes) took part in this study. Driving performance was assessed during 14 min of urban commuting using a driving simulator. While completing the simulated driving task and UFOV test, the physiological responses were monitored using an electrocardiograph (ECG) to document heart rate variability (HRV). Varsity soccer players showed more risky behaviors at the wheel compared to their nonathlete student peers. Varsity soccer players spent more time over the speed limit, committed more driving errors, and adopted fewer safe and legal behaviors. However, no difference was observed between both groups on driving skill variables (i.e., vehicle control, vehicle mobility, ecodriving). For subtests 1 and 2 of the UFOV (i.e., processing speed, divided attention), both groups performed identically (i.e., 17 ms). The nonathlete group tended to perform better on the selective attention task (i.e., subtest 3 of UFOV test; 63.2 ± 6.2 ms vs. 87.2 ± 10.7 ms, respectively; this difference was not significant, P = .76). Preventive driving measures should be enforced in this high-risk population to develop strategies for risk reduction in male team athletes.

#5 Methodological Issues in Soccer Talent Identification Research
Reference: Sports Med. 2019 Jun 3. doi: 10.1007/s40279-019-01113-w. [Epub ahead of print]
Authors: Bergkamp TLG, Niessen ASM, den Hartigh RJR, Frencken WGP, Meijer RR
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Summary: Talent identification research in soccer comprises the prediction of elite soccer performance. While many studies in this field have aimed to empirically relate performance characteristics to subsequent soccer success, a critical evaluation of the methodology of these studies has mostly been absent in the literature. In this position paper, we discuss advantages and limitations of the design, validity, and utility of current soccer talent identification research. Specifically, we draw on principles from selection psychology that can contribute to best practices in the context of making selection decisions across domains. Based on an extensive search of the soccer literature, we identify four methodological issues from this framework that are relevant for talent identification research, i.e. (1) the operationalization of criterion variables (the performance to be predicted) as performance levels; (2) the focus on isolated performance indicators as predictors of soccer performance; (3) the effects of range restriction on the predictive validity of predictors used in talent identification; and (4) the effect of the base rate on the utility of talent identification procedures. Based on these four issues, we highlight opportunities and challenges for future soccer talent identification studies that may contribute to developing evidence-based selection procedures. We suggest for future research to consider the use of individual soccer criterion measures, to adopt representative, high-fidelity predictors of soccer performance, and to take restriction of range and the base rate into account.

#6 Effects of plyometric jump training on the physical fitness of young male soccer players: Modulation of response by inter-set recovery interval and maturation status
Reference: J Sports Sci. 2019 Jun 3:1-8. doi: 10.1080/02640414.2019.1626049. [Epub ahead of print]
Authors: Ramirez-Campillo R, Alvarez C, Sanchez-Sanchez J, Slimani M, Gentil P, Chelly MS, Shephard RJ
Summary: The effects of plyometric jump training on the physical fitness of male youth (age = 10-17 years) soccer players was examined in relation to inter-set recovery intervals and the maturity of the players in a single-blind, randomized-and controlled crossover trial. Jumping tests and kicking velocities were measured before (T0), after a 6 week control period (T1), after 6 weeks of plyometrics (T2), after 6 weeks of wash-out (T3), and after a further 6 weeks of plyometrics (T4). Subjects were divided into pre- and post- peak-height-velocity (PHV) groups, and were randomly assigned to 30 s or 120 s inter-set intervals during periods T2 and T4. Any changes in jumping and maximum kicking velocities during T1 and T3, had trivial effect sizes (0.01-0.15), but small to moderate improvements (effect size = 0.20-0.99) were observed in both groups during T2 and T4. Gains in pre-PHV players were similar for the two inter-set intervals, but gains in post-PHV players were greater (p < 0.05) with an inter-set recovery of 120 s than with a 30 s recovery. We conclude that plyometric jump training improves the physical fitness of adolescents, irrespective of their maturity, but that in older individuals gains are greater with a longer inter-set recovery interval.

#7 How Does the Adjustment of Training Task Difficulty Level Influence Tactical Behavior in Soccer?
Reference: Res Q Exerc Sport. 2019 Jun 3:1-14. doi: 10.1080/02701367.2019.1612511. [Epub ahead of print]
Authors: Machado JC, Barreira D, Teoldo I, Travassos B, Júnior JB, Santos JOLD, Scaglia AJ
Summary: This study aimed to investigate if player tactical skill level and age category influence team performance and player exploratory behavior in tasks with different difficulty levels. In total, 48 youth male soccer players participated in the study (U15, n = 24, mean age = 13.06 ± 1.53 years; U17, n = 24, mean age = 16.89 ± 0.11 years). Player tactical skills were evaluated through the System of Tactical Assessment in Soccer (FUT-SAT), allowing them to be organized into three groups according to tactical efficiency: Higher tactical skill level (Group 01), Intermediate tactical skill level (Group 02), and Lower tactical skill level (Group 03). Next, Group 01 and Group 03 of both categories performed six Small-Sided and Conditioned Games (SSCG) each, namely three High difficulty SSCGs and three Low difficulty SSCGs. Team performance and players' exploratory behavior were analyzed through the Offensive Sequences Characterization System and Lag Sequential Analysis, respectively. We found that team performance and players' exploratory behavior were influenced both by the age and tactical skill level of the players, as well as by task difficulty level. Therefore, in an attempt to improve player performance, practitioners must carefully manipulate key task constraints to adapt training task difficulty levels to player age and tactical skill level.

#8 Influence of Whole-Body Electrostimulation on the Deformability of Density-Separated Red Blood Cells in Soccer Players
Reference: Front Physiol. 2019 May 9;10:548. doi: 10.3389/fphys.2019.00548. eCollection 2019.
Authors: Filipovic A, Bizjak D, Tomschi F, Bloch W, Grau M
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Summary: Red blood cell nitric oxide synthase (RBC-NOS) dependent NO production positively affects RBC deformability which is known to improve oxygen supply to the working tissue. Whole-body electrostimulation (WB-EMS) has been shown to improve maximum strength, sprinting and jumping performance, and to increase deformability in elite soccer players during the season. The aim of the present study was to investigate whether WB-EMS affects RBC turnover which might affect overall deformability of circulating RBC by rejuvenation of the RBC population and if this might be related to improved endurance capacity. Thirty male field soccer players were assigned in either a WB-EMS group (EG, n = 10), a training group (TG, n = 10), or a control group (CG, n = 10). EG performed 3 × 10 squat jumps superimposed with WB-EMS twice per week in concurrent to 2-4 soccer training sessions and one match per week. TG only performed 3 × 10 squat jumps without EMS in addition to their soccer routine and the CG only performed the usual soccer training and match per week. Subjects were tested before (Baseline) and in week 7 (wk-7), with blood sampling before (Pre), 15-30 min after (Post), and 24 h after (24 h post) the training. Endurance capacity was determined before and directly after the training period. The key findings of the investigation indicate an increase in young RBC in the EG group along with improved overall RBC deformability, represented by decreased SS1/2:EImax Ratio. Analysis of the different RBC subfractions revealed improved RBC deformability of old RBC during study period. This improvement was not only observed in the EG but also in TG and CG. Changes in RBC deformability were not associated to altered RBC-NOS/NO signaling pathway. Endurance capacity remained unchanged during study period. In summary, the effect of WB-EMS on RBC physiology seems to be rather low and results are only in part comparable to previous findings. According to the lower training volume of the present study it can be speculated that the soccer specific training load in addition to the WB-EMS was too low to induce changes in RBC physiology.

#9 Comparison of Selected CD45+ Cell Subsets' Response and Cytokine Levels on Exhaustive Effort Among Soccer Players
Reference: J Med Biochem. 2019 May 11;38(3):256-267. doi: 10.2478/jomb-2018-0029. eCollection 2019 Jul.
Authors: Kostrzewa-Nowak D, Buryta R, Nowak R
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Summary: Immunological alterations may led to the reduction in capacity and endurance levels in elite athletes by e.g. increased susceptibility to infections. There is a need to explain the impact of intensive physical effort on the CD4+ memory T cell subsets. Fourteen participants median aged 19 years old (range 17-21 years) were recruited form Pogoń Szczecin S.A., soccer club. They performed progressive efficiency test on mechanical treadmill until exhaustion twice: during preparatory phases to spring and autumn competition rounds. We examined the influence of exhaustive effort on the selected CD45+, especially CD4+ memory T cell subsets and inflammation markers determined before, just after the test and during recovery time. Significant changes in total CD45+ cells and decrease in T lymphocytes percentage after the run was observed. Significant fluctuations in T cells' distribution were related not only to the changes in Th or Tc subsets but also to increase in naïve T cell percentage during recovery. Increase in TNF-α and IL-8 post-exercise, IL-6 and IL-10 plasma levels in recovery was also found. The novel finding of our study is that the run performed on mechanical treadmill caused a significant release of CD4+ T naïve cells into circulation. Post-exercise increase in circulating NK cells is related with fast biological response to maximal effort. However, at the same time an alternative mechanism enhancing inflammation is involved.

#10 Chronic traumatic encephalopathy is a common co-morbidity, but less frequent primary dementia in former soccer and rugby players
Reference: Acta Neuropathol. 2019 Jun 1. doi: 10.1007/s00401-019-02030-y. [Epub ahead of print]
Authors: Lee EB, Kinch K, Johnson VE, Trojanowski JQ, Smith DH, Stewart W
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Summary: Chronic traumatic encephalopathy (CTE) is reported at high prevalence in selected autopsy case series of former contact sports athletes. Nevertheless, the contribution of CTE pathology to clinical presentation and its interaction with co-morbid neurodegenerative pathologies remain unclear. To address these issues, we performed comprehensive neuropathology assessments on the brains of former athletes with dementia and considered these findings together with detailed clinical histories to derive an integrated clinicopathological diagnosis for each case. Consecutive, autopsy-acquired brains from former soccer and rugby players with dementia were assessed for neurodegenerative pathologies using established and preliminary consensus protocols. Thereafter, next of kin interviews were conducted to obtain detailed accounts of the patient's clinical presentation and course of disease to inform a final, integrated clinicopathological diagnosis. Neuropathologic change consistent with CTE (CTE-NC) was confirmed in five of seven former soccer and three of four former rugby players' brains, invariably in combination with mixed, often multiple neurodegenerative pathologies. However, in just three cases was the integrated dementia diagnosis consistent with CTE, the remainder having alternate diagnoses, with the most frequent integrated diagnosis Alzheimer's disease (AD) (four cases; one as mixed AD and vascular dementia). This consecutive autopsy series identifies neuropathologic change consistent with preliminary diagnostic criteria for CTE (CTE-NC) in a high proportion of former soccer and rugby players dying with dementia. However, in the majority, CTE-NC appears as a co-morbidity rather than the primary, dementia causing pathology. As such, we suggest that while CTE-NC might be common in former athletes with dementia, in many cases its clinical significance remains uncertain.

#11 Enhanced sprint performance analysis in soccer: New insights from a GPS-based tracking system
Reference: PLoS One. 2019 May 31;14(5):e0217782. doi: 10.1371/journal.pone.0217782. eCollection 2019.
Authors: Reinhardt L, Schwesig R, Lauenroth A, Schulze S, Kurz E
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Summary: The aim of this investigation was to establish the validity of a GPS-based tracking system (Polar Team Pro System, PTPS) for estimating sprint performance and to evaluate additional diagnostic indices derived from the temporal course of the movement velocity. Thirty-four male soccer players (20 ± 4 years) performed a 20 m sprint test measured by timing gates (TG), and while wearing the PTPS. To evaluate the relevance of additional velocity-based parameters to discriminate between faster and slower athletes, the median-split method was applied to the 20-m times. Practical relevance was estimated using standardized mean differences (d) between the subgroups. Differences between the criterion reference (TG) and PTPS for the 10 and 20 m splits did not vary from zero (dt10: -0.01 ± 0.07 s, P = 0.7, d < -0.1; dt20: -0.01 ± 0.08 s, P = 0.4, d < -0.2). Although subgroups revealed large differences in their sprint times (d = -2.5), the average accelerations between 5 and 20 km/h as well as 20 and 25 km/h showed merely small effects (d < 0.5). Consequently, analyses of velocity curves derived from PTPS may help to clarify the occurrence of performance in outdoor sports. Thus, training consequences can be drawn which contribute to the differentiation and individualization of sprint training.

#12 Epidemiology of injuries in professional football: a systematic review and meta-analysis
Reference: Br J Sports Med. 2019 Jun 6. pii: bjsports-2018-099577. doi: 10.1136/bjsports-2018-099577. [Epub ahead of print]
Authors: López-Valenciano A, Ruiz-Pérez I, Garcia-Gómez A, Vera-Garcia FJ, De Ste Croix M, Myer GD, Ayala F
Summary: We performed a systematic review and meta-analysis of epidemiological data of injuries in professional male football. Forty-four studies have reported the incidence of injuries in football. Two reviewers independently extracted data and assessed trial quality using the Strengthening the Reporting of Observational Studies in Epidemiology statement and Newcastle Ottawa Scale. Studies were combined in a pooled analysis using a Poisson random effects regression model. The overall incidence of injuries in professional male football players was 8.1 injuries/1000 hours of exposure. Match injury incidence (36 injuries/1000 hours of exposure) was almost 10 times higher than training injury incidence rate (3.7 injuries/1000 hours of exposure). Lower extremity injuries had the highest incidence rates (6.8 injuries/1000 hours of exposure). The most common types of injuries were muscle/tendon (4.6 injuries/1000 hours of exposure), which were frequently associated with traumatic incidents. Minor injuries (1-3 days of time loss) were the most common. The incidence rate of injuries in the top 5 European professional leagues was not different to that of the professional leagues in other countries (6.8 vs 7.6 injuries/1000 hours of exposure, respectively). Professional male football players have a substantial risk of sustaining injuries, especially during matches.

#13 Physical workload and glycemia changes during football matches in adolescents with type 1 diabetes can be comparable
Reference: Acta Diabetol. 2019 Jun 4. doi: 10.1007/s00592-019-01371-0. [Epub ahead of print]
Authors: Gawrecki A, Michalak A, Gałczyński S, Dachowska I, Zozulińska-Ziółkiewicz D, Szadkowska A
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Summary: The purpose was to analyze physical performance and diabetes-related outcomes in adolescents with type 1 diabetes (T1DM) during two semi-competitive football matches utilising precise physical activity monitoring. The study was conducted during an annual summer camp for adolescents with T1DM. After physical examination and glycated hemoglobin measurement, 16 adolescent players completed Cooper's 12-min running test and, in the following days, took part in two football matches while wearing heart rate (HR) monitors coupled with global positioning system (GPS) tracking. Both matches were comparable in terms of covered distances, number of sprints, achieved velocities and heart rate responses. During both games, capillary blood lactate increased significantly (Match 1: 1.75 ± 0.16-6.13 ± 1.73 mmol/l; Match 2: 1.77 ± 0.18-3.91 ± 0.63 mmol/l, p = 0.004). No significant differences in blood glucose were observed between the matches (p = 0.83) or over each match (p = 0.78). Clinically significant hypoglycemia (< 54 mg/dl) occurred in two children during the first match. None of the players experienced severe hypoglycemia. Despite similar workloads, players consumed significantly less carbohydrates during Match 2 [median difference: - 20 g (25-75%: - 40 to 0), p = 0.006]. HR monitoring and GPS-based tracking can effectively parameterize physical activity during a football match. In T1DM patients, exercise workload and glycemic changes during similar matches are comparable, which provides an opportunity to develop individual recommendations for players with T1DM.

#14 Brief in-play cooling breaks reduce thermal strain during football in hot conditions
Reference: J Sci Med Sport. 2019 May 4. pii: S1440-2440(18)31272-6. doi: 10.1016/j.jsams.2019.04.009. [Epub ahead of print]
Authors: Chalmers S, Siegler J, Lovell R, Lynch G, Gregson W, Marshall P, Jay O
Summary: The study examined if three feasible strategies involving additional in-play cooling periods attenuate the core (rectal) temperature rise during simulated football matches. Four counterbalanced experimental trials in an environmental chamber set to 35 °C ambient temperature, 55% relative humidity, and 30 °C WBGT were utilized. Twelve healthy well-trained football players completed a regular simulated match (REG), regular simulated match with additional 3-min cooling periods at the 30-min mark of each half inclusive of chilled water consumption (COOLwater), regular simulated match with additional 3-min cooling periods at the 30-min mark of each half inclusive of chilled water consumption and the application of an ice towel around the neck (COOLtowel), regular simulated match with an extended (+5 min; total of 20-min) half-time break (HTextended). The difference in rectal temperature change was significantly lower in the COOLwater (-0.25 °C), COOLtowel (-0.28 °C), and HTextended (-0.21 °C) trials in comparison to the REG (all p < 0.05). Exercising heart rate and session rating of perceived exertion was lower in the COOLwater (-13 bpm; -1.4 au), COOLtowel (-10 bpm; -1.3 au), and HTextended (-8 bpm; -0.9 au) trials in comparison to the REG trial (all p < 0.05). The cooling interventions did not significantly change skin temperature or thermal sensation in comparison to the REG (all p > 0.05). All three cooling interventions attenuated core body thermal strain during simulated matches. The laboratory-based study supports the use of brief in-play cooling periods as a means to attenuate the rise in core temperature during matches in hot and humid conditions.





Latest research in football - week 21 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Activity Profiles by Position in Youth Elite Soccer Players in Official Matches
Reference: Sports Med Int Open. 2019 May 28;3(1):E19-E24. doi: 10.1055/a-0883-5540. eCollection 2019 Jan.
Authors: Pettersen SA, Brenn T
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Summary: In order to investigate activity profiles and external load patterns in elite youth soccer players, we studied high-intensity activity patterns, maximum running speed, and temporary and end-of-match decline in external load in 54 U17 players (96 match observations) over a full season of official match play. Wide midfielders covered most high-intensity running (HIR) distance (1044.2 m), most sprinting distance (224.4 m), and the highest number of accelerations (185.2); center defenders had the lowest values for these activities (10 396.8 m, 508.3 m, 85.1 m, and 119.0), respectively. Wide midfielders had the highest and center defenders had the lowest maximum speed (30.3 km·h -1 and 28.6 km·h -1 ), respectively. During the matches, players in all playing positions displayed a significant drop in HIR distance, sprinting distance, and number of accelerations. This was especially pronounced in the 5 min following the 5-min peak period and in the last 5-min period for sprinting distance. There are substantial differences in activity profiles by positions, but all players show temporary and end-of-match drop in external load. The variation in activity profiles by playing position in this study may aid in the design of training programs. The considerable end-of-match drop in external load observed raises the question of the favorability of 90 min match times for U17 players.

#2 Russian and Low-Frequency Currents Training Programs Induced Neuromuscular Adaptations in Soccer Players: Randomized Controlled Trial
Reference: J Sport Rehabil. 2019 May 29:1-25. doi: 10.1123/jsr.2018-0314. [Epub ahead of print]
Authors: Modesto KAG, de Oliveira PFA, Fonseca HG, Azevedo KP, Guzzoni V, Bottaro MF, Babault N, Durigan JLQ
Summary: Neuromuscular electrical stimulation (NMES) is widely used to induce muscular strength increase, however, no study has compared Russian current (RC) with Pulsed current (PC) effects after a training program. We studied the effects of different neuromuscular electrical stimulation (NMES) currents, Russian current (RC) and Pulsed current (PC) on the neuromuscular system after a six-week training period. Twenty-seven male soccer players (22.2±2.2 years, 74.2±10.0 kg, 177±0 cm, BMI: 23.7±2.9 kg/cm for the control group, 22.1±3.1 years, 69.7±5.7 kg, 174±0 cm, 23.0±2.5 kg/cm for the PC group, and 23.0±3.4 years, 72.1±10.7 kg,175±0 cm, 23.5±3.4 kg/cm for the RC group) were randomized into three groups: 1) control group, 2) RC (2500 Hz, burst 100 Hz, phase duration 200 μs), and 3) PC (100 Hz and 200 μs). Intervention: The experimental groups trained for six weeks, with three sessions per week with NMES. Maximal voluntary isometric contraction (MVIC) and evoked torque, muscle architecture, sensory discomfort (VAS), and electromyographic activity (EMG) were evaluated before and after the six-week period. Evoked torque increased in the RC (169.5±78.2 %, p<0.01) and PC groups (248.7±81.1 %, p<0.01). Muscle thickness and pennation angle increased in the RC (8.7±3.8 % and 16.7±9.0%, p<0.01) and PC groups (16.1±8.0 % and 27.4±11.0 %, p<0.01). The PC demonstrated lower values for VAS (38.8±17.1 %, p<0.01). There was no significant time difference for MVIC and RMS (root mean square) values (p>0.05). For all these variables, there was no difference between the RC and PC (p>0.05). Despite the widespread use of RC in clinical practice, RC and PC training programs produced similar neuromuscular adaptations in soccer players. Nonetheless, as PC generated less perceived discomfort it could be preferred after several training sessions.

#3 Commentary: Interpersonal Coordination in Soccer: Interpreting Literature to Enhance the Representativeness of Task Design, From Dyads to Teams
Reference: Front Psychol. 2019 May 14;10:1093. doi: 10.3389/fpsyg.2019.01093. eCollection 2019.
Authors: Gesbert V, Hauw D
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#4 Oral Ingestion of Deep Ocean Minerals Increases High-Intensity Intermittent Running Capacity in Soccer Players after Short-Term Post-Exercise Recovery: A Double-Blind, Placebo-Controlled Crossover Trial
Reference: Mar Drugs. 2019 May 24;17(5). pii: E309. doi: 10.3390/md17050309.
Authors: Higgins MF, Rudkin B, Kuo CH
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Summary: This study examined whether deep ocean mineral (DOM) supplementation improved high-intensity intermittent running capacity after short-term recovery from an initial bout of prolonged high-intensity running in thermoneutral environmental conditions. Nine healthy recreational male soccer players (age: 22 ± 1 y; stature: 181 ± 5 cm; and body mass 80 ± 11 kg) completed a graded incremental test to ascertain peak oxygen uptake (V·O2PEAK), two familiarisation trials, and two experimental trials following a double-blind, repeated measures, crossover and counterbalanced design. All trials were separated by seven days and at ambient room temperature (i.e., 20 °C). During the 2 h recovery period after the initial ~60 min running at 75% V·O2PEAK, participants were provided with 1.38 ± 0.51 L of either deep ocean mineral water (DOM) or a taste-matched placebo (PLA), both mixed with 6% sucrose. DOM increased high-intensity running capacity by ~25% compared to PLA. There were no differences between DOM and PLA for blood lactate concentration, blood glucose concentration, or urine osmolality. The minerals and trace elements within DOM, either individually or synergistically, appear to have augmented high-intensity running capacity in healthy, recreationally active male soccer players after short-term recovery from an initial bout of prolonged, high-intensity running in thermoneutral environmental conditions.

#5 Running Performance of Soccer Players During Matches in the 2018 FIFA World Cup: Differences Among Confederations
Reference: Front Psychol. 2019 May 7;10:1044. doi: 10.3389/fpsyg.2019.01044. eCollection 2019.
Authors: Tuo Q, Wang L, Huang G, Zhang H, Liu H
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Summary: With the purpose of quantifying the differences in the running performance of soccer players during matches from different continental confederations, data of 1508 match observations generated from 559 players in 59 matches at the 2018 FIFA World Cup held in Russia were analyzed. Generalized mixed linear modeling was carried out to estimate the effect of confederations on each of the selected thirteen match running performance related variables (total distance covered, top speed achieved, number of sprints, distance covered and time spent in walking, jogging, low-speed running, moderate-speed running, and high-speed running), controlling the effects of match result, competition phase, and team and opponent strength. Results showed that the differences in the match running performance of UEFA and CONMEBOL players were trivial (ES between 0.04 and 0.14); players from AFC, CAF, and CONCACAF covered less total distance (ES between 0.26 and 0.54), spent less playing time, and covered less distance in jogging and low-speed running (ES between 0.20 and 0.53), whereas they spent more time walking (ES between 0.27 and 0.41) as compared with players from UEFA and CONMEBOL; top speed achieved, number of sprints made, and time spent and distance covered in the moderate- and high-speed running intensity zones by players from all confederations were similar (ES between 0.01 and 0.15), with an exception that high-speed-running distance covered by CONCACAF players was less than that by CAF players (2.0 ± 1.5 m/min vs. 2.3 ± 1.7 m/min, ES = 0.23, ±90% CL: ±0.21).

#6 Evaluating the impact of a coach development intervention for improving coaching practices in junior football (soccer): The "MASTER" pilot study
Reference: J Sports Sci. 2019 May 25:1-13. doi: 10.1080/02640414.2019.1621002. [Epub ahead of print]
Authors: Eather N, Jones B, Miller A, Morgan PJ
Summary: The aim of this pilot study was to evaluate the impact of a novel coach development intervention (MASTER) on coaching practices of football coaches. The study involved six coaches (of 10-12 year old) from one representative football club (Australia February-July 2017). The 15-week multi-component intervention included a face-to-face workshop, ongoing mentoring, modelled training sessions, peer assessments and group discussions. MASTER is underpinned by positive coaching and game-based coaching practices and aimed to educate coaches on how to implement and operationalise a number of evidence-based coaching elements. At each of baseline and immediate post-intervention coaches were filmed three times and evaluated using a modified version of the Coach Analysis Intervention System. Using linear mixed model analysis, significant changes were observed for time spent performing playing-form activities [+15.4% (95% CI 6.01-24.79)(t(15) = 3.5, P = 0.003], with significant changes in the type of interventions undertaken and the nature of feedback given to athletes. Program feasibility was examined using measures of recruitment, retention, adherence and satisfaction. Results indicate program feasibility and high coach evaluation ratings. MASTER demonstrated effectiveness for improving coaching practices of football coaches during training sessions. Further large-scale trials will build evidence for the utility of MASTER for guiding coaching practices in football and other sporting codes.

#7 Medical assessment of potential concussion in elite football: video analysis of the 2016 UEFA European championship
Reference: BMJ Open. 2019 May 30;9(5):e024607. doi: 10.1136/bmjopen-2018-024607.
Authors: Abraham KJ, Casey J, Subotic A, Tarzi C, Zhu A, Cusimano MD
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Summary: The objective is to determine if suspected concussions in elite football are medically assessed according to the International Conferences on Concussion in Sport consensus statement recommendations. Potential concussive events (PCEs) were defined as direct head collision incidents resulting in the athlete being unable to immediately resume play following impact. PCEs identified and description of PCE assessment and outcome were accomplished through direct standardised observation of video footage by trained observers in 51 games played in the Men's UEFA European Championship (10 June-10 July 2016). Sixty-nine total PCEs (1.35 per match) were identified in 51 games played during the 2016 Men's UEFA European Championship. Forty-eight PCEs (69.6%) resulted in two observable signs of concussion, 13 (18.8%) resulted in three signs and 1 (1.4%) resulted in four signs in the injured athletes. Nineteen (27.5%) PCEs were medically assessed by sideline healthcare personnel while 50 (72.5%) were not. Of the 50 PCEs that were not medically assessed, 44 (88%) PCEs resulted in two or more signs of concussion among injured athletes. Of the 19 medically assessed PCEs, 8 resulted in 3 signs of concussion, and 1 resulted in 4 signs; all assessments concluded in the same-game return for the injured athletes. PCEs were frequent events in the 2016 UEFA Euro championship, but were rarely assessed concordant with the International Conferences on Concussion in Sport consensus statement recommendations. There is an imperative need to improve the assessment and management of players suspected of concussion in elite football.

#8 Effects of Adding Vertical or Horizontal Force-Vector Exercises to In-season General Strength Training on Jumping and Sprinting Performance of Youth Football Players
Reference: J Strength Cond Res. 2019 May 27. doi: 10.1519/JSC.0000000000003221. [Epub ahead of print]
Authors: Abade E, Silva N, Ferreira R, Baptista J, Gonçalves B, Osório S, Viana J
Summary: Football is characterized by short-term high-intensity triaxial activities that require optimized neuromuscular capacity. Thus, training routines must consider the direction of force application, particularly when strength exercises are performed. This study aimed to explore the effects of adding vertical or horizontal force-vector exercises to a 20-week in-season general strength training program on jumping and sprinting performance of youth football players. Twenty-four well-trained male under-17 players participated in this study and were randomly assigned to a control, vertical, or horizontal training group. Control group performed a general strength training program (free weights, eccentric-overload, and body mass exercises) once a week during 20 weeks. Vertical and horizontal groups additionally performed back-half-squat or barbell hip-thrust, respectively. Vertical group improved vertical jump (VJ) (squat jump, likely 4.5; ±4.4% and countermovement jump, likely 4.9; ±4.1%), horizontal jump (HJ) (most likely 7.5; ±2.7%), and sprint (10 m, likely -1.6; ±2.0% and 20 m, very likely -3.3; ±1.6%). The horizontal group showed unclear results in VJ; however, large improvements were observed in HJ (most likely, 13.0; ±4.8%), 10 m and 20 m (very likely -3.0; ±1.8% and most likely -3.8; ±1.0%, respectively). Back-squat and hip-thrust showed an important transference effect to both jumping and sprinting performance. If considering the effects of back-squat on VJ, hip-thrust improved HJ and sprint to a greater extent. This study reinforces the importance of performing both vertical and horizontal force-vector exercises to enhance physical performance during football in-season, even when performed only once a week.

#9 Evaluating the impact of a coach development intervention for improving coaching practices in junior football (soccer): The "MASTER" pilot study
Reference: J Sports Sci. 2019 May 25:1-13. doi: 10.1080/02640414.2019.1621002. [Epub ahead of print]
Authors: Eather N, Jones B, Miller A, Morgan PJ
Summary: The aim of this pilot study was to evaluate the impact of a novel coach development intervention (MASTER) on coaching practices of football coaches. The study involved six coaches (of 10-12 year old) from one representative football club (Australia February-July 2017). The 15-week multi-component intervention included a face-to-face workshop, ongoing mentoring, modelled training sessions, peer assessments and group discussions. MASTER is underpinned by positive coaching and game-based coaching practices and aimed to educate coaches on how to implement and operationalise a number of evidence-based coaching elements. At each of baseline and immediate post-intervention coaches were filmed three times and evaluated using a modified version of the Coach Analysis Intervention System. Using linear mixed model analysis, significant changes were observed for time spent performing playing-form activities [+15.4% (95% CI 6.01-24.79)(t(15) = 3.5, P = 0.003], with significant changes in the type of interventions undertaken and the nature of feedback given to athletes. Program feasibility was examined using measures of recruitment, retention, adherence and satisfaction. Results indicate program feasibility and high coach evaluation ratings. MASTER demonstrated effectiveness for improving coaching practices of football coaches during training sessions. Further large-scale trials will build evidence for the utility of MASTER for guiding coaching practices in football and other sporting codes.

#10 Training load and submaximal heart rate testing throughout a competitive period in a top-level male football team
Reference: J Sports Sci. 2019 May 26:1-8. doi: 10.1080/02640414.2019.1618534. [Epub ahead of print]
Authors: Rago V, Krustrup P, Martín-Acero R, Rebelo A, Mohr M
Summary: The aim of this study was to investigate training load and cardiorespiratory fitness in a top-level Spanish (LaLiga) football team (n = 17). The submaximal Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1SUB) was performed in four moments of the competitive period from early February (E1) to early May (E4). Training load was quantified using a 10-Hz global positioning system and heart rate (HR) recording (n = 837 individual training sessions), while match load was quantified using semi-automated cameras (n = 216 individual match observations). Cardiorespiratory fitness moderately improved as the season progressed (P < 0.05; effect sizes = 0.8 to 1.2). Cumulative total distance covered during training between E1 and E4 was negatively correlated with percentage of changes in mean HR during the last 30 s of Yo-Yo IR1SUB (P = 0.049; r = -0.47 [-0.71; -0.14]; moderate). HR during the last 30 s of Yo-Yo IR1SUB was negatively correlated to total distance covered during the match (P = 0.024; r = -0.56 [-0.80; -0.17]; moderate). Yo-Yo IRSUB can be used to monitor seasonal changes in cardiorespiratory fitness without the need to have players work until exhaustion. Cardiorespiratory fitness given by mean HR during the last 30 s of the test seems meaningful in relation to match performance.

#11 Attitudes, beliefs and knowledge related to doping in different categories of football players
Reference: J Sci Med Sport. 2019 May 18. pii: S1440-2440(18)31034-X. doi: 10.1016/j.jsams.2019.05.010. [Epub ahead of print]
Authors: Morente-Sánchez J, Zandonai T, Zabala Díaz M
Summary: The aim of this study was to study and compare attitudes, beliefs and knowledge about doping of footballers, from elite to under-18 categories. The descriptive exploratory design used an instrument combining a validated questionnaire (Performance Enhancement Attitude Scale: PEAS) with qualitative open-ended questions. A total of 1324 Spanish football players (average age 22.56 ± 5.62 years) from 88 football teams that ranged from elite to under-18 categories: Elite (ELI, n = 304), non-elite Professional (PRO, n = 308), top Amateur (AMA, n = 330), elite Under-18 (U18, n = 334) and elite Female (FEM, n = 48) composed the sample. PEAS overall scores (range 17-102, with higher scores representing more permissive attitudes) was 34.02 ± 11.08. The overall scores for all groups analysed were: FEM: 33.75 ± 14.73; ELI: 30.61 ± 9.91; PRO: 34.23 ± 11.13; AMA: 35.05 ± 10.35; and U18: 35.93 ± 11.50. Significant differences were observed between ELI and PRO (p < 0.001), ELI and AMA (p < 0.001), and ELI and U18 (p < 0.001). 95% of participants did not know the meaning of WADA; 97.4% did not know the Prohibited List; 5% admitted having used banned substances and 23.7% knew dopers. This study showed different an important lack of knowledge about doping and an high levels of supplement use in this sample of footballers assessed. It which clearly reinforces the idea of implementing a wide educational doping prevention programme in football environment.

#12 Acute high-intensity football games can improve children's inhibitory control & neurophysiological measures of attention
Reference: Scand J Med Sci Sports. 2019 May 24. doi: 10.1111/sms.13485. [Epub ahead of print]
Authors: Rasmussen Lind R, Beck MM, Wikman J, Malarski K, Krustrup P, Lundbye-Jensen J, Sparre Geertsen S
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Summary: Recent studies suggest that a single bout of exercise can lead to transient performance improvements in specific cognitive domains in children. However, more knowledge is needed to determine the key exercise characteristics for obtaining these effects and how they translate into real-world settings. In the present study, we investigate how small-sided football games of either high or moderate-intensity affect measures of inhibitory control in a school setting. Eighty-one children (mean age 11.8, 48 boys) were randomly allocated to three groups performing 20-min of high-intensity small-sided real football games (SRF), moderate-intensity small-sided walking football games (SWF) or resting (RF). Behavioural measures of inhibitory control and neurophysiological measures of attention (P300 latency and amplitude) were obtained during a flanker task performed at baseline and 20 minutes following the intervention. Retention of declarative memory was assessed in a visual memory task 7 days after the intervention. Measures of inhibitory control improved more in children performing SRF compared to SWF 19ms, 95% CI [7, 31ms], (p=0.041). This was paralleled by larger increases in P300 amplitudes at Fz in children performing SRF compared both to RF in congruent (3.54μV, 95% CI [0.85, 6.23 μV], p=0.039) and incongruent trials (5.56μV, 95% CI [2.87, 8.25 μV], p<0.001) and compared to SWF in incongruent trials (4.10μV, 95% CI [1.41, 6.68 μV], p=0.010). No effects were found in measures of declarative memory. Together this indicate that acute high-intensity small-sided football games can transiently improve measures of inhibitory control and neurophysiological correlates of attention. Intense small-sided football games are easily implementable and can be employed by practitioners, e.g. during breaks throughout the school day.

#13 Influence of the structural components of artificial turf systems on impact attenuation in amateur football players
Reference: Sci Rep. 2019 May 23;9(1):7774. doi: 10.1038/s41598-019-44270-8.
Authors: Sánchez-Sánchez J, Gallardo-Guerrero AM, García-Gallart A, Sánchez-Sáez JA, Felipe JL, Encarnación-Martínez A
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Summary: The purpose of this research was to evaluate the influence of the structural components of different 3rd generation artificial turf football field systems on the biomechanical response of impact attenuation in amateur football players. A total of 12 amateur football players (24.3 ± 3.7 years, 73.5 ± 5.5 kg, 178.3 ± 4.1 cm and 13.7 ± 4.3 years of sport experience) were evaluated on three third generation artificial turf systems (ATS) with different structural components. ATS were composed of asphalt sub-base and 45 mm of fibre height with (ATS1) and without (ATS2) elastic layer or compacted granular sub-base, 60 mm of fibre height without elastic layer (ATS3). Two triaxial accelerometers were firmly taped to the forehead and the distal end of the right tibia of each individual. The results reveal a higher force reduction on ATS3 in comparison to ATS1 (+6.24%, CI95%: 1.67 to 10.92, ES: 1.07; p < 0.05) and ATS2 (+21.08%, CI95%: 16.51 to 25.66, ES: 2.98; p < 0.05) elastic layer. Tibia acceleration rate was lower on ATS3 than ATS1 (-0.32, CI95%: -0.60 to -0.03, ES: 4.23; p < 0.05) and ATS2 (-0.35, CI95%: -0.64 to -0.06; ES: 4.69; p < 0.05) at 3.3 m/s. A very large correlation (r = 0.7 to 0.9; p < 0.05) was found between energy restitution and fibre height in both head and tibial peak acceleration and stride time. In conclusion, structural components (fibre height, infill, sub-base and elastic layer) determine the mechanical properties of artificial turf fields. A higher force reduction and lower energy restitution diminished the impact received by the player which could protect against injuries associated with impacts compared to harder artificial turf surfaces.

#14 Comparison of Static and Dynamic Balance in Male Football and Basketball Players
Reference: Foot Ankle Spec. 2019 May 23:1938640019850618. doi: 10.1177/1938640019850618. [Epub ahead of print]
Authors: Halabchi F, Abbasian L, Mirshahi M, Mazaheri R, Pourgharib Shahi MH, Mansournia MA
Summary: The aim of the present study was to compare static and dynamic balance among professional athletes in football and basketball. In this cross-sectional study, 47 professional, male football and basketball players from Pro League in Iran participated. They were divided into 3 groups. Group 1 included 16 participants with history of grade 1 or 2 single ankle sprain within the past 6 months. Group 2 included 17 participants with recurrent ankle sprain. Group 3 included 14 participants without history of ankle sprain. Static and dynamic balance were measured by the Balance Error Scoring System (BESS) and modified Star Excursion Balance Test (SEBT), respectively. For the single-leg stance on a firm surface, group 2 scored errors with a high mean value of 3.94 compared with the other 2 groups, and the difference was statistically significant (P = .03). Significant differences in BESS scores are observed on both surfaces across the tandem limb between groups 2 and 3. The measures from the SEBTs may not reflect the balance performance especially in well-trained athletes who have a better balance when performing sport-related skills. However, BESS includes static postures, and it may reflect postural deficits better than dynamic tests in the more experienced athlete.





Latest research in football - week 20 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 The Relationship between Change of Direction Tests in Elite Youth Soccer Players
Reference: Sports (Basel). 2019 May 14;7(5). pii: E111. doi: 10.3390/sports7050111.
Authors: Kadlubowski B, Keiner M, Hartmann H, Wirth K, Frick U
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Summary: Change of direction (COD) is a performance-limiting factor in team sports. However, there are no exact definitions describing which physical abilities limit COD performance in soccer. Nevertheless, different COD tests are used or have been recommended as being equally effective in the professional practice of measuring COD performance. Therefore, the aim of this study was to evaluate the relationship between different COD tests, and to test the independence and generalizability of these COD tests in soccer. As such, 27 elite youth soccer players were randomly recruited and were tested in different COD tests (i.e., Illinois agility test (IAT), T agility test (TT), 505 agility test (505), Gewandtheitslauf (GewT), triangle test (Tri-t), and square test (SQT)). Bivariate Pearson correlation analysis was used to assess the relationships between the COD tests. The Benjamini-Hochberg method was used to control for the false discovery rate of the study at 0.05. This investigation calculated explained variances of 10% to 55% between performances in the different COD tests. This suggested that the tests covered different aspects or task-specific characteristics of the COD. Therefore, coaches and sport scientists should review and select different tests with a logical validity, based on the requirement profiles of the corresponding sport.

#2 Does soccer headgear reduce the incidence of sport-related concussion? A cluster, randomised controlled trial of adolescent athletes
Reference: Br J Sports Med. 2019 May 14. pii: bjsports-2018-100238. doi: 10.1136/bjsports-2018-100238. [Epub ahead of print]
Authors: McGuine T, Post E, Pfaller AY, Hetzel S, Schwarz A, Brooks MA, Kliethermes SA
Summary: There have been no large randomised controlled trials to determine whether soccer headgear reduces the incidence or severity of sport-related concussion (SRC) in US high school athletes. We aimed to determine whether headgear reduces the incidence or severity (days out from soccer) of SRCs in soccer players. 2766 participants (67% female, age 15.6±1.2) (who undertook 3050 participant years) participated in this cluster randomised trial. Athletes in the headgear (HG) group wore headgear during the season, while those in the no headgear (NoHG) group did not. Staff recorded SRC and non-SRC injuries and soccer exposures. Multivariate Cox proportional hazards models were used to examine time-to-SRC between groups, while severity was compared with a Wilcoxon rank-sum test. 130 participants (5.3% female, 2.2% male) sustained an SRC. The incidence of SRC was not different between the HG and NoHG groups for males (HR: 2.00 (0.63-6.43) p=0.242) and females (HR: 0.86 (0.54-1.36) p=0.520). Days lost from SRC were not different (p=0.583) between the HG group (13.5 (11.0-018.8) days) and the NoHG group (13.0 (9.0-18.8) days). Soccer headgear did not reduce the incidence or severity of SRC in high school soccer players.

#3 Maximum acceleration performance of professional soccer players in linear sprints: Is there a direct connection with change-of-direction ability?
Reference: PLoS One. 2019 May 14;14(5):e0216806. doi: 10.1371/journal.pone.0216806. eCollection 2019.
Authors: Loturco I, A Pereira L, T Freitas T, E Alcaraz P, Zanetti V, Bishop C, Jeffreys I
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Summary: The purpose of this study was to examine the selective influences of the maximum acceleration capability on change of direction (COD) speed, COD deficit, linear sprint speed, sprint momentum, and loaded and unloaded vertical jump performances in forty-nine male professional soccer players (24.3 ± 4.2 years; 75.4 ± 5.4 kg; 177.9 ± 6.4 cm). Soccer players performed the assessments in the following order: 1) squat and countermovement jumps; 2) 20-m sprinting speed test; 3) Zigzag COD ability test; and 4) bar-power outputs in the jump squat exercise. Athletes were divided, using a median split analysis, into two different groups according to their maximum acceleration rates from zero to 5-m (e.g., higher and lower ACC 0-5-m). Magnitude-based inference was used to compare the differences in the physical test results between "higher" and "lower" acceleration groups. A selective influence of the maximum acceleration ability on speed-power tests was observed, as the higher acceleration group demonstrated likely to almost certain higher performances than the lower acceleration group in all measurements (effect sizes varying from 0.66 [for sprint momentum in 20-m] to 2.39 [for sprint velocity in 5-m]). Conversely, the higher acceleration group demonstrated a higher COD deficit when compared to the lower acceleration group (ES = 0.55). This indicates compromised efficiency to perform COD maneuvers in this group of players. In summary, it was observed that soccer players with higher maximum acceleration rates are equally able to jump higher, sprint faster (over short distances), and achieve higher COD velocities than their slower counterparts. However, they appear to be less efficient at changing direction, which may be related to their reduced ability to deal with greater entry and exit velocities, or counterbalance the associated mechanical consequences (i.e., greater inertia) of being faster and more powerful.

#4 Relationship Between Resting Heart Rate Variability and Intermittent Endurance Performance in Novice Soccer Players
Reference: Res Q Exerc Sport. 2019 May 13:1-7. doi: 10.1080/02701367.2019.1601666. [Epub ahead of print]
Authors: Pereira LA, Abad CCC, Leiva DF, Oliveira G, Carmo EC, Kobal R, Loturco I
Summary: This study examined the relationships between the Yo-Yo Intermittent Recovery Test level 1 (Yo-Yo IR1) and resting heart rate variability (HRV) and submaximal 5'-5' test derived measures in novice male soccer players. Forty players (11.54 ± 0.58 years) from a soccer academy participated in this study, performing physical tests on two different days, separated by 48 h, as follows: (day 1) resting HRV and Yo-Yo IR1 test, and (day 2) anthropometric assessments (for peak height velocity assessment [PHV]) and the 5'-5' test. The Pearson product-moment correlation coefficient was used to determine the correlations between Yo-Yo IR1 performance and the remaining variables. A partial correlation analysis was further performed using age, stature, body mass, distance to PHV, and age at PHV as "confounders." The highest correlation score was observed between Yo-Yo IR1 performance and resting HRV, when the absolute age was used as confounder (r = 0.72; p < .05). We observed that a practical measure of parasympathetic activity at rest is largely associated with performance obtained during a traditional intermittent endurance performance test.

#5 Shorter Small-Sided Game Sets May Increase the Intensity of Internal and External Load Measures: A Study in Amateur Soccer Players
Reference: Sports (Basel). 2019 May 9;7(5). pii: E107. doi: 10.3390/sports7050107.
Authors: Clemente FM, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The purpose of this study was to compare internal and external load measures during two regimens (6 x 3' and 3 x 6') of a 5 vs. 5 format of play. Moreover, within-regimen changes (between sets) were also tested. Ten amateur soccer players (age: 19.8 ± 1.6 years; experience: 8.3 ± 2.1 years; height: 177.4 ± 3.8 cm; weight: 71.7 ± 4.2 kg) participated in the experiment. Internal load was measured using the CR-10 scale as the rated of perceived exertion (RPE) scale and a heart rate (HR) monitor. The measurements of total (TD), running (RD) and sprinting (SD) distances were also collected using a 10-Hz validated and reliable GPS. Comparisons between regimens revealed that the 3 x 6' regimen was significantly more intense in terms of RPE than the 6 x 3' regimen (p = 0.028; d = 0.351), although no significant differences were found in HR. Significantly greater averages of TD (p = 0.000; d = 0.871) and RD (p = 0.004; d = 0.491) were found in the 6 x 3' regimen. In both regimens, the RPE was significantly lower during the first set than in the remaining sets. On the other hand, the TD was significantly shorter in the last sets than in the earlier. In summary, the present study suggests that shorter sets may be beneficial for maintaining higher internal and external load intensities during 5 vs. 5 formats, and that a drop-in performance may occur throughout the sets in both regimens.

#6 Maximal heart rate assessment in recreational football players. A study involving a multiple testing approach
Reference: Scand J Med Sci Sports. 2019 May 21. doi: 10.1111/sms.13472. [Epub ahead of print]
Authors: Póvoas SCA, Krustrup P, Pereira R, Vieira S, Carneiro I, Magalhães J, Castagna C
Summary: This study aimed at examining the suitability of a standard treadmill test (TT), popular intermittent field tests and small-sided recreational football matches to induce maximal heart rate (HRmax ) in recreational football players. Sixty-six male sedentary untrained subjects (age 39.3±5.8 years, VO2max 41.3±6.2 ml·kg-1 ·min-1 , body mass 81.9±10.8 kg, height 173.2±6.4 cm) were evaluated. On separate occasions, the players were randomly submitted to a progressive VO2max TT, to the Yo-Yo intermittent endurance level 1 (YYIE1) and level 2 (YYIE2) tests, to the Yo-Yo intermittent recovery level 1 (YYIR1) test, and to 7v7 (43x27 m pitch, 83 m2 /player) football matches (45 min; 2-4 matches/player). To ensure data consistency, exercise HR was recorded using the same HR monitors in all the experimental conditions. A total of 73, 24, 18, 17 and 30% of players achieved HRmax during the YYIE1, YYIE2, YYIR1, TT and the small-sided football matches, respectively. The probability of achieving HRmax increased proportionally to test duration, with 7.8 min as the cut-off time. Variations in HRpeak of ±2 b. min-1 should be regarded as of practical relevance. YYIE1 HRpeak provided the most accurate estimation of a subject's individual HRmax and much higher probability of reaching HRmax . Nevertheless, the results of this study suggest caution in considering a reference test for HRmax assessment in this population. The use of confirmation tests is still highly advisable when the test duration is shorter than 7.8 min. In this regard, field tests seem to be suitable and accurate for individual HRmax assessment in recreational football players.

#7 The effect of the change of football turf on knee kinematics of adolescent male football players
Reference: J Sports Med Phys Fitness. 2019 May 20. doi: 10.23736/S0022-4707.19.09774-3. [Epub ahead of print]
Authors: Zhou B, Li B, Bai L
Summary: The aim of this study was to investigate the effect of the change of football turf on knee kinematics of adolescent male football players. Thirteen adolescent male football players were tested by a portable infrared motion analysis system based on markers. The angular displacements of flexion/extension,valgus/ varus and internal/external rotation were calculated respectively when players performed 90° shuttle running on artificial turf and natural turf. The maximum valgus angle and range of valgus/varus were larger when they were changed from artificial turf to natural turf (P<0.05). There were no significant differences in the maximum flexion angle, maximum extension angle,range of flexion/extension,maximum varus angle,maximum internal rotation angle, maximum external rotation angle and range of internal/external rotation(P>0.05). The change of football turf has a significant effect on knee kinematics of adolescent male football players.The risk of noncontact anterior cruciate ligament(ACL) injury is increased when players who are changed from artificial turf to natural turf.

#8 The Relationship Between Cognitive Functions and Sport-Specific Motor Skills in Elite Youth Soccer Players
Reference: Front Psychol. 2019 Apr 25;10:817. doi: 10.3389/fpsyg.2019.00817. eCollection 2019.
Authors: Scharfen HE, Memmert D
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Summary: The aim of the present study was to examine the relationship between basic cognitive functions and sport-specific motor skills in elite youth soccer players. A total of 15 elite youth soccer players aged 11-13 years performed a computer-based test battery measuring the attention window (AW), perceptual load (PL), working memory capacity (WMC), and multiple object tracking (MOT). Another set of tests was used to asses speed abilities and football-specific technical skills (sprint, change of direction, dribbling, ball control, shooting, and juggling). Spearman's correlation tests showed that the diagonal AW was positively associated with dribbling skills (rs = 0.656) which indicates that a broader AW could be beneficial for highly demanding motor skills like dribbling. WMC was positively related to dribbling (rs = 0.562), ball control (rs = 0.669), and ball juggling (rs = 0.727). Additionally, the cumulated score of all cognitive tests was positively related to the cumulated motor test score (rs = 0.614) which supports the interplay of physical and psychological skills. Our findings highlight the need for more, and especially longitudinal, studies to enhance the knowledge of cognition-motor skill relationships for talent identification, talent development, and performance in soccer.

#9 Physical and Physiological Responses during the Stop-Ball Rule During Small-Sided Games in Soccer Players
Reference: Sports (Basel). 2019 May 17;7(5). pii: E117. doi: 10.3390/sports7050117.
Authors: Halouani J, Ghattasi K, Bouzid MA, Rosemann T, Nikolaidis PT, Chtourou H, Knechtle B
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Summary: Small-sided games (SSGs) are a recommended training method for significant performance enhancement, and training efficiency. The stop-ball (SSG-SB) effects on physical responses (e.g., acceleration, deceleration, sprints, total distance, and indicator of workload) have not been investigated yet. This study aimed to investigate the effects of the SSG-SB compared to the small-goals SSG (SSG-SG) on physical and heart rate (HR) responses at high intensity (total distance (>18 km/h)), sprints (>18 km/h), and acceleration and deceleration (>3 m/s²) during a 4 vs. 4 SSG format in youth professional soccer players. Sixteen male elite young soccer players (mean ± SD body height, 176.5 ± 6.3 cm; age, 18.3 ± 0.7 years; body weight, 73.4 ± 7.2 kg) performed two forms of SSGs, i.e., SSG-SB or SSG-SG, for 4 × 4 min with a recovery of 2 min between sets. Data were compared using the t-test. The SSG-SB induced a significantly higher mean HR (180.0 ± 2.0 vs. 173.0 ± 3.0 beats per minute; p < 0.05) compared to the SSG-SG. Likewise, the SSG-SB was significantly higher compared to the SSG-SG for total distance (2580 ± 220.3 vs. 2230 ± 210 m; p < 0.001), player load (98.07 ± 12.5 vs. 89.4 ± 10.5; p < 0.05), sprint distance (7.9 ± 2.3 vs. 5.2 ± 2.0 m; p < 0.05), acceleration (15.6 ± 2.75 vs. 12.5 ± 1.75; p < 0.05), and deceleration (17.3 ± 3.20 vs. 14.4 ± 2.55; p < 0.05). However, no significant difference was found between the SSG-SG and the SSG-SB for maximal velocity, power, and sprints duration. This study provides new information about the effectiveness of the SSG-SB as a training stimulus for soccer.

#10 Comparative Effects of Game Profile-Based Training and Small-Sided Games on Physical Performance of Elite Young Soccer Players
Reference: J Strength Cond Res. 2019 May 27. doi: 10.1519/JSC.0000000000003225. [Epub ahead of print]
Authors: Dello Iacono A, Beato M, Unnithan V
Summary: This study was designed to investigate and compare the effects of game profile-based training (GPBT) and small-sided game (SSG) training on physical performances of elite youth soccer players during the in-season period. Twenty young soccer players (18.6 ± 0.6) were randomly assigned to either GPBT or SSG protocols performed twice a week for 8 weeks. The GPBT consisted of 2 sets of 6-10 minutes of intermittent soccer-specific circuits. The SSG training consisted of 3-5 sets of 5 vs. 5 SSGs played on a 42 × 30-m pitch. Before and after the training program, the following physical performances were assessed: repeated sprint ability, change of direction (COD), linear sprinting on 10 m and 20 m, countermovement jump, and intermittent running (YYIRL1). Significant improvements were found in all the assessed variables after both training interventions (p < 0.05). The GPBT group improved more than the SSG group in the 10-m and 20-m sprint tests by 2.4% (g = 0.4; small effect) and 4% (g = 0.9; large effect), respectively. Conversely, the SSG group jumped 4% higher (g = 0.4; small effect) and resulted 6.7% quicker than the GPBT (g = 1.5; large effect) in completing the COD task. These results suggest both GPBT and SSGs to be effective for fitness development among elite young soccer players during the competitive season. More importantly, these 2 conditioning methodologies may be considered in terms of specificity for selectively improving or maintaining specific soccer fitness-related performances in the latter phase of the season.

#11 The Experiences of Young Men, Their Families, and Their Coaches Following a Soccer and Vocational Training Intervention to Prevent HIV and Drug Abuse in South Africa
Reference: AIDS Educ Prev. 2019 Jun;31(3):224-236. doi: 10.1521/aeap.2019.31.3.224.
Authors: Swendeman D, Bantjes J, Mindry D, Stewart J, Tomlinson M, Rotheram-Borus MJ, Medich M
Summary: Young men in South Africa are at high-risk for HIV, substance abuse, and gender-based violence. This article presents qualitative results from a pilot study testing soccer leagues and vocational training to engage young-adult township men to deliver preventive interventions, including rapid HIV and alcohol/drug testing, shifting attitudes toward gender-based violence, and promoting other prosocial behaviors. Three groups participated in focus groups and in-depth interviews on experiences with the program: (1) a subset of 15 participants, (2) 15 family members, and (3) five intervention coaches. Results suggest that participants first reduced substance use on tournament days and then gradually reduced to practice days and beyond. Families suggested that "keeping young men occupied" and encouragement of prosocial behaviors was critical to risk reduction and led to increased community respect for the men. Coaches noted that behavioral and attitudinal changes were incremental and slow. The use of incentives was problematic and more research is needed to understand how incentives can be used in interventions of this nature.





Latest research in football - week 19 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Acute and chronic effects of competition on ankle dorsiflexion ROM in professional football players
Reference: Eur J Sport Sci. 2019 May 9:1-10. doi: 10.1080/17461391.2019.1611930. [Epub ahead of print]
Authors: Moreno-Pérez V, Soler A, Ansa A, López-Samanes Á, Madruga-Parera M, Beato M, Romero-Rodríguez D
Summary: The aim of this study was to investigate the acute (a football match) and chronic (a whole season) effects of competition on ankle dorsiflexion ROM in professional football players. Forty football players participated in this study. Ankle dorsiflexion ROM was recorded to examine acute (pre-match, immediately post-match and 48 h post-match) and chronic (pre-season, mid-season and post-season) effects of competitive football. In addition, it was found that players had restricted mobility measures on ankle dorsiflexion as >2 cm change between baseline measures (pre-match and pre-season). The training load of all played matches was estimated using a global positioning system (GPS) and RPE. Pre-season ankle dorsiflexion ROM was greater compared to mid-season (8.1% in the dominant, and 9.6% in the non-dominant leg) and post-season (13.8% in the dominant, and 12.5% in the non-dominant leg). In addition, around 30% of all players showed restricted ankle dorsiflexion ROM values in post-season compared with pre-season. Related to acute effects, ankle dorsiflexion ROM increased after a match (5.8%) in the dominant ankle, and this value decreased (2.65%) 48 h post-match when post-match measurements in both dominant and non-dominant ankles were compared. The progressive decrease in ankle dorsiflexion ROM throughout a season can be an indicator of increased risk of injury and may be reinforce the need of prevention actions such as stretching exercises and eccentric strength training in professional football players. In addition, these findings suggest to implement specific recovery strategies aiming at minimizing alteration in ankle dorsiflexion ROM 48 h post-match.

#2 The effect of compression shorts on pain and performance in male football players with groin pain - A double blinded randomized controlled trial
Reference: Phys Ther Sport. 2019 Apr 25;38:87-95. doi: 10.1016/j.ptsp.2019.04.013. [Epub ahead of print]
Authors: Otten R, Stam S, Langhout R, Weir A, Tak I
Summary: The purpose was to investigate the effects of compression shorts on pain and performance in football players with groin pain. Thirty-four male football players with groin pain participated in this study. The effect of wearing zoned high compression shorts (ZHC-shorts), non-zoned low compression shorts (NZLC-shorts), and normal sports clothes on pain measured with the Numeric Pain Rating Scale (NPRS) and performance during the Copenhagen 5-s squeeze test (CS), the Illinois Agility test (IAT), and maximum shooting (ST). The effects of wearing ZHC versus NZLC shorts on symptoms were measured using the Hip and groin outcome score (HAGOS) during actual football activities. Wearing ZHC-shorts reduced pain during the IAT (1.4, ES = 0.58, p= <0.01) and ST (1.2, ES = 0.47, p= <0.01) compared to wearing normal sports clothes, but did not negatively affect performance. Compared to the baseline HAGOS scores a clinically significant improvement in the symptoms (9.7, ES = 0.63, p= <0.01) and sport/recreation (13.2, ES = 0.68, p = 0.01) subscales was found when wearing the ZHC-short during football activities. Wearing zoned high compression shorts could be useful in reducing groin pain in football players during their football activities.

#3 Jump height as performance indicator for the selection of youth football players to national teams
Reference: J Sports Med Phys Fitness. 2019 May 2. doi: 10.23736/S0022-4707.19.09739-1. [Epub ahead of print]
Authors: Ryman Augustsson S, Arvidsson J, Haglund E
Summary: Different jump tests such as the Countermovement Jump (CMJ), Abalakov Jump (AJ) and Standing Long Jump (SLJ) are often used in practice to evaluate muscular power and functional performance in football. These tests are also used in different selection processes and talent identification, but the significance of the tests for the selection of youth players to national teams are relatively unknown. The aim of this study was to compare jump ability between youth football players selected or not selected for the national team. In this cross-sectional study, 22 players (aged 17±2 years), 11 national players (NP) and 11 non- national players (NNP) were evaluated in three different jump tests; CMJ, AJ and SLJ. Mean scores for the tests were analysed and compared. Significant differences were found between the groups regarding jump height in favour of the NP group in both the CMJ (NP 39.9±5.0 cm vs NNP 34.2±4.9 cm, p=0.013) and the AJ (NP 47.1±5.4 vs NNP 40.9±4.7, p=0.010). No group difference was found regarding jump length in SLJ (NP 246.2±17.9 vs NNP 232.9±16.5, p=0.084). The results suggest that tests, measuring jump height, could be used as a performance indicator and part of the selection process of youth football players to national teams, whereas the use of jump length could be questioned.

