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Latest research in football - week 46 - 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 public data set of spatio-temporal match events in soccer competitions
Reference: Sci Data. 2019 Oct 28;6(1):236. doi: 10.1038/s41597-019-0247-7.
Authors: Pappalardo L, Cintia P, Rossi A, Massucco E, Ferragina P, Pedreschi D, Giannotti F
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Summary: Soccer analytics is attracting increasing interest in academia and industry, thanks to the availability of sensing technologies that provide high-fidelity data streams for every match. Unfortunately, these detailed data are owned by specialized companies and hence are rarely publicly available for scientific research. To fill this gap, this paper describes the largest open collection of soccer-logs ever released, containing all the spatio-temporal events (passes, shots, fouls, etc.) that occured during each match for an entire season of seven prominent soccer competitions. Each match event contains information about its position, time, outcome, player and characteristics. The nature of team sports like soccer, halfway between the abstraction of a game and the reality of complex social systems, combined with the unique size and composition of this dataset, provide an ideal ground for tackling a wide range of data science problems, including the measurement and evaluation of performance, both at individual and at collective level, and the determinants of success and failure.

#2 Soccer Injuries in Children and Adolescents
Reference: Pediatrics. 2019 Nov;144(5). pii: e20192759. doi: 10.1542/peds.2019-2759.
Authors: Watson A, Mjaanes JM
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Summary: Participation in youth soccer in the United States continues to increase steadily, with a greater percentage of preadolescent participants than perhaps any other youth sport. Despite the wide-ranging health benefits of participation in organized sports, injuries occur and represent a threat to the health and performance of young athletes. Youth soccer has a greater reported injury rate than many other contact sports, and recent studies suggest that injury rates are increasing. Large increases in the incidence of concussions in youth soccer have been reported, and anterior cruciate ligament injuries remain a significant problem in this sport, particularly among female athletes. Considerable new research has identified a number of modifiable risk factors for lower-extremity injuries and concussion, and several prevention programs have been identified to reduce the risk of injury. Rule enforcement and fair play also serve an important role in reducing the risk of injury among youth soccer participants. This report provides an updated review of the relevant literature as well as recommendations to promote the safe participation of children and adolescents in soccer.

#3 Arachnoid cyst in young soccer players complicated by chronic subdural hematoma: personal experience and review of the literature
Reference: Acta Neurol Belg. 2019 Oct 25. doi: 10.1007/s13760-019-01224-1. [Epub ahead of print]
Authors: Gregori F, Colistra D, Mancarella C, Chiarella V, Marotta N, Domenicucci M
Summary: Arachnoid cysts (ACs) are congenital intracranial benign cavities originating from the meninges during embryological development. Several studies have shown the existence of a relationship between AC and a higher risk to develop ipsilateral chronic subdural hematoma (CSH) especially in a young population. In the presence of an AC, the practice of sport activities may expose young patients to minor head trauma and to an increased risk of developing CSH. We describe three cases of young soccer players with AC associated with CSH. Then, we performed a literature review of all the reported cases in the literature of patients younger than 18 years with AC-associated CSH related to sport practice. A total of 33 cases, including the three cases reported by us, are analyzed. Soccer is the most represented sport activity in this association (39% of cases). The treatment of choice is surgical in all patients, with burr hole or craniotomy in similar proportions. In one-third of patients, the AC has been fenestrated. Outcome is good in all the reported cases. We reviewed the main pathogenic theories, the main surgical strategies described in literature, as well as recurrence rate of CSH, the association of AC and cranial deformities, and the clinical outcome. AC might be associated with skull deformities, but their real incidence remains unclear. The clinical detection of such anomalies should suggest performing further radiological investigations. If the presence of AC is confirmed, the practice of sport activities should not be avoided, as the real incidence of AC-associated CSH is not clear yet and the reported outcomes in literature are good. Surgical treatment of AC-associated CSH should be hematoma removal through burr hole, reserving AC fenestration only for cases with intracystic bleeding or recurrences. The surgeon should adequately advise and inform the young patients and their families that they could have an increased risk of developing CSH given by the presence of the AC, and that they should be referred to a neurosurgical center if they become symptomatic.

#4 Prevalence of Relative Age Effect in Russian Soccer: The Role of Chronological Age and Performance
Reference: Int J Environ Res Public Health. 2019 Oct 23;16(21). pii: E4055. doi: 10.3390/ijerph16214055.
Authors: Bezuglov EN, Nikolaidis PT, Khaitin V, Usmanova E, Luibushkina A, Repetiuk A, Waśkiewicz Z, Gerasimuk D, Rosemann T, Knechtle B
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Summary: The relative age effect (RAE) has been well studied in adolescent and adult soccer players; however, less information has been available about children engaged in regular soccer training and the role of performance. Thus, the aim of the present study was to examine the prevalence of RAE in children and adolescent soccer players, as well as the role of age and performance. Russian soccer players (n = 10,446) of various ages, playing positions and performance levels were examined for their date of birth. It was observed that RAE was widespread in Russian soccer teams of all age groups. RAE was most pronounced in children teams of the top tier Russian soccer academies and junior Russia national teams, where the proportions of soccer players born in the first quarter were 43.9% and 39.8%, respectively, whereas those born in the fourth quarter of the year were 7.7% and 6.3%, respectively. In top tier soccer academies, RAE did not vary by age group. In the middle tier soccer academies, RAE was less pronounced. It was still prevalent in the junior teams of the top tier clubs of the Russian Premier League, where 14.3% of the soccer players were born in the fourth quarter of the year compared to 42.9% born in the first quarter of the year. RAE can be observed in the top tier Russian adult teams as well, although it is less pronounced there. In summary, RAE is highly prevalent in Russian children and junior soccer and is associated with the level of competitiveness. At the same time, the proportion of players born in the fourth quarter of the year is higher in adult teams than in junior and youth teams, which is most likely due to the wider selection of players, not limited by their age and place of residence. In junior teams, RAE results in a bias towards selection of players who are more physically mature, whereas children who may be more talented but are less developed due to their younger chronological age tend to be overlooked.

#5 Women Are at Higher Risk for Concussions Due to Ball or Equipment Contact in Soccer and Lacrosse
Reference: Clin Orthop Relat Res. 2019 Oct 17. doi: 10.1097/CORR.0000000000000995. [Epub ahead of print]
Authors: Ling DI, Cheng J, Santiago K, Ammerman B, Jivanelli B, Hannafin J, Casey E
Summary: There is ample evidence to suggest sex- and gender-based differences in the incidence of sports-related concussions. The mechanisms of concussion may vary between male and female athletes and contribute to this observed difference. Understanding the underlying etiology by pooling data from primary studies across different settings and sport types will inform interventions that can reduce concussion rates. Specifically, we asked: (1) In which sports are female athletes less likely to experience concussions from player contact? (2) In which sports are female athletes more likely to experience concussions because of ball or equipment contact? PubMed, EMBASE, and Cochrane Library databases were searched to identify articles published from January 2000 to December 2018. Ten studies met the inclusion criteria, which were studies that reported concussion incidence by mechanism for both male and female athletes. Exclusion criteria included non-English studies, conference abstracts, and studies on non-sports related concussions. The sports represented by the 10 studies included ice hockey (n = 4), soccer (n = 5), basketball (n = 4), baseball/softball (n = 4), and lacrosse (n = 5). The rate ratio was calculated as the incidence rate in female athletes/male athletes for each concussion mechanism or activity. Data were pooled using the DerSimonian-Laird random-effects model. Study quality was assessed with the Newcastle-Ottawa Scale. Female athletes were at lower risk of player-contact-induced concussions in lacrosse (pooled rate ratio 0.33 [95% CI 0.25 to 0.43]; p < 0.001), basketball (pooled rate ratio 0.86 [95% CI 0.76 to 0.97]; p = 0.01), ice hockey (pooled rate ratio 0.64 [95% CI 0.56 to 0.73]; p < 0.001), soccer (pooled rate ratio 0.70 [95% CI 0.66 to 0.75]; p < 0.001), and soccer heading (pooled rate ratio 0.80 [95% CI 0.72 to 0.90]; p < 0.001); in these sports, men were at higher risk of concussions from player contact. Female athletes were more likely to experience concussions because of ball or equipment contact in lacrosse (pooled rate ratio 3.24 [95% CI 2.10 to 4.99]; p < 0.001), soccer (pooled rate ratio 2.04 [95% CI 1.67 to 2.49]; p < 0.001), and soccer heading (pooled rate ratio 2.63 [95% CI 1.84 to 3.77]; p < 0.001). The mechanism or activity underlying concussions differs between male and female athletes across different sports. This finding remains the same regardless of whether there are rule differences between the men's and women's games. The implementation of other interventions are required to further ensure player safety, including protective head equipment, concussion prevention training, or rules limiting player contact in the men's game.

#6 Jump performance in male and female football players
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Oct 30. doi: 10.1007/s00167-019-05747-1. [Epub ahead of print]
Authors: Arundale AJH, Kvist J, Hägglund M, Fältström A
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Summary: The purpose was to examine differences between men and women football players in clinically feasible jumping measures. Female football players (N = 46, ages 16-25) were matched based on age, training frequency, and playing position with 46 male players. All players performed the tuck jump and drop vertical jump (DVJ). DVJ was assessed quantitatively for valgus knee motion and probability of a high peak knee abduction moment (pKAM), as well as sagittal plane hip, knee, and ankle angles, and qualitatively with visual assessment of the player's knees upon landing; graded as good, reduced, or poor control. Women had higher total tuck jump scores (5 ± 2) (more technique flaws), than men (3 ± 2, P < 0.01). The quantitative analysis of the DVJ found that men had greater asymmetries between limbs, but women landed bilaterally in more knee valgus (interaction P = 0.04, main effect of sex P = 0.02). There was no difference in pKAM (interaction n.s.). Women also landed in less hip flexion (P = 0.01) and ankle dorsiflexion (P = 0.01) than men. The qualitative DVJ analysis found that more women (48%) had poor knee control compared to men (11%, P < 0.01). The results indicate that women perform worse on the tuck jump assessment than men. The results support previous findings that women land in more knee valgus than men, but also found that men may have larger asymmetries in knee valgus. These results from clinically feasible measures provide some suggestions for clinicians to consider during ACL reconstruction rehabilitation to enhance performance.

#7 Game-specific abilities in elite youth football players: validity and sensitivity to change in subjective coach ratings compared to objectively assessed data
Reference: J Sports Med Phys Fitness. 2019 Oct 25. doi: 10.23736/S0022-4707.19.10084-9. [Epub ahead of print]
Authors: Niederer D, Damm M, Grigereit A, Banzer W, Vogt L
Summary: Little is known on the accuracy of coaches' ratings of game-specific physical abilities in elite youth football players. The present study on elite youth football players aims to assess whether 1) the coaches' subjective assessment of the level of performance of each athlete within the team is in accordance with objectively collected data and 2) the coaches rate changes in the athletes'' performance level accurately or not. Data on jumping ability, sprinting speed, change of direction and strength were collected in seven age groups at a football youth academy (n = 150). The diagnostic battery was repeated after seven months (n = 138). Before the second session, the head coaches completed Likert-scaled closed questions on 1) the importance of running speed and reactive strength components and their relevance to the individual game performance of each of their athletes, 2) level of performance of their athletes, and 3) the change between the first and second performance testing results. Validity and sensitivity of change of their ratings in comparison to the performance data were calculated using analyses of interrelationship. The data of the head coaches showed a low to medium effect size in the agreement with the performance data (Cohen's W = .33 - .71). The evaluation of the change in level of performance was poorer (Cohen's W =.04 - .2; n.s.). Our results underline that functional/physical testing twice during a season may be crucial for displaying performance levels of elite youth football players. Simple self-reported ratings by the coach may be valid in recent performance level assessment but not for performance changes.

#8 Internal training load monitoring in professional football: a systematic review of methods using rating of perceived exertion
Reference: J Sports Med Phys Fitness. 2019 Oct 24. doi: 10.23736/S0022-4707.19.10000-X. [Epub ahead of print]
Authors: Rago V, Brito J, Figueiredo P, Costa J, Krustrup P, Rebelo A
Summary: The rate of perceived exertion (RPE) is widely adopted to quantify internal training load (ITL) in professional football. The aim of this study was to systematically review the use RPE-based methods in professional football. Observational studies conducted during training routines of professional football players over a minimum of one- week were selected based on the preferred reporting items for systematic reviews and meta-analyses statement. Thirty-eight articles met the inclusion criteria (average qualitative score was 6.3 out of 10 [3 to 9]). The main deficiencies identified concerned the poor description of study design (~52% of the studies), and the non-quantification of match load (~44%). Ten studies complemented RPE-based ITL information with time-motion analysis (~26%) and seven studies added HR recordings (~18%). Nine studies collected RPE data after complementary training, separately to field sessions (~3%). Operational questions (e.g. How was your workout? ~71%) were preferred to instructions (e.g. Please rate the intensity of today's session; ~8%). Session-RPE (s-RPE; RPE multiplied by training duration) was more commonly adopted as measure of exercise intensity than isolated RPE (~76 vs. ~8%). RPE-derived variables calculated on weekly values included absolute week-to-week change, acute: chronic workload ratio, monotony and strain and were not frequently used (7 to 15%). Four studies (~11%) divided RPE in two components: respiratory and muscular. There is a lack of consensus for the use of RPE in professional football and "good practices" are warranted. This review might help practitioners regarding procedures to adopt in RPE data collection and interpretation.

#9 No association between perceived exertion and session duration with hamstring injury occurrence in professional football
Reference: Scand J Med Sci Sports. 2019 Oct 30. doi: 10.1111/sms.13591. [Epub ahead of print]
Authors: Lolli L, Bahr R, Weston M, Whiteley R, Tabben M, Bonanno D, Gregson W, Chamari K, Di Salvo V, van Dyk N
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Summary: Training and competition loads have emerged as modifiable composite risk factors of non-contact injury. Hamstring strains are the most common injuries in football with substantial burden on the individual player and club. Nevertheless, robust evidence of a consistent load-hamstring injury relationship in professional football is lacking. Using available data from the Qatar Stars League over three competitive seasons, this study investigated the separate and combined effects of perceived exertion and session duration on hamstring injury occurrence in a sample of 30 outfield football players. Load variables were calculated into 7-day, 14-day, 21-day, 28-day periods of data, and week-to-week changes for average ratings of perceived exertion (RPE; au) score and session-RPE (s-RPE; session-duration X score), plus the cumulative training and match minutes and s-RPE, respectively. Conditional logistic regression models estimated load-injury relationships per 2-within-subject standard deviation increments in each candidate variable. Associations were declared practically important based on the location of the confidence interval in relation to thresholds of 0.90 and 1.11 defining small beneficial and harmful effects, respectively. The uncertainty for the corrected odds ratios show that typically high within-subject increments in each candidate variable were not practically important for training- and match-related hamstring injury (95% confidence intervals range: 0.85 to 1.16). We found limited exploratory evidence regarding the value of perceived exertion and session duration as aetiological factors of hamstring injury in Middle-East professional football. Monitoring remains valuable to inform player load management strategies, but our exploratory findings suggest its role for type-specific injury risk determination appears empirically unsupported.

#10 Risk of acute and overuse injuries in youth elite soccer players: Body size and growth matter
Reference: J Sci Med Sport. 2019 Oct 10. pii: S1440-2440(19)30355-X. doi: 10.1016/j.jsams.2019.10.001. [Epub ahead of print]
Authors: Rommers N, Rössler R, Goossens L, Vaeyens R, Lenoir M, Witvrouw E, D'Hondt E
Summary: This study investigated anthropometric measures and growth as risk factors for overuse and acute injuries in younger (U10-U12) and older (U13-U15) elite level soccer players. Height, weight, and sitting height were measured at the start and the end of the 2016-2017 competitive season and growth velocities were calculated. Throughout the season, injuries were registered continuously by the (para-)medical staff of the included clubs. We analyzed the injury risk using multilevel Poisson regression models, accounting for club and team clustering. Of the included 314 players (11.7±1.7 years of age), 160 players sustained 133 overuse and 163 acute injuries (i.e. 106 injuries in 69 players of the younger group, 190 in 91 players of the older group). In the younger group, risk of overuse injuries was associated with an increase in leg length over the season (incidence rate ratio (IRR) 1.620 [95% CI 1.230-2.117]) and risk of acute injuries with relatively younger age (IRR 1.003 [95% CI 1.000-1.006]). In the older group, a higher leg length was associated with an increased risk of overuse injuries (IRR 1.055 [95% CI 1.011-1.108]), and a higher weight and a lower growth rate with an increased risk of acute injuries (IRR 1.043 [95% CI 1.021-1.067] and 0.903 [95% CI 0.831-0.981], respectively). Injury risk factors differ by age group and type of injury. The age-specific anthropometric and growth-related risk factors should be monitored and these risk profiles should be considered to manage injury risk effectively.

#11 Effects of Ramadan fasting on physical performances in soccer players: a systematic review
Reference: Tunis Med. 2019 Oct;97(10):1114-1131.
Authors: Chtourou H, Trabelsi K, Boukhris O, Ammar A, Shephard RJ, Bragazzi NL.
Summary: The purpose was to evaluate the effects of Ramadan fasting on physical performance measures in soccer players through a systematic appraisal of the literature. Systematic review Data sources: The entire content of two databases, PubMed/MEDLINE and Web of Science. Eligibility criteria for selecting studies: Both singlegroup, pre-post and crossover design studies published in any language before March 15, 2019 were included. Assessments of physical performance were accepted for analysis. study appraisal: The methodological quality of the included studies was assessed using 'QualSyst'. Of 18 selected articles, 16 were generally of strong quality and the remaining studies (n=2) were rated as moderate, although most lacked significant details about the Ramadan fasting. Most studies showed that Ramadan fasting did not impair short-term maximal performances in soccer players (i.e., vertical jump, sprint performance, maximal voluntary contraction, hand grip, agility performance). During the 30-s Wingate test, the repeated sprint exercise (RSE) tasks, and the long-duration incremental and non-incremental exercises, most studies reported some negative effects of Ramadan fasting even when the training load was maintained. For the soccer specific skills and test with ball, most studies reported that there was no significant negative effects of the fasting month on performance when the training load was maintained or slightly reduced during the Ramadan. The continuance of training during Ramadan fasting, with maintained training load, has no negative effects on short-term maximal performances and soccer specific skills and test with ball. However, performances of the 30-s Wingate test, the RSE tasks, and the long-duration incremental and non-incremental exercises were significantly impaired during Ramadan fasting even when the training load was maintained.





Latest research in football - week 45 - 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 Improvements in strength and functional performance after Kinesio taping in semi-professional male soccer players with and without functional ankle instability
Reference: Foot (Edinb). 2019 Jun 27;41:12-18. doi: 10.1016/j.foot.2019.06.006. [Epub ahead of print]
Authors: Fereydounnia S, Shadmehr A, Attarbashi Moghadam B, Talebian Moghadam S, Mir SM, Salemi S, Pourkazemi F
Summary: The objectives of this study were to compare the immediate effects of two methods of Kinesio taping on muscle strength, functional performance, and balance in athletes with and without functional ankle instability (FAI). The present study investigated the effects of distal taping (muscle application over peroneus longus) and proximal- distal taping (muscle application over gluteus medius and peroneus longus) on the strength of evertor and hip abductor muscles, side hop test, figure of 8 hop test, and star excursion balance test in semi-professional male soccer players with and without FAI (n=15 in each group). A Multifactorial repeated measure ANOVA was used for comparison. There were significant differences for factor effect in all outcome measures (P<0.05), except for the figure of 8 hop test. No significant differences for group effects and group by factor interaction effects (P>0.05) was observed except for the side hop test. Kinesio taping had immediate effects on improving strength, performance and balance. However, there were no differences on the method of application. Clinicians can consider the application Kinesio taping during the rehabilitation process of athletes with FAI, to improve balance and strength. The long-term impacts of taping on the functional, balance and strength measures should be investigated in future studies.

#2 Hip Range of Motion: Which Plane of Motion Is More Predictive of Lower Extremity Injury in Elite Soccer Players? A Prospective Study
Reference: J Surg Orthop Adv. 2019 Fall;28(3):201-208.
Authors: Shah SS, Testa EJ, Gammal I, Sullivan J, Gerland RW, Goldstein J, Sheridan B, Mashura M, Shah AS, Goodwillie A, Cohn RM
Summary: The objective of this study was to determine which plane of hip motion (rotational or sagittal) is more predictive of lower extremity (LE) injury in elite soccer players. A total of 69 athletes (43 professional and 26 collegiate) were examined (mean age, 22.6 years). Bilateral hip internal rotation (IR), external rotation, extension, and flexion measurements were taken along with the modified Thomas test during preseason physicals. There were 42 LE injuries (injury rate 3.74/1000 athlete exposures). Mean IR was 25.2. and 29.9° for injured versus noninjured extremities, respectively (p = .009). There was a significant association between decreased IR (categorized as IR < 28°) and incidence of ipsilateral LE injury (p = .042). Extremities with IR < 28° were 2.81 times more likely to sustain a LE injury (95% CI,; p = .023). With a utilitarian focus, the current study has identified a measurement of decreased hip IR with potential for substantial clinical value in collegiate and professional soccer players. (Journal of Surgical Orthopaedic Advances 28(3):201-208, 2019).

#3 Italian consensus statement (2020) on return to play after lower limb muscle injury in football (soccer)
Reference: BMJ Open Sport Exerc Med. 2019 Oct 15;5(1):e000505. doi: 10.1136/bmjsem-2018-000505. eCollection 2019.
Authors: Bisciotti GN, Volpi P, Alberti G, Aprato A, Artina M, Auci A, Bait C, Belli A, Bellistri G, Bettinsoli P, Bisciotti A, Bisciotti A, Bona S, Bresciani M, Bruzzone A, Buda R, Buffoli M, Callini M, Canata G, Cardinali D, Cassaghi G, Castagnetti L, Clerici S, Corradini B, Corsini A, D'Agostino C, Dellasette E, Di Pietto F, Enrica D, Eirale C, Foglia A, Franceschi F, Frizziero A, Galbiati A, Giammatei C, Landreau P, Mazzola C, Moretti B, Muratore M, Nanni G, Niccolai R, Orizio C, Pantalone A, Parra F, Pasta G, Patroni P, Pelella D, Pulici L, Quaglia A, Respizzi S, Ricciotti L, Rispoli A, Rosa F, Rossato A, Sannicandro I, Sprenger C, Tarantola C, Tenconi FG, Tognini G, Tosi F, Trinchese GF, Vago P, Zappia M, Vuckovich Z, Zini R, Trainini M, Chamari K
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Summary: Return to play (RTP) decisions in football are currently based on expert opinion. No consensus guideline has been published to demonstrate an evidence-based decision-making process in football (soccer). Our aim was to provide a framework for evidence-based decision-making in RTP following lower limb muscle injuries sustained in football. A 1-day consensus meeting was held in Milan, on 31 August 2018, involving 66 national and international experts from various academic backgrounds. A narrative review of the current evidence for RTP decision-making in football was provided to delegates. Assembled experts came to a consensus on the best practice for managing RTP following lower limb muscle injuries via the Delphi process. Consensus was reached on (1) the definitions of 'return to training' and 'return to play' in football. We agreed on 'return to training' and RTP in football, the appropriate use of clinical and imaging assessments, and laboratory and field tests for return to training following lower limb muscle injury, and identified objective criteria for RTP based on global positioning system technology. Level of evidence IV, grade of recommendation D.

#4 Physical Performance Differences Between Starter and Non-Starter Players During Professional Soccer Friendly Matches
Reference: J Hum Kinet. 2019 Oct 18;69:283-291. doi: 10.2478/hukin-2019-0018. eCollection 2019 Oct.
Authors: Giménez JV, Leicht AS, Gomez MA
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Summary: The aim of this study was to investigate the physical performance differences between players that started (i.e. starters, ≥65 minutes played) and those that were substituted into (i.e. non-starter) soccer friendly matches. Fourteen professional players (age: 23.2 ± 2.7 years, body height: 178 ± 6 cm, body mass: 73.2 ± 6.9 kg) took part in this study. Twenty, physical performance-related match variables (e.g. distance covered at different intensities, accelerations and decelerations, player load, maximal running speed, exertion index, work-to-rest ratio and rating of perceived exertion) were collected during two matches. Results were analysed using effect sizes (ES) and magnitude based inferences. Compared to starters, non-starters covered greater match distance within the following intensity categories: >3.3≤4.2m/s (very likely), >4.2≤5 m/s (likely) and >5≤6.9 m/s (likely). In contrast, similar match average acceleration and deceleration values were identified for starters and non-starters (trivial). Indicators of workloads including player loads (very likely), the exertion index (very likely), and the work-to-rest ratio (very likely) were greater, while self- reported ratings of perceived exertion were lower (likely) for non-starters compared to starters. The current study demonstrates that substantial physical performance differences during friendly soccer matches exist between starters and non-starters. Identification of these differences enables coaches and analysts to potentially prescribe optimal training loads and microcycles based upon player's match starting status.

#5 Player Load and Metabolic Power Dynamics as Load Quantifiers in Soccer
Reference: J Hum Kinet. 2019 Oct 18;69:259-269. doi: 10.2478/hukin-2018-0072. eCollection 2019 Oct.
Authors: Reche-Soto P, Cardona-Nieto D, Diaz-Suarez A, Bastida-Castillo A, Gomez-Carmona C, Garcia-Rubio J, Pino-Ortega J
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Summary: There has recently been an increase in quantification and objective analysis of soccer performance due to improvements in technology using load indexes such as Player Load (PL) and Metabolic Power (MP). The objectives of this study were: (1) to describe the performance of PL and MP in competition according to the specific role, match-to- match variation, periods of play, game location and match status according to game periods, and (2) to analyze the relationship between both indexes. Twenty-one national-level soccer players were distributed in the following specific positional roles: external defenders (ED) (n = 4), central defenders (CD) (n = 4), midfielders (M) (n = 5), external midfielders (EM) (n = 4) and attackers (A) (n = 4). A total of 12 matches played by a Spanish Third Division team during the 2016/2017 season were analyzed. WIMU PROTM inertial devices (RealTrack System, Almeria, Spain) were used for recording the data. The main results were: (1) a performance reduction in both variables over the course of match time, (2) significant differences in both variables based on the specific position, (3) differences in physical demands during the season matches, (4) winning during a game period and the condition of being the visitor team provoked higher demands, and (5) a high correlation between both variables in soccer. In conclusion, different contextual variables influence the external load demands; both indexes are related so they could be used for external load quantification, and it is necessary to analyze physical demands of the competition for a specific and individualized load design in training sessions.

#6 Combined Small-Sided Game and High-Intensity Interval Training in Soccer Players: The Effect of Exercise Order
Reference: J Hum Kinet. 2019 Oct 18;69:249-257. doi: 10.2478/hukin-2018-0092. eCollection 2019 Oct.
Authors: Rabbani A, Clemente FM, Kargarfard M, Jahangiri S
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Summary: The aim of the present study was to compare combined small-sided game (SSG) and high-intensity interval training (HIT) with different order. Twenty-one semi-professional soccer players were divided into two groups: SSG+HIT (n = 10) and HIT+SSG (n = 11), and underwent similar four-week training programs. Players completed the 30-15 Intermittent Fitness Test (30-15IFT) before and after the experiment; maximum speed (VIFT) was recorded. During the experiment, seven sessions of SSG (3 vs 3) and HIT (15"-15" with 95-100% VIFT) were implemented. Weekly accumulated training loads for both groups during the experiment were similar. Moderate improvements in VIFT were observed in both SSG+HIT (+6.2%, 90% confidence limits, [CL] 4.6; 7.7 and Effect Size, [ES] +0.96) and HIT+SSG (+6.9%, 90% CL 4.6; 9.3 and ES +0.97) groups. Between-group difference in changes of VIFT was trivial (+0.7%, 90% CL -1.8; 3.3 and ES +0.11). Combining SSG and HIT in different order elicited the same enhancement in high-intensity intermittent performance in soccer players.

#7 Trends of Goal Scoring Patterns in Soccer: A Retrospective Analysis of Five Successive FIFA World Cup Tournaments
Reference: J Hum Kinet. 2019 Oct 18;69:231-238. doi: 10.2478/hukin-2019-0015. eCollection 2019 Oct.
Authors: Kubayi A, Toriola A
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Summary: This study analysed the 795 goals scored during a total of 320 matches played in five successive FIFA World Cup tournaments (1998-2014). Data were obtained through YouTube videos and analysed by means of Longomatch software. The variables analysed included the number of goals scored per half (45-min period), per 15-min period, and per 30-min period of extra time, goal scoring zones, goals scored by substitutes, types of goals scored, and goals scored according to the playing position. With regard to 15-min period analysis, most goals were scored between the 76th and 90th minutes (24.7%) of the game in all five World Cup competitions. Chi-square analyses showed no significant (p > 0.05) differences in the frequency of goal scoring patterns per 45-min and 15-min periods in the five World Cup tournaments. Most goals were scored from inside the goal (23.8%) and penalty (14.6%) areas. The greatest number of goals was scored by strikers (54.2%), followed by midfielders (33.3%) and defenders (2.3%). These findings provide practical implications for improving goal-scoring performance in soccer.

