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Club revenue highlights

Chapter 8 was about the UEFA clubs and their revenue.

Generally, revenue has grown over the last year with an average of more than 9% per year. The club’s revenue are now six times the level of 1996.



Interestingly, the average English Premier League club having five times more revenue than the average Italian Serie A or French Ligue 1 club.

The average six-year club growth was the greatest in England followed by Germany, Spain and Italy. On average, every club in England extended its revenue by 99.2 mio Euros, followed by German clubs (48.1), Spanish club (27.4) and Italy (19.0).



So how much do the clubs earn on average?

According to UEFA, the ability of clubs to generate revenue varies enormously. For example a club in England generate ~220 mio, followed by Germany ~135 mio, Spain wit ~102 and Italy ~95 mio Euros.

As a consequence its not surprising that England aggregated 4.4 bn in its top division, followed by Germany (2.4 bn), Spain (2.0 bn), Italy (1.9 bn) and France (1.4 bn). In 2015 there were 46 clubs with an annual revenue of 100+ mio Euros.

The map shows where the wealth in football is concentrated.



So what are the top clubs in terms of total revenue in 2015?

The greatest revenue was generated by Real Madrid (578 mio), followed by Barcelona (561 mio) and ManU (521 mio). Juventus as the first Italian club ranked 10th with 325 mio Euros. Zenit Petersburg comes in with 196 mio at 15th place and Galatasaray with 148 mio at rank 26.



The club’s revenue come from diverse income streams. Number one is domestic broadcasting (34%), followed by Sponsorships (24%), Gate receipts (16%), revenues from UEFA and commercials (both 9%) and other revenues (8%).

The picture below shows broadcast revenues for the six largest domestic leagues. Obviously, the broadcast revenues in England exceeded 100 mio per club, comfortably more than double the Italian and triple the Spanish and German average. Interestingly, the 36.1 mio per club in Germany displays 27% “only” of the total revenue, while 47.7 mio equals 50% of the total revenue in Italy.



While 17 out of the 20 top clubs by broadcast revenues are from England, the top two are Barca and Real Madrid from Spain. Both clubs receiving 3.8 – 3.9 times the league average (equaling ~142 mio Euros).


Another income source was the UEFA price money, which is determined in part by the clubs sporting performance. While the UEFA price money equals ~51% of the clubs revenue in Bulgaria (10th place), its about 4% (in England) and 10% (in Spain) leading to a club average of 10.5 mio Euros.

The top 20 clubs receiving from UEFA can be seen in the slide below.



Gate receipts as the third highest income stream for clubs in different countries are as follows in the next slide.



Real Madrid receives the greatest amount (compared to other clubs) from gate receipts having 4.9 mio per match which is about six times the Spanish league average. There seemed to big differences in the ability to generate revenue from gate receipts. Five clubs, all with 60.000+ stadium capacities generated more than 100 mio Euros with an average per home game between 4.2 and 5.1, however, Juventus in 5th place generating only half of that.



Sponsorship, as the second biggest income stream provided at least 20% (19.3 mio in Italy), but not more than 66% (2.6 mio in Azerbaijan) of the total revenue. The highest club average of 64.8 mio was received in England.



The last part of the UEFA club revenue highlights was about transfer proceeds. Sorted after the total amount of transfer proceeds, Real Madrid sat in front with 111 mio Euros, however, spending 186 mio which ends-up in a total of net transfer proceeds of -75 mio. Genoa CFC was the club that created the greatest net transfer proceeds with 68 mio Euros. However, having a closer look on the original transfer costs and the achieved revenue, FC Porto created the highest profit with 49 mio Euros.



Three English clubs ManCity, ManU and Chelsea have to be named as the top clubs selling players for “marked-down”, with -95, -74 and -42 mio Euros respectively. Interestingly, there are no “country” trend for this part, meaning that we will find clubs of different countries (England, Portugal, France, Italy, Germany, Spain, Ukrain) inside the top 20 of club transfer proceeds. Interestingly, ManU spend 198 mio in transfers resulting in a net transfer proceed of -144 mio. The top 20 clubs aggregated a net transfer proceed of -341 mio Euros.

The last two slides is about the revenue mix in (and outside) the top 20 leagues sorted after aggregate revenue. Clubs in Italy and England (on average) depend on domestic broadcasting with an average of 50 and 49%. However, transfer proceeds made up of 75% of the clubs revenue in Portugal.



Revenue mix outside the Top 20 leagues showed that transfer proceeds (relative to revenue) were the highest in Croatian (85%) and Serbian clubs (82%). Revenue from UEFA club competition is highly significant for clubs in most middle-income and lower-earning leagues.








Latest research in football - week 14 - 2017

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 Injuries in male and female semi-professional football (soccer) players in Nigeria: prospective study of a National Tournament
Reference: BMC Res Notes. 2017 Mar 21;10(1):133. doi: 10.1186/s13104-017-2451-x.
Authors: Owoeye OB, Aiyegbusi AI, Fapojuwo OA, Badru OA, Babalola AR
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Summary: Research on the epidemiology of football injuries in Africa is very sparse despite its importance for injury prevention planning in a continent with limited sports medicine resources. The vast majority of studies available in literature were conducted in Europe and only a very few studies have prospectively reported the pattern of football injury in Africa. The purpose of this study was to evaluate the incidence and pattern of injuries in a cohort of male and female semi-professional football players in Nigeria. A prospective cohort design was conducted, in which a total of 756 players with an age range of 18-32 years (356 males and 300 females) from 22 different teams (12 male and 10 female teams), were prospectively followed in a National Football Tournament. Physiotherapists recorded team exposure and injuries. Injuries were documented using the consensus protocol for data collection in studies relating to football injury surveillance. An overall incidence of 113.4 injuries/1000 h (95% CI 93.7-136.0) equivalent to 3.7 injuries/match and time-loss incidence of 15.6 injuries/1000 h were recorded for male players and 65.9 injuries/1000 h (95% CI 48.9-86.8) equivalent to 2.2 injuries/match and time-loss incidence of 7.9 injuries/1000 h were recorded for female players. Male players had a significantly higher risk of injuries [IRR = 1.72 (95% CI 1.23-2.45)]. Injuries mostly affected the lower extremity for both genders (n = 81, 70% and n = 31, 62% for males and females respectively). Lower leg contusion (n = 22, 19%) and knee sprain (n = 9, 18%) were the most common specific injury types for male and female players respectively. Most of the injuries were as a result of contact with another player (n = 102, 88%-males; n = 48, 96%-females). Time-loss injuries were mostly estimated as minimal (n = 11, 69%) for male players and severe (n = 4, 66%) for female players. The overall incidence of injuries among Nigerian semi-professional football players is high but most of the injuries do not result in time-loss. Pattern of injuries is mostly consistent with previous studies. More prospective studies are needed to establish injury prevention initiatives among African players.

#2 Geographical Variations in the Interaction of Relative Age Effects in Youth and Adult Elite Soccer
Reference: Front Psychol. 2017 Mar 7;8:278. doi: 10.3389/fpsyg.2017.00278. eCollection 2017.
Authors: Steingrover C, Wattie N, Baker J, Helsen WF, Schorer J
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Summary: Selection biases based on the use of cut-off dates and the timing of athletes' birthdates have been termed relative age effects. These effects have been shown to differentially affect individuals involved in sport. For example, young male soccer players born early in their age group are overrepresented in elite teams while studies in adult soccer indicated potential carry-over effects from talent development systems. This two-study approach focuses on the processes within multi-year age groups in youth and adult elite soccer and on the role of players' age position within the age band with regard to players' birth year and birth month. Study 1 tests for an interaction of two different types of relative age effects among data from participants in the last five Under-17 FIFA World Cups (2007-2015). Analyses revealed a significant global within-year effect and varying birthdate distributions were found between confederations. Even stronger effects were found for constituent year effects. For the total sample, a multi-way frequency analysis (MFA) revealed an interaction with a pattern of a stronger within-year effect for the younger year group. This study highlights the need to consider interactions between different types of age effects. The main aim of Study 2 was to test for carry-over effects from previously found constituent year effects among players participating in the 2014 soccer World Cup and, therefore, to test for long-term effects of age grouping structures used during earlier stages of talent development. A secondary purpose of this study was to replicate findings on the existence of within-year effects and to test whether effects vary between continental confederations. No significant interaction between constituent year and within-year effects was shown by the MFA among the World Cup sample and previous findings on varying within-year effects were replicated. Results indicate that long-term effects of age grouping structures in earlier high-level talent development structures exist.

#3 The effects of an increased calorie breakfast consumed prior to simulated match-play in Academy soccer players
Reference: Eur J Sport Sci. 2017 Mar 21:1-9. doi: 10.1080/17461391.2017.1301560. [Epub ahead of print]
Authors: Briggs MA, Harper LD, McNamee G, Cockburn E, Rumbold PL, Stevenson EJ, Russell M
Summary: Dietary analysis of Academy soccer players highlights that total energy and carbohydrate intakes are less than optimal, especially, on match-days. As UK Academy matches predominantly kick-off at ∼11:00 h, breakfast is likely the last pre-exercise meal and thus may provide an intervention opportunity on match-day. Accordingly, the physiological and performance effects of an increased calorie breakfast consumed ∼135-min before soccer-specific exercise was investigated. English Premier League Academy soccer players (n = 7) repeated a 90-min soccer match simulation on two occasions after consumption of habitual (Bhab; ∼1100 kJ) or increased (Binc; ∼2100 kJ) energy breakfasts standardised for macronutrient contributions (∼60% carbohydrates, ∼15% proteins and ∼25% fats). Countermovement jump height, sprint velocities (15-m and 30-m), 30-m repeated sprint maintenance, gut fullness, abdominal discomfort and soccer dribbling performances were measured. Blood samples were taken at rest, pre-exercise, half-time and every 15-min during exercise. Although dribbling precision (P = .522; 29.9 ± 5.5 cm) and success (P = .505; 94 ± 8%) were unchanged throughout all time-points, mean dribbling speed was faster (4.3 ± 5.7%) in Binc relative to Bhab (P = .023; 2.84 vs 2.75 m s-1). Greater feelings of gut fullness (67 ± 17%, P = .001) were observed in Binc without changes in abdominal discomfort (P = .595). All other physical performance measures and blood lactate and glucose concentrations were comparable between trials (all P > .05). Findings demonstrate that Academy soccer players were able to increase pre-match energy intake without experiencing abdominal discomfort; thus, likely contributing to the amelioration of energy deficits on match-days. Furthermore, whilst Binc produced limited benefits to physical performance, increased dribbling speed was identified, which may be of benefit to match-play.

#4 Effects of Plyometric Training on Physical Fitness in Prepuberal Soccer Athletes
Reference: Int J Sports Med. 2017 Mar 17. doi: 10.1055/s-0042-122337. [Epub ahead of print]
Authors: Negra Y, Chaabene H, Sammoud S, Bouguezzi R, Abbes MA, Hachana Y, Granacher U
Summary: This study aimed at examining the effects of plyometric training on stable (SPT) vs. unstable (UPT) surfaces on physical fitness in prepuberal soccer players. Male athletes were randomly assigned to SPT (n=18; age=12.7±0.2 years) or UPT (n=16; age=12.2±0.5 years). Both groups conducted 3 regular soccer training sessions per week combined with either 2 SPT or UPT sessions. Assessment of jumping ability (countermovement jump [CMJ], and standing long jump [SLJ]), speed (10-m, 20-m, 30-m sprint), agility (Illinois agility test [IAT]), and balance (stable [SSBT], unstable [USBT] stork balance test; stable [SYBT], unstable [UYBT] Y balance test) was conducted pre-and post-training. An ANCOVA model was used to test for between-group differences (SPT vs. UPT) at post-test using baseline values as covariates. No significant differences were found for CMJ height (p>0.05, d=0.54), SLJ (p>0.05; d=0.81), 10-m, 20-m, and 30-m sprint performances (p>0.05, d=0.00-0.24), IAT (p>0.05, d=0.48), and dynamic balance (SYBT and UYBT, both p>0.05, d=0.39, 0.08, respectively). Statistically significant between-group differences were detected for the USBT (p<0.01, d=1.86) and the SSBT (p<0.01, d=1.75) in favor of UPT. Following 8 weeks of SPT or UPT in prepuberal athletes, similar performance levels were observed in both groups for measures of jumping ability, speed, dynamic balance, and agility. However, if the goal is to additionally enhance static balance, UPT has an advantage over SPT.

#5 Interrelationships among Jumping Power, Sprinting Power and Pubertal Status after Controlling for Size in Young Male Soccer Players
Reference: Percept Mot Skills. 2017 Apr;124(2):329-350. doi: 10.1177/0031512516686720. Epub 2017 Jan 16.
Authors: Cunha GS, Cumming SP, Valente-Dos-Santos J, Duarte JP, Silva G, Dourado AC, Leites GT, Gaya AC, Reischak-Oliveira A, Coelho-E-Silva M
Summary: This study examined power output on jumping and sprinting tests in young soccer players of differing pubertal status, while controlling for body size with allometric scaling exponents. A total of 46 males aged 12-18 years (14.17 years) were divided into three groups: pre-pubescent ( n = 12), pubescent ( n = 22), and post-pubescent ( n = 12). Participants performed a series of tests, including the squat jump (SJ), countermovement jump (CMJ), and 10-meter and 30-meter sprint test protocols. The Post-PUB group was older ( F = 112.411, p < 0.001), more experienced in competitive soccer ( F = 8.055, p = 0.001), taller ( F = 28.940, p < 0.001), and heavier ( F = 20.618, p < 0.001), when compared to peers in the other groups. Mean differences in jumping and sprinting performances suggested a significant effect for pubertal status on performance in the 10-meter sprint (large effect size, F = 8.191, p < 0.001) and 30-meter sprint (large effect size, F = 8.093, p < 0.001) after allometric scaling. Power output derived from SJ (small effect size, F = 0.536, p = 0.001) and CMJ (small effect size, F = 1.058, p = 0.356) showed no significant differences across players of varying pubertal status. Biological maturation showed a large effect on maximal power output for sprints, but not for jumps, when the effect of body size was adjusted by statistically derived allometric exponents in young male soccer players.

#6 Redox status alterations during the competitive season in élite soccer players: focus on peripheral leukocyte-derived ROS
Reference: Intern Emerg Med. 2017 Mar 30. doi: 10.1007/s11739-017-1653-5. [Epub ahead of print]
Authors: Becatti M, Mannucci A, Barygina V, Mascherini G, Emmi G, Silvestri E, Wright D, Taddei N, Galanti G, Fiorillo C
Summary: It is well known that exercise training can deeply affect redox homeostasis by enhancing antioxidant defenses. However, exhaustive exercise can induce excessive reactive oxygen species (ROS) production, leading to oxidative stress-related tissue injury and impaired muscle contractility. Hence, ROS represent important signaling molecules whose level has to be maintained to preserve normal cellular function, but which can also accumulate in response to repetitive muscle contraction. In fact, low levels of oxidants have been suggested to be essential for muscle contraction. Both aerobic and anaerobic exercise induce ROS production from several sources (mitochondria, NADPH oxidases and xanthine oxidases); however, the exact mechanisms underlying exercise-induced oxidative stress remain undefined. Professional athletes show a high risk for oxidative stress, and consequently muscle injury or decreased performance. Based on this background, we investigated leukocyte redox homeostasis alterations during the soccer season in élite soccer players. Overall blood redox status was investigated in twenty-seven male soccer players from primary division (Italian "Serie A" team) at four critical time points during the soccer season: T0: just before the first team training session; T1: at the beginning of the season; T2: in the middle of the season and T3: at the end of the season. The main markers of muscular damage (CK, myoglobin, LDH), assessed by standard routine methods, are significantly altered at the considered time points (T0 vs T1 P < 0.01). In peripheral leukocyte subpopulations, ROS production shows significant alterations at the considered time points during the soccer season, and strictly and significantly correlates with CK values at every considered time point. Our experimental data indicate that deep redox homeostasis alterations are evident during the soccer season in élite soccer players, and that oxidative stress can be easily monitored, besides using the standard plasma biochemical parameters, by leukocyte ROS production analysis.

#7 Return to play after hamstring injuries in football (soccer): a worldwide Delphi procedure regarding definition, medical criteria and decision-making
Reference: Br J Sports Med. 2017 Mar 30. pii: bjsports-2016-097206. doi: 10.1136/bjsports-2016-097206. [Epub ahead of print]
Authors: van der Horst N, Backx F, Goedhart EA, Huisstede BM; HIPS-Delphi Group
Summary: There are three major questions about return to play (RTP) after hamstring injuries: How should RTP be defined? Which medical criteria should support the RTP decision? And who should make the RTP decision? The study aimed to provide a clear RTP definition and medical criteria for RTP and to clarify RTP consultation and responsibilities after hamstring injury. The study used the Delphi procedure. The results of a systematic review were used as a starting point for the Delphi procedure. Fifty-eight experts in the field of hamstring injury management selected by 28 FIFA Medical Centres of Excellence worldwide participated. Each Delphi round consisted of a questionnaire, an analysis and an anonymised feedback report. After four Delphi rounds, with more than 83% response for each round, consensus was achieved that RTP should be defined as 'the moment a player has received criteria-based medical clearance and is mentally ready for full availability for match selection and/or full training'. The experts reached consensus on the following criteria to support the RTP decision: medical staff clearance, absence of pain on palpation, absence of pain during strength and flexibility testing, absence of pain during/after functional testing, similar hamstring flexibility, performance on field testing, and psychological readiness. It was also agreed that RTP decisions should be based on shared decision-making, primarily via consultation with the athlete, sports physician, physiotherapist, fitness trainer and team coach. The consensus regarding aspects of RTP should provide clarity and facilitate the assessment of when RTP is appropriate after hamstring injury, so as to avoid or reduce the risk of injury recurrence because of a premature RTP.

#8 Repeated sprint ability is not enhanced by caffeine, arginine, and branched-chain amino acids in moderately trained soccer players
Reference: J Exerc Rehabil. 2017 Feb 28;13(1):55-61. doi: 10.12965/jer.1732722.361. eCollection 2017.
Authors: Ermolao A, Zanotto T, Carraro N, Fornasier T, Zaccaria M, Neunhaeuserer D, Bergamin M
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Summary: The aim was to investigate the effect of a dietary supplementation on the repeated sprint ability (RSA) performance in recreationally trained team sports athletes. Twelve young men underwent a RSA exercise protocol in five trials, in which participants ingested carbohydrates (CHO) plus caffeine (Caf), CHO plus arginine (Arg), CHO plus branched-chain amino acids (BCAA), CHO plus Caf, Arg, and BCAA (ALL), and CHO only. Heart rate, oxygen saturation, hematic lactate, ratings of perceived exertion, average sprint time, total time, best sprint time, peak power, and average power were taken. Data revealed no significant effects neither on physiological nor performance parameters with any of the supplements.

#9 Within Session Sequence of Balance and Plyometric Exercises Does Not Affect Training Adaptations with Youth Soccer Athletes
Reference: J Sports Sci Med. 2017 Mar 1;16(1):125-136. eCollection 2017.
Authors: Chaouachi M, Granacher U, Makhlouf I, Hammami R, Behm DG, Chaouachi A
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Summary: The integration of balance and plyometric training has been shown to provide significant improvements in sprint, jump, agility, and other performance measures in young athletes. It is not known if a specific within session balance and plyometric exercise sequence provides more effective training adaptations. The objective of the present study was to investigate the effects of using a sequence of alternating pairs of exercises versus a block (series) of all balance exercises followed by a block of plyometric exercises on components of physical fitness such as muscle strength, power, speed, agility, and balance. Twenty-six male adolescent soccer players (13.9 ± 0.3 years) participated in an 8-week training program that either alternated individual balance (e.g., exercises on unstable surfaces) and plyometric (e.g., jumps, hops, rebounds) exercises or performed a block of balance exercises prior to a block of plyometric exercises within each training session. Pre- and post-training measures included proxies of strength, power, agility, sprint, and balance such as countermovement jumps, isometric back and knee extension strength, standing long jump, 10 and 30-m sprints, agility, standing stork, and Y-balance tests. Both groups exhibited significant, generally large magnitude (effect sizes) training improvements for all measures with mean performance increases of approximately >30%. There were no significant differences between the training groups over time. The results demonstrate the effectiveness of combining balance and plyometric exercises within a training session on components of physical fitness with young adolescents. The improved performance outcomes were not significantly influenced by the within session exercise sequence.

#10 Comparison of Skillful vs. Less Skilled Young Soccer Players on Anthropometric, Maturation, Physical Fitness and Time of Practice
Reference: Int J Sports Med. 2017 Mar 24. doi: 10.1055/s-0042-122815. [Epub ahead of print]
Authors: Gouvea MA, Cyrino ES, Valente-Dos-Santos J, Ribeiro AS, Silva DR, Ohara D, Coelho-E-Silva MJ, Ronque ER
Summary: This study compared maturation, body composition and physical fitness between youth soccer athletes with different technical skills levels. Sixty-two young athletes (11-17 years) were categorized dichotomously in more skilled (n=31) and less skilled (n=31) groups based on 3 specific technical tests (Dribbling Speed Test [DST], Shuttle Dribble Test [SDT] and Slalom Dribble Test [SLDT]). Chronological and skeletal age, time of practice, body composition and 4 physical fitness tests were performed for comparisons. As expected, the 3 technical tests were correlated (r=0.47-0.54, P<0.05). More skilled subjects in DST and SDT showed (respectively) higher time of practice (effect size [ES]=0.72 and 0.90), and greater performance sit-ups (ES=1.23 and 0.81), squat jump (ES=1.10 and 1.08), countermovement jump (ES=1.11 and 1.10), and Yo-Yo test (ES=1.17 and 1.40) compared to the less skilled subjects (P<0.05). However, more skilled subjects in SLDT showed greater performance (P<0.05) only in the squat jump (ES=0.67) and Yo-Yo tests (ES=0.83). The results suggest that technical performance is associated with greater time of practice and some physical capabilities. Moreover, the DST and SDT tests seem to be good options to discriminate technical performance in youth soccer athletes.


#11 Preferred Hip Strategy During Landing Reduces Knee Abduction Moment In Collegiate Female Soccer Players
Reference: J Sport Rehabil. 2017 Mar 24:1-19. doi: 10.1123/jsr.2016-0026. [Epub ahead of print]
Authors: Nguyen AD, Taylor JB, Wimbish TG, Keith JL, Ford KR
Summary: Hip focused interventions are aimed to decrease frontal plane knee loading related to anterior cruciate ligament (ACL) injuries. Whether a preferred hip landing strategy decreases frontal plane knee loading is unknown. The objective was to determine if a preferred hip landing strategy during a drop vertical jump (DVJ) is utilized during a single leg landing (SLL) task and whether differences in frontal plane knee loading are consistent between a DVJ and a SLL task. Participants were dichotomized into a hip (HIP, n=9) or knee/ankle (KA, n=14) strategy group based on the percentage distribution of each lower extremity joint relative to the summated moment (% distribution) during the DVJ. Separate one-way ANOVAs examined the differences in joint specific % distribution and external knee abduction moment between the HIP and KA groups. The HIP group had significantly greater % distribution of hip moment and less % distribution of knee moment compared to the KA group during the DVJ and SLL. External knee abduction moment was also significantly less in the HIP group compared to the KA group during the DVJ. Female soccer athletes who land with a preferred hip strategy during a DVJ also land with a preferred hip strategy during a SLL. The preferred hip strategy also resulted in less external knee abduction moments during the DVJ.

#12 Effects of Bout Duration on Players' Internal and External Loads During Small-Sided Games in Young Soccer Players
Reference: Int J Sports Physiol Perform. 2017 Mar 24:1-23. doi: 10.1123/ijspp.2016-0584. [Epub ahead of print]
Authors: Koklu Y, Alemdaroglu U, Cihan H, Wong DP
Summary: This study investigated the effects of different bout durations on internal and external loads of young soccer players during different small-sided games (SSGs). Fifteen male young soccer players (average age 17 ± 1 years) participated in 2 vs 2, 3 vs 3 and 4 vs 4 SSGs. All games lasted 12 min playing time in total, but each SSG format further consisted of four bout durations: continuous (CON: 1 bout x 12 min) or interval with short (SBD: 6 bouts x 2 min), medium (MBD: 3 bouts x 4 min) or long (LBD: 2 bouts x 6 min) bout durations. During the SSGs, heart rate (HR) responses, and distance covered in different speed zones - walking, low-intensity, moderate-intensity and high-intensity running were measured. Rating of Perceived Exertion (RPE) and blood lactate (La-) were determined at the end of each SSG. The SBD format elicited significantly lower %HRmax responses compared to LBD and CON in all formats (p<0.05). The SBD format also showed significantly shorter distances covered in walking and greater distances covered in moderate-intensity running as well as significantly greater total distance covered compared to LBD and CON in all formats (p<0.05). In addition, LBD produced significantly lower La- and RPE responses than SBD and CON in all formats (p<0.05). These results suggest that coaches and sports scientists who want to achieve higher internal loads could use SBD and CON timing protocols, while those who want to achieve higher external loads might prefer to use SBD and MBD when planning to all SSG formats.


American Football

#1 The effect of repetitive subconcussive collisions on brain integrity in collegiate football players over a single football season: A multi-modal neuroimaging study
Reference: Neuroimage Clin. 2017 Mar 21;14:708-718. doi: 10.1016/j.nicl.2017.03.006. eCollection 2017
Authors: Slobounov SM, Walter A, Breiter HC, Zhu DC, Bai X, Bream T, Seidenberg P, Mao X, Johnson B, Talavage TM
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Summary: The cumulative effect of repetitive subconcussive collisions on the structural and functional integrity of the brain remains largely unknown. Athletes in collision sports, like football, experience a large number of impacts across a single season of play. The majority of these impacts, however, are generally overlooked, and their long-term consequences remain poorly understood. This study sought to examine the effects of repetitive collisions across a single competitive season in NCAA Football Bowl Subdivision athletes using advanced neuroimaging approaches. Players were evaluated before and after the season using multiple MRI sequences, including T1-weighted imaging, diffusion tensor imaging (DTI), arterial spin labeling (ASL), resting-state functional MRI (rs-fMRI), and susceptibility weighted imaging (SWI). While no significant differences were found between pre- and post-season for DTI metrics or cortical volumes, seed-based analysis of rs-fMRI revealed significant (p < 0.05) changes in functional connections to right isthmus of the cingulate cortex (ICC), left ICC, and left hippocampus. ASL data revealed significant (p < 0.05) increases in global cerebral blood flow (CBF), with a specific regional increase in right postcentral gyrus. SWI data revealed that 44% of the players exhibited outlier rates (p < 0.05) of regional decreases in SWI signal. Of key interest, athletes in whom changes in rs-fMRI, CBF and SWI were observed were more likely to have experienced high G impacts on a daily basis. These findings are indicative of potential pathophysiological changes in brain integrity arising from only a single season of participation in the NCAA Football Bowl Subdivision, even in the absence of clinical symptoms or a diagnosis of concussion. Whether these changes reflect compensatory adaptation to cumulative head impacts or more lasting alteration of brain integrity remains to be further explored.

#2 Changes in Creatine Kinase and Hormones over the Course of an American Football Season
Reference: J Strength Cond Res. 2017 Apr 4. doi: 10.1519/JSC.0000000000001920. [Epub ahead of print]
Authors: Stone JD, Kreutzer A, Mata JD, Nystrom MG, Jagim AR, Jones MT, Oliver JM.
Summary: The purpose of this study was to examine changes in creatine kinase and hormones over the course of an entire season of American football. A secondary purpose was to determine differences between starters and non-starters. Fasting blood samples were obtained from nineteen National Collegiate Athletic Association Division I (n = 19; 20 ± 1 years) football athletes over the course of a season beginning prior to the start of summer off-season conditioning (T1), before (T2) and after pre-season (T3) football camp, with remaining samples taken throughout the competitive season (T4-T8). A magnitude-based inference approach was used to define outcomes. Testosterone was higher in starters prior to the start of the season (T1, Effect Size [ES] = 0.8) and during pre-conference (T4; ES = 0.7). Post-Camp (T3) testosterone was lower in all players, though greater in starters (starters, 0.0%/0.3%/99.7%; non-starters, 0.2%/2.9%/96.9%). An increase cortisol relative to baseline (T1) was observed in starters early in season (T4, ES = 0.7; T5, ES = 0.5). Creatine kinase was elevated at all time-points in all athletes, with starters having higher circulating levels throughout season. These data demonstrate that changes in hormonal markers may be experienced over a season of football and differ by playing status. Differences between starters and non-starters may be indicative of greater damage and stress experienced by starters, which may result from a greater number of repetitions.

#3 Influence of Glenoid Defect Size and Bone Fragment Size on the Clinical Outcome After Arthroscopic Bankart Repair in Male Collision/Contact Athletes
Reference: Am J Sports Med. 2017 Apr 1:363546517700864. doi: 10.1177/0363546517700864. [Epub ahead of print]
Authors: Nakagawa S, Mae T, Yoneda K, Kinugasa K, Nakamura H
Summary: The usefulness of arthroscopic Bankart repair for collision/contact athletes has varied in previous reports. The purpose of the study was to investigate the influence of glenoid rim morphologic characteristics on the clinical outcome after arthroscopic Bankart repair without additional reinforcement procedures in male collision/contact athletes, including athletes with a large glenoid defect. Eighty-six athletes (93 shoulders) followed for a minimum of 2 years were retrospectively investigated. The sports were rugby (36 shoulders), American football (29 shoulders), and other collision/contact sports (28 shoulders). Preoperative glenoid defect size, bone fragment size, and bone union after bony Bankart repair were investigated regarding factors influencing postoperative recurrence. Postoperative changes in glenoid defect size and bone fragment size were investigated as well as their influence on the clinical outcome. Postoperative recurrence of instability was noted in 22 shoulders (23.7%). The recurrence rate was 33.3% in rugby, 17.2% in American football, and 17.9% in other collision/contact sports. The recurrence rate was only 7.1% in 28 shoulders without a preoperative glenoid defect, but it increased to 43.8% in 16 shoulders that did not have a bone fragment even though there was a preoperative glenoid defect. Additionally, the recurrence rate was 7.7% in 26 shoulders with bone union after arthroscopic bony Bankart repair but rose to 45% in 20 shoulders without bone union. In the shoulders with bone union, the mean bone fragment size increased from 8.2% preoperatively to 15.2% postoperatively, while the mean glenoid defect size decreased from 18.0% to 2.8%, respectively. The recurrence rate was 8.3% in shoulders with a final glenoid defect 5% or less versus 38.1% in shoulders with a defect greater than 5%. While the recurrence rate was low among athletes other than rugby players with a final defect of 10% or less, it was low in only the rugby players with a defect of 0%. In male collision/contact athletes, while the overall clinical outcome was unsatisfactory, a favorable outcome was achieved in athletes without a preoperative glenoid defect and athletes with bone union. The glenoid defect decreased in size postoperatively due to remodeling of the united bone fragment, and the recurrence rate was low when the final glenoid defect size was 5% or less.

#4 Epidemiology of Knee Sprains in Youth, High School, and Collegiate American Football Players
Reference: J Athl Train. 2017 Apr 17. doi: 10.4085/1062-6050-52.3.09. [Epub ahead of print]
Authors: Clifton DR, Onate JA, Schussler E, Djoko A, Dompier TP, Kerr ZY
Summary: Variations in knee-sprain incidence among competition levels are unclear but may help inform prevention strategies in American football players. The purpose of the study was to describe the epidemiology of knee sprains in youth, high school, and collegiate football players. Injury and athlete-exposure (AE) data were collected from 3 injury-surveillance programs at the youth, high school, and collegiate competition levels. Data from 310 youth, 184 high school, and 71 collegiate football team-seasons were collected during the 2012 through 2014 seasons. Knee-sprain rates and risks were calculated for each competition level. Injury rate ratios (IRRs) and risk ratios (RRs) compared knee-sprain rates by competition level. Injury proportion ratios (IPRs) compared differences in surgery needs, recurrence, injury mechanism, and injury activity by competition level. Knee-sprain rates in youth, high school, and collegiate football were 0.16/1000 AEs, 0.25/1000 AEs, and 0.69/1000 AEs, respectively. Knee-sprain rates increased as the competition level increased (high school versus youth: IRR = 1.60; 95% confidence interval [CI] = 1.12, 2.30; collegiate versus high school: IRR = 2.73; 95% CI = 2.38, 3.96). Knee-sprain risk was highest in collegiate (4.3%), followed by high school (2.0%) and youth (0.5%) athletes. Knee-sprain risk increased as the competition level increased (high school versus youth: RR = 3.73; 95% CI = 2.60, 5.34; collegiate versus high school: RR = 2.14; 95% CI = 1.83, 2.51). Collegiate football had the lowest proportion of knee sprains that were noncontact injuries (collegiate versus youth: IPR = 0.54; 95% CI = 0.31, 0.95; collegiate versus high school: IPR = 0.59; 95% CI = 0.44, 0.79) and the lowest proportion that occurred while being tackled (collegiate versus youth: IPR = 0.44; 95% CI = 0.26, 0.76; collegiate versus high school: IPR = 0.71; 95% CI = 0.51, 0.98). Knee-sprain incidence was highest in collegiate football. However, level-specific variations in the distributions of knee sprains by injury activity may highlight the need to develop level-specific policies and prevention strategies that ensure safe sports play.

#5 Long-Term Cognitive and Neuropsychiatric Consequences of Repetitive Concussion and Head-Impact Exposure
Reference: J Athl Train. 2017 Mar;52(3):309-317. doi: 10.4085/1062-6050-52.1.14.
Authors: McAllister T, McCrea M
Summary: Initially, interest in sport-related concussion arose from the premise that the study of athletes engaged in sports associated with high rates of concussion could provide insight into the mechanisms, phenomenology, and recovery from mild traumatic brain injury. Over the last decade, concerns have focused on the possibility that, for some athletes, repetitive concussions may raise the long-term risk for cognitive decline, neurobehavioral changes, and neurodegenerative disease. First conceptualized as a discrete event with variable recovery trajectories, concussion is now viewed by some as a trigger of neurobiological events that may influence neurobehavioral function over the course of the life span. Furthermore, advances in technology now permit us to gain a detailed understanding of the frequency and intensity of repetitive head impacts associated with contact sports (eg, football, ice hockey). Helmet-based sensors can be used to characterize the kinematic features of concussive impacts, as well as the profiles of typical head-impact exposures experienced by athletes in routine sport participation. Many large-magnitude impacts are not associated with diagnosed concussions, whereas many diagnosed concussions are associated with more modest impacts. Therefore, a full understanding of this topic requires attention to not only the effects of repetitive concussions but also overall exposure to repetitive head impacts. This article is a review of the current state of the science on the long-term neurocognitive and neurobehavioral effects of repetitive concussion and head-impact exposure in contact sports.


Australian football

#1 Competition Sleep Is Not Compromised Compared To Habitual In Elite Australian Footballers
Reference: Int J Sports Physiol Perform. 2017 Apr 19:1-23. doi: 10.1123/ijspp.2016-0776. [Epub ahead of print]
Authors: Lalor BJ, Halson SL, Tran J, Kemp JG, Cormack SJ
Summary: The purpose was to assess the impact of match start time and days relative to match compared to the habitual sleep characteristics of elite Australian Football (AF) players. 45 elite male AF players were assessed during the pre-season (habitual) and across four home matches during the season. Players wore an activity monitor the night before (-1), night of (0), one night after (+1), and two nights (+2) after each match and completed a self-reported rating of sleep quality. A two-way ANOVA with Tukey's post hoc was used to determine differences in sleep characteristics between match start times and days relative to the match. Two-way nested ANOVA was conducted to examine differences between competition and habitual phases. The Effect size ± 90% confidence interval (ES ± 90% CI) was calculated to quantify the magnitude of pairwise differences. Differences observed in sleep onset latency (ES=0.11 ± 0.16), sleep rating (ES=0.08 ± 0.14) and sleep duration (ES=0.08 ± 0.01) between competition and habitual periods were trivial. Sleep efficiency (%) was almost certainly higher during competition than habitual, however this was not reflected in the subjective rating of sleep quality. Elite AF competition does not cause substantial disruption to sleep characteristics compared to habitual sleep. Whilst match start time has some impact on sleep variables, it appears that the match itself is more of a disruption than the start time. Subjective ratings of sleep from well-being questionnaires appear limited in their ability to accurately provide an indication of sleep quality.

#2 The association between fundamental athletic movements and physical fitness in elite junior Australian footballers
Reference: J Sports Sci. 2017 Apr 13:1-6. doi: 10.1080/02640414.2017.1313996. [Epub ahead of print]
Authors: Woods CT, McKeown I, Keogh J, Robertson S
Summary: This study investigated the associations between fundamental athletic movement and physical fitness in junior Australian football (AF). Forty-four under 18 players performed a fundamental athletic movement assessment consisting of an overhead squat, double lunge, single leg Romanian deadlift and a push up. Movements were scored on three assessment criterions using a three-point scale. Additionally, participants performed five physical fitness tests commonly used for talent identification in AF. A Spearman's nonparametric correlation matrix was built, with correlation coefficients being visualised using a circularly rendered correlogram. Score on the overhead squat was moderately positively associated with dynamic vertical jump height on left (rs = 0.40; P ≤ 0.05) and right (rs = 0.30; P ≤ 0.05) leg take-off, stationary vertical jump (rs = 0.32; P ≤ 0.05) and negatively associated with 20-m sprint time (rs = -0.35; P ≤ 0.05). Score on the double lunge (left/right side) was moderately positively associated with the same physical fitness tests as well as score on the multistage fitness test. Results suggest that improvements in physical fitness qualities may occur through concurrent increases in fundamental athletic movement skill, namely the overhead squat and double lunge movements. These findings may assist with the identification and development of talent.





Latest research in football - week 13 - 2017

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 effects of menstrual cycle phase on physical performance in female soccer players

Reference: PLoS One. 2017 Mar 13;12(3):e0173951. doi: 10.1371/journal.pone.0173951. eCollection 2017.

Authors: Julian R, Hecksteden A, Fullagar HH, Meyer T

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Summary: Female soccer has grown extensively in recent years, however differences in gender-specific physiology have rarely been considered. The female reproductive hormones which rise and fall throughout the menstrual cycle, are known to affect numerous cardiovascular, respiratory, thermoregulatory and metabolic parameters, which in turn, may have implications on exercise physiology and soccer performance. Therefore, the main aim of the present study was to investigate potential effects of menstrual cycle phase on performance in soccer specific tests. Nine sub elite female soccer players, all of whom have menstrual cycles of physiological length; performed a series of physical performance tests (Yo-Yo Intermittent endurance test (Yo-Yo IET), counter movement jump (CMJ) and 3x30 m sprints). These were conducted at distinct time points during two main phases of the menstrual cycle (early follicular phase (FP) and mid luteal phase (LP)) where hormones contrasted at their greatest magnitude. Yo-Yo IET performance was considerably lower during the mid LP (2833±896 m) as compared to the early FP (3288±800 m). A trend towards significance was observed (p = 0.07) and the magnitude based inferences suggested probabilities of 0/61/39 for superiority/equality/inferiority of performance during the mid LP, leading to the inference of a possibly harmful effect. For CMJ (early FP, 20.0±3.9 cm; mid LP 29.6±3.0 cm, p = 0.33) and sprint (early FP, 4.7±0.1 s; mid LP, 4.7±0.1 s, p = 0.96) performances the results were unclear (8/24/68, 48/0/52, respectively). The results of this study are in support of a reduction in maximal endurance performance during the mid LP of the menstrual cycle. However, the same effect was not observed for jumping and sprint performance. Therefore, consideration of cycle phase when monitoring a player's endurance capacity may be worthwhile.



#2 A low-dose, 6-week bovine colostrum supplementation maintains performance and attenuates inflammatory indices following a Loughborough Intermittent Shuttle Test in soccer players

Reference: Eur J Nutr. 2017 Mar 11. doi: 10.1007/s00394-017-1401-7. [Epub ahead of print]

Authors: Kotsis Y, Mikellidi A, Aresti C, Persia E, Sotiropoulos A, Panagiotakos DB, Antonopoulou S, Nomikos T

Download link:*~hmac=3f7f58f091a6de3a21206ef1d8a6bea314b2dd47a6825f26470927fb8f96f216

 Summary: The aim of the study was to investigate the effect of a 6-week, low-dose bovine colostrum (BC) supplementation on exercise-induced muscle damage (EIMD) and performance decline in soccer players following the Loughborough Intermittent Shuttle Test (LIST) during a competitive season period. In a double-blind, randomized, placebo-controlled design, two groups of soccer players were allocated to a 3.2 g/day of whey protein (WP, N=8) or BC (N=10) and performed a pre- and a post-supplementation LIST. Maximum isometric voluntary contraction, squat jump (SQJ), countermovement jump, muscle soreness, blood cell counts, creatine kinase (CK), C-reactive protein (CRP) and interleukin-6 (IL-6) were monitored for 2, 24, 48, 72 h post-LIST. LIST induced transient increases in leukocytes, granulocytes, CK, muscle soreness, CRP, IL-6 and declines in lymphocytes and performance indices. Supplementation resulted in a faster recovery of SQJ, CK and CRP compared to pre-supplementation kinetics (trial × time: p=0.001, 0.056, 0.014, respectively) and lower incremental area under the curve (iAUC) for IL-6, only in the BC group [pre-: 31.1 (6.78-46.9), post-: 14.0 (-0.16 to 23.5) pg h/ml, p=0.034]. Direct comparison of the two groups after supplementation demonstrated higher iAUC of SQJ [WP: -195.2 (-229.0 to (-52.5)), BC: -15.8 (-93.2 to 16.8) cm h, p=0.034], a trend for lower iAUC of CK in the BC group [WP: 18,785 (4651-41,357), BC: 8842 (4807-14,802) U h/L, p=0.081] and a significant intervention × time interaction for CRP (p=0.038) in favor of BC. Post-exercise EIMD may be reduced and performance better maintained by a low dose of BC administration following LIST in soccer players.



#3 Developing Evidence for Football (Soccer) Reminiscence Interventions Within Long-term Care: A Co-operative Approach Applied in Scotland and Spain

Reference: J Am Med Dir Assoc. 2017 Apr 1;18(4):355-360. doi: 10.1016/j.jamda.2017.01.013. Epub 2017 Mar 7.

Authors: Coll-Planas L, Watchman K, Domenech S, McGillivray D, O'Donnell H, Tolson D

Summary: Loneliness is a common experience within long-term care and, to promote well-being and quality of life among people with dementia, it is important to draw upon a repertoire of strategies that provide social stimulation, companionship, and enjoyment. This paper describes and reflects on a program of co-operative social participatory research that sought to introduce football-focused (ie, soccer-based) reminiscence based in 4 community settings within Spain and Scotland. Findings are reported and inform an original conceptual model that supports the introduction of sustainable approaches to the development of football-focused reminiscence with and for people with dementia.



#4 Kinesio taping does not alter muscle torque, muscle activity or jumping performance in professional soccer players: A randomized, placebo-controlled, blind, clinical trial

Reference: J Back Musculoskelet Rehabil. 2017 Mar 3. doi: 10.3233/BMR-160556. [Epub ahead of print]

Authors: Dos Santos Gloria IP, de Oliveira Gonzalez T, de Oliveira Gonzalez T, Junior EC, de Paula Gomes CA, Herpich CM, Antonialli FC, Serenza F, de Souza Calheira L, Arruda EE, Lucareli PR, Biasotto-Gonzalez DA

 Summary: Kinesio taping consists of the attachment of a thin elastic tape over specific muscles, the thickness of which is similar to that of the epidermis. The aim of the present study was to compare the effect of Kinesio taping and placebo taping on muscle torque, muscle activity and jumping performance soccer players.Thirty athletes were randomly allocated to two groups (Group A: Kinesio taping and Group B: placebo taping). The participants were instructed to perform the Hop test's and were submitted to an isokinetic evaluation of the knee extensors as well as an electromyographic evaluation of the retus femoris muscle of the dominant lower limb. Next, Kinesio taping was performed for the activation of the rectus femoris muscle in Group A and placebo taping was performed in Group B. The participants were reevaluated 30 minutes after taping and 24 hours after the first evaluation using the same tests. Intra-group and inter-group comparisons were made considering the three evaluation times. No statistically significant differences were found between groups at any evaluation time regarding the Hop test's, root mean square of the electromyographic signal or peak torque of the knee extensors of the dominant lower limb (p>0.05). Kinesio taping for the activation of the rectus femoris muscle has no effect on peak muscle torque, muscle activity or jumping performance among soccer players.



#5 Changes of the psychophysical state and feeling of wellness of professional soccer players during pre-season and in-season periods

Reference: Res Sports Med. 2016 Oct-Dec;24(4):375-386. Epub 2016 Aug 30.

Authors: Fessi MS, Nouira S, Dellal A, Owen A, Elloumi M, Moalla W

Summary: Perceived changes due to training monotony, strain, sleep, stress, fatigue, muscle soreness and the influence of specific training sessions on the affective valence were explored in professional soccer players. Seventeen players completed the Hooper questionnaire, the ratings of perceived exertion and feeling scale (FS) every training/match day before and during the soccer season. Higher players' training loads were recorded during pre-season when compared with in-season period (2558.1 ± 262.4 vs. 1642.8 ± 169.3 a.u., p < 0.01; respectively). The ratings of sleep, stress, fatigue and muscle soreness in pre-season were higher than those observed during in-season (p < 0.01) whereas the feeling score was lower (p < 0.01). Furthermore, training sessions, including technical/tactical work, induced an improved feeling score but linked with a lower training load when compared with sessions focus on physical emphasis (p < 0.01). Pre-season period of training induces a significantly more strenuous and exhausting demands on professional soccer players compared with the in-season period at the elite level.



#6 Longitudinal changes in linguistic complexity among professional football players

Reference: Brain Lang. 2017 Mar 16;169:57-63. doi: 10.1016/j.bandl.2017.02.003. [Epub ahead of print]

Authors: Berisha V, Wang S, LaCross A, Liss J, Garcia-Filion P

Summary: Reductions in spoken language complexity have been associated with the onset of various neurological disorders. The objective of this study is to analyze whether similar trends are found in professional football players who are at risk for chronic traumatic encephalopathy. We compare changes in linguistic complexity (as indexed by the type-to-token ratio and lexical density) measured from the interview transcripts of players in the National Football League (NFL) to those measured from interview transcripts of coaches and/or front-office NFL executives who have never played professional football. A multilevel mixed model analysis reveals that exposure to the high-impact sport (vs no exposure) was associated with an overall decline in language complexity scores over time. This trend persists even after controlling for age as a potential confound. The results set the stage for a prospective study to test the hypothesis that language complexity decline is a harbinger of chronic traumatic encephalopathy.



#7 Safety regulation in professional football: Empirical evidence of intended and unintended consequences

Reference: J Health Econ. 2017 Jan 29;53:87-99. doi: 10.1016/j.jhealeco.2017.01.004. [Epub ahead of print]

Authors: Hanson A, Jolly NA, Peterson J

Summary: In response to increasing public awareness and negative long-term health effects of concussions, the National Football League implemented the "Crown-of-the-Helmet Rule" (CHR). The CHR imposes penalties on players who initiate contact using the top of the helmet. This paper examines the intended effect of this policy and its potential for unintended consequences. We find evidence supporting the intended effect of the policy- a reduction in weekly concussion reports among defensive players by as much as 32% (34% for all head and neck injuries), but also evidence of an increase in weekly lower extremity injury reports for offensive players by as much as 34%.



#8 Walking football as sustainable exercise for older adults - A pilot investigation

Reference: Eur J Sport Sci. 2017 Mar 19:1-8. doi: 10.1080/17461391.2017.1298671. [Epub ahead of print]

Authors: Reddy P, Dias I, Holland C, Campbell N, Nagar I, Connolly L, Krustrup P, Hubball H

Summary: The health benefits of playing football and the importance of exercise and social contact for healthy ageing are well established, but few older adults in the UK take enough exercise. Football is popular, flexible in format and draws players into engrossing, effortful and social exercise, but the physical demands of play at full speed may make it unsustainable for some older adults. Restricted to walking pace, will play still be engaging? Will health benefits be retained? Will physical demands remain manageable? This pilot study aims to investigate: (1) the experience of older adults playing walking football every week, is it sustainable and rewarding, (2) the intensity and locomotor pattern of walking football, (3) the scale and nature of walking football health benefits and (4) possible cognitive benefits of playing walking football through measures of processing speed, selective and divided attention and updating and inhibition components of executive function.
 'Walking football' and 'waiting list' groups were compared before and after 12 weeks of one-hour per week football. Walking football was found to be engaging, sustainable for older adults and moderately intensive; however, selective health and cognitive benefits were not found from this brief intervention.



#9 Evaluating erroneous offside calls in soccer

Reference: PLoS One. 2017 Mar 23;12(3):e0174358. doi: 10.1371/journal.pone.0174358. eCollection 2017.

Authors: Huttermann S, Noel B, Memmert D

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Summary: The ability to simultaneously attend to multiple objects declines with increases in the visual angle separating distant objects. We explored whether these laboratory-measured limits on visual attentional spread generalize to a real life context: offside calls by soccer assistant referees. We coded all offside calls from a full year of first division German soccer matches. By determining the x-y coordinates of the relevant players and assistant referee on the soccer field we were able to calculate how far assistant referees had to spread their visual attention to perform well. Counterintuitively, assistant referees made fewer errors when they were farther away from the action due to an advantageous (smaller) visual angle on the game action. The pattern held even when we accounted for individual differences in a laboratory-based attentional spread measure of ten of the assistant referees. Our finding that errors are linked to smaller visual angles may explain the complaints of fans in some situations: Those seated directly behind the assistant referee, further from the players, might actually have it easier to make the right call because the relevant players would form a smaller visual angle.



#10 The Effect of Standard Strength vs. Contrast Strength Training on the Development of Sprint, Agility, Repeated Change of Direction, and Jump in Junior Male Soccer Players

Reference: J Strength Cond Res. 2017 Apr;31(4):901-912. doi: 10.1519/JSC.0000000000001815.

Authors: Hammami M, Negra Y, Shephard RJ, Chelly MS

Summary: The aim was to compare the impact of 2 differing strength training (ST) programs on the athletic performance of junior male soccer players at a critical phase during their competitive season. Participants aged 16.0 ± 0.5 years were randomly assigned between control (C, n = 12), standard ST (n = 16), and contrast strength training (CST, n = 16), each performed twice a week. Athletic performance was assessed before and after the intervention using 8 tests: 40-m sprint, 4 × 5-m sprint (S4 × 5), 9-3-6-3-9 m sprint with 180° turns (S180°), 9-3-6-3-9 m sprint with backward and forward running (SBF), repeated shuttle sprint ability (RSSA), repeated change of direction (RCOD), squat jump (SJ), and countermovement jump (CMJ). The control group's (CG) performance tended to improve in some tests and decrease in others, but these changes were not statistically significant. Both training programs enhanced all sprint performances relative to controls (p ≤ 0.05). The strength training group (SG) and the CST group (CSG) increased significantly in S180°, SBF, and S4 × 5 relative to CG, although the S4 × 5 also increased in CSG relative to SG (p ≤ 0.05). No intergroup difference of RSSA performance was observed. The RCOD parameters increased significantly in CSG relative to both SG and CG (p ≤ 0.05). The SJ and CMJ height increased significantly in both experimental groups (p < 0.000). We conclude that during the competitive season, some measures of athletic performance in male soccer players were increased more by 8 weeks of CST than by ST.



#11 Beetroot Juice Supplementation Improves High-Intensity Intermittent Type Exercise Performance in Trained Soccer Players

Reference: Nutrients. 2017 Mar 22;9(3). pii: E314. doi: 10.3390/nu9030314.

Authors: Nyakayiru J, Jonvik KL, Trommelen J, Pinckaers PJ, Senden JM, van Loon LJ, Verdijk LB

Summary: It has been shown that nitrate supplementation can enhance endurance exercise performance. Recent work suggests that nitrate ingestion can also increase intermittent type exercise performance in recreational athletes. We hypothesized that six days of nitrate supplementation can improve high-intensity intermittent type exercise performance in trained soccer players. Thirty-two male soccer players (age: 23 ± 1 years, height: 181 ± 1 m, weight: 77 ± 1 kg, playing experience: 15.2 ± 0.5 years, playing in the first team of a 2nd or 3rd Dutch amateur league club) participated in this randomized, double-blind cross-over study. All subjects participated in two test days in which high-intensity intermittent running performance was assessed using the Yo-Yo IR1 test. Subjects ingested nitrate-rich (140 mL; ~800 mg nitrate/day; BR) or a nitrate-depleted beetroot juice (PLA) for six subsequent days, with at least eight days of wash-out between trials. The distance covered during the Yo-Yo IR1 was the primary outcome measure, while heart rate (HR) was measured continuously throughout the test, and a single blood and saliva sample were collected just prior to the test. Six days of BR ingestion increased plasma and salivary nitrate and nitrite concentrations in comparison to PLA (p < 0.001), and enhanced Yo-Yo IR1 test performance by 3.4 ± 1.3% (from 1574 ± 47 to 1623 ± 48 m; p = 0.027). Mean HR was lower in the BR (172 ± 2) vs. PLA trial (175 ± 2; p = 0.014). Six days of BR ingestion effectively improves high-intensity intermittent type exercise performance in trained soccer players.






Borussia Dortmund UEFA Champions League Pre-Match Warm-Up

Due to a good friend I was able to visit the UEFA Champions league match of Borussia Dortmund against AS Monaco.


Unfortunately, and due to the bomb-attacks on the team bus I had to travel to the Signal-Iduna-Park at Dortmund twice.


Despite (and probably especially due) the terrible incidents the day before, the BVB fans tried to have a "normal" CL game and pushed their team the entire game.



The stadium was sold out and AS Monaco won the game.



As usual when visiting a football match, I filmed the warm-up of both teams and the one of Borussia Dortmund can be seen below.






Latest research in football - week 12 - 2017

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 Pneumomediastinum in a College-Aged Soccer Player: A Case Report
Reference: Curr Sports Med Rep. 2017 Mar/Apr;16(2):71-73. doi: 10.1249/JSR.0000000000000338.
Authors: Zarandy E, Counts S, Clemow C.
Download link:|ExpireAbsolute;source|Journals;ttl|1489387698829;payload|mY8D3u1TCCsNvP5E421JYK6N6XICDamxByyYpaNzk7FKjTaa1Yz22MivkHZqjGP4kdS2v0J76WGAnHACH69s21Csk0OpQi3YbjEMdSoz2UhVybFqQxA7lKwSUlA502zQZr96TQRwhVlocEp/sJ586aVbcBFlltKNKo+tbuMfL73hiPqJliudqs17cHeLcLbV/CqjlP3IO0jGHlHQtJWcICDdAyGJMnpi6RlbEJaRheGeh5z5uvqz3FLHgPKVXJzdtavZhyL1R7GZ07U38xM5S/usr4L5LXmcxbNZRxgtepo=;hash|fhHlEk29gZDjZAC0saV15A==

#2 Proximal Neuromuscular Control Protects Against Hamstring Injuries in Male Soccer Players
Reference: Am J Sports Med. 2017 Mar 1:363546516687750. doi: 10.1177/0363546516687750. [Epub ahead of print]
Authors: Schuermans J, Danneels L, Van Tiggelen D, Palmans T, Witvrouw E
Summary: With their unremittingly high incidence rate and detrimental functional repercussions, hamstring injuries remain a substantial problem in male soccer. Proximal neuromuscular control ("core stability") is considered to be of key importance in primary and secondary hamstring injury prevention, although scientific evidence and insights on the exact nature of the core-hamstring association are nonexistent at present. The authors hypothesize that the muscle activation pattern throughout the running cycle would not differ between participants based on injury occurrence during follow-up. Sixty amateur soccer players participated in a multimuscle surface electromyography (sEMG) assessment during maximal acceleration to full-speed sprinting. Subsequently, hamstring injury occurrence was registered during a 1.5-season follow-up period. Hamstring, gluteal, and trunk muscle activity time series during the airborne and stance phases of acceleration were evaluated and statistically explored for a possible causal association with injury occurrence and absence from sport during follow-up. Players who did not experience a hamstring injury during follow-up had significantly higher amounts of gluteal muscle activity during the front swing phase ( P = .027) and higher amounts of trunk muscle activity during the backswing phase of sprinting ( P = .042). In particular, the risk of sustaining a hamstring injury during follow-up lowered by 20% and 6%, with a 10% increment in normalized muscle activity of the gluteus maximus during the front swing and the trunk muscles during the backswing, respectively ( P < .024). Muscle activity of the core unit during explosive running appeared to be associated with hamstring injury occurrence in male soccer players. Higher amounts of gluteal and trunk muscle activity during the airborne phases of sprinting were associated with a lower risk of hamstring injuries during follow-up. Hence, the present results provide a basis for improved, evidence-based rehabilitation and prevention, particularly focusing on increasing neuromuscular control of the gluteal and trunk muscles during sport-specific activities (eg, sprint drills, agility drills).

#3 Who runs the fastest? Anthropometric and physiological correlates of 20 m sprint performance in male soccer players
Reference: Res Sports Med. 2016 Oct-Dec;24(4):341-351. Epub 2016 Aug 22.
Authors: Nikolaidis PT, Ruano MA, de Oliveira NC, Portes LA, Freiwald J, Lepretre PM, Knechtle B
Summary: The aim of the present study was to examine the relationship of 20 m sprint performance with anthropometrical and physiological parameters in male soccer players. A hundred and 81 soccer players from the region of Athens (age 23.4 ± 5.0 yrs, body mass 73.4 ± 7.7 kg, height 180.0 ± 5.9 cm, body fat (BF) 14.4 ± 3.6%), classified into quartiles according to 20 m sprint time (group A, 2.84-3.03 s; group B, 3.04-3.09 s; group C, 3.10-3.18 s; group D, 3.19-3.61 s), participated. Soccer players in group A were younger and had better performance in vertical jumps and in the Wingate anaerobic test (WAnT, p < 0.05). Sprint time correlated to age (r = 0.27), body mass (r = 0.23), body height (r = 0.20), BF (r = 0.23), vertical jumps (-0.58 ≤ r ≤ -0.50) and the WAnT (-0.45 ≤ r ≤ -0.30, p < 0.05). In summary, the magnitude of correlations of sprint time with measures of lower limbs muscle strength and power (WAnT and jumps) was larger than with anthropometric measures (body mass and BF).

#4 The specificity of the Loughborough Intermittent Shuttle Test for recreational soccer players is independent of their intermittent running ability
Reference: Res Sports Med. 2016 Oct-Dec;24(4):363-374. Epub 2016 Aug 22.
Authors: Coratella G, Beato M, Schena F
Summary: The aim of the present study was to evaluate whether or not recreational soccer players (SP) and non-soccer players (non-SP) with similar intermittent-running ability had similar physiological responses to a soccer match-simulation protocol. Twenty-two recreational SP and 19 fitness-matched non-SP participated. Yo-Yo level 1 assessed intermittent-running ability, while the Loughborough Intermittent Shuttle Test served as soccer match-simulation protocol. Heart rate (HR), blood lactate concentration [La-] and rating of perceived exertion (RPE) were recorded after each bout (1-5, plus an exhaustive task). SP had lower HR after the third, fourth and fifth bout, compared to non-SP. Similarly, SP had lower [La-] after the third, fourth and the fifth bout. SP also had lower RPE after the third, fourth and fifth bout. The appropriateness of intermittent-running ability as the main determinant of physical performance in SP was questioned.

#5 Effects of horizontal plyometric training volume on soccer players' performance
Reference: Res Sports Med. 2016 Oct-Dec;24(4):308-319. Epub 2016 Aug 22.
Authors: Yanci J, Los Arcos A, Camara J, Castillo D, García A, Castagna C
Summary: The aim of this study was to examine the dose response effect of strength and conditioning programmes, involving horizontally oriented plyometric exercises, on relevant soccer performance variables. Sixteen soccer players were randomly allocated to two 6-week plyometric training groups (G1 and G2) differing by imposed (twice a week) training volume. Post-training G1 (4.13%; d = 0.43) and G2 (2.45%; d = 0.53) moderately improved their horizontal countermovement jump performance. Significant between-group differences (p < 0.01) in the vertical countermovement jump for force production time (T2) were detected post-training. No significant and practical (p > 0.05, d = trivial or small) post-training improvements in sprint, change of direction ability (CODA) and horizontal arm swing countermovement jump were reported in either group. Horizontal plyometric training was effective in promoting improvement in injury prevention variables. Doubling the volume of a horizontal plyometric training protocol was shown to have no additional effect over functional aspects of soccer players' performance.

#6 The effect of slope on repeated sprint ability in young soccer players
Reference: Res Sports Med. 2016 Oct-Dec;24(4):320-330. Epub 2016 Aug 18.
Authors: Padulo J, Ardigo LP, Attene G, Cava C, Wong DP, Chamari K, Migliaccio GM
Summary: This study aimed to describe a gradient repeated sprint ability (RSA) test in comparison with a standard level one by investigating performance, metabolic demand and muscular jumping performance as a proxy for running mechanics. Eighteen athletes performed two level RSA tests (40 m × 6) - for reliability evaluation - and one ±5% gradient RSA test, second leg downhill (RSAgrad). Rating of perceived exertion (RPE), blood lactate concentration (BLa) concentration, vertical jump heights were assessed as well. Level test measures resulted highly reliable (Intra-class correlation coefficient (ICC) ≥0.96). RSAgrad worsened only first sprints' performance (-2%) but not overall test performance (~45 s). RSAgrad resulted to be less deteriorating in terms of fatigue index (FI) (-36%), BLa (-23%), RPE (-11%), jumping performance (RSAgrad post-/pre-squat jump, countermovement jump heights (CMJh): -3%, -6%, respectively). RSAgrad could be used to diversify common training protocol without stressing excessively athletes' current metabolic-anaerobic capacity. Such physical conditioning procedures could improve acceleration/braking capability.

#7 Physical and technical performances are not associated with tactical prominence in U14 soccer matches
Reference: Res Sports Med. 2016 Oct-Dec;24(4):352-362. Epub 2016 Aug 17.
Authors: Clemente FM, Figueiredo AJ, Martins FM, Mendes RS, Wong DP
Summary: The aim of this study was to analyse the association between physical/technical variables and the tactical prominence variables in U14 soccer matches. Twenty-two young amateur soccer players (13.5 [Formula: see text] 0.5 years old, 5.4 [Formula: see text] 0.5 years of practice, 163.3 [Formula: see text] 9.8 cm in body height) from two teams of the Portuguese regional league volunteered for the study. Our results showed positive and moderate correlation between dribbling test and betweenness centrality (r = 0.324; p = 0.142), and negative moderate correlation between %fatigue index and betweenness centrality (r = -0.390; p = 0.073). Physical and technical variables had no statistical differences among tactical positions. Nevertheless, when tactical prominence of players from four tactical positions were compared, significant differences were found in terms of degree prestige (p = 0.001) and degree centrality (p = 0.002). This pilot study did not find strong correlations between physical/technical levels and tactical prominence in soccer matches.

#8 Predicting football injuries using size and ratio of the multifidus and quadratus lumborum muscles
Reference: Scand J Med Sci Sports. 2017 Apr;27(4):440-447. doi: 10.1111/sms.12643.
Authors: Hides JA, Stanton WR
Summary: Deficits in muscles of the lumbo-pelvic region, such as a relatively small multifidus muscle, have been used to predict lower limb injuries in professional football players. Results have been less consistent for the size of the quadratus lumborum (QL) muscle. Changes in size of the multifidus and QL muscles could be functionally related to each other, and modeling this relationship could improve prediction of lower limb injuries. Ultrasound imaging examinations were performed on male elite football players at the start of the Australian Football League (AFL) pre-season and playing season. Injury data were obtained from records collected by each club. Results indicated that the cross-sectional area of the multifidus muscle was related to the occurrence of an injury in the pre-season (odds ratio [OR] = 2.08/cm2 decrease below the mean; OR for dichotomized measure = 12.2) and in the season (OR = 2.43/cm2 ). The size of the QL muscle was significantly related to an injury in the pre-season (OR = 2.12/cm2 increase above the mean; OR for dichotomized measure = 7.26) but not in the season. A significant link was found between the ratio of the multifidus and QL muscles, and the incidence of pre-season (OR = 14.71) and season injuries (OR = 5.29). The sensitivity and specificity of the model in the pre-season were 75% and 85.7%, respectively; values for the playing season were 88.4% and 62.5%. A model was developed for prediction of lower limb injuries in football players. Combining size measurements of the multifidus and QL muscles improved predictive power. This information may have clinical implications for injury screening and prevention.

#9 Circannual rhythm of plasmatic vitamin D levels and the association with markers of psychophysical stress in a cohort of Italian professional soccer players
Reference: Chronobiol Int. 2017 Mar 17:1-9. doi: 10.1080/07420528.2017.1297820. [Epub ahead of print]
Authors: Lombardi G, Vitale JA, Logoluso S, Logoluso G, Cocco N, Cocco G, Cocco A, Banfi G
Summary: Adequate plasmatic Vitamin D levels are crucial to maintain calcium homeostasis and bone metabolism both in the general population and in athletes. Correct dietary supply and a regular sun exposure are fundamental for allowing the desired and effective fitness level. Past studies highlighted a scenario of Vitamin D insufficiency among professional soccer players in several countries, especially in North Europe, whilst a real deficiency in athletes is rare. The typical seasonal fluctuations of Vitamin D are wrongly described transversally in athletes belonging to teams that play at different latitudes and a chronobiologic approach studying the Vitamin D circannual rhythm in soccer players has not been described yet. Therefore, we studied plasma vitamin D, cortisol, testosterone, and creatin kinase (CK) concentrations in three different Italian professional teams training at the same latitude during a period of two consecutive competitive seasons (2013 and 2014). In this retrospective observational study, 167 professional soccer players were recruited (mean age at sampling 25.1 ± 4.7 years) and a total of 667 blood drawings were carried out to determine plasma 25(OH)D, serum cortisol, serum testosterone and CK levels. Testosterone to cortisol ratio (TC) was calculated based as a surrogate marker of overtraining and psychophysical stress and each athlete was drawn until a maximum of 5 times per season. Data extracted by a subgroup of players that underwent at least 4 sample drawings along a year (N = 45) were processed with the single and population mean cosinor tests to evaluate the presence of circannual rhythms: the amplitude (A), acrophase (Φ) and the MESOR (M) are described. In total, 55 players (32.9%) had an insufficient level of 25(OH)D during the seasons and other 15 athletes (9.0%) showed, at least once, a deficiency status of Vitamin D. The rhythmometric analyses applied to the data of Vitamin D revealed the presence of a significant circannual rhythm (p < 0.001) with the acrophase that occurred in August; the rhythms of Vitamin D levels were not different neither among the three soccer teams nor between competitive seasons. Cortisol, testosterone and TC showed significant circannual rhythms (p < 0.001): cortisol registered an acrophase during winter (February) while testosterone and TC registered their peaks in the summer months (July). On the contrary, CK did not display any seasonal fluctuations. In addition, we observed weak but significant correlations between 25(OH)D versus testosterone (r = 0.29 and p < 0.001), cortisol (r = -0.27 and p < 0.001) and TC (r = 0.37 and p < 0.001). No correlation was detected between Vitamin D and CK. In conclusion, the correct chronobiologic approach in the study of annual variations of Vitamin D, cortisol and testosterone could be decisive in the development of more specific supplementation and injury prevention strategies by athletic trainers and physicians.