#4 Anterior cruciate ligament injury risk factors in football: a narrative review
Reference: J Sports Med Phys Fitness. 2019 Apr 30. doi: 10.23736/S0022-4707.19.09563-X. [Epub ahead of print]
Authors: Bisciotti GN, Chamari K, Cena E, Bisciotti A, Bisciotti A, Corsini A, Volpi P
Summary: Anterior cruciate ligament (ACL) lesion represents one of the most dramatic injuries in a football (soccer) player's career. There are many injury risk factors related to intrinsic (non-modifiable) and/or extrinsic (modifiable) factors of ACL-injury. To date, evidence from the literature suggests that the risk of ACL-injury is multifactorial and involves biomechanical, anatomical, hormonal, and neuromuscular factors. Despite this relative complexity, the mechanisms of injury are well known and rationally classified into two categories: mechanisms of injury based on contact or on non- contact with another player, with the non-contact injury mechanisms clearly prevailing over the mechanisms of contact injury. One of the most frequent biomechanical risk factors, associated with ACL non-contact injury, is represented by the valgus knee in the pivoting and cutting movements and in the landing phase after jumping. Gender related risk factors show female populations to have a higher predisposition to ACL-injury than males However, there are still some theoretical and practical aspects that need further investigation such as; genetic risks together with the role of oestrogen and progesterone receptors in female populations, and the in vivo interaction shoe- playing surface. In particular, the genetic risk factors of ACL lesion seem to be an interesting and promising field of investigation, where considerable progress has still to be made. This narrative review provides an insight into the risk factors of ACL-injury that could be used by practitioners for preventing injury in football (soccer).

#5 Misbehavior During Penalty Kicks and Goalkeepers Holding the Ball Too Long as Trivial Offenses in Football
Reference: Front Psychol. 2019 Apr 18;10:844. doi: 10.3389/fpsyg.2019.00844. eCollection 2019.
Authors: Kolbinger O, Stöckl M
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Summary: Rule violations occur in every sport and the respective book of rules prescribes how match officials need to sanction them. However, there are some rule violations that are nearly never penalized, even if they are perceived by the match officials. A phenomenon that has been neglected in the scientific community so far, for which we want to introduce the term trivial offenses. This research focuses on two potential trivial offenses in football: rule violations regarding the six-seconds rule, the time a goalkeeper is allowed to control the ball with his hands, and rule violations during the performance of penalty kicks. The aim is to provide empirical proof of the existence of those trivial offenses and describe the respective patterns. For this purpose, two observation systems were constructed; one to investigate 45 games from the German Bundesliga with respect to the six-seconds rule and one to study rule violations during 618 penalty kicks from four European football leagues and one cup event. The following variables were collected: Goalkeeper, MatchLocation, Minute (representing the minute of the game), PreviousAction, CurrentScore, Time (representing the time the goalkeeper controlled the ball with his hands), and Penalization for the six-seconds study; Responsibility for infringement, Decision of the referee, and Outcome for the penalty study. Reliability tests showed almost perfect agreement for the data of both samples. On average, goalkeepers control the ball 6.0 s (SD:4.54) with their hands and the six-second rule was violated in 38.4% of the situations, none of which was penalized. This duration was significantly influenced by CurrentScore (p < 0.001), which indicates a tactical abuse of this situation. None of the investigated penalty kicks was conducted without a rule violation either. In most incidents (96.3%) outfield players from both teams as well as the goalkeeper commit offenses. The umpire only judges 2.8% of these incidents correctly, most of them by approving the scored goal. In total, this research proves the existence of trivial offenses in football and shows how methods and tools of performance analysis can serve to investigate and even solve this issue.

#6 The ball kicking speed: A new, efficient performance indicator in youth soccer
Reference: PLoS One. 2019 May 17;14(5):e0217101. doi: 10.1371/journal.pone.0217101. eCollection 2019.
Authors: Rađa A, Kuvačić G, De Giorgio A, Sellami M, Ardigò LP, Bragazzi NL, Padulo J
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Summary: Success in different soccer skills like kicking depends on motor abilities achieved. Kicking is a soccer fundamental, which depends on many different and complex factors (technique, foot-ball interaction, ball flight, etc.). Therefore, it is important to identify players that are able to perform faster kicks using both dominant and non-dominant leg. The current study investigated some basic variables of different soccer kicking speed and their relevance to success in youth soccer academy. 119 players from the first and the second division participated to this study. They were randomly divided into age groups (U-15, U-17, and U19) and team status (first team, reserves). The diagnostic ability of the different ball kicking speed tests in capturing differences between first team players and reserves among different age categories were computed using the receiver operating characteristics analysis. Results demonstrated that first team players achieved better results when comparing to reserves in each category. In addition, differences were greater in the U-15 and the U-17 than in the U-19 age group. In conclusion, ball kicking speed could be one of the possible identification tools to evaluate players' success in youth soccer.

#7 Hamstring rate of torque development is more affected than maximal voluntary contraction after a professional soccer match
Reference: Eur J Sport Sci. 2019 May 17:1-16. doi: 10.1080/17461391.2019.1620863. [Epub ahead of print]
Authors: Grazioli R, Lopez P, Andersen LL, Machado CLF, Pinto MD, Cadore EL, Pinto RS
Summary: Match-induced fatigue of knee muscle strength and agonist-antagonist strength-ratios may affect both performance and risk of injury in soccer players. Once explosive tasks are imperative in soccer as well as hamstring strain injuries occur during high-velocity moments, rapid force capacity of this muscle group is especially important. This study evaluated the effect of match-induced fatigue on knee muscle strength and strength-ratio parameters after a single professional soccer match. Male professional soccer players (n = 16; 24.2 ± 3.9 years) were tested before and after a soccer match (56.2 ± 22.6 minutes of playing) for knee flexors (hamstring) and extensors (quadriceps) isometric peak torque (MVC) and rate of torque development (RTD) - as well as the hamstring-to-quadriceps ratio (H:Q) - at 30° of knee flexion. Knee injuries often occur at this joint angle, which is common in sprinting, pivoting, sidecutting, and jumping. Match-induced fatigue caused a left shift in the knee extensors torque-time curve with no significant change in both early (i.e. 0 to 50 ms) and late (i.e. 0 to 200 ms) RTD, and a right shift in the knee flexors torque-time curve with a decrease in early RTD (∼16%, P = 0.029) and late RTD (∼11%, P = 0.011). Knee extensors and knee flexors peak torque remained unchanged (P > 0.05). Early RTD H:Q decreased by∼24% (P = 0.027), while late RTD H:Q and MVC H:Q remained unchanged (P > 0.05). In conclusion, match-induced fatigue impaired the ability to rapidly produce force at an angle where injuries are most susceptible to occur. Important information is missed if only the traditional H:Q is considered.

#8 Age-related physical and technical match performance changes in elite soccer players
Reference: Scand J Med Sci Sports. 2019 May 17. doi: 10.1111/sms.13463. [Epub ahead of print]
Authors: Sal de Rellán-Guerra A, Rey E, Kalén A, Lago-Peñas C
Summary: The age of peak performance is likely to vary between sports and competitions, affected by the specific skills and attributes needed to succeed in the particular competition. However, no studies using modern tracking techniques have examined on the effects of age on competitive match play performance. Thus, the purpose of this study was to evaluate the effects of age on match physical and technical performance using a large-scale analysis of match performance in professional soccer players. A total of 14,546 individual match observations were undertaken in the first German league (Bundesliga) during the 2012-13, 2013-14, and 2014-15 seasons using a computerized tracking system (VISTRACK, by Impire Corp., Germany). Differences on physical and technical match performance of soccer players were analysed for the following variables: total distance covered, number of fast runs, number of sprints and percentage of successful passes. Professional soccer players aged >30 years showed a significant lower performance in the total distance covered, the number of fast runs, and the number of sprints compared with younger players (≤30 years). Conversely, the player's ability to make successful passes increased with age. These effects were observed in all positional roles except wide midfielders. These findings may help coaches and managers to better understand the effects of age on match-related physical and technical performance and may have the potential to assist in decisions such as, for example, when a new contract would be signed, the duration of the contract, the salary or when to replace or transfer a player depending on their age.

#9 Effects of Taping and Balance Exercises on Knee and Lower Extremity Function in Amateur Soccer Players: A Randomized Controlled Trial
Reference: J Sport Rehabil. 2019 May 16:1-25. doi: 10.1123/jsr.2018-0452. [Epub ahead of print]
Authors: Espí-López GV, Serra-Añó P, Cobo-Pascual D, Zarzoso M, Suso-Martí L, Cuenca-Martínez F, Inglés M
Summary: Knee injury prevention is a critical aspect in sport rehabilitation sciences and taping is a widely used technique in this field. Nevertheless, the role and effectiveness of a long-term application of Kinesio Taping on knee function, disability and injury prevention remains unclear. The objective was to determine the effect of Kinesio Taping, alone or in combination with balance exercises, on dynamic and static knee balance and flexibility. 48 male amateur soccer players were assigned to three groups: Sham KT (sKT) + BE; KT + BE; and KT in isolation. The intervention period lasted 4 weeks. Three evaluations were performed: at baseline (pre), at two weeks (mid) and at four weeks post-treatment (post). Y-Balance Test (YBT), Unipedal Stance Test (UST), the Toe Touch Test (TTT) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were utilized as main outcome measures.  Both sKT + BE and KT + BE groups achieved significant pre-post improvements in SEBT, UST and TTT. The KT group only showed significant intra-group differences in the left and right UST variable (p<0.05, d=0.76, d=0.62 respectively). The sham KT group obtained the strongest results in all physical variables. Regarding the KOOS, pre-post significant changes were found in the sham group (p<0.05, d=0.28). Both sham and real KT in combination with BE achieved significant improvements on all physical variables, and these differences were significantly greater compared to those found in the KT in isolation group, suggesting that benefits in knee function are due to the BE.

#10 Effects of Plyometric vs Optimum Power Training on Components of Physical Fitness in Young Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 May 16:1-27. doi: 10.1123/ijspp.2019-0039. [Epub ahead of print]
Authors: Ribeiro J, Teixeira L, Lemos R, Teixeira AS, Moreira V, Silva P, Nakamura FY
Summary: The current study aimed to compare the effects of plyometric (PT) vs. optimum power load (OPL) training on physical performance of young high-level soccer players. Athletes were randomly divided into PT (horizontal and vertical drills) and OPL (squat+hip thrust exercises at the load of maximum power output) interventions, applied over 7 weeks during the in-season period. Squat (SJ) and countermovement (CMJ) jumps, maximal sprint (10 and 30 m) and change of direction (COD; agility T test) were the pre-and post-training measured performance variables. Magnitude-based inference was used for within-and between-group comparisons. OPL training induced moderate improvements in vertical SJ (ES:0.97; 90%CI:0.32-1.61) and CMJ (ES:1.02; 90%CI:0.46-1.57), 30 m sprint speed (ES:1.02; 90%CI:0.09-1.95) and COD performance (ES:0.93; 90%CI:0.50-1.36). After PT training method, vertical SJ (ES:1.08; 90%CI:0.66-1.51) and CMJ (ES:0.62; 90%CI:0.18-1.06) were moderately increased, while small enhancements were noticed for 30 m sprint speed (ES:0.21; 90%CI:-0.02-0.45) and COD performance (ES:0.53; 90%CI:0.24-0.81). The 10 m sprint speed possibly increased after PT intervention (small ES: 0.25; 90%CI:-0.05-0.54), but no substantial change (small ES:0.36; 90%CI:-0.40-1.13) was noticed in OPL. For between-group analyses, the COD ability and 30 m sprint performances were possibly (small ES:0.30; 90%CI:-0.20-0.81; Δ=+1.88%) and likely (moderate ES:0.81; 90%CI:-0.16-1.78; Δ=+2.38%) more improved in the OPL than in the PT intervention, respectively. The two different training programs improved physical performance outcomes during the in-season period. However, the combination of vertically-and horizontally-based training exercises (squat+hip thrust) at optimum power zone led to superior gains in COD and 30 m linear sprint performances.

#11 Dynamic Warm-up With a Weighted Vest: Improvement of Repeated Change-of-Direction Performance in Young Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 May 16:1-28. doi: 10.1123/ijspp.2018-0800. [Epub ahead of print]
Authors: Turki O, Dhahbi W, Gueid S, Hmaied S, Souaifi M, Khalifa R
Summary: This study aims to explore the effect of 4 different warm-up strategies using weighted vests, and to determine the specific optimal recovery duration required to optimize the repeated change of direction (RCOD) performance in young soccer players. Nineteen male soccer players (age: 18±0.88 years, body-mass: 69.85±7.68 kg, body-height: 1.75±0.07 m, body-mass-index: 22.87±2.23 kg·m-2 and body-fat-percentage: 12.53±2.59 %), completed the following loaded warm-up protocols in a randomized, counterbalanced cross-over, within participants order and on separate days: weighted-vest with a loading of 5% (WUV5%), 10% (WUV10%), 15% (WUV15%) body-mass, and an unloaded condition (control). RCOD performance (total time, peak time and fatigue index) was collected during the pre-intervention phase (5 min after the dynamic stretching sequence) for baseline values and immediately (at 15ths), at the 4th and 8th min post-warm-up intervention. For each post-warm-up tested, recovery-times (i.e., 15-s, 4-min, and 8-min), both total, and peak times were faster following WUV5%, WUV10%, and WUV15%, compared to the unloaded condition (P [<0.001-0.031], d [1.28-2.31] [large]). There were no significant differences (P [0.09-1.00], d [0.03-0.72] [trivial-moderate]) in-between recovery times in both total and peak times following WUV5%, WUV10% and WUV15%. However, baseline fatigue index score was significantly worse than all other scores (P [<0.001-0.002], d [1.35-2.46] [large]) following the loaded conditions. The findings demonstrated that a dynamic loaded warm-up increases an athlete's initial RCOD performance up to the 8th min post-warm-up intervention. Therefore, strength coaches need to consider using weighted-vests during the warm-up for trained athletes in order to acutely optimize RCODs.

#12 The Increased Effectiveness of Loaded Versus Unloaded Plyometric-Jump Training in Improving Muscle Power, Speed, Change-of-Direction, and Kicking-Distance Performance in Prepubertal Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 May 16:1-25. doi: 10.1123/ijspp.2018-0866. [Epub ahead of print]
Authors: Negra Y, Chaabene H, Sammoud S, Prieske O, Moran J, Ramirez-Campillo R, Nejmaoui A, Granacher U
Summary: This study examined the effects of loaded (LPJT) and unloaded (UPJT) plyometric jump training programmes on measures of muscle power, speed, change-of-direction and kicking-distance performance in prepubertal male soccer players. Participants (N=29) were randomly assigned to a LPJT group (n=13; age=13.0±0.7 years) using weighted vests or UPJT group (n=16; age=13.0±0.5 years) using body mass only. Before and after the intervention, tests for the assessment of proxies of muscle power (i.e., countermovement-jump [CMJ], standing-long-jump [SLJ]), speed (i.e., 5-m, 10-m, and 20-m sprint), change-of-direction (i.e., Illinois change-of-direction test [ICoDT], modified 505 agility test), and kicking-distance test were conducted. Data were analysed using magnitude-based inferences. Within-group analyses for the LPJT group showed large and very large improvements for 10-m sprint-time (effect size [ES]=2.00) and modified 505 CoD (ES=2.83) tests, respectively. For the same group, moderate improvements were observed in ICoDT (ES=0.61), 5- and 20-m sprint-time (ES=1.00 for both tests), CMJ (ES=1.00) and MKD (ES=0.90). Small enhancements in the SLJ (ES=0.50) test were apparent. Regarding the UPJT group, small improvements were observed for all tests (ES=0.33 to 0.57) except 5-m and 10-m sprint-time (ES=1.00 and 0.63, respectively). Between-group analyses favored the LPJT group for the modified 505 CoD (ES=0.61), SLJ (ES=0.50), and MKD (ES=0.57) tests, but not for 5-m sprint-time (ES=1.00). Only trivial between-group differences were shown for the remaining tests (ES=0.00 to 0.09). Overall, LPJT appears to be more effective than UPJT in improving measures of muscle power, speed, change-of-direction and kicking-distance performance in prepubertal male soccer players.





Latest research in football - week 18 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Relationship of Pre-season Training Load With In-Season Biochemical Markers, Injuries and Performance in Professional Soccer Players
Reference: Front Physiol. 2019 Apr 12;10:409. doi: 10.3389/fphys.2019.00409. eCollection 2019.
Authors: Coppalle S, Rave G, Ben Abderrahman A, Ali A, Salhi I, Zouita S, Zouita A, Brughelli M, Granacher U, Zouhal H
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Summary: There is controversy in the literature in regards of the link between training load and injury rate. Thus, the aims of this non-interventional study were to evaluate relationships between pre-season training load with biochemical markers, injury incidence and performance during the first month of the competitive period in professional soccer players. Healthy professional soccer players were enrolled in this study over two pre-season periods. Data sets were available from 26 players during the first season (2014-2015) and 24 players during the second season (2015-2016) who completed two pre-season periods (6 weeks each). External training load was assessed from all athletes during training using Global Positioning System (GPS). Internal training load was monitored after each training session using rate of perceived exertion (RPE). Before and after each pre-season, blood samples were taken to determine plasma lactate dehydrogenase (LDH), creatine kinase (CK) and C-reactive protein (CRP). Injury incidence and overall performance (ranking of the team after the first five official games of the championship) were recorded for both seasons separately. There was no statistically significant difference in mean RPE values of the two-preparation periods (2737 ± 452 and 2629 ± 786 AU, p = 0.492). The correlational analysis did not reveal significant associations between internal and external training load (RPE and GPS data) and biological markers. There was a significant positive correlation between RPE and LDH during the 2015/2016 season (r = 0.974, p = 0.001). In addition, a significant negative correlation was found between total distance >20 km/h and CRP during the 2015-2016 season (r = -0.863, p = 0.027). The injury rates for the two seasons were 1.76 and 1.06 per 1000 h exposure for the 2014-2015 and 2015-2016 seasons, respectively (p = 0.127). Our study showed that pre-season training load is not associated with overall team performance. This association is most likely multifactorial and other factors (e.g., technical and tactical level of the team, opponents, environment) may play an important role for the collective team performance. Our findings may help coaches to better prepare their athletes during pre-season.

#2 Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football
Reference: PLoS One. 2019 Apr 30;14(4):e0216364. doi: 10.1371/journal.pone.0216364. eCollection 2019.
Authors: Thomson A, Whiteley R, Wilson M, Bleakley C
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Summary: An optimal range of shoe-surface traction (grip) exists to improve performance and minimise injury risk. Little information exists regarding the magnitude of traction forces at shoe-surface interface across a full season of elite football (soccer) using common football shoes. The objective was to assess variation in shoe-surface traction of six different football shoe models throughout a full playing season in Qatar encompassing climatic and grass species variations. Football shoes were loaded onto a portable shoe-surface traction testing machine at five individual testing time points to collect traction data (rotational and translational) on a soccer playing surface across one season. Surface mechanical properties (surface hardness, soil moisture) and climate data (temperature and humidity) were collected at each testing time point. Peak rotational traction was significantly different across shoe models (F = 218, df = 5, p <0.0001), shoe outsole groups (F = 316.2, df = 2, p < .0001), and grass species (F = 202.8, df = 4, p < 0.0001). No main effect for shoe model was found for translational traction (F = 2.392, p = 0.07). The rotational (but not translational) traction varied substantially across different shoe types, outsole groups, and grass species. Highest rotational traction values were seen with soft ground outsole (screw-in metal studs) shoes tested on warm season grass. This objective data allows more informed footwear choices for football played in warm/hot climates on sand-based elite football playing surfaces. Further research is required to confirm if these findings extend across other football shoe brands.

#3 When Better Seems Bigger: Perceived Performance of Adult Professional Football Players Is Positively Associated With Perceptions of Their Body Size
Reference: Evol Psychol. 2019 Apr-Jun;17(2):1474704919841914. doi: 10.1177/1474704919841914.
Authors: Knapen JEP, Pollet TV, van Vugt M
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Summary: Research has shown a positive association between cues of physical formidability and perceptions of status, supporting a generic "bigger-is-better" heuristic. However, does better also lead to appraisals as bigger? Recent research suggests that the perceptual association between body size and social status can also be explained in terms of prestige. To test whether perceptions of prestige lead to higher appraisals of body size, we examined whether people apply a "better is bigger bias" (BBB) in football, where performance and body size tend to be uncorrelated. In two studies, we examined real coalitional sports groups on a national (Study 1) and team level (Study 2), and we manipulated target performance in an experimental third study. Results suggest that perceived performance significantly predicted both the perceived height (Studies 2 and 3) and perceived weight (Studies 1 and 2) of professional football players, supporting the BBB. Support for the team had a positive effect on body size estimations of the players; however, we did not find any support for winner or loser effects. We discuss these results in light of individual versus team performance and coalitional affiliation.

#4 Efficacy of using non-linear pedagogy to support attacking players' individual learning objectives in elite-youth football: A randomised cross-over trial
Reference: J Sports Sci. 2019 Apr 27:1-11. doi: 10.1080/02640414.2019.1609894. [Epub ahead of print]
Authors: Roberts SJ, Rudd JR, Reeves MJ
Summary: The present study examined the efficacy of a coaching curriculum, based on non-linear pedagogy, on improving attacking players' individual learning objectives (ILOs) in elite-youth football. Participants included 22 attacking players (i.e., centre-forwards, wide-players and attacking midfield players) from a professional football academy in England. The players were randomly appointed to both control (CON) and intervention (INT) periods following baseline measures. The INT (non-linear) and CON (linear) periods were both designed to support the ILOs provided to each player as part of the elite player performance plan. The study adopted a randomised cross-over design and ILOs considered important for attacking players (i.e., strong foot finishing, weak foot finishing, 1-v-1 and decision-making) were evaluated using the Loughborough Shooting Skill Test. The results showed significant differences for INT in 1-v-1 (P< 0.02) and decision-making (P< 0.01). However, there were no significant differences for strong foot finishing, weak foot finishing or time taken. These results support non-linear pedagogy in developing 1-v-1 game play and decision-making but not for technical shooting proficiency.

#5 Injury Prevention in Amateur Soccer: A Nation-Wide Study on Implementation and Associations with Injury Incidence
Reference: Int J Environ Res Public Health. 2019 May 7;16(9). pii: E1593. doi: 10.3390/ijerph16091593.
Authors: Gebert A, Gerber M, Pühse U, Stamm H, Lamprecht M
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Summary: Prevention programmes can reduce injury risk in amateur soccer. Hence, we examined the implementation of injury prevention in the real-world context of Swiss amateur soccer. In 2004 (n = 1029), 2008 (n = 705) and 2015 (n = 1008), a representative sample of Swiss amateur soccer coaches was interviewed by telephone about the frequency of injuries in their teams, the implementation of preventive measures and the use of injury prevention programmes. In the 2015 survey, 86.1% of amateur coaches stated that injury prevention is important and 85.3% of amateur coaches reported that they would implement some kind of preventive measures. The proportion of teams which performed a prevention programme according to minimal standards remained unchanged between 2008 (21.7%) and 2015 (21.9%), although a second prevention programme was made available in 2011. Only 8.6% of the 30+/40+ league teams, which are composed as a function of age, implemented a programme. Overall, the level of implementation of prevention programmes in this real-world context is still unsatisfactory. Offering an additional programme did not lead to a higher willingness to implement such programmes among the coaches. Concerted efforts are needed to remove barriers that hinder the use of such programmes, particularly among coaches of 30+/40+ league teams.

#6 Validity and reliability of a 6-a-side small-sided game as an indicator of match-related physical performance in elite youth Brazilian soccer players
Reference: J Sports Sci. 2019 May 7:1-6. doi: 10.1080/02640414.2019.1608895. [Epub ahead of print]
Authors: Aquino R, Melli-Neto B, Ferrari JVS, Bedo BLS, Vieira LHP, Santiago PRP, Gonçalves LGC, Oliveira LP, Puggina EF
Summary: The aims of this study were: (i) to compare the external and internal load during a 6-a-side small-sided game (6v6-SSG) according to age-group; (ii) to relate these parameters between the 6v6-SSG and official matches; and (iii) to test the reliability of the 6v6-SSG. A total of 51 Brazilian youth soccer players participated in this study (U11 [n = 16]; U13 [n = 10]; U15 [n = 9]; U17 [n = 8]; U20 [n = 8]). Three experiments were conducted. Experiment A: fifty-one U11 to U20 players were submitted to 6v6-SSGs (n = 10 games; two for each age-group). Experiment B: thirty-two players were randomized to also play official matches (n = 6 matches). Experiment C: thirty-five youth players played the 6v6-SSG twice for test and retest reliability analysis. External load was obtained using Global Positioning Systems and the internal load parameter was calculated through mean heart rate. Statistical approaches showed progressive increases in all parameters according to categories (U11< U13< U15< U17< U20; p < 0.05; ES = 0.42-23.68). Even controlling for chronological age, all parameters showed likely to almost certain correlations between 6v6-SSG and official matches (r = 0.25-0.92). Collectively, the proposed protocol indicates good reliability (CV% = 2.0-12.6; TE% = 2.3-2.7%; ICC = 0.78-0.90). This research suggests that the 6v6-SSG is an alternative tool to indicate match-related physical performance in youth soccer players.

#7 Improvements in soccer specific fitness and exercise tolerance following 8 weeks of inspiratory muscle training in adolescent males
Reference: J Sports Med Phys Fitness. 2019 Apr 30. doi: 10.23736/S0022-4707.19.09578-1. [Epub ahead of print]
Authors: Najafi A, Ebrahim K, Ahmadizad S, Jahani Ghaeh Ghashlagh GR, Javidi M, Hackett D
Summary: Inspiratory muscle training has been shown to improve exercise performance, however there is limited evidence for its effectiveness in soccer players. This study investigates the effect of inspiratory muscle training on soccer-specific fitness and exercise tolerance in adolescent male players. Thirty highly trained soccer players (16-19 y) were randomly assigned into one of three groups: experimental 1 (n=10), experimental 2 (n=10) and sham-control (sham, n=10). All groups performed inspiratory muscle training twice per day and five times per week for 8 weeks. Experimental 1 performed 25-35 breaths at 55% maximal inspiratory pressure, experimental 2 performed 45-55 breaths at 40% maximal inspiratory pressure, whereas sham performed 30 breaths at 15% maximal inspiratory pressure. Measures before and after the intervention involved the Yo-Yo intermittent recovery test level 1, running-based anaerobic test, repeated high-intensity endurance test, and maximal inspiratory pressure, and spirometry. Yo-Yo intermittent recovery test level 1 distance increased for experimental groups 1 and 2 compared to sham (P = 0.012 and P = 0.031, respectively), with no difference between experimental groups. Fatigue index calculated from running-based anaerobic test improved for experimental groups 1 and 2 compared to sham (P = 0.014 and P = 0.011, respectively), with no difference between experimental groups. Exercise tolerance (i.e. blood lactate concentration, perceived exertion and perceived breathlessness) following the repeated high-intensity endurance test decreased in experimental groups 1 and 2 compared to sham (P <0.05), with no difference between experimental groups. Maximal inspiratory pressure increased for experimental groups 1 and 2 compared to sham (P = 0.000), with no difference between experimental groups. There were no changes for the spirometry measures. Improvements in soccer-specific fitness and exercise tolerance can be achieved using inspiratory muscle training protocols of varying intensities and volumes.

#8 Effects of Strength Training on Body Composition in Young Male Professional Soccer Players
Reference: Sports (Basel). 2019 May 5;7(5). pii: E104. doi: 10.3390/sports7050104.
Authors: Suarez-Arrones L, Lara-Lopez P, Torreno N, Saez de Villarreal E, Di Salvo V, Mendez-Villanueva A
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Summary: The present prospective cohort study investigated changes in body composition (BC) in young male football players (n = 18, 16.1 ± 0.8 years; 181.0 ± 0.1 cm; 71.3 ± 4.9 kg) after combined football and strength training (ST) during a whole in-season period (26 weeks). BC was measured at whole-body absolute and regional levels by dual-energy X-ray absorptiometry in eighteen players at the beginning and at the end of the competitive period. The ST was organized into three different session types: ST in the gym, specific ST on the field, and individual ST (weak points). The results of the present study indicated that fat-free mass (FFM) was substantially higher following the competitive period (5.1% ± 1.2%), while percentage of fat showed no changes during the competitive period. At the regional level, arms' and legs' FFM increased at the end of the season, and bone mineral content (BMC) and density (BMD) increased in arms, legs, pelvis, thoracic spine, and lumbar spine. In conclusion, within the limitation of the potential positive impact of growth and/or maturation, present results seem to indicate that an ST program that supplements football-related training sessions could be an effective option to increase FFM, BMC, and BMD at both whole-body and regional level across the competitive season in young male professional football players.

#9 Dose-Response Relationship Between External Load Variables, Body Composition, and Fitness Variables in Professional Soccer Players
Reference: Front Physiol. 2019 Apr 17;10:443. doi: 10.3389/fphys.2019.00443. eCollection 2019.
Authors: Clemente FM, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The aim of this study was to test associations between accumulated external load and changes in body composition, isokinetic strength, and aerobic capacity of soccer players. Twenty-three professional soccer players (age: 24.7 ± 2.8 years; height: 179.2 ± 6.3; experience: 9.7 ± 2.1 years) participated in this study. This pre-post study design was performed during 10 weeks from July to August of 2017 (4 weeks of pre-season and 6 weeks during the early season). Players were monitored daily by GPS technology and were assessed before and after a 10-week period in terms of body mass (BM), fat mass, lean mass, isokinetic strength at 60°/s, VO2max, and HRmax. Large-to-very large positive correlations were found between the sum of sprinting distance and % differences of BM [0.70, (-0.09;0.95)], HRmax [0.51, (-0.37;0.91)], agonist (quadriceps)/antagonist (hamstrings) left ratio [0.84, (0.27;0.97)] and agonist/antagonist right ratio [0.92, (0.58;0.99)]. Large positive correlations were found between the acceleration sum and % differences of VO2max [0.58, (-0.29;0.92)], quadriceps left peak torque [0.66, (-0.16;0.94)], hamstrings left peak torque [0.68, (-0.13;0.94)] and hamstrings right peak torque [0.62, (-0.22;0.93)]. Sprinting load was largely and positively associated with changes in knee strength asymmetries. Acceleration sum was largely and positively correlated with variations at VO2max and peak torques at hamstrings. In addition, dose-response relationships using external load variables were identified in professional soccer players.

#10 Biological maturation and match running performance: A national football (soccer) federation perspective
Reference: J Sci Med Sport. 2019 Apr 22. pii: S1440-2440(18)30984-8. doi: 10.1016/j.jsams.2019.04.007. [Epub ahead of print]
Authors: Lovell R, Fransen J, Ryan R, Massard T, Cross R, Eggers T, Duffield R
Summary: The purpose was to examine the influence of maturation and its interaction with playing position upon physical match performances in U15 footballers from a national federation. 278 male outfield players competing in a national tournament were assessed for somatic maturity and match physical performances according to playing position. Stature, sitting height, and body mass were measured and entered into an algorithm to estimate the age at peak height velocity (APHV). Players match movements were recorded by Global Positioning System devices (10 Hz), to determine peak speed, and total- (TD), low-speed running (LSR; ≤13.0 km h-1), high-speed running (HSR; 13.1-16.0 km h-1), very high-speed running (VHSR; 16.1-20.0 km h-1) and sprint distances (SPR; >20.0 km h-1) expressed relative to match exposure (m min-1). Linear-mixed models using log transformed response variables revealed a significant contribution of estimated APHV upon TD (1.01; 95% CI: 0.99-1.02 m·min-1; p < 0.001), HSR (1.05; 95% CI: 0.98-1.13 m min-1; p < 0.001) and VHSR (1.07; 95% CI: 1.00-1.14 m min-1; p = 0.047). An increase by one year in APHV was associated with an increase of 0.6, 5.4 and 6.9% in TD, HSR and VHSR respectively. No effects of APHV were observed for LSR, SPR, and peak speed. Further, no APHV effects were observed relative to players' field position. Later maturing players covered substantially more higher-intensity (HSR and VHSR) running in matches, irrespective of playing position. The greater match intensity of later maturing players may inform talent identification and athletic development processes within a national federation.

#11 Short-Term Cardiac Autonomic Recovery after a Repeated Sprint Test in Young Soccer Players
Reference: Sports (Basel). 2019 Apr 30;7(5). pii: E102. doi: 10.3390/sports7050102.
Authors: Abad CCC, Pereira LA, Zanetti V, Kobal R, Loturco I, Nakamura FY
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Summary: The aim of this study was to describe the time course (within 2 h post-exercise) of heart rate variability (HRV) recovery following a traditional repeated sprint ability (RSA) test applied to youth soccer players. Twenty-four young soccer players (18.4 ± 0.5 years) undertook the following assessments: (1) 10 min rest in the seated position for HRV assessment; (2) a repeated sprint ability (RSA) test; (3) passive recovery in the seated position for 10 min, immediately after finishing the RSA test and 1 h and 2 h post-RSA test. During the HRV measurements (using the natural log of root mean square difference of successive normal RR intervals-lnRMSSD) the participants were instructed to assume a comfortable sitting position, remaining awake and breathing spontaneously for 10 min. Magnitude-based inference was used in the analyses. After the RSA test, the post-1 h measure was almost certainly lower than the resting measure, but almost certainly higher than the lnRMSSD measured post-RSA test. The lnRMSSD post-2 h was likely lower than the resting lnRMSSD and very likely higher than post-1 h. In conclusion, lnRMSSD is severely depressed after performing an RSA test, and reactivation is incomplete after 2 h of passive recovery. This result should be considered by practitioners when applying successive training sessions within intervals shorter than 2 h.

#12 A comparison of the isometric force fatigue-recovery profile in two posterior chain lower limb tests following simulated soccer competition
Reference: PLoS One. 2019 May 3;14(5):e0206561. doi: 10.1371/journal.pone.0206561. eCollection 2019.
Authors: Matinlauri A, Alcaraz PE, Freitas TT, Mendiguchia J, Abedin-Maghanaki A, Castillo A, Martínez-Ruiz E, Carlos-Vivas J, Cohen DD
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Summary: The aim was to evaluate the reliability of isometric peak force (IPF) in a novel "long-length" 90°Hip:20°Knee (90:20) strength test and to compare the simulated soccer match induced fatigue-recovery profile of IPF in this test with that of an isometric 90°Hip:90°Knee (90:90) position test. Twenty semi-professional soccer players volunteered for the study of which 14 participated in the first part of the study which assessed 90:20 reliability (age = 21.3 ± 2.5 years, height = 1.79 ± 0.07 m, body mass = 73.2 ± 8.8 kg), while 17 completed the second part of the study evaluating fatigue-recovery (age 21.2±2.4 yrs., height = 180 ± 0.09 m, body mass 73.8 ± 8.9 kg). We evaluated the inter-session reliability of IPF in two 90:20 test protocols (hands on the wall (HW); and hands on chest (HC)) both performed on two occasions, 7 days apart. We then assessed 90:20 (HC) and 90:90 IPF immediately before (PRE) and after (POST) after a simulated soccer match protocol (BEAST90mod) and 48 (+48 h) and 72 hours (+72 h) later. Part one: the 90:20 showed moderate to high overall reliability (CV's of 7.3% to 11.0%) across test positions and limbs. CV's were lower in the HW than HC in the dominant (7.3% vs 11.0%) but the opposite happened in the non-dominant limb where CV's were higher in the HW than HC (9.7% vs 7.3%). Based on these results, the HC position was used in part two of the study. Part two: 90:20 and 90:90 IPF was significantly lower POST compared to PRE BEAST90mod across all testing positions (p<0.001). IPF was significantly lower at +48 h compared to PRE in the 90:20 in both limbs (Dominant: p<0.01,Non-dominant: p≤0.05), but not in the 90:90. At +72 h, IPF was not significantly different from PRE in either test. Simple to implement posterior IPF tests can help to define recovery from competition and training load in football and, potentially, in other multiple sprint athletes. Testing posterior chain IPF in a more knee extended 90:20 position may provide greater sensitivity to fatigue at 48 h post simulated competition than testing in the 90:90 position, but also may require greater degree of familiarization due to more functional testing position.





Latest research in football - week 17 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 In-season internal and external training load quantification of an elite European soccer team
Reference: PLoS One. 2019 Apr 22;14(4):e0209393. doi: 10.1371/journal.pone.0209393. eCollection 2019.
Authors: Oliveira R, Brito JP, Martins A, Mendes B, Marinho DA, Ferraz R, Marques MC
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Summary: Elite soccer teams that participate in European competitions need to have players in the best physical and psychological status possible to play matches. As a consequence of congestive schedule, controlling the training load (TL) and thus the level of effort and fatigue of players to reach higher performances during the matches is therefore critical. Therefore, the aim of the current study was to provide the first report of seasonal internal and external training load that included Hooper Index (HI) scores in elite soccer players during an in-season period. Nineteen elite soccer players were sampled, using global position system to collect total distance, high-speed distance (HSD) and average speed (AvS). It was also collected session rating of perceived exertion (s-RPE) and HI scores during the daily training sessions throughout the 2015-2016 in-season period. Data were analysed across ten mesocycles (M: 1 to 10) and collected according to the number of days prior to a one-match week. Total daily distance covered was higher at the start (M1 and M3) compared to the final mesocycle (M10) of the season. M1 (5589m) reached a greater distance than M5 (4473m) (ES = 9.33 [12.70, 5.95]) and M10 (4545m) (ES = 9.84 [13.39, 6.29]). M3 (5691m) reached a greater distance than M5 (ES = 9.07 [12.36, 5.78]), M7 (ES = 6.13 [8.48, 3.79]) and M10 (ES = 9.37 [12.76, 5.98]). High-speed running distance was greater in M1 (227m), than M5 (92m) (ES = 27.95 [37.68, 18.22]) and M10 (138m) (ES = 8.46 [11.55, 5.37]). Interestingly, the s-RPE response was higher in M1 (331au) in comparison to the last mesocycle (M10, 239au). HI showed minor variations across mesocycles and in days prior to the match. Every day prior to a match, all internal and external TL variables expressed significant lower values to other days prior to a match (p<0.01). In general, there were no differences between player positions. Conclusions: Our results reveal that despite the existence of some significant differences between mesocycles, there were minor changes across the in-season period for the internal and external TL variables used. Furthermore, it was observed that MD-1 presented a reduction of external TL (regardless of mesocycle) while internal TL variables did not have the same record during in-season match-day-minus.

#2 Comparison of Physical Fitness and Anthropometrical Profiles Among Brazilian Female Soccer National Teams From U15 to Senior Categories
Reference: J Strength Cond Res. 2019 Apr 11. doi: 10.1519/JSC.0000000000003140. [Epub ahead of print]
Authors: Ramos GP, Nakamura FY, Penna EM, Mendes TT, Mahseredjian F, Lima AM, Garcia ES, Prado LS, Coimbra CC
Summary: This study aimed to compare anthropometric and physical fitness of Brazilian female national team soccer players from the U15 to senior categories, and to compare the physical performance between selected and nonselected players. Subjects included 231 athletes (U15, n = 46, U17, n = 49, U20, n = 98, and Senior, n = 38). Body mass, height, sum of skinfolds, squat jump (SJ), countermovement jump (CMJ), 20-m linear sprint, and Yo-Yo IR1 were assessed. The U15 players were shorter than all other groups (p < 0.01) and lighter than U20 players (p < 0.01). Regarding physical tests, Senior athletes presented higher SJ compared with U20, and both showed higher CMJ and SJ compared with the U15 and U17 (p < 0.05). Senior athletes were also faster than players of all other categories in 20-m sprint (p < 0.01) and covered the greatest distance in the Yo-Yo IR1 (p < 0.05). U20 were better in the Yo-Yo IR1 than the younger groups (p < 0.05). When comparing selected and nonselected players, no differences were identified in anthropometric measures (p > 0.05). However, selected players from U17, U20, and Senior teams showed better performance in Yo-Yo IR1 than nonselected ones (p < 0.05). Finally, selected senior athletes also presented higher CMJ and SJ than nonselected players (p < 0.05). These results suggest that, although there is a tendency for maintenance in anthropometric measures from the age of 15 years, there are substantial improvements in speed, lower-body power, and aerobic capacity from U20 age group. In addition, it seems that intermittent aerobic fitness contributes to the selection of players to international tournaments in national teams.

#3 Effects of Interlimb Asymmetries on Acceleration and Change of Direction Speed: A Between-Sport Comparison of Professional Soccer and Cricket Athletes
Reference: J Strength Cond Res. 2019 Apr 16. doi: 10.1519/JSC.0000000000003135. [Epub ahead of print]
Authors: Bishop C, Read P, Brazier J, Jarvis P, Chavda S, Bromley T, Turner A
Summary: The first aim of this study was to quantify and compare asymmetries among professional soccer and cricket athletes. The second aim was to examine the association between asymmetries and performance within both groups. Professional soccer (n = 18) and cricket (n = 23) athletes performed single-leg countermovement jumps, single-leg drop jumps (SLDJs), a 10-m sprint, and 505 change of direction speed (CODS) tests. Interlimb asymmetries were calculated as a standard percentage difference, Mann-Whitney U tests conducted to establish systematic bias between groups, and Spearman's r correlations used to establish the relationship between asymmetry scores and speed and CODS performance. Soccer athletes sprinted faster, jumped higher, and had a greater reactive strength index (RSI) score than cricket athletes (p < 0.05). However, cricketers showed reduced ground contact times compared with footballers during the SLDJ (p < 0.05). The cricket group showed significantly greater jump height (asymmetry = 11.49 vs. 6.51%; p = 0.015) and RSI (asymmetry = 10.37 vs. 5.95%; p = 0.014) asymmetries compared with soccer players. These metrics were also associated with slower 505 times in the cricket group only (r = 0.56 -0.74; p < 0.01). These results show that between-limb asymmetries exhibit no association with speed and CODS in elite soccer players but are associated with reduced CODS in elite cricketers. Thus, the reduction of interlimb asymmetries may be of greater consideration when working with cricket vs. soccer athletes.

#4 Dose-Response Relationship Between Internal Training Load and Changes in Performance During the Preseason in Youth Soccer Players
Reference: J Strength Cond Res. 2019 Apr 16. doi: 10.1519/JSC.0000000000003126. [Epub ahead of print]
Authors: Figueiredo DH, Figueiredo DH, Moreira A, Gonçalves HR, Dourado AC
Summary: The aim of this study was to describe training intensity distribution based on the session rating of perceived exertion (sRPE) and heart rate (HR) methods and examine the dose-response relation between internal training load (ITL) and change in performance of 16 youth soccer players (mean ± SD age: 18.75 ± 0.68 years, height: 175.3 ± 5.5 cm, body mass: 68.7 ± 6.5 kg, and body fat: 10.7 ± 1.2%) belonging to a Brazilian first division team during a 3-week preseason. The sRPE and HR data were registered daily to calculate the ITL and the training intensity distribution, in 3 intensity zones (low, moderate, and high). The Yo-yo Intermittent Recovery Level 1 (Yo-yo IR1) was evaluated before and after experimental period. The total time spent in the low-intensity zone (HR method) was greater (p < 0.01) compared with the moderate- and high-intensity zones. No difference was observed between training intensity zones determined by the sRPE method (p > 0.05). Negative correlations were observed between weekly mean sRPE-TL (r = -0.69), Edward's-TL (r = -0.50), and change in Yo-yo IR1. Linear regression indicated that weekly mean sRPE-TL (F1;14 = 13.3; p < 0.01) and Edward's-TL (F1;14 = 4.8; p < 0.05) predicted 48.7 and 25.5% of the variance in performance change, respectively. Stepwise linear regression revealed that these 2-predictor variables (F2;13 = 18.9; p < 0.001) explained 74.5% of the variance in performance change. The results suggest that the sRPE and HR methods cannot be used interchangeably to determine training intensity distribution. Moreover, sRPE-TL seems to be more effective than the HR-based TL method to predict changes in performance in youth soccer players.

#5 Activity Profiles of Top-Class Players and Referees and Accuracy in Foul Decision-Making During Korean National League Soccer Games
Reference: J Strength Cond Res. 2019 Apr 16. doi: 10.1519/JSC.0000000000003083. [Epub ahead of print]
Authors: Joo CH, Jee H
Summary: The aims of this study were to compare the activity profiles between the top-class referees and players and elucidate the factors related to foul decision-making. Three hundred thirty-five elite-level players and referees were analyzed for distance covered during 20 matches of nationally held 2016 Korean league competitions. Distance covered by the players and referees was analyzed for the activity zones (slow walking, walking, jogging, running, high-intensity running, and sprinting) and 15-minute match periods. Mean distance between foul play and referee locations, foul plays, and 15-minute match periods were compared with the foul decision errors. Foul play and decision error rates (%) were also analyzed per segmented pitch zone. Although the total distance covered during a match and distances covered by jogging, running, and sprinting were significantly different between the players and referees, differences were within 1%. Significant differences in the distance covered before and after halftime were observed. The greatest distance between the foul play and referee locations, number of foul plays, and number of foul decision errors were observed at the 75-minute match period. Finally, the greater number of foul plays was observed in the neutral and attacking zones, and the foul decision errors were observed in the right defensive and left attacking zones 1. In conclusion, although the activity profiles may be different, referees should maintain certain level of physical fitness to match that of the players. To reduce the number of foul decision errors, factors such as match time, foul occurring location, and distance between foul play and referee locations should be considered.

#6 Are specific players more likely to be involved in high-magnitude head impacts in youth football?
Reference: J Neurosurg Pediatr. 2019 Apr 26:1-7. doi: 10.3171/2019.2.PEDS18176. [Epub ahead of print]
Authors: Gellner RA, Campolettano ET, Smith EP, Rowson S
Summary: Youth football attracts approximately 3.5 million participants every year, but concern has recently arisen about the long-term effects of experiencing repetitive head accelerations from a young age due to participation in football. The objective of this study was to quantify total involvement in high-magnitude impacts among individual players in youth football practices. The authors explored the relationship between the total number of high-magnitude accelerations in which players were involved (experienced either by themselves or by other players) during practices and the number of high-magnitude accelerations players experienced. local cohort of 94 youth football players (mean age 11.9 ± 1.5, mean body mass 50.3 ± 16.4 kg) from 4 different teams were recruited and outfitted with helmet-mounted accelerometer arrays. The teams were followed for one season each for a total of 128 sessions (practices, games, and scrimmages). All players involved in high-magnitude (greater than 40g) head accelerations were subsequently identified through analysis of practice film. Players who experienced more high-magnitude accelerations were more likely to be involved in impacts associated with high-magnitude accelerations in other players. A small subset of 6 players (6%) were collectively involved in 230 (53%) high-magnitude impacts during practice, were involved in but did not experience a high-magnitude acceleration 78 times (21% of the 370 one-sided high-magnitude impacts), and experienced 152 (30%) of the 502 high-magnitude accelerations measured. Quarterbacks/running backs/linebackers were involved in the greatest number of high-magnitude impacts in practice and experienced the greatest number of high-magnitude accelerations. Which team a player was on was an important factor, as one team showed much greater head impact exposure than all others. This study showed that targeting the most impact-prone players for individualized interventions could reduce high-magnitude acceleration exposure for entire teams. These data will help to further quantify elevated head acceleration exposure and enable data-driven interventions that modify exposure for individual players and entire teams.

#7 Bilateral Simultaneous Tibial Tubercle Avulsion in an Adolescent Football Player with Previous Bilateral Osgood-Schlatter Disease
Reference: Case Rep Orthop. 2019 Mar 24;2019:8535370. doi: 10.1155/2019/8535370. eCollection 2019.
Authors: Dalla Rosa Nogales J, Nogales Zafra JJ
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Summary: Tibial tubercle avulsion fractures are a very uncommon injury, accounting between 0.4 and 2.7% of all epiphyseal injuries. Bilateral lesions are extremely rare with only 20 cases described in the literature. They occur more frequently in male adolescents and during sport activities that require jumping and sprinting, such as football or basketball. We report the case of a 13-year-old boy who sustained simultaneous bilateral tibial avulsion fractures on the background of a previous conservatively managed bilateral Osgood-Schlatter disease.

#8 Working Memory Training in Professional Football Players: A Small-Scale Descriptive Feasibility Study-The Importance of Personality, Psychological Well-Being, and Motivational Factors
Reference: Sports (Basel). 2019 Apr 18;7(4). pii: E89. doi: 10.3390/sports7040089.
Authors: In de Braek D, Deckers K, Kleinhesselink T, Banning L, Ponds R
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Summary: Working memory training (WMT) programs can improve working memory (WM). In football players, this could lead to improved performance on the pitch. Eighteen professional football players of Maatschappelijke Voetbal Vereniging Maastricht (MVV) participated and followed an online, computerized WMT program. Neuropsychological performance, psychological wellbeing, self-efficacy, and football skills (Loughborough Soccer Passing Test; LSPT) were assessed at three time points, before and after WMT and at three-month follow-up. Descriptive data are reported. Baseline characteristics were roughly similar for both groups. Participants performed better on the trained WM tasks, but performance for other neuropsychological test measures or the LSPT did not change. Low compliance rates were observed, showing differences in personality and well-being between compliers and non-compliers. WMT is not a feasible and effective strategy to improve non-trained cognitive measures and football performance. However, this study indicates that it is important to take individual characteristics into account.

#9 Are Hip Physical Examination Findings Predictive of Future Lower Body Injury Rates in Elite Adolescent Female Soccer Athletes at Minimum 5-Year Follow-Up?
Reference: J Sport Rehabil. 2019 Apr 29:1-26. doi: 10.1123/jsr.2018-0350. [Epub ahead of print]
Authors: Cheng AL, Merlo JA, Hunt D, Yemm T, Brophy RH, Prather H
Summary: While elite adolescent female soccer athletes have unique injury risk factors and management challenges, limited epidemiological data exist for this population. Describe lower body injury patterns and determine whether a screening hip physical examination is predictive of future injuries in elite adolescent female soccer athletes. One hundred seventy-seven female soccer athletes ages 10-18 years old (mean 14.6±1.8 years) completed a demographic questionnaire and screening hip physical examination which included range of motion and provocative tests. At least five years after baseline screening, athletes completed an electronic follow-up injury survey. Injury was defined as pain that interfered with sporting activity. In addition to descriptive analyses of athletes' injury profiles, associations between players' baseline demographics and subsequent injury profiles were evaluated using chi-square tests, and potential predictors of injury based on players' baseline hip examinations were evaluated using multivariable logistic regression. Ninety-four of 177 athletes (53%) were contacted for follow-up, and 88/94 (93.6%) completed the survey. With mean follow-up of 91.9±9.3 months (range 66-108 months), 42/88 (47.7%) reported sustaining a new lower body injury. The low back was the most commonly injury region (16/42, 38.1%). Almost half of all injured athletes (20/42, 47.6%) sustained overuse injuries, and 16/42 (38.1%) had an incomplete recovery. Higher body mass index and reaching menarche were associated with sustaining an injury (p=0.03 and 0.04, respectively). Athletes' baseline hip examinations were not predictive of their subsequent rate of lower body, lumbopelvic, overuse, or incomplete recovery injury (all p>0.05). Lower body injuries were common in elite adolescent female soccer athletes, with over one third of injured athletes reporting permanent negative impact of the injury on their playing ability. Baseline hip physical examinations were not associated with future injury rate.

#10 Respiratory Frequency as a Marker of Physical Effort During High-Intensity Interval Training in Soccer Players
Reference:  Int J Sports Physiol Perform. 2019 Apr 29:1-24. doi: 10.1123/ijspp.2019-0028. [Epub ahead of print]
Authors: Nicolò A, Montini M, Girardi M, Felici F, Bazzucchi I, Sacchetti M
Summary: Variables currently used in soccer training monitoring fail to represent the physiological demand of the player during movements like accelerations, decelerations and directional changes performed at high intensity. We tested the hypothesis that respiratory frequency (fR) is a marker of physical effort during soccer-related high-intensity exercise. Twelve male soccer players performed a preliminary intermittent incremental test and two shuttle-run high-intensity interval training (HIIT) protocols, in separate visits. The two HIIT protocols consisted of 12 repetitions over 9 min and differed in the work-recovery ratio (15:30s vs. 30:15s). Work rate was self-paced by participants to achieve the longest possible total distance in each HIIT protocol. Work-phase average metabolic power was higher (P < 0.001) in the 15:30s (31.7 ± 3.0 W·kg-1) compared to the 30:15s (22.8 ± 2.0 W·kg-1). Unlike heart rate and V̇O2, fR showed a fast response to the work-recovery alternation during both HIIT protocols, resembling changes in metabolic power even at supramaximal intensities. Large correlations (P < 0.001) were observed between fR and rating of perceived exertion during both 15:30s (r = 0.87) and 30:15s (r = 0.85). Our findings suggest that fR is a good marker of physical effort during shuttle-run HIIT in soccer players. These findings have implications for monitoring training in soccer and other team sports.

#11 Case Study: Muscle Atrophy, Hypertrophy and Energy Expenditure of a Premier League Soccer Player During Rehabilitation From ACL Injury
Reference: Int J Sport Nutr Exerc Metab. 2019 Apr 29:1-17. doi: 10.1123/ijsnem.2018-0391. [Epub ahead of print]
Authors: Anderson L, Close GL, Konopinksi M, Rydings D, Milsom J, Hambly C, Speakman JR, Drust B, Morton JP
Summary: Maintaining muscle mass and function during rehabilitation from anterior cruciate ligament (ACL) injury is complicated by the challenge of accurately prescribing daily energy intakes aligned to energy expenditure. Accordingly, we present a 38-week case study characterizing whole body and regional rates of muscle atrophy and hypertrophy (as inferred by assessments of fat free mass from DXA) in a professional male soccer player from the English Premier League. Additionally, in week 6 we also quantified energy intake (via the remote food photographic method) and energy expenditure using the doubly labeled water method. Mean daily energy intake (CHO: 1.9-3.2, Protein: 1.7-3.3 and Fat: 1.4-2.7 and energy expenditure was 2765 ± 474 and 3178 kcal.d-1 respectively. In accordance with an apparent energy deficit, total body mass decreased by 1.9 kg during week 1-6 where FFM loss in the injured and non-injured limb was 0.9 and 0.6 kg, respectively, yet, trunk FFM increased by 0.7 kg. In weeks 7-28, the athlete was advised to increased daily CHO intake (4-6 to facilitate an increased daily energy intake. Throughout this period, total body mass increased by 3.6 kg (attributable to a 2.9 and 0.7 kg increase in fat-free and fat mass, respectively). Our data suggest it may be advantageous to avoid excessive reductions in energy intake during the initial 6-8 weeks post-ACL surgery so as to limit muscle atrophy.





Latest research in football - week 16 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Effects of Creatine Supplementation on Athletic Performance in Soccer Players: A Systematic Review and Meta-Analysis
Reference: Nutrients. 2019 Mar 31;11(4). pii: E757. doi: 10.3390/nu11040757.
Authors: Mielgo-Ayuso J, Calleja-Gonzalez J, Marqués-Jiménez D, Caballero-García A, Córdova A, Fernández-Lázaro D
Summary: Studies have shown that creatine supplementation increases intramuscular creatine concentrations, favoring the energy system of phosphagens, which may help explain the observed improvements in high-intensity exercise performance. However, research on physical performance in soccer has shown controversial results, in part because the energy system used is not taken into account. The main aim of this investigation was to perform a systematic review and meta-analysis to determine the efficacy of creatine supplementation for increasing performance in skills related to soccer depending upon the type of metabolism used (aerobic, phosphagen, and anaerobic metabolism). A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in the Medline/PubMed and Web of Science, Cochrane Library, and Scopus databases until January 2019. The search included studies with a double-blind and randomized experimental design in which creatine supplementation was compared to an identical placebo situation (dose, duration, timing, and drug appearance). There were no filters applied to the soccer players' level, gender, or age. A final meta-analysis was performed using the random effects model and pooled standardized mean differences (SMD) (Hedges's g). Nine studies published were included in the meta-analysis. This revealed that creatine supplementation did not present beneficial effects on aerobic performance tests (SMD, -0.05; 95% confidence interval (CI), -0.37 to 0.28; p = 0.78) and phosphagen metabolism performance tests (strength, single jump, single sprint, and agility tests: SMD, 0.21; 95% CI, -0.03 to 0.45; p = 0.08). However, creatine supplementation showed beneficial effects on anaerobic performance tests (SMD, 1.23; 95% CI, 0.55⁻1.91; p <0.001). Concretely, creatine demonstrated a large and significant effect on Wingate test performance (SMD, 2.26; 95% CI, 1.40⁻3.11; p <0.001). In conclusion, creatine supplementation with a loading dose of 20⁻30 g/day, divided 3⁻4 times per day, ingested for 6 to 7 days, and followed by 5 g/day for 9 weeks or with a low dose of 3 mg/kg/day for 14 days presents positive effects on improving physical performance tests related to anaerobic metabolism, especially anaerobic power, in soccer players.

#2 Dietary Intake of Polish Female Soccer Players
Reference: Int J Environ Res Public Health. 2019 Mar 29;16(7). pii: E1134. doi: 10.3390/ijerph16071134.
Authors: Dobrowolski H, Włodarek D
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Summary: The aim of the study was to evaluate the energy expenditure and fulfillment of nutritional needs of female soccer players. Participants in this research were 41 professional soccer players from the three Polish female soccer league levels: Ekstraleague, I League and II League. The participants had their height and body mass measured. Total Energy Expenditure was measured by means of a SenseWear Pro3 Armband device. Data related to the food-intake energy values and the consumption of macro- and micronutrients were obtained through systematic recording of results, which was conducted over a three-day-long period at the start of the competitive season. The average age of the participants was 21 ± 5 years, the average height was 167.5 ± 5 cm, and the average body mass was 62.53 ± 9.8 kg. The average energy expenditure of the participants was 2811 ± 493 kcal/day, and their average energy intake was 1476 ± 434 kcal/day. The average consumption of carbohydrates, fats, and proteins was 199 ± 20.6, 47.3 ± 20.7, and 72.3 ± 24.2 g/day, respectively. There was a prevalence of inadequate intake of potassium, calcium, magnesium, iodine, vitamins D, E and B1, and folate in the diet of the examined group. The remaining micronutrients were consumed in the prescribed amounts by at least 50% of the examined group. The participants demonstrated low energy intakes, and consequently, low consumption of macronutrients and a large number of micronutrients.

#3 Sport-Related Structural Brain Injury in High School Soccer: Epidural Hemorrhage After a "Header"
Reference: World Neurosurg. 2019 Mar 27. pii: S1878-8750(19)30878-2. doi: 10.1016/j.wneu.2019.03.198. [Epub ahead of print]
Authors: Mummareddy N, Legarreta AD, Yengo-Kahn AM, Bow HC, Solomon GS, Naftel RP, Zuckerman SL
Summary: Sport-related structural brain injury (SRSBI) is a rare but potentially catastrophic injury. Limited data exists outlining its epidemiology, pathophysiology, and outcomes. We present the case of an epidural hematoma (EDH) suffered during a high school soccer game. A 16-year-old male experienced a head-to-ball collision and head-to-head collision with another player. He denied loss of consciousness, endorsed retrograde amnesia, and complained of a minor headache. On the sidelines, he subsequently passed brief orientation and physical exertion tests. Upon returning to play, he experienced blurry vision, along with headache and nausea/vomiting. At the local hospital, he was found to have a 2.6cm right frontal EDH. After transfer to our institution, increasing somnolence was noted, prompting emergent evacuation of the EDH. His post-operative course was unremarkable, and he was discharged on post-operative day 2. At the 2-week and 3-month follow up visits, he did not express any complaints or residual deficits and was cleared for full sporting activity. This case highlights one of the few SRSBIs that have occurred in soccer. Due to their rarity and severity, a concerted effort should be made to report these cases of SRSBIs regarding mechanism, post-collision symptoms, and long-term outcomes.