#8 Variability of Technical Actions During Small-Sided Games in Young Soccer Players
Reference: J Hum Kinet. 2019 Oct 18;69:201-212. doi: 10.2478/hukin-2019-0013. eCollection 2019 Oct.
Authors: Clemente FM, Sarmento H, Costa IT, Enes AR, Lima R
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Summary: The purpose of this study was three-fold: (i) to test the between-sessions variability of 3 vs. 3 and 6 vs. 6 formats in under-11 players, (ii) to assess the within-session variability of 3 vs. 3 and 6 vs. 6 formats, and (iii) to investigate the variations of technical actions between formats. Sixteen soccer players (10.1 ± 0.3 years old) participated in this study. Both formats of play were played twice within an interval of one week to test the between-session variability and the variables of conquered balls (CBs), received balls (RBs), lost balls (LBs), attacking balls/passes (ABs) and shots (Ss) were analyzed using the Performance Assessment in Team Sports instrument in all matches. Moderate variations on the sum of sets during the 3 vs. 3 and 6 vs. 6 formats were observed in all variables. Considering the variations of technical actions made between sets in the 3 vs. 3 format, likely moderate increases were found in set 2 vs. 1 in terms of RB (37.5%, [-2.7;94.2]), and likely small decreases were found in set 3 vs. 2 for the same variable (-18.3%, [-37.8;7.3]). In the 6 vs. 6 format, only possibly small increases were found for set 3 vs. 1 in S (22.5%, [-7.0;61.3]). Generally (sum of sets), the variables standardized per minute revealed almost certain very large decreases in the 6 vs. 6 vs. the 3 vs. 3 format in the variables of CB (-67.9%, [-75.3;-55.9]), LB (-66.0%, [-73.9;-55.7]), RB (-65.6%, [-74.8;- 53.1]) and S (-87.6%, [-93.1;-77.7]). The results of this study suggest that both formats of play are too noisy to be reproducible. The 3 vs. 3 format largely increased the number of individual technical actions.

#9 Analysis of Successful Offensive Play Patterns by the Spanish Soccer Team
Authors: Amatria M, Maneiro R, Anguera MT
Reference: J Hum Kinet. 2019 Oct 18;69:191-200. doi: 10.2478/hukin-2019-0011. eCollection 2019 Oct.
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Summary: Victory is the ultimate aim in soccer and therefore when a team wins an elite European or world championship, attempts will invariably be made to emulate the winning team's style of play. In this study, we performed an in-depth analysis of play by the Spanish soccer team during the 2012 UEFA European Championship, where it was crowned champion. Using observational methodology and T-pattern analysis, we identified hidden patterns of play that ended in a goal for the Spanish team. A generalizability coefficient (e2) of 0.986 demonstrated that the offensive patterns detected are robust and highly generalizable. These patterns were formed by technical actions consisting of ball control and pass, with alternations between short and long passes, in the central area of the rival pitch, with use of both wings to achieve width of play and prioritization of width over depth of play. We also found patterns showing that goals and shots at goal were made on a ball delivered from the opposite direction to the shot and were not preceded by a technical action.

#10 Practical Use of the Navigate Pain Application for the Assessment of the Area, Location, and Frequency of the Pain Location in Young Soccer Goalkeepers
Reference: J Hum Kinet. 2019 Oct 18;69:125-135. doi: 10.2478/hukin-2019-0091. eCollection 2019 Oct.
Authors: Muracki J, Kumorek M, Kisilewicz A, Pożarowszczyk B, Larsen DB, Kawczyński A, Boudreau S
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Summary: Next to winning, minimizing injuries during training and matches is one of the primary goals of professional team sports games. Soreness and pain can be early indicators and risk factors for acute or long-term injuries. Monitoring pain intensity and duration, as well as potential sources, are useful for planning practices and can be effective means for preventing injury. The aim of this study was to assess the areas and locations of pain in young soccer goalkeepers during a training camp, and to differentiate the area and frequency between pain arising from the muscles (MP), joints (JP), or as a result of an impact (IP). Recordings of the MP, JP, and IP location along with the area were performed using digital body mapping software (Navigate Pain Android app, Aalborg University, Denmark) installed on a tablet personal computer at the end of each training day across a 5-day training camp. There was a significant difference in the area between the three types of pain (p < 0.001). The post hoc analysis revealed statistically significant differences between the pixel areas of IP versus JP (p < 0.001), IP versus MP (p < 0.001), and JP versus MP (p < 0.001). There was no significant time-effect for the IP area between 1-5 days of training (p = 0.610), neither for MP (p = 0.118) or JP (p = 0.797) and no significant difference for all three pain areas between the front and the back side of the body. The body regions most often reported for MP were thighs, while for JP they were groin and hips, and for IP the hips, shoulders, and forearms were most frequently indicated. This is the first study to map and report the pain distribution associated with training across a 5-day training camp in soccer goalkeepers, and these findings emphasize the value of using digital pain drawings clinically as well as for monitoring the health status of soccer players.

#11 Relationships between the Expression of the ACTN3 Gene and Explosive Power of Soccer Players
Reference: J Hum Kinet. 2019 Oct 18;69:79-87. doi: 10.2478/hukin-2019-0020. eCollection 2019 Oct.
Authors: Domańska-Senderowska D, Szmigielska P, Snochowska A, Jastrzębski Z, Jegier A, Kiszałkiewicz J, Jastrzębska J, Pastuszak-Lewandoska D, Cięszczyk P, Suchanecka A, Wilk M, Brzeziański M, Brzeziańska-Lasota E
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Summary: Muscle strength and maximal speed are factors determining athlete's results during competition. Their association with ACTN3 gene activity has been documented. The purpose of this study was the analysis of ACTN3 gene expression during a 2 month training cycle of soccer players and its correlation with the countermovement jump (CMJ) and squat jump (SJ). The study group consisted of 22 soccer players (aged 17-18). The study material included peripheral blood lymphocytes. The relative expression (RQ) of the ACTN3 gene was analyzed by qPCR and performed before and after the two-month training cycle. Before the training cycle low expression levels of ACTN3 (median RQ = 0.95) were observed, yet after the training cycle they were elevated (median RQ = 1.98) ( p = 0.003). There was an increase in performance of both jumps: SJ (p = 0.020) and CMJ (p = 0.012) at the end of the training cycle. A simultaneous increase in the ACTN3 gene expression level and height in both jump tests was observed in 73% of athletes (p > 0.05). There were no significant relationships between the ACTN3 gene expression level and the results of the CMJ and SJ. However, explosive strength is a complex feature shaped by many different factors and it could be the reason why we did not observe correlations between these variables.

#12 Correlations between body composition, aerobic capacity, speed and distance covered among professional soccer players during official matches
Reference: J Sports Med Phys Fitness. 2019 Oct 24. doi: 10.23736/S0022-4707.19.09979-1. [Epub ahead of print]
Authors: Radzimiński Ł, Szwarc A, Padrón-Cabo A, Jastrzębski Z
Summary: The importance of sprinting and high-speed running activities during a soccer match is indisputable. The main purpose of this study was to investigate the relations between the players' speed, aerobic capacity, body composition and distance covered in different speed zones during official soccer matches and to compare the match performance variables according to playing position. Twenty-three professional soccer players (age: 27.9 ± 4.58 y, body mass: 78.8 ± 7.35 kg, height: 181.7 ± 6.53 cm) participated in this study. During 13 weeks of the competitive season, players participated in 16 official matches and completed body composition analyses, sprint tests, multistage shuttle run tests (MST), and incremental running tests (IRTs). Significant negative correlations were found between sprint distance and percent of fat mass (FM; r = -0.57, p < 0.0001), MST (r = 0.45, p < 0.001), maximal speed (r = 0.44, p < 0.001). High-speed running (HSR) distance covered by the players during the matches was significantly correlated with FM (r = -0.38, p < 0.001) and MST distance (r = 0.30, p < 0.01). These data indicate that professional soccer players with lower fat content and higher levels of aerobic capacity are able to cover longer distances in sprinting and HSR during official matches.

#13 Knee muscle and tendon stiffness in professional soccer players: a shear-wave elastography study
Reference: J Sports Med Phys Fitness. 2019 Oct 24. doi: 10.23736/S0022-4707.19.09938-9. [Epub ahead of print]
Authors: Taş S, Özkan Ö, Karaçoban L, Dönmez G, Çetin A, Korkusuz F
Summary: It is well known that several risk factors such as fatigue, previous injury, muscle strength deficit or imbalance are related to a higher incidence of knee injuries in professional soccer players. Knee muscle and tendon stiffness may be another factor that is related to knee injuries in professional soccer players. Therefore, the aim of the present study was to investigate the differences between professional soccer players and healthy sedentary males in terms of the stiffness of patellar tendon (PT), quadriceps tendon (QT), and rectus femoris muscle (RF) and vastus medialis muscle (VM). The study group was comprised of 17 professional male soccer players in age range of 24-37 years. The control group was comprised of 22 healthy sedentary males in an age range of 21-36 years. Shear-Wave Velocity (SWV) measurements of the selected muscles and tendons were performed using an ultrasonography device with a lineal probe. The professional soccer players had lower SWV of PT (p=0.024) and QT (p<0.001) in the dominant leg compared to the control group; however, SWV of PT (p=0.455) and QT (p=0.827) in the non-dominant leg were similar in both groups. SWV of RF was higher in both dominant and non-dominant legs in professional soccer players compared to the control group (p<0.05); however, SWV of VM was similar in both groups (p>0.05). Professional soccer players had lower PT and QT stiffness. On the other hand, they had higher RF stiffness compared to sedentary individuals. Furthermore, VM stiffness was similar in both groups.





Latest research in football - week 44 - 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 Effect of the FIFA 11+ on Landing Patterns and Baseline Movement Errors in Elite Male Youth Soccer Players
Reference: J Sport Rehabil. 2019 Oct 18:1-8. doi: 10.1123/jsr.2018-0374. [Epub ahead of print]
Authors: Akbari H, Sahebozamani M, Daneshjoo A, Amiri-Khorasani M, Shimokochi Y.
Summary: There is no evidence regarding the effect of the FIFA 11+ on landing kinematics in male soccer players, and few studies exist regarding the evaluating progress of interventions based on the initial biomechanical profile. The aim was to investigate the effect of the FIFA 11+ program on landing patterns in soccer players classified as at low or high risk for noncontact anterior cruciate ligament injuries. Field-based functional movement screening performed at the soccer field was measured in a total of 24 elite male youth soccer players participated in this study. The intervention group performed the FIFA 11+ program 3 times per week for 8 weeks, whereas the control group performed their regular warm-up.Before and after the intervention, all participants were assessed for landing mechanics using the Landing Error Scoring System. Pretraining Landing Error Scoring System scores were used to determine risk groups. The FIFA 11+ group had greater improvement than the control group in terms of improving the landing pattern; there was a significant intergroup difference (F1,20 = 28.86, P < .001, ηp2=.591). Soccer players categorized as being at high risk displayed greater improvement from the FIFA 11+ program than those at low risk (P = .03). However, there was no significant difference in the proportion of risk category following the routine warm-up program (P = 1.000). The present study provides evidence of the usefulness of the FIFA 11+ program for reducing risk factors associated with noncontact anterior cruciate ligament injuries. The authors' results also suggest that soccer players with the higher risk profile would benefit more than those with lower risk profiles and that targeting them may improve the efficacy of the FIFA 11+ program.

#2 Neurodegenerative Disease Mortality among Former Professional Soccer Players
Reference: N Engl J Med. 2019 Oct 21. doi: 10.1056/NEJMoa1908483. [Epub ahead of print]
Authors: Mackay DF, Russell ER, Stewart K, MacLean JA, Pell JP, Stewart W
Summary: Neurodegenerative disorders have been reported in elite athletes who participated in contact sports. The incidence of neurodegenerative disease among former professional soccer players has not been well characterized. We conducted a retrospective cohort study to compare mortality from neurodegenerative disease among 7676 former professional soccer players (identified from databases of Scottish players) with that among 23,028 controls from the general population who were matched to the players on the basis of sex, age, and degree of social deprivation. Causes of death were determined from death certificates. Data on medications dispensed for the treatment of dementia in the two cohorts were also compared. Prescription information was obtained from the national Prescribing Information System. Over a median of 18 years, 1180 former soccer players (15.4%) and 3807 controls (16.5%) died. All-cause mortality was lower among former players than among controls up to the age of 70 years and was higher thereafter. Mortality from ischemic heart disease was lower among former players than among controls (hazard ratio, 0.80; 95% confidence interval [CI], 0.66 to 0.97; P = 0.02), as was mortality from lung cancer (hazard ratio, 0.53; 95% CI, 0.40 to 0.70; P<0.001). Mortality with neurodegenerative disease listed as the primary cause was 1.7% among former soccer players and 0.5% among controls (subhazard ratio [the hazard ratio adjusted for competing risks of death from ischemic heart disease and death from any cancer], 3.45; 95% CI, 2.11 to 5.62; P<0.001). Among former players, mortality with neurodegenerative disease listed as the primary or a contributory cause on the death certificate varied according to disease subtype and was highest among those with Alzheimer's disease (hazard ratio [former players vs. controls], 5.07; 95% CI, 2.92 to 8.82; P<0.001) and lowest among those with Parkinson's disease (hazard ratio, 2.15; 95% CI, 1.17 to 3.96; P = 0.01). Dementia-related medications were prescribed more frequently to former players than to controls (odds ratio, 4.90; 95% CI, 3.81 to 6.31; P<0.001). Mortality with neurodegenerative disease listed as the primary or a contributory cause did not differ significantly between goalkeepers and outfield players (hazard ratio, 0.73; 95% CI, 0.43 to 1.24; P = 0.24), but dementia-related medications were prescribed less frequently to goalkeepers (odds ratio, 0.41; 95% CI, 0.19 to 0.89; P = 0.02). In this retrospective epidemiologic analysis, mortality from neurodegenerative disease was higher and mortality from other common diseases lower among former Scottish professional soccer players than among matched controls. Dementia-related medications were prescribed more frequently to former players than to controls. These observations need to be confirmed in prospective matched-cohort studies. (Funded by the Football Association and Professional Footballers' Association.).

#3 Sport Specialization and Coordination Differences in Multisport Adolescent Female Basketball, Soccer, and Volleyball Athletes
Reference: J Athl Train. 2019 Oct;54(10):1105-1114. doi: 10.4085/1062-6050-407-18.
Authors: DiCesare CA, Montalvo A, Foss KDB, Thomas SM, Hewett TE, Jayanthi NA, Myer GD
Summary: Early sport specialization, or the participation in 1 sport year-round to the exclusion of all others, is a growing concern in youth athletics because of its possible association with musculoskeletal injury. The underlying injury risk may be the result of coordination differences that sport-specialized athletes have been speculated to exhibit relative to multisport athletes; however, little evidence exists to support or refute this notion. The aim was to examine relative hip- and knee-joint angular-motion variability among adolescent sport-specialized and multisport female adolescent athletes to determine how sport specialization may affect coordination. A total of 366 sport-specialized and 366 multisport adolescent female basketball, soccer, and volleyball players participated in this study with an drop-vertical-jump (DVJ) assessment. Average coupling-angle variability (CAV) for hip flexion and knee flexion, knee flexion and ankle flexion, hip flexion and knee abduction, knee flexion and knee abduction, knee flexion and knee internal rotation, and knee abduction and knee internal rotation. The sport-specialized group exhibited increased coupling variability in dominant-limb hip flexion and knee flexion (P = .015), knee flexion and knee abduction (P = .014), and knee flexion and knee internal rotation (P = .048) while landing during the DVJ, although they had small effect sizes (η2 = 0.010, 0.010, and 0.007, respectively). No differences were present between groups for any of the other CAV measures of the dominant limb, and no differences were found for any CAV measures of the nondominant limb (all P values > .05). Sport specialization was associated with increased variability of critical hip- and knee-joint couplings responsible for effective landing during the DVJ. Altered coordination strategies that involve the hip and knee joints may underlie unstable landings, inefficient force-absorption strategies, or greater contact forces that can place the lower extremities at risk for injury (or a combination of these).

#4 Evaluation for the effects of nutritional education on Chinese elite male young soccer players: The application of adjusted dietary balance index (DBI)
Reference: J Exerc Sci Fit. 2020 Jan;18(1):1-6. doi: 10.1016/j.jesf.2019.08.004. Epub 2019 Aug 20.
Authors: Zeng D, Fang ZL, Qin L, Yu AQ, Ren YB, Xue BY, Zhou X, Gao ZY, Ding M, An N, Wang QR
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Summary: The aim of this study was to evaluate the effect of nutrition education on Chinese elite male young soccer players through the knowledge, attitude, behavior (KAP) survey and an adjusted dietary balance index (DBI). 30 Chinese elite male young soccer players were randomly divided into two groups: lecture group (N = 15, Age: 16.7 ± 1.8 years, Height: 173.9 ± 9.0 cm; Weight: 62.4 ± 13.0 kg; Training years: 5.6 ± 2.7 years) and non-lecture group (N = 15, Age: 16.8 ± 1.7 years, Height: 175.5 ± 7.9 cm; Weight: 62.5 ± 12.3 kg; Training years: 6.2 ± 3.3). The comics book was given to the non-lecture group, while the a four-week nutritional quality education along with comic books were given to the lecture group. Before and after 4 weeks nutritional education, dietary nutritional status of both groups was assessed. The main outcome measurements included the scores for each part of the KAP survey, diet status (food-weighing method) and the dietary index in the adjusted DBI-07 system (DBI-low bound score, LBS; DBI-high bound score, HBS; and DBI-diet quality distance, DQD). In the lecture group, significant differences were found in the scores of general nutrition knowledge, sports nutrition knowledge and total scores of KAP dietary questionnaire after 4 weeks nutritional education (P < 0.01). However, there is no significant difference in dietary attitude and dietary behavior (P > 0.05) on both two groups. There is no significant change in the DBI-low bound score (LBS), DBI-high bound score (HBS) and DBI-diet quality distance (DQD) of dietary quality index (P > 0.05) in both two groups. Four weeks nutritional quality education improved the understanding of dietary nutrition among Chinese elite male young soccer players.

#5 Analysis of the Association between Running Performance and Game Performance Indicators in Professional Soccer Players
Reference: Int J Environ Res Public Health. 2019 Oct 21;16(20). pii: E4032. doi: 10.3390/ijerph16204032.
Authors: Modric T, Versic S, Sekulic D, Liposek S
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Summary: Running performance (RP) and game performance indicators (GPI) are important determinants of success in soccer (football), but there is an evident lack of knowledge about the possible associations between RP and GPI. This study aimed to identify associations between RP and GPI in professional soccer players and to compare RP and GPI among soccer playing positions. One hundred one match performances were observed over the course of half of a season at the highest level of national competition in Croatia. Players (mean ± SD, age: 23.85 ± 2.88 years; body height: 183.05 ± 8.88 cm; body mass: 78.69 ± 7.17 kg) were classified into five playing positions (central defenders (n = 26), full-backs (n = 24), central midfielders (n = 33), wide midfielders (n = 10), and forwards (n = 8). RP, as measured by global positioning system, included the total distance covered, distance covered in five speed categories (walking, jogging, running, high-speed running, and maximal sprinting), total number of accelerations, number of high-intensity accelerations, total number of decelerations, and number of high-intensity decelerations. The GPI were collected by the position-specific performance statistics index (InStat index). The average total distance was 10,298.4 ± 928.7 m, with central defenders having the shortest and central midfielders having the greatest covered distances. The running (r = 0.419, p = 0.03) and high-intensity accelerations (r = 0.493, p = 0.01) were correlated with the InStat index for central defenders. The number of decelerations of full-backs (r = -0.43, p = 0.04) and the distance covered during sprinting of forwards (r = 0.80, p = 0.02) were associated with their GPI obtained by InStat index. The specific correlations between RP and GPI should be considered during the conditioning process in soccer. The soccer training should follow the specific requirements of the playing positions established herein, which will allow players to meet the game demands and to perform successfully.

#6 Working memory capacity does not always promote dual-task motor performance: The case of juggling in soccer
Reference: Scand J Psychol. 2019 Oct 21. doi: 10.1111/sjop.12589. [Epub ahead of print]
Authors: Laurin R, Finez L
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Summary: The aim of this research was to refine our understanding of the role of working memory capacity (WMC) on motor performances that require attentional control in dual-task situations. Three studies were carried out on soccer players. Each participant had to perform a juggling task in both normal and dual-task conditions. In Study 1, the interfering task was a mental calculation test performed under time pressure (strong cognitive load). In Study 2, the interfering task was a count-down test (low cognitive load). In Study 3 an intra-individual design in which participants perform dual-tasks increasingly complex has been proposed. Results showed a positive relationship between participants' WMC and their dual-task motor performance when the cognitive load was low and a negative relationship when the cognitive load was high. This paper highlights the role of the WMC in the activation of different modes of processing and its importance on the performance in dual-task.

#7 Injury Profile of Elite Male Young Soccer Players in a Spanish Professional Soccer Club: A Prospective Study During 4 Consecutive Seasons
Reference: J Sport Rehabil. 2019 Oct 18:1-7. doi: 10.1123/jsr.2019-0113. [Epub ahead of print]
Authors: Raya-González J, Suárez-Arrones L, Navandar A, Balsalobre-Fernández C, Sáez de Villarreal E.
Summary: As the number of injuries in young soccer players increases, an epidemiological study is the first step in improving preventive strategies. The aim was to analyze the injury profile of a Spanish professional soccer club's academy during 4 consecutive seasons and to examine the injury incidence across different chronological age groups. Aggregate injury and exposure data collected during 4 consecutive seasons were collected of three hundred nine elite male young soccer players. Injuries that led to participation time missed from training and match play prospectively reported by medical or coaching staff of the club were used as outcome measures. A total of 464 time-loss injuries were observed during this study period. The overall injury incidence was 2.93 injuries per 1000 hours, with higher incidence during matches than during training (10.16 vs 2.10 injuries/1000 h; rate ratio [RR] = 0.21; 95% confidence interval [CI], 0.17-0.25; P < .05), with the U14 age group presenting the lowest injury rate (2.39 injuries/1000 h; RR = 1.15-1.57; P < .05). In terms of injury severity, moderate injuries were the most frequent (1.42 injuries/1000 h). Muscle injuries were the most common type of injuries (57.7%; 2.75 injuries/1000 h; RR = 1.84-13.4; P < .05), and hamstrings (93/268) were the most affected muscle group (0.58 injuries/1000 h; RR = 1.58-2.91; P < .05). Injury incidence showed a seasonal variation as indicated by peaks in August and October. In matches, specifically, the match period between 75 and 90 minutes showed the highest injury incidence (10.29 injuries/1000 h; RR = 1.89-6.38; P < .01). The findings of this study suggest that specific preventive strategies must be implemented to try to reduce the injury incidence in Spanish elite young soccer players attending to the characteristics of each age group.

#8 Elite Players' Perceptions of Football Playing Surfaces: A Qualitative Study
Reference: Res Q Exerc Sport. 2019 Oct 24:1-13. doi: 10.1080/02701367.2019.1660757. [Epub ahead of print]
Authors: Roberts JR, Osei-Owusu P, Mears AC, Harland AR
Summary: The decision by the International Football Association Board in 2004 to approve the use of artificial surfaces in elite football (soccer) competitions remains controversial amongst many players, managers and coaching staff. The aim of this study was to conduct a comprehensive assessment of players' opinions to better understand the influence of playing surfaces on the game of football and identify factors that may contribute to differences of opinion. Qualitative data were collected from 103 elite footballers and 21 coaching staff during a series of interviews and focus groups. A thematic analysis was conducted to identify patterns in the data. Players considered that the type and condition of a playing surface influenced ball-surface interactions, game play, tactics/strategy, footwear selection, movement, risk of injury and fatigue. Together these influence a player's perception of the suitability of a surface and also their mindset, which could ultimately affect their performance. The majority of participants in this study expressed a higher preference for natural grass over artificial turf pitches. A perceived increased risk of injury on artificial turf remains a primary concern despite a lack of supporting evidence in research studies. To address this discrepancy, the reporting of muscle soreness and the effect of constant surface switching merit further consideration. Not all participants shared the same views and player characteristics such as age, surface experience, injury history and playing style/position were found to be potential factors that could account for differences in elite players' opinions regarding the surfaces used in football.

#9 Acute effects of differential learning on football kicking performance and in countermovement jump
Reference: PLoS One. 2019 Oct 23;14(10):e0224280. doi: 10.1371/journal.pone.0224280. eCollection 2019.
Authors: Gaspar A, Santos S, Coutinho D, Gonçalves B, Sampaio J, Leite N
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Summary: The aim of this study was to identify the acute effects of a differential-learning training program on football kicking performance and countermovement jump. Twenty youth Portuguese under-15 football players participated in this study. All players were exposed to two training approaches: i) traditional, in which the players performed a total of 36 kicks in a blocked and repetitive approach; and ii) differential learning, which consisted in the 36 kicks using differential variations in each kick. Football kicking impact and velocity were assessed using a Stalker radar gun, while the kicking accuracy was assessed by aggregating the total number of points achieved during 12 kicks into a goal, which was divided into quantifiable scoring zones. Lastly, leg power was measured using a countermovement jump. Measurements were performed at baseline, post-intervention, and following a 35-minute training match. The comparisons between the baseline and post-test revealed that the differential learning approach promoted a possibly ~5% increase in the countermovement jump (small effects) and a likely ~3% increase in the average velocity (small effects) when compared with the traditional training approach. From the accuracy perspective, there was a moderate decrease from the baseline to the post-test and post-match in accurate kicks into zone 1 (centre of the goal) and a moderate decrease from the baseline to the post-match in accurate kicks into zone 5 (lateral zones at short height) in the differential intervention. In turn, a small increase in the accurate kicks into zones 4 and 6 (lateral zones of the goal and nearest to the bar, respectively) was found from the baseline to the post-match in the differential intervention. Overall, the differential learning intervention was more beneficial than a traditional training protocol with respect to acute improvements in countermovement jump performance, football kicking velocity and higher scoring zones kicking accuracy.

#10 Testing the functionality of peripheral vision in a mixed-methods football field study
Reference: J Sports Sci. 2019 Dec;37(24):2789-2797. doi: 10.1080/02640414.2019.1664100. Epub 2019 Sep 6.
Authors: Vater C, Luginbühl S, Magnaguagno L
Summary: In team sports, peripheral vision might be useful to simultaneously monitor movements of opponents and teammates. Until now, however, little is known about the perceptual-cognitive processes underlying peripheral vision in a sporting task. Therefore, we used a mixed-methods approach with in-situ decision making (3 vs. 3 situations) and retrospective verbal reports to identify perceptual strategies used for optimal information pick-up in high- and low-skilled football players. Our results show that the use of peripheral vision by central defenders depends on the position of the ball and the position of the direct opponent. Players were shown to either use a pivot strategy, whereby they frequently look at the direct opponent if he is not in the possession of the ball in addition to making saccades to monitor other players, or they employ a more direct strategy, in which gaze is anchored on this location, avoiding saccades and monitoring the other players with peripheral vision. Based on our findings we make recommendations about how these gaze strategies can be further tested in future research and how sports practice can benefit from these results.

#11 The Relationship Between Personality Traits and Muscle Injuries in Swedish Elite Male Football Players
Reference: J Sport Rehabil. 2019 Oct 18:1-6. doi: 10.1123/jsr.2018-0473. [Epub ahead of print]
Authors: Eckerman M, Svensson K, Edman G, Alricsson M.
Summary: The physical and mental demands of an elite football player are complex, which may explain why injuries are common in football. At elite level, muscle injuries of the lower-extremity are the most common among male football players, and the research hitherto is limited. The aim was to investigate whether personality traits affect the incidence of muscle injuries among male football players from the first league in Sweden. A male football team from the first league in Sweden was prospectively followed, in terms of muscle injuries of the lower-extremity during 8 seasons, between 2007 and 2015. All muscle injuries included in this study were evaluated and diagnosed with ultrasonography. Players from the team filled out the Swedish Universities Scales of Personality questionnaire. Swedish Universities Scales of Personality questionnaire consists of 91 items and is divided into 13 categories. The raw values of each scale were linearly transformed to T scores, having a mean (SD) of 50 (10). All variables were summarized with standard descriptive statistics, such as frequency, mean, and SD. As data were of interval scale and no variable distribution was severely skewed, differences between noninjured players, rarely injured players, and frequently injured players were analyzed with 1-way analysis of variance with post hoc tests by Tukey honestly significant difference test. No significant difference in personality traits were observed between noninjured players, rarely injured players, and frequently injured players regarding number of muscle injuries (P > .05). However, a trend (P = .07) was seen, where frequently injured players scored higher on stress susceptibility than rarely injured players. A player's stress susceptibility should be taken into consideration by the player, coaches, and medical staff when assessing the risk of a muscle injury. Also, preventive measures available for these players may need to be considered.





Latest research in football - week 43 - 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 sleep hygiene strategy improves objective sleep latency following a late-evening soccer-specific training session: A randomized controlled trial
Reference: J Sports Sci. 2019 Dec;37(23):2711-2719. doi: 10.1080/02640414.2019.1661938. Epub 2019 Sep 6.
Authors: Vitale JA, La Torre A, Banfi G, Bonato M
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Summary: The aim of this study was to evaluate the effects of sleep hygiene (SH) education on sleep quality in soccer players after a late-evening small-sided-game (SSG) training session. Twenty-nine non-professional players were recruited and allocated to either an experimental group (EG, n = 17) that received SH education, or a control group (CG, n = 12). SSG consisted of 3 × 4 min in a 4vs4, with 3 min of recovery and was performed at 8.00 p.m. Sleep quality was monitored via actigraphy and sleep diary entries before (PRE) and two nights after (POST1, POST2) the SSG. Sleep latency (SL) differed between the two groups at POST1 (4.9 ± 5.4 vs. 15.5 ± 16.1 for EG and CG, respectively; p = 0.017, effect size [ES] = 2.0); SL values were lower at POST1 compared to PRE for the EG (-47%; p = 0.021, ES = 0.6). Subjective sleep quality was better in the EG than the CG at POST1 (8.6 ± 1.0 vs. 7.1 ± 2.0 for EG and CG, respectively; p = 0.016, ES = 0.9) with a significant improvement over PRE-values (+11.0%, p = 0.004, ES = 0.8). Although SL and subjective sleep quality did not decrease significantly from POST1 to POST2 values at POST2 no longer differed significantly form baseline and, hence, indicate that observed effects may be short-lasting. No other objective sleep indices were influenced by late-evening training or SH practices implemented by the EG. Soccer players may benefit from acute SH strategies to reduce the time to sleep onset after late-evening training sessions.