#10 Predictors Of Linear And Multidirectional Acceleration In Elite Soccer Players
Reference: J Strength Cond Res. 2017 Mar 13. doi: 10.1519/JSC.0000000000001897. [Epub ahead of print]
Authors: Jonathan N, Russell M, Shearer D, Cook C, Kilduff L
Summary: Linear and multidirectional acceleration underpins success in professional soccer match-play. However, the physical qualities that determine these performance indicators are poorly understood in elite players. English Premier League players (n=26) performed isometric mid-thigh pulls (IMTP), bilateral and unilateral drop jumps (DJ; from 40 and 20 cm, respectively), bilateral and unilateral countermovement jumps (CMJ) and assessments of linear (5-, 10-, 20-m) and multidirectional (left/right pre-planned and reactive) acceleration. Regression analyses highlighted that 21% of variance in 5-m sprint time (1.02±0.07 s) was explained by relative peak power output (PPO) in bilateral CMJ (54.5±5.3 W·kg). A 5.4 W·kg increase in CMJ predicted a 0.03 s decrease in 5-m sprint time (P=0.02). For 10-m sprint time (1.72±0.09 s), 44% of variance was explained by isometric relative peak force (PF; 30.4±4.9 N·kg) and bilateral relative CMJ PPO (54.5±5.3 W·kg). A 5.4 W·kg increase in CMJ predicted reduced 10-m sprint times by 0.04 s (P=0.01). For 20-m sprint time (2.94±0.11 s), 55% of the total variance was explained by isometric relative PF (30.4±4.9 N·kg) and relative CMJ PPO (54.5±5.3 W·kg). Increases of 5.4 W·kg in bilateral CMJ predicted an improvement of 20-m sprint time by 0.06 s (P=0.002). Contributions were insignificant (P>0.05) for pre-planned and reactive multidirectional acceleration. Relativized indices, especially those related to force production during CMJ and IMTP tests, likely underpin linear but not multidirectional acceleration performance in professional soccer players. When linear acceleration is a training focus, practitioners should seek to monitor CMJ and IMTP test performance.

#11 Groin Problems in Male Soccer Players Are More Common Than Previously Reported
Reference: Am J Sports Med. 2017 Feb 1:363546516687539. doi: 10.1177/0363546516687539. [Epub ahead of print]
Authors: Haroy J, Clarsen B, Thorborg K, Holmich P, Bahr R, Andersen TE
Summary: The majority of surveillance studies in soccer have used a time-;loss injury definition, and many groin problems result from overuse, leading to gradually increasing pain and/or reduced performance without necessarily causing an absence from soccer training or match play. Thus, the magnitude of groin problems in soccer has probably been underestimated in previous studies based on traditional injury surveillance methods. The purpose of the study was to investigate the prevalence of groin problems among soccer players of both sexes and among male soccer players at different levels of play through a new surveillance method developed to capture acute and overuse problems. We registered groin problems during a 6-;week period of match congestion using the Oslo Sports Trauma Research Center Overuse Injury Questionnaire. A total of 240 players from 15 teams across different levels of play and from both sexes were included, and they responded to the weekly questionnaire. We calculated the average weekly prevalence of all groin problems and substantial groin problems. Of the 240 players, 112 male players (59%) and 20 female players (45%) reported at least 1 episode of groin problems. The average weekly prevalence of any groin problem and substantial groin problem for all male players was 29% (range, 23%-32% across different levels) and 10% (7%-13%), respectively. Elite male players had an increased risk of experiencing groin problems (odds ratio: 3.1, 95% CI: 1.5-6.4, P = .03) compared with elite female players. There was no difference in the risk of experiencing groin problems among elite, subelite, and amateur male players. For substantial problems, there was no difference between elite male and elite female players or among levels of play for senior male soccer players. We found a high prevalence of groin problems among male soccer players during a period with match congestion. Time-loss definition as used in previous injury surveillance studies captured only one-;third of the male groin problems registered with the new method. Elite male players had 3 times' higher risk of reporting groin problems as compared with elite female players, while playing level did not influence the risk of reporting a groin problem among males.





Latest research in football - week 11 - 2017

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 Monitoring Elite Soccer Players External Loads Using Real-Time Data
Reference: Int J Sports Physiol Perform. 2017 Mar 2:1-10. doi: 10.1123/ijspp.2016-0516. [Epub ahead of print]
Authors: Barrett S
Summary: The principle aim of the study was to assess the validity of measuring locomotor activities and PlayerLoad using Real-Time (RT) data collection during soccer training. Twenty-nine (n=29) English soccer players participated. Each player wore the same MEMS device (S5, Optimeye, CatapultSports, Melbourne, Australia) during twenty-one training sessions (n= 331 data sets) in the 2015/2016 and 2016/2017 season. A Real-Time receiver (TRX, Catapultsports, Melbourne, Australia) was used to collect the locomotor activities and PlayerLoad data in RT and compared with the post-event downloaded (PED) data. PlayerLoad and locomotor activities (total distance covered, TDC; total high speed running distance covered, >5.5m/s, HSR; total sprinting distance covered, >7m/s, SP; maximum velocity, VEL) were analysed. Correlations were near perfect for all variables analysed (r=0.98-1.00), with a varied level of noise between RT and PED also (0.3-9.7% CV). Locomotor activities and PlayerLoad can be used both RT and PED concurrently to quantify a players physical output during a training session. Caution should be taken with higher velocity based locomotor activities during RT compared to PED.

#2 Long Sprint Abilities in Soccer: Ball vs Running Drills
Reference: Int J Sports Physiol Perform. 2017 Mar 2:1-22. doi: 10.1123/ijspp.2016-0565. [Epub ahead of print]
Authors: Castagna C, Francini L, Póvoas SC, D'Ottavio S
Summary: The purpose of the study was to examine the acute effects of generic (Running Drills, RD) and specific (Small-Sided Games, SSG) Long Sprint Ability (LSA) drills on internal and external load of male soccer-players. Fourteen academy-level soccer-players (mean±SD; age 17.6±0.61 years, height 1.81±0.63 m, body-mass 69.53±4.65 kg) performed four 30s LSA bouts for maintenance (work:rest, 1:2) and production (1:5) with RD and SSG drills. Players' external-load was tracked with GPS technology (20Hz) and heart-rate (HR), blood-lactate concentrations (BLc) and rate of perceived exertion (RPE) were used to characterize players' internal-load. Individual peak BLc was assessed with a 30s all-out test on a non-motorized treadmill (NMT). Compared to SSGs the RDs had a greater effect on external-load and BLc (large and small, respectively). During SSGs players covered more distance with high-intensity decelerations (moderate-to-small). Muscular-RPE was higher (small-to-large) in RD than in SSG. The production mode exerted a moderate effect on BLc while the maintenance condition elicited higher cardiovascular effects (small-to-large). The results of this study showed the superiority of generic over specific drills in inducing LSA related physiological responses. In this regard production RD showed the higher post-exercise BLc. Interestingly, individual peak blood-lactate responses were found after the NMT 30s all-out test, suggesting this drill as a valid option to RD bouts. The practical physiological diversity among the generic and specific LSA drills here considered, enable fitness trainers to modulate prescription of RD and SSG drills for LSA according to training schedule.

#3 Changes in body composition and bone of female collegiate soccer players through the competitive season and off-season

Reference: J Musculoskelet Neuronal Interact. 2017 Mar 1;17(1):386-398.
Authors: Minett MM, Binkley TB, Weidauer LA, Specker BL
Summary: The purpose of the study was to assess body composition and bone changes pre- to post-season (pre-post) and post- to off-season (post-off) in female soccer athletes (SC).
Outcomes were assessed using DXA and pQCT in 23 SC and 17 controls at three times throughout season. SC, non-starters in particular, lost lean mass pre-post (-0.9±0.2 kg, p<0.01; not different from controls, p=0.2) and gained fat mass post-off (1.4±0.3 kg, p<0.01; differed from controls, p=0.01). Baseline femoral neck and hip aBMD were higher in SC than controls (both,p<0.04), but increased in controls more than SC in pre-post and decreased post-off. SC cortical bone mineral content (BMC), cortical area and periosteal circumference increased pre-post (all, p<0.01; differed from controls, p<0.05) and trabecular vBMD decreased post-off (-3.0±1.3 mg/cm3; p=0.02; not different from controls, p=0.4). Both SC and controls increased cortical BMC, cortical area, and thickness post-off (all, p<0.01). Soccer players lost lean mass over the competitive season that was not recovered during off-season. Bone size increased pre- to post-season. Female soccer athletes experience body composition and bone geometry changes that differ depending on the time of season and on athlete's playing status. Evaluations of athletes at key times across the training season are necessary to understand changes that occur.

#4 The assessment of neuromuscular fatigue during 120 min of simulated soccer exercise
Reference: Eur J Appl Physiol. 2017 Feb 28. doi: 10.1007/s00421-017-3561-9. [Epub ahead of print]
Authors: Goodall S, Thomas K, Harper LD, Hunter R, Parker P, Stevenson E, West D, Russell M, Howatson G
Download link:*~hmac=5dd338e5036a46152a7d9f94e33901a365f57c98ec7ccb3aa84adee932e5d4e7
Summary: This investigation examined the development of neuromuscular fatigue during a simulated soccer match incorporating a period of extra time (ET) and the reliability of these responses on repeated test occasions. Ten male amateur football players completed a 120 min soccer match simulation (SMS). Before, at half time (HT), full time (FT), and following a period of ET, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation (TMS) were obtained from the knee-extensors to measure neuromuscular fatigue. Within 7 days of the first SMS, a second 120 min SMS was performed by eight of the original ten participants to assess the reliability of the fatigue response. At HT, FT, and ET, reductions in maximal voluntary force (MVC; -11, -20 and -27%, respectively, P ≤ 0.01), potentiated twitch force (-15, -23 and -23%, respectively, P < 0.05), voluntary activation (FT, -15 and ET, -18%, P ≤ 0.01), and voluntary activation measured with TMS (-11, -15 and -17%, respectively, P ≤ 0.01) were evident. The fatigue response was robust across both trials; the change in MVC at each time point demonstrated a good level of reliability (CV range 6-11%; ICC2,1 0.83-0.94), whilst the responses identified with motor nerve stimulation showed a moderate level of reliability (CV range 5-18%; ICC2,1 0.63-0.89) and the data obtained with motor cortex stimulation showed an excellent level of reliability (CV range 3-6%; ICC2,1 0.90-0.98). Simulated soccer exercise induces a significant level of fatigue, which is consistent on repeat tests, and involves both central and peripheral mechanisms.

#5 Soccer and head injuries: What is the risk?
Reference: Neurology. 2017 Feb 28;88(9):e74-e77. doi: 10.1212/WNL.0000000000003669.
Authors: Allen B, Karceski S.
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#6 Lack of eye discipline during headers in high school girls soccer: A possible mechanism for increased concussion rates
Reference: Med Hypotheses. 2017 Mar;100:10-14. doi: 10.1016/j.mehy.2016.12.016. Epub 2017 Jan 5.
Authors: Clark JF, Elgendy-Peerman HT, Divine JG, Mangine RE, Hasselfeld KA, Khoury JC, Colosimo AJ
Summary: The sport of soccer is the fastest growing and most popular sport worldwide. With this growth and popularity, attention needs to be given to this athletic population. Sports related concussions is a topic that has gained attention both in the media and by governmental organizations, with growing initiatives in diagnosis, prevention and treatment. The act of soccer heading is thought to contribute to increased concussion incidence. Current evidence reveals that within the high school soccer athletic population, female athletes incur a higher concussion rate than males. This is often attributed to many things including differing cervical spinal musculature, skull thickness, etc., but a definitive reason has not yet been found. Other behaviors, such as field awareness and eye discipline™ on the field of play, may also be contributing factors that result in females incurring a greater concussion rate than males. For the purposes of this paper we define eye discipline™ as the ability to keep the eyes engaged in sporting activity with high risk potential. We present our hypothesis that high school female soccer players are more likely to have their eyes closed when in position for heading the ball as compared to high school male soccer players and this lack of visual awareness may increase the risk of concussion. Should these differences be substantiated between males and females, it may initiate and promote discussion of the need for vision training in the high school athletic setting. As a tool for injury prevention, vision training may improve specific visual parameters improving athletes' abilities to process the field of play and prepare for or avoid injury causing situations. Through ocular motor and visual conditioning, an athlete may become more eye disciplined™, and more likely to have their eyes open during heading of the ball, and more likely to avoid concussions.

#7 Youth Football Injuries: A Prospective Cohort
Reference: Orthop J Sports Med. 2017 Feb 10;5(2):2325967116686784. doi: 10.1177/2325967116686784. eCollection 2017.
Authors: Peterson AR, Kruse AJ, Meester SM, Olson TS, Riedle BN, Slayman TG, Domeyer TJ, Cavanaugh JE, Smoot MK
Download link:
Summary: There are approximately 2.8 million youth football players between the ages of 7 and 14 years in the United States. Rates of injury in this population are poorly described. Recent studies have reported injury rates between 2.3% and 30.4% per season and between 8.5 and 43 per 1000 exposures. Youth flag football has a lower injury rate than youth tackle football. The concussion rates in flag football are lower than in tackle football. Three large youth (grades 2-7) football leagues with a total of 3794 players were enrolled. Research personnel partnered with the leagues to provide electronic attendance and injury reporting systems. Researchers had access to deidentified player data and injury information. Injury rates for both the tackle and flag leagues were calculated and compared using Poisson regression with a log link. The probability an injury was severe and an injury resulted in a concussion were modeled using logistic regression. For these 2 responses, best subset model selection was performed, and the model with the minimum Akaike information criterion value was chosen as best. Kaplan-Meier curves were examined to compare time loss due to injury for various subgroups of the population. Finally, time loss was modeled using Cox proportional hazards regression models. A total of 46,416 exposures and 128 injuries were reported. The mean age at injury was 10.64 years. The hazard ratio for tackle football (compared with flag football) was 0.45 (95% CI, 0.25-0.80; P = .0065). The rate of severe injuries per exposure for tackle football was 1.1 (95% CI, 0.33-3.4; P = .93) times that of the flag league. The rate for concussions in tackle football per exposure was 0.51 (95% CI, 0.16-1.7; P = .27) times that of the flag league. Injury is more likely to occur in youth flag football than in youth tackle football. Severe injuries and concussions were not significantly different between leagues. Concussion was more likely to occur during games than during practice. Players in the sixth or seventh grade were more likely to suffer a concussion than were younger players.

#8 Football nutrition: time for a new consensus?
Reference: Br J Sports Med. 2017 Mar 2. pii: bjsports-2016-097260. doi: 10.1136/bjsports-2016-097260. [Epub ahead of print]
Authors: Collins J, McCall A, Bilsborough J, Maughan R
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#9 Effect of lifelong football training on the expression of muscle molecular markers involved in healthy longevity
Reference: Eur J Appl Physiol. 2017 Mar 1. doi: 10.1007/s00421-017-3562-8. [Epub ahead of print]
Authors: Mancini A, Vitucci D, Labruna G, Imperlini E, Randers MB, Schmidt JF, Hagman M, Andersen TR, Russo R, Orru S, Krustrup P, Salvatore F, Buono P
Summary: We investigated whether lifelong football training affects the expression of healthy longevity-related muscle molecular markers. Biopsies were collected from the vastus lateralis muscle of 10 lifelong football-trained men (68.2 ± 3.0 years) and of 10 active untrained healthy men (66.7 ± 1.3 years). Gene and protein expression was measured by RTqPCR on RNA and by western blotting on protein extracts from muscle biopsies, respectively. The expression of AMPKα1/α2, NAMPT, TFAM and PGC1α, which are markers of oxidative metabolism, and MyHC β isoform expression was higher in the muscle of football-trained men vs untrained men. Also citrate synthase activity was higher in trained than in untrained men (109.3 ± 9.2 vs 75.1 ± 9.2 mU/mg). These findings were associated with a healthier body composition in trained than in untrained men [body weight: 78.2 ± 6.5 vs 91.2 ± 11.2 kg; body mass index BMI: 24.4 ± 1.6 vs 28.8 ± 4.0 kg m-2; fat%: 22.6 ± 8.0 vs 31.4 ± 5.0%)] and with a higher maximal oxygen uptake (VO2max: 34.7 ± 3.8 vs 27.3 ± 4.0 ml/min/kg). Also the expression of proteins involved in DNA repair and in senescence suppression (Erk1/2, Akt and FoxM1) was higher in trained than in untrained men. At BMI- and age-adjusted multiple linear regression analysis, fat percentage was independently associated with Akt protein expression, and VO2max was independently associated with TFAM mRNA and with Erk1/2 protein expression. Lifelong football training increases the expression of key markers involved in muscle oxidative metabolism, and in the DNA repair and senescence suppression pathways, thus providing the molecular basis for healthy longevity.

#10 Increased Training Volume Improves Bone Density and Cortical Area in Adolescent Football Players
Reference: Int J Sports Med. 2017 Mar 1. doi: 10.1055/s-0042-124510. [Epub ahead of print]
Authors: Varley I, Hughes DC, Greeves JP, Fraser WD, Sale C
Summary: Habitual football participation has been shown to be osteogenic, although the specific volume of football participation required to cause bone adaptations are not well established. The aim of the present study is to investigate tibial bone adaptations in response to 12 weeks of increased training volume in elite adolescents who are already accustomed to irregular impact training. 99 male adolescent elite footballers participated (age 16±0 y; height 1.76±0.66 m; body mass 70.2±8.3 kg). Tibial scans were performed using peripheral quantitative computed tomography immediately before and 12 weeks after an increase in football training volume. Scans were obtained at 4, 14, 38 and 66% of tibial length. Trabecular density (mg/cm3), cortical density (mg/cm3), cross-sectional area, cortical area (mm2), cortical thickness (mm) and strength strain index (mm3) were assessed. Trabecular (4%) and cortical density (14, 38%), cortical cross-sectional area (14, 38%), total cross-sectional area (66%), cortical thickness (14, 38%) and strength strain index (14, 38%) increased following 12 weeks of augmented volume training (P<0.05). Increased density of trabecular and cortical compartments and cortical thickening were shown following an increased volume of training. These adaptive responses may have been enhanced by the adolescent status of the cohort, supporting the role of early exercise intervention in improving bone strength.

#11 Return to play criteria after hamstring muscle injury in professional football: a Delphi consensus study
Reference: Br J Sports Med. 2017 Feb 28. pii: bjsports-2016-097131. doi: 10.1136/bjsports-2016-097131. [Epub ahead of print]
Authors: Zambaldi M, Beasley I, Rushton A
Summary: Hamstring muscle injury (HMI) is the most common injury in professional football and has a high re-injury rate. Despite this, there are no validated criteria to support return to play (RTP) decisions. The purpose was to use the Delphi method to reach expert consensus on RTP criteria after HMI in professional football. All professional football clubs in England (n=92) were invited to participate in a 3-round Delphi study. Round 1 requested a list of criteria used for RTP decisions after HMI. Responses were independently collated by 2 researchers under univocal definitions of RTP criteria. In round 2 participants rated their agreement for each RTP criterion on a 1-5 Likert Scale. In round 3 participants re-rated the criteria that had reached consensus in round 2. Descriptive statistics and Kendall's coefficient of concordance enabled interpretation of consensus. Participation rate was limited at 21.7% (n=20), while retention rate was high throughout the 3 rounds (90.0%, 85.0%, 90.0%). Round 1 identified 108 entries with varying definitions that were collated into a list of 14 RTP criteria. Rounds 2 and 3 identified 13 and 12 criteria reaching consensus, respectively. Five domains of RTP assessment were identified: functional performance, strength, flexibility, pain and player's confidence. The highest-rated criteria were in the functional performance domain, with particular importance given to sprint ability. This study defined a list of consensually agreed RTP criteria for HMI in professional football. Further work is now required to determine the validity of the identified criteria.





Latest research in football - week 10 - 2017

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 Hormonal responses during two different concurrent-training trials in youth elite soccer players: does changing the organisation of training impact the hormonal response to concurrent exercise?
Reference: J Sports Med Phys Fitness. 2017 Feb 22. doi: 10.23736/S0022-4707.17.07198-5. [Epub ahead of print]
Authors: Enright K, Morton J, Iga J, Drust B
Summary: There are no data describing the acute hormonal responses to concurrent- training programmes in youth elite soccer players. Therefore, the aim of this study was to describe the total testosterone (T), cortisol (C), and growth hormone (hGH) responses during two same-day concurrent-training (CT) trials in elite soccer players. Thirteen youth elite players (age: 17.0±0.2 yrs; height, 1.80±0.07 m; body mass, 73.1±5.7 kg; VO2 max, 64.4± from an English premier league soccer club completed two CT trials. 'Trial 1' (CT1); E (10.30h) followed by S (14.00h) and Trial 2 (CT2); strength-training (S) 09.00h followed by a soccer-specific endurance-training session (E) at 10.30h. Venous blood samples were collected at 5 time-points around training and food intake (T1; 08.00h, T2; 09.45h, T3; 12.30h, T4; 13.45h and T5; 15.15h) and analysed for T (nmol/L) and C (nmol/L) and hGH (ug/L). There was no main effects found between exercise conditions for any hormones (T; P=0.22, C; P=0.07, hGH; P=0.21). Effect size analysis revealed a moderate effect for T at T3 (ES=0.63, CT1; 18.4±3.8, CT2; 15.7±4.7 nmol/L-1). A moderate effect for T area under the curve (AUC) was observed between conditions (CT1; 300±76 versus CT2; 244 ± 81 [AU]; ES=0.71). A moderate effect was apparent for C concentrations T4 in (ES=-0.95, CT1; 230±69, CT2; 314±105 nmol/L-1). Moderate effect sizes were observed at T3 and T4 (ES=0.82, CT1; 1.28±1.17, CT2; 0.47±0.75, ES=0.72, CT1; 0.11±0.05, CT2; 0.07±0.06 ug/L-1 respectively). A moderate effect for hGH AUC was observed between trials (CT1; 14±11 versus CT2; 5±9; [AU], ES=-1.08). The organisation of the concurrent-training protocols used in this study has a negligible impact upon the acute T, C and hGH in youth elite soccer players.

#2 The periodization of resistance training in soccer players: changes in maximal strength, lower extremity power, body composition, and muscle volume
Reference: J Sports Med Phys Fitness. 2017 Feb 22. doi: 10.23736/S0022-4707.17.07129-8. [Epub ahead of print]
Authors: Barjaste A, Mirzaei B
Summary: The purpose of this study was to investigate the effect of 12-weeks traditional periodized resistance training on some physical capacities of soccer players. Eighteen amateur soccer players with very little experience in resistance training voluntarily participated in this study. Subjects were assigned into two groups; Experimental (EX) group (n: 10) that conducted a traditional linear periodized resistance training program and a control (C) group (n: 8) that did not participate in any resistance training. Periodized resistance training in two mesocycles was used in this study: general or anatomical adaptation phase (6 wk, 65%-75% of 1RM, eleven exercises in each session) and maximal strength phase (6 wk, 85%-95% of 1RM, three to four exercises in each session). One Repetition Maximum (1RM) strength in lower and upper body, Vertical Jump (VJ) height, Body Composition, and Muscle Volume were measured at three different time points; baseline, after general phase, and after maximal strength phase. The average of the increase in 1RM all exercises in general phase was greater than the maximal strength phase, on average 29.38% and 9.67% respectively (P≤0.05). Also, the Percentage of change in VJ height in general phase was greater than the maximal strength phase (11.93% vs 3.97% respectively) (P≤0.05). The results of this study indicated that muscle strength and explosive performance in players with the little experience in resistance training can be significantly improved with the completion of general phase of resistance training periodization using moderate loads.

#3 Nonlinear sprint performance differentiates professional from young soccer players
Reference: J Sports Med Phys Fitness. 2017 Feb 22. doi: 10.23736/S0022-4707.17.07116-X. [Epub ahead of print]
Authors: Cardoso de Araujo M, Baumgart C, Freiwald J, Hoppe MW
Summary: Linear and nonlinear sprinting activities are relevant physical capacities in soccer. This study aimed (1) to compare linear and nonlinear sprint performance between professional and young soccer players and (2) to investigate relationships between both sprint types. Sixty-eight German male elite field soccer players were grouped based on age as professional (PRO, n = 20), under-23 (U23, n = 16), under-19 (U19, n = 18), and under-17 (U17, n = 14). All players were tested for 30 m linear (split-times at 5, 10, and 20 m) and 22 m nonlinear sprint performance. In linear sprint, PRO players were moderately to very largely faster than U17 players at all distances and also than U19 players at 20 m (effect size [ES] = 0.90-2.06, p ≤ 0.04). U23 players were moderately to largely faster than U17 players at 5 and 10 m (ES = 0.93-1.74, p ≤ 0.04). In nonlinear sprint, PRO players were moderately to largely faster than all other groups (ES = 1.04-1.84, p ≤ 0.02). Moderate to large correlations were found between linear and nonlinear sprint performance for all players (r = 0.48-0.50, p < 0.01). Within groups, moderate to large correlations were evident only for PRO at 5-20 m (r = 0.45-0.61, p ≤ 0.05) and U23 at 30 m (r = 0.55, p = 0.03). The findings indicate that nonlinear sprint performance is a key physical capacity in professional soccer. Therefore, training programs should focus to increase this capacity in younger players. Furthermore, linear and nonlinear sprint performance should be independently tested and trained in elite players.

#4 Sex Differences in Anthropometrics and Heading Kinematics Among Division I Soccer Athletes
Reference: Sports Health. 2017 Mar/Apr;9(2):168-173. doi: 10.1177/1941738116678615. Epub 2016 Nov 15.
Authors: Bretzin AC, Mansell JL, Tierney RT, McDevitt JK
Summary: Soccer players head the ball repetitively throughout their careers; this is also a potential mechanism for a concussion. Although not all soccer headers result in a concussion, these subconcussive impacts may impart acceleration, deceleration, and rotational forces on the brain, leaving structural and functional deficits. Stronger neck musculature may reduce head-neck segment kinematics. The relationship between anthropometrics and soccer heading kinematics will not differ between sexes. The relationship between anthropometrics and soccer heading kinematics will not differ between ball speeds. Division I soccer athletes (5 male, 8 female) were assessed for head-neck anthropometric and neck strength measurements in 6 directions (ie, flexion, extension, right and left lateral flexions and rotations). Participants headed the ball 10 times (25 or 40 mph) while wearing an accelerometer secured to their head. Kinematic measurements (ie, linear acceleration and rotational velocity) were recorded at 2 ball speeds. Sex differences were observed in neck girth ( t = 5.09, P < 0.001), flexor and left lateral flexor strength ( t = 3.006, P = 0.012 and t = 4.182, P = 0.002, respectively), and rotational velocity at both speeds ( t = -2.628, P = 0.024 and t = -2.227, P = 0.048). Neck girth had negative correlations with both linear acceleration ( r = -0.599, P = 0.031) and rotational velocity at both speeds ( r = -0.551, P = 0.012 and r = -0.652, P = 0.016). Also, stronger muscle groups had lower linear accelerations at both speeds ( P < 0.05). There was a significant relationship between anthropometrics and soccer heading kinematics for sex and ball speeds.

#5 The effects of "Prevent Injury and Enhance Performance Program" in a female soccer team
Reference: J Sports Med Phys Fitness. 2017 Feb 21. doi: 10.23736/S0022-4707.17.07024-4. [Epub ahead of print]
Authors: Rodriguez C, Echegoyen S, Aoyama T
Summary: The purpose of this study is to evaluate the changes of muscle strength in lower limbs and knee valgus alignment using the Prevent Injury and Enhance Performance Program (PEP program) to prevent ACL injuries in female soccer players during an entire season. A longitudinal and prospective study was done in twenty female soccer players at the Universidad Nacional Autónoma de México, from a senior team. During 24 weeks the training program was applied three times a week as a part of the team workouts. Video analysis of dynamic knee valgus alignment and maximal strength of quadriceps, hamstrings and gastrocnemius were evaluated pre and post training. Quadriceps and hamstring strength increased on the right pelvic limb (p<0.001). In addition the quadriceps/hamstrings ratio decreased from 3.38 to 2.3 in the right side, and from 1.99 to 1.09 in the left side. The mechanics of jump improved in 20% of the female soccer players. Muscle strength in quadriceps and hamstrings increased in right pelvic limb (p<0.001), and the quadriceps/hamstrings ratio decreased from 3.38 to 2.3 in right side and from 1.99 to 1.09 in left side. Although injuries did not decrease during this period no ACL injury was registered. Until now there are no reports about muscle strength and jump technique assessment with the application of the PEP program. The neuromuscular training and muscle balance are important to prevent ACL injuries. We advise that this program is integrated to women ́s soccer training.

#6 Soccer-related performance in eumenorrheic Tunisian high-level soccer players: effects of menstrual cycle phase and moment of day
Reference: J Sports Med Phys Fitness. 2017 Feb 21. doi: 10.23736/S0022-4707.17.06958-4. [Epub ahead of print]
Authors: Tounsi M, Jaafar H, Aloui A, Souissi N
Summary: This study aimed to examine the combined effects of menstrual cycle phase and moment of day on female soccer players' performances in the five-jump test (5JT), the repeated shuttle- sprint ability test (RSSA), and the Yo-Yo intermittent recovery test level 1 (YYIRT1). Eleven eumenorrheic Tunisian high-level soccer players volunteered to participate. Each subject individually participated in three testing periods: one in the early follicular phase (menses), one in the late follicular phase, and another in the luteal phase. In each period, two test sessions were conducted: one at 07:30 h and another at 17:30 h. The testing routines included the 5JT, the RSSA, and the YYIRT1. None of the measured variables were altered due to menstrual cycle phase (all P > 0.05). Mean time during RSSA was significantly lower in the afternoon session compared to the morning session (8.48 ± 0.27 s and 8.77 ± 0.34 s, respectively, P < 0.001), while 5JT performance was significantly higher in the afternoon compared to the morning (9.08 ± 0.58 m and 8.60 ± 0.56 m, respectively, P < 0.001). Soccer-specific endurance as well as jumping and repeated sprinting ability of Tunisian female high-level soccer players are not affected due to menstrual cycle phase neither in the morning nor in the afternoon.

#7 Neuroplus biofeedback improves attention, resilience, and injury prevention in elite soccer players
Reference: Psychophysiology. 2017 Feb 21. doi: 10.1111/psyp.12847. [Epub ahead of print]
Authors: Rusciano A, Corradini G, Stoianov I
Summary: Performance and injury prevention in elite soccer players are typically investigated from physical-tactical, biomechanical, and metabolic perspectives. However, executive functions, visuospatial abilities, and psychophysiological adaptability or resilience are also fundamental for efficiency and well-being in sports. Based on previous research associating autonomic flexibility with prefrontal cortical control, we designed a novel integrated autonomic biofeedback training method called Neuroplus to improve resilience, visual attention, and injury prevention. Herein, we introduce the method and provide an evaluation of 20 elite soccer players from the Italian Soccer High Division (Serie-A): 10 players trained with Neuroplus and 10 trained with a control treatment. The assessments included psychophysiological stress profiles, a visual search task, and indexes of injury prevention, which were measured pre- and posttreatment. The analysis showed a significant enhancement of physiological adaptability, recovery following stress, visual selective attention, and injury prevention that were specific to the Neuroplus group. Enhancing the interplay between autonomic and cognitive functions through biofeedback may become a key principle for obtaining excellence and well-being in sports. To our knowledge, this is the first evidence that shows improvement in visual selective attention following intense autonomic biofeedback.

#8 Relative Age, Maturation and Physical Biases on Position Allocation in Elite-Youth Soccer
Reference: Int J Sports Med. 2017 Feb 20. doi: 10.1055/s-0042-119029. [Epub ahead of print]
Authors: Towlson C, Cobley S, Midgley AW, Garrett A, Parkin G, Lovell R
Summary: This study assessed the contribution of relative age, anthropometry, maturation, and physical fitness characteristics on soccer playing position (goalkeeper [GK], central-defender [CD], lateral-defender [LD], central-midfield [CM], lateral-midfielder [LM], and forward [FWD]) for 465 elite-youth players (U13-U18's). U13-14 CD were relatively older than LD and CM (likely small effects). CD and GK were generally taller and heavier (likely small to very-likely moderate effects) than other players at each developmental stage and were advanced maturers at U13-14 (very-likely small to likely moderate effects). GK had inferior agility (very-likely small to likely moderate effects), endurance (very-likely small to likely moderate effects), and sprint capacities (likely small-moderate effects) vs. outfield positions at U13-14, but deficits in anaerobic phenotypes were diminished in U15-16 and U17-18. Position specific fitness characteristics were distinguished at U15-16 (likely small) and U17-18 (likely moderate), where LM were faster than their central counterparts. In summary, relative age, maturation and anthropometric characteristics appear to bias the allocation of players into key defensive roles from an early development stage, whereas position-specific physical attributes do not become apparent until the latter stages of talent development in outfield players. Given the inter-individual trajectories of physical development according to biological maturation, playing position allocation might be considered 'plastic' by selectors, until complete-maturity is achieved.

#9 The intra- and inter-reliability of the soccer injury movement screen (SIMS)
Reference: Int J Sports Phys Ther. 2017 Feb;12(1):53-66.
Authors: McCunn R, Aus der Funten K, Govus A, Julian R, Schimpchen J, Meyer T
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Summary: The growing volume of movement screening research reveals a belief among practitioners and researchers alike that movement quality may have an association with injury risk. However, existing movement screening tools have not considered the sport-specific movement and injury patterns relevant to soccer. The present study introduces the Soccer Injury Movement Screen (SIMS), which has been designed specifically for use within soccer. Furthermore, the purpose of the present study was to assess the intra- and inter-rater reliability of the SIMS and determine its suitability for use in further research. The study utilized a test-retest design to discern reliablility. Twenty-five (11 males, 14 females) healthy, recreationally active university students (age 25.5 ± 4.0 years, height 171 ± 9 cm, weight 64.7 ± 12.6 kg) agreed to participate. The SIMS contains five sub-tests: the anterior reach, single-leg deadlift, in-line lunge, single-leg hop for distance and tuck jump. Each movement was scored out of 10 points and summed to produce a composite score out of 50. The anterior reach and single-leg hop for distance were scored in real-time while the remaining tests were filmed and scored retrospectively. Three raters conducted the SIMS with each participant on three occasions separated by an average of three and a half days (minimum one day, maximum seven days). Rater 1 re-scored the filmed movements for all participants on all occasions six months later to establish the 'pure' intra-rater (intra-occasion) reliability for those movements. Intraclass correlation coefficient (ICC) values for intra- and inter-rater composite score reliability ranged from 0.66-0.72 and 0.79-0.86 respectively. Weighted kappa values representing the intra- and inter-rater reliability of the individual sub-tests ranged from 0.35-0.91 indicating fair to almost perfect agreement. Establishing the reliability of the SIMS is a prerequisite for further research seeking to investigate the relationship between test score and subsequent injury. The present results indicate acceptable reliability for this purpose; however, room for further development of the intra-rater reliability exists for some of the individual sub-tests.

#10 Effects of a small-sided game-based training programme on repeated sprint and change of direction abilities in recreationally-trained football players
Reference: J Sports Med Phys Fitness. 2017 Feb 21. doi: 10.23736/S0022-4707.17.07044-X. [Epub ahead of print]
Authors: Bujalance-Moreno P, Garcia-Pinillos F, Latorre-Roman PA
Summary: The purpose of the study was to examine the effects of 6-week periodized small-sided game (SSG) training intervention on change of direction [COD], sprint and repeated sprint ability [RSA] in recreational male football players. Twenty-three young football players (age: 20.86 years) were randomized in a control group (n = 11) and an experimental group (n = 12). The SSG programme was included in the experimental group's training sessions. The players completed two variations of a SSG (i.e. 2 vs. 2 and 4 vs. 4 players) during intervention. To examine the changes in physical performance after the 6-week periodized SSG training intervention, all players were tested 6 weeks apart (i.e. pre-test and post-test) in sprint, COD ability test, and RSA shuttle test. A 2x2 ANOVA showed that 6-week SSG training intervention induced significant improvements (P<0.05, ES>0.7) in COD ability test, and variables related to both sprint test and RSA in the experimental group, whereas the control group remained unchanged (P≥0.05, ES<0.4). Regarding the response to the RSA test - in terms of BLa, both the experimental group (P=0.001, ES=1.270) and the control group (P=0.010, ES=0.939) increased BLa after the intervention. The current study indicates that a 6-week SSG-based training programme could improve decisive parameters in performance in football, such as COD, RSA and sprint in recreationally trained football players.

#11 Risk factors of anterior cruciate ligament injury in football players: a systematic review of the literature
Reference: Muscles Ligaments Tendons J. 2016 Feb 12;6(4):480-485. doi: 10.11138/mltj/2016.6.4.480.
Authors: Volpi P, Bisciotti GN, Chamari K, Cena E, Carimati G, Bragazzi NL
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Summary: The ACL lesion represents one of the most dramatic injuries in a sportsman's career. There are many injury risk factors related to intrinsic, or non-modifiable, and extrinsic, or modifiable, factors. In literature at today current evidence suggests that ACL injury risk is multifactorial and involves biomechanical, anatomical, hormonal and neuromuscular factors. The purpose of the study was to perform a systematic review of the literature concerning the ACL injury risk factors in soccer. The injury risk factors show a low level of evidence, further studies in the field are needed.

#12 ACL injury in football: a literature overview of the prevention programs
Reference: Muscles Ligaments Tendons J. 2016 Feb 12;6(4):473-479. doi: 10.11138/mltj/2016.6.4.473.
Authors: Bisciotti GN, Chamari K, Cena E, Carimati G, Volpi P
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Summary: The ACL prevention programs are addressed to the control and/or modification of the so-called "modifiable risk factors". All these programs focus on different intervention strategies aimed to decrease the ACL injury risk, particularly in female athletes population. The purpose of the study was to furnish an overview of the most used ACL injury prevention program through a narrative review. In literature there are many reports on prevention programs whose common denominator is the proper alignment of the lower limb joints and proper motor control during movements that are considered at risk for ACL integrity, as the landing phase after a jump. Nevertheless, some programs would appear more effective than others. In any cases a major problem remains the lack of sufficient compliance in respect of prevention programs. Finally, it is important to remember that the ethiology of ACL injuries is multifactorial. For this reason a prevention program able to prevent all the risk situations is utopian.

#13 Where biomedicalisation and magic meet: Therapeutic innovations of elite sports injury in British professional football and cycling
Reference: Soc Sci Med. 2017 Feb 9;178:136-143. doi: 10.1016/j.socscimed.2017.02.011. [Epub ahead of print]
Authors: Faulkner A, McNamee M, Coveney C, Gabe J
Summary: Injury is a conspicuous feature of the practice and public spectacle of contemporary elite sports. The paper argues that the 'biomedicalisation' thesis (medico-industrial nexus, techno-scientific drivers, medical optimisation, biologisation, the rise of evidence and health surveillance) goes some way to capturing the use in elite sports injury of some highly specialised mainstream therapies and some highly maverick biological therapies, which are described. Nevertheless, these main strands of biomedicalisation do not capture the full range of these phenomena in the contexts of sports medicine and athletes' practices in accessing innovative, controversial therapies. Drawing on multi-method qualitative research on top-level professional football and cycling in the UK, 2014-2016, we argue that concepts of 'magic' and faith-based healing, mediated by notions of networking behaviour and referral systems, furnish a fuller explanation. We touch on the concept of 'medical pluralism', concluding that this should be revised in order to take account of belief-based access to innovative bio-therapies amongst elite sportspeople and organisations.





Latest research in football - week 9 - 2017

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 Injuries of the obturator muscles in professional soccer players
Reference: Knee Surg Sports Traumatol Arthrosc. 2017 Feb 10. doi: 10.1007/s00167-017-4453-6. [Epub ahead of print]
Authors: Wong-On M, Turmo-Garuz A, Arriaza R, Gonzalez de Suso JM, Til-Perez L, Yanguas-Leite X, Diaz-Cueli D, Gasol-Santa X
Summary: Obturator externus and internus muscular tears are uncommon injuries. Only a few case reports exist, mainly in high-level athletes. Our aim is to describe a series of obturator externus and internus muscular tears in professional soccer players. Injury data from four teams from the First Division of the Spanish Soccer League were collected over a total of four seasons. Any soccer player who sustained an injury to either the obturator externus or internus identified on magnetic resonance (MRI) was included. All injured players were treated non-operatively with a goal of returning to play as fast as possible. Sixteen players sustained injuries to the obturator externus and internus during matches or training sessions. The main complaint was anterior hip pain with a physical examination showing pain during internal rotation or external rotation of the flexed hip. The MRI documented 12 muscular tears of the obturator externus, and 4 muscular tears of the obturator internus. All injuries were treated conservatively based on physical therapy, analgesic medications, and underwent a symptoms-based rehabilitation protocol. Mean return to play was 11.5  ±  8.8 days. Although uncommon, tears of the obturator externus and internus occur in professional soccer players. The MRI scan was essential to the location, classification, and evaluation of the injury size. The clinical relevance of our investigation is based on the relatively benign prognosis of these injuries.

#2 Torque-angle-velocity Relationships and Muscle Performance of Professional and Youth Soccer Players
Reference: Int J Sports Med. 2016 Nov;37(12):992-996. Epub 2016 Aug 1.
Authors: Mazuquin BF, Dela Bela LF, Pelegrinelli AR, Dias JM, Carregaro RL, Moura FA, Selfe J, Richards J, Brown LE, Cardoso JR
Summary: Soccer matches consist of a variety of different activities, including repeated sprints. Time to attain velocity (TTAV), load range (LR) and the torque-angle-velocity relationship (TAV3D) represent an important measurement of muscle performance, however there are few related studies. The aim of this study was to compare these outcomes between soccer players of different age category. 17 professional (PRO) and 17 under-17 (U17) soccer players were assessed for concentric knee flexion/extension at 60, 120 and 300°/s. For the extensor muscles, differences were found in favor of the U17 group for TTAV and LR outcomes at 120°/s, however, the PRO group maintained higher torques in both movement directions in comparison to the U17 in TAV3D evaluation. These results suggest that muscle performance of the PRO group is more efficient than the U17 group.

#3 What's in a game? A systems approach to enhancing performance analysis in football
Reference: PLoS One. 2017 Feb 17;12(2):e0172565. doi: 10.1371/journal.pone.0172565. eCollection 2017.
Authors: McLean S, Salmon PM, Gorman AD, Read GJ, Solomon C
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Summary: Performance analysis (PA) in football is considered to be an integral component of understanding the requirements for optimal performance. Despite vast amounts of research in this area key gaps remain, including what comprises PA in football, and methods to minimise research-practitioner gaps. The aim of this study was to develop a model of the football match system in order to better describe and understand the components of football performance. Such a model could inform the design of new PA methods. Eight elite level football Subject Method Experts (SME's) participated in two workshops to develop a systems model of the football match system. The model was developed using a first-of-its-kind application of Cognitive Work Analysis (CWA) in football. CWA has been used in many other non-sporting domains to analyse and understand complex systems. Using CWA, a model of the football match 'system' was developed. The model enabled identification of several PA measures not currently utilised, including communication between team members, adaptability of teams, playing at the appropriate tempo, as well as attacking and defending related measures.The results indicate that football is characteristic of a complex sociotechnical system, and revealed potential new and unique PA measures regarded as important by SME's, yet not currently measured. Importantly, these results have identified a gap between the current PA research and the information that is meaningful to football coaches and practitioners.

#4 Football APP based on smart phone with FES in drop-foot rehabilitation
Reference: Technol Health Care. 2016 Feb 3. doi: 10.3233/THC-160730. [Epub ahead of print]
Authors: Ciou SH, Hwang YS, Chen CC, Luh JJ, Chen SC, Chen YL
Summary: Long-term, sustained progress is necessary in drop foot rehabilitation. The necessary inconvenient body training movements, the return trips to the hospital and repetitive boring training using functional electrical simulation (FES) often results in the patient suspending their training. The patient's drop foot rehabilitation will not progress if training is suspended. A fast spread, highly portable drop foot rehabilitation training device based on the smart phone is presented. This device is combined with a self-made football APP and feedback controlled FES. The drop foot patient can easily engage in long term rehabilitation training that is more convenient and interesting. An interactive game is established on the smart phone with the Android system using the originally built-in wireless communications. The ankle angle information is detected by an external portable device as the game input signal. The electrical stimulation command to the external device is supplemented with FES simulation for inadequate ankle efforts. After six-weeks training using six cases, the results indicated that this training device showed significant performance improvement (p< 0.05) in the patient's ankle dorsiflexion strength, ankle dorsiflexion angle, control timing and Timed Up and Go. Preliminary results show that this training device provides significant positive help to drop foot patients. Moreover, this device is based on existing and universally popular mobile processing, which can be rapidly promoted. The responses of clinical cases also show this system is easy to operate, convenient and entertaining. All of these features can improve the patient's willingness to engage in long term rehabilitation.

#5 A comparison of injuries in elite male and female football players: A 5-Season prospective study
Reference: Scand J Med Sci Sports. 2017 Feb 16. doi: 10.1111/sms.12860. [Epub ahead of print]
Authors: Larruskain J, Lekue JA, Diaz N, Odriozola A, Gil SM
Summary: The aim was to compare the epidemiology of injuries between elite male and female football players from the same club. Injuries and individual exposure time in a male team and a female team, both playing in the Spanish first division, were prospectively recorded by the club's medical staff for five seasons (2010-2015) following the FIFA consensus statement. Total, training and match exposure hours per player-season were 20% higher for men compared to women (P < 0.01). Total, training and match injury incidence were 30-40% higher in men (P ≤ 0.04) mainly due to a 4.82 [95% confidence interval (CI) 2.30-10.08] times higher incidence of contusions, as there were no differences in the incidence of muscle and joint/ligament injuries (P ≥ 0.44). The total number of absence days was 21% larger in women owing to a 5.36 (95% CI 1.11-25.79) times higher incidence of severe knee and ankle ligament injuries. Hamstring strains and pubalgia cases were 1.93 (95% CI 1.16-3.20) and 11.10 (95% CI 1.48-83.44) times more frequent in men, respectively; whereas quadriceps strains, anterior cruciate ligament ruptures and ankle syndesmosis injuries were 2.25 (95% CI 1.22-4.17), 4.59 (95% CI 0.93-22.76) and 5.36 (95% CI 1.11-25.79) times more common in women, respectively. In conclusion, prevention strategies should be tailored to the needs of male and female football players, with men more predisposed to hamstring strains and hip/groin injuries, and women to quadriceps strains and severe knee and ankle ligament injuries.

#6 Hip strength and range of motion: Normal values from a professional football league
Reference: J Sci Med Sport. 2016 Aug 23. pii: S1440-2440(16)30106-2. doi: 10.1016/j.jsams.2016.05.010. [Epub ahead of print]
Authors: Mosler AB, Crossley KM, Thorborg K, Whiteley RJ, Weir A, Serner A, Holmich P
Summary: The objective of the study was to determine the normal profiles for hip strength and range of motion (ROM) in a professional football league in Qatar, and examine the effect of leg dominance, age, past history of injury, and ethnicity on these profiles. Participants included 394 asymptomatic, male professional football players, aged 18-40 years. Strength was measured using a hand held dynamometer with an eccentric test in side-lying for hip adduction and abduction, and the squeeze test in supine with 45° hip flexion. Range of motion measures included: hip internal and external rotation in 90° flexion, hip IR in prone, bent knee fall out and hip abduction in side-lying. Demographic information was collected and the effect on the profiles was analysed using linear mixed models with repeated measures. Strength values (mean±SD) were: adduction=3.0±0.6Nm/kg, abduction=2.6±0.4Nm/kg, adduction/abduction ratio=1.2±0.2, Squeeze test=3.6±0.8N/kg. Range of motion values: internal rotation in flexion=32±8°, external rotation=38±8°, internal rotation in prone=38±8°, bent knee fall out=13±4.4cm, abduction in side-lying=50±7.3°. Leg dominance had no clinically relevant effect on these profiles. Multivariate analysis demonstrated that age had a minor influence on squeeze strength (-0.03N/kg/year), external rotation (-0.30°/year) and abduction range (-0.19°/year) but past history of injury, and ethnicity did not. Normal values are documented for hip strength and range of motion that can be used as reference profiles in the clinical assessment, screening, and management of professional football players. Leg dominance, recent past injury history and ethnicity do not need to be accounted for when using these profiles for comparison purposes.

#7 One ACL injury is enough! Focus on female football players
Reference: Br J Sports Med. 2017 Feb 9. pii: bjsports-2016-097179. doi: 10.1136/bjsports-2016-097179. [Epub ahead of print]
Authors: Faltstrom A

#8 Injury mechanism of midfacial fractures in football causes in over 40% typical neurological symptoms of minor brain injuries
Reference: Knee Surg Sports Traumatol Arthrosc. 2017 Feb 8. doi: 10.1007/s00167-017-4431-z. [Epub ahead of print]
Authors: Krutsch V, Gesslein M, Loose O, Weber J, Nerlich M, Gaensslen A, Bonkowsky V, Krutsch W
Summary: The injury mechanisms of midfacial fractures may be typical causes of concussion, but hardly any scientific data on midfacial injuries sustained in football are available. Head and brain trauma represent frequent injuries in athletes of different sports that require appropriate treatment by sports and trauma physicians. This study investigated the management of midfacial fractures in football and the association of such fractures with concomitant brain injury. In a prospective cohort study lasting 24 months (2012 to 2013), midfacial injuries of football players were analysed with regard to the injury mechanisms, first aid procedures on the field, treatment and return-to-play. To analyse concomitant and potentially overlooked minor brain injuries due to the trauma, we retrospectively investigated the neurological symptoms of the study population. The study included 132 football players (37 semi-professionals and 95 amateurs) with midfacial fractures. The main injury mechanisms were head-to-head and head-to-elbow trauma. The mean period of return-to-play after trauma was 33.5 days, which was significantly shortened if a protective face mask was worn (mean 10.4 days earlier, p = 0.0006). Semi-professional football players returned to play earlier (p = 0.009) and more often used protective face masks (p = 0.001). 55 players (41.6%) had neurological symptoms immediately after trauma as a possible sign of concomitant minor brain injury. 5 of 132 players with concussion had been hospitalised for 24 h, but no persistent neurological symptoms were detected. In football, midfacial fractures represent moderate-to-severe injuries with time away from sports of more than 4 weeks. Over 40% of athletes with a midfacial fracture showed concomitant neurological symptoms as a sign of minor brain injury. Therefore, sports physicians and other staff supervising athletes in daily practice should be aware of the presence of neurological symptoms.






Latest research in football - week 8 - 2017

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 Mixed pathologies including chronic traumatic encephalopathy account for dementia in retired association football (soccer) players
Reference: Acta Neuropathol. 2017 Feb 15. doi: 10.1007/s00401-017-1680-3. [Epub ahead of print]
Authors: Ling H, Morris HR, Neal JW, Lees AJ, Hardy J, Holton JL, Revesz T, Williams DD
Summary: In retired professional association football (soccer) players with a past history of repetitive head impacts, chronic traumatic encephalopathy (CTE) is a potential neurodegenerative cause of dementia and motor impairments. From 1980 to 2010, 14 retired footballers with dementia were followed up regularly until death. Their clinical data, playing career, and concussion history were prospectively collected. Next-of-kin provided consent for six to have post-mortem brain examination. Of the 14 male participants, 13 were professional and 1 was a committed amateur. All were skilled headers of the ball and had played football for an average of 26 years. Concussion rate was limited in six cases to one episode each during their careers. All cases developed progressive cognitive impairment with an average age at onset of 63.6 years and disease duration of 10 years. Neuropathological examination revealed septal abnormalities in all six post-mortem cases, supportive of a history of chronic repetitive head impacts. Four cases had pathologically confirmed CTE; concomitant pathologies included Alzheimer's disease (N = 6), TDP-43 (N = 6), cerebral amyloid angiopathy (N = 5), hippocampal sclerosis (N = 2), corticobasal degeneration (N = 1), dementia with Lewy bodies (N = 1), and vascular pathology (N = 1); and all would have contributed synergistically to the clinical manifestations. The pathological diagnosis of CTE was established in four individuals according to the latest consensus diagnostic criteria. This finding is probably related to their past prolonged exposure to repetitive head impacts from head-to-player collisions and heading the ball thousands of time throughout their careers. Alzheimer's disease and TDP-43 pathologies are common concomitant findings in CTE, both of which are increasingly considered as part of the CTE pathological entity in older individuals. Association football is the most popular sport in the world and the potential link between repetitive head impacts from playing football and CTE as indicated from our findings is of considerable public health interest. Clearly, a definitive link cannot be established in this clinico-pathological series, but our findings support the need for further systematic investigation, including large-scale case-control studies to identify at risk groups of footballers which will justify for the implementation of protective strategies.

#2 Head accelerations across collegiate, high school and youth female and male soccer players
Reference: Br J Sports Med. 2017 Feb 16. pii: bjsports-2016-097118. doi: 10.1136/bjsports-2016-097118. [Epub ahead of print]
Authors: Caccese JB

#3 Surgical Management of Rectus Femoris Avulsion Among Professional Soccer Players
Reference: Orthop J Sports Med. 2017 Jan 23;5(1):2325967116683940. doi: 10.1177/2325967116683940. eCollection 2017.
Authors: Sonnery-Cottet B, Barbosa NC, Tuteja S, Gardon R, Daggett M, Monnot D, Kajetanek C, Thaunat M
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Summary: Rectus femoris injuries are common among athletes, especially in kicking sports such as soccer; however, proximal rectus femoris avulsions in athletes are a relatively rare entity. The purpose of this study was to describe and report the results of an original technique of surgical excision of the proximal tendon remnant followed by a muscular suture repair. Our hypothesis was that this technique limits the risk of recurrence in high-level athletes and allows for rapid recovery without loss of quadriceps strength. Our retrospective series included 5 players aged 31.8 ± 3.9 years with acute proximal rectus femoris avulsion injuries who underwent a surgical resection of the proximal tendon between March 2012 and June 2014. Four of these players had recurrent rectus femoris injuries in the 9 months before surgery, while 1 player had surgery after a first injury. Mean follow-up was 18.2 ± 12.6 months, and minimum follow-up was 9 months. We analyzed the age, sex distribution, physical examination outcomes, type and mechanism of injury, diagnosis, treatment and complications during surgery, postoperative follow-up, and time to return to play. The Lower Extremity Functional Scale (LEFS) and Marx scores were obtained at 3-month follow-up, and isokinetic tests were performed before return to sports. A telephone interview was completed to determine the presence of recurrence at an average follow-up of 18.2 months. At 3-month follow-up, all patients had Marx activity scores of 16 and LEFS scores of 80. Return to the previous level of play occurred at a mean of 15.8 ± 2.6 weeks after surgery, and none of the athletes suffered a recurrence. Isokinetic test results were comparable between both sides. The surgical treatment of proximal rectus femoris avulsions, consisting of resection of the tendinous part of the muscle, is a reliable and safe technique allowing a fast recovery in professional athletes.

#4 A Comparison of Players' and Coaches' Perceptions of the Coach-Created Motivational Climate within Youth Soccer Teams
Reference: Front Psychol. 2017 Feb 1;8:109. doi: 10.3389/fpsyg.2017.00109. eCollection 2017.
Autors: Mollerlokken NE, Loras H, Pedersen AV
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Summary: The coach-created motivational climate within youth sports teams has been shown to be of great importance for the quality of youths' sports experiences as well as their motivation for continuing or discontinuing sport participation. While the player's perspective on motivational climates has been studied extensively, the coach's perspective has received considerably less attention. Thus, little is known about the concordance of perceptions of the motivational climate between coaches and their players, or the lack thereof. The purpose of the present study was to directly compare players' and coaches' perceptions of the motivational climate within their respective teams. To this end, 256 male and female soccer players (15-17 years of age) from 17 different teams and their coaches (n = 29) responded to the Perceived Motivational Climate in Sports Questionnaire-2 (PMCSQ-2). The study design included responses from both coaches and players to the same questionnaire, and both groups were aware of the other part's participation. Statistical analyses revealed significant differences between players' and coaches' perceptions of the motivational climate. Specifically, players of both sexes perceived the motivational climate to be significantly more performance-oriented and significantly less mastery-oriented compared with the coaches. These findings may advance our understanding of the coach-athlete relationship, and may be of importance for understanding players' motivation for persistence or discontinuation of the sport.

#5 Left ventricular longitudinal strain in soccer referees
Reference: Oncotarget. 2017 Feb 9. doi: 10.18632/oncotarget.15242. [Epub ahead of print]
Authors: Gianturco L, Bodini B, Gianturco V, Lippo G, Solbiati A, Turiel M
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Summary: Along the years, the analysis of soccer referees perfomance has interested the experts and we can find several types of studies in literature using in particular cardiac imaging. The aim of this retrospective study was to observe relationship between VO2max uptake and some conventional and not-conventional echocardiographic parameters. In order to perform this evaluation, we have enrolled 20 referees, belonging to Italian Soccer Referees' Association and we have investigated cardiovascular profile of them. We found a strong direct relationship between VO2max and global longitudinal strain of left ventricle assessed by means of speckle tracking echocardiographic analysis (R2=0.8464). The most common classic echocardiographic indexes have showed mild relations (respectively, VO2max vs EF: R2=0.4444; VO2max vs LV indexed mass: R2=0.2268). Therefore, our study suggests that longitudinal strain could be proposed as a specific echocardiographic parameter to evaluate the soccer referees performance.

#6 Short- or long-rest intervals during repeated-sprint training in soccer?
Reference: PLoS One. 2017 Feb 15;12(2):e0171462. doi: 10.1371/journal.pone.0171462. eCollection 2017
Authors: Iaia FM, Fiorenza M, Larghi L, Alberti G, Millet GP, Girard O
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Summary: The present study compared the effects of two repeated-sprint training (RST) programs, differing in duration of the between-sprint rest intervals, on various soccer-related exercise performances. For 5 weeks during the competitive season, twenty-nine young trained male soccer players either replaced two of their habitual fitness conditioning sessions with RST characterized by short (5-15; n = 9) or long (5-30; n = 10) rest intervals, or served as control (n = 10). The 5-15 and 5-30 protocols consisted of 6 repetitions of 30-m (~5 s) straight-line sprints interspersed with 15 s or 30 s of passive recovery, respectively. 5-15 improved 200-m sprint time (2.0±1.5%; p<0.05) and had a likely positive impact on 20-m sprint performance, whereas 5-30 lowered the 20-m sprint time (2.7±1.6%; p<0.05) but was only possibly effective for enhancing the 200-m sprint performance. The distance covered during the Yo-Yo Intermittent Recovery Test Level 2 increased following 5-15 (11.4±5.0%; p<0.05), which was possibly better than the non-significant 6.5% enhancement observed in 5-30. Improvements in the total time of a repeated-sprint ability test were possibly greater following 5-30 (3.6±0.9%; p<0.05) compared to 5-15 (2.6±1.1%; p<0.05). Both RST interventions led to similar beneficial (p<0.05) reductions in the percentage decrement score (~30%) of the repeated-sprint ability test as well as in blood lactate concentration during submaximal exercise (17-18%). No changes occurred in the control group. In soccer players, RST over a 5-week in-season period is an efficient means to simultaneously develop different components of fitness relevant to match performance, with different benefits induced by shorter compared to longer rest intervals.

#7 Relationship between field tests and match running performance in high-level young brazilian soccer players
Reference: J Sports Med Phys Fitness. 2017 Feb 14. doi: 10.23736/S0022-4707.17.06651-8. [Epub ahead of print]
Authors: Aquino R, Palucci Vieira LH, de Paula Oliveira L, Cruz Goncalves LG, Pereira Santiago PR
Summary: The main aim of this study was to analyse the relationship between field tests and match running performance using computational tracking technology in high-level young Brazilian soccer players. Twenty-five young male Brazilian soccer players participated in this study (U-15, n = 13; U-17, n = 12). In the same week the players were submitted to field tests and actual matches. The field tests were: Maximum Speed (10m-30m), Zig-Zag, Running-based Anaerobic Sprint Test, and Yo-Yo Intermittent Recovery Test level 1. Additionally, participants performed actual soccer match-play. Match running performance was collected using a fixed video-camera. Subsequently, computerized tracking video-analysis (30 Hz) was utilized to identify each physical performance indicator. Pearson's correlation and linear regression were used for statistical analysis. The results showed that the majority of field tests were not related to match running performance. The Zig-Zag Test, Running-based Anaerobic Sprint Test, and Yo-Yo Intermittent Recovery Test level 1 seem to be the most specific tests (r = 0.41-0.47), however the explanatory powers of these field tests in relation to match running performance were low (R2 = 17-22%). Assessment of match running performance should be included in the evaluation periods of young soccer players, together with the most specific tests reported.

#8 Role of vision in sighted and blind soccer players in adapting to an unstable balance task
Reference: Exp Brain Res. 2017 Feb 14. doi: 10.1007/s00221-017-4885-8. [Epub ahead of print]
Authors: Campayo-Piernas M, Caballero C, Barbado D, Reina R
Summary: This study tested whether a compensatory hypothesis exists on postural control during standing unstable balance tasks comparing blind soccer players (n = 7) to sighted soccer players (n = 15) and sighted sedentary individuals (n = 6). All subjects performed a pre-test, a training of ten practice trials on a single day, and a post-test balance test. All tests were performed on an unstable surface placed on a force platform and under closed-eyes conditions, and a final test was performed with open eyes. Balance performance was assessed by resultant distance (RD) and the magnitude of mean velocity (MV) of the centre of pressure (CoP) displacement, and EMG signals from the gastrocnemius lateralis, tibialis anterior, rectus femoris, and peroneus longus were measured with surface electromyography. Principal component analysis (PCA) on EMG muscular activation was used to assess EMG pattern differences during the balance tasks. All groups improved their performance, obtaining low scores for the closed-eyes condition balance task after the training period in RD, VM, and aids received to keep balance in the novel task, and no differences were found between groups or in interaction effects. Sighted individuals and the control group showed significantly lower RD and VM scores under open-eyes conditions than blind participants. As regards neuromuscular behaviour, three principal patterns explained 84.15% of the variability in the measured data. The theoretical improvement of the other senses caused by visual deprivation does not allow blind individuals to obtain better balance than sighted individuals under closed-eyes conditions, thereby reinforcing the prominent role of vision in integrating and processing the other sensory inputs. In addition, blind individuals seem to increase their muscular co-activation as a safety strategy, but this behaviour is not different to that shown by sighted people under closed-eyes conditions.

#9 Neuromuscular Coordination Deficit Persists 12 Months after ACL Reconstruction But Can Be Modulated by 6 Weeks of Kettlebell Training: A Case Study in Women's Elite Soccer
Reference: Case Rep Orthop. 2017;2017:4269575. doi: 10.1155/2017/4269575. Epub 2017 Jan 18.
Authors: Zebis MK, Andersen CH, Bencke J, Orntoft C, Linnebjerg C, Holmich P, Thorborg K, Aagaard P, Andersen LL
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Summary: The aim of the present single-case study was to investigate the effect of 6 weeks' kettlebell training on the neuromuscular risk profile for ACL injury in a high-risk athlete returning to sport after ACL reconstruction. A female elite soccer player (age 21 years) with no previous history of ACL injury went through neuromuscular screening as measured by EMG preactivity of vastus lateralis and semitendinosus during a standardized sidecutting maneuver. Subsequently, the player experienced a noncontact ACL injury. The player was screened again following postreconstruction rehabilitation, then underwent 6-week kettlebell training, and was subsequently screened again at 6-week follow-up. Prior to and after postreconstruction rehabilitation the player demonstrated a neuromuscular profile during sidecutting known to increase the risk for noncontact ACL injury, that is, reduced EMG preactivity for semitendinosus and elevated EMG preactivity for vastus lateralis. Subsequently, the 6-week kettlebell training increased semitendinosus muscle preactivity during sidecutting by 38 percentage points to a level equivalent to a neuromuscular low-risk profile. An ACL rehabilitated female athlete with a high-risk neuromuscular profile changed to low-risk in response to 6 weeks of kettlebell training. Thus, short-term kettlebell exercise with documented high levels of medial hamstring activation was found to transfer into high medial hamstring preactivation during a sidecutting maneuver.

#10 Explosive strength and endurance adaptations in young elite soccer players during two soccer seasons
Reference: PLoS One. 2017 Feb 13;12(2):e0171734. doi: 10.1371/journal.pone.0171734. eCollection 2017.
Authors: Di Giminiani R, Visca C
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Summary: The purpose of the present study was to investigate the explosive strength and endurance adaptations in young elite soccer players who underwent a supervised training program for a period of two years. Nineteen players, with seven years of training experience (age: 13.3 ± 0.1 years; body weight: 57.9 ± 4.9 kg; height: 168.9 ± 4.7 cm; BMI: 20.1 ± 1.1 kg/m2), voluntarily participated in the present study. The testing sessions were performed at the beginning of the preparation period in the first (T1), second (T2), and third year (T3). The following performance variables were measured: explosive strength [squat-jump (SJ) and counter-movement-jump (CMJ)], pre-stretch augmentation (CMJ-SJ), leg stiffness [hopping test (HT)], short sprint performance [15 m (SSP15) and 30 m (SSP30)], aerobic endurance [test of Leger (VO2max)], maximal heart rate [at the last step of Leger (HR)], and speed-strength endurance [continuous counter-movement-jumps (CCMJ)]. A significant main effect on the VO2Max (+5.72%; F(2.49) = 3.822; p = 0.029; ES = 1.00), HR (-1.70%; F(2.54) = 3.472; p = 0.038; ES = 0.97), CCMJ (+7.64%; F(2.54) = 5.438; p = 0.007; ES = 1.15), SJ (+10.26%; F(2.54) = 15.254; p = 0.0001; ES = 1.53), CMJ (+7.36; F(2.54) = 8.270; p = 0.001; ES = 1.33), HT (+8.34%; F(2.48) = 3.297; p = 0.046; ES = 1.01), SSP15 (-3.50%; F(2.44) = 12.760; p = 0.0001; ES = 1.53), and SSP30 (-4.44%; F(2.44) = 5.797; p = 0.006; ES = 1.16) was observed in the two soccer seasons. These results highlight that, in long-term training, the monitoring of the adaptive responses in relation to the training load may provide a guideline to optimize the trainability of some performance variables in young elite soccer players (13-15 years). In the present study, we cannot exclude the influence of growth and maturation on some performance variables; therefore, the monitored adaptive responses should be considered as the possible results of an interaction between the applied training load and maturation.

#11 Higher Drop in Speed during a Repeated Sprint Test in Soccer Players Reporting Former Hamstring Strain Injury
Reference: Front Physiol. 2017 Jan 27;8:25. doi: 10.3389/fphys.2017.00025. eCollection 2017.
Authors: Roksund OD, Kristoffersen M, Bogen BE, Wisnes A, Engeseth MS, Nilsen AK, Iversen VV, Maland S, Gundersen H
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Summary: The aim of the study was to evaluate the physical capacity of players who have and have not suffered from hamstring strain injury in a sample of semi-professional and professional Norwegian soccer players in order to evaluate characteristics and to identify possible indications of insufficient rehabilitation. Seventy-five semi-professional and professional soccer players (19 ± 3 years) playing at the second and third level in the Norwegian league participated in the study. All players answered a questionnaire, including one question about hamstring strain injury (yes/no) during the previous 2 years. They also performed a 40 m maximal sprint test, a repeated sprint test (8 × 20 m), a countermovement jump, a maximal oxygen consumption (VO2max) test, strength tests and flexibility tests. Independent sample t-tests were used to evaluate differences in the physical capacity of the players who had suffered from hamstring strain injury and those who had not. Mixed between-within subject's analyses of variance was used to compare changes in speed during the repeated sprint test between groups. Players who reported hamstring strain injury during the previous two years (16%) had a significantly higher drop in speed (0.07 vs. 0.02 s, p = 0.007) during the repeated sprint test, compared to players reporting no previous hamstring strain injury. In addition, there was a significant interaction (groups × time) (F = 3.22, p = 0.002), showing that speed in the two groups changed differently during the repeated sprint test. There were no significant differences in relations to age, weight, height, body fat, linear speed, countermovement jump height, leg strength, VO2max, or hamstring flexibility between the groups. Soccer players who reported hamstring strain injury during the previous 2 years showed significant higher drop in speed during the repeated sprint test compared to players with no hamstring strain injury. The maximal speed, leg strength, ability to produce maximal power, endurance capacity, and hamstring flexibility was similar for both groups. Thus, a repeated sprint test consisting of 8 × 20 m could be used as a field-based diagnostic tool to identify players in need of reconditioning programs to ensure complete post-injury rehabilitation.