#4 Travel fatigue and sleep/wake behaviors of professional soccer players during international competition
Reference: Sleep Health. 2019 Apr;5(2):141-147. doi: 10.1016/j.sleh.2018.10.013. Epub 2018 Dec 12.
Authors: Lastella M, Roach GD, Sargent C
Summary: The magnitude of travel completed by professional Australian soccer teams during domestic competition is substantial. The inclusion of Australian soccer teams into the Asian Champions league has seen additional stress placed on soccer players' training and competition schedules. For management staff, the complexity of organizing training and travel schedules during domestic competition and the Asian Champions league is challenging. Seven male professional soccer players (mean ± SD: age 25.2 ± 3.2 years, height 182.8 ± 5.2 cm, body mass 84.6 ± 7.4 kg) participated in this study which examined the sleep and fatigue levels of Australian soccer players during an intensive home and away travel schedule during the Asian Champions league. Seven male professional soccer players' (mean ± SD: age 25.2 ± 3.2 years, height 182.8 ± 5.2 cm, body mass 84.6 ± 7.4 kg) sleep/wake behavior was assessed using sleep diaries and wrist activity monitors for 19 days, including 9 days before, 5 days during, and 4 days after a home and away group stage match of the Asian Champions league. Analyses examined differences in sleep/wake behavior and fatigue levels between day type (training day, rest day, pregame, and postgame) and between sleep location (Adelaide, during flight, and Hiroshima). Sleep/wake behavior and fatigue levels were poorest the night immediately after games compared to the night before games, training days, and rest days. Soccer players' sleep/wake behaviors were disrupted during flights such that they obtained 3.6 hours less sleep during flights compared to sleep in Adelaide (7.0 ± 1.6 hours) and Hiroshima (7.0 ± 2.1 hours). The sleep/wake behaviors of professional soccer players are compromised when they are required to travel and compete in multiple matches within a short period of time.

#5 Medial collateral ligament injuries of the knee in male professional football players: a prospective three-season study of 130 cases from the UEFA Elite Club Injury Study
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Apr 4. doi: 10.1007/s00167-019-05491-6. [Epub ahead of print]
Authors: Lundblad M, Hägglund M, Thomeé C, Hamrin Senorski E, Ekstrand J, Karlsson J, Waldén M
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Summary: Medial collateral ligament (MCL) injury is the single most common traumatic knee injury in football. The purpose of this study was to study the epidemiology and mechanisms of MCL injury in men's professional football and to evaluate the diagnostic and treatment methods used. Fifty-one teams were followed prospectively between one and three full seasons (2013/2014-2015/2016). Individual player exposure and time-loss injuries were recorded by the teams' medical staffs. Moreover, details on clinical grading, imaging findings and specific treatments were recorded for all injuries with MCL injury of the knee as the main diagnosis. Agreement between magnetic resonance imaging (MRI) and clinical grading (grades I-III) was described by weighted kappa. One hundred and thirty of 4364 registered injuries (3%) were MCL injuries. Most MCL injuries (98 injuries, 75%) occurred with a contact mechanism, where the two most common playing situations were being tackled (38 injuries, 29%) and tackling (15 injuries, 12%). MRI was used in 88 (68%) of the injuries, while 33 (25%) were diagnosed by clinical examination alone. In the 88 cases in which both MRI and clinical examination were used to evaluate the grading of MCL injury, 80 (92% agreement) were equally evaluated with a weighted kappa of 0.87 (95% CI 0.77-0.96). Using a stabilising knee brace in players who sustained a grade II MCL injury was associated with a longer lay-off period compared with players who did not use a brace (41.5 (SD 13.2) vs. 31.5 (SD 20.3) days, p = 0.010). Three-quarter of the MCL injuries occurred with a contact mechanism. The clinical grading of MCL injuries showed almost perfect agreement with MRI grading, in cases where the MCL injury is the primary diagnosis. Not all grade II MCL injuries were treated with a brace and may thus indicate that routine bracing should not be necessary in milder cases.

#6 Involving research-invested clinicians in data collection affects injury incidence in youth football
Reference: Scand J Med Sci Sports. 2019 Apr 2. doi: 10.1111/sms.13427. [Epub ahead of print]
Authors: Wik EH, Materne O, Chamari K, Duque JDP, Horobeanu C, Salcinovic B, Bahr R, Johnson A
Summary: It is well established that differences in injury definition and recording methodology restrict comparisons between injury surveillance programmes. There is, however, little documentation of the variation that can exist between data recorders. The aim of this study was therefore to explore the effect on reported injuries when team recorders or supervisors are involved in research. Injury data collected prospectively over five seasons for the U16, U17 and U18 age groups in a youth football (soccer) academy were used to compare different recording settings based on the research involvement of the clinicians. A research-invested team physiotherapist reported an 8.8 times greater incidence (p<0.001) of non-time-loss injuries and a 2.5 times greater incidence (p<0.001) of minimal injuries (1-3 days lost) compared to a setting where neither the team physiotherapists or the supervisor relied on the collected data for research purposes. When team physiotherapists were not invested in research themselves but were supervised by a researcher, the incidence of non-time-loss injuries and minimal injuries was 2.5 times (p<0.001) and 2.0 times greater (p<0.01) than in the non-invested setting, respectively. However, there were no differences between recording settings for overall incidence of time-loss injuries. The results from this study demonstrate that involving clinicians that are relying on the collected data for research purposes can significantly affect the reported rates of non-time-loss and minimal injuries. Time-loss injuries overall were not affected by research investment, and should therefore be preferred for comparisons between teams and seasons. This article is protected by copyright. All rights reserved.

#7 Possession in Football: More Than a Quantitative Aspect - A Mixed Method Study
Reference: Front Psychol. 2019 Mar 18;10:501. doi: 10.3389/fpsyg.2019.00501. eCollection 2019.
Authors: Casal CA, Anguera MT, Maneiro R, Losada JL
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Summary: The aim of the present study was to identify and differentiate the factors that determine the possession times of successful and unsuccessful elite football teams, with the purpose of identifying a more effective possession model. For this, match corresponding to the round of eighth-finals, quarter-finals, semi-finals and final of the 2016 UEFA Euro France in which 2,636 offensive sequences occurred, were analyzed. Video recordings of matches were analyzed and coded post-event using systematic observation. The performance indicators recorded and analyzed were: phase; match period; type of start-up; interaction context; intention; field zone; possession time, passes, attack outcome; match status and final outcome. An ANOVA was performed to analyze data in order to study the influence of a set of variables. A Box-Cox transformation was applied on the variable explained to achieve normal conditions. A study of the main effects and significant interactions was also carried out, complemented with a set of predictions with the variables that were more significant. It is hypothesized that possession analysis from a mixed methods perspective will identify a more effective offensive playstyle. Results show how, in successful teams, possession time is influenced by: Type of start-up, intention and field zone. On the other hand, in unsuccessful teams, possession time is determined fundamentally by intention and match status. In terms of the results of the predictive models, in the case of successful teams, they will have longer possessions in the offensive zone with the score in favor and, in the defensive zone with a draw score, in both situations, initiated with the intention of progressing by means of a transition. For unsuccessful teams, possessions will be of longer duration in the defensive zone with a draw score, regardless of the type of start-up and, in the offensive zone, losing and initiating the play by means of a set ball action and winning by means of a transition. Results obtained in this work identify key factors that determine possession time in teams and allow to differentiate the possessions of successful and unsuccessful teams, identifying a more effective ball possession model. This information can be used to design a possession model with greater probabilities of success and increase the offensive performance of teams.

#8 Influence of Aerobic Power on Youth Players' Tactical Behavior and Network Properties during Football Small-Sided Games
Reference: Sports (Basel). 2019 Mar 25;7(3). pii: E73. doi: 10.3390/sports7030073.
Authors: Praça GM, Sousa RBE, Greco PJ
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Summary: This study aimed to compare the incidence of tactical principles, the percentage of successful tactical principles, and the network properties between higher and lower aerobic power in young football players during small-sided games. Eighteen Under-17 Brazilian players were recruited. Firstly, they performed the Yo-Yo Intermittent Recovery Test Level 2, which was used to split them into two groups with higher and lower aerobic power. In the sequence, they played three vs three small-sided games within each group. The System of Tactical Assessment in Soccer was used to analyze the tactical behavior demonstrated by measuring the incidence of tactical principles and the percentage of successful principles, while the macro variables, density and clustering coefficient from social network analysis for team sports was used to analyze players' interactions. No differences were reported for the incidence of tactical principles (p > 0.05, small or small-to-moderate effect sizes), the percentage of successful offensive principles (p = 0.122, small-to-moderate effect size), or the network variables (p > 0.05; small effect sizes). The lower aerobic power group demonstrated a higher percentage of successful defensive tactical principles (p = 0.043; small-to-moderate effect size). We concluded that aerobic power has a limited impact on player behavior, indicating that players' actions within a small-sided game are mostly constrained by other parameters.

#9 Antioxidant vitamin supplementation prevents oxidative stress but does not enhance performance in young football athletes
Reference: Nutrition. 2019 Jan 24;63-64:29-35. doi: 10.1016/j.nut.2019.01.007. [Epub ahead of print]
Authors: de Oliveira DCX, Rosa FT, Simões-Ambrósio L, Jordao AA, Deminice R
Summary: The aim of this study was to verify the effects of supplementation with antioxidants (vitamins C and E) on oxidative stress, delayed-onset muscle soreness (DOMS), and performance in football players during a recovery period after an exercise-induced oxidative stress protocol. Twenty-one football athletes were randomly assigned to two groups: placebo and antioxidant-supplemented. Supplementation was performed in a double-blind, controlled manner using vitamin C (500 mg/d) and E (400 UI/d) for 15 d. After 7 d of supplementation, athletes were submitted to an exercise-induced oxidative stress protocol consisting of plyometric jumping and strength resistance sets to exhaustion. Blood samples, performance tests, and DOMS were determined before and 24, 48, and 72 h after exercise. Antioxidant supplementation was continued during the recuperation week and for a total of 15 d. Antioxidant supplementation caused a significant increase in plasma vitamins C and E. The antioxidant supplementation could inhibit oxidative stress characterized by elevated lipid peroxidation markers malondialdehyde and total lipid peroxidation as well as reduced ratio of glutathione to oxidized glutathione promoted by exercise. Antioxidant supplementation, however, did not significantly reduce the plasma creatine kinesis concentration or DOMS during the recovery days. Likewise, supplementation with vitamin C and E did not improve lower body power, agility, or anaerobic power, nor did it provide any indication of faster muscle recovery. Antioxidant supplementation does not attenuate elevated markers of muscle damage or muscle soreness promoted by acute exercise and do not exert any ergogenic effect on football performance of young athletes, although it reduced oxidative stress.

#10 The Effects of a Physically Active Lifestyle on the Health of Former Professional Football Players
Reference: Sports (Basel). 2019 Mar 28;7(4). pii: E75. doi: 10.3390/sports7040075.
Authors: Melekoğlu T, Sezgin E, Işın A, Türk A
Summary: The purpose of this investigation was to determine if a physically active lifestyle affects the health of former football players. Sixty former professional football players aged 40⁻50 years and who ended their sports career at least ten years ago were recruited for the study and grouped into two groups based on their physical activity habits after their retirement. Health and lifestyle characteristics were collected through a questionnaire to obtain information about recreational physical activity levels, diseases, family medical history, smoking, alcohol intake and dietary habits. Furthermore, lung functions, blood parameters and cardiovascular health were evaluated. Our results showed that body weight and body fat percentage were significantly higher in retired footballers who had a sedentary lifestyle compared to those who were physically active. The absolute and predicted values for forced expiratory volume in one-second values were higher in the active group. Twelve retired athletes were found to have intraventricular conduction delay. The findings suggest that former footballers who have higher levels of physical activity have advanced body composition, respiratory functions and serum lipids compared to former footballers with less active lifestyles. It is recommended that former elite athletes should maintain physically active lifestyles to sustain their health and reduce the risk of disease and disability in the later years of life.

#11 Scaling Demands of Soccer According to Anthropometric and Physiological Sex Differences: A Fairer Comparison of Men's and Women's Soccer
Reference: Front Psychol. 2019 Apr 9;10:762. doi: 10.3389/fpsyg.2019.00762. eCollection 2019.
Authors: Pedersen AV, Aksdal IM, Stalsberg R
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Summary: Spectators frequently harass female soccer players, and women's soccer is frequently compared negatively to men's soccer by writers who make the comparison without the backing of any data and without taking into account anthropometric and physiological differences between the sexes. This affects female soccer players' self-confidence negatively and contributes to an undeservedly negative image of women's soccer. In the present paper, we argue that most differences between men's and women's soccer can be explained by women having to adapt to rules and regulations that are suited for men and their physical attributes. Thus, games are much more demanding for women. Furthermore, we argue that if men had to play with a degree of adaptation similar to that which women do today, they would have to alter their style of play radically. As support for our argument, we scale game demands for male and female soccer players according to anthropometric and physiological differences in order to highlight the differences, and use these to predict what would be the most appropriate adaptations. Finally, we show that our predictions are largely supported by the scarce pool of comparable data across the sexes.





Latest research in football - week 15 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 And at the end, the Germans always win, don't they? An evaluation of country-specific scoring behaviour in the dying seconds of international club soccer games
Reference: PLoS One. 2019 Apr 16;14(4):e0202852. doi: 10.1371/journal.pone.0202852. eCollection 2019.
Authors: Van Den Broucke L, Baert S
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Summary: This article contributes to the literature on performance determinants in soccer by investigating country differences in goal scoring in the dying seconds of international soccer games (i.e. in the 90th minute or later). We analyse this goal-scoring behaviour in 1,008 recent soccer games played in the Union of European Football Associations (UEFA) Champions League and Europa League. In contrast to Gary Lineker's well-known quote that "at the end, the Germans always win", no significant evidence is found for German teams scoring a goal in the dying seconds more often than other teams. Our results indicate, however, that European clubs do have an interest in learning from the end-of-game tactics used by French and Spanish clubs in recent international games as these teams were less likely to concede a goal during the dying seconds. English teams were also in this situation but only if they had an English coach.

#2 Maximum Oxygen Uptake of Male Soccer Players According to their Competitive Level, Playing Position and Age Group: Implication from a Network Meta-Analysis
Reference: J Hum Kinet. 2019 Mar 27;66:233-245. doi: 10.2478/hukin-2018-0060. eCollection 2019 Mar.
Authors: Slimani M, Znazen H, Miarka B, Bragazzi NL
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Summary: The aim of the present meta-analysis was to compare the maximum oxygen uptake (VO2max) characteristics of male soccer players relative to their competitive level, playing position and age group and the interaction between them. The meta-analysis was based on 16 studies, employing 2385 soccer players aged 10-39 years. Higher-level soccer players showed greater (ES = 0.58 [95% CI 0.08-1.08], SE = 0.25, var = 0.06, z = 2.29, p = 0.022) VO2max performance with respect to their lower level counterparts. Furthermore, lower VO2max values in goalkeepers than defenders (ES = 1.31 (SE 0.46) [95% CI 0.41-2.21], var = 0.21, z = 2.84, p = 0.004) and midfielders (ES = 1.37 (SE 0.41) [95% CI 0.58 to 2.17], var = 0.16, z = 3.40, p = 0.001) were found. Thus, VO2max increased significantly with age (all, p < 0.01): Under 10 versus Under 11 years, Under 11 versus Under 12 years, Under 12 versus Under 13 years, Under 13 versus Under 14 years, Under 14 versus Under 15 years and Under 16-18 versus Under 20-23 years. VO2max performance is the most powerful discriminator between higher and lower-level soccer players. These findings indicate also the need for sports scientists and conditioning professionals to take the VO2max performance of soccer players into account when designing individualized position specific training programs.

#3 Characteristics of Very High Intensity Runs of Soccer Players in Relation to their Playing Position and Playing Half in the 2013-14 Spanish La Liga Season
Reference: J Hum Kinet. 2019 Mar 27;66:213-222. doi: 10.2478/hukin-2018-0058. eCollection 2019 Mar.
Authors: Rivilla-García J, Calvo LC, Jiménez-Rubio S, Paredes-Hernández V, Muñoz A, van den Tillaar R, Navandar A
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Summary: The objective of this study was to carry out a detailed quantitative analysis of the very high intensity runs during actual play in the 2013-2014 Spanish First Division, at a general level and according to the specific playing position and half. 380 matches of the Spanish First Division in the 2013 - 2014 season were monitored using the Mediacoach video motion analysis tool. Total distance, very high intensity (above 21 km/h) running distance and the number of runs at very high intensity of 230 players from 20 teams in the Spanish First Division were analysed. The main findings of the study were that the performance indicators at very high intensities decreased from the first half to the second half for all outfield players (covered distance: 4694 ± 538 m vs 4485 ± 437 m, sprint distance: 256 ± 72 m vs 239 ± 67 m, number of sprints: 14.3 ± 3.5 vs 13.2 ± 3.1), except the central defenders (sprint distance: 166 ± 37 vs 166 ± 40 m, number of sprints: 10.0 ± 2.1 vs 9.8 ± 3.8). Secondly, although wide defenders (9759 ± 665 m) and central midfielders (9776 ± 942 m) covered the most distance during matches, it were the wide defenders (30 ± 5), centre-forwards (28 ± 7) and wide midfielders (31 ± 8) who performed the most runs at very high intensity. Consequently, the distance they ran at these very high intensity runs followed the same pattern. Such results enable general and specific profiles by demarcation to be established based on the demands of the game at high-level competitive play.

#4 The Influence of Situational Variables on Ball Possession in the South African Premier Soccer League
Reference: J Hum Kinet. 2019 Mar 27;66:175-181. doi: 10.2478/hukin-2018-0056. eCollection 2019 Mar.
Authors: Kubayi A, Toriola A
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Summary: Although the influence of ball possession in soccer has been well studied in other leagues, such information is sparse concerning the South African Premier Soccer League (PSL). The purpose of this study was to assess the impact of situational variables on ball possession in the PSL. Thirty-two matches played during the 2016-2017 PSL season were analysed using a multiple-camera match analysis system (InStat®). Three situational variables (match outcome, match location, and quality of opposition) and team performance variables (percentage of ball possession, ball possession <5 s, ball possession 5-15 s, ball possession 15-45 s, and ball possession >45 s) were examined. The results showed that losing teams had the highest ball possession (52.35 ± 5.90%) compared to winning (47.65 ± 5.90%) and drawing (50.00 ± 9.98%) teams. Playing away significantly (p < 0.05) decreased ball possession by 5.21% compared to playing at home. Playing against weak opposition was associated with increased ball possession by 4.09%. Conclusively, soccer coaches should be aware of the potential role of situational variables in determining successful team performance in a league season.

#5 Characterization of the Weekly External Load Profile of Professional Soccer Teams from Portugal and the Netherlands
Reference: J Hum Kinet. 2019 Mar 27;66:155-164. doi: 10.2478/hukin-2018-0054. eCollection 2019 Mar.
Authors: Clemente FM, Owen A, Serra-Olivares J, Nikolaidis PT, van der Linden CMI, Mendes B
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Summary: The purpose of this study was to analyze the day-to-day variance of a typical weekly external training workload of two professional soccer teams from different countries. Twenty-nine players from two professional teams from Portugal and the Netherlands participated in this study. The players' external load was monitored for 7 weeks, by means of portable GPS devices (10 Hz, JOHAN, Noordwijk, Netherlands). Results revealed that match day -1 (MD-1), i.e. the training day before a match, had significantly (p = 0.001) less training volume (4584.50 m) than the other days. MD-5 (training five days before a match), MD-4 (four days before a match) and MD-3 (three days before a match) were the most intense (390.83, 176.90 and 247.32 m of sprinting distance, respectively) and with large volume (7062.66, 6077.30 and 6919.49 m, respectively). Interestingly, significant differences were found between clubs of different countries (p < 0.05) with the Portuguese team showing significantly higher intensity (sprinting distance) and volume (total distance) in all days with exception of MD-1 than the Dutch team. The results of this study possibly allow for the identification of different training workloads and tapering strategies between countries in relation to volume and intensity. It should be noted, however, that both clubs used a significant tapering phase in the last two days before the competition in an attempt to reduce residual fatigue accumulation.

#6 A New Approach to the Analysis of Pitch-Positions in Professional Soccer
Reference: J Hum Kinet. 2019 Mar 27;66:143-153. doi: 10.2478/hukin-2018-0067. eCollection 2019 Mar
Authors: Konefał M, Chmura P, Zając T, Chmura J, Kowalczuk E, Andrzejewski M
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Summary: The purpose of the study was to examine how various playing positions affected the number of (and percentage breakdowns for) physical and technical activities of soccer players in the Germany's Bundesliga. A further objective was to identify and present features distinguishing between the activities of players within the Defender, Midfielder and Forward formations. The study sample comprised 4426 individual match observations of 473 soccer players competing in the Bundesliga during the 2016/2017 domestic season. Data from the Impire AG motion analysis system, and the so-called "heat maps" it supplies, revealed areas in which players spent most time during a match, with 22 different playing positions on the pitch identified in consequence. Players in the formation comprising Defenders did not differ significantly in relation to the number of accelerations, the number of shots or the percentage of duels won. Furthermore, there were no significant differences among Midfielders in regard to total distance covered, mean running speed, the number of accelerations, the number of duels and the percentage of duels won. Likewise, Forwards did not differ in distances covered at ≥24 km/h, average running speed, the number of sprints, the number of shots, the proportion of on-target passes, the number of duels, or the percentage share of duels won. Irrespective of the formation or position on the pitch, today's game of soccer also pays great importance to the number of accelerations, as well as the number of duels engaged in, and their effectiveness.

#7 Anthropometric and Motor Characteristics of South African National Level Female Soccer Players
Reference: J Hum Kinet. 2019 Mar 27;66:121-129. doi: 10.1515/hukin-2017-0189. eCollection 2019 Mar.
Authors: Booysen MJ, Gradidge PJ, Constantinou D
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Summary: Data regarding anthropometric and motor characteristics of elite national level female soccer players are scarce. Determining these characteristics may likely assist in evaluating the specificity of current training programmes, identify players who might lack specific qualities deemed critical for the successful execution of their tactical roles, and benchmark norms for developing future playing talent. Therefore, the aims of this study were to describe anthropometric and motor characteristics of South African national level female soccer players (n = 37) and determine possible differences with regard to their playing position. The following measurements and tests were performed: anthropometry (body mass index and sum-of-skinfolds), the countermovement jump, sprints (10 m, 20 m and 40 m), upper body muscle endurance (push-ups) and the Yo-Yo Intermittent Recovery Test - level 1. One-way analysis of variance revealed few differences in the main outcome variables. Fischer Least Significant Difference (LSD) showed that strikers had a greater body mass index than midfielders and defenders (both p = 0.04) and goalkeepers were heavier than defenders (p = 0.02). Goalkeepers were slower than strikers and defenders over 10 m (p = 0.01; p = 0.03) and 20 m (p = 0.001; p = 0.01). Midfielders were slower than strikers over 20 m (p = 0.02), and with strikers and defenders over 40 m (both p = 0.04). Defenders performed better than goalkeepers in the upper body muscle endurance test (p = 0.02). In conclusion, both strikers and defenders require speed to win ball possession, which may explain their fast sprint times. However, the similarity of certain motor characteristics across playing positions may suggest that conditioning coaches train players similarly, irrespective of their tactical position. The authors suggest that South African fitness professionals, particularly at a club level, develop physical conditioning programs specific to each field position. Furthermore, fitness assessments should occur on a continuous basis and comparisons should be made with existing normative data in order to guide the development of players over the course of their careers.

#8 Physiological and Psychological Changes at the End of the Soccer Season in Elite Female Athletes
Reference: J Hum Kinet. 2019 Mar 27;66:99-109. doi: 10.2478/hukin-2018-0051. eCollection 2019 Mar.
Authors: Morales J, Roman V, Yáñez A, Solana-Tramunt M, Álamo J, Fíguls A
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Summary: This study compares and describes relationships among stress-recovery indices, the heart rate variability index, and the Cooper and Yo-Yo IR1 tests among female soccer players during the last six weeks of the competitive season. Sixteen female soccer players engaged in a pre-test of all of the variables. After having their training monitored for six weeks, a post-test was administered. The results revealed significant (p < 0.05) differences in the specific stress-recovery scales of the RESTQ-sport and in the frequency-domain variables of the HRV, although there were no significant differences in the general stress or general recovery scales. The Yo-Yo IR1 test, the Cooper test scores, and the means of the time-domain HRV variables did not exhibit any significant differences between the pre- and the post-test. The RMSSD variations exhibited very large and large correlations with the performance test and the RESTQ-sport variables, respectively. The variations in the HRV frequency-domain variables exhibited significant moderate and large correlations among the variations of the RESTQ-sport scales. Monitoring athletes at the end of the season may reveal contradictions between some variables. To help with the interpretation of these scales, some external aspects, such as athlete strain and monotony of training, should be considered.

#9 Strength Profile of Hip Abductor and Adductor Muscles in Youth Elite Soccer Players
Reference: J Hum Kinet. 2019 Mar 27;66:31-41. doi: 10.2478/hukin-2018-0069. eCollection 2019 Mar.
Authors: Karatrantou K, Gerodimos V, Katsareli E, Manouras N, Ioakimidis P, Famisis K
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Summary: The main objective of this study was to provide an extensive isokinetic profile of the hip joint in youth soccer players, where the literature is limited. Additionally, this study investigated the effect of age on isokinetic peak torque values of hip abductor and adductor muscles and on reciprocal muscle group torque ratios in youth soccer players at different angular velocities (30 vs. 90o/s) and muscle actions (concentric vs. eccentric). Sixty young elite male soccer players were assigned into three equal groups (n = 20): children, young adolescents and older adolescents, and performed five maximal concentric and eccentric hip-abductions and adductions at 30o/s and 90o/s. The results showed a significant increase (p < 0.05) in peak torque values from childhood to adolescence, with the exception of young adolescents vs. older adolescents where no differences were observed. The reciprocal ratios were not affected by age, but improved with an increase in angular velocity with the exception of the CON/ECC ratio that was higher at 30o/s. The data presented in this study provide an extensive isokinetic profile of hip abductor and adductor muscle strength in youth soccer players to assist both coaches and sports medicine professionals in strength monitoring and training.

#10 Effects of 7-Week Hip Thrust Versus Back Squat Resistance Training on Performance in Adolescent Female Soccer Players
Reference: Sports (Basel). 2019 Apr 3;7(4). pii: E80. doi: 10.3390/sports7040080.
Authors: González-García J, Morencos E, Balsalobre-Fernández C, Cuéllar-Rayo Á, Romero-Moraleda B
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Summary: Hip thrust (HT) is a loaded bridging exercise that requires more hip extension than a back squat (SQ) does, while in a back squat, triple flex extension occurs. Due to the specificity of each exercise, it is claimed that HT gains can be better transferred to actions where hip extension occurs. In addition, strength improvements during squatting can be transferred in a greater way to vertical plane movement, such as vertical jumping. However, its effects on the performance of female soccer players are unclear. For this reason, the purpose of this study was to analyze a 7-week training program on performance variables using either HT or SQ exercises in female adolescent soccer players without lifting experience (N = 24, age = 16.82 ± 1.56 years, height = 1.64 ± 0.55 cm, body mass = 58.35 ± 6.28 kg). Players were randomized into three groups: A back squat group (SQG; N = 8), hip thrust group (HTG; N = 8), and control group (CG; N = 8). Participants in the HTG and SQG joined a progressive resistance training program twice per week for 7 weeks with either HT or SQ exercises. A countermovement jump, 10-20 m sprint, T-test, and barbell velocity during HTs and SQs (with the load that represents ~60 and ~80% RM) were measured before and after the intervention. The HTG showed greater improvements in the 10-m sprint (d = 0.7), 20-m sprint (d = 0.46), T-test (d = 0.36), and barbell velocity at 80% repetition maximal (RM) (d = 0.53) and 60% RM (d = 1.02) during hip thrusts, while the SQG showed higher barbell velocity at 80% RM (d = -0.7) during back squats. These results may be useful for strength and conditioning coaches working with adolescent female soccer athletes, since both strengthening exercises improved performance in different ways due to the nature of the exercise.

#11 Fat-Free Mass and Bone Mineral Density of Young Soccer Players: Proposal of Equations Based on Anthropometric Variables
Reference: Front Psychol. 2019 Mar 29;10:522. doi: 10.3389/fpsyg.2019.00522. eCollection 2019.
Authors: Gomez-Campos R, Santi-Maria T, Arruda M, Maldonado T, Albernaz A, Schiavo M, Cossio-Bolaños M
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Summary: The assessment of body composition may assist in optimizing competitive efficiency and monitoring the success of training regimes for young soccer players. The purpose of this study was to determine the predictors for Fat-Free Mass (FFM) and Bone Mineral Density (BMD) of young soccer players. Also, the goal was to propose regression equations to estimate FFM and BDM through anthropometric variables. One hundred and sixty-seven young soccer players ages 10.0 to 19.9 years old were studied. Weight, height, trunk-cephalic length, right arm circumference, diameter of the humerus, and length of the foot were assessed. FFM and BDM were determined by using dual X-ray absorptiometry (DXA). Maturity status using Peak Height Velocity (PHV) was calculated. Maturity status, weight, and circumference of the relaxed arm positively related to the FFM (R 2 = 41-66%). Similarly, PHV, weight, diameter of the humerus, and length of the foot explained BDM in both groups of soccer players (goalkeepers and filed players) (R 2 = 45-82%). Six equations to predict FFM (R 2 = 62-69%) and six to predict BDM (R 2 = 69-90%) were created. Chronological age had a limited use for predicting FFM and BDM. Results suggested the use and application of the regression equations as a non-invasive alternative for everyday use in soccer clubs.

#12 Changes Over a Decade in Anthropometry and Fitness of Elite Austrian Youth Soccer Players
Reference: Front Physiol. 2019 Mar 28;10:333. doi: 10.3389/fphys.2019.00333. eCollection 2019.
Authors: Gonaus C, Birklbauer J, Lindinger SJ, Stöggl TL, Müller E
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Summary: Increases in physical (e.g., high-intensity running and sprinting), technical (e.g., passing rate), and tactical (e.g., player density) aspects made elite level soccer more challenging within the past years. The aim of the study was to evaluate whether these evolutions are also been reflected in changes in anthropometric and fitness characteristics between former (2002 to 2005) and current (2012 to 2015) elite Austrian youth development center (U13 to U14) and soccer academy (U15 to U18) players. A battery of anthropometric, general and soccer-specific fitness tests was conducted annually at the end of each year. Independent t-test and Cohen's d (ES) were calculated to compare the two four-year periods (2530 vs. 2611 players) at each age group separately. Current players were significantly faster in 20 m sprint (ES = 0.26-0.50) and reaction test (ES = 0.15-0.39, except for U18), but less flexible at sit-and-reach (ES = -0.19 to -0.55), in all age categories. Whereas height (ES = 0.26-0.32), body mass (ES = 0.11-0.18) and countermovement jump (ES = 0.24-0.26) increased significantly at youth development center level, current academy players performed superior at shuttle sprint (ES = 0.21-0.59), hurdles agility run (ES = 0.24-0.49), and endurance run (ES = 0.11-0.20). These changes over time in speed, change-of-direction ability, lower-body power, coordination, and endurance were attributed to modern training approaches (e.g., modified games and change-of-direction drills) and modifications in selection politics (e.g., coaches favor speed and decision-making skills).

#13 Recovery profiles following single and multiple matches per week in professional football
Reference: Eur J Sport Sci. 2019 Apr 18:1-9. doi: 10.1080/17461391.2019.1601260. [Epub ahead of print]
Authors: Howle K, Waterson A, Duffield R
Summary: The purpose was to investigate player responses 48 h post single (SM) and multi-match (MM) weeks on two subjective and three objective outcome measures to infer recovery status. From 42 professional players over 2 seasons, outcome measures relevant to recovery status were collected 48 h following matches, as well as during pre-season training weeks as a comparative baseline. These included (1) 5-item subjective wellness questionnaire, (2) total quality recovery (TQR) scale, (3) hip adduction squeeze test, ankle knee to wall (KTW) test, and active knee extension (AKE) flexibility test. These outcome measures 48 h post-match were compared for SM (n = 79) and MM (n = 86) weeks where players completed >75 min of match time in only one (SM) or if both matches were played and had <96 h recovery (MM). Internal match load was collected from each match based on session rating of perceived exertion (sRPE) multiplied by match duration. Subjective wellness (specifically fatigue, sleep and soreness), TQR and hip adduction squeeze test were all significantly reduced following match 1 at 48 h post for both SM and MM (p < 0.05), and further reduced following match 2 in MM (p < 0.05). No other outcome measures to infer recovery showed significant differences (p > 0.05) within or between-conditions. Subjective wellness, TQR and hip adduction strength showed reduction 48 h post match for players competing in multiple matches with <96 h recovery. Therefore, these outcome measures may be of use to practitioners to assess readiness to compete during congested competition schedules.

#14 Effects of Creatine Supplementation on Athletic Performance in Soccer Players: A Systematic Review and Meta-Analysis
Reference: Nutrients. 2019 Mar 31;11(4). pii: E757. doi: 10.3390/nu11040757.
Authors: Mielgo-Ayuso J, Calleja-Gonzalez J, Marqués-Jiménez D, Caballero-García A, Córdova A, Fernández-Lázaro D
Summary: Studies have shown that creatine supplementation increases intramuscular creatine concentrations, favoring the energy system of phosphagens, which may help explain the observed improvements in high-intensity exercise performance. However, research on physical performance in soccer has shown controversial results, in part because the energy system used is not taken into account. The main aim of this investigation was to perform a systematic review and meta-analysis to determine the efficacy of creatine supplementation for increasing performance in skills related to soccer depending upon the type of metabolism used (aerobic, phosphagen, and anaerobic metabolism). A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in the Medline/PubMed and Web of Science, Cochrane Library, and Scopus databases until January 2019. The search included studies with a double-blind and randomized experimental design in which creatine supplementation was compared to an identical placebo situation (dose, duration, timing, and drug appearance). There were no filters applied to the soccer players' level, gender, or age. A final meta-analysis was performed using the random effects model and pooled standardized mean differences (SMD) (Hedges's g). Nine studies published were included in the meta-analysis. This revealed that creatine supplementation did not present beneficial effects on aerobic performance tests (SMD, -0.05; 95% confidence interval (CI), -0.37 to 0.28; p = 0.78) and phosphagen metabolism performance tests (strength, single jump, single sprint, and agility tests: SMD, 0.21; 95% CI, -0.03 to 0.45; p = 0.08). However, creatine supplementation showed beneficial effects on anaerobic performance tests (SMD, 1.23; 95% CI, 0.55⁻1.91; p <0.001). Concretely, creatine demonstrated a large and significant effect on Wingate test performance (SMD, 2.26; 95% CI, 1.40⁻3.11; p <0.001). In conclusion, creatine supplementation with a loading dose of 20⁻30 g/day, divided 3⁻4 times per day, ingested for 6 to 7 days, and followed by 5 g/day for 9 weeks or with a low dose of 3 mg/kg/day for 14 days presents positive effects on improving physical performance tests related to anaerobic metabolism, especially anaerobic power, in soccer players.





Latest research in football - week 14 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 The Lower Limb Assessment Score: A valid measure of hypermobility in elite football?
Reference: Phys Ther Sport. 2019 Mar 15;37:86-90. doi: 10.1016/j.ptsp.2019.03.007. [Epub ahead of print]
Authors: Paul Johnson A, Ward S, Simmonds J
Summary: This study aims to validate the Lower Limb Assessment Score against the current gold standard Beighton Scale within an adult elite footballing population to allow for future research to explore the influence of lower limb specific hypermobility on injury incidence. Thirty-six male, professional footballers aged between 18 and 37 years old participated in this study. The Sensitivity, specificity, positive predictive value, negative predictive value and Spearman's rank correlation between the LLAS and Beighton Scale were used as outcome measures. There was significant strong correlation between LLAS and Beighton Scale scores (ρ = 0.732; p < 0.001). The LLAS displayed a sensitivity of 67% and specificity of 94% when a cut off of ≥4/12 was applied to the screening data. This cut off point also yielded moderate Positive Predictive Validity (50%) and excellent Negative Predictive Validity (97%). The present study suggests that the LLAS is a valid test for identifying lower limb hypermobility within an adult male footballing population when a cut off of ≥4/12 is used.

#2 Soccer Footedness and Between-Limbs Muscle Strength: Systematic Review and Meta-Analysis
Reference: Int J Sports Physiol Perform. 2019 Apr 11:1-12. doi: 10.1123/ijspp.2018-0336. [Epub ahead of print]
Authors: DeLang MD, Rouissi M, Bragazzi NL, Chamari K, Salamh PA.
Summary: Limb dominance and consequent between-limbs muscle strength in soccer players should be explored to determine a standard musculoskeletal profile to maintain and establish during screening protocols and postinjury rehabilitation. The primary aim of this review was to identify dominant- vs non-dominant-lower-extremity muscle-strength characteristics of healthy soccer players, with secondary aims to consider available between-limbs outcome measures and directions for future research. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Five electronic databases were used for study identification with guidance from a medical librarian. Inclusion criteria consisted of studies employing a cross-sectional design assessing soccer players of all ages, genders, and levels of play that identified limb dominance and associated lower-extremity muscle strength as a main purpose of the experiment. The literature search identified 3471 articles. After screening titles, abstracts, and full texts, 17 articles were included in the review. Peak torques and hamstring-to-quadriceps ratios via isokinetic dynamometry were commonly used, and subsequent meta-analyses were conducted to yield remarkable between-limbs symmetry. Additional results of individual studies also demonstrate symmetry, except 1 article of velocity-dependent measures that reported greater strength in the dominant limb. In soccer, between-limbs muscle strength measured by maximal isokinetic dynamometry demonstrates symmetry across ages, genders, and levels of play. Future testing using alternative measures that more specifically replicate the movement demands of soccer players may further classify between-limbs characteristics.

#3 Player Migration and Soccer Performance
Reference: Front Psychol. 2019 Mar 21;10:616. doi: 10.3389/fpsyg.2019.00616. eCollection 2019.
Authors: Lago-Peñas C, Lago-Peñas S, Lago I
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Summary: The aim of this study is to examine the relationship between migrating soccer players and the annual ranking of the national teams according to the World Football Elo Rating. The sample includes annual data for 243 countries over the period 1994-2018. Migration is captured with the number of migrating players by country in the "big-five" leagues. The causal relationship between the two variables is examined by using Granger causality test. Four control variables are included: the political regime, per capita income, population, and regional soccer confederations. It was hypothesized that (i) the better the ranking of the national teams in the Elo rating, the higher the number of migrating players in the "big-five" leagues (shop-window hypotheses) and that (ii) while the shop-window effect takes place in the short-run, the annual Elo rating of a national team is positively affected by expatriate players in the medium or long-run, but not in the short-run (blending hypotheses). The results shed light on two crucial issues. First, causality mainly goes from national soccer performance to migrating soccer players rather than the other way around. Second, the timing of the two effects is quite different. While those players giving an outstanding performance when their national team is doing well are immediately bought by clubs from more highly ranked leagues (the shop-window effect), it takes at least 4 years for the additional skills acquired by migrated players to have a positive effect on the national soccer performance (the blending effect).

#4 Test-retest reliability of a hip strength assessment system in varsity soccer players
Reference: Phys Ther Sport. 2019 Mar 28;37:138-143. doi: 10.1016/j.ptsp.2019.03.013. [Epub ahead of print]
Authors: Desmyttere G, Gaudet S, Begon M
Summary: The purpose was to investigate test-retest reliability of a hip strength assessment system (GroinBar).  Twenty asymptomatic varsity soccer players participated in this study. Maximal isometric hip strength (adduction, abduction, internal and external rotation, flexion and extension) was assessed using the GroinBar. Intraclass correlation coefficient (ICC) and relative standard error of measurement (SEM) were calculated to evaluate reliability of peak (ICC3,1) (highest peak within 3 trials) and average peak (ICC3,3) (average of 3 trials) force and rate of force development (RFD). Hotelling's T2, were also used to compare bilateral and reciprocal ratios between dominant and non-dominant leg. ICC for both peak force and RFD values revealed moderate to good reliability (0.53-0.88 and 0.61-0.84, respectively), whereas reliability was good to excellent regarding their average values (0.77-0.95 and 0.81-0.92, respectively). SEM of average peak force and RFD values (4.1-9.4% and 8.2-13.9%, respectively) were lower than that of peak force and RFD values (5.7-13.0% and 10.7-19.1%, respectively). No significant difference was found in bilateral and reciprocal force ratios between dominant and non-dominant leg. The GroinBar is a reliable tool to assess hip muscle function in athletic populations and could be used for player screening and follow-up.

#5 A season long investigation into the effects of injury, match selection and training load on mental wellbeing in professional under 23 soccer players: A team case study
Reference: Eur J Sport Sci. 2019 Apr 6:1-7. doi: 10.1080/17461391.2019.1600586. [Epub ahead of print]
Authors: Abbott W, Brownlee TE, Harper LD, Naughton RJ, Richardson A, Clifford T
Summary: This study examined the influence of injury, match selection and training load on mental wellbeing (MW) in a squad of professional soccer players. Using a longitudinal design, twenty-five male soccer players (age, 20 ± 1 years, height, 1.80 ± 5.79 m, body mass 76.33 ± 7.52 kg) from the under 23 squad playing in the Premier League 2 division in the UK completed the Warwick-Edinburgh Mental Well-being Scale (WEMWBS) each week of the 2017/2018 season (37 weeks in total). Injury and non-selection for the match squad were the only significant predictors of MW (P < 0.05). Injury had the biggest influence on MW that was lower when injured vs. not injured (43.6 ± 5.0 vs. 49.9 ± 3.5, respectively, P = 0.001, ES = 1.48), accounting for 40% of the variation in MW. This increased to 50% when not being selected to play games was also considered. Weekly training loads measured by GPS (total distance, sprint distance and total duration) and individual player win rate did not influence MW (P > 0.05). These findings highlight the importance of monitoring MW in professional soccer players and suggest that injured players and those rarely selected for the match squad should be educated on the strategies available for managing their mental health and wellbeing.

#6 Tibial fractures following participation in recreational football: Incidence and outcome
Reference: Niger J Clin Pract. 2019 Apr;22(4):492-495. doi: 10.4103/njcp.njcp_148_18.
Authors: Nwosu C
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Summary: Football is responsible for 3.5%-10% of all injuries treated in hospital, but this may reflect the popularity of the sport rather than its dangers. Young people are particularly at risk of sports injury because of high levels of exposure at a time of major physiological change. Soccer players are susceptible to a variety of injuries due to contact, aggressive tackle, and high-speed collisions. The aim of this study was to determine the pattern of presentation, treatment, and outcome of tibial fractures following participation in recreational football activity; with the hope that knowledge gained from this study will help in preventing or reducing its occurrence. This is a retrospective study of all cases of tibial fractures following participation in recreational football presenting to the Orthopedic Unit of Federal Medical Center and Surgery Department of Sir Yahaya Memorial Hospital all in Birnin Kebbi, Kebbi State, north western Nigeria; from January 2012 to December 2017. Data were extracted from the accident and emergency register, operation register, and patients' case folders on biodata, diagnosis, mechanism of injury, associated injuries, type of surgical procedure, site of surgery, date of surgery, and postoperative complications. Data collected were analyzed using the Statistical Package for Social Sciences for Windows version 22. Results were presented with descriptive statistics. In total, 37 patients were included in the study. All of them were males. The age range is from 14 to 33 years with mean age of 23.6. 17 (45.9%) of the patients are in the 21- to 30-year age group. The right tibia was affected in 34 (91.9%) patients. None of the patients used shin guard. The mechanism of injury in all the cases was direct contact. About 31 (83.8%) of the fractures were closed. Seven (18.9%) of these patients were discharged against medical advice. Nineteen (51.3%) patients were managed nonoperatively with plaster of Paris casts. Ten (27.1%) of these patients had internal fixation with locked intramedullary nail. Tibial fractures following football occur mostly in males especially adolescents and youths. The right tibia was commonly affected and most of the injuries are closed. The most common mechanism of injury was direct contact.

#7 The Effect of the "11+ Kids" on the Isokinetic Strength of Young Football Players
Reference: Int J Sports Physiol Perform. 2019 Apr 8:1-19. doi: 10.1123/ijspp.2018-0827. [Epub ahead of print]
Authors: Zarei M, Abbasi H, Daneshjoo A, Gheitasi M, Johari K, Faude O, Rommers N, Rössler R
Summary: The "11+ Kids" injury prevention programme has shown to reduce injuries and related costs in youth football players under 14 years of age. A major argument to convince coaches to use this exercise-based injury prevention programme, is a potential performance enhancement of the players. Therefore, this study investigated the effects of the "11+ Kids" programme on isokinetic strength. Two teams were randomly assigned to the intervention and control group. The intervention group replaced their warm-up by the "11+ Kids" and the control group warmed-up as usual. Two days before and after the 10-week intervention, isokinetic strength of the hip adductors and abductors, knee flexors and extensors, and ankle invertors and evertors was tested. Thirty-one players (mean age 11.5 ± 0.8 years) completed the study. The intervention group showed large improvements in all isokinetic strength measures (p < 0.001 for all measures, Cohen's d 0.8 to 1.4), whereas the control group only showed negligible to medium positive effects (p-values from 0.006 to 0.718, Cohen's d -0.1 to 0.7). The intervention was beneficial compared to the control group regarding isokinetic strength of the hip adductors (p < 0.001), knee flexors (p = 0.002), as well as ankle evertors (p < 0.001) and invertors (p = 0.005). Given the relatively short intervention period of 10 weeks, the observed improvements relate to a practically meaningful effect of the intervention. The gain in strength may improve players' performance and may contribute to a reduction of injury risk in the long-term application.

#8 Assessment of Safety and Glycemic Control During Football Tournament in Children and Adolescents With Type 1 Diabetes-Results of GoalDiab Study
Reference: Pediatr Exerc Sci. 2019 Apr 7:1-7. doi: 10.1123/pes.2018-0264. [Epub ahead of print]
Authors: Gawrecki A, Araszkiewicz A, Szadkowska A, Biegański G, Konarski J, Domaszewska K, Michalak A, Skowrońska B, Adamska A, Naskręt D, Jarosz-Chobot P, Szypowska A, Klupa T, Zozulińska-Ziółkiewicz D
Summary: The purpose was to assess glycemic control and safety of children and adolescents with type 1 diabetes participating in a 2-day football tournament. In total, 189 children with type 1 diabetes from 11 diabetes care centers, in Poland, participated in a football tournament in 3 age categories: 7-9 (21.2%), 10-13 (42.9%), and 14-17 (36%) years. Participants were qualified and organized in 23 football teams, played 4 to 6 matches of 30 minutes, and were supervised by a medical team. Data on insulin dose and glycemia were downloaded from personal pumps, glucose meters, continuous glucose monitoring, and flash glucose monitoring systems. The median level of blood glucose before the matches was 6.78 (4.89-9.39) mmol/L, and after the matches, it was 7.39 (5.5-9.87) mmol/L (P = .001). There were no episodes of severe hypoglycemia or ketoacidosis. The number of episodes of low glucose value (blood glucose ≤3.9 mmol/L) was higher during the tournament versus 30 days before: 1.2 (0-1.5) versus 0.7 (0.3-1.1) event/person/day, P < .001. Lactate levels increased during the matches (2.2 [1.6-4.0] mmol/L to 4.4 [2.6-8.5] mmol/L after the matches, P < .001). Large football tournaments can be organized safely for children with type 1 diabetes. For the majority of children, moderate mixed aerobic-anaerobic effort did not adversely affect glycemic results and metabolic safety.

#9 The effects of TeaCrine® and caffeine on endurance and cognitive performance during a simulated match in high-level soccer players
Reference: J Int Soc Sports Nutr. 2019 Apr 18;16(1):20. doi: 10.1186/s12970-019-0287-6.
Authors: Bello ML, Walker AJ, McFadden BA, Sanders DJ, Arent SM
Summary: Theacrine (1,3,7,9-tetramethyluric-acid) is a pure alkaloid with a similar structure to caffeine and acts comparably as an adenosine receptor antagonist. Early studies have shown non-habituating effects, including increases in energy and focus in response to Teacrine®, the compound containing pure theacrine. The purpose of this study was to determine and compare the effects of Teacrine® and caffeine on cognitive performance and time-to-exhaustion during a simulated soccer game in high-level male and female athletes. Male and female soccer players (N = 24; MAge = 20.96 ± 2.05y, MMaleVO2max = 55.31 ± 3.39 mL/O2/kg, MFemaleVO2max = 50.97 ± 3.90 mL/O2/kg) completed a 90-min simulated treadmill soccer match over four randomized sessions (TeaCrine®, caffeine, TeaCrine® + caffeine, placebo). Cognitive testing at halftime and end-of-game including simple reaction time (SRT), choice RT (CRT), and cognitive-load RT with distraction questions (COGRT/COGRTWrong) was performed, with a run time-to-exhaustion (TTE) at 85% VO2max following end-of-game cognitive testing. Session times and pre-exercise nutrition were controlled. RM-MANOVAs with univariate follow-ups were conducted and significance was set at P < 0.05. TTE trended towards significance in TeaCrine® and TeaCrine® + caffeine conditions compared to placebo (P < 0.052). A condition main effect (P < 0.05) occurred with faster CRT in caffeine and TeaCrine® + caffeine compared to placebo. COGRTWrong showed a significant time main effect, with better accuracy at end-of-game compared to halftime (P < 0.05). A time x condition interaction in SRT (P < 0.05) showed placebo improved from halftime to end-of-game. The 27-38% improvements in TTE reflect increased performance capacity that may have important implications for overtime scenarios. These findings suggest TeaCrine® favorably impacts endurance and the combination with caffeine provides greater benefits on cognitive function than either supplement independently.

#10 Comparison of lateral abdominal muscle thickness of young male soccer players with and without low back pain
Reference:  Int J Sports Phys Ther. 2019 Apr;14(2):273-281.
Authors: Noormohammadpour P, Mirzaei S, Moghadam N, Mansournia MA, Kordi R
Summary: While researchers have investigated low back pain (LBP) and its association with the thickness of trunk muscles in the general population, few articles have studied this relationship in athletes. The purpose was to compare the lateral abdominal muscle thickness and other possible functional risk factors in young soccer players with and without LBP. Thirty young male soccer players, with and without LBP, from the Premier League participated in this study. The thicknesses of the external oblique, internal oblique and transversus abdominis muscles were measured via musculoskeletal ultrasound imaging, bilaterally. In addition, hamstring flexibility, lumbar spine flexion range of motion, and trunk extensor muscle endurance were measured and were compared in those with and without the history of LBP. The mean age of the subjects was 17.4 (+/- 1.1) years. There was no statistically significant difference between groups (p > 0.05). Subjects with a history of LBP during their lifetime of sports participation (sports life), within the prior year, and within the prior month had statistically significant lower external oblique muscle thickness bilaterally (p<0.05). Subjects with a sports life history of LBP had lower internal oblique muscle thickness on both sides (p<0.05). Moreover, those with a sports life history of LBP had significantly less hamstring flexibility than the non-LBP group on the dominant limb (p < 0.05). In this sample group of young soccer players, abdominal muscle ultrasound measurements were different between players with and without LBP. Further longitudinal studies are needed to evaluate the role of these muscles as LBP risk factor for soccer players.

#11 The effects of training on hormonal concentrations in young soccer players
Reference: J Cell Physiol. 2019 Apr 16. doi: 10.1002/jcp.28673. [Epub ahead of print]
Authors: Muscella A, Vetrugno C, Spedicato M, Stefàno E, Marsigliante S
Summary: The purpose was to test the hypothesis that football training would be accompanied by physiological adaptations and hormonal changes, we analyzed the effects of a whole football season on physical fitness and hormonal concentrations in youth football players. Male football players (n = 29, age 16.51 ± 0.7 years) in a regional professional league and male healthy control subjects (n = 30, age 17.1 ± 1 years) participated to the study. Blood cortisol, testosterone, and growth hormone (hGH) concentrations were assayed before the beginning of the training period (T0), just after the training period (T1), at the middle of the season (T2), and at the end of the season (T3). In each period physical tests and anthropometric measurements were also performed. Results showed significant differences in basal values of cortisol, testosterone, and growth hormone (hGH) in the four time points evaluated (P < 0.01). In addition, the concentrations of hGH were higher in the soccer players group than in control subjects (P < 0.001). Between the start of the training period and the end of the football season significant differences were observed in the anthropometric characteristics and in the physical form of the football players. Furthermore, the hormonal status was significantly correlated with the indicators of the lower limb power (squat-jump [SqJ], and counter-movement-jump [CMJ]) and those of aerobic performance (Yo-Yo intermittent recovery test level 1 (YYIRT1) and maximal oxygen consumption (VO2max )).These data underscore the importance of establishing training protocols that present the potential to promote positive adaptations without, at the same time, provoking overtraining of young players.

#12 Sport Participation and Specialization Characteristics Among Pediatric Soccer Athletes
Reference: Orthop J Sports Med. 2019 Mar 27;7(3):2325967119832399. doi: 10.1177/2325967119832399. eCollection 2019 Mar.
Authors: McLeod TV, Israel M, Christino MA, Chung JS, McKay SD, Lang PJ, Bell DR; PRiSM Sports Specialization Research Interest Group, Chan CM, Crepeau A, Davis E, Fletcher AL, Laniak J, McCaffrey K, Pacicca D, Riederer M, Rizzone K, Rush JK, Zaslow T
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Summary: Soccer is an increasingly popular sport for children and adolescents in the United States. Little is known about participation patterns related to sport specialization. The purpose was to investigate soccer participation levels and sport specialization characteristics among youth soccer athletes. Adolescent athletes aged between 12 and 18 years completed an online survey addressing participant demographics, sports and soccer participation history, and level of specialization. Descriptive analyses characterized participation, while chi-square and Kruskal-Wallis tests assessed the influence of specialization, sex, and grade on survey variables. Overall, 83.7% of 746 respondents participated in an organized soccer league outside of school, and 37% played in multiple leagues concurrently. Nearly three-quarters of respondents trained in soccer more than 8 months of the year, with those who participated in club soccer being more likely to train more than 8 months of the year. More respondents were classified as high specialization (37.5%), followed by moderate (35.6%) and low (28.6%) specialization. No differences between sexes were noted for level of specialization or quitting other sports to specialize in soccer, but male athletes were more likely to train more than 8 months per year compared with female athletes. Respondents in older grades (9th-10th and 11th-12th grades) were more likely to be highly specialized and quit other sports to focus on soccer. No differences between grade levels were found among respondents training more than 8 months per year. The study findings suggest that many youth soccer athletes participated in multiple teams or leagues at the same time and trained more than 8 months of the year. Characteristics including participation on a club team, level of specialization, and male sex were associated with a greater likelihood of exceeding the 8-month training recommendation.

#13 The relative age effect in European elite soccer: A practical guide to Poisson regression modelling
Reference: PLoS One. 2019 Apr 3;14(4):e0213988. doi: 10.1371/journal.pone.0213988. eCollection 2019.
Authors: Doyle JR, Bottomley PA
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Summary: Many disciplines of scholarship are interested in the Relative Age Effect (RAE), whereby age-banding confers advantages on older members of the cohort over younger ones. Most research does not test this relationship in a manner consistent with theory (which requires a decline in frequency across the cohort year), instead resorting to non-parametric, non-directional approaches. In this article, the authors address this disconnect, provide an overview of the benefits associated with Poisson regression modelling, and two managerially useful measures for quantifying RAE bias, namely the Indices of Discrimination and Wastage. In a tutorial-like exposition, applications and extensions of this approach are illustrated using data on professional soccer players competing in the top two tiers of the "Big Five" European football leagues in the search to identify paragon clubs, leagues, and countries from which others may learn to mitigate this form of age-discrimination in the talent identification process. As with OLS regression, Poisson regression may include more than one independent variable. In this way we test competing explanations of RAE; control for unwanted sources of covariation; model interaction effects (that different clubs and countries may not all be subject to RAE to the same degree); and test for non-monotonic versions of RAE suggested in the literature.





Latest research in football - week 13 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Risk diagnosis of minor muscle injuries in professional football players: when imaging cannot help out biology might
Reference: BMJ Open Sport Exerc Med. 2019 Feb 26;5(1):e000479. doi: 10.1136/bmjsem-2018-000479. eCollection 2019.
Authors: Volpi P, Chamari K, Bisciotti GN
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#2 Epidemiology of hip and groin injuries in Swedish male first football league
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Mar 20. doi: 10.1007/s00167-019-05470-x. [Epub ahead of print]
Authors: Lundgårdh F, Svensson K, Alricsson M
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Summary: This study aimed to investigate the incidence, pattern, and burden of hip/groin injuries in Swedish professional male football players over five consecutive seasons. Injury history from 16 football teams in the Swedish male first football league was evaluated during five consecutive seasons. The team's medical staff recorded team exposure and time-loss injuries prospectively between 2012 and 2016. In total, 467 time-loss injuries located in the hip/groin area were recorded among 1,687 professional male football players, with an overall incidence and burden of 0.82/1,000 h and 15.6/1,000 h, respectively. There appeared to be an increased risk of hip/groin injuries during the last two seasons (2015-2016); however, the difference was not statistically significant (n.s). Recurrent injury rate was relatively low (14%), and overuse injuries accounted for the majority of injuries and absence days. Muscle injuries were the main injury type, while kicking and sprinting/running were the primary causes of injury. Goalkeepers had the lowest percentage of injuries and absence days. Hip/groin injuries are a substantial problem in football, but does not seem to be an increasing phenomenon in the Swedish male first football league. Index and overuse injuries accounted for the majority of injuries and absence days. Thus, the focus should be on preventing hip/groin injuries to lower the injury rate. These new findings should be taken into consideration when designing and implementing preventive training interventions.

#3 Network-based centrality measures and physical demands in football regarding player position: Is there a connection? A preliminary study
Reference: J Sports Sci. 2019 Mar 20:1-8. doi: 10.1080/02640414.2019.1589919. [Epub ahead of print]
Authors: Castellano J, Echeazarra I
Summary: This study's main objective is to analyse the relationship between network-based centrality measures and physical demands in elite football players. Thirty-six matches from La Liga, the Spanish league, were analysed in the 2017/18 season. The analysis of networks formed by team players passing the ball included: degree-prestige (DP), degree-centrality (DC), betweenness-centrality (BC), page-rank (PRP) and closeness-centrality (IRCC). A video-based system was used for analysing total distance (TDpos) and distance run >21Km/h (TD21pos) when the team was in possession of the ball. A magnitude-based inference and correlation analysis were applied. There were different styles of play, team-A was characterized by greater ball circulation (e.g. higher values of DP, DC, BC and IRCC) while team-B used a more direct game (lower values in centrality-metrics except with PRP). Furthermore, TDpos was higher in team-A than in team-B, but those differences disappeared for TD21pos between teams with the exception of the forwards. Finally, the correlation among centrality measures and physical performance were higher in team-B. Coaches could identify the key opponents and players who are linked to them, allowing to adjust performance strategies. Furthermore, interaction patterns between teammates can be used to identify preferential paths of cooperation and to take decisions regarding these relations in order to optimize team performance.

#4 Unison of movements in football players with different nervous systems
Reference: Rev Assoc Med Bras (1992). 2019 Feb;65(2):211-215. doi: 10.1590/1806-9282.65.2.211.
Author: Polevoy G
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Summary: In this study, we investigated the effect of typological features of nervous system properties on the ability to unite the movements of young football players. A total of 36 young football players aged 11-12 years participated in this experiment. Of them, 18 were engaged in an experimental differentiated method, which is based on using the same exercise and methods for developing the ability to unite movements but with different load components; for players with a strong nervous system (9 children), the load was intensive, but for players with a weak nervous system (9 children) - the load was volumetric. The other 18 athletes made up the control group. After 8 months of the experiment, we observed positive changes in terms of the ability to unite movements in young football players. In the control group, these changes were not significant (P>0.05). In the experimental group studied according to a special method, the indicators changed considerably. The performance of football players with a strong nervous system improved from 6.4±0.2 s to 5.7±0.1 s (P<0.05), and for football players with a weak nervous system from 6.2±0.2 s to 5.6±0.2 s (P<0.05). The study proved the effectiveness of the use of the typological properties of the nervous system as a differentiated method for developing the ability to unite movements in young football players. This approach allows for the improvement of the quality of technical training of young athletes.