#2 New curve sprint test for soccer players: Reliability and relationship with linear sprint
Reference: J Sports Sci. 2019 Oct 13:1-6. doi: 10.1080/02640414.2019.1677391. [Epub ahead of print]
Authors: Fílter A, Olivares J, Santalla A, Nakamura FY, Loturco I, Requena B
Summary: The speed performance is involved not only in linear sprints, but also in a wide spectrum of multi-directional movements, such as curve sprinting. Curved sprint can be defined as sprint with gradual and continuous change of direction (COD). Although ~85% of the actions performed at maximum velocity in a professional soccer league are curvilinear sprints, there is not any specific test to assess this ability. This study aimed to analyse the reliability of a new curve sprint test, and compare its results with those obtained by soccer players in linear sprint. Forty experienced soccer players performed 3 attempts of curve sprint (using the penalty arc) to right and left side (17 m), and 3 linear sprints (17 m) in two different days. The ICCs (inter-session reliability) were 0.93 for sprint curve right side (CSRS) and 0.89 for sprint curve left side (CSLS), considered "acceptable". The CVs (intra-session reliability) were 0.87% in CSRS and 1.15% in CSLS. The coefficient of determination (R2) between linear and curve sprinting was ~35%. The association between curve sides was "very large" (r = 0.878; p < 0.01). In summary, we showed that "curve sprint test" is highly reliable, and that curvilinear and linear sprints are different and independent actions.

#3 The most demanding passages of play in football competition: a comparison between halves
Reference: Biol Sport. 2019 Sep;36(3):233-240. doi: 10.5114/biolsport.2019.86005. Epub 2019 Jun 14.
Authors: Casamichana D, Castellano J, Diaz AG, Gabbett TJ, Martin-Garcia A
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Summary: The purpose of this investigation was to determine the differences between halves in the most demanding passages of play in football players according to playing position and duration-specific activity. Global positioning system data were collected from twenty-three football players from a reserve squad of the Spanish La Liga. A total of 265 individual match half data were analysed across the competitive season. Players were categorised based on positional groups: full-back (FB), central defender (CD), midfielder (MF), offensive midfielder (OMF) and forwards (FW). The most demanding passage of match play was analysed using a rolling average method, where maximal values were calculated for five different time durations (1, 3, 5, 10 min and half completed) using distance (m·min-1), high metabolic load distance (HMLD; m·min-1) and average metabolic power (AMP; W·kg-1) as variables of interest. The differences between the first and second half increased as the rolling duration increased, reaching the greatest difference between halves in the complete half (45 min) in all the variables studied (ES = 0.54 ± 0.15, 0.75 ± 0.15 and 0.76 ± 0.15 in distance, HMLD and AMP). The CDs were the players that presented the greatest differences, and it was in the AMP variable where the greatest differences between the first and second half were found. Large decreases in AMP were found for CD (ES = -1.30 ± 0.36) and moderate decreases were found in AMP for FB (ES = -0.84 ± 0.30) and OMF (ES = -0.78 ± 0.37). These results provide insight into the most demanding passages of play to inform training practices for specific football playing positions.

#4 A method for predicting background advertisement exposure parameters in sporting events: Televised football game approach
Reference: PLoS One. 2019 Oct 17;14(10):e0223662. doi: 10.1371/journal.pone.0223662. eCollection 2019.
Authors: Xiao Y, John C, Ren X, Zhang P
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Summary: The background advertisement exposure parameters (BAEP) forms a premise for sponsorship negotiation and the basis for estimating the sponsorship value of background advertising. Prediction of the BAEP has a great contribution to the sporting events organizers and sponsors in terms of negotiating, decision-making for bidding, and income-generating. Virtual Reality (VR), technology was utilized to construct a virtual three-dimensional model of the sports venue and simulate the telecast of the event. Based on VR technology and computer graphics theory, a pre-event prediction method for estimating the background advertisement exposure parameters of sporting events was put forward. The pre and post measures of the thirty BAEP of televised football games were compared to verify the effectiveness of the prediction method. There was no significant difference between the pre- and post-measurement results for the same football game. The pre- and post-measurement results of the thirty BAEP of televised football games were tightly matched. Using the prediction method can predict the BAEP of televised football games effectively and overcomes the shortcomings of current prediction methods that inhibits the effectiveness of the prediction of exposure parameters due to changes such as the type of the sporting events, the size of the sports venue, the layout of the background advertisements, and the placement of the television cameras, etc.

#5 Trait Self-Control Discriminates Between Youth Football Players Selected and Not Selected for the German Talent Program: A Bayesian Analysis
Reference: Front Psychol. 2019 Sep 26;10:2203. doi: 10.3389/fpsyg.2019.02203. eCollection 2019.
Authors: Wolff W, Bertrams A, Schüler J
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Summary: Trait self-control predicts success in various walks of life. Sports is a prototypical domain, where self-control is required, and there is evidence that successful athletes display superior self-control. Here, we assess if self-control already differs between athletes that were selected for a talent development program and non-selected athletes. Self-reported trait self-control was assessed in n = 25 (7 = female, 13.2 ± 1.7 years) youth football players who were part of the German talent development program and in n = 27 (6 = female, 13.6 ± 1.8 years) age and sex matched youth football players, who trained at the same clubs but had not been selected for the program. A one-sided Bayesian two-sample t-test yielded a Bayes factor of 54.99, indicating very strong evidence for the hypothesis that elite youth football players have higher trait self-control than non-elite youth football players. The 95% credibility interval indicates that the true value of δ lies between 0.28 and 1.42, indicating some uncertainty regarding the effects' magnitude. We show that already at young age, elite athletes display higher levels of self-control than their less successful peers. This underlines the importance of self-control as an important personality factor for success. These findings might have implications for talent selection and for sport psychological training.

#6 Clinical Features and isokinetic Parameters in Assessing Injury Risk in elite Football Players
Reference: Int J Sports Med. 2019 Oct 15. doi: 10.1055/a-1014-2911. [Epub ahead of print]
Authors: Liporaci RF, Saad M, Grossi DB, Riberto M
Summary: Football players frequently face the occurrence of non-contact injuries. Although there are likely multiple factors that contribute to increased risk of non-contact injury, it remains a challenge to correlate all these factors. However, it is not clear how much of individual training abilities may interfere in these events. As such, the primary aim of the present study was to determine whether the reduction of functional performance of the thigh in the isokinetic knee tests, anthropometric and morbid history can establish risk factors for lower-limb musculoskeletal injuries throughout the season. The incidence of injuries and odds ratios were calculated for suspected risk factors. Hamstring/Quadriceps conventional ratio outside of the safety range (55-64%) may be involved in the occurrence of non-contact muscle injuries and the risk for any musculoskeletal injuries in the lower extremities is 16 times higher when extensor peak of torque exceeds 10% and 12 times higher when flexor peak of torque difference was greater than 10%. This kind of evaluation can result in intervention programs that may decrease the risk of lower-limb musculoskeletal injuries. Based on these results we can establish a specific and individualized exercise program for each athlete and thus protect them during the season.

#7 Psychological characteristics of developing excellence in elite youth football players in English professional academies
Reference: J Sports Sci. 2019 Oct 13:1-7. doi: 10.1080/02640414.2019.1676526. [Epub ahead of print]
Authors: Saward C, Morris JG, Nevill ME, Minniti AM, Sunderland C
Summary: This mixed-longitudinal prospective study examined the development of psychological characteristics of developing excellence in relation to the career progression of elite youth football players. In a 20-month period, 111 academy football players aged 11-16 completed the Psychological Characteristics of Developing Excellence Questionnaire (PCDEQ) on 1-5 occasions. This combination of single and repeated assessments resulted in a mixed-longitudinal sample of 226 completed PCDEQs. Players were then prospectively tracked, and their scholarship status assessed at follow-up, at age U17. Multilevel modelling revealed that coping with performance and developmental pressures scores increased with age, and that Category 1-2 academy scholars (4.35 ± 0.61) scored higher than Category 3-4 academy scholars (3.99 ± 0.67) and non-scholars (4.02 ± 0.78) (p < .05). Evaluating performances and working on weaknesses scores increased with age for Category 1-2 academy scholars (U12-U14 vs. U15-U16 = 5.16 ± 0.48 vs. 5.38 ± 0.45), compared to non-scholars (U12-U14 vs. U15-U16 = 5.11 ± 0.59 vs. 5.03 ± 0.71) (p < .05). Imagery use during practice and competition scores decreased with age (U12-U14 vs. U15-U16 = 4.45 ± 0.66 vs. 4.29 ± 0.70) (p < .05). A blend of PCDEs may facilitate optimal career progression. Football academies should develop players' PCDEs, with a particular focus on developing their coping skills and their ability to realistically evaluate performances and work on weaknesses.

#8 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, Klatt 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.

#9 The effect of age on between-match physical performance variability in professional soccer players
Reference: Res Sports Med. 2019 Oct 20:1-9. doi: 10.1080/15438627.2019.1680985. [Epub ahead of print]
Authors: Lorenzo-Martínez M, Rey E, Padrón-Cabo A
Summary: This study aimed to analyse the effect of age on between-match variability of physical performance in professional soccer players. For this purpose, observations on entire match performance were collected on 787 professional soccer players competing in the first or second division of Spanish league during the 2017-2018 season. Players were classified into six groups according to their age: G1 (≤22.5 years), G2 (22.6-25.1 years), G3 (25.2-27.5 years), G4 (27.6-30.1 years), G5 (30.2-33.1 years) and G6 (≥33.2 years). Coefficients of variation (CVs) were calculated individually for each player and performance variable: total distance, low- intensity, medium-intensity, high-intensity running (HIR), sprinting, number of HIR, number of sprints, average speed and maximal speed. The main finding of this study was that players under 25.2 years (G1 and G2) showed lower CVs for high-intensity activities (HIR and sprinting) in comparison with players over 33.1 years (G6). These findings provide useful information for soccer coaches, who could put extra attention on physical performance of the oldest players when they have to play an entire match, because their performance is more variable and uncertain in comparison with the youngest.

#10 Basal Serum Cortisol and Testosterone/Cortisol Ratio Are Related to Rate of Na+ Lost During Exercise in Elite Soccer Players
Reference: Int J Sport Nutr Exerc Metab. 2019 Oct 17:1-6. doi: 10.1123/ijsnem.2019-0129. [Epub ahead of print]
Authors: Castro-Sepulveda M, Cancino J, Fernández-Verdejo R, Pérez-Luco C, Jannas-Vela S, Ramirez-Campillo R, Del Coso J, Zbinden-Foncea H
Summary: During exercise, the human body maintains optimal body temperature through thermoregulatory sweating, which implies the loss of water, sodium (Na+), and other electrolytes. Sweat rate and sweat Na+ concentration show high interindividual variability, even in individuals exercising under similar conditions. Testosterone and cortisol may regulate sweat Na+ loss by modifying the expression/activity of the cystic fibrosis transmembrane conductance regulator. This has not been tested. As a first approximation, the authors aimed to determine whether basal serum concentrations of testosterone or cortisol, or the testosterone/cortisol ratio relate to sweat Na+ loss during exercise. A total of 22 male elite soccer players participated in the study. Testosterone and cortisol were measured in blood samples before exercise (basal). Sweat samples were collected during a training session, and sweat Na+ concentration was determined. The basal serum concentrations of testosterone and cortisol and their ratio were (mean [SD]) 13.6 (3.3) pg/ml, 228.9 (41.4) ng/ml, and 0.06 (0.02), respectively. During exercise, the rate of Na+ loss was related to cortisol (r = .43; p < .05) and to the testosterone/cortisol ratio (r = -.46; p < .01), independently of the sweating rate. The results suggest that cortisol and the testosterone/cortisol ratio may influence Na+ loss during exercise. It is unknown whether this regulation depends on the cystic fibrosis transmembrane conductance regulator.

#11 Comparison of Drop Jump and Tuck Jump Knee Joint Kinematics in Elite Male Youth Soccer Players: Implications for Injury Risk Screening
Reference: J Sport Rehabil. 2019 Oct 18:1-6. doi: 10.1123/jsr.2019-0077. [Epub ahead of print]
Authors: Lloyd RS, Oliver JL, Myer GD, De Ste Croix MB, Wass J, Read PJ.
Summary: Despite the popularity of jump-landing tasks being used to identify injury risk factors, minimal data currently exist examining differences in knee kinematics during commonly used bilateral jumping tasks. This is especially the case for rebounding-based protocols involving young athletes. The aim was to compare the frontal plane projection angles (FPPAs) during the drop vertical jump (DVJ) and tuck jump assessment (TJA) in a cohort of elite male youth soccer players of varying maturity status. A total of 57 male youth soccer players from an English championship soccer club participated in this study. Participants performed 3 trials of the DVJ and TJA, during which movement was recorded with 2-dimensional video cameras. FPPA for both right (FPPA-r) and left (FPPA-l) legs, with values <180° indicative of medial knee displacement. On a whole-group level, FPPA-r (172.7° [7.4°] vs 177.2° [11.7°]; P < .05; effect size [ES] = 0.46) and FPPA-l (173.4° [7.3°] vs 179.2° [11.0°]; P < .05; ES = 0.62) were significantly greater for both limbs in the TJA compared with the DVJ; however, these differences were less consistent when grouped by maturity status. FPPA-r during the TJA was significantly and moderately greater in the circa-peak height velocity (PHV) group compared with the post-PHV cohorts (169.4° [6.4°] vs 175.3° [7.8°]; P < .05; ES = 0.49). Whole-group data showed moderate relationships for FPPA-r and FPPA-l between the TJA and DVJ; however, stronger relationships were shown in circa- and post-PHV players compared with the pre-PHV cohort. Considering that the TJA exposed players to a larger FPPA and was sensitive to between-group differences in FPPA-r, the TJA could be viewed as a more suitable screen for identifying FPPA in young male soccer players.





Latest research in football - week 42 - 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 Return-to-Play Practices Following Hamstring Injury: A Worldwide Survey of 131 Premier League Football Teams
Reference: Sports Med. 2019 Oct 8. doi: 10.1007/s40279-019-01199-2. [Epub ahead of print]
Authors: Dunlop G, Ardern CL, Andersen TE, Lewin C, Dupont G, Ashworth B, O'Driscoll G, Rolls A, Brown S, McCall A
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Summary: Return-to-play (RTP) is an on-going challenge in professional football. Return-to-play related research is increasing. However, it is unknown to what extent the recommendations presented within research are being implemented by professional football teams, and where there are gaps between research and practice. The purposes of this study were (1) to determine if premier-league football teams worldwide follow a RTP continuum, (2) to identify RTP criteria used and (3) to understand how RTP decision-making occurs in applied practice. We sent a structured online survey to practitioners responsible for the RTP programme in 310 professional teams from 34 premier-leagues worldwide. The survey comprised four sections, based on hamstring muscle injury: (1) criteria used throughout RTP phases, (2) the frequency with which progression criteria were achieved, (3) RTP decision-making process and (4) challenges to decision-making. One-hundred and thirty-one teams responded with a completed survey (42%). One-hundred and twenty-four teams (95%) used a continuum to guide RTP, assessing a combination of clinical, functional and psychological criteria to inform decisions to progress. One-hundred and five (80%) teams reported using a shared decision-making approach considering the input of multiple stakeholders. Team hierarchy, match- and player-related factors were common challenges perceived to influence decision-making. General research recommendations for RTP and the beliefs and practices of practitioners appear to match with, the majority of teams assessing functional, clinical and psychological criteria throughout a RTP continuum to inform decision-making which is also shared among key stakeholders. However, specific criteria, metrics and thresholds used, and the specific involvement, dynamics and interactions of staff during decision-making are not clear.

#2 Match Running Performance on Three Different Competitive Standards in Norwegian Soccer
Reference: Sports Med Int Open. 2019 Oct 16;3(3):E82-E88. doi: 10.1055/a-0943-3682. eCollection 2019 Dec.
Authors: Sæterbakken A, Haug V, Fransson D, Grendstad HN, Gundersen HS, Moe VF, Ylvisaker E, Shaw M, Riiser A, Andersen V
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Summary: The aim of the study was to compare running performance of three competitive standards and to examine the effects of being promoted to a higher league in Norwegian football. One club's first and second team were included. The first team consisted of professional soccer players playing at Level 2 (2015 season) and Level 1 (2016 season). The second team consisted of amateurs playing at Level 4. A fully automatic tracking system was used to examine running performance, divided into different running-speed categories and playing position. Forty-one matches were included containing 278 observations. Level 1 performed 61 and 51% sprinting compared to Level 2 and Level 4 but similar high-speed running. Similar high-speed running distances were observed only for the different playing positions at Level 1 compared to Level 2 and 4. The sprinting distance was greater for the central defender and attacker, and the number of accelerations was greater for central midfielders and wide midfielders' playing at Level 1 compared to lower competitive standards. In conclusion, better competitive standards resulted in greater high-intensity actions than lower leagues in Norwegian soccer. Furthermore, only central defenders and attackers increased their high-intensity locomotions when the team was promoted.

#3 Effects of different repeated sprint-training frequencies in youth soccer players
Reference: Biol Sport. 2019 Sep;36(3):257-264. doi: 10.5114/biolsport.2019.87047. Epub 2019 Jul 31.
Authors: Rey E, Padrón-Cabo A, Costa PB, Lago-Fuentes C
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Summary: The aim of this study was to determine the effects of 2 different repeated-sprint ability (RSA) training frequencies (2 RSA sessions per week [RSA2D] or 1 RSA session [RSA1D]) under volume-equated conditions on sprint and RSA performance in under-15 (U15) soccer players. Twenty-seven youth male soccer players (age: 12.29±0.47 years; height: 158.35±10.86 cm; weight: 45.08±8.05 kg) were randomly assigned to RSA2D (n=14) or RSA1D (n=13) groups. The players performed the same RSA training for 6 weeks, and only the training frequency differed between the groups. Before and after the training period, 5 m sprint, 10 m sprint, 20 m sprint and the RSA test were assessed. No significant time × group interactions were observed (p>0.05). Within-group analysis showed significant improvements in 20 m sprint (p=0.046, partial eta squared [η p 2 ] = 0.150, large) and RSA average time (p=0.001, η p 2 =0.438, large), fastest time (p=0.012, η p 2 =0.229, large), and total time (p=0.001, η p 2 =0.438, large) from pre-test to post-test in RSA1D and RSA2D groups. However, no significant pre-post changes (p>0.05) were found in 5 m and 10 m sprint tests. In the between-group analysis, there were no significant differences between RSA1D and RSA2D groups in any variable. In conclusion, the current findings suggest that 6 weeks of RSA training 1 or 2 times per week in addition to typical soccer training produced significant and similar improvements in sprint and RSA performances. This information could be useful for coaches when planning training sessions during congested fixtures of soccer competitions or in periods when the emphasis should be placed on other physical qualities.

#4 Running technique is more effective than soccer-specific training for improving the sprint and agility performances with ball possession of prepubescent soccer players
Reference: Biol Sport. 2019 Sep;36(3):249-255. doi: 10.5114/biolsport.2019.87046. Epub 2019 Jul 31.
Authors: Lupo C, Ungureanu AN, Varalda M, Brustio PR
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Summary: Soccer-specific training is easily associable to players' sprint abilities demonstrated during a match. However, no clear evidence has been provided to show whether this approach is more effective than training focused on running techniques for sprints in prepubescent soccer players. Thus, the present study aimed at comparing the effects of these two training approaches on prepubescent soccer players' sprint performances. Ninety-five players (10±2 years) competing in local (Piedmont, Italy) Under-9 (N=21), -10 (N=24), -11 (N=25) and -13 (N=25) championships were recruited for the study. Sixty-three and 32 players were included in the running training group (RTG) and soccer-specific group (SSG), respectively. Before (PRE) and after (POST) the training period (2 weekly sessions for 12 weeks), sprint abilities were evaluated by means of four 20-m sprint tests: linear sprint (20-mL), linear sprint with ball possession (20-mLB), sprint with change of direction (20-mCoD), sprint with change of direction and with ball possession (20-mCoDB). A linear mixed model was applied to evaluate differences (P≤0.05) between the RTG and SSG in the four tests and categories, comparing PRE and POST performances. A main effect emerged for the interaction between groups, sessions (p=0.014; Between PRE ES range=0.03, 0.85; Within PRE-POST ES range=-0.45, 0.09), highlighting a POST improvement of RTG for the 20-mLB (Δ=-7.9%; ES=0.85) and 20-mCoDB (Δ=-5.9%; ES=0.33). In contrast, no improvements emerged for the SSG. The present findings indicate that the training approach of the RTG is more able to improve prepubescent soccer players' sprint performances than that of the SSG, with the emphasis on ball possession executions, which are particularly game-related.

#5 Effects of in-season enhanced negative work-based vs traditional weight training on change of direction and hamstrings-to-quadriceps ratio in soccer players
Reference: Biol Sport. 2019 Sep;36(3):241-248. doi: 10.5114/biolsport.2019.87045. Epub 2019 Jul 31.
Authors: Coratella G, Beato M, Cè E, Scurati R, Milanese C, Schena F, Esposito F
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Summary: The present study investigated the effects of in-season enhanced negative work-based training (ENT) vs weight training in the change of direction (COD), sprinting and jumping ability, muscle mass and strength in semi-professional soccer players. Forty male soccer players participated in the eight-week, 1 d/w intervention consisting of 48 squat repetitions for ENT using a flywheel device (inertia=0.11 kg·m -2 ) or weight training (80%1 RM) as a control group (CON). Agility T-test, 20+20 m shuttle, 10 m and 30 m sprint, squat jump (SJ) and countermovement jump (CMJ), lean mass, quadriceps and hamstrings strength and the hamstrings-to-quadriceps ratio were measured. Time on agility T-test and 20+20 m shuttle decreased in ENT (effect-size =-1.44, 95% CI -2.24/-0.68 and -0.75, -1.09/-0.42 respectively) but not in CON (-0.33, -0.87/0.19 and -0.13, -0.58/0.32). SJ and CMJ height increased in both ENT (0.71, 0.45/0.97 and 0.65, 0.38/0.93) and CON (0.41, 0.23/0.60 and 0.36, 0.12/0.70). Overall, quadriceps and hamstrings strength increased in both ENT and CON (0.38/0.79), but the hamstrings-to-quadriceps ratio increased in ENT (0.31, 0.22/0.40) but not in CON (0.03, -0.18/0.24). Lean mass increased in both ENT (0.41, 0.26/0.57) and CON (0.29, 0.14/0.44). The repeated negative actions performed in ENT may have led to improvements in braking ability, a key point in COD performance. Semi-professional soccer players may benefit from in-season ENT to enhance COD and the negative-specific adaptations in muscle strength and hamstrings-to-quadriceps ratio.

#6 Do asymmetry scores influence speed and power performance in elite female soccer players?
Reference: Biol Sport. 2019 Sep;36(3):209-216. doi: 10.5114/biolsport.2019.85454. Epub 2019 May 30.
Authors: Loturco I, Pereira LA, Kobal R, Abad CCC, Rosseti M, Carpes FP, Bishop C
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Summary: This study examined the relationships between vertical jump asymmetries and speed and power performance in elite female soccer athletes. Sixteen professional female soccer players (age: 23.0 ± 3.8 years; body mass: 60.2 ± 7.3 kg; height: 165.1 ± 5.5 cm) from the same professional club participated in this study. Athletes performed unilateral and bilateral squat jumps (SJ) and countermovement jumps (CMJ) on a portable force plate; 30-m sprinting test; Zigzag change-of-direction (COD) test; and muscle power testing using the jump squat (JS) exercise. Asymmetry scores were obtained from the results of the unilateral SJ and CMJ by the percentage difference between the dominant and non-dominant legs. The Pearson product-moment coefficient of correlation was used to analyse the correlations between the bilateral and unilateral vertical jump variables and the physical tests. The bilateral vertical jump performance (in both SJ and CMJ) was closely related to sprinting and JS power performances (r values ranging from 0.50 to 0.73; P< 0.05). In contrast, no significant associations were found between jump asymmetries and performance measures. Our data suggest that asymmetry scores derived from unilateral vertical jumps are not capable of influencing the speed-power performance of professional female soccer players.

#7 Adolescent female soccer players' soccer-specific warm-up effects on performance and inter-limb asymmetries
Reference: Biol Sport. 2019 Sep;36(3):199-207. doi: 10.5114/biolsport.2019.85453. Epub 2019 May 28.
Authors: Pardos-Mainer E, Casajús JA, Gonzalo-Skok O
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Summary: No studies have assessed whether changes in physical performance and inter-limb asymmetries (ILA) can be achieved with the FIFA 11+ prevention programme in adolescent female soccer players. The aim of this study was to assess the effect of the FIFA 11+ programme compared with a standard warm-up on physical performance and ILA in adolescent female soccer players. Thirty-six adolescent female soccer players were randomly assigned to an experimental (EG; n = 19) or a control group (CG; n = 17). Unilateral/bilateral countermovement jump (CMJ), drop jump (DJ) and horizontal jump tests, two different change of direction tests, an ankle dorsiflexion test, the Y-Balance test (YBT) and inter-limb asymmetries were measured before and after 10 weeks of training. The results revealed no significant group-by-time interactions in the vast majority of variables (p>0.05). Paired t-test revealed significant improvements of the right [effect size (ES):0.56] and left (ES:0.49) CMJ, right (ES:0.74) and left (ES:0.54) DJ (ES:0.74), right (ES:1.27) and left (ES:1.26) posteromedial direction and right (ES:0.89) and left (ES:0.84) posterolateral direction in the YBT in the EG (p < 0.05). Right anterior direction in the YBT and V-cut test were significantly improved in both groups (p<0.05). For inter-limb asymmetry variables, no significant group-by-time interactions (ES:0 to 0.93) and an improvement between pre- and post-tests (ES:-0.76 to 0.49) were observed. Therefore, the FIFA 11+ programme led to improved unilateral jumping, dynamic balance and reduced lower extremity symmetries of several tests in adolescent female soccer players.

#8 Retraction Note: Assessing cardiorespiratory fitness of soccer players: is test specificity the issue?-a review
Reference: Sports Med Open. 2019 Oct 17;5(1):42. doi: 10.1186/s40798-019-0217-9.
Authors: Jemni M, Prince MS, Baker JS
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#9 Effect of Kinesio Taping and balance exercises on postural control in amateur soccer players: A randomised control trial
Reference: J Sports Sci. 2019 Dec;37(24):2853-2862. doi: 10.1080/02640414.2019.1677016. Epub 2019 Oct 15.
Authors: Inglés M, Serra-Añó P, Méndez ÀG, Zarzoso M, Aguilar-Rodríguez M, Suso-Martí L, Cuenca-Martínez F, Espí-López GV
Summary: The objective of this study was to determine the effect of Kinesio Taping (KT), alone or together with balance exercises (BE), on parameters related to postural control, such as dynamic balance, static balance and flexibility. Forty-four male amateur soccer players (mean age 24.45 (4.79) years) were randomly allocated to 3 groups: KT+BE that received KT and BE (n = 16); KTp+BE, in which the KT was used as a placebo (n = 15) and KT alone (n = 13). The intervention period lasted 4 weeks. Star Excursion Balance Test (SEBT), Unipedal Stance Test (UST) and the Toe Touch Test (TTT) were assessed at baseline (pre), two weeks after beginning the treatment (mid) and after the intervention (post). We observed a significant improvement on the SEBT (mid and post-treatment) and the UST (post-treatment), but not on the TTT in either KT+BE or KTp+BE groups post treatment. No differences were found either in KT group at any time point or between groups in any variable studied. In conclusion, KT functional correction technique does not improve static and dynamic balance when applied alone, whereas BE alone or combined with KT significantly improves these variables. None of these techniques has any effect on flexibility.

#10 Pediatric retinal damage due to soccer-ball-related injury: Results from the last decade
Reference: Eur J Ophthalmol. 2019 Oct 15:1120672119882332. doi: 10.1177/1120672119882332. [Epub ahead of print]
Authors: Leshno A, Alhalel A, Fogel-Levin M, Zloto O, Moisseiev J, Vidne-Hay O
Summary: The aim was to outline the incidence of posterior segment injuries related to soccer-ball blunt trauma in children. Retrospective search of the computerized hospital medical database between the years 2007 and 2017. All pediatric trauma cases were reviewed and cases with blunt trauma related to direct orbital/ocular hit from a soccer-ball were included. Cases were divided into two groups (non-severe and severe) based on the presence of sight-threatening findings on presentation (e.g. retinal tear, vitreous hemorrhage, retinal detachment, and macular edema). Out of 343 pediatric patients with relevant diagnoses, 14 (4.1%) were treated for injuries related to soccer-ball trauma. All patients were males at their early-to-mid teens (14.3 ± 2.1 years). The most common funduscopic finding was peripheral commotio retina (13, 93%). There was equal distribution between the two groups (seven each). Retinal injury in the severe group included retinal tear (3), vitreous hemorrhage (4), retinal detachment (1), and macular hole (1). Five patients in this group presented with visual acuity of 20/25 or better. Rate of external signs of injury were similar in both groups. Soccer-ball blunt trauma in children can cause significant posterior segment injuries regardless of the presence of external injury or ocular complaints. A thorough ocular exam is mandatory in all cases for the detection of vision-threatening retinal injuries.

#11 Acute sleep hygiene strategy improves objective sleep latency following a late-evening soccer-specific training session: A randomized controlled trial
Reference: J Sports Sci. 2019 Dec;37(23):2711-2719. doi: 10.1080/02640414.2019.1661938. Epub 2019 Sep 6.
Authors: Vitale JA, La Torre A, Banfi G, Bonato M
Summary: The aim of this study was to evaluate the effects of sleep hygiene (SH) education on sleep quality in soccer players after a late-evening small-sided-game (SSG) training session. Twenty-nine non-professional players were recruited and allocated to either an experimental group (EG, n = 17) that received SH education, or a control group (CG, n = 12). SSG consisted of 3 × 4 min in a 4vs4, with 3 min of recovery and was performed at 8.00 p.m. Sleep quality was monitored via actigraphy and sleep diary entries before (PRE) and two nights after (POST1, POST2) the SSG. Sleep latency (SL) differed between the two groups at POST1 (4.9 ± 5.4 vs. 15.5 ± 16.1 for EG and CG, respectively; p = 0.017, effect size [ES] = 2.0); SL values were lower at POST1 compared to PRE for the EG (-47%; p = 0.021, ES = 0.6). Subjective sleep quality was better in the EG than the CG at POST1 (8.6 ± 1.0 vs. 7.1 ± 2.0 for EG and CG, respectively; p = 0.016, ES = 0.9) with a significant improvement over PRE-values (+11.0%, p = 0.004, ES = 0.8). Although SL and subjective sleep quality did not decrease significantly from POST1 to POST2 values at POST2 no longer differed significantly form baseline and, hence, indicate that observed effects may be short-lasting. No other objective sleep indices were influenced by late-evening training or SH practices implemented by the EG. Soccer players may benefit from acute SH strategies to reduce the time to sleep onset after late-evening training sessions.