#12 Effect of low dose, short-term creatine supplementation on muscle power output in elite youth soccer players
Reference: J Int Soc Sports Nutr. 2017 Feb 7;14:5. doi: 10.1186/s12970-017-0162-2. eCollection 2017
Authors: Yanez-Silva A, Buzzachera CF, Picarro ID, Januario RS, Ferreira LH, McAnulty SR, Utter AC, Souza-Junior TP
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Summary: The purpose of the study was to determine the effects of a low dose, short-term Creatine monohydrate (Cr) supplementation (0.03 during 14 d) on muscle power output in elite youth soccer players. Using a two-group matched, double blind, placebo-controlled design, nineteen male soccer players (mean age = 17.0 ± 0.5 years) were randomly assigned to either Cr (N = 9) or placebo (N = 10) group. Before and after supplementation, participants performed a 30s Wingate Anaerobic Test (WAnT) to assess peak power output (PPO), mean power output (MPO), fatigue index (FI), and total work. There were significant increases in both PPO and MPO after the Cr supplementation period (P  ≤ 0.05) but not the placebo period. There were also significant increases in total work, but not FI, after the Cr supplementation and placebo periods (P ≤ 0.05). Notably, there were differences in total work between the Cr and placebo groups after (P ≤ 0.05) but not before the 14 d supplementation period. There is substantial evidence to indicate that a low-dose, short-term oral Cr supplementation beneficially affected muscle power output in elite youth soccer players.





Latest research in football - week 7 - 2017

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 light-load maximal lifting velocity weight training vs. combined weight training and plyometrics on sprint, vertical jump and strength performance in adult soccer players
Reference: J Sci Med Sport. 2017 Jan 24. pii: S1440-2440(17)30241-4. doi: 10.1016/j.jsams.2016.11.010. [Epub ahead of print]
Authors: Rodriguez-Rosell D, Torres-Torrelo J, Franco-Marquez F, Gonzalez-Suarez JM, Gonzalez-Badillo JJ
Summary: The purpose of this study was to compare the effects of combined light-load maximal lifting velocity weight training (WT) and plyometric training (PT) with WT alone on strength, jump and sprint performance in semiprofessional soccer players. Thirty adult soccer players were randomly assigned into three groups: WT alone (FSG, n=10), WT combined to jump and sprint exercises (COM, n=10) and control group (CG, n=10). WT consisted of full squat with low load (∼45-60% 1RM) and low volume (4-6 repetitions). Training program was performed twice a week for 6 weeks of competitive season in addition to 4 soccer sessions a week. Sprint time in 10 and 20m, jump height (CMJ), estimated one-repetition maximum (1RMest) and velocity developed against different absolute loads in full squat were measured before and after training period. Both experimental groups showed significant improvements in 1RMest (17.4-13.4%; p<0.001), CMJ (7.1-5.2%; p<0.001), sprint time (3.6-0.7%; p<0.05-0.001) and force-velocity relationships (16.9-6.1%; p<0.05-0.001), whereas no significant gains were found in CG. No significant differences were found between FSG and COM. Despite FSG resulted of greater increases in strength variables than COM, this may not translate into superior improvements in the sport-related performance. In fact, COM showed higher efficacy of transfer of strength gains to sprint ability. Therefore, these findings suggest that a combined WT and PT program could represent a more efficient method for improving activities which involve acceleration, deceleration and jumps compared to WT alone.

#2 Between-Session Reliability Of Isometric Mid-Thigh Pull Kinetics And Maximal Power Clean Performance In Male Youth Soccer Players
Reference: J Strength Cond Res. 2017 Feb 1. doi: 10.1519/JSC.0000000000001830. [Epub ahead of print]
Authors: Dos'Santos T, Thomas C, Comfort P, McMahon JJ, Jones PA, Oakley NP, Young AL
Summary: The aim of the study was to determine the between-session reliability of isometric mid-thigh pull (IMTP) kinetics and maximal weight lifted during the power clean (PC) in male youth soccer players, and to identify the smallest detectable differences between sessions. Thirteen male youth soccer players (age: 16.7 ± 0.5 years, height: 1.80 ± 0.08 m, mass: 70.5 ± 9.4 kg) performed three IMTP trials, while only ten soccer players performed maximal power cleans. These were performed twice, separated by 48 hours to examine the between-session reliability. Intraclass correlation coefficients (ICC) and coefficient of variation (CV) demonstrated high levels of within-session (ICC = 0.84-0.98, CV = 4.05-10.00%) and between-session reliability (ICC = 0.86-0.96, CV = 3.76-7.87%) for IMTP kinetics (peak force and time-specific force values 30-250 ms) and maximal PC (ICC = 0.96, CV = 3.23%), all meeting minimum acceptable reliability criteria. No significant differences (p>0.05, effect size ≤0.22) were revealed between sessions for IMTP kinetics and maximal PC performance. Strength and conditioning coaches and practitioners should consider changes of >6.04% in maximal PC and changes in IMTP kinetics of >14.31% in force at 30 ms, > 14.73% in force at 50 ms, >12.36% in force at 90 ms, >12.37% in force at 100 ms, >14.51% in force at 150 ms, >11.71% in force at 200 ms, >7.23% in force at 250 ms and >8.50% in absolute peak force as meaningful improvements in male youth soccer players. Decrements in the IMTP kinetics greater than aforementioned values could possibly be used as an indicator of neuromuscular fatigue and preparedness for training or competition.

#3 Coach-led preventive training program in youth soccer players improves movement technique
Reference: J Sci Med Sport. 2017 Jan 24. pii: S1440-2440(17)30265-7. doi: 10.1016/j.jsams.2017.01.235. [Epub ahead of print]
Authors: Pryor JL, Root HJ, Vandermark LW, Pryor RR, Martinez JC, Trojian TH, Denegar CR, DiStefano LJ
Summary: Long-term implementation of preventive training programs (PTP) in youth sport requires coach involvement. However, the optimal training of coaches to effectively implement a PTP remains unknown. It is also unknown if the benefits of PTP can be enhanced with multiple sport seasons of exposure. The objective of the study was to evaluate the influence of prior PTP exposure on movement technique in youth soccer players after completing a coach-led PTP. Twelve youth soccer teams (n=89; age range 8-14 years) were divided into groups with (Experience (EXP); 6 teams [n=18 females, n=25 males]) and without (Novice (NOV); 6 teams [n=30 females, n=16 males]) previous professional-led PTP experience. The coaches and players of the EXP teams were exposed to an eight-week professional-led PTP before the coach-led PTP. EXP and NOV coaches attended the educational workshop prior to implementing the coach-led PTP. The Landing Error Scoring System (LESS) was used to evaluate movement technique. Both groups improved LESS scores over time (mean difference±SD [post-pre]=-0.8±0.2, 95%CI [-1.2, -0.4], p=0.0001). Of the 64 participants classified as high risk for injury (LESS ≥5) prior to PTP implementation, a greater proportion of EXP (n=14) compared to NOV (n=7) participants changed risk classification from high to low (LESSΔ≥1 and LESS <5; p=0.03). Our PTP enhanced movement technique regardless of PTP experience, but the benefits of the PTP impacted a proportionally greater number of players with previous PTP experience supporting continued PTP implementation. Coaches effectively implemented an exercise-based PTP after attending a training workshop regardless of previous PTP experience.

#4 Injury mechanism of midfacial fractures in football causes in over 40% typical neurological symptoms of minor brain injuries
Reference: Knee Surg Sports Traumatol Arthrosc. 2017 Feb 8. doi: 10.1007/s00167-017-4431-z. [Epub ahead of print]
Authors: Krutsch V, Gesslein M, Loose O, Weber J, Nerlich M, Gaensslen A, Bonkowsky V, Krutsch W
Summary: The injury mechanisms of midfacial fractures may be typical causes of concussion, but hardly any scientific data on midfacial injuries sustained in football are available. Head and brain trauma represent frequent injuries in athletes of different sports that require appropriate treatment by sports and trauma physicians. This study investigated the management of midfacial fractures in football and the association of such fractures with concomitant brain injury. In a prospective cohort study lasting 24 months (2012 to 2013), midfacial injuries of football players were analysed with regard to the injury mechanisms, first aid procedures on the field, treatment and return-to-play. To analyse concomitant and potentially overlooked minor brain injuries due to the trauma, we retrospectively investigated the neurological symptoms of the study population. The study included 132 football players (37 semi-professionals and 95 amateurs) with midfacial fractures. The main injury mechanisms were head-to-head and head-to-elbow trauma. The mean period of return-to-play after trauma was 33.5 days, which was significantly shortened if a protective face mask was worn (mean 10.4 days earlier, p = 0.0006). Semi-professional football players returned to play earlier (p = 0.009) and more often used protective face masks (p = 0.001). 55 players (41.6%) had neurological symptoms immediately after trauma as a possible sign of concomitant minor brain injury. 5 of 132 players with concussion had been hospitalised for 24 h, but no persistent neurological symptoms were detected. In football, midfacial fractures represent moderate-to-severe injuries with time away from sports of more than 4 weeks. Over 40% of athletes with a midfacial fracture showed concomitant neurological symptoms as a sign of minor brain injury. Therefore, sports physicians and other staff supervising athletes in daily practice should be aware of the presence of neurological symptoms.

#5 Visual search behaviors of association football referees during assessment of foul play situations
Reference: Cogn Res Princ Implic. 2016;1(1):12. doi: 10.1186/s41235-016-0013-8. Epub 2016 Oct 31
Authors: Spitz J, Put K, Wagemans J, Williams AM, Helsen WF
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Summary: It is well reported that expert athletes have refined perceptual-cognitive skills and fixate on more informative areas during representative tasks. These perceptual-cognitive skills are also crucial to performance within the domain of sports officials. We examined the visual scan patterns of elite and sub-elite association football referees while assessing foul play situations. These foul play situations (open play and corner kick situations) were presented on a Tobii T120 Eye Tracking monitor. The elite referees made more accurate decisions and differences in their visual search behaviors were observed. For the open play situations, referees in the elite group spent significantly more time fixating the most informative area of the attacking player (contact zone) and less time fixating the body part that was not involved in the infringement (non-contact zone). Furthermore, the average total fixation time in the contact zone and non-contact zone tended to differ between the elite and sub-elite referees in corner kick situations. In conclusion, elite level referees have learned to discern relevant from less-relevant information in the same way as expert athletes. Findings have implications for the development of perceptual training programs for sport officials.

#6 The acceleration and deceleration profiles of elite female soccer players during competitive matches
Reference: J Sci Med Sport. 2017 Jan 24. pii: S1440-2440(17)30268-2. doi: 10.1016/j.jsams.2016.12.078. [Epub ahead of print]
Authors: Mara JK, Thompson KG, Pumpa KL, Morgan S
Summary: The aim of this study was to determine the acceleration (≥2ms-2) and deceleration (≤-2ms-2) profiles of elite female soccer players during competitive matches. An Optical Player Tracking system was used to determine acceleration (≥2ms-2) and deceleration (≤-2ms-2) variables for twelve elite female players across seven competitive matches. In total, players performed 423 (±126) accelerations and 430 (±125) decelerations per match. It was shown that the number of accelerations (p=0.003-0.034, partial η2=0.229-321) and decelerations (p=0.012-0.031, partial η2=0.233-275) at different intensities (based on the start and final velocity) varied according to player position. Mean and maximum distance per effort was 1-4m and 2-8m, respectively, and differed between each intensity category (p<0.001, partial η2=0.753-0.908). The mean time between efforts was 14s for both accelerations (±5s) and decelerations (±4s) and fluctuated between 15min time periods (p<0.001, partial η2=0.148-0.206). The acceleration and deceleration profiles varied according to player position and time period of the match. The results of this study can be used to design match-specific acceleration and deceleration drills to enhance change of speed ability.

#7 The influence of genetic polymorphisms on performance, cardiac and hemodynamic parameters among Brazilian soccer players
Reference: Appl Physiol Nutr Metab. 2017 Jan 24. doi: 10.1139/apnm-2016-0608. [Epub ahead of print]
Authors: Dionisio TJ, Thiengo CR, Brozoski DT, Dionisio EJ, Talamoni GA, Silva RB, Garlet GP, Santos CF, Amaral SL
Summary: This study investigated whether ACTN3 R577X, AMPD1 C34T, I/D ACE and M235T AGT polymorphisms can affect performance tests such as jumping, sprinting and endurance in 220 young male athletes from professional minor league soccer team from São Paulo Futebol Clube, Brazil. I/D ACE and M235T AGT polymorphisms were also analyzed according to cardiac and hemodynamic parameters. Athletes were grouped or not by age. DNA from saliva and Taqman® assays were used for genotyping 220 athletes and the results were associated with performance tests. Ventricle mass, ventricle end-diastolic diameter, end diastolic volume and ejection fraction were assessed by echocardiogram. Arterial pressure, heart rate and oximetry were assessed by a cardioscope. The main results of this study were that athletes who carried RR/RX (ACTN3) and DD (ACE) genotypes presented better performance during jump and sprint tests. On the other hand, athletes with ID/II genotype presented better results during endurance test, while AGT genotypes did not seem to favor the athletes during the evaluated physical tests. CC genotype (AMPD1) only favored the athletes during 10-m sprint test. Although there are environmental interactions influencing performance, the present results suggest that RR/RX ACTN3 and ACE DD genotypes may benefit athletes in activities that require strength and speed, while II ACE genotype may benefit athletes in endurance activities. This information could help coaches to plan the training session in order to improve the athletes' performance.

#8 Free-sugar, total-sugar, fibre and micronutrient intake within elite youth British soccer players: a nutritional transition from schoolboy to fulltime soccer player
Reference: Appl Physiol Nutr Metab. 2017 Jan 10. doi: 10.1139/apnm-2016-0459. [Epub ahead of print]
Authors: Naughton RJ, Drust B, O'Boyle A, Abayomi J, Mahon E, Morton JP, Davies IG
Summary: It is recommended that soccer players consume a high carbohydrate (CHO) diet to augment performance. However, growing evidence suggests that there is a link between high free-sugar (FS) intake (>5% total energy intake; TEI) and metabolic diseases. Furthermore, foods that are often high in sugar, such as processed foods, are typically lacking in nutrient quality. We therefore analysed total- and FS, dietary fibre and micronutrient intake of players from an English Premier League academy under(U) 18 (n=13); U15/16 (n=25); U13/14 (n=21) using a 7-day food diary. Data was compared to current UK dietary reference value (DRV) for free-sugar via a t-test. The U13/14s (1018 %) and U15/16s (1130 %) both consumed higher amounts of free-sugar in comparison to the UK DRV of 5% TEI 5% (P<0.01), conversely, the U18s did not exceed the DRV (513 %). Furthermore, FS intake of the U18s was significantly lower than the U13/14s and U15/16s (P<0.01). Dietary fibre was below the DRV (25g/d for U13/14 & U15/16s; 30g/d for U18s) for all squads (19.04.7; 19.68.3; 17.14.2 g/d, respectively), but not different between squads. Additionally, micronutrient reference intakes were generally met. In conclusion, we provide novel data on dietary sugar, fibre and micronutrient intake within elite youth soccer players. We report an apparent 'nutritional transition' from schoolboy to fulltime soccer player, with U18s showing a significantly lower intake of sugar in comparison to younger squads, and a similar intake of FS to the UK DRVs. Practitioners should target improving player education around sugar and fibre consumption.

#9 Core executive functions are associated with success in young elite soccer players
Reference: PLoS One. 2017 Feb 8;12(2):e0170845. doi: 10.1371/journal.pone.0170845. eCollection 2017.
Authors: Vestberg T, Reinebo G, Maurex L, Ingvar M, Petrovic P
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Summary: Physical capacity and coordination cannot alone predict success in team sports such as soccer. Instead, more focus has been directed towards the importance of cognitive abilities, and it has been suggested that executive functions (EF) are fundamentally important for success in soccer. However, executive functions are going through a steep development from adolescence to adulthood. Moreover, more complex EF involving manipulation of information (higher level EF) develop later than simple executive functions such as those linked to simple working memory capacity (Core EF). The link between EF and success in young soccer players is therefore not obvious. In the present study we investigated whether EF are associated with success in soccer in young elite soccer players. We performed tests measuring core EF (a demanding working memory task involving a variable n-back task; dWM) and higher level EF (Design Fluency test; DF). Color-Word Interference Test and Trail Making Test were performed on an exploratory level as they contain a linguistic element. The lower level EF test (dWM) was taken from CogStateSport computerized concussion testing and the higher level EF test (DF) was from Delis-Kaplan Executive Function System test battery (D-KEFS). In a group of young elite soccer players (n = 30; aged 12-19 years) we show that they perform better than the norm in both the dWM (+0.49 SD) and DF (+0.86 SD). Moreover, we could show that both dWM and DF correlate with the number of goals the players perform during the season. The effect was more prominent for dWM (r = 0.437) than for DF (r = 0.349), but strongest for a combined measurement (r = 0.550). The effect was still present when we controlled for intelligence, length and age in a partial correlation analysis. Thus, our study suggests that both core and higher level EF may predict success in soccer also in young players.

#10 Commentary: "How Much is that Player in the Window? The One with the Early Birthday?" Relative Age Influences the Value of the Best Soccer Players, but Not the Best Businesspeople
Reference: Front Psychol. 2017 Jan 25;8:58. doi: 10.3389/fpsyg.2017.00058. eCollection 2017.
Authors: Fumarco L, Gibbs BG
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#11 The Effect of Plyometric Training Volume in Prepubertal Male Soccer Players' Athletic Performance
Reference: Int J Sports Physiol Perform. 2017 Feb 9:1-22. doi: 10.1123/ijspp.2016-0372. [Epub ahead of print]
Authors: Chaabene H, Negra Y
Summary: The aim of this study was to assess and to compare the effects of 8-weeks in-season (2 sessions per-week) low and high-volume plyometric training (PT) on measures of physical fitness in prepubertal male soccer players. A total of twenty-five soccer players were randomly assigned to low-volume plyometric training group (LPT; n=13; age = 12.68 ± 0.23 years; age at peak height velocity (APHV) = 14.25 ± 0.29 years, maturity-offset = -1.57 ± 0.29 years) and high-volume plyometric training group (HPT; n=12; age = 12.72 ± 0.27 years; APHV = 14.33 ± 0.77 years, maturity-offset = -1.61 ± 0.76 years). Linear sprint test (5-m, 10-m, 20-m, and 30-m), change of direction test (T-test), vertical (squat-jump [SJ] and counter-movement-jump [CMJ]), and horizontal (standing-long-jump [SLJ]) jump ability were carried out pre and post 8-weeks of PT. A significant main effect of time for sprint outcomes (5-m: p=0.005, ES=0.86; 10-m: p=0.006, ES=0.85; 20-m: p=0.03, ES=0.64, and 30-m: p=0.05, ES=0.57), change of direction (p = 0.002, ES=0.96), vertical (SJ: p=0.008, ES= 0.81); CMJ: p=0.01, ES= 0.73), and horizontal jump ability (SLJ: p = 0.007, ES = 0.83). There were no significant training group × time interactions in all the measured outcomes. Following 8-weeks of training, results showed similar performance improvement on measures of sprint time, change of direction, and jumping ability between LPT and HPT groups. From a time efficiency perspective, it is recommended to use LPT in prepubertal male soccer players so as to improve their proxies of athletic performance.





Latest research in football - week 6 - 2017

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 Mechanisms and situations of anterior cruciate ligament injuries in professional male soccer players: a YouTube-based video analysis
Reference: Eur J Orthop Surg Traumatol. 2017 Jan 25. doi: 10.1007/s00590-017-1905-0. [Epub ahead of print]
Authors: Grassi A, Smiley SP, Roberti di Sarsina T, Signorelli C, Marcheggiani Muccioli GM, Bondi A, Romagnoli M, Agostini A, Zaffagnini S
Summary: Soccer is considered the most popular sport in the world concerning both audience and athlete participation, and the incidence of ACL injury in this sport is high. The understanding of injury situations and mechanisms could be useful as substratum for preventive actions. The purpose was to conduct a video analysis evaluating the situations and mechanisms of ACL injury in a homogeneous population of professional male soccer players, through a search entirely performed on the Web site focusing on the most recent years. A video analysis was conducted obtaining videos of ACL injury in professional male soccer players from the Web site YouTube. Details regarding injured players, events and situations were obtained. The mechanism of injury was defined on the basis of the action, duel type, contact or non-contact injury, and on the hip, knee and foot position. Thirty-four videos were analyzed, mostly from the 2014-2015 season. Injuries occurred mostly in the first 9 min of the match (26%), in the penalty area (32%) or near the side-lines (44%), and in non-rainy conditions (97%). Non-contact injuries occurred in 44% of cases, while indirect injuries occurred in 65%, mostly during pressing, dribbling or tackling. The most recurrent mechanism was with an abducted and flexed hip, with knee at first degrees of flexion and under valgus stress. Through a YouTube-based video analysis, it was possible to delineate recurrent temporal, spatial and mechanical characteristics of ACL injury in male professional soccer players.

#2 Timing Effect on Training Session Rating of Perceived Exertion in Top-Class Soccer Referees
Reference: Int J Sports Physiol Perform. 2017 Jan 25:1-18. doi: 10.1123/ijspp.2016-0626. [Epub ahead of print]
Authors: Castagna C, Bizzini M, Povoas SC, D'Ottavio S
Summary: The purpose was to examine the effect of recall timing on training session rating of perceived exertion (S-RPE) in a population of method procedures well-familiarized athletes, during a 5-days training micro-cycle. Fifty-one top class Field Referees (FR, age 38.4±3.3 years; height 181±5.6 cm; body mass 76.8±6.8 kg; body max index, 23.4±1.7 kg·m2; body fat 20.4±3.6%; international refereeing experience 5±3.5 years) from 43 National Football Associations worldwide, preselected by FIFA Refereeing Department for officiating during the FIFA WC 2014 Brazil volunteered for this study. The FR were randomly allocated into three assessment groups (n=17 each), defined according to the timing of the S-RPE, i.e., immediately at the end, 30 min or 7 hours after the training sessions' ending (G0min, G30min and G7h, respectively). The CR10 Börg scale was used to rate the training sessions (n=5). All FR rated again each training session of the 5-days training micro-cycle in the consecutive morning (~20h after) for confirmation (absolute and relative reliability). No significant timing effect was found between and within groups. Relative reliability ranged from large to very large with trivial within and between groups differences. This study showed no effect of recall timing on post-exercise RPE when well familiarized athletes are submitted to training during a weekly micro-cycle. Post-training RPE was reported to be a reliable subjective measure, however, specific timing is advisable to reduce magnitude difference in RPE values.

#3 Analysis of physical fitness and technical skills of youth soccer players according to playing position
Reference: J Exerc Rehabil. 2016 Dec 31;12(6):548-552. doi: 10.12965/jer.1632730.365. eCollection 2016.
Authors: Joo CH, Seo DI
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Summary: The purpose of this study was to compare performance factors of youth soccer players according to position. A total of 101 high school soccer players were selected and were classified into goalkeeper (n=7), defense (n=37), midfield (n=39), and forward (n=18) positions. All subjects were subjected to the Wingate test for anaerobic capacity, shuttle run test for aerobic capacity, and pass, kick, dribble, and shooting tests for soccer skills. There was no significant difference in aerobic capacity according to position. However, anaerobic capacity was significantly higher in defenders than midfielders (P<0.05), and soccer skills were significant lower in goalies than in other positions (P<0.01). The results show significant differences in anaerobic capacity and soccer skills according to position in youth soccer players. Therefore, we suggest that middle and high school soccer players should improve aerobic, an-aerobic capacity, and soccer skills irrespective position to achieve high-level soccer performance.

#4 Director's Cut: Analysis and Annotation of Soccer Matches
Reference: IEEE Comput Graph Appl. 2016 Sep-Oct;36(5):50-60. doi: 10.1109/MCG.2016.102.
Authors: Stein M, Janetzko H, Breitkreutz T, Seebacher D, Schreck T, Grossniklaus M, Couzin ID, Keim DA.
Summary: For development and alignment of tactics and strategies, professional soccer analysts spend up to three working days manually analyzing and annotating professional soccer matches. In an effort to improve soccer player and match analysis, a visual-interactive and data-analysis support system focuses on key situations by using rule-based filtering and automatically annotating key types of soccer match elements. The authors evaluate the proposed approach by analyzing real-world soccer matches and several expert studies. Quantitative measures show the proposed methods can significantly outperform naive solutions.

#5 Combination of Recreational Soccer and Caloric Restricted Diet Reduces Markers of Protein Catabolism and Cardiovascular Risk in Patients with Type 2 Diabetes
Reference: J Nutr Health Aging. 2017;21(2):180-186. doi: 10.1007/s12603-015-0708-4.
Authors: Vieira de Sousa M, Fukui R, Krustrup P, Dagogo-Jack S, Rossi da Silva ME
Summary: Moderate calorie-restricted diets and exercise training prevent loss of lean mass and cardiovascular risk. Because adherence to routine exercise recommendation is generally poor, we utilized recreational soccer training as a novel therapeutic exercise intervention in type 2 diabetes (T2D) patients. The objective of the study was to compare the effects of acute and chronic soccer training plus calorie-restricted diet on protein catabolism and cardiovascular risk markers in T2D. Fifty-one T2D patients (61.1±6.4 years, 29 females: 22 males) were randomly allocated to the soccer+diet-group (SDG) or to the diet-group (DG). The 40-min soccer sessions were held 3 times per week for 12 weeks. Nineteen participants attended 100% of scheduled soccer sessions, and none suffered any injuries. The SDG group showed higher levels of growth hormone (GH), free fatty acids and ammonia compared with DG. After 12 weeks, insulin-like growth factor binding protein (IGFPB)-3 and glucose levels were lower in SDG, whereas insulin-like growth factor (IGF)-1/ IGFBP-3 ratio increased in both groups. After the last training session, an increase in IGF-1/IGFBP-3 and attenuation in ammonia levels were suggestive of lower muscle protein catabolism. Recreational soccer training was popular and safe, and was associated with decreased plasma glucose and IGFBP-3 levels, decreased ammoniagenesis, and increased lipolytic activity and IGF-1/IGFBP-3 ratio, all indicative of attenuated catabolism.

#6 The Athletic Shoe in Football
Reference: Sports Health. 2017 Feb 1:1941738117690717. doi: 10.1177/1941738117690717. [Epub ahead of print]
Authors: Jastifer J, Kent R, Crandall J, Sherwood C, Lessley D, McCullough KA, Coughlin MJ, Anderson RB
Summary: Foot and ankle injuries are common in sports, particularly in cleated athletes. Traditionally, the athletic shoe has not been regarded as a piece of protective equipment but rather as a part of the uniform, with a primary focus on performance and subjective feedback measures of comfort. Changes in turf and shoe design have poorly understood implications on the health and safety of players. A literature search of the MEDLINE and PubMed databases was conducted. Keywords included athletic shoewear, cleated shoe, football shoes, and shoewear, and search parameters were between the years 2000 and 2016. The athletic shoe is an important piece of protective sports equipment. There are several important structural considerations of shoe design, including biomechanical compliance, cleat and turf interaction, and shoe sizing/fit, that affect the way an athlete engages with the playing surface and carry important potential implications regarding player safety if not understood and addressed. Athletic footwear should be considered an integral piece of protective equipment rather than simply an extension of the uniform apparel. More research is needed to define optimal shoe sizing, the effect that design has on mechanical load, and how cleat properties, including pattern and structure, interact with the variety of playing surfaces.

#7 No association between static and dynamic postural control and ACL injury risk among female elite handball and football players: a prospective study of 838 players
Reference: Br J Sports Med. 2017 Feb;51(4):253-259. doi: 10.1136/bjsports-2016-097068
Authors: Steffen K, Nilstad A, Krosshaug T, Pasanen K, Killingmo A, Bahr R
Summary: Research on balance measures as potential risk factors for ACL injury is limited. The objective was to assess whether postural control was associated with an increased risk for ACL injuries in female elite handball and football players. Premier league players were tested in the preseason and followed prospectively for ACL injury risk from 2007 through 2015. At baseline, we recorded player demographics, playing experience, ACL and ankle injury history. We measured centre of pressure velocity in single-leg stabilisation tests and reach distances in the Star Excursion Balance Test. To examine the stability of postural control measures over time, we examined their short-term and long-term reproducibility. We generated logistic regression models, 1 for each of the proposed risk factors. A total of 55 (6.6%) out of 838 players (age 21±4 years; height 170±6 cm; body mass 66±8 kg) sustained a non-contact ACL injury after baseline testing (1.8±1.8 years). When comparing normalised balance measures between injured and uninjured players in univariate analyses, none of the variables were statistically associated with ACL injury risk. Short-term and long-term reproducibility of the selected variables was poor. Players with a previous ACL injury had a 3-fold higher risk of sustaining a new ACL injury compared with previously uninjured players (OR 2.9, CI 1.4 to 5.7). None of postural control measures examined were associated with increased ACL injury risk among female elite handball and football players. Hence, as measured in the current investigation, the variables included cannot be used to predict ACL injury risk.

#8 Exploring Team Passing Networks and Player Movement Dynamics in Youth Association Football
Reference: PLoS One. 2017 Jan 31;12(1):e0171156. doi: 10.1371/journal.pone.0171156. eCollection 2017
Authors: Goncalves B, Coutinho D, Santos S, Lago-Penas C, Jimenez S, Sampaio J
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Summary: Understanding how youth football players base their game interactions may constitute a solid criterion for fine-tuning the training process and, ultimately, to achieve better individual and team performances during competition. The present study aims to explore how passing networks and positioning variables can be linked to the match outcome in youth elite association football. The participants included 44 male elite players from under-15 and under-17 age groups. A passing network approach within positioning-derived variables was computed to identify the contributions of individual players for the overall team behaviour outcome during a simulated match. Results suggested that lower team passing dependency for a given player (expressed by lower betweenness network centrality scores) and high intra-team well-connected passing relations (expressed by higher closeness network centrality scores) were related to better outcomes. The correlation between the dyads' positioning regularity and the passing density showed a most likely higher correlation in under-15 (moderate effect), indicating a possible more dependence of the ball position rather than in the under-17 teams (small/unclear effects). Overall, this study emphasizes the potential of coupling notational analyses with spatial-temporal relations to produce a more functional and holistic understanding of teams' sports performance.

#9 Assessment of P wave duration and P wave dispersion in high level football referees
Reference: J Sports Med Phys Fitness. 2017 Jan-Feb;57(1-2):162. doi: 10.23736/S0022-4707.16.05983-1
Authors: Yucesir I, Sahin Yildiz B, Coskun O, Yakal S, Bayraktar B, Metin G, Altan M, Yildiz M

#10 Short versus long small-sided game training during Ramadan in soccer players
Reference: Phys Ther Sport. 2016 Oct 24;24:20-25. doi: 10.1016/j.ptsp.2016.10.002. [Epub ahead of print]
Authors: Baklouti H, Rejeb N, Aloui A, Jaafar H, Ammar A, Chtourou H, Girard O, Souissi N
Summary: The purpose was to compare the effects of two small-sided game (SSG) training formats (4 × 4 min (SSG-S) and 2 × 8 min (SSG-L)) conducted during Ramadan on Hoff and five-jump (5JT) tests' performances and session rating of perceived exertion. Twenty-four male soccer players were divided into 3 groups: 2 groups undertaking 4 weeks of SSG-S (n = 8) or SSG-L (n = 8) during Ramadan and a control group (n = 8) participated in this studz. The Profile of Mood States (POMS) and Hooper questionnaires' scores and 5JT and Hoff test's performances were measured before (BR) and at the end of Ramadan (R4). Compared to BR, fatigue estimated by POMS and Hooper questionnaires was higher at R4 in all groups (ES = 0.77-1.57, p < 0.05). Hoff test distance increased to the same extent in SSG-S and SSG-L groups (+7.38-7.39%, ES = 1.49-1.93, p < 0.001). Mean sRPE scores measured during Ramadan were higher after SSG-L (6.49 ± 0.38) than SSG-S (5.61 ± 0.14) sessions (+15.58%, ES = 2.79, p < 0.001). SSG training can be implemented as an efficient intervention to avoid detraining and equally improve soccer-specific physical performance during Ramadan. Given the lower perceptual responses associated with shorter SSG sequences, this modality would be better tolerated during the fasting month, and therefore is recommended.





Al-Kass U17 Tournament Pre-match Warm-ups

The 6th edition of the annual Al-Kass U17 international tournament was held in Doha in January.

My former colleague Ioannis Grammos was able to visit some games and kind to record some warm-up procedures of PSG and the Aspire Academy.



Aspire Academy





Latest research in football - week 5 - 2017

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 among Repeated Sprint Ability, Chronological Age and Puberty in young soccer players
Reference: J Strength Cond Res. 2016 Jan 19. doi: 10.1519/JSC.0000000000001799. [Epub ahead of print]
Authors: Perroni F, Pintus A, Frandino M, Guidetti L, Baldari C
Summary: The aim of this study was to analyzed the relationship of Repeated Sprinting Ability (RSA) with chronological age and puberty in 100 young soccer players (Age: 13 ± 3 yr - 160 ± 33 month-; High: 159 ± 16 cm, Weight: 49.7 ± 14.1 kg; BMI 19.2 ± 2.5 kg/m) grouped on "Pulcini" (9 - 10 yrs), "Esordienti" (11 - 12 yrs), "Giovanissimi" (13 - 14 yrs), "Allievi" (15 - 16 yrs) and "Juniores" (> 17 yrs) categories. Anthropometric (Weight, Height, BMI), RSA (7x30 m sprint with 25s active rest: Total Time -TT, the lowest sprinting time (LST) and the fatigue index percentage -%IF), and Development (Self-Administered Rating Scale for pubertal development - PDS; Puberty) parameters were measured. ANOVA among categories was applied to asses differences (p<0.05) in TT and %IF. When a significant effect was found, Bonferroni's post hoc analysis was used. Pearson correlation among all variables was calculated considering all subjects and also within categories. Among categories, statistical analysis showed a significant differences (p< 0.001) in TT and a considerable trend toward significance (p=0.06) in %IF. Significant correlations among variables was found in all subjects and within categories. In particular, TT showed large significant correlation with PDS (r=-0.66) and Puberty (r=-0.67) only in "Esordienti". This study provides useful information for the coach in order to porpose an appropriate training and to obtain the optimal training effect and to minimise the risk of injury and overtraining during the different phases of growth and maturation.

#2 Heart rate variability discriminates competitive levels in professional soccer players
Reference: J Strength Cond Res. 2017 Jan 20. doi: 10.1519/JSC.0000000000001795. [Epub ahead of print]
Authors: Proietti R, di Fronso S, Lucas AP, Bortoli L, Robazza C, Fabio YN, Bertollo M
Summary: Heart rate variability (HRV) has been increasingly used to monitor team sports athletes. Besides the traditional time domain indices (i.e., the standard deviation of successive RR intervals [SDNN] and the root mean square difference of successive normal RR intervals [RMSSD]), recently it has been proposed the use of the stress score (SS), which is an inverse function of the standard deviation 2 index derived from the Poincaré plot, and the sympathetic/parasympathetic ratio (S/PS) to monitor soccer players. However, the reliability of these new indices and the ability of HRV to differentiate between soccer competitive levels are unknown. The aim of this study was to analyze the reliability of the different HRV-derived indices in professional soccer players during the competitive period and to compare HRV of professional soccer players from three teams of distinct competitive levels (i.e., Italian Second Division [2D], European League [EL] and Champions League [CL]). Fifty-four male professional soccer players from three different teams of two European countries (Italy and Germany) participated in the study. The intraclass correlation coefficient (ICC) values of the HRV indices varied from 0.78 (very large) to 0.90 (near perfect). The coefficient of variation (CV) values for RMSSD and SDNN were all <5.00%, while the CV for SS was 6.13% and for S/PS 21.33%. Both the CL and EL groups, assumed to be internationally qualified, presented higher lnRMSSD and lnSDNN and lower lnSS and S/PS than the 2D. Therefore, the HRV can be considered reliable in professional soccer players and able to differentiate between international and national level players.

#3 Effects of knowing the task duration on players' pacing patterns during soccer small-sided games
Reference: J Sports Sci. 2017 Jan 30:1-7. doi: 10.1080/24733938.2017.1283433. [Epub ahead of print]
Authors: Ferraz R, Gonçalves B, Van Den Tillaar R, Jiménez Saiz S, Sampaio J, Cardoso Marques M
Summary: The aim of this study was to identify the influence of prior knowledge of exercise duration on players' pacing patterns during soccer small-sided games. Twenty semi-professional male soccer players participated in this study. In the first game scenario, players were not informed how long they would be required to play the small-sided game and the activity was terminated after 20 min (Unknown Condition). In the second game scenario, players were told that they would play the small-sided game for 10 min, but immediately after completing the 10-min game, they were asked to complete another 10 min (Partially Condition). In the third game scenario, players were instructed that they would play the small-sided game for 20 min and then they completed the 20-min game (Known Condition). The results presented a tendency of higher values in all performance variables in the [0'-10'] min compared with the [10'-20'] min. As the players' previous knowledge about the tasks duration increased, the performance between two moments tended to be similar. Considering the entire 20-min game duration, the Partially Condition of the exercise was the most demanding condition. In conclusion, the knowledge of shorter durations of the exercise seems to lead to an increase of exercise duration demand, and longer exercise durations possibly tend to decrease differences between full knowledge and not knowing the exercise duration.

#4 Broad-spectrum health improvements with one year of soccer training in inactive mildly hypertensive middle-aged women
Reference: Scand J Med Sci Sports. 2017 Jan 25. doi: 10.1111/sms.12829. [Epub ahead of print]
Authors: Krustrup P, Skoradal MB, Randers MB, Weihe P, Uth J, Mortensen J, Mohr M
Summary: The study tested the hypothesis that long-term soccer training has positive impact on cardiovascular profile, body composition, bone health, and physical capacity in inactive, pre-menopausal women with mild hypertension. The study applied a randomized controlled design in which physically inactive middle-aged women were separated into a soccer training group (n=19; SOC) and a control group (n=12; CON). SOC performed 128±29 (±SD) one-h small-sided soccer training sessions over one year. Blood pressure, body composition, blood lipid profile, and fitness level were determined pre- and post-intervention. Over one year, mean arterial pressure decreased more in SOC than in CON (-5±7 vs +4±5 mmHg; P<.05). Total-body fat mass decreased more (P<.05) in SOC than in CON (-2.5±2.5 vs +0.6±3.2 kg; P<.05), while the change scores for lean body mass were not significantly different in SOC (2.6±2.7 kg) compared to CON (1.1±1.9 kg, P=.09). Over one year, change scores in whole-body bone mineral density (0.004±0.032 vs -0.019±0.026 g·cm2 ) as well as bone mineral content (30±70 vs -39±113 g) were positive in SOC compared to CON (P<.05). Post-intervention plasma triglycerides decreased more (-0.1±0.7 vs +0.2±0.2 mmol·L-1 ) and HDL cholesterol increased more (0.2±0.7 vs -0.2±0.2 mmol·L-1 ) in SOC than in CON (P<.05). Yo-Yo intermittent endurance level 1 (122±105 vs 2±21%) and 20-m sprint performance (6±6 vs -1±2%) increased more (P<.05) in SOC than in CON. In conclusion, long-term soccer training resulted in broad-spectrum improvements in the health profile of untrained, pre-menopausal women with mild hypertension, including cardiovascular, metabolic, and musculo-skeletal benefits.

#5 Osteoarthritis and joint replacements of the lower limb and spine in ex-professional soccer players: A systematic review
Reference: Scand J Med Sci Sports. 2017 Feb 2. doi: 10.1111/sms.12846. [Epub ahead of print]
Authors: Lohkamp M, Kromer TO, Schmitt H
Summary: After a professional career as a soccer player, the risk of developing osteoarthritis (OA) in different joints of the spine and lower limb might be increased. The extent of this problem to date is not clear. Therefore, the aim of this systematic review is to summarise the prevalence of OA and joint replacement of the lower limb and spine in former professional soccer players. Relevant databases were searched with different combinations of key words: e.g. osteoarthritis, hip, knee, ankle, foot, joint replacement, soccer. Studies were included if they were original research, included a sample of former professional male soccer players, had OA in the lower limb and/or spine, OA was diagnosed either through questionnaires or x-rays, article in English, Dutch or German. Sixteen studies with 1576 former players and 2153 control subjects were included in the review. Studies agreed that the prevalence of hip OA and hip replacements is significantly higher in former players compared to the control group. For the ankle and spine there is only limited information and for the prevalence of knee OA and knee replacement the results are contradictory. The quality of the included studies was moderate. Future studies should have a prospective design to control for confounding factors, to identify possible risk factors and consequences for the individuals, and to be able to develop a prevention programme.

#6 Repeated Dribbling Ability in Young Soccer Players: Reproducibility and Variation by the Competitive Level
Reference: J Hum Kinet. 2016 Oct 14;53:155-166. doi: 10.1515/hukin-2016-0019. eCollection 2016.
Authors: Duarte JP, Tavares O, Valente-Dos-Santos J, Severino V, Ahmed A, Rebelo-Gonçalves R, Pereira JR, Vaz V, Povoas S, Seabra A, Cumming SP, Coelho-E-Silva MJ
Summary: The intermittent nature of match performance in youth soccer supports relevance of ability to repeatedly produce high-intensity actions with short recovery periods. This study was aimed to examine the reproducibility of a repeated dribbling ability protocol and, additionally, to estimate the contribution of concurrent tests to explain inter-individual variability in repeated dribbling output. The total sample comprised 98 players who were assessed as two independent samples: 31 players were assessed twice to examine reliability of the protocol; and 67 juveniles aged 16.1 ± 0.6 years were compared by the competitive level (local, n = 34; national, n = 33) to examine construct validity. All single measurements appeared to be reasonably reliable: total (ICC = 0.924; 95%CI: 0.841 to 0.963); ideal (ICC = 0.913; 95%CI: 0.820 to 0.958); worst (ICC = 0.813; 95%CI: 0.611 to 0.910). In addition, the percentage of the coefficient of variation was below the critical value of 5% for total (%CV = 3.84; TEM = 2.51 s); ideal (%CV = 3.90, TEM = 2.48 s). Comparisons between local and national players suggested magnitude effects as follows: moderate (d-value ranged from 0.63 to 0.89) for all repeated sprint ability scores; large for total (d = 1.87), ideal (d = 1.72), worst (d = 1.28) and moderate for composite scores: the fatigue index (d = 0.69) and the decrement score (d = 0.67). In summary, the dribbling protocol presented reasonable reproducibility properties and output extracted from the protocol seemed to be independent from biological maturation.

#7 Role of Vertical Jumps and Anthropometric Variables in Maximal Kicking Ball Velocities in Elite Soccer Players
Reference: J Hum Kinet. 2016 Oct 15;53:143-154. doi: 10.1515/hukin-2016-0018. eCollection 2016.
Authors: Rodriguez-Lorenzo L, Fernandez-Del-Olmo M, Sanchez-Molina JA, Martín-Acero R
Summary: Kicking is one of the most important skills in soccer and the ability to achieve ma ximal kicking velocity with both legs leads to an advantage for the soccer player. This study examined the relationship be tween kicking ball velocity with both legs using anthropometric measurements and vertical jumps (a squat jump (SJ); a countermovement jump without (CMJ) and with the arm swing (CMJA) and a reactive jump (RJ)). Anthropome tric measurements did not correlate with kicking ball velocity. Vertical jumps correlated significantly with kicking ball velocity using the dominant leg only (r = .47, r = .58, r = .44, r = .51, for SJ, CMJ, CMJA and RJ, respectively) . Maximal kicking velocity with the dominant leg was significantly higher than with the non-dominant leg (t = 18.0 4, p < 0.001). Our results suggest that vertical jumps may be an optimal test to assess neuromuscular skills involved in kicking at maximal speed. Lack of the relationship between vertical jumps and kicking velocity with the non-dominant leg may reflect a difficulty to exhibit the neuromuscular skills during dominant leg kicking.

#8 Monitoring Salivary Immunoglobulin A Responses to Official and Simulated Matches In Elite Young Soccer Players
Reference: J Hum Kinet. 2016 Oct 14;53:107-115. doi: 10.1515/hukin-2016-0015. eCollection 2016.
Authors: Freitas CG, Aoki MS, Arruda AF, Franciscon C, Moreira A
Summary: The purpose of the present study was to examine SIgA responses (concentration [SIgAabs] and a secretion rate [SIgArate]) to official and simulated competitive matches in young soccer players. The sample was composed of 26 male soccer players (age 15.6 ± 1.1 yrs, stature 177.0 ± 6.1 cm, body mass 70.5 ± 5.7 kg). Four soccer matches (two simulated matches [SM] and two official matches [OM]) were conducted. The matches consisted of two halves of 35 min with a 10 min rest interval. Each assessed player participated in only one SM and one OM. All matches were performed in the same week, during the competitive season, and at the same time of the day (9:00 am), separated by 48 h. Saliva samples were collected before and after every match. The session rating of perceived exertion was reported 30 min after each match in order to determine the internal training load (ITL). A significant decrease in SIgAabs and SIgArate after OM was observed when compared to the pre-match value. In addition, the SIgArate was higher at pre-OM when compared to pre-SM. A higher ITL for OM was observed compared to SM. The current findings indicate that OM may lead to a decrease in the main mucosal immunity function parameter of young soccer players that could increase the risk of URTI. Coaches should be aware of it in order to plan appropriate training loads and recovery procedures to avoid or minimize the likelihood of upper respiratory tract infection occurrences.

#9 The Importance of Postural Control in Relation to Technical Abilities in Small-Sided Soccer Games
Reference: J Hum Kinet. 2016 Oct 14;53:51-61. doi: 10.1515/hukin-2016-0010. eCollection 2016.
Authors: Edis ÇC, Vural F, Vurgun H
Summary: Making assessments regarding postural control and balance is very important for injury prevention in soccer. However, there has been no study that has associated postural control variables with branch-specific technical properties in a game. The aim of the present study was to determine the relationships between variables designating postural control levels and technical performance variables in different (1:1, 2:2 and 3:3) small-sided games (SSGs). Sixteen trained male amateur soccer players volunteered to take part in the study (age 17.2 ± 1.02 years, body height 176.25 ± 0.07 m, body mass 67.67 ± 13.27 kg). Following familiarization sessions, postural control was evaluated using one-leg and both-leg quiet-stance positions by measuring postural sway with a Tekscan HR Mat™ in anterior-posterior and medial-lateral directions. Later, 1:1, 2:2 and 3:3 SSGs were performed at two-day intervals and the technical variables specified for each game were analyzed. A Spearman's rank-order correlation analysis demonstrated the relationship between postural control and soccer-specific technical variables in 1:1 (r-values ranging from 0.582 to 0.776), 2:2 (rvalues ranging from 0.511 to 0.740) and 3:3 (r-values ranging from 0.502 to 0.834) SSGs. In addition, a Wilcoxon signed rank test revealed differences between SSGs in terms of several variables. The results of the study showed that higher postural control levels are among the important variables that affect success in the performance of technical skills under rival pressure and suddenly changing conditions. Therefore, it is recommended that in addition to its use for injury prevention purposes, balance training should be conducted to improve branch-specific technical skills and to increase the levels of their successful performance in a game.

#10 Determinants of feedback retention in soccer players
Reference: J Hum Kinet. 2016 Jul 2;51:235-241. doi: 10.1515/hukin-2015-0187. eCollection 2016
Authors: Januario N, Rosado A, Mesquita I, Gallego J, Aguilar-Parra JM
Summary: This study analyzed soccer players' retention of coaches' feedback during training sessions. We intended to determine if the retention of information was influenced by the athletes' personal characteristic (age, gender and the sports level), the quantity of information included in coach's feedback (the number of ideas and redundancy), athletes' perception of the relevance of the feedback information and athletes' motivation as well as the attention level. The study that was conducted over the course of 18 sessions of soccer practice, involved 12 coaches (8 males, 4 females) and 342 athletes (246 males, 96 females), aged between 10 and 18 years old. All coach and athlete interventions were transposed to a written protocol and submitted to content analysis. Descriptive statistics and multiple linear regression were calculated. The results showed that a substantial part of the information was not retained by the athletes; in 65.5% of cases, athletes experienced difficulty in completely reproducing the ideas of the coaches and, on average, the value of feedback retention was 57.0%. Six variables with a statistically significant value were found: gender, the athletes' sports level, redundancy, the number of transmitted ideas, athletes' perception of the relevance of the feedback information and the athletes' motivation level.

#11 Comparison between two types of anaerobic speed endurance training in competitive soccer players
Reference: J Hum Kinet. 2016 Jul 2;51:183-192. doi: 10.1515/hukin-2015-0181. eCollection 2016
Authors: Mohr M, Krustrup P
Summary: The purpose of the present study was to examine the effects of additional in-season speed endurance production versus speed endurance maintenance training regimes on performance in competitive male soccer players. In a randomised controlled trial 18 male sub-elite players were exposed to additional speed endurance production (SEP) or speed endurance maintenance (SEM) training (two additional sessions/wk for 4 weeks) during the competitive season. Players performed the Yo-Yo intermittent recovery level 2 test (YYIR2) and a repeated sprint test (RST) pre- and post-intervention. Yo-Yo IR2 performance increased (p<0.001) by 50 ± 8% and 26 ± 5% in SEP and SEM, respectively, with greater (p=0.03) improvement in SEP. RST performance improved by 2.1 ± 0.3% and 1.3 ± 0.4% in SEP and SEM, respectively, while the RST fatigue index decreased (4.4 ± 0.8 to 3.4 ± 0.5%; p<0.04) in SEP only. Peak and average speed during training were higher (p<0.001) in SEP than in SEM (24.5 ± 0.3 vs 19.2 ± 0.3 and 15.5 ± 0.1 km·h-1 vs 9.4 ± 0.1 km·h-1). Additional in-season anaerobic speed endurance production and maintenance training improves high-intensity exercise performance in competitive soccer players with superior effects of speed endurance production training.

#12 Effect of the pitch size and presence of goalkeepers on the work load of players during small-sided soccer games
Reference: J Hum Kinet. 2016 Jul 2;51:175-181. doi: 10.1515/hukin-2015-0180. eCollection 2016
Authors: Hulka K, Weisser R, Belka J
Summary: Small-sided games (SSGs) are spontaneous forms of specific training where exercise intensity can be manipulated by modifying external factors. To ensure suitable usage of small-sided games in practice, we have to know which variables can influence internal responses and external loads. The aim of the present study was to determine the influence of presence of a goalkeeper and the pitch size on internal responses and the external load during five-a-side soccer games. Twenty nine junior soccer players (age: 18.11 ± 1.31 years; body mass index: 21.04 ± 2.58 kg·m-2; peak heart rate: 199.53 ± 7.51 beats·min-1) participated in the study. The heart rate, distance covered and the rate of perceived exertion were monitored. We found significantly higher average heart rates of players in 5v5 SSGs without goalkeepers than with them on a small pitch. Analysis showed significant differences in the time spent in 65-85% of the peak heart rate zone and ˂65% of the peak heart rate zone on the small pitch. Furthermore, we found significantly higher distance covered by players during five-a-side games with goalkeepers than without them played on the small pitch. Our results indicate that the pitch size is a very important variable that influences the work load of players. The inclusion of the goalkeeper decreases the work load of the player on a small pitch (28 × 20 m; 560 m2), but not on a medium or large pitch.

#13 The influence of scoring targets and outer-floaters on attacking and defending team dispersion, shape and creation of space during small-sided soccer games
Reference: J Hum Kinet. 2016 Jul 2;51:153-163. doi: 10.1515/hukin-2015-0178. eCollection 2016
Authors: Castellano J, Silva P, Usabiaga O, Barreira D
Summary: The effect of altered game formats on team performances during soccer practice can be harnessed by coaches to stimulate specific tactical behaviours. The aim of the present study was to analyse the influence of using (i) small goals [SG], (ii) goalkeepers [7G] and (iii) floaters [7GF] on the dispersion, shape and available space of teams during small-sided games (SSGs). Twenty-four male soccer players were distributed into four teams composed of five players, two goalkeepers and two floaters that performed six SSG bouts of 6 min, interspersed with 6 min of passive recovery. Offensive and defensive phases were also analysed separately in order to verify the preservation of basic principles of attacking (teams more stretched to create free space) and defending (teams more compact to tie-up space) during SSGs. The variables used to characterize the collective behaviour were: length [L], width [W], team shape [Sh], and team separateness [TS]. Results revealed that the teams showed different collective behaviours depending on SSG format and a playing phase: a) L and W were higher in attack than in defence in all SSGs; b) team shapes were more elongated in defence in all SSGs except SG; c) the space separating players from their closest opponents (TS) was shorter in 7G; and d) SG and 7GF elicited greater defensive openness due to increased team width. The results suggest that manipulating task constraints, such as goal size, presence or absence of goalkeepers and floaters can be harnessed by coaches to shape distinct team tactical behaviours in SSGs while preserving the basic principles of attacking and defending.

#14 The effect of the MTHFR C677T mutation on athletic performance and the homocysteine level of soccer players and sedentary individuals
Reference: J Hum Kinet. 2016 Jul 2;51:61-69. doi: 10.1515/hukin-2015-0171. eCollection 2016
Authors: Dinc N, Yucel SB, Taneli F, Sayın MV
Summary: This study investigated athletic performance and homocysteine (Hcy) levels in relation to the methylenetetrahydrofolate reductase (MTHFR) C677T mutation and explored the relationship between this mutation and other cardiac risk factors in soccer players and sedentary individuals. The study groups consisted of randomly selected soccer players (n=48) from the Turkish Super and Major League and sedentary male students (n=48) aged 18-27. Anthropometric variables, aerobic and anaerobic thresholds were measured, furthermore, biochemical assays were performed. The level of HDL cholesterol, LDL cholesterol, triglyceride, Hcy, folate, vitamin B12, hemogram and MTHFR C677T was investigated. The results showed that there was a statistical difference between the two groups in terms of body mass, body fat, the BMI, the aerobic threshold heart rate (ATHR), aerobic threshold velocity (ATVL) and anaerobic threshold velocity (ANTVL). The soccer players were found to have lower levels of triglyceride, total cholesterol and LDL cholesterol, and higher levels of folate than the sedentary participants. The analysis of the alleles of the MTHFR C677T polymorphism showed that the participants that carried TT genotypes had a lower level of vitamin B12 and folate, and a higher level of Hcy than the participants carrying CC and CT genotypes. In conclusion, the baseline homocysteine and cardiovascular fitness levels of healthy young males with the TT genotypes of the MTHFR C677T genotype were found to strongly correlate with their levels of Hcy.





Latest research in football - week 4 - 2017

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 Symptoms from repeated intentional and unintentional head impact in soccer players
Reference: Neurology. 2017 Feb 1. pii: 10.1212/WNL.0000000000003657. doi: 10.1212/WNL.0000000000003657. [Epub ahead of print]
Authors: Stewart WF, Kim N, Ifrah CS, Lipton RB, Bachrach TA, Zimmerman ME, Kim M, Lipton ML
Summary: The purpose was to determine the rate and differential contribution of heading vs unintentional head impacts (e.g., head to head, goal post) to CNS symptoms in adult amateur soccer players. Amateur soccer players completed baseline and serial on-line 2-week recall questionnaires (HeadCount) and reported (1) soccer practice and games, (2) heading and unintentional soccer head trauma, and (3) frequency and severity (mild to very severe) of CNS symptoms. For analysis, CNS symptoms were affirmed if one or more moderate, severe, or very severe episodes were reported in a 2-week period. Repeated measures logistic regression was used to assess if 2-week heading exposure (i.e., 4 quartiles) or unintentional head impacts (i.e., 0, 1, 2+) were associated with CNS symptoms. A total of 222 soccer players (79% male) completed 470 HeadCount questionnaires. Mean (median) heading/2 weeks was 44 (18) for men and 27 (9.5) for women. One or more unintentional head impacts were reported by 37% of men and 43% of women. Heading-related symptoms were reported in 20% (93 out of 470) of the HeadCounts. Heading in the highest quartile was significantly associated with CNS symptoms (odds ratio [OR] 3.17, 95% confidence interval [CI] 1.57-6.37) when controlling for unintentional exposure. Those with 2+ unintentional exposures were at increased risk for CNS symptoms (OR 6.09, 95% CI 3.33-11.17) as were those with a single exposure (OR 2.98, 95% CI 1.69-5.26) when controlling for heading. Intentional (i.e., heading) and unintentional head impacts are each independently associated with moderate to very severe CNS symptoms.

#2 No Effect of Generalized Joint Hypermobility on Injury Risk in Elite Female Soccer Players
Reference: Am J Sports Med. 2017 Feb;45(2):286-293. doi: 10.1177/0363546516676051. Epub 2016 Dec 14.
Authors: Blokland D, Thijs KM, Backx FJ, Goedhart EA, Huisstede BM
Summary: Although it has been suggested that generalized joint hypermobility (GJH) is a risk factor for injury in soccer players, it remains unclear whether this applies to elite female soccer players. The purpose was to investigate whether GJH is a risk factor for injury in elite female soccer players. Elite female soccer players in the Netherlands were screened at the start of the 2014-2015 competitive season. GJH was assessed using the Beighton score. Soccer injuries and soccer exposure were registered throughout the entire season. Poisson regression was performed to calculate incidence risk ratios (IRRs) using different cutoff points of the Beighton score (≥3, ≥4, and ≥5) to indicate GJH. Of the 114 players included in the study, 20 were classified as hypermobile (Beighton score ≥4). The mean (±SD) injury incidence per player was 8.40 ± 9.17 injuries/1000 hours of soccer, with no significant difference between hypermobile and nonhypermobile players. GJH was not a risk factor for injuries when using Beighton score cutoff points of ≥3 (IRR = 1.06 [95% CI, 0.74-1.50]; P = .762), ≥4 (IRR = 1.10 [95% CI, 0.72-1.68]; P = .662), or ≥5 (IRR = 1.15 [95% CI, 0.68-1.95]; P = .602). Similarly, GJH was not a significant risk factor for thigh, knee, or ankle injuries evaluated separately. This study indicates that GJH is not a risk factor for injuries in elite female soccer players, irrespective of Beighton score cutoff point. Hypermobile players at this elite level might have improved their active stability and/or used braces to compensate for joint laxity.

#3 Functional Performance Among Active Female Soccer Players After Unilateral Primary Anterior Cruciate Ligament Reconstruction Compared With Knee-Healthy Controls
Reference: Am J Sports Med. 2017 Feb;45(2):377-385. doi: 10.1177/0363546516667266. Epub 2016 Oct 7.
Authors: Faltstrom A, Hagglund M, Kvist J
Summary: Good functional performance with limb symmetry is believed to be important to minimize the risk of injury after a return to pivoting and contact sports after anterior cruciate ligament reconstruction (ACLR). This study aimed to investigate any side-to-side limb differences in functional performance and movement asymmetries in female soccer players with a primary unilateral anterior cruciate ligament (ACL)-reconstructed knee and to compare these players with knee-healthy controls from the same soccer teams. This study included 77 active female soccer players at a median of 18 months after ACLR (interquartile range [IQR], 14.5 months; range, 7-39 months) and 77 knee-healthy female soccer players. The mean age was 20.1 ± 2.3 years for players with an ACL-reconstructed knee and 19.5 ± 2.2 years for controls. We used a battery of tests to assess postural control (Star Excursion Balance Test) and hop performance (1-legged hop for distance, 5-jump test, and side hop). Movement asymmetries in the lower limbs and trunk were assessed with the drop vertical jump and the tuck jump using 2-dimensional analyses. The reconstructed and uninvolved limbs did not differ in any of the tests. In the 5-jump test, players with an ACL-reconstructed knee performed worse than controls (mean 8.75 ± 1.05 m vs 9.09 ± 0.89 m; P = .034). On the drop vertical jump test, the ACL-reconstructed limb had significantly less knee valgus motion in the frontal plane (median 0.028 m [IQR, 0.049 m] vs 0.045 m [IQR, 0.043 m]; P = .004) and a lower probability of a high knee abduction moment (pKAM) (median 69.2% [IQR, 44.4%] vs 79.8% [IQR, 44.8%]; P = .043) compared with the control players' matched limb (for leg dominance). Results showed that 9% to 49% of players in both groups performed outside recommended guidelines on the different tests. Only 14 players with an ACL-reconstructed knee (18%) and 15 controls (19%) had results that met the recommended guidelines for all 5 tests ( P = .837). The reconstructed and uninvolved limbs did not differ, and players with an ACL-reconstructed knee and controls differed only minimally on the functional performance tests, indicating similar function. It is worth noting that many players with an ACL-reconstructed knee and controls had movement asymmetries and a high pKAM pattern, which have previously been associated with an increased risk for both primary and secondary ACL injury in female athletes.

#4 The influence of football shoe characteristics on athletic performance and injury risk – a review
Reference: Footwear Science, Received 21 Oct 2016, Accepted 16 Jan 2017, Published online: 03 Feb 2017
Author: Kulessa DJ, Gollhofer A, Gehring D
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Summary: Footwear is the most relevant tool of a footballer's gear and has to cope with the individual sport-specific demands of the athlete. The challenge in the development of a football shoe is to fine-tune its functional parameters to meet criteria of injury prevention and performance enhancement. There exists a contradiction between those two set-targets that needs to be addressed. The objective of the review is to provide a literature survey about the scientific knowledge on how football shoe characteristics influence performance and injury risk. Almost 100 scientific publications are included in a qualitative synthesis. The outsole configuration and its influence on traction can be regarded as the most studied functional shoe parameter and has been scientifically proven to affect the player's performance in translational locomotion and the injury risk in rotational movements. The second main aspect consists of the interaction between shoe and ball, which can be divided into the influence of shoe construction on kicking velocity, accuracy and ball control. Footwear properties, such as bending and torsional stiffness, cushioning and comfort, have barely been studied, if at all. The present literature survey shows a substantial influence of football footwear on the athlete. Currently available literature suggests that outsole design influences shoe–surface interaction, which has implications regarding performance and injury risk. Additionally, shoe upper seems to play a crucial role with regard to the performance in ball interactions. However, further research is needed on shoe–foot interactions and on footwear requirements for female, adolescent and indoor players.

#5 Evaluating injury risk in first and second league professional Portuguese soccer: muscular strength and asymmetry
Reference: J Hum Kinet. 2016 Jul 2;51:19-26. doi: 10.1515/hukin-2015-0166. eCollection 2016
Authors: Carvalho A, Brown S, Abade E
Summary: Strength imbalances between the hamstrings and quadriceps are an essential predictor for hamstring strain in soccer. The study aimed to investigate and compare the muscle strength imbalances of professional soccer players of different performance levels. One hundred and fifty nine senior male professional soccer players from first (n = 75) and second league (n = 84) Portuguese clubs participated in this study. Muscle strength was evaluated with a REV9000 isokinetic dynamometer. Maximal peak torque data were used to calculate quadriceps and hamstrings strength during concentric and eccentric actions, bilateral asymmetry, conventional strength ratios and dynamic control ratios. Second league athletes produced slightly lower conventional strength ratios in the right and left legs (ES = 0.22, p = 0.17 and ES = 0.36, p = 0.023, respectively) compared to the first league athletes. No significant differences were found in dynamic control ratios or in bilateral asymmetry among first and second league athletes. These findings do not show a clear link between the competitive level and injury risk in soccer players. However, some of the differences found, particularly in conventional strength ratios, highlight the importance of performing off-season and pre-season strength assessments to prescribe and adjust individual strength training programs among professional soccer players.

#6 Muscle Strength and Speed Performance in Youth Soccer Players
Reference: J Hum Kinet. 2016 Apr 13;50:203-210. doi: 10.1515/hukin-2015-0157. eCollection 2016
Authors: Penailillo L, Espildora F, Jannas-Vela S, Mujika I, Zbinden-Foncea H
Summary: This study aimed to examine the relationship between maximum leg extension strength and sprinting performance in youth elite male soccer players. Sixty-three youth players (12.5 ± 1.3 years) performed 5 m, flying 15 m and 20 m sprint tests and a zigzag agility test on a grass field using timing gates. Two days later, subjects performed a one-repetition maximum leg extension test (79.3 ± 26.9 kg). Weak to strong correlations were found between leg extension strength and the time to perform 5 m (r = -0.39, p = 0.001), flying 15 m (r = -0.72, p < 0.001) and 20 m (r = -0.67, p < 0.001) sprints; between body mass and 5 m (r = -0.43, p < 0.001), flying 15 m (r = -0.75, p < 0.001), 20 m (r = -0.65, p < 0.001) sprints and agility (r =-0.29, p < 0.001); and between height and 5 m (r = -0.33, p < 0.01) and flying 15 m (r = -0.74, p < 0.001) sprints. Our results show that leg muscle strength and anthropometric variables strongly correlate with sprinting ability. This suggests that anthropometric characteristics should be considered to compare among youth players, and that youth players should undergo strength training to improve running speed.

#7 Acute Effect of Different Combined Stretching Methods on Acceleration and Speed in Soccer Players
Reference: J Hum Kinet. 2016 Apr 13;50:179-186. doi: 10.1515/hukin-2015-0154. eCollection 2016
Authors: Amiri-Khorasani M, Calleja-Gonzalez J, Mogharabi-Manzari M
Summary: The purpose of this study was to investigate the acute effect of different stretching methods, during a warm-up, on the acceleration and speed of soccer players. The acceleration performance of 20 collegiate soccer players (body height: 177.25 ± 5.31 cm; body mass: 65.10 ± 5.62 kg; age: 16.85 ± 0.87 years; BMI: 20.70 ± 5.54; experience: 8.46 ± 1.49 years) was evaluated after different warm-up procedures, using 10 and 20 m tests. Subjects performed five types of a warm-up: static, dynamic, combined static + dynamic, combined dynamic + static, and no-stretching. Subjects were divided into five groups. Each group performed five different warm-up protocols in five non-consecutive days. The warm-up protocol used for each group was randomly assigned. The protocols consisted of 4 min jogging, a 1 min stretching program (except for the no-stretching protocol), and 2 min rest periods, followed by the 10 and 20 m sprint test, on the same day. The current findings showed significant differences in the 10 and 20 m tests after dynamic stretching compared with static, combined, and no-stretching protocols. There were also significant differences between the combined stretching compared with static and no-stretching protocols. We concluded that soccer players performed better with respect to acceleration and speed, after dynamic and combined stretching, as they were able to produce more force for a faster execution.

#8 Preseason Strategies of Italian First League Soccer Clubs in Relation to their Championship Ranking: A Five-Year Analysis
Reference: J Hum Kinet. 2016 Apr 13;50:145-155. doi: 10.1515/hukin-2015-0151. eCollection 2016
Authors: Francioni FM, Figueiredo AJ, Lupo C, Conte D, Capranica L, Tessitore A
Summary: This study is focused on the strategies adopted by Italian 'Serie A' soccer clubs during the non-competitive period. Thus, duration (i.e., number of days) of the specific non-competitive periods (i.e., off- plus pre-season, off-season, pre-season, summer camp), the number of games (i.e., friendly, official and polled games) and days between games (i.e., ≤ 3, 4-5, or ≥ 6 days between two consecutive games) of the entire non-competitive period were recorded and compared by clubs participating in the European Championships (EU), only 'Serie A' (A) and promoted from 'Serie B' (B) during five and single seasons (i.e., 2009/10-2013/14). Due to the short B off-season duration (2009/10-2013/14, 2010/11, 2011/12, 2012/13, 2013/14, p≤.001), effects between clubs emerged also for the off- plus preseason (2009/10-2013/14, EU vs A, p≤.01, EU vs B, p≤.01, A vs B, p≤.001; 2011/12, 2012/13, 2013/14, p≤.001). Nevertheless, no difference between clubs resulted for the pre-season. Reduced duration of summer camps was reported by the EU (i.e., 2009/10-2013/14, 2009/10, 2013/14, p≤.001). A higher number of official games were played by EU than A (i.e., 2009/10-2013/14, p≤.001; 2010/11, p≤.01). No effect emerged for the days between games. Therefore, despite the longer 'Serie B' schedule and EU preliminary UEFA games that determined the off-season restriction, clubs demonstrated the tendency to guarantee satisfactory pre-season duration.