#5 Relationship between External Load and Perceptual Responses to Training in Professional Football: Effects of Quantification Method
Reference: Sports (Basel). 2019 Mar 17;7(3). pii: E68. doi: 10.3390/sports7030068.
Authors: Rago V, Brito J, Figueiredo P, Krustrup P, Rebelo A
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Summary: We examined the within-player correlation between external training load (ETL) and perceptual responses to training in a professional male football team (n = 13 outfield players) over an eight-week competitive period. ETL was collected using 10-Hz GPS, whereas perceptual responses were accessed through rating of perceived exertion (RPE) questionnaires. Moderate-speed running (MSR), high-speed running (HSR) and sprinting were defined using arbitrary (fixed) and individualised speed zones (based on maximal aerobic speed and maximal sprinting speed). When ETL was expressed as actual distance covered within the training session, perceptual responses were moderately correlated to MSR and HSR quantified using the arbitrary method (p < 0.05; r = 0.53 to 0.59). However, the magnitude of correlations tended to increase when the individualised method was used (p < 0.05; r = 0.58 to 0.67). Distance covered by sprinting was moderately correlated to perceptual responses only when the individualised method was used (p < 0.05; 0.55 [0.05; 0.83] and 0.53 [0.02; 0.82]). Perceptual responses were largely correlated to the sum of distance covered within all three speed running zones, irrespective of the quantification method (p < 0.05; r = 0.58 to 0.68). When ETL was expressed as percentage of total distance covered within the training session, no significant correlations were observed (p > 0.05). Perceptual responses to training load seem to be better associated with ETL, when the latter is adjusted to individual fitness capacities. Moreover, reporting ETL as actual values of distance covered within the training session instead of percentual values inform better about players' perceptual responses to training load.

#6 Reducing risk of head injury in youth soccer: An extension of behavioral skills training for heading
Reference: J Appl Behav Anal. 2019 Mar 29. doi: 10.1002/jaba.557. [Epub ahead of print]
Authors: Quintero LM, Moore JW, Yeager MG, Rowsey K, Olmi DJ, Britton-Slater J, Harper ML, Zezenski LE
Summary: Recently, concerns regarding sport-related concussions have increased within the research literature, the media, and popular culture. One potential source of soccer-related concussions involves the purposeful striking of the ball with one's head (i.e., heading). There is currently limited research on an effective teaching method to improve safe heading technique. In the current study, Behavior Skills Training (BST) was evaluated as a method to teach correct heading techniques to youth soccer players. BST increased the percentage of correct steps for each player based on a task analysis of heading. Based on social validity questionnaires administered to players and the coach, BST was rated as an acceptable form of training. After the final training session, experienced coaches rated each player as having improved from baseline to training.

#7 Effects of season long participation on ACL volume in female intercollegiate soccer athletes
Reference: J Exp Orthop. 2019 Mar 28;6(1):12. doi: 10.1186/s40634-019-0182-8.
Authors: Myrick KM, Voss A, Feinn RS, Martin T, Mele BM, Garbalosa JC
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Summary: The aim of this study was to characterize the volumetric changes of the anterior cruciate ligament over the course of a competitive soccer season in female athletes. Seventeen Division-I collegiate soccer players were recruited. Two data collection sessions were conducted. The first data collection occurred prior to the start of the soccer season. Each subject completed a brief questionnaire, had height and weight measured, underwent a clinical assessment of their anterior cruciate ligaments and an eight sequence magnetic resonance imagery of their knees. Contours of the anterior cruciate ligaments were outlined in sagittal T-2 weighted MR images and volumes were calculated using Medical Image Processing, Analysis, and Visualization software. Presence or absence of edema within the ligament was determined in pre and post season scans. All subjects were followed during the season to determine if a lower extremity injury had been sustained. Mean ligament volume significantly increased from preseason to postseason (p=.006). There was a 10% increase in the percentage of knees with edema pre to post season. The physical demand of a competitive soccer season in female collegiate athletes appears to cause an increase in volume of the anterior cruciate ligament. The increase in volume may be related to the accumulation of microscopic tears over the course of the season which induce inflammation and edema. The volumetric changes in the ligament may have significant clinical implications, however further studies must be done to determine the relationship between anterior cruciate ligament volume and risk of injury.

#8 Comparing accuracy between global positioning systems and ultra-wideband-based position tracking systems used for tactical analyses in soccer
Reference: Eur J Sport Sci. 2019 Mar 28:1-9. doi: 10.1080/17461391.2019.1584248. [Epub ahead of print]
Authors: Bastida-Castillo A, Gómez-Carmona CD, De La Cruz Sánchez E, Pino-Ortega J
Summary: Current studies have reported high accuracy in global positioning system (GPS) and recently developed ultra-wideband (UWB)-based tracking systems for monitoring time - motion patterns. The accuracy and reliability of both systems may be different in tactical analysis application, an aspect that has never been studied previously. The aims of the present study were: (i) to determine and compare the accuracy of GPS and UWB technologies in soccer players' positions (ii) to compare the tactical application of both systems. Following institutional ethical approval and familiarisation, 14 well-trained soccer players performed tests around five courses: (a) field perimeter, (b) halfway line, (c) centre circle, (d) perimeter of the penalty area, and (e) semicircle penalty area. Also, a small-sided game was played monitored with WIMUPRO™ to determine real and practical differences in accuracy of both systems in tactical analysis. For the GPS, the mean absolute error (N = 9445) of "x" and "y" coordinates was 41.23 ± 17.31 cm and 47.6 ± 8.97 cm, respectively. For UWB, it was 9.57 ± 2.66 cm and 7.15 ± 2.62 cm. The results of the "x" and "y" accuracy comparison were significantly lower in all cases (p < 0.05) with an ES of 0.78 and 0.95, respectively. In a real practical application, the differences of both systems reached 8.31% in typical tactical variables (ES = 0.11). In contrast to GPS-10Hz, UWB WIMUPRO™-20 Hz has been demonstrated to be an acceptable technology to estimate the position of players on the pitch with high accuracy and be a useful, automatic, and portable instrument for tactical analysis measurement.

#9 Comparative Study of Two Intervention Programmes for Teaching Soccer to School-Age Students
Reference: Sports (Basel). 2019 Mar 26;7(3). pii: E74. doi: 10.3390/sports7030074.
Authors: García-Ceberino JM, Feu S, Ibáñez SJ
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Summary: The objective of this study was to design and analyse the differences and/or similarities of two homogeneous intervention programmes (didactic units) based on two different teaching methods, Direct Instruction (DI) and Tactical Games Approach (TGA), for teaching school-age soccer. The sample was composed of 58 tasks, 29 for each intervention programme. The pedagogical and external Training Load (eTL) variables recorded in the Integral System for Training Tasks Analysis (SIATE) were studied. The two intervention programmes were compared using Chi-Square, Mann-Whitney U and the Adjusted Standardized Residuals statistical tests. Likewise, the strength of association of the variables under study was calculated using Cramer's Phi and Cramer's V coefficients. Both intervention programmes had the same number of tasks (n = 29), sessions (n = 12), game phases (x² = 0.000; p = 1.000), specific contents (x² = 5.311; p = 0.968) and didactic objectives, as well as different levels of eTL (U = 145.000; p = 0.000; d = 1.357); which are necessary requirements to be considered similar. The differences and/or similarities between both intervention programmes will offer teachers guidelines to develop different didactic units using the specific DI and TGA methodologies.

#10 Stress fractures of the medial malleolus in the professional soccer player demonstrate excellent outcomes when treated with open reduction internal fixation and arthroscopic spur debridement
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Mar 26. doi: 10.1007/s00167-019-05483-6. [Epub ahead of print]
Authors: Nguyen A, Beasley I, Calder J
Summary: Despite a debilitating effect on athletic performance and an incidence of up to 4% of all stress fractures, there have been only 31 documented cases of medial malleolus stress fractures (MMSF) to our knowledge in the literature. The largest series to date is presented in this study, of 16 professional soccer players undergoing uniform operative treatment. The authors attempt to justify their preferred treatment of MMSFs in the professional soccer player, with an emphasis on patient satisfaction, clinical and radiographic union, and return to high level sport. The authors aim to prove an association between lower limb varus alignment and the development of MMSFs. Sixteen professional soccer players of mean age 23.6 years were analysed. A biomechanic assessment was performed. Preoperative CT+-MRI scan were performed to assess fracture lines and the presence of anteromedial tibial and/or talar spurs; which are the likely pathognomic lesion in the development of MMSFs. All patients underwent open reduction and internal fixation with three screws, as well as arthroscopic debridement of impringement spurs, and concentrated bone marrow aspirate into the fracture site. Patients completed the Ogilvie-Harris score, and all patients had CT scans at 3 months and until union. All the patients in this cohort had causative bony spurs that were debrided at surgery. All of the cohort achieved clinical union. All patients were able to return to professional football; at the same level as prior to the injury. There was complete cohort follow up; and 81% of patients were graded as excellent and 19% as good by the Ogilvie-Harris score. We noted 50% of our cohort demonstrated varus malalignment, either genu varum or hindfoot varus. The authors conclude that open reduction and internal fixation of MMSFs with screws combined with arthroscopic spur debridement results in excellent clinical outcomes. It can be concluded that varus lower limb malalignment is a risk factor for MMSFs. Given the treatment controversy for these injuries, the results herein demonstrate that aggressive multimodal operative treatment produces excellent outcomes in high demand professional footballers. This study is the first to report a biomechanic association, which can alert the clinician to preventative measures; such as hindfoot orthoses.

#11 No Evidence of Association Between Soccer Heading and Cognitive Performance in Professional Soccer Players: Cross-Sectional Results
Reference: Front Neurol. 2019 Mar 12;10:209. doi: 10.3389/fneur.2019.00209. eCollection 2019.
Authors: Rodrigues AC, Lima MDM, de Souza LC, Furtado C, Marques CE, Gonçalves L, Lima MV, Lasmar RP, Caramelli P
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Summary: Although the scientific community has focused on the effects of concussions in contact sports, the role of subconcussive impacts, as it can occur during soccer heading, has recently gained attention, considering that it may represent an additional mechanism of cumulative brain injury. The aim of this study is to investigate the effects of soccer heading on cognitive functioning in active professional soccer players. Male soccer players (n = 44), from two soccer teams that play in the Brazilian A Series Championship, and non-athletes (n = 47), comparable in age and education, were submitted to cognitive assessment, consisting of computerized and conventional neuropsychological testing (Neupsilin battery). In the computerized cognitive assessment, soccer players performed better than controls on reaction time measures in general motor coordination, executive functioning and memory tests, and on accuracy measures in executive functioning tests. There were no significant differences between groups on the Neupsilin battery. A comparison between two sub-groups of soccer players, based on the self-reported number of headings, did not show significant differences on tests performance. No significant correlations were found between an estimate of exposure to heading during professional soccer career and cognitive performance. Our data demonstrate no evidence of cognitive impairment in soccer players, compared to non-athletes, and no association between heading exposure and performance on neuropsychological tests. Longitudinal investigations, including neuroimaging assessment, will help to clarify whether soccer heading may be associated with brain injury and cognitive dysfunction.

#12 Effect of Creatine Supplementation on the Airways of Youth Elite Soccer Players
Reference: Med Sci Sports Exerc. 2019 Mar 19. doi: 10.1249/MSS.0000000000001979. [Epub ahead of print]
Authors: Simpson AJ, Horne S, Sharp P, Sharps R, Kippelen P
Summary: Owing to its well-established ergogenic potential, creatine is a highly popular food supplement in sports. As an oral supplement, creatine is considered safe and ethical. However, no data exist on the safety of creatine on lung function in athletes. The aim of this project was to evaluate the effects of a standard course of creatine on the airways of youth elite athletes. Nineteen elite soccer players, aged 16-21yr, completed a stratified, randomized, double-blind, placebo-controlled, parallel-group trial. The creatine group (n=9) ingested 0.3 g/kg/d of creatine monohydrate (CM) for 1wk (loading phase) and 5 g/d for 7wk (maintenance phase), and the placebo group (n=10) received the same dosages of maltodextrin. Airway inflammation (assessed by exhaled nitric oxide, FENO) and airway responsiveness (to dry air hyperpnoea) were measured pre- and post-supplementation. Mild, unfavorable changes in FENO were noticed by trend over the supplementation period in the CM group only (P=0.056 for interaction, η=0.199), with a mean group change of 9 ± 13 ppb in the CM group versus -5 ± 16 ppb in the placebo group (P=0.056, d=0.695). Further, the maximum fall in forced expiratory volume in 1 sec (FEV1) after dry air hyperpnoea was larger by trend post-supplementation in the CM group compared to the placebo group: 9.7 ± 7.5% versus 4.4 ± 1.4%, respectively (P=0.070, d=0.975). These adverse effects were more pronounced when atopic players only (n=15) were considered. Based on the observed trends and medium-to-large effect sizes, we cannot exclude that creatine supplementation has an adverse effect on the airways of elite athletes, particularly in those with allergic sensitization. Further safety profiling of the ergogenic food supplement is warranted.

#13 Effect of Overload and Tapering on Individual Heart Rate Variability, Stress Tolerance, and Intermittent Running Performance in Soccer Players During a Preseason
Reference: J Strength Cond Res. 2019 Mar 20. doi: 10.1519/JSC.0000000000003127. [Epub ahead of print]
Authors: Figueiredo DH, Figueiredo DH, Moreira A, Gonçalves HR, Stanganelli LCR
Summary:  This study evaluates the weekly natural log of the root-mean-square difference of successive R-R intervals (lnRMSSDmean), its coefficient of variation (lnRMSSDcv), training load (TL), stress tolerance (ST), and changes in intermittent running performance in response to a 2-week overload (OL) followed by a 1-week taper (TP) during a preseason. Additionally, we determined the relationships between these variables. Ultra-short lnRMSSD, psychometric responses, and ratings of perceived exertion were evaluated daily among 16 under-19 soccer players. At the end of each training phase, the athletes performed the Yo-Yo Intermittent Recovery test level 1 (Yo-Yo). Group analysis showed a decrease in lnRMSSDmean and ST, increases in lnRMSSDcv, and decreases in the Yo-Yo during OL, with a return to baseline levels and a trivial increase in the Yo-Yo during TP. Small to very large correlations were found between lnRMSSDmean and lnRMSSDcv values, with changes in Yo-Yo, TL, monotony, and strain during the preseason (r values ranging from -0.27 to 0.82). No correlation was found between lnRMSSD responses and ST. During OL, athletes with decreases in lnRMSSDmean and increases in lnRMSSDcv accumulated higher perceived TL, with higher monotony and overall stress, and presented a decrease in ST and intermittent running performance, interpreted as a negative adaptation in response to the maintenance of higher TL. During TP, these responses were reversed, leading to an increase in intermittent running performance. In addition, subjective measures of ST may be used to provide early indicators of training adaptation in soccer players.

#14 Influence of Different Small-Sided Game Formats on Physical and Physiological Demands and Physical Performance in Young Soccer Players
Reference: J Strength Cond Res. 2019 Mar 15. doi: 10.1519/JSC.0000000000003114. [Epub ahead of print]
Authors: Castillo D, Rodríguez-Fernández A, Nakamura FY, Sanchez-Sanchez J, Ramirez-Campillo R, Yanci J, Zubillaga A, Raya-González J
Summary: The aim of this study was to quantify the acute impact of bout duration and individual interaction space on physical and physiological demands and on physical performance. Ten young male soccer players (age: 14.8 ± 0.6 years) from the same team playing in the National U-16 Division participated. Physical (total distance [TD]; distance covered at different speeds; and maximum velocity [Velmax]) and physiological (peak [HRpeak] and mean [HRmean] heart rate) parameters were collected for every bout during each small-sided game (SSG) format. Moreover, the effects of SSGs on horizontal jump (HJ) and 30-m sprint performances were evaluated. The SSG formats were composed of 6 players a side (including goalkeepers) and included 4 repetitions of 6 minutes in a space of 100 m (SSG1) or 200 m (SSG2) and 6 repetitions of 4 minutes in 100 m (SSG3) or 200 m (SSG4). The TD, the distance covered at different speeds, and Velmax were greater (p < 0.01, effect size [ES] = 1.25-5.95, large) in SSG2 and SSG4 than SSG1 and SSG3, respectively. Furthermore, the HRmean and HRpeak were lower (p < 0.05, ES = 1.53-2.23, large) during SSG3 than other SSGs. In addition, while a significant (p < 0.05, ES = 0.70-2.04, moderate to large) increase in SPR30 time in SSG1 and SSG3 was observed, HJ performance was not affected (p > 0.05, ES = 0.03-0.54, trivial to moderate) by any SSG format. These findings suggest increasing pitch size to induce greater physical demands and to use SSGs with smaller pitch size, and independently of the bout duration, to induce neuromuscular fatigue.





Latest research in football - week 12 -2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Vertical Jump Performance in Hungarian Male Elite Junior Soccer Players
Reference: Res Q Exerc Sport. 2019 Mar 22:1-7. doi: 10.1080/02701367.2019.1588934. [Epub ahead of print]
Authors: Petridis L, Utczás K, Tróznai Z, Kalabiska I, Pálinkás G, Szabó T
Summary: Vertical jump is a common test to measure impulsive ability in soccer; however, limited normative data have been published on young soccer players from vertical jump measurements on a force platform. The purpose of this study was to provide normative values for three chronological age groups of male junior soccer players (U16, U17 and, U18 years). Vertical jump performance of 365 soccer players (16.4 ± 0.8 years) was assessed using a force platform measurement system. Net impulse, force, power, jump height (impulse-momentum), jump height (flight time) were reported for each age group for squat jump (SJ) and countermovement jump (CMJ). Mean values ± SD of jump height were 32.9 ± 4.1, 33.5 ± 4.0, and 33.9 ± 4.2 cm for the three age groups respectively in SJ and 36.3 ± 3.8, 37.5 ± 3.9, and 38.6 ± 4.4 cm in the CMJ. Mean values of all age groups for maximum force and maximum power were 1559 ± 211 N and 3261 ± 492 watt respectively for SJ and 1598 ± 241 N and 3287 ± 502 watt for CMJ. Based on descriptive data, percentiles were reported for all examined variables. Jump height and relative values were less sensitive discriminator variables between age groups in the studied age range, while maximum impulse, maximum force, and maximum power were more sensitive to changes in maturational status. Normative values can be used by the coaches in the interpretation and evaluation of their athletes' performance and for training and talent identification purposes.

#2 Effect of a 4-week detraining period followed by a 4-week strength program on isokinetic strength in elite youth soccer players
Reference: J Exerc Rehabil. 2019 Feb 25;15(1):67-73. doi: 10.12965/jer.1836538.269. eCollection 2019 Feb.
Authors: Vassilis S, Yiannis M, Athanasios M, Dimitrios M, Ioannis G, Thomas M
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Summary: The aim of the present study was to determine if 4 weeks of training cessation (detraining) followed by a 4-week strength training program can affect the isokinetic strength of elite youth soccer players. There were 13 players who participated in the study. The players performed anthropometric measurements and lower limb isokinetic strength measurements 3 times, before the training cessation, after the training cessation and after the 4-week strength training program. No significant differences were observed in the anthropometric and strength measurements (P>0.05) after the detraining period and after the training program (P>0.05). These results indicate that 4 weeks of detraining in elite youth soccer players does not have any significant effects according to their anthropometric characteristics and isokinetic strength of their lower limbs. Furthermore, neither the 4-week training program affected the parameters above. Perhaps, youth players can maintain the benefits of training better than adults due to their neural adaptations. The duration of the strength training program could be the reason of the lack of adaptations.

#3 The relationship between ACTN3 R577X gene polymorphism and physical performance in amateur soccer players and sedentary individuals
Reference: Biol Sport. 2019 Mar;36(1):9-16. doi: 10.5114/biolsport.2018.78900. Epub 2018 Oct 5.
Authors: Koku FE, Karamızrak SO, Çiftçi AS, Taşlıdere H, Durmaz B, Çoğulu Ö
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Summary: The aim of this study was to determine the distribution of ACTN3 R577X gene polymorphism in soccer players and sedentary individuals, and to investigate the relationship of this distribution with performance tests. A total of 100 soccer players and 101 sedentary individuals were enrolled in the study. Standing long jump and countermovement jump (with arm swing, without arm swing and repeated) scores were recorded, using a jump meter. Maximum VO2 levels were measured using a treadmill-connected cardiopulmonary exercise device, Masterscreen CPX. ACTN3 R577X polymorphism was evaluated by real-time PCR. ACTN3 R577X genotype distribution was found to be similar in soccer players and controls (p>0.05). The only statistically significant finding was a shorter countermovement jump with arm swing scores in the RR-genotyped soccer players, compared with their RX genotyped counterparts (p<0.05). In the soccer player group, RX-genotyped subjects were observed to have lower respiratory threshold values compared with RR-genotyped subjects (p<0.05). No significant correlation was detected between this distribution and performance test results. ACTN3 R577X genotype distribution was found to have no effect on sprint and endurance characteristics in amateur soccer players. The ACTN3 R577X polymorphism may not be a specific enough genetic marker to determine athletic performance in soccer.

#4 Lack of impact moderating movement adaptation when soccer players perform game specific tasks on a third-generation artificial surface without a cushioning underlay
Reference: Sports Biomech. 2019 Mar 21:1-15. doi: 10.1080/14763141.2019.1579365. [Epub ahead of print]
Authors: Lozano-Berges G, Clansey AC, Casajús JA, Lake MJ
Summary: The objective of this study was to investigate how the inclusion of a cushioning underlay in a third-generation artificial turf (3G) affects player biomechanics during soccer-specific tasks. Twelve soccer players (9 males/3 females; 22.6 ± 2.3 y) participated in this study. Mechanical impact testing of each 3G surface; without (3G-NCU) and with cushioning underlay (3G-CU) were conducted. Impact force characteristics, joint kinematics and joint kinetics variables were calculated on each surface condition during a sprint 90° cut (90CUT), a sprint 180° cut (180CUT), a drop jump (DROP) and a sprint with quick deceleration (STOP). For all tasks, greater peak resultant force, peak knee extensor moment and peak ankle dorsi-flexion moment were found in 3G-NCU than 3G-CU (p < 0.05). During 90CUT and STOP, loading rates were higher in 3G-NCU than 3G-CU (p < 0.05). During 180CUT, higher hip, knee and ankle ranges of motion were found in 3G-NCU (p < 0.05). These findings showed that the inclusion of cushioning underlay in 3G reduces impact loading forces and lower limb joint loading in soccer players across game-specific tasks. Overall, players were not attempting to reduce higher lower limb impact loading associated with a lack of surface cushioning underlay.

#5 Maturity status effects on torque and muscle architecture of young soccer players
Reference: J Sports Sci. 2019 Mar 21:1-10. doi: 10.1080/02640414.2019.1589908. [Epub ahead of print]
Authors: Cunha GDS, Vaz MA, Herzog W, Geremia JM, Leites GT, Reischak-Oliveira Á
Summary: This study investigated the effects of maturity status on knee extensor torque and vastus lateralis architecture of young soccer players. Thirty-four males aged 13-18 years were divided into two groups: pubescent (PUB, n = 15) and postpubescent (POSP, n = 19). Torque by angle interaction was established for absolute [F(2.649, 84.771) = 9.066, p < 0.05] and relative to body mass [F(2.704, 86.533) = 4.050, p < 0.05] isometric torque with the POSP group showing greater values. Muscle volume torque-angle relationship was similar between groups. Absolute, relative to body mass, and relative to muscle volume concentric and eccentric torque-velocity relationship showed a non-significant interaction but a significant group effect in favour the POSP group for absolute and concentric torque relative to body mass. Torque-angle and torque-velocity relationship normalized by body mass allometric exponents showed a non-significant interactions and group effects. Muscle thickness (3.6 ± 0.6 vs. 3.8 ± 0.6 cm), fascicle length (8.3 ± 1.4 vs. 8.9 ± 1.6 cm) and pennation angle (15.0 ± 2.3 vs. 14.3 ± 3.2 degrees) was similar between PUB and POSP groups, respectively. Maturity status did not show a significant effect on muscle architecture and on isometric and dynamic torques when allometrically normalized.

#6 Repeated Sprint Ability and Muscular Responses According to the Age Category in Elite Youth Soccer Players
Reference: Front Physiol. 2019 Mar 6;10:175. doi: 10.3389/fphys.2019.00175. eCollection 2019.
Authors: Sánchez-Sánchez J, García-Unanue J, Hernando E, López-Fernández J, Colino E, León-Jiménez M, Gallardo L
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Summary: The aim of this study was to analyse the influence of age category on the performance and muscle response after a Repeated Sprint Ability (RSA) test in elite youth soccer players. 62 soccer players from three different age categories (Under 14 [n = 21], Under 16 [n = 20], and Under 18 [n = 21]) were selected to participate in this study. Players completed an RSA test (7 × 30 m) with a 20-s recovery between sprints. The muscular response to an electrical stimulus before and after the test of both the biceps femoris (BF) and the rectus femoris (RF) were evaluated using tensiomyography. A two-way ANOVA was used to analyse the differences in RSA parameters in each of the four distance-intervals (0-5; 5-25; 25-30; 0-30 m) between sprint and age category. The U14 age category (5.30 ± 0.30 s) showed higher mean sprint times than U16 (4.62 ± 0.20 s) and U18 (4.46 ± 0.17 s) throughout the entire test (p < 0.01). U16 players revealed a worse best sprints time (RSABEST) than U18 players (+0.12 s, CI95%: to 0.01 to 0.24; ES: 1.09, p = 0.03). The muscular contractile properties were similar in the three age categories analyzed (p > 0.05), although the delay time (Td) of the muscle was significantly lower after the RSA test in U16 players (-1.53 ms, CI95%: -2.607 to -0.452; ES: 0.38) and U18 players (-1.11 ms, CI95%: -2.10 to -0.12; ES: 0.22). In conclusion, this study revealed an increase in physical performance and muscle response variability after a repeated sprint ability test in the U16's and over. The fatigue induced by the RSA test did not show differences depending on the age of the players, although muscle mechanical properties were altered after the RSA test in U16 and U18 soccer players. Physical performance and muscle response can be complementary variables in managing fatigue according to the age category in soccer players.

#7 Leadership and Motivational Climate: The Relationship with Objectives, Commitment, and Satisfaction in Base Soccer Players
Reference: Behav Sci (Basel). 2019 Mar 19;9(3). pii: E29. doi: 10.3390/bs9030029.
Authors: Calvo C, Topa G
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Summary: The objective of the present study is to analyze non-professional soccer players' preferences regarding coach leadership style and motivational climate and to determine the relationship of these variables with players' satisfaction, sport commitment, and sport objectives. The participants were 151 players, aged between 10 and 24 years, divided into five categories: Alevín, Infantil, Cadet, Feminine, and Juvenile, all belonging to the Aragonese Soccer Federation. The participants completed questionnaires assessing their perception of their coach's leadership style, the team's motivational climate, their individual satisfaction, degree of sport commitment, and sport objectives. The results show that the leadership styles of training and instruction (M = 3.98, SD = 0.43) and positive feedback (M = 4.02, SD = 0.53) are the most valued by the players in all categories. The training and instruction leadership style had the highest correlations with task-oriented motivational climate (r = 0.40). The findings of the regression analysis show that a training and instruction leadership style and a task-oriented motivational climate significantly predict players' satisfaction (13.3%) and sport commitment (14.5%).

#8 Monitoring Training and Match Physical Load in Junior Soccer Players: Starters versus Substitutes
Reference: Sports (Basel). 2019 Mar 19;7(3). pii: E70. doi: 10.3390/sports7030070.
Authors: Dalen T, Lorås H
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Summary: The aim of this study was to investigate differences in the physical (locomotor activities) and physiological (Banister's training impulse) in-season training load between starters and substitutes in a well-trained junior soccer team. Physical performance variables from the Polar Team Pro system were collected and analyzed from a sample of junior soccer players (N = 18; age = 15.7 ± 0.5 years; stature, 177.9 ± 4.6 cm; body mass, 67.1 ± 5.5 kg). The study analyzed a total of 10 matches and 38 training sessions during the 2018 season with linear mixed models. The players from the starting line-ups demonstrated significantly higher average weekly physical load compared to the non-starters with respect to all variables: distance (total, running, high-speed running, and sprint) [F (1, 573) ≥ 66, p < 0.001, eta = 0.10], number of accelerations and sprints [F (1, 573) ≥ 66, p < 0.001, eta = 0.10], as well as Banister's training impulse (TRIMP) [F (1, 569) = 10, p < 0.001, eta = 0.02]. Evidence from this study indicates that a large amount of weekly accumulated high-speed running and sprint distances is related to match playing time. Therefore, weekly fitness-related adaptations in running at high speeds seem to favor the starters in a soccer team.

#9 Determinants of concussion diagnosis, symptomology, and resolution time in U.S. high school soccer players
Reference: Res Sports Med. 2019 Mar 20:1-13. doi: 10.1080/15438627.2019.1590834. [Epub ahead of print]
Authors: Chandran A, Elmi A, Young H, DiPietro L
Summary: Determinants of concussion diagnosis, symptomology, and other sequelae have not been examined in high school soccer players. Using a sample of soccer-related head/neck injuries from the NATION Surveillance Program, we evaluated potential determinants (sex, injury history, injury mechanism, setting) of concussion characteristics. A total of 378 head/neck injuries were recorded, and 189 (50.0%) injuries from this sample, resulted in a concussion diagnosis. Odds of concussion diagnosis were 84% higher among female players compared with their male counterparts, and over two-fold higher in game settings compared with practice settings. We also observed several significant symptom dependencies, such as higher odds of difficulty concentrating (OR = 5.84, 95% CI = [2.99, 11.42]) given concurrent light sensitivity. Furthermore, we identified injury mechanism as a determinant of concussion symptom resolution time. Our results suggest that determinants of soccer-related concussions and their sequelae are multifactorial, and extend the existing literature with the potential to inform clinical practice.

#10 Tracking and Comparing Self-Determined Motivation in Elite Youth Soccer: Influence of Developmental Activities, Age, and Skill
Reference: Front Psychol. 2019 Mar 5;10:304. doi: 10.3389/fpsyg.2019.00304. eCollection 2019.
Authors: Hendry DT, Crocker PRE, Williams AM, Hodges NJ
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Summary: Our aim was to determine if self-determined motivation (SDM) in elite, men's soccer changes over time and differs as a function of age, skill-grouping, and engagement in soccer play and practice. We tested predictions from the Developmental Model of Sport Participation (DMSP) regarding relations between practice and play and SDM among both elite and non-elite samples. Elite youth soccer players in the United Kingdom (n = 31; from the Under 13/U13 and U15 years age groups) completed practice history and motivation questionnaires at time 1 (T1) and ∼2 years later (T2: now U15 and U17 years). Non-elite players (n = 32; from U15 and U17 years) completed the same questionnaires at T2 only. For the elite groups, global SDM decreased over time for the current U17 group (from U15), but no change was seen for the current U15 group (from U13). Age group differences at T2 mirrored these data, with U17 players showing lower global SDM and higher controlled motivation than U15 elites. The non-elite players did not show age group differences, but elites scored higher for global SDM and autonomous motivation than non-elites. The recent hours accumulated in practice negatively correlated with global SDM in elite and non-elite groups, but play was unrelated to measures of motivation. Conclusion: Differences in SDM as a function of age and skill point toward the dynamic nature of these motivations over time, likely a result of proximity to external rewards related to professional status. Although high volumes of practice are related to lower global SDM in both skill groups, the absence of any relations between SDM and soccer play does not support a key prediction related to the DMSP.

#11 Modelling the Acceleration and Deceleration Profile of Elite-level Soccer Players
Reference: Int J Sports Med. 2019 Mar 18. doi: 10.1055/a-0853-7676. [Epub ahead of print]
Authors: Newans T, Bellinger P, Dodd K, Minahan C
Summary: The ability to change velocity rapidly is a key element of field-based sports. This study quantified the acceleration and deceleration profiles of soccer players during match play. Global positioning system measures were collected from 20 male soccer players competing in the Australian Hyundai A-League during 58 matches. Match data were organized into ten 9 min periods (i. e., P1: 0-9 min) and the time spent at moderate (1-2 m·s-2) and high (>2 m·s-2) acceleration and deceleration thresholds were quantified. Additionally, a novel deceleration: acceleration ratio was quantified to identify the transient nature of deceleration activity. Linear mixed models were used to model the acceleration and deceleration profiles. All acceleration and deceleration metrics displayed negative logarithmic curves within each half. There was no change in the ratio of high deceleration: acceleration; however, a significant increase in the ratio of moderate deceleration:acceleration was evident. Using negative logarithmic curves to illustrate the acceleration and deceleration decay provides a novel methodological approach to quantify the high-intensity actions during match play. A decrease in the time spent decelerating throughout a match may be attributed to a lack of opportunity. Practitioners can use the coefficients, intercepts, and deceleration: acceleration ratios to monitor a player's deceleration profile in match play.

#12 Relationship of Training Load with High-intensity Running in Professional Soccer Players
Reference: Int J Sports Med. 2019 Mar 18. doi: 10.1055/a-0855-3843. [Epub ahead of print]
Authors: Lee M, Mukherjee S
Summary: This study determined the training load (TL) and its relationship with high-intensity running performance across the season in professional soccer players. The TL, YoYo Intermittent Recovery Test Level 2 (YYIR 2) and repeated sprint ability (RSA) were monitored in 29 players (age 26.2±3.8 years, height 173.6±5.6 cm, body mass 68.5±8.6 kg). In the mid in-season (MS), Lucia TRIMP (TRIMPL) was inversely correlated with YYIR 2 (r=-0.6, p<0.05), with total distance (TD), work-rate (WR), low-intensity distance (LID) and player load (PL) showing correlation with YYIR 2 (r=0.81, 0.77, 0.88, 0.67; p<0.05) in the late in-season (LS). In pre-season (PS), TD, WR and moderate-intensity distance (MID) were correlated with YYIR 2 (r=0.65, 0.80, 0.83, p<0.05), whereas in early in-season (ES), TD, WR, LID were correlated with YYIR 2 performance (r=0.58, 0.67, 0.55, p<0.05). There was no significant relationship (p>0.05) between TL and RSA. The findings showed the volume, intensity and types of TL accrued influences the relationship with physical performance that suggest the significance of phase-specific monitoring of TL for maximizing performance in soccer players.

#13 A Coding System to Quantify Powerful Actions in Soccer Match Play: A Pilot Study
Reference: Res Q Exerc Sport. 2019 Mar 18:1-10. doi: 10.1080/02701367.2019.1576838. [Epub ahead of print]
Authors: Murtagh CF, Naughton RJ, McRobert AP, O'Boyle A, Morgans R, Drust B, Erskine RM
Summary: The powerful activity profile of elite soccer match play has not been documented appropriately to inform specific maximal power assessment and development criteria. The aims of the current study were to develop a reliable  soccer-specific powerful action (SSPA) notational analysis coding system that could be used to compare frequency and durations of powerful actions during elite youth soccer match play. Sixteen elite male English Premier League (EPL) Academy players (19 ± 1 yrs) were recorded by an individual camera during 16 competitive EPL U18 and U21 games. Video footage was analyzed using performance analysis software and SSPAs were coded according to the following categories: initial acceleration, leading acceleration, sprint, unilateral jump and bilateral jump. The SSPA coding system demonstrated very good inter- and intra-rater reliability (kappa coefficients ≥ 0.827). Elite youth EPL soccer players undertook significantly more initial (31 ± 9) and leading (37 ± 12) accelerations than sprints (8 ± 3; p = .014, d = 1.7, and p < .001, d = 1.7, respectively) and jumps (6 ± 5; p = .002, d = 1.7 and p < .001, d = 1.7, respectively). Players performed a significantly greater number of initial and leading accelerations with action durations below 1.5 s compared to above 1.5 s (p = .001, d = 1.6, and p = .002, d = 1.4), respectively. Our SSPA coding system provides a reliable observational instrument for quantifying the frequency and duration of powerful actions performed during elite soccer match play. In our sample of elite youth soccer players, horizontal accelerations of short duration (< 1.5 s) from different starting speeds appear the most dominant powerful action in elite youth soccer match play.

#14 Characterizing head impact exposure in youth female soccer with a custom-instrumented mouthpiece
Reference: Res Sports Med. 2019 Mar 16:1-17. doi: 10.1080/15438627.2019.1590833. [Epub ahead of print]
Authors: Miller LE, Pinkerton EK, Fabian KC, Wu LC, Espeland MA, Lamond LC, Miles CM, Camarillo DB, Stitzel JD, Urban JE
Summary: While many research efforts have focused on head impact exposure in professional soccer, there have been few studies characterizing exposure at the youth level. The aim of this study is to evaluate a new instrumentation approach and collect some of the first head impact exposure data for youth female soccer players. Athletes were instrumented with custom-fit mouthpieces that measure head impacts. Detailed video analysis was conducted to identify characteristics describing impact source (e.g., kick, header, throw). A total of 763 verified head impacts were collected over 23 practices and 8 games from 7 athletes. The median peak linear accelerations, rotational velocities, and rotational accelerations of all impacts were 9.4 g, 4.1 rad/s, and 689 rad/s2, respectively. Pairwise comparisons resulted in statistically significant differences in kinematics by impact source. Headers following a kicked ball had the highest accelerations and velocity when compared to headers from thrown or another header.

#15 Partial-body cryostimulation after training improves sleep quality in professional soccer players
Reference: BMC Res Notes. 2019 Mar 15;12(1):141. doi: 10.1186/s13104-019-4172-9.
Authors: Douzi W, Dupuy O, Theurot D, Boucard G, Dugué B
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Summary: The aim of the present investigation was to determine whether using cryostimulation (partial-body cryostimulation) impacts sleep quality in professional soccer players. Different exposure durations at - 180 °C were tested randomly after standardized training sessions in nine professional soccer players (no cryostimulation, 180-s exposure, two 90-s exposures separated by a 5-min rest at room temperature, and 90-s exposure), and the effects on sleep quality using 3-dimensional accelerometers worn during sleep were assessed. The number of movements during the night after partial-body cryostimulation was significantly reduced only in the 180-s exposure condition (p < 0.05, very large effect size) compared with the control condition. Partial-body cryostimulation seems to induce a positive impact on sleep quality that may be dose-dependent. Trial registration Australia and New Zealand Clinical Trials Registry (ANZCTR), ACTRN12619000330145, date of registration: 4/03/2019. Retrospectively registered.





Latest research in football - week 11 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 A Preventive Model For Hamstring Injuries in Professional Soccer: Learning Algorithms
Reference: Int J Sports Med. 2019 Mar 14. doi: 10.1055/a-0826-1955. [Epub ahead of print]
Authors: Ayala F, López-Valenciano A, Gámez Martín JA, De Ste Croix M, Vera-Garcia FJ, García-Vaquero MDP, Ruiz-Pérez I, Myer GD
Summary: Hamstring strain injury (HSI) is one of the most prevalent and severe injury in professional soccer. The purpose was to analyze and compare the predictive ability of a range of machine learning techniques to select the best performing injury risk factor model to identify professional soccer players at high risk of HSIs. A total of 96 male professional soccer players underwent a pre-season screening evaluation that included a large number of individual, psychological and neuromuscular measurements. Injury surveillance was prospectively employed to capture all the HSI occurring in the 2013/2014 season. There were 18 HSIs. Injury distribution was 55.6% dominant leg and 44.4% non-dominant leg. The model generated by the SmooteBoostM1 technique with a cost-sensitive ADTree as the base classifier reported the best evaluation criteria (area under the receiver operating characteristic curve score=0.837, true positive rate=77.8%, true negative rate=83.8%) and hence was considered the best for predicting HSI. The prediction model showed moderate to high accuracy for identifying professional soccer players at risk of HSI during pre-season screenings. Therefore, the model developed might help coaches, physical trainers and medical practitioners in the decision-making process for injury prevention.

#2 Effects of Small-Sided Games vs. Conventional Endurance Training on Endurance Performance in Male Youth Soccer Players: A Meta-Analytical Comparison
Reference: Sports Med. 2019 Mar 13. doi: 10.1007/s40279-019-01086-w. [Epub ahead of print]
Authors: Moran J, Blagrove RC, Drury B, Fernandes JFT, Paxton K, Chaabene H, Ramirez-Campillo R
Summary: Small-sided games have been suggested as a viable alternative to conventional endurance training to enhance endurance performance in youth soccer players. This has important implications for long-term athlete development because it suggests that players can increase aerobic endurance through activities that closely resemble their sport of choice. The objectives of this meta-analysis were to compare male youth soccer players' adaptability to small-sided games vs. conventional endurance training and to establish exercise prescription guidelines for this population. The data sources utilised were Google Scholar, PubMed and Microsoft Academic. Studies were eligible for inclusion if interventions were carried out in male soccer players (aged < 18 years) and compared the effects of small-sided games and conventional endurance training on aerobic endurance performance. We defined small-sided games as "modified [soccer] games played on reduced pitch areas, often using adapted rules and involving a smaller number of players than traditional games". We defined conventional endurance training as continuous running or extensive interval training consisting of work durations > 3 min. The inverse-variance random-effects model for meta-analyses was used because it allocates a proportionate weight to trials based on the size of their individual standard errors and facilitates analysis whilst accounting for heterogeneity across studies. Effect sizes were represented by the standardised mean difference and presented alongside 95% confidence intervals. Seven studies were included in this meta-analysis. Both modes of training were effective in increasing endurance performance. Within-mode effect sizes were both of moderate magnitude [small-sided games: 0.82 (95% confidence interval 0.05, 1.60), Z = 2.07 (p = 0.04); conventional endurance training: 0.89 (95% confidence interval 0.06, 1.72), Z = 2.10 (p = 0.04)]. There were only trivial differences [0.04 (95% confidence interval - 0.36, 0.43), Z = 0.18 (p = 0.86)] between the effects on aerobic endurance performance of small-sided games and conventional endurance training. Subgroup analyses showed mostly trivial differences between the training methods across key programming variables such as set duration (≥ or < 4 min) and recovery period between sets (≥ or < 3 min). Programmes that were longer than 8 weeks favoured small-sided games [effect size = 0.45 (95% confidence interval - 0.12, 1.02), Z = 1.54 (p = 0.12)], with the opposite being true for conventional endurance training [effect size = - 0.33 (95% confidence interval - 0.79, 0.14), Z = 1.39 (p = 0.16)]. Programmes with more than 4 sets per session favoured small-sided games [effect size = 0.53 (95% confidence interval - 0.52, 1.58), Z = 0.98 (p = 0.33)] with only a trivial difference between those with 4, or fewer, sets [effect size = - 0.13 (95% confidence interval - 0.52, 0.26), Z = 0.65 (p = 0.52)]. Small-sided games are as effective as conventional endurance training for increasing aerobic endurance performance in male youth soccer players. This is important for practitioners as it means that small-sided games can allow both endurance and skills training to be carried out simultaneously, thus providing a more efficient training stimulus. Small-sided games offer the same benefits as conventional endurance training with two sessions per week, with ≥ 4 sets of 4 min of activity, interspersed with recovery periods of 3 min, recommended in this population.

#3 Management succession and success in a professional soccer team
Reference: PLoS One. 2019 Mar 13;14(3):e0212634. doi: 10.1371/journal.pone.0212634. eCollection 2019.
Authors: Kattuman P, Loch C, Kurchian C
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Summary: Research into sports team performance has shown that across many sports and league competitions, teams that change their coaches after a decline in performance do rebound, but fare no better on average than teams that have not changed their coach in a similar situation. A similar lack of succession benefits has been reported in studies of manager and CEO succession: it has not been established that changing a team's leader improves a declining team's performance. We study the effect of a change of coach on the performance of a professional soccer team. Based on rarely obtained access to a whole season (one year) of daily close observation of the team and coaching staff in practice and matches, this study uses quantitative and qualitative data to go beyond the "average" pattern reported in the literature. We document in detail how, in a single team case study over an entire season, the processes in leadership behavior changed with a change of coach, the effect this had on the state of mind of the team, how the match behaviors of the players changed, and how these changes translated into improved performance. The process effects of a leadership change on the performance of a sports team may hold insights for leader succession in management: in addition to the aggregate organizational and experience fit of the new team leader, the specific leadership processes introduced by the new leader are critical for performance effects.

#4 Prevalence and severity of traumatic dental injuries among young amateur soccer players: a screening investigation
Reference: Dent Traumatol. 2019 Mar 13. doi: 10.1111/edt.12470. [Epub ahead of print]
Authors: Qudeimat MA, AlHasan AA, AlHasan MA, Al-Khayat K, Andersson L
Summary: Traumatic dental injuries (TDI) are prevalent among soccer players. In Kuwait, no studies of TDI among soccer players have been carried out. The aim of this study was to investigate the prevalence, type, and causes of soccer-related traumatic dental injuries among 7-18-year-old amateur soccer players. All amateur soccer players who were registered in the 14 sports clubs in the country were invited to participate in this screening study. Players who were present in the club on the assigned examination day were included. The players were examined by two trained and calibrated paediatric dentists for signs of injury to the oral tissues. Injury diagnosis was made according to the Andreasen (2007) epidemiological dental injury classification. The history of any dental injury present at the time of examination was recorded. The timing and nature of any dental advice or treatment sought was also noted. Six hundred sixty-seven (48% inclusion rate) male players were included (mean age of 13.4 ± 2.6 years). In total, 213 injured teeth were observed among 169 (25%) players. The prevalence of soccer-related injuries was 11% and a greater number of injuries were observed in older players. Maxillary central incisors were the most frequently injured teeth (91%), and enamel-only fractures represented 60% of all injured teeth. Slightly more TDIs were soccer-related (44%) compared to non-soccer-related injuries (39%) and a large number of TDIs (39%) occurred inside the sports clubs. The prevalence of reported soft tissue injuries was 18%. The majority of the players (75%) did not receive dental care for their injuries. A significant number of young Kuwaiti amateur soccer players suffered TDIs. In addition, a high percentage of traumatic injuries were not treated, and there was a lack of the use of protective mouthguards.

#5 Effects of morning and nocturnal soccer matches on levels of some trace elements in young trained males
Reference: Cell Mol Biol (Noisy-le-grand). 2019 Feb 28;65(2):32-36.
Authors: Algul S, Bengu AS, Baltaci SB, Ozcelik O
Summary: The aim of this study was to comparatively evaluate effect of morning and nocturnal soccer matches induced metabolic stress on plasma levels of iron (Fe), copper (Cu) and zinc (Zn). Twenty male footballers performed two soccer matches in morning and at night on different days. Blood samples were taken before and after match. The levels of Fe, Zn and Cu were measured through an atomic absorption spectrophotometry. Metabolic stress was evaluated by altered malondialdehyde (MDA) levels that measured using High Performance Liquid Chromatography. In morning and at nocturnal soccer matches, levels of MDA (36% and 27%), Fe (37.4% and 38.9%) and Cu (34.8% and 26.8%) were all increased in all subjects, respectively. However, Zn level decreased -4.5 % in morning (n=10 subjects) and -9.4% at nocturnal (n=12 subjects) soccer matches. In addition, Cu/Zn ratio increased significantly 46.6% in morning and 36.6% at nocturnal soccer matches. Soccer match has significant effects on levels of MDA, Fe and Cu but not Zn levels. The results of this study showed that morning soccer match significantly alters levels of MDA and Cu and Cu/Zn ratio compared to nocturnal soccer match.

#6 A Comparison of Three Different Unilateral Strength Training Strategies to Enhance Jumping Performance and Decrease Inter-Limb Asymmetries in Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Mar 12:1-26. doi: 10.1123/ijspp.2018-0920. [Epub ahead of print]
Authors: Gonzalo-Skok O, Moreno-Azze A, Arjol-Serrano JL, Tous-Fajardo J, Bishop C
Summary: This study compared the effects of performing different unilateral strength training interventions on unilateral and bilateral jumping performance and their related asymmetries in young soccer players. Forty-five male young (U-17) soccer players were randomly assigned to three eccentric overload training programs: The first group executed the same volume with both legs starting with the weaker leg (SVW, n=15), the second group carried out the double volume with the weaker leg and also starting with the weaker leg (DVW, n=15), and the third group performed the same volume with both legs starting with the stronger leg (SVS, n=15). Jumping performance assessment included a single-leg horizontal jump test, a triple single-leg horizontal jump test, a bilateral countermovement (CMJ) jump test and unilateral countermovement jump test. Asymmetries were also analyzed in the unilateral jumping tests. CMJ was improved (effect size [ES]: 0.27-0.48) and CMJ asymmetry was possibly reduced (ES: 0.08-0.24) in all groups. Substantial improvements were found in triple hop (ES: 0.52-0.71) in SVW and DVW, and triple hop asymmetry was substantially decreased (ES: 0.88) in DVW. Between-group analysis showed a substantial better performance in triple hop and horizontal hop with right leg in SVW and DVW compared to SVS. Unilateral strength training programs were shown to substantially improve bilateral jumping performance, while unilateral jumping was substantially enhanced in those groups that started the training session with the weaker leg. Finally, between-limbs asymmetries in the triple hop were mainly reduced through performing the double volume with the weaker leg.

#7 The Effects of Long Sprint Ability Oriented Small-Sided Games Using Different Players-to-Pitch Area on Internal and External Load in Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Mar 12:1-23. doi: 10.1123/ijspp.2018-0645. [Epub ahead of print]
Authors: Castagna C, D'Ottavio S, Cappelli S, Póvoas SCA
Summary: The aim of this study was to examine the internal and external load imposed by Long Sprint Ability (LSA) oriented small-sided games (SSG) using different players-to-pitch area ratio (densities) in soccer players. Nineteen professional soccer players from the same soccer club (age 17.1±0.3 years, height 1.76±0.69 m, body mass 69.7±9.4 kg) participated in this study. Players performed 4x30s (150s recovery) all-out 1v1 SSG considering 300, 200 and 100 m2 per player (48h apart). Players' external-load was tracked with GPS technology (20Hz). Heart rate, blood lactate concentration (BLc) and rating of perceived exertion characterized players' internal-load. Peak BLc was assessed with a 30s all-out test on a non-motorized treadmill (NMT). SSG300 produced higher BLc than SSG200 (moderate) and SSG100 (large). The SSG300, SSG200 and SSG100 BLc were 97.8±34.8 (trivial), 74.7±24.9 (moderate) and 43.4±15.7% (large) of the NMT30s peak BLc, respectively. Players covered more distance at high-intensity during the SSG300 than in other SSG conditions (huge to very-large differences).. High-intensity deceleration distance was largely lower in SSG200 than in SSG300. SSG100 elicit very-large to huge and large to very-large lower external load values than SSG300 and SSG200, respectively. The main finding of this study showed an inverse association between ball-drill density and internal/external loads in LSA oriented SSG. The SSG300 attested to provide BLc closer to individual maximal, and thus, satisfying the all-out construct assumed for LSA development. Further studies using the SSG300 as training intervention and/or investigating other different SSG formats using the same density are warranted.

#8 Application of a Preventive Training Program Implementation Framework to Youth Soccer and Basketball Organizations
Reference: J Athl Train. 2019 Mar 11. doi: 10.4085/1062-6050-375-17. [Epub ahead of print]
Authors: Root HJ, Frank BS, Denegar CR, Casa DJ, Gregorio DI, Mazerolle SM, DiStefano LJ
Summary: Preventive training programs (PTPs) can reduce injury rates and improve neuromuscular control and sport performance. However, PTPs must be implemented correctly and consistently over time for athletes to benefit. Coaches represent the best long-term option for implementing PTPs. Youth athletes are at the optimal age for developing good habits before maturation. Although frameworks have been proposed to guide implementation efforts, little is known regarding the feasibility and real-world context of PTP implementation at the youth sport level. The aim was to evaluate the application of the 7-Step framework for promoting implementation of a preseason PTP workshop. Youth soccer and basketball organizations were utilized for this study. Organizations with at least 1 team of athletes aged 8 to 14 years were invited to participate in a free preseason coaches' education workshop on PTP implementation. The 7-Step framework was used to guide PTP education and implementation for each organization. Personnel at organizations that agreed to participate attended a single preseason workshop for coaches. Research staff were available as a resource throughout the season but did not actively implement or monitor the PTPs. Retrospective evaluation of each organization's completion of steps 1 through 5 of the 7-Step framework were used as main outcome measures.  A total of 62 youth soccer (n = 40) and basketball (n = 22) organizations were invited to participate. Twelve organizations completed steps 1 through 4 and steps 5a through 5d. The highest drop-off rate occurred during step 1, "Establishing Administrative Support". No organization completed all components of steps 1 through 5. To better understand how to successfully promote PTP adoption, we must identify the implementation steps that may present the most challenges. Because the highest drop-off rate was seen during the initial step, establishing administrative support and strengthening initial engagement are necessary to improve PTP implementation.

#9 Dissociation between changes in sprinting performance and Nordic hamstring strength in professional male football players
Reference:  PLoS One. 2019 Mar 14;14(3):e0213375. doi: 10.1371/journal.pone.0213375. eCollection 2019.
Authors: Suarez-Arrones L, Lara-Lopez P, Rodriguez-Sanchez P, Lazaro-Ramirez JL, Di Salvo V, Guitart M, Fuentes-Nieto C, Rodas G, Mendez-Villanueva A
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Summary: The aim of the present study was to evaluate the consequence of implementing a Nordic Hamstring exercise (NHE) protocol during the first 15 to 17 weeks of the season to assess the effect on sprinting and NHE strength (NHEs) in professional football players. The study examined 50 healthy male professional football players (age 18.8±0.8yr; height 176.8±6.9cm; weight 71.3±5.7kg) belonging to 3 of the reserve squads of three Spanish La-Liga clubs divided in 2 intervention teams [Nordic-Group1 (NG-1) and Nordic-Group2 (NG-2, extensive experience in NHE)] and 1 team as a control-group (CG). NHEs and linear sprint (T5, T10, T20-m) were evaluated at the beginning of the season and at the end of an intervention period of conditioning and football training, supplemented with a NHE protocol (24 sessions for NG-1 and 22 sessions for NG-2) or without using the NHE at all (CG). Sprint times were substantially improved in all groups (ES from -2.24±0.75 to -0.60±0.37). NHEs was enhanced absolute and relative to body-mass only in NG-1 after the training period (ES from 0.84±0.32 to 0.74±0.26), while in the NG-2 there were only improvements in average NHEs relative to body-mass (ES = 0.39±0.36). The improvements in T20-m were substantially greater in NG-2 vs. NG-1, and there were no differences in sprint performance changes between NG-1 and CG. Changes in sprinting performance and NHEs were unrelated. NHEs was largely correlated with the body-mass of the players. Results indicate that the improvements in sprint are not dependent on the NHEs changes, with no relationships between NHEs and sprint performance, and between sprint changes and changes in NHEs.

#10 Developing a theory-driven framework for a football intervention for men with severe, moderate or enduring mental health problems: a participatory realist synthesis
Reference: J Ment Health. 2019 Mar 12:1-12. doi: 10.1080/09638237.2019.1581339. [Epub ahead of print]
Authors: Such E, Burton H, Copeland RJ, Davies R, Goyder E, Jeanes R, Kesterton S, Mackenzie K, Magee J
Summary: Physical activity interventions are an important adjunct therapy for people with severe to moderate and/or enduring mental health problems. Football is particularly popular for men in this group. Several interventions have emerged over the past decade and there is a need to clearly articulate how they are intended to work, for whom and in what circumstances. The aim was to develop a theory-driven framework for a football intervention for men with severe, moderate and/or enduring mental health problems using a participatory realist approach. A participatory literature review on playing football as a means of promoting mental health recovery with a realist synthesis. It included the accounts and input of 12 mental health service users and the contributions of other stakeholders including football coaches and occupational therapists. Fourteen papers were included in the review. Analysis revealed that interventional mechanisms were social connectedness, identity security, normalising experiences and positive affectivity. These supported mental health recovery. Outcomes were moderated by social stigma and several interventional factors such as over-competitiveness. The context mechanism outcome configuration framework for these interventions map well onto social models of mental health recovery and provide insight into how they work. This now requires testing.

#11 Adductor squeeze test and groin injuries in elite football players: A prospective study
Reference: Phys Ther Sport. 2019 Mar 2;37:54-59. doi: 10.1016/j.ptsp.2019.03.001. [Epub ahead of print]
Authors: Moreno-Pérez V, Travassos B, Calado A, Gonzalo-Skok O, Del Coso J, Mendez-Villanueva A
Summary: The aim was to examining the relationship between hip adductor strength and groin injury incidence during the competitive season of professional football teams. Seventy-one players volunteered to participate. In the pre-season, maximal hip adductor strength was measured by means of the isometric adductor squeeze test. Hip adductor strength, normalized by body mass, was compared between players who suffered a groin injury (n = 18) vs uninjured players (n = 53). Risk ratios (RR) were used to evaluate the likelihood of players to suffer this type of injury. Most of the reported groin injuries occurred during competitive matches (5.5 per 1000 match hours). Maximal isometric hip adductor strength was lower in the groin-injured group compared with their uninjured counterparts (429.8 ± 100 vs 564 ± 58.7 N, d = -1.58 and 5.40 ± 1.27 vs 7.71 ± 0.89 N/kg, d = -1.88, respectively). Results revealed that values of maximal isometric adductor strength lower than 465.33 N increased the probability to suffer a groin injury by 72%. Furthermore, values of force relative to body mass lower than 6.971 N/kg increased the probability to suffer a groin injury by 83%. The assessment of Hip adductor strength, in addition to other measurements, might help practitioners to determine the probability of suffering an overuse groin injuries in elite football players.

#12 Application of multivariant decision tree technique in high performance football: The female and male corner kick
Reference: PLoS One. 2019 Mar 11;14(3):e0212549. doi: 10.1371/journal.pone.0212549. eCollection 2019.
Authors: Maneiro R, Casal CA, Ardá A, Losada JL
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Summary: The use of multidimensional statistical technique based on decision trees is of recent application in sports science. In the case of football, this technique has not yet been sufficiently proven. The aim of the present study was to search for different success models for the corners in the FIFA World Cup 2014 and FIFA Women's World Cup 2015. For this, the statistical analysis focused on the search for classification models for the different criteria considered (shot, shot between the three posts and goal), based on the creation of different decision trees that allow the most important variables to be identified quickly and efficiently. For this, 1117 corners were collected between the two competitions, performed in 116 international matches. It has been possible to establish multivariate models for the "shot" and "shot between the three posts" criteria, allowing, in some cases, to quadruple the potential for offensive success. On the other hand, we have been able to identify significant differences in the male and female model of execution. These findings suggest the need to continue deepening the study of tactical behavior in women's soccer from a multivariate perspective, and also propose a better optimization of the management and training of this type of actions for both male and female football. In addition, it has allowed to test the decision tree statistical technique in the analysis of high performance football, with satisfactory results and of great relevance in the applied field.





Latest research in football - week 10 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Lateral foot pain due to os vesalianum pedis in a young football player; a case report and review of the current literature
Reference: Skeletal Radiol. 2019 Feb 27. doi: 10.1007/s00256-019-03190-4. [Epub ahead of print]
Authors: Aykanat F, Vincenten C, Cankus MC, Kose O, Sindel M
Summary: Os vesalianum pedis is a rare accessory ossicle located at the 5th metatarsal base. This anatomic variation is typically asymptomatic and usually detected incidentally on routine foot radiographs. However, it may be a source of lateral foot pain and rarely become symptomatic following traumatic ankle injuries such as an inversion ankle sprain. To date, seven symptomatic os vesalianum pedis cases that required surgical treatment have been reported in the current literature. Herein, a 17-year-old professional football player with a symptomatic os vesalianum pedis was presented. The ossicle was surgically removed upon failure of conservative treatment. At the sixth month, the patient returned to sport without any restriction or pain. Clinical presentation, diagnosis, and treatment options of symptomatic os vesalianum pedis were discussed with an extensive literature review.