Latest research in football - week 41 - 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 Isometric Posterior Chain Peak Force Recovery Response Following Match-Play in Elite Youth Soccer Players: Associations with Relative Posterior Chain Strength
Reference: Sports (Basel). 2019 Oct 1;7(10). pii: E218. doi: 10.3390/sports7100218.
Authors: Constantine E, Taberner M, Richter C, Willett M, Cohen DD
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Summary: The purpose of this study was to determine changes in two tests of lower limb isometric posterior chain force (IPC-F) following 90 min of match-play in elite youth soccer players and the interaction between relative strength and recovery profile. 14 players (age: 16 ± 2 years) performed 3 × 3 second IPC-F tests unilaterally at 30° and 90° of knee and hip flexion pre- and post-match, +24 h, +48 h, and +72 h post-match. Peak force was recorded for both limbs, combined and expressed relative to bodyweight (N/kg). A two-way repeated measures analysis of variance was performed to determine differences in force output between joint angles, time intervals and subjects. As there was no interaction between angle and time (p = 0.260), we report the change between timepoints as mean Δ in 90° + 30° IPC-F. Relative to pre-match IPC-F, there were significant decreases post (Δ = -18%; p > 0.001) and at +24 h (Δ = -8%; p = 0.040), no significant difference at +48 h (Δ = 0%; p = 0.992) and a significant increase at +72 h (Δ = +12%; p = 0.005). There was a large inter-individual variability in recovery profile at both angles and substantial differences between post-match deficits at 90° (-10.8%) compared to 30° (-20.7%). Higher pre-match IPC-F was correlated with the magnitude of IPC-F deficits at both angles and all time points (r = 0.56 to 0.70, p = < 0.01) except for post-match 90°. Regular IPC-F monitoring to determine the magnitude of match-induced fatigue and track recovery may help inform decision-making regarding modifications to individual players training load, particularly as there is a large inter-individual variability in response to competition. Further research is warranted to better understand and address the finding that stronger players showed larger force deficits and slower recovery following match-play.

#2 Investigating the Clinical Effect of Kinesio Tape on Muscle Performance in Healthy Young Soccer Players - A Prospective Cohort Study
Reference: Clinics (Sao Paulo). 2019 Sep 26;74:e1158. doi: 10.6061/clinics/2019/e1158. eCollection 2019.
Authors: Alrawaili SM
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Summary: Kinesio tape (KT) is a visible adhesive restorative tape that has typically been utilized for injury prevention, recovery, and even performance improvement, but limited studies have assessed the effect of KT on muscle performance. The purpose of this study was to investigate the clinical impact of KT on muscle performance in healthy young soccer players. Between 25 March and 21 April 2017, sixteen healthy soccer players with a mean age of 20±2.17 were enrolled in this prospective cohort study. All participants were selected from the college football team of Prince Sattam Bin Abdulaziz University. The muscle performance of the players was evaluated with an isokinetic dynamometer for the following three conditions: without tape, immediately after applying KT, and 8 hrs post-KT application while the tape remained on the same site. The differences in peak torque and total work among the three conditions were nonsignificant (p>0.05). Additionally, applying KT to the thigh muscles did not decrease or increase the performance of non injured healthy soccer players (p>0.05). KT does not lead to beneficial outcomes of muscle performance in healthy young soccer players.

#3 Biomechanical mechanisms of jumping performance in youth elite female soccer players
Reference: J Sports Sci. 2019 Oct 1:1-7. doi: 10.1080/02640414.2019.1674526. [Epub ahead of print]
Authors: Jeras NMJ, Bovend'Eerdt TJH, McCrum C
Summary: We aimed to determine key biomechanical parameters explaining age-related jumping performance differences in youth elite female soccer players. Multiple biomechanical parameters from countermovement (CMJ) squat (SJ) and drop (DJ) jump testing of elite female soccer players (n = 60) within the same national training centre were analysed across ages 9-11y, 12-14y and 15-19y. Effects of age group and jump type on jump height were found, with the older jumping higher than the younger groups in all jumps (P < 0.05). For DJ, higher reactive strength index was found for older, compared to each younger group (P < 0.001). For CMJ and SJ, peak power was the most decisive characteristic, with significant differences between each group for absolute peak power (P < 0.0001) and body-weight-normalised peak power in CMJ (57 ± 7W/kg, 50 ± 7W/kg, 44.7 ± 5.5W/kg; P < 0.05) and between the older and each younger group in SJ (56.7 ± 7.1W/kg, 48.9 ± 7.1W/kg, 44.6 ± 6W/kg; P < 0.01). Age-related differences in jumping performance in youth elite female soccer players appear to be due to power production during standing jumps and by the ability to jump with shorter ground contact times during reactive jumps.

#4 Effect of Match Location, Team Ranking, Match Status and Tactical Dimensions on the Offensive Performance in Spanish 'La Liga' Soccer Matches
Reference: Front Psychol. 2019 Sep 12;10:2089. doi: 10.3389/fpsyg.2019.02089. eCollection 2019.
Authors: González-Rodenas J, Aranda-Malavés R, Tudela-Desantes A, Calabuig Moreno F, Casal CA, Aranda R

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Summary: The aim of this paper was to study the combined effects of tactical and contextual dimensions on achieving offensive performance in open play possessions from Spanish "La Liga" soccer matches. 1860 team possessions from 20 random matches were evaluated by means of multidimensional observation. Multilevel regression models were constructed to predict the probability to achieve offensive performance according to the tactical and contextual dimensions registered in each possession. Performing penetrative actions after recovering the ball (OR = 1.497; 95% CI: 1.022-2.192; P < 0.05), and progressing by fast attacks (OR = 3.588; 95% CI: 2.045-6.294; p < 0.001) or counterattacks (OR = 7.097; 95% CI: 3.530-14.269; P < 0.001) was more effective to create scoring opportunities than performing a non-penetrative action and progressing by combinative attack, respectively. Also, progressing by long possessions (OR = 5.057; 95% CI: 2.406-10.627; p < 0.001) was more effective than progressing by short possessions to create scoring opportunities. As for contextual dimensions, multivariate analyses showed how playing at home and against high-ranked opponents registered more likelihood of achieving offensive penetration, although no associations were found in the production of scoring opportunities. Tactical dimensions as initial penetration, type of attack and possession length played an important role on achieving offensive penetration and goal scoring opportunities in Spanish Soccer "La Liga".

#5 Transformational Leadership, Task-Involving Climate, and Their Implications in Male Junior Soccer Players: A Multilevel Approach
Reference: Int J Environ Res Public Health. 2019 Sep 28;16(19). pii: E3649. doi: 10.3390/ijerph16193649.
Authors: Álvarez O, Castillo I, Molina-García V, Tomás I
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Summary: Despite the well-known positive consequences of transformational coaches in sport, there is still little research exploring the mechanisms through which coaches' transformational leadership exerts its impact on athletes. Multilevel SEM was used to examine the relationship between coaches' transformational leadership style, a task-involving climate, and leadership effectiveness outcome criteria (i.e., players' extra effort, coach effectiveness, and satisfaction with their coach), separately estimating between and within effects. A representative sample of 625 Spanish male soccer players ranging from 16 to 18 years old and nested in 50 teams completed a questionnaire package tapping the variables of interest. Results confirmed that at the team level, team perceptions of transformational leadership positively predicted teams' perceptions of task climate, which in turn positively predicted the three outcome criteria. At the individual level, players' perceptions of transformational leadership positively predicted teams' perceptions of task climate, which in turn positively predicted teams' extra effort and coach effectiveness. Mediation effects appeared at the team level for all the outcome criteria, and at the individual only for extra effort. Transformational leadership is recommended to enhance task climate, in order to increase players' extra effort, their perceptions of the effectiveness of their coach, and their satisfaction with his/her leadership style.

#6 Inspiratory muscle training improves performance of a repeated sprints ability test in professional soccer players
Reference: J Bodyw Mov Ther. 2019 Jul;23(3):452-455. doi: 10.1016/j.jbmt.2019.01.016. Epub 2019 Jan 30.
Authors: Cavalcante Silva RL, Hall E, Maior AS
Summary: The aim of this study was to investigate the effects of IMT on exercise tolerance, repeated sprint ability (RSA) performance, maximal inspiratory pressure (MIP), and peak inspiratory flow (PIF) in a cohort of professional male soccer players. Twenty-two healthy male professional soccer players (18.3 ± 1.4 years; 174.5 ± 6.1 cm; 70.5 kg ± 4.6 kg; body fat 10.1 ± 4.2%) from a club in the Brazilian first division soccer league participated in this study. IMT consisted of 15 and 30 self-paced inspiratory breaths (each to 50% maximal static inspiratory pressure [P0]) in the 1-and 2-week intervention period, respectively. IMT was performed prior to soccer training (1 sets.d-1; 6 d.wk-1) with repeated sprint ability (RSA) assessed pre- and post- the 2-week period of IMT. Statistical analyses identified a significant (p < 0.001) decrease in sprint time post-IMT. Additionally, RSAbest, RSAmean, total sprint time and percentage of RSA performance decrement (RSA % dec) also showed significant decreases (p < 0.0001) post-IMT. Additional measures including MIP and PIF were also significantly elevated (p < 0.0002) following the 2-week period of IMT. In conclusion, our results raise two important issues. Firstly, IMT demonstrated enhanced inspiratory muscle strength in professional soccer players. Secondly, this increase in inspiratory muscle efficiency led to a decrease in sprint time and improved exercise tolerance. We recommend that a standard training protocol be developed and tested in an experimental and control group with a large representative sample.

#7 Regarding: "Inspiratory muscle training improves performance of a repeated sprints ability test in professional soccer players"
Reference: J Bodyw Mov Ther. 2019 Jul;23(3):443-444. doi: 10.1016/j.jbmt.2019.03.012. Epub 2019 Apr 2.
Authors: Matte DL, Ribeiro GS, Esquivel MS, Karsten M
Summary: The Journal of Bodywork & Movement Therapies recently published an article by Silva et al., entitled "Inspiratory muscle training improves performance of a repeated sprints ability test in professional soccer players" (Silva et al., 2019). After close reading we find that the new findings of Silva et al., (2019) are relevant and provide a promising indication that IMT can improve the performance of young male soccer players. However, some additional important points must be considered when interpreting these positive findings.

#8 Session-To-Session Variations of External Load Measures of Youth Soccer Players in Medium-Sided Games
Reference: Int J Environ Res Public Health. 2019 Sep 26;16(19). pii: E3612. doi: 10.3390/ijerph16193612.
Authors: Clemente FM, Rabbani A, Kargarfard M, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The aim of this study was to analyze the variability of time-motion variables during five vs. five games when completed within the same session as, and between, two different sessions. Ten under-19 male soccer players (18.27 ± 0.47 years old) participated in this study. The five vs. five matches (3 × 5 min) were played twice with a 3-day interval of rest in the same week. Moderate between-session variations were observed for TD (total distance) (range coefficient of variation (CV), 6.9; 8.3%, confidence interval (CI), (5.0; 14.0), standardized typical error (STE), 0.68; 1.06, (0.64; 1.75)) and RD (running distance) (range CV, 53.3; 145.7%, (36.6; 338.9), STE, 0.83; 1.09, (0.60; 1.76)). PL (player load) showed small variations (range CV, 4.9; 6.0%, [3.6; 10.1], STE, 0.37; 0.43, (0.27; 0.71)). In within-session analyses for examining the differences between sets, a small decrease was observed in RD in set 3 versus set 2 (-14.8%, 90% CI (-32.1; 6.9%); standardized difference (ES): -0.39 (0.95; 0.16)). TD decreased with moderate (-3.5%, (-6.8; -0.1%); ES: -0.65(-1.30; -0.01)) and large (-8.2%, (-11.4; -4.9%); ES: -1.58(-2.24; -0.92)) effects in sets 2 and 3, respectively, versus set 1. Our results suggest that PL is the most stable performance variable. It was also verified that measures had a progressive decreasing tendency within a session.

#9 Head impact exposure in youth football - are current interventions hitting the target?
Reference: Scand J Med Sci Sports. 2019 Oct 4. doi: 10.1111/sms.13562. [Epub ahead of print]
Authors: Sandmo SB, Andersen TE, Koerte IK, Bahr R
Summary: Restrictions on heading in youth football have been implemented in some countries to limit head-impact exposure. However, current interventions remain poorly guided by evidence. Our objective was to quantify heading exposure in youth football, assessing the effects of sex and age. Football matches played during an international youth football tournament with no heading restrictions were directly observed, including players from both sexes (11-19 years). The elite senior level was included for comparison, using video analysis. All heading events were registered, classified and assigned to individual players. Heading rates were calculated for each sex and age group. We observed a total of 267 matches, corresponding to 4011 player hours (1927 player hours for females, 2083 player hours for males). Males headed more frequently than females (2.7 vs. 1.8 headers/player hour; p<0.001). Heading rates increased with age (ANOVA, p<0.001), approaching the elite senior level for players 16 years and older. There was substantial variation within teams for all age and sex groups, with the widest range (1-18 headers) observed for girls aged 19. Girls younger than 12 years had the lowest exposure, with an average of less than two players per team heading the ball, each with 1-2 headers. In conclusion, age and sex influence head-impact exposure in youth football, and warrants careful consideration when introducing injury prevention measures. Males are more frequently exposed than females, heading rates increase with age, and there is substantial variation between players. Heading is a rare event in the youngest age groups, especially among females.

#10 Trapezoid Fracture Associated with Scaphoid Fracture in a Football Goalkeeper
Reference: Case Rep Orthop. 2019 Sep 5;2019:7949754. doi: 10.1155/2019/7949754. eCollection 2019.
Authors: Yamamoto T, Matsushita T, Ito K, Matsushima S, Yoshida K, Kuroda R
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Summary: A 19-year-old male who played as a football goalkeeper visited our hospital with complaints of sustained pain from the right wrist to the hand after punching a ball. Scaphoid fracture was diagnosed on plain radiographs, whereas trapezoid fracture was overlooked. Computed tomography revealed a displaced trapezoid fracture associated with a scaphoid fracture. Both fractures were successfully treated by open reduction and internal fixation using cannulated screws. Almost complete bone union was achieved at 5 months after surgery. The patient returned to play as a football goalkeeper. The simultaneous occurrence of trapezoid and scaphoid fractures has never been reported. Trapezoid fractures are rare and can be overlooked on plain radiographs, as what happened in the present case, because the trapezoid is small and overlaps with other carpal bones on plain radiographs. If there is sustained pain in the wrist and hand after punching, combined trapezoid and scaphoid fractures should be considered as the possible injury.

#11 Is Physical Performance a Differentiating Element between More or Less Successful Football Teams?
Reference: Sports (Basel). 2019 Sep 30;7(10). pii: E216. doi: 10.3390/sports7100216.
Authors: Asian Clemente JA, Requena B, Jukic I, Nayler J, Hernández AS, Carling C
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Summary: This study investigated the time-motion characteristics of football teams in the Spanish first division, in relation to their final competitive level as defined by league position (Champions League, Europa League, Upper mid-table, lower mid-table and relegation). Match observations (n = 9641) were collected using a multiple-camera computerized tracking system during the 2013-2014 competitive season. The following match parameters were analyzed: total distance, relative distance (m·min-1), distance < 14 km·h-1, >14 km·h-1, between 14-21 km·h-1, >21 km·h-1, and >24 km·h-1. Total distance and distance at different velocities (>14, 21, and 24 km·h-1) in and out of ball possession were also analyzed. A repeated analysis of variance and a comparison of effect sizes were carried out to compare the performance of the teams. The analysis of the data showed differences in physical performance characteristics between competitive levels. The volume of distance covered in the variables analyzed did not relate to success in soccer. Both successful and unsuccessful teams presented the same running requirements at higher velocities. These findings provide valuable information about the physical demands of the running requirements according to their final position in the league table.

#12 Community-based football in men with prostate cancer: 1-year follow-up on a pragmatic, multicentre randomised controlled trial
Reference: PLoS Med. 2019 Oct 1;16(10):e1002936. doi: 10.1371/journal.pmed.1002936. eCollection 2019 Oct.
Authors: Bjerre ED, Petersen TH, Jørgensen AB, Johansen C, Krustrup P, Langdahl B, Poulsen MH, Madsen SS, Østergren PB, Borre M, Rørth M, Brasso K, Midtgaard J
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Summary: Physical exercise has been shown to be effective in relation to fatigue, aerobic fitness, and lower body strength in men with prostate cancer. However, research into the clinically relevant effects of interventions conducted in heterogeneous patient populations and in real-life clinical practice settings is warranted. We conducted a pragmatic, multicentre, parallel randomised controlled trial in 5 Danish urological departments. Recruitment began in May 2015, the first participant was randomised in June 2015, and the last participant was included in February 2017. In total, 214 men with prostate cancer were randomly assigned to either 6 months of free-of-charge football training twice weekly at a local club (football group [FG]) (n = 109) or usual care (usual care group [UG]) (n = 105), including brief information on physical activity recommendations at randomisation. Participants were on average 68.4 (SD 6.2) years old, 157 (73%) were retired, 87 (41%) were on castration-based treatment, 19 (9%) had received chemotherapy, and 41 (19%) had skeletal metastases at baseline. In this 1-year follow-up study, we evaluated the effects of community-based football training on the following outcomes: primary outcome, quality of life; secondary outcomes: continuation of football after 6 months, hip and lumbar spine bone mineral density (BMD), mental health score, fat and lean body mass, and safety outcomes, i.e., fractures, falls, and hospital admissions. Intention to treat (ITT) and per protocol (PP) analyses were conducted. No statistically significant between-group difference was observed in change in prostate-cancer-specific quality of life (ITT: 1.9 points [95% CI -1.9 to 5.8], p = 0.325; PP: 3.6 points [95% CI -0.9 to 8.2], p = 0.119). A statistically significant between-group difference was observed in change in total hip BMD, in favour of FG (0.007 g/cm2 [95% CI 0.004 to 0.013], p = 0.037). No differences were observed in change in lumbar spine BMD or lean body mass. Among patients allocated to football, 59% chose to continue playing football after the end of the 6-month intervention period. At 1-year follow-up in the PP population, FG participants had more improvement on the Mental Component Summary (2.9 [95% CI 0.0 to 5.7], p = 0.048 points higher) than UG participants, as well as a greater loss of fat mass (-0.9 kg [95% CI -1.7 to -0.1], p = 0.029). There were no differences between groups in relation to fractures or falls. Hospital admissions were more frequent in UG compared to FG (33 versus 20; the odds ratio based on PP analysis was 0.34 for FG compared to UG). There were 3 deaths in FG and 4 in UG. Main limitations of the study were the physically active control group and assessment of physical activity by means of self-report. In this trial, participants allocated to football appeared to have improved hip BMD and fewer hospital admissions. Men who played football more than once a week for 1 year lost fat mass and reported improved mental health. Community-based football proved to be acceptable, even when club membership was not subsidised.





Latest research in football - week 40 - 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 Is Playing Soccer More Osteogenic for Females Before the Pubertal Spurt?
Reference: J Hum Kinet. 2019 Jul 5;67:153-161. doi: 10.2478/hukin-2018-0074. eCollection 2019 Jun.
Authors: Lozano-Berges G, Matute-Llorente Á, Gómez-Bruton A, González-Agüero A, Vicente-Rodríguez G, Casajús JA
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Summary: The aims of this study were to assess bone mass in children and adolescent soccer players and to evaluate the influence of both gender and pubertal status on bone mass. A total of 110 soccer players (75 males / 35 females; 12.73 ± 0.65 / 12.76 ± 0.59 years) participated in this cross-sectional study. They were divided into two groups according to their pubertal status. Bone and lean masses were measured with Dual-energy X-ray Absorptiometry. An independent t-test and an adjusted by subtotal lean and training experience multivariate analysis of covariance were used to analyse the differences in bone mass values between genders and maturity status. Female soccer players presented higher bone mass values than their male counterparts in most of the measured weight-bearing sites. Moreover, when stratifying by pubertal status, peripubertal and postpubertal females had higher subtotal body and lumbar spine bone mass than males. Comparing between pubertal status groups before adjustment, both male and female postpubertal players showed higher bone mass than their pubertal counterparts. After adjusting, these differences disappeared and, in fact results were inverted as bone mass at the femoral neck was higher in both male and female peripubertal soccer players than in postpubertal players. Bone mass seems to be more intensely stimulated by playing soccer in female than male players, particularly in the lumbar spine. The results of peripubertal players showing higher bone mass at the femoral neck after adjusting suggest that playing soccer during the peripubertal stage could

#2 Decrease in Attentional Performance After Repeated Bouts of High Intensity Exercise in Association-Football Referees and Assistant Referees
Reference: Front Psychol. 2019 Sep 6;10:2014. doi: 10.3389/fpsyg.2019.02014. eCollection 2019.
Authors: Schmidt SL, Schmidt GJ, Padilla CS, Simões EN, Tolentino JC, Barroso PR, Narciso JH, Godoy ES, Costa Filho RL
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Summary: Referees and assistant referees are submitted to high physical stress during matches. Pressure to make decisions in front of large crowds is another potential stressor. These two stressors can impair attention executive control, depending on physical fitness and individual vulnerability or resilience to situational pressure. Error percentage for referees and assistants may reach around 14% during a soccer match. Although previous studies have suggested that soccer referees and assistants should take cognitive assessments, they are only required by Fédération Internationale de Football Association (FIFA) to demonstrate knowledge of the rules and pass annually in a fitness test (FIFA-Test). This study aimed to assess attention performance in referees and assistants before and after the mandatory FIFA-Test. It is hypothesized that the high physical demands associated with the pressure to pass the FIFA-Test would interfere with attention performance. The sample included 33 referees and 20 assistants. The Continuous Visual Attention Test (CVAT) consisted of a 15-min Go/No-go task. Performance in the CVAT is based on four variables: omission and commission errors, reaction time, and variability of reaction time (VRT). Failure in the CVAT was defined by a performance below the 5th percentile of the age- and sex-matched normative data in at least one variable of the CVAT. Before the FIFA-Test all participants performed the CVAT. The second CVAT began 3-7 min directly following completion of the FIFA-test. Considering only the officials who passed both the FIFA-Test and the first CVAT (19 referees and 15 assistants), 44% (9 referees and 6 assistants) exhibited a performance decline in the second CVAT. A significant increase in VRT was found after the high intensity exercise. As increase in VRT is thought to reflect executive dysfunctions and lapses of attention, we concluded that physical fitness alone may not be enough to help officials cope with the physical and contextual stresses associated with the FIFA-Test. These data suggest that over 35% of soccer referees and their assistants who were considered physically able to referee matches may not be mentally prepared for the attentional demands of refereeing soccer matches.

#3 You Don't Bend It Like Beckham if You're Female and Reminded of It: Stereotype Threat Among Female Football Players
Reference: Front Psychol. 2019 Aug 28;10:1963. doi: 10.3389/fpsyg.2019.01963. eCollection 2019.
Authors: Grabow H, Kühl M
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Summary: Originally, the stereotype threat effect - poorer performance due to a fear of fulfilling a negative stereotype about one's group - was demonstrated for cognitive tasks (e.g. Steele and Aronson, 1995, or Steele, 1997). Drawing on the widespread stereotype of women being unable to play football we experimentally tested (N = 80) whether a respective threat affected female football players' goal scoring precision, i.e. a complex and demanding motor task. Those participants who were reminded of the stereotype scored significantly less hits than those not reminded. Additionally, deviations from the instruction during task execution (e.g. shooting from another distance than demanded or using the wrong foot) were recorded. Stereotype threat did not affect this comparatively more cognitive task of following instructions correctly. In order to explore underlying mechanisms of the observed stereotype effect, several potential mediators, e.g. measures of cognitive interference, or collective identification, were tested. None emerged as an unquestionable link between threat and motor performance. We discuss, however, why collective identification - in comparison to cognitive demand - appears to be the more promising explanatory concept.

#4 Corrigendum: Football Players Do Not Show "Neural Efficiency" in Cortical Activity Related to Visuospatial Information Processing During Football Scenes: An EEG Mapping Study
Reference: Front Psychol. 2019 Aug 27;10:1877. doi: 10.3389/fpsyg.2019.01877. eCollection 2019.
Authors: Del Percio C, Franzetti M, De Matti AJ, Noce G, Lizio R, Lopez S, Soricelli A, Ferri R, Pascarelli MT, Rizzo M, Triggiani AI, Stocchi F, Limatola C, Babiloni C
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#5 Strategies for Maintaining the Coach-Analyst Relationship Within Professional Football Utilizing the COMPASS Model: The Performance Analyst's Perspective
Reference: Front Psychol. 2019 Sep 10;10:2064. doi: 10.3389/fpsyg.2019.02064. eCollection 2019.
Authors: Bateman M, Jones G
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Summary: There is a considerable body of research by that has investigated the coach-athlete relationship in sport. However, given the multi-disciplinary nature of modern elite coaching, there is a scarcity of research focusing on the relationship between coaches and other members of the coaching and support team. This study examined the perceptions of six elite professional football analyst's relationships with their respective coaches. Semi structured interviews utilizing the COMPASS Framework were conducted focusing on Conflict, Openness, Motivation, Preventative Strategies, Assurance, Support, and Social Networks. The results verified that the COMPASS Model of relationship maintenance was applicable to this dyad. Content analysis indicated that there was 215 raw data units comprising of 16 higher order themes across the model which was further broken down into 29 lower order themes. All aspects of the model were found to contribute toward a positively maintained relationship. Having an open relationship underpinned by honesty and being able to provide an opinion was seen as the highest rated attribute that was closely followed by supporting the coach by understanding their requirements for successful coaching practice. Not meeting the coach's expectations was found to cause conflict and was further highlighted by an inductive analysis that revealed the existence of a relationship that is fundamentally dictated by the coach. Implications of this investigation are that professionals which support elite performers need to set out clear expectations of working practice and hierarchies in order to minimize the chance of internal conflict that can impact on the service levels received by the performer.

#6 A study protocol for the development and internal validation of a multivariable prognostic model to determine lower extremity muscle injury risk in elite football (soccer) players, with further exploration of prognostic factors
Reference: Diagn Progn Res. 2019 Sep 19;3:19. doi: 10.1186/s41512-019-0063-8. eCollection 2019.
Authors: Hughes T, Riley R, Sergeant JC, Callaghan MJ
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Summary: Indirect muscle injuries (IMIs) are a considerable burden to elite football (soccer) teams, and prevention of these injuries offers many benefits. Preseason medical, musculoskeletal and performance screening (termed periodic health examination (PHE)) can be used to help determine players at risk of injuries such as IMIs, where identification of PHE-derived prognostic factors (PF) may inform IMI prevention strategies. Furthermore, using several PFs in combination within a multivariable prognostic model may allow individualised IMI risk estimation and specific targeting of prevention strategies, based upon an individual's PF profile. No such models have been developed in elite football and the current IMI prognostic factor evidence is limited. This study aims to (1) develop and internally validate a prognostic model for individualised IMI risk prediction within a season in elite footballers, using the extent of the prognostic evidence and clinical reasoning; and (2) explore potential PHE-derived PFs associated with IMI outcomes in elite footballers, using available PHE data from a professional team. This is a protocol for a retrospective cohort study. PHE and injury data were routinely collected over 5 seasons (1 July 2013 to 19 May 2018), from a population of elite male players aged 16-40 years old. Of 60 candidate PFs, 15 were excluded. Twelve variables (derived from 10 PFs) will be included in model development that were identified from a systematic review, missing data assessment, measurement reliability evaluation and clinical reasoning. A full multivariable logistic regression model will be fitted, to ensure adjustment before backward elimination. The performance and internal validation of the model will be assessed. The remaining 35 candidate PFs are eligible for further exploration, using univariable logistic regression to obtain unadjusted risk estimates. Exploratory PFs will also be incorporated into multivariable logistic regression models to determine risk estimates whilst adjusting for age, height and body weight. This study will offer insights into clinical usefulness of a model to predict IMI risk in elite football and highlight the practicalities of model development in this setting. Further exploration may identify other relevant PFs for future confirmatory studies and model updating, or influence future injury prevention research.

#7 Limited positive effects on jump-landing technique in girls but not in boys after 8 weeks of injury prevention exercise training in youth football
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Sep 20. doi: 10.1007/s00167-019-05721-x. [Epub ahead of print]
Authors: Lindblom H, Waldén M, Carlfjord S, Hägglund M
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Summary: The aim was to evaluate changes in jump-landing technique in football-playing boys and girls after 8 weeks of injury prevention training. Four boys' and four girls' teams (mean age 14.1 ± 0.8 years) were instructed to use either the original Knee Control injury prevention exercise programme (IPEP) or a further developed IPEP, Knee Control + , at every training session for 8 weeks. Baseline and follow-up testing of jump-landing technique included drop vertical jumps (DVJ), assessed subjectively and with two-dimensional movement analysis, and tuck jump assessment (TJA). Only minor differences in intervention effects were seen between the two IPEPs, and results are therefore presented for both intervention groups combined. At baseline 30% of the boys showed good knee control during the DVJ, normalised knee separation distances of 77-96% (versus hip) and a median of 3 flaws during the TJA. Among girls, 22% showed good knee control, normalised knee separation distances of 67-86% and a median of 4 flaws during the TJA. At follow-up, boys and girls performed significantly more jumps during TJA. No changes in jump-landing technique were seen in boys, whereas girls improved their knee flexion angle at initial contact in the DVJ (mean change + 4.7°, p < 0.001, 95% CI 2.36-6.99, d = 0.7) and their TJA total score (- 1 point, p = 0.045, r = - 0.4). The study showed small positive effects on jump-landing technique in girls, but not in boys, after 8 weeks of injury prevention training.