#9 Prevalence of Dehydration Before Training Sessions, Friendly and Official Matches in Elite Female Soccer Players
Reference: J Hum Kinet. 2016 Apr 13;50:79-84. doi: 10.1515/hukin-2015-0145. eCollection 2016
Authors: Castro-Sepulveda M, Astudillo J, Letelier P, Zbinden-Foncea H
Summary: This study aimed to evaluate and compare the hydration states prior to different sporting events (training sessions, friendly and official matches) in elite female soccer players and relate that to the importance that the player attached to the hydration state as a determinant of sports performance. The hydration state of 17 female elite soccer players (age: 21.5 ± 3 years; body mass: 62 ± 6 kg; body height: 165 ± 9 cm) was determined by measuring their urine specific gravity (USG) prior to three different sports events: training sessions (PT), friendly (PF) and official (PO) matches. The importance that each player attached to the hydration state as a determinant of sports performance was evaluated through a simple questionnaire. An average of 47.05% of the soccer players were severely dehydrated (USG > 1.030), 33.33% were significantly dehydrated (USG > 1.020), 17.64% were mildly dehydrated (USG > 1.010) and 1.96% were euhydrated (USG < 1.010). The average USG was 1.027 ± 0.007 (PT = 1.029 ± 0.009; PF = 1.023 ± 0.010 and PO = 1.030 ± 0.006). Differences were found between urine specific gravity prior to a friendly and an official match (p = 0.03). No relationship was found between urine specific gravity and the importance each player attached to the hydration state as a determinant of sports performance. The results show that dehydration is the most prevalent hydration state of elite soccer players before training sessions, friendly and official matches. Players were most dehydrated prior to official matches, which was unlinked to the players' perceived importance of hydration for sports performance.

#10 Comparison of Lateral Abdominal Muscle Thickness and Cross Sectional Area of Multifidus in Adolescent Soccer Players with and without Low Back Pain: A Case Control Study
Reference: Asian J Sports Med. 2016 Oct 4;7(4):e38318. doi: 10.5812/asjsm.38318. eCollection 2016
Authors: Noormohammadpour P, Hosseini Khezri A, Linek P, Mansournia MA, Hassannejad A, Younesian A, Farahbakhsh F, Kordi R
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Summary: Low back pain (LBP) is a common complaint amongst adolescent athletes. While different studies have shown association between LBP and trunk muscle thickness in the general population, few articles have studied it in adolescent athletes. The aim of this study is to compare lateral abdominal muscle thickness and function, and cross sectional area (CSA) of lumbar multifidus (LM) in adolescent soccer players with and without LBP. In total, 28 adolescent soccer players with and without LBP, from the premier league participated in this study. The thickness of external oblique, internal oblique and transversus abdominis and the CSA of the LM muscles at L4 level on both sides were measured at rest and contraction via ultrasound imaging (USI). In addition, leg length discrepancy, hamstring flexibility, active lumbar forward flexion, and isometric muscle endurance of trunk extensors were measured in both groups. (study design/setting: case control study). The mean (SD) age in LBP group and non-LBP group were 14.0 (1.1) and 14.1 (0.9) years, respectively. There was no significant difference in baseline characteristics of participants between groups. Findings showed no significant difference between LBP and non-LBP groups comparing all measured variables. The data obtained support that there is not a correlation between abdominal muscle thickness and CSA of the lumbar multifidi and LBP in adolescent soccer players. These findings suggest that other factors rather than the thickness of deep trunk muscles may play a more significant role in the etiology of LBP in adolescent soccer players.

#11 Temporal Changes in Technical and Physical Performances During a Small-Sided Game in Elite Youth Soccer Players
Reference: Asian J Sports Med. 2016 Oct 16;7(4):e35411. doi: 10.5812/asjsm.35411. eCollection 2016.
Authors: Moreira A, Saldanha Aoki M, Carling C, Alan Rodrigues Lopes R, Felipe Schultz de Arruda A, Lima M, Cesar Correa U, Bradley PS
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Summary: There have been claims that small-sided games (SSG) may generate an appropriate environment to develop youth players' technical performance associated to game-related problem solving. However, the temporal change in technical performance parameters of youth players during SSG is still unknown. The aim of this study was to examine temporal changes in technical and physical performances during a small-sided game (SSG) in elite soccer players. Sixty elite youth players (age 14.8 ± 0.2 yr; stature 177 ± 5 cm; body mass 66.2 ± 4.7 kg) completed a 5 v 5 SSG using two repetitions of 8 minutes interspersed by 3 minutes of passive recovery. To evaluate temporal changes in performance, the data were analysed across 4 minutes quarters. Physical performance parameters included the total distance covered (TDC), the frequency of sprints (>18 km•h-1), accelerations and decelerations (> 2.0 m•s-2 and - 2.0 m•s-2), metabolic power (W•kg-1), training impulse (TRIMP), TDC: TRIMP, number of impacts, and body load. Technical performance parameters included goal attempts, total number of tackles, tackles and interceptions, total number of passes, and passes effectiveness. All physical performance parameters decreased from the first to the last quarter with notable declines in TDC, metabolic power and the frequency of sprints, accelerations and decelerations (P < 0.05; moderate to very large ES: 1.08 - 3.30). However, technical performance parameters did not vary across quarters (P > 0.05; trivial ES for 1st v 4th quarters: 0.15 - 0.33). The data demonstrate that technical performance is maintained despite substantial declines in physical performance during a SSG in elite youth players. This finding may have implications for designing SSG's for elite youth players to ensure physical, technical and tactical capabilities are optimized. Modifications in player number, pitch dimensions, rules, coach encouragement, for instance, should be included taking into account the main aim of a given session and then focused on overloading physical or technical elements.





Club ownership

The fifth chapter of the UEFA Club Footballing Landscape was about (foreign) club ownership.


Forty-four clubs in major European leagues are now under foreign ownership, by owners of 18 different nationalities.

Foreign ownership is still centered in England, where more than half of the clubs in the top two leagues now have foreign owners.

2016 was the most active year for foreign club takeovers, with ten new acquisitions by November, including eight new Chinese owners.


Foreign ownership increased over recent years predominantly in England (first and second tier) (75 and 54%) respectively. However, an opposite trend was observed in France, Spain and Italy.

More than three-quarters of clubs in Germany, Portugal and Turkey do not have controlling parties as the clubs are predominantly associations. This ownership structure is also quite dominant in the Netherlands and Spain with some cases also seen in Belgium, France, Switzerland and Ukraine. Interestingly, Russia and Italy have the highest share of domestic club owners.


Where are the owners coming from?


The Asian region provides the largest source of foreign investment, with 17 clubs under majority foreign ownership. As of November 2016, nine clubs are under Chinese control and Chinese owners are present in six different leagues, making them the most widespread of any nationality. In addition, six clubs have received significant non-controlling Chinese investments.


North America, and more specifically the USA, is the second largest source of investment in European clubs. As of November 2016, 10 clubs across 4 different leagues (the English Premier League and Championship, Italy’s Serie A and most recently the French Ligue 1 ) are under American ownership.


A total of 20% of total foreign investment comes directly from within Europe. Meaning European investors who either own or invest in a European league club of a different nationality. The two most prominent nationalities in this investor groups are Russian and Italian. As of November 2016 there are four clubs owned by Russian investors in three leagues outside Russia (Ligue 1, EPL & Eredivise) and Italian ownership in Englands top two leagues.


The largest share of foreign ownership in European club football comes from Asia. As the timeline shows, Asian ownership has mainly emerged over the last season (2015/16). Of the ten new owners that invested in clubs in Europe’s top leagues in 2016, eight came from China. It is also worth noting that Chinese investors have invested in clubs in five different leagues in the first 11 months of 2016 (shaded area, additionally, AC Milans change in ownership was not confirmed by the time of release of this document).


The second largest source of foreign ownership comes from North America, mainly the USA. Of the 13 clubs in the English Premier League, six are under American ownership. Americans were the first foreign owners to come from a continent other than Europe and their influx has been fairly consistent over time.

Nine foreign owners are European. These owners come from five different countries, and four of them are Russian. In this sample of clubs from 13 leagues, Russian investment has also accounted for the longest- standing active ownership (since 2003).

The fourth and smallest source of foreign ownership is the Middle East, with four clubs under Middle Eastern ownership. These four clubs come from four different leagues: the English Premier League, the English Championship, the French Ligue 1 and Spain’s La Liga.






Latest research in football - week 3 - 2017

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 Exercise Training under Hyperbaric Oxygen on Oxidative Stress Markers and Endurance Performance in Young Soccer Players: A Pilot Study
Reference: J Nutr Metab. 2016;2016:5647407. doi: 10.1155/2016/5647407. Epub 2016 Dec 19.
Authors: Burgos C, Henriquez-Olguin C, Andrade DC1, Ramirez-Campillo R, Araneda OF, White A, Cerda-Kohler H
Summary: The aim of the present study was to determine the effects of three weeks of hyperbaric oxygen (HBO2) training on oxidative stress markers and endurance performance in young soccer players. Participants (18.6 ± 1.6 years) were randomized into hyperbaric-hyperoxic (HH) training (n = 6) and normobaric normoxic (NN) training (n = 6) groups. Immediately before and after the 5th, 10th, and 15th training sessions, plasma oxidative stress markers (lipid hydroperoxides and uric acid), plasma antioxidant capacity (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid [TROLOX]), arterial blood gases, acid-base balance, bases excess (BE), and blood lactate analyses were performed. Before and after intervention, maximal oxygen uptake (VO2max) and peak power output (PPO) were determined. Neither HH nor NN experienced significant changes on oxidative stress markers or antioxidant capacity during intervention. VO2max and PPO were improved (moderate effect size) after HH training. The results suggest that HBO2 endurance training does not increase oxidative stress markers and improves endurance performance in young soccer players. Our findings warrant future investigation to corroborate that HBO2 endurance training could be a potential training approach for highly competitive young soccer players.

#2 Ecologically Valid Carbohydrate Intake during Soccer-Specific Exercise Does Not Affect Running Performance in a Fed State
Reference: Nutrients. 2017 Jan 5;9(1). pii: E39. doi: 10.3390/nu9010039.
Authors: Funnell MP, Dykes NR, Owen EJ, Mears SA, Rollo I, James LJ
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Summary: This study assessed the effect of carbohydrate intake on self-selected soccer-specific running performance. Sixteen male soccer players (age 23 ± 4 years; body mass 76.9 ± 7.2 kg; predicted VO2max = 54.2 ± 2.9 mL∙kg-1∙min-1; soccer experience 13 ± 4 years) completed a progressive multistage fitness test, familiarisation trial and two experimental trials, involving a modified version of the Loughborough Intermittent Shuttle Test (LIST) to simulate a soccer match in a fed state. Subjects completed six 15 min blocks (two halves of 45 min) of intermittent shuttle running, with a 15-min half-time. Blocks 3 and 6, allowed self-selection of running speeds and sprint times, were assessed throughout. Subjects consumed 250 mL of either a 12% carbohydrate solution (CHO) or a non-caloric taste matched placebo (PLA) before and at half-time of the LIST. Sprint times were not different between trials (CHO 2.71 ± 0.15 s, PLA 2.70 ± 0.14 s; p = 0.202). Total distance covered in self-selected blocks (block 3: CHO 2.07 ± 0.06 km; PLA 2.09 ± 0.08 km; block 6: CHO 2.04 ± 0.09 km; PLA 2.06 ± 0.08 km; p = 0.122) was not different between trials. There was no difference between trials for distance covered (p ≥ 0.297) or mean speed (p ≥ 0.172) for jogging or cruising. Blood glucose concentration was greater (p < 0.001) at the end of half-time during the CHO trial. In conclusion, consumption of 250 mL of 12% CHO solution before and at half-time of a simulated soccer match does not affect self-selected running or sprint performance in a fed state.

#3 Observations of youth football training: How do coaches structure training sessions for player development?
Reference: J Sports Sci. 2017 Jan 7:1-9. doi: 10.1080/02640414.2016.1277034. [Epub ahead of print]
Authors: O'Connor D, Larkin P, Williams AM
Summary: We used systematic observation tools to explore the structure (i.e., activity and inactivity) and sequencing (i.e., the types of activities used) of football coaching sessions in Australia following the implementation of a new National Curriculum. Youth soccer coaches (n = 34), coaching within the Skill Acquisition (U11-U13 n = 19) and Game Training (U14-U17 n = 15) phases of the Football Federation Australia National Curriculum participated. Participants were filmed during a regular coaching session, with systematic observation of the session undertaken to provide a detailed analysis of the practice activities and coach behaviours. Findings indicated a session comprised of Playing Form activities (40.9%), Training Form activities (22.3%), inactivity (31%), and transitions between activities (5.8%). Coaches prescribed more Training Form activities (e.g., individual (5.4%) and drills (15.1%)) early in the session and progressed to Playing Form activities (i.e., small-sided games (15.3%) then larger games (24.8%)) later in the session. Most inactivity reflected the players listening to the coach - either in a team huddle (9.9%) or frozen on the spot during an activity (16.5%). In addition, coaches generally spent over 3 min communicating to players prior to explaining and introducing an activity regardless of when in the session the activity was scheduled.

#4 Do Neurocognitive SCAT3 Baseline Test Scores Differ Between Footballers (Soccer) Living With and Without Disability? A Cross-Sectional Study
Reference: Clin J Sport Med. 2017 Jan 17. doi: 10.1097/JSM.0000000000000407. [Epub ahead of print]
Authors: Weiler R, van Mechelen W, Fuller C, Ahmed OH, Verhagen E
Summary: The purpose was to determine if baseline Sport Concussion Assessment Tool, third Edition (SCAT3) scores differ between athletes with and without disability. Team doctors and physiotherapists supporting England football teams recorded players' SCAT 3 baseline tests from August 1, 2013 to July 31, 2014. A convenience sample of 249 England footballers, of whom 185 were players without disability (male: 119; female: 66) and 64 were players with disability (male learning disability: 17; male cerebral palsy: 28; male blind: 10; female deaf: 9). Between-group comparisons of median SCAT3 total and section scores were made using nonparametric Mann-Whitney-Wilcoxon ranked-sum test. All footballers with disability scored higher symptom severity scores compared with male players without disability. Male footballers with learning disability demonstrated no significant difference in the total number of symptoms, but recorded significantly lower scores on immediate memory and delayed recall compared with male players without disability. Male blind footballers' scored significantly higher for total concentration and delayed recall, and male footballers with cerebral palsy scored significantly higher on balance testing and immediate memory, when compared with male players without disability. Female footballers with deafness scored significantly higher for total concentration and balance testing than female footballers without disability. This study suggests that significant differences exist between SCAT3 baseline section scores for footballers with and without disability. Concussion consensus guidelines should recognize these differences and produce guidelines that are specific for the growing number of athletes living with disability.

#5 Effects of leg contrast strength training on sprint, agility and repeated change of direction performance in male soccer players
Reference: J Sports Med Phys Fitness. 2017 Jan 17. doi: 10.23736/S0022-4707.17.06951-1. [Epub ahead of print]
Authors: Hammami M, Negra Y, Shephard RJ, Souhaiel Chelly M
Summary: Contrast training is popular technique among individuals who are involved in dynamic sports, having as its goal an increase in dynamic muscular performance. It is characterized by the use of high and low loads in the same strength training session. The present investigation aimed to determine the effects of adding 8--weeks of contrast strength training (CSTP) to regular soccer practice in U--17 male soccer players during the competitive season. We hypothesized that CSTP would enhance their performance. Subjects were divided randomly divided between a control group (CG, n=12) and a contrast strength group (CSG, n=19). The 2 groups trained together; controls followed the regular soccer program, which was replaced by a contrast strength training program for the experimental group. Performance was assessed before and after training, using 10 measures : 5--10--, 20-- 30--, and 40--m sprints, a 4 x 5 m sprint (S4 x 5), a 9--3--6--3--9 m sprint with 180° turns (S180° ), a 9--3--6--3--9 m sprint with backward and forward running (SBF), a repeated--shuttle--sprint ability test (RSSA), and a repeated change of direction test (RCOD). CSG showed gains relative to controls in 5--m (p<0.000), 10--m (p<0.001), 20--m (p<0.001), 30--m (p<0.05) and 40-m (p<0.05) sprints. There were also significant gains in S180°, SBF, and S4 x 5 agility tests (p<0.01), and all RCOD parameters (p's <0.05) except RCOD--FI (p=0.055) but no significant change in any RSSA parameters. We conclude that biweekly contrast strength training can be commended to U--17 male soccer players as a means of improving many important components of athletic performance relative to standard in--season training.

#6 Agility training in young elite soccer players: promising results compared to change of direction drills
Reference: Biol Sport. 2016 Dec;33(4):345-351. doi: 10.5604/20831862.1217924. Epub 2016 Sep 10.
Authors: Chaalali A, Rouissi M, Chtara M, Owen A, Bragazzi NL, Moalla W, Chaouachi A, Amri M, Chamari K
Download link:
Summary: The aim of this study was to compare the effect of two different training programmes - change of direction (COD) vs. agility (AG) - on straight sprint (SS), COD and AG test performances in young elite soccer players. Thirty-two soccer players (age: 14.5±0.9 years; height: 171.2±5.1 cm; body mass: 56.4±7.1 kg, body fat: 10.3±2.3%) participated in a short-term (6 weeks) training study. Players were randomly assigned to two experimental groups - training with change of direction drills (COD-G, n=11) or using agility training (AG-G, n= 11) - and to a control group (CON-G, n=10). All players completed the following tests before and after training: straight sprint (15m SS), 15 m agility run with (15m-AR-B) and without a ball (15m-AR), 5-0-5 agility test, reactive agility test (RAT), and RAT test with ball (RAT-B). A significant group effect was observed for all tests (p<0.001; η2=large). In 15m SS, COD-G and AG-G improved significantly (2.21; ES=0.57 and 2.18%; ES=0.89 respectively) more than CON-G (0.59%; ES=0.14). In the 15m-AR and 5-0-5 agility test, COD-G improved significantly more (5.41%; ES=1.15 and 3.41; ES=0.55 respectively) than AG-G (3.65%; ES=1.05 and 2.24; ES=0.35 respectively) and CON-G (1.62%; ES=0.96 and 0.97; ES=0.19 respectively). Improvements in RAT and RAT-B were larger (9.37%; ES=2.28 and 7.73%; ES=2.99 respectively) in RAT-G than the other groups. In conclusion, agility performance amongst young elite soccer could be improved using COD training. Nevertheless, including a conditioning programme for agility may allow a high level of athletic performance to be achieved.

#7 Knee function among elite handball and football players 1 to 6 years after anterior cruciate ligament injury
Reference: Scand J Med Sci Sports. 2017 Jan 20. doi: 10.1111/sms.12842. [Epub ahead of print]
Authors: Myklebust G, Bahr R, Nilstad A, Steffen K
Summary: The aim of the study was to describe objective and self-reported knee function for athletes who have returned to elite handball and football play after an ACL injury, comparing these to non-injured players at the same level. A total of 414 handball and 444 football players completed baseline tests from 2007 through 2014, examining lower extremity strength, dynamic balance, knee laxity, and knee function (KOOS questionnaire). Measures were compared between injured and non-injured legs, and between injured legs and legs of controls. Eighty (9.3%) of the 858 players reported a previous ACL injury, 1 to 6 yrs post-injury (3.5±2.5 yrs), 49 handball (61.3%) and, 31 football players (38.7%). We found no difference in strength or dynamic balance between previously ACL-injured (N=80) and non-injured players legs (N=1556). However, lower quadriceps (6.3%, 95% CI: 3.2 to 9.2) and hamstrings muscle strength (6.1%, 95% CI: 3.3 to 8.1) was observed in previously ACL-injured legs compared to the non-injured contralateral side (N=80). ACL-injured knees displayed greater joint laxity than for the contralateral knee (N=80, 17%, 95% CI: 8 to 26) and healthy knees (N=1556, 23%, 95% CI: 14 to 33). KOOS scores were significantly lower for injured knees compared to knees of non-injured players. ACL-injured players who have successfully returned to elite sport have comparable strength and balance measures as their non-injured teammates. Subjective perception of knee function is strongly affected by injury history, with clinically relevant lower scores for the KOOS sub-scores Pain, Function, Sport and Quality Of Life.

#8 Non-surgical treatment of pubic overload and groin pain in amateur football players: a prospective double-blinded randomised controlled study
Reference: Knee Surg Sports Traumatol Arthrosc. 2017 Jan 16. doi: 10.1007/s00167-017-4423-z. [Epub ahead of print]
Authors: Schoberl M, Prantl L, Loose O, Zellner J, Angele P, Zeman F, Spreitzer M, Nerlich M, Krutsch W
Summary: The incidence of groin pain in athletes is steadily increasing. Symptomatic pubic overload with groin pain and aseptic osteitis pubis represent well-known and frequently misdiagnosed overuse injuries in athletes. This study investigated the benefits of standardised non-surgical treatment for swift return-to-football. In a prospective double-blinded controlled study, 143 amateur football players with groin pain as well as radiological signs and clinical symptoms of pubic overload were analysed for 1 year. Two randomised study groups participated in an intensive physical rehabilitation programme, either with or without shock wave therapy. The control group did not participate in any standardised rehabilitation programme but only stopped participating in sports activity. Follow-up examinations took place 1, 3 months and 1 year after the beginning of therapy. Endpoints were visual analogue scale (VAS), functional tests, the time of return-to-football, recurrent complaints and changes in the MR image. Forty-four football players with groin pain and aseptic osteitis pubis were randomised into two study groups; 26 received shock wave therapy, 18 did not. Clinical examination showed pubic overload as a multi-located disease. Players receiving shock wave therapy showed earlier pain relief in the VAS (p < 0.001) and returned to football significantly earlier (p = 0.048) than players without this therapy. Forty-two of 44 players of both study groups returned to football within 4 months after the beginning of therapy and had no recurrent groin pain within 1 year after trauma. Fifty-one players of the control group returned to football after 240 days (p < 0.001), of whom 26 (51%) experienced recurrent groin pain. Follow-up MRI scans did not show any effect of shock wave therapy. Non-surgical therapy is successful in treating pubic overload and osteitis pubis in athletes. Shock wave therapy as a local treatment significantly reduced pain, thus enabling return-to-football within 3 months after trauma. Early and correct diagnosis is essential for successful intensive physiotherapy.

#9 Effect of specific exercise-based football injury prevention programmes on the overall injury rate in football: a systematic review and meta-analysis of the FIFA 11 and 11+ programmes
Reference: Br J Sports Med. 2017 Jan 13. pii: bjsports-2016-097066. doi: 10.1136/bjsports-2016-097066. [Epub ahead of print]
Authors: Thorborg K, Krommes KK, Esteve E, Clausen MB, Bartels EM, Rathleff MS
Summary: The purpose was to investigate the effect of FIFA injury prevention programmes in football (FIFA 11 and FIFA 11+). Randomised controlled trials comparing the FIFA injury prevention programmes with a control (no or sham intervention) among football players. Databases such as MEDLINE via PubMed, EMBASE via OVID, CINAHL via Ebsco, Web of Science, SportDiscus and Cochrane Central Register of Controlled Trials, from 2004 to 14 March 2016 were utilized. Six cluster-randomised controlled trials had assessed the effect of FIFA injury prevention programmes compared with controls on the overall football injury incidence in recreational/subelite football. These studies included 2 specific exercise-based injury prevention programmes: FIFA 11 (2 studies) and FIFA 11+ (4 studies). The primary analysis showed a reduction in the overall injury risk ratio of 0.75 (95% CI 0.57 to 0.98), p=0.04, in favour of the FIFA injury prevention programmes. Secondary analyses revealed that when pooling the 4 studies applying the FIFA 11+ prevention programme, a reduction in the overall injury risk ratio (incidence rate ratio (IRR) 0.61; 95% CI 0.48 to 0.77, p<0.001) was present in favour of the FIFA 11+ prevention programme. No reduction was present when pooling the 2 studies including the FIFA 11 prevention programme (IRR 0.99; 95% CI 0.80 to 1.23, p=0.940). An injury-preventing effect of the FIFA injury prevention programmes compared with controls was shown in football. This effect was induced by the FIFA 11+ prevention programme which has a substantial injury-preventing effect by reducing football injuries by 39%, whereas a preventive effect of the FIFA 11 prevention programme could not be documented.






Chapter 4 of the UEFA Club Footballing Landscape was about the supporters.

Over 170 mio people went to European league matches in 2015/2016 with 55 mio in England and Germany alone. Overall there was a significant increase and 14 leagues achieved their best attendance figures in more than 10 years.

The highest aggregate and average crowds were once again found in the English Premier League and the German Bundesliga in 2015/16. All eight clubs that recorded home match attendances of more than 1 million play in the top tier in England, Germany or Spain, and four of the top ten European leagues by total attendance were second or third-tier leagues in England, Germany and Spain, emphasising the strength and depth of supporter interest and stadium capacity in these three traditional powerhouses.


Attendances at European football matches (domestic and UEFA) exceeded 170 million in 2015/16. Including lower league attendances, German and English clubs attracted 55 million spectators between them. The trend in the top divisions was largely positive, with 34 leagues reporting increased crowds, compared with 17 that reported a drop. Combined top division attendances increased by more than 2.6 million between 2014/15 and 2015/16. In total, 13 top-tier leagues added at least 100,000 to their total crowds between 2014/15 and 2015/16, contributing to a net top-division increase of more than 2.6 million.


Nine clubs added 5,000 or more to their average season match attendance between 2014/15 and 2015/16. At the top of the list is Manchester City FC, which benefitted from increased stadium capacity, as did Udinese Calcio and Olympique Lyonnais.



There is a clear link between average attendance trends and on-pitch performance, as measured by changes in final league position. On average, moving one position up the league table added 3% to average attendance, with each position lost resulting in an equivalent 3% drop in attendance.
A significant improvement or deterioration in performance (moving three places or more in the table), as seen more than 2,000 times across European leagues in the last decade, has led on average to crowds increasing by 15% or decreasing by 9%.






Al-Kass U17 International Tournament Pre-match Warm-ups

The 6th edition of the annual Al-Kass U17 international tournament was held in Doha until today.

My former colleague Ioannis Grammos was able to visit some games and kind to record some warm-up procedures of Eintracht Frankfurt, AS Roma and Kashiwa Reysol.

Eintracht Frankfurt

AS Roma

Kashiwa Reysol

HERE are the teams and their warm-up from last year.





Latest research in football - week 1 - 2017

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 Optimization of Game Formats in U-10 Soccer Using Logistic Regression Analysis
Reference: J Hum Kinet. 2016 Dec 15;54:163-171. doi: 10.1515/hukin-2016-0047. eCollection 2016.
Authors: Amatria M, Lapresa D, Arana J, Anguera MT, Garzon B
Download link:
Summary: Small-sided games provide young soccer players with better opportunities to develop their skills and progress as individual and team players. There is, however, little evidence on the effectiveness of different game formats in different age groups, and furthermore, these formats can vary between and even within countries. The Royal Spanish Soccer Association replaced the traditional grassroots 7-a-side format (F-7) with the 8-a-side format (F-8) in the 2011-12 season and the country's regional federations gradually followed suit. The aim of this observational methodology study was to investigate which of these formats best suited the learning needs of U-10 players transitioning from 5-aside futsal. We built a multiple logistic regression model to predict the success of offensive moves depending on the game format and the area of the pitch in which the move was initiated. Success was defined as a shot at the goal. We also built two simple logistic regression models to evaluate how the game format influenced the acquisition of technicaltactical skills. It was found that the probability of a shot at the goal was higher in F-7 than in F-8 for moves initiated in the Creation Sector-Own Half (0.08 vs 0.07) and the Creation Sector-Opponent's Half (0.18 vs 0.16). The probability was the same (0.04) in the Safety Sector. Children also had more opportunities to control the ball and pass or take a shot in the F-7 format (0.24 vs 0.20), and these were also more likely to be successful in this format (0.28 vs 0.19).

#2 Nonverbal Communication of Confidence in Soccer Referees: An Experimental Test of Darwin's Leakage Hypothesis
Reference: J Sport Exerc Psychol. 2016 Dec 29:1-24. doi: 10.1123/jsep.2016-0192. [Epub ahead of print]
Authors: Furley P, Schweizer G
Summary: The goal of the present paper was to investigate whether soccer referees' nonverbal behavior (NVB) differed based on the difficulty of their decisions and whether perceivers could detect these systematic variations. On the one hand, communicating confidence via NVB is emphasized in referee training. On the other hand, it seems feasible from a theoretical point of view that particularly following relatively difficult decisions referees have problems controlling their NVB. We conducted three experiments in order to investigate into this question. Experiment 1 (N = 40) and Experiment 2 (N = 60) provided evidence that perceivers regard referees' NVB as less confident following ambiguous decisions as compared to following unambigous decisions. Experiment 3 (N = 58) suggested that perceivers were more likely to debate with the referee when referees nonverbally communicated less confidence. We discuss consequences for referee training.

#3 Etiology and Recovery of Neuromuscular Fatigue following Simulated Soccer Match-Play
Reference: Med Sci Sports Exerc. 2017 Jan 3. doi: 10.1249/MSS.0000000000001196. [Epub ahead of print]
Authors: Thomas K, Dent J, Howatson G, Goodall S
Summary: We profiled the etiology and recovery of neuromuscular fatigue post-simulated-soccer-match-play. Fifteen semi-professional players completed a 90 min simulated soccer match. Pre-, immediately-post and at 24, 48 and 72 h participants completed a battery of neuromuscular, physical and perceptual tests. Perceived fatigue and muscle soreness were assessed via visual analogue scales. Maximum voluntary contraction (MVC) and twitch responses to electrical (femoral nerve) and magnetic (motor cortex) stimulation during isometric knee-extensor contractions and at rest were measured to assess central (voluntary activation, VA) and peripheral (quadriceps potentiated twitch force, Qtw,pot) fatigue, and responses to single and paired-magnetic stimuli were assessed to quantify corticospinal excitability and short-intracortical inhibition (SICI), respectively. Countermovement jump, reactive strength index and sprint performance were assessed to profile the recovery of physical function. Simulated match-play elicited decrements in MVC that remained unresolved at 72 h (P = 0.01). Central fatigue was prominent immediately post-exercise (-9% reduction in VA) and remained depressed at 48 h (-2%, P = 0.03). Qtw,pot declined by 14% post-exercise, remained similarly depressed at 24 h and had not fully recovered by 72 h post (-5%, P = 0.01). Corticospinal excitability was reduced at 24 h (P = 0.047) only, and no change in SICI was observed. Measures of jump performance and self-reported fatigue followed a similar time-course recovery to neuromuscular fatigue. Central processes contribute significantly to the neuromuscular fatigue experienced in the days post-soccer-match-play, but the magnitude and slower recovery of peripheral fatigue indicates that it is the resolution of muscle function that primarily explains the recovery of neuromuscular fatigue post- soccer match-play.

#4 Laterality related to the successive selection of Dutch national youth soccer players
Reference: J Sports Sci. 2017 Jan 6:1-5. doi: 10.1080/02640414.2016.1262544. [Epub ahead of print]
Authors: Verbeek J, Elferink-Gemser MT, Jonker L, Huijgen BC, Visscher C
Summary: In the general population, estimates of left-foot preference are around 20%. In soccer, specific tasks create positional demands, requiring 40% of the players to be left-footed. Whether and how this is related to the selection of players is unknown. To examine the successive selection of soccer players for Dutch national youth teams in relation to foot preference, 280 youth players (age = 16.2 ± 1.08 years) were monitored from the U16 through the U19 teams over the last 5 years. No difference in successive selection between left- and right-footed players was found (p < 0.05). Regardless of foot preference, more than 50% of the selected players were deselected out of a national youth team after 2 years. On average, 31% of the national youth players were left-footed, which is higher than expected, based on population estimates (χ2 (1) = 37.49, p < 0.001, w = 0.27). However, there was an under-representation of left-footed players, based on expected positional demands (i.e., attack, midfield, defence) (χ2 (1) = 16.83, p < 0.001, w = 0.18). The conclusion is that left-foot preference increases the probability of selection in Dutch national youth soccer teams.

#5 Energy Intake and Expenditure of Professional Soccer Players of the English Premier League: Evidence of Carbohydrate Periodization
Reference: Int J Sport Nutr Exerc Metab. 2017 Jan 4:1-25. doi: 10.1123/ijsnem.2016-0259. [Epub ahead of print]
Authors: Anderson L, Orme P, Naughton RJ, Close GL, Milsom J, Rydings D, O'Boyle A, Di Michele R, Louis J, Hambley C, Speakman JR, Morgans R, Drust B, Morton JP
Summary: In an attempt to better identify and inform the energy requirements of elite soccer players, we quantified the energy expenditure (EE) of players from the English Premier League (n=6) via the doubly labeled water method (DLW) over a 7-day in-season period. Energy intake (EI) was also assessed using food diaries, supported by the remote food photographic method and 24 h recalls. The 7-day period consisted of 5 training days (TD) and 2 match days (MD). Although mean daily EI (3186 ± 367 kcals) was not different from (P>0.05) daily EE (3566 ± 585 kcals), EI was greater (P<0.05) on MD (3789 ± 532 kcal; 61.1 ± 11.4 LBM) compared with TD (2956 ± 374 kcal; 45.2 ± 9.3 LBM, respectively). Differences in EI were reflective of greater (P<0.05) daily CHO intake on MD (6.4 ± 2.2 compared with TD (4.2 ± 1.4 Exogenous CHO intake was also different (P<0.01) during training sessions (3.1 ± 4.4 g.h-1) versus matches (32.3 ± 21.9 g.h-1). In contrast, daily protein (205 ± 30, P=0.29) and fat intake (101 ± 20, P=0.16) did not display any evidence of daily periodization. Although players readily achieve current guidelines for daily protein and fat intake, data suggest that CHO intake on the day prior to and in recovery from match play was not in accordance with guidelines to promote muscle glycogen storage.

#6 Anterior Inferior Iliac Spine Morphology and Outcomes of Hip Arthroscopy in Soccer Athletes: A Comparison to Nonkicking Athletes
Reference: Arthroscopy. 2016 Dec 31. pii: S0749-8063(16)30891-X. doi: 10.1016/j.arthro.2016.10.019. [Epub ahead of print]
Authors: Nawabi DH, Degen RM, Fields KG, Wentzel CS, Adeoye O, Kelly BT
Summary: The aim of the study was to describe the anterior inferior iliac spine (AIIS) morphology and clinical outcomes following arthroscopic surgical decompression in a group of high-level soccer athletes presenting with symptomatic hip impingement when compared with a control group of nonkicking athletes. From 2009 to 2012, we retrospectively reviewed our prospective hip registry for soccer athletes who underwent arthroscopic treatment for femoroacetabular impingement (FAI) with 2-year follow-up, comparing with a control group of nonkicking athletes. Demographics were collected and radiographic studies (plain radiograph and computed tomographic scan) reviewed for several parameters, including AIIS morphology. Patient-reported outcome scores, including modified Harris Hip Score (mHHS), Hip Outcome Score-Activities of Daily Living (HOS-ADL) and Sport-Specific Subscale (HOS-SSS), and International Hip Outcome Tool-33 (iHOT-33), were administered preoperatively, at 6 months, and at 1, 2, and 3 years postoperatively. Twenty-six soccer players (34 hips) and 87 nonkicking athletes (115) hips were identified. Demographics, including age (19.2 ± 4.1 vs 20.1 ± 3.8 years) and gender distribution (53.8% vs 51.7% male), were similar between the soccer and nonkicking athletes (P = .288, .849). Eighty-four percent of soccer players demonstrated some abnormality of the AIIS extending to (type II, 52%) or below the anterior acetabular rim (type III, 32%), compared with 52% nonkicking athletes (P < .001). At a mean follow-up of 35 months (range, 24-57 months) there was significant improvement in all outcome scores in both groups from pre- to postoperation (P < .001). There was no evidence of differences in outcome scores between groups (mHSS: 89 ± 14.6 vs 88.2 ± 14.4, P = .804; HOS-ADL: 94.1 ± 9.1 vs 92.2 ± 11.1, P = .431; HOS-SSS: 86 ± 17.1 vs 81.3 ± 24.3, P = .362) with the exception of iHOT-33 (81.7 ± 19 vs 70.3 ± 23.6, P = .027). High-level soccer players have a significantly higher rate of subspine impingement compared with nonkicking athletes. There should be a high index of suspicion when treating soccer players for FAI, where appropriate recognition and treatment of subspine impingement can yield excellent clinical results.

#7 Acute Effects of Three Neuromuscular Warm-Up Strategies on Several Physical Performance Measures in Football Players
Reference: PLoS One. 2017 Jan 6;12(1):e0169660. doi: 10.1371/journal.pone.0169660. eCollection 2017.
Authors: Ayala F, Calderon-Lopez A, Delgado-Gosalbez JC, Parra-Sanchez S, Pomares-Noguera C, Hernandez-Sanchez S, Lopez-Valenciano A, De Ste Croix M
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Summary: No studies have analysed the acute effects of the FIFA 11+ and Harmoknee warm-up programmes on major physical performance measures. The aim of this study was to analyse the acute (post-exercise) effects of the FIFA 11+, Harmoknee and dynamic warm-up routines on several physical performance measures in amateur football players. A randomized, crossover and counterbalanced study design was used to address the purpose of this study. A total of sixteen amateur football players completed the following protocols in a randomized order on separate days: a) FIFA 11+; b) Harmoknee; and c) dynamic warm-up (DWU). In each experimental session, 19 physical performance measures (joint range of motion, hamstring to quadriceps [H/Q] strength ratios, dynamic postural control, 10 and 20 m sprint times, jump height and reactive strength index) were assessed. Measures were compared via a magnitude-based inference analysis. The results of this study showed no main effects between paired comparisons (FIFA 11+ vs. DWU, Harmoknee vs. DWU and Harmoknee vs. FIFA 11+) for joint range of motions, dynamic postural control, H/Q ratios, jumping height and reactive strength index measures. However, significant main effects (likely effects with a probability of >75-99%) were found for 10 (1.7%) and 20 (2.4%) m sprint times, demonstrating that both the FIFA 11+ and Harmoknee resulted in slower sprint times in comparison with the DWU. Therefore, neither the FIFA 11+ nor the Harmoknee routines appear to be preferable to dynamic warm-up routines currently performed by most football players prior to training sessions and matches.

#8 Head injuries in children's football - results from two prospective cohort studies in four European countries
Reference: Scand J Med Sci Sports. 2017 Jan 4. doi: 10.1111/sms.12839. [Epub ahead of print]
Authors: Faude O, Rossler R, Junge A, Aus der Funten K, Chomiak J, Verhagen E, Beaudouin F, Dvorak J, Feddermann-Demont N
Summary: Head injuries are considered harmful in children. We analysed head and neck injuries in organised football in 7 to 12 year old children. Data for this analysis were obtained from a prospective cohort study over two consecutive football seasons in two European countries, and a randomised intervention trial over one season in four European countries. Football exposure and injuries were documented through an online database. Detailed information regarding injury characteristics and medical follow-up was retrieved from coaches, children and parents by phone. Thirty-nine head injuries and one neck injury (5% of all 791 injuries) were documented during 9,933 player-seasons (total football exposure 688,045 h). The incidence was 0.25 [95%CI 0.15, 0.35] head/neck injuries per 1,000 match hours (N=23 match injuries) and 0.03 [95%CI 0.02, 0.03] per 1,000 training hours. Eleven concussions (27.5%), nine head contusions (22.5%), eight lacerations or abrasions (20%), two nose fractures (2.5%) and two dental injuries (2.5%) occurred. The remaining eight injuries were nose bleeding or other minor injuries. Thirty injuries (75%) resulted from contact with another player, ten injuries were due to collision with an object, falling or a hit by the ball. Whereas 70% of all head injuries (N=28) were due to frontal impacts, 73% of concussions (N=8) resulted from an impact to the occiput. The incidence and severity of head injuries in children's football is low. Coaches and parents, however, should be sensitised regarding the potential of concussions, particularly after an impact to the occiput.

#9 Physiological, Perceptual and Performance Responses Associated With Self-Selected Versus Standardized Recovery Periods During a Repeated Sprint Protocol in Elite Youth Football Players: A Preliminary Study
Reference: Pediatr Exerc Sci. 2017 Jan 4:1-20. doi: 10.1123/pes.2016-0130. [Epub ahead of print]
Authors: Gibson N, Brownstein C, Ball D, Twist C
Summary: The purpose was to examine the physiological and perceptual responses of youth footballers to a repeated sprint protocol employing standardized and self-selected recovery. Eleven male participants (13.7 ± 1.1 years) performed a repeated sprint assessment comprising 10 x 30 m efforts. Employing a randomized crossover design, repeated sprints were performed using 30 s and self-selected recovery periods. Heart rate was monitored continuously with ratings of perceived exertion (RPE) and lower body muscle power measured 2 min after the final sprint. The concentration of blood lactate was measured at 2, 5 and 7 minutes post sprinting. Magnitude of effects were reported using effect size (ES) statistics ± 90% confidence interval and percentage differences. Differences between trials were examined using paired student t-tests (p < 0.05). Self-selected recovery resulted in most likely shorter recovery times (57.7%; ES 1.55 ± 0.5; p < 0.01), a most likely increase in percentage decrement (65%; ES 0.36 ±1 0.21; p = 0.12), very likely lower heart rate recovery (-58.9%; ES -1.10 ± 0.72; p = 0.05), and likely higher blood lactate concentration (p = 0.08-0.02). Differences in lower body power and RPE were unclear (p > 0.05). Self-selected recovery periods compromise repeated sprint performance.





Player profiles and use of domestic/foreign players

The second big part of the "The European Club Footballing Landscape", from the 2014/2015 season, was about the players.


The average age of first-team squads (in January 2016) can be seen in the following maps below. It seems that the talent-importing leagues tend to have a higher average first team squad compared to talent exporters (such as Netherlands and the Balkan countries).

Russia (27.1) and Turkey (27.1) have the oldest average player age in Europe with the second Dutch league comfortable the youngest (23.1).

The big five have the following average player age: England (26.9), Italy (26.9), Spain (26.9), France (26.0) and Germany (25.4).



The data from around the globe paints the following picture:

The Philippines (27.3), Qatar (27.2) and Mexico (27.1) having the oldest players and New Zealands ASB Premiership (24.1) the youngest top tier outside Europe.



The English Premier League has the highest percentage of expatriate players at almost 70%.

Other countries of the big five were Serie A (55.5%) and Bundesliga (49.2%).

Brazilian players represents ~25% of players in the top tier in Portugal.



Another topic about players is about the recruitment and the market value.



A strong majoriy (25.1 bn or 82%) of global talent (30.6 bn) is concentrated in European leagues with 48% playing in England, Germany, Italy of Spain. Interestingly, this includes five Italian, four German, four English and three Turkish leagues.



And here is the worldwide perspective.

The remaining 5.5 bn from the global talent pool is spread outside Europe. The Brazilian first and second tier, the Argentinian first tier and the first and second Mexican tier holding the greatest value.









Head coach stability

The head coach plays a paramount role in every football club. Consequently, UEFA investigated different topics "around" the head coach in its release "The European Club Footballing Landscape".


The manuscript highlighted some data evaluated from the the 2014/2015 season.


First topic was about "Head coach security" and it seems that it remains a problem and it i getting worse in many places. Please have a look at the first European and global maps below.


At least one head coach was replaced in 2015 in every one of the 60 European leagues analyzed in this section.



The security map clearly demonstrates less patience the further south east you go in Europe.


There are some interesting information with regards to a worldwide perspective. Coaches in Costa Rica and Brazil will have a hard time to survive.



The ages' of the head coaches were also analyzed. It seems that there is no obvious regional tendency towards young or old coaches. The wealthier leagues tend towards older head coaches. England (52 years of age), France (51 years) and Turkey (51.3 years) were among the highest of the 60 leagues. Northern Ireland had the youngest average age of head coaches with 40.6 years.



Here is the worldwide perspective with regards to average head coach ages.



The following picture shows the number of expatriate head coach by region. England shows the highest proportion of foreign head coaches in Europe (75%), Ecuador the highest in the American leagues (83%) and Qatar the highest in the AFC (100%).


Italian and Serbien head coaches are the most widely spread.








Latest research in football - week 51 - 2016

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 Nine-year study of US high school soccer injuries: data from a national sports injury surveillance programme
Reference: Br J Sports Med. 2016 Dec 28. pii: bjsports-2015-095946. doi: 10.1136/bjsports-2015-095946. [Epub ahead of print]
Authors: Khodaee M, Currie DW, Asif IM, Comstock RD
Summary: Research on high school soccer injury epidemiology is sparse. Therefore the purpose was to describe high school soccer injury rates, trends and patterns by type of athlete exposure (AE), position and sex. This descriptive epidemiological study used data from a large national high school sports injury surveillance programme to describe rates and patterns of soccer-related injuries including concussion sustained from 2005/2006 to 2013/2014. Injury rates are calculated per 1000 AEs. Overall, 6154 soccer injuries occurred during 2 985 991 AEs; injury rate=2.06 per 1000 AEs. Injury rates were higher during competition (4.42) than practice (1.05; rate ratio (RR)=4.19; 95% CI 3.98 to 4.41), and in girls (2.33) than boys (1.83; RR=1.27, 95% CI 1.21 to 1.34). Boys' non-concussion injury rates decreased significantly (p=0.001) during the study period while reported concussion rates increased significantly (p=0.002). Girls' non-concussion rates were relatively stable and reported concussion rates increased significantly (p=0.004). Player-player contact was the injury mechanism that led to the most competition injuries (injury proportion ratio (IPR)=2.87; 95% CI 2.57 to 3.21), while non-contact injuries were the most common mechanisms among practice injuries (IPR=2.10; 95% CI 1.86 to 2.38). Recovery from concussion was >7 days in a third of the cases. Injury patterns were similar between sexes with respect to position played and location on the field at the time of injury. High school soccer injury rates vary by sex and type of exposure, while injury patterns are more similar across sexes. Reported concussion rates increased significantly over the study period in male and female athletes.

#2 Effectiveness of a stress management pilot program aimed at reducing the incidence of sports injuries in young football (soccer) players
Reference: Phys Ther Sport. 2016 Sep 6. pii: S1466-853X(16)30097-9. doi: 10.1016/j.ptsp.2016.09.003. [Epub ahead of print]
Authors: Olmedilla-Zafra A, Rubio VJ, Ortega E, García-Mas A
Summary: Several attempts to reduce the incidence of sport injuries using psychosocial interventions produced fruitful, although inconclusive results. This paper presents the effectiveness and implementation issues of a pilot 3-month stress-management and muscle relaxation program aimed at reducing sport injury incidence. The program was administered by a trained psychologist on a once-a-week, 1-h session basis. Seventy-four male soccer players from four National Youth league teams voluntarily participated. Teams were randomly assigned to either treatment/non-treatment group. Injury protocol, Self-monitoring cards, Athletes' satisfaction and commitment survey, Coaches' interview were used as data measures.  Group main effect and Time-Group interaction effect were both statistically significant, F(1,60) = 8.30, p = 0.005, η2p = 0.121, with the average number of injuries larger in the post-treatment phase of non-treatment group (p = 0.005, η2p = 0.077). There was a significant decrease in the average number of injuries for the intervention group before and after implementing the program (p < 0.001, η2p = 0.309). A controlled implementation of a psychosocial program was effective in reducing youth soccer sport injuries, with a high level of satisfaction and commitment from the athletes, as well as high acceptance from the coaches.

#3 Exercise Intensity During Power Wheelchair Soccer
Reference: Arch Phys Med Rehabil. 2016 Nov;97(11):1938-1944. doi: 10.1016/j.apmr.2016.05.012. Epub 2016 Jun 8.
Authors: Barfield JP, Newsome L, Malone LA
Summary: The purpose was to determine exercise intensity during power wheelchair soccer among a sample of persons with mobility impairments. Participants with severe mobility impairments (N=30) (mean ± SD, age: 29.40±15.51y, body mass index: 24.11±6.47kg/m2, power soccer experience: 7.91±3.93y, disability sport experience: 12.44±9.73y) were recruited from multiple power wheelchair soccer teams. Portable metabolic carts were used to collect oxygen consumption (V˙o2) data during resting and game play conditions. Average V˙o2 (expressed in metabolic equivalent tasks [METs]) during resting and game play conditions and rating of perceived exertion for game play. V˙o2 increased from 1.35±0.47 METs at rest to 1.81±0.65 METs during game play. This 34% increase in exercise intensity was significant (P<.01) and supported by a mean perceived exertion score of approximately 13 (somewhat hard). Although not able to sustain an intensity associated with reduced secondary disease risk (ie, 3 METs), the documented light-intensity exercise in the current study surpassed an intensity threshold associated with improved functional capacity and performance of daily living activities (ie, 1.5 METs).

#4 Real Time Quantification of Dangerousity in Football Using Spatiotemporal Tracking Data
Reference: PLoS One. 2016 Dec 30;11(12):e0168768. doi: 10.1371/journal.pone.0168768. eCollection 2016.
Authors: Link D, Lang S, Seidenschwarz P

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Summary: This study describes an approach to quantification of attacking performance in football. Our procedure determines a quantitative representation of the probability of a goal being scored for every point in time at which a player is in possession of the ball-we refer to this as dangerousity. The calculation is based on the spatial constellation of the player and the ball, and comprises four components: (1) Zone describes the danger of a goal being scored from the position of the player on the ball, (2) Control stands for the extent to which the player can implement his tactical intention on the basis of the ball dynamics, (3) Pressure represents the possibility that the defending team prevent the player from completing an action with the ball and (4) Density is the chance of being able to defend the ball after the action. Other metrics can be derived from dangerousity by means of which questions relating to analysis of the play can be answered. Action Value represents the extent to which the player can make a situation more dangerous through his possession of the ball. Performance quantifies the number and quality of the attacks by a team over a period of time, while Dominance describes the difference in performance between teams. The evaluation uses the correlation between probability of winning the match (derived from betting odds) and performance indicators, and indicates that among Goal difference (r = .55), difference in Shots on Goal (r = .58), difference in Passing Accuracy (r = .56), Tackling Rate (r = .24) Ball Possession (r = .71) and Dominance (r = .82), the latter makes the largest contribution to explaining the skill of teams. We use these metrics to analyse individual actions in a match, to describe passages of play, and to characterise the performance and efficiency of teams over the season. For future studies, they provide a criterion that does not depend on chance or results to investigate the influence of central events in a match, various playing systems or tactical group concepts on success.

#5 Content Validity and Psychometric Properties of the Nomination Scale for Identifying Football Talent (NSIFT): Application to Coaches, Parents and Players
Reference: Sports 2017, 5(1), 2; doi:10.3390/sports5010002
Authors: Prieto-Ayuso A, Pastor-Vicedo JC, Contreras-Jordan O
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Summary: The identification of football talent is a critical issue both for clubs and the families of players. However, despite its importance in a sporting, economic and social sense, there appears to be a lack of instruments that can reliably measure talent performance. The aim of this study was to design and validate the Nomination Scale for Identifying Football Talent (NSIFT), with the aim of optimising the processes for identifying said talent. The scale was first validated through expert judgment, and then statistically, by means of an exploratory factor analysis (EFA), confirmatory factor analysis (CFA), internal reliability and convergent validity. The results reveal the presence of three factors in the scale’s factor matrix, with these results being confirmed by the CFA. The scale revealed suitable internal reliability and homogeneity indices. Convergent validity showed that it is teammates who are best able to identify football talent, followed by coaches and parents. It can be concluded that the NSIFT is suitable for use in the football world. Future studies should seek to confirm these results in different contexts by means of further CFAs.

#6 Comparison of T2* relaxation times of articular cartilage of the knee in elite professional football players and age-and BMI-matched amateur athletes
Reference: Eur J Radiol. 2017 Jan;86:105-111. doi: 10.1016/j.ejrad.2016.10.028. Epub 2016 Oct 27.
Authors: Behzadi C, Welsch GH, Laqmani A, Henes FO, Kaul MG, Schoen G, Adam G, Regier M
Summary: Recent investigation has underlined the potential of quantitative MR imaging to be used as a complementary tool for the diagnosis of cartilage degeneration at an early state. The presented study analyses T2* relaxation times of articular cartilage of the knee in professional athletes and compares the results to age- and BMI (Body Mass Index)-matched healthy amateur athletes. 22 professional football players and 22 age- and BMI-matched individuals were underwent knee Magnetic Resonance Imaging (MRI) at 3T including qualitative and quantitative analysis. Qualitative analysis included e.g. meniscal tears, joint effusion and bone edema. For quantitative analysis T2* (22 ET: 4.6-53.6ms) measurements in 3D data acquisition were performed. Deep and superficial layers of 22 predefined cartilage segments were analysed. All data sets were postprocessed using a dedicated software tool. Statistical analysis included Student t-test, confidence intervals and a random effects model. In both groups, T2* relaxation times were significantly higher in the superficial compared to the deep layers (p<0.001). Professional athletes had significantly higher relaxation times in eight superficial and three deep cartilage layers in the predefined cartilage segments (p<0.05). Highly significant differences were found in the weight-bearing segments of the lateral superficial femoral condyle (p<0.001). Elevated T2* values in cartilage layers of professional football players compared to amateur athletes were noted. The effects seem to predominate in superficial cartilage layers.

#7 Short Duration Small Sided Football and to a Lesser Extent Whole Body Vibration Exercise Induce Acute Changes in Markers of Bone Turnover
Reference: Biomed Res Int. 2016;2016:3574258. doi: 10.1155/2016/3574258. Epub 2016 Nov 29.
Authors: Bowtell JL, Jackman SR, Scott S, Connolly LJ, Mohr M, Ermidis G, Julian R, Yousefian F, Helge EW, Jorgensen NR, Fulford J, Knapp KM, Krustrup P
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Summary: We aimed to study whether short-duration vibration exercise or football sessions of two different durations acutely changed plasma markers of bone turnover and muscle strain. Inactive premenopausal women (n = 56) were randomized to complete a single bout of short (FG15) or long duration (FG60) small sided football or low magnitude whole body vibration training (VIB). Procollagen type 1 amino-terminal propeptide (P1NP) was increased during exercise for FG15 (51.6 ± 23.0 to 56.5 ± 22.5 μg·L-1, mean ± SD, P < 0.05) and FG60 (42.6 ± 11.8 to 50.2 ± 12.8 μg·L-1, P < 0.05) but not for VIB (38.8 ± 15.1 to 36.6 ± 14.7 μg·L-1, P > 0.05). An increase in osteocalcin was observed 48 h after exercise (P < 0.05), which did not differ between exercise groups. C-terminal telopeptide of type 1 collagen was not affected by exercise. Blood lactate concentration increased during exercise for FG15 (0.6 ± 0.2 to 3.4 ± 1.2 mM) and FG60 (0.6 ± 0.2 to 3.3 ± 2.0 mM), but not for VIB (0.6 ± 0.2 to 0.8 ± 0.4 mM) (P < 0.05). Plasma creatine kinase increased by 55 ± 63% and 137 ± 119% 48 h after FG15 and FG60 (P < 0.05), but not after VIB (26 ± 54%, NS). In contrast to the minor elevation in osteocalcin in response to a single session of vibration exercise, both short and longer durations of small sided football acutely increased plasma P1NP, osteocalcin, and creatine kinase. This may contribute to favorable effects of chronic training on musculoskeletal health.

#8 Examining the relationships between challenge and threat cognitive appraisals and coaching behaviours in football coaches
Reference: J Sports Sci. 2016 Dec 26:1-7. doi: 10.1080/02640414.2016.1273538. [Epub ahead of print]
Authors: Dixon M, Turner MJ, Gillman J
Summary: Previous research demonstrates that sports coaching is a stressful activity. This article investigates coaches' challenge and threat cognitive appraisals of stressful situations and their impact on coaching behaviour, using Blascovich and Mendes' (2000) biopsychosocial model as a theoretical framework. A cross-sectional correlational design was utilised to examine the relationships between irrational beliefs (Shortened general attitude and belief scale), challenge and threat appraisals (Appraisal of life events scale), and coaching behaviours (Leadership scale for sports) of 105 professional football academy coaches. Findings reveal significant positive associations between challenge appraisals and social support, and between threat appraisals and autocratic behaviour, and a significant negative association between threat appraisals and positive feedback. Results also show that higher irrational beliefs are associated with greater threat, and lesser challenge cognitive appraisals. However, no associations were revealed between irrational beliefs and challenge cognitive appraisals. Additionally, findings demonstrate a positive relationship between age and training and instruction. Results suggest that practitioners should help coaches to appraise stressful situations as a challenge to promote positive coaching behaviours.

#9 Somatic, Endurance Performance and Heart Rate Variability Profiles of Professional Soccer Players Grouped According to Age
Reference: J Hum Kinet. 2016 Dec 15;54:65-74. doi: 10.1515/hukin-2016-0035. eCollection 2016.
Authors: Botek M, Krejcj J, McKune AJ, Klimesova
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Summary: This cross-sectional study compared somatic, endurance performance determinants and heart rate variability (HRV) profiles of professional soccer players divided into different age groups: GI (17-19.9 years; n = 23), GII (20-24.9 years; n = 45), GIII (25-29.9 years; n = 30), and GIV (30-39 years; n = 26). Players underwent somatic and HRV assessment and maximal exercise testing. HRV was analyzed by spectral analysis of HRV, and high (HF) and low (LF) frequency power was transformed by a natural logarithm (Ln). Players in GIV (83 ± 7 kg) were heavier (p < 0.05) compared to both GI (73 ± 6 kg), and GII (78 ± 6 kg). Significantly lower maximal oxygen uptake (VO2max, ml•kg-1•min-1) was observed for GIV (56.6 ± 3.8) compared to GI (59.6 ± 3.9), GII (59.4 ± 4.2) and GIV (59.7 ± 4.1). All agegroups, except for GII, demonstrated comparable relative maximal power output (Pmax). For supine HRV, significantly lower Ln HF (ms2) was identified in both GIII (7.1 ± 0.8) and GIV (6.9 ± 1.0) compared to GI (7.9 ± 0.6) and GII (7.7 ± 0.9). In conclusion, soccer players aged >25 years showed negligible differences in Pmax unlike the age group differences demonstrated in VO2max. A shift towards relative sympathetic dominance, particularly due to reduced vagal activity, was apparent after approximately 8 years of competing at the professional level.

#10 Developing Talented Soccer Players: An Analysis of Socio-Spatial Factors as Possible Key Constraints
Reference: J Hum Kinet. 2016 Dec 15;54:227-236. doi: 10.1515/hukin-2016-0050. eCollection 2016.
Authors: Serra-Olivares J, Pastor-Vicedo JC, Gonzalez-Víllora S, Teoldo da Costa I
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Summary: Most studies on the identification and development of soccer talent have been one-dimensional in nature. Although some multi-dimensional analyses have been conducted, few research studies have assessed in any depth the socio-spatial factors influencing talent development. The aim of this particular study was to analyse variations in the international representation of clubs (n = 821) and countries (n = 59) in the development of players who took part in the 2014 FIFA Soccer World Cup. Clubs and countries were ranked and divided into quartiles according to the number of players developed between the ages of 15 and 21 (clubs and countries that developed players for at least three years between these ages) and the number of official league matches played by these players up to the age of 23. Significant variations were observed between clubs in terms of the number of developed players who took part in the World Cup and the number of official league matches played by these players up to the age of 23 (p < .05), and also between countries (p < .05). The findings reveal the need to carry out more in-depth studies into the type of training and competition engaged in by elite players in the period of development between the ages of 15 and 21. It may be the case that these factors are potentially decisive socio-spatial constraints in the development of soccer talent.

#11 Soccer Players Cultural Capital and Its Impact on Migration
Reference: J Hum Kinet. 2016 Dec 15;54:195-206. doi: 10.1515/hukin-2016-0052. eCollection 2016.
Authors: Krizaj J, Leskosek B, Vodicar J, Topic MD
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Summary: The purpose of this study was to identify factors that constituted the cultural capital among soccer players. We assumed that in the increasingly globalized world of professional soccer, a player's success would often depend on migrating and adjusting to life in other countries. Willingness to migrate and successful adjustment are tied to player's previous attitudes and/or behaviours (habitus), significant support from others, including family members, and previous experiences and success in sports and education. Our hypothesised model of the cultural capital was based on the Pierre Bourdieu's theoretical framework. It consisted of 26 variables related to three sets of factors: soccer experiences, a family context and support, and educational achievements of the players and their parents. The model was tested using a sample of 79 current soccer coaches who also had been players at the elite level. A factor analysis was used to empirically verify the content of the hypothetical model of the soccer players' cultural capital. Nine latent factors were extracted and together, they accounted for 55.01% of the total model variance. Individual factors obtained showed a sufficient level of substantial connection. The Cronbach's alpha value of 0.77 confirmed the internal consistency of the operationalised variables in the hypothetical model. In addition, the impact of these aforementioned life dimensions on the migration of soccer players was studied. The results of the binary logistic regression analysis showed that the first factor of the hypothetical model (F1) had 2.2 times and the second factor (F8) had 3.9 times higher odds for migration abroad. Sociocultural findings using this new assessment approach could help create better "success conditions" in the talent development of young players.





Latest research in football - week 50 - 2016

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 Emergence of Exploratory, Technical and Tactical Behavior in Small-Sided Soccer Games when Manipulating the Number of Teammates and Opponents
Reference: PLoS One. 2016 Dec 22;11(12):e0168866. doi: 10.1371/journal.pone.0168866. eCollection 2016.
Authors: Torrents C, Ric A, Hristovski R, Torres-Ronda L, Vicente E, Sampaio J
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Summary: The effects that different constraints have on the exploratory behavior, measured by the variety and quantity of different responses within a game situation, is of the utmost importance for successful performance in team sports. The aim of this study was to determine how the number of teammates and opponents affects the exploratory behavior of both professional and amateur players in small-sided soccer games. Twenty-two professional (age 25.6 ± 4.9 years) and 22 amateur (age 23.1 ± 0.7 years) male soccer players played three small-sided game formats (4 vs. 3, 4 vs. 5, and 4 vs. 7). These trials were video-recorded and a systematic observation instrument was used to notate the actions, which were subsequently analyzed by means of a principal component analysis and the dynamic overlap order parameter (measure to identify the rate and breadth of exploratory behavior on different time scales). Results revealed that a higher the number of opponents required for more frequent ball controls. Moreover, with a higher number of teammates, there were more defensive actions focused on protecting the goal, with more players balancing. In relation to attack, an increase in the number of opponents produced a decrease in passing, driving and controlling actions, while an increase in the number of teammates led to more time being spent in attacking situations. A numerical advantage led to less exploratory behavior, an effect that was especially clear when playing within a team of seven players against four opponents. All teams showed strong effects of the number of teammates on the exploratory behavior when comparing 5 vs 7 or 3 vs 7 teammates. These results seem to be independent of the players' level.

#2 Assessment of myocardial function in elite athlete's heart at rest - 2D speckle tracking echocardiography in Korean elite soccer players
Reference: Sci Rep. 2016 Dec 22;6:39772. doi: 10.1038/srep39772.
Authors: Eun LY, Chae HW
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Summary: The purpose of this study was to investigate Korean elite soccer players' myocardial function using the conventional and advanced speckle tracking imaging to compare the difference with the normal controls. We used 2D echocardiography speckle tracking echocardiography (STE) to evaluate LV regional strain in 29 elite soccer players compared to 29 age-matched healthy controls. Conventional, tissue Doppler, and STI echocardiography was performed, for strain at base and apex, rotation and torsion. There is no difference in longitudinal strain (-17.6 ± 1.8 vs -17.3 ± 2.9, p = ns), and basal radial strain. However, the significant increases were noticed in basal circumferential strain (-17.5 ± 2.6 vs -15.5 ± 8.9, p = 0.05), apical radial strain (33.1 ± 20.5 vs 22.5 ± 19.4, p = 0.02), and apical circumferential strain in soccer players (-21.4 ± 4.8 vs -16.8 ± 7.6, p = 0.005). Soccer players showed the higher rotation at base (-3.9 ± 1.9 vs -2.6 ± 3.2, p = 0.03), and apex (6.98 ± 2.62 vs 6.21 ± 3.81, p = 0.05), higher torsion (10.9 ± 3.7 vs 8.8 ± 6.3, p = 0.05). In conclusion, the elite soccer players' heart demonstrated the unique ventricular adaptation. These alterations could benefit the cardiovascular adjustment to exercise without much loss of myocardial energy expenditure.

#3 "There is soccer but we have to watch": the embodied consequences of rhetorics of inclusion for South African children with cerebral palsy
Reference: J Community Appl Soc Psychol. 2015 Nov-Dec;25(6):474-486. doi: 10.1002/casp.2225. Epub 2015 Jan 19.
Authors: Bantjes J, Swartz L, Conchar L, Derman W
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Summary: Twenty years after the advent of democracy in South Africa (SA), there have been some successes in the achievement of greater equality, access and inclusion for many persons with disabilities. The move towards inclusive education may, however, have had unanticipated embodied consequences for people positioned discursively as included, but who in fact may in some respects be further marginalised than they had been under apartheid. We describe ethnographic research conducted in a special needs school in SA to explore the lived experiences of children with cerebral palsy and their involvement in physical activity. Our study shows how inclusive educational practices in SA have impeded involvement in sport for some children with motor impairments because of resource limitations and other historic reasons. This paper raises important questions about the role of community psychology in recognising, naming and contributing to action around injustices, which may be hard to see but which can have profound effects on the lives and bodies of those who experience exclusion.

#4 Game-profile-based Training in Soccer: A New Field Approach
Reference: J Strength Cond Res. 2016 Dec 8. doi: 10.1519/JSC.0000000000001768. [Epub ahead of print]
Authors: Iacono AD, Martone D, Cular D, Milic M, Padulo J
Summary: The aim of the study was to profile and compare the time-motion, physiological, and neuromuscular responses of both national youth league (NYL) and UEFA Youth League (UYL) matches with those of an experimental game-profile-based training (GPBT) protocol. Time-motion traits and physiological, perceptual, and neuromuscular responses were investigated in 24 male soccer players across 14 matches and 6 GPBT training sessions, for a total of 420 samples. The GPBT had a greater influence on time-motion traits and perceptual responses than the NYL and UYL matches (all p< 0.001). No significant GPBT vs. matches differences were found for mean heart rate (%HR) or BLa (F= 1.228, p= 0.304 and F= 0.978, p= 0.385, respectively). Finally, the GPBT protocol led to greater impairment of the neuromuscular explosive performances when compared to those of the post-match scores (SJ: F= 19.991, p< 0.001; CMJ: F= 61.703, p< 0.001). Results identified the GPBT protocol as characterized by relatively greater high-intensity workloads than official NYL and UYL matches, requiring increased demanding efforts. In light of these outcomes, the GPBT protocol can be considered an advantageous training method for elite soccer players, capable of stimulating the physical effort and physiological capabilities required during a match. This approach is favorable when designing a training intervention according to the principle of sport specificity, as it is based on the specific metabolic demands.

#5 Changes in dynamic balance and hip-strength after an eight-week conditioning program in NCAA Division I Female soccer (Football) athletes
Reference: Int J Sports Phys Ther. 2016 Dec;11(7):1054-1064.
Authors: Ness BM, Comstock BA, Schweinle WE
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Summary: Lower extremity injury commonly affects female soccer athletes. Decreased dynamic balance and hip strength are identified risk factors for lower extremity injury. Little is known about how these factors adapt to a training stimulus in this population. The purpose of the study was to retrospectively investigate changes in lower extremity dynamic balance and isometric hip strength in Division I collegiate female soccer athletes after participating in an eight-week strength and conditioning program. As part of a standard testing battery, soccer athletes completed athletic performance pre- and post-testing separated by an eight-week off-season conditioning program consisting of overall strength and technical skill development. Testing included lower extremity dynamic balance assessment through the Star Excursion Balance Test (SEBT) and isometric hip abduction and external rotation (ER) strength testing, normalized to limb length and percent body mass, respectively. Athletes rested for one week prior to post-testing. Seventeen healthy Division I female soccer athletes (age: 18.8 ± 0.9 years, height: 1.7 ± 0.06 m, mass: 68.0 ± 8.2 kg) completed the protocol. Significant improvements in SEBT composite reach distance were observed in the dominant (DOM) (3.6 ± 4.8%, 95% CI: 1.1 to 6.0) and nondominant (NDOM) (4.8 ± 6.1%, 95% CI: 1.7 to 7.9) limbs. Significant improvements in DOM hip ER strength (2.4 ± 2.3%, 95% CI: 1.3 to 3.6) and DOM SEBT anterior reach (2.1 ± 2.8%, 95% CI: 0.6 to 3.5) were observed. Large effect sizes were observed for DOM and NDOM hip ER strength gains (0.87 - 1.0), while small-moderate effect sizes were noted for the anterior reach direction (0.40 - 0.66). Further, DOM hip ER strength gains were significantly associated with DOM anterior reach performance improvements (r2 = 0.37, p<.01). DOM hip ER strength gains appear to be associated with improved lower extremity dynamic balance on the ipsilateral limb for the SEBT anterior reach direction in collegiate, Division I female soccer athletes after an eight-week conditioning program. Future investigations should prospectively investigate intervention strategies to modify lower extremity injury risk factors in this population.