#2 Applying the New Teaching Methodologies in Youth Football Players: Toward a Healthier Sport
Reference: Front Physiol. 2019 Feb 13;10:121. doi: 10.3389/fphys.2019.00121. eCollection 2019.
Authors: García-Angulo A, García-Angulo FJ, Torres-Luque G, Ortega-Toro E
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Summary: At early ages (6-12 years), the levels of physical activity developed in sports initiation and Physical Education often fall short of optimal levels. Ecological models of education seek, among other things, to make up for this deficit by modifying the structural elements of sport, bringing play closer to the child's developmental characteristics. In this sense, Nonlinear Pedagogy is a model of active pedagogy that seeks the integral development of young players through a sport more in line with their abilities, and that for this is based on a system of constraints on the environment, the task and the player himself. However, there are no studies that analyze the effects of these methodologies on the parameters of physical activity at such an early age. The aim of this study was to analyze the impact of a learning methodology based on Nonlinear Pedagogy on health-related levels of physical activity (heart rate) in young football players (U-11). A quasi-experimental study was developed in which three tasks were applied using structural modifications of the football elements related to Nonlinear Pedagogy (modification of the number of players related to situations of inferiority, equality and numerical superiority; dimensions of the field of play). The sample studied was composed of football players, U-11 n = 32), age: 10.35 ± 0.54 years; years of experience: 2.14 ± 0.768 years. The players carried out each task for 10 min. Physical activity levels were measured by controlling heart rate using heart rate monitors (Polar Team2). The results showed very high levels of vigorous and very vigorous physical activity in all the tasks designed. These data show that the use of these new teaching methodologies has an impact on levels of physical activity in accordance with the recommended parameters.

#3 A combination of oral L-citrulline and L-arginine improved 10-min full-power cycling test performance in male collegiate soccer players: a randomized crossover trial
Reference: Eur J Appl Physiol. 2019 Feb 16. doi: 10.1007/s00421-019-04097-7. [Epub ahead of print]
Authors: Suzuki I, Sakuraba K, Horiike T, Kishi T, Yabe J, Suzuki T, Morita M, Nishimura A, Suzuki Y
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Summary: The purpose of the study was to investigate Oral L-citrulline (Cit) that increases plasma L-arginine (Arg) concentration and the production of nitric oxide (NO). NO dilates blood vessels and potentially improves sports performance. The combination of oral Arg and Cit (Arg + Cit) immediately and synergistically increases plasma Arg and nitrite/nitrate (NOx) concentrations more than either Cit or Arg alone. This prompted us to assess the effects of oral Arg + Cit on 10-min cycling performance in a double-blind, randomized, placebo-controlled crossover trial. Twenty-four male soccer players ingested either Cit + Arg or placebo (both 1.2 g/day each) for 6 days. On day 7, they ingested Cit + Arg 1 h before performing a 10-min full-power pedaling test on a bicycle ergometer. Plasma NOx and amino acid levels were measured before and after the test, as well as the participants' subjective perception of physical exertion. Power output was significantly greater with Cit + Arg than in the placebo group (242 ± 24 vs. 231 ± 21 W; p < 0.05). Plasma concentrations of post-exercise NOx (p < 0.05), Cit (p < 0.01) and Arg (p < 0.01) were significantly higher in the Cit + Arg than in the placebo group, whereas exercise upregulated plasma NOx concentrations in both groups (p < 0.05). Cit + Arg also gave improved post-exercise subjective perception of "leg muscle soreness" and "ease of pedaling" (both p < 0.05). Seven days of oral Citrulline (1.2 g/d) and Arginine (1.2 g/d) ingestion improved 10-min cycling performance and the perception of physical exertion in male collegiate soccer players.

#4 Fat Oxidation Rates in Professional Soccer Players
Reference: Med Sci Sports Exerc. 2019 Mar 4. doi: 10.1249/MSS.0000000000001973. [Epub ahead of print]
Authors: Randell RK, Carter JM, Jeukendrup AE, Lizarraga MA, Yanguas JI, Rollo I
Summary: Large inter-individual variation exists in maximal fat oxidation rates (MFO) and the exercise intensity at which it occurs (FATMAX). However, there is no data describing the shape of the fat oxidation curve or, if individual differences exist when tested on separate occasions. Furthermore, there is limited data on fat metabolism in professional team sport athletes. Therefore, the aim of this study was to test-retest the concavity (shape) and intercept (height) of fat oxidation curves within a group of professional soccer players. On two occasions 16 professional male soccer players completed a graded exercise test in a fasted state (≥5 h). Rates of fat oxidation were determined using indirect calorimetry. Maximal oxygen uptake (VO2max) was measured to calculate FATMAX (%VO2max). The shape of the fat oxidation curves were modelled on an individual basis using third degree polynomial. Test-by-test differences, in the shape and vertical shift of the fat oxidation curves, were established to assess within-individual variability. Average absolute MFO was 0.69 ± 0.15 g[BULLET OPERATOR]min (range 0.45 - 0.99g[BULLET OPERATOR]min). On a group level, no significant differences were found in MFO between the two tests. No differences were found (p>0.05) in the shape of the fat oxidation curves in 13/16 players (Test1 vs. Test2). There were also no differences (p>0.05) in the vertical shift of the fat oxidation curves in 10 players. In general, the shape of the fat oxidation curve does not change within an individual however the vertical shift is more susceptible to change, which may be due to training status and body composition. Understanding a player's metabolism may be of value to practitioners working within sport, with regards to personalising nutrition strategies.

#5 Adolescent characteristics of youth soccer players: do they vary with playing status in young adulthood?
Reference: Res Sports Med. 2019 Mar 6:1-12. doi: 10.1080/15438627.2019.1586704. [Epub ahead of print]
Authors: Figueiredo AJ, Coelho-E-Silva MJ, Sarmento H, Moya J, Malina RM
Summary: Adolescent characteristics of young adult soccer players (n = 35) were compared with those of youth teammates (n = 124) no longer involved in soccer. Former U-13 players active in soccer as young adults were slightly later in maturation and performed better in several functional and soccer skills than youth teammates. Former U-15 players active in soccer as young adults did not differ in maturity status from youth teammates but were chronologically older and performed better in agility and ball control. Young adult regional and national players in both age groups were rated significantly higher on the potential for success by their youth coaches, and national players were rated significantly higher than regional players. The results highlight the need for study of interactions among coaches, youth training and playing environments and the growth, maturity, functional, skill and behavioural characteristics of youth players, and how these interactions may influence persistence in soccer and later playing status.

#6 Match Fatigue Time-Course Assessment Over Four Days: Usefulness of the Hooper Index and Heart Rate Variability in Professional Soccer Players
Reference: Front Physiol. 2019 Feb 19;10:109. doi: 10.3389/fphys.2019.00109. eCollection 2019.
Authors: Rabbani A, Clemente FM, Kargarfard M, Chamari K
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Summary: The aims of the present study were to (a) examine recovery time-course and (b) analyze the usefulness of the Hooper-Index (wellness index) and resting heart rate variability (HRV) in professional soccer players during an in-season phase. The Hooper-Index and resting HRV were collected on matchday and on the four following days in three consecutive in-season weeks in nine players (25.2 ± 4.3-years). The usefulness of monitoring variables was assessed by (a) comparing noise (typical error, TE) to the smallest worthwhile change (SWC) (TE/SWC) and (b) comparing match-related changes (i.e., signal) to TE (i.e., signal-to-noise ratio). Between-days standardized differences in the changes of Hooper-Index and HRV were compared to the SWC using magnitude-based inferences. The magnitudes of TE were small and moderate for the Hooper-Index and HRV, respectively. The Hooper-Index showed to be more useful than HRV for monitoring match-induced fatigue as having a lower TE/SWC (3.1 versus 4.4) and a higher signal-to-noise ratio (5.5 versus 1.5). Small-to-very large [range of effect sizes, 0.48; 2.43, confidence limits (0.22; 2.91)] and moderate-to-large [-1.71; -0.61 (-2.44; -0.03)] detrimental changes in Hooper-Index and HRV, respectively, were observed on the days following matchday. While group analyses showed a similar pattern for recovery time-course, more individual players responded, similarly when tracked using the Hooper -Index compared to when they were tracked using HRV. An inverse moderate within-individual relationship was observed between changes in the Hooper index and HRV [r = -0.41, (-0.60, 0.18)]. The Hooper index is an easy-to-use, no-cost, and non-invasive monitoring tool and seems promising for tracking match-induced fatigue during in the season in professional soccer.

#7 Epidemiological profile of soccer-related injuries in a state Brazilian championship: An observational study of 2014-15 season
Reference: J Clin Orthop Trauma. 2019 Mar-Apr;10(2):374-379. doi: 10.1016/j.jcot.2018.05.006. Epub 2018 May 14.
Authors: Gaspar-Junior JJ, Onaka GM, Barbosa FSS, Martinez PF, Oliveira-Junior SA
Summary: Soccer related injuries are often reported in studies, but epidemiological research on this theme is rare in Brazil, Furthermore, the conditions in which athletes have returned to sports practice, namely, either symptomatic or asymptomatic, have been neglected in research. The aim of this study was to describe the epidemiological features of injuries among professional Brazilian soccer players in relation to location, type, mechanism, severity, recurrence, treatment and, lastly, symptoms in return to sport. 116 male professional athletes of teams from a Brazilian state championship were interviewed and information about injuries was recorded using a retrospective reported morbidity questionnaire. Data were analyzed in mean ± SD for physical characteristics and sports practice history in absolute and relative frequencies (chi-square test with Bonferroni's correction) for characterization of soccer injuries in terms of type, location, severity, recurrence and symptoms in return to sport. The numbers of injuries per athlete and per injured athlete were 0.92 and 1.43 respectively. The injuries of muscle-tendon unit and the joint types localized on lower limbs constituted the most important clinical occurrences with significant difference both in relation to other types (p < 0.05). Moderate and severe injuries were the most frequent occurrences. In relation to mechanisms for each type of injury, body contact was at least three times more responsible for injury cases. This type of mechanism was associated with a significantly greater impairment of joint structures. Concerning occurrence and recurrence of cases, the number of recurrent injuries of the muscle-tendon unit reached about 7.5% of the first-time injuries, while the number of joint recurrent injuries integrated almost 40% of the first-time cases. Significant differences between first-time injuries and recurrent injuries were found only for muscle-tendon and joint structures (p < 0.05), while significant differences among the type of injuries within each type of occurrence (first-time or recurrent injuries) were also found between muscle-tendon and joint injuries (p < 0.05). In relation to athletes with symptoms, in return to sport, 77.6% of them were treated for their injuries but more than half of them returned with symptoms still present when compared to those who returned without any symptoms. Among athletes who did not receive treatment, a lower percentage (58.3%) returned to the sport with symptoms still present. Significant associations between treatment and symptomatology were not found.

#8 Looking for Complementary Intensity Variables in Different Training Games in Football
Reference: J Strength Cond Res. 2019 Mar 5. doi: 10.1519/JSC.0000000000003025. [Epub ahead of print]
Authors: Casamichana D, Castellano J, Gómez Díaz A, Martín-García A
Summary: The main aim of this study was to identify which combination of external intensity training load (iTL) metrics capture similar or unique information for different training game (TG) formats and official matches (OMs) in football using principal component (PC) analysis. Ten metrics of iTL were collected from 24 professional male football players using global positioning technology. A total of 348, 383, 120, 127, 148, and 207 individual files for small-sided possession games, medium-sided possession games, small-sided games, medium-sided games, large-sided games, and OMs, respectively, were studied. Principal component analysis was conducted on each game format. Extraction criteria were set at an eigenvalue of greater than one. Varimax rotation mode was used to extract more than one PC. Intensity training load metrics with PC "loadings" above 0.7 were deemed to possess well-defined relationships with the extracted PC. In each TG and OM, 3 PCs were identified. For the first PC, eigenvalues for each game format ranged from 3.89 to 4.45, which explained 39-44% of the information (i.e., variance) provided by the 10 iTL metrics. For the second PC, eigenvalues ranged from 2.17 to 2.47, explaining 22-26% of iTL information. For the third PC, eigenvalues ranged from 1.41 to 1.98, explaining 14-20% of iTL information. This would suggest that TG and OM have multidimensional demands; so, the use of only a single iTL could potentially lead to an underestimation of the physical demands. Consequently, a combination of 3 iTL metrics is required during professional football game formats.

#9 Assessing the Return on Investment of Injury Prevention Procedures in Professional Football
Reference: Sports Med. 2019 Mar 6. doi: 10.1007/s40279-019-01083-z. [Epub ahead of print]
Authors: Fuller CW
Summary: The aim of this study was to develop a quick and simple screening procedure for evaluating the return on investment provided by injury prevention programmes in professional football. Injury prevention in sport has usually been considered in isolation of other management responsibilities, and interventions are published irrespective of whether their impact is worthwhile and irrespective of the return on players' time investment in the programme. This approach is naive from a business perspective and is not an approach normally adopted by commercial organisations. In professional football, the overwhelming cost associated with implementing an injury prevention programme is the players' time commitment, and the major benefit is the players' increased availability, achieved through the reduction in the number of injuries. A comparison of these time-based costs and benefits provides the basis for the evaluation process presented. Applying the evaluation process to a number of published injury prevention programmes recommended for football demonstrates that they are unlikely to provide an adequate return on investment. Researchers should focus on developing injury prevention programmes that provide an adequate return on players' time investment, otherwise there is no incentive for clubs to implement the programmes. Reporting that an injury prevention programme produces a statistically significant reduction in the incidence of injury, for example, is insufficient information. Injury prevention programmes should focus on 'at risk' players to increase the return on investment, and researchers should evaluate and report on the utility of prevention programmes within the intended sports setting.

#10 Lifelong Football Training: Effects on Autophagy and Healthy Longevity Promotion
Reference: Front Physiol. 2019 Feb 19;10:132. doi: 10.3389/fphys.2019.00132. eCollection 2019.
Authors: Mancini A, Vitucci D, Randers MB, Schmidt JF, Hagman M, Andersen TR, Imperlini E, Mandola A, Orrù S, Krustrup P, Buono P
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Summary: Aging is a physiological process characterized by a progressive decline of biological functions and an increase in destructive processes in cells and organs. Physical activity and exercise positively affects the expression of skeletal muscle markers involved in longevity pathways. Recently, a new mechanism, autophagy, was introduced to the adaptations induced by acute and chronic exercise as responsible of positive metabolic modification and health-longevity promotion. However, the molecular mechanisms regulating autophagy in response to physical activity and exercise are sparsely described. We investigated the long-term adaptations resulting from lifelong recreational football training on the expression of skeletal muscle markers involved in autophagy signaling. We demonstrated that lifelong football training increased the expression of messengers: RAD23A, HSPB6, RAB1B, TRAP1, SIRT2, and HSBPB1, involved in the auto-lysosomal and proteasome-mediated protein degradation machinery; of RPL1, RPL4, RPL36, MRLP37, involved in cellular growth and differentiation processes; of the Bcl-2, HSP70, HSP90, PSMD13, and of the ATG5-ATG12 protein complex, involved in proteasome promotion and autophagy processes in muscle samples from lifelong trained subjects compared to age-matched untrained controls. In conclusion, our results indicated that lifelong football training positively influence exercise-induced autophagy processes and protein quality control in skeletal muscle, thus promoting healthy aging.

#11 The FIFA 11 programme reduces the costs associated with ankle and hamstring injuries in amateur Spanish football players: A retrospective cohort study
Reference: Eur J Sport Sci. 2019 Mar 4:1-7. doi: 10.1080/17461391.2019.1577495. [Epub ahead of print]
Authors: Nouni-Garcia R, Asensio-Garcia MR, Orozco-Beltran D, Lopez-Pineda A, Gil-Guillen VF, Quesada JA, Bernabeu Casas RC, Carratala-Munuera C
Summary: This study aimed to assess the cost-effectiveness of the "Fédération Internationale de Football Association (FIFA) 11" injury prevention programme for ankle and hamstring injuries. This retrospective cohort study included eighty-four male amateur football players aged 18-40 years. The exposed group performed the FIFA 11 protocol twice a week throughout the 2010-2011 and 2011-2012 seasons; the unexposed group performed the usual training during the 2008-2009 and 2009-2010 seasons. Lateral ankle ligament and hamstring injuries were recorded over the whole study period. We compared the mean costs associated with lateral ankle ligament and hamstring injuries in the two groups. The mean cost per player and lateral ankle injury was EUR 928 in the unexposed group versus EUR 647 in the exposed group (p = 0.19). The mean cost of hamstring injury per player was EUR 1271 in the unexposed group versus EUR 742 in the exposed group (p = 0.028). The mean total cost per player was EUR 2199 in the unexposed group versus EUR 1273 in the exposed group (p = 0.008). We concluded that the use of the FIFA 11 injury prevention programme reduced both the direct and indirect costs associated with lateral ankle ligament and hamstring injuries.





Latest research in football - week 9 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Does maturation influence neuromuscular performance and muscle damage after competitive match-play in youth male soccer players?
Reference: Eur J Sport Sci. 2019 Feb 18:1-10. doi: 10.1080/17461391.2019.1575913. [Epub ahead of print]
Authors: De Ste Croix M, Lehnert M, Maixnerova E, Zaatar A, Svoboda Z, Botek M, Varekova R, Stastny P
Summary: Poor neuromuscular control and fatigue have been proposed as a risk factor for non-contact injuries especially around peak height velocity (PHV). This study explored the effects of competitive soccer match-play on neuromuscular performance and muscle damage in male youth soccer players. 24 youth players aged 13-16y were split into a PHV group (-0.5 to 0.5y) and post PHV group (1.0-2.5y) based on maturity off-set. Leg stiffness, reactive strength index (RSI), muscle activation, creatine kinase (CK), and muscle soreness were determined pre and post a competitive soccer match. Paired t-tests were used to explore differences pre and post competitive match play and independent sample t-tests for between groups differences for all outcome measures. There was no significant fatigue-related change in absolute and relative leg stiffness or muscle activation in both groups, except for the gastrocnemius in the post PHV group. RSI, CK and perceived muscle soreness were significantly different after soccer match-play in both groups with small to large effects observed (ES:0.41-2.82). There were no significant differences between the groups pre match-play except for absolute and relative leg stiffness (P < 0.001; ES = 1.16 and 0.63 respectively). No significant differences were observed in the fatigue related responses to competitive match play between groups except for perceived muscle soreness. The influence of competitive match-play on neuromuscular function and muscle damage is similar in male youth around the time of PHV and those post-PHV indicating that other factors must contribute to the heightened injury risk around PHV.

#2 Spikes in acute:chronic workload ratio (ACWR) associated with a 5-7 times greater injury rate in English Premier League football players: a comprehensive 3-year study
Reference: Br J Sports Med. 2019 Feb 21. pii: bjsports-2018-099422. doi: 10.1136/bjsports-2018-099422. [Epub ahead of print]
Authors: Bowen L, Gross AS, Gimpel M, Bruce-Low S, Li FX
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Summary: We examined the relation between global positioning system (GPS)-derived workloads and injury in English Premier League football players (n=33) over three seasons. Workload and injury data were collected over three consecutive seasons. Cumulative (1-weekly, 2-weekly, 3-weekly and 4-weekly) loads in addition to acute:chronic workload ratios (ACWR) (acute workload (1-week workload)) divided by chronic workload (previous 4-week average acute workload) were classified into discrete ranges by z-scores. Relative risk (RR) for each range was then calculated between injured and non-injured players using specific GPS variables: total distance, low-intensity distance, high-speed running distance, sprint distance, accelerations and decelerations. The greatest non-contact injury risk was when the chronic exposure to decelerations was low (<1731) and the ACWR was >2.0 (RR=6.7). Non-contact injury risk was also 5-6 times higher for accelerations and low-intensity distance when the chronic workloads were categorised as low and the ACWR was >2.0 (RR=5.4-6.6), compared with ACWRs below this. When all chronic workloads were included, an ACWR >2.0 was associated with a significant but lesser injury risk for the same metrics, plus total distance (RR=3.7-3.9). We recommend that practitioners involved in planning training for performance and injury prevention monitor the ACWR, increase chronic exposure to load and avoid spikes that approach or exceed 2.0.

#3 Measurements and Coach Assessments for Efficient Talent Selection in Elite Youth Football Science or Coaches' Eye? - Both! Beneficial Collaboration of Multidimensional
Reference: J Sports Sci Med. 2019 Feb 11;18(1):32-43. eCollection 2019 Mar.
Authors: Sieghartsleitner R, Zuber C, Zibung M, Conzelmann A
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Summary: Due to the tremendous popularity of youth football, practitioners in this domain face the ongoing question of the most effective solutions in early talent selection. Although the scientific community has suggested multidimensional models for some time, coach assessments and motor performance tests remain common. Earlier research has determined the strengths and weaknesses within these different approaches. The current investigation directly compared the effectiveness of each approach in talent selection (coach assessment vs. motor performance tests vs. multidimensional data). A sample of 117 youth football players, their parents, and coaches participated in multidimensional measurements in the U14 age category (coach assessments, motor performance tests, psychological characteristics, familial support, training history, and biological maturation). The area under the curve (AUC [95% CI]) from receiver operating characteristic indicated the prognostic validity of each approach in predicting U19 player status five years after the assessments (professional vs. non-professional). Motor performance tests (0.71 [0.58; 0.84]) showed a lower AUC than the multidimensional data (0.85 [0.76; 0.94], p = 0.02), whilst coach assessments did not differ from the two others (.82 [.74; .90]). Further, combined talent selection approaches, especially the use of coach assessments and multidimensional data together, were significantly better at predicting U19 player status (0.93 [0.87; 0.98], p = 0.02 vs. multidimensional data only). Although certain limitations may impede further insights (summation of data, skipped use of non-linear statistics), scientific claims for using multidimensionality within talent selection were confirmed to be fruitful. In particular, the combination of the subjective coaches' eye with scientific data may buffer the mutual weaknesses of these different approaches. Future research should focus on optimizing the output of promising multidimensional models. Knowledge of detailed values relating to specific dimensions within these models and the implementation of enhanced non-linear statistics may enable further improvements in the field of talent selection.

#4 Playing football on artificial turf as a risk factor for fifth metatarsal stress fracture: a retrospective cohort study
Reference: BMJ Open. 2019 Feb 20;9(2):e022864. doi: 10.1136/bmjopen-2018-022864.
Authors: Miyamori T, Nagao M, Sawa R, Tumilty S, Yoshimura M, Saita Y, Ikeda H, Kaneko K
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Summary: The fifth metatarsal stress fracture is a common injury among football players. Although several risk factors have been proposed, the association between the playing surface and development of fifth metatarsal stress fractures (MT-5) has not been evaluated. We conducted an epidemiological study using a computer-based survey to investigate the association between the playing surface and development of MT-5. This study included 1854 football players, of which 41 experienced MT-5 within the past 24 months. Baseline demographic data and the percentage of time spent playing on artificial turf and clay fields were compared between the non-MT-5 and MT-5 player groups, and the risks for development of MT-5 associated with the playing surfaces were estimated by univariate and multivariate analyses. There were significant differences in body mass index, years of play, playing categories and playing time on artificial turf between non-MT-5 and MT-5 groups (p<0.05). Generalised estimating equations analyses adjusted for multiple confounders demonstrated that relative to the risk of playing <20% of the time on each surface, the OR (OR: 95% CI) for MT-5 for playing on artificial turf >80% of the time increased (3.44: 1.65 to 7.18), and for playing on a clay field 61%-80% of the time, the OR decreased (0.25: 0.11 to 0.59). A higher percentage of playing time on an artificial turf was a risk factor for developing MT-5 in football players. This finding could be beneficial for creating strategies to prevent MT-5.

#5 Physical Fitness Characteristics of High-level Youth Football Players: Influence of Playing Position
Reference: Sports (Basel). 2019 Feb 16;7(2). pii: E46. doi: 10.3390/sports7020046.
Authors: Bujnovky D, Maly T, Ford KR, Sugimoto D, Kunzmann E, Hank M, Zahalka F
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Summary: The aim of this study was to determine whether the speed, agility, aerobic and anaerobic capacities of football players varied by playing positions. Elite youth football players (n = 123, age = 15.7 ± 0.5 years) who played in six different positions, as goalkeepers (GK), full backs (FB), central defenders (CD), wide midfielders (WM), central midfielders (CM), and attackers (AT), were assessed. Multivariate analysis of variances was used to compare the following variables: Linear running sprint for 5 m (S5) and 10 m (S10), flying sprint for 20 m (F20), agility 505 test with turn on the dominant (A505D) and non-dominant leg (A505N), agility K-test, Yo-Yo intermittent recovery (YYIR1) test and repeat sprint ability (RSA) test. The results showed significant influence of playing positions on linear-running sprint performance (F1,123 = 6.19, p < 0.01, ηp² = 0.23). Midfielders reached significantly higher performance levels (CM = 2.44 ± 0.08 s, WM = 2.47 ± 0.13 s) in the A505N test compared to GK (2.61 ± 0.23 s). Outfield players had significantly higher performance in both YYIR1 and RSA tests compared to GK (p < 0.01). The results of this study may provide insightful strategies for coaches and clinical practitioners for developing position-specific conditioning programs.

#6 Energy expenditure and dietary intake in professional football players in the Dutch Premier League: Implications for nutritional counselling
Reference: J Sports Sci. 2019 Feb 16:1-9. doi: 10.1080/02640414.2019.1576256. [Epub ahead of print]
Authors: Brinkmans NYJ, Iedema N, Plasqui G, Wouters L, Saris WHM, van Loon LJC, van Dijk JW
Summary: Selecting effective dietary strategies for professional football players requires comprehensive information on their energy expenditure (EE) and dietary intake. This observational study aimed to assess EE and dietary intake over a 14-day period in a representative group (n = 41) of professional football players playing in the Dutch Premier League (Eredivisie). Daily EE, as assessed by doubly labelled water, was 13.8 ± 1.5 MJ/day, representing a physical activity level (PAL) of 1.75 ± 0.13. Weighted mean energy intake (EI), as assessed by three face-to-face 24-h recalls, was 11.1 ± 2.9 MJ/day, indicating 18 ± 15% underreporting of EI. Daily EI was higher on match days (13.1 ± 4.1 MJ) compared with training (11.1 ± 3.4 MJ; P < 0.01) and rest days (10.5 ± 3.1 MJ; P < 0.001). Daily carbohydrate intake was significantly higher during match days (5.1 ± 1.7 g/kg body mass (BM)) compared with training (3.9 ± 1.5 g/kg BM; P < 0.001) and rest days (3.7 ± 1.4 g/kg BM; P < 0.001). Weighted mean protein intake was 1.7 ± 0.5 g/kg BM. Daytime distribution of protein intake was skewed, with lowest intakes at breakfast and highest at dinner. In conclusion, daily EE and PAL of professional football players are modest. Daily carbohydrate intake should be increased to maximize performance and recovery. Daily protein intake seems more than adequate, but could be distributed more evenly throughout the day.

#7 Listening to neutral or self-selected motivational music during warm-up to improve short-term maximal performance in soccer players: Effect of time of day
Reference: Physiol Behav. 2019 Feb 25. pii: S0031-9384(18)30924-7. doi: 10.1016/j.physbeh.2019.02.033. [Epub ahead of print]
Authors: Belkhir Y, Rekik G, Chtourou H, Souissi N
Summary: The present experiment examined the effects of listening to different types of music during warm-up on the diurnal variation of short-term maximal performance (STMP) in soccer players, using a 3 × 2 mixed design with factors "Condition" (warm-up with self-selected motivational-music (WUMM) vs. warm-up with neutral-music (WUNM) vs. warm-up without-music (WUWM) and "Time of Day" (07 h00 vs. 17 h00). In a random order, twelve male soccer players performed a 5-m shuttle run test after a 10 min of WUMM, a 10 min of WUNM and a 10 min WUWM at 07 h00 and 17 h00. The higher distance (HD) and total distance (TD) were measured during the test, and the rated perceived exertion (RPE) and the feelings states (FS) were obtained immediately after the warm-up and the test. The results revealed that HD and TD were higher at 17 h00 than 07 h00 in all conditions (p < .01). At 07 h00 and 17 h00, TD and HD were higher after WUMM and WUNM than WUWM and after WUMM than WUNM (p < .01). This improvement was greater at 07 h00 than 17 h00 (e.g., 6.97% vs. 5.26% for TD). Moreover, FS were more positive after WUNM than WUWM only at 07 h00, after WUMM than WUWM at the two time-of-day (p < .01), and after WUMM than WUNM at 17 h00 (p < .01). After the 5-m shuttle run test, FS were more negative and the RPE scores were higher with WUMM than WUWM at 07 h00 (p < .01). The findings suggested that STMP and feelings depend on types of music listened during a warm-up. A warm-up with self-selected motivational-music improves STMP and feelings at 07 h00 and 17 h00 with greater enhancement in the morning. However, a warm-up with neutral-music improves STMP and feelings only at 07 h00.

#8 Effects of a Soccer Tournament on the Psychohormonal States of Collegiate Female Players
Reference: J Strength Cond Res. 2019 Feb 18. doi: 10.1519/JSC.0000000000002993. [Epub ahead of print]
Authors: Broodryk A, Pienaar C, Edwards D, Sparks M
Summary: A gap exists in the literature concerning the connection between soccer players' hormonal and psychological responses when playing a tournament, or even a match, and its outcome (victory or defeat). This study evaluates the effects of a week-long tournament on the psychohormonal states of collegiate female soccer players. Eight players' cortisol (saliva sample), mood states (Incredibly Short Profile of Mood States [ISP]), and state-anxiety (state subscale of the State-Trait Anxiety Inventory) were assessed 1 hour before and 15 minutes after every game. Cortisol increased significantly after most matches, with intramatch differences observed (p < 0.05, d > 1.2). Match intensity influenced cortisol secretion, with greater secretion as intensity increased. The ISP demonstrated intramatch differences for the subscales' fatigue, depression, tension, and vigor (p < 0.05). Matches lost produced a higher total mood disturbance (TMD) index compared with matches won (p = 0.001, d = 1.4). Cortisol correlated with the TMD and various mood subscales before a winning outcome, with the ISP correlating at all times with the anxiety scores (p < 0.05). In conclusion, these results indicate that physiological and psychological variables combine to contribute to the stress response during a tournament. Focusing on high-intensity activities and minimizing fatigue are important, as both are associated with raised cortisol and negative mood states. Finally, implementing a mood questionnaire over a tournament can be beneficial, as sensitive information on players' hormonal and perceived anxiety states, which subsequently affect physical performance, can be obtained.

#8 Concurrent changes in eccentric hamstring strength and knee joint kinematics induced by soccer-specific fatigue
Reference: Phys Ther Sport. 2019 Feb 18;37:21-26. doi: 10.1016/j.ptsp.2019.02.003. [Epub ahead of print]
Author: Greig M
Summary: The purpose was to investigate the influence of soccer-specific fatigue on concurrent changes in knee joint kinematics and hamstring strength, given the increased risk of injury during the latter stages of match-play and the prevalence of knee joint and hamstring muscular injury. Ten male professional soccer players participated in this study. Reactive inversion, eversion and neutral hop tasks were completed at 15 min intervals during a soccer-specific protocol, with touchdown knee joint kinematics in the frontal and sagittal planes calculated at 200 Hz. In a separate trial, players completed maximal eccentric knee flexions at 160°·s-1 (reflecting average knee angular velocity in the functional task) at 15 min intervals, quantifying peak torque. All trials were characterized by knee varus at touchdown, with ∼4° greater mal-alignment elicited over the final 15 min of the protocol (P ≤ 0.05). Peak eccentric hamstring strength was significantly (P = 0.045) reduced throughout the 2nd half. The coincident impairment of eccentric hamstring strength and increased knee varus at touchdown predisposes the player to injury, supporting epidemiological observations. Knee varus in these elite male players is in marked contrast to the valgus associated with ACL injury risk in female players.

#9 Evaluation of an In-Ear Sensor for Quantifying Head Impacts in Youth Soccer
Reference: Am J Sports Med. 2019 Feb 25:363546519826953. doi: 10.1177/0363546519826953. [Epub ahead of print]
Authors: Sandmo SB, McIntosh AS, Andersen TE, Koerte IK, Bahr R
Summary: Wearable sensor systems have the potential to quantify head kinematic responses of head impacts in soccer. However, on-field use of sensors (eg, accelerometers) remains challenging, owing to poor coupling to the head and difficulties discriminating low-severity direct head impacts from inertial loading of the head from human movements, such as jumping and landing. The purpose of the study was to test the validity of an in-ear sensor for quantifying head impacts in youth soccer. First, the sensor was mounted to a Hybrid III headform and impacted with a linear impactor or a soccer ball. Peak linear acceleration (PLA), peak rotational acceleration (PRA), and peak rotational velocity (PRV) were obtained from both systems; random and systematic errors were calculated with Hybrid III as reference. Then, 6 youth soccer players wore sensors and performed a structured training protocol, including heading and nonheading exercises; they also completed 2 regular soccer sessions. For each accelerative event recorded, PLA, PRA, and PRV outputs were compared with video recordings. Receiver operating characteristic curves were used to determine the sensor's discriminatory capacity in both on-field settings, establishing cutoff values for predicting outcomes. For the laboratory tests, the random error was 11% for PLA, 20% for PRA, and 5% for PRV; the systematic error was 11%, 19%, and 5%, respectively. For the structured training protocol, heading events resulted in higher absolute values (PLA = 15.6 g± 11.8 g) than nonheading events (PLA = 4.6 g± 1.2 g); the area under the curve was 0.98 for PLA. In regular training sessions, the area under the curve was >0.99 for PLA. A 9 g cutoff value yielded a positive predictive value of 100% in the structured training protocol versus 65% in the regular soccer sessions. The in-ear sensor displayed considerable random error and substantially overestimated head impact exposure. Despite the sensor's excellent on-field accuracy for discriminating headings from other accelerative events in youth soccer, absolute values must be interpreted with caution, and there is a need for secondary means of verification (eg, video analysis) in real-life settings. Wearable sensor systems can potentially provide valuable insights into head impact exposures in contact sports, but their limitations require careful consideration.

#10 Workload and injury incidence in elite football academy players
Reference: J Sports Sci. 2019 Mar 1:1-6. doi: 10.1080/02640414.2019.1584954. [Epub ahead of print]
Authors: Delecroix B, Delaval B, Dawson B, Berthoin S, Dupont G
Summary: The aim of this study was to prospectively analyse the relationship between workloads and injury in elite football academy players. Elite football academy players (n = 122) from under-19 (U19) and under-21 (U21) of a professional football team competing in UEFA European Cups were followed during 5 seasons. Injuries were collected and absolute workload and workload ratios (4-weeks, 3-weeks, 2-weeks and week-to-week) calculated using a rolling days method with the help of the session Rate of Perceived Exertion. There was no association between absolute workload or workload ratio with the injury incidence in the U19. In the U21, the level of cumulative absolute workloads during 3-weeks (RR = 1.39, p = 0.026) and during 4-weeks (RR = 1.40, p = 0.019) were associated with an increase in injury. There was no association between workload ratio and injury in U21. The significant link between high cumulated 3-weeks and 4 weeks workloads and injury in U21 confirmed the requirement to monitor the internal subjective workload in U21 in order to prevent injury. Further studies exploring the relationships between workload and injury are required in football academy.





Latest research in footbal - week 8 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Finding Roles of Players in Football Using Automatic Particle Swarm Optimization-Clustering Algorithm
Reference: Big Data. 2019 Feb 15. doi: 10.1089/big.2018.0069. [Epub ahead of print]
Authors: Behravan I, Zahiri SH, Razavi SM, Trasarti R
Summary: Recently, professional team sport organizations have invested their resources to analyze their own and opponents' performance. So, developing methods and algorithms for analyzing team sports has become one of the most popular topics among data scientists. Analyzing football is hard because of its complexity, number of events in each match, and constant flow of circulation of the ball. Finding roles of players with the purpose of analyzing the performance of a team or making a meaningful comparison between players is crucial. In this article, an automatic big data clustering method, based on a swarm intelligence algorithm, is proposed to automatically cluster the data set of players' performance centers in different matches and extract different kinds of roles in football. The proposed method created using particle swarm optimization algorithm has two phases. In the first phase, the algorithm searches the solution space to find the number of clusters and, in the second phase, it finds the positions of the centroids. To show the effectiveness of the algorithm, it is tested on six synthetic data sets and its performance is compared with two other conventional clustering methods. After that, the algorithm is used to find clusters of a data set containing 93,000 objects, which are the centers of players' performance in about 4900 matches in different European leagues.

#2 Shared Knowledge and Verbal Communication in Football: Changes in Team Cognition Through Collective Training
Reference: Front Psychol. 2019 Jan 31;10:77. doi: 10.3389/fpsyg.2019.00077. eCollection 2019.
Authors: Blaser MA, Seiler R
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Summary: One of the psychological mechanisms that contribute to effective and efficient team actions is team cognition, defined either as shared knowledge states about game situations, teammates' skills, and action probabilities or direct communication processes in the team action itself. Particularly in interactive team sports (e.g., football), characterized by highly complex, dynamic, and uncertain situations, sharing a common understanding concerning potential future actions and how to coordinate these actions may be an advantage. Otherwise, team members must communicate their thoughts and ideas on the fly, which might be impossible due to time pressure, cognitive costs or noisy environments. This study examined if shared knowledge and verbal communication change through collective training. Forty-six under-18 and under-21 youth football players performed a football task in teams of two. The task consisted of passing and running elements common in football. After a training phase, and before two testing phases, players evaluated their actions and the actions of their assigned teammate regarding action type, location, and timing. Out of these evaluations, two indices of common understanding were computed. Furthermore, verbal communication during the task was video-and audio-recorded. Data analysis showed that shared knowledge considerably increased over time and with practice. Simultaneously, overall verbal communication and verbal communication consisting of orienting information was significantly reduced. Additionally, there was a tendency for a correlation that when shared knowledge increased, orienting verbal communication decreased. Overall, the players used orienting communications the most (77%). The study revealed that shared knowledge states and verbal communication change through collective training and that there might be a relation between the level of shared knowledge and the use of orienting verbal communication. Further studies in and off the field are needed to disentangle the complex interplay of team cognitions.

#3 Echocardiographic diagnosis of congenital coronary artery abnormalities in a continuous series of adolescent football players
Reference:  Eur J Prev Cardiol. 2019 Feb 12:2047487319825520. doi: 10.1177/2047487319825520. [Epub ahead of print]
Authors: Gerling S, Loose O, Zant R, Michel H, Melter M, Gündisch C, Krutsch V, Krutsch W
Summary: Sudden cardiac death (SCD) in children and adolescents is rare. Several studies have reported a higher risk of SCD during athletic competition. High risk congenital coronary artery abnormalities are the second leading cause of SCD in young athletes in the USA. Echocardiographic assessment of coronary arteries has not been routinely used in screening programmes for junior athletes so far. All athletes underwent a standardized cardiovascular screening protocol with a medical history, a physical examination, 12-lead resting electrocardiogram and a complete transthoracic 2D-echocardiography. Two athletes (0.19%) showed a high-risk coronary artery abnormality (CAA) with a right coronary artery originating abnormal from the aorta and coursing inter-arterial. Low-risk CAAs were found in 16 athletes (1.53%). There was an ectasia of the left coronary artery (+3.9z and +4.3z) and a fistula from the left coronary artery in two cases (0.19%), respectively. In 1.05% ( n = 11) we found a high take-off (2.3-6.8 mm) and in one case (0.096%) there was a tangential take-off of the right main coronary artery. Variants of coronary arterial anatomy were identified in 335 of 1045 athletes (32.06%). Basic pre-participation screening tests including 12-lead or exercise electrocardiogram do not safely identify high-risk CAAs. In adolescent athletes an expert cardiologist is able to describe the origin and the proximal course of the coronary arteries and identify major abnormalities in most of the cases by transthoracic 2D-echocardiography.

#4 Complete Rupture of the Triceps Tendon and Ulnar Collateral Ligament of the Elbow in a 13-Year-Old Football Player: A Case Report
Reference: J Orthop Case Rep. 2018 Sep-Oct;8(5):15-18. doi: 10.13107/jocr.2250-0685.1188.
Authors: Khalil LS, Alkhelaifi K, Meta F, Lizzio VA, Shehab R, Makhni EC
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Summary: With the increasing number of children and adolescents participating in sports, pathologies once reserved for high-level athletes are now emerging in this younger population. Distal triceps tendon tears represent an injury infrequently seen even among older, skeletally mature athletes. We report a case of distal triceps tendon tear with concomitant ulnar collateral ligament (UCL) injury in a skeletally-immature football player. This is a rare case of traumatic triceps tendon tear with UCL injury in a 13-year-old male football player during a fall and hyperextension of his elbow. Management included surgical treatment of the triceps tear with suture anchors in double row technique. The concomitant UCL injury was treated conservatively. This case suggests that this type of injury can occur in young athletes, but good prognosis can be expected with prompt management. Surgical repair of a functionally deficient triceps tendon tear and conservative management of associated UCL injury can result in returntoplay within 6 months.

#5 A Meta-Comparison of the Effects of High-Intensity Interval Training to Those of Small-Sided Games and Other Training Protocols on Parameters Related to the Physiology and Performance of Youth Soccer Players
Reference: Sports Med Open. 2019 Feb 21;5(1):7. doi: 10.1186/s40798-019-0180-5.
Authors: Kunz P, Engel FA, Holmberg HC, Sperlich B
Summary: High-intensity interval training (HIIT) is frequently employed to improve the endurance of various types of athletes. To determine whether youth soccer players may benefit from the intermittent load and time efficiency of HIIT, we performed a meta-analysis of the relevant scientific literature. Our primary objective was to compare changes in various physiological parameters related to the performance of youth soccer players in response to running-based HIIT to the effects of other common training protocols (i.e., small-sided games, technical training and soccer-specific training, or high-volume endurance training). A secondary objective was to compare specifically running-based HIIT to a soccer-specific form of HIIT known as small-sided games (SSG) in this same respect, since this latter type of training is being discussed extensively by coaches. A systematic search of the PubMed, SPORTDiscus, and Web of Science databases was performed in August of 2017 and updated during the review process in December of 2018. The criteria for inclusion of articles for analysis were as follows: (1) comparison of HIIT to SSG or some other training protocol employing a pre-post design, (2) involvement of healthy young athletes (≤ 18 years old), and (3) assessment of variables related to endurance or soccer performance. Hedges' g effect size (dppc2) and associated 95% confidence intervals for the comparison of the responses to HIIT and other interventions were calculated. Nine studies, involving 232 young soccer players (mean age 16.2 ± 1.6 years), were examined. Endurance training in the form of HIIT or SSG produced similar positive effects on most parameters assessed, including peak oxygen uptake and maximal running performance during incremental running (expressed as Vmax or maximal aerobic speed (MAS)), shuttle runs (expressed as the distance covered or time to exhaustion), and time-trials, as well as submaximal variables such as running economy and running velocity at the lactate threshold. HIIT induced a moderate improvement in soccer-related tests involving technical exercises with the soccer ball and other game-specific parameters (i.e., total distance covered, number of sprints, and number of involvements with the ball). Neuromuscular parameters were largely unaffected by HIIT or SSG. The present meta-analysis indicates that HIIT and SSG have equally beneficial impacts on variables related to the endurance and soccer-specific performance of youth soccer players, but little influence on neuromuscular performance.

#6 Caffeine Supplementation and Physical Performance, Muscle Damage and Perception of Fatigue in Soccer Players: A Systematic Review
Reference: Nutrients. 2019 Feb 20;11(2). pii: E440. doi: 10.3390/nu11020440.
Authors: Mielgo-Ayuso J, Calleja-Gonzalez J, Del Coso J, Urdampilleta A, León-Guereño P, Fernández-Lázaro D
Summary: Soccer is a complex team sport and success in this discipline depends on different factors such as physical fitness, player technique and team tactics, among others. In the last few years, several studies have described the impact of caffeine intake on soccer physical performance, but the results of these investigations have not been properly reviewed and summarized. The main objective of this review was to evaluate critically the effectiveness of a moderate dose of caffeine on soccer physical performance. A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in the Medline/PubMed and Web of Science databases from January 2007 to November 2018. The search included studies with a cross-over and randomized experimental design in which the intake of caffeine (either from caffeinated drinks or pills) was compared to an identical placebo situation. There were no filters applied to the soccer players' level, gender or age. This review included 17 articles that investigated the effects of caffeine on soccer-specific abilities (n = 12) or on muscle damage (n = 5). The review concluded that 5 investigations (100% of the number of investigations on this topic) had found ergogenic effects of caffeine on jump performance, 4 (100%) on repeated sprint ability and 2 (100%) on running distance during a simulated soccer game. However, only 1 investigation (25%) found as an effect of caffeine to increase serum markers of muscle damage, while no investigation reported an effect of caffeine to reduce perceived fatigue after soccer practice. In conclusion, a single and moderate dose of caffeine, ingested 5⁻60 min before a soccer practice, might produce valuable improvements in certain abilities related to enhanced soccer physical performance. However, caffeine does not seem to cause increased markers of muscle damage or changes in perceived exertion during soccer practice.

#7 Defining the Early, Mid, and Late Subsections of Sprint Acceleration in Division I Men's Soccer Players
Reference: J Strength Cond Res. 2019 Feb 14. doi: 10.1519/JSC.0000000000003088. [Epub ahead of print]
Authors: Bellon CR, DeWeese BH, Sato K, Clark KP, Stone MH
Summary: The purpose of this study was to investigate whether the acceleration phase of sprinting could be split into subphases specific to the competitive demands of a soccer match by comparing sprint metrics at various sprint distances in Division I men's soccer players. Twenty-three Division I men's soccer athletes completed 2 maximal-effort 20-m sprints from a standing start position through an optical measurement system. Sprint metrics measured included sprint velocity (SV), step length (SL), step frequency (SF), and ground contact time (GCT). Each metric was recorded at approximately 2.5, 6, and 12 m. Sprint metrics at each distance were compared using a 2-tailed, 1-way repeated-measures analysis of variance. The results indicated that SV, SL, and SF were statistically greater at 12 m in comparison with 6 m (p < 0.001) and 2.5 m (p < 0.001), whereas GCT was statistically shorter at 12 m compared with 6 m (p < 0.001) and 2.5 m (p < 0.001). In addition, sprint metrics at 6 m also displayed the same relationships when compared to 2.5 m, with SV, SL, and SF being statistically greater (p < 0.001) at this distance, and GCT being statistically shorter (p < 0.001) as well. These results suggest that the acceleration phase may effectively be differentiated into early, mid, and late subphases based on differences in key sprint metrics at distances of 2.5, 6, and 12 m, respectively, in Division I men's soccer athletes.

#8 Compression Stockings Used During Two Soccer Matches Improve Perceived Muscle Soreness and High-Intensity Performance
Reference: J Strength Cond Res. 2019 Feb 14. doi: 10.1519/JSC.0000000000003048. [Epub ahead of print]
Authors: Gimenes SV, Marocolo M, Pavin LN, Spigolon LMP, Barbosa Neto O, da Silva BVC, Duffield R, da Mota GR
Summary: Evidence on the use of compression stockings (CS) during soccer matches is limited. Thus, we evaluated the acute effects of CS on match-based physical performance indicators and perceptual responses during 2 consecutive soccer matches with 72-hour recovery. Twenty outfield players were randomly allocated to the CS group (20-30 mm Hg) or control group (non-CS) and performed 2 matches (5 players using CS or regular socks per team/match). Match loads {rating of perceived exertion × minutes; CS ∼830 vs. control 843 (arbitrary units [AU])} and heart rate (HR) responses (both CS and control ∼86% HRpeak) did not differ (p > 0.05) between CS and control groups. Although total distance covered did not differ (p > 0.05) between groups, CS increased distances (effect size [ES] = 0.9-1.32) in higher-speed zones (>19 km·h CS ∼550 m vs. control ∼373 m) alongside an increased number of accelerations (-50.0 to -3.0 m·s) than control (CS: 33.7 ± 11.2 vs. control: 23.8 ± 7.9; p = 0.003; ES = 1.04). Perceived recovery did not differ (p > 0.05) between groups for either match but was worse in the second match for both groups. Perceived muscle soreness increased in control after match 2 (from 3.1 ± 1.9 to 6.3 ± 1.6 AU; p < 0.0010) but did not in CS (from 2.8 ± 1.4 to 4.1 ± 1.9 AU; p = 0.6275; ES = 1.24 CS vs. control after match). Accordingly, CS use during 2 soccer matches with 72-hour recovery reduces perceived muscle soreness in the second match and increases higher-speed match running performance.

#9 Are Linear Speed and Jumping Ability Determinants of Change of Direction Movements in Young Male Soccer Players?
Reference: J Sports Sci Med. 2019 Feb 11;18(1):109-117. eCollection 2019 Mar.
Authors: Popowczak M, Rokita A, Świerzko K, Szczepan S, Michalski R, Maćkała K
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Summary: The study was undertaken to investigate the relationships between linear speed, change of direction, and explosive power in the lower limbs of young soccer players. We aimed to determine the variables associated with effective change-of-direction speeds (time) based on the 30-m ZigZag (cutting maneuver) under 60° (CODS1), and 30 m sprint divided into forward-backward-forward movement (CODS2). Sixty young soccer players (age: 17.4 ± 0.7 years, height: 1.76 ± 0.06 m, weight: 68.1 ± 8.9 kg) from soccer sport clubs were included. The participants performed 30-m change-of-direction sprints and 30-m backward and forward sprints. For the maximum speed evaluation, a straight-line 30-m sprint test was performed. Counter-movement jumps and standing broad jumps were used to assess jumping ability. Pearson's linear correlation and a multiple stepwise linear regression model were used to adjust for variations related to the influence of functional speed and explosive power variables, which were analyzed based on the CODS1 and CODS2 data. Our results showed that 30-m CODS2 and standing broad jumps were associated with CODS1. The variation for the 30-m change-of-direction maneuvers under 60° could be explained by the results of 30-m forward-backward-forward change-of-direction. The standing broad jump explained 10% variation for the performances in change-of-direction sprint decrements and 9% variation for the 5-m change-of-direction with the best times, whereas straight-line sprinting was related to forward-backward-forward change-of-direction. The 10-m sprint explained 50% variation of the performances in the first 10-m forward running in the CODS2 and 12% variation for 10-m backward-forward change-of-direction. The 30-m sprint explained 36% variation for 30-m forward-backward-forward change-of-direction. The 30-m sprint and overall body mass also explained 58% variation for 10-m forward-backward change-of-direction. For coaching purposes, we report that forward-backward-forward and cutting maneuver change-of-direction movements are independent and highly useful skills. This information can help to provide better training prescriptions.

#10 The Use of GPS Analysis to Quantify the Internal and External Match Demands of Semi-Elite Level Female Soccer Players during a Tournament
Reference: J Sports Sci Med. 2019 Feb 11;18(1):73-81. eCollection 2019 Mar.
Authors: Strauss A, Sparks M, Pienaar C
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Summary: The purpose of this study was to make use of global positioning system technology to quantify the internal and external match demands of sub-elite female soccer players. Secondly, the study aims to describe the magnitude of change of these variables within and between matches over the course of a tournament to determine the effect of player fatigue. Thirty sub-elite female soccer players were assessed throughout a local tournament. Differences in match demands within and between matches were assessed using percent difference, effect size and 90% confidence intervals. One-way ANOVA was used to compare differences in the match demands and running intensities among playing positions and Bonferroni corrections were used to determine differences where significant effects of position were observed. A paired sample t-test in conjunction with the Cohen effect size was used to compare changes in match performance. Total distance covered averaged 5917 m. Midfielders covered the greatest absolute and relative total distances, and achieved the highest low-intensity activity and player load per minute of play. Defenders covered significantly (p ≤ 0.05) less relative distance and low-intensity activity per minute of play compared to midfielders. Forwards covered the greatest distance at high-intensity, while the greatest percentage of time at high-intensity heart rate was measured among the defenders. Within match comparisons revealed that player load decreased significantly (p ≤ 0.05) in the second half (ES: 0.4). Relative distance, low-intensity activity and high-intensity activity also decreased in the second half with possibly trivial to likely small changes. Small to large differences in variables were observed throughout the tournament. The biggest magnitude of change was seen with a large decrease (ES: -1.2) in relative distance covered between match 2 and 5. Despite generally small reductions in performance measures, there is evidence that accumulated fatigue throughout a multi-day tournament would affect performance negatively.

#11 Preseason Dynamic Balance Performance in Healthy Elite Male Soccer Players
Reference: Am J Mens Health. 2019 Jan-Feb;13(1):1557988319831920. doi: 10.1177/1557988319831920.
Authors: Onofrei RR, Amaricai E, Petroman R, Surducan D, Suciu O
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Summary: Lower limb musculoskeletal injuries in sports are linked with balance abnormalities and altered postural control. Dynamic balance screening should be performed in order to identify athletes at risk. The purpose of the study was to evaluate the preseason dynamic balance performance and side-to-side asymmetry of healthy elite male soccer players, using modified Star Excursion Balance Test (mSEBT). Seventy-three elite soccer players (23.8 ± 5.4 years) were evaluated using the mSEBT. Normalized reach distances, side-to-side asymmetries, and composite scores were determined. The composite scores were 93.33% ± 8.99% for dominant leg and 93.36% ± 9.23% for nondominant leg. No significant differences were found between dominant and nondominant limb in any direction. The mSEBT is an easy-to-use tool to measure the dynamic balance performance in elite athletes. It can be applied successfully during preseason physical examinations. Future studies are needed to establish predictive cutoff points in order to increase mSEBT use in screening soccer players for dynamic balance abnormalities and identify those at risk for noncontact lower limb injuries.






Latest research in football - week 7 - 2018

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Ankle Structures of Professional Soccer (Football) Players With Proximal Diaphyseal Stress Fractures of the Fifth Metatarsal
Reference: J Foot Ankle Surg. 2019 Feb 11. pii: S1067-2516(18)30428-9. doi: 10.1053/j.jfas.2018.09.024. [Epub ahead of print]
Authors: Kizaki K, Yamashita F, Mori D, Funakoshi N
Summary: Despite a high incidence of proximal diaphyseal stress fractures of the fifth metatarsal (zone 3) in soccer (football) players, studies that examine risk factors of the fractures in professional soccer players are scarce; in particular, ankle structures have not yet been investigated. This study was designed to investigate ankle structures of professional soccer players with proximal diaphyseal stress fractures of the fifth metatarsal. We reviewed the ankle radiographs of 100 professional soccer players (stress fractures n = 15; controls n = 85) and measured the medial malleolar slip angle (MMSA), the ratio of the medial malleolar length to the width of the talar dome (MML:TD ratio), the ratio of the lateral malleolar length to the width of the TD (LML:TD ratio), and the ratio of the MML to the LML (MML:LML ratio). The MMSA (p < .01: 28.7° ± 5.8° versus 23.0° ± 4.9°) in the stress fractures was significantly wider and the MML:TD ratio (p = .08: 0.49 ± 0.08 versus 0.52 ± 0.07) had a trend to be smaller compared with the values of the controls. Logistic regression analysis revealed that a wider malleolar slip angle became a factor associated with stress fractures in professional soccer players (p < .01: odds ratio 1.27, 95% confidence interval 1.110 to 1.463). Receiver operating characteristic curve with MMSA for the stress fractures was depicted with an area under the curve of 0.778, and the suitable cut-off point was set at MMSA >27° with a positive likelihood ratio of 3.67 (95% confidence interval 2.173 to 6.188). Our study results show that a wide MMSA was associated with proximal diaphyseal stress fractures of the fifth metatarsal in professional soccer players.

#2 The acute effects of a short technique-intense training period on side-foot kick performance among elite female soccer players
Reference: J Sports Med Phys Fitness. 2019 Feb 13. doi: 10.23736/S0022-4707.19.09449-0. [Epub ahead of print]
Authors: Carlsson M, Isberg J, Nilsson J, Carlsson T
Summary: Previously, it was shown that elite soccer teams were 24% more likely to win matches if their passing effectiveness were increased by 1%. However, research interventions aiming to improve passing performance are scarce. The current study aimed to investigate the effect of a short technique-intense training period on side-foot kick performance among elite female soccer players. Four side-foot kick tests were completed before and after a training period: kicking a stationary ball using match-relevant (SBRS) and maximal ball speed (SBMS), passing the ball on the move using match-relevant ball speed (RBRS), and repeated side-foot kicks onto a rebound-box with continuously increasing passing distance (RRB). The players were assigned to either the intervention group or the control group. The training intervention consisted of six 55-min training sessions with five side-foot kick exercises. Within-group and between-group differences were investigated using paired-samples t-test and Mann-Whitney U test, respectively. The intervention group improved the performance in the RBRS and RRB tests (both P < 0.05), but no differences were found for the SBRS and SBMS tests (both P > 0.05). No improvements were found for the control group independent of test condition (all P > 0.05). Significant between-group differences were found for the RBRS and RRB tests (both P < 0.05), whereas no differences were found for the SBRS and SBMS tests (both P > 0.05). The fundamental soccer skill of passing a moving ball was improved in elite female soccer players by a short technique-intense training period.

#3 Head Injury in Soccer: From Science to the Field; summary of the head injury summit held in April 2017 in New York City, New York
Reference: Br J Sports Med. 2019 Feb 13. pii: bjsports-2018-100232. doi: 10.1136/bjsports-2018-100232. [Epub ahead of print]
Authors: Putukian M, Echemendia RJ, Chiampas G, Dvorak J, Mandelbaum B, Lemak LJ, Kirkendall D
Summary: There has been an increased focus and awareness of head injury and sport-related concussion (SRC) across all sports from the medical and scientific communities, sports organisations, legislators, the media and the general population. Soccer, in particular, has been a focus of attention due to the popularity of the game, the frequency of SRC and the hypothesised effects of repetitive heading of the ball. Major League Soccer, US Soccer and the National Women's Soccer League jointly hosted a conference entitled, 'Head Injury in Soccer: From Science to the Field', on 21-22 April 2017 in New York City, New York. The mission of this conference was to identify, discuss and disseminate evidence-based science related to the findings and conclusions of the fifth International Conference on Concussion in Sport held by the Concussion in Sport Group and apply them to the sport of soccer. In addition, we reviewed information regarding the epidemiology and mechanism of head injuries in soccer at all levels of play, data regarding the biomechanics and effects of repetitive head impacts and other soccer-specific considerations. We discussed how to release the information raised during the summit to key stakeholders including athletes, parents, coaches and healthcare providers. We identified future areas for research and collaboration to enhance the health and safety of soccer (football) players.

#4 The use of adaptive neuro-stimulation for rebalancing posture and muscular tone in a soccer team
Reference: J Sports Med Phys Fitness. 2019 Feb 12. doi: 10.23736/S0022-4707.19.09311-3. [Epub ahead of print]
Authors: Barassi G, Bellomo RG, Porreca A, Giannuzzo G, Giannandrea N, Pezzi L, Crudeli M, Visciano C, Saggini R
Summary: Posture and somatic structure could positively influence athletic gestures for their biomechanical implications. Working on neuromuscular activity, offers the possibility of intervention on postural control. The aim is demonstrating the possibility of interacting with the human body system through the spinal reflex pathway, starting from the stimulation of cutaneous receptors. In this study, developed inside the Chair in Physical and Rehabilitative Medicine, at G. d'Annunzio University, twenty soccer players were recruited. Males between 25.5 ± 10.6 years old participated in this study. Patients were divided using a single-blind criterion into two groups, each containing ten subjects. The experimental group was treated with 2 pre-set programs 4 times a week with an Adaptive Neuro-Stimulation (ANS) able to interact with cutaneous receptors through an ENF Physio® device with a range of electrical frequency of about 15-350 Hz; the placebo-controlled group received the treatment with the device switched off. Patients performed a myometric evaluation with the MyotonPRO® system and a postural one with the Rarog system at T0 before the treatment and at T1 after the four-week treatment. After our intervention, we identified an improvement in muscular tone, in particular in the hamstring muscles (17.69%, R p<0.01 / L p<0.05 ) and a rebalancing of the principal bone points in the postural system (shoulder 71%, p<0.05, hips 65.6%, p=0.056, sagittal "AP" and frontal "LL" centre of gravity, respectively 40%, p<0.05 and 52.7%, p=0.01 ). In conclusion, we could hypothesise the usefulness of an Adaptive Neuro-Stimulation to act on these parameters. Clinical rehabilitation impact - Adaptive Neuro-Stimulation could be used not only for treatment of injuries but also in the field of prevention.