#8 Prevention of severe knee injuries in men's elite football by implementing specific training modules
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Sep 20. doi: 10.1007/s00167-019-05706-w. [Epub ahead of print]
Authors: Krutsch W, Lehmann J, Jansen P, Angele P, Fellner B, Achenbach L, Krutsch V, Nerlich M, Alt V, Loose O
Summary: Injury prevention of knee injuries by means of training and warm-up exercises has been investigated in several studies in amateur football. However, the number of investigations in elite football is limited despite the currently higher injury incidence of severe knee injuries. Therefore, the purpose of this study was to investigate whether specifically adapted preventive training modules may reduce severe knee injuries in elite football. In a prospective controlled cohort study of elite football players in Germany, an injury prevention programme with 5 modules was implemented in the season of 2015-2016. The training modules were specifically adapted to this skill level and based on scientific evidence, team coach preferences, and the specific environment of this playing level. Of the 62 teams taking part in this study, 26 used the new trainings modules and 36 continued their standard programme as a control group. Success of the programme was documented by means of an injury report over one season. The primary outcome was reduction in severe knee injuries. A pre-seasonal investigation had identified five modules to be implemented in the training routine. Postural stability, mobilisation of lower extremity joints, leg and trunk stabilisation, jumping, and landing exercises as well as agility movements were incorporated into the programme to prevent severe knee injuries in elite football. Over the season, the study group (529 players) with the adapted training modules had sustained 52 severe knee injuries (incidence: 0.38 per 1000 h football exposure; prevalence: 9.8%) compared to 108 severe knee injuries in the control group (601 players) using the standard programme (incidence: 0.68 per 1000 h football exposure; prevalence: 18.0%; p < 0.05). The overall injury incidence for any other type of injury was comparable between the two groups (3.3 vs. 3.4 in h 1000 football, n.s.). Appropriate preventive training modules reduce severe knee injuries in elite football significantly. The key for the sustainability of preventive training measures are programmes specifically adapted to the demands of the playing level and to the preferences of the coaches

#9 Professional football clubs' involvement in health promotion in Spain: an audit of current practices
Reference: Health Promot Int. 2019 Sep 20. pii: daz097. doi: 10.1093/heapro/daz097. [Epub ahead of print]
Authors: Lozano-Sufrategui L, Pringle A, Zwolinsky S, Drew KJ
Summary: The implementation of effective community-based health interventions within Spanish football clubs has the potential to positively influence the public health agenda and enable the healthcare system in Spain to be more successful and sustainable. This paper aims to explore the involvement of Spanish football clubs in health promotion activities, their potential for future involvement and what that would require. A mixed methods explanatory sequential design, with a purposive sample of La Liga clubs. Data collection included online questionnaires and phone interviews. Quantitative methods enabled us to describe the number and types of programmes the clubs are currently involved in. Qualitative data was useful to further unpick the processes followed by the clubs in planning and developing health promotion programmes, while identifying any determinants to change. Seventeen clubs completed questionnaires and 11 participated in interviews. Clubs generally support inclusive programmes that target disadvantaged groups. Health-related programmes focus on healthy eating, physical activity and blood donation. Thematic analysis of interviews with 11 representatives of La Liga clubs resulted in three-key themes. These related to: (i) Diversity of programmes; (ii) (Lack of) evidence-based approaches to intervention design and evaluation and (iii) Contrasting views about a club's role in health promotion interventions. Spanish football clubs have potential to reach into communities that are currently underserved. However, there is limited infrastructure and understanding within the clubs to do this. Nevertheless, there is huge opportunity for organizations with public health responsibility in Spain to implement translational approaches within football-based settings.

#10 Defining a historic football team: Using Network Science to analyze Guardiola's F.C. Barcelona
Reference:  Sci Rep. 2019 Sep 19;9(1):13602. doi: 10.1038/s41598-019-49969-2.
Authors: Buldú JM, Busquets J, Echegoyen I, Seirul Lo F
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Summary: The application of Network Science to social systems has introduced new methodologies to analyze classical problems such as the emergence of epidemics, the arousal of cooperation between individuals or the propagation of information along social networks. More recently, the organization of football teams and their performance have been unveiled using metrics coming from Network Science, where a team is considered as a complex network whose nodes (i.e., players) interact with the aim of overcoming the opponent network. Here, we combine the use of different network metrics to extract the particular signature of the F.C. Barcelona coached by Guardiola, which has been considered one of the best teams along football history. We have first compared the network organization of Guardiola's team with their opponents along one season of the Spanish national league, identifying those metrics with statistically significant differences and relating them with the Guardiola's game. Next, we have focused on the temporal nature of football passing networks and calculated the evolution of all network properties along a match, instead of considering their average. In this way, we are able to identify those network metrics that enhance the probability of scoring/receiving a goal, showing that not all teams behave in the same way and how the organization Guardiola's F.C. Barcelona is different from the rest, including its clustering coefficient, shortest-path length, largest eigenvalue of the adjacency matrix, algebraic connectivity and centrality distribution.

#11 Improved maximal strength is not associated with improvements in sprint time or jump height in high-level female football players: a clusterrendomized controlled trial
Reference: BMC Sports Sci Med Rehabil. 2019 Sep 17;11:20. doi: 10.1186/s13102-019-0133-9. eCollection 2019.
Authors: Pedersen S, Heitmann KA, Sagelv EH, Johansen D, Pettersen SA
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Summary: Maximal strength increments are reported to result in improvements in sprint speed and jump height in elite male football players. Although similar effects are expected in females, this is yet to be elucidated. The aim of this study was to examine the effect of maximal strength training on sprint speed and jump height in high-level female football players. Two female football teams were team-cluster-randomized to a training group (TG) performing maximal strength training (MST) twice a week for 5 weeks, or control group (CG) doing their regular pre-season preparations. The MST consisted of 3-4 sets of 4-6 repetitions at ≥85% of 1 repetitions maximum (1RM) in a squat exercise. Sprint speed and jump height were assessed in 5-, 10- and 15 m sprints and a counter-movement jump (CMJ) test, respectively. Nineteen participants in TG (18.3 ± 2.7 years) and 14 in CG (18.3 ± 2.4 years) completed pre- and posttests and were carried forward for final analyses. There was no improvement in neither of the sprint times (p > 0.36), nor jump height (p = 0.87). The players increased their 1RM in squats (main of effect of time: p < 0.00, pη2 = 0.704), and an interaction effect of time x group was observed (p < 0.00, pη2 = 0.516) where the TG increased their 1RM more than the CT (between subjects effects: p < 0.001, pη2 = 0.965). MST improved maximal strength in female football players to a large extent; however, the improvement in maximal strength did not result in any transference to sprint speed or jump height.

#12 Acute Surgical Excision of a Traumatic Fat Fracture in a Professional Soccer Player
Reference: J Orthop Case Rep. 2019;9(3):68-71. doi: 10.13107/jocr.2250-0685.1426.
Authors: Kayani B, Ayuob A, Onochie E, Haddad FS
Summary: Surgical excision of fat fractures is often reserved for patients with large chronic deformities to improve cosmetic appearance. To our knowledge, the acute surgical management of a traumatic fat fracture has not been previously reported. This case report describes the management of a professional soccer player that developed a traumatic fat fracture over the lateral thigh. The patient presented with persistent pain, reduced range of movement, and inability to participate in sporting activity. Symptoms were refractory to non-operative treatment. Following acute surgical excision of the fat fracture, the patient was able to make an early return to sporting activity with no complications at short-term follow-up. Acute surgical excision of a traumatic fat fracture may be used as an avenue for improving pain, enhancing functional rehabilitation, and facilitating early return to pre-injury level of function.

#13 The Influence of Caffeine Expectancies on Simulated Soccer Performance in Recreational Individuals
Reference: Nutrients. 2019 Sep 25;11(10). pii: E2289. doi: 10.3390/nu11102289.
Authors: Shabir A, Hooton A, Spencer G, Storey M, Ensor O, Sandford L, Tallis J, Higgins MF
Summary: Caffeine (CAF) has been reported to improve various facets associated with successful soccer play, including gross motor skill performance, endurance capacity and cognition. These benefits are primarily attributed to pharmacological mechanisms. However, evidence assessing CAF's overall effects on soccer performance are sparse with no studies accounting for CAF's potential psychological impact. Therefore, the aim of this study was to assess CAF's psychological vs. pharmacological influence on various facets of simulated soccer performance. Utilising a double-dissociation design, eight male recreational soccer players (age: 22 ± 5 years, body mass: 78 ± 16 kg, height: 178 ± 6 cm) consumed CAF (3 mg/kg/body mass) or placebo (PLA) capsules, 60 minutes prior to performing the Loughborough Intermittent Shuttle Test (LIST) interspersed with a collection of ratings of perceived exertion (RPE), blood glucose and lactate, heart rate and performing the Loughborough Soccer Passing Test (LSPT). Whole-body dynamic reaction time (DRT) was assessed pre- and post- LIST, and endurance capacity (TLIM) post, time-matched LIST. Statistical analysis was performed using IBM SPSS (v24) whilst subjective perceptions were explored using template analysis. Mean TLIM was greatest (p < 0.001) for synergism (given CAF/told CAF) (672 ± 132 s) vs. placebo (given PLA/told PLA) (533 ± 79 s). However, when isolated, TLIM was greater (p = 0.012) for CAF psychology (given PLA/told CAF) (623 ± 117 s) vs. pharmacology (given CAF/told PLA) (578 ± 99 s), potentially, via reduced RPE. Although DRT performance was greater (p = 0.024) post-ingestion (+5 hits) and post-exercise (+7 hits) for pharmacology vs. placebo, psychology and synergism appeared to improve LSPT performance vs. pharmacology. Interestingly, positive perceptions during psychology inhibited LSPT and DRT performance via potential CAF over-reliance, with the opposite occurring following negative perceptions. The benefits associated with CAF expectancies may better suit tasks that entail lesser cognitive-/skill-specific attributes but greater gross motor function and this is likely due to reduced RPE. In isolation, these effects appear greater vs. CAF pharmacology. However, an additive benefit may be observed after combining expectancy with CAF pharmacology (i.e. synergism).





Latest research in football - week 39 - 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 Preseason Hip/Groin Strength and HAGOS Scores Are Associated With Subsequent Injury in Professional Male Soccer Players
Reference: J Orthop Sports Phys Ther. 2019 Sep 17:1-34. doi: 10.2519/jospt.2020.9022. [Epub ahead of print]
Authors: Bourne MN, Williams M, Jackson J, Williams KL, Timmins RG, Pizzari T
Summary: Hip and groin injuries are a significant cause of time lost from training and competition in elite soccer. Therefore the aim was to explore the association between pre-season assessments of 1) isometric hip adductor and abductor strength using a novel field-test; and 2) the Copenhagen Hip and Groin Outcome Score (HAGOS), and subsequent hip/groin injury in professional male soccer players. In total, 204 elite male soccer players from ten professional Hyundai A-League and English Championship League clubs had assessments of hip adductor and abductor strength and completed the HAGOS in the 2017-18 pre-season. In-season hip/groin injuries were reported by team medical staff. Data reduction was conducted using principal component analysis. The principal component for HAGOS and three principal components for strength and imbalance measures were entered with age and prior hip/groin injury into a multivariable logistic regression model to determine their association with prospectively occurring hip/groin injury. Twenty-four players suffered at least one hip/groin injury throughout the 2017-18 season. The principal component for between-limb abduction imbalance (peak strength in the preferred [kicking] limb - non-preferred limb) (OR = 0.58, 95% CI = 0.38 to 0.90, p = 0.011), the principal component for peak adduction and abduction strength (OR = 0.71, 95% CI = 0.50 to 1.00, p=0.045), and the principal component for HAGOS (OR = 0.77, 95% CI = 0.62 to 0.96, p = 0.022), were independently associated with a reduced risk of future hip/groin injury. Receiver operator curve analysis of the whole model revealed an area under the curve of 0.76, which indicates a fair combined sensitivity and specificity of the included variables but an inability to correctly identify all subsequently injured players. Hip abduction imbalance, favouring the preferred kicking limb, higher levels of hip adductor and abductor strength, and superior HAGOS values, were associated with a reduced likelihood of future hip/groin injury in professional soccer players.

#2 Intra-individual variability of sleep and nocturnal cardiac autonomic activity in elite female soccer players during an international tournament
Reference: PLoS One. 2019 Sep 17;14(9):e0218635. doi: 10.1371/journal.pone.0218635. eCollection 2019.
Authors: Costa J, Figueiredo P, Nakamura F, Rago V, Rebelo A, Brito J
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Summary: The aim was to describe individual sleeping patterns and nocturnal cardiac autonomic activity of National team female soccer players during an international tournament. Twenty elite female soccer players (aged 25.2±3.1 years) wore wrist actigraph units and heart rate (HR) monitors during night-sleep throughout 9 consecutive days (6 day-time training sessions [DT], 2 day-time matches [DM], and 1 evening-time match [EM]) of an international tournament. Training and match loads were monitored using the session-rating of perceived exertion (s-RPE) and wearable 18-Hz GPS (total distance covered [TD], training and match exposure time, and high-speed running [HSR]) to characterize training and match loads. Individually, s-RPE, TD, exposure time, and HSR during training sessions ranged from 20 to 680 arbitrary units (AU), 892 to 5176 m, 20 to 76 min, and 80 to 1140 m, respectively. During matches, s-RPE, TD, exposure time, and HSR ranged from 149 to 876 AU, 2236 to 11210 m, 20 to 98 min, and 629 to 3213 m, respectively. Individually, players slept less than recommended (<7 hours) on several days of the tournament, especially after EM (n = 8; TST ranging between 6:00-6:54 h). Total sleep time coefficient of variation (CV) ranged between 3.1 and 18.7%. However, all players presented good sleep quality (i.e., sleep efficiency ≥75%; individual range between: 75-98%) on each day of the tournament. Most of the players presented small fluctuations in nocturnal cardiac autonomic activity (individual nocturnal heart rate variability [HRV] ranged from 3.91-5.37 ms and HRV CV ranged from 2.8-9.0%), while two players presented higher HRV CV (11.5 and 11.7%; respectively). Overall, this study highlights the substantial individual variability in sleep and HRV measures, suggesting the adoption of an individual approach to monitor sleep, training and match loads and recovery, to better understand how players cope with highly demanding competitions.

#3 The neuromuscular, endocrine and mood responses to a single versus double training session day in soccer players
Reference: J Sci Med Sport. 2019 Sep 5. pii: S1440-2440(18)31114-9. doi: 10.1016/j.jsams.2019.08.291. [Epub ahead of print]
Authors: Sparkes W, Turner AN, Cook CJ, Weston M, Russell M, Johnston MJ, Kilduff LP
Summary: This study profiled the 24h neuromuscular, endocrine and mood responses to a single versus a double training day in soccer players. Twelve semi-professional soccer players performed small-sided-games (SSG's; 4 vs 4+goalkeepers; 6×7-min, 2-min inter-set recovery) with neuromuscular (peak-power output, PPO; jump height, JH), endocrine (salivary testosterone, cortisol), and mood measures collected before (pre) and after (0h, +24h). The following week, the same SSG protocol was performed with an additional lower body strength training session (back-squat, Romanian deadlift, barbell hip thrust; 4×4 repetitions, 4-min inter-set recovery; 85% 1 rep-max) added at 2h after the SSG's. Between-trial comparisons revealed possible to likely small impairments in PPO (2.5±2.2Wkg-1; 90% Confidence Limits: ±2.2Wkg-1), JH (-1.3; ±2.0cm) and mood (4.6; ±6.1AU) in response to the double versus single sessions at +24h. Likely to very likely small favourable responses occurred following the single session for testosterone (-15.2; ±6.1pgml-1), cortisol (0.072; ±0.034ugdl-1) and testosterone/cortisol ratio (-96.6; ±36.7AU) at +24h compared to the double session trial. These data highlight that performance of two training sessions within a day resulted in possible to very likely small impairments of neuromuscular performance, mood score and endocrine markers at +24h relative to a single training session day. A strategy of alternating high intensity explosive training days containing multiple sessions with days emphasising submaximal technical/tactical activities may be beneficial for those responsible for the design and delivery of soccer training programs.

#4 Pre-exercise hypohydration prevalence in soccer players: a quantitative systematic review
Reference: Eur J Sport Sci. 2019 Sep 17:1-18. doi: 10.1080/17461391.2019.1669716. [Epub ahead of print]
Authors: Chapelle L, Tassignon B, Rommers N, Mertens E, Mullie P, Clarys P
Summary: Pre-exercise hypohydration can impair soccer performance and has been extensively studied in different soccer populations. Therefore, the aim of this systematic review was to report hypohydration prevalence, measured by blood or urine samples, in different soccer populations based on sex (males and females), performance level (professional and recreational players) and context (training sessions and games). The Pubmed, Web of Science and SPORTDiscus databases were systematically searched until November 2018. Data were pooled to compare hypohydration prevalence between the different subgroups. Following the systematic search selection process, 24 studies were included. The results indicated that overall pre-exercise hypohydration prevalence was 63.3 %, 37.4 % and 58.8 % for urine specific gravity (USG), urine osmolality (U Osm) and urine colour, respectively. Furthermore, no study implemented blood samples to examine hypohydration prevalence in soccer players. The subgroup analyses using USG data indicated that pre-exercise hypohydration prevalence was significantly higher amongst males (66.0 %; p = 0.001), professional soccer players (66.2 %; p = 0.020) and before a training session (79.6 %; p < 0.001). Pre-exercise hypohydration prevalence was 46.8 % among female soccer players, 55.6 % in recreational soccer players and 41,3 % before a game. The subgroup analyses using U Osm data indicated that hypohydration prevalence was significantly higher before a training session (52.6 %; p = 0.023). Based on these results, it can be concluded that hypohydration prevalence in soccer players is of major concern. Future research should explore how pre-exercise hydration status can be improved in a sustainable way.

#5 Analysis of static balance performance and dynamic postural priority according to playing position in elite soccer players
Reference: Gait Posture. 2019 Sep 5;74:148-153. doi: 10.1016/j.gaitpost.2019.09.008. [Epub ahead of print]
Authors: Jadczak Ł, Grygorowicz M, Wieczorek A, Śliwowski R
Summary: Balance performance and postural priority are important components of motor skill development. No published reports have investigated the differences in static balance abilities and postural priority among professional soccer players according to field position. We hypothesized that static balance as well as dynamic postural priority is influenced by playing position in professional soccer players. The study covered a group of 101 elite professional soccer players who were divided into six subgroups according to playing positions: goalkeepers (G) (n = 10), central defenders (CD) (n = 15), external defenders (ED) (n = 15), central midfielders (CM) (n = 23), external midfielders (EM) (n = 15) and forwards (F) (n = 23). All participants completed the Delos Postural System Test using the standard protocol. The tests were performed unilaterally on non-dominant (NL) and dominant leg (DL) under static conditions (with open and closed eyes) standing on a stable platform and under dynamic conditions on an unstable base. In the static test with open eyes (ST OE) there were no statistically significant differences between the legs and positions. In the static test with closed eyes (ST CE), the differences are statistically significant only between positions. Players on the CM position have significantly higher differences than G. In the dynamic postural priority test (DPPT) there is a difference between positions and legs. In fact, the statistically higher differentiation refers to players in the CM position relative to ED, CD, EM and F. We noticed a significantly greater difference in the NL compared to the DL. Static balance performance and postural priority varied with playing position in elite soccer players. Midfield players have better postural priority than players in other positions. Professional soccer players present greater balance postural priority on the non-dominant leg.

#6 Contextual Factors Influencing External and Internal Training Loads in Collegiate Men's Soccer
Reference: J Strength Cond Res. 2019 Sep 12. doi: 10.1519/JSC.0000000000003361. [Epub ahead of print]
Authors: Curtis RM, Huggins RA, Benjamin CL, Sekiguchi Y, Adams WM, Arent SM, Jain R, Miller SJ, Walker AJ, Casa DJ
Summary: This study investigated factors influencing training loads (TL) in collegiate men's soccer. Total distance, high-speed running distance (>14.4 km·h), high-intensity heart-rate zone duration (HI HRZ, >70% heart rate relative to maximum), and session rating of perceived exertion were assessed daily from 107 male soccer players competing for 5 National Collegiate Athletics Association Division I teams. Differences between athlete role (starter and reserve), position (defender, midfielder, and forward), season phase (preseason, in-season, and postseason), days relative to match (MD-1 to MD-5+), days between matches (<4, 4-5, >5 days), previous match outcome (win, loss, and draw), and upcoming opponent relative ranking (weaker, trivial, and stronger) were examined. Mean differences (MD) and effect sizes (ESs) with 90% confidence intervals were reported. There were trivial and insignificant differences by player role, position, or upcoming opponent strength, and small-moderate increases in preseason TL compared with in-season (ES [range] = 0.4-0.9). TLs were lower for MD-1 and higher for MD-5+ (ES [range] = 0.4-1.3) when compared with MD-2-4. External loads (ES = -0.40 ± 0.20) were less after wins compared with losses. TLs are increased in the preseason, when training sessions occur greater than 5 days from a match and after losses. Contextualizing factors affecting TLs has implications for developing workload prescription and recovery strategies.

#7 The isokinetic strength profile of semi-professional soccer players according to low back pain
Reference: J Back Musculoskelet Rehabil. 2019 Aug 30. doi: 10.3233/BMR-171109. [Epub ahead of print]
Authors: Madić D, Obradović B, Golik-Perić D, Marinković D, Trajković N, Gojković Z
Summary: Soccer as a sport has a very high injury rate and low back pain (LBP) is considered to be the most common overuse injury typically occurring in the back and spine in elite soccer players. The objective was to investigate differences in knee muscle strength and muscle imbalances in soccer players according to lower back pain. One hundred and thirty-six male professional soccer players (20.49 ± 3.73 years, 76.57 ± 8.24 kg, 182.63 ± 6.73 cm) volunteered for the study. The isokinetic dynamometer PrimaDOC (EASYTECH, Italy) was used to assess the hamstring and quadriceps strength at the selected speeds of 60∘/s, whereas the Roland-Morris Disability Questionnaire (RDQ) was used as a health status measure to assess physical disability caused by low back pain. A univariate analysis of variance has shown that there is a statistically significant difference among the groups divided into Absolut peak torque right knee flexors, Absolut peak torque left knee flexors, Ratio between hamstrings and quadriceps strength right leg, Ratio between hamstrings and quadriceps strength left leg based on the RDQ scores. On the other hand, no other significant differences among the groups were found in other parameters. The current study indicates that knee muscle strength variables, resulting from an isokinetic testing, have the potential to discriminate between soccer players with and without a history of low back pain. However, low back pain is a multidimensional phenomenon and knee muscle strength or imbalance alone cannot be expected to explain low back pain.

#8 Physical Performance During Soccer-7 Competition and Small-Sided Games in U12 Players
Reference: J Hum Kinet. 2019 Jul 5;67:281-290. doi: 10.2478/hukin-2018-0082. eCollection 2019 Jun.
Authors: Sanchez-Sanchez J, Sanchez M, Hernández D, Gonzalo-Skok O, Casamichana D, Ramirez-Campillo R, Nakamura FY
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Summary: The aim of this study was to compare the activity profile (external loads) during soccer-7 competition versus 6 vs 6 small-sided games ( SSGs) in U12 players. Peak velocity (Vmax), total distance completed (DT), total distance relative to match duration, the percentage of DT in acceleration (%DAC) and in deceleration (%DEA), and the percentage of DT at different speeds were recorded. Six types of SSGs were randomly implemented: without pitch orientation-delimitation and with a limit of three ball-contacts per player (3TOU), with no limit of ball-contacts (MAN), with a greater number of players as internal-offensive wildcard players (2WI) or external-offensive wildcard players (4WE); and with pitch orientation-delimitation and crossing the rival goal-line while dribbling the ball without goalkeepers (INV) or using official goalkeepers (GKP). The physical demands of SSGs were compared with the average of two soccer-7 match plays. During soccer-7 match plays a lower %DAC and %DEA (p < 0.05) were observed compared to 2WI, 4WE, INV and GKP, and to INV and GKP, respectively. The Vmax and %HI were greater (p < 0.05) in soccer-7 match plays compared to all SSGs. In conclusion, the demands imposed on U12 players during different formats of SSGs differ from the soccer-7 match play demands, presenting a low stimulation of the actions performed at high-speed and an adequate simulation of acceleration-deceleration actions.

#9 Effects of Slackline Training on Acceleration, Agility, Jump Performance and Postural Control in Youth Soccer Players
Reference: J Hum Kinet. 2019 Jul 5;67:235-245. doi: 10.2478/hukin-2018-0078. eCollection 2019 Jun.
Authors: Fernández-Rio J, Santos L, Fernández-García B, Robles R, Casquero I, Paredes R
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Summary: The goal of this study was to assess the effects of a supervised slackline training program in a group of soccer players. Thirty-four male division I under-19 players (16.64 ± 0.81 years) agreed to participate in the study. They were randomly divided into an experimental group (EG) and a control group (CG). The first group (EG) followed a 6-week supervised slackline training program (3 sessions/week; 5-9 min/session), while the CG performed only regular soccer training. Several variables were assessed in all participants: acceleration (20-m sprint test), agility (90º turns test), jump performance (squat jump, countermovement jump), and postural control (Center of Pressure ( CoP) testing: length, area, speed, Xmean, Ymean, Xspeed, Yspeed, Xdeviation, Ydeviation). Ratings of perceived exertion and local muscle ratings of perceived exertions were also recorded after each slackline training session. At post-tests, there was a significant increase only in the EG in acceleration, agility, squat jump and countermovement jump performance, as well as several CoP variables: area in the bipedal support on a firm surface, and length, area and speed in the left leg on a firm surface. The program was rated as "somewhat hard" by the players, while quadriceps, gastrocnemius and tibialis anterior were the most exerted muscles while slacklining. In conclusion, slackline training can be an effective training tool for young, high-level soccer players.

#10 The Yo-Yo Intermittent Endurance Level 2 Test: Reliability of Performance Scores, Physiological Responses and Overload Characteristics in Competitive Soccer, Basketball and Volleyball Players
Reference: J Hum Kinet. 2019 Jul 5;67:223-233. doi: 10.2478/hukin-2018-0091. eCollection 2019 Jun.
Authors: Papanikolaou K, Chatzinikolaou A, Pontidis T, Avloniti A, Deli CK, Leontsini D, Draganidis D, Tsimeas PD, Rafailakis L, Jamurtas AZ, Krustrup P, Mohr M, Fatouros IG
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Summary: The purpose of this study was to evaluate the reliability and reproducibility of the physiological and overload features of the Yo-Yo intermittent endurance test level 2 (Yo-Yo IE2) in competitive male soccer (n = 20), basketball (n = 11), and volleyball players (n = 10). The participants completed Yo-Yo IE2 tests on three separate occasions with assessment of performance, heart rate, running speed, accelerations, decelerations and body load using GPS instrumentation. The intra-class correlation coefficient index, confidence intervals and coefficients of variation were calculated to assess the reliability of the test. Intra-class correlation coefficients for test-retest trials in the total sample ranged from large to nearly perfect (total distance: 0.896; mean speed: 0.535; maximum speed: 0.715; mean HR: 0.876; maximum HR: 0.866; body load: 0.865). The coefficients of variation for distance, mean speed, HR response, as well as acceleration and deceleration scores for test-retest trials ranged from 1.2 to 12.5% with no differences observed among particular sport disciplines. The CV for shuttles performed ranged from 4.4 to 5.5% in all sports. Similar results were obtained for the three different categories of players tested. These results suggest that the Yo-Yo IE2 test appears to be a reliable alternative for evaluating the ability to perform intermittent high-intensity running in different outdoor and indoor team sports. Players may need one or two familiarization tests to ensure valid assessment of intermittent endurance capacity. It appears that the Yo-Yo IE2 test incorporates accelerations and decelerations in a consistent and reproducible fashion.

#11 Repeated Sprint Ability in Youth Soccer Players: Independent and Combined Effects of Relative Age and Biological Maturity
Reference: J Hum Kinet. 2019 Jul 5;67:209-221. doi: 10.2478/hukin-2018-0090. eCollection 2019 Jun.
Authors: Duarte JP, Coelho-E-Silva MJ, Costa D, Martinho D, Luz LGO, Rebelo-Gonçalves R, Valente-Dos-Santos J, Figueiredo A, Seabra A, Malina RM
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Summary: The objective of the study was to examine the effects of the relative age effect (RAE) and predicted maturity status on body size and repeated sprint ability (RSA: 7 x 34.2 m / 25 s interval) in youth soccer. The sample was composed of 197 male players aged 13-14 years. Body mass, stature, and sitting height were measured, RSA was assessed in the field, and age at peak height velocity (APHV) was predicted. Factorial ANOVA tested the independent and combined effects of RAE given by birth quarters (BQs) and maturity status on dependent variables. Players born in the second birth quarter (BQ2) were significantly taller (F = 4.28, p < 0.01) than their peers born in BQ1 and BQ3. Additionally, players born in BQ2 performed better than players born in BQ4 in RSA total time and ideal time (F ranged between 4.81 and 4.90, p < 0.01), while players born in BQ1 exhibited a lower RSA fatigue index compared to those born in BQ4 (F = 2.90, p < 0.05). The interaction of the BQ and maturity status was a significant source of inter-individual variation for body size (F ranged between 64.92 and 105.57; p < 0.01) and RSA output (F ranged between 4.082 and 6.76; p < 0.05). In summary, being relatively older and, simultaneously, advanced in maturity status corresponds to a substantial advantage in characteristics that are related to soccer-specific fitness.