#6 Analysis of Gauntlet Test Performance and Injury Risk in Intercollegiate Division I Female Soccer (Football) Players: A Retrospective Study
Reference: J Sport Rehabil. 2016 Dec 19:1-21. [Epub ahead of print]
Authors: Ness BM, Zimney K, Schweinle WE
Summary: Injury risk factors and relevant assessments have been identified in women's soccer athletes. Other tests assess fitness, e.g. the Gauntlet Test (GT). However, little empirical support exists for the utility of the GT to predict time loss injury. The aim of the study was to examine the GT as a predictor of injury in intercollegiate Division I female soccer athletes. 71 female division I soccer athletes (age 19.6 ± 1.24, BMI 23.0 ± 2.19) participated in this study. GT, demographic, and injury data was collected over three consecutive seasons. GT trials were administered by coaching staff each pre-season. Participation in team-based activities (practices, matches) was restricted until a successful GT trial. Soccer-related injuries that resulted in time loss from participation were recorded. 71 subjects met the inclusion criteria, with 12 lower body time loss injuries sustained. Logistic regression models indicated that with each unsuccessful GT attempt, the odds of sustaining an injury increased by a factor of 3.5 (P < .02). The Youden index was 2 GT trials for success, at which sensitivity = .92 and specificity = .46. For successive GT trials before success (1, 2, or 3), the predicted probabilities for injury were .063, .194, and .463. The GT appears to be a convenient and predictive screen for potential lower body injuries among female soccer athletes in this cohort. Further investigation into the appropriate application of the GT for injury prediction is warranted given the scope of this study.

#7 Construct validity of tests that measure kick performance for young soccer players based on cluster analysis: exploring the relationship between coaches rating and actual measures
Reference: J Sports Med Phys Fitness. 2016 Dec 16. [Epub ahead of print]
Authors: Vieira LH, DE Andrade VL, Aquino RL, Moraes R, Barbieri FA, Cunha SA, Bedo BL, Santiago PR
Summary: The main aim of this study was to verify the relationship between the classification of coaches and actual performance in field tests that measure the kicking performance in young soccer players, using the K--means clustering technique. Twenty--three U--14 players performed eight tests to measure their kicking performance. Four experienced coaches provided a rating for each player as follows: 1--poor, 2--below average, 3--average, 4--very good, 5-excellent as related to three parameters (i.e. accuracy, power and ability to put spin on the ball). The scores interval established from k--means cluster metric was useful to originating five groups of performance level, since ANOVA revealed significant differences between clusters generated (p < 0.01). Accuracy seems to be moderately predicted by the penalty kick, free kick, kicking the ball rolling and Wall Volley Test (0.44 ≤ r ≤ 0.56), while the ability to put spin on the ball can be measured by the free kick and the corner kick tests (0.52 ≤ r ≤ 0.61). Body measurements, age and PHV did not systematically influence the performance. The Wall Volley Test seems to be a good predictor of other tests. Five tests showed reasonable construct validity and can be used to predict the accuracy (penalty kick, free kick, kicking a rolling ball and Wall Volley Test) and ability to put spin on the ball (free kick and corner kick tests) when kicking in soccer. In contrast, the goal kick, kicking the ball when airborne and the vertical kick tests exhibited low power of discrimination and using them should be viewed with caution.

#8 Quantifying Inter-Segmental Coordination during the Instep Soccer Kicks
Reference: Int J Exerc Sci. 2016 Nov 1;9(5):646-656. eCollection 2016.
Authors: Li Y, Alexander M, Glazebrook C, Leiter J
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Summary: In order to generate a high ball speed in soccer, the inter-segmental coordination of the kicking leg is critical. The purpose of this study was to quantify the coordination between the thigh and shank movement in the sagittal plane during instep kicks. Eleven female soccer players were video recorded using a high-speed (80 Hz) video camera during penalty kicks. Hip, knee and ankle joint centers of the right leg were digitized, and the movement was analyzed using Dartfish TeamPro (6.0). The thigh and shank segment angles were generated, and the coordination was quantified using the cross-correlation and the vector coding method. Four coordination patterns were defined based on coupling angles: in-phase, anti-phase, thigh-phase and shank-phase. The time spent in each coordination pattern was analyzed. The cross-correlation coefficient was positive for all the participants, indicating that the two segments rotated with similar patterns. Based on the vector coding method, we observed dominant coordination patterns of shank-phase and in-phase during the backswing and forward swing phase, respectively. We hope the outcomes of our study could provide a better understanding of soccer kicking coordination and benefit training young soccer players. Future studies may use the methodology and outcomes in the present study to investigate the coordination of different levels of players to better understand the process of skill acquisition.

#9 Meta-analytical review of the effects of football heading
Reference: Br J Sports Med. 2016 Dec 21. pii: bjsports-2016-096276. doi: 10.1136/bjsports-2016-096276. [Epub ahead of print]
Authors: Kontos AP, Braithwaite R, Chrisman SP, McAllister-Deitrick J, Symington L, Reeves VL, Collins MW
Summary: The objective of this study was to provide a meta-analysis examining the effects of football heading. Combinations of the key terms were entered into the following electronic database search engines: Cochrane Libraries, PyscARTICLE, PyscINFO, PubMed, ProQuest, SPORTDiscus and Web of Science on 7 July 2016. The following inclusion criteria were used to determine eligibility for studies: (1) the study examined and reported on soccer athletes; (2) the population's age, sex and sport position was described; (3) cognitive function, symptoms, balance or other outcomes were quantitatively measured; (4) football heading exposure was quantitatively measured between at least two groups and (5) the study was written in the English language after December 1979. The literature search process identified 467 unique studies. After applying exclusion criteria, 28 studies remained. Included studies had a total of 2288 participants (female participants =933, male participants =1355), aged 13-70 years. The overall results of random effects modelling of football heading were found to be inconclusive across all outcomes, groups and time points. No moderating variables related to methodological, sample or study characteristics were supported in the analysis; age was a potential moderating variable. We provide the first meta-analytical review of football heading effects aggregated from multiple studies and extended findings from a recent systematic review of the effects of football heading. Our analysis indicates no overall effect for heading a football on adverse outcomes.

#10 Traditional vs. sport-specific vertical jump tests: reliability, validity, and relationship with the legs strength and sprint performance in adult and teen soccer and basketball players
Reference: J Strength Cond Res 31(1): 196–206, 2017
Authors: Rodríguez-Rosell, D, Mora-Custodio, R, Franco-Márquez, F, Yáñez-García, JM, González-Badillo, JJ
Summary: The vertical jump is considered an essential motor skill in many team sports. Many protocols have been used to assess vertical jump ability. However, controversy regarding test selection still exists based on the reliability and specificity of the tests. The main aim of this study was to analyze the reliability and validity of 2 standardized (countermovement jump [CMJ] and Abalakov jump [AJ]) and 2 sport-specific (run-up with 2 [2-LEGS] or 1 leg [1-LEG] take-off jump) vertical jump tests, and their usefulness as predictors of sprint and strength performance for soccer (n = 127) and basketball (n = 59) players in 3 different categories (Under-15, Under-18, and Adults). Three attempts for each of the 4 jump tests were recorded. Twenty-meter sprint time and estimated 1 repetition maximum in full squat were also evaluated. All jump tests showed high intraclass correlation coefficients (0.969–0.995) and low coefficients of variation (1.54–4.82%), although 1-LEG was the jump test with the lowest absolute and relative reliability. All selected jump tests were significantly correlated (r = 0.580–0.983). Factor analysis resulted in the extraction of one principal component, which explained 82.90–95.79% of the variance of all jump tests. The 1-LEG test showed the lowest associations with sprint and strength performance. The results of this study suggest that CMJ and AJ are the most reliable tests for the estimation of explosive force in soccer and basketball players in different age categories.

#11 Influence of rest intervals after assisted sprinting on bodyweight sprint times in female collegiate soccer players
Reference: J Strength Cond Res 31(1): 88–94, 2017
Authors: Nealer AL, Dunnick DD, Malyszek KK, Wong MA, Costa PB, Coburn JW, Brown LE
Summary: Speed is a crucial element an athlete must possess to be successful. In soccer, the ability to accelerate faster than your opponent can result in being first to reach a ball on a breakaway or stopping a counter attack. A unique way to train explosive movements is to evoke postactivation potentiation (PAP) in the working muscles. Traditionally, an overload stimulus with a long rest period is used, but a model using an overspeed stimulus with shorter rest periods is less understood. Therefore, the purpose of this study was to determine the acute effects of varied rest intervals after assisted sprinting on bodyweight sprint time. Twenty-four female soccer players were split into 2 groups: recreational (n:11; age:20 ± 1.67 year; ht:162.30 ± 4.35 cm; mass:61.02 ± 8.78 kg) and collegiate athletes (n:13; age:19.76 ± 0.83 year; ht:166.85 ± 5.98 cm; mass:61.23 ± 3.77 kg). All participants attended 5 separate sessions, performed a dynamic warm up, then executed one 20 m sprint (with 5 m splits) at 30% bodyweight assistance (BWA). They then rested for 30 seconds, 1, 2, or 4 minutes in random order, followed by one bodyweight sprint with no BWA. Baseline sprint times were measured without BWA on the initial session of testing. Results revealed no difference in sprint time for the full 20 m distance in either group. However, sprint time was significantly decreased for the 0–5 m split only for the athletes after 1 minute (1.15 ± 0.06 second) and 2 minute (1.16 ± 0.06 second) rest compared with baseline (1.21 ± 0.04 second). Therefore, trained athletes should rest 1 or 2 minutes after 30% BWA supramaximal sprinting for increased bodyweight sprint speed.





Latest research in football - week 49 - 2016

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 Yo-Yo Intermittent Recovery Test Level 2 and its Relationship to other Typical Soccer Field Tests in Female Collegiate Soccer Players
Reference: J Strength Cond Res. 2016 Nov 19. [Epub ahead of print]
Authors: Lockie RG, Jalilvand F, Moreno MR, Orjalo AJ, Risso FG, Nimphius S
Summary: The ability to complete high-intensity running is essential for soccer. The Yo-Yo Intermittent Recovery Test Level 2 (YYIRT2) can measure this capacity, but there is limited information regarding this assessment in collegiate female soccer players. This study investigated the YYIRT2 as a measure of high-intensity running in this population, and its relationship to other soccer field tests. Twenty-one players from a Division I team were recruited. In addition to the YYIRT2, subjects completed linear (0-5, 0-10, 0-30 m sprint intervals) and change-of-direction (pro-agility and 60-yard shuttle) speed tests, as well as the YYIRT Level 1 (YYIRT1), to assess relationships with YYIRT2 via correlations (p < 0.05). The correlation of YYIRT1 with the speed tests was also assessed. YYIRT1 and YYIRT2 were standardized via z-scores for comparison to elite benchmarks to investigate relative performance on each test. YYIRT2 and YYIRT1 distance did not significantly correlate with the speed tests (r = -0.251-0.274). There was a large relationship between YYIRT2 and YYIRT1 distance (r = 0.582), although the explained variance was low (33.87%). Mean YYIRT2 z-scores (-4.29 ± 1.66) indicated a performance further from elite benchmarks than the YYIRT1 (-1.92 ± 1.61), and 90.5% (19 of 21) subjects performed relatively better in the YYIRT1 than YYIRT2. The YYIRT2 provided a more specific measure of high-intensity running to that of the YYIRT1 in collegiate female soccer players. Coaches may consider using the YYIRT2 to gauge and track progress of high-intensity running capabilities, and create training programs to improve this ability in female players.

#2 Enhancing Collegiate Women's Soccer Psychosocial and Performance Outcomes by Promoting Intrinsic Sources of Sport Enjoyment
Reference: J Sports Sci Med. 2016 Dec 1;15(4):678-687. eCollection 2016.
Authors: Barnicle SP, Burton D
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Summary: This study examined the effectiveness of an applied mental skills training (MST) intervention utilizing mental skills to enhance intrinsic sources of enjoyment (ISOEs) as a means of promoting self-confidence, motivational style, and athletic performance, while also decreasing trait anxiety. The intervention project was designed to increase intrinsic SOE using a systematic and individualized mental training protocol, and then examine its relationships to mental skills and soccer performance. A Division 1 collegiate women's soccer team was randomly assigned to treatment (n = 8) and control (n = 11) groups, equally distributed by academic year, position, and pre-season coach-evaluated starters and non-starts. Results revealed that the MST intervention significantly increased intrinsic enjoyment targeted psychological and competitive outcomes, both in practice and competition within the treatment group as compared to the control group. This study's support for the impact mental skills training may have had on ISOEs, as well as other psychosocial outcomes and athletic performance can serve to highlight a mental skill often overlooked by consultants and coaches.

#3 Effects of a Whole-Body Electrostimulation Program on Strength, Sprinting, Jumping, and Kicking Capacity in Elite Soccer Players
Reference: J Sports Sci Med. 2016 Dec 1;15(4):639-648. eCollection 2016.
Authors: Filipovic A, Grau M, Kleinöder H, Zimmer P, Hollmann W, Bloch W
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Summary: The aim of the present study was to investigate the effect of a 14-week dynamic Whole-Body Electrostimulation (WB-EMS) training program on muscular strength, soccer relevant sprint, jump and kicking velocity performance in elite soccer players during competitive season. Twenty-two field-players were assigned to 2 groups: WB-EMS group (EG, n = 12), jump-training group (TG, n = 10). The training programs were conducted twice a week concurrent to 6-7 soccer training sessions during the 2nd half of the season. Participants were tested before (baseline), during (wk-7) and after (wk-14). Blood serum samples for analyzing IGF-1 and CK were taken before each testing, 15-30min post and 24h post the training program. Our findings of the present study were that a 14-week in-season WB-EMS program significant increased one-leg maximal strength (1RM) at the leg press machine (1.99 vs. 1.66 kg/kg, p = 0.001), and improved linear sprinting (5m: 1.01 vs. 1.04s, p=0.039), sprinting with direction changes (3.07 vs. 3.25s, p = 0.024), and vertical jumping performance (SJ: 38.8 vs. 35.9cm p = 0.021) as well as kicking velocity (1step: 93.8 vs. 83.9 km·h-1, p < 0.001). The TG showed no changes in strength and performance. The EG revealed significantly increased CK levels 24h post training and yielded significantly higher CK levels compared to the TG. IGF-1 serum levels neither changed in the EG nor in the TG. The results give first hints that two sessions of a dynamic WB-EMS training in addition to 6-7 soccer sessions per week can be effective for significantly enhancing soccer relevant performance capacities in professional players during competitive season.

#4 Subjective well-being and training load predict in-season injury and illness risk in female youth soccer players
Reference: Br J Sports Med. 2016 Dec 5. pii: bjsports-2016-096584. doi: 10.1136/bjsports-2016-096584. [Epub ahead of print]
Authors: Watson A, Brickson S, Brooks A, Dunn W
Summary: The purpose of this study was to evaluate the effects of training load (TL) and well-being on injury and illness risk in youth soccer players. Throughout a 20-week season, 75 female adolescent soccer players reported mood, fatigue, stress, soreness, sleep quality, sleep hours, TL, injuries and illnesses. Well-being measures were recorded from -3 (worst) to +3 (best). TL was expressed as daily, weekly and monthly, as well as an acute:chronic workload ratio (weekly divided by monthly). Variables were compared between days with and without an injury, and with or without an illness. Poisson regression models were developed to predict daily injuries and illnesses using well-being and TL (z-scores) as predictors. 36 injuries and 52 illnesses were recorded. Days with an injury had lower (worse) daily mood (1.24±0.2 vs 1.16±0.1, p=0.012) and higher daily TL (517±138 vs 440±158, p=0.010). Average monthly TL was higher preceding days with an illness (12 442 ±409 vs 12 627 ±403, p=0.043), while no differences were found with respect to other measures of TL or well-being. Worse daily mood (p=0.011, OR=0.012), higher daily TL (p<0.001, OR=1.98), and higher prior day TL (p=0.040, OR=1.34) were independent predictors of injury, while weekly (p=0.005, OR=1.50) and monthly TL (p=0.007, OR=1.54) were predictors of illness. Lower mood and higher acute TL are associated with increased injury risk, while higher chronic TL increases the risk of illness. Monitoring well-being and TL may facilitate intervention to reduce in-season injury and illness.

#5 The Influence of Changes in Acute Training Load on Daily Sensitivity of Morning-measured Fatigue Variables in Elite Soccer Players
Reference: Int J Sports Physiol Perform. 2016 Dec 5:1-23. [Epub ahead of print]
Authors: Thorpe RT, Strudwick AJ, Buchheit M, Atkinson G, Drust B, Gregson W
Summary: The purpose was to determine the sensitivity of a range of potential fatigue measures to daily training load accumulated over the previous two, three and four days during a short in-season competitive period in elite senior soccer players (n=10). Total high-speed running distance, perceived ratings of wellness (fatigue, muscle soreness, sleep quality), counter-movement jump height (CMJ), submaximal heart rate (HRex), post-exercise heart rate recovery (HRR) and heart rate variability (HRV: Ln rMSSD) were analysed during an in-season competitive period (17 days). General linear models were used to evaluate the influence of two, three and four day total high-speed running distance accumulation on fatigue measures. Fluctuations in perceived ratings of fatigue were correlated with fluctuations in total high-speed running distance accumulation covered on the previous 2-days (r=-0.31; small), 3 -days (r=-0.42; moderate) and 4-days (r=-0.28; small) (p<0.05). Changes in HRex (r=0.28; small; p= 0.02) were correlated with changes in 4-day total high-speed running distance accumulation only. Correlations between variability in muscle soreness, sleep quality, CMJ, HRR% and HRV and total high-speed running distance were negligible and not statistically significant for all accumulation training loads. Perceived ratings of fatigue and HRex were sensitive to fluctuations in acute total high-speed running distance accumulation, although, sensitivity was not systematically influenced by the number of previous days over which the training load was accumulated. The present findings indicate that the sensitivity of morning-measured fatigue variables to changes in training load is generally not improved when compared with training loads beyond the previous days training.

#6 Relationships Between Internal and External Match Load Indicators in Soccer Match Officials
Reference: Int J Sports Physiol Perform. 2016 Dec 5:1-21. [Epub ahead of print]
Authors: Castillo D, Weston M, McLaren SJ, Cámara J, Yanci J
Summary: The aims of this study were to describe the internal and external match load (ML) of refereeing activity during official matches and also to investigate the relationship among the methods of ML quantification across a competitive soccer season. A further aim was to examine the usefulness of differential perceived exertion (dRPE) as a tool for monitoring internal ML in soccer referees. Twenty field referees (FR) and 43 assistant referees (AR) participated in this study. Data were collected from 30 competitive matches (FR = 20 observations, AR = 43 observations) and included measures of internal (Edwards' heart rate derived training impulse [TRIMPEDW]), external (total distance covered [TD], distance covered at high speeds [HSR] and player load [PL]) ML, differentiated ratings of perceived respiratory [sRPEres ML] and leg muscle [sRPEmus ML] exertion). Internal and external ML were all greater for FR when compared to AR (-19.7 to -72.5); with differences ranging from very likely very large to most likely extremely large. The relationships between internal ML and external ML indicators were, in most cases, unclear for FR (r < .35) and small to moderate for AR (r < .40). We found substantial differences between RPEres and RPEmus scores in both FR (.6 AU; ±90% confidence limits .4 AU) and AR (.4; ±.3 AU). These data demonstrate the multifaceted demands of soccer refereeing and thereby highlight the importance of monitoring both internal and external ML. Moreover, dRPE represent distinct dimensions of effort and may be useful in monitoring soccer referees ML during official matches.

#7 Seasonal changes in soccer players' body composition and dietary intake practices
Reference: J Strength Cond Res. 2016 Nov 29. [Epub ahead of print]
Authors: Devlin BL, Kingsley M, Leveritt MD, Belski R
Summary: The aims of this study were two-fold: to determine seasonal changes in dietary intake and body composition in elite soccer players and to evaluate the influence of self-determined individual body composition goals on dietary intake and body composition. This longitudinal, observational study assessed body composition (total mass, fat-free soft tissue mass and fat mass) using dual-energy x-ray absorptiometry and dietary intake (energy and macronutrients) via multiple pass 24-hour recalls, at four time points over a competitive season in elite soccer players from one professional club in the Australian A-League competition. Self-reported body composition goals were also recorded. Eighteen elite male soccer players took part (25 ± 5 years, 180.5 ± 7.4 cm, 75.6 ± 6.5 kg). Majority (≥67%) reported the goal to maintain weight. Fat-free soft tissue mass increased from the start of preseason (55278 ± 5475 g) to the start of competitive season (56784 ± 5168 g; p<0.001) and these gains were maintained until the end of the season. Fat mass decreased over the preseason period (10072 ± 2493 g to 8712 ± 1432 g; p<0.001), but increased during the latter part of the competitive season. Dietary intake practices on training days were consistent over time and low compared to sport nutrition recommendations. The self-reported body composition goals did not strongly influence dietary intake practices or changes in body composition. This study has demonstrated that body composition changes over the course of a soccer season are subtle in elite soccer players despite relatively low self-reported intakes of energy and carbohydrate.

#8 Assessing the effectiveness of the Functional Movement Screen (FMS™) in predicting non-contact injury rates in soccer players
Reference: J Strength Cond Res. 2016 Dec 7. [Epub ahead of print]
Authors: Smith PD, Hanlon M
Summary: This study assessed if the Functional Movement Screen (FMS™) can accurately predict non-contact injury in adult soccer players when normalizing non-contact injury occurrence against match exposure levels. Senior male players (n=89) from five League of Ireland semi-professional clubs participated in the study (mean age=23.2 ± 4.4 years; mean height=179.5 ± 6.6 cm; mean body mass=77.5 ± 7.8 kg). Participants performed the FMS™ during preseason and their injury occurrence rates and match minutes were tracked throughout one season. In total, 66 non-contact injuries were recorded. No significant difference was found in FMS™ composite scores between players receiving non-contact injuries and players not suffering a non-contact injury (p=0.96). There was no significant difference in exposure-normalized non-contact injury incidence between those scoring 14 or below and those scoring above 14 on the FMS™ (0.36 vs. 0.29 non-contact injuries per player per 1000 match minutes). Players scoring 14 or below on the FMS™ had an odds ratio of 0.63 (p=0.45; CI 95%=0.19- 2.07) of receiving a non contact injury. Despite previous research showing links between low FMS™ composite scores and subsequent injury, these results suggest the FMS™ cannot accurately predict a male soccer player's likelihood of receiving a non-contact injury and that a lower FMS™ composite score does not significantly increase their non-contact injury incidence rate per 1000 match minutes. Caution should therefore be used when employing the FMS™ as a predictor of non-contact injury, and pain prevalence during the FMS™, previous injuries, and training/match exposure levels should also be taken into account.

#9 Intra-articular injections of HYADD4-G in male professional soccer players with traumatic or degenerative knee chondropathy. A pilot, prospective study
Reference: J Sports Med Phys Fitness. 2016 Dec;56(12):1534-1539.
Authors: Tamburrino P, Castellacci E
Summary: Knee injuries are very common in some sports and particularly in soccer due to the highly repetitive loading of the mechanical stress involved in this practice. Knee-joint injuries account for 40% of all different kinds of lesions. Traumatic or degenerative patellofemoral or tibialfemoral chondropaties of knee cause disabling symptoms, joint pain and/or dysfunctions. The aim of the study was to evaluate the effects of HYADD4-G, a hydrogel based on a hyaluronic acid derivative, in professional soccer players affected by traumatic or degenerative knee chondropathy. Thirty male professional soccer players participants in the Italian League 2014-2015, affected by traumatic or degenerative knee patellofemoral (N.=12) or tibiofemoral (N.=18) chondropathy assessed through MRI and/or arthroscopy of knee joints and the ICRS staging (International Cartilage Repair Society ≤3a), were enrolled in this pilot prospective study. Patients underwent 2 intra-articular (IA) injections of HYADD4-G (3 mL of 8 mg/mL) at one week interval. Patients were prospectively evaluated at baseline and then at 1, 3 and 6 months after the treatment by the Osteoarthritis Outcome Score (KOOS) Score (main outcome) and by the Visual Analog Scale (VAS) to evaluate pain. A significant improvement in all clinical endpoints from pretreatment to different times of evaluation was found in all patients. ANOVA with repeated measure using the SPSS has showed significantly better results in term of KOOS and VAS scores at 1, 3 and 6 months compared to the pre-injection value (P<0.05). IA HYADD4-G is highly effective to improve resting and walking pain in professional male soccer players with traumatic or degenerative knee chondropathy.

#10 Sex-Based Differences in Cognitive Deficits and Symptom Reporting Among Acutely Concussed Adolescent Lacrosse and Soccer Players
Reference: Am J Sports Med. 2016 Dec 9. pii: 0363546516677246. [Epub ahead of print]
Authors: Sandel NK, Schatz P, Goldberg KB, Lazar M
Summary: Research on the acute effects of a concussion among lacrosse players is limited, and postconcussion patterns between male and female athletes have yet to be clearly established. Differences in the style of play and protective gear worn among male and female lacrosse players potentially confound a direct comparison of sex-based differences in this population. The purpose was to explore sex-based differences in postconcussive neurocognitive functioning and symptom reporting outcomes in concussed adolescent male and female lacrosse players compared with a group of soccer players. A total of 224 adolescent lacrosse players (112 male, 112 female) aged 13 to 17 years (mean [±SD] age, 15.43 ± 1.09 years) were included in this study. A comparison group of soccer players was added and matched to lacrosse players based on age and sex to address confounding sport differences in male and female versions of lacrosse. All athletes underwent baseline and postinjury testing within 3 days of an injury using the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) tool. Data were analyzed at baseline using a multivariate analysis of variance (MANOVA) with sport and sex as between-participant factors. A 2 × 2 × 2 mixed-factorial MANOVA was also conducted for sex and sport comparisons at baseline versus after a concussion. Ancillary analyses evaluated sex-based differences in exceeded reliable change indices (RCIs) using an independent-samples t test and established postinjury cutoff scores reflective of a protracted recovery using chi-square tests. All athletes had a significantly worse cognitive profile and greater endorsement of symptoms after an injury (F5,216 = 30.30, P < .001, ηρ2 = .41). Sport yielded a significant main effect (F5,216 = 2.36, P = .04, ηρ2 = .05), but subsequent univariate analyses were nonsignificant (P > .05) across all neurocognitive and symptom outcome variables. Likewise, there were no significant interaction effects for sport × time (F5,216 = 1.46, P = .21, ηρ2 = .03) or sport × sex × time (F5,216 = 2.09, P = .07, ηρ2 = .05), indicating that lacrosse and soccer players respond similarly on neurocognitive testing and symptom reporting after sustaining a concussion. Regarding sex-based differences, female athletes had a significantly greater neurocognitive decline and increased symptoms after a concussion relative to male athletes, regardless of the sport type (sex × time interaction effect: F5,216 = 3.86, P = .002, ηρ2 = .08), with the relationship between concussions and sex demonstrating a medium- to large-sized effect. Female athletes demonstrated a significantly greater number of exceeded RCIs (t(216.16) = -3.732, P < .001), with 59% of male and 74% of female athletes with at least 1 RCI decline. Approximately 13% of male athletes, compared with 30% of female athletes, demonstrated scores indicative of protracted recovery at a 75% sensitivity (χ2 (1, N = 224) = 9.43, P = .002). Athletes performed more poorly on computerized cognitive screening tools and reported greater symptoms after an acute concussion relative to their baseline performance. Female sex may be a modifier of an acute concussion outcome, given that female athletes in this study performed significantly worse than male athletes across all neurocognitive measures and reported greater symptoms relative to their baseline testing compared with male athletes, regardless of the sport played. Female athletes were also more likely than male athletes to demonstrate scores on neurocognitive testing that exceeded reliable change cutoffs and were predictive of a protracted recovery. The practical significance of these findings should be further verified by prospective longitudinal research given the medium- to large-sized effect demonstrated for the overall relationship between sex and concussions.

#11 Identification of Sensitive Measures of Recovery Following External Load From Football Match Play
Reference: Int J Sports Physiol Perform. 2016 Dec 14:1-25. [Epub ahead of print]
Authors: Rowell AE, Aughey RJ, Hopkins WG, Stewart AM, Cormack SJ
Summary: Objective measures of recovery from football match-play could be useful for assessing athletes' readiness to train, if sensitive to preceding match load. The purpose of the study was to identify the sensitivity of countermovement-jump (CMJ) performance and concentration of salivary testosterone and cortisol relative to elite football match load. CMJ performance and salivary hormones were measured in 18 elite football players before (27-, 1-h) and after (0.5-, 18-, 42-, 66-, 90-h) three consecutive matches. Match load was determined via accelerometer derived PlayerLoad™ and praised into tertiles. Sensitivity of CMJ performance and hormone concentrations to match load was quantified with t-statistics and magnitude-based inferences (change in mean as % ± 90% confidence interval (CI)) derived with a linear mixed model. Jump height was reduced in medium- and high-load at 0.5-h (10% ± 7% and 16% ± 8%) and 18-h (7% ± 4% and 9% ± 5%) post match. There was a 12% ± 7% reduction in Flight time:contraction time (FT:CT) ratio in high-load at 0.5-h post, with reductions in medium- and high-load at 18-h. Reductions in FT:CT persisted at later post-match time-points than changes in Jump height. Increased cortisol (range: 55% to 165%) and testosterone (range: 17% to 20%) was observed in all match loads at 0.5-h post with individual variability thereafter. Measures of CMJ performance and hormonal concentrations were sensitive to levels of A-League football match load. Although jump height was reduced immediately post-match, FT:CT provided a more sensitive measure of recovery. Football match play induces an acute hormonal response with substantial individual variability thereafter.





Latest research in football - week 48 - 2016

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 Injury incidence in a Premier League youth soccer academy using the consensus statement: a prospective cohort study
Reference: BMJ Open Sport Exerc Med. 2016 Oct 26;2(1):e000132. eCollection 2016.
Authors: Renshaw A, Goodwin PC
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Summary: There is an established risk of injury to young athletes exposed to high training loads. Identifying and monitoring injury risk is essential to aid prevention. The aim of this study was to use the consensus statement to determine the incidence and pattern of injury in 1 English Premier League soccer academy during 1 season. A prospective cohort study included 181 elite academy soccer players during the 2012-2013 season. Players were divided into 5 age groups between 9 and 18 years. The number, type and incidence of injuries were recorded during matches and training. Incidence was calculated per 1000 hours of exposure. 127 injuries occurred during 29 346 hours of soccer exposure. 72% of injuries were non-contact related. Under (U)18 players sustained the highest number of match injuries. U12-14 players sustained the highest number of training injuries and injuries overall. U16 players sustained the highest number of severe injuries, and U18 players sustained the highest number of moderate injuries. U18 players sustained the highest number of injuries/1000 hours of training and overall. U15 players sustained the highest number of injuries/1000 hours of matches, the highest number of recurrent injuries and the highest incidence of recurrence. The most common injuries were muscle injuries in U15 and U18 players. The most common injury location was the anterior thigh, with the majority of these occurring in training. Using the consensus statement, this study used a repeatable method to identify the injury profile of elite academy-level soccer players.

#2 Injury prevention exercise programmes in professional youth soccer: understanding the perceptions of programme deliverers
Reference: BMJ Open Sport Exerc Med. 2016 Jan 4;2(1):e000075. eCollection 2016.
Authors: O'Brien J, Finch CF
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Summary: There are well-known challenges to implementing injury prevention strategies in amateur soccer, but information from other soccer settings is scarce. This cross-sectional survey analysed the injury prevention perceptions of soccer coaches, fitness coaches and physiotherapists from 4 male teams in a professional youth soccer academy. The respondents (n=18) completed a web-based survey relating to lower limb (LL) soccer injuries, the value and practicality of injury prevention exercise programmes (IPEPs) in general and, more specifically, the IPEP endorsed by FIFA, the FIFA 11+. There were very high levels of agreement regarding players' susceptibility to LL injury and the seriousness of these injuries. Respondents agreed unanimously that players should perform evidence-based injury prevention exercises. Despite 61% of respondents having previously heard of the FIFA 11+, just 6% reported current use of the full programme, with a further 22% reporting modified use. 22% believed the FIFA 11+ contained adequate variation and progression for their team and 78% felt it needed improvement. Respondents identified multiple barriers and facilitators to maintaining IPEPs, relating either to the programme content (eg, exercise variation), or the delivery and support of the programme (eg, coach acceptance). The coaches, fitness coaches and physiotherapists of professional youth teams support the use of IPEPs, but enhancing their impact requires tailoring of programme content, along with adequate delivery and support at multiple levels. The findings suggest that the FIFA 11+ needs modification for use in professional youth soccer teams.

#3 Concurrent validity of the Gyko inertial sensor system for the assessment of vertical jump height in female sub-elite youth soccer players
Reference: BMC Sports Sci Med Rehabil. 2016 Nov 11;8:35. eCollection 2016.
Authors: Lesinski M, Muehlbauer T, Granacher U
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Summary: The aim of the present study was to verify concurrent validity of the Gyko inertial sensor system for the assessment of vertical jump height. Nineteen female sub-elite youth soccer players (mean age: 14.7 ± 0.6 years) performed three trials of countermovement (CMJ) and squat jumps (SJ), respectively. Maximal vertical jump height was simultaneously quantified with the Gyko system, a Kistler force-plate (i.e., gold standard), and another criterion device that is frequently used in the field, the Optojump system. Compared to the force-plate, the Gyko system determined significant systematic bias for mean CMJ (-0.66 cm, p < 0.01, d = 1.41) and mean SJ (-0.91 cm, p < 0.01, d  = 1.69) height. Random bias was ± 3.2 cm for CMJ and ± 4.0 cm for SJ height and intraclass correlation coefficients (ICCs) were "excellent" (ICC = 0.87 for CMJ and 0.81 for SJ). Compared to the Optojump device, the Gyko system detected a significant systematic bias for mean CMJ (0.55 cm, p < 0.05, d = 0.94) but not for mean SJ (0.39 cm) height. Random bias was ± 3.3 cm for CMJ and ± 4.2 cm for SJ height and ICC values were "excellent" (ICC = 0.86 for CMJ and 0.82 for SJ). Consequently, apparatus specific regression equations were provided to estimate true vertical jump height for the Kistler force-plate and the Optojump device from Gyko-derived data. Our findings indicate that the Gyko system cannot be used interchangeably with a Kistler force-plate and the Optojump device in trained individuals. It is suggested that practitioners apply the correction equations to estimate vertical jump height for the force-plate and the Optojump system from Gyko-derived data.

#4 Effect of oxygen therapy on myocardial salvage in ST elevation myocardial infarction: the randomized SOCCER trial
Reference: Eur J Emerg Med. 2016 Nov 23. [Epub ahead of print]
Authors: Khoshnood A, Carlsson M, Akbarzadeh M, Bhiladvala P, Roijer A, Nordlund D, Höglund P, Zughaft D, Todorova L, Mokhtari A, Arheden H, Erlinge D, Ekelund U.
Summary: Recent studies suggest that administration of O2 in patients with acute myocardial infarction may have negative effects. With the use of cardiac MRI (CMR), we evaluated the effects of supplemental O2 in patients with ST elevation myocardial infarction (STEMI) accepted for acute percutaneous coronary intervention (PCI). This study was a randomized-controlled trial conducted at two university hospitals in Sweden. Normoxic STEMI patients were randomized in the ambulance to either supplemental O2 (10 l/min) or room air until the conclusion of the PCI. CMR was performed 2-6 days after the inclusion. The primary endpoint was the myocardial salvage index assessed by CMR. The secondary endpoints included infarct size and myocardium at risk. At inclusion, the O2 (n=46) and air (n=49) patient groups had similar patient characteristics. There were no significant differences in myocardial salvage index [53.9±25.1 vs. 49.3±24.0%; 95% confidence interval (CI): -5.4 to 14.6], myocardium at risk (31.9±10.0% of the left ventricle in the O2 group vs. 30.0±11.8% in the air group; 95% CI: -2.6 to 6.3), or infarct size (15.6±10.4% of the left ventricle vs. 16.0±11.0%; 95% CI: -4.7 to 4.1). In STEMI patients undergoing acute PCI, we found no effect of high-flow oxygen compared with room air on the size of ischemia before PCI, myocardial salvage, or the resulting infarct size. These results support the safety of withholding supplemental oxygen in normoxic STEMI patients.

#5 Effects of Sprint Training With and Without Weighted Vest on Speed and Repeated Sprint Ability in Male Soccer Players
Reference: J Strength Cond Res. 2016 Nov 16. [Epub ahead of print]
Authors: Rey E, Padrón-Cabo A, Fernández-Penedo D
Summary: The purpose of this study was to assess the effect resisted sprint training using weighted vests (WV) compared with unresisted sprint training (US) on physical fitness (countermovement jump, 10 m sprint, 30 m sprint and repeated sprint ability (RSA)) in amateur male soccer players. 19 soccer players (age: 23.7±4.5 years; height: 178.3±5.8 cm; body mass: 72.9±5.2 kg) were randomly assigned to a WV (n= 10) or a US (n= 9) group. The intervention program had to be carried out 2 times a week over 6 weeks. The only difference between the two interventions was that the WV group performed all the sprints with an additional weight of 18.9% ± 2.1% of body mass. Within-group analysis showed significant improvements (p<0.001) in 10 m and 30 m sprint performance from pretest to post-test in WB (+9.42% and +6.04%) and CTU (+10.87% and +5.10%). Players in both WV and US also showed significant enhancements in RSA average time, fastest time, and total time from pretest to posttest. Percentage changes in 30 m sprint performance, for both groups combined, had a very large correlation with percentage changes in average time of RSA. In the between-groups analysis, there were no differences between the sprint training groups (WV vs US) in any variable. In conclusion, the findings of this study indicate that both sprint training methods used seem to be effective to improve soccer related performance measures, and could be beneficial to players and coaches in field settings.

#6 Leg Stiffness In Female Soccer Players: Inter-Session Reliability And The Fatiguing Effects Of Soccer-Specific Exercise
Reference: J Strength Cond Res. 2016 Nov 16. [Epub ahead of print]
Authors: De Ste Croix M, Hughes J, Lloyd RS, Oliver JL, Read P
Summary: Low levels of leg stiffness and reduced leg stiffness when fatigue is present compromise physical performance and increase injury risk. The purpose of this study was to (a) determine the reliability of leg stiffness measures obtained from contact mat data and (b) explore age-related differences in leg stiffness following exposure to a soccer-specific fatigue protocol in young female soccer players. 37 uninjured female youth soccer players divided into 3 sub-groups based on chronological age (U13, U15 and U17 year olds) volunteered to participate in the study. Following baseline data collection during which relative leg stiffness, contact time, flight time was collected, participants completed an age-appropriate soccer-specific fatigue protocol (SAFT). Upon completion of the fatigue protocol, subjects were immediately re-tested. Inter-session reliability was acceptable and could be considered capable of detecting worthwhile changes in performance. Results showed that leg stiffness decreased in the U13 year olds, was maintained in the U15 age group and increased in the U17 players. Contact times and flight times did not change in the U13 and U15 year olds, but significantly decreased and increased respectively in the U17 age group. The data suggests that age-related changes in the neuromuscular control of leg stiffness are present in youth female soccer players. Practitioners should be aware of these discrepancies in neuromuscular responses to soccer-specific fatigue, and should tailor training programs to meet the needs of individuals which may subsequently enhance performance and reduce injury risk.

#7 A topography of free kicks in soccer
Reference: J Sports Sci. 2016 Dec;34(24):2312-2320.
Authors: Link D, Kolbinger O, Weber H, Stöckl M
Summary: This study investigates the spatial relationship of performance variables for soccer free kicks. In order to suggest ways in which players might optimise their performance, we collected data from free kicks (<35 m to goal line) of two German Bundesliga seasons (2013/14, 2014/15) (n = 1624). In the analysis, we applied the ISO-map approach using colour gradients to visualise the mean values of a variable on a 2D-map of the pitch. Additionally, variograms were used to describe the degree of spatial dependence of the free kick variables. Results show that DENSITY, TYPE OF PLAY, PLAYERS IN WALL, DISTANCE TO WALL and RULE VIOLATION were strongly spatially dependent. Centrality and proximity to the goal increased the variables PLAYERS IN WALL, RULE VIOLATIONS and INTERRUPTION TIME, and the ratio of goals scored increased from 5.9% (central far) to 10.9% (central near). In 70.9% of the shots, players preferred a switched laterality, which did not result in a higher success rate. Furthermore, there was no statistical advantage for the defensive team when DISTANCE TO WALL was below 9.15 m or when there was a RULE VIOLATION. Crosses had a success rate (i.e., first controlled ball contact after the cross) of 20.8%. Played with natural laterality, they were 5% more successful than with switched laterality. Crosses from the right side outside the penalty box were 10% more successful than from the left side. Therefore, it might be worthwhile practising the defence of balls coming from this side.

#8 Endoscopic debridement and fibrin glue injection of a chronic Morel-Lavallée lesion of the knee in a professional soccer player: A case report and literature review
Reference: Knee. 2016 Nov 22. pii: S0968-0160(16)30183-1. doi: 10.1016/j.knee.2016.10.017. [Epub ahead of print]
Authors: Koc BB, Somorjai N, P M Kiesouw E, Vanderdood K, Meesters-Caberg M, Draijer FW, Jansen EJ
Summary: A Morel-Lavallée lesion is a post-traumatic closed degloving injury of soft tissue. The lesion is due to a shearing trauma with separation of subcutaneous tissue from underlying fascia. When conservative treatment fails, surgical treatment is imperative. Commonly, open drainage and debridement is performed. This case report describes a Morel-Lavallée lesion of the knee in a professional soccer player who was successfully treated with endoscopic debridement and fibrin glue injection after failure of conservative management. This method achieves the goal of an open surgical debridement without exposing patients to an increased morbidity.

#9 Symptoms and risk factors of depression during and after the football career of elite female players
Reference: BMJ Open Sport Exerc Med. 2016 May 31;2(1):e000124. eCollection 2016.
Authors: Prinz B, Dvořák J, Junge A
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Summary: The mental health of elite athletes has received increasing attention in recent years, but no study has evaluated the career-time prevalence of depression, and very few have analysed risk factors of mental health problems during or after the career. 157 (response rate 64.1%) female players who played in the German First League answered an anonymous online survey on details of their football career, stressful and helpful conditions, depression and need of psychotherapeutic support during and after the football career. The career-time prevalence of depression symptoms was 32.3%. Significant differences in the average depression score were observed for playing positions (F=2.75; p<0.05) and levels of play (F=3.53; p<0.01). About half of the players (49.7%) stated 'conflicts with coach/management' as an important reason for their low in moods, followed by 'low in performance/injury' (48.4%) and 'too little support/acknowledgement by the coach' (40.0%). 'Psychological strain/stress' (46.5%) was (after injury) the second most important reason for lows in performance. During their career, almost 40% of players wanted or needed psychological support, but only 10% received it. After their career, the percentage of players wanting or needing psychological support decreased to 24%, of whom 90% received it. The high prevalence of depression symptoms in combination with low use of psychotherapy during the career shows the need for de-stigmatisation of mental health issues in elite football. Furthermore, it seems very important to educate coaches, physicians, physiotherapists and club managers to recognise and prevent mental health problems of their players.

#10 Prevalence of depression and anxiety in top-level male and female football players
Reference: BMJ Open Sport Exerc Med. 2016 Jan 19;2(1):e000087. eCollection 2016.
Authors: Junge A, Feddermann-Demont N
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Summary: Scientific studies on the prevalence of mental health problems in elite athletes are rare, and most have had considerable methodological limitations, such as low response rate and heterogeneous samples. The aim of the study was to evaluate the prevalence of depression and anxiety in top-level football players in comparison to the general population, and to analyse potential risk factors. Players of all first league (FL) and of four U-21 football teams in Switzerland were asked to answer a questionnaire on player's characteristics, the Centre of Epidemiologic Studies Depression Scale (CES-D) and the Generalized Anxiety Disorder (GAD-7) scale. All 10 women's FL teams, 9 of 10 men's FL teams and 4 male U-21 teams (n=471 football players) took part in the study. The CES-D score indicated a mild to moderate depression in 33 (7.6%) players and a major depression in 13 (3.0%) players. The GAD-7 score indicated an at least moderate anxiety disorder in 6 (1.4%) players. Compared to the general population, the prevalence of depression was similar and the prevalence of anxiety disorders was significantly (χ2=16.7; p<0.001) lower in football players. Significant differences were observed with regard to player characteristics, such as age, gender, player position, level of play and current injury. Swiss FL football players had the same prevalence of depression as the general population, while male U-21 players had a higher prevalence of depression. It is important to raise awareness and knowledge of athletes' mental health problems in coaches and team physicians, and to provide adequate treatment to athletes.

#11 Sympathetic enhancement in futsal players but not in football players after repeated sprint ability test
Reference: BMJ Open Sport Exerc Med. 2015 Nov 27;1(1):e000049. eCollection 2015.
Authors: Chen YS, Liao CJ, Lu WA, Kuo CD
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Summary: Heart rate variability (HRV) can disclose the specific adaptation of sympathovagal modulation to exercise. This study investigated the change in HRV measures after anaerobic and aerobic intermittent exercises in university football and futsal players. 36 male university students with physically active lifestyle (n=14), football (n=12), and futsal (n=10) participated in this study. The participants completed the repeated sprint ability (RSA) test and Yo-Yo (YY) intermittent recovery test level 1 in randomised order. ECG signals of the participants were recorded in supine position 15 min before and 30 min after exercises. Before exercise, and 5 and 30 min after exercise, the blood pressures were also taken. In the RSA protocol, the percentage changes in normalised high-frequency power (nHFP) were significantly decreased, while the percentage changes in the very low/high frequency power ratio (VLHR) and low/high frequency power ratio (LHR) were significantly increased in futsal players after exercise, as compared with the controls. No significant changes in all HRV indices were found in the YY protocol, except the respiratory frequency. After exercise, the percent decrease in vagal modulation in futsal players was significantly reduced, while the percentage increase in sympathetic modulation in futsal players was significantly enhanced in the RSA test, but not in the YY test, as compared with the control group. The increase in sympathetic activity and the decrease in vagal activity in the futsal players were greater than the corresponding increase and decrease in the football players in the RSA test.

#12 Heart Rate, Technical Performance And Session-Rpe In Elite Youth Soccer Small-Sided Games Played With Wildcard Player
Reference: J Strength Cond Res. 2016 Nov 19. [Epub ahead of print]
Authors: Sanchez-Sanchez J, Hernández D, Casamichana D, Martínez-Salazar C, Ramirez-Campillo R, Sampaio J
Summary: The aim of this study was to compare heart rate (HR), perceived exertion (RPE) and technical-tactical actions during small-sided games (SSG) played without (CTR), with internal (IW) and with IW and external (IEW) wildcard players. A total of 22 young male soccer players (age 17.2±0.9 y) randomly completed six 4vs4 SSG situations. The control conditions occurred with goals scored without goalkeeper (4vs4-NO) and with goalkeeper (4vs4-GK). During the experimental conditions the situations incorporated 2 IW (4vs4+2IW-NO, 4vs4+2IW-GK) and 2 IEW (4vs4+2IW+2IEW-NO, 4vs4+2IW+2IEW-GK). Processed results did not included data from goalkeepers, IW and IEW players. The HR was divided in intensity-zones (Z1, Z2 and Z3, for <80%, 80-90% and >90% of maximal HR, respectively) and the analyzed technical-tactical actions were the pass, dribbling, collective success and pause. The effects of IW and IEW were analyzed thought repeated-measures ANOVA. During 4vs4+2IW+2IEW-NO greater time was recorded in Z1 (p<0.05) compared to 4vs4-NO and 4s4+2IW-NO. During 4vs4+2IW+2IEW-GK greater time was recorded in Z1 and less in Z3 (p<0.05) compared to 4vs4-GK. Greater RPE was reported in 4vs4-NO (p<0.01) and 4vs4+2IW-NO (p<0.01) compared to 4vs4+2IW+2IEW-NO, and during 4vs4-GK (p<0.01) than 4vs4+2IW+2IEW-GK. Greater number of dribbling situations were recorded during 4vs4-NO (p<0.05) compared to 4vs4+2IW+2IEW-NO. In conclusion, compared to the control condition of 4vs4, the incorporation of IEW reduced HR, RPE and dribbling actions.





Latest research in football - week 47 - 2016

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 Plantar pressure asymmetry and risk of stress injuries in the foot of young soccer players
Reference: Phys Ther Sport. 2016 Oct 24. pii: S1466-853X(16)30129-8. doi: 10.1016/j.ptsp.2016.10.001. [Epub ahead of print]
Authors: Azevedo RR, da Rocha ES, Franco PS, Carpes FP
Summary: Asymmetries in the magnitude of plantar pressure are considered a risk factor for stress fracture of the fifth metatarsal in soccer athletes. The objective was to investigate the presence of plantar pressure asymmetries among young soccer athletes. Thirty young adolescents divided into a soccer player group (n = 15) or a matched control group (n = 15) participated in this study. Mean plantar pressure was determined for seven different regions of the foot. Data were compared between the preferred and non-preferred foot, and between the groups, during barefoot standing on a pressure mat system. Higher pressure was found in the hallux, 5th metatarsal and medial rearfoot of the non-preferred foot in the young soccer players. These asymmetries were not observed in the control group. Magnitudes of plantar pressure did not differ between the groups. Young soccer players present asymmetries in plantar pressure in the hallux, 5th metatarsal and medial rearfoot, with higher pressure observed in the non-preferred foot.

#2 The acute:chonic workload ratio in relation to injury risk in professional soccer
Reference: J Sci Med Sport. 2016 Nov 9. pii: S1440-2440(16)30230-4. doi: 10.1016/j.jsams.2016.10.014. [Epub ahead of print]
Authors: Malone S, Owen A, Newton M, Mendes B, Collins KD, Gabbett TJ
Summary: The objective was to examine the association between combined sRPE measures and injury risk in elite professional soccer. Forty-eight professional soccer players (mean±SD age of 25.3±3.1 yr) from two elite European teams were involved within a one season study. Players completed a test of intermittent-aerobic capacity (Yo-YoIR1) to assess player's injury risk in relation to intermittent aerobic capacity. Weekly workload measures and time loss injuries were recorded during the entire period. Rolling weekly sums and week-to-week changes in workload were measured, allowing for the calculation of the acute:chronic workload ratio, which was calculated by dividing the acute (1-weekly) and chronic (4-weekly) workloads. All derived workload measures were modelled against injury data using logistic regression. Odds ratios (OR) were reported against a reference group. Players who exerted pre-season 1-weekly loads of ≥1500 to ≤2120AU were at significantly higher risk of injury compared to the reference group of ≤1500AU (OR=1.95, p=0.006). Players with increased intermittent-aerobic capacity were better able to tolerate increased 1-weekly absolute changes in training load than players with lower fitness levels (OR=4.52, p=0.011). Players who exerted in-season acute:chronic workload ratios of >1.00 to <1.25 (OR=0.68, p=0.006) were at significantly lower risk of injury compared to the reference group (≤0.85). These findings demonstrate that an acute:chronic workload of between 1.00 and 1.25 is protective for professional soccer players. A higher intermittent-aerobic capacity appears to offer greater injury protection when players are exposed to rapid changes in workload in elite soccer players. Moderate workloads, coupled with moderate-low to moderate-high acute:chronic workload ratios, appear to be protective for professional soccer players.

#3 The Relationship Between Coach and Player Training Load Perceptions in Professional Soccer
Reference: Percept Mot Skills. 2016 Nov 17. pii: 0031512516678727. [Epub ahead of print]
Authors: Redkva PE, Gregorio da Silva S, Paes MR, Dos-Santos JW
Summary: The training load imposed and perceived by coaches and soccer players, respectively, was compared for three weeks of the basic preparatory period of a professional soccer team through session ratings of perceived exertion (S-RPE). Participants were 24 professional Brazilian soccer players (all males, age: 24.1 ± 3.4 years) and their coaches. Athletes responded to the scale of perceived exertion (scores from 0 to10) after the training, while the coaches completed the scale prior to the training session, based on prior planning. The t-test for independent samples was used to compare S-RPE responses, and the Pearson correlation test was used to examine possible correlations between the parameters analyzed. There were no statistical differences between perceptions of prescribed (coaches) and experienced (players) S-RPE, and moderate correlations were found between these parameters (r = .60; p = .003). No statistically significant group differences were found in the perceived exertion during any of three types of training: physical, technical, or tactical. The results suggest that the S-RPE prescribed during the preseason period (by coaches) was not different from that perceived by professional soccer players.

#4 The Independent Influence of Concussive and Sub-concussive Impacts on Soccer Players' Neurophysiological and Neuropsychological Function
Reference: Int J Psychophysiol. 2016 Nov 17. pii: S0167-8760(16)30795-4. doi: 10.1016/j.ijpsycho.2016.11.011. [Epub ahead of print]
Authors: Moore RD, Lepine J, Ellemberg D
Summary: Accumulating research demonstrates that repetitive sub-concussive impacts can alter the structure, function and connectivity of the brain. However, the functional significance of these alterations as well as the independent contribution of concussive and sub-concussive impacts to neurophysiological and neuropsychological health are unclear. Accordingly, we compared the neurophysiological and neuropsychological function of contact athletes with (concussion group) and without (sub-concussion group) a history of concussion, to non-contact athletes. We evaluated event-related brain potentials (ERPs) elicited during an oddball task and performance on a targeted battery of neuropsychological tasks. Athletes in the sub-concussion and concussion groups exhibited similar amplitude reductions in the ERP indices of attentional resource allocation (P3b) and attentional orienting (P3a) relative to non-contact athletes. However, only athletes in the concussion group exhibited reduced amplitude in the ERP index of perceptual attention (N1). Athletes in the sub-concussion and concussion groups also exhibited deficits in memory recall relative to non-contact athletes, but athletes in the concussion group also exhibited significantly more recall errors than athletes in the sub-concussion group. Additionally, only athletes in the concussion group exhibited response delays during the oddball task. The current findings suggest that sub-concussive impacts are associated with alterations in the neurophysiological and neuropsychological indices of essential cognitive functions, albeit to a lesser degree than the combination of sub-concussive and concussive impacts.

#5 Incidence, Mechanisms, and Severity of Match-Related Collegiate Men's Soccer Injuries on FieldTurf and Natural Grass Surfaces: A 6-Year Prospective Study
Reference: Am J Sports Med. 2016 Nov 21. pii: 0363546516671715. [Epub ahead of print]
Authors: Meyers MC
Summary: Numerous injuries have been attributed to playing on artificial turf. More recently, newer generations of artificial turf have been developed to duplicate the playing characteristics of natural grass. Although artificial turf has been deemed safer than natural grass in some studies, few long-term studies have been conducted comparing match-related collegiate soccer injuries between the 2 playing surfaces. The authors hypothesize that Collegiate male soccer athletes do not experience any difference in the incidence, mechanisms, or severity of match-related injuries between FieldTurf and natural grass. Male soccer athletes from 11 universities were evaluated over 6 seasons. Demographic features and predictors included player position, cleat design, player weight, turf age, and environmental factors. Outcomes of interest included injury incidence, injury category, time loss, injury mechanism and situation, type of injury, injury grade and anatomic location, injury severity, head and lower extremity trauma, and elective medical procedures. All match-related injuries were evaluated by the attending head athletic trainer and team physicians on site and subsequently in the physician's office when further follow-up and treatment were deemed necessary. In sum, 765 collegiate games were evaluated for match-related soccer injuries sustained on FieldTurf or natural grass during 6 seasons. Overall, 380 team games (49.7%) were played on FieldTurf versus 385 team games (50.3%) played on natural grass. A total of 722 injuries were documented, with 268 (37.1%) occurring on FieldTurf and 454 (62.9%) on natural grass. Multivariate analysis per 10 team games indicated a significant playing surface effect: F2,720 = 7.260, P = .001. A significantly lower total injury incidence rate (IIR) of 7.1 (95% CI, 6.6-7.5) versus 11.8 (95% CI, 11.3-12.2; P < .0001) and lower rate of substantial injuries, 0.7 (95% CI, 0.5-1.0) versus 1.9 (95% CI, 1.5-2.3; P < .03), were documented on FieldTurf versus natural grass, respectively. Analyses also indicated significantly less trauma on FieldTurf when comparing injury category, time loss, player position, injury mechanism and situation, injuries under various environmental conditions, cleat design, turf age, anatomic location, and elective medical procedures. No significant difference (F11,710 = 0.822, P = .618) between surfaces by knee injury was observed, with the majority of knee injuries involving patellar tendinopathies/syndromes followed by medial collateral ligament injuries on both surfaces. Although similarities existed between FieldTurf and natural grass during competitive match play, FieldTurf is, in many cases, safer than natural grass when comparing injuries in collegiate men's soccer. The findings of this study, however, may not be generalizable to other levels of competition or to other artificial surfaces.

#6 Changes in lumbopelvic rhythm during trunk extension in adolescent soccer players
Reference: Gait Posture. 2016 Nov 15;52:72-75. doi: 10.1016/j.gaitpost.2016.11.026. [Epub ahead of print]
Authors: Tojima M, Torii S
Summary: Many adolescent athletes experience low back pain (LBP). Its causative factors include lower limb muscle tightness and hip-spine in coordination. Hip-spine coordination [or lumbopelvic rhythm, LPR] can be used to assess lower-limb and spine functions. We assessed the presence/absence of LBP in adolescent soccer players before and after a six-month period and divided them into four groups: no LBP both before and after the period (NBP group); LBP before but not after (PN group); LBP after but not before (NP group); and LBP both before and after (LBP group). We used a 3D motion analysis system during trunk extension to measure the lumbar spine and hip ranges of motion (ROMs). On comparing the results obtained before and after the six-month period, lumbar spine ROM decreased in the NP group, hip ROM increased in the LBP group. From before to after the period, the linear prediction indicated that, when the hip extends by 1°, the lumbar spine extends by 3.5°-3.2° for the PN group and by 3.4°-2.8° for the NP group. The NP group extended their lumbar spine excessively compared with the hip before the period, which could cause LBP, but decreased the extension after the period. Lumbar extension relative to hip extension decreased in the PN group, which could decrease excessive load on the lumbar spine and eliminate LBP. These findings suggest that to prevent LBP in adolescent soccer players, it is important to restrict lumbar spine extension relative to hip extension.

#7 Reliability, Validity and Usefulness of 30-15 Intermittent Fitness Test in Female Soccer Players
Reference: Front Physiol. 2016 Nov 17;7:510. eCollection 2016.
Authors: Čović N, Jelešković E, Alić H, Rađo I, Kafedžić E, Sporiš G, McMaster DT, Milanović Z
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Summary: The aim of this study was to examine the reliability, validity and usefulness of the 30-15IFT in competitive female soccer players. Seventeen elite female soccer players participated in the study. A within subject test-retest study design was utilized to assess the reliability of the 30-15 intermittent fitness test (IFT). Seven days prior to 30-15IFT, subjects performed a continuous aerobic running test (CT) under laboratory conditions to assess the criterion validity of the 30-15IFT. End running velocity (VCT and VIFT), peak heart rate (HRpeak) and maximal oxygen consumption (VO2max) were collected and/or estimated for both tests. VIFT (ICC = 0.91; CV = 1.8%), HRpeak (ICC = 0.94; CV = 1.2%), and VO2max (ICC = 0.94; CV = 1.6%) obtained from the 30-15IFT were all deemed highly reliable (p > 0.05). Pearson product moment correlations between the CT and 30-15IFT for VO2max, HRpeak and end running velocity were large (r = 0.67, p = 0.013), very large (r = 0.77, p = 0.02) and large (r = 0.57, p = 0.042), respectively. Current findings suggest that the 30-15IFT is a valid and reliable intermittent aerobic fitness test of elite female soccer players. The findings have also provided practitioners with evidence to support the accurate detection of meaningful individual changes in VIFT of 0.5 km/h (1 stage) and HRpeak of 2 bpm. This information may assist coaches in monitoring "real" aerobic fitness changes to better inform training of female intermittent team sport athletes. Lastly, coaches could use the 30-15IFT as a practical alternative to laboratory based assessments to assess and monitor intermittent aerobic fitness changes in their athletes.

#8 Do Elite and Amateur Soccer Players Outperform Non-Athletes on Neurocognitive Functioning? A Study Among 8-12 Year Old Children
Reference: PLoS One. 2016 Dec 1;11(12):e0165741. doi: 10.1371/journal.pone.0165741. eCollection 2016.
Authors: Verburgh L, Scherder EJ, Van Lange PA, Oosterlaan J
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Summary: Research suggested a positive association between physical fitness and neurocognitive functioning in children. Aim of the present study is to investigate possible dose-response relationships between diverse daily physical activities and a broad range of neurocognitive functions in preadolescent children. Furthermore, the relationship between several sedentary behaviours, including TV-watching, gaming and computer time, and neurocognitive functioning will be investigated in this group of children. A total of 168 preadolescent boys, aged 8 to 12 years, were recruited from various locations, including primary schools, an amateur soccer club, and a professional soccer club, to increase variability in the amount of participation in sports. All children performed neurocognitive tasks measuring inhibition, short term memory, working memory, attention and information processing speed. Regression analyses examined the predictive power of a broad range of physical activities, including sports, active transport to school, physical education (PE), outdoor play, and sedentary behaviour such as TV-watching and gaming, for neurocognitive functioning. Time spent in sports significantly accounted for the variance in inhibition, short term memory, working memory and lapses of attention, where more time spent in sports was associated with better performance. Outdoor play was also positively associated with working memory. In contrast, time spent on the computer was negatively associated with inhibition. Results of the current study suggest a positive relationship between participation in sports and several important neurocognitive functions. Interventions are recommended to increase sports participation and to reduce sedentary behaviour in preadolescent children.

#9 Sleep quality and high intensity interval training at two different times of day: A crossover study on the influence of the chronotype in male collegiate soccer players

Reference: Chronobiol Int. 2016 Dec 1:1-9. [Epub ahead of print]
Authors: Vitale JA, Bonato M, Galasso L, La Torre A, Merati G, Montaruli A, Roveda E, Carandente F
Summary: The influence of the chronotype on the sleep quality in male collegiate soccer players in response to acute high intensity interval training (HIIT) performed at two different times of day was evaluated. The sleep quality was poorer in the morning-type than in the evening-type players after the evening HIIT session, whereas no significant changes in the sleep quality of the two chronotypes after the morning HIIT session was observed. The results suggest that an athlete's chronotype should be taken into account when scheduling training sessions and to promote faster recovery processes.

#10 The efficacy, and characteristics, of warm-up and re-warm-up practices in soccer players: a systematic review
Reference: J Sports Med Phys Fitness. 2016 Nov 30. [Epub ahead of print]
Authors: Hammami A, Zois J, Slimani M, Russel M, Bouhlel E
Summary: This review aimed (i) to evaluate the current research that examines the efficacy of warm-up (WU) and re-warm-up (RWU) on physical performance, and (ii) to highlight the WU and RWU characteristics that optimise subsequent performance in soccer players. A computerized search was performed in the PubMed, ScienceDirect and Google Scholar (from 1995 to December 2015) for English-language, peer- reviewed investigations using the terms "soccer" OR "football" AND "warm-up" OR "stretching" OR "post-activation potentiation" OR "pre-activity" OR "re-warm-up" AND "performance" OR "jump" OR "sprint" OR "running". Twenty seven articles were retrieved. Particularly, 22 articles examined the effects of WU on soccer performance and 5 articles focused on the effects of RWU. Clear evidence exists supporting the inclusion of dynamic stretching or postactivation potentiation-based exercises within a WU as acute performance enhancements were reported (pooled estimate changes of +3.46% and +4.21%, respectively). The FIFA 11+ WU also significantly increases strength, jump, speed and explosive performances (changes from 1 to 20%). At half-time, active RWU protocols including postactivation potentiation practices and multidirectional speed drills attenuate temperature and performance reductions induced by habitual practice. The data obtained in the present review showed that the level of play did not moderate the effectiveness of WU and RWU on soccer performance. This review demonstrated that a static stretching WU reduced acute subsequent performance, while WU activities that include dynamic stretching, PAP-based exercises, and the FIFA 11+ can elicit positive effects in soccer players. The efficacy of an active RWU during half-time is also justified.

#11 Cardiac parasympathetic reactivation after small-sided soccer games and repeated sprints in untrained healthy adolescents
Reference: J Sports Med Phys Fitness. 2016 Nov 30. [Epub ahead of print]
Authors: Hammami A, Kasmi S, Yousfi N, Bouamra M, Tabka Z, Bouhlel E
Summary: It has been shown that recreational soccer was a highly motivating and social activity which produces large improvements in health-related indices in sedentary healthy and unhealthy subjects. The purpose of this study was to compare the acute parasympathetic reactivation after small-sided soccer games (SSG) and repeated sprints training (RST) sessions. Eight post-pubertal untrained adolescents (age 15.8 ± 0.6 years, body mass 59.1 ± 3.7 kg, height 1.7 ± 0.1 m) performed a RST, SSG and a control session in a counterbalanced order. Heart rate variability (HRV) indices in time and frequency domain, heart rate recovery and rating of perceived exertion (RPE) were evaluated. RPE was significantly lower after SSGs compared with RST (P = 0.02, ES = 1.1). There was a significant decrease in mean R-R intervals after RST (difference: -19.6%, P < 0.01, ES = 1.7) and after SSG (-19.2%, P < 0.01, ES = 2.3). A significant decrease was also noted in SDNN after RST (-26.6%, P = 0.02, ES = 1.8) and SSG (-37.8%, P = 0.01, ES = 1.1). For RMSSD, a significant decrease was observed only after SSG (48%, P = 0.01, ES = 1.3). No significant change in all HRV indices after the control condition. SSG and RST elicited high and similar heart rates responses. A low parasympathetic reactivation during early recovery was noted after both RST and SSG. These results were important especially for clinician looking to prescribe repeated sprint or small-sided game for sedentary subjects.

#12 Elastin: a possible genetic biomarker for more severe ligament injuries in elite soccer. A pilot study
Reference: Muscles Ligaments Tendons J. 2016 Sep 17;6(2):188-192.
Authors: Artells R, Pruna R, Dellal A, Maffulli N
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Summary: The study of new genetic biomarkers in genes related to connective tissue repair and regeneration may help to identify individuals with greater predisposition to injury, who may benefit from targeted preventive measures, and those who require longer recovery time following a muscle, ligament or tendon injury. The present study investigated whether single nucleotide polymorphisms of the Elastin gene could be related to MCL injury. 60 top class football players were studied to identify single nucleotide polymorphisms for the Elastin (ELN) gene using Allelic Discrimination analysis. Each player was followed for 7 seasons, and each MCL injury was noted. Ligament injury rate, severity and recovery time are related to specific genotypes observed in the elastin gene, especially the ELN-AA (16 MCL) and the ELN-AG (3 MCL). Players with the ELN-GG genotype sustained no MCL injury during the 7 seasons of the study. The identification of polymorphisms in the ELN gene may be used as a novel tool to better define an athlete's genotype, and help to plan training and rehabilitation programmes to prevent or minimize MCL ligament injuries, and optimize the therapeutic and rehabilitation process after soft tissue injuries, and manage the workloads during trainings and matches.