#5 Plantar pressures in male adolescent soccer players and its associations with bone geometry and strength
Reference: J Sports Med Phys Fitness. 2019 Feb 12. doi: 10.23736/S0022-4707.19.09267-3. [Epub ahead of print]
Authors: Lozano-Berges G, Matute-Llorente Á, Gómez-Bruton A, Alfaro-Santafé V, González-Agüero A, Vicente-Rodríguez G, Casajús JA
Summary: Mechanical loads exerted by soccer-specific actions increase bone remodeling activity. Nevertheless, little is known about the relationship between plantar pressure and bone structure. Therefore, the aim of this study was to compare bone geometry and strength between soccer players who exhibited different maximum values of the average pressures (MP) when performing a combination of soccer-specific tasks. Forty male adolescent soccer players (mean age 13.20.5 y) and 13 controls (mean age 13.10.9 y) participated in this study. Biofoot system was used to measure MP at the non-dominant foot during a circuit of soccer-specific tasks. Cluster analysis was performed to classify players into groups of similar MP profiles resulting two different groups as follows: 15 players with high MP (SOC-HP; mean MP: 392.768.2 kPa) and 25 with low MP (SOC-LP; mean MP: 261.049.6 kPa). Total and cortical volumetric bone mineral content (Tt.BMC/Ct.BMC), cross-sectional area (Tt.Ar/Ct.Ar), cortical thickness (Ct.Th), fracture load in X-axis, and polar strength index (SSIp) were measured at 38% of the non-dominant tibia by peripheral quantitative computed tomography. Bone geometry and strength comparisons between SOC-HP and SOC-LP were performed using analyses of covariance controlling by weight and tibia length. Greater Tt.BMC, Ct.BMC and Tt.Ar. were found in SOC-HP compared to CG (Tt.BMC: 3.22vs2.95 g, Ct.BMC: 2.95vs2.68 g, Ct.Ar: 280vs253 mm2; p<.05). Nevertheless, no significant bone geometry and strength differences were found between soccer groups and between SOC-LP and CG (p>.05). Developing high MP when training and playing soccer might be favourable to bone development.

#6 Sex-Related Hip Strength Measures Among Professional Soccer Players
Reference: J Strength Cond Res. 2019 Feb 7. doi: 10.1519/JSC.0000000000003003. [Epub ahead of print]
Authors: Hedt CA, Pearson JM, Lambert BS, McCulloch PC, Harris JD
Summary: Lower-extremity musculoskeletal injuries in soccer are common among sexes. However, it remains unknown whether differences between sexes exist with regard to absolute or relative hip strength and how these differences may relate to injury. In the current study, we performed a retrospective cross-sectional analysis of pre-season data from male (♂n = 21) and female (♀n = 19) professional United States soccer organizations. Two years of pre-season data were collected for peak strength of lower extremity and hip musculature (no duplicates used). A 2 × 2 multivariate analysis of variance was used to detect differences in hip strength between sexes and dominant compared with nondominant legs. For all significant multivariate effects indicated by Wilks lambda and follow-up univariate analysis, a Tukey's post hoc test was used for pairwise univariate comparisons. A 2-tailed independent-samples T-test was used for comparison of height, body mass, body mass index (BMI), mean leg length, and strength ratios between dominant and nondominant limbs between sexes. Type I error was set at α = 0.05 for all analyses. Height (♂183.1 ± 6.8 cm, ♀170.0 ± 5.5 cm), body mass (♂79.0 ± 8.7 kg, ♀65.1 ± 5.6 kg), BMI (♂23.5 ± 1.3 kg·m, ♀22.5 ± 1.4 kg·m), and mean leg length (♂95.5 ± 4.34 cm, ♀ 88.3 ± 3.24 cm) differed between groups (p < 0.05). Sex differences (p < 0.05) were also found for hip abduction (dominant ♂19.5 ± 3.6 kg, ♀17.3 ± 2.2 kg; nondominant ♂18.5 ± 3.7 kg, ♀16.0 ± 2.3 kg), adduction (dominant ♂19.8 ± 3.0 kg, ♀16.7 ± 2.3 kg; nondominant ♂20.1 ± 2.9 kg, ♀17.6 ± 2.9 kg), external rotation (dominant ♂21.7 ± 3.4 kg, ♀17.7 ± 2.4 kg; nondominant ♂21.6 ± 3.9 kg, ♀16.8 ± 2.1 kg), and dominant hamstring strength (♂27.9 ± 6.5 kg, ♀23.0 ± 4.9 kg). The ratio of hip internal to external rotation strength differed in the nondominant leg (♂1.1 ± 0.2, ♀0.9 ± 0.2, p < 0.05). No significant differences were found between males and females when measures were normalized to body mass. These findings provide baseline pre-season normative data for professional soccer athletes and indicate that strength differences can be expected among different sexes, but are attenuated with attention to body mass. Further research should indicate how pre-season strength measures relate to injury.

#7 Prevalence of Hamstring Strain Injury Risk Factors in Professional and Under-20 Male Football (Soccer) Players
Reference: J Sport Rehabil. 2019 Feb 12:1-23. doi: 10.1123/jsr.2018-0084. [Epub ahead of print]
Authors: Ribeiro-Alvares JB, Dornelles MP, Fritsch CG, de Lima-E-Silva FX, Medeiros TM, Severo-Silveira L, Marques VB, Baroni BM
Summary: Hamstring strain injury (HSI) is the most prevalent injury in football (soccer), and a few intrinsic factors have been associated with higher injury rates. The purpose was to describe the prevalence of the main intrinsic risk factors for HSI in professional and under-20 football players. One-hundred and one football players (52 professionals; 49 under-20) participated in this study. Anamnesis, hamstrings ultrasonography, passive straight-leg raise test, functional movement screen, and isokinetic dynamometry were performed. Eleven HSI risk factors for each leg were assessed, besides the player's age as a systemic risk factor. Reports were delivered to the coaching staff. Professionals had greater prevalence of HSI history compared to under-20 players (40% vs. 18%). No between-group differences were found for the other screening tests. Altogether, thirty percent of players had already sustained at least one HSI; 58% had history of injuries in adjacent regions; 49% had short biceps femoris fascicles; 66% and 21% had poor passive and active flexibility, respectively; 42% and 29% had deficits in functional movements and core stability, respectively; 7% and 26% presented bilateral imbalance for hamstring concentric and eccentric strength, respectively; 87% and 94% obtained low values for hamstring-to-quadriceps conventional and functional ratios, respectively. Two-thirds of players had 3 to 5 risk factors per leg. None of the players was fully free of HSI risk factors. Most football players present multiple risk factors for sustaining an HSI. Hamstring weakness is the most prevalent risk factor, but the teams should also be aware of deficits in flexibility, core stability, functional movements, and hamstring fascicle length.

#8 Hydrothermally Modified Corn Starch Ingestion Attenuates Soccer Skill Performance Decrements in the Second Half of a Simulated Soccer Match
Reference: Int J Sport Nutr Exerc Metab. 2019 Feb 12:1-26. doi: 10.1123/ijsnem.2018-0217. [Epub ahead of print]
Authors: Quinones MD, Lemon PWR
Summary: Hydrothermally modified non-GMO corn starch (HMS) ingestion may enhance endurance exercise performance via sparing carbohydrate oxidation. To determine whether similar effects occur with intermittent, high intensity exercise we investigated the effects of HMS ingestion prior to and at half time on soccer skill performance and repeated sprint ability during the later stages of a simulated soccer match. Eleven, male, university varsity, soccer players (177.7±6.8 cm, 77.3±7.9 kg, 22±3 y, 12.8±4.9 %BF, V̇O2max = 57.1±3.9 ml∙kg BM-1∙min-1) completed the match with HMS (8% CHO containing a total of 0.7 g∙kg BM-1∙h-1; 2.8 kcal∙kg BM-1∙h-1) or isoenergetic dextrose (DEX). Blood glucose was lower (p<0.001) with HMS at 15 (5.3 vs 7.7 mmol∙L-1) and 30 min (5.6 vs 8.3 mmol∙L-1) following ingestion, there were no treatment differences in blood lactate, and the respiratory exchange ratio was lower with HMS at 15 (0.84 vs 0.86, p = 0.003), 30 (0.83 vs 0.85, p = 0.004) and 45 min (0.83 vs 0.85, p = 0.007) of the first half. Repeated sprint performance was similar for both treatments (p>0.05) but soccer dribbling time was slower with DEX vs baseline (15.63 s vs 14.43 s, p < 0.05) but not so with HMS (15.04 vs 14.43 s, p > 0.05). Further, during the passing test, penalty time was reduced (4.27 s vs 7.73 s, p = 0.004) with HMS. During situations where glycogen availability is expected to become limiting, HMS ingestion pre-match and at half time could attenuate the decline in skill performance often seen late in contests.

#9 Are Soccer Players Older Now Than Before? Aging Trends and Market Value in the Last Three Decades of the UEFA Champions League
Reference: Front Psychol. 2019 Jan 28;10:76. doi: 10.3389/fpsyg.2019.00076. eCollection 2019.
Authors: Kalén A, Rey E, de Rellán-Guerra AS, Lago-Peñas C
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Summary: The aims of the current study were to analyze the evolution of players' age in the UEFA Champions League since the start of its modern-day format in 1992-1993 up until 2017-2018 and to determine how the players' age relates to their market value. The sample consisted of all players participating in the UEFA Champions League from the 1992-1993 to 2017-2018 seasons (n = 16062). The following variables were used in this study: players' age, number of seasons in the club, number of Champions Leagues won, team performance, and market value of the player in the season. Data were examined using a one-way ANOVA and a linear regression. The main finding of the current study is that an aging trend has occurred in the last three decades in the Champions League. A significant increase in average players' age (>1.6 years) was observed, rising from an age of 24.9 to 26.5 years. Goalkeepers and Center Backs tend to peak later than attackers, and their peak performance can last until an age of about 31 years. Finally, an inverted-U curve defines the association between market value and age, with peak value appearing in the 26-30 age range. These results provide useful information regarding at which age soccer players are likely to perform at the highest level, as well as the age they are likely to have the highest market value.

#10 Young Soccer Players With Higher Tactical Knowledge Display Lower Cognitive Effort
Reference: Percept Mot Skills. 2019 Feb 11:31512519826437. doi: 10.1177/0031512519826437. [Epub ahead of print]
Authors: Cardoso FDSL, González-Víllora S, Guilherme J, Teoldo I
Summary: The present study aimed to investigate whether the form and amount of declarative tactical knowledge (DTK) and procedural tactical knowledge (PTK) influence cognitive effort during soccer performance among young players. We assessed 36 male players from a Brazilian first-division soccer club; participants averaged 14.89 ( SD = 1.42) years of age. We evaluated DTK from video simulation tests and PTK through the System of Tactical Assessment in Soccer. We assessed cognitive effort by measures of pupil diameter using Mobile Eye Tracking-XG while players viewed soccer video scenes and made game-related play decisions. After the assessment of tactical knowledge, we categorized the sample according to players' tactical knowledge into participants with higher and lower PTK and higher and lower DTK. Subsequently, we examined the both PTK and DTK groups on cognitive effort. Our results suggest that tactical knowledge influences cognitive effort in that players with higher PTK and DTK displayed less cognitive effort during soccer performance tasks. In conclusion, we observed that PTK and DTK influenced the cognitive effort younger soccer players expended while viewing soccer scenes and making soccer performance decisions.

#11 Differences in Acceleration and High-Intensity Activities Between Small-Sided Games and Peak Periods of Official Matches in Elite Soccer Players
Reference: J Strength Cond Res. 2019 Feb 6. doi: 10.1519/JSC.0000000000003081. [Epub ahead of print]
Authors: Dalen T, Sandmæl S, Stevens TGA, Hjelde GH, Kjøsnes TN, Wisløff U
Summary: The purpose of this study was to compare whether the physical performance of players during 4 vs. 4 + goalkeeper (4 vs. 4) and 6 vs. 6 + goalkeeper (6 vs. 6) small-sided games (SSGs) is equivalent to those experienced during the most intense 5-minute period of soccer match play. Twenty-six male soccer players from an elite Norwegian league team took part. Players were monitored during 18 matches, 56 SSGs: twenty-eight 4 vs. 4 and twenty-eight 6 vs. 6 games. The ZXY Sport Tracking System was used to measure for each player the total distance covered, high-intensity running distance, sprint distance, number of accelerations, and player load (all expressed per minute). To compare the physical performance variables on players during the SSGs formats and match play, a 1-way analysis of variance with repeated measures was used. Players performed the same number of accelerations and player load in 4 vs. 4 (1.7 and 248, respectively) as in peak match (1.6 and 227, respectively), whereas in 6 vs. 6, there were 63% fewer accelerations and 15% lower player load (1.2 and 198, respectively), than in peak match. High-intensity running and sprint distance were significantly lower than mean match values in both 4 vs. 4 (4.1 and 0.2 m vs. 8.2 and 1.7 m) and 6 vs. 6 games (2.7 and 0.21 m vs. 8.2 and 1.7 m) (p < 0.05). In conclusion, only 4 vs. 4 SSGs are highly valuable, and in that, they elicit player load and accelerations to a level that is (at least) equivalent with peak periods of official match play.

#12 Effects of Plyometric Training on Physical Performance of Young Male Soccer Players: Potential Effects of Different Drop Jump Heights
Reference: Pediatr Exerc Sci. 2019 Feb 8:1-8. doi: 10.1123/pes.2018-0207. [Epub ahead of print]
Authors: Ramirez-Campillo R, Alvarez C, García-Pinillos F, Gentil P, Moran J, Pereira LA, Loturco I
Summary: The purpose was to compare the effects of plyometric drop jump (DJ) training against those induced by regular soccer training and assess the transference effect coefficient (TEC) of DJs ("trained exercises") performed from 20- (DJ20) and 40-cm (DJ40) height boxes with respect to different physical qualities (jumping, linear and change of direction speed, kicking, endurance, and maximal strength) in youth male soccer players. Participants were randomly divided into a control group (n = 20; age: 13.5 [1.9] y) and a DJ training group (n = 19; age: 13.2 [1.8] y), and trained for 7 weeks. A 2-way analysis of variance for repeated measures with the within-subject factor time (preintervention and postintervention) and between-subject factor group (intervention vs control) was performed. To calculate the TECs between the trained exercises (DJ20 and DJ40) and the physical tests, the ratio between the "result gains" (effect size [ES]) in the analyzed physical qualities and the result gains in the trained exercises were calculated. The TECs were only calculated for variables presenting an ES ≥ 0.2. Significant improvements (ES = 0.21-0.46; P < .05) were observed in the DJ training group, except in linear sprint performance. The control group improved only the maximal strength (ES = 0.28; P < .05). Significant differences were observed in all variables (ES = 0.20-0.55; P < .05) in favor of the DJ training group, except for maximal strength (group × time interaction). A plyometric training scheme based on DJs was able to significantly improve the physical performance of youth male soccer players. Overall, greater TECs were observed for DJ40 (0.58-1.28) than DJ20 (0.55-1.21).

#13 Vitamin D Supplementation and Physical Activity of Young Soccer Players during High-Intensity Training
Reference: Nutrients. 2019 Feb 6;11(2). pii: E349. doi: 10.3390/nu11020349.
Authors: Skalska M, Nikolaidis PT, Knechtle B, Rosemann TJ, Radzimiński Ł, Jastrzębska J, Kaczmarczyk M, Myśliwiec A, Dragos P, López-Sánchez GF, Jastrzębski Z
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Summary: The aim of this study was to confirm that vitamin D supplementation of young soccer players during eight-week high-intensity training would have a significant effect on their motion activity. The subjects were divided into two groups: the experimental one, which was supplemented with vitamin D (SG, n = 20), and the placebo group (PG, n = 16), which was not supplemented with vitamin D. All the players were subjected to the same soccer training, described as High-Intensity Interval Training (HIIT). The data of the vitamin D status, time motion parameters and heart rate were collected just before and after the intervention. A significant increase in 25(OH)D concentration (119%) was observed in the supplemented group, while the non-supplemented group showed a decrease of 8.4%. Based on the obtained results, it was found that physical activity indicators in the players were significantly improved during small-sided games at the last stage of the experiment. However, taking into account the effect of supplementation with vitamin D, there were no statistically significant differences between the placebo and the supplemented groups; thus, the effect size of the conducted experiment was trivial.





Latest research in football - week 6 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Design, Validation, and Reliability of an Observation Instrument for Technical and Tactical Actions of the Offense Phase in Soccer
Reference: Front Psychol. 2019 Jan 24;10:22. doi: 10.3389/fpsyg.2019.00022. eCollection 2019.
Authors: Ortega-Toro E, García-Angulo A, Giménez-Egido JM, García-Angulo FJ, Palao JM
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Summary: The use of observational methodology in the sports context provides coaches and other sports professionals with flexible tools that adapt to their needs. In collective sports, the use of these instruments is common for the technical and tactical analysis of the game. Based on the importance of data quality in these instruments, the purpose was to design, validate, and test the reliability of a mixed observational instrument of field formats and category systems to analyze technical and tactical actions in the offense phase in soccer. The instrument collects information regarding the actions with the ball, moment of the play (start, development, and end), and contextual situation for the offensive team and for the goalkeeper. The instrument design, validation, and reliability calculation were done in four stages: (a) review of the literature, (b) design the first draft of the instrument, (c) experts' qualitative and quantitative review of the instrument, and (d) observer training test (reliability calculation). The content validity was established by 12 experts (Ph.D. in sports science or soccer coach with at least of 10 years of coaching experience). The Delphi methodology was used. Experts did a quantitative (scale 0-10) and qualitative evaluation. Experts were asked about: (a) comprehension of the criteria, categorical cores, degree of openness, and their definitions, (b) pertinence of categorical cores and degree of openness, and (c) whether to include other categorical cores or degree of openness in the observation instrument. The lowest Aiken's V index was 0.91 for the categorical core "numerical situation with opponent goalkeeper." The inter- and intra-observer reliability presented good levels of agreement. The lowest Kappa index was 0.96 for the inter-reliability in the categorical core "defensive pressing lines" and was 0.98 for the intra-reliability in the categorical core "ball height (start of ball possession)," "distance of the defensive player," "ball height (end of ball possession)," "numerical situation," and "defensive pressing lines." The coefficients of the generalizability analysis showed a high level of accuracy, validity and reliability of the instrument. The results show that the instrument allows to obtain objective, valid and reliable information about the offensive phase in soccer.

#2 Change-of-direction, speed and jump performance in soccer players: a comparison across different age-categories
Reference: J Sports Sci. 2019 Feb 6:1-7. doi: 10.1080/02640414.2019.1574276. [Epub ahead of print]
Authors: Loturco I, Jeffreys I, Abad CCC, Kobal R, Zanetti V, Pereira LA, Nimphius S
Summary: This study examined the age-specific development of vertical jump height, straight and change-of-direction (COD) speed, and COD deficit in one-hundred and eighty-two elite soccer players from different age-categories (U15, U17, U20, and Senior). All participants were players of two distinct clubs and were undertaking different training routines, as planned by their technical staff members. For this purpose, the soccer players performed: (1) squat and countermovement jumps; (2) a maximal 20-m linear sprint speed test, and (3) the Zigzag COD test. The magnitude-based inference approach and standardized differences were used to compare the age-groups. Sprint speed at longer distances (20-m) increased progressively across the age-ranges. In contrast, speed and acceleration performances at shorter distances (5-m) were better in U15 than in the other age-categories. The COD speed did not change throughout the younger categories but presented a meaningful decrease in the Senior category. Surprisingly, despite the progressive increase in volume and intensity of neuromuscular training from younger to older categories, the COD deficit presented a gradual increase across the age-groups. It is possible that simple modulation of the strength-power training program during the maturation process is not sufficient to produce faster adult players with enhanced ability to change direction. Therefore, coaches are strongly encouraged to implement specific COD training practices to tolerate braking at increasing running speeds and appropriate volume and intensity of soccer specific training throughout the players' specialization process.

#3 Prevalence of labrum and articular cartilage injuries of the hip on 3T magnetic resonance imaging of asymptomatic elite soccer players
Reference: Rev Esp Cir Ortop Traumatol. 2019 Feb 2. pii: S1888-4415(18)30173-5. doi: 10.1016/j.recot.2018.10.008. [Epub ahead of print] [Article in English, Spanish]
Authors: Márquez WH, Gómez-Hoyos J, Gallo JA, Espinosa B, Rivas N, Llano JF, Osorio J, Martin HD
Summary: The purpose was to establish the prevalence of lesions of the labrum and articular cartilage of the hip in asymptomatic elite soccer players by performing 3T magnetic resonance imaging. Eighty-four asymptomatic hips of 42 professional soccer players were evaluated. Male subjects older than 18 years were included. Cam and pincer deformity were defined as an alpha angle greater than 55 degrees and a lateral centre edge angle greater than 39 degrees, respectively. Labral injuries were classified with the Czerny classification and cartilage damage was classified with the Outerbridge classification. Specific statistical tests were used to establish the relationship between anatomical variances of the hip and the presence of chondral and labral injuries. FAI morphology prevalence was 25%. Abnormalities such as cam (22.5%) and labral injuries (33.8%) were found. Those cases with reported labral injury were predominantly intrasubstance damage (18.8%). Anatomical features of FAI were found to be related to lesions of the femoral cartilage (P<.001), chondrolabral damage (P=.042), or both injuries (P<.001). Asymptomatic labral or cartilaginous injuries of the hip were reported in 25% of the included professional soccer players. These injuries were associated with anatomical features of FAI.

#4 Effects of playing position, pitch location, opposition ability and team ability on the technical performance of elite soccer players in different score line states
Reference: PLoS One. 2019 Feb 5;14(2):e0211707. doi: 10.1371/journal.pone.0211707. eCollection 2019.
Authors: Redwood-Brown AJ, O'Donoghue PG, Nevill AM, Saward C, Sunderland C
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Summary: The purpose of this study was to investigate the effects of playing position, pitch location, team ability and opposition ability on technical performance variables (pass, cross, corner, free kick accuracy) of English Premier League Soccer players in difference score line states. A validated automatic tracking system (Venatrack) was used to code player actions in real time for passing accuracy, cross accuracy, corner accuracy and free kick accuracy. In total 376 of the 380 games played during the 2011-12 English premier League season were recorded, resulting in activity profiles of 570 players and over 35'000 rows of data. These data were analysed using multi-level modelling. Multi-level regression revealed a "u" shaped association between passing accuracy and goal difference (GD) with greater accuracy occurring at extremes of GD e.g., when the score was either positive or negative. The same pattern was seen for corner accuracy away from home e.g., corner accuracy was lowest when the score was close with the lowest accuracy at extremes of GD. Although free kicks were not associated with GD, team ability, playing position and pitch location were found to predict accuracy. No temporal variables were found to predict cross accuracy. A number of score line effects were present across the temporal factors which should be considered by coaches and managers when preparing and selecting teams in order to maximise performance. The current study highlighted the need for more sensitive score line definitions in which to consider score line effects.

#5 Age-related differences in flexibility in soccer players 8-19 years old
Reference: PeerJ. 2019 Jan 29;7:e6236. doi: 10.7717/peerj.6236. eCollection 2019.
Authors: Cejudo A, Robles-Palazón FJ, Ayala F, De Ste Croix M, Ortega-Toro E, Santonja-Medina F, Sainz de Baranda P
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Summary: Muscle flexibility is a main component of health-related fitness and one of the basic components of fitness for the performance in some sports. Sport and health professionals require the flexibility profile of soccer to define quantitative aims in the training of flexibility. The aim of this study was to identify age-related differences in lower extremity flexibility in youth soccer players. Seventy-two young male soccer players (age: 13.0 ± 3.1 y; body mass: 50.5 ± 15.3 kg; stature 158.2 ± 16.8 cm; BMI: 19.6 ± 2.6 kg/m2) completed this study. Measures of eleven passive hip (hip extension (HE), hip adduction with hip flexed 90°(HAD-HF90°), hip flexion with knee flexed (HF-KF) and extended (HF-KE), hip abduction with hip neutral (HAB) and hip flexed 90°(HAB-HF90°), hip external (HER) and internal (HIR) rotation), knee (knee flexion (KF)) and ankle dorsiflexion (ankle dorsiflexion with knee flexed (ADF-KF) and extended (ADF-KE)) ranges of motion (ROM) were taken. Descriptive statistics were calculated for hip, knee and ankle ROM measured separately by leg (dominant and non-dominant) and age-group (U10, U12, U14, U16 and U19). The data was analysed using a one-way analysis of variance (ANOVA) to examine the interaction of 11 ROM in the different players' age-group. Generally, U10 and/or U12 soccer players obtain the highest mean value in almost all ROM evaluated (U10: HAD-HF [39.6° ± 4.3°], ADF-KE [32.3° ± 4.1°], HER [63.5° ± 5.6°] and HAB-HF90°[64.1° ± 7.5°]; U12: HE [17.7° ± 6.2°], HAB [35.6° ± 3.0], HIR [60.8° ± 4.7°] and KF [133.8° ± 7.1°]). Nonetheless, significant differences between the players' age-groups are just found in HAD-HF90°(p = .042; ES = .136), HAB (p = .001; ES = .252), HIR (p = .001; ES = .251), HER (p < .001; ES = .321) and HAB-HF90°(p < .001; ES = .376) ROM, showing a progressive and irregular decrease in these ROM until the U19 team. The findings of this study reinforce the necessity of prescribing exercises aimed at improving HAD-HF90°  ROM in U16, HAB ROM in U14, HIR ROM in U16 and U19, HER ROM in U12 and U19, and HAB-HF90°  ROM in U16 and U19 players within everyday soccer training routines.

#6 Effects of the long-term consumption of hydrogen-rich water on the antioxidant activity and the gut flora in female juvenile soccer players from Suzhou, China
Reference: Med Gas Res. 2019 Jan 9;8(4):135-143. doi: 10.4103/2045-9912.248263. eCollection 2018 Oct-Dec.
Authors: Sha JB, Zhang SS, Lu YM, Gong WJ, Jiang XP, Wang JJ, Qiao TL, Zhang HH, Zhao MQ, Wang DP, Xia H, Li ZW, Chen JL, Zhang L, Zhang CG
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Summary: Expending a considerable amount of physical energy inevitably leads to fatigue during both training and competition in football. An increasing number of experimental findings have confirmed the relationship between the generation and clearance of free radicals, fatigue, and exercise injury. Recently, hydrogen was identified as a new selective antioxidant with potential beneficial applications in sports. The present study evaluated the effect of 2-month consumption of hydrogen-rich water on the gut flora in juvenile female soccer players from Suzhou. As demonstrated by enzyme linked immunosorbent assay and 16S rDNA sequence analysis of stool samples, the consumption of hydrogen-rich water for two months significantly reduced serum malondialdehyde, interleukin-1, interleukin-6, tumour necrosis factor-α levels; then significantly increased serum superoxide dismutase, total antioxidant capacity levels and haemoglobin levels of whole blood. Furthermore, the consumption of hydrogen-rich water improved the diversity and abundance of the gut flora in athletes. All examined indices, including the shannon, sobs, ace, and chao indices, were higher in the control group than those proposed to result from hydrogen-rich water consumption prior to the trial, but these indices were all reversed and were higher than those in the controls after the 2-month intervention. Nevertheless, there were some differences in the gut flora components of these two groups before the trial, whereas there were no significant changes in the gut flora composition during the trial period. Thus, the consumption of hydrogen-rich water for two months might play a role modulating in the gut flora of athletes based on its selective antioxidant and anti-inflammatory activities.

#7 Effects of a multifactorial injuries prevention program in young Spanish football players
Reference: J Sports Med Phys Fitness. 2019 Feb 5. doi: 10.23736/S0022-4707.19.09219-3. [Epub ahead of print]
Authors: Chena M, Rodríguez ML, Bores AJ, Ramos-Campo DJ
Summary: The high injury rate in football has highlighted the need to research strategies that allow the modification of the dynamic risk factors. Most of the preventive proposals have focused on standardized protocols. However, the aim of this study was to evaluate the effect of a multifactorial injuries prevention program (MC-7) in Spanish football players. A total of 219 Spanish football male players aged 16-23 were studied. The study was conducted over two consecutive seasons (2012-2013, 2013-2014). The first season was the control season (SC) and the second one was the experimental season (ES). Injuries were recorded prospectively during the two seasons in accordance with the criteria established by the consensus statement. During CS the injuries were just observed, while during ES, the players participated in the MC-7: training methodology, specific warm-up protocol (FIFA 11+), basic injury recovery strategies, continuous training of coaches, conferences for parents/family and education sessions for players. The frequency of injuries was significantly reduced by 63.8% in the ES. Muscle-tendon and joint injuries were reduced by 65% and 56.7% respectively, with a significant decrease in the lower-limbs injuries. The incidence of injuries was reduced by 71.4%, with significant differences in the typology, location and severity of injuries. The rate of injury in football is reduced when multifactorial strategies are applied. Reducing the frequency and severity of injuries allowed players to greatly increase their available for sports practice.

#8 ACTN3 single nucleotide polymorphism is associated with non-contact musculoskeletal soft-tissue injury incidence in elite professional football players
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Feb 5. doi: 10.1007/s00167-019-05381-x. [Epub ahead of print]
Authors: Clos E, Pruna R, Lundblad M, Artells R, Esquirol Caussa J
Summary: Muscle injuries are common in professional football, even though prevention protocols are being implemented. Genetics constitutes a novel field for studying intrinsic injury risks and performance. Since previous studies involving single nucleotide polymorphisms (SNPs) have shown that SNPs influence muscle injury rate, injury severity and recovery time, the aim was to study the association the SNP of ACTN3 has with those parameters in professional football players. The medical staff team recorded non-contact musculoskeletal soft-tissue injuries in 43 professional football players in 7 different seasons (2007-2012 and 2015-2016). Injury rate, injury severity and injury recovery times were established. Players were genotyped by extracting DNA from a blood sample and using a polymerase chain reaction. Injury rate was associated with the SNP of ACTN3 (p = 0.003). The 577R allele was more frequent in subjects than in a normal population by showing presence in 93% of the subjects and suggesting that it could influence football performance. No statistically significant differences in injury severity and recovery time were associated with the SNP of ACTN3. Genetics is gaining in importance when assessing injury risk and performance in professional football. ACTN3 can be regarded as a biomarker of injury susceptibility in this discipline. Identifying those players with the highest injury susceptibility through genetics could lead football teams to individualise workloads and prevention protocols.

#9 Relationships between Anxiety, Emotional Intelligence, and Motivational Climate among Adolescent Football Players
Reference: Sports (Basel). 2019 Feb 1;7(2). pii: E34. doi: 10.3390/sports7020034.
Authors: Castro-Sánchez M, Zurita-Ortega F, Ubago-Jiménez JL, González-Valero G, Chacón-Cuberos R
Summary: Emotional and motivational factors are fundamental in the context of sport, as they directly relate to sports performance and anxiety. The present study aimed to analyze the relationships between motivational climate (MC), emotional intelligence (EI), and anxiety within a sample of footballers playing at a low level. The sample was composed of 282 registered football players aged between 16 and 18 years old (16.96 ± 0.77), playing in the lower tier in the province of Jaen (Spain). Data were self-reported, with participants responding to the Perceived Motivational Climate in Sport Questionnaire (PMCSQ-2), the Schutte Self-Report Inventory (SSRI), and the State Trait Anxiety Inventory (STAI). The results showed that footballers who reported higher levels of state anxiety and trait anxiety also demonstrated lower EI and more negatively perceived and regulated their emotions. Moreover, an ego-oriented climate was associated with higher levels of anxiety, while a task-oriented climate was related to lower levels of anxiety and higher levels of EI. No relationship was identified between the emotional aspects of young footballers and holding a motivational orientation toward an ego climate. Football players who more greatly perceived a task-oriented climate had higher EI and usually reported lower levels of anxiety related to sport performance. It is therefore important to promote intrinsic motivations and develop the capacity of footballers to regulate their own emotions.

#10 A Brazilian Football Player Still on the Pitch After 10 Years of Parkinson's Disease with Severe Freezing of Gait
Reference: Mov Disord Clin Pract. 2014 Dec 6;2(1):43-44. doi: 10.1002/mdc3.12110. eCollection 2015 Mar.
Authors: Vale TC, Pedroso JL, Barsottini OG, Lees AJ
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Latest research in football - week 5 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Immediate effects and one-week follow-up after neuromuscular electric stimulation alone or combined with stretching on hamstrings extensibility in healthy football players with hamstring shortening
Reference: J Bodyw Mov Ther. 2019 Jan;23(1):16-22. doi: 10.1016/j.jbmt.2018.01.017. Epub 2018 Feb 2.
Authors: Espejo-Antúnez L, Carracedo-Rodríguez M, Ribeiro F, Venâncio J, De la Cruz-Torres B, Albornoz-Cabello M
Summary: The purpose was to assess the immediate and mid-term (after 7 days) effects of electric current combined with simultaneous muscle stretching (EME technique) per comparison to the isolated use of the same current (without applying simultaneous muscle stretching), over the hamstring extensibility in football players with hamstring shortening, and to estimate the clinical benefit of the interventions according to the muscular extensibility. Forty-eight participants were randomized to receive one session of EME technique (n = 26) or one session of the electrical current (EC) alone (n = 22). The measurement of the hamstrings extensibility through the active knee test was carried out before and immediately after each intervention and one week later. A significant interaction group x time was observed (F2,84 = 7.112, p = 0.001; partial eta squared = 0.145). The hamstrings extensibility changed significantly immediately after the EME technique (147.3° ± 16.4° to 153.5° ± 14.2°, p < 0.05), but not after the EC only (144.2 ± 10.2° to 141.7 ± 7.8°, p > 0.05). One week after the intervention no significant differences were found to the baseline values in both groups. The number needed to treat to prevent one new case of hamstring shortening was 3. The combination of electric current with simultaneous stretching is an effective technique to acutely increase the hamstring extensibility of football players with hamstring shortness.

#2 Sudden cardiac death in football players: Towards a new pre-participation algorithm
Reference: Exp Ther Med. 2019 Feb;17(2):1143-1148. doi: 10.3892/etm.2018.7041. Epub 2018 Nov 30.
Authors: Mavrogeni SI, Tsarouhas K, Spandidos DA, Kanaka-Gantenbein C, Bacopoulou F
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Summary: Athletic pre-participation screening is essential for minimizing the risk for sudden cardiac death (SCD) in athletes participating in either competitive or leisure sporting activities. The primary causes of SCD in young athletes (<35 years of age) include hypertrophic cardiomyopathy, congenital anomalies of the coronary artery and arrhythmogenic right ventricular cardiomyopathy. Other abnormalities, such as malignant arrhythmia due to blunt trauma to the chest (commotio cordis), myocarditis, valvular disease, aortic rupture (in Marfan syndrome) and ion channelopathies (catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, long or short QT syndrome), also contribute to a lesser degree to SCD. Currently, clinical assessment, electrocardiogram (ECG) and echocardiography are the cornerstones of the pre-participation athletic evaluation. However, their low sensitivity raises queries as regards the need for the application of more sophisticated modalities, such as cardiovascular magnetic resonance (CMR). CMR offers precise biventricular assessment and is greatly reproducible without the inherent limitations of echocardiography; i.e., low quality of images due to the lack of appropriate acoustic window or operator's experience. Furthermore, myocardium replacement fibrosis, indicative of patients' increased risk for future cardiac events, can be effectively detected by late gadolinium enhanced (LGE) images, acquired 15 min post-contrast injection. Finally, diffuse myocardial fibrosis not identified by LGE, can also be detected by pre-contrast (native) T1, post-contrast T1 mapping and extracellular volume images, which provide detailed information about the underlying pathophysiologic background. Therefore, CMR is recommended in all football players with a positive family or personal history of syncope or SCD, abnormal/doubtful ECG or echocardiogram.

#3 Asthma and youth soccer: an investigation into the level of asthma awareness and training among youth soccer coaches
Reference: Open Access J Sports Med. 2019 Jan 15;10:17-31. doi: 10.2147/OAJSM.S182178. eCollection 2019.
Authors: Sadasivan C, Cave A
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Summary: Asthma is the most common chronic disease among children. Exercise-induced bronchoconstriction which is common in asthmatic patients also occurs in individuals with no prior asthma diagnosis. Despite this and the fact that soccer is a high ventilation sport, there are no validated asthma management protocols in place for soccer coaches. This study aims to address 1) soccer coaches' current knowledge on asthma, 2) whether there is a need for asthma-related training, and 3) any barriers to administration of such training. A total of 2,300 volunteer youth soccer coaches from the Edmonton Minor Soccer Association (EMSA) were invited to participate in completing a 22-question online survey. The survey was open for 1 month from June 8, 2018, to July 8, 2018. There was a response rate of 22% (513 of 2,300). Respondents were on average, inexperienced coaches, coached younger age groups, and approximately one-third of respondents had personal experience with asthma (either themselves or their child had asthma). 93% of respondents had not received any asthma-related training at any coaching level, whether it be from EMSA or the Alberta Soccer Association. Coaches had strong knowledge on how to treat asthma attacks, but mixed levels of knowledge on asthma attack prevention. Experienced coaches were better at identifying the number of players with asthma on their team and the number of asthma-related incidents they had encountered as coaches. Coaches demonstrated a receptive attitude toward receiving asthma-related training, with 91% of respondents saying training would be beneficial and 69% of respondents saying training should be mandatory. The results of this study indicate that soccer coaches have limited knowledge regarding asthma management, acknowledge a need for asthma-related training, and are willing to participate in and could benefit from educational interventions as it pertains to their roles as coaches.

#4 Electrocardiographic and echocardiographic evaluation of a large cohort of peri-pubertal soccer players during pre-participation screening
Reference: Eur J Prev Cardiol. 2019 Jan 29:2047487319826312. doi: 10.1177/2047487319826312. [Epub ahead of print]
Authors: Calò L, Martino A, Tranchita E, Sperandii F, Guerra E, Quaranta F, Parisi A, Nigro A, Sciarra L, Ruvo E, Casasco M, Pigozzi F
Summary: The early diagnosis of cardiac abnormalities in young athletes may be helpful not only to identify subjects potentially at risk of sudden cardiac death but also to prevent stress-related cardiac dysfunction and cardiovascular events during the life of these subjects. The aim of our study was to investigate the prevalence of cardiac abnormalities in a population of young male soccer players undergoing pre-participation screening through electrocardiogram and trans-thoracic echocardiography. All consecutive male football players undergoing pre-participation screening comprehensive of medical history, physical examination, 12-lead electrocardiogram and trans-thoracic echocardiography at the FMSI Sport Medicine Institute in Rome between January 2008-March 2009 were enrolled in the study. Overall, 2261 consecutive young athletes aged 12.4 ± 2.6 years were evaluated. Training-unrelated electrocardiogram abnormalities were observed in 65 (2.9%) athletes. Abnormal trans-thoracic echocardiography was observed in 102 athletes (4.5%), including two cases of hypertrophic cardiomyopathy, eight of mild left ventricular hypertrophy, six of mild left ventricular dilation and 17 of bicuspid aortic valve. An abnormal electrocardiogram was associated with anomalous trans-thoracic echocardiography in 11/65 (16.9%) cases. All athletes requiring sport disqualification were identified by electrocardiogram. Notably, among 2216 athletes with a normal electrocardiogram, 91 had abnormal trans-thoracic echocardiography, including six cases of left ventricular dilation and six of ventricular hypertrophy. In a wide population of peri-pubertal male athletes, evaluation of the electrocardiogram identified all cardiac diseases requiring sport disqualification. Trans-thoracic echocardiography alone allowed the identification of cardiac abnormalities potentially leading to cardiomyopathies or major cardiovascular events over time.

#5 Ecological and Construct Validity of a Repeated Sprint Test in Male Youth Soccer Players
Reference: J Strength Cond Res. 2019 Jan 23. doi: 10.1519/JSC.0000000000003047. [Epub ahead of print]
Authors: Fernandes-Da-Silva J, Castagna C, Teixeira AS, Carminatti LJ, Francini L, Póvoas SCA, Antonacci Guglielmo LG
Summary: This study aimed to examine the relationship between a repeated sprint ability (RSA) test (5 bouts of 30-m sprints interspersed by 30 seconds of recovery) and match-related physical performance in male youth soccer players. Although 60 outfield players were evaluated, only data from players who participated in the full matches (n = 39) were retained (8 central defenders, 7 external defenders, 8 central midfielders, 8 external midfielders, and 8 forwards). To verify the ecological validity of this RSA protocol, the association between the best (RSAbest) and mean (RSAmean) sprint time in the 5 × 30-m and physical match performance during friendly youth soccer games was examined. Physical match demands were assessed using global positioning system technology (10 Hz) considering distance covered in selected arbitrary speed categories. The absolute speed thresholds were the same for all the players. Players were categorized into 2 groups based on the 5 × 30-m performance: RSAmean times below (i.e., faster) and above (i.e., slower) the median value. Players with faster RSAmean times covered significantly more distance sprinting during friendly matches (606 ± 204 m, +47.0%; t = 4.953; effect size = 1.88, 1.24; 2.52, p ≤ 0.001) compared to their slower counterparts (322 ± 145 m). A large negative correlation (r = -0.63, -0.77; -0.44, p ≤ 0.001) was found between RSAbest time (4.59 ± 0.27 seconds) and match sprint distance (457 ± 229 m). Likewise, RSAmean time (4.76 ± 0.25 seconds) was also largely associated (r = -0.60, -0.75; -0.39; p ≤ 0.001) with in-game sprinting performance. The results of this study provided evidence to support the construct and ecological validity of the 5 × 30-m protocol in male youth soccer players. Furthermore, differences in 5 × 30-m performance explained the amount of sprinting activity performed during the match.

#6 Accuracy of Anthropometric Equations to Estimate DXA-Derived Skeletal Muscle Mass in Professional Male Soccer Players
Reference: J Sports Med (Hindawi Publ Corp). 2019 Jan 1;2019:4387636. doi: 10.1155/2019/4387636. eCollection 2019.
Authors: González-Mendoza RG, Gaytán-González A, Jiménez-Alvarado JA, Villegas-Balcázar M, Jáuregui-Ulloa EE, Torres-Naranjo F, López-Taylor JR
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Summary: Several anthropometric equations that estimate skeletal muscle mass (SMM) have been published, but their applicability and accuracy among athletes are still uncertain. The purpose was to assess the accuracy of different anthropometric equations that estimate SMM in professional male soccer players, as compared to dual-energy X-ray absorptiometry (DXA) as the reference method. In this cross-sectional study, we evaluated 179 professional male soccer players aged between 18 and 37 years. Anthropometric measurements (height, body weight, skinfold thicknesses, and girths) and a DXA whole body scan were performed the same day for each participant, and SMM was estimated with nine anthropometric equations (Heymsfield, Martin, Doupe, Kerr, Drinkwater, Lee, De Rose, and two equations published by Kuriyan). To determine differences between SMM estimated with anthropometric equations and SMM evaluated with DXA, a Kruskal-Wallis test was performed using Dunn's test as post hoc. The significance level was set at p < 0.05. We calculated the mean difference and 95% limits of agreement for the analyzed equations (Equation - DXA). Only Heymsfield's and Lee's equations showed no significant differences with DXA. Heymsfield's equation had the smallest mean difference (-0.17 kg), but wider limits of agreement with DXA (-6.61 to 6.94 kg). Lee's equation had a small mean difference (1.10 kg) but narrower limits of agreement with DXA (-1.83 to 4.03 kg). In this study, the prediction equation published by Lee et al. showed the best agreement with DXA and is able to estimate SMM accurately in professional male soccer players.

#7 Management of concussion in soccer
Reference: Acta Neurochir (Wien). 2019 Jan 28. doi: 10.1007/s00701-019-03807-6. [Epub ahead of print]
Authors: Hubertus V, Marklund N, Vajkoczy P
Summary: When participating in contact sports, (mild) head trauma is a common incident-observed in both professional and amateur sports. When head trauma results in transient neurological impairment, a sports-related concussion has occurred. Acute concussion, repetitive concussions, as well as cumulative "sub-concussive" head impacts may increase the risk of developing cognitive and behavioral deficits for athletes, as well as accelerated cerebral degeneration. While this concept has been well established for classic contact sports like American Football, Rugby, or Boxing, there is still an awareness gap for the role of sports-related concussion in the context of the world's most popular sport-Soccer. Here, we review the relevance of sport-related concussion for Soccer as well as its diagnosis and management. Finally, we provide insight into future directions for research in this field. Soccer fulfills the criteria of a contact sport and is characterized by a high incidence of concussion. There is ample evidence that these events cause functional and structural cerebral disorders. Furthermore, heading, as a repeat sub-concussive impact, has been linked to structural brain changes and neurocognitive impairment. As a consequence, recommendations for the diagnosis and management of concussion in soccer have been formulated by consensus groups. In order to minimize the risk of repetitive concussion in soccer the rapid and reliable side-line diagnosis of concussion with adoption of a strict remove-from-play protocol is essential, followed by a supervised, graduated return-to-play protocol. Recent studies, however, demonstrate that adherence to these recommendations by players, coaches, clubs, and officials is insufficient, calling for stricter enforcement. In addition, future research to solidify the pathophysiological relevance of concussion for soccer athletes seems to be needed. Advanced neuroimaging and neurochemical biomarker analyses (e.g. S100β, tau and neurofilament light (NfL)) may assist in detecting concussion-related structural brain changes and selecting athletes at risk for irreversible damage. Sports-related concussion represents a genuine neurosurgical field of interest. Given the high socioeconomic relevance, neurosurgeons should get involved in prevention and management of concussion in soccer.

#8 Training Loads and RSA and Aerobic Performance Changes During the Preseason in Youth Soccer Squads
Reference: J Hum Kinet. 2018 Dec 31;65:235-248. doi: 10.2478/hukin-2018-0032. eCollection 2018 Dec.
Authors: Cetolin T, Teixeira AS, Netto AS, Haupenthal A, Nakamura FY, Guglielmo LGA, da Silva JF
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Summary: The aims of this study were to compare the internal training load (ITL) in soccer players of two competitive age groups (under-15 [U-15] and under-19 [U-19]) during an 8-week preseason training period and compare the associated changes in physical performance measures. Eighteen U-15 and twelve U-19 players were monitored over an 8-week period during the preseason phase. The ITL was monitored using the session rating of perceived exertion (RPE) method. Before and after the preseason period, physical performance was assessed by best (RSAbest) and mean (RSAmean) times in a repeated sprint ability (RSA) test and peak velocity derived from the Carminatti test (PVT-CAR). Total weekly ITL increased with age (U-15: 13770 ± 874 AU vs. U-19: 33584 ± 2506 AU; p < 0.001). In addition, U-19 players perceived training sessions as heavier than U-15 players (6.1 ± 0.3 vs. 5.3 ± 0.3 AU, respectively; p < 0.001). After the preseason period, very likely to almost certainly positive changes were observed for all performance measures in both age groups. However, the U-15 group had possibly superior gains in RSAbest (+1.40%, 90%CL -0.29 to 3.05, with ES = 0.35) and likely higher effects in RSAmean (+1.89%, 90%CL 0.04 to 3.70, with ES = 0.53) and PVT-CAR (+2.71%, 90%CL 0.35 to 5.01, with ES = 0.37) compared to the U-19 group. In conclusion, our findings demonstrate that the U-19 group accumulate higher total weekly ITLs than the U-15 group during the preseason phase due to longer and heavier training sessions. However, the U-15 group obtained superior gains in soccer-specific physical abilities while accumulating half the total ITLs during lighter training sessions.

#9 Relative Age Effect and Long-Term Success in the Spanish Soccer and Basketball National Teams
Reference: J Hum Kinet. 2018 Dec 31;65:197-204. doi: 10.2478/hukin-2018-0027. eCollection 2018 Dec.
Authors: López de Subijana C, Lorenzo J
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Summary: The aims of this study were: i) to analyze whether relative age effect occurs in the athletes of the junior national teams and professional athletes in Spain in general and in soccer and basketball, and ii) to compare the long-term success of the players selected for the junior national team between these sports. The samples for this study were Spanish professional soccer (n = 461) and basketball (n = 250) players in the 2013-2014 premier league and players from the junior Spanish soccer (i.e., n = 273; U-17: n = 107; U-19: n = 166) and basketball (i.e., n = 240; U-18: n = 120, U-16: n = 120) teams that classified to play in the European Championships (from 2004 to 2013). Junior players (42.3%) were more frequently born in the 1st quarter of the year than the professional players (30.7%) (χ2(3) = 30.07; p = .001; Vc = .157). This was found in both basketball (χ2(3) = 12.2.; p = .007; Vc = .158) and soccer (χ2(3) = 20.13; p < .001; Vc = .166). Long-term success is more frequent in soccer, where 59.9% of the juniors selected for the national team played later in the premier league, while in basketball that percentage was 39.6% (χ2(1) = 14.64; p < .001; Vc = .201). On the other hand, 79.4% and 39.8% of the professional soccer and basketball players had been previously selected for junior national teams (χ2(1) = 60.2; p < .001; Vc = .386), respectively. The talent selection process should be reviewed as players born in the second half of the year have fewer opportunities to stand out.

#10 Effects of the Pitch Surface on Displacement of Youth Players During Soccer Match-Play
Reference: J Hum Kinet. 2018 Dec 31;65:175-185. doi: 10.2478/hukin-2018-0046. eCollection 2018 Dec.
Authors: Brito Â, Roriz P, Silva P, Duarte R, Garganta J
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Summary: The aim of this study was to analyze the effect of different pitch surfaces (artificial turf, natural turf and dirt field) on positioning and displacement of young soccer players (age: 13.4 ± 0.5 yrs; body height: 161.82 ± 7.52 cm; body mass: 50.79 ± 7.22 kg and playing experience: 3.5 ± 1.4 yrs). Data were collected using GPS units which allowed to calculate spatial distribution variability, assessed by measuring entropy of individual distribution maps (ShannEn). Ellipsoidal areas (m2) representing players' displacement on the pitch, centred on the average players' positional coordinates, were also calculated, with axes corresponding to the standard deviations of the displacement in the longitudinal and lateral directions. Analysis of variance (ANOVA) was used to evaluate differences between pitch surfaces and across players' positions. There was significant effect in positioning (η2 = 0.146; p < 0.001) and displacement (η2 = 0.063; p < 0.05) by the players between pitch surfaces. A dirt field condition induced an increase in the players' movement variability, while players' displacement was more restricted when playing on artificial turf. Also, there were significant effects on positioning (η2 = 0.496; p < 0.001) and displacement (η2 = 0.339; p < 0.001) across players' positions. Central midfielders presented the greatest movement variability and displacement while fullbacks showed the lowest variability. Subsequently, the results may contribute to implement strategies that optimise players' performance in different surface conditions.

#11 Work-rate Analysis of Substitute Players in Professional Soccer: Analysis of Seasonal Variations
Reference: J Hum Kinet. 2018 Dec 31;65:165-174. doi: 10.2478/hukin-2018-0025. eCollection 2018 Dec.
Authors: Padrón-Cabo A, Rey E, Vidal B, García-Nuñez J
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Summary: The aims of this study were to evaluate physical performance of substitute players versus those replaced or completing the entire match, determine physical performance of substitute players across different playing positions and examine variations in match-related running performance in substitute players throughout the entire competitive season. The sample was composed of 943 observations of professional players who participated in the first division of the Spanish League (La Liga) during the 2014-2015 season. The players were divided into three different groups: players who completed the entire match (n = 519), players who were replaced (n = 212) and substitute players (n = 212). Substitute players covered greater distances at medium and high intensity compared to the players who played the entire match and those who were replaced. Position-specific trends indicated that attackers and central midfielder increased the distance covered at high-intensity running compared to their peers who played the whole match. During the competitive season, it was observed that substitute players attained greater match running performance during the mid-season period, allowing them to cover more distance for different variables of running performance compared to the start and end of the season.

#12 Analysis of elite soccer players' performance before and after signing a new contract
Reference: PLoS One. 2019 Jan 25;14(1):e0211058. doi: 10.1371/journal.pone.0211058. eCollection 2019.
Authors: Gómez MÁ, Lago C, Gómez MT, Furley P
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Summary: The aim of the current study was to analyse performance differences of football players 2-years prior and the year after signing a new contract (the following year) while taking playing position, nationality, player's role, team ability, and age into account. The sample was comprised of 249 players (n = 109 defenders, n = 113 midfielders; and n = 27 forwards) from four of the major European Leagues (Bundesliga, English FA Premier League, Ligue 1, and La Liga) during the seasons 2008 to 2015. The dependent variables studied were: shooting accuracy, defense (the sum of defensive actions, tackles, blocks, and interceptions), yellow cards, red cards, passing accuracy, tackle success, and minutes played per match. Two-step cluster analysis allowed classifying the sample into three groups of defenders (national important, foreign important, and less important players) and four groups of midfielders and forwards (national important, foreign important, national less important, and foreign less important players). Magnitude Based Inference (MBI) was used to test the differences between player's performances during the years of analyses. The main results (very likely and most likely effects) showed better performance in the year prior to signing a new contract than the previous year for foreign important defenders (decreased number of red cards), national important midfielders (increased number of minutes played), foreign important forwards (increased minutes played and defense), and national important forwards (increased minutes played). In addition, performance was lower the year after signing the contract compared to the previous one for less important defenders (decreasing defense), national less important midfielders (decreased minutes played), and foreign less important forwards (decreased defense). On the other hand, the players showed better performance in defense and more minutes played the year after signing the contract for less important defenders, national less important midfielders, and foreign less important forwards. These results may assist coaches to decide on when a new contract should be signed or the duration of the contract.

#13 Assessing the Validity of the MyJump2 App for Measuring Different Jumps in Professional Cerebral Palsy Football Players: An Experimental Study
Reference: JMIR Mhealth Uhealth. 2019 Jan 30;7(1):e11099. doi: 10.2196/11099.
Authors: Coswig V, Silva AACE, Barbalho M, Faria FR, Nogueira CD, Borges M, Buratti JR, Vieira IB, Román FJL, Gorla JI
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Summary: Vertical jumps can be used to assess neuromuscular status in sports performance. This is particularly important in Cerebral Palsy Football (CP Football) because players are exposed to high injury risk, but it may be complicated because the gold standard for assessing jump performance is scarce in field evaluation. Thus, field techniques, such as mobile apps, have been proposed as an alternative method for solving this problem. This study aims to evaluate the reliability of the measures of the MyJump2 app to assess vertical jump performance in professional CP Football. We assessed 40 male CP Football athletes (age 28.1 [SD 1.4] years, weight 72.5 [SD 6.2] kg, and height 176 [SD 4.2] cm) through the countermovement jump (CMJ) and squat jump (SJ) using a contact mat. At the same time, we assessed the athletes using the MyJump2 app. There were no significant differences between the instruments in SJ height (P=.12) and flight time (P=.15). Additionally, there were no significant differences between the instruments for CMJ in jump height (P=.16) and flight time (P=.13). In addition, it was observed that there were significant and strong intraclass correlations in all SJ variables varying from 0.86 to 0.89 (both P<.001), which was classified as "almost perfect." Similar results were observed in all variables from the CMJ, varying from 0.92 to 0.96 (both P ≤.001). We conclude that the MyJump2 app presents high validity and reliability for measuring jump height and flight time of the SJ and CMJ in CP Football athletes.

#14 Does the Environment Influence the Frequency of Concussion Incidence in Professional Football?
Reference: Cureus. 2018 Nov 23;10(11):e3627. doi: 10.7759/cureus.3627.
Authors: Haider S, Kaye-Kauderer HP, Maniya AY, Dai JB, Li AY, Post AF, Sobotka S, Adams R, Gometz A, Lovell MR, Choudhri TF
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Summary: Background Sports-related concussion is a major cause of mild traumatic brain injury (mTBI). It is possible that environmental factors, such as temperature, humidity, and stadium's altitude, may influence the overall incidence of concussions during a game. Purpose To examine the impact of environmental factors, such as temperature, humidity, barometric pressure, and dew point, on concussion incidence. Methods Public Broadcasting Service (PBS) FRONTLINE Concussion Watch was used to collect injury data on 32 NFL teams during regular season games from 2012 to 2015. Weather data points were collected from Weather Underground. Concussion incidence per game, the probability of a concussion during a game, and a difference in mean game-day temperature, humidity, dew point, and barometric pressure between concussion and concussion-free games were calculated. Our analysis included t-tests, analysis of variance (ANOVA), multivariate correlation tests, and logistic and Poisson regression.  Results Overall, 564 concussions were reported. There were 411 games with concussions and 549 games without concussions. We observed a significant decrease in concussion incidence with increasing temperature, both when the temperature was divided into 20oF increments or into quartiles (p = 0.005 and p = 0.002, respectively). We identified a statistically significant lower mean-game day temperature in concussion games compared to concussion-free games (p < 0.0006). We also observed a significant decrease in the incidence of concussion per game with increasing dew point. There was no significant difference in concussion incidence in barometric pressure and humidity. The logistic regression model predicted a decrease in the probability of a concussion in games with higher temperatures and dew points. Conclusions National Football League (NFL) players experienced an increased risk of concussion during football games played in colder temperatures and at lower dew points. Further research on environmental effects on concussions may aid in improving player safety in football leagues.





Latest research in football - week 4 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Head impact magnitudes that occur from purposeful soccer heading depend on the game scenario and head impact location
Reference: Musculoskelet Sci Pract. 2019 Jan 24;40:53-57. doi: 10.1016/j.msksp.2019.01.009. [Epub ahead of print]
Authors: Harriss A, Johnson AM, Walton DM, Dickey JP
Summary: This study quantified the linear and angular kinematics that result from purposeful heading during youth soccer games, and the influence of game scenario and head impact location on these magnitudes. This observational study recruited thirty-six female soccer players (13.4 ± 0.9 years old) from three elite youth soccer teams (U13, U14, U15) and followed for an entire soccer season. Players wore wireless sensors during each game to quantify head impact magnitudes. A total of 60 regular season games (20 games per team) were video recorded, and purposeful heading events were categorized by game scenario (e.g. throw in), and head impact location (e.g. front of head). Game scenario had a statistically significant effect on the linear head acceleration, and rotational head velocity, that resulted from purposeful headers. Rotational velocity from purposeful headers varied significantly between head impact locations, with impacts to the top of the head (improper technique) resulting in larger peak rotational velocities than impacts to the front of the head (proper technique); this was also the case for the linear acceleration for punts. Our findings suggest that the magnitude for both linear and angular head impact kinematics depend on the game scenario and head impact location. Headers performed with the top of the head (improper technique) result in larger rotational velocities compared to the front of the head (proper technique). Accordingly, youth players should be educated on how to execute proper heading technique to reduce head impact accelerations.

#2 Jumping Asymmetries Are Associated With Speed, Change of Direction Speed, and Jump Performance in Elite Academy Soccer Players
Reference: J Strength Cond Res. 2019 Jan 30. doi: 10.1519/JSC.0000000000003058. [Epub ahead of print]
Authors: Bishop C, Brashill C, Abbott W, Read P, Lake J, Turner A
Summary: The aim of this study was to establish interlimb asymmetries across different age groups in elite academy male soccer players and to examine any relationships between asymmetry and measures of physical performance. Fifty-one players from an English Premier League soccer academy were split into under-23 (n = 21), under-18 (n = 14), and under-16 (n = 16) groups and performed bilateral and unilateral countermovement jumps, 5-, 10-, and 20-m sprints, and a 505 change of direction speed tests. All tests showed low variability (coefficient of variation ≤ 2.5%) and good to excellent reliability (intraclass correlation coefficient = 0.80-0.99). A 1-way analysis of variance showed that the under-23 group was significantly faster than the under-16 group during the 20-m sprint (2.90 vs. 2.98 s; p = 0.02; effect size = 0.94). No other significant differences were present between groups. Interlimb asymmetry was quantified from the single-leg countermovement jump, and no significant differences in the magnitude of asymmetry were present between groups. However, multiple significant correlations were present in each age group between asymmetry and physical performance tests, all of which were indicative of reduced athletic performance. Results from this study show that although interlimb asymmetry scores are comparable across age groups in elite academy soccer players, differences as low as 5% are associated with reduced physical performance during jumping, sprinting, and change of direction speed tasks. This study suggests the importance of monitoring jump height asymmetries in elite academy soccer players.