Latest research in football - week 38 - 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 Longitudinal emotional process among adolescent soccer player in intensive training centre
Reference: J Sports Sci. 2019 Sep 9:1-12. doi: 10.1080/02640414.2019.1662538. [Epub ahead of print]
Authors: Saby Y, Pupier Y, Guillet-Descas E, Nicolas M, Martinent G
Summary: Grounded in Lazarus's (1999) cognitive motivational relational theory of emotions, this study aimed to explore longitudinal relationships between appraisals, everyday emotions related to the competitive environment and emotional regulation strategies during a competitive season. Forty adolescent soccer players (Mage = 15.8) involved in an intensive training centre from a professional club voluntarily participated to the study. A series of hierarchical linear modelling analyses were conducted upon the 9 measurement times to: (a) examine the relationships between appraisals (threat, challenge, loss), pleasant (happiness, excitement) and unpleasant (anxiety, dejection, anger) emotions, and emotional regulation strategies (adaptive and less adaptive); and (b) ascertain whether the relationships between appraisals and emotions were mediated by emotion regulation strategies. The results of the random coefficient regression models showed: (a) positive relationships between challenge appraisal, adaptive emotion regulation, and pleasant emotions as well as between threat and loss appraisals, less adaptive emotion regulation and unpleasant emotions; and (b) mediating effects of emotional regulation strategies in the appraisals - emotions relationships. As a whole, this study furthered knowledge base about the competitive environment in showing that appraisals, emotion regulation and emotions are intertwined psychological constructs in a dynamic relationship allowing athletes to continuously adjust to their constantly changing everyday demands.

#2 Artificial-turf surfaces for sport and recreational activities: microbiota analysis and 16S sequencing signature of synthetic vs natural soccer fields
Reference: Heliyon. 2019 Aug 29;5(8):e02334. doi: 10.1016/j.heliyon.2019.e02334. eCollection 2019 Aug.
Authors: Valeriani F, Margarucci LM, Gianfranceschi G, Ciccarelli A, Tajani F, Mucci N, Ripani M, Romano Spica V
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Summary: Synthetic fibres are used in place of the natural grass worldwide, for realizing playgrounds, soccer fields and even domestic gardens or recreational structures. An intensive use of artificial turf is currently observed in sports facilities, due to lower costs, higher sustainability in recycling of materials, and advantages related to athletic practice and performance. However, even if chemical and physical risks were studied, the microbiological component was not fully addressed, especially considering a comprehensive evaluation of the microbiota in synthetic vs natural playground surfaces. Here, we investigated the microbial community present on soccer fields, using Next Generation Sequencing and a 16S amplicon sequencing approach. Artificial and natural turfs show own ecosystems with different microbial profiles and a mean Shannon's diversity value of 2.176 and 2.475, respectively. The bacterial community is significantly different between facilities (ANOSIM: R = 0.179; p < 0.001) and surface materials (ANOSIM: R = 0.172; p < 0.005). The relative abundance of potentially pathogenic bacterial OTUs was higher in synthetic than in natural samples (ANOVA, F = 2.2). Soccer fields are characterized by their own microbiota, showing a different 16S amplicon sequencing signature between natural and artificial turfs.

#3 The Running and Technical Performance of U13 to U18 Elite Japanese Soccer Players During Match Play
Reference: J Strength Cond Res. 2019 Sep 6. doi: 10.1519/JSC.0000000000003300. [Epub ahead of print]
Authors: Goto H, Saward C
Summary: The aims of the current study were (a) to examine age-related differences in match running performance with 2 different approaches (speed vs. metabolic power) in U13-U18 Japanese elite soccer players and (b) to examine age-related differences in technical match performance in U13-U18 Japanese elite soccer players. Participants were 110 outfield players from academies of 2 professional soccer clubs in Japan. Forty-eight 11-a-side official league matches (13, 6, 9, 7, 6, and 7 matches for U13, U14, U15, U16, U17, and U18 age-groups, respectively) were analyzed (152 complete match files). Global positioning system (15 Hz) and video analysis were used to analyze running and technical performance during matches, respectively. Total distance covered in absolute terms (U13 < [U14 and U15] < [U16-U18]; p < 0.05 for all), high-intensity running distance ([U13-U15] < [U16-U18]; p < 0.05 for all), and distance covered during the metabolic power zone of ≥35 W·kg relative to match playing time ([U13 < U16], [U13-U15] < [U17 and U18]; p < 0.05 for all) increased with age. The speed zone based approach (high-intensity running distance, ≥4.0 m·s) underestimated high-intensity demands compared with the metabolic power zone based approach (≥20 W·kg) by ∼33 to ∼57% (p < 0.01 for all), with the underestimation declining with age (p < 0.001). Pass accuracy improved with age from 73% at U13 to 85% at U18 (p < 0.001). Therefore, distance covered at high speeds and at high metabolic powers, and pass accuracy increase with age. Moreover, the speed zone based approach underestimates the demands of match play in Japanese elite youth soccer players. The current results could support coaches to develop players, identify talent, and produce age-specific training programs.

#4 The Reliability of Potential Fatigue-Monitoring Measures in Elite Youth Soccer Players
Reference: J Strength Cond Res. 2019 Sep 6. doi: 10.1519/JSC.0000000000003317. [Epub ahead of print]
Authors: Fitzpatrick JF, Hicks KM, Russell M, Hayes PR
Summary:  Monitoring fatigue is of vital importance to practitioners; however, logistics and concerns about reliability may impede the use of certain measures. This study aimed to quantify the reliability of potential measures of fatigue; a subjective wellness questionnaire, jump performance tests, and tri-axial accelerometer variables derived during submaximal shuttle running in elite youth soccer players. A secondary aim was to establish the minimum test duration that could be used for the submaximal shuttle run while maintaining good reliability. Seventeen male youth team players (age: 17.4 ± 0.5 years) were assessed on 2 occasions, spaced 7 days apart. Typical error, coefficient of variation (CV%), interclass correlation (ICC), and minimum detectable change were calculated for a subjective wellness questionnaire, countermovement jump (CMJ), squat jump (SJ) and drop jump contact time (DJ-CT), drop jump height (DJ-JH), and reactive strength (DJ-RSI). A novel submaximal shuttle running test was also used to assess tri-axial accelerometer data reliability. Results suggest that CMJ, SJ, DJ-CT, and DJ-RSI have good test-retest reliability (CV% = 4.5-7.7; ICC = 0.80-0.88); however DJ-JH did not show acceptable reliability (CV% = 6.0; ICC = 0.76). Good reliability was found for all tri-axial accelerometer variables during a 3-minute (2-minute analysis) submaximal shuttle run (CV% = 2.4-8.0; ICC = 0.81-0.95), except for % PlayerLoad anterior-posterior (%PLAP) (CV% = 7.2; ICC = 0.63). The subjective wellness questionnaire demonstrated poor reliability for all items (CV% = 11.2-30.0; ICC = 0.00-0.78). The findings from this study provide practitioners with valuable information about the reliability of a range of potential fatigue-monitoring measures. This can be used to help make accurate decisions about the magnitude of change in these assessments when used in practice.

#5 Effects of a blocked versus an alternated sequence of balance and plyometric training on physical performance in youth soccer players
Reference: BMC Sports Sci Med Rehabil. 2019 Sep 2;11:18. doi: 10.1186/s13102-019-0131-y. eCollection 2019.
Authors: Muehlbauer T, Wagner V, Brueckner D, Schedler S, Schwiertz G, Kiss R, Hagen M
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Summary: The sequence of blocked balance training (BT) followed by blocked plyometric training (PT) showed greater improvements in physical performance than vice versa and is explained by a preconditioning effect of BT-related adaptations on subsequent adaptations induced by PT. However, it remains unclear whether beneficial effects can also be induced using alternating instead of blocked BT and PT exercise sequences. Thus, we examined the effects of a blocked versus an alternated sequence of BT and PT on physical performance in trained individuals. Twenty young soccer players (13 years) were randomly assigned to a blocked (n = 10) or an alternated (n = 10) intervention group. Both groups trained balance and plyometric exercises for six weeks (two sessions/week). The exercises were conducted in a blocked (three weeks of BT followed by three weeks of PT) or an alternated sequence (weekly change of BT and PT). Assessment of pre- and post-training performance included measures of balance, muscle power, speed, and agility. Mainly significant main effects of Test (i.e., pre- to post-test improvements) were observed for the Y-balance test (p ≤ 0.014, 1.3 ≤ Cohen's d ≤ 1.81), the squat jump (p = 0.029, d = 1.36), the countermovement jump (p = 0.002, d = 2.21), the drop jump (p = 0.004, d = 1.96), the split times/total time over 15-m sprinting (p ≤ 0.001, 2.02 ≤ d ≤ 3.08), and the figure-T agility run (p < 0.001, d = 3.80). Further, tendencies toward significant Test x Group interactions were found for several items of the Y-balance test and for SJ height in favor of the blocked BTPT group. Our results indicate that the combined training of balance and plyometric exercises is effective to improve proxies of physical performance in youth soccer players. In addition, there is a limited advantage in some parameters of balance and muscle power for the blocked as compared to the alternated sequence of BT and PT.

#6 Assessment of Selected Exercise-induced CD3+ Cell Subsets and Cell Death Parameters Among Soccer Players
Reference: J Med Biochem. 2019 Mar 26;38(4):437-444. doi: 10.2478/jomb-2019-0013. eCollection 2019 Oct.
Authors: Nowak R, Kostrzewa-Nowak D
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Summary: Molecular mechanisms of biological adaptation to training in professional soccer players are unclear. The aim of this study was to assess the impact of progressive physical effort on peripheral T-cells and their molecular response. Thirteen soccer players form Pogo Szczecin S.A., a top league soccer club, (median age 21, range 18- 31, years old) performed progressive efficiency tests on a mechanical treadmill until exhaustion at the start (period 1) and the end (period 2) of a competition round. Venous blood T-lymphocyte subsets, selected hallmarks of cell death and plasma cytokine levels were determined by flow cytometry three times: pre-exercise, post-exercise, and in recovery. Although significant changes in T, Tc and Tc-naïve cell percentages were found in both periods, Th-naïve cell percentages were altered only in period 1. Post-exercise IL-10 plasma levels were higher than pre-exercise, while an increase in TNF-α levels was noticed in recovery from both periods. An increase in recovery IL-12p70 levels was observed in the second period. Increases in the percentage of T-cells with disrupted mitochondrial membrane potentials, elevated levels of phosphorylated H2AX histones and increases in early apoptotic T-cells were also observed. The immune system in soccer players creates space for naïve CD3+CD8+ cells by inducing mechanisms of cell death. It seems that the cumulative effect of physical activity during a competition round induced an adaptive mechanism, since the cell death process was induced faster during period 2.

#7 Clustering algorithm for formations in football games
Reference: Sci Rep. 2019 Sep 11;9(1):13172. doi: 10.1038/s41598-019-48623-1.
Authors: Narizuka T, Yamazaki Y
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Summary: In competitive team sports, players maintain a certain formation during a game to achieve effective attacks and defenses. For the quantitative game analysis and assessment of team styles, we need a general framework that can characterize such formation structures dynamically. This paper develops a clustering algorithm for formations of multiple football (soccer) games based on the Delaunay method, which defines the formation of a team as an adjacency matrix of Delaunay triangulation. We first show that heat maps of entire football games can be clustered into several average formations: "442", "4141", "433", "541", and "343". Then, using hierarchical clustering, each average formation is further divided into more specific patterns (clusters) in which the configurations of players are different. Our method enables the visualization, quantitative comparison, and time-series analysis for formations in different time scales by focusing on transitions between clusters at each hierarchy. In particular, we can extract team styles from multiple games regarding the positional exchange of players within the formations. Applying our algorithm to the datasets comprising football games, we extract typical transition patterns of the formation for a particular team.

#8 Effects of Temporary Numerical Imbalances on Collective Exploratory Behavior of Young and Professional Football Players
Reference: Front Psychol. 2019 Aug 27;10:1968. doi: 10.3389/fpsyg.2019.01968. eCollection 2019.
Authors: Canton A, Torrents C, Ric A, Gonçalves B, Sampaio J, Hristovski R
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Summary: The aim of this study was to explore how the use of temporary numerical imbalances during small-sided Game SSGs affects team's exploratory behaviors (i.e., variety and quantity of responses given in an ever-changing game context and its rate of change) in different age groups. Two different age groups (under-15 and under-23) of football players participated in the study. For each age group, three teams of five players played six small-sided games of 5 min duration in different conditions: (i) numerical balance (GK + 4 vs. 4 + GK); (ii) temporary numerical imbalance, which consisted of a numerical change of teammates and opponents every one minute. Latitude and longitude GPS coordinates were used to determine the positioning-derived variables. The dynamic overlap (i.e. the measure of average similarity of the game patterns that take place in increasingly larger time intervals) was used to provide information of the rate and breadth of exploratory behavior. The results revealed that the long-term exploratory breadth increased for the under-23 age group. Non-clear effects were found for the short-term rate of exploration, but with an increasing trend. In the under-15 group, the exploratory behavior was more likely to increase in the long term. The increase for the short-term rate of exploration was unclear, but it follows an increasing trend. These results suggest that the use of temporary numerical imbalances could offer coaches more dynamic training situations and different adaptive training environments similar to matches.

#9 Correction to: Injury Incidence, Prevalence and Severity in High-Level Male Youth Football: A Systematic Review
Reference: Sports Med. 2019 Sep 9. doi: 10.1007/s40279-019-01182-x. [Epub ahead of print]
Authors: Jones S, Almousa S, Gibb A, Allamby N, Mullen R, Andersen TE, Williams M
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#10 The association between watching football matches and the risk of cardiovascular events: A meta-analysis
Reference: J Sports Sci. 2019 Sep 9:1-9. doi: 10.1080/02640414.2019.1665246. [Epub ahead of print]
Authors: Lin LL, Gu HY, Yao YY, Zhu J, Niu YM, Luo J, Zhang C
Summary: The aim was to comprehensively shed light on whether viewing football games is associated with a higher risk of cardiovascular disease (CVD). Electronic databases were searched through 17 May 2018. All studies focusing on the association between viewing football matches and the fatal or non-fatal CVD were identified. Viewing football matches was associated with a higher risk of fatal overall CVD (RR: 1.06, 95%CI: 1.01-1.12) in both men (RR: 1.13, 95%CI: 1.004-1.28) and women (RR: 1.08, 95%CI: 1.01-1.15). Subgroup analysis showed that failure of the team has a higher risk of fatal overall CVD (RR: 1.29, 95%CI: 1.15-1.45). However, lower risk of fatal overall CVD from spectators was observed when team obtained a victory (RR: 0.80, 95%CI: 0.66-0.96). For non-fatal CVD, viewing football matches was associated with a higher risk of non-fatal overall CVD (RR: 1.24, 95%CI: 1.09-1.41) in both men (RR: 1.73, 95%CI: 1.12-2.69) and women (RR: 1.25, 95%CI: 1.08-1.45). Subgroup analysis showed that viewing football matches was associated with a higher risk of non-fatal myocardial infarction (RR: 1.20, 95%CI: 1.04-1.38) in both men and women (RR: 1.51, 95%CI: 0.99-2.28; RR: 1.21, 95%CI: 1.08-1.36, respectively). No significant increase was found in fatal or non-fatal stroke. Viewing football matches was associated with a higher risk of the fatal and non-fatal CVD, especially in male spectators. The victory of team could have a lower risk of fatal CVD. Therefore, precautionary measures should be required for the reduction of healthcare burden in football matches.

#11 Effect of poor cooperation between coaching and medical staff on muscle re-injury in professional football over 15 seasons
Reference: Open Access J Sports Med. 2019 Aug 5;10:107-113. doi: 10.2147/OAJSM.S221292. eCollection 2019.
Authors: Ghrairi M1,2,3, Loney T1, Pruna R2,4, Malliaropoulos N2,5, Valle X2,4.
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Summary: Muscle injury is the most common type of injury in football. Previous research has focused on traditional risk factors (eg, age, injury history, muscle imbalance/inflexibility) contributing to muscle re-injury. The effect of poor cooperation between the coaching and medical teams on the risk of re-injury remains unexplored in the sports medicine football literature. Examine the effect of poor cooperation between coaching and medical teams on muscle re-injury in professional football. Retrospective review of the medical files of 97 footballers of a professional team in Dubai over 15 consecutive seasons (2002-2017). Medical team recorded all injuries in each player's file. Data on the perceived level of cooperation between coaching and medical teams were available in the daily meeting notes from the head of the medical team. The level of perceived cooperation was ranked on a three-point Likert scale by the head of the medical team and depended on whether the coaching team accepted the player injury (excellent cooperation), brought some suggestion after discussion with the medical team (normal cooperation) or rejected it (poor cooperation). In total, 338 indirect muscle injuries (21 re-injuries) were recorded during 15 consecutive seasons., There was a significant increase in the mean number of total injuries (mean ± SE, 95% CI; 16±2, 12-21; P<0.0001), mean number of indirect muscle injuries (12±1, 95% CI 10-14; P<0.0001), and indirect muscle re-injuries (4±1, 95% CI 3-5; P<0.0001) during seasons with a poor perceived level of cooperation compared to seasons with a normal/excellent perceived level of cooperation. Findings suggest that poor cooperation between coaching and medical teams may increase the risk of muscle re-injury in professional football. Future studies conducted in different clubs, leagues, countries, and even sports are required to further explore the effect of cooperation between coaching and medical teams on the risk of re-injury.





Latest research in football - week 37 - 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 Single Session of Straight Line and Change-of-Direction Sprinting per Week Does Not Lead to Different Fitness Improvements in Elite Young Soccer Players
Reference: J Strength Cond Res. 2019 Sep 2. doi: 10.1519/JSC.0000000000003369. [Epub ahead of print]
Authors: Beato M, Bianchi M, Coratella G, Merlini M, Drust B
Summary: Effective prescription is especially important in elite soccer players, who have a very limited time to dedicate to specific physical development as a consequence of factors such as congested match schedules and travel. The aim of this study was to compare the effectiveness of one repeated-sprint training (RST) session per week over an 8-week period on physical performance. A second aim was to compare the effect of RST involving straight sprints (RST-SS) or changes of direction (RST-COD). This study used a randomized pre-post parallel group trial design. The elite soccer players were randomly assigned to either an RST-SS (10 players) or RST-COD (10 players). RST-SS was 3 sets of 7 × 30-m sprints with 20-second and 4-minute recovery between sprints and sets, respectively. RST-COD was 3 sets of 7 × 20 + 20 m (one COD of 180°) shuttle sprints with 20-second and 4-minute recovery between sprints and sets, respectively. The physical tests selected were long jump, repeated-sprint ability (RSA) best, RSA mean, 505 agility test, Yo-Yo recovery level 1, 10, 30, and 40 m sprints. RST-SS reported unclear variations in long jump, sprint 30 m, sprint 40 m, RSA best, and RSA mean, whereas RST-COD showed unclear and trivial variations in sprint 10 m, sprint 30 m, sprint 40 m, RSA best, and RSA mean. The between-group analysis did not report any statistical difference. In conclusion, a single session of RST-SS and RST-COD do not improve soccer-specific fitness indicators in elite youth players during the season.

#2 The Effects of Six-Weeks Change of Direction Speed and Technique Modification Training on Cutting Performance and Movement Quality in Male Youth Soccer Players
Reference: Sports (Basel). 2019 Sep 6;7(9). pii: E205. doi: 10.3390/sports7090205.
Authors: Dos'Santos T, McBurnie A, Comfort P, Jones PA
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Summary: Cutting manoeuvres are important actions associated with soccer performance and a key action associated with non-contact anterior cruciate ligament injury; thus, training interventions that can improve cutting performance and movement quality are of great interest. The aim of this study, therefore, was to determine the effects of a six-week change of dire[ction (COD) speed and technique modification training intervention on cutting performance and movement quality in male youth soccer players (U17s, n = 8) in comparison to a control group (CG) (U18s, n = 11) who continued 'normal' training. Cutting performance was assessed based on completion time and COD deficit, and the field-based cutting movement assessment score (CMAS) qualitative screening tool was used to assess cutting movement quality. Significant main effects for time (pre-to-post changes) (p ≤ 0.041, η2 = 0.224-0.839) and significant interaction effects of time and group were observed for cutting completion times, COD deficits, and CMASs. Improvements in completion time (p < 0.001, g = 1.63-1.90, -9% to -11% vs. -5% to 6%) and COD deficit (p ≤ 0.012, g = -1.63 to -2.43, -40-52% vs. -22% to -28%) for the COD intervention group (IG) were approximately two-times greater than the CG. Furthermore, lower CMASs (i.e., improved cutting movement quality) were only observed in the IG (p ≤ 0.025, g = -0.85 to -1.46, -23% to -34% vs. 6-19%) compared to the CG. The positive changes in CMASs were attributed to improved cutting technique and reduced incidences of high-risk deficits such as lateral trunk flexion, extended knee postures, knee valgus, hip internal rotation, and improved braking strategies. The results of this study indicate that COD speed and technique modification training, in addition to normal skills and strength training, improves cutting performance and movement quality in male youth soccer players. Practitioners working with male youth soccer players should implement COD speed and technique modification training to improve cutting performance and movement quality, which may decrease potential injury-risk.

#3 Comparing Balance Control Between Soccer Players and Non-Athletes During a Dynamic Lower Limb Reaching Task
Reference: Res Q Exerc Sport. 2019 Sep 3:1-6. doi: 10.1080/02701367.2019.1649356. [Epub ahead of print]
Authors: Snyder N, Cinelli M
Summary: Balance control is an essential element of locomotion that enhances biomotor abilities and physical performance. Individuals with extensive soccer experience display superior static single leg balance control compared to athletes of other sports as well as non-athletes. However, during a match, players often encounter greater challenges to single leg balance that require rapid decision-making skills and dynamic stability. The purpose of this study was to determine if individuals with extensive soccer training demonstrate superior single-leg balance control compared to non-athletes during a dynamic lower limb reaching task. 22 varsity soccer players were matched with 21 non-athlete controls. Single-leg balance control was assessed during a Go/No-Go lower limb reaching task. Centre of pressure displacement (dCOP) was measured for both the dominant and non-dominant feet and compared between groups. Soccer players displayed reduced dCOP during All Go trials compared to non-athletes, particularly in the medial-lateral plane. Additionally, soccer players displayed reduced anterior-posterior dCOP during Go/No-Go trials compared to non-athletes, particularly on their dominant foot. Athletes with soccer-specific training demonstrate improved executive control and use of proprioceptive information, which results in an improved ability to maintain single-support balance and corral COP during a dynamic visuomotor lower limb-reaching task. As such, balance training may be a useful addition to athlete training regimes to improve sport-specific performance. Future research would compare these results to athletes of other sports to explore balance control during a visuomotor reaching task and how it may differ based on sport training history.

#4 Lactate Equivalent for Maximal Lactate Steady State Determination in Soccer
Reference: Res Q Exerc Sport. 2019 Sep 3:1-12. doi: 10.1080/02701367.2019.1643446. [Epub ahead of print]
Authors: Garcia-Tabar I, Rampinini E, Gorostiaga EM
Summary: The association between an overlooked classical Lactate Threshold (LT), named "Minimum Lactate Equivalent" (LEmin), with Maximal Lactate Steady State (MLSS) has been recently described with good MLSS prediction results in endurance-trained runners. This study aimed to determine the applicability of LEmin to predict MLSS in lower aerobic-conditioned individuals compared to well-established blood lactate-related thresholds (BLTs). Fifteen soccer players [velocity at MLSS (MLSSV) 13.2 ± 1.0 km·h-1; coefficient of variation (CV) 7.6%] conducted a submaximal discontinuous incremental running test to determine BLTs and 3-6 constant velocity running tests to determine MLSSV. LEmin did not differ from conventional LTs (p > .05) and was 24% lower than MLSS (p < .001; ES: 3.26). Among LTs, LEmin best predicted MLSSV (r = 0.83; p < .001; SEE = 0.59 km·h-1). There was no statistical difference between MLSS and estimated MLSS using LEmin prediction formula (p = .99; ES: 0.001). Mean bias and limits of agreement were 0.00 ± 0.58 km·h-1 and ±1.13 km·h-1, respectively. LEmin best predicted MLSSV (r = 0.92; p < .001; SEE = 0.54 km·h-1) in the pooled data of soccer players and endurance-trained runners of the previous study (n = 28; MLSSV range 11.2-16.5 km·h-1; CV 9.8%). Results support LEmin to be one of the best single predictors of MLSS. This study is the sole study providing specific operational regression equations to estimate the impractical gold standard MLSSV in soccer players by means of a BLT measured during a submaximal single-session test.

#5 Creative and Intuitive Decision-Making Processes: A Comparison of Brazilian and German Soccer Coaches and Players
Reference: Res Q Exerc Sport. 2019 Sep 3:1-15. doi: 10.1080/02701367.2019.1642994. [Epub ahead of print]
Authors: Klatt S, Noël B, Musculus L, Werner K, Laborde S, Lopes MC, Greco PJ, Memmert D, Raab M
Summary:  The concepts of creativity and intuition have been well studied in isolation, but less is known about their distinctive contributions to option generation in decision making. We examined the relation between creative and intuitive decision making in two studies-one involving coaches and one involving soccer players-using video footage of real soccer matches. Additionally, we analyzed whether this relation is culture generic or culture specific by conducting matched cross-cultural studies in a European and a South American country. In Study 1, results indicate a conceptual overlap of creativity and intuition for Brazilian and German soccer coaches. Furthermore, coaches did not differ in their evaluation of creative and intuitive actions of players of both cultures. In Study 2, we found that for both subsamples the total number of generated options was positively correlated with the quality of the first and the final option and that the quality of players' first (intuitive) option was higher than that of options generated later. Moreover, results indicate a positive correlation between a player's creativity score and the quality of the first generated option for the whole sample. Overall, our findings provide meaningful information regarding athletes' and coaches' option-generation processes in decision making in complex team sports.

#6 Should you let your child play football? What about soccer or hockey?
Reference: Appl Neuropsychol Child. 2019 Sep 2:1-6. doi: 10.1080/21622965.2019.1654385. [Epub ahead of print]
Authors: Ferraro FR, Cuccolo K, Wise RA
Summary: College students (n = 120) answered 18 yes-no questions that varied the child's gender (male, female), grade (grade school, high school, college), and sport (football, soccer, hockey). The format of the 18 yes or no questions was "If you had a child in (grade school, high school, college) would you let (him, her) play (football, soccer, hockey)"? Similar to a previous study, a large percentage (78.8%) of the respondents answered yes to the questions about football, indicating that they would permit their children to play football despite the risk of concussion (96% yes for male children, 67% yes for female children). Although the number of respondents who would allow their male child to play soccer (98% for male children, 99% for female children) or hockey (92% for male children, 89% for female children) was similar to the percentage of respondents that would allow their male child to play football, significantly more respondents would allow their female child to play soccer or hockey than football. This result is potentially problematic because soccer and hockey have high rates of concussion, especially for females, which suggests that the respondents may have been unaware of this fact.

#7 Psychological characteristics in women football players: Skills, mental toughness, and anxiety
Reference: Scand J Psychol. 2019 Sep 6. doi: 10.1111/sjop.12571. [Epub ahead of print]
Authors: Kristjánsdóttir H, Jóhannsdóttir KR, Pic M, Saavedra JM
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Summary: Women's football has been far less studied than men's. This work's objectives were to: (1) analyze the differences in psychological skills, mental toughness (MT), and anxiety in women football players according to their level (national team, first division, and second division); and (2) predict those three levels (using a multivariate model) according to the players' psychological skills, mental toughness, and anxiety. One hundred and forty-two Icelandic women football players (23.5 ± 3.5 years) participated in the study. They were classified into three groups according to their level: national team, and first and second divisions. Three questionnaires were used: the Test of Performance Strategies Questionnaire, the Sport Mental Toughness Questionnaire, and the Sport Anxiety Scale-2 questionnaire. A one-way ANOVA with Bonferroni post hoc correction was used to examine differences between teams. Applying a classification tree analysis, the participants were classified into three groups according to their level. There were few differences between the three groups in psychological skills, but in mental toughness and anxiety the national team had the highest and lowest values respectively, and the first and second division players differed in relaxation in competition (TOPS), total score and confidence (SMTQ), and worry (SAS-2). The classification tree correctly classified 54.9% of the sample with the variables total score (SMTQ) and activation in practice (TOPS). Therefore, given the relevance that psychological attributes appear to have for women football players' performance, it would seem indispensable to incorporate the figure of the sports psychologist into national and club teams.

#8 Different Marks in the Pitch Constraint Youth Players' Performances During Football Small-sided Games
Reference: Res Q Exerc Sport. 2019 Sep 3:1-9. doi: 10.1080/02701367.2019.1645938. [Epub ahead of print]
Authors: Coutinho D, Gonçalves B, Travassos B, Folgado H, Figueira B, Sampaio J

Summary: This study aimed to compare players' performances when manipulating the external markings of the pitch during football small-sided games. Ten under-15 players performed a 5-a-side (plus goalkeepers) under three conditions: (i) Lines, the game was played in a pitch in which the external boundaries were painted with full lines; (ii) Dashed, the game was played in a pitch in which the external boundaries were painted with dashed lines; (iii) Corners, the game was played in a pitch were the external boundaries were delimited by one marker at each pitch corner. Players' positional data was used to compute tactical and time-motion variables. Also, technical analysis was comprised using video footage. Results showed similar tactical, physical and technical performances between the Lines and Dashed conditions. In contrast, the Lines condition showed small higher effects than Corners scenario in the time spent synchronized in longitudinal and lateral displacements, game pace, total distance covered, distance covered while jogging, number successful dribbles and shots on target. The Lines scenario has also revealed a lower effective playing space, distance covered at walking and running and a lower number of passes (small effects) compared to Corners. These results highlight that these changes in informational perception constraints modify players movement behavior. Accordingly, pitches with more visible boundaries were likely to decrease team dispersion, which may optimize team synchrony and technical performances, while decreasing the distance covered at higher speeds. Coaches may use this information to modify the types of pitch external boundaries markings, exposing the players to different environmental information.