Latest research in football - week 46 - 2016

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 Applying the acute:chronic workload ratio in elite football: worth the effort?
Reference: Br J Sports Med. 2016 Nov 16. pii: bjsports-2016-097017. doi: 10.1136/bjsports-2016-097017. [Epub ahead of print]
Authors: Buchheit M
Summary: The use of the acute:chronic workload ratio (A/C) has received a growing interest in the past 2 years to monitor injury risk in a variety of team sports.1 ,2 This ratio is generally computed over 28 days (ie, load accumulated during the current week/load accumulated weekly over the past 28 days), using both internal (session-rate of perceive exertion (Session-RPE)×duration) and external (tracking variables, often Global Positioning System (GPS)-related, such as high-speed running and acceleration variables) measures of competitive and training load. While the potential benefit of such a metric is straight forward for practitioners, there remain several limitations to (1) the assessment of relative external load and in turn, injury risk in players differing in locomotor profiles and (2) the effective monitoring of overall load across all training and matches throughout the year. In turn, these limitations likely compromise the usefulness of the A/C ratio in elite football (soccer).

#2 Treatment of muscle injuries in football
Reference: J Sports Sci. 2016 Nov 16:1-9. [Epub ahead of print]
Authors: Ueblacker P, Haensel L, Mueller-Wohlfahrt HW
Summary: Muscle injuries are frequent and represent one of the most substantial medical problems in professional football. They can have both traumatic and overuse causes with direct practical consequence due to differences in terms of the post-primary care regimen and prognosis. An accurate diagnosis is the first step towards a specific treatment and usually allows to predict return to play (RTP). Current treatment principles have no firm scientific basis; they are practiced largely as empirical medicine due to a lack of prospective randomised studies. Immediate treatment usually follows the PRICE-principle (protection, rest, ice, compression, elevation). Depending on the type of the muscle injury, specific physical and physiotherapeutical procedures as well as rehabilitative exercises and gradual training therapy are used to recondition the injured structure, to restore coordination and proprioception, and to normalise movement patterns. Injection therapy with various substances is frequently used, with positive results empirically, but evidence in form of prospective randomised studies is lacking. A precise rehabilitation plan should be developed for every muscle injury, including recommendations for sport-specific training with increasing intensity. Since there are no guidelines regarding safe RTP, regular follow-up examinations on the current muscle status are crucial to evaluate the progress made in terms of healing and to determine when the injured muscle can be exposed to the next step of load. This narrative review describes the various factors that a medical team should consider during assessment, treatment and rehabilitation of a muscle injury with particular focus on professional football.

#3 Ghost or Real Musculoskeletal Asymmetries in Football Players?
Reference: Med Sci Sports Exerc. 2016 Dec;48(12):2580.
Authors: Sanchis-Moysi J, Calbet JA

#4 Hip Strength as an Intrinsic Risk Factor for Lateral Ankle Sprains in Youth Soccer Players: A 3-Season Prospective Study
Reference: Am J Sports Med. 2016 Nov 16. pii: 0363546516672650. [Epub ahead of print]
Authors: De Ridder R, Witvrouw E, Dolphens M, Roosen P, Van Ginckel A
Summary: Numerous epidemiological studies have emphasized the burden of lateral ankle sprains in youth soccer players. However, no prospective study has identified intrinsic physical and modifiable risk factors for these injuries in this particular population. Although injury prevention programs in soccer incorporate proximal hip and core stability exercises, it is striking that the relationship between impaired proximal hip function and ankle sprains has not yet been prospectively investigated in youth soccer players. This prospective study aimed to examine whether hip muscle strength is a risk factor for sustaining a lateral ankle sprain in youth soccer players. We hypothesized that decreased hip muscle strength would predispose youth soccer players to an increased risk of lateral ankle sprains. This study included a total of 133 male youth soccer players (age divisions U11-U17) for analysis. At the beginning of the season, anthropometric characteristics were collected and hip muscle strength was assessed using a handheld dynamometer. Injury registration was performed by the team medical staff during 3 consecutive seasons. A principal-component, multivariate Cox regression analysis was performed to identify potential risk factors for sustaining a lateral ankle sprain. Twelve participants (18% of all reported injuries) sustained a lateral ankle sprain (0.36 per 1000 athletic-exposure hours). After adjustment for body size dependencies and other hip muscle forces, an increase in hip muscle extension force was associated with a significant decrease in the hazard of the injury (hazard ratio, 0.3; 95% confidence interval, 0.1-0.9; P = .028). No other study variable could be identified as a risk factor for lateral ankle sprains. Reduced hip extension muscle strength is an independent risk factor for lateral ankle sprains in male youth soccer players. Other hip muscle strength outcomes were not identified as risk factors. Replication in larger samples with more injured cases is warranted to further ascertain the importance of this risk factor.

#5 The Challenge of Evaluating the Intensity of Short Actions in Soccer: A New Methodological Approach Using Percentage Acceleration
Reference: PLoS One. 2016 Nov 15;11(11):e0166534. doi: 10.1371/journal.pone.0166534. eCollection 2016.
Authors: Sonderegger K, Tschopp M, Taube W
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Summary: There are several approaches to quantifying physical load in team sports using positional data. Distances in different speed zones are most commonly used. Recent studies have used acceleration data in addition in order to take short intense actions into account. However, the fact that acceleration decreases with increasing initial running speed is ignored and therefore introduces a bias. The aim of our study was to develop a new methodological approach that removes this bias. For this purpose, percentage acceleration was calculated as the ratio of the maximal acceleration of the action (amax,action) and the maximal voluntary acceleration (amax) that can be achieved for a particular initial running speed (percentage acceleration [%] = amax,action / amax * 100). To define amax, seventy-two highly trained junior male soccer players (17.1 ± 0.6 years) completed maximal sprints from standing and three different constant initial running speeds (vinit; trotting: ~6.0 km·h-1; jogging: ~10.8 km·h-1; running: ~15.0 km·h-1). The amax was 6.01 ± 0.55 from a standing start, 4.33 ± 0.40 from trotting, 3.20 ± 0.49 from jogging and 2.29 ± 0.34 m·s-2 from running. The amax correlated significantly with vinit (r = -0.98) and the linear regression equation of highly-trained junior soccer players was: amax = -0.23 * vinit + 5.99. Using linear regression analysis, we propose to classify high-intensity actions as accelerations >75% of the amax, corresponding to acceleration values for our population of >4.51 initiated from standing, >3.25 from trotting, >2.40 from jogging, and >1.72 m·s-2 from running. The use of percentage acceleration avoids the bias of underestimating actions with high and overestimating actions with low initial running speed. Furthermore, percentage acceleration allows determining individual intensity thresholds that are specific for one population or one single player.

#6 Do cognitive training strategies improve motor and positive psychological skills development in soccer players? Insights from a systematic review
Reference: J Sports Sci. 2016 Nov 15:1-12. [Epub ahead of print]
Authors: Slimani M, Bragazzi NL, Tod D, Dellal A, Hue O, Cheour F, Taylor L, Chamari K
Summary: Soccer players are required to have well-developed physical, technical and cognitive abilities. The present systematic review, adhering to Preferred Reporting Items for Systematic reviews and Meta-Analysis guidelines, examined the effects of cognitive training strategies on motor and positive psychological skills development in soccer performance and identified the potential moderators of the "cognitive training-soccer performance" relationship. Thirteen databases were systematically searched using keywords related to psychological or cognitive training in soccer players. The review is based on 18 studies, employing 584 soccer players aged 7-39 years. Cognitive strategies, particularly imagery, appear to improve sports performance in soccer players. Regarding imagery, the combination of two different types of cognitive imagery training (i.e., cognitive general and cognitive specific) has a positive influence on soccer performance during training, whereas motivational imagery (i.e., motivational general-arousal, motivational general-mastery and motivational specific) enhance competition performance. Younger soccer players employ cognitive general and cognitive specific imagery techniques to a greater extent than older soccer players. Combined cognitive training strategies were more beneficial than a single cognitive strategy relative to motor skills enhancement in elite (particularly midfielders) and amateur (i.e., when practising complex and specific soccer skills in precompetitive period) soccer players. In conclusion, it appears that there are differences in cognitive/psychological training interventions, and their efficacy, according to whether they are directed towards training or competition, and the age, standard and playing position of the players.

#7 Sequencing effects of balance and plyometric training on physical performance in youth soccer athletes
Reference: J Strength Cond Res 30(12): 3278–3289, 2016

Authors: Hammami R, Granacher U, Makhlouf I, Behm DG, Chaouachi A
Summary: Balance training may have a preconditioning effect on subsequent power training with youth. There are no studies examining whether the sequencing of balance and plyometric training has additional training benefits. The objective was to examine the effect of sequencing balance and plyometric training on the performance of 12- to 13-year-old athletes. Twenty-four young elite soccer players trained twice per week for 8 weeks either with an initial 4 weeks of balance training followed by 4 weeks of plyometric training (BPT) or 4 weeks of plyometric training proceeded by 4 weeks of balance training (PBT). Testing was conducted pre- and posttraining and included medicine ball throw; horizontal and vertical jumps; reactive strength; leg stiffness; agility; 10-, 20-, and 30-m sprints; Standing Stork balance test; and Y-Balance test. Results indicated that BPT provided significantly greater improvements with reactive strength index, absolute and relative leg stiffness, triple hop test, and a trend for the Y-Balance test (p = 0.054) compared with PBT. Although all other measures had similar changes for both groups, the average relative improvement for the BPT was 22.4% (d = 1.5) vs. 15.0% (d = 1.1) for the PBT. BPT effect sizes were greater with 8 of 13 measures. In conclusion, although either sequence of BPT or PBT improved jumping, hopping, sprint acceleration, and Standing Stork and Y-Balance, BPT initiated greater training improvements in reactive strength index, absolute and relative leg stiffness, triple hop test, and the Y-Balance test. BPT may provide either similar or superior performance enhancements compared with PBT.

#8 Effects of high-velocity resistance training on athletic performance in prepuberal male soccer athletes
Reference: J Strength Cond Res 30(12): 3290–3297, 2016
Authors: Negra Y, Chaabene H, Hammami M, Hachana Y, Granacher U
Summary: The aim of this study was to assess the effectiveness of a 12-week in-season low-to-moderate load high-velocity resistance training (HVRT) in addition to soccer training as compared with soccer training only on proxies of athletic performance in prepubertal soccer players. Twenty-four male soccer players performed 2 different protocols: (a) regular soccer training with 5 sessions per week (n = 11; age = 12.7 ± 0.3 years) and (b) regular soccer training with 3 sessions per week and HVRT with 2 sessions per week (n = 13; age = 12.8 ± 0.2 years). The outcome measures included tests for the assessment of muscle strength (e.g., 1 repetition maximum [1RM] half-squat tests), jump ability (e.g., countermovement jump, squat jump [SJ], standing long jump [SLJ], and multiple 5-bound tests [MB5s]), linear speed (e.g., 5-, 10-, 20-, and 30-m sprint tests), and change of direction (e.g., T-test and Illinois change of direction test). Results revealed significant group × test interactions for the SJ test (p ≤ 0.05, d = 0.59) and the SLJ test (p < 0.01, d = 0.83). Post hoc tests illustrated significant pre-post changes in the HVRT group (SJ: [INCREMENT]22%, p < 0.001, d = 1.26; SLJ: [INCREMENT]15%, p < 0.001, d = 1.30) but not in the control group. In addition, tendencies toward significant interaction effects were found for the 1RM half-squat (p = 0.08, d = 0.54) and the 10-m sprint test (p = 0.06, d = 0.57). Significant pre-post changes were found for both parameters in the HVRT group only (1RM: [INCREMENT]25%, p < 0.001, d = 1.23; 10-m sprint: [INCREMENT]7%, p < 0.0001, d = 1.47). In summary, in-season low-to-moderate load HVRT conducted in combination with regular soccer training is a safe and feasible intervention that has positive effects on maximal strength, vertical and horizontal jump and sprint performance as compared with soccer training only.

#9 Technical actions, heart rate, and locomotor activity in 7v7 and 8v8 games for female youth soccer players
Reference: J Strength Cond Res 30(12): 3298–3303, 2016
Authors: Ørntoft C, Larsen MN, Andersen TB, Rasmussen LS, Póvoas SCA, Randers MB, Krustrup P
Summary: The purpose of this study was to evaluate technical performance, heart rate (HR), and activity profile in 7v7 and 8v8 soccer games for 9- to 10-year-old girls (U11). A total of 24 female youth players participated in the study, all playing 20-minute 7v7 and 8v8 games with 160 and 223 m2 per player, respectively. Technical actions, HR, and activity profile were measured during the games using video filming, HR monitors, and 5-Hz Global positioning system (GPS) units. The number of technical actions was higher in 7v7 than in 8v8 games (34 ± 19 vs. 28 ± 14; p = 0.03; d = 0.37), as was the number of successful actions (25 ± 16 vs. 20 ± 12; p = 0.01; d = 0.35), with no difference in success rate for technical actions (70 ± 13 vs. 69 ± 14%; p = 0.63; d = 0.07). No differences were found between 7v7 and 8v8 in total distance covered (1,574 ± 251 and 1,622 ± 281 m; p = 0.66; d = 0.18), peak speed (19.5 ± 2.6 and 20.7 ± 1.5 km·h−1; p = 0.16; d = 0.56), mean HR values (85 ± 5 and 86 ± 6%HRpeak; p = 0.85; d = 0.18), and time of >90% HRpeak (37 ± 16 and 35 ± 14% of playing time; p = 0.70; d = 0.13). Distance covered at the highest running speeds of >16 km·h−1 was lower in 7v7 than in 8v8 games (34 ± 24 vs. 63 ± 34 m; p = 0.018; d = 0.98), as was the number of entries into this speed zone (8 ± 5 vs. 13 ± 7; p = 0.006; d = 0.82). In conclusion, more technical actions and successful actions were observed in 7v7 than in 8v8 games, but players covered more ground with high-speed running in 8v8 games. This study also revealed that HR values were high in both game formats for U11 adolescent female players, with no difference between formats.

#10 Consistency of field-based measures of neuromuscular control using force-plate diagnostics in elite male youth soccer players
Reference: J Strength Cond Res 30(12): 3304–3311, 2016
Authors: Read P, Oliver JL, Croix MD, Myer GD, Lloyd, RS
Summary: Deficits in neuromuscular control during movement patterns such as landing are suggested pathomechanics that underlie sport-related injury. A common mode of assessment is measurement of landing forces during jumping tasks; however, these measures have been used less frequently in male youth soccer players, and reliability data are sparse. The aim of this study was to examine the reliability of a field-based neuromuscular control screening battery using force-plate diagnostics in this cohort. Twenty-six pre–peak height velocity (PHV) and 25 post-PHV elite male youth soccer players completed a drop vertical jump (DVJ), single-leg 75% horizontal hop and stick (75%HOP), and single-leg countermovement jump (SLCMJ). Measures of peak landing vertical ground reaction force (pVGRF), time to stabilization, time to pVGRF, and pVGRF asymmetry were recorded. A test-retest design was used, and reliability statistics included change in mean, intraclass correlation coefficient, and coefficient of variation (CV). No significant differences in mean score were reported for any of the assessed variables between test sessions. In both groups, pVGRF and asymmetry during the 75%HOP and SLCMJ demonstrated largely acceptable reliability (CV ≤ 10%). Greater variability was evident in DVJ pVGRF and all other assessed variables, across the 3 protocols (CV range = 13.8–49.7%). Intraclass correlation coefficient values ranged from small to large and were generally higher in the post-PHV players. The results of this study suggest that pVGRF and asymmetry can be reliably assessed using a 75%HOP and SLCMJ in this cohort. These measures could be used to support a screening battery for elite male youth soccer players and for test-retest comparison.

#11 Effects of an in-season plyometric training program on repeated change of direction and sprint performance in the junior soccer player
Reference: J Strength Cond Res 30(12): 3312–3320, 2016
Authors: Hammami M, Negra Y, Aouadi R, Shephard RJ, Chelly MS
Summary: We aimed to determine the gains in explosive movements of male junior soccer players induced by incorporating an 8-week plyometric training program (PTP) into a standard soccer conditioning regimen 5 months after the beginning of the competitive season. Our hypothesis was that PTP would enhance explosive movements, and thus sprint running, repeated shuttle sprint ability (RSSA), agility and the ability to make repeated changes of direction (RCOD). A group of junior soccer players were randomly divided into 2 groups: an experimental group (E, n = 15, age 15.7 ± 0.2 years) and a control group (C, n = 13, age 15.8 ± 0.2 years). The participants in E and C performed training exercises and matches together, but for an 8-week period in the latter part of the season, the experimental group replaced a part of the normal regimen (the tactical session) by a biweekly course of PTP (hurdle and drop jumps). Two familiarization sessions were held 2 weeks before definitive testing. The ability of the players was assessed by 3 agility tests (a sprint test with 180° turns, a 9-3-6-3-9 m sprint with backward and forward running, and a four 5-m sprint test with turns); 2 repeated sprint tests (RSSA and RCOD); and running times over 5-, 10-, 20-, 30-, and 40-m distances. Participants in E showed gains relative to C in sprint times (p ≤ 0.05 for 5, 10, and 20 m), and 2 of 3 the RCOD parameters (RCOD best, p ≤ 0.001; RCOD total, p ≤ 0.05). However, with the pattern of plyometric training that we adopted, and perhaps because participants were in good initial physical condition, the agility and RSSA test scores remained unchanged. Nevertheless, we conclude that our PTP can be commended to junior soccer players as a means of improving important components of their physical performance.





Latest research in football - week 45 - 2016

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 muscle damage, inflammation, and fatigue-related parameters in young elite soccer players after a match
Reference: J Sports Med Phys Fitness. 2016 Oct;56(10):1198-1205. Epub 2015 Nov 11.
Authors: Romagnoli M, Sanchis-Gomar F, Alis R, Risso-Ballester J, Bosio A, Graziani RL, Rampinini E
Summary: Professional soccer players are subjected to substantial physical loads during competitive seasons. We aimed to explore the changes induced by a soccer match on muscle damage and inflammation biomarkers, and their relationship with fatigue parameters. Twenty young male professional in-field soccer players from an Italian Serie A team (age 17-20 years, weight 73.0±7.0 kg, height 1.81±0.05m) played a 90-minute soccer match. Players' distances and velocities were recorded during the match. Before the match and 30 minutes, 24 and 48 hours after the match, blood samples were drawn and a full blood cell count was determined, along with serum creatine kinase (CK), interleukin 6 (hsIL-6), cortisol and testosterone. At the same time intervals, counter-movement jump (CMJ) performance was recorded. The players covered fewer meters at low velocities in the second period while the meters covered at higher intensity remained unchanged. CMJ height was lower at all postgame time-points compared to the pregame measurement. Immediately after the match, CK, hs-IL6 and neutrophil counts were elevated. 24 and 48 hours after the match, CK and neutrophil counts remained significantly elevated. The distance covered during the game was found to be correlated with the values for postmatch hsIL-6 (ρ=0.521, P=0.027), post 24-hour cortisol (r=0.502, P=0.034) and the increase in cortisol at 48 hours with respect to prematch values (r=0.515, P=0.029). A soccer match provokes a transient systemic imbalance that results in muscle damage and inflammatory and performance-related parameter changes. HsIL-6 and cortisol could be used to monitor recovery processes and as fatigue markers, even for short time periods.

#2 New score based on early repolarization in precordial leads for detection of left ventricular hypertrophy in young soccer players
Reference: J Sports Med Phys Fitness. 2016 Oct;56(10):1258-1259. Epub 2015 Nov 10.
Authors: Fabregat-Andrés Ó, Muñoz-Macho A, Pina-Buded S, Cal Vente-Nomdedeu A, Soriano-Navarro CJ, Usó H

#3 The effects of anthropometry and leg muscle power on drive and transition phase of acceleration: a longitudinal study on young soccer players
Reference: J Sports Med Phys Fitness. 2016 Oct;56(10):1156-1162. Epub 2015 Sep 23.
Authors: Nikolaidis PT, Ingebrigtsen J, Jeffreys I
Summary: The aim of this study was to examine the effect of anthropometry and leg muscle power on accelerative ability and its phases (drive and transition). Thirty-six soccer players (age 12.4±1.2 years, body mass 49.9±8.9 kg and height 154.2±10.3 cm) were tested twice, in the beginning and in the end of competitive season, for anthropometric characteristics, countermovement jump and 20-meter acceleration (split 0-10 meters and 10-20 meters, indices of drive and transition, respectively). The soccer players were grouped according to seasonal changes in 20-meter acceleration (Δacc) in responders (Δacc≤-0.10 s), control (-0.05≤Δacc≤0.08 s) and non-responders (Δacc≥0.10 s). Compared with the non-responders at baseline, the responders were younger (-2.0 years [-2.8;-1.1]), shorter (-10.1 cm [-19.4;-0.7]), with higher body fat percentage (7.7% [2.7%;12.6%]) and fat mass (4.1 kg [0.7;7.4]), and lower performance in the countermovement jump (-8.9 cm [-13.9;-4.0]) and 20 m acceleration (0.63 s [0.39;0.87]); during the season they had smaller body mass gain (-2.8 kg [-5.4;-0.1]), decreased Body Mass Index (BMI, -1.0 kg/m2 [-1.9;0]) and greater improvement in the 20-meter acceleration (-0.33 s [-0.38;-0.28]). The effect size for these between-group differences was large (η2≥0.18). The Δacc and Δ10-20 were moderately correlated with body mass difference (r=0.48 and r=0.53, P<0.01, respectively) and ΔBMI (r=0.50 and r=0.51, P<0.01, respectively), whereas the Δ0-10 was correlated with ΔBMI (r=0.34, P<0.05) and ΔCMJ (r=-0.34, P<0.05). The findings indicated that the changes in body mass had the largest effect on changes in accelerative ability and on both two phases (drive and transition). On the contrary, changes in leg muscle power had impact only on the drive phase of the acceleration.

#4 Physical and anthropometric changes during pre- and in-season in professional soccer players
Reference: J Sports Med Phys Fitness. 2016 Oct;56(10):1163-1170. Epub 2015 Sep 10.
Authors: Fessi MS, Zarrouk N, Filetti C, Rebai H, Elloumi M, Moalla W.
Summary: The purpose of this study was to examine the changes in anthropometric and physical fitness characteristics in professional soccer players at the beginning of the season, after preseason camp and during in-season. Seventeen players were evaluated on three different periods (June: T0, August: T1 and December: T2). Each evaluation consisted of anthropometric measurements (body mass, height, and body fat) and physical fitness tests (counter movement jump [CMJ], counter movement jump with arm (CMJA), 10-m sprint, 30-m sprint and maximal aerobic speed [MAS]). Comparatively with T0, all physical performances achieved in T1 were significantly improved (MAS: P<0.01, 10-m sprint: P<0.05, 30-m sprint: P<0.05, CMJ: P<0.01, and CMJA: P<0.05). The decrease in training load during in-season is associated by significant decrement in MAS (P<0.05) and preserved performances in 10 (P=0.85) and 30-m sprint (P=0.99), CMJ (P=0.34) and CMJA (P=0.87) completed in T2 comparatively with T1. Physical fitness performances achieved in T2 remain higher than that obtained in T0 (MAS: P<0.01, 10-m sprint: P<0.01, 30-m sprint: P<0.05 and CMJ: P<0.05) and remain similar for CMJA (P=0.13). No significant changes were observed in anthropometric measurements throughout the study. The main finding of this study was that a greater training load accomplished during preseason could lead to an improvement in the physical fitness during in-season in professional soccer players. We suggest that this higher training load meets the needed required for the professional soccer although the training loads are declined during in-season.

#5 Relationship Between Pre-Season Training Load and In-Season Availability in Elite Australian Football Players
Reference: Int J Sports Physiol Perform. 2016 Nov 11:1-21. [Epub ahead of print]
Authors: Murray NB, Gabbett TJ, Townshend AD
Summary: Investigate the relationship between the proportion of pre-season training sessions completed, and load and injury during the ensuing Australian Football League season. Forty-six elite male Australian football players from one club participated in this study. Players were divided into three equal groups based on the amount of pre-season training completed (high, HTL, >85% sessions completed; medium, MTL, 50-85% sessions completed, and low, LTL, <50% sessions completed). Global Positioning System (GPS) technology was used to record training and game loads, with all injuries recorded and classified by club medical staff. Differences between groups were analysed using a two-way (group x training/competition phase) repeated measures ANOVA, along with magnitude-based inferences. Injury incidence was expressed as injuries per 1,000 hours. The HTL and MTL group completed a greater proportion of in-season training sessions (81.1% and 74.2%) and matches (76.7% and 76.1%) than the LTL (56.9% and 52.7%) group. Total distance and Player load were significantly greater during the first half of the in-season period for the HTL (p=0.03, ES=0.88) and MTL (p=0.02, ES=0.93) groups than the LTL group. The relative risk of injury for the LTL group (26.8/1,000 hours) was 1.9 times greater than the HTL group (14.2/1,000 hours) (χ2=3.48, df=2, p=0.17). Completing a greater proportion of pre-season training resulted in higher training loads and greater participation in training and competition during the competitive phase of the season.

#6 The Prevalence of Selected Intrinsic Risk Factors for Ankle Sprain Among Elite Football and Basketball Players
Reference: Asian J Sports Med. 2016 May 23;7(3):e35287. eCollection 2016.
Authors: Halabchi F, Angoorani H, Mirshahi M, Pourgharib Shahi MH, Mansournia MA
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Summary: Lateral ankle sprains (LAS) are among the most common sports- related injuries and the reinjury rate is very high. This study aimed to evaluate the prevalence of some intrinsic risk factors among professional football and basketball players with or without history of acute or recurrent ankle sprain.One hundred and six professional football and basketball players who were referred for pre-participation examinations were recruited in this study. Prepared checklist was completed for each participant. Athletes were asked for any history of previous ankle sprain and the severity (based of self-description of signs and symptoms by the athlete), level and number of injuries in the last two years. All players were assessed for measures of foot posture index- 6, foot length and width, Beighton generalized joint laxity score, anterior drawer and talar tilt tests, star excursion and single leg balance tests and goniometric assessment of ankle plantarflexion, ankle dorsiflexion and first metatarsophalangeal dorsiflexion. Forty eight basketball players (45.3%) and 58 football players (54.7%) with mean (SD) age of 19.8 (4.5) years participated. About 58.5% and 14.2% of athletes had a history of ankle sprain and recurrent sprain in at least one extremity, respectively. Sprains were more prevalent in basketball players and in dominant leg. There was no significant difference in assessed risk factors between athletes with and without history of ankle sprain, except for positive single leg balance test which was more prevalent in athletes with history of ankle sprain and also for positive talar tilt test and decreased ankle plantarflexion range of motion in acute and recurrent injury of left ankle. Some intrinsic risk factors including lateral ankle ligaments laxity, balance and ankle plantarflexion seem to be related to acute or recurrent LAS in athletes. Further research is needed to reveal the role of different arthrokinematics following lateral ankle sprain.

#7 Persistent effects of playing football and associated (subconcussive) head trauma on brain structure and function: a systematic review of the literature
Reference: Br J Sports Med. 2016 Nov 4. pii: bjsports-2016-096593. doi: 10.1136/bjsports-2016-096593. [Epub ahead of print]
Authors: Tarnutzer AA, Straumann D, Brugger P, Feddermann-Demont N
Summary: There is ongoing controversy about persistent neurological deficits in active and former football (soccer) players. We reviewed the literature for associations between football activities (including heading/head injuries) and decline in brain structure/function. MEDLINE, Embase, PsycINFO, CINAHL, Cochrane-CRCT, SportDiscus, Cochrane-DSR=4 (accessed 2 August 2016) database were searched. Original studies reporting on football-related persistent effects on brain structure/function. Results from neurocognitive testing, neuroimaging and EEG were compared with controls and/or correlated with heading frequency and/or head injuries. Methodological quality was rated for risk-of-bias, including appropriateness of controls, correction for multiple statistical testing and assessment of heading frequency and head injuries. 30 studies with 1691 players were included. Those 57% (8/14) of case-control studies reporting persistent neurocognitive impairment had higher odds for inappropriate control of type 1 errors (OR=17.35 (95% CI (10.61 to 28.36)) and for inappropriate selection of controls (OR=1.72 (1.22 to 2.43)) than studies observing no impairment. Studies reporting a correlation between heading frequency and neurocognitive deficits (6/17) had lower quality of heading assessment (OR=14.20 (9.01 to 22.39)) than studies reporting no such correlation. In 7 of 13 studies (54%), the number of head injuries correlated with the degree of neurocognitive impairment. Abnormalities on neuroimaging (6/8 studies) were associated with subclinical neurocognitive deficits in 3 of 4 studies. Various methodological shortcomings limit the evidence for persistent effects of football play on brain structure/function. Sources of bias include low-quality assessment of heading frequency, inappropriate control for type 1 errors and inappropriate selection of controls. Combining neuroimaging techniques with neurocognitive testing in prospective studies seems most promising to further clarify on the impact of football on the brain.

#8 Football and dementia: A qualitative investigation of a community based sports group for men with early onset dementia
Reference: Dementia (London). 2016 Nov;15(6):1358-1376. Epub 2014 Nov 26.
Authors: Carone L, Tischler V, Dening T
Summary: This study investigates the impact of a weekly group providing sport and physical activities for men with early onset dementia established by Notts County Football in the Community (NCFC). There were three aims: to investigate the effect of early onset dementia on individuals with the condition and their carers; to examine the perceptions of current levels of service provision for people with early onset dementia; and to analyse the impact of the group. Men with dementia (n = 5) attending the sessions, their carers (n = 5), NCFC coaching staff (n = 5) and people organizing/facilitating the sessions (n = 5) were interviewed. Semi-structured interviews explored the participants' experiences of dementia, their opinions on current service provisions and on the sessions. Data were analysed using thematic analysis. Four main themes were found: loss related to the condition of dementia and its impact on relationships ('Loss'); lack of age-appropriate services for people with early onset dementia ('Lack of Resources'); enjoyment and positive anticipation related to the group for all involved ('Enjoyment and Anticipation'); and 'the Notts County Effect' which attributed the success of the sessions to the strong brand of the football club, and to personalized service in a "dementia-free" environment. The NCFC sessions provided a safe low-cost intervention with positive effects upon quality of life for both people with early onset dementia, their carers and the staff involved. This suggests that the service may be valuable to a wider range of people living in different areas.

#9 Index of fatigue quadriceps in soccer athletes after anterior cruciate ligament reconstruction
Reference: Rev Bras Ortop. 2016 Aug 17;51(5):535-540.
Authors: Cavalcante ML, Teixeira PR, Sousa TC, Lima PO, Oliveira RR
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Summary: The present study aimed to evaluate the muscle fatigue of the quadriceps muscle in high-performance soccer players undergoing (anterior cruciate ligament) ACL reconstruction. We evaluated 17 high-performance soccer players from three professional soccer teams of a state in Brazil from August 2011 to July 2012. All subjects were evaluated between 5.5 and 7 months after ACL reconstruction with a Biodex® isokinetic dynamometer (System 4 Pro) with test protocol CON/CON at 60°/s and 300°/s with 5 and 15 repetitions, respectively. In the calculation of local muscle fatigue, the fatigue index was used, which is calculated by dividing the labor done in the first one-third of the repetitions by that done at the final one-third of the repetitions, and multiplying by 100 to express a unit in percentage (i.e., as a discrete quantitative variable). All subjects were male, with a mean age of 21.3 ± 4.4 years and mean BMI 23.4 ± 1.53 cm; left dominance was observed in 47% (n = 8) of athletes, and right dominance, in 53% (n = 9) of athletes; and the limb involved in the lesion was the dominant in 29% (n = 5) and the non-dominant in 71% (n = 12). Fatigue rates were 19.6% in the involved limb and 29.0% in the non-involved limb. The results allow us to conclude that there was no significant difference between the limbs involved and not in ACL injuries regarding local muscle fatigue. No association was observed between the dominant side and the limb involved in the ACL injury.

#10 Physical and balance performance following exercise induced muscle damage in male soccer players
Reference: J Phys Ther Sci. 2016 Oct;28(10):2942-2949. Epub 2016 Oct 28.
Authors: Khan MA, Moiz JA, Raza S, Verma S, Shareef MY, Anwer S, Alghadir A
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Summary: The present study aimed to determine the changes in physical and balance performance following exercise-induced muscle damage using a sport-specific protocol. Fifteen collegiate soccer players were asked to perform a sport-specific sprint protocol to induce muscle damage. The markers of muscle damage (soreness, range of motion, limb girth, muscle strength, creatine kinase and lactate dehydrogenase), physical performance (speed, agility and power) and balance (static and dynamic balance) were assessed at baseline and 24, 48 and 72 hours following the sprint protocol. All variables, including the markers of muscle damage, physical performance and balance showed a significant difference when assessed at the 4 time points. [Conclusion] The study demonstrated that both the physical and balance performance were affected following repeated sprint protocol in soccer players. It is recommended the balance performance of an athlete be continually assessed following exercise-induced muscle damage so as to determine the appropriate return to sport decision thereby, minimizing the risk of further injury.

#11 No Association Between Return to Play After Injury and Increased Rate of Anterior Cruciate Ligament Injury in Men's Professional Soccer
Reference: Orthop J Sports Med. 2016 Oct 27;4(10):2325967116669708. eCollection 2016.
Authors: Lundblad M, Waldén M, Hägglund M, Ekstrand J, Thomeé C, Karlsson J
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Summary: Studies have shown that previous injury, not necessarily anatomically related, is an important injury risk factor. However, it is not known whether a player runs an increased risk of anterior cruciate ligament (ACL) injury after returning to play from other injury types. The purpose was to analyze whether professional soccer players are more susceptible to ACL injury after returning to play from any previous injury. A total of 101 elite male soccer players suffering a first-time complete ACL injury between 2001 and 2014 were included and matched according to team, age, and playing position with control players who did not have a current injury (1:1 match). For each injured player, the 90-day period prior to the ACL injury was analyzed for injuries and compared with that of control players by using odds ratios (ORs) and 95% CIs. The odds of a player with an ACL injury sustaining a previous injury in the 90-day period did not differ significantly from that of controls (OR, 1.20; 95% CI, 0.66-2.17; P = .65). Testing the frequency of absence periods due to injury between the groups revealed that the odds of a player with an ACL injury having a previous period of absence due to injury did not differ compared with controls (OR, 1.14; 95% CI, 0.64-2.01; P = .77). Players with ACL injury did not have a greater occurrence of absence due to injury in the 3 months preceding their ACL injury compared with matched controls. This indicates that previous injury of any type does not increase the risk of suffering an ACL injury.

#12 Very-Heavy Sled Training for Improving Horizontal Force Output in Soccer Players
Reference: Int J Sports Physiol Perform. 2016 Nov 11:1-13. [Epub ahead of print]
Authors: Morin JB, Petrakos G, Jimenez-Reyes P, Brown SR, Samozino P, Cross MR
Summary: Sprint running acceleration is a key feature of physical performance in team sports, and recent literature shows that the ability to generate large magnitudes of horizontal ground reaction force and mechanical effectiveness of force application are paramount. We tested the hypothesis that very-heavy loaded sled sprint training would induce an improvement in horizontal force production, via an increased effectiveness of application. Training-induced changes in sprint performance and mechanical outputs were computed using a field method based on velocity-time data, before and after an 8-week protocol (16 sessions of 10x20-m sprints). 16 male amateur soccer players were assigned to either a very-heavy sled (80% body-mass sled load) or a control group (unresisted sprints). The main outcome of this pilot study is that very-heavy sled resisted sprint training, using much greater loads than traditionally recommended, clearly increased maximal horizontal force production compared to standard unloaded sprint training (effect size of 0.80 vs 0.20 for controls, unclear between-group difference) and mechanical effectiveness (i.e. more horizontally applied force; effect size of 0.95 vs -0.11, moderate between-group difference). In addition, 5-m and 20-m sprint performance improvement were moderate and small for the very-heavy sled group, and small and trivial for the control group, respectively. This brief report highlights the usefulness of very-heavy sled (80% body-mass) training, which may suggest value for practical improvement of mechanical effectiveness and maximal horizontal force capabilities in soccer players and other team sport athletes. This study may encourage further research to confirm the usefulness of very-heavy sled in this context.





Latest research in football - week 44 - 2016

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 Test-Retest Reliability of Physiological and Performance Responses to 120 Minutes of Simulated Soccer Match Play
Reference: J Strength Cond Res. 2016 Nov;30(11):3178-3186.
Author: Harper LD, Hunter R, Parker P, Goodall S, Thomas K, Howatson G, West DJ, Stevenson E, Russell M
Summary: This study investigated the test-retest reliability of physiological and performance responses to 120 minutes (90 minutes plus 30 minutes extra-time [ET]) of the soccer match simulation (SMS). Ten university-standard soccer players completed the SMS on 2 occasions under standardized conditions. Capillary and venous blood was taken pre-exercise, at half-time, and at 90 and 120 minutes, with further capillary samples taken every 15 minutes throughout the exercise. Core temperature (Tcore), physical (20- and 15-m sprint speeds and countermovement jump height), and technical (soccer dribbling) performance was also assessed during each trial. All variables except blood lactate demonstrated no systematic bias between trials (p > 0.05). During the last 15 minutes of ET, test-rest reliability (coefficient of variation %, Pearson's r, respectively) was moderate to strong for 20-m sprint speed (3.5%, 0.71), countermovement jump height (4.9%, 0.90), dribble speed (2.8%, 0.90), and blood glucose (7.1%, 0.93), and very strong for Tcore (1.2%, 0.99). Moderate reliability was demonstrated for 15-m sprint speed (4.6%, 0.36), dribble precision (11.5%, 0.30), plasma insulin (10.3%, 0.96), creatine kinase ([CK] 28.1%, 0.38), interleukin-6 (24%, 0.99), nonesterified fatty acids ([NEFA] 13.2%, 0.73), glycerol (12.5%, 0.86), and blood lactate (18.6%, 0.79). In the last 15 minutes of ET, concentrations of blood glucose and lactate and sprint and jump performances were reduced, whereas Tcore, NEFA, glycerol, and CK concentrations were elevated (p ≤ 0.05). The SMS is a reliable protocol for measuring responses across the full 120 minutes of soccer-specific exercise. Deleterious effects on performance and physiological responses occur during ET.

#2 Failure of Internal Fixation for Painful Bipartite Navicular in Two Adolescent Soccer Players: A Report of Two Cases
Reference: J Foot Ankle Surg. 2016 Nov - Dec;55(6):1323-1326. doi: 10.1053/j.jfas.2016.01.015. Epub 2016 Feb 6.
Authors: Yamaguchi S, Niki H, Akagi R, Yamamoto Y, Sasho T
Summary: Bipartite navicular bone is an uncommon condition that can cause midfoot pain in children and adolescents. No treatment methods, other than conservative management, have been reported. We report the cases of 2 adolescent soccer players who underwent internal fixation of the painful bipartite fragments, resulting in nonunion. After failure of conservative management, the patients underwent surgery. Curettage of the junction between the 2 bone fragments was performed, and autologous cancellous bone was grafted. Next, the fragments were fixed with variable-threaded screws. Bone union of the bipartite fragments was once achieved on computed tomography in both cases at 3 and 5 months after surgery, respectively. However, separation of the fragment occurred in both cases after the patients had returned to sports. Although the patients were able to return to sports activities, they still had mild midfoot pain 3 and 2 years after surgery, respectively. Internal fixation using screws and an autologous bone graft for painful bipartite navicular bone in adolescent athletes is not recommended, and other surgeries should be considered to achieve bony union.

#3 Effects of the FIFA 11 training program on injury prevention and performance in football players: A systematic review and meta-analysis
Reference: Clin Rehabil. 2016 Nov 2. pii: 0269215516675906. [Epub ahead of print]
Authors: Gomes Neto M, Conceição CS, de Lima Brasileiro AJ, de Sousa CS, Carvalho VO, de Jesus FL
Summary: The purpose was to investigate the effects of FIFA 11 training on injury prevention and performance in football players. We conducted a systematic search using four databases (CINAHL, Cochrane Library, EMBASE, and PubMed) to find controlled trials evaluating the effects of FIFA 11 on injury prevention and performance among football players. Weighted mean differences, standard mean differences, risk ratios, and 95% confidence intervals were calculated, and heterogeneity was assessed using the I2 test. We analyzed 11 trials, including 4700 participants. FIFA 11 resulted in a significant reduction in injury risk (risk ratio = 0.69; 95% confidence interval, 0.49-0.98; P = 0.02) and improvements in dynamic balance (weighted mean difference = 2.68; 95% confidence interval, 0.44-4.92; P = 0.02) and agility (standard mean difference = -0.36; 95% confidence interval, 0.70-0.02; P = 0.04). The meta-analysis indicated a non-significant improvement in jump height (standard mean difference = 0.25; 95% confidence interval, 0.08-0.59; P = 0.14) and running sprint (standard mean difference = -0.24; 95% confidence interval, 0.58-0.10; P = 0.17) in the FIFA 11 group. FIFA 11 can be considered as a tool to reduce the risk of injury. It may improve dynamic balance and agility and can be considered for inclusion in the training of football players.

#4 Recreational football training improved health-related physical fitness in 9- to 10-year-old boys
Reference: J Sports Med Phys Fitness. 2016 Oct 28. [Epub ahead of print]
Authors: Wang J, Cao L, Xie P, Wang J
Summary: Recreational football is an aerobic/anaerobic intermittent sport with altering exercise periods at high or low intensity. Various football drills and body movement in this exercise may easily attract children to take part in. The purpose of this study was to test the hypothesis that recreational football training would improve the health-related physical fitness in healthy 9- to 10-year-old boys, compared to the outcome from non-exercise boys. Forty boys were randomly allocated into the football and control groups. Body composition, predicted maximal oxygen uptake, heart rate responses during submaximal exercise, running ability, muscle strengths, and body balance and flexibility were measured before and after the experimental period. No dietary modification was suggested to the boys in this study. Following 10 weeks of recreational football training, the football group achieved significant improvements in body fat% (-2.42%), fat mass (-0.93kg), abdominal fat (-0.06kg), 50-meter run (-0.9s), long jump (+7.6cm), core muscle strengths (front bridge increased 10.9s and side bridge increased 5.6s), and body balance (single-leg standing time increased 5.2s). The heart function during submaximal exercise and predicted maximal oxygen uptake were also significantly improved in the trained boys. There were no changes in these variables of the control group. There was no sport injury occurred during the training program. The daily energy intake was not changed for all boys before and after the interventions. the 10-week recreational football training is an effective method to improve the health-related physical fitness in 9- to 10-year-old boys.

#5 Foot and Ankle Kinematics and Dynamic Electromyography: Quantitative Analysis of Recovery From Peroneal Neuropathy in a Professional Football Player
Reference: J Surg Orthop Adv. 2016 Fall;25(3):180-186.
Authors: Prasad NK, Coleman Wood KA, Spinner RJ, Kaufman KR
Summary: The assessment of neuromuscular recovery after peripheral nerve surgery has typically been a subjective physical examination. The purpose of this report was to assess the value of gait analysis in documenting recovery quantitatively. A professional football player underwent gait analysis before and after surgery for a peroneal intraneural ganglion cyst causing a left-sided foot drop. Surface electromyography (SEMG) recording from surface electrodes and motion parameter acquisition from a computerized motion capture system consisting of 10 infrared cameras were performed simultaneously. A comparison between SEMG recordings before and after surgery showed a progression from disorganized activation in the left tibialis anterior and peroneus longus muscles to temporally appropriate activation for the phase of the gait cycle. Kinematic analysis of ankle motion planes showed resolution from a complete foot drop preoperatively to phase-appropriate dorsiflexion postoperatively. Gait analysis with dynamic SEMG and motion capture complements physical examination when assessing postoperative recovery in athletes.

#6 Training loads and injury risk in Australian football-differing acute: chronic workload ratios influence match injury risk
Reference: Br J Sports Med. 2016 Oct 27. pii: bjsports-2016-096309. doi: 10.1136/bjsports-2016-096309. [Epub ahead of print]
Authors: Carey DL, Blanch P, Ong KL, Crossley KM, Crow J, Morris ME
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Summary: The purpose was to investigate whether a daily acute:chronic workload ratio informs injury risk in Australian football players; (2) to identify which combination of workload variable, acute and chronic time window best explains injury likelihood. Workload and injury data were collected from 53 athletes over 2 seasons in a professional Australian football club. Acute:chronic workload ratios were calculated daily for each athlete, and modelled against non-contact injury likelihood using a quadratic relationship. 6 workload variables, 8 acute time windows (2-9 days) and 7 chronic time windows (14-35 days) were considered (336 combinations). Each parameter combination was compared for injury likelihood fit (using R2). The ratio of moderate speed running workload (18-24 km/h) in the previous 3 days (acute time window) compared with the previous 21 days (chronic time window) best explained the injury likelihood in matches (R2=0.79) and in the immediate 2 or 5 days following matches (R2=0.76-0.82). The 3:21 acute:chronic workload ratio discriminated between high-risk and low-risk athletes (relative risk=1.98-2.43). Using the previous 6 days to calculate the acute workload time window yielded similar results. The choice of acute time window significantly influenced model performance and appeared to reflect the competition and training schedule. Daily workload ratios can inform injury risk in Australian football. Clinicians and conditioning coaches should consider the sport-specific schedule of competition and training when choosing acute and chronic time windows. For Australian football, the ratio of moderate speed running in a 3-day or 6-day acute time window and a 21-day chronic time window best explained injury risk.

#7 Physical and Physiological Responses of Amateur Football Players on Third-Generation Artificial Turf Systems During Simulated Game Situations
Reference: J Strength Cond Res. 2016 Nov;30(11):3165-3177
Authors: Sánchez-Sánchez J, García-Unanue J, Felipe JL, Jiménez-Reyes P, Viejo-Romero D, Gómez-López M, Hernando E, Burillo P, Gallardo L
Summary: The aim of this study is to evaluate the physical and physiological load imposed on amateur football players in a simulated game situation on different artificial turf systems. For that purpose, 20 football players (21.65 ± 3.10 year old) were monitored with Global Positioning Systems and heart rate bands during 45-minutes games on 4 selected artificial turf systems. The results show more covered distance in high-intensity ranges on the system with lower levels of damping and higher rates of rotational traction (p ≤ 0.05). Likewise, this system of artificial turf demonstrated a high number of sprints (12.65 ± 5.67) and more elevated maximum speed peaks during the last part of the game (28.16 ± 2.90 km·h) in contrast to the systems with better damping capacity (p ≤ 0.05). On the other hand, the physiological load was similar across the 4 artificial turf systems (p > 0.05). Finally, the regression analysis demonstrated a significant influence of the mechanical properties of the surface on global distance (15.4%), number (12.6%), and maximum speed (16.6%) of the sprints. To conclude, the mechanical variability of the artificial turf systems resulted in differences in the activity profiles and the players' perceptions during simulated football games.

#8 Factors associated with playing football after anterior cruciate ligament reconstruction in female football players
Reference: Scand J Med Sci Sports. 2016 Nov;26(11):1343-1352. doi: 10.1111/sms.12588. Epub 2015 Nov 21.
Authors: Fältström A, Hägglund M, Kvist J
Summary: This study investigated whether player-related factors (demographic, personality, or psychological factors) or the characteristics of the anterior cruciate ligament (ACL) injury were associated with the return to playing football in females after ACL reconstruction (ACLR). We also compared current knee function, knee related quality of life and readiness to return to sport between females who returned to football and those who had not returned. Females who sustained a primary ACL rupture while playing football and underwent ACLR 6-36 months ago were eligible. Of the 460 contacted, 274 (60%) completed a battery of questionnaires, and 182 were included a median of 18 months (IQR 13) after ACLR. Of these, 94 (52%) returned to football and were currently playing, and 88 (48%) had not returned. Multiple logistic regression analysis identified two factors associated with returning to football: short time between injury and ACLR (0-3 months, OR 5.6; 3-12 months OR 4.7 vs reference group > 12 months) and high motivation. Current players showed higher ratings for current knee function, knee-related quality of life, and psychological readiness to return to sport (P < 0.001). Undergoing ACLR sooner after injury and high motivation to return to sports may impact a player's return to football after ACLR.

#9 Large eccentric strength increase using the Copenhagen Adduction exercise in football: A randomized controlled trial
Reference: Scand J Med Sci Sports. 2016 Nov;26(11):1334-1342. doi: 10.1111/sms.12585. Epub 2015 Nov 21.
Authors: Ishøi L, Sørensen CN, Kaae NM, Jørgensen LB, Hölmich P, Serner A
Summary: Hip adductor injuries are frequent in football, and players with low adductor strength appear to be at increased risk of injury. High adductor muscle activity has been shown in the Copenhagen Adduction exercise (CA); however, an associated strength gain has not been investigated. This study aims to examine the eccentric hip adduction strength (EHAD) gain using the CA in-season. Two U-19 sub-elite football teams, including 24 football players, were randomized to either an 8-week supervised progressive training program in addition to the usual training (intervention) or to continue training as usual (control). EHAD, eccentric hip abduction strength (EHAB), and side-bridge endurance were measured using reliable test procedures at baseline and follow-up by a blinded tester. There was a significant interaction between group and time on EHAD, EHAB, and EHAD/EHAB ratio (P < 0.025). The intervention group demonstrated a 35.7% increase in EHAD (P < 0.001); a 20.3% increase in EHAB (P = 0.003), and 12.3% increase in EHAD/EHAB ratio (P = 0.019). No significant within-group differences were found in the control group (P > 0.335). Compliance was 91.25%, and median muscle soreness ranged from 0 to 2. The CA implemented in-season with an 8-week progressive training program elicited a large significant increase in EHAD, EHAB, and EHAD/EHAB ratio.

#10 Economic impact study: neuromuscular training reduces the burden of injuries and costs compared to standard warm-up in youth soccer
Reference: Br J Sports Med. 2016 Nov;50(22):1388-1393. doi: 10.1136/bjsports-2015-095666. Epub 2016 Mar 31.
Authors: Marshall DA, Lopatina E, Lacny S, Emery CA
Summary: There is randomised controlled trial (RCT) evidence that neuromuscular training (NMT) programmes can reduce the risk of injury in youth soccer. We evaluated the cost-effectiveness of such an NMT prevention strategy compared to a standard of practice warm-up. A cost-effectiveness analysis was conducted alongside a cluster RCT. Injury incidence rates were adjusted for cluster using Poisson regression analyses. Direct healthcare costs and injury incidence proportions were adjusted for cluster using bootstrapping. The joint uncertainty surrounding the cost and injury rate and proportion differences was estimated using bootstrapping with 10 000 replicates. Along with a 38% reduction in injury risk (rate difference=-1.27/1000 player hours (95% CI -0.33 to -2.2)), healthcare costs were reduced by 43% in the NMT group (-$689/1000 player hours (95% CI -$1741 to $234)) compared with the control group. 90% of the bootstrapped ratios were in the south-west quadrant of the cost-effectiveness plane, showing that the NMT programme was dominant (more effective and less costly) over standard warm-up. Projecting results onto 58 100 Alberta youth soccer players, an estimated 4965 injuries and over $2.7 million in healthcare costs would be conservatively avoided in one season with implementation of a neuromuscular training prevention programme. Implementation of an NMT prevention programme in youth soccer is effective in reducing the burden of injury and leads to considerable reduction in costs. These findings inform practice and policy supporting the implementation of NMT prevention strategies in youth soccer nationally and internationally.





Latest research in football - week 43 - 2016

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 effect of high-speed strength training on physical performance in young soccer players of different ages
Reference: J Strength Cond Res. 2016 Oct 28. [Epub ahead of print]
Authors: Rodriguez-Rosell D, Franco-Márquez F, Mora-Custodio R, González-Badillo JJ
Summary: The aim of the present study was to compare the effectiveness of low-load, low-volume weight training combined with plyometrics on strength, sprint and jump performance in soccer players of different ages. Eighty-six soccer players from the same academy were categorized into 3 groups by age (under 13 year, U13, n = 30; under 15, U15, n = 28; under 17, U17, n = 28) and then randomly assigned into two subgroups: a strength training group (STG) and a control group (CG). The strength training program was performed twice a week for 6 weeks and consisted of full squats (load: 45-60% 1RM; volume: 3 set of 8-4 repetitions), jumps and straight line sprint exercises. After training intervention, the STGs showed significant improvements in maximal strength (7.5-54.5%; p < 0.001), jump height (5.7-12.5%; p < 0.01 - 0.001) and sprint time (-3.7 to -1.2%; p < 0.05 - 0.001), whereas no significant gains were found for any variable in the CGs. Comparison between experimental groups resulted in a greater magnitude of change for U13 compared to U15 (ES: 0.10-0.53) and U17 (ES: 0.14-1.41) soccer players in most variables, whereas U15 showed higher improvements in jump and strength parameters than U17 (ES: 0.25-0.90) soccer players. Thus, although our results indicates that a combined weight training and plyometrics program may be effective in eliciting gains in strength, jump and sprint in soccer players of different ages, the training program used appears to be generally less effective as the age of the soccer players increased. Therefore, it appears that training characteristics (mainly volume, intensity and type of exercise) should be modified in relation to maturity status and initial strength level.

#2 Effects of pitch area-restrictions on tactical behavior, physical and physiological performances in soccer large-sided games
Reference: J Strength Cond Res. 2016 Oct 27. [Epub ahead of print]
Authors: Gonçalves B, Esteves P, Folgado H, Ric A, Torrents C, Sampaio J
Summary: The aim of this study was to identify how pitch area-restrictions affects the tactical behavior, physical and physiological performances of players during soccer large-sided games. A 10 vs. 9 large-sided game was performed under three experimental conditions: (i) restricted-spacing, the pitch was divided into specific areas where players were assigned and they should not leave it; (ii) contiguous-spacing, the pitch was divided into specific areas where the players were only allowed to move to a neighboring one; (iii) free-spacing, the players had no restrictions in space occupation. The positional data were used to compute players' spatial exploration index and also the distance, coefficient of variation, approximate entropy and frequency of near-in-phase displacements synchronization of players' dyads formed by the outfield teammates. Players' physical and physiological performances were assessed by the distance covered at different speed categories, game pace and heart rate. Most likely higher values were found in players' spatial exploration index under free-spacing conditions. The synchronization between dyads' displacements showed higher values for contiguous-spacing and free-spacing conditions. In contrast, for the jogging and running intensity zones, restricted-spacing demanded a moderate effect and most likely decrease compared to other scenarios (∼20-50% to jogging and ∼60-90% to running). Overall, the effects of limiting players' spatial exploration greatly impaired the co-adaptation between teammates' positioning while decreasing the physical and physiological performances. These results allow for a better understanding of players' decision-making process according to specific task rules and can be relevant to enrich practice task design, such that coaches acknowledge the differential effect by using specific pitch-position areas restrictions.

#3 Assessment of Technical Skills in Young Soccer Goalkeepers: Reliability and Validity of Two Goalkeeper-Specific Tests
Reference: J Sports Sci Med. 2016 Aug 5;15(3):516-523. eCollection 2016.
Authors: Rebelo-Gonçalves R, Figueiredo AJ, Coelho-E-Silva MJ, Tessitore A
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Summary: The purpose of this study was to evaluate the reproducibility and validity of two new tests designed to examine goalkeeper-specific technique. Twenty-six goalkeepers (14.49 ± 2.52 years old) completed two trial sessions, each separated by one week, to evaluate the reproducibility of the Sprint-Keeper Test (S-Keeper) and the Lateral Shuffle-Keeper Test (LS-Keeper). Construct validity was assessed among forty goalkeepers (14.49 ± 1.71 years old) by competitive level (elite versus non-elite), after controlling for chronological age. All participants were examined in vertical jump (CMJ and CMJ-free arms), acceleration (5-m and 10-m sprint) and goalkeeper-specific technique. The S-Keeper requires the goalkeeper to accelerate during 3 m and dive over a stationary ball after performing a change of direction in a total distance of 10 m. The LS-Keeper involves three changes of direction and a diving save over a stationary ball, in a total distance of 12.55 m. Performance was respectively measured as total time for the right and left sides in each protocol. Bivariate correlations between repeated measures were high and significant (r = 0.835 - 0.912). Test-retest results for the S-Keeper and LS-Keeper showed good reliability (reliability coefficients > 0.88, intra-class correlation coefficient > 0.908 and coefficients of variation < 4.37%), even though participants tended to improve performance when diving to their right side (p < 0.05). Both tests were able to detect significant differences between elite and non-elite goalkeepers, particularly to the left side (p < 0.05). These findings suggest that the S-Keeper and LS-Keeper are reliable and valid tests for assessing goalkeeper-specific technique. Both protocols can be used as a practical tool to provide relevant information about the influence of several components of performance in the overall execution of a diving save, particularly movement patterns, take-off movements and possible asymmetries.

#4 Muscle Contraction Velocity: A Suitable Approach to Analyze the Functional Adaptations in Elite Soccer Players
Reference: J Sports Sci Med. 2016 Aug 5;15(3):483-491. eCollection 2016.
Authors: Loturco I, Pereira LA, Kobal R, Kitamura K, Ramírez-Campillo R, Zanetti V, Abad CC, Nakamura FY
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Summary: Tensiomyography (TMG) has been used as a simple and non-invasive tool to assess the mechanical properties of skeletal muscles. The TMG-derived velocity of contraction (Vc), which can be calculated from the ratio between maximal radial displacement and the sum of contraction time and delay time, has been proposed for evaluating athletes. However, its sensitivity to training effects and possible relation with changes in soccer players' neuromuscular performance have not yet been addressed. To test this possibility, twenty-two male Brazilian elite soccer players were assessed using TMG-derived Vc, unloaded squat jump, countermovement jump and drop jump at 45 cm, loaded jump squat and linear (20 m) and change of direction (COD) sprint tests, prior to and after an 8-week period, between two consecutive official tournaments, during which the concurrency between endurance and strength-power training commonly impairs neuromuscular capacities. Magnitude-based inference was used to detect meaningful training effects. From pre- to post-tests, it was observed likely to almost certainly improvements in all modes of jumping tests. In addition, we could verify decrements in the 20-m and COD sprint performances, which were rated as very likely and almost certainly, respectively. Finally, both rectus femoris and biceps femoris muscles presented a likely reduction in Vc. Therefore, chronic decreases in sprinting speed are possibly accompanied by a reduced TMG-derived Vc. From a practical standpoint, the TMG-derived Vc can be used to monitor negative specific-soccer training effects related to potential impairments in maximum speed.

#5 Perceptual-cognitive skill and the in-situ performance of soccer players
Reference: Q J Exp Psychol (Hove). 2016 Nov 1:1-44. [Epub ahead of print]
Authors: van Maarseveen MJ, Oudejans RR, Mann DL, Savelsbergh GJ
Summary: Many studies have shown that experts possess better perceptual-cognitive skills than novices (e.g., in anticipation, decision making, pattern recall), but it remains unclear whether a relationship exists between performance on those tests of perceptual-cognitive skill and actual on-field performance. In this study, we assessed the in-situ performance of skilled soccer players and related the outcomes to measures of anticipation, decision-making, and pattern recall. In addition, we examined gaze behaviour when performing the perceptual-cognitive tests to better understand whether the underlying processes were related when performing those perceptual-cognitive tasks. The results revealed that on-field performance could not be predicted on the basis of performance on the perceptual-cognitive tests. Moreover, there were no strong correlations between the level of performance on the different tests. The analysis of gaze behaviour revealed differences in search rate, fixation duration, fixation order, gaze entropy, and percentage viewing time when performing the test of pattern recall, suggesting that it is driven by different processes to that used for anticipation and decision making. Altogether, the results suggest that the perceptual-cognitive tests may not be as strong determinants of actual performance as may have previously been assumed.

#6 Biomechanical Effects of an Injury Prevention Program in Preadolescent Female Soccer Athletes
Reference: Am J Sports Med. 2016 Oct 28. pii: 0363546516669326. [Epub ahead of print]
Authors: Thompson JA, Tran AA, Gatewood CT, Shultz R, Silder A, Delp SL, Dragoo JL
Summary: Anterior cruciate ligament (ACL) injuries are common, and children as young as 10 years of age exhibit movement patterns associated with an ACL injury risk. Prevention programs have been shown to reduce injury rates, but the mechanisms behind these programs are largely unknown. Few studies have investigated biomechanical changes after injury prevention programs in children. The purpose was to investigate the effects of the F-MARC 11+ injury prevention warm-up program on changes to biomechanical risk factors for an ACL injury in preadolescent female soccer players. We hypothesized that the primary ACL injury risk factor of peak knee valgus moment would improve after training. In addition, we explored other kinematic and kinetic variables associated with ACL injuries. A total of 51 female athletes aged 10 to 12 years were recruited from soccer clubs and were placed into an intervention group (n = 28; mean [±SD] age, 11.8 ± 0.8 years) and a control group (n = 23; mean age, 11.2 ± 0.6 years). The intervention group participated in 15 in-season sessions of the F-MARC 11+ program (2 times/wk). Pre- and postseason motion capture data were collected during preplanned cutting, unanticipated cutting, double-leg jump, and single-leg jump tasks. Lower extremity joint angles and moments were estimated using OpenSim, a biomechanical modeling system. Athletes in the intervention group reduced their peak knee valgus moment compared with the control group during the double-leg jump (mean [±standard error of the mean] pre- to posttest change, -0.57 ± 0.27 %BW×HT vs 0.25 ± 0.25 %BW×HT, respectively; P = .034). No significant differences in the change in peak knee valgus moment were found between the groups for any other activity; however, the intervention group displayed a significant pre- to posttest increase in peak knee valgus moment during unanticipated cutting (P = .044). Additional analyses revealed an improvement in peak ankle eversion moment after training during preplanned cutting (P = .015), unanticipated cutting (P = .004), and the double-leg jump (P = .016) compared with the control group. Other secondary risk factors did not significantly improve after training, although the peak knee valgus angle improved in the control group compared with the intervention group during unanticipated cutting (P = .018). The F-MARC 11+ program may be effective in improving some risk factors for an ACL injury during a double-leg jump in preadolescent athletes, most notably by reducing peak knee valgus moment. This study provides motivation for enhancing injury prevention programs to produce improvement in other ACL risk factors, particularly during cutting and single-leg tasks.

#7 Evidence for Acute Electrophysiological and Cognitive Changes Following Routine Soccer Heading
Reference: EBioMedicine. 2016 Oct 23. pii: S2352-3964(16)30490-X. doi: 10.1016/j.ebiom.2016.10.029. [Epub ahead of print]
Authors: Di Virgilio TG, Hunter A, Wilson L, Stewart W, Goodall S, Howatson G, Donaldson DI, Ietswaart M
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Summary: There is growing concern around the effects of concussion and sub-concussive impacts in sport. Routine game-play in soccer involves intentional and repeated head impacts through ball heading. Although heading is frequently cited as a risk to brain health, little data exist regarding the consequences of this activity. This study aims to assess the immediate outcomes of routine football heading using direct and sensitive measures of brain function. Nineteen amateur football players (5 females; age 22±3y) headed machine-projected soccer balls at standardized speeds, modelling routine soccer practice. The primary outcome measure of corticomotor inhibition measured using transcranial magnetic stimulation, was assessed prior to heading and repeated immediately, 24h, 48h and 2weeks post-heading. Secondary outcome measures were cortical excitability, postural control, and cognitive function. Immediately following heading an increase in corticomotor inhibition was detected; further to these electrophysiological alterations, measurable reduction memory function were also found. These acute changes appear transient, with values normalizing 24h post-heading. Sub-concussive head impacts routine in soccer heading are associated with immediate, measurable electrophysiological and cognitive impairments. Although these changes in brain function were transient, these effects may signal direct consequences of routine soccer heading on (long-term) brain health which requires further study.

#8 Validation and calibration of HeadCount, a self-report measure for quantifying heading exposure in soccer players
Reference: Res Sports Med. 2016 Oct-Dec;24(4):416-425. Epub 2016 Sep 22.
Authors: Catenaccio E, Caccese J, Wakschlag N, Fleysher R, Kim N, Kim M, Buckley TA, Stewart WF, Lipton RB, Kaminski T, Lipton ML
Summary: The long-term effects of repetitive head impacts due to heading are an area of increasing concern, and exposure must be accurately measured; however, the validity of self-report of cumulative soccer heading is not known. In order to validate HeadCount, a 2-week recall questionnaire, the number of player-reported headers was compared to the number of headers observed by trained raters for a men's and a women's collegiate soccer teams during an entire season of competitive play using Spearman's correlations and intraclass correlation coefficients (ICCs), and calibrated using a generalized estimating equation. The average Spearman's rho was 0.85 for men and 0.79 for women. The average ICC was 0.75 in men and 0.38 in women. The calibration analysis demonstrated that men tend to report heading accurately while women tend to overestimate. HeadCount is a valid instrument for tracking heading behaviour, but may have to be calibrated in women.

#9 Does kinesiology taping of the ankles affect proprioceptive control in professional football (soccer) players?
Reference: Phys Ther Sport. 2016 Sep 3. pii: S1466-853X(16)30095-5. doi: 10.1016/j.ptsp.2016.09.001. [Epub ahead of print]
Authors: Bailey D, Firth P
Summary: The purpose of the study was to determine whether the bilateral application of kinesiology tape (KT) to professional footballers' ankles can improve their lower limb proprioception. Participants were randomly assigned to complete a proprioception test in either a taped or not taped condition first. Following a wash out period, participants were then re-tested in the alternate condition. Twenty male professional football players over the age of 18, currently match fit with no injuries. Proprioception was assessed by participants undertaking the moving target program on the balance module attached to a Kin-Com 125AP isokinetic dynamometer. A paired sample two tailed t-test was used to assess whether there was a significant difference between the participants test scores in the not taped and taped conditions. The bilateral application of KT to professional footballers' ankles did not bring about a significant change in participants' scores when tested with a fine movement and balance control test. Percentage accuracy score mean difference 4.2 (p = 0.285). The results of this study do not support the use of KT when applied to the ankles of healthy footballers as a method of improving proprioception.

#10 The Neurophysiological Response Following Sub-Concussive Soccer Heading
Reference: EBioMedicine. 2016 Nov 2. pii: S2352-3964(16)30504-7. doi: 10.1016/j.ebiom.2016.10.043. [Epub ahead of print]
Author: Pearce AJ
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Latest research in football - week 42 - 2016

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 One-year follow-up of blood viscosity factors and hematocrit/viscosity ratio in elite soccer players
Reference: Clin Hemorheol Microcirc. 2016 Oct 15. [Epub ahead of print]
Authors: Jean-Frédéric B, Emmanuelle VM, Christine F, de Mauverger Eric R
Summary: We investigated to what extent a prediction of the 'ideal' hematocrit based on individual hemorheological profile with an equation of viscosity is relevant in trained athletes, and how the agreement between theoretical and actual values is modified by changes in training volume and performance. Elite soccer players (national level: 18-32 yr, weight 61-83 kg, body mass index 20.9-25.8 kg/m2) were seen twice at one year interval. Hemorheologic parameters were measured with the MT90 viscometer and the Myrenne aggregometer the theoretical bell-shaped curve of hematocrit/viscosity ratio as a function of hematocrit was reconstructed with Quemada's equation using actual plasma viscosity and red cell rigidity to predict hematocrit/viscosity at various hematocrit levels. RBC aggregation is correlated at baseline with fat mass (M1 = 0.552 p < 0.02) and changes in aggregation are related to changes in fat mass (M = 0.652, p < 0.05; M1 = 0.647, p < 0.05). Predicted and actual hematocrit are correlated (r = 0.644, p < 0.05) but exhibit discrepancies (mean difference -1% range [3.24 to 1.24]) and those discrepancies are inversely correlated to the level of predicted hematocrit (r = -0.912, p < 0.01), to systolic blood pressure (r = -0.626, p < 0.05), and to the overtraining score (r = -0.693, p < 0.05). After one year changes in hematocrit are a close reflect of the change in training volume (r = -0.877, p < 0.01) but are not correlated to fitness changes. Therefore in these athletes i) systemic hematocrit is close to its predicted 'ideal value", suggesting the accuracy of the prediction; ii) red cell aggregation is correlated to fat mass even in nonobese subjects; iii) hematocrit is lower than predicted by the model when markers of sympathetic tone (systolic blood pressure, overtraining score) are increased; iv) weekly training volume appears the main determinant of the reduction of hematocrit.