#3 Coaching Efficacy, Player Perceptions of Coaches' Leadership Styles, and Team Performance in Premier League Soccer
Reference: Res Q Exerc Sport. 2019 Feb 1:1-9. doi: 10.1080/02701367.2018.1563277. [Epub ahead of print]
Authors: Keatlholetswe L, Malete L
Summary: The coaching competency research has demonstrated the role of coaching efficacy and coaching behaviors on various athlete outcomes. However, athlete perceptions of these relationships and how they affect performance are less understood. This study examined if coaching efficacy is predictive of player perceptions of coaches' leadership styles, team atmosphere, and team performance in a soccer season. Fifteen male premier league soccer coaches (Mage = 45.27, SD = 6.07) and 226 players (Mage = 25.66, SD = 3.96) from Botswana participated in the study. All participants completed a background information questionnaire. Coaches completed the Coaching Efficacy Scale. Players rated their coaches' leadership styles using the Revised Leadership Scale for Sports as well as team atmosphere. Team performance was based on position in the league log and player ratings of the teams' performance. Findings showed that coaches' self-ratings on technique efficacy predicted player perceptions of the coaches' use of all six leadership styles. Game strategy efficacy predicted higher team atmosphere and team performance. Motivation efficacy was not significantly associated with player perceptions of the coaches' use of any of the leadership styles, while character building efficacy was negatively associated with the various leadership styles. Findings provide support to previous research evidence linking higher coaching efficacy, leadership styles, and team outcomes. The study expands the emergent research within the coaching competency literature that examines player perceptions of coaches' behaviors and leadership styles.

#4 The Effect of In-Season Traditional and Explosive Resistance Training Programs on Strength, Jump Height, and Speed in Recreational Soccer Players
Reference: Res Q Exerc Sport. 2019 Feb 1:1-8. doi: 10.1080/02701367.2018.1563276. [Epub ahead of print]
Authors: Griffiths B, Grant J, Langdown L, Gentil P, Fisher J, Steele J
Summary: Resistance training is often performed in a traditional training style using deliberate relatively longer repetition durations or in an explosive training style using maximal intended velocities and relatively shorter repetition durations. Both improve strength, "power" (impulsivity), and speed. This study compared explosive and traditional training over a 6-week intervention in 30 healthy young adult male recreational soccer players. Full body supervised resistance training was performed 2 times a week using 3 sets of each exercise at 80% of one repetition maximum to momentary failure. Outcomes were Smith machine squat 1 repetition maximum, 10 meter sprint time, and countermovement jump. Both groups significantly improved all outcomes based on 95% confidence intervals not crossing zero. There were no between-group differences for squat 1 RM (TRAD = 6.3[5.1 to 7.6] kg, EXP = 5.2[3.9 to 6.4] kg) or 10 meter sprint (TRAD = -0.05[-0.07 to -0.04] s, EXP = -0.05[-0.06 to -0.03] s). Explosive group had a significantly greater increase in countermovement jump compared to the traditional group (TRAD = 0.7[0.3 to 1.1] cm, EXP = 1.3[0.9 to 1.7] cm). Both the traditional training and explosive training performed to momentary failure produced significant improvements in strength, speed, and jump performance. Strength gains are similar independent of intended movement speed. However, speed and jump performance changes are marginal with resistance training.

#5 A match-day analysis of the movement profiles of substitutes from a professional soccer club before and after pitch-entry
Reference:  PLoS One. 2019 Jan 31;14(1):e0211563. doi: 10.1371/journal.pone.0211563. eCollection 2019.
Authors: Hills SP, Barrett S, Feltbower RG, Barwood MJ, Radcliffe JN, Cooke CB, Kilduff LP, Cook CJ, Russell M
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Summary: Whilst the movement demands of players completing a whole soccer match have been well-documented, comparable information relating to substitutes is sparse. Therefore, this study profiled the match-day physical activities performed by soccer substitutes, focusing separately on the pre and post pitch-entry periods. Seventeen English Championship soccer players were monitored using 10 Hz Micromechanical Electrical Systems (MEMS) devices during 13 matches in which they participated as substitutes (35 observations). Twenty physical variables were examined and data were organised by bouts of warm-up activity (pre pitch-entry), and five min epochs of match-play (post pitch-entry). Linear mixed modelling assessed the influence of time (i.e., 'bout' and 'epoch'), playing position, and match scoreline. Substitutes performed 3±1 rewarm-up bouts∙player-1∙match-1. Compared to the initial warm-up, each rewarm-up was shorter (-19.7 to -22.9 min) and elicited less distance (-606 to -741 m), whilst relative total distances were higher (+26 to +69 m∙min-1). Relative total (+13.4 m∙min-1) and high-speed (+0.4 m∙min-1) distances covered during rewarm-ups increased (p <0.001) with proximity to pitch-entry. Players covered more (+3.2 m; p = 0.047) high-speed distance per rewarm-up when the assessed team was losing compared with when winning at the time of pitch-entry. For 10 out of 20 variables measured after pitch-entry, values reduced from 0-5 min thereafter, and substitutes covered greater (p ˂0.05) total (+67 to +93 m) and high-speed (+14 to +33 m) distances during the first five min of match-play versus all subsequent epochs. Midfielders covered more distance (+41 m) per five min epoch than both attackers (p ˂0.001) and defenders (p = 0.016). Acknowledging the limitations of a solely movement data approach and the potential influence of other match-specific factors, such findings provide novel insights into the match-day demands faced by substitute soccer players. Future research opportunities exist to better understand the match-day practices of this population.

#6 Effect of Heavy Resisted Sled Sprint Training During the Competitive Season on Sprint and Change-of-Direction Performance in Professional Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Jan 31:1-25. doi: 10.1123/ijspp.2018-0592. [Epub ahead of print]
Authors: McMorrow BJ, Ditroilo M, Egan B
Summary: Resisted sled sprinting (RSS) is an effective tool for improving sprint performance over short distances, but the effect on change-of-direction (COD) performance is largely unknown. The present study investigated the effect of heavy RSS training during the competitive season on sprint and COD performance in professional soccer players. Over six weeks in-season, a RSS training group (n=6) performed RSS at a sled load of 30% of body mass for a total programme running distance of 800 m, while an unresisted sprint (URS) training group (n=7) performed the same distance of unresisted sprinting. A 20 m maximal sprint with split times measured at 5, 10 and 20 m, and the sprint 9-3-6-3-9 m with 180° turns COD test were performed before and after the intervention. Sprint performance (mean; 95% confidence limits; qualitative inference) was improved in both groups over 5 m (URS, 5.1%; -2.4, 12.7; likely moderate; RSS, 5.4%; 0.5, 10.4; likely moderate), 10 m (URS, 3.9%; -0.3, 8.1; very likely moderate; RSS, 5.0%; 1.8, 8.0; very likely large), and 20 m (URS, 2.0%; -0.6, 4.5; likely moderate; RSS (3.0%; 1.7, 4.4; very likely moderate). COD was improved in both groups (URS, 3.7%; 2.2, 5.2; most likely large; RSS, 3.3%; 1.6, 5.0; most likely moderate). Between-group differences were unclear. Heavy RSS or URS training matched for running distance were similarly effective at improving sprint and COD performance in professional soccer players when performed in the competitive phase of the season.

#7 Predicting Future Perceived Wellness in Professional Soccer: The Role of Preceding Load and Wellness
Reference: Int J Sports Physiol Perform. 2019 Jan 31:1-25. doi: 10.1123/ijspp.2017-0864. [Epub ahead of print]
Authors: Jaspers A, De Beéck TO, Brink MS, Frencken WGP, Staes F, Davis JJ, Helsen WF
Summary: The influence of preceding load and perceived wellness on the future perceived wellness of professional soccer players is unexamined. This paper simultaneously evaluates the external and internal load for different time frames in combination with pre-session wellness to predict future perceived wellness using machine learning techniques. Training and match data were collected from a professional soccer team. The external load was measured using global positioning system technology and accelerometry. The internal load was obtained using the RPE multiplied by duration. Predictive models were constructed using gradient boosted regression trees (GBRT) and one naive baseline method. The individual predictions of future wellness items (i.e., fatigue, sleep quality, general muscle soreness, stress levels, and mood) were based on a set of external and internal load indicators in combination with pre-session wellness. The external and internal load was computed for acute and cumulative time frames. The GBRT model's performance on predicting the reported future wellness was compared to the naive baseline's performance by means of absolute prediction error and effect size. The GBRT model outperformed the baseline for the wellness items fatigue, general muscle soreness, stress levels and mood. Additionally, only the combination of external load, internal load, and pre-session perceived wellness resulted in non-trivial effects for predicting future wellness. Including the cumulative load did not improve the predictive performances. The findings may indicate the importance of including both acute load and pre-session perceived wellness in a broad monitoring approach in professional soccer.

#8 A tactical comparison of the 4-2-3-1 and 3-5-2 formation in soccer: A theory-oriented, experimental approach based on positional data in an 11 vs. 11 game set-up
Reference: PLoS One. 2019 Jan 30;14(1):e0210191. doi: 10.1371/journal.pone.0210191. eCollection 2019.
Authors: Memmert D, Raabe D, Schwab S, Rein R
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Summary: The presented field experiment in an 11 vs. 11 soccer game set-up is the first to examine the impact of different formations (e.g. 4-2-3-1 vs. 3-5-2) on tactical key performance indicators (KPIs) using positional data in a controlled experiment. The data were gathered using player tracking systems (1 Hz) in a standardized 11 vs. 11 soccer game. The KPIs were measured using dynamical positioning variables like Effective Playing Space, Player Length per Width ratio, Team Separateness, Space Control Gain, and Pressure Passing Efficiency. Within the experimental positional data analysis paradigm, neither of the team formations showed differences in Effective Playing Space, Team Separateness, or Space Control Gain. However, as a theory-based approach predicted, a 3-5-2 formation for the Player Length per Width ratio and Pressure Passing Efficiency exceeded the 4-2-3-1 formation. Practice task designs which manipulate team formations therefore significantly influence the emergent behavioral dynamics and need to be considered when planning and monitoring performance. Accordingly, an experimental positional data analysis paradigm is a useful approach to enable the development and validation of theory-oriented models in the area of performance analysis in sports games.

#9 Time Trends of Head Injuries Over Multiple Seasons in Professional Male Football (Soccer)
Reference: Sports Med Int Open. 2019 Jan 28;3(1):E6-E11. doi: 10.1055/a-0808-2551. eCollection 2019 Jan.
Authors: Beaudouin F, der Fünten KA, Tröß T, Reinsberger C, Meyer T
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Summary: The present study aimed to investigate time trends of head injuries and their injury mechanisms since a rule change as monitoring may help to identify causes of head injuries and may advance head injury prevention efforts. Based on continuously recorded data from the German football magazine "kicker Sportmagazin ® " as well as other media sources, a database of head injuries in the 1 st German male Bundesliga was generated comprising 11 seasons (2006/07-2016/17). Injury mechanisms were analysed from video recordings. Injury incidence rates (IR) and 95% confidence intervals (95% CI) were calculated. Time trends were analysed via linear regression. Two hundred thirty-eight match head injuries occurred (IR 1.77/1000 match hours, 95% CI 1.56-2.01). There were no significant seasonal changes, expressed as annual average year-on-year change, in IRs over the 11-year period for total head injuries (p=0.693), facial/head fractures (p=0.455), lacerations/abrasions (p=0.162), and head contusions (p=0.106). The annual average year-on-year increase for concussion was 6.4% (p=0.004). Five head injury mechanisms were identified. There were no seasonal changes in injury mechanisms over the study period. The concussion subcategory increased slightly over the seasons, which may either be a result of increasing match dynamics or raised awareness among team physicians and players.





Latest research in football - week 3 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Effects of Resisted Sprint With Changes of Direction Training Through Several Relative Loads on Physical Performance in Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Jan 24:1-20. doi: 10.1123/ijspp.2018-0702. [Epub ahead of print]
Authors: Rodríguez-Osorio D, Gonzalo-Skok O, Pareja-Blanco F
Summary: The purpose was to compare the effects of resisted change of direction (COD) movements, using several relative loads, on soccer players' physical performance. Fifty-four male soccer players were randomly assigned to one of the following 3 groups, which differed only in the magnitude of the external load used during the COD training: COD training without external load (COD-0; n = 16); COD training with a 12.5% body mass (BM) external load (COD-12.5; n = 19); and COD training with a 50% BM external load (COD-50; n = 19). Participants performed the specific COD training twice per week for 6 weeks. Before and after the training period a battery of tests was completed: countermovement jump (CMJ); 30 m running sprint (time in 10-m [T10], 20-m [T20] and 30-m [T30]); L-RUN test; and V-CUT test. Within-group comparisons showed substantial improvements in CMJ and T10 (likely) in COD-0, whereas CMJ, T10 and T20 were substantially enhanced (possibly to likely) in COD-50. COD-12.5 induced substantial improvements in all analyzed variables (likely to most likely). Between-groups comparisons showed better effects on all analyzed variables for COD-12.5 compared to COD-0 group (possibly to very likely), whereas COD-50 only showed possibly better effects than COD-0 on T10. In addition, COD-12.5 induced a better effect on L-RUN and V-CUT tests than COD-50 (possibly to likely). These results indicate that COD training, especially moderate load (12.5% BM) resisted COD training, may have a positive effect on COD skills, running sprint performance and jumping ability in young soccer players.

#2 The Arrowhead Agility Test: Reliability, Minimum Detectable Change, and Practical Applications in Soccer Players
Reference: J Strength Cond Res. 2019 Jan 22. doi: 10.1519/JSC.0000000000002987. [Epub ahead of print]
Authors: Rago V, Brito J, Figueiredo P, Ermidis G, Barreira D, Rebelo A
Summary: Four independent studies were conducted to examine the utility of the arrowhead agility test (AAT) to measure change of direction (COD) capacity in soccer players, specifically, (a) intersession reliability and minimum detectable change (n = 24); (b) power-dependent abilities associated with AAT performance (n = 56); and (c) fatigue sensitivity (n = 20); differences between competitive levels and age groups (n = 264). Irrespective of the AAT outcome measure (skillful side, less-skillful side, sum of both), intersession reliability and the ability to detect changes in performance were good (ICC = 0.80-0.83; CV = 1.25-2.21%; smallest worthwhile change, 0.06-0.12 >SEM, 0.01-0.03) except for the asymmetry index. A 15-m sprint explained a significant amount of variance in COD (p < 0.01; R = 0.42). Arrowhead agility test performance did not change from the prematch toward half time (p = 0.21). However, reduced COD performance was observed after an intense period in the second half and after the game, compared with prematch and half-time performance (p < 0.05; effect size [ES] = -0.85 to 0.42). Irrespective of age group, national players were more agile than regional players (p < 0.05; ES = -1.97 to -0.36). Moreover, independently of their competitive level, senior and U18 players had a better performance than U16 (p < 0.05; ES = -2.33 to -0.84), whereas no significant differences were observed between senior and U18. Percentiles were also reported in the results. The AAT is reliable to measure COD in soccer players. The test may simultaneously encompass 15-m sprint testing but should be implemented independently to countermovement jump. Furthermore, the test is sensitive to match-induced fatigue during the second half and discriminates players from different competitive levels.

#3 External Cueing Influences Drop Jump Performance in Trained Young Soccer Players
Reference: J Strength Cond Res. 2019 Jan 22. doi: 10.1519/JSC.0000000000002935. [Epub ahead of print]
Authors: Oliver JL, Barillas SR, Lloyd RS, Moore I, Pedley J
Summary: Drop jump (DJ) characteristics provide insight on power production and injury risk. The purpose of this study was to investigate the effect of external cueing on DJ characteristics in young male soccer players. Fourteen academy soccer players performed DJs with 4 different conditions, control (CONT), contact cue (CC), height cue (HC), and quiet cue (QC). Performance measures were reactive strength index (RSI), jump height, ground contact time (GCT), and take-off impulse, with injury risk reflected by impact peak, impact timing, and landing impulse. Contact cue showed a very large significant reduction in GCT (effect size [ES] > 2.0, p < 0.05), and moderate to large increase in RSI, landing impulse, and push-off impulse (ES 0.70-1.55, p < 0.05) compared with all other conditions. Contact cue also moderately increased impact peak when compared with HC and QC (ES ≥ 0.78, p < 0.05). Height cue led to a significant increase in jump height that was moderately greater than other external cues (ES ≥ 0.87, p < 0.05), but with only a small nonsignificant increase compared (ES 0.54, p > 0.05) with CONT. The data showed that all cues provided a specific response; CC reduced GCT and increased RSI, HC increased jump height, and QC reduced outcomes associated with injury risk. Height cue may be advantageous for young soccer players with a low training age because it shows a small to moderate increase in jump height without increasing injury risk. Young players may need to be safely progressed to be able to use a CC to facilitate high reactive strength without being exposed to undue injury risk.

#4 Measuring the Hip Adductor to Abductor Strength Ratio in Ice Hockey and Soccer Players: A Critically Appraised Topic
Reference: J Sport Rehabil. 2019 Jan 24:1-18. doi: 10.1123/jsr.2018-0250. [Epub ahead of print]
Author: Rodriguez R
Summary: Ice hockey and soccer are both dynamic sports that involve continuous, unpredictable play. These athletes consistently demonstrate higher rates of groin strains compared to other contact sports. Measuring the hip adductor/abductor ratio has the potential to expose at-risk players, reduce injury rates, and preserve groin health in players with chronic strains. What is the clinical utility of measuring the hip adductor/abductor ratio for pre-season and in-season ice hockey and soccer players? Three studies, all of which were prospective cohort designs, were included. One study involved assessing preseason strength and flexibility as a risk factor for adductor strains in professional ice hockey players. Another study performed in the same professional hockey team used preseason hip adductor/abductor strength ratios to screen for those players who would benefit from a strengthening intervention aimed at reducing the incidence of adductor strains. The final study, which was performed in elite U17 soccer players, assessed the effectiveness of monthly in-season strength monitoring as a guide to trigger in-season interventions to decrease injury incidence. Measuring the hip adductor/abductor strength ratio in hockey and soccer players can be a beneficial pre-season and in-season tool to predict future groin strain risk and screen for athletes who might benefit from a strengthening intervention. Evidence exists to support monitoring the hip adductor/abductor strength ratio to assess and reduce the risk of adductor strains in ice hockey and soccer players.

#5 Realistic Soccer-Specific Virtual Environment Exposes High-Risk Lower Extremity Biomechanics
Reference: J Sport Rehabil. 2019 Jan 24:1-23. doi: 10.1123/jsr.2018-0237. [Epub ahead of print]
Authors: DiCesare CA, Kiefer AW, Bonnette SH, Myer GD
Summary: Laboratory-based biomechanical analyses of sport-relevant movements such as landing and cutting have classically been used to quantify kinematic and kinetic factors in the context of injury risk, which are then used to inform targeted interventions designed to improve risky movement patterns during sport. However, the non-contextual nature of standard assessments presents challenges for assessing sport-relevant skill transfer. It may be more effective to examine injury-risk biomechanics on individuals performing sport-specific tasks within the actual sport environment, or more feasibly, within a simulated sport environment using virtual reality (VR). The purpose of this study was to examine biomechanical differences exhibited by athletes during a jump-landing task performed as part of both a standard biomechanical assessment and a sport-specific VR-based assessment.  22 female adolescent soccer athletes (age = 16.0 ± 1.4 years; height = 165.6 ± 4.9 cm; weight = 60.2 ± 11.4 kg) participated in this study. The landing performance of was analyzed for a drop vertical jump task and a VR-based, soccer-specific corner-kick scenario in which the athletes were required to jump to head a virtual soccer ball and land. Hip, knee and ankle joint kinematic differences in the frontal and sagittal planes were used as main outcome measures. Athletes exhibited reduced hip and ankle flexion, hip abduction, and frontal plane ankle excursion during landing in realistic sport scenario compared to the standard drop vertical jump task. VR-based assessments can provide a sport-specific context in which to assess biomechanical deficits that predispose athletes for lower extremity injury and offer a promising approach to better evaluate skill transfer to sport which can guide future injury prevention efforts.

#6 Associations Between Selected Training Stress Measures and Fitness Changes in Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Jan 24:1-23. doi: 10.1123/ijspp.2018-0462. [Epub ahead of print]
Authors: Rabbani A, Kargarfard M, Castagna C, Clemente FM, Twist C
Summary: The purpose of this study was to investigate the relationship of accumulated Global Positioning System (GPS)-accelerometer-based and heart rate (HR)-based training metrics to changes in high-intensity intermittent running capacity during an in-season phase in professional soccer players. Eleven male professional players (mean ± SD, age: 27.2 ± 4.5 years) performed the 30-15 Intermittent Fitness Test (30-15IFT) before and after a five-week in-season training phase, and the final velocity (VIFT) was considered as players' high-intensity intermittent running capacity. During all sessions, Edwards' training impulse (Edwards' TRIMP), Banister's TRIMP, Z5 TRIMP, training duration, total distance covered, New Body Load (NBL), high-intensity running performance (distance covered above 14.4 km·h-1), and very high-intensity running performance (distance covered above 19.8 km·h-1) were recorded. The players' VIFT showed a most likely moderate improvement (+4.3%, 90% confidence limits [3.1; 5.5%], effect size ES, 0.70 [0.51; 0.89]). Accumulated NBL, Banister's TRIMP and Edwards' TRIMP showed large associations (r = 0.51 to 0.54) with changes in VIFT. Very large relationship was also observed between accumulated Z5 TRIMP (r= 0.72) with changes in VIFT. Large-to-nearly perfect within-individual relationships were observed between NBL and some of the other training metrics (i.e., Edwards' TRIMP, Banister's TRIMP, training duration, and total distance) in 10 out of 11 players. HR-based training metrics can be used to monitor high-intensity intermittent running capacity changes in professional soccer players. The dose-response relationship is also largely detected using accelerometer-based metrics (i.e., NBL) to track changes in high-intensity intermittent running capacity of professional soccer players.

#7 Learning to Rate Player Positioning in Soccer
Reference: Big Data. 2019 Jan 23. doi: 10.1089/big.2018.0054. [Epub ahead of print]
Authors: Dick U, Brefeld U
Summary: We investigate how to learn functions that rate game situations on a soccer pitch according to their potential to lead to successful attacks. We follow a purely data-driven approach using techniques from deep reinforcement learning to valuate multiplayer positionings based on positional data. Empirically, the predicted scores highly correlate with dangerousness of actual situations and show that rating of player positioning without expert knowledge is possible.

#8 Match Running Performance in Young Soccer Players: A Systematic Review
Reference: Sports Med. 2019 Jan 22. doi: 10.1007/s40279-018-01048-8. [Epub ahead of print]
Authors: Palucci Vieira LH, Carling C, Barbieri FA, Aquino R, Santiago PRP
Summary: To date, athletic performance has been extensively assessed in youth soccer players through laboratory and field testing. Only recently has running performance via time-motion analysis been assessed during match play. Match running data are often useful in a practical context to aid game understanding and decision making regarding training content and prescriptions. A plethora of previous reviews have collated and appraised the literature on time-motion analysis in professional senior players, but none have solely examined youth players. The aim of the present systematic review was to provide a critical appraisal and summary of the original research articles that have evaluated match running performance in young male soccer players. Following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement, literature searches were performed in four databases: PubMed, ISI Web of Science, SPORTDiscus and SciELO. We used the following descriptors: soccer, football, young, youth, junior, physical performance, running performance, match running performance, movement patterns, time-motion analysis, distances covered, activity profile, work rate, match analysis, and match performance. Articles were included only if they were original articles written in the English language, studied populations of male children and/or adolescents (aged ≤ 20 years), were published/ahead of print on or before 31 December 2017 and showed at least one outcome measure regarding match running performance, such as total distance covered, peak game speed or indicators of activities performed at established speed thresholds. A total of 5801 records were found. After duplicates were removed and exclusion and inclusion criteria applied, 50 articles were included (n = 2615 participants). Their outcome measures were extracted and findings were synthesized. The majority of the reviewed papers covered the European continent (62%) and used global positioning systems (GPS) (64%). Measurement error of the tools used to obtain position data and running metrics was systematically overlooked among the studies. The main aims of studies were to examine differences across playing positions (20%), age groups (26%) and match halves (36%). Consistent findings pointed to the existence of positional role and age effects on match running output (using fixed running speed thresholds), but there was no clear consensus about reductions in activity over the course of match play. Congested schedules negatively affected players' running performance. While over 32% of all studies assessed the relationships between match running performance and physical capacity, biochemical markers and body composition, ~ 70% of these did not account for playing position. This review collated scientific evidence that can aid soccer conditioning professionals in understanding external match loads across youth categories. Coaches working with youth development programs should consider that data derived from a given population may not be relevant for other populations, since game rules, match format and configuration are essentially unstandardized among studies for age-matched players. Despite limited evidence, periodization training emphasizing technical-tactical content can improve match running performance. Occurrence of acute and residual impairments in the running performance of young soccer players is common. Prescription of postmatch recovery strategies, such as cold water immersion and spa treatment, can potentially help reduce these declines, although additional research is warranted. This review also highlighted areas requiring further investigation, such as the possible influence of environmental and contextual constraints and a more integrative approach combining tactical and technical data.

#9 Drop Jump Asymmetry is Associated with Reduced Sprint and Change-of-Direction Speed Performance in Adult Female Soccer Players
Reference: Sports (Basel). 2019 Jan 21;7(1). pii: E29. doi: 10.3390/sports7010029.
Authors: Bishop C, Turner A, Maloney S, Lake J, Loturco I, Bromley T, Read P
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Summary: Studies that examine the effects of inter-limb asymmetry on measures of physical performance are scarce, especially in adult female populations. The aim of the present study was to establish the relationship between inter-limb asymmetry and speed and change-of-direction speed (CODS) in adult female soccer players. Sixteen adult players performed a preseason test battery consisting of unilateral countermovement jump (CMJ), unilateral drop jump (DJ), 10 m, 30 m, and 505 CODS tests. Inter-limb asymmetry was calculated using a standard percentage difference equation for jump and CODS tests, and Pearson's r correlations were used to establish a relationship between asymmetry and physical performance as well as asymmetry scores themselves across tests. Jump-height asymmetry from the CMJ (8.65%) and DJ (9.16%) tests were significantly greater (p < 0.05) than asymmetry during the 505 test (2.39%). CMJ-height asymmetry showed no association with speed or CODS. However, DJ asymmetries were significantly associated with slower 10 m (r = 0.52; p < 0.05), 30 m (r = 0.58; p < 0.05), and 505 (r = 0.52⁻0.66; p < 0.05) performance. No significant relationships were present between asymmetry scores across tests. These findings suggest that the DJ is a useful test for detecting existent between-limb asymmetry that might in turn be detrimental to speed and CODS performance. Furthermore, the lack of relationships present between different asymmetry scores indicates the individual nature of asymmetry and precludes the use of a single test for the assessment of inter-limb differences.

#10 Hip Arthroscopic Management Can Improve Osteitis Pubis and Bone Marrow Edema in Competitive Soccer Players With Femoroacetabular Impingement
Reference: Am J Sports Med. 2019 Jan 21:363546518819099. doi: 10.1177/0363546518819099. [Epub ahead of print]
Authors: Saito M, Utsunomiya H, Hatakeyama A, Nakashima H, Nishimura H, Matsuda DK, Sakai A, Uchida S
Summary: There is a dearth of knowledge regarding the correlation between femoroacetabular impingement (FAI) and osteitis pubis (OP) among symptomatic soccer players. The purpose was to elucidate whether arthroscopic FAI correction is effective for young competitive soccer players with FAI combined with OP or perisymphyseal pubic bone marrow edema (BME). A total of 577 consecutive patients who underwent arthroscopic FAI correction were retrospectively reviewed with a minimum 2-year follow-up. Competitive soccer players who were professional, college, and high school athletes were included. The authors assessed the modified Harris Hip Score and Nonarthritic Hip Score preoperatively and at 6 months, 1 year, and 2 years after surgery. In addition, players were divided into groups according to radiographic evidence of OP and BME (2 groups each). Clinical outcomes, return to play, and radiographic assessments were compared between groups. Twenty-eight hips met the inclusion criteria. The median modified Harris Hip Score significantly improved after hip arthroscopy (81.4, preoperatively; 95.7 at 6 months, P = .0065; 100 at 1 year, P = .0098; 100 at 2 years, P = .013). The median Nonarthritic Hip Score also significantly improved (75.0, preoperatively; 96.3 at 6 months, P = .015; 98.8 at 1 year, P = .0029; 100 at 2 years, P = .015). Furthermore, 92.0% of players returned to play soccer at the same or higher level of competition at a median 5.5 months (range, 4-15 months); 67.8% had radiological confirmation of OP; and 35.7% had pubic BME. The alpha angle was significantly higher in pubic BME group than the no-pubic BME group (64.8° vs 59.2°, P = .027), although there was no significant difference between the OP and no-OP groups. The prevalence of tenderness of the pubic symphysis significantly decreased preoperatively (32.1%) to postoperatively (3.6%). Magnetic resonance imaging findings confirmed that pubic BME disappeared in all players at a median 11 months (range, 6-36) after initial surgery. Arthroscopic management for FAI provides favorable clinical outcomes, a high rate of return to sports, and, when present, resolution of pubic BME among competitive soccer players.

#11 Effects of Combined Surfaces vs. Single-Surface Plyometric Training on Soccer Players' Physical Fitness
Reference: J Strength Cond Res. 2019 Jan 17. doi: 10.1519/JSC.0000000000002929. [Epub ahead of print]
Authors: Ramirez-Campillo R, Álvarez C, García-Pinillos F, García-Ramos A, Loturco I, Chaabene H, Granacher U
Summary: The aim of this study was to compare the effects of a 8-week plyometric jump training (PJT) performed on different surfaces (grass, land-dirt, sand, wood, gym mat, and tartan-track) vs. a single-surface PJT (grass) on components of physical fitness (muscle power, speed, and change-of-direction speed [CODS] tasks) and sport-specific performance (i.e., maximal kicking velocity [MKV]) in male soccer players aged 11-14 years. Athletes were randomly assigned to a combined surfaces PJT (PJTc, n = 8), a single-surface PJT (PJTs, n = 8), or an active control (CON, n = 7). Although the PJT group trained on grass, the PJTc trained on 6 different surfaces and equally distributed the total jump volume according to the surface. Pre-post tests were conducted on grass. Significant main effects of time were observed for the countermovement jump, the standing-long-jump, the 20-cm drop jump, 30-m sprint time, CODS, and MKV (all p < 0.001; d = 0.53-0.87). Group × time interactions were identified for all jump tests, MKV, 30-m sprint time, and CODS (all p < 0.001; d = 0.58-0.71) in favor of PJTc. No significant pre-post changes were observed in the CON (all p > 0.05; d = 0.07-0.1). In conclusion, PJT is effective in improving physical fitness in young soccer players when conducted in combination with regular soccer training. Although general fitness testing and PJTs were performed on grass, larger physical fitness improvements were found after PJTc. Thus, PJTc is recommended, as it provides a better overload stimulus compared with more conventional training overload (e.g., increase in training volume or intensity). Future studies still have to address the underlying physiological adaptations after PJTc.

#12 Effect of deep oscillation as a recovery method after fatiguing soccer training: A randomized cross-over study
Reference: J Exerc Sci Fit. 2018 Dec;16(3):112-117. doi: 10.1016/j.jesf.2018.10.004. Epub 2018 Oct 16.
Authors: von Stengel S, Teschler M, Weissenfels A, Willert S, Kemmler W
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Summary: In soccer the recovery time between matches is often not long enough for complete restoration. Insufficient recovery can result in reduced performance and a higher risk of injuries. The purpose of this study was to evaluate the potential of Deep Oscillation (DO) as a recovery method. In a randomized crossover study including 8 male soccer players (22 ± 3.3 years) the following parameters were evaluated directly before and 48 h after a fatiguing soccer-specific exercise: Maximum isokinetic strength of the leg and hip extensors and flexors (Con-Trex® Leg Press, Physiomed, Germany), rating of perceived exertion (RPE) during isokinetic testing (Borg scale 6-20), creatine kinase (CK) serum levels and Delayed Onset Muscle Soreness (DOMS; visual analogue scale 1-10). By random allocation, half of the group performed a DO self-treatment twice daily (4 applications of 15min each), whilst the other half received no intervention. 4 weeks later a cross-over was conducted. Two-way repeated measures analysis of variance was used to compare treatment versus control. A significant treatment effect was observed for maximum leg flexion strength (p = 0.03; DO: 125 ± 206 N vs. CG: -115 ± 194; p = 0.03) and for RPE (DO: -0.13 ± 0.64; vs. CG: +1.13 ± 1.36; p = 0.03). There was a trend to better recovery for maximum leg extension strength (DO: -31 ± 165 N vs. CG: -138 ± 212; p = 0.028), CK values (DO: 72 ± 331 U/ml vs. CG: 535 ± 797 U/ml; p = 0.15) and DOMS (DO: 3.4 ± 1.5 vs. CG: 4.1 ± 2.6; p = 0.49). In the present study we found significant effects of DO on maximum leg flexion strength and perceived rate of exertion. Other variables showed a consistent trend in favour of DO compared with the control without significance. DO seems to be a promising method to accelerate the time-course of peripheral recovery of muscle which should be addressed in larger studies in future.

#13 In season adaptations to intense intermittent training and sprint interval training in sub-elite football players
Reference: Scand J Med Sci Sports. 2019 Jan 24. doi: 10.1111/sms.13395. [Epub ahead of print]
Authors: Hostrup M, Gunnarsson TP, Fiorenza M, Mørch K, Onslev J, Pedersen KM, Bangsbo J
Summary: This study investigated the in-season effect of intensified training comparing the efficacy of duration-matched intense intermittent exercise training with sprint interval training in increasing intermittent running performance, sprint ability, and muscle content of proteins related to ion handling and metabolism in football players. After the first two weeks in the season, 20 sub-elite football players completed either 10 weeks of intense intermittent training using the 10-20-30 training concept (10-20-30, n=12) or sprint interval training (SIT, n=10; work/rest-ratio: 6-s/54-s) three times weekly, with a ~20% reduction in weekly training time. Before and after the intervention, players performed a Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) and a 30-m sprint test. Furthermore, players had a muscle biopsy taken from the vastus lateralis. Yo-Yo IR1 performance increased by 330 m (95%CI: 178-482, P≤0.01) in 10-20-30, whereas no change was observed in SIT. Sprint time did not change in 10-20-30, but decreased by 0.04 s (95%CI: 0.00-0.09, P≤0.05) in SIT. Muscle content of HADHA (24%, P≤0.01), PDH-E1α (40%, P≤0.01), complex I-V of the electron transport chain (ETC) (51%, P≤0.01) and Na+ ,K+ -ATPase subunits α2 (33%, P≤0.05) and β1 (27%, P≤0.05) increased in 10-20-30, whereas content of DHPR (27%, P≤0.01) and complex I-V of the ETC (31%, P≤0.05) increased in SIT. Intense intermittent training, combining short sprints and a high aerobic load, is superior to regular sprint interval training in increasing intense intermittent running performance during a Yo-Yo IR1 test and muscle content of PDH-E1α and HADHA in sub-elite football players.





Latest research in football - week 2 - 2018

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Impact of Sports-Related Subconcussive Injuries in Soccer Players
Reference: Semin Speech Lang. 2019 Feb;40(1):57-64. doi: 10.1055/s-0038-1676365. Epub 2019 Jan 7.
Authors: Díaz-Rodríguez YI, Salvatore AP
Summary: Sports-related subconcussive impacts to the head are receiving increased interest. Recent evidence indicates that subconcussive impacts will have greater relevance across time because of the number of repetitive impacts. Soccer players are at risk of receiving at least one impact during a soccer game. The authors review the cognitive-communication functioning following subconcussive head injuries in youth and recommendations for baseline assessments and cognitive-communication dysfunctions after subconcussive impacts in youth. The review is followed by a description and discussion of a study that assessed the cognitive-communicative dysfunction in young soccer players prior to and following a series of soccer matches and recommendations for monitoring recovery of cognitive-communication.

#2 Practical Torso Cooling During Soccer-Specific Exercise in the Heat
Reference: J Athl Train. 2018 Nov;53(11):1089-1097. doi: 10.4085/1062-6050-417-17. Epub 2019 Jan 7.
Authors: Parris K, Tyler CJ
Summary: Precooling and midevent cooling of the torso using cooling vests can improve exercise performance in the heat with or without physiological changes; however, the effects of such cooling during intermittent exercise in the heat are unknown. The objective of the study was to investigate the effects of torso cooling during intermittent exercise in the heat (35°C, 50% relative humdity) on sprint performance and the physiological and perceptual responses to the exercise. Ten non-heat-acclimated, male soccer players (age = 25 ± 2 years, height = 1.77 ± 0.06 m, mass = 72.9 ± 7.6 kg) participated in this study. Two 90-minute bouts of soccer-specific intermittent running in the heat: 1 trial with a cooling vest worn during the exercise and 1 trial without a cooling vest. Each trial comprised two 45-minute periods separated by approximately 15 minutes of seated rest in cool conditions (approximately 23°C, 50% relative humdity). Peak sprint speed, rectal temperature (Tr), mean-weighted skin temperature (Tsk), heart rate (HR), rating of perceived exertion (RPE), and thermal sensation (TS) were measured every 5 minutes. Peak sprint performance was largely unaffected by the cooling vest. The Tr, Tsk, HR, RPE, and TS were unaffected in the cooling-vest trial during the first 45 minutes, but Tr rose at a slower rate in the cooling-vest trial (0.026°C.min-1 ± 0.008°C.min-1) than in the no-vest trial (0.032°C.min-1 ± 0.009°C.min-1). During the second 45-minute period, Tr, Tr rate of rise, Tsk, RPE, and TS were lower in the cooling-vest trial (Hedges g range, 0.55-0.84), but mean HR was unaffected. Wearing a cooling vest during soccer-specific intermittent running in the heat reduced physiological and perceptual strain but did not increase peak sprint speed.

#3 Bone quality in young adults with intellectual disability involved in adapted competitive football
Reference: Eur J Sport Sci. 2019 Jan 9:1-10. doi: 10.1080/17461391.2018.1563633. [Epub ahead of print]
Authors: Lizondo V, Caplliure-Llopis J, Escrivá D, De La Rubia JE, Barrios C
Summary: The objective of this study was to analyse bone quality parameters of football players with intellectual disability (ID) participating in adapted competitive football. Sixty-seven male football players with ID were studied: 22 with Down syndrome (DS) and 45 without DS. The average age was 26 years (range: 16 ̶ 50 years). A group of 25 age-matched sedentary individuals with ID (11 DS and 14 non-DS) and another group of 20 healthy participants of the same age group not involved in competitive football were comparatively analysed. There were no differences in the bone quality parameters when the healthy sedentary individuals were compared with both the sedentary and the football players with ID. However, the speed of sound (SOS), T-score, and estimated bone mineral density (BMD) were of higher values in the football players with ID than in the sedentary ID group (p < 0.05). On comparing the football players with non-DS ID with the sedentary non-DS individuals, significant differences were noted in SOS (p < 0.01), T-scores (p < 0.01), and estimated BMD (p < 0.01). Four of the 45 non-DS (8.9%) and none of the football players with DS had T-scores less than -1.5. Two of the 14 sedentary non-DS participants (14.3%) had T-scores indicating osteoporosis. In summary, the ID population actively involved in football showed higher values of bone mass parameters than their sedentary ID and healthy peers. The participants with non-DS ID showed a higher prevalence of osteoporosis than the football players with DS. Participation in sports seems to prevent bone loss in individuals with ID.

#4 Dual Kinect v2 system can capture lower limb kinematics reasonably well in a clinical setting: concurrent validity of a dual camera markerless motion capture system in professional football players
Reference: BMJ Open Sport Exerc Med. 2018 Dec 17;4(1):e000441. doi: 10.1136/bmjsem-2018-000441. eCollection 2018.
Authors: Kotsifaki A, Whiteley R, Hansen C
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Summary: The purpose was to determine whether a dual-camera markerless motion capture system can be used for lower limb kinematic evaluation in athletes in a preseason screening setting. Thirty-four (n=34) healthy athletes participated. Three dimensional lower limb kinematics during three functional tests: Single Leg Squat (SLS), Single Leg Jump, Modified Counter-movement Jump. The tests were simultaneously recorded using both a marker-based motion capture system and two Kinect v2 cameras using iPi Mocap Studio software. Excellent agreement between systems for the flexion/extension range of motion of the shin during all tests and for the thigh abduction/adduction during SLS were seen. For peak angles, results showed excellent agreement for knee flexion. Poor correlation was seen for the rotation movements. This study supports the use of dual Kinect v2 configuration with the iPi software as a valid tool for assessment of sagittal and frontal plane hip and knee kinematic parameters but not axial rotation in athletes.

#5 Don't Turn Blind! The Relationship Between Exploration Before Ball Possession and On-Ball Performance in Association Football
Reference: Front Psychol. 2018 Dec 10;9:2520. doi: 10.3389/fpsyg.2018.02520. eCollection 2018.
Authors: McGuckian TB, Cole MH, Jordet G, Chalkley D, Pepping GJ
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Summary: Visual exploratory action - scanning movements expressed through left and right rotation of the head - allows perception of a surrounding environment and supports prospective actions. In the dynamically changing football environment, the extent to which exploratory action benefits a player's subsequent performance with the ball is likely influenced by how and when the exploratory action occurs. Although few studies have examined the relationship between visual exploration and on-pitch football performance, it has been reported that a higher frequency of exploratory head movement up to 10-s before receiving the ball increases the likelihood of successful performance with the ball. This study investigated the relationship between head turn frequency and head turn excursion, and how and when exploratory head movement - within 10-s before ball possession - is related to performance with the ball in 11v11 match-play. Thirty-two semi-elite football players competed in 11v11 match-play. Head turn frequency and head turn excursion before ball possession were quantified with wearable inertial measurement units, and actions with the ball were coded via notational analysis. Odds ratio calculations were conducted to determine the associations between exploration variables and on-ball performance outcomes. A total of 783 actions with the ball were analyzed. Results revealed a strong relationship between head turn frequency and head turn excursion. Further, a higher than average head turn frequency and head turn excursion before receiving the ball resulted in a higher likelihood of turning with the ball, playing a pass in the attacking direction, and playing a pass to an area that is opposite to which it was received from. The strength of these outcomes varied for different time periods before receiving the ball. When players explored their environment with higher than average head turn frequency and excursion, they used more complex action opportunities afforded by the surrounding environment. Considerations for future research and practical implications are discussed.

#6 Use of viscosupplementation for the recovery of active football players complaining of knee pain
Reference: Open Access J Sports Med. 2018 Dec 24;10:11-15. doi: 10.2147/OAJSM.S164693. eCollection 2019.
Authors: Migliore A, Giannini S, Bizzi E, Massafra U, Cassol M, Abilius MJM, Boni G
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Summary: The aim of this study is to investigate the effect of intra-articular hyaluronic acid administration in active football players complaining of knee pain after sports activity. Efficacy and safety profiles of intra-articular hyaluronic acid and time needed for football players to recover and restart sports activity were examined. Clinical data of active football players reporting knee pain after sports activity were included in this retrospective study. All patients who received an intra-articular injection at time 0 and after 2 weeks were included in the study. Patients underwent laboratory examination, knee X-ray, ultrasound, and clinical examination before receiving the intra-articular injection. Effusions or cysts were drained before injections. Lequesne index score, pain visual analog scale (VAS) score, and patient's global assessment score were recorded at time 0 (day of the first injection), 1 and 2 days after the first injection, at 2 weeks (day of the second injection), and at follow-up visits. Only data from patients completing the follow-up were analyzed. Data from 17 patients were analyzed: 16 males and one female, of which three were professional players (two males and one female) and 14 were nonprofessional players. The mean age of patients was 39.8±11.8 years. Two patients (one male and one female) showed joint effusion. Two patients reported relevant joint pain after injection that regressed without any medication. At the first week, all parameters examined indicated improvement that was maintained until the end of follow-up. One day after the first and second injection, patients reported a slight increase in pain VAS score, which was not statistically significant, and the pain resolved after 1 day. All patients successfully restarted playing after the first injection within 3.1±2.0 days and kept playing after the second injection following our indication (1 day of break). The use of a medium-molecular weight hyaluronic acid in football players affected by knee osteoarthritis seems efficacious and safe and resulted, in our experience, a stable improvement of symptoms; moreover, it allowed a rapid restart of sports activity. Larger studies on larger populations are needed to confirm these findings.

#7 The value of tibial mounted inertial measurement units to quantify running kinetics in elite football (soccer) players. A reliability and agreement study using a research orientated and a clinically orientated system
Reference: J Electromyogr Kinesiol. 2019 Jan 7;44:156-164. doi: 10.1016/j.jelekin.2019.01.001. [Epub ahead of print]
Authors: Hughes T, Jones RK, Starbuck C, Sergeant JC, Callaghan MJ
Summary: In elite football, measurement of running kinetics with inertial measurement units (IMUs) may be useful as a component of periodic health examination (PHE). This study determined the reliability of, and agreement between a research orientated IMU and clinically orientated IMU system for initial peak acceleration (IPA) and IPA symmetry index (SI) measurement during running in elite footballers. On consecutive days, 16 participants performed treadmill running at 14kmph and 18kmph. Both IMUs measured IPA and IPA SI concurrently. All measurements had good or excellent within-session reliability (intraclass correlation coefficient (ICC2,1) range = 0.79-0.96, IPA standard error of measurement (SEM) range = 0.19-0.62 g, IPA SI SEM range = 2.50-8.05%). Only the research orientated IMU demonstrated acceptable minimal detectable changes (MDCs) for IPA at 14kmph (range = 7.46-9.80%) and IPA SI at both speeds (range = 6.92-9.21%). Considering both systems, between-session IPA reliability ranged from fair to good (ICC2,1 range = 0.63-0.87, SEM range = 0.51-1.10 g) and poor to fair for IPA SI (ICC2,1 range = 0.32-0.65, SEM range = 8.07-11.18%). All MDCs were >10%. For IPA and SI, the 95% levels of agreement indicated poor between system agreement. Therefore, the use of IMUs to evaluate treadmill running kinetics cannot be recommended in this population as a PHE test to identify prognostic factors for injuries or for rehabilitation purposes.

#8 Premenstrual Syndrome, Inflammatory Status, and Mood States in Soccer Players
Reference: Neuroimmunomodulation. 2019 Jan 17:1-6. doi: 10.1159/000494559. [Epub ahead of print]
Authors: Foster R, Vaisberg M, Bachi ALL, Dos Santos JMB, de Paula Vieira R, Luna-Junior LA, Araújo MP, Parmigiano TR, Borges F, Di-Bella ZIKJ
Summary: The aim was to evaluate the relationship between the inflammatory profile and mood states in the different phases of the menstrual cycle in soccer players with and without premenstrual syndrome (PMS). Data on the menstrual cycle and mood states were collected using the Daily Symptom Report and the Brunel Mood Scale. Cytokine and stress hormone concentrations were measured in urine by flow cytometry before and after a game in the luteal phase and in the follicular phase of one menstrual cycle. In all, 59.6% of the athletes had PMS. The PMS group showed higher concentrations of interleukin (IL)-1β, IL-6, and IL-8 than the athletes without PMS. After the game, IL-6 decreased in the follicular phase and the luteal phase. The tumor necrosis factor-α levels were higher in the group without PMS during the post-game follicular phase than before the game. In the PMS group, tension was higher in the follicular phase before the game and depression was higher in the pre-game luteal phase than in the group without PMS. The PMS group also presented a negative correlation between depression and IL-10 levels in the pre-game follicular phase. Finally, in the pre-game luteal phase were found positive correlations between growth hormone and IL-10. PMS influences the inflammatory condition related to mood states and stress hormones in female soccer players.

#9 Nutrition-Related Considerations in Soccer: A Review
Reference: Am J Orthop (Belle Mead NJ). 2018 Dec;47(12). doi: 10.12788/ajo.2018.0100.
Authors: Keen R
Summary: Soccer is the world's most popular sport. As the sport has grown, so have the physical demands and the search for ways to edge out the competition with the use of sports science and nutrition. The demands, which include intense training, ≥90 minutes matches, congested fixtures, and travel, lead to increased energy and nutrient requirements, stress on the body, and risk of impaired sleep cycles. Identifying key areas to enhance a player's performance is an ongoing effort because of individual differences. Moreover, new information is being discovered via research, and advancing technology to measure performance is always evolving. This article focuses on the core nutrition principles known to lay the foundation for a better soccer player. These principles are obvious for some; however, nutrition and hydration are often undervalued, leaving the individual player with the responsibility to eat right. This review addresses the most applicable nutrition-related recommendations for soccer players.

#10 Limb Differences in Unipedal Balance Performance in Young Male Soccer Players with Different Ages
Reference: Sports (Basel). 2019 Jan 11;7(1). pii: E20. doi: 10.3390/sports7010020.
Authors: Muehlbauer T, Schwiertz G, Brueckner D, Kiss R, Panzer S
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Summary: In soccer, the dominant leg is frequently used for passing and kicking while standing on the non-dominant leg. Consequently, postural control in the standing leg might be superior compared to the kicking leg and is further enhanced with increasing age (i.e., level of playing experience). Unfortunately, leg differences in postural control are associated with an increased risk of injuries. Thus, we examined differences between limbs in unipedal balance performance in young soccer players at different ages. Performance in the Lower Quarter Y Balance Test (YBT-LQ) of the dominant and non-dominant leg and anthropometry was assessed in 76 young male soccer players (under-13 years [U13]: n = 19, U15: n = 14, U17: n = 21, U19: n = 22). Maximal reach distances (% leg length) and the composite scores were used for further analyses. Statistical analyses yielded no statistically significant main effects of leg or significant Leg × Age interactions, irrespective of the measure investigated. However, limb differences in the anterior reach direction were above the proposed cut-off value of >4 cm, which is indicative of increased injury risk. Further, statistically significant main effects of age were found for all investigated parameters, indicating larger reach distances in older (U19) compared to younger (U13) players (except for U15 players). Although reach differences between legs were non-significant, the value in the anterior reach direction was higher than the cut-off value of >4 cm in all age groups. This is indicative of an increased injury risk, and thus injury prevention programs should be part of the training of young soccer players.

#11 Recruiting Older Men to Walking Football: A Pilot Feasibility Study
Reference: Explore (NY). 2018 Dec 11. pii: S1550-8307(18)30194-0. doi: 10.1016/j.explore.2018.12.001. [Epub ahead of print]
Authors: McEwan G, Buchan D, Cowan D, Arthur R, Sanderson M, Macrae E
Summary: Walking football (soccer) has recently emerged as a physical activity option targeted at older males to enhance health and wellbeing. This pilot study aimed to examine the feasibility of recruiting and retaining males aged 50 years and over to an 8-week walking football programme in a professional football club. Participants were recruited via social media and assigned to an intervention group or a wait-list control group. The intervention group engaged in 1 h of walking football a week led by a community coach from the professional football club, followed by an optional social session in the club facility. Physiological and psychological outcome measures were obtained onsite at the football club facility (aiding compliance and retention) at baseline and following 8-weeks, from both groups. Semi-structured interviews were conducted after the 8-week programme and 1 year later, to explore motivations for engagement and the social impact. The opportunity to engage in football and the link to a professional football club were key attractions. All participants recruited were overweight, sedentary, exhibited blood pressures outside normal ranges, and all but two were hypertensive. Adherence to the programme was 90% over 8 weeks, and of the participants who were contacted after one year, all (n = 6) had maintained engagement in walking football. Walking football is therefore a feasible, cost-effective method of recruiting and retaining males aged 50 years and over to a physical activity programme, though attrition is to be expected.





Latest research in football - week 1 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Visualizing a Team's Goal Chances in Soccer from Attacking Events: A Bayesian Inference Approach
Reference: Big Data. 2018 Dec 1;6(4):271-290. doi: 10.1089/big.2018.0071. Epub 2018 Dec 13.
Authors: Whitaker GA, Silva R, Edwards D
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Summary: We consider the task of determining the number of chances a soccer team creates, along with the composite nature of each chance-the players involved and the locations on the pitch of the assist and the chance. We infer this information using data consisting solely of attacking events, which the authors believe to be the first approach of its kind. We propose an interpretable Bayesian inference approach and implement a Poisson model to capture chance occurrences, from which we infer team abilities. We then use a Gaussian mixture model to capture the areas on the pitch a player makes an assist/takes a chance. This approach allows the visualization of differences between players in the way they approach attacking play (making assists/taking chances). We apply the resulting scheme to the 2016/2017 English Premier League, capturing team abilities to create chances, before highlighting key areas where players have most impact.

#2 Predicting the defensive performance of individual players in one vs. one soccer games
Reference: PLoS One. 2018 Dec 31;13(12):e0209822. doi: 10.1371/journal.pone.0209822. eCollection 2018.
Authors: Wilson RS, Smith NMA, Santiago PRP, Camata T, Ramos SP, Caetano FG, Cunha SA, Sandes de Souza AP, Moura FA
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Summary: The aim of this study was to use technical skill and physical performance and coaches' rankings to predict the defensive performance of junior soccer players. Twenty-one male players (mean age 17.2 years, SD = 1.1) were recruited from the Londrina Junior Team Football Academy in Brazil. Data were collected during regular training sessions. After participants had warmed up, players were asked to either dribble the ball or sprint through five custom circuits that varied in average curvature (0-1.37 radians.m-1). In addition, four coaches were asked to rank the players from best to worst in defensive ability. Dribbling, sprinting, and coaches' rankings were then compared with defending performance as assessed in the one vs. one competitions (N = 1090 paired-trials: 40-65 trials per individual), in which they acted as defender or attacker in turn. When defending, the objective was to steal the ball or prevent the attacker from running around them with the ball into a scoring zone. Testing occurred over three days. Overall, dribbling performance (r = 0.56; P = 0.008) and coaches' ranking (r = 0.59; P = 0.004) were significantly related to defensive ability; sprinting performance was not (r = 0.20; P = 0.38). Though dribbling performance and coaches' ranking each explained 30% and 37% of the variance in defensive performance, respectively, the two predictors were not related (r = 0.27; P = 0.23), so combined these traits explained more than half the variance in defensive performance. In conclusion, the current study demonstrates that including only one metric of closed-skill performance-dribbling speed-doubles the ability of coaches to identify their best defensive players in one vs. one scenarios.

#3 Patellar and Achilles Tendon Stiffness in Elite Soccer Players Assessed Using Myotonometric Measurements
Reference: Sports Health. 2019 Jan 2:1941738118820517. doi: 10.1177/1941738118820517. [Epub ahead of print]
Authors: Cristi-Sánchez I, Danes-Daetz C, Neira A, Ferrada W, Yáñez Díaz R, Silvestre Aguirre R
Summary: Tendon overuse injuries are an issue in elite footballers (soccer players) and may affect tendon function. Achilles and patellar tendinopathy are the most frequent pathologies. Tendon stiffness, the relationship between the force applied to a tendon and the displacement exerted, may help represent tendon function. Stiffness is affected by training and pathology. Nevertheless, information regarding this mechanical property is lacking for elite soccer athletes. Achilles and patellar tendon stiffness assessed using myotonometric measurements will be greater in elite soccer athletes than in control participants. Forty-nine elite soccer athletes and 49 control participants were evaluated during the 2017 preseason. A handheld device was used to measure Achilles and patellar tendon stiffness. Dominant and nondominant limbs were assessed for both groups. A significantly stiffer patellar tendon was found for both the dominant and the nondominant limb in the elite soccer athletes compared with the control group. Nevertheless, no differences were found in Achilles tendon stiffness between groups. When comparing between playing positions in soccer athletes, no significant differences were found for both tendons. Greater patellar tendon stiffness may be related to an improvement in force transmission during muscle contraction. On the other hand, it seems that after years of professional training, Achilles tendon stiffness does not change, conserving the storing-releasing function of elastic energy. The nonsignificant differences between positions may be attributable to the years of homogeneous training that the players underwent. The present study shows another technique for measuring mechanical properties of tendons in soccer athletes that could be used in clinical settings. In the future, this technique may help clinicians choose the best exercise protocol to address impairments in tendon stiffness.

#4 Examination of Physical Characteristics and Positional Differences in Professional Soccer Players in Qatar
Reference: Sports (Basel). 2018 Dec 31;7(1). pii: E9. doi: 10.3390/sports7010009.
Authors: Wik EH, Auliffe SM, Read PJ
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Summary: Physical characteristics in professional soccer differ between competition levels and playing positions, and normative data aid practitioners in profiling their players to optimize performance and reduce injury risk. Given the paucity of research in Arabic soccer populations, the purpose of this study was to provide position-specific normative values for professional players competing in the Qatar Stars League. One hundred and ninety-five players completed a musculoskeletal assessment as part of an annual periodic health examination. Tests included measures of range of motion (hip, ankle, and hamstring), bilateral and unilateral jump performance, and quadriceps/hamstring (isokinetic/NordBord), hip adduction/abduction (eccentric), and groin (isometric) strength. Descriptive data were examined, and positional differences were analyzed using a one-way analysis of variance (ANOVA). Goalkeepers were significantly heavier (p < 0.01), had a higher body mass index (p < 0.05) than outfield positions and demonstrated greater absolute strength. Defenders were the strongest relative to body mass, and these differences were significant (p < 0.05) versus goalkeepers and strikers. No meaningful between-group comparisons were apparent for jumping or range of motion tests. Compared to mean values from other professional leagues, soccer players in Qatar appear to be shorter, lighter and display inferior strength and jump capacities. These data can be used to tailor training and rehabilitation programs to the specifics of the league and position in which the athletes compete.

#5 Photobiomodulation therapy as a tool to prevent hamstring strain injuries by reducing soccer-induced fatigue on hamstring muscles
Reference: Lasers Med Sci. 2019 Jan 3. doi: 10.1007/s10103-018-02709-w. [Epub ahead of print]
Authors: Dornelles MP, Fritsch CG, Sonda FC, Johnson DS, Leal-Junior ECP, Vaz MA, Baroni BM
Summary: Muscle fatigue is a potential risk factor for hamstring strain injuries in soccer players. The aim of this study was to verify the effect of photobiomodulation therapy (PBMT) on the hamstrings' muscle fatigue of soccer players during a simulated match. Twelve male amateur soccer players (~ 25 years) participated in this randomized, crossover, double-blinded, placebo-controlled trial. The volunteers were evaluated in two sessions, with a minimum 7-day interval. At each session, volunteers received either PBMT (300 J per thigh) or placebo treatment on the hamstrings prior to the simulated soccer match. Muscle strength and functional capacity were evaluated through isokinetic dynamometry and countermovement jump (CMJ) tests, respectively, before and immediately after the simulated soccer match. Players had lower reductions on hamstring eccentric peak torque [4.85% (ES = 0.31) vs. 8.72% (ES = 0.50)], hamstring-to-quadriceps torque ratio [3.60% (ES = 0.24) vs. 7.75% (ES = 0.50)], and CMJ height [1.77% (ES = 0.09) vs. 5.47% (ES = 0.32)] when treated with PBMT compared to placebo. Magnitude-based inference supports that PBMT promoted 75%, 69%, and 53% chances for beneficial effects on hamstring eccentric peak torque, hamstring-to-quadriceps torque ratio, and CMJ height, respectively, compared to placebo treatment. In conclusion, PBMT applied before a simulated soccer match proved to be effective in attenuating the hamstrings' muscle fatigue. These findings support PBMT as a promising tool to prevent hamstring strain injury in soccer players.