#9 Return to play after surgery for isolated unstable syndesmotic ankle injuries (West Point grade IIB and III) in 110 male professional football players: a retrospective cohort study
Reference: Br J Sports Med. 2019 Aug 31. pii: bjsports-2018-100298. doi: 10.1136/bjsports-2018-100298. [Epub ahead of print]
Authors: D'Hooghe P, Grassi A, Alkhelaifi K, Calder J, Baltes TP, Zaffagnini S, Ekstrand J
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Summary: The purpose was to evaluate time to return to play following surgical stabilisation of isolated unstable syndesmosis injuries in a cohort of professional male football players. All professional football players undergoing surgery for isolated unstable syndesmosis injury (West Point grade ≥IIB) at a specialised Orthopaedic and Sports Medicine Hospital were followed up until return to play (minimum ≥6 months). Players with a stable syndesmosis, injuries older than 6 weeks, concomitant medial or lateral malleolar fracture or previous ankle surgery were excluded. During rehabilitation, time required to return to sports-specific rehabilitation, team training and first match play, were recorded. Between January 2012 and December 2017, a total of 110 male professional football players were included. The mean time required to begin on field rehabilitation was 37±12 days, while the mean time to return to team training was 72±28 days. The first official match was played on average 103±28 days postoperatively. Multivariable analysis revealed that the severity of injury, the concomitant presence of talar cartilage injury and the age of the player were significantly associated (p<0.00001) with time to return to on field rehabilitation, team training and match play. In this cohort of professional football players, surgical stabilisation of isolated unstable syndesmosis injuries (West Point grade ≥IIB) allowed for relatively quick return to play. High grade injury (West Point grade III), concomitant cartilage injury and greater age were associated with longer return to play times.

#10 Blood Biomarkers of Recovery Efficiency in Soccer Players
Reference: Int J Environ Res Public Health. 2019 Sep 6;16(18). pii: E3279. doi: 10.3390/ijerph16183279.
Authors: Nowakowska A, Kostrzewa-Nowak D, Buryta R, Nowak R
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Summary: Physical exercise strongly affects human metabolism and causes biochemical changes. This study aimed to investigate the relationship between routine plasma biomarker levels and recovery efficiency in soccer players during an entire competitive match season. The players participating in the study were divided into a midfielder/defender group (seven midfielders and seven defenders) and a goalie/substitute group (six persons-goalkeepers and players with a short cumulative match-time). The fasting capillary blood samples were taken 17-24 h after each competitive match. The blood plasma was used to determine the creatinine, urea, alkaline phosphatase, creatine kinase, lactate dehydrogenase, aspartate and alanine aminotransferase, iron and magnesium levels of the athletes. The levels of (AST) (aspartate aminotransferase), (ALT) (alanine aminotransferase) and (Cr) creatinine were higher in the midfielder/defender group than in the control group, but only AST and Cr significantly varied over time (AST decreased, and Cr increased with time). The (LDH) (lactate dehydrogenase) activity and urea level were significantly lower in the midfielder/defender group than in the goalie/substitute group, and it significantly varied over time (LDH decreased, and urea increased with time). No differences in the (CK) creatine kinase and (ALP) alkaline phosphatase activities between the groups was found, although CK increased significantly with time in the midfielder/defender group (particularly midfielders in the spring round). In midfielders, the AST activity and the iron level were significantly lower in the spring than in the autumn round. On the contrary, ALT, CK, urea and magnesium levels were significantly higher in the spring than in autumn round. A long-term measurement of biochemical parameters in elite soccer players indicated that AST, CK, LDH and creatinine levels, when analyzed together, could constitute a useful set of markers for monitoring recovery periods.

#11 Effect of Pre-training and Post-training Nordic Exercise on Hamstring Injury Prevention, Recurrence, and Severity in Soccer Players
Reference:  Ann Rehabil Med. 2019 Aug;43(4):465-473. doi: 10.5535/arm.2019.43.4.465. Epub 2019 Aug 31.
Authors: Elerian AE, El-Sayyad MM, Dorgham HAA
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Summary: The purpose was to investigate the effect of adding Nordic exercise as post-training in decreasing hamstring initial, recurrent injuries rates, and their severity. In this randomly controlled trial study, 34 professional football players aged 21 to 35 years were randomly assigned into two groups (17 players each) from Sporting clubs at Alexandria, Egypt. For group one, Nordic hamstring exercise (NHE) was performed pre-training and post-training. For group two, NHE was only performed pre-training. The control group was the same team during the previous season. Length of the trial was 12 weeks. The Australian football association injury form was used to collect incidence of injuries for each subject in both groups. Pooled results based on total injuries showed that group one had significantly less hamstring initial injuries (92% less) than the previous season, while group two had 80% less initial injuries and 85% less recurrent injuries than previous season. Regarding the severity of injuries in term of mean number of absent days, it was 1 day for group one and 2.7 days for group two while it was 7.95 days for the previous season during total risk time of 116.3±13.2 and 117.6±5.7 exposure hours for group one and group two, respectively. The use of NHE as a prevention protocol was effective in reducing all hamstring injuries with the use of NHE during pre-training and post-training having the greatest effect.

#12 Pressure pain sensitivity over nerve trunk areas and physical performance in amateur male soccer players with and without chronic ankle instability
Reference: Phys Ther Sport. 2019 Sep 4;40:91-98. doi: 10.1016/j.ptsp.2019.09.002. [Epub ahead of print]
Authors: Navarro-Santana MJ, Albert-Lucena D, Gómez-Chiguano GF, Plaza-Manzano G, Fernández-de-Las-Peñas C, Cleland J, Pérez-Silvestre Á, Asín-Izquierdo I
Summary: Chronic ankle instability (CAI) is reported after ankle sprain. Our aim was to assess differences in mechanical pain sensitivity of lower extremity nerve trunks and physical performance between amateur soccer players with and without CAI. Fifty-five male soccer players, 28 with and 27 without CAI participated in this stud. The perceived instability was assessed with the Cumberland Ankle Instability Tool (CAIT). Pressure pain thresholds (PPTs) on the common peroneal and tibialis nerve trunks, vertical jump, lateral step-down test and joint position sense of the knee were assessed by a blinded assessor.Soccer players with CAI showed lower PPTs over the common peroneal nerve than those without CAI (between-groups mean difference: 1.0 ± 0.8 kg/cm2, P < 0.001). No differences for PPT over the tibialis posterior (P = 0.078) or any physical performance outcome (knee joint positioning sense [P = 0.798], lateral step-down test [P = 0.580] and vertical jump variables [all, P > 0.310]) were found. PPT over the common peroneal nerve exhibited a significant moderate correlation with the CAIT score (r = 0.528, P < 0.001).Amateur soccer players with CAI have higher pressure pain sensitivity over the common peroneal nerve but exhibit similar physical performance to amateur soccer players without CAI.





Latest research in football - week 36 - 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 Combined Resistance and Plyometric Training Is More Effective Than Plyometric Training Alone for Improving Physical Fitness of Pubertal Soccer Players
Reference: Front Physiol. 2019 Aug 7;10:1026. doi: 10.3389/fphys.2019.01026. eCollection 2019.
Authors: Zghal F, Colson SS, Blain G, Behm DG, Granacher U, Chaouachi A
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Summary: The purpose of this study was to compare the effects of combined resistance and plyometric/sprint training with plyometric/sprint training or typical soccer training alone on muscle strength and power, speed, change-of-direction ability in young soccer players. Thirty-one young (14.5 ± 0.52 years; tanner stage 3-4) soccer players were randomly assigned to either a combined- (COMB, n = 14), plyometric-training (PLYO, n = 9) or an active control group (CONT, n = 8). Two training sessions were added to the regular soccer training consisting of one session of light-load high-velocity resistance exercises combined with one session of plyometric/sprint training (COMB), two sessions of plyometric/sprint training (PLYO) or two soccer training sessions (CONT). Training volume was similar between the experimental groups. Before and after 7-weeks of training, peak torque, as well as absolute and relative (normalized to torque; RTD r ) rate of torque development (RTD) during maximal voluntary isometric contraction of the knee extensors (KE) were monitored at time intervals from the onset of contraction to 200 ms. Jump height, sprinting speed at 5, 10, 20-m and change-of-direction ability performances were also assessed. There were no significant between-group baseline differences. Both COMB and PLYO significantly increased their jump height (Δ14.3%; ES = 0.94; Δ12.1%; ES = 0.54, respectively) and RTD at mid to late phases but with greater within effect sizes in COMB in comparison with PLYO. However, significant increases in peak torque (Δ16.9%; p < 0.001; ES = 0.58), RTD (Δ44.3%; ES = 0.71), RTD r (Δ27.3%; ES = 0.62) and sprint performance at 5-m (Δ-4.7%; p < 0.001; ES = 0.73) were found in COMB without any significant pre-to-post change in PLYO and CONT groups. Our results suggest that COMB is more effective than PLYO or CONT for enhancing strength, sprint and jump performances.

#2 Training/Match External Load Ratios in Professional Soccer Players: A Full-Season Study
Reference: Int J Environ Res Public Health. 2019 Aug 23;16(17). pii: E3057. doi: 10.3390/ijerph16173057.
Authors: Clemente FM, Rabbani A, Conte D, Castillo D, Afonso J, Truman Clark CC, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The aim of this study was two-fold: (i) to describe the training/match ratios of different external load measures during a full professional soccer season while analyzing the variations between different types of weeks (three, four and five training sessions/week) and (ii) to investigate the relationship between weekly accumulated training loads and the match demands of the same week. Twenty-seven professional soccer players (24.9 ± 3.5 years old) were monitored daily using a 10-Hz global positioning system with a 100-Hz accelerometer. Total distance (TD), running distance (RD), high-speed running (HSR), sprinting distance (SD), player load (PL), number of high accelerations (ACC), and number of high decelerations (DEC) were recorded during training sessions and matches. An individual training/match ratio (TMr) was calculated for each external load measure. Weeks with five training sessions (5dW) presented meaningfully greater TMr than weeks with four (4dW) or three (3dW) training sessions. Additionally, TDratio (TDr) was significantly greater in 5dW than in 3dW (mean differences dif: 1.23 arbitray units A.U.) and 4dW (dif: 0.80 A.U.); HSRr was significantly greater in 5dW than in 3dW (dif: 0.90 A.U.) and 4dW (dif: 0.68 A.U.); and SDr was significantly greater in 5dW than in 3dW (dif: 0.77 A.U.) and 4dW (dif: 0.90 A.U.). Correlations between the weekly training loads and the match demands of the same week were small for PL (r = 0.250 [0.13;0.36]), ACC (r = 0.292 [0.17;0.40]) and DEC (r = 0.236 [0.11;0.35]). This study reveals that ratios of above 1 were observed for specific measures (e.g., HSR, SD). It was also observed that training sessions are not adjusted according to weekly variations in match demands.

#3 Variations of Internal and External Load Variables between Intermittent Small-Sided Soccer Game Training Regimens
Reference: Int J Environ Res Public Health. 2019 Aug 15;16(16). pii: E2923. doi: 10.3390/ijerph16162923.
Authors: Clemente FM, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The purpose of this study was twofold: (i) analyze the variations of internal and external load between intermittent regimens (6 × 3' and 3 × 6') during a small-sided game (SSG); and (ii) analyze the variations of internal and external load within-intermittent regimens (between sets). Ten male amateur soccer players (age: 21.7 ± 2.1 years) participated in this study. Almost certain large decreases in total distance (-8.6%, [-12.3; -4.8], Effect Size (ES): -1.51, [-2.20; -0.82]) and running distance (-34.0%, [47.0; -17.8], ES: -2.23, [-3.40; -1.05]) were observed when comparing the 3 × 6' and 6 × 3'. Very likely moderate and large decreases in total accelerations (-24.0%, [-35.1; -10.9]; ES: -1.11, [-1.75; -0.47]) and total of decelerations (-26.7%, [-38.8; -12.1]; ES:-1.49, [-2.36; -0.62]), respectively, were found when comparing the 3 × 6' and 6 × 3'. Very likely increases in rated of perceived exertion in the set 3 in comparison to the 1st during the 3 × 6' SSG (34.5%, [12.4; 61.0], ES: 1.35, [0.53; 2.16]) and the 6 × 3' (29.9%, [11.6; 51.2]; ES: 1.17, [0.49; 1.85]). Longer sets increase the perception of effort and contribute to a large decrease in total and running distances, and total of accelerations and decelerations. Meaningful decreases in time-motion demands occur between sets 2 and 3 while perceived effort increases.

#4 Physical Performance Measures Correlate with Head Impact Exposure in Youth Football
Reference: Med Sci Sports Exerc. 2019 Aug 28. doi: 10.1249/MSS.0000000000002144. [Epub ahead of print]
Authors: Kelley ME, Jones DA, Espeland MA, Rosenberg ML, Miles CM, Whitlow CT, Maldjian JA, Stitzel JD, Urban JE
Summary: Head impact exposure (HIE) (i.e., magnitude and frequency of impacts) can vary considerably among individuals within a single football team. To better understand individual-specific factors that may explain variation in head impact biomechanics, this study aimed to evaluate the relationship between physical performance measures and HIE metrics in youth football players. Head impact data were collected from youth football players using the Head Impact Telemetry (HIT) System. HIE was quantified in terms of impact frequency, linear and rotational head acceleration, and risk-weighted cumulative exposure metrics (RWELinear, RWERotational, and RWECP). Study participants completed 4 physical performance tests: vertical jump, shuttle run, 3-cone, and 40 yard sprint. The relationships between performance measures and HIE metrics were evaluated using linear regression analyses. A total of 51 youth football athletes (ages: 9-13 years old) completed performance testing and received a combined 13,770 head impacts measured with the HIT System for a full season. All performance measures were significantly correlated with total number of impacts in a season, RWELinear-Season, and all RWE-Game metrics. The strongest relationships were between 40 yard sprint speed and all RWE-Game metrics (all p≤0.0001 and partial R>0.3). The only significant relationships among HIE metrics in practice were between shuttle run speed and total practice impacts and RWELinear-Practices, 40 yard sprint speed and total number of practice impacts, and 3-cone speed and 95th percentile number of impacts/practice. Generally, higher vertical jump height and faster times in speed and agility drills were associated with higher HIE, especially in games. Physical performance explained less variation in HIE in practices, where drills and other factors, such as coaching style, may have a larger influence on HIE.

#5 Proprioception is not associated with lower extremity injuries in U21 high-level football players
Reference: Eur J Sport Sci. 2019 Aug 30:1-20. doi: 10.1080/17461391.2019.1662492. [Epub ahead of print]
Authors: Namazi P, Zarei M, Abbasi H, Hovanloo F, Rommers N, Rössler R
Summary: Football is a contact sport with a significant risk of injury. Although proprioception is well studied in rehabilitation, little is known about the association between proprioception and the occurrence of sport injuries. The purpose of this study was to look into the association between ankle and knee proprioception and lower extremity injuries in young football players. 73 football players from the highest U-21 league in Iran volunteered to participate in this study. Before the start of the 2017-2018 competitive season, joint position sense was measured at 30°, 60° and 90° knee flexion and at 10° and 15° ankle dorsiflexion, and inversion using the Biodex Isokinetic pro 4 system. The teams' medical staff recorded football-related lower extremity injuries. We used mixed effects Cox regression models to calculate hazard ratios (HRs) with 95% CIs, acknowledging the clustered data structure. 22 players (30.1%) suffered one or more lower extremity injuries during the season. None of the proprioception measures examined was significantly associated with the risk of lower extremity injuries. Based on these results of our sample, joint position sense does not seem to be associated with lower extremity injuries in young male football players.

#6 Few training sessions between return to play and first match appearance are associated with an increased propensity for injury: a prospective cohort study of male professional football players during 16 consecutive seasons
Reference: Br J Sports Med. 2019 Aug 29. pii: bjsports-2019-100655. doi: 10.1136/bjsports-2019-100655. [Epub ahead of print]
Authors: Bengtsson H, Ekstrand J, Waldén M, Hägglund M
Summary: It has been hypothesised that injury risk after return to play following an injury absence is influenced by the amount of training completed before return to competition. The aim was to analyse if the number of completed training sessions between return to play and the first subsequent match appearance was associated with the odds of injury in men's professional football. From a cohort study, including 303 637 individual matches, 4805 first match appearances after return to play following moderate to severe injuries (≥8 days absence) were analysed. Rate ratios (RRs) were used to compare injury rates in the first match appearances with the average seasonal match injury rate. Odds ratios (ORs) were used to analyse associations between the number of completed training sessions and general (all injuries), muscle, and non-muscle injury odds. Injury rate in the first match after return to play was increased by 87% compared with the average seasonal match injury rate (46.9 vs 25.0/1000 hours, RR=1.87; 95% CI 1.64 to 2.14). The odds of injury dropped 7% with each training session before the first match (OR 0.93; 95% CI 0.87 to 0.98). The same association was found for muscle injuries (OR 0.87; 95% CI 0.79 to 0.95) but not for non-muscle injuries (OR 0.99; 95% CI 0.91 to 1.07). Injury rates in the first match after injury are higher than the average seasonal match injury rate, but the propensity for player injury is decreased when players complete more training sessions before their first match.

#7 C-Reactive Protein Serum Levels as an Internal Load Indicator of Sprints in Competitive Football Matches
Reference: Int J Sports Med. 2019 Aug 29. doi: 10.1055/a-0985-4464. [Epub ahead of print]
Authors: Jatene P, Dos Santos GS, Portella DL
Summary: This study compared internal load variable dynamics across three consecutive football matches and investigated its relationship with the number of sprints performed by players. Twenty-three male players had blood and salivary samples collected for hormonal concentration (testosterone, cortisol, and testosterone-cortisol ratio), and serum analysis (interleukin-6, interleukin-1-beta, and c-reactive-protein), respectively. Sprints were measured through Global Position System devices. Testosterone and testosterone-cortisol-ratio presented a decreasing behavior up to the second match, and all other indicators presented an increasing behavior during the same period, c-reactive-protein was the only indicator observed to significantly rise up to the third match as well (0.38±0.02 mg/L; 0.49±0.05 mg/L; 0.69±0.05 mg/L; 0.89±0.08 mg/L). C-reactive-protein showed strong correlations with sprints in the second and third matches (p<0.01, r=0.71 and 0.79), and weak-to-moderate in the first one (p<0.05, r=0.59). Interleukin-6 and interleukin-1-beta presented weak-to-moderate correlation in every match (p<0.05, r=0.48 to 0.51; r=0.51 to 0.55) while testosterone-cortisol ratio presented weak-to-moderate correlation only in the third one (p<0.05, r=0.42). Multilevel linear regression showed that c-reactive-protein had a higher R2 than other biomarker in any regression model (R2=0.624; p<0.001). Therefore, c-reactive-protein can be a valid and reliable indicator of sprinting in competitive football. Future research should explore longer periods of monitoring and/or others external load variables so that other behaviors may arise to knowledge.

#8 Radiographic analysis of lower limb alignment in professional football players
Reference: Arch Orthop Trauma Surg. 2019 Aug 28. doi: 10.1007/s00402-019-03266-9. [Epub ahead of print]
Authors: Krajnc Z, Drobnič M
Summary: The purpose was to radiographically analyze lower limb alignment in adult asymptomatic professional football players and to correlate these values to clinical measurements. Twenty-four asymptomatic players [24.2 (3.6) years] were enrolled. Standard bilateral lower limb anteroposterior weight-bearing radiographs were acquired and clinical measurement of intercondylar/intermalleolar (ICD/IMD) distance was performed. Coronal plane mechanical alignment was assessed by five angles: leg mechanical axis (LMA), lateral proximal femoral angle (LPFA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and lateral distal tibial angle (LDTA). Their values were compared to the reference values for adult population. An inter-individual comparison between right/left and dominant/non-dominant leg was added. The sum of bilateral LMA was correlated against ICD/IMD and against ICD/IMD adjusted for body height. Football players presented with ICD/IMD of 46.5 (19.8) mm. Two, out of five, lower leg coronal angles showed significant differences (p < 0.001) compared to reference data from literature: LMA 5.8 (3.0)º vs.1.2 (2.2)º and MPTA 83.5 (2.6)º vs. 87.2 (1.5)º. No significant differences between left/right leg and dominant/non-dominant leg were established. Summed up bilateral LMA showed a high correlation to IMD/ICD (r = 0.8395; R2 = 0.7048), and even higher to ICD/IMD adjusted for body height (r = 0.8543; R2 = 0.7298). This study was radiographically confirming increased varus of elite football players toward general population. Apex of the varus deformity was located in the proximal tibia. Clinical measurement of ICD/IMD adjusted for body height highly correlated with the radiographic values of coronal alignment; therefore, it may be used in population studies.

#9 Short term effects of a weight loss and healthy lifestyle programme for overweight and obese men delivered by German football clubs
Reference: Eur J Sport Sci. 2019 Aug 28:1-35. doi: 10.1080/17461391.2019.1660809. [Epub ahead of print]
Authors: Pietsch B, Weisser B, Hanewinkel R, Gray C, Hunt K, Wyke S, Morgenstern M
Summary: Numbers of obese and overweight people continue to grow in Germany as they do worldwide. Men are affected more often but do less about it and few weight loss services attract men in particular. To evaluate the effectiveness of a men-only weight loss program, Football Fans in Training (FFIT), delivered by football clubs in the German Bundesliga, we did a non-randomized trial with a waiting list control group. Participants' data were collected between January 2017 and July 2018. FFIT is a 12-week, group-based, weight loss program and was delivered in stadia and facilities of 15 professional German Bundesliga clubs. Inclusion criteria were age 35-65 years, BMI ≥ 28 and waist circumference ≥100 cm. Clubs recruited participants through Social Media, E-Mail and match day advertisement. 477 German male football fans were allocated to the intervention group by order of registration date at their respective clubs. 84 participants on waiting list were allocated to the control group. Primary outcome was mean difference in weight loss with treatment condition over time as independent variable. We performed a multilevel mixed-effects linear regression analysis. Results were based on Intention-to-treat (ITT) analysis with Multiple Imputation. After 12 weeks, the mean weight loss of the intervention group adjusted for club, course and participants' age was 6.24 kg (95% CI 5.82 to 6.66) against 0.50 kg (-0.47 to 1.49) in the comparison group (p < 0.001). The results indicate that Football Fans in Training effectively helped German men to reduce their weight and waist circumference.

#10 Use of functional performance tests in sports: Evaluation proposal for football players in the rehabilitation phase
Reference: Turk J Phys Med Rehabil. 2018 May 15;64(2):148-154. doi: 10.5606/tftrd.2018.1462. eCollection 2018 Jun.
Authors: Gomez-Piqueras P, Gonzalez-Rubio J, Sainz de Baranda P, Najera A
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Summary: Based on the criteria of a group of experts, this study aims to select a set of functional performance tests which can be applied to evaluate the functional status of a football player in the recovery process and make a decision in relation to their return to practice. A total of 16 experts were selected by the coordinator group to judge an initial list of functional performance tests and, thus, reach a consensus about the tests which are best suited to the needs of the injured player. Each of the experts had to evaluate each one of the tests in a scale from 1 to 5 in relation to their suitability. Delphi method was used to reach consensus in the expert group. From the initial list of 25, the tests which obtained the best evaluation were: Counter movement jump (4.3±0.9), Single hop test (4.1±0.8), Triple hop test (4.1±0.9), Crossover hop test (4.1±0.7), Yo-Yo intermittent recovery (4.2±0.6), Barrow test (4.1±0.6), Shuttle run 8¥5 m (4.1±0.8). Star excursion balance test (4±0.7) and Y balance test (4.1±0.7). In the opinion of the experts selected here, these tests are the ones which best respond to the needs involved in a complex decision such as RTP.

#11 Injury Incidence, Prevalence and Severity in High-Level Male Youth Football: A Systematic Review
Reference: Sports Med. 2019 Aug 26. doi: 10.1007/s40279-019-01169-8. [Epub ahead of print]
Authors: Jones S, Almousa S, Gibb A, Allamby N, Mullen R, Andersen TE, Williams M
Summary: At a young age, high-level youth footballers enter structured practice where they engage in regular training and matches. The academy system is considered fundamental to a young footballer's tactical, technical and physical development. Yet, with regular training and matches, high-level youth footballers may be exposed to the risk of injury. This systematic review analyses and summarises published scientific information on high-level youth football injury characteristics and calculates the risk of them sustaining an injury over the course of a typical season. The search was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Of the 1346 studies found, 23 fulfilled the inclusion criteria. Quality assurance scores for the selected research articles ranged between two and five out of eight. A high degree of heterogeneity between studies was observed. The probability of sustaining a time-loss injury during a high-level youth season ranged between < 1% and 96% for under 9- to under 16-year age groups and 50% and 91% for under 18- to under 21-year age groups. Pooled estimates for total (training and match) incidence per 1000 h was 5.8 for youth players aged under 9 to under 21 years, 7.9 for older players (under 17-under 21 years) and 3.7 for younger aged players (under 9-under 16 years). Training injury incidence rate ranged from 0.69 to 7.9 per 1000 h for all age groups in youth football. Match injury incidence rate for high-level youth players ranged from 0.4 to 80.0 per 1000 h. Close to one-fifth (18%) of all high-level youth football injuries were classified as severe and required > 28 days recovery time. Muscle strain injury accounted for 37% of all injuries reported in youth football. High probabilities (> 90%) of sustaining a time-loss injury over one typical high-level football season were found. High-level youth players lose large portions of the seasonal development to injury, with players seemingly suffering long absences from training and matches, consequently affecting health and well-being and possibly burdening club/parental finances and healthcare systems.





Latest research in football - week 35 - 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 Influence of poor preparation and sleep deficit on injury incidence in amateur small field football of both gender
Reference: Arch Orthop Trauma Surg. 2019 Aug 17. doi: 10.1007/s00402-019-03261-0. [Epub ahead of print]
Authors: Krutsch V, Clement A, Heising T, Achenbach L, Zellner J, Gesslein M, Weber-Spickschen S, Krutsch W
Summary: Amateur small-field football tournaments are rather common worldwide. Adequate preparation is essential for injury prevention. The consequences of insufficient injury preparation at this level are still unclear. This study investigates the factors influencing injuries in this football population. In 2017, medical students participating in a national amateur football tournament were analysed in a prospective cohort study. Injury incidence, injury pattern and factors influencing injuries were investigated according to the statement on data collection and injury definition of Fuller et al. (Br J Sports Med 40:193-201, 2006). Preparation for the tournament was assessed for both sexes by means of hours of sleep, alcohol consumption, training level and warm-up performance. Of 694 amateur football players (423 men and 271 women) with a mean age of 23 years (SD 2.5), 321 (21.1%) injuries happened during the tournament. 60% of injuries affected the lower extremity. The most common types of traumatic injury were skin abrasions (40.0%) and muscle strains (23.3%). The injury incidence of male players during match exposure was 469 per 1000 h football and significantly higher than in female players 313 (p = 0.025). One potential reason for the higher injury rate of male players as measure for inadequate preparation was significantly higher alcohol consumption the evening before the tournament (p < 0.001) and the after-effects on match day (p < 0.001). Additionally, male players reported less and inadequate sleep the night before the tournament (p < 0.007) and a lower warm-up rate before the matches compared to female players (p < 0.001). Small-field tournaments in football have a high injury incidence. Male players have a higher injury incidence than female players and show additionally a lack of sleep and alcohol consumption the night before the tournament and poor warm-up performance on match day. Adequate preparation for a football tournament is the key factor for preventing injuries, also in recreational football.

#2 Tattoos among elite football players during the 2019 FIFA Women's World Cup France
Reference: J Eur Acad Dermatol Venereol. 2019 Aug 17. doi: 10.1111/jdv.15890. [Epub ahead of print]
Authors: Kluger N
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Summary: Thirty-four percent of the men players harbored visible tattoos, without notable impact on performance or discipline on the field during the 2018 FIFA World Cup (FWC), [1]. In a spirit of gender equality, we performed the same study among elite women footballers enrolled in the 2019 FWC France with the same methodology [1]. Players' visible tattoos (location, colours) were reviewed using the Getty Images website [2]. We collected players and teams' statistics using the official FIFA website.

#3 Distribution of External Load During Acquisition Training Sessions and Match Play of a Professional Soccer Team
Reference: J Strength Cond Res. 2019 Aug 29. doi: 10.1519/JSC.0000000000003363. [Epub ahead of print]
Authors: Castillo D, Raya-González J, Weston M, Yanci J
Summary: The aim of this study was to use global position systems to analyze the external loads of the 3 different acquisition training sessions (ATS) with competitive matches in professional soccer players over a 6-week period. Sixteen professional soccer players participated in the study, which analyzed the distribution of external load during the training microcycle of a professional soccer team. The 3 types of ATS undertaken by the players were as follows: ATS1 (strength), ATS2 (endurance), and ATS3 (speed). The total distance covered, the distance covered at above 14 km·h, the distance covered >21 km·h, the number of high accelerations (>3 m·s), and player load were recorded. The results showed that external loads were consistently higher during matches when compared with all training sessions (range of effect sizes: 1.06-3.38). Between training session comparisons revealed higher external loads during ATS1 and ATS2, when compared with ATS3 (range of effect sizes: 0.60-2.41). The only external load variable that differed between ATS1 and ATS2 was the distance covered >21 km·h, which was higher for ATS1. Our findings suggest that technical staff should consider the physical demands of weekly periodization to understand the training process regarding optimizing player physical performance.

#4 Relationship Among Biological Maturation, Physical Characteristics, and Motor Abilities in Youth Elite Soccer Players
Reference:  J Strength Cond Res. 2019 Aug 29. doi: 10.1519/JSC.0000000000003346. [Epub ahead of print]
Authors: Itoh R, Hirose N
Summary: Studies investigating skeletal maturity and motor abilities in youth Asian elite soccer players are lacking. We aimed to investigate the cross-sectional relationship among skeletal age (SA), physical characteristics, and motor abilities in youth elite soccer players. Skeletal age is commonly used to estimate the maturity status of youth athletes using a hand-wrist radiograph. We enrolled 49 youth elite male soccer players (12.7 ± 0.2 years). Height, body mass, body fat percentage, circumference (thigh/calf), flexibility, 10-m/50-m sprint, 10-m × 5 shuttle run, the crank test, 5-step bounding, Yo-Yo intermittent recovery test level 2, and cooper run were measured. Participants were divided into early (n = 14), average (n = 22), and late (n = 13) maturation groups according to their chronological age (CA) and SA based on the following criteria: SA-CA < -1 year, SA-CA = ±1 year, and SA-CA > +1 year, respectively. The difference in parameters among the groups was analyzed using one-way analysis of variance and Tukey's post hoc test. Statistical significance was set at p < 0.05. The early and average maturation groups were taller and heavier and had a larger circumference than the late maturation group (p < 0.05). Conversely, the early and average groups were significantly faster in 50-m sprint (p < 0.05) and scored higher in 5-step bounding (p < 0.05) than the late group. There was no difference in other parameters among the groups. In conclusion, the difference in biological maturity influences physical and physiological development, particularly height and muscular power, in youth elite soccer players.