#2 Match analysis of an elite beach soccer team
Reference: J Sports Med Phys Fitness. 2016 Oct 20. [Epub ahead of print]
Authors: Scarfone R, Ammendolia A
Summary: The aim of this study was to investigate the physiological demands and technical-tactical performances of field players in Italian elite beach soccer team. Three official matches of the Italian First Division beach soccer tournament were analyzed to evaluate the heart rate (HR) and time-motion analysis considering: standing, walking, jogging, running and sprinting, and technical-tactical aspects. Repeated-measures ANOVAs were used to determine the effects of time on the physiological measures and time motion analysis. The mean heart rate (HR) was 161±20 b·min-1corresponding to an overall mean of 84.3±10.5% of maximum heart rate (HRmax). Beach soccer players spent 52.5% of the time exercising at HR >85% of their HRmax. The time motion analysis results showed that for 50% of the match the players performed very low intensity activities. The notational analysis showed that during the 52.8% of the offensive actions 2 players were involved and the 42.6% of the offensive actions was performed by one pass. These findings demonstrate that the beach soccer is an intermittent high intensity sport with a significant involvement of anaerobic metabolism. The results of time motion analysis and notational analysis underscored that the sand does not support the movements of players overall high intensity running. Team work is difficult to implement due to irregular rebounds and it does not consent precise passes. Furthermore this study suggests that it is important to include an intermittent training with high intensity and short recovery to improve the athlete's performance.

#3 Future Achievements, Passion and Motivation in the Transition from Junior-to-Senior Sport in Spanish Young Elite Soccer Players
Reference: Span J Psychol. 2016 Oct 20;19:E69.
Authors: Chamorro JL, Torregrosa M, Sánchez Oliva D, García Calvo T, León B
Summary: Within the context of the transition from junior-to-senior sport, this study aims in first place to explore differences in young Spanish elite soccer players based on the importance given to getting different achievements in their future (including sport, studies and private life) and, in second place, to explore differences among those players in levels of passion, motivation and basic psychological need. 478 elite youth soccer filled out a questionnaire based on the presented theoretical models. A cluster analysis shows a sport oriented group (N = 98) only interested in becoming a professional, a life spheres balance group (N = 288) characterized by balancing the importance of achievements in the sport sphere, as well as in education and a private life and a group (N = 91) only interested in private life achievements. The life spheres balance group shows higher levels of harmonious passion (η2 = .06, F(2, 475) = 9.990, p < .001) than the players of the other groups. The life spheres balance group shows higher levels of autonomous motivation (η2 = .10, F(2, 475) = 13.597, p < .001), autonomy (η2 = .07, F(2, 475) = 6.592, p < .01) and relatedness satisfaction (η2 = .07, F(2, 475) = 5.603, p < .01) than the sport oriented group as well as lower levels of amotivation (η2 = .04, F(2, 475) = 6.665, p < .01) than the private life oriented group. This study suggests players who perceive equal future importance in their life spheres appear to be more resourceful than the other two groups regarding athletes' internal resources, such as passion and motivation, to cope with the transition to professional soccer.

#4 Increasing Performance of Professional Soccer Players and Elite Track and Field Athletes with Peak Performance Training and Biofeedback: A Pilot Study
Reference: Appl Psychophysiol Biofeedback. 2016 Oct 19. [Epub ahead of print]
Authors: Rijken NH, Soer R, de Maar E, Prins H, Teeuw WB, Peuscher J, Oosterveld FG
Summary: The aim of this pilot study was to investigate the effects of an intervention consisting of mental coaching combined with either electro encephalogram (EEG) alpha power feedback or heart rate variability (HRV) feedback on HRV, EEG outcomes and self-reported factors related to stress, performance, recovery and sleep quality in elite athletes. A prospective pilot study was performed with two distinct cohorts. Soccer players were provided with four sessions of mental coaching combined with daily HRV biofeedback (Group A); track and field athletes were provided with four sessions of mental coaching in combination with daily neurofeedback (Group B). Measurements were performed at baseline, post intervention and at 5 weeks follow-up. Objective measures: EEG and ECG. Subjective measures: Numeric Rating Scale for performance, Pittsburgh Sleep Quality Index, Rest and Stress Questionnaire and Sports Improvement-60. Group characteristics were too distinct to compare the interventions. Linear mixed models were used to analyze differences within groups over time. In Group A, significant changes over time were present in alpha power at 5 of 7 EEG locations (p < 0.01-0.03). LF/HF ratio significantly increased (p = 0.02) and the concentration (p = 0.02) and emotional scale (p = 0.03) of the SIM-60 increased significantly (p = 0.04). In Group B, the HRV low frequency power and recovery scale of the REST-Q significantly increased (p = 0.02 and <0.01 resp.). Other measures remained stable or improved non-significantly. A mental coaching program combined with either HRV or EEG alpha power feedback may increase HRV and alpha power and may lead to better performance-related outcomes and stress reduction. Further research is needed to elucidate the effects of either type of feedback and to compare effects with a control group.

#5 Soft-assembled Multilevel Dynamics of Tactical Behaviors in Soccer
Reference: Front Psychol. 2016 Oct 5;7:1513. eCollection 2016.
Authors: Ric A, Torrents C, Gonçalves B, Sampaio J, Hristovski R
Summary: This study aimed to identify the tactical patterns and the timescales of variables during a soccer match, allowing understanding the multilevel organization of tactical behaviors, and to determine the similarity of patterns performed by different groups of teammates during the first and second halves. Positional data from 20 professional male soccer players from the same team were collected using high frequency global positioning systems (5 Hz). Twenty-nine categories of tactical behaviors were determined from eight positioning-derived variables creating multivariate binary (Boolean) time-series matrices. Hierarchical principal component analysis (PCA) was used to identify the multilevel structure of tactical behaviors. The sequential reduction of each set level of principal components revealed a sole principal component as the slowest collective variable, forming the global basin of attraction of tactical patterns during each half of the match. In addition, the mean dwell time of each positioning-derived variable helped to understand the multilevel organization of collective tactical behavior during a soccer match. This approach warrants further investigations to analyze the influence of task constraints on the emergence of tactical behavior. Furthermore, PCA can help coaches to design representative training tasks according to those tactical patterns captured during match competitions and to compare them depending on situational variables.

#6 The relationship between trunk endurance plan tests and athletic performance tests in adolescent soccer players
Reference: Int J Sports Phys Ther. 2016 Oct;11(5):718-724.
Authors: Imai A, Kaneoka K
Summary: Although it is believed that trunk function is important for athletic performance, few researchers have demonstrated a significant relationship between the trunk function and athletic performance. Recently, the prone plank and side plank tests have been used to assess trunk function. The purpose of this study was to investigate the relationships between trunk endurance plank tests and athletic performance tests, including whether there is a relationship between long distance running and trunk endurance plank tests in adolescent male soccer players. Fifty-five adolescent male soccer players performed prone and side plank tests and seven performance tests: the Cooper test, the Yo-Yo intermittent recovery test, the step 50 agility test, a 30-m sprint test, a vertical countermovement jump, a standing five-step jump, and a rebound jump. The relationships between each individual plank test, the combined score of both plank tests, and performance tests were analyzed using the Pearson correlation coefficient. The combined score of plank tests was highly correlated with the Yo-Yo intermittent recovery test (r = 0.710, p < 0.001), and was moderately correlated with the Cooper test (r = 0.567, p < 0.001). Poor correlation was observed between the prone plank test and step 50 agility test (r = -0.436, p = 0.001) and no significant correlations were observed between plank tests and jump performance tests. The results suggest that trunk endurance plank tests are positively correlated with the Yo-Yo intermittent recovery test, the Cooper test, and the step 50 agility test.

#7 Effect of Injury Prevention Programs that Include the Nordic Hamstring Exercise on Hamstring Injury Rates in Soccer Players: A Systematic Review and Meta-Analysis
Reference: Sports Med. 2016 Oct 17. [Epub ahead of print]
Authors: Al Attar WS, Soomro N, Sinclair PJ, Pappas E, Sanders RH
Summary: Hamstring injuries are among the most common non-contact injuries in sports. The Nordic hamstring (NH) exercise has been shown to decrease risk by increasing eccentric hamstring strength. The purpose of this systematic review and meta-analysis was to investigate the effectiveness of the injury prevention programs that included the NH exercise on reducing hamstring injury rates while factoring in athlete workload. Two researchers independently searched for eligible studies using the following databases: the Cochrane Central Register of Controlled Trials via OvidSP, AMED (Allied and Complementary Medicine) via OvidSP, EMBASE, PubMed, MEDLINE, SPORTDiscus, Web of Science, CINAHL and AusSportMed, from inception to December 2015. The keyword domains used during the search were Nordic, hamstring, injury prevention programs, sports and variations of these keywords. The initial search resulted in 3242 articles which were filtered to five articles that met the inclusion criteria. The main inclusion criteria were randomized controlled trials or interventional studies on use of an injury prevention program that included the NH exercise while the primary outcome was hamstring injury rate. Extracted data were subjected to meta-analysis using a random effects model. The pooled results based on total injuries per 1000 h of exposure showed that programs that included the NH exercise had a statistically significant reduction in hamstring injury risk ratio [IRR] of 0.490 (95 % confidence interval [CI] 0.291-0.827, p = 0.008). Teams using injury prevention programs that included the NH exercise reduced hamstring injury rates up to 51 % in the long term compared with the teams that did not use any injury prevention measures. This systematic review and meta-analysis demonstrates that injury prevention programs that include NH exercises decrease the risk of hamstring injuries among soccer players.

#8 Maximal sprinting speed of elite soccer players during training and matches
Reference: J Strength Cond Res. 2016 Sep 23. [Epub ahead of print]
Authors: Djaoui L, Chamari K, Owen A, Dellal A
Summary: The aim of the present study was to compare 1) the maximal sprinting speed (MSS) attained by soccer players during matches (MSSmatch) according to their level of play (professional 1st French division vs. elite amateur 4th French division) and the playing positions; and 2) the MSS attained by professional soccer players during 14 different types of small-sided games (SSG, MSSSSG) and match-play. All players monitored through the study performed a 40-m sprint test to assess individual MSS (MSStest) and compare it to the training and match activity, with the calculation of the percentage of MSStest (%MSStest) reached. No differences were found according to the level of play, however positionally, wide players achieved a higher MSSmatch, %MSStest, and MSSSSG compared to central players (both defenders and midfielders) during matches and SSG. MSSmatch were higher than all MSSSSG, and MSSSSG were positively correlated with the area of the pitch (0.45, p<0.001), its length (0.53, p<0.001) and the number of players involved (0.38, p<0.001). The closer SSG was to match situation in term of rules, the higher the MSSSSG. Wide players reached higher MSS in match and SSG than central players, confirming the relevance of using SSG close to match situation to specifically prepare elite players to the maximal running speed demand of the match.

#9 How does lower leg alignment differ between soccer players, other athletes, and non-athletic controls?
Reference: Knee Surg Sports Traumatol Arthrosc. 2016 Oct 14. [Epub ahead of print]
Authors: Colyn W, Agricola R, Arnout N, Verhaar JA, Bellemans J
Summary: The influence of type and intensity of sports during growth on knee alignment was investigated. The second aim was to ascertain whether the distal femur or proximal tibia contribute most to knee alignment. Also, the influence of field position and leg dominancy on knee alignment in soccer players was audited. Standardized full-leg standing digital radiographs were obtained from 100 males and 100 females on which 8 different alignment parameters were measured. Participants were questioned on their sports activities during different stages of growth. Sports activities were graded according to the Tegner score. The mean (±SD) hip-knee-ankle angle (HKA) was significantly lower (p < 0.001) in high-activity male athletes (-2.8° ± 2.4°) than in low-activity male athletes (-0.9° ± 1.9°). No differences in HKA were observed between different activity levels in females. Males who practiced soccer between 10-12 years and 15-17 years had, in turn, a lower HKA than athletes practicing other high-activity sports in these age categories (mean difference ≥1.2°, p ≤ 0.046). The most contributing factor for the varus alignment in male soccer players was a lower medial proximal tibial angle (MPTA). High-activity sports participation during youth is associated with varus alignment at the end of growth in males. The most pronounced bowlegs were observed in male soccer players, and this was primarily determined by the proximal tibia. Adjustments in loads applied to the knees during skeletal growth in males might prevent the development of varus alignment and associated pathology, but further studies are required.





Latest research in football - week 41 - 2016

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 Muscle Fatigue Induced by CMJ on Efficacy Parameters of Instep Ball Kicking in Soccer
Reference: J Appl Biomech. 2016 Oct 13:1-24. [Epub ahead of print]
Authors: Torreblanca-Martínez V, Otero-Saborido FM, González-Jurado JA
Summary: The purpose was to study the effects of muscle fatigue induced by countermovement jumps (CMJ) on instep kick foot velocity in young male soccer players. Fifteen under-18 soccer players of a professional club, performed maximal velocity instep kicks before and after a fatigue protocol that consisted of continuous CMJ (countermovement jump). Foot velocity at impact without fatigue, foot velocity at impact with fatigue, CMJ height without fatigue, maximum jump height in fatigue test, and CMJ height change in fatigue test on a dynamometric platform, were measured. There was a significant difference between jump height with and without fatigue (p = 0.00; ES = 0.8), but there were no significant differences between kicking with fatigue and without fatigue (p = 0.580, ES = 0.10). In conclusion, although the protocol was intense enough to generate fatigue in the muscles involved in CMJ, there were no significant differences in kicking velocity under fatigue conditions with respect to kicking without fatigue in the soccer players studied.

#2 Dynamic balance ability in young elite soccer players: implication of isometric strength
Reference: J Sports Med Phys Fitness. 2016 Oct 11. [Epub ahead of print]
Authors: Chtara M, Rouissi M, Bragazzi NL, Owen AL, Haddad M, Chamari K
Summary: Soccer requires maintaining unilateral balance when executing movement with the contralateral leg. Despite the fact that balance requires standing with maintaining isometric posture with the support leg, currently there is a lack of studies regarding the implication of isometric strength on dynamic balance's performance among young soccer players. Therefore, the aim of this study was to examine the relationship between the Y- balance test and 12 lower limbs isometric strength tests. 26 right footed soccer players (mean±SD, age=16.2±1.6 years, height=175±4.2 cm, body mass = 68.8±6.1 kg) performed a dynamic balance test (star excursion balance-test [SEBT] with dominant- (DL) and nondominant-legs (NDL). Furthermore, maximal isometric contraction tests of 12 lower limb muscle groups were assessed in DL and NDL. Correlations analysis reported a significant positive relationship between some of isometric strength tests (with DL and NDL) and the Y-balance test. Furthermore, stepwise multiple regression analysis showed that maximal isometric strength explained between 21.9% and 49.4% of the variance of the Y-balance test. Moreover, maximal isometric strength was dependent upon the reaching angle of the Y-balance test and the leg used to support body weight. This study showed a significant implication of maximal isometric strength of the lower limb and the Y-balance test. Moreover, the present investigation suggests the implementation of specific lower limb strengthening exercises depending on players' deficit in each reaching direction and leg. This result suggests that further studies should experiment if increasing lower limbs isometric strength could improve dynamic balance ability among young soccer players.

#3 Health problems in former elite female football players: Prevalence and risk factors
Reference: Scand J Med Sci Sports. 2016 Oct 17. doi: 10.1111/sms.12747. [Epub ahead of print]
Authors: Prien A, Prinz B, Dvořák J, Junge A
Summary: The aim of this study was to assess the prevalence of health problems and associated risk factors in former elite female football players. A cross-sectional research design was employed, using an online questionnaire on personal characteristics and health complaints during/after the career. One hundred fifty-two (response rate: 62.0%) former first German league players answered the survey. Around 70% described their current health as good or very good. Over half (57.9%) reported knee problems during the last 4 weeks while exercising and a third (33.6%) during normal daily activities. The second most common location for complaints was the head (53.3%). Almost one quarter (23.7%) of players suffered from osteoarthritis (OA). Regression analysis showed that OA in knee/ankle and physical complaints (PC) in knee/ankle/head were significantly predicted by number and severity of previous injuries (P < 0.05). Further, increases in age, training volume, and level of play were associated with an increased likelihood of presenting with OA (P < 0.05), but not PC. In conclusion, a football career may lead to specific long-term health problems in elite female players. Prevention strategies should focus on knee, ankle, and head injuries. Future studies are needed to clinically assess the prevalence rates of OA and possible neurocognitive changes.

#4 The efficacy of exercise in preventing injury in adult male football: a systematic review of randomised controlled trials
Reference: Sports Med Open. 2015 Dec;1(1):4. Epub 2015 Jan 20.
Authors: Porter T, Rushton A
Download link:
Summary: Injury prevention measures might reduce the impact of injury on footballers and football clubs. Increasing research has evaluated the use of exercise for injury prevention. However, research has focused on adolescent females. No high-quality systematic reviews have evaluated the efficacy of all forms of exercise on preventing injury in adult male football. Our objective was to conduct a systematic review to evaluate the efficacy of exercise in preventing injury in adult male football. Comprehensive searches of electronic databases CINAHL (Cumulative Index to Nursing and Allied Health Literature), MEDLINE, Embase, AMED (The Allied and Complementary Medicine Database), the Cochrane Central Register of Controlled Trials, PEDro (The Physiotherapy Evidence Database), SPORTDiscus™, the National Research Register, Current Controlled Trials website (York), and were conducted using predefined search terms to identify relevant studies published up to 1 March 2013. Screening of references, searches of grey literature, and hand searches of relevant journals were also employed. Included studies were randomized controlled trials using injury incidence as an outcome measure to evaluate the efficacy of an exercise intervention on uninjured male footballers aged 16 years and over. Articles not written in English were excluded. Two researchers independently searched data sources, screened studies for eligibility, evaluated risk of bias, and extracted data using predefined criteria. Risk of bias of included trials was assessed using the Cochrane Collaboration's tool for assessing risk of bias. There was insufficient trial comparability (outcome measures, interventions, injury type) for meta-analysis, and a qualitative analysis was performed. Eight trials (n = 3,355) from five countries met the inclusion criteria. All trials were assessed as having a high risk of bias. Two trials reported statistically significant reductions in hamstring injuries with eccentric exercise, and two reported statistically significant reductions in recurrent ankle sprains with proprioceptive exercise. Four trials showed no statistically significant difference in injury incidence with exercise interventions targeting a range of injuries. Notable limitations of included trials included poor reporting and limited blinding. A high risk of bias and insufficient comparability across trials prevented quantitative data synthesis. Limitations in the context of study quality and heterogeneity resulted in an inability to reach a clear conclusion regarding efficacy of exercise for injury prevention in adult male football. Future low risk of bias, properly powered, and comprehensively reported trials are warranted to evaluate the efficacy of exercise on injury prevention. The use of eccentric hamstring exercise for hamstring injury prevention and proprioceptive training for recurrent ankle sprain prevention might be a good focus for future trials, as existing trials with a high risk of bias suggest an effect.

#5 Symptoms of common mental disorders among professional football referees: a one-season prospective study across Europe
Reference: Phys Sportsmed. 2016 Oct 14. [Epub ahead of print]
Authors: Gouttebarge V, Johnson U, Rochcongar P, Rosier P, Kerkhoffs G
Summary: The primary aim of this study was to determine the prevalence and one-season incidence of symptoms of common mental disorders (CMD; distress, anxiety/depression, sleep disturbance, eating disorders, adverse alcohol use) among European professional football referees. A secondary aim was to explore the view of European professional football referees on consequences, support and needs related to these symptoms.An observational prospective cohort study with three measurements over a follow-up period of one season (2015-2016) was conducted among central or assistant professional football referees from Belgium, Finland, France, Germany, Norway, Russia, Scotland and Sweden. Using validated questionnaires to assess symptoms of CMD (self-reported and not clinically diagnosed), an electronic questionnaire in English and French was set up and distributed by the eight football federations involved. A total of 391 referees (mean age of 33 years old; mean career duration of 7 years) were enrolled, of which 292 completed the follow-up period. Baseline 4-week prevalence rates were 6% for distress, 12% for anxiety/depression, 9% for sleep disturbance, 19% for eating disorders and 17% for adverse alcohol use. The one-season incidence of symptoms of CMD was 10% for distress, 16% for anxiety/depression, 14% for sleep disturbance, 29% for eating disorders and 8% for adverse alcohol use. While symptoms of CMD occur among professional football referees and can influence negatively refereeing performances, the development of specific support measures for referees are needed in order to manage properly these symptoms of CMD.

#6 Effect of Instructions Prioritizing Speed or Accuracy on Kinematics and Kicking Performance in Football Players
Reference: J Mot Behav. 2016 Oct 14:1-8. [Epub ahead of print]
Authors: van den Tillaar R, Fuglstad P
Summary: The authors' purpose was to investigate if there is a speed accuracy trade-off in soccer kicking by using instructions prioritizing velocity, accuracy, or both upon soccer kicking performance and kicking direction in experienced soccer players. In addition, kinematics were measured to investigate the eventual differences in performance. Thirteen experienced male footballers performed penalty kicks with different instructions prioritizing velocity, accuracy or both. Three-dimensional kinematics, together with maximal ball velocity and hitting accuracy, were measured on all kicks. The main findings were that when the main aim was accuracy, accuracy increased, while the velocity reduced, which supports Fitts' law (Fitts, 1954 ). In addition, kicking accuracy was higher when kicking to the contralateral side. The slower ball velocity was caused by lower segmental and in run velocities. These lower segmental velocities were mainly caused by the lower maximal knee extension and pelvis rotation during the accuracy priority kicks.


#7 Validation of the FASH (Functional Assessment Scale for Acute Hamstring Injuries) questionnaire for German-speaking football players
Reference: J Orthop Surg Res. 2016 Oct 24;11(1):130.
Authors: Lohrer H, Nauck T, Korakakis V, Malliaropoulos N
Download link: linkl
Summary: The FASH (Functional Assessment Scale for Acute Hamstring Injuries) questionnaire has been recently developed as a disease-specific self-administered questionnaire for use in Greek, English, and German languages. Its psychometric qualities (validity and reliability) were tested only in Greek-speaking patients mainly representing track and field athletes. As hamstring injuries represent the most common football injury, we tested the validity and reliability of the FASH-G (G = German version) questionnaire in German-speaking footballers suffering from acute hamstring injuries. The FASH-G questionnaire was tested for reliability and validity, in 16 footballers with hamstring injuries (patients' group), 77 asymptomatic footballers (healthy group), and 19 field hockey players (at-risk group). Known-group validity was tested by comparing the total FASH-G scores of the injured and non-injured groups. Reliability of the FASH-G questionnaire was analysed in 18 asymptomatic footballers using the intra-class coefficient. Known-group validity was demonstrated by significant differences between injured and non-injured participants (p < 0.001). The FASH-G exhibited very good test-retest reliability (intra-class correlation coefficient = 0.982, p < 0.001). Internal consistency was excellent (α = 0.938). Compared with the results presented in the original publication, no statistical differences were found between healthy athletes (p = 0.257), but patients' groups and at-risk groups presented scoring differences (p = 0.040 and <0.001, respectively). The FASH-G is a valid and reliable instrument to assess and determine the severity of hamstring injuries in German footballers.

#8 Relationship Between Running Performance and Recovery-Stress State in Collegiate Soccer Players
Reference: J Strength Cond Res. 2016 Oct 17. [Epub ahead of print]
Authors: Coker NA, Ake KM, Griffin DL, Rossi SJ, McMillan JL, Wells AJ.
Summary: The purpose of this study was to evaluate the relationship between changes in running performance and the stress-recovery state in collegiate soccer players. Running performance was evaluated in seven Division I NCAA male soccer players (179.39±5.24 cm; 75.46±5.98 kg; 20.37±1.41 yrs.) via global positioning system over the course of 12 competitive games in a single season. The regular season was divided into four competitive blocks: B1 (n=3), B2 (n=3), B3 (n=3) and B4 (n=3). Total distance and distance covered while engaging in walking, jogging, low-speed running, high-speed running, sprinting, low-intensity running and high-intensity running were assessed during each block. The RESTQ 52 Sport was administered twice during each block to evaluate measures of stress and recovery. Total distance was greater during B4 compared to B1 (p=0.027). Jogging and low-speed running were greater during B4 compared to all other time points (p's ≤ 0.05). Low-intensity running distance was greater during B4 compared to B1 (p=0.034). Sport-specific recovery decreased significantly during B4 compared to B1 (p=0.035). Correlational analysis indicated that high-velocity running was associated with increased stress, while low-velocity running was associated with greater recovery. However, changes in sport specific recovery did not correlate with changes in running performance from B1 to B4. Results of this study indicate that running performance decreased across the season. Changes in running performance coincided with a decrease in sport specific recovery. Practitioners may benefit from including the RESTQ as part of an assessment battery to monitor the stress/recovery state of athletes.

#9 Influence of Rest Intervals Following Assisted Sprinting on Bodyweight Sprint Times in Female Collegiate Soccer Players
Reference: J Strength Cond Res. 2016 Oct 6. [Epub ahead of print]
Authors: Nealer AL, Dunnick DD, Malyszek KK, Wong MA, Costa PB, Coburn JW, Brown LE
Summary: Speed is a crucial element an athlete must possess to be successful. In soccer, the ability to accelerate faster than your opponent can result in being first to reach a ball on a breakaway or stopping a counter attack. A unique way to train explosive movements is to evoke postactivation potentiation (PAP) in the working muscles. Traditionally, an overload stimulus with a long rest period is used, but a model utilizing an overspeed stimulus with shorter rest periods is less understood. Therefore, the purpose of this study was to determine the acute effects of varied rest intervals following assisted sprinting on bodyweight sprint time. Twenty-four female soccer players were split into two groups: recreational (n:11; age:20±1.67yrs; ht:162.30±4.35cm; mass:61.02±8.78kg) and collegiate athletes (n:13; age:19.76±0.83yrs; ht:166.85±5.98cm; mass:61.23±3.77kg). All participants attended five separate sessions, performed a dynamic warm up, then executed one 20m sprint (with 5m splits) at 30% bodyweight assistance (BWA). They then rested for 30s, one, two, or 4min in random order, followed by one bodyweight sprint with no BWA. Baseline sprint times were measured without BWA on the initial session of testing. Results revealed no difference in sprint time for the full 20m distance in either group. However, sprint time was significantly decreased for the 0-5m split only for the athletes following 1min (1.15±0.06s) and 2min (1.16±0.06s) rest compared to baseline (1.21±0.04s). Therefore, trained athletes should rest one or two minutes after 30% BWA supramaximal sprinting for increased bodyweight sprint speed.





Latest research in football - week 40 - 2016

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 test of basic psychological needs theory in young soccer players: time-lagged design at the individual and team levels
Reference: Scand J Med Sci Sports. 2016 Sep 27. doi: 10.1111/sms.12778. [Epub ahead of print]
Authors: González L, Tomás I, Castillo I, Duda JL, Balaguer I
Summary: Within the framework of basic psychological needs theory (Deci & Ryan, 2000), multilevel structural equation modeling (MSEM) with a time-lagged design was used to test a mediation model examining the relationship between perceptions of coaches' interpersonal styles (autonomy supportive and controlling), athletes' basic psychological needs (satisfaction and thwarting), and indicators of well-being (subjective vitality) and ill-being (burnout), estimating separately between and within effects. The participants were 597 Spanish male soccer players aged between 11 and 14 years (M = 12.57, SD = 0.54) from 40 teams who completed a questionnaire package at two time points in a competitive season. Results revealed that at the individual level, athletes' perceptions of autonomy support positively predicted athletes' need satisfaction (autonomy, competence, and relatedness), whereas athletes' perceptions of controlling style positively predicted athletes' need thwarting (autonomy, competence, and relatedness). In turn, all three athletes' need satisfaction dimensions predicted athletes' subjective vitality and burnout (positively and negatively, respectively), whereas competence thwarting negatively predicted subjective vitality and competence and relatedness positively predicted burnout. At the team level, team perceptions of autonomy supportive style positively predicted team autonomy and relatedness satisfaction. Mediation effects only appeared at the individual level.

#2 Vertical and Horizontal Impact Force Comparison During Jump-Landings With and Without Rotation in NCAA Division 1 Male Soccer Players
Reference: J Strength Cond Res. 2016 Sep 22. [Epub ahead of print]
Authors: Harry JR, Barker LA, Mercer JA, Dufek JS
Summary: There is a wealth of research on impact force characteristics when landing from a jump. However, there are no data on impact forces during landing from a jump with an airborne rotation about the vertical axis. We examined impact force parameters in the vertical and horizontal axes during vertical jump (VJ) landings and vertical jump landings with a 180-degree rotation (VJR). Twenty-four Division 1 male soccer players performed three VJ and VJR landings on a dual-force platform system. Paired-samples t-tests (α=0.05) compared differences in the first (F1) and second (F2) peak vertical ground reaction forces, times to F1 (tF1), F2 (tF2), and the end of the impact phase, vertical impulse, and anterior-posterior and medial-lateral force couples. Effect sizes (ES; large >0.8) were computed to determine the magnitude of the differences. Lower jump height (41.60±4.03 cm, VJ landings; 39.40±4.05 cm, VJR landings; p=0.002; ES=0.39), greater F2 (55.71±11.95 N•kg-1, VJ; 68.16±14.82 N•kg-1; p<0.001; ES=0.94), faster tF2 (0.057±0.012 sec, VJ; 0.047±0.011 sec, VJR; p=0.001; ES=0.89), greater anterior-posterior (0.06±0.03 N•s•kg-1, VJ; 0.56±0.15 N•s•kg-1, VJR; p<0.001; ES=1.83) and medial-lateral force couples (0.29±0.11 N•s•kg-1, VJ; 0.56±0.14 N•s•kg-1, VJR; p<0.001; ES=1.46) occurred during VJR landings. No other differences were identified. This kinetic analysis determined that landing from a jump with 180-degree airborne rotation is different than landing from a jump without an airborne rotation. Male Division 1 soccer players could benefit from increasing the volume of VJR landings during training to address the differences in jump height and force parameters compared to VJ landings.

#3 Influence of physical maturity status on sprinting speed among youth soccer players
Reference: J Strength Cond Res. 2016 Sep 21. [Epub ahead of print]
Authors: McCunn R, Weston M, Hill JK, Johnston RD, Gibson NV
Summary: The relative age effect is well documented with the maturation-selection hypothesis the most common explanation; however, conflicting evidence exists. We observed the birth-date distribution within an elite junior soccer academy. The influence of physical maturity status on anthropometric variables and sprinting ability was also investigated. Annual fitness testing was conducted over an eight-year period with a total of 306 players (age: 12.5 ± 1.7 y [range: 9.7 - 16.6 y]; stature: 156.9 ± 12.9 cm; mass: 46.5 ± 12.5 kg) drawn from six age categories (under-11s to -17s) who attended the same Scottish Premiership club academy. Measurements included mass, stature, maturity offset and 0-15 m sprint. Odds ratios revealed a clear bias towards recruitment of players born in quartile one compared to quartile four. The overall effect (all squads combined) of birth quartile was very likely small for maturity offset (0.85 years; 90% confidence interval 0.44 years to 1.26 years) and stature (6.2 cm; 90% confidence interval 2.8 cm to 9.6 cm), and likely small for mass (5.1 kg; 90% confidence interval 1.7 kg to 8.4 kg). The magnitude of the relationship between maturity offset and 15 m sprinting speed ranged from trivial for under-11s (r = 0.01; 90% confidence interval -0.14 to 0.16) to very likely large for under-15s (r = -0.62; -0.71 to -0.51). Making decisions about which players to retain and release should not be based on sprinting ability around the under-14 and under-15 age categories since any inter-individual differences may be confounded by transient inequalities in maturity offset.

#4 Analysis of the predictive qualities of betting odds and FIFA World Ranking: evidence from the 2006, 2010 and 2014 Football World Cups
Reference: J Sports Sci. 2016 Aug 11:1-9. [Epub ahead of print]
Authors: Wunderlich F, Memmert D
Summary: The present study aims to investigate the ability of a new framework enabling to derive more detailed model-based predictions from ranking systems. These were compared to predictions from the bet market including data from the World Cups 2006, 2010, and 2014. The results revealed that the FIFA World Ranking has essentially improved its predictive qualities compared to the bet market since the mode of calculation was changed in 2006. While both predictors were useful to obtain accurate predictions in general, the world ranking was able to outperform the bet market significantly for the World Cup 2014 and when the data from the World Cups 2010 and 2014 were pooled. Our new framework can be extended in future research to more detailed prediction tasks (i.e., predicting the final scores of a match or the tournament progress of a team).

#5 The use and modification of injury prevention exercises by professional youth soccer teams
Reference: Scand J Med Sci Sports. 2016 Oct 7. doi: 10.1111/sms.12756. [Epub ahead of print]
Authors: O'Brien J, Young W, Finch CF
Summary: The efficacy of injury prevention exercise programs (IPEPs) for amateur youth soccer has been established, but little is known about their adaptability to other soccer populations. This study aimed to assess the use of individual injury prevention exercises by professional youth soccer teams, against the industry-standard, FIFA 11+ program. Four teams' chosen IPEPs were observed across one season and documented on a standardized form. The use of each FIFA 11+ exercise was coded as "performed", "performed modified" or "not performed". The proportion of the 160 observed sessions containing each individual exercise was calculated. Staff provided reasons for their use and modification of FIFA 11+ exercises. On average, individual FIFA 11+ exercises were conducted in original form in 12% of the sessions (range 0-33%), and in modified form in 28% of sessions (range 2-62%). The five most frequently observed exercises, in either original or modified form, were "bench" (72%), "squats" (69%), "running straight" (68%), "single-leg stance" (66%), and "sideways bench" (64%). Staff modified exercises to add variation, progression, and individualization, and to align with specific training formats and goals. Professional youth soccer teams often use injury prevention exercises similar to those in the FIFA 11+, but tailor them considerably to fit their implementation context.

#6 Relationship between daily training load and psychometric status of professional soccer players
Reference: Res Sports Med. 2016 Oct 7:1-8. [Epub ahead of print]
Authors: Moalla W, Fessi MS, Farhat F, Nouira S, Wong DP, Dupont G
Summary: We studied the relationship between daily training load (TL) experienced by professional soccer players and the Hooper questionnaire reflecting their perceived quality of sleep, fatigue, stress and delayed onset muscle soreness. During a 16-week training period, the rating of perceived exertion and duration were collected after each training session, and daily TL was calculated from 14 professional soccer players. The Hooper questionnaire was completed every day before the first training session and the Hooper's score (HS) was then calculated. The daily TL and HS were 379.9 ± 198.3 AU and 16.2 ± 5.1, respectively. Pearson correlation showed significant relationships (p < 0.01) between TL and perceived fatigue, muscle soreness, sleep and stress. Our findings revealed that the perceived sleep, stress, fatigue and muscle soreness are moderately related to the daily TL in professional soccer players. The Hooper questionnaire is both a simple and useful tool for monitoring perceived wellness and psychometric players' status of professional soccer players.

#7 Dietary Intake, Body Composition and Nutrition Knowledge of Australian Football and Soccer Players: Implications for Sports Nutrition Professionals in Practice
Reference: Int J Sport Nutr Exerc Metab. 2016 Oct 6:1-21. [Epub ahead of print]
Authors: Devlin BL, Leveritt MD, Kingsley M, Belski R
Summary: Sports nutrition professionals aim to influence nutrition knowledge, dietary intake and body composition to improve athletic performance. Understanding the interrelationships between these factors and how they vary across sports has the potential to facilitate better-informed and targeted sports nutrition practice. This observational study assessed body composition (DXA), dietary intake (multiple-pass 24-hour recall) and nutrition knowledge (two previously validated tools) of elite and sub-elite male players involved in two team-based sports; Australian football (AF) and soccer. Differences in, and relationships between, nutrition knowledge, dietary intake and body composition between elite AF, sub-elite AF and elite soccer players were assessed. A total of 66 (23 ± 4 years, 82.0 ± 9.2 kg, 184.7 ± 7.7 cm) players participated. Areas of weaknesses in nutrition knowledge are evident (57% mean score obtained) yet nutrition knowledge was not different between elite and sub-elite AF and soccer players (58%, 57% and 56%, respectively, p > 0.05). Dietary intake was not consistent with recommendations in some areas; carbohydrate intake was lower (4.6 ± 1.5 g/kg/day, 4.5 ± 1.2 g/kg/day and 2.9 ± 1.1 g/kg/day for elite and sub-elite AF and elite soccer players, respectively) and protein intake was higher (3.4 ± 1.1 g/kg/day, 2.1 ± 0.7 g/kg/day and 1.9 ± 0.5 g/kg/day for elite and sub-elite AF and elite soccer players, respectively) than recommendations. Nutrition knowledge was positively correlated with fat-free soft tissue mass (n = 66; r2 = 0.051, p = 0.039). This insight into known modifiable factors may assist sports nutrition professionals to be more specific and targeted in their approach to supporting players to achieve enhanced performance.

#8 Traditional Periodization versus Optimum Training Load Applied to Soccer Players: Effects on Neuromuscular Abilities
Reference: Int J Sports Med. 2016 Oct 5. [Epub ahead of print]
Authors: Loturco I, Nakamura FY, Kobal R, Gil S, Pivetti B, Pereira LA, Roschel H
Summary: It is unknown whether traditional periodization of strength-power training involving accumulation, transformation and realization blocks is superior to other simpler and more practical training schemes. The purpose of this study was thus to investigate changes in strength/power/speed characteristics of elite soccer players in response to either classic strength-power periodization (TSP) or optimum power load (OPL). 23 professional soccer players were randomly assigned to TSP or OPL for 6 weeks in-season regular training (3 times per week). TSP involved half squats or jump squats, depending on the respective training block, while OPL involved only jump squats at the optimum power load. Results revealed that both groups presented similar significant (P<0.05) improvements in squat one repetition maximum, squat and countermovement jump heights and change of direction speed. In addition, although both groups reported significant increases in sprinting speed (P<0.05); delta change scores demonstrated a superior effect of OPL to improve 10- and 20-m speed. Similarly, OPL presented greater delta change in mean propulsive power in the jump squat. Therefore, training continuously at the optimum power zone resulted in superior performance improvements compared to training under classic strength-power periodization.

#9 Continued Sex-Differences in the Rate and Severity of Knee Injuries among Collegiate Soccer Players: The NCAA Injury Surveillance System, 2004-2009
Reference: Int J Sports Med. 2016 Oct 5. [Epub ahead of print]
Authors: Fulstone D, Chandran A, Barron M, DiPietro L
Summary: We extend previous analyses and examined sex-differences in the rate and severity of knee injuries among collegiate soccer players between 2004 and 2009. Data from the National Collegiate Athletic Association Injury Surveillance System (NCAA ISS) were used to calculate injury incidence density (ID) per 1 000 athletic exposures (AE). Multivariable regression modeling then tested the relation between sex and knee injury incidence and severity among all injured soccer players, while controlling for contact, setting, and division level, as well as for the interactions among these variables. The rate of knee injuries was 1.19 per 1 000 AEs in women and 0.91 per 1 000 AEs in men (RR=1.31, 95% Wald CI=[1.16, 1.47]). In the multivariable modeling, women continued to experience significantly higher odds of knee injury compared with men (aOR=1.44, 95% CI=[1.27,1.63]). Also, the adjusted odds of a knee injury that resulted in surgery remained higher in women compared with men (aOR=1.61 (1.00, 2.58), as well as the amount of time lost from participation (beta=0.129; p=0.05). Given the prominence of soccer play in the United States, continued efforts to evaluate and improve knee injury prevention practices and policies may be especially important for female players.

#10 A Comparison of Body Segment Inertial Parameter Estimation Methods and Joint Moment and Power Calculations During a Drop Vertical Jump in Collegiate Female Soccer Players
Reference: J Appl Biomech. 2016 Oct 5:1-15. [Epub ahead of print]
Authors: Arena SL, McLaughlin K, Nguyen AD, Smoliga JM, Ford KR
Summary: Athletic individuals may differ in body segment inertial parameter (BSIP) estimates due to differences in body composition, and this may influence calculation of joint kinetics. The purposes of this study were to 1) compare BSIPs predicted by the method introduced by de Leva1 with DXA-derived BSIPs in collegiate female soccer players, and 2) examine the effects of these BSIPs estimation methods on joint moment and power calculations during a drop vertical jump (DVJ). Twenty female NCAA Division 1 soccer players were recruited. BSIPs of the shank and thigh (mass, COM location, and radius of gyration) were determined using de Leva's method and analysis of whole-body DXA scans. These estimates were used to determine peak knee joint moments and power during the DVJ. Compared to DXA, de Leva's method located the COM more distally in the shank (p = 0.008) and more proximally in the thigh (p < 0.001), and the radius of gyration of the thigh to be further from the thigh COM (p < 0.001). All knee joint moment and power measures were similar between methods. These findings suggest that BSIP estimation may vary between methods, but the impact on joint moment calculations during a dynamic task is negligible.

#11 Effectiveness of community-based football compared to usual care in men with prostate cancer: Protocol for a randomised, controlled, parallel group, multicenter superiority trial (The FC Prostate Community Trial)
Reference: BMC Cancer. 2016 Oct 3;16(1):767.
Authors: Bjerre E, Bruun DM, Tolver A, Brasso K, Krustrup P, Johansen C, Christensen R, Rørth M, Midtgaard J
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Summary: Prostate cancer is the most common non-cutaneous malignancy in men. Today most patients may expect to live years following the diagnosis and may thus experience significant morbidity due to disease progression and treatment toxicity. In order to address some of these problems exercise has been suggested and previously studies have shown improvements of disease specific quality of life and a reduction in treatment-related toxicity. Cohort studies with long term follow up have suggested that physical activity is associated with improved survival in prostate cancer patients. Previously one randomised controlled trial has examined the efficacy of football in prostate cancer patients undergoing androgen deprivation therapy to usual care and reported positive effects on lean body mass and bone markers. Against this background, we wish to examine the effectiveness of community-based football for men diagnosed with prostate cancer. Using a randomised controlled parallel group, multicenter, superiority trial design, two hundred prostate cancer patients will be recruited and randomised (1:1) to either community-based football one hour twice weekly or to a control group. The intervention period will be six months. The primary outcome is quality of life assessed after 12 weeks based on the change from baseline in the Functional Assessment of Cancer Therapy-Prostate questionnaire. Secondary outcomes are change from baseline to six months in quality of life, lean body mass, fat mass, whole body and regional bone markers, as well as physical activity and functional capacity at 12 weeks and six months. Safety outcome variables will be falls resulting in seeking medical assessment and fractures during the six-month period. Football is viewed as a case for non-professional, supervised community-based team sport for promoting long-term physical activity in men diagnosed with prostate cancer. This randomised trial will provide data on effectiveness and safety for men with prostate cancer when football training is delivered in local football clubs.

#12 Comparison of Two Different Modes of Active Recovery on Muscles Performance after Fatiguing Exercise in Mountain Canoeist and Football Players
Reference: PLoS One. 2016 Oct 5;11(10):e0164216. doi: 10.1371/journal.pone.0164216. eCollection 2016.
Authors: Mika A, Oleksy Ł, Kielnar R, Wodka-Natkaniec E, Twardowska M, Kamiński K, Małek Z
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Summary: The aim of this study is to assess if the application of different methods of active recovery (working the same or different muscle groups from those which were active during fatiguing exercise) results in significant differences in muscle performance and if the efficiency of the active recovery method is dependent upon the specific sport activity (training loads). Thirteen mountain canoeists and twelve football players participated in this study. Measurements of the bioelectrical activity, torque, work and power of the vastus lateralis oblique, vastus medialis oblique, and rectus femoris muscles were performed during isokinetic tests at a velocity of 90°/s. Active legs recovery in both groups was effective in reducing fatigue from evaluated muscles, where a significant decrease in fatigue index was observed. The muscles peak torque, work and power parameters did not change significantly after both modes of active recovery, but in both groups significant decrease was seen after passive recovery. We suggest that 20 minutes of post-exercise active recovery involving the same muscles that were active during the fatiguing exercise is more effective in fatigue recovery than active exercise using the muscles that were not involved in the exercise. Active arm exercises were less effective in both groups which indicates a lack of a relationship between the different training regimens and the part of the body which is principally used during training.






Latest research in football - week 39 - 2016

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 Repeated-sprint sequences during female soccer matches using fixed and individual speed thresholds
Reference: J Strength Cond Res. 2016 Sep 20. [Epub ahead of print]
Authors: Nakamura FY, Pereira LA, Loturco I, Rosseti M, Moura FA, Bradley PS
Summary: The main objective of this study was to characterize the occurrence of single sprint and repeated-sprint sequences (RSS) during elite female soccer matches, using fixed (20 kmh) and individually based speed thresholds (>90% of the mean speed from a 20 m sprint test). Eleven elite female soccer players from the same team participated in the study. All players performed a 20 m linear sprint test, and were assessed in up to 10 official matches using Global Positioning System (GPS) technology. Magnitude-based inferences were used to test for meaningful differences. Results revealed that irrespective of adopting fixed or individual speed thresholds, female players produced only a few RSS during matches (2.3 ± 2.4 sequences using the fixed threshold and 3.3 ± 3.0 sequences using the individually based threshold), with most sequences composing of just two sprints. Additionally, central defenders performed fewer sprints (10.2 ± 4.1) than other positions (full backs: 28.1 ± 5.5; midfielders: 21.9 ± 10.5; forwards: 31.9 ± 11.1; with likely to almost certainly differences associated with effect sizes ranging from 1.65 to 2.72) and sprinting ability declined in the second half. The data do not support the notion that RSS occurs frequently during soccer matches in female players, irrespective of using fixed or individual speed thresholds to define sprint occurrence. However, repeated sprint ability development cannot be ruled out from soccer training programs due to its association with match-related performance.

#2 The use of vanishing spray reduces the extent of rule violations in soccer
Reference: Springerplus. 2016 Sep 15;5(1):1572. doi: 10.1186/s40064-016-3274-2. eCollection 2016
Authors: Kolbinger O, Link D
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Summary: More and more sport associations introduce innovative devices to support referees and umpires respectively, affecting a strong need for the evaluation of these devices. This study evaluates the use of the new vanishing spray for free kicks in the German Bundesliga. In more detail, the aim of the study is to investigate if the spray reduces violations of the required minimum distance and consequently the respective punishments, if it reduces errors concerning the distance set by the referee and if it leads to a higher success rate of free kicks. Therefore, 1833 free kicks of the 2013/2014 and 2014/2015 season of the German Bundesliga were screened using a self-designed observational system. For the statistical analysis two parallel samples were built of 299 free kicks each. The results showed no decrease of free kicks with distance violations but a significantly lower extent of these violations (χ(2) = 4.58; p < .05). However, none of these violations were punished appropriately. Concerning the success of free kicks, no significant impact was found neither for shots nor for crosses. In addition, no influence on the distance set by the referee could be identified. The main objective of the vanishing spray was basically realized, but the use didn't lead to any further positive (side) effects. Due to the lack of punishment, the authors raise concerns about the current application of the minimum distance rule.

#3 Flu vaccination in elite athletes: A survey among Serie A soccer teams
Reference: Acta Biomed. 2016 Sep 13;87(2):117-20.
Authors: Signorelli C, Odone A, Miduri A, Cella P, Pasquarella C, Gozzini A, Tamburrino P, Castellacci E
Summary: Scant data is available on immunization policies and practices among professional athletes. Following up on a recent review on the topic, we conducted a survey among Italian Serie A soccer teams during the influenza season 2015-16, to explore vaccination practices and attitudes as well as influenza vaccine uptake. The survey covered a sample of over 600 professional athletes from 20 teams and was carried out in collaboration with the Italian Association of Physicians of Professional Football Teams (L.A.M.I.CA.). For each team, the head of the medical staff was interviewed (structured telephone interviews, 100% response rate). Seasonal influenza vaccine was actively offered in 75% of Serie A teams with a median coverage rate of 40% (range 0%-100%). Vaccines are often administered after matches or training sessions. We report vaccine hesitancy associated with fear of adverse events, poor communication and other selected determinants. Vaccination in elite athletes, if correctly managed, represents a powerful, cost-effective and long lasting preventive tool. In times where vaccines are losing public confidence, our findings are a useful basis to inform the planning, implementation and evaluation of interventions to promote prevention in sports medicine.

#4 The effect of low back pain on trunk muscle size/function and hip strength in elite football (soccer) players
Reference: J Sports Sci. 2016 Sep 19:1-9. [Epub ahead of print]
Authors: Hides JA, Oostenbroek T, Franettovich Smith MM, Mendis MD
Summary: Low back pain (LBP) is a common problem in football (soccer) players. The effect of LBP on the trunk and hip muscles in this group is unknown. The relationship between LBP and trunk muscle size and function in football players across the preseason was examined. A secondary aim was to assess hip muscle strength. Twenty-five elite soccer players participated in the study, with assessments conducted on 23 players at both the start and end of the preseason. LBP was assessed with questionnaires and ultrasound imaging was used to assess size and function of trunk muscles at the start and end of preseason. Dynamometry was used to assess hip muscle strength at the start of the preseason. At the start of the preseason, 28% of players reported the presence of LBP and this was associated with reduced size of the multifidus, increased contraction of the transversus abdominis and multifidus muscles. LBP decreased across the preseason, and size of the multifidus muscle improved over the preseason. Ability to contract the abdominal and multifidus muscles did not alter across the preseason. Asymmetry in hip adductor and abductor muscle strength was found between players with and without LBP. Identifying modifiable factors in players with LBP may allow development of more targeted preseason rehabilitation programmes.

#5 Quantifying the high-speed running and sprinting profiles of elite female soccer players during competitive matches using an Optical Player Tracking System
Reference: J Strength Cond Res. 2016 Sep 6. [Epub ahead of print]
Authors: Mara JK, Thompson KG, Pumpa KL, Morgan S
Summary: The aim of this study was to determine the high-speed running and sprinting profiles of elite female soccer players during competitive matches using a new Optical Player Tracking System. Eight stationary video cameras were positioned at vantage points surrounding the soccer field so that when each camera view was combined the entire field could be viewed simultaneously. Following each match, an optical player tracking system detected the coordinates (x,y) of each player for every video frame. Algorithms applied to the x and y coordinates were used to determine activity variables for twelve elite female players across seven competitive matches. Players covered 9,220-10,581 m of total distance, 1,772-2,917 m of high-speed running (3.4-5.3 m·s) distance and 417-850 m of sprinting (>5.4 m·s) distance, with variations between positional groups (p < 0.001, partial η = 0.444-0.488). Similarly, the number of high-speed runs differed between positional groups (p = 0.002, partial η = 0.342) and a large proportion of high-speed runs (81-84 %) and sprints (71-78 %) were performed over distances less than 10 m. Mean time between high-speed runs (13.9 s ± 4.4) and sprints (86.5 s ± 38.0) varied according to playing position (p < 0.001, partial η = 0.409) and time period of the match (p < 0.001, partial η = 0.113 - 0.310). The results of this study can be used to design match-specific conditioning drills, and shows that coaches should take an individualised approach to training load monitoring according to position.

#6 The peak velocity derived from the Carminatti Test is related to physical match performance in young soccer players
Reference: J Sports Sci. 2016 Aug 10:1-8. [Epub ahead of print]
Authors: Fernandes-da-Silva J, Castagna C, Teixeira AS, Carminatti LJ, Guglielmo LG
Summary: The aim of this study was to examine the relationship between the peak velocity derived from the Carminatti Test (T-CAR) (PVT-CAR) and physical match performance in young soccer players. Thirty-three youth soccer players were recruited from 2 non-professional clubs. Friendly matches and small-sided game were performed. Physical match demands were assessed using Global Positioning System (GPS) technology. On a separate occasion, the players were submitted to the T-CAR. Players were categorised into 3 groups based on their T-CAR performance: Low (PVT-CAR ≤ P33), Intermediate (P33 > PVT-CAR < P66) and High (PVT-CAR ≥ P66). The PVT-CAR (15.5 ± 0.7 km·h-1) was significantly related to high-intensity activities (HIA; r = 0.78, P < 0.001), high-intensity running (HIR; r = 0.66, P < 0.001), sprinting (r = 0.62, P < 0.001) and total distance (TD) covered (r = 0.47, P < 0.01) during friendly matches. The PVT-CAR was strongly correlated with the amount of HIA (r = 0.81, P < 0.001), HIR (r = 0.85, P < 0.001) and TD covered (r = 0.81, P < 0.001) during small-sided game. No significant correlation was observed between the PVT-CAR and distance of sprinting (r = 0.49, P = 0.067) during small-side game. Furthermore, players in the High group covered significantly more TD (10%) and did more HIA (42%), sprinting (31%) and HIR (25%) during friendly matches compared to the players classified as having Low performance on the T-CAR. These differences still remained after adjusting for chronological age (CA), maturity and body size. In conclusion, the current study gives empirical support to the ecological and construct validity of this novel field test (T-CAR) as an indicator of match-related physical performance in young soccer players during pubertal years.

#7 Effect of Dry Needling on Thigh Muscle Strength and Hip Flexion in Elite Soccer Players
Reference: Med Sci Sports Exerc. 2016 Sep 28. [Epub ahead of print]
Authors: Haser C, Stöggl T, Kriner M, Mikoleit J, Wolfahrt B, Scherr J, Halle M, Pfab F
Summary: Increase in muscle force, endurance and flexibility is desired in elite athletes in order to improve performance and avoid injuries but often hindered by occurence of myofascial trigger points. Dry needling (DN) has been shown effective in eliminating myofascial trigger points. This randomized controlled study in 30 elite youth soccer players of a professional soccer Bundesliga Club investigated the effects of four weekly sessions of DN plus water-pressure-massage on thigh muscle force and range-of-motion of hip flexion. A group receiving placebo-LASER plus water-pressure-massage and a group with no intervention served as controls. Data was collected at baseline (M1), treatment end (M2) and four-week follow-up (M3). Furthermore a 5-month muscle injury follow-up was performed. DN showed significant improvement of muscular endurance of knee extensors at M2 (p=0.039) and M3 (p=0.008) compared to M1 (M1:294.6±15.4nm/s, M2:311±25Nm/s; M3:316.0±28.6nm/s) and knee flexors at M2 compared to M1 (M1:163.5±10.9Nm/s, M2:188.5±16.3Nm/s) as well as hip flexion (M1:81.5±3.3°, M2:89.8±2.8°; M3:91.8±3.8°). Compared to placebo (3.8±3.8°) and control (1.4±2.9°) DN (10.3±3.5°) showed a significant (p=0.01 and p=0.0002) effect at M3 compared to M1 on hip flexion; compared to non-treatment control (-10±11.9Nm) DN (5.2±10.2Nm) also significantly (p=0.049) improved maximum force of knee extensors at M3 compared to M1. During the rest of the season muscle injuries were less frequent in the DN group compared to control groups. DN showed a significant effect on muscular endurance and hip flexion range-of-motion that persisted 4 weeks post-treatment. Compared to placebo it showed a significant effect on hip flexion that persisted 4 weeks post-treatment and compared to non-intervention control a significant effect on maximum force of knee extensors 4 weeks post-treatment in elite soccer players.

#8 Epidemiology of football (soccer) injuries in the 2012/2013 and 2013/2014 seasons of the Italian Serie A
Reference: Res Sports Med. 2016 Sep 29:1-7. [Epub ahead of print]
Authors: Falese L, Della Valle P, Federico B
Summary: Epidemiological studies on football (soccer) injuries are needed to assess both the magnitude of the problem and the effectiveness of preventive programmes. However, few data are available for Italy, which hosts one of the main football leagues in Europe. In this study, we aimed to describe the epidemiology of football injuries in the 2012/2013 and 2013/2014 seasons of the Italian Serie A. Information about injury location, type, date of occurrence and duration of absence was obtained from , a free collaborative international database on football. Overall, 363 injuries occurred throughout the two seasons affecting 286 players. The most commonly reported injuries were thigh-strain and knee injury, which accounted for 42% and 19% of all injuries, respectively. Injury incidence increased with age and was particularly higher from August to October. Results suggest that injury prevention strategies should be introduced from the preseason to reduce the risk of injuries, especially muscle strains.

#9 Isokinetic hip in soccer players: Moroccan experience about 36 cases
Reference: Ann Phys Rehabil Med. 2016 Sep;59S:e16. doi: 10.1016/
Authors: Belhaj K, Meftah S, Zahi S, Lmidmani F, Elfatimi A
Summary: Isokinetic evaluation allows accurate and reproducible measurement of dynamic muscle strength. It has several application areas, especially in sports, it allows the evaluation, rehabilitation and re-entrainment. It is rarely used for the hip joint. The objective of this study was to report the isokinetic profile of the abductor and adductor muscles of the hip in Moroccan professional players, while comparing players with a history of groin for those without medical history at the hip. This is a prospective study in physical medicine and rehabilitation, including 36 professional footballers who have been performed concentric isokinetic evaluation mode abductor and adductor muscles of the hip at 60°/s and 120°/s. The distribution of variables was verified by the normality test of Shapiro, Wilk. The Wilcoxon test and U Mann-Whitney test were used to compare different isokinetic variables of the two groups evaluated. There was no statistically significant difference between dominant and non-dominant side in terms of the maximum peak torque, work, power, and adductor/abductor ratios. There was a significant difference between the players with a history of groin and those who showed no pathological history at the hip. A weak adductors compared to hip abductors may be involved in the development of the groin, especially an eccentric force deficit. The isokinetic allows the establishment of specific profiles and can be applied preventively early in the season to objectify and correct anomalies, particularly agonists/antagonists imbalances sometimes responsible for further damage. It allows a customized physical preparation, predicting the return to competition.

#10 Hormonal (cortical-gonadotropic axis) and physical changes with two years intense exercise training in elite young soccer players
Reference: J Strength Cond Res. 2016 Sep 23. [Epub ahead of print]
Authors: Ali Hammami M, Abderrahman AB, Hackney AC, Kebsi W, Owen AL, Nebigh A, Racil G, Tabka Z, Zouhal H
Summary: The aim of this study was to investigate the effects of two soccer-training seasons on physical fitness and hormone concentrations in elite youth soccer players. Twenty male elite soccer players (SP, age 14.5 ± 0.4 years) and 20 male control subjects (CS, age 14.3 ± 0.3years) participated to the study. Anthropometric measurements, aerobic (Yo-Yo Intermittent Recovery Test Level 1 (YYIRT1)) and anaerobic soccer relevant performances (jump and sprint tests), blood testosterone (T), cortisol (C),sex hormone binding globulin (SHBG) and T/C ratio were assessed 5 times (from T0 to T4) during two competitive seasons. Significant differences from basal values (Δ) of T, SHBG and C between SP and CS were observed (p<0.01). Additionally, T and T/C ratio changes were positively correlated to physical performance (p<0.05). In conclusion, as expected, higher T concentration and greater power performance were observed in the soccer players group compared to controls. Our findings also show that the T concentrations and power performance outcomes covary positively over the two soccer seasons in soccer players.






Latest research in football - week 38 - 2016

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 Soccer-Related Injuries Treated in Emergency Departments: 1990-2014
Reference: Pediatrics. 2016 Sep 12. pii: e20160346. [Epub ahead of print]
Authors: Smith NA, Chounthirath T, Xiang H
Summary: The purpose was to investigate the epidemiology of youth soccer-related injuries treated in emergency departments in the United States. A retrospective analysis was conducted of soccer-related injuries among children 7 through 17 years of age from 1990 through 2014 with data from the National Electronic Injury Surveillance System. Injury rates were calculated from soccer participation data. An estimated 2 995 765 (95% confidence interval [CI], 2 309 112-3 682 418) children 7 through 17 years old were treated in US emergency departments for soccer-related injuries during the 25-year study period, averaging 119 831 (95% CI, 92 364-147 297) annually. The annual injury rate per 10 000 soccer participants increased significantly, by 111.4%, from 1990 to 2014. Patients 12 to 17 years old accounted for 72.7% of injuries, 55.5% of patients were male, and most injuries occurred in a place of sport or recreation (68.5%) or school (25.7%). Struck by (38.5%) and fell (28.7%) were the leading mechanisms of injury. Injuries most commonly were diagnosed as sprain or strain (34.6%), fracture (23.2%), and soft tissue injury (21.9%), and occurred to the upper extremity (20.7%), ankle (17.8%), and head or neck (17.7%). Concussions or other closed head injuries accounted for 7.3% of the injuries, but the annual rate of concussions/closed head injuries per 10 000 participants increased significantly, by 1595.6%, from 1990 to 2014. This study is the first to comprehensively investigate soccer-related injuries and calculate injury rates based on soccer participation data among children at the national level. The increasing number and rate of pediatric soccer-related injuries, especially soccer-related concussions/closed head injuries, underscore the need for increased efforts to prevent these injuries.

#2 Five-week sensory motor training program improves functional performance and postural control in young male soccer players - A blind randomized clinical trial
Reference: Phys Ther Sport. 2016 May 10;22:74-80. doi: 10.1016/j.ptsp.2016.05.004. [Epub ahead of print]
Authors: Heleno LR, da Silva RA, Shigaki L, Araújo CG, Coelho Candido CR, Okazaki VH, Frisseli A, Macedo CS
Summary: Sensory motor training programs are used in the rehabilitation and prevention of injuries among soccer players. Inconsistencies are found in the literature regarding the duration of the protocols and the exercises and equipment used. The objective was to evaluate the benefits of a five-week sensory motor training program on the functional performance and postural control of young soccer players. The study sample comprised 22 young male soccer players who were evaluated using: the Figure-of-Eight Test (F8), Side Hop Test (SHT), Star Excursion Balance Test (SEBT), and a force platform. The players were randomly divided into a control group (N = 10), who continued their soccer practice sessions and an intervention group (N = 12), who continued their soccer practice sessions and were also enrolled in a supervised five-week sensory motor training program. After the five-week training program, the intervention group obtained significant results in the F8, SHT and SEBT, as well as in the following parameters: area of pressure of sway center (COP), mean velocity and mean frequency of COP. The five-week sensory motor training program, carried out with easily available and low cost equipment, was effective at improving functional performance and postural control in young soccer players.

#3 Soccer-Related Facial Trauma: A Nationwide Perspective
Reference: Ann Otol Rhinol Laryngol. 2016 Sep 12. pii: 0003489416668195. [Epub ahead of print]
Authors: Bobian MR, Hanba CJ, Svider PF, Hojjat H, Folbe AJ, Eloy JA, Shkoukani MA
Summary: Soccer participation continues to increase among all ages in the US. Our objective was to analyze trends in soccer-related facial injury epidemiology, demographics, and mechanisms of injury. The National Electronic Injury Surveillance System was evaluated for soccer-related facial injuries from 2010 through 2014. Results for product code "soccer" were filtered for injures to the face. Number of injuries was extrapolated, and data were analyzed for age, sex, specific injury diagnoses, locations, and mechanisms. In all, 2054 soccer-related facial trauma entries were analyzed. During this time, the number of injures remained relatively stable. Lacerations were the most common diagnosis (44.2%), followed by contusions and fractures. The most common sites of fracture were the nose (75.1%). Of fractures with a reported mechanism of injury, the most common was head-to-head collisions (39.0%). Patients <19 years accounted for 66.9% of injuries, and athletes over 18 years old had a higher risk of fractures. The incidence of soccer-related facial trauma has remained stable, but the severity of such injuries remain a danger. Facial protection in soccer is virtually absent, and our findings reinforce the need to educate athletes, families, and physicians on injury awareness and prevention.

#4 The Evaluation of the Match External Load in Soccer: Methods Comparison
Reference: Int J Sports Physiol Perform. 2016 Sep 6. [Epub ahead of print]
Authors: Castagna C, Varley M, Póvoas Araújo SC, D'Ottavio S
Summary: The aim of this study was to test the interchangeability of two match-analysis approaches for external-load detection considering arbitrary selected speeds and metabolic power (MP) thresholds in male top-class level soccer. Data analyses were performed considering match physical performance of 120 team data (1200 player cases) of randomly selected Spanish, German and English first division championship matches (2013-14 season). Match analysis was performed with a validated semi-automated multi-camera system operating at 25 Hz. During a match players covered 10673±348m of which 1778±208m and 2759±241m were performed at High-Intensity using the speed (≥16 km·h-1, HI) and metabolic power notations (≥20 watt·kg-1, MPHI). High-intensity notations were nearly perfect associated (r=0.93, p<0.0001). A huge method bias (980.63± 87.82m. d=11.67) was found when considering MPHI and HI. Very large correlations were found between match total distance covered and MPHI (r=0.84, p<0.0001) and HI (r=0.74, p<0.0001). Players high-intensity decelerations (≥-2 m·s2) coverage was very largely associated with MPHI (r=0.73, p<0.0001). The results of this study showed that the speed and MP methods are highly interchangeable at relative (magnitude rank) but not absolute (measure magnitude) level. The two physical match analysis methods can be independently used to track match external-load in elite level players. However match-analyst decisions must be based on single method use in order to avoid bias in external-load determination.

#5 Effects of Velocity Loss During Resistance Training on Performance in Professional Soccer Players
Reference: Int J Sports Physiol Perform. 2016 Sep 6. [Epub ahead of print]
Authors: Pareja-Blanco F, Sánchez-Medina L, Suárez-Arrones L, González-Badillo JJ
Summary: The purpose was to analyze the effects of two resistance training (RT) programs that used the same relative loading but different repetition volume, using the velocity loss during the set as the independent variable: 15% (VL15) vs. 30% (VL30). Sixteen professional soccer players with RT experience (age 23.8 ± 3.5 years, body mass 75.5 ± 8.6 kg) were randomly assigned to two groups: VL15 (n = 8) or VL30 (n = 8) that followed a 6-week (18 sessions) velocity-based squat training program. Repetition velocity was monitored in all sessions. Assessments performed before (Pre) and after training (Post) included: estimated one-repetition maximum (1RM) and change in average mean propulsive velocity (AMPV) against absolute loads common to Pre and Post tests; countermovement jump (CMJ); 30-m sprint (T30); and Yo-yo intermittent recovery test (YYIRT). Null-hypothesis significance testing and magnitude-based inference statistical analyses were performed. VL15 obtained greater gains in CMJ height than VL30 (P < 0.05), with no significant differences between groups for the remaining variables. VL15 showed a likely/possibly positive effect on 1RM (91/9/0%), AMPV (73/25/2%) and CMJ (87/12/1%), whereas VL30 showed possibly/unclear positive effects on 1RM (65/33/2%) and AMPV (46/36/18%) and possibly negative effects on CMJ (4/38/57%). The effects on T30 performance were unclear/unlikely for both groups, whereas both groups showed most likely/likely positive effects on YYIRT. A velocity-based RT program characterized by a low degree of fatigue (15% velocity loss in each set) is effective to induce improvements in neuromuscular performance in professional soccer players with previous RT experience.

#6 The biomechanical and physiological response to repeated soccer-specific simulations interspersed by 48 or 72 hours recovery
Reference: Phys Ther Sport. 2016 Jul 4;22:81-87. doi: 10.1016/j.ptsp.2016.06.011. [Epub ahead of print]
Authors: Page RM, Marrin K, Brogden CM, Greig M
Summary: The purpose was to assess the residual fatigue response associated with the completion of two successive soccer-specific exercise protocols (SSEP). Twenty male soccer players were pair-matched before completing SSEPs, interspersed by either 48 or 72 h. Outcome variables were measured every 15 min, and comprised uni-axial measures of PlayerLoad, mean (HR) and peak heart rate (HRpeak), blood lactate concentration, mean and peak (V˙O2peak) oxygen consumption, and rating of perceived exertion (RPE). No significant (P > 0.05) group interactions were identified for any outcome variables. Uni-axial (and total) PlayerLoad exhibited a significant (P < 0.05) main effect for time, with the exception of the relative contribution of medial lateral PlayerLoad™. Total PlayerLoad during the final 15 min (222.23 ± 15.16 a.u) was significantly higher than all other time points. All other outcome variables also exhibited a significant main effect for time, with HR, HRpeak and V˙O2peak also exhibiting significantly higher values in the first trial. There was also a significant (P = 0.003) trial*time interaction for RPE. With equivalence at baseline, there was no difference in the fatigue response associated with two SSEPs interspersed by either 48 or 72 h recovery. The current study has implications for the design and micro management of training and competition schedules.