#6 Accelerations - a new approach to quantify physical performance decline in male elite soccer?
Reference: Eur J Sport Sci. 2019 Jan 11:1-9. doi: 10.1080/17461391.2019.1566403. [Epub ahead of print]
Authors: Dalen T, Lorås H, Hjelde GH, Kjøsnes TN, Wisløff U
Summary: The aim of the current study was (1) to investigate whether the number of accelerations is a more precise estimate of performance decline in soccer compared to distances with high-speed running (HSR) and (2) to compare changes in the number of accelerations and HSR distances across playing positions in order to examine whether the match profiles of the physical measures are consistent or demonstrate high interposition variability. The dataset includes domestic home games (N = 34) over three full seasons (2012-2014) for a team in the Norwegian Elite League. The change in the number of accelerations throughout the match demonstrates a more clear pattern compared to the distance covered by HSR. In numbers of accelerations, a systematic and linear decrease can be observed throughout the match, with 34% less accelerations from the first to the last 5-minute period of the game (6.7 vs. 4.4 accelerations). This pattern of results captures the change in the number of accelerations across all positions. HSR distance had more variability during the match. All five positions investigated displayed a similar trend in accelerations and HSR profiles after the peak periods in each half. In contrast to the absolute number of accelerations, there were major positional differences in the mean HSR distance during the match. Our data suggest a more visible performance decline in the number of accelerations from the start to the end of the game, than the decline in the distance covered by HSR distance.

#7 A Nationwide Follow-up Survey on the Effectiveness of an Implemented Neuromuscular Training Program to Reduce Acute Knee Injuries in Soccer Players
Reference: Orthop J Sports Med. 2018 Dec 21;6(12):2325967118813841. doi: 10.1177/2325967118813841. eCollection 2018 Dec.
Authors: Åman M, Larsén K, Forssblad M, Näsmark A, Waldén M, Hägglund M
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Summary: A cruciate ligament (CL) injury is a severe injury in soccer. Neuromuscular training programs have a well-documented preventive effect, but there are few studies on the effectiveness of such a program at a national level. The Swedish Knee Control Program (KCP) was found to be effective in preventing CL injuries in youth female soccer players. The KCP was implemented nationwide in Sweden in 2010. The purpose was to evaluate the effectiveness of the Swedish KCP in reducing acute knee injuries in soccer players at a nationwide level. All licensed soccer players in Sweden are covered by the same insurance company. Using this insurance database, around 17,500 acute knee injuries that were reported to the insurance company between 2006 and 2015 were included in the study. By matching the number of licensed soccer players with the number of reported injuries each year, the annual incidence of knee and CL injuries was able to be calculated. To evaluate the spread of the KCP nationally, a questionnaire was sent to all 24 Swedish district football associations (FAs) with questions regarding KCP education. The number of downloads of the KCP mobile application (app) was obtained. The incidence of CL injuries decreased during the study period for both male (from 2.9 to 2.4 per 1000 player-years) and female players (from 4.9 to 3.9 per 1000 player-years). The overall incidence of knee injuries decreased in both male (from 5.6 to 4.6 per 1000 player-years) and female players (from 8.7 to 6.4 per 1000 player-years). Comparing before and after the nationwide implementation of the KCP, there was a decrease in the incidence of CL injuries by 6% (rate ratio [RR], 0.94 [95% CI, 0.89-0.98]) in male players and 13% (RR, 0.87 [95% CI, 0.81-0.92]) in female players and a decrease in the incidence of knee injuries by 8% (RR, 0.92 [95% CI, 0.89-0.96]) and 21% (RR, 0.79 [95% CI, 0.75-0.83]), respectively (P < .01 for all). This trend corresponded to a reduction of approximately 100 CL injuries each year in Sweden. A total of 21 of 24 district FAs held organized KCP educational courses during the study period. The percentage of district FAs holding KCP courses was between 46% and 79% each year. There were 101,236 downloads of the KCP app. The KCP can be considered partially implemented nationwide, and the incidence of knee and CL injuries has decreased in both sexes at a nationwide level.

#8 Cardio respiratory response: Validation of new modifications of Bruce protocol for exercise testing and training in elite Saudi triathlon and soccer players
Reference: Saudi J Biol Sci. 2019 Jan;26(1):105-111. doi: 10.1016/j.sjbs.2017.05.009. Epub 2017 May 19.
Authors: Badawy MM, Muaidi QI
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Summary: The Bruce protocol is the traditional method used to assess maximal fitness level, although it may have limitations, such as its short duration and large work rate increases, with very high levels of exertion that consist of speed/incline combinations. Modifications have been added to elicit similar maximal fitness achievements. The authors of this experimental trial have proposed a new treadmill protocol that allows optimal test duration in conjunction with peak oxygen consumption 'VO2max', and with appropriate patient comfort and safety during both exercise testing and training. Twenty-two elite Saudi players, comprising eleven Saudi triathlon athletes, and eleven Saudi elite soccer players, BMI, body fat mass percentage, body fat free mass percentage. cardiovascular parameter; including, absolute and relative "VO2max" as well as maximal heart rate "HR max", were assessed during a graded treadmill running modified protocol, using a Quark Cardio Pulmonary Exercise Testing Unit (CPET). Descriptive statistics were used to obtain the anthropometric characteristics, including comparisons between the means, independent sample T-test and a regression analysis, to test the association of the protocol duration and the corresponding, dependent variables. It is often difficult to achieve a high cardiorespiratory response, VO2max, without an association to high values of HR max, and peak perceived exertion. This may lead to cardiovascular risk. Our new modifications can provide a practical, valid alternative protocol to be used comfortably both during exercise testing and training, rather than performance testing only, to achieve high VO2max with minimal cardiovascular stress.

#9 Knee Angle Affects Posterior Chain Muscle Activation During an Isometric Test Used in Soccer Players
Reference: Sports (Basel). 2019 Jan 4;7(1). pii: E13. doi: 10.3390/sports7010013.
Authors: Read PJ, Turner AN, Clarke R, Applebee S, Hughes J
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Summary: It has been suggested that altering the knee flexion angle during a commonly used supine isometric strength test developed with professional soccer players changes preferential hamstring muscle recruitment. The aim of this study was to examine the electromyography (EMG) knee joint-angle relationship during this test, as these data are currently unknown. Ten recreational male soccer athletes (age: 28 ± 2.4 years) were recruited and performed a supine isometric strength test on their dominant leg with the knee placed at two pre-selected flexion angles (30° and 90°). The surface EMG of the gluteus maximus, biceps femoris, semitendinosus, and medial gastrocnemius was measured, in addition to the within-session reliability (intraclass correlation coefficient (ICC) and coefficient of variation (CV)). Within-session reliability showed large variation dependent upon the test position and muscle measured (CV% = 8.8⁻36.1) Absolute mean EMG activity and percentage of maximum voluntary isometric contraction (MVIC) indicated different magnitudes of activation between the two test positions; however, significant mean differences were present for the biceps femoris only with greater activation recorded at the 30° knee angle (% MVIC: 31 ± 9 vs. 22 ± 7; p = 0.002). These differences (30% mean difference) were greater than the observed typical measurement error (CV% = 13.1⁻14.3 for the 90° and 30° test positions, respectively). Furthermore, the percentage MVIC showed a trend of heightened activation of all muscles with the knee positioned at 30°, but there was also more within-subject variation, and this was more pronounced for the gluteus maximus (CV% = 36.1 vs. 19.8) and medial gastrocnemius (CV% 31 vs. 22.6). These results indicate that biceps femoris and overall posterior chain muscle activation is increased with the knee positioned at 30° of flexion; however, the 90° angle displayed less variation in performance within individual participants, especially in the gluteus maximus and medial gastrocnemius. Thus, practitioners using this test to assess hamstring muscle strength should ensure appropriate familiarisation is afforded, and then may wish to prioritise the 30° knee position.

#10 Interpersonal Coordination in Soccer: Interpreting Literature to Enhance the Representativeness of Task Design, From Dyads to Teams
Reference: Front Psychol. 2018 Dec 11;9:2550. doi: 10.3389/fpsyg.2018.02550. eCollection 2018.
Authors: Santos R, Duarte R, Davids K, Teoldo I
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Summary: Interpersonal coordination in soccer has become a trending topic in sports sciences, and several studies have examined how interpersonal coordination unfolds at different levels (i.e., dyads, sub-groups, teams). Investigations have largely focused on interactional behaviors at micro and macro levels through tasks from dyadic (i.e., 1 vs. 1) to team (i.e., 11 vs. 11) levels. However, as the degree of representativeness of a task depends on the magnitude of the relationship between simulated and intended environments, it is necessary to address a discussion on the correspondence between competitive and practice/experimental settings in soccer. The aims of this paper are to: (i) provide a brief description of the main concepts underlying the subject of interpersonal coordination in sports teams; (ii) demonstrate, through exemplar research findings, how interpersonal coordination in soccer unfolds at different scales; and (iii), discuss how coaches and researchers may ensure representativeness for practice and experimental tasks. We observed that papers addressing the analysis of interpersonal coordination tendencies in soccer often resort to dyadic (one vs. one) or sub-group (many vs. many) experimental tasks, instead of full-sized (11 vs. 11) games. Consequently, the extent to which such patterns reflect those observed in competition is somewhat uncertain. The design of practice and/or experimental tasks that rely on sub-phases of the game (e.g., 1 vs. 1, 4 vs. 4) should ensure the preservation of players' behavior patterns in intended match conditions (11 vs. 11). This can be accomplished by measuring the level of action fidelity of the task, ensuring correspondence and successful transfer across contexts.

#12 Use of Saliva in Alternative to Serum Sampling to Monitor Biomarkers Modifications in Professional Soccer Players
Reference: Front Physiol. 2018 Dec 20;9:1828. doi: 10.3389/fphys.2018.01828. eCollection 2018.
Authors: Francavilla VC, Vitale F, Ciaccio M, Bongiovanni T, Marotta C, Caldarella R, Todaro L, Zarcone M, Muratore R, Bellia C, Francavilla G, Mazzucco W
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Summary: We aimed to investigate the correlation between serum and salivary concentrations of steroid hormones and IgA, and the variation in concentrations of these biomarkers, across a soccer competitive season in a sample of players playing for an Italian major League team. Thirty-five elite male soccer players were recruited and assessed for salivary hormones (cortisol, testosterone, T/C‰ and DHEA-S) and IgA at three different time-points: (t1) after the pre-season period and 16 official matches played; (t2) after a winter break and three official matches played; (t3) 2 days after the final match of the championship and 19 matches played. Players were also tested for blood biomarkers (ser-C, ser-T, ser-T/C‰, ser-IgA, ACTH) at two detection times (t1 and t3). Blood samples were collected immediately after saliva sampling. The Spearman's rank correlation was used to explore the correlation between blood and salivary concentrations of cortisol, free testosterone and IgA in the different time points. One-way ANOVA and permutation test were performed to explore changes by time of hormones and IgA concentrations over the competitive season. We documented a positive correlation between serum and saliva concentrations for Cortisol at t1 (+58.2%; p-value = 0.002) and t3 (+54.2%; p-value = 0.018) and for Testosterone at t1 (+42.0%; p-value = 0.033). Moreover, a positive variation was documented across the season (D = t3-t1) for Cortisol (D = +6.83; SEM = ±2.70; Var% = +37.6; p-value = 0.032), Testosterone (D = +0.33; SEM = ±0.07; Var% = +27.3; p-value = 0.002) and DHEA-S (D = +44.48; SEM = ±18.54; Var% = +82.0; p-value = 0.042), while a decrease of sal-T/C ratio and no variation in salivary IgA concentrations were reported. In conclusion, our findings support for experimental use of saliva samples to monitor steroid hormones modifications in professional soccer players across a competitive season.





Latest research in football - week 52 - 2018

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Reliability and validity of field-based fitness tests in youth soccer players
Reference: Eur J Sport Sci. 2018 Dec 27:1-12. doi: 10.1080/17461391.2018.1556739. [Epub ahead of print]
Authors: Dugdale JH, Arthur CA, Sanders D, Hunter AM
Summary: This study aimed to establish between-day reliability and validity of commonly used field-based fitness tests in youth soccer players of varied age and playing standards, and to discriminate between players without ("unidentified") or with ("identified") a direct route to professional football through their existing club pathway. Three-hundred-and-seventy-three Scottish youth soccer players (U11-U17) from three different playing standards (amateur, development, performance) completed a battery of commonly used generic field-based fitness tests (grip dynamometry, standing broad jump, countermovement vertical jump, 505 (505COD) and T-Drill (T-Test) change of direction and 10/20 m sprint tests) on two separate occasions within 7-14 days. The majority of field-based fitness tests selected within this study proved to be reliable measures of physical performance (ICC = 0.83-0.97; p < .01). However, COD tests showed weaker reliability in younger participants (ICC = 0.57-0.79; p < .01). The field-based fitness testing battery significantly discriminated between the unidentified and identified players; χ2 (7) = 101.646, p < .001, with 70.2% of players being correctly classified. We have shown field-based fitness tests to be reliable measures of physical performance in youth soccer players. However, results from the 505COD and T-Test change of direction tests may be more variable in younger players, potentially due to complex demands of these tests and the limited training age established by these players. While the testing battery selected in this study was able to discriminate between unidentified and identified players, findings were inconsistent when attempting to differentiate between individual playing standards within the "identified" player group (development vs. performance).

#2 Factors influencing hydration status during a National Collegiate Athletics Association division 1 soccer preseason
Reference: J Sci Med Sport. 2018 Dec 14. pii: S1440-2440(18)31245-3. doi: 10.1016/j.jsams.2018.12.005. [Epub ahead of print]
Authors: Sekiguchi Y, Adams WM, Curtis RM, Benjamin CL, Casa DJ
Summary: The purpose was to investigate the roles that training load and environmental conditions have on fluid balance during a collegiate men's soccer preseason. Twenty-eight male collegiate soccer players (mean±SD; age, 20±1.7y; body mass (BM), 79.9±7.3kg; height, 180.9±6.8cm; body fat, 12.7±3.1%; VO2max, 50.7±4.3ml·kg-1·min-1) participated in this study. Prior to (PRE) and following (POST) each team session, BM, percent BM loss (%BML) and hydration status was measured. Participants donned a heart rate and GPS enabled monitor to measure training load. For all team activities, ambient temperature (TAMB) and relative humidity (RH) were obtained from the nearest local weather station. Participants consumed 500mL of water as part of the team-based hydration strategy before and after training session. Stepwise linear regression was used to identify the variables that predicted %BML. Significance was set a-priori p<0.05. Total distance covered predicted %BML during all preseason activities (r2=0.253, p<0.001), with TAMB and RH further adding to the model (r2=0.302, p<0.001). %BML never exceeded 2% of BM during any one session and daily variation in BM was <1% from baseline measures. Urine specific gravity was greater than 1.020 on 12/15days and UCOL was above 4 on 13/15days, indicating a state of hypohydration. Total distance covered was the best predictor for the extent of body water losses during a collegiate preseason. While the team-based hydration strategy during preseason was successful in minimizing fluid losses during activity, participants arrived hypohydrated 80% of the time, necessitating a greater focus on daily fluid needs.

#3 Assessing the validity of a video-based decision-making assessment for talent identification in youth soccer
Reference: J Sci Med Sport. 2018 Dec 21. pii: S1440-2440(18)30435-3. doi: 10.1016/j.jsams.2018.12.011. [Epub ahead of print]
Authors: Bennett KJM, Novak AR, Pluss MA, Coutts AJ, Fransen J
Summary: The aim was to investigate the construct and discriminant validity of a video-based decision-making assessment for talent identification in youth soccer. A total of 328 academy youth soccer players (tier one, tier two, and tier three) from three developmental stages (late childhood, early adolescence, and mid-adolescence) participated in this study. The control group consisted of 59 youth athletes with no soccer experience in the last five years. Players completed a video-based decision-making assessment on an iPad, with response accuracy and response time recorded for various attacking situations (2 vs. 1, 3 vs. 1, 3 vs. 2, 4 vs. 3, and 5 vs. 3). The video-based decision-making assessment showed some construct validity. Response times were significantly faster in early and mid-adolescent players when compared to those in the late childhood group. Furthermore, an overall decline in decision-making performance (i.e. decrease in response accuracy and increase in response time) was observed from the 2 vs. 1 to the 4 vs. 3 situations. The video-based decision-making assessment lacked discriminant validity as minimal differences between academies were evident for response accuracy and response time. Only response accuracy was able to discriminate youth academy soccer players from the control group to some extent. Coaches and sporting professionals should apply caution when interpreting data from practical, video-based decision-making assessments. There is currently limited conclusive evidence supporting the effectiveness of these assessments for talent identification.

#4 Influences of Synchronized Metronome Training on Soccer Players' Timing Ability, Performance Accuracy, and Lower-Limb Kinematics
Reference: Front Psychol. 2018 Dec 7;9:2469. doi: 10.3389/fpsyg.2018.02469. eCollection 2018.
Authors: Rönnqvist L, McDonald R, Sommer M
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Summary: Planning and performance of all complex movement requires timing, integration, and coordination between sensory-perception and motor production to be successful. Despite this, there is limited research into "if" and "how" timing training may influence movement performance in athletes. The aim of the present study was to investigate the effect of synchronized metronome training (SMT) on sensorimotor timing ability, and in view of that, if improved timing may be transferred to lower-limb movement planning, precision performance, and kinematics. The sample consisted of 24 female elite- and semi-elite soccer players, randomly assigned to receive SMT and a control group. The SMT group received 12 sessions of Interactive Metronome® (IM) training over 4 weeks. At pre- and post-test, timing-precision was assessed through hand and feet movement synchronization with rhythmic sound; and leg-movements performance accuracy, duration, and kinematics were recorded during embodied high cognitive-load stepping task (6 trials×20 s) by use of a optoelectronic motion capture system. Pre- to post-test comparisons showed significant timing improvements as an effect of the IM training. Significant pre- to post-test improvements on the stepping task performance were seen in an increasing number of accurate foot taps during the stepping task sequence and by shorter duration for the SMT-group only. No evident pre- to post-test effects of SMT on the kinematic parameters investigated were found. These findings signify that the guided attention and working-memory functioning may be positively affected by SMT training; thereby, resulting in better motor planning, performance, and movement precision. Still, independent of group and test-occasion, significant correlations were found between the participants' outcome performance differences and the kinematic parameters. It was found that a decreasing 3D movement distance and less segmented movements correlating negatively, and increasing velocity (speed) positively, with accuracy and performance duration, respectively. These findings are likely associated with inter-individual variations in the nature of higher-order cognitive processing capacity due to the highly cognitive demanding stepping task.

#5 Amyotrophic Lateral Sclerosis and soccer: an internet survey of 29 Italian players
Reference: Ann Ist Super Sanita. 2018 Oct-Dec;54(4):364-369. doi: 10.4415/ANN_18_04_14.
Authors: Vanacore N, Barbariol P, Caffari B, Lacorte E, Bacigalupo I, Spila Alegiani S
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Summary: Previous epidemiological studies reported a significantly higher risk of Amyotrophic Lateral Sclerosis (ALS) in Italian male soccer players. As a consequence, sports newspapers and news agencies focused on this issue and spread the news of 51 male soccer players with a reported diagnosis of ALS. We searched news on male Italian national soccer players with a reported diagnosis of ALS quoted from January 1, 1950 to July 31, 2016 in at least two Internet web sites or in books by journalists. A total of 39 male soccer players with a reported diagnosis of ALS were identified. Subjects were born from 1905 to 1973, 32 were currently deceased, 6 were still living, while the status of 1 player was unknown. All gathered information was available for 29 soccer players. The group had a mean age at diagnosis of 45.3 ± 12.2 years, a mean age at onset of symptoms of 46.4 ± 12.1 years, and a mean age at death of 50.9 ± 12.3 years. A significant inverse correlation between year of birth and age at onset of symptoms was observed, with a younger age at onset of symptoms in soccer players born in more recent years (r = -0.65, p < 0.01). Italian male soccer players with a reported diagnosis of ALS have a significantly younger age at diagnosis when compared to other European patients with ALS. Results support a possible relationship between soccer and the risk of ALS. We believe that further research is urgently needed in this field.

#6 Dark Chocolate Intake Positively Modulates Redox Status and Markers of Muscular Damage in Elite Football Athletes: A Randomized Controlled Study
Reference: Oxid Med Cell Longev. 2018 Nov 21;2018:4061901. doi: 10.1155/2018/4061901. eCollection 2018.
Authors: Cavarretta E, Peruzzi M, Del Vescovo R, Di Pilla F, Gobbi G, Serdoz A, Ferrara R, Schirone L, Sciarretta S, Nocella C, De Falco E, Schiavon S, Biondi-Zoccai G, Frati G, Carnevale R
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Summary: Intensive physical exercise may cause increase oxidative stress and muscular injury in elite football athletes. The aim of this study was to exploit the effect of cocoa polyphenols on oxidative stress and muscular injuries induced by intensive physical exercise in elite football players. Oxidant/antioxidant status and markers of muscle damage were evaluated in 24 elite football players and 15 controls. Furthermore, the 24 elite football players were randomly assigned to either a dark chocolate (>85% cocoa) intake (n = 12) or a control group (n = 12) for 30 days in a randomized controlled trial. Oxidative stress, antioxidant status, and muscle damage were assessed at baseline and after 30 days of chocolate intake. Compared to controls, elite football players showed lower antioxidant power and higher oxidative stress paralleled by an increase in muscle damage markers. After 30 days of dark chocolate intake, an increased antioxidant power was found in elite athletes assuming dark chocolate. Moreover, a significant reduction in muscle damage markers (CK and LDH, p < 0.001) was observed. In the control group, no changes were observed with the exception of an increase of sNox2-dp, H2O2, and myoglobin. A simple linear regression analysis showed that sNox2-dp was associated with a significant increase in muscle damage biomarker release (p = 0.001). An in vitro study also confirmed that polyphenol extracts significantly decreased oxidative stress in murine myoblast cell line C2C12-derived. These results indicate that polyphenol-rich nutrient supplementation by means of dark chocolate positively modulates redox status and reduced exercise-induced muscular injury biomarkers in elite football athletes.

#7 "Macro-structure" of developmental participation histories and "micro-structure" of practice of German female world-class and national-class football players
Reference: J Sports Sci. 2018 Dec 24:1-9. doi: 10.1080/02640414.2018.1558744. [Epub ahead of print]
Authors: Güllich A
Summary: The study examined the "micro-structure" of football practice and the "macro-structure" of participation history of female professional football players. Participants were 29 German 1st league (Bundesliga) players, 14 of whom played on the senior national team (Olympic Champion in 2016). A questionnaire recorded the players' positions, proportions of physical conditioning, drill-type skill exercises and playing forms within coach-led football practice, and the volume of coach-led practice and peer-led play, in both football and other sports, from childhood to adulthood. Analyses revealed that most athletes played various attacker and defender positions during development. National team players differed from their Bundesliga peers by less physical conditioning and greater proportions of playing forms within football practice. National team players also accumulated less total football practice until age 18 years, but more peer-led football and coach-led practice in other sports compared to their Bundesliga counterparts. Based on these variables, a binary logistic regression classified 93% of the national team and Bundesliga players correctly. Conclusion: A combination of long-term coach-led football practice involving a relatively large proportion of playing forms with considerable childhood/adolescent peer-led football play and coach-led practice in other sports may have facilitated adult performance among German female world-class football players.

#8 Comparison of head impact exposure in practice drills among multiple youth football teams
Reference: J Neurosurg Pediatr. 2018 Dec 21:1-9. doi: 10.3171/2018.9.PEDS18314. [Epub ahead of print]
Authors: Kelley ME, Espeland MA, Flood WC, Powers AK, Whitlow CT, Maldjian JA, Stitzel JD, Urban JE
Summary: Limiting contact in football practice can reduce the number of head impacts a player receives, but further research is needed to inform the modification of optimal drills that mitigate head impact exposure (HIE) while the player develops the skills needed to safely play the game. This study aimed to compare HIE in practice drills among 6 youth football teams and to evaluate the effect of a team on HIE. On-field head impact data were collected from athletes (ages 10-13 years) playing on 6 local youth football teams (teams A-F) during all practices using the Head Impact Telemetry System. Video was recorded and analyzed to verify and assign impacts to a specific drill. Drills were identified as follows: dummy/sled tackling, half install, install, install walk through, multiplayer tackle, Oklahoma, one-on-one, open field tackling, other, passing, position skill work, scrimmage, special teams, tackling drill stations, and technique. HIE was quantified in terms of impacts per player per minute (ppm) and peak linear and rotational head acceleration. Generalized linear models were used to assess differences in head impact magnitude and frequency among drills as well as among teams within the most common drills. Among 67 athlete-seasons, a total of 14,718 impacts during contact practices were collected and evaluated in this study. Among all 6 teams, the mean linear (p < 0.0001) and rotational (p < 0.0001) acceleration varied significantly among all drills. Open field tackling had significantly (p < 0.001) higher mean linear acceleration than all other drills. Multiplayer tackle had the highest mean impact rate (0.35 ppm). Significant variations in linear acceleration and impact rate were observed among teams within specific drills. Team A had the highest mean linear acceleration in install, one-on-one, and open field tackling and the highest mean impact rate in Oklahoma and position skill work. Although team A spent the greatest proportion of their practice on minimal- or no-player versus player contact drills (27%) compared to other teams, they had the highest median (20.2g) and 95th percentile (56.4g) linear acceleration in practice. Full-speed tackling and blocking drills resulted in the highest HIE. Reducing time spent on contact drills relative to minimal or no contact drills may not lower overall HIE. Instead, interventions such as reducing the speed of players engaged in contact, correcting tackling technique, and progressing to contact may reduce HIE more effectively.





Latest research in football - week 51 - 2018

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Pre-Practice Hydration Status in Soccer (Football) Players in a Cool Environment
Reference: Medicina (Kaunas). 2018 Dec 5;54(6). pii: E102. doi: 10.3390/medicina54060102.
Authors: Kiitam U, Voitkevica L, Timpmann S, Pontaga I, Ereline J, Unt E, Ööpik V
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Summary: Only a few studies have reported the pre-practice hydration status in soccer players (SPs) who train in a cool climate. The primary purpose of this study was to examine the hydration status of male semiprofessional SPs immediately before their regular training session in winter. The secondary purpose was to compare the urinary indices of the hydration status of Estonian and Latvian SPs. Pre-training urine samples were collected from 40 Estonian (age 22.1 ± 3.4 years, soccer training experience 13.7 ± 3.9 years) and 41 Latvian (age 20.8 ± 3.4 years, soccer training experience 13.3 ± 3.0 years) SPs and analyzed for urine specific gravity (USG). The average outdoor temperature during the sample collection period (January⁻March) was between -5.1 °C and 0.2 °C (Estonia) and -1.9 °C and -5.0 °C (Latvia). Results: The average pre-training USG of Estonian and Latvian SPs did not differ (P = 0.464). Pooling the data of Estonian and Latvian SPs yielded a mean USG value of 1.021 ± 0.007. Hypohydration (defined as a USG ≥ 1.020) was evident altogether in fifty SPs (61.7%) and one of them had a USG value greater than 1.030. Estonian and Latvian SPs do not differ in respect of USG and the prevalence of pre-training hypohydration is high in this athletic cohort. These findings suggest that SPs as well as their coaches, athletic trainers, and sports physicians should be better educated to recognize the importance of maintaining euhydration during the daily training routine in wintertime and to apply appropriate measures to avoid hypohydration.

#2 Injury Risk and Injury Burden Are Related to Age Group and Peak Height Velocity Among Talented Male Youth Soccer Players
Reference: Orthop J Sports Med. 2018 Dec 11;6(12):2325967118811042. doi: 10.1177/2325967118811042. eCollection 2018 Dec.
Authors: Bult HJ, Barendrecht M, Tak IJR
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Summary: The relationship between injury risk (IR) in age groups and periods around peak height velocity (PHV) remains unclear. PHV is defined as the moment of the largest increase in body height. The purpose was to investigate injury risk and injury burden as functions of growth velocity (periods around PHV) and chronological age groupings (under 12 years [U12] to U19) in talented youth male soccer players. Cohort study; Level of evidence, 2. A total of 170 players from the youth academy of a Dutch soccer club (highest professional league: Eredivisie) were observed for 1 to 3 seasons. Injuries, exposure, PHV age, and chronological age were registered. The injury incidence density (IID) and injury burden per 1000 hours of soccer participation, with 95% CIs, were calculated for 5 PHV periods and 7 age groups. These were compared with the overall cohort results using incidence ratios (IRs) and burden ratios (BRs) with 95% CIs. The mean age at PHV was 14.4 ± 0.65 years (range, 12.8-16.5 years). The mean IID for the total cohort was 8.34 injuries per 1000 hours (95% CI, 7.71-9.02). Compared with the overall mean, a significantly higher IID was found for PHV period 4+5 (IR, 1.31 [95% CI, 1.00-1.71]; P = .049) and for the U15 group (IR, 1.49 [95% CI, 1.24-1.79]; P < .001). The overall injury burden was 58.37 injury days per 1000 hours (95% CI, 56.66-60.13). In PHV period 4+5, the injury burden was significantly higher (BR, 1.53 [95% CI, 1.39-1.68]; P < .001) when compared with the overall mean. Also, compared with the overall mean, the injury burden was higher in the U16 (BR, 1.48 [95% CI, 1.39-1.58]; P < .001), U15 (BR, 1.28 [95% CI, 1.19-1.38]; P < .001), and U17 groups (BR, 1.21 [95% CI, 1.13-1.31]; P < .001). Talented young soccer players were more prone to injuries during the 6 months after PHV (31% above overall mean) as well as in the U15 group (49% above overall mean). Based on the higher injury burden in the U16 (48%), U15 (28%), and U17 (21%) groups, we suggest that research on injury risk factors and preventive measures should primarily target these age groups. Additional interventions based on PHV may be of limited value from a screening perspective. Further research is needed on the interaction between age groups and PHV periods.

#3 Anthropometry, Physical and Movement Features, and Repeated-sprint Ability in Soccer Players
Reference: Int J Sports Med. 2018 Dec 17. doi: 10.1055/a-0781-2473. [Epub ahead of print]
Authors: Campa F, Semprini G, Júdice PB, Messina G, Toselli S
Summary: This study aimed to evaluate the associations of anthropometry, functional movement patterns (FMP) and physical performance characteristics with repeated-sprint ability (RSA) in male youth soccer players. Thirty six athletes (ages 16.6±0.5 years, BMI 22.0±1.3 kg/m2) completed the RSA test and other physical tests including countermovement jump with (CMJA) and without the help of arms (CMJ), 10-m and 20-m straight-line sprints, Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo), and functional movement screen (FMS). In addition, a battery of anthropometric variables was measured. RSA performance components such as best time (BT), mean time (MT) and sprint decrement were calculated. Results showed that measures of physical performance derived from horizontal plane in 10-m and 20-m sprints, were more strongly associated (p<0.01) with RSA performance than those obtained with CMJ or CMJA (p<0.05). High correlations (p<0.01) were found between MT, BT and Yo-Yo distance (r=-0.79, r=-0.67, respectively), as well as with FMS scores (r=-0.68, r=-0.58, respectively). Anthropometric measures, such as fat mass, upper fat area, thigh fat area, calf muscle area, and endomorphy were associated with RSA components (p<0.05). Predictors for the RSA performance identified in the stepwise multivariate analysis included Yo-Yo distance, time in sprints, FMP, and calf muscle area.

#4 Do male and female soccer players differ in helping? A study on prosocial behavior among young players
Reference: PLoS One. 2018 Dec 17;13(12):e0209168. doi: 10.1371/journal.pone.0209168. eCollection 2018.
Authors: Van Lange PAM, Manesi Z, Meershoek RWJ, Yuan M, Dong M, Van Doesum NJ
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Summary: Acting prosocially can be quite challenging in one of the most salient intergroup contexts in contemporary society: Soccer. When winning is the ultimate goal, balancing self-interest with helping a fellow player in distress can be a tough decision; yet it happens. To date, we know little about what motivates soccer players to offer such help in the heat of the game. We propose that sex and what is at stake will matter in such prosocial dilemma situations. A pilot study (N = 107) indicated that female players may be more likely to help than male players, but this difference was only observed when the players are close to scoring position rather than far away from the goal (midfield). The main study (N = 366) finds that young soccer players show elevated inclinations to help in low-stakes situations, for example when their team is winning or when the outcome of the game seems pretty much decided. Contrariwise, helping intentions decline in high-stakes situations, for example when one's own team is losing, when one is close to a scoring position in the offense (rather than at the midfield), or when the outcome of the game is still uncertain. Furthermore, female players show somewhat greater inclinations to help than their male counterparts. The current data point at some differences for male and female soccer players, albeit small in effect size. In contrast, we conclude that especially quick cost-benefit judgments regarding the stakes can play a major role in decisions to help or not to help another player on the soccer field.

#5 Internal and External Loads in Training Week Before the Competition in U19 High-Level Soccer Players
Reference: J Strength Cond Res. 2018 Dec 14. doi: 10.1519/JSC.0000000000002975. [Epub ahead of print]
Authors: Martín-López Á, Mendes RS, Castillo-Rodríguez A
Summary: Nowadays, the information about the load in training sessions (TRs) and the relationship of these TRs with official competition are necessary to gain the sport success in soccer. The aim of this study was to quantify the different loads in TRs according to days before the competition (P-4, P-2, and P-1) on soccer players U19 based on their playing position and their sport success. Twenty-four male Spanish high-level players (age: 16.5 ± 0.5 years; height: 1.69 ± 0.04 m; and body mass: 63.0 ± 6.3 kg) participated in the study. They were grouped according to their playing position: external defenders, internal defenders (ID), external midfielders, internal midfielders (IM), and forwards (FO). To conduct the study, global positioning system technology was used, and a 1-way analysis of variance and Pearson correlation were performed. The main results revealed that the highest physical and physiological responses in the TRs were shown by ID, IM, and players without sport success (p < 0.05), and during P-2. In addition, sport success is predicted by the mean heart rate (R = 0.33; p < 0.001). As conclusion, players covering central positions in the playing field performed higher physical and physiological demands than players covering exterior or forward positions. Furthermore, physical and physiological responses during the TRs P-2 may be similar to the responses produced in competition match and are notably different depending on the sport success of the soccer player.

#6 The team's influence on physical and technical demands of elite goalkeepers in LaLiga: a longitudinal study in professional soccer
Reference: Res Sports Med. 2018 Dec 16:1-15. doi: 10.1080/15438627.2018.1555755. [Epub ahead of print]
Authors: Serrano C, Paredes-Hernández V, Sánchez-Sánchez J, Gallardo-Pérez J, Da Silva R, Porcel D, Colino E, García-Unanue J, Gallardo L
Summary: This study examined physical and technical demands and the influence of the team's level on elite goalkeepers' performance during six consecutive seasons in Spanish Professional Soccer League. The goalkeepers' performance data were obtained by analyzing a total of 3,874 matches using a multiple-camera computerized tracking system. The physical and technical match variables registered were: distance traveled; distance Sprinted and the number of sprints; total number of passes; successful passes; pass percentage; recovered balls; lost balls; ratio lost balls: recovered balls, and number of saves. The results showed that the number of saves made has shown a significant reduction (p < 0.001). When comparing between the teams' level, the goalkeepers of the worst classified teams showed a greater distance traveled by sprint (+3.72 m, IC95%: 1.00-6.44, ES: 0.41, p = 0.008). In conclusion, the results the influence of the team's level on the technical and physical parameters of the goalkeepers during the last six seasons

#7 Intra-seasonal variation of injury patterns among German Bundesliga soccer players
Reference: J Sci Med Sport. 2018 Dec 6. pii: S1440-2440(18)30449-3. doi: 10.1016/j.jsams.2018.12.001. [Epub ahead of print]
Authors: Leventer L, Eek F, Lames M
Summary: High fluctuations in injury-risk during the playing season in soccer have been reported. As seasons are structured in periods with homogenous loads and intensities, we investigated injury-risk over season periods, contrarily to previous studies adopting a month-based approach. Incidence-rate ratios (IRRs) for match and training injuries were compared across six consecutive seasons of German Bundesliga, divided into six periods each: Pre-season (PS), winter-break (WB), quarter 1-4: (Q1-Q4). Significant variations in injury-risk were observed for match and training injuries. IRRs in matches was 1.30 (95% CI: 1.11-1.53) times higher in Q3 and 1.53 (95% CI: 1.31-1.78) higher in Q4 compared to Q1. For training injuries, IRR peaked in Q1 and Q3 followed by a marked decrease in each subsequent quarter. Compared to Q4, IRR was 1.62 (95% CI: 1.40-1.86) times higher during Q3 and 1.78 (95% CI: 1.53-2.07) times higher in Q1. IRR was significantly higher in the competitive season compared to pre-season across match (IRR: 2.00, 95% CI: 1.30-3.00) and training (IRR: 1.27, 95% CI: 1.11-1.43) injuries. The increased match IRRs later during the season indicate that, in practice, coaches should consider putting even more emphasis on recovery in the last part of the season. Moreover, training injuries seem to indicate a carry-over effect. Further studies need to investigate how training during preparatory phases can be implemented in a way that prevents injuries during the competitive season.

#8 Changes in injury incidences and causes in Swiss amateur soccer between the years 2004 and 2015
Reference: Swiss Med Wkly. 2018 Dec 15;148:w14690. doi: smw.2018.14690. eCollection 2018 Dec 3.
Authors: Gebert A, Gerber M, Pühse U, Faude O, Stamm H, Lamprecht M
Summary: Injury prevention in amateur soccer has been promoted in recent years, but only a few studies have addressed long-term changes in injury incidence in amateur soccer. However, better knowledge of changes with respect to injury incidences and causes could make an important contribution to improving prevention strategies. The aim of this study was to investigate the long-term development of injury incidence in Swiss amateur soccer with respect to level of play, injury causes and injury characteristics. A representative sample of about 1000 Swiss amateur soccer coaches was interviewed by telephone in 2004, 2008 and 2015. They were asked to recall their last game and to report details on all injuries. For every injury, the coaches were asked to remember injury characteristics and causes. The same procedure was repeated for all games that took place during the previous 4 weeks. Additionally, all training injuries in the previous 4 weeks were recorded in detail. The incidence of game injuries decreased between the years 2004 and 2008 from 15.1 (95% confidence interval [CI] 14.2&ndash;16.0) to 13.3 (95% CI 12.4&ndash;14.2) injuries per 1000 hours, and increased between the years 2008 and 2015 to 16.5 (95% CI 15.5&ndash;17.4) injuries per 1000 hours. Between 2004 and 2015, the rate of contact injuries during games increased by 19.1%. The incidence of foul play injuries in games increased by 25.5% between 2008 and 2015. The rise in total training injury incidence between the years 2004 (2.4, 95% CI 2.2&ndash;2.7) and 2015 (2.9, 95% CI 2.6&ndash;3.1) was caused by a 22.2% higher rate of noncontact injuries. During the same period, game and training injury incidences increased across all amateur soccer leagues without exception, but these changes did not reach statistical significance. In 2015, the incidence of injuries leading to medical attention was higher than in 2004 (game 20.0%, training 37.5%). There is evidence that injury incidence in Swiss amateur soccer has increased in past years. &nbsp.

#9 The Effect of Block Versus Daily Undulating Periodization on Strength and Performance in Adolescent Football Players
Reference: Int J Sports Physiol Perform. 2018 Dec 20:1-25. doi: 10.1123/ijspp.2018-0609. [Epub ahead of print]
Authors: Gavanda S, Geisler S, Quittmann OJ, Schiffer T
Summary: Muscle mass, strength and power are important factors for performance. To improve these characteristics, periodized resistance training is used. However, there is no consensus regarding the most effective periodization model. Therefore the purpose of this study was to compare the effects of block (BLOCK) versus daily undulating periodization (DUP) on body composition, hypertrophy, strength, performance and power in adolescent American football players. Forty-seven subjects participated in this study (M±SD age = 17±0.8 years; strength training experience = 0.93±0.99 years). Pre- and post-measurements consisted of body mass (BM), fat mass (FMkg), body fat percentage (relFM), fat-free mass (FFM), muscle mass (MM) and muscle thickness of the M. vastus lateralis (VL), M. rectus femoris (RF) and M. triceps brachii (TB), one repetition maximum (1-RM) back squat (BS) and bench press (BP), countermovement jump (CMJ), estimated peak power from vertical jump performance (Wpeak), medicine ball put (MBP) and 40 yd sprint. Subjects were randomly assigned in either the BLOCK or DUP group prior to the 12 week intervention period consisting of 3 full-body sessions per week. Both groups displayed significantly higher BM (p<0.001), relFM (p=0.005), FFM (p<0.001), MM (p<0.001), RF (p<0.001), VL (p<0.001), TB (p<0.001), BS (p<0.001), BP (p<0.001), CMJ (p<0.001), Wpeak (p<0.001) and significant lower sprint times (p<0.001) following twelve weeks of resistance training with no difference between groups. Resistance training was effective to increase muscle mass, strength, power and performance in adolescent athletes. BLOCK and DUP affect anthropometric measures and physical performance equally.

#10 Transfer market activities and sportive performance in European first football leagues: A dynamic network approach
Reference: PLoS One. 2018 Dec 19;13(12):e0209362. doi: 10.1371/journal.pone.0209362. eCollection 2018.
Authors: Matesanz D, Holzmayer F, Torgler B, Schmidt SL, Ortega GJ
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Summary: Professional football is a globalized game in which players are the most valuable assets for clubs. In this study, we explore the evolution of the football players' transfer network among 21 European first leagues between the seasons 1996/1997 and 2015/2016. From a topological point of view, we show that this network achieved an upper limit expansion around season 2007/2008, thereafter becoming more connected and dense. Using a machine learning approach based on Self-Organizing Maps and Principal Component Analysis we confirm that European competitions, such as the UEFA Champions League or UEFA Europa League, are indeed a "money game" where the clubs with the highest transfer spending achieve better sportive performance. Some clubs' transfer market activities also affect domestic performance. We conclude from our findings that the relationship between transfer spending and domestic or international sportive performance might lead to substantial inequality between clubs and leagues, while potentially creating a virtuous (vicious) circle in which these variables reinforce (weaken) each other.





Latest research in football - week 50 - 2018

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Current Soccer Footwear, Its Role in Injuries and Potential for Improvement
Reference: Sports Med Int Open. 2018 May 25;2(2):E52-E61. doi: 10.1055/a-0608-4229. eCollection 2018 Apr.
Authors: Blanchard S, Palestri J, Guer JL, Behr M
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Summary: Soccer is the most popular sport in the world and generates great financial revenue. It is also a sport whose practice has evolved considerably in terms of intensity and commitment, and in which the intrinsic risk of injury (not directly related to an interaction with the environment) is particularly high. In this context, the cleated shoe as a major component of soccer equipment may play a key role in the overexposure to injury. Soccer shoe evolution is all the more challenging, because design and mechanical structure differ in many points compared to other modern shoes developed for sports such as running, tennis and basketball. This critical review aims to elucidate the characteristics of modern soccer footwear and their possible link to soccer-specific injuries, focusing on the following areas: (1) ergonomics, comfort and proprioception; (2) shoe mechanical characteristics; (3) field surfaces and shoe design.

#2 Does a bounding exercise program prevent hamstring injuries in adult male soccer players? - A cluster -RCT
Reference: Scand J Med Sci Sports. 2018 Dec 9. doi: 10.1111/sms.13353. [Epub ahead of print]
Authors: van de Hoef PAS, Brink MSM, Huisstede BMAB, van Smeden MM, de Vries NN, Goedhart EAE, Gouttebarge VV, Backx FJGF
Summary: Although the Nordic Hamstring Exercise (NHE) prevents hamstring injury in soccer players effectively, the annual incidence of these injuries still increases. This may be because of poor long-term compliance with the program. Furthermore, the timing and amplitude of gluteal and core muscle activation seem to play an important role in hamstring injury prevention, the NHE program was not designed to improve activation of these muscles. Therefore, we propose plyometric training as an alternative to reduce hamstring injuries soccer players. The purpose was to determine the preventive effect of the Bounding Exercise Program (BEP) on hamstring injury incidence and severity in adult male amateur soccer players. Thirty-two soccer teams competing in the first-class amateur league were cluster-randomized into the intervention or control group. Both groups were instructed to perform their regular training program, and the intervention group additionally performed BEP. Information about player characteristics was gathered at baseline and exposure, hamstring injuries and BEP compliance were weekly registered during one season (2016-2017). The data of 400 players were analyzed. In total, 57 players sustained 65 hamstring injuries. The injury incidence was 1.12/1000 hours in the intervention group and 1.39/1000 hours in the control group. There were no statistically significant differences in hamstring injury incidence (OR=0.89, 95% CI 0.46-1.75) or severity between the groups (p>0.48). In this large cluster-randomized controlled trial, no evidence was found for plyometric training in its current form to reduce hamstring injuries in amateur soccer players.

#3 Professional Soccer Players' Return to Play and Performance After Operative Repair of Achilles Tendon Rupture
Reference: Orthop J Sports Med. 2018 Nov 28;6(11):2325967118810772. doi: 10.1177/2325967118810772. eCollection 2018 Nov.
Authors: Trofa DP, Noback PC, Caldwell JE, Miller JC, Greisberg JK, Ahmad CS, Vosseller JT
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Summary: The majority of Achilles tendon ruptures are sports related; however, no investigation has examined the impact of surgical repair for complete ruptures on professional soccer players. The purpose was to examine the return to play, playing time, and performance of professional soccer players following Achilles tendon repair. Union of European Football Associations (UEFA) and Major League Soccer (MLS) athletes who sustained a primary complete Achilles tendon rupture and were treated surgically between 1988 and 2014 were identified via public injury reports. Demographic information and performance-related statistics for the identified athletes were recorded for the season before surgery and 2 seasons after surgery and were compared with information for matched controls. Statistical analyses were used to assess differences in recorded metrics. A total of 24 athletes with Achilles ruptures met inclusion criteria, 17 (70.8%) of whom were able to return to play. On average, players had 8.3 years of professional-level experience prior to sustaining an Achilles rupture. Among athletes who returned to play, no differences were found in the number of games played or started, minutes played, or goals scored 1 year postoperatively compared with the year prior to injury. However, 2 years postoperatively, these athletes played 28.3% (P = .028) fewer minutes compared with their preoperative season, despite starting and playing in an equivalent number of games. Matched controls had baseline playing time and performance statistics similar to those of players. However, controls played and started in significantly more games and played more minutes at 1 and 2 years compared with players (P < .05). No differences were found in goals scored at any time point. This is the first investigation examining the effect of an Achilles repair on the career of professional soccer players. This is a difficult injury that most commonly occurs in veteran players and prevents 29.2% of players from returning to play despite surgical management. Additionally, athletes able to return to play were found to play fewer minutes 2 years postoperatively compared with their baseline as well as playing less at 1 and 2 years postoperatively compared with uninjured matched controls. The reduction in playing time following an Achilles repair has significant implications for professional players and teams.

#4 Changes in Echocardiographic Parameters among Beninese Soccer Referees during the Division 1 Championship in 2016
Reference: J Sports Med (Hindawi Publ Corp). 2018 Nov 7;2018:6024574. doi: 10.1155/2018/6024574. eCollection 2018.
Authors: Coffi Q, Arnaud S, Polycarpe G, Hyacinthe A, Folly M, Basile N, Murielle H, Martin HD
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Summary: The goal of this study was to describe the echocardiographic parameters of soccer referees and to examine the changes in these parameters after a period of intensive physical exercise. We conducted a prospective study that included Beninese soccer referees. The study of the geometry and function of the left ventricle (LV) was made at the beginning and end of the national Division 1 championship, which was held during the course of 10 weeks. There were 37 referees included in this study; 20 at the national level (G1: 27.8 ± 6.6 years) and 17 at the international level (G2: 32.1 ± 6.4 years). Dimensions of the LV were normal for all the referees. At the beginning of the championship, 51.3% of the referees had a normal LV geometry, 37.8% had concentric remodelling, 2.7% had concentric hypertrophy, and 8.1% had eccentric hypertrophy. In the group of referees with normal LV geometry, a modification in concentric remodelling at the end of the championship was seen in 30% of the referees in G1, 33.3% of the referees in G2, and 31.6% of the whole sample. In the group of subjects who presented concentric LV remodelling, a modification in the normal geometry was observed in 37.5% of those in G1, in 0% of those in G2, and in 21.4% of the whole sample. The cases of LV hypertrophy showed no change regardless of the group considered. An LV ejection fraction of more than 50% and an E/E' ratio less than 8 were found in all referees. All the referees studied had normal cardiac morphology and function. The intensity of the physical load was insufficient to impact this morphology.

#5 In-season training load quantification of one-, two- and three-game week schedules in a top European professional soccer team
Reference: Physiol Behav. 2018 Dec 6. pii: S0031-9384(18)30585-7. doi: 10.1016/j.physbeh.2018.11.036. [Epub ahead of print]
Authors: Oliveira R, Brito J, Martins A, Mendes B, Calvete F, Carriço S, Ferraz R, Marques M
Summary: Top European soccer teams that play in UEFA competitions often participate in one, two- or three-games per week. Therefore, it is necessary to understand the variations in training load (TL) according to each team's competitive schedule. The aim of this study was to quantify internal and external TLs within five microcycles: M4 and M5 - one-game weeks; M1 and M3 - two-game weeks; M2 - three-game week). The sample consisted of thirteen elite soccer players. A global positioning system (GPS) was used to measure the total distance covered and distances of different exercise training zones (1-5), the session ratings of perceived exertion (s-RPE) scores and the amount of creatine kinase (CK) created during daily training sessions for the 2015-2016 in-season period. The data were analysed with respect to the number of days prior to a given match. The main results indicate that there was a significant difference in training intensity for zone 1 between M5 and M3 (4010.2 ± 103.5 and 4507.6 ± 133.0 m, respectively); a significant difference in training intensity for zone 3 between M4 and M2 (686.1 ± 42.8 and 801.2 ± 61.2 m, respectively); a significant difference in the duration of the training sessions and matches between M5 and M2 (69.2 ± 2.1 and 79.6 ± 2.3) and M1 and M2 (69.7 ± 1.0 and 79.6 ± 2.3); and finally, there was a significant difference in CK between M1 and M5 (325.5 ± 155.0 and 194.4 ± 48.9). Moreover, there was a significant decrease in TL in the last day prior to a match, for all microcycles and all variables. There was no significant difference with respect to s-RPE. This study provides the first report of daily external and internal TLs and weekly accumulated load (training sessions and match demands) during one, two, and three-game week schedules in a group of elite soccer players. Expected significant differences are found in daily and accumulated loads for within- and between-game schedules. A similar pattern is exhibited for one- and two-game week microcycles regarding the day before the match, which exhibits a decrease in all variables.

#6 Estimating fat-free mass in elite youth male soccer players: cross-validation of different field methods and development of prediction equation
Reference: J Sports Sci. 2018 Dec 11:1-8. doi: 10.1080/02640414.2018.1551045. [Epub ahead of print]
Authors: Munguía-Izquierdo D, Suárez-Arrones L, Di Salvo V, Paredes-Hernández V, Ara I, Mendez-Villanueva A
Summary: This study determined the most effective field method for quantifying fat-free mass (FFM) in elite youth male soccer players compared to dual X-ray absorptiometry (DXA) values and to develop prediction equations for FFM based on anthropometric variables. Forty-one male elite-standard youth soccer players, ages 16.2-18.0 years, undertook FFM assessments including bioelectrical impedance analysis, and different skinfold-based prediction equations. DXA provided a criterion measure of FFM. Correlation coefficients, bias, limits of agreement, and differences were used as validity measures, and regression analyses to develop soccer-specific prediction equations. Slaughter et al (1988), Durnin and Wormersley (1974), and Sarria et al (1998) equations showed the lowest biases, and no significant, standardized, and substantial differences against DXA. The new youth soccer-specific anthropometric equation explained 91% of the DXA-derived FFM variance using three circumferences, eight skinfolds, and one bone breadth. All field methods compared in this study may not be adequate for estimating FFM in elite youth male soccer players, except the equations of Slaughter et al (1988), Durnin and Wormersley (1974), and Sarria et al (1998). We recommend the use of the new soccer-specific equation proposed in this study as a valid alternative to DXA to quantify FFM among elite youth male players.

#7 Dynamic and Static Assessment of Single Leg Postural Control in Female Soccer Players
Reference: J Sport Rehabil. 2018 Dec 11:1-19. doi: 10.1123/jsr.2018-0072. [Epub ahead of print]
Authors: Meiners KM, Loudon JK
Summary: Various methods are available for assessment of static and dynamic postural stability. The purpose of this study was to investigate the relationship between dynamic postural stability as measured by the Star Excursion Balance Test (SEBT) and static postural sway assessment as measured by the Technobody™ Prokin in female soccer players. A secondary purpose was to determine side-to-side symmetry in this cohort. 18 female soccer players completed testing on the SEBT and TechnobodyTM Prokin balance device. Outcome measures were: anterior, posterior medial, and posterior lateral reaches from the SEBT and Center of Pressure (COP) in the X and Y axis and Standard Deviation of movement in the forward-backward and medial-lateral directions from the force plate on left and right legs. Bivariate correlations were determined between the 8 measures. Additionally, paired Wilcoxon Signed Ranks were performed to determine similarity between limb scores. All measures on both the SEBT and postural sway assessment were significantly correlated when comparing dominant to non-dominant lower extremities with exception of SD of movement in both X and Y axis. When correlating results of the SEBT with postural sway assessment, a significant correlation was found between SEBT right lower extremity posterior lateral reach (r=.567, p<.05) and summed SEBT (r=.486, p<.05) and the COP in the Y axis. A significant correlation was also found on the left lower extremity, with Standard Deviation of movement forward-backward and SEBT posterior medial reach (r=-.511, p<.05). Dynamic postural tests and static postural tests provide different information to the overall assessment of balance in the female soccer player. Relationship between variables differed based on the subject's lower extremity dominance.

#8 Validation study of the Functional Assessment Scale for Acute Hamstring injuries in Spanish professional soccer players
Reference: Clin Rehabil. 2018 Dec 10:269215518815540. doi: 10.1177/0269215518815540. [Epub ahead of print]
Authors: Hernández-Sanchez S, Korakakis V, Malliaropoulos N, Moreno-Perez V
Summary: The purpose of the study was to cross-culturally adapt and validate the Functional Assessment Scale for acute hamstring injury for professional Spanish-speaking soccer players. Clinical measurement study. Cross-cultural adaptation was conducted following international recommendations. Indicators of validity, reliability and responsiveness are provided. The Spanish version of the Functional Assessment Scale for acute hamstring injury scale was administered to 165 participants: 45 professional soccer players with acute hamstring muscle injury diagnosis, 40 healthy subjects, 40 individuals at-risk for a hamstring muscle injury and 40 patients with injuries of the lower limb other than hamstring muscle injury. The Functional Assessment Scale for acute hamstring injury were main outcome measures. Spanish version of the Quality of Life Short-Form 36 questionnaire (SF-36) and the Lower Limb Functional Index (LLFI) were used as the reference measures. Cronbach's alpha (internal consistency) for the Spanish version of the Functional Assessment Scale for acute hamstring injury scale was >0.8. The intraclass correlation coefficient using the two-way random model (ICC2,1) (test-retest) was 0.993 (95% confidence interval (CI): 0.991-0.995; P < 0.05). In the exploratory factor analysis, a one-factor solution explained 85% of the variance. Subjects with hamstring muscle injury scored significantly lower than the other groups in the Spanish version of the Functional Assessment Scale for acute hamstring injury scale ( P < 0.001). The Spanish version of the Functional Assessment Scale for acute hamstring injury scale score within the hamstring muscle injury group showed moderate and significant correlations with SF-36 physical components (Spearman's rs > 0.6; P < 0.001), and LLFI score at baseline ( rs = 0.42; P < 0.01). The standard error of measurement (SEM) and minimum detectable change threshold (MDC95%) were 2.6 and 7.2 points, respectively. The responsiveness indicators have an effect size of 3.62, and the standardized response mean is 3.24. The Spanish version of the Functional Assessment Scale for acute hamstring injury scale showed satisfactory psychometric properties. It can be considered a reliable and valid instrument to assess the functional impact of acute hamstring muscle injury in professional Spanish-speaking football players.

#9 Effective But Not Adhered to: How Can We Improve Adherence to Evidence-Based Hamstring Injury Prevention in Amateur Football?
Reference: Clin J Sport Med. 2018 Dec 13. doi: 10.1097/JSM.0000000000000710. [Epub ahead of print]
Authors: van der Horst N, Hoef SV, Otterloo PV, Klein M, Brink M, Backx F
Summary: The purpose was to investigate adherence to a Nordic hamstring exercise (NHE) program in a real-world context of male amateur football, and the perceptions of end users (players) and intervention deliverers (coaches and medical staff) about adherence to this proven effective program.
Dutch amateur football. Two hundred sixty-four players, 23 coaches, and 29 medical staff from Dutch amateur football teams that participated in a national randomized controlled trial 2 years earlier. Nordic hamstring exercise program were used as the independent variable. Main outcome measures were the Nordic hamstring exercise program adherence during 2014 and 2015. Intervention or control group allocation during the trial, transfers, and personal perception about adherence to the program were also examined. Of all players, 69% reported never, 16% sometimes, 6% frequently, 5% often, and 4% always performing exercises of the NHE program. Adherence to the NHE program was higher among players who had been in the NHE arm of the previous trial and among players who had not been transferred to another club compared with players who had been transferred. Key factors in stimulating players to adhere to the NHE program were knowledge of the NHE and personal motivation. Coaches and medical staff members also mentioned personal motivation and consensus with team staff as key factors to encourage NHE adherence. Among high-level male amateur football players, adherence to an evidence-based hamstring injury-prevention program was very low. It is essential to recognize factors that stimulate or limit adherence to injury-prevention programs for effective programs to actually lead to a reduction in hamstring injuries in a real-world context.

#10 Does Night-Training Load Affect Sleep Patterns and Nocturnal Cardiac Autonomic Activity in High-Level Female Soccer Players?
Reference: Int J Sports Physiol Perform. 2018 Dec 20:1-26. doi: 10.1123/ijspp.2018-0652. [Epub ahead of print]
Authors: Costa JA, Brito J, Nakamura FY, Oliveira EM, Costa OP, Rebelo AN
Summary: The purpose was to analyse whether exercise training conducted at night disturbs sleep and affects nocturnal cardiac autonomic control in high-level female athletes. Eighteen high-level female soccer players (mean±SD; age: 20.4±2.1 years) wore actigraphs and heart rate (HR) monitors during night-sleep throughout night-training days (n=8) and resting days (n=8), for 3 consecutive weeks. This was a longitudinal study that measured internal training load, sleep, nocturnal cardiac autonomic activity, and well-being ratings prior to training sessions. Training load varied across training days (e.g., training impulse range; mean±SD; ES [95% confidence interval]: 72.9±18.8 to 138.4±29.6 a.u.; F(4,62)=32.331; ηp2=0.673 [0.001-0.16], large effect; p<0.001). However, no differences in subjective well-being ratings were observed, although ES was large. Total sleep time (training days vs. resting days: 7:17±0:47 hours vs. 7:51±0:42 hours; ES=0.742 [0.59-0.92], p=0.005; moderate effect) and sleep onset time (00:58±0:19 vs. 00:44±0:16 hours; ES=0.802 [0.68-0.94], p=0.001; moderate effect) were negatively affected after night-training. In addition, small effects were detected for wake up time, time in bed, and sleep latency (p>0.05). No differences were detected in HR variability (HRV) during sleep (range of lnRMSSD: 4.3±0.4 to 4.5±0.4 ln[ms] vs. 4.6±0.3 to 4.5±0.4 ln[ms]; F(3,52)=2.148; p>0.05; ηp2=0.112 [0.01-0.25], medium effect), but the HR during sleep was significantly higher after training days (range of HR: 56±4 to 63±7 vs. 54±4 to 57±6 b.p.m; F(2,32) = 15.956; p<0.001 ηp2=0.484 [0.20-0.63], large effect). Overall, the results indicate that exercise training conducted at night may disturb sleep and affect HR, whereas limited effects can be expected in HRV assessed during sleep in high-level female soccer players.