#5 Competencies for rating perceived exertion in amateur soccer players with and without intellectual disabilities
Reference: J Appl Res Intellect Disabil. 2019 Aug 30. doi: 10.1111/jar.12668. [Epub ahead of print]
Authors: Schmitz G, Meis JM, Hafferkamp M, Schmitz S
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Summary: Perception of exertion is essential for self-regulation in sports. The ability to rate perceived exertion (RPE) is regarded as psychophysiological competence, although cognitive components of RPE are largely unknown. The present study tested the hypothesis that cognitive processing speed, perseveration and figural fluency correlate with RPE. The present study tested relationships between the performance in neuropsychological tests and the competence for RPE assessed during soccer training in 30 adults with and 22 adults without intellectual disabilities. Mean correlation coefficients for RPE and heart rate differed significantly between participants with intellectual disabilities (r = .41) and participants without intellectual disabilities (r = .71). The variance of RPE could be partially explained by neuropsychological performance measures reflecting cognitive processing speed and perseveration and by age. The results point to an impaired perception of exertion in people with intellectual disabilities, which can be partially explained by individual neuropsychological competencies.

#6 Sports Specialization Is Not Associated With Greater Odds of Previous Injury in Elite Male Youth Soccer Players
Reference: Clin J Sport Med. 2019 Sep;29(5):368-373. doi: 10.1097/JSM.0000000000000643.
Authors: Frome D, Rychlik K, Fokas J, Chiampas G, Jayanthi N, LaBella C
Summary: The purpose was to determine the relationship between sport specialization and previous injury in elite male youth soccer players. Male youth soccer players (N = 2123) participated in this study.  Sport specialization, weekly training volume, training ratio, and age were utilized as risk factors. Previous sports-related injury, injury type (traumatic vs overuse), injury severity, and injury location were main outcomes measures.  Of 2099 participants (average age 13.2 ± 1.8 years), 61.7% were specialized in soccer (played soccer >8 mo/yr and no other sports) and 38.3% were nonspecialized (played soccer >8 mo/yr and also played other organized sports). Specialized athletes were older than nonspecialized athletes (13.7 ± 1.9 vs 12.5 ± 1.4, P < 0.0001). Thirty-three percent (690/2099) of athletes reported at least one previous sports-related injury for a total of 765 traumatic injuries and 25 overuse injuries. Distribution of injury type was similar for specialized and nonspecialized athletes. Among athletes with overuse injuries, nonspecialized athletes were more likely to report upper-extremity and trunk overuse injuries than specialized athletes. After accounting for age and weekly training volume, specialized athletes had decreased odds of reporting any previous injury compared with nonspecialized athletes [odds ratio (OR), 0.78; 95% confidence interval (CI), 0.64-0.95], and similar odds of reporting a previous lower-extremity (LE) overuse injury as nonspecialized athletes (OR, 0.70; 95% CI, 0.56-1.1). However, specialized athletes missed more practices due to injury than nonspecialized players [median = 3, interquartile range (IQR) 2-4 vs median = 2, IQR 2-4, P = 0.0003]. In this national sample of elite, male youth soccer players, after accounting for age and weekly training volume, specialized athletes had decreased odds of reporting any previous injury and similar odds of reporting a previous LE overuse injury as nonspecialized athletes. These data suggest the need for further research to determine whether injury risk related to sports specialization depends on sex, chosen sport, and skill/competitive level.

#7 Comparative efficacy of active recovery and cold water immersion as post-match recovery interventions in elite youth soccer
Reference: J Sports Sci. 2019 Aug 28:1-9. doi: 10.1080/02640414.2019.1660448. [Epub ahead of print]
Authors: Pooley S, Spendiff O, Allen M, Moir HJ
Summary: The current study compared cold-water immersion (CWI) and active recovery (AR) to static stretching (SS) on muscle recovery post-competitive soccer matches in elite youth players (n = 15). In a controlled crossover design, participants played a total of nine competitive soccer games, comprising three 80 minute games for each intervention (SS, CWI and AR). Muscle oedema, creatine kinase (CK), countermovement jump performance (CMJA) and perceived muscle soreness (PMS) were assessed pre-, immediately post-, and 48 hours post-match and compared across time-intervals and between interventions. Following SS, all markers of muscle damage remained significantly elevated (P < 0.05) compared to baseline at 48 hours post-match. Following AR and CWI, CMJA returned to baseline at 48 hours post-match, whilst CK returned to baseline following CWI at 48 hours post-match only. Analysis between recovery interventions revealed a significant improvement in PMS (P < 0.05) at 48 hours post-match when comparing AR and CWI to SS, with no significant differences between AR and CWI observed (P > 0.05). Analysis of %change for CK and CMJA revealed significant improvements for AR and CWI compared to SS. The present study indicated both AR and CWI are beneficial recovery interventions for elite young soccer players following competitive soccer matches, of which were superior to SS.

#8 Does soccer play lower blood pressure?
Reference: Dtsch Med Wochenschr. 2019 Aug;144(17):1229-1232. doi: 10.1055/a-0953-6509. Epub 2019 Aug 27. [Article in German]
Summary: Playing football leads to a sustainable improvement of cardiovascular risk factors, especially to a reduction of blood pressure in hypertension. For certain target groups football is more attractive with its team character than individual sports. However, the existing studies are not sufficient for an evidence-based recommendation. Therefore, no medical society explicitly recommends football for lowering blood pressure. Urgent studies are needed to adequately evaluate the value of football as a health sport. This includes a special training program and rules, the involvement of football clubs in these programs, the training of appropriate coaches and the involvement of interested physicians. Football could, with its popularity, motivate more people to exercise and contribute to a sustained reduction in cardiovascular disease.

#9 Seasonal Accumulated Workloads in Collegiate Men's Soccer: A Comparison of Starters and Reserves
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003257. [Epub ahead of print]
Authors: Curtis RM, Huggins RA, Benjamin CL, Sekiguchi Y, M Arent S, C Armwald B, Pullara JM, West CA, Casa DJ
Summary: The purpose of this investigation was to quantify and compare player's season total-, match-, and training-accumulated workload by player status characteristics (i.e., starter vs. reserve) in American collegiate men's soccer. Global positioning system (GPS) and heart rate (HR)-derived workloads were analyzed from 82 collegiate male soccer athletes from 5 separate teams over the 2016 and 2017 seasons. Differences in total physical and physiological workloads (i.e., total distance, accelerations, and weighted HR-zone training impulse [TRIMP] score) as well as workloads over a range of intensity zones were examined using multilevel mixed models, with mean difference (MD) and effect size (ES) reported. Starters accumulated substantially more total distance (MD = 82 km, ES = 1.23), TRIMP (MD = 2,210 au, ES = 0.63), and total accelerations (MD = 6,324 n, ES = 0.66) over the season. Total accumulated distance in all velocity zones (ES [range] = 0.87-1.08), all accelerations zones (ES [range] = 0.54-0.74), and time spent at 70-90% HRmax (ES [range] = 0.60-1.12) was also greater for starters. Reserves accumulated substantially more total distance (MD = 20 km, ES = 0.43) and TRIMP (MD = 1,683 au, ES = 0.79) during training. Although reserves show elevated physical and physiological loads during training compared with starters, there is an imbalance in overall workloads between player roles, with starters incurring substantially more match and total seasonal workloads. These results indicate managing player workloads in soccer requires attention to potential imbalances between players receiving variable match times. Coaches and practitioners in collegiate men's soccer may consider implementing strategies to reduce discrepancies in loading between starters and reserves. Individualized monitoring of training and match workloads may assist in the implementation of more balanced load management programs.

#10 Contextual Variables and Training Load Throughout a Competitive Period in a Top-Level Male Soccer Team
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003258. [Epub ahead of print]
Authors: Rago V, Rebelo A, Krustrup P, Mohr M
Summary: The aim of the present study was to investigate and quantify the weekly training load (TL) according to different match-related contextual factors in a professional male soccer team (n = 23). Training load was quantified using a 10-Hz global positioning system with integrated 100-Hz accelerometer and heart rate recordings over a 3-month competitive period. Total distance (TD) covered and high-speed running (HSR, >16 km·h) during training were higher in the week after playing against a bottom-level or top-level opponent compared to a medium-level opponent (p < 0.05; effect size [ES] = 0.30-1.04). TD was also higher when preparing for a match against a bottom-level opponent (p < 0.05; ES = 0.39-0.76). In addition, the percentage of HSR was higher after playing a bottom-level compared to a medium-level opponent (p < 0.001; ES = 0.49 [0.27; 0.71]). TD covered was higher in the week following a draw or a win, and higher before a loss compared to a draw (p < 0.05, ES = 0.32-0.81). Both absolute HSR and HSR expressed as percentage of TD were higher before losing and winning a match compared to a draw (p < 0.05; ES = 0.72-0.98). Weekly TL seems to be slightly affected by match-related contextual variables, with special emphasis on the opponent standard and match outcome. Higher training volume was observed before and after playing against a top-level opponent, and after losing a match, whereas the volume of high-intensity training seems to be higher when preparing for a game against a top-level opponent. Future experimental research should clarify the interaction between match-related contextual variables (e.g., cause) and weekly TL (e.g., effect).

#11 Relative Age Effect in Collegiate Soccer: Influence of Nationality, Playing Position, and Class
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003356. [Epub ahead of print]
Authors: Hurley E, Comstock BA, Haile L, Beyer KS
Summary: The purpose of this study was to evaluate the existence of relative age effects (RAEs) in collegiate soccer. In addition, the impact of nationality, position, class, and National Collegiate Athletic Association (NCAA) tournament qualification status on the prevalence of RAEs was assessed. Birth dates from male NCAA Division I soccer athletes (n = 4,082) from the 2017/2018 season were categorized into quarters based on calendar and scholastic quarters. All athlete birth-date distributions were compared with the expected birth-date distributions for the United States. International-born athletes (INT) displayed a significant difference in birth-date distribution when assessed with calendar quarters, whereas American-born athletes (USA) showed a significant difference in birth-date distributions when assessed with scholastic quarters. Furthermore, INT showed significant RAEs for midfielders and defenders, whereas USA showed significant RAEs midfielders and goalkeepers. In terms of class, INT had significant RAEs for all classes, whereas USA had significant RAEs only for freshmen and sophomores. All INT had significant RAEs regardless of tournament qualification status; however, USA had significant RAEs only for nontournament teams. In summary, significant RAEs exist in male Division I college soccer; however, the presence of RAEs is influenced by nationality, position, class, and NCAA tournament qualification status. Coaches should be aware of RAEs during the recruitment process to avoid potential selection bias.

#12 High-intensity endurance capacity assessment as a tool for talent identification in elite youth female soccer
Reference: J Sports Sci. 2019 Aug 26:1-7. doi: 10.1080/02640414.2019.1656323. [Epub ahead of print]
Authors: Datson N, Weston M, Drust B, Gregson W, Lolli L
Summary: Talent identification and development programmes have received broad attention in the last decades, yet evidence regarding the predictive utility of physical performance in female soccer players is limited. Using a retrospective design, we appraised the predictive value of performance-related measures in a sample of 228 youth female soccer players previously involved in residential Elite Performance Camps (age range: 12.7-15.3 years). With 10-m sprinting, 30-m sprinting, counter-movement jump height, and Yo-Yo Intermittent Recovery Test Level 1 (IR1) distance as primary predictor variables, the Akaike Information Criterion (AIC) assessed the relative quality of four penalised logistic regression models for determining future competitive international squads U17-U20 level selection. The model including Yo-Yo IR1 was the best for predicting career outcome. Predicted probabilities of future selection to the international squad increased with higher Yo-Yo IR1 distances, from 4.5% (95% confidence interval, 0.8 to 8.2%) for a distance lower than 440 m to 64.7% (95% confidence interval, 47.3 to 82.1%) for a score of 2040 m. The present study highlights the predictive utility of high-intensity endurance capacity for informing career progression in elite youth female soccer and provides reference values for staff involved in the talent development of elite youth female soccer players.





Latest research in football - week 34 - 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 Eccentric-concentric Ratio: A Key Factor for Defining Strength Training in Soccer
Reference: Int J Sports Med. 2019 Aug 21. doi: 10.1055/a-0977-5478. [Epub ahead of print]
Authors: Nuñez FJ, Hoyo M, López AM, Sañudo B, Otero-Esquina C, Sanchez H, Gonzalo-Skok O
Summary: The aims of this study were to analyse the effect of chronic strength training over concentric power (CON), eccentric power (ECC), ECC/CON ratio, and 20 m linear sprint performance in elite young soccer players. Twenty young elite Spanish soccer players were assigned to an experimental group (CPG) which performed a front-step exercise using a conical pulley, 2-3 sets of 6 repetitions each leg, during 9 weeks (CPG, n=10) in addition to its usual strength training, or to a control group (CG, n=10). The improvements in the ECC mean power (36%, ES=1.61), and ECC / CON ratio (17%, ES=1.77) were substantially greater in the CPG than in the CG while the CON mean power (16%, ES=0.83) was substantially greater in the CG than in the CPG. The sprinting time for 10 m (2.8%, ES=0.78) and the 10 m flying time between 10-20 m (1.72%, ES=0.41) were substantially enhanced in CPG and CG respectively. To be efficient when defining a functional strength training and performance increments using an inertial device, the mean power output need to be measured during the CON and ECC phases and an analysis of the ECC / CON ratio should be included.

#2 Progressive strength training restores quadriceps and hamstring muscle strength within 7 months after ACL reconstruction in amateur male soccer players
Reference: Phys Ther Sport. 2019 Aug 9;40:10-18. doi: 10.1016/j.ptsp.2019.08.004. [Epub ahead of print]
Authors: Welling W, Benjaminse A, Lemmink K, Dingenen B, Gokeler A
Summary: The purpose of the current study was to compare the results of a progressive strength training protocol for soccer players after anterior cruciate ligament reconstruction (ACLR) with healthy controls, and to investigate the effects of the strength training protocol on peak quadriceps and hamstring muscle strength. Thirty-eight amateur male soccer players after ACLR were included. Thirty age-matched amateur male soccer players served as control group. Quadriceps and hamstring muscle strength was measured at three time points during the rehabilitation. Limb symmetry index (LSI) > 90% was used as cut-off criteria. Soccer players after ACLR had no significant differences in peak quadriceps and hamstring muscle strength in the injured leg at 7 months after ACLR compared to the dominant leg of the control group. Furthermore, 65.8% of soccer players after ACLR passed LSI >90% at 10 months for quadriceps muscle strength. Amateur male soccer players after ACLR can achieve similar quadriceps and hamstring muscle strength at 7 months compared to healthy controls. These findings highlight the potential of progressive strength training in rehabilitation after ACLR that may mitigate commonly reported strength deficits.

#3 Analysis of Playing Area Dimensions in Spanish Professional Soccer: Extrapolation to the Design of Small-Sided Games With Tactical Applications
Reference: J Strength Cond Res. 2019 Aug 15. doi: 10.1519/JSC.0000000000003226. [Epub ahead of print]
Authors: Caro O, Zubillaga A, Fradua L, Fernandez-Navarro J
Summary: The aims of this study were to examine (a) the width and length dimensions of the playing area in 4v4 situations during competition, (b) the influence of the pitch zone where the ball is on 4v4 dimensions, and (c) the influence of match status on the dimensions of 4v4 situations. Data were collected from 25 matches from the Spanish La Liga of the 2007-2008 season using the Amisco system. Length, width, and individual playing area (IPA) of the rectangle that included the nearest 4 players to the ball from each team were collected in a total of 8,727 4v4 game situations. The pitch zone and match status were also considered for these 4v4 situations. To determine factors that affect 4v4 game situations, 1-way analysis of variance was used. The influence of the pitch zone where 4v4 situations took place showed significant differences (p < 0.001) between the zones where different principles of the game apply. The areas of the 4v4 situations ranged from 14.70 ± 4.69 × 17.18 ± 6 to 17.09 ± 5.16 × 20.34 ± 5.93 m, and the IPA of the 4v4 playing rectangle ranged from 46.33 ± 20 to 35.48 ± 16.95 m, being larger in the central zones of the pitch. The length of the 4v4 rectangle showed a significant reduction in the closer zones to the goal. Match status did not affect the dimensions of these 4v4 game situations significantly. The findings of this study suggest that the size of 4v4 situations proposed for training should be designed according to the pitch zone where playing actions take place.

#4 Augmented-Feedback Training Improves Cognitive Motor Performance of Soccer Players
Reference: Med Sci Sports Exerc. 2019 Aug 16. doi: 10.1249/MSS.0000000000002118. [Epub ahead of print]
Authors: Hicheur H, Chauvin A, Cavin V, Fuchslocher J, Tschopp M, Taube W
Summary: In this study, we tested the hypothesis that augmented feedback (AF) training can improve both perceptual-cognitive and/or motor skills specific to soccer. Three groups of young elite players (U14-U15 categories) performed a test consisting in passing the ball as accurately and as quickly as possible towards a visual target moving briefly across a large screen located at 6 meters from the player. The performed task required players to correctly perceive the target, anticipate its future location and to adequately adjust the pass direction and power. The control group (CON) performed normal soccer training and was compared with two visuomotor training groups (AF and No-Feedback NF) that followed the same training regime but integrated series of 32 passes three times per week over a seventeen-day period into their normal soccer training. Objective measurements of the passing performance were provided using a high-technology system (COGNIFOOT) prior to, during and after training. During training, only players of the AF-group received visuo-auditory feedback immediately after each trial informing them about the accuracy of their passes. The results show that only players of the AF-group significantly improved passing accuracy, reactiveness, and global passing performance (+22 %) whereas the NF-group only improved passing accuracy. None of these parameters was improved in the CON-group. The objectively measured changes in passing performance were compared to the more subjectively judged passing performance provided by coaches and players. Coaches' judgments were more reliable than players' judgments and exhibited a training group effect comparable to the ones objectively measured by COGNIFOOT. This study provides evidence that the training of cognitive motor performance in soccer players highly benefits from the use of augmented feedback.

#5 Effects of mental fatigue on passing decision-making performance in professional soccer athletes
Reference: Eur J Sport Sci. 2019 Aug 19:1-21. doi: 10.1080/17461391.2019.1656781. [Epub ahead of print]
Authors: Gantois P, Caputo Ferreira ME, Lima-Junior D, Nakamura FY, Batista GR, Fonseca FS, de Sousa Fortes L
Summary: The aim of this study was to analyze the effect of mental fatigue on passing decision-making in professional soccer athletes. A controlled and counterbalanced cross-over design was adopted consisting of three visits with a 1-week interval between sessions. Twenty (20) professional soccer male athletes participated in three randomized conditions divided into three visits: control, 15-min Stroop task, and 30-min Stroop task. Inhibitory control was accessed by the Stroop task (accuracy and response time) before and after induced mental fatigue protocol. The athletes played a training match (90-min) following the experimental conditions. The Game Performance Assessment Instrument (GPAI) was used for the passing decision-making analysis. The GPAI analysis showed impaired passing decision-making performance following the 30-min Stroop task compared with the 15-min and control condition (F(2,17) = 6.99, p = .01). Moreover, an increase in response time during the Stroop task was found following 30-min Stroop task condition (F(2,17) = 6.57, p = .03) compared to 15-min of Stroop task and control conditions. Prolonged cognitive tasks may be considered a mediating factor in passing decision-making performance in male professional soccer athletes throughout a full-length training match. Thus, athletes should avoid highly demanding-cognitive tasks before a soccer match. Future studies are required to explore more ecological cognitive tasks to induce mental fatigue (i.e. smartphones and video-games) and their effects on other performance indicators (e.g., physical, technical, tactical) in a full-length training match setting.

#6 Using differential ratings of perceived exertion to assess agreement between coach and player perceptions of soccer training intensity: An exploratory investigation
Reference: J Sports Sci. 2019 Aug 19:1-6. doi: 10.1080/02640414.2019.1653423. [Epub ahead of print]
Authors: Macpherson TW, McLaren SJ, Gregson W, Lolli L, Drust B, Weston M
Summary: We aimed to assess the coach-player agreement of subjective soccer training loads via differential ratings of perceived exertion (dRPE). The coach initially underwent quantifiable familiarisation (blackness test) with the Borg CR100 scale. Data were collected from 16 semi-professional soccer players across seven consecutive training sessions. For the measurement of subjective training load, the coach and players provided dRPE (CR100) for legs (RPE-L), breathlessness (RPE-B) and technical exertion (RPE-T). Coach-prescribed dRPE were recorded prior to training, with coach observed and player reported dRPE collected post training. Statistical equivalence bounds for agreement between coach (prescribed and observed) and player reported dRPE scores were 4 arbitrary units on the CR100 and we used a probability outcome of likely (≥75%) to infer realistic equivalence. Following three familiarisation sessions, the coach improved their blackness test score from 39% to 83%. Coach observed and player reported RPE-T scores were likely equivalent, with all other comparisons not realistically equivalent. Since training prescription is coach-led, our data highlight the importance of accurate internal load measurement and feedback in soccer. The improved accuracy and precision of coach intensity estimation after three attempts at the blackness test suggests that this method could be worthwhile to researchers and practitioners employing dRPE.

#7 The effects of detraining and retraining periods on fat-mass and fat-free mass in elite male soccer players
Reference: PeerJ. 2019 Aug 13;7:e7466. doi: 10.7717/peerj.7466. eCollection 2019.
Authors: Suarez-Arrones L, Lara-Lopez P, Maldonado R, Torreno N, De Hoyo M, Nakamura FY, Di Salvo V, Mendez-Villanueva A
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Summary: The aim of the study was to examine the effects of a detraining period (DTP) (i.e., off-season) with an individually prescribed training program, and a retraining period (RTP) (i.e., pre-season) combining soccer and flywheel-based strength training on fat-free mass (FFM) and fat-mass (FM) in 10 elite professional male soccer players. The present study used a controlled repeated-measures research design to investigate the changes in FFM and FM using dual-energy X-ray absorptiometry. Whole body %FM increased (effect size (ES) = 0.87 ± 0.46) and FFM reduced after DTP (ES = -0.30 ± 0.19), returning to values comparable to the end of the previous season after RTP. At regional levels, arms, legs, and trunk %FM increased (ES = from 0.42 to 1.29) while trunk-FFM was reduced (ES = -0.40 ± 0.26) after DTP, returning to the values observed at the end of the previous season after RTP. Legs-FFM did not change after DTP, with a substantial increase after RTP in comparison with pre-season values (ES = 0.34 ± 0.29 and 0.53 ± 0.36 for the right and left leg, respectively). Despite the small sample size of the present study, the findings indicate that elite soccer players can be allowed 2 weeks of rest during a five-week DTP, since the changes in %FM and FFM were relatively small, and FM and FFM returned to the optimal initial values for competition after the proposed RTP during the pre-season.

#8 The Effects of a Single Versus Three Consecutive Sessions of Football Training on Postprandial Lipemia: a Randomized, Controlled Trial in Healthy, Recreationally Active Males
Reference: Sports Med Open. 2019 Aug 22;5(1):38. doi: 10.1186/s40798-019-0212-1.
Authors: Paul DJ, Bangsbo J, Cherif A, Nassis GP
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Summary: Exercise frequency is important for maintaining health; however, its effects on postprandial responses remain largely unknown. Better understanding this during popular sports activities such as football may influence exercise habits. Therefore, the aim of the present study was to examine the effects of playing one single versus three consecutive days of 60-min small-sided football matches on postprandial lipemia. Fifteen males performed either one (1FOOT; n = 7) or three 60-min football (3FOOT; n = 8) sessions across an 8-day trial period. On day 1, a blood sample was collected at fasted (0 min) and 0.75, 2, 4, 6 h after a high-fat meal. Participants were then randomly allocated to the 1FOOT (day 7) or 3FOOT (days 5, 6, 7) condition. On day 8, they repeated the high-fat meal and blood sampling for 6 h following the meal. Postprandial total and incremental area under the curve (AUC, iAUC, respectively) were calculated. The postprandial triglyceride iAUC was 41% lower from pre- to post-measures for the 1FOOT (p < 0.05; ES = 1.02) and 15.7% lower for the 3FOOT (ns; ES = 0.41). Total triglyceride AUC was lower (26%) post-football matches in the 3FOOT group only (p < 0.01; ES = 1.23). In 3FOOT, insulin concentration was lower for post- compared to pre-measures at 0.75 and 2 h, respectively (p < 0.001). One single 60-min small-sided football match lowered postprandial TG incremental area under the curve while performing three consecutive days of football matches did not result in a greater attenuation.

#9 The Dependence of Running Speed and Muscle Strength on the Serum Concentration of Vitamin D in Young Male Professional Football Players Residing in the Russian Federation
Reference: Nutrients. 2019 Aug 21;11(9). pii: E1960. doi: 10.3390/nu11091960.
Authors: Bezuglov E, Tikhonova A, Zueva A, Khaitin V, Lyubushkina A, Achkasov E, Waśkiewicz Z, Gerasimuk D, Żebrowska A, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: Vitamin D insufficiency is prevalent among athletes, and it can negatively affect physical performance. At the same time, most of the available data were obtained from untrained individuals of various ages, and published studies performed in athletes led to contradictory conclusions. This cohort prospective study examined the serum concentration of 25-hydroxycalciferol (25(OH)D) and its association with running speed and muscle power in 131 young football players (mean age 15.6 ± 2.4 years). 25(OH)D levels were below reference in 42.8% (serum 25(OH)D <30 ng/mL) and above reference in 30.5% of the participants (serum 25(OH)D 61-130 ng/mL). A comparison of the results of 5, 15, and 30 m sprint tests and the standing long jump test found no statistically significant differences between the two groups. Athletes from the 25(OH)D-insufficient group were treated with 5000 IU cholecalciferol supplement daily for 60 days. After the treatment, the 25(OH)D concentration increased by 79.2% and was within reference in 84% of the treated athletes (serum 25(OH)D 30-60 ng/mL). Testing was repeated after the end of treatment, and a statistically significant increase in the results of the 5, 15, and 30 m sprint tests was observed (Cohen's d was 0.46, 0.33, and 0.34, respectively), while the results of the standing long jump test remained unchanged. Body height, body weight, and lean body mass of the football players also increased. These findings indicate that there is likely no correlation between serum levels of 25(OH)D, muscle power, and running speed in young professional football players, and the changes observed post-treatment might have been caused by changes in the anthropometric parameters. During the study, all the anthropometric parameters changed, but the amount of lean body mass only correlated with the results of the 5 m sprint.

#10 Extracting spatial-temporal features that describe a team match demands when considering the effects of the quality of opposition in elite football
Reference: PLoS One. 2019 Aug 22;14(8):e0221368. doi: 10.1371/journal.pone.0221368. eCollection 2019.
Authors: Gonçalves B, Coutinho D, Exel J, Travassos B, Lago C, Sampaio J
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Summary: Spatiotemporal patterns of play can be extracted from competitive environments to design representative training tasks and underlying processes that sustain performance outcomes. To support this statement, the aims of this study were: (i) describe the collective behavioural patterns that relies upon the use of player positioning in interaction with teammates, opponents and ball positioning; (ii) and define the underlying structure among the variables through application of a factorial analysis. The sample comprised a total of 1,413 ball possession sequences, obtained from twelve elite football matches from one team (the team ended the season in the top-5 position). The dynamic position of the players (from both competing teams), as well as the ball, were captured and transformed to two-dimensional coordinates. Data included the ball possession sequences from six matches played against top opponents (TOP, the three teams classified in the first 3 places at the end of the season) and six matches against bottom opponents (BOTTOM, the three teams classified in the last 3 at the end of the season). The variables calculated for each ball possession were the following: ball position; team space in possession; game space (comprising the outfield players of both teams); position and space at the end of ball possession. Statistical comparisons were carried with magnitude-based decisions and null-hypothesis analysis and factor analysis to define the underlying structure among variables according to the considered contexts. Results showed that playing against TOP opponents, there was ~38 meters game length per ~43 meters game width with 12% of coefficient of variation (%). Ball possessions lasted for ~28 seconds and tended to end at ~83m of pitch length. Against BOTTOM opponents, a decrease in the game length with an increase in game width and in the deepest location was observed in comparison with playing against TOP opponents. The duration of ball possession increased considerable (~37 seconds), and the ball speed entropy was higher, suggesting lower levels of regularity in comparison with TOP opponents. The BOTTOM teams revealed a small EPS. The Principal Component Analysis showed a strong association of the ball speed, entropy of the ball speed and the coefficient of variation (%) of the ball speed. The EPS of the team in possession was well correlated with the game space, especially the game width facing TOP opponents. Against BOTTOM opponents, there was a strong association of ball possession duration, game width, distance covered by the ball, and length/width ratio of the ball movement. The overall approach carried out in this study may serve as the starting point to elaborate normative models of positioning behaviours measures to support the coaches' operating decisions.

#11 Physical and Tactical Demands of the Goalkeeper in Football in Different Small-Sided Games
Reference: Sensors (Basel). 2019 Aug 19;19(16). pii: E3605. doi: 10.3390/s19163605.
Authors: Jara D, Ortega E, Gómez-Ruano MÁ, Weigelt M, Nikolic B, Sainz de Baranda P
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Summary: Several studies have examined the differences between the different small-sided game (SSG) formats. However, only one study has analysed how the different variables that define SSGs can modify the goalkeeper's behavior. The aim of the present study was to analyze how the modification of the pitch size in SSGs affects the physical demands of the goalkeepers. Three professional male football goalkeepers participated in this study. Three different SSG were analysed (62 m × 44 m for a large pitch; 50 m × 35 m for a medium pitch and 32 m × 23 m for a small pitch). Positional data of each goalkeeper was gathered using an 18.18 Hz global positioning system. The data gathered was used to compute players' spatial exploration index, standard ellipse area, prediction ellipse area The distance covered, distance covered in different intensities and accelerations/decelerations were used to assess the players' physical performance. There were differences between small and large SSGs in relation to the distances covered at different intensities and pitch exploration. Intensities were lower when the pitch size was larger. Besides that, the pitch exploration variables increased along with the increment of the pitch size.





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 depend