#7 Assessment and Training of Visuomotor Reaction Time for Football Injury Prevention
Reference: J Sport Rehabil. 2016 Aug 24:1-26. [Epub ahead of print]
Authors: Wilkerson GB, Simpson KA, Clark RA
Summary: Neurocognitive reaction time has been associated with musculoskeletal injury risk, but visuomotor reaction time (VMRT) derived from tests that present greater challenges to visual stimulus detection and motor response execution may have a stronger association. The purposes of this study were to assess VMRT as a predictor of injury and the extent to which improvement may result from VMRT training. Seventy-six NCAA Division-I FCS football players (19.5 ±1.4 years; 1.85 ± 0.06 m; 102.98 ±19.06 kg) participated in this study. Pre-participation and post-season assessments. A subset of players who exhibited slowest VMRT in relation to the cohort's post-season median value participated in a 6-week training program. Injury occurrence was related to pre-participation VMRT, which was represented by both number of target hits in 60 s and average elapsed time between hits (ms). Receiver operating characteristic analysis identified the optimum cut point for a binary injury risk classification. A non-parametric repeated measures analysis of ranks procedure was used to compare post-training VMRT values for slow players who completed at least half of the training sessions (n=15) to those for untrained fast players (n=27). A pre-participation cut point of ≤ 85 hits (≥ 705 ms) discriminated injured from non-injured players with OR = 2.30 (90% CI: 1.05, 5.06). Slow players who completed the training exhibited significant improvement in visuomotor performance compared to baseline (SRM = 2.53), whereas untrained players exhibited a small performance decrement (group x trial interaction effect, L2 = 28.74; P < .001). Slow VMRT appears to be an important and modifiable injury risk factor for college football players. More research is needed to refine visuomotor reaction time screening and training methods and to determine the extent to which improved performance values can reduce injury incidence.

#8 Small-sided football games on sand are more physical-demanding but less technical-specific compared to artificial turf
Reference: J Sports Med Phys Fitness. 2016 Sep 15. [Epub ahead of print]
Authors: Rago V, Rebelo AN, Pizzuto F, Barreira D
Summary: The use of sand has been suggested as fitness-enhancing surface in field-based team sports. However, concerns have arisen in regard whether physical responses associated to sand training are sport-specific. We compared physical and technical demands during small-sided football games (4v4 + goalkeeper; SSGs) played on artificial turf and on sand. Movement patterns, rating of perceived exertion (RPE) and technical parameters were obtained from eight adult male footballers (20.1±1.0 years, 176±4 cm and 70.1±2.0 kg) using Global Positioning Systems, Visual Analogue Scale questionnaires and Notational analysis respectively. High-intensity actions (high intensity running, high intensity activities), low changes of speed, as well as peak and average speed were higher on artificial turf (p<0.05; Effect sizes (ES) from 0.41 to 0.82). In contrast, time spent by jogging as well as high and maximum changes of speed was higher on sand (p<0.05; ES from 0.59 to 0.82). Moreover, players perceived more demanding to play on sand (p<0.05; ES=0.72). Rating of successful actions was higher during turf SSGs than sand SSGs (p<0.05; ES from 0.44 to 0.73), whereas actions requiring lifting the ball were higher on sand (p<0.05; ES from 0.47 to 0.50). The use of sand can be considered as complemental to on-turf football training, when the training goal is to tax lower-limb muscle strength or to require high-ball situations. Nonetheless, sand training is not appropriate when the achievement of maximal speed is desired. Further research should clarify the suitability of sand training within football conditioning programmes.

#9 A new clinical test for measurement of lower limb specific range of motion in football players: Design, reliability and reference findings in non-injured players and those with long-standing adductor-related groin pain
Reference: Phys Ther Sport. 2016 Jul 31. pii: S1466-853X(16)30063-3. doi: 10.1016/j.ptsp.2016.07.007. [Epub ahead of print]
Authors: Tak IJ, Langhout RF, Groters S, Weir A, Stubbe JH, Kerkhoffs GM
Summary: The association between groin pain and range of motion is poorly understood. The aim of this study was to develop a test to measure sport specific range of motion (SSROM) of the lower limb, to evaluate its reliability and describe findings in non-injured (NI) and injured football players. 6 Dutch elite clubs, 6 amateur clubs and a sports medicine practice consisting of 103 NI elite and 83 NI amateurs and 57 football players with unilateral adductor-related groin pain participated in this study. Sport specific hip extension, adduction, abduction, internal and external rotation of both legs were examined with inclinometers. Test-retest reliability (ICC), standard error of measurement (SEM) and minimal detectable change (MDC) were calculated. Non-injured players were compared with the injured group. Intra and inter tester ICCs were acceptable and ranged from 0.90 to 0.98 and 0.50-0.88. SEM ranged from 1.3 to 9.2° and MDC from 3.7 to 25.6° for single directions and total SSROM. Both non-injured elite and amateur players had very similar total SSROM in non-dominant and dominant legs (188-190, SD ± 25). Injured players had significant (p < 0.05) total SSROM deficits with 187(SD ± 31)° on the healthy and 135(SD ± 29)° on the injured side. The SSROM test shows acceptable reliability. Loss of SSROM is found on the injured side in football players with unilateral adductor-related groin pain. Whether this is the cause or effect of groin pain cannot be stated due to the study design. Whether restoration of SSROM in injured players leads to improved outcomes should be investigated in new studies.





Latest research in football - week 37 - 2016

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 Daily Distribution of Carbohydrate, Protein and Fat Intake in Elite Youth Academy Soccer Players Over a 7-day Training Period
Reference: Int J Sport Nutr Exerc Metab. 2016 Aug 24:1-20. [Epub ahead of print]
Authors: Naughton RJ, Drust B, O'Boyle A, Morgans R, Abayomi J, Davies IG, Morton JP, Mahon E
Summary: While traditional approaches to dietary analysis in athletes have focused on total daily energy and macronutrient intake, it is now thought that daily distribution of these parameters can also influence training adaptations. Using seven-day food diaries, we quantified the total daily macronutrient intake and distribution in elite youth soccer players from the English Premier League in U18 (n=13), U15/16 (n=25) and U13/14 squads (n=21). Total energy (43.1±10.3, 32.6±7.9, 28.1±6.8 kcal·kg-1·day-1), CHO (6±1.2, 4.7±1.4, 3.2±1.3 g·kg-1·day-1) and fat (1.3±0.5, 0.9±0.3, 0.9±0.3 g·kg-1·day-1) intake exhibited hierarchical differences (P<0.05) such that U13/14>U15/16>U18. Additionally, CHO intake in U18s was lower (P<0.05) at breakfast, dinner and snacks when compared with both squads but no differences were apparent at lunch. Furthermore, the U15/16s reported lower relative daily protein intake than the U13/14s and U18s (1.6±0.3 vs. 2.2±0.5, 2.0±0.3 g·kg-1). A skewed distribution (p<0.05) of daily protein intake was observed in all squads, with a hierarchical order of dinner (~0.6 g·kg-1) > lunch (~0.5 g·kg-1) > breakfast (~0.3 g·kg-1). We conclude elite youth soccer players do not meet current CHO guidelines. Although daily protein targets are achieved, we report a skewed daily distribution in all ages such that dinner>lunch>breakfast. Our data suggest that dietary advice for elite youth players should focus on both total daily macronutrient intake and optimal daily distribution patterns.

#2 Vitamin D in relation to bone health and muscle function in young female soccer players
Reference: Eur J Sport Sci. 2016 Sep 15:1-8. [Epub ahead of print]
Authors: Brännström A, Yu JG, Jonsson P, Åkerfeldt T, Stridsberg M, Svensson M
Summary: The present work investigated serum vitamin D (25(OH)D) status in relation to bone and muscle qualities and functions in 19 female soccer players (13-16 years) resident at northern latitude with very low sun exposure (∼32-36 h/month) during winter season (late January to early March). Serum 25(OH)D, parathyroid hormone and bone turnover markers osteocalcin (OC) and beta carboxy-terminal collagen cross-links (β-Ctx), as well as body composition and muscle performance were examined. Hormones were tested using routine laboratory methods. Fat mass, lean mass, and bone mineral density in whole body, as well as femur and lumbar spine were evaluated with dual-energy X-ray absorptiometry. Muscle performance was assessed through isokinetic knee extension and flexion, countermovement jump, and sprint running. 25(OH)D was low (50.5 ±   12.8 nmol l-1), whereas the values of bone turnover markers were markedly high (OC: 59.4 ±   18.6 µg l-1; β-Ctx: 1075 ±   408 ng l-1). All bone and muscle measurements were normal or above normal. 25(OH)D was not significantly correlated with most of the parameters of bone and muscle quality or function, except the knee extension time to peak torque (r   =   -0.50, p =   .03). In conclusion, the level of vitamin D is markedly low in adolescent female soccer players during the winter in Sweden. However, vitamin D levels did not significantly correlate with measures of bone and muscle except a moderate correlation in time to peak torque in the knee extensors. The practical implication of low vitamin D levels in young growing female athletes remains unclear.

#3 Associations between Functional and Isolated Performance Measures in Collegiate Women's Soccer Players
Reference: J Sport Rehabil. 2016 Aug 24:1-29. [Epub ahead of print]
Authors: McCann RS, Kosik KB, Terada M, Beard MQ, Buskirk GE, Gribble PA
Summary: The Star Excursion Balance Test (SEBT) and Functional Movement Screen (FMS) are functional performance measures capable of predicting lower extremity injury risk. While suboptimal SEBT and FMS performances are influenced by multiple factors, the contribution of hip strength and flexibility to these tests is mostly unknown. Examination of hip strength and flexibility influences on the SEBT and FMS may direct clinicians to better methods of correcting functional deficits. The objective of the study was to determine the relationships of isometric hip strength and hip passive range of motion (PROM) with functional performance measures. Forty-three NCAA Division I women's soccer players (19.65±1.12yrs; 166.93±3.84cm; 60.99±4.31kg) volunteered. All participants were tested bilaterally in the SEBT; the deep squat, in-line lunge, hurdle step, and straight leg raise, comprising a lower extremity FMS (FMS-LE); hip internal and external rotation PROM; and isometric hip extension strength (HEXT). The mean of the three averaged, normalized SEBT scores was used as a composite score. Pearson product moment correlations assessed relationships of SEBT and FMS-LE scores with PROM and HEXT. Significance was set a priori at P<0.05. Pearson correlations revealed anterior (ANT) SEBT scores had a low negative association with HEXT (r=-0.33,P=0.004) and a low positive association with hip internal rotation PROM (PROM-IR) (r=0.43,P=0.0032). All other correlations were negligible. Flexibility training aimed at PROM-IR may contribute to improved ANT scores. Targeting HEXT and hip external rotation PROM are likely not preferred means of correcting deficits in SEBT and FMS-LE performance.

#4 Longitudinal Changes in Hip Strength and Range of Motion in Female Youth Soccer Players: Implications for ACL Injury. A Pilot Study
Reference: J Sport Rehabil. 2016 Aug 24:1-23. [Epub ahead of print]
Authors: Nguyena AD, Zuka EF, Baellowa AL, Pfileb KR, DiStefanoc LJ, Bolingd MC
Summary: Risk of ACL injuries in young female athletes increases with age, appearing to peak during maturation. Changes in hip muscle strength and range of motion (ROM) during this time may contribute to altered dynamic movement patterns that are known to increase risk of ACL injuries. Understanding the longitudinal changes in hip strength and ROM is needed in order to develop appropriate interventions to reduce the risk of ACL injuries. The objective was to examine the longitudinal changes in hip strength and ROM in female youth soccer players. Fourteen female youth soccer athletes (14.1± 1.1yrs, 165.8± 5.3cm, 57.5± 9.9kg) volunteered as part of a multi-year risk factor screening project. Clinical measures of hip strength and ROM were collected annually over three consecutive years. Passive hip internal rotation (IR), external rotation (ER), abduction (ABD), and adduction (ADD) ROM were measured with a digital inclinometer. Isometric hip ABD and extension (EXT) strength were evaluated using a hand-held dynamometer. Separate repeated measures ANOVAs compared hip strength and ROM values across 3 consecutive years (P<0.05). As youth female soccer players increased in age, there were no changes in normalized hip ABD (P=0.830) or EXT strength (P=0.062) across three consecutive years. Longitudinal changes in hip ROM were observed with increases in hip IR (P=0.001) and ABD (P<0.001), while hip ADD (P=0.009) and ER (P<0.001) decreased. Anatomical changes at the hip occur as youth female soccer players increase in age. While there are no changes in hip strength, there is an increase in hip IR and ABD ROM with a concomitant decrease in hip ER and ADD ROM. The resulting asymmetries in hip ROM may decrease the activation and force producing capabilities of the hip muscles during dynamic activities, contributing to altered lower extremity mechanics known to increase the risk of ACL injuries.

#5 Eccentric Exercises Reduce Hamstring Strains in Elite Adult Male Soccer Players: A Critically Appraised Topic
Reference: J Sport Rehabil. 2016 Aug 24:1-11. [Epub ahead of print]
Authors: Shadle IB, Cacolice PA

#6 Soccer helps in controlling the development of psoriasis in Italian second league players
Reference: J Eur Acad Dermatol Venereol. 2016 Sep 15. doi: 10.1111/jdv.13971. [Epub ahead of print]
Authors: Megna M, Lobasso A, Napolitano M, Rossi FW, Balato A, Matucci-Cerinic C, Braconaro F, Prignano F, Monfrecola G, Balato N, Paulis A
Summary: Psoriasis is a systemic disease linked to a general state of inflammation and increased risk to develop metabolic and cardiovascular diseases such as obesity, diabetes, and hypertension.1,2 Physical activity, a vital component in prevention and management of these diseases, is reported to be potentially associated in a negative way with psoriasis, since the latter often cause significant restriction of social activities.3 The interest in the relationship between exercise and psoriasis is constantly growing. Recently, we have shown that regular physical activity may lower the risk of psoriasis and have a beneficial effect on the natural course of the disease.

#7 Comparison of the Kinematic Patterns of Kick Between Brazilian and Japanese Young Soccer Players
Reference: Asian J Sports Med. 2016 Jun 1;7(2):e33645. doi: 10.5812/asjsm.33645. eCollection 2016.
Authors: Pereira Santiago PR, Palucci Vieira LH, Barbieri FA, Moura FA, Exel Santana J, de Andrade VL, de Souza Bedo BL, Cunha SA
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Summary: Kicking performance is the most studied technical action in soccer and lower limbs kinematics is closely related to success in kicking, mainly because they are essential in imparting high velocity to the ball. Previous studies demonstrated that soccer leagues in different countries exhibit different physical demands and technical requirements during the matches. However, evidencewhether nationality has any influence in the kinematics of soccer-related skills has not yet been reported. The nationality of the players is an aspect that might be also relevant to the performance in kicking. The aim of this study was to compare the lower limbs kinematic patterns during kicking, between Brazilian and Japanese young top soccer players. Seven Brazilian (GA) and seven Japanese (GB) U-17 players performed 15 side-foot kicks each, with a distance of 20 m away from the goal, aiming a target of 1 × 1 m in upper corner, constrained by a defensive wall (1.8 × 2 m). Four digital video cameras (120 Hz) recorded the performance for further 3D reconstruction of thigh, shank and foot segments of both kicking and support limbs. The selected kicking cycle was characterized by the toe-off of the kicking limb to the end of the kicking foot when it came in contact with the ball. Stereographical projection of each segment was applied to obtain the representative curves of kicking as function of time for each participant in each trial. Cluster analysis was performed to identify the mean GA and GB curves for each segment. Silhouette coefficient (SC) was calculated, in order to determine the degree of separation between the two groups' curves. Comparison between the median confidence intervals of the SC showed no differences between groups as regards lower limb patterns of movements. Task accuracy was determined by the relative frequency that the ball reached the target for all attempts and no differences were found (GA: 10.48 ± 14.33%; GB: 9.52 ± 6.51%; P = 0.88). We conclude that lower limb kinematic patterns, in support and ball contact phases, are similar in young Brazilian and Japanese soccer players during free kicks when adopting the side-foot kick style.

#8 Asymmetry of the Modified Illinois Change of Direction Test Impacts Young Elite Soccer Players' Performance
Reference: Asian J Sports Med. 2016 Jun 11;7(2):e33598. doi: 10.5812/asjsm.33598. eCollection 2016.
Authors: Rouissi M, Chtara M, Berriri A, Owen A, Chamari K
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Summary: The modified Illinois change of direction test (MICODT) is an asymmetrical test because the numbers of changes of direction performed to the right and to the left are unequal. Therefore, it is possible that the asymmetry of this test may influence agility performance testing. The aim of this study was to compare two opposite/mirrored versions of the modified Illinois change of direction test. Forty-six right-footed soccer players (17.2 ± 1.6 years-old) participated in the study. Players performed a modified Illinois change of direction test and a mirrored version of this test "inverted modified Illinois change of direction test" (I/MICODT) in a randomized and counter-balanced order. Paired t-test was used to determine whether significant differences existed between time performances of the tests as a within-subjects measure. Players were thereafter stratified into MICODT group or I/MICODT group according to their best performance and independent t-tests were used to determine differences between groups. The analysis revealed no significant difference in time performance between the two versions of test as a within-subjects measure (P > 0.05, ES = 0.05). However, significant better time performances among inverted modified Illinois change of direction group (52% of players) were found when compared to the modified Illinois change of direction group (48% of players) (P < 0.04, ES = 0.66). The modified Illinois change of direction test must be considered as an asymmetrical test because it underestimates more than half of the players' agility performances. Therefore, fitness coaches should take these results into account when using this test.

#9 The hydration status of elite youth female soccer players during an official tournament
Reference: J Sports Med Phys Fitness. 2016 Sep 13. [Epub ahead of print]
Authors: Chapelle L, Tassignon B, Aerenhouts D, Mullie P, Clarys P
Summary: The hydration status of elite female soccer players is a concern, especially during high-volume training periods or tournaments. Furthermore, scientific literature on this topic is scarce to non-existent. Therefore, the primary aim of this study was to evaluate the hydration status in elite youth female soccer players during an official tournament. The secondary aim was to identify a possible relationship between pre-training hydration status and fluid intake. Eighteen players were followed during eight consecutive days. Urine specific gravity was used to assess hydration status. Body weight was monitored before and after every training and match, whilst individual fluid intake was only registered during training. The players were informed about their hydration status on day 5. On days 1 to 4, the percentage of players who were at least minimally hypohydrated ranged between 44% and 78%. On day 5 (rest day), all the players were at least minimally hypohydrated. After the information session on day 5, the relative number of euhydrated players increased to 89% on both day 6 (training day) and day 7 (match day). On the final day (rest day), all players were either minimally hypohydrated or hypohydrated. Furthermore, a moderate and significant negative correlation (r = -0.44; N = 54; p = 0.01) was found between fluid intake during and USG value before the training sessions. The data illustrates that the hydration status of this population of elite youth female soccer players may be suboptimal and is of substantial concern on rest days during this tournament under temperate conditions. Receiving personal advice about rehydration seems to have a positive effect.





Latest research in football - week 36 - 2016

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 Time series of ground reaction forces following a single leg drop jump landing in elite youth soccer players consist of four distinct phases
Reference: Gait Posture. 2016 Sep 4;50:137-144. doi: 10.1016/j.gaitpost.2016.09.002. [Epub ahead of print]
Authors: Fransz DP, Huurnink A, de Boode VA, Kingma I, van Dieën JH
Summary: The single leg drop jump landing test may assess dynamic and static balance abilities in different phases of the landing. However objective definitions of different phases following landing and associated reliability are lacking. Therefore, we determined the existence of possible distinct phases of single leg drop jump landing on a force plate in 82 elite youth soccer players. Three outcome measures were calculated over moving windows of five sizes: center of pressure (COP) speed, COP sway and horizontal ground reaction force (GRF). Per outcome measure, a Factor Analysis was employed with all windows as input variables. It showed that four factors (patterns of variance) largely (>75%) explained the variance across subjects/trials along the 12s time series. Each factor was highly associated with a distinct phase of the time series signal: dynamic (0.4-2.7s), late dynamic (2.5-5.0s), static 1 (5.0-8.3s) and static 2 (8.1-11.7s). Intra-class correlations (ICC) between trials were lower for the dynamic phases (0.45-0.68) than for the static phases (0.60-0.86). The COP speed showed higher ICC's (0.63-0.86) than COP sway (0.45-0.61) and GRF (0.57-0.71) for all four phases. In conclusion, following a drop jump landing unique information is available in four distinct phases. The COP speed is most reliable, with higher reliability in the static phases compared to the dynamic phases. Future studies should assess the sensitivity of information from dynamic, late dynamic and static phases.

#2 Big data and tactical analysis in elite soccer: future challenges and opportunities for sports science
Reference: Springerplus. 2016 Aug 24;5(1):1410. doi: 10.1186/s40064-016-3108-2. eCollection 2016.
Authors: Rein R, Memmert D
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Summary: Until recently tactical analysis in elite soccer were based on observational data using variables which discard most contextual information. Analyses of team tactics require however detailed data from various sources including technical skill, individual physiological performance, and team formations among others to represent the complex processes underlying team tactical behavior. Accordingly, little is known about how these different factors influence team tactical behavior in elite soccer. In parts, this has also been due to the lack of available data. Increasingly however, detailed game logs obtained through next-generation tracking technologies in addition to physiological training data collected through novel miniature sensor technologies have become available for research. This leads however to the opposite problem where the shear amount of data becomes an obstacle in itself as methodological guidelines as well as theoretical modelling of tactical decision making in team sports is lacking. The present paper discusses how big data and modern machine learning technologies may help to address these issues and aid in developing a theoretical model for tactical decision making in team sports. As experience from medical applications show, significant organizational obstacles regarding data governance and access to technologies must be overcome first. The present work discusses these issues with respect to tactical analyses in elite soccer and propose a technological stack which aims to introduce big data technologies into elite soccer research. The proposed approach could also serve as a guideline for other sports science domains as increasing data size is becoming a wide-spread phenomenon.

#3 Ankle Injury Prevention Programs for Soccer Athletes Are Protective: A Level-I Meta-Analysis
Reference: J Bone Joint Surg Am. 2016 Sep 7;98(17):1436-43. doi: 10.2106/JBJS.15.00933.
Authors: Grimm NL, Jacobs JC Jr, Kim J, Amendola A, Shea KG
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Summary: Soccer has one of the highest rates of ankle injury in sports for both males and females. Several injury prevention programs have been developed to address this concern. The purposes of this study were to conduct a meta-analysis of ankle injury prevention programs for soccer players, assess the heterogeneity among the studies, and evaluate the reported effectiveness of the prevention programs. A systematic search of the literature was conducted in PubMed (MEDLINE), Embase, CINAHL (Cumulative Index to Nursing and Allied Health), and the Cochrane Central Register of Controlled Trials (CENTRAL) database. Studies were limited to clinical investigations of injury prevention programs specific to the ankle in soccer players. Title, abstract, and full-text review were utilized to identify articles that met the inclusion criteria. The Cochrane Q test and I(2) index were independently used to assess heterogeneity among the studies. Sensitivity analyses were performed to assess heterogeneity. The pooled risk difference was calculated by random-effects models with use of the DerSimonian-Laird method. Publication bias was assessed with a funnel plot and Egger weighted regression technique. Ten studies met the inclusion criteria as randomized controlled trials. A total of 4,121 female and male soccer athletes were analyzed for ankle injuries. Significant heterogeneity was found among studies of ankle injury prevention (p = 0.002), with an I(2) index of 65.2%. For studies of ankle injury prevention programs, the risk ratio was 0.60 (95% confidence interval, 0.40 to 0.92) and a significant reduction in the risk of ankle injury was found in the prevention group (p = 0.002). No evidence of publication bias was found among the included studies. This meta-analysis of studies regarding ankle injury prevention programs identified a significant reduction in the risk of ankle injury. Future high-quality research designs with a low risk of bias are necessary to further evaluate the effectiveness of specific exercises and the optimal timing and age at intervention for the prevention of ankle injuries in the athletic soccer player.

#4 Effects of far infrared rays emitting clothing on recovery after an intense plyometric exercise bout applied to elite soccer players: a randomized double-blind placebo-controlled trial
Reference: Biol Sport. 2016 Sep;33(3):277-83. doi: 10.5604/20831862.1208479. Epub 2016 Jul 2.
Authors: Loturco I, Abad C, Nakamura FY, Ramos SP, Kobal R, Gil S, Pereira LA, Burini F, Roschel H, Ugrinowitsch C, Tricoli V
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Summary: The aim was to investigate the effects of far infrared (FIR) ray emitting clothes on indirect markers of exercise-induced muscle damage and physical performance recovery after a plyometric bout applied to soccer players. Twenty-one male players (18.9±0.6 years; 70.8±5.01 kg; 178.3±0.06 cm) performed 100 drop-jumps. Six hours after the bout, athletes put on FIR clothes (FIR) (density of 225 g·m(-2), 88% far infrared rays emitting polyamide 66 Emana yarn (PA66) fibre, 12% Spandex, emissivity of 0.88 and power emitted of 341 W/m2µm at 37°C in the 5-20 µm wavelength range, patent WO 2009/077834 A2) (N = 10) or placebo clothes (PLA) (N = 11). Mid-thigh circumferences, creatine kinase (CK), and delayed-onset muscle soreness (DOMS) were assessed before, immediately after and 24, 48, and 72 h after the bout. Squat (SJ) and countermovement jump (CMJ) heights were measured before and at 24, 48, and 72 h after, while 1RM leg press (maximum strength) was measured before and at 72 h after the plyometrics. No differences between groups were found in mid-thigh circumferences, SJ, CMJ or 1RM. CK increased significantly 24 h after the plyometrics in comparison to before (p < 0.05) in both groups. PLA showed significant DOMS increases at 24, 48, and 72 h, while FIR showed significant increases at 24 and 48 h (p < 0.05). DOMS effect sizes were greater in FIR (moderate at 48 h, ES = 0.737 and large at 72 h, ES = 0.844), suggesting that FIR clothes may reduce perceived DOMS after an intense plyometric session performed by soccer players.

#5 The Hoff circuit test is more specific than an incremental treadmill test to assess endurance with the ball in youth soccer players
Reference: Biol Sport. 2016 Sep;33(3):263-8. doi: 10.5604/20831862.1201913. Epub 2016 May 11.
Authors: Zagatto AM, Papoti M, Da Silva A, Barbieri RA, Campos EZ, Ferreira EC, Loures JP, Chamari K
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Summary: The assessment of aerobic endurance is important for training prescription in soccer, and is usually measured by straight running without the ball on a track or treadmill. Due to the ball control and technical demands during a specific soccer test, the running speeds are likely to be lower compared to a continuous incremental test. The aim of the present study was to compare the heart rate (HR), rating of perceived exertion (RPE) and speeds corresponding to 2.0 mmol∙L(-1), 3.5 mmol∙L(-1), lactate threshold (Dmax method) and peak lactate determined in the laboratory and in the Hoff circuit soccer-specific test. Sixteen soccer players (16±1 years) underwent two incremental tests (laboratory and Hoff circuit tests). The speeds were significantly higher in the treadmill test than on the Hoff circuit (2.0 mmol∙L(-1): 9.5±1.2 and 8.1±1.0 km∙h(-1); 3.5 mmol∙L(-1): 12.0±1.2 and 10.2±1.1 km∙h(-1); Dmax: 11.4±1.4 and 9.3±0.4 km∙h(-1); peak lactate: 14.9±1.6 and 10.9±0.8 km∙h(-1)). The HR corresponding to 3.5 mmol∙L-1 was significantly higher on the Hoff circuit compared to the laboratory test (187.5±18.0 and 178.2±17.6 bpm, respectively; P <0.001), while the RPE at the last incremental stage was lower on the Hoff circuit (P < 0.01). The speeds during the Hoff specific soccer test and the HR corresponding to 2.0 mmol∙L(-1), 3.5 mmol∙L(-1) and Dmax/threshold were different compared with the laboratory test. The present study shows that it is possible to assess submaximal endurance related variables specifically in soccer players.

#6 Assessment of hydration status of elite young male soccer players with different methods and new approach method of substitute urine strip
Reference: J Int Soc Sports Nutr. 2016 Sep 2;13(1):34. doi: 10.1186/s12970-016-0145-8. eCollection 2016.
Authors: Ersoy N, Ersoy G, Kutlu M
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Summary: The purpose of the study is to determine and compare the hydration status with different methods and determine fluid intake, dehydration percentages and sweat rate of 26 young male soccer players (15 ± 1.2 years) before an important competition. More specifically, the study aims at validating the urine strip and advising the players to use it as an easy and practical method. Measurements of urine analysis were taken from the urine sample of the participants before breakfast and conducted for 3 consecutive days before the competition. Hydration status was assessed through analysis of urine color, urine specific gravity (USG) (laboratory, strip, refractometry), and osmolality. The players' dehydration percentages and sweat ratio were calculated. The average values for all samples were 3 ± 1 for color, and 1.021 ± 4 g/cm(3) for USG (laboratory), and 1.021 ± 3 g/cm(3) for USG (strip), and 1.021 ± 4 for USG (refractometry), and 903 ± 133 mOsm/kg for osmolality. USG (strip) was highly correlated with USG (laboratory), USG (refractometry) (r = 0.8; P < 0.01) and osmolality (r = 0.7; P < 0.01), and moderately correlated with urine color (r = 0.4; P < 0.05). The mean dehydration percentage and sweat rate of the soccer players were observed as 0.5 % and 582.3 ± 232.0 mL/h, respectively. We found that youth soccer players are under a slight risk of dehydration under moderate weather conditions. As indicated by the research results, determination of hydration status of athletes must be taken into account more carefully under moderate and hot weather conditions. In addition, hydration methods were compatible with one another as measured in this study.

#7 Spontaneous Intracranial Hypotension Following Soccer Game: Potential Role of MRI in The Treatment Response
Reference: Turk Neurosurg. 2015 Sep 21. doi: 10.5137/1019-5149.JTN.15549-15.0. [Epub ahead of print]
Authors: Acar T, Gölen MK, Gölen M.
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#8 Agility profile in sub-elite under-11 soccer players: is SAQ training adequate to improve sprint, change of direction speed and reactive agility performance?
Reference: Res Sports Med. 2016 Sep 3:1-10. [Epub ahead of print]
Authors: Trecroci A, Milanović Z, Rossi A, Broggi M, Formenti D, Alberti G
Summary: The purpose of this study was to examine the effects of speed, agility and quickness (SAQ) training on acceleration (5 and 20 m), change of direction speed (CODS) and reactive agility in preadolescent soccer players. Thirty-five participants (age = 10.57 ± 0.26, body mass = 36.78 ± 5.34 kg, body height = 1.42 ± 0.05 m), randomly assigned to experimental (EG, n = 20) and control groups (CG, n = 15), completed a 12-week training intervention, 2 day/week. A significant interaction was found in 5-m sprint (P < 0.05, part η2 = 0.117) and reactive agility (P < 0.01, part η2 = 0.248) between EG and CG. In both groups, 20-m sprint time improved significantly (P < 0.05, effect size = 0.3-0.4) while performance on CODS remained unchanged after 12 weeks. These findings indicated that SAQ training could positively affect cognitive skills and initial sprint acceleration through the middle childhood, offering useful guidance to soccer coaches.

#9 Offensive strategies in the European Football Championship 2012
Reference: Percept Mot Skills. 2016 Sep 8. pii: 0031512516667455. [Epub ahead of print]
Authors: Sgrò F, Aiello F, Casella A, Lipoma M
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Summary: The aim of this study was to identify the independent and interactive effects of possession strategy, pitch location, and game period on the offensive actions performed by the winning teams in the 2012 European Football Championship. The non-clinical magnitude-based inferences method was used to interpret the true effect of the performance indicators on the response variable. The offensive team possessions were grouped into winning (n = 2035) and losing (n = 2071). The winning teams performed offensive processes mainly using the possession play strategy (OR: 0.75, very likely negative effect of the direct play). When the analysis included the pitch location, negative interaction effect was found for the direct play, which ended up in the central path (OR: 0.70, very likely negative effect). On the contrary, the direct play in the second half of the match seemed to produce an effect on the probability of the winning teams performing offensive processes (OR: 1.59, most likely positive effect). The results of multivariate analyses showed that the offensive team possession profiles required a careful investigation because the possession strategy changed under the conjoint effect of pitch location and game period.

#10 Interseason variability of a functional movement test, the 9+ screening battery, in professional male football players
Reference: Br J Sports Med. 2016 Sep 6. pii: bjsports-2016-096570. doi: 10.1136/bjsports-2016-096570. [Epub ahead of print]
Authors: Bakken A, Targett S, Bere T, Eirale C, Farooq A, Tol JL, Whiteley R, Witvrouw E, Khan KM, Bahr R
Summary: The Nine Plus screening battery test (9+) is a functional movement test intended to identify limitations in fundamental movement patterns predisposing athletes to injury. However, the interseason variability is unknown.
The aim of the study was to examine the variability of the 9+ test between 2 consecutive seasons in professional male football players. Asymptomatic Qatar Star League players (n=220) completed the 9+ at the beginning of the 2013 and 2014 seasons. Time-loss injuries in training and matches were obtained from the Aspetar Injury and Illness Surveillance Program. No intervention was initiated between test occasions. A significant increase in the mean total score of 1.6 points (95% CI 1.0 to 2.2, p<0.001) was found from season 1 (22.2±4.1 (SD)) to season 2 (23.8±3.3). The variability was large, as shown by an intraclass correlation coefficient (ICC) of 0.24 (95% CI 0.11 to 0.36) and a minimal detectable change (MDC) of 8.7 points. Of the 220 players, 136 (61.8%) suffered a time-loss injury between the 2 tests. There was an improvement in mean total scores in the injured (+2.0±0.4 (SE), p<0.001) group but not in the uninjured group (+0.9±0.5, p=0.089). The variability from season 1 to season 2 was large both in the injured (ICC 0.25, 0.09 to 0.40, MDC 8.3) and uninjured (ICC 0.24, 0.02 to 0.43, MDC 9.1) groups. The 9+ demonstrated substantial intraindividual variability in the total score between 2 consecutive seasons, irrespective of injury. A change above 8 points is necessary to represent a real change in the 9+ test between seasons.

#11 Mechanical Player Load™ using trunk-mounted accelerometry in football: Is it a reliable, task- and player-specific observation?
Reference: J Sports Sci. 2016 Sep 6:1-8. [Epub ahead of print]
Authors: Barreira P, Robinson MA, Drust B, Nedergaard N, Raja Azidin RM, Vanrenterghem J
Summary: The aim of the present study was to examine reliability and construct convergent validity of Player Load™ (PL) from trunk-mounted accelerometry, expressed as a cumulative measure and an intensity measure (PL · min-1). Fifteen male participants twice performed an overground football match simulation that included four different multidirectional football actions (jog, side cut, stride and sprint) whilst wearing a trunk-mounted accelerometer inbuilt in a global positioning system unit. Results showed a moderate-to-high reliability as indicated by the intra-class correlation coefficient (0.806-0.949) and limits of agreement. Convergent validity analysis showed considerable between-participant variation (coefficient of variation range 14.5-24.5%), which was not explained from participant demographics despite a negative association with body height for the stride task. Between-task variations generally showed a moderate correlation between ranking of participants for PL (0.593-0.764) and PL · min-1 (0.282-0.736). It was concluded that monitoring PL® in football multidirectional actions presents moderate-to-high reliability, that between-participant variability most likely relies on the individual's locomotive skills and not their anthropometrics, and that the intensity of a task expressed by PL · min-1 is largely related to the running velocity of the task.





Latest research in football - week 35 - 2016

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 Common Anthropometric Measurements and Isokinetic Strength in Men's College Soccer Team
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):668. doi: 10.1249/01.mss.0000487004.11907.df.
Authors: Felton SD, Burkett PA, Cordova ML
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#2 Impact Of "Extra-time" On Performance And Physiological Responses To Simulated Soccer Match-play
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):667-8. doi: 10.1249/01.mss.0000487003.73788.9b.
Authors: Harper LD, Parker P, Hunter R, Goodall S, Thomas K, Howatson G, West DJ, Stevenson E, Russell M
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#3 Effect of Rest Time in Sprint Training in Young Soccer Players
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):667. doi: 10.1249/01.mss.0000487002.73788.d2.
Authors: Mazza JC, Festa RR, Groppo C, Ruffo L, Maggiolo L, Mangione P, Cosolito P, Grossi G
Download link:|ExpireAbsolute;source|Journals;ttl|1473662175881;payload|mY8D3u1TCCsNvP5E421JYK6N6XICDamxByyYpaNzk7FKjTaa1Yz22MivkHZqjGP4kdS2v0J76WGAnHACH69s21Csk0OpQi3YbjEMdSoz2UhVybFqQxA7lKwSUlA502zQZr96TQRwhVlocEp/sJ586aVbcBFlltKNKo+tbuMfL73hiPqJliudqs17cHeLcLbV/CqjlP3IO0jGHlHQtJWcICDdAyGJMnpi6RlbEJaRheGeh5z5uvqz3FLHgPKVXJzdKVgAgQT2Xde+Z+1EdY8MswkChdn/oaKSHzz572m32Mw=;hash|Gfd6z8EorUqOWYeIZiomlw==

#4 A Test Battery to Identify Elite Talent Among Youth International Soccer Players
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):667. doi: 10.1249/01.mss.0000487001.66165.2c.
Authors: O'Reilly J, Wong SH
Download link:|ExpireAbsolute;source|Journals;ttl|1473662274047;payload|mY8D3u1TCCsNvP5E421JYK6N6XICDamxByyYpaNzk7FKjTaa1Yz22MivkHZqjGP4kdS2v0J76WGAnHACH69s21Csk0OpQi3YbjEMdSoz2UhVybFqQxA7lKwSUlA502zQZr96TQRwhVlocEp/sJ586aVbcBFlltKNKo+tbuMfL73hiPqJliudqs17cHeLcLbV/CqjlP3IO0jGHlHQtJWcICDdAyGJMnpi6RlbEJaRheGeh5z5uvqz3FLHgPKVXJzdKVgAgQT2Xde+Z+1EdY8Ms85MawwtfLsaNSRiFaGpRss=;hash|YULjbeWuycURfTbumRYilg==

#5 Neuromuscular Fatigue In Response To 120 Minutes Of Soccer-specific Exercise
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):666-7. doi: 10.1249/01.mss.0000487000.89035.ed.
Authors: Goodall S, Thomas K, Hunter R, Parker P, Woolley G, Harper L, Stevenson E, West D, Russell M, Howatson G.
Download link:|ExpireAbsolute;source|Journals;ttl|1473662305533;payload|mY8D3u1TCCsNvP5E421JYK6N6XICDamxByyYpaNzk7FKjTaa1Yz22MivkHZqjGP4kdS2v0J76WGAnHACH69s21Csk0OpQi3YbjEMdSoz2UhVybFqQxA7lKwSUlA502zQZr96TQRwhVlocEp/sJ586aVbcBFlltKNKo+tbuMfL73hiPqJliudqs17cHeLcLbV/CqjlP3IO0jGHlHQtJWcICDdAyGJMnpi6RlbEJaRheGeh5z5uvqz3FLHgPKVXJzdKVgAgQT2Xde+Z+1EdY8Ms2OZ4KCUVnrCUJS+OcgcOy4=;hash|rvqqClLzDRr+NZ8rR7VpuQ==

#6 Heart Rate Variability And Autonomic Activity In A Nonfunctional Overreached Professional Soccer Player
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):666. doi: 10.1249/01.mss.0000486999.81412.ea.
Authors: Vilamitjana JJ, Lentini NA, Verde PE, Perez MF Jr
Download link:|ExpireAbsolute;source|Journals;ttl|1473662338577;payload|mY8D3u1TCCsNvP5E421JYK6N6XICDamxByyYpaNzk7FKjTaa1Yz22MivkHZqjGP4kdS2v0J76WGAnHACH69s21Csk0OpQi3YbjEMdSoz2UhVybFqQxA7lKwSUlA502zQZr96TQRwhVlocEp/sJ586aVbcBFlltKNKo+tbuMfL73hiPqJliudqs17cHeLcLbV/CqjlP3IO0jGHlHQtJWcICDdAyGJMnpi6RlbEJaRheGeh5z5uvqz3FLHgPKVXJzdKVgAgQT2Xde+Z+1EdY8MswDKIXv1XX+D8a0O/tpP4aI=;hash|x0d/3gotaPn4NNzMHdpOnw==

#7 Changes in Performance, HRV, and Inflammation Following an Individualized Soccer Specific Training Program
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):666. doi: 10.1249/01.mss.0000486998.81412.a3.
Authors: Berry NT, Cone JR, Ritsche K, Wideman L
Download link:,_HRV,_and_Inflammation.1992.pdf?token=method|ExpireAbsolute;source|Journals;ttl|1473662383616;payload|mY8D3u1TCCsNvP5E421JYK6N6XICDamxByyYpaNzk7FKjTaa1Yz22MivkHZqjGP4kdS2v0J76WGAnHACH69s21Csk0OpQi3YbjEMdSoz2UhVybFqQxA7lKwSUlA502zQZr96TQRwhVlocEp/sJ586aVbcBFlltKNKo+tbuMfL73hiPqJliudqs17cHeLcLbV/CqjlP3IO0jGHlHQtJWcICDdAyGJMnpi6RlbEJaRheGeh5z5uvqz3FLHgPKVXJzdKVgAgQT2Xde+Z+1EdY8Ms/vhfWL9H7EYHV3epZAq7ok=;hash|8cSBxbIxJJbV7qf+jmnoaw==

#8 Effects of Training on ACL Volume in Female Intercollegiate Soccer Athletes
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):492. doi: 10.1249/01.mss.0000486479.39854.47.
Authors: Kim G, Mele B, Myrick K, Feinn R, Gonzales R, Garbalosa JC
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#9 Cardiac Systolic And Diastolic Function During Incremental Exercise In Highly-trained Youth Soccer Players
Reference: Med Sci Sports Exerc. 2016 May;48(5 Suppl 1):479. doi: 10.1249/01.mss.0000486440.58987.51.
Authors: Unnithan V, Rowland T, George K, Oxborough D
Download link:|ExpireAbsolute;source|Journals;ttl|1473662458182;payload|mY8D3u1TCCsNvP5E421JYK6N6XICDamxByyYpaNzk7FKjTaa1Yz22MivkHZqjGP4kdS2v0J76WGAnHACH69s21Csk0OpQi3YbjEMdSoz2UhVybFqQxA7lKwSUlA502zQZr96TQRwhVlocEp/sJ586aVbcBFlltKNKo+tbuMfL73hiPqJliudqs17cHeLcLbV/CqjlP3IO0jGHlHQtJWcICDdAyGJMnpi6RlbEJaRheGeh5z5uvqz3FLHgPKVXJzdKVgAgQT2Xde+Z+1EdY8Mswpz/9YwNuOG4m30Q/BcWv0=;hash|4v4vd+BLy2ZpJbZZgBUKfg==

#10 MRI-Based Regional Muscle Use during Hamstring Strengthening Exercises in Elite Soccer Players
Reference: PLoS One. 2016 Sep 1;11(9):e0161356. doi: 10.1371/journal.pone.0161356. eCollection 2016.
Authors: Mendez-Villanueva A, Suarez-Arrones L, Rodas G, Fernandez-Gonzalo R, Tesch P, Linnehan R, Kreider R, Di Salvo V
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Summary: The present study examined site-specific hamstring muscles use with functional magnetic resonance imaging (MRI) in elite soccer players during strength training. Thirty-six players were randomized into four groups, each performing either Nordic hamstring, flywheel leg-curl, Russian belt or the hip-extension conic-pulley exercise. The transverse relaxation time (T2) shift from pre- to post-MRI were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. T2 values increased substantially after flywheel leg-curl in all regions of the BFl (from 9±8 to 16±8%), BFs (41±6-71±11%), and ST (60±1-69±7%). Nordic hamstring induced a substantial T2 increase in all regions of the BFs (13±8-16±5%) and ST (15±7-17±5%). T2 values after the Russian belt deadlift substantially increased in all regions of the BFl (6±4-7±5%), ST (8±3-11±2%), SM (6±4-10±4%), and proximal and distal regions of BFs (6±6-8±5%). T2 values substantially increased after hip-extension conic-pulley only in proximal and middle regions of BFl (11±5-7±5%) and ST (7±3-12±4%). The relevance of such MRI-based inter- and intra-muscle use in designing more effective resistance training for improving hamstring function and preventing hamstring injuries in elite soccer players should be explored with more mechanistic studies.

#11 No Relationship Between Hamstring Flexibility and Hamstring Injuries in Male Amateur Soccer Players: A Prospective Study
Reference: Am J Sports Med. 2016 Aug 31. pii: 0363546516664162. [Epub ahead of print]
Authors: van Doormaal MC, van der Horst N, Backx FJ, Smits DW, Huisstede BM
Summary: In soccer, although hamstring flexibility is thought to play a major role in preventing hamstring injuries, the relationship between hamstring flexibility and hamstring injuries remains unclear. The purpose of the study was to investigate the relationship between hamstring flexibility and hamstring injuries in male amateur soccer players. This study included 450 male first-class amateur soccer players (mean age, 24.5 years). Hamstring flexibility was measured by performing the sit-and-reach test (SRT). The relationship between hamstring flexibility and the occurrence of hamstring injuries in the following year, while adjusting for the possible confounding effects of age and previous hamstring injuries, was determined with a multivariate logistic regression analysis. Of the 450 soccer players, 21.8% reported a hamstring injury in the previous year. The mean (±SD) baseline score for the SRT was 21.2 ± 9.2 cm. During the 1-year follow-up period, 23 participants (5.1%) suffered a hamstring injury. In the multivariate analysis, while adjusting for age and previous injuries, no significant relationship was found between hamstring flexibility and hamstring injuries (P = .493). In this group of soccer players, hamstring flexibility (measured with the SRT) was not related to hamstring injuries. Age and previous hamstring injuries as possible confounders did not appear to influence this relationship. Other etiological factors need to be examined to further elucidate the mechanism of hamstring injuries.

#12 Dynamic balance is impaired after a match in young elite soccer players
Reference: Phys Ther Sport. 2016 May 21;22:11-15. doi: 10.1016/j.ptsp.2016.05.008. [Epub ahead of print]
Authors: Pau M, Mereu F, Melis M, Leban B, Corona F, Ibba G
Summary: The aim of this study is to assess the effect of actual match effort on dynamic balance abilities in young elite soccer players. Seventeen Under 15 male players who compete at national level participated in the study. Their dynamic balance was assessed by having them jump starting with both feet on the ground in a standing position and land on one foot only. Their vertical time to stabilization (vTTS) and postural sway were calculated before and after 35 min of an unofficial match. Postural sway was assessed on the basis of center-of-pressure (COP) trajectories. Parameters considered were sway area, COP displacements in the antero-posterior (AP) and medio-lateral (ML) directions and COP path length. After the match, a significant increase in vTTS (p = 0.007) COP path length (p = 0.001) and COP displacements in ML (p < 0.001) was observed. Such effects involve both non-dominant (vTTS, path length) and dominant limb (COP displacements). The physical effort associated with the match induces significant impairments of players' dynamic balance abilities. On the basis of such findings, coaches might consider integrating training sessions with specific balance exercises as well as performing injury-prevention routines even when players are fatigued, to better adapt them to match conditions.

#13 Changes of the psychophysical state and feeling of wellness of professional soccer players during pre-season and in-season periods
Reference: Res Sports Med. 2016 Aug 30:1-12. [Epub ahead of print]
Authors: Fessi MS, Nouira S, Dellal A, Owen A, Elloumi M, Moalla W
Summary: Perceived changes due to training monotony, strain, sleep, stress, fatigue, muscle soreness and the influence of specific training sessions on the affective valence were explored in professional soccer players. Seventeen players completed the Hooper questionnaire, the ratings of perceived exertion and feeling scale (FS) every training/match day before and during the soccer season. Higher players' training loads were recorded during pre-season when compared with in-season period (2558.1 ± 262.4 vs. 1642.8 ± 169.3 a.u., p < 0.01; respectively). The ratings of sleep, stress, fatigue and muscle soreness in pre-season were higher than those observed during in-season (p < 0.01) whereas the feeling score was lower (p < 0.01). Furthermore, training sessions, including technical/tactical work, induced an improved feeling score but linked with a lower training load when compared with sessions focus on physical emphasis (p < 0.01). Pre-season period of training induces a significantly more strenuous and exhausting demands on professional soccer players compared with the in-season period at the elite level.

#14 Relationship Between Internal Load Indicators And Changes On Intermittent Performance After The Preseason In Professional Soccer Players
Reference: J Strength Cond Res. 2016 Aug 22. [Epub ahead of print]
Authors: Campos-Vazquez MA, Toscano-Bendala FJ, Mora-Ferrera JC, Suarez-Arrones L.
Summary: The aim of this study was to examine the effects of accumulated internal training load during the preseason (4 weeks) on changes in the intermittent performance, in a professional soccer team. Twelve professionals soccer players (Mean±SD age 27.7±4.3 years; height: 177.1±6.2 cm; body mass: 73.1±5.2 kg; % body fat (Faulkner): 10.2±1.2) belonging to a Spanish second division team (2013-2014) participated in this study. The 30-15 intermittent fitness test was performed before and after the preseason, and the speed for the last period completed by each player was recorded (VIFT). During the preseason, the team alternated practice of training sessions (TRNs) with friendly matches (FMs). Session rating of perceived exertion (sRPE), heart rate (HR) and HR reserve were analized every TRN and FM in order to calculate internal training load (ITL: sRPE-TL, Edward's-TL and Edward's-TLres). The players' VIFT substantially increased after the preseason period (20.1±0.8 vs. 21.1±0.8 km·h; Effect Size [ES]=1.15±0.25; almost certainly). The average value of sRPE throughout FMs was substantially greater than the value of the TRNs (7.4±0.9 vs. 5.25±0.2; ES=2.31±2.45; almost certainly). sRPE-TL, practice volume and sum of RPE during the preseason were positively and largely correlated (r=0.70-0.75) with changes on intermittent performance. No relationships were found between HR-derived measures of exercise load and changes on intermittent fitness. The present results suggest that practice volume and subjective measures of TL, related better than HR-based TL methods to changes on intermittent performance after the preseason, in professional soccer players.





Champions League Prize Money

With the first game of the 2016/2017 UEFA Champions League group stage played I thought its time to shine some light on the possible prize money the clubs (possibly) earn.

As the picture indicates, a possible 62.2 mio Euros are possible with winning all games.

However, the so-called “market-pool” distribution will further increase the money that the clubs will receive. That means, based on their “market value” clubs will receive money accordingly to the proportion value of each TV market (Country/League). So the market-pool awarded to each country’s league will be distributed among the teams from that league according to their performance in previous league season and how many matches they will play in the given champions league season.

That means Real Madrid will earn more as Basel for example.

Secondly, depending on the number of teams from each country, the teams have to share.  For example clubs from Spain will have to share the market-pool, while Basel, as the only team from Suisse, will not need to share (a smaller amount however).






Latest research in football - week 34 - 2016

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 specificity of the Loughborough Intermittent Shuttle Test for recreational soccer players is independent of their intermittent running ability
Reference: Res Sports Med. 2016 Aug 22:1-12. [Epub ahead of print]
Authors: Coratella G, Beato M, Schena F
Summary: The aim of the present study was to evaluate whether or not recreational soccer players (SP) and non-soccer players (non-SP) with similar intermittent-running ability had similar physiological responses to a soccer match-simulation protocol. Twenty-two recreational SP and 19 fitness-matched non-SP participated. Yo-Yo level 1 assessed intermittent-running ability, while the Loughborough Intermittent Shuttle Test served as soccer match-simulation protocol. Heart rate (HR), blood lactate concentration [La-] and rating of perceived exertion (RPE) were recorded after each bout (1-5, plus an exhaustive task). SP had lower HR after the third, fourth and fifth bout, compared to non-SP. Similarly, SP had lower [La-] after the third, fourth and the fifth bout. SP also had lower RPE after the third, fourth and fifth bout. The appropriateness of intermittent-running ability as the main determinant of physical performance in SP was questioned.

#2 Effects of horizontal plyometric training volume on soccer players' performance
Reference: Res Sports Med. 2016 Aug 22:1-12. [Epub ahead of print]
Authors: Yanci J, Los Arcos A, Camara J, Castillo D, García A, Castagna C
Summary: The aim of this study was to examine the dose response effect of strength and conditioning programmes, involving horizontally oriented plyometric exercises, on relevant soccer performance variables. Sixteen soccer players were randomly allocated to two 6-week plyometric training groups (G1 and G2) differing by imposed (twice a week) training volume. Post-training G1 (4.13%; d = 0.43) and G2 (2.45%; d = 0.53) moderately improved their horizontal countermovement jump performance. Significant between-group differences (p < 0.01) in the vertical countermovement jump for force production time (T2) were detected post-training. No significant and practical (p > 0.05, d = trivial or small) post-training improvements in sprint, change of direction ability (CODA) and horizontal arm swing countermovement jump were reported in either group. Horizontal plyometric training was effective in promoting improvement in injury prevention variables. Doubling the volume of a horizontal plyometric training protocol was shown to have no additional effect over functional aspects of soccer players' performance.

#3 Periodontal status and serum creatine kinase levels among young soccer players: A preliminary report
Reference: Niger J Clin Pract. 2016 Sep-Oct;19(5):655-8. doi: 10.4103/1119-3077.188708.
Authors: Alshail F, Aljohar A, Alshehri M
Summary: It is hypothesized that soccer players with periodontal disease exhibit raised serum creatine kinase (CK) levels as compared to those without periodontal disease. We assessed the clinical gingival status and serum CK levels among young soccer players. Demographic data were collected through a structured questionnaire. Full mouth bleeding on probing (BOP) and probing pocket depth (PPD) were assessed. Blood samples (4 mL) were collected for measurement of serum CK levels. All blood samples were collected from a vein in the antecubital region. Total CK activities in serum were determined with an optimized spectrophotometric method. Statistical analysis was performed using one-way analysis of variance, and P< 0.05 was considered statistically significant. Twenty-seven male soccer players volunteered to participate in the present study. The mean age of the participants in Groups 1 (n = 14) and 2 (n = 13) were 18.2 ± 2.3 years and 19.1 ± 0.6 years, respectively. Mean scores of BOP were significantly higher among individuals in Group 2 (56.8%) compared with individuals in Group 1 (19.4%) (P < 0.001). Mean scores of PPD ≥4 mm were significantly higher among subjects in Group 2 (12.1%) as compared to individuals in Group 1 (0.8%) (P < 0.001). Levels of CK were significantly higher among individuals in Group 2 (292.7 U/L) as compared to those in Group 1 (52.3 U/L) (P < 0.01).

#4 The effect of slope on repeated sprint ability in young soccer players
Reference: Res Sports Med. 2016 Aug 18:1-11. [Epub ahead of print]
Authors: Padulo J, Ardigò LP, Attene G, Cava C, Wong DP, Chamari K, Migliaccio GM
Summary: This study aimed to describe a gradient repeated sprint ability (RSA) test in comparison with a standard level one by investigating performance, metabolic demand and muscular jumping performance as a proxy for running mechanics. Eighteen athletes performed two level RSA tests (40 m × 6) - for reliability evaluation - and one ±5% gradient RSA test, second leg downhill (RSAgrad). Rating of perceived exertion (RPE), blood lactate concentration (BLa) concentration, vertical jump heights were assessed as well. Level test measures resulted highly reliable (Intra-class correlation coefficient (ICC) ≥0.96). RSAgrad worsened only first sprints' performance (-2%) but not overall test performance (~45 s). RSAgrad resulted to be less deteriorating in terms of fatigue index (FI) (-36%), BLa (-23%), RPE (-11%), jumping performance (RSAgrad post-/pre-squat jump, countermovement jump heights (CMJh): -3%, -6%, respectively). RSAgrad could be used to diversify common training protocol without stressing excessively athletes' current metabolic-anaerobic capacity. Such physical conditioning procedures could improve acceleration/braking capability.

#5 Risk assessment of back pain in youth soccer players
Reference: Res Sports Med. 2016 Aug 18:1-12. [Epub ahead of print]
Authors: Haag TB, Mayer HM, Schneider AS, Rumpf MC, Handel M, Schneider C
Summary: The purpose of this study is to identify several responsible parameters for back pain (BP) in youth soccer players to create a risk assessment tool for early prevention. An iPad-based survey was used to screen for parameters in a cross-sectional study. This questionnaire includes items regarding anthropometric data, training habits and sports injuries and was put into practice with 1110 athletes. Sex (odds ratio (OR): 1.84), age group (1.48) and playing surface (1.56) were significantly associated with BP. A history of injuries especially to the spine and hip/groin increased the likelihood for evolving recurrent BP (1.74/1.40). Overall 15 factors seem to influence the appearance of pain and were integrated into a feasible nomogram. The nomogram provides a practical tool to identify the risks of developing BP for youth soccer players. Although most factors we identified are non-modifiable, this method allows to rank the importance of factors and especially their prevention treatments for athletes.

#6 High-intensity efforts in elite soccer matches and associated movement patterns, technical skills and tactical actions. Information for position-specific training drills
Reference: J Sports Sci. 2016 Aug 18:1-10. [Epub ahead of print]
Authors: Ade J, Fitzpatrick J, Bradley PS
Summary: This study aimed to translate movement patterns, technical skills and tactical actions associated with high-intensity efforts into metrics that could potentially be used to construct position-specific conditioning drills. A total of 20 individual English Premier League players' high-intensity running profiles were observed multiple times (n = 100) using a computerised tracking system. Data were analysed using a novel high-intensity movement programme across five positions (centre back [CB], full-back [FB], central midfielder [CM], wide midfielder [WM] and centre forward [CF]). High-intensity efforts in contact with the ball and the average speed of efforts were greater in WMs than CBs, CMs and CFs (effect sizes [ES]: 0.9-2.1, P < 0.05). WMs produced more repeated efforts than CBs and CMs (ES: 0.6-1.3, P < 0.05). In possession, WMs executed more tricks post effort than CBs and CMs (ES: 1.2-1.3, P < 0.01). FBs and WMs performed more crosses post effort than other positions (ES: 1.1-2.0, P < 0.01). Out of possession, CFs completed more efforts closing down the opposition (ES: 1.4-5.0, P < 0.01) but less tracking opposition runners than other positions (ES: 1.5-1.8, P < 0.01). CFs performed more arc runs before efforts compared to CBs, FBs and WMs (ES: 0.9-1.4, P < 0.05), however, CBs completed more 0-90° turns compared to FBs, CMs and WMs (ES: 0.9-1.1, P < 0.01). The data demonstrate unique high-intensity trends in and out of possession that could assist practitioners when devising position-specific drills.

#7 Physical and technical performances are not associated with tactical prominence in U14 soccer matches
Reference: Res Sports Med. 2016 Aug 17:1-11. [Epub ahead of print]
Authors: Clemente FM, Figueiredo AJ, Martins FM, Mendes RS, Wong DP
Summary: The aim of this study was to analyse the association between physical/technical variables and the tactical prominence variables in U14 soccer matches. Twenty-two young amateur soccer players (13.5 [Formula: see text] 0.5 years old, 5.4 [Formula: see text] 0.5 years of practice, 163.3 [Formula: see text] 9.8 cm in body height) from two teams of the Portuguese regional league volunteered for the study. Our results showed positive and moderate correlation between dribbling test and betweenness centrality (r = 0.324; p = 0.142), and negative moderate correlation between %fatigue index and betweenness centrality (r = -0.390; p = 0.073). Physical and technical variables had no statistical differences among tactical positions. Nevertheless, when tactical prominence of players from four tactical positions were compared, significant differences were found in terms of degree prestige (p = 0.001) and degree centrality (p = 0.002). This pilot study did not find strong correlations between physical/technical levels and tactical prominence in soccer matches.

#8 Time Trends in Incidence and Severity of Injury Among Collegiate Soccer Players in the United States: NCAA Injury Surveillance System, 1990-1996 and 2004-2009
Reference: Am J Sports Med. 2016 Aug 15. pii: 0363546516659879. [Epub ahead of print]
Authors: Chandran A, Barron MJ, Westerman BJ, DiPietro L
Summary: A number of sociocultural and environmental changes have occurred over the past several decades that may affect the risk of injury among young athletes playing soccer. The purpose of the study was to identify trends in injury incidence and severity between 2 time periods (1990-1996 and 2004-2009) in both male and female National Collegiate Athletic Association (NCAA) soccer players in the United States. Data were analyzed from the NCAA Injury Surveillance System. The rate ratio (RR), along with the 95% Wald CI, compared incidence density in 2004-2009 relative to that in 1990-1996. Overall sex-pooled injury rates were significantly lower in the 2004-2009 cohort compared with the 1990-1996 cohort (RR = 0.88; 95% CI = 0.86-0.91), and this was true for almost every category of injury studied. We observed only 1 significant sex difference between the time periods with regard to noncontact injuries, as men experienced a significant increase in rate of noncontact injuries between 1990-1996 and 2004-2009 (RR = 1.09; 95% CI = 1.02-1.17), whereas women experienced a significant decrease (RR = 0.70; 95% CI = 0.67-0.75). These surveillance data show decreasing trends in collegiate soccer injuries. Whether these decreases are attributable to greater resources being allocated toward athlete health, injury management, or the safety of the playing environment cannot be determined. Given the prominence of soccer play in the United States, public health efforts should promote the use of this surveillance system to better inform and evaluate injury prevention practices and policies directed toward player safety.

#9 Kicking Velocity and Effect on Match Performance When using a Smaller, Lighter Ball in Women's Football
Reference: Int J Sports Med. 2016 Aug 23. [Epub ahead of print]
Authors: Andersen TB, Krustrup P, Bendiksen M, Orntoft CO, Randers MB, Pettersen SA
Summary: The present study evaluated the effect of a smaller, lighter ball on kicking speed and technical-tactical and physical match performance in high-level adult female footballers. In the laboratory test setting, the peak ball velocity was 6% higher with the new ball (NB) than the standard ball (SB) (26.5±0.5 vs. 25.1±0.5 m·s-1, p<0.05). However, during match-play, no differences were observed in mean heart rate (87±5 vs. 87±5%HRmax; p>0.05), blood lactate (90 min: 4.7±1.7 and 4.0±1.7 mmol·l-1; p>0.05), total distance covered (10.6±0.9 and 10.4±0.8 km; p>0.05), intense running (>16 km/h) (2.08±0.42 and 1.94±0.38 km; p>0.05) and match-induced decrement in Yo-Yo IR1 performance (28 vs. 31%, respectively, p<0.05) using NB compared to SB. Likewise, no difference was observed in the number of short, medium-range or long passes during matches played with the 2 ball types, and there was no difference in passing success rate (NB: 68±1% and SB: 68±1%, p>0.05). In conclusion, high-level adult female footballers had a higher kicking speed when using a smaller, lighter ball, but no differences were observed during match-play with the 2 ball types in respect of technical-tactical and physical match performance. The physical loading was high for the players when playing with both ball types.

#10 Tactical expertise assessment in youth football using representative tasks
Reference: Springerplus. 2016 Aug 9;5(1):1301. doi: 10.1186/s40064-016-2955-1. eCollection 2016.
Authors: Serra-Olivares J, Clemente FM, González-Víllora S
Download link:
Summary: Specific football drills improve the development of technical/tactical and physical variables in players. Based on this principle, in recent years it has been possible to observe in daily training a growing volume of small-sided and conditioned games. These games are smaller and modified forms of formal games that augment players' perception of specific tactics. Despite this approach, the assessment of players' knowledge and tactical execution has not been well documented, due mainly to the difficulty in measuring tactical behavior. For that reason, this study aims to provide a narrative review about the tactical assessment of football training by using representative tasks to measure the tactical expertise of youth football players during small-sided and conditioned games. This study gives an overview of the ecological approach to training and the principles used for representative task design, providing relevant contribution and direction for future research into the assessment of tactical expertise in youth football.

#11 High prevalence of dysfunctional, asymmetrical, and painful movement in elite junior Australian Football players assessed using the Functional Movement Screen
Reference: J Sci Med Sport. 2016 May 21. pii: S1440-2440(16)30064-0. doi: 10.1016/j.jsams.2016.05.003. [Epub ahead of print]
Authors: Fuller JT, Chalmers S, Debenedictis TA, Townsley S, Lynagh M, Gleeson C, Zacharia A, Thomson S, Magarey M
Summary: The purpose of this study was to describe the prevalence of dysfunctional, asymmetrical, and painful movement in junior Australian Football players using the Functional Movement Screen (FMS). Elite junior male Australian Football players (n=301) aged 15-18 years completed pre-season FMS testing. The FMS consists of 7 sub-tests: deep squat, hurdle step, in-line lunge, shoulder mobility, active straight leg raise, trunk stability push-up (TSPU) and rotary stability. The shoulder mobility, TSPU, and rotary stability tests were combined with an accompanying clearing test to assess pain. Each sub-test was scored on an ordinal scale from 0 to 3 and summed to give a composite score out of 21. Composite scores ≤14 were operationally defined as indicating dysfunctional movement. Players scoring differently on left and right sides were considered asymmetrical. Players reported whether they missed any games due to injury in the preceding 22 game season. Sixty percent of players (n=182) had composite scores ≤14, 65% of players (n=196) had at least one asymmetrical sub-test, and 38% of players (n=113) had at least one painful sub-test. Forty-two percent of players (n=126) missed at least one game in the previous season due to injury. Previous injury did not influence composite score (p=0.951) or asymmetry (p=0.629). Players reporting an injury during the previous season were more likely to experience pain during FMS testing (odds ratio 1.97, 95% confidence interval 1.23-3.18; p=0.005). Junior Australian Football players demonstrate a high prevalence of dysfunctional, asymmetrical, and painful movement during FMS testing.

#12 Injuries in professional male football players in Kosovo: a descriptive epidemiological study
Reference: BMC Musculoskelet Disord. 2016 Aug 12;17:338. doi: 10.1186/s12891-016-1202-9.
Authors: Shalaj I, Tishukaj F, Bachl N, Tschan H, Wessner B, Csapo R
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Summary: The incidence and severity of football-related injuries has been found to differ strongly between professional leagues from different countries. The aims of this study were to record the incidence, type and severity of injuries in Kosovarian football players and investigate the relationship between injury incidence rates (IRs), players' age and playing positions. Players' age, anthropometric characteristics and playing positions, training and match exposure as well as injury occurrences were monitored in 11 teams (143 players) of Kosovo's top division during the 2013/14 season. The exact type, severity and duration of football-related injuries were documented following International Federation of Football Associations (FIFA) recommendations. A total of 272 injuries were observed, with traumatic injuries accounting for 71 %. The overall injury IR was 7.38 (CI: 7.14, 7.63) injuries per 1,000 exposure hours and ~11x lower during training as opposed to matches. Strains and ruptures of thigh muscles, ligamentous injuries of the knee as well as meniscus or other cartilage tears represented the most frequent differential diagnoses. While no statistical differences were found between players engaged in different playing positions, injury IR was found to be higher by 10-13 % in younger (IR = 7.63; CI: 7.39, 7.87) as compared to middle-aged (IR = 6.95; CI: 6.41, 7.54) and older players (IR = 6.76; CI: 5.71, 8.00). The total injury IR in elite football in Kosovo is slightly lower than the international average, which may be related to lesser match exposure. Typical injury patterns agree well with previously reported data. Our finding that injury IR was greater in younger players is related to a higher rate of traumatic injuries and may indicate a more aggressive and risky style of play in this age group.





Europe’s Top 20 – The clubs with the most spectators

Below is a list of Europe’s football clubs ranked based on their average spectator attendance for the 2015/2016 season.

Interestingly, 9 clubs are from Germany, 4 from England, 3 from Spain, 2 from Netherlands, 1 from France and 1 from Portugal.


#1: Borussia Dortmund - 80.761
#2: FC Barcelona - 79.464
#3: Manchester United - 75.286
#4: FC Bayern München - 75.018
#5: Real Madrid - 70.411
#6: FC Schalke 04 - 61.077
#7: FC Arsenal - 59.944
#8: Manchester City - 54.041
#9: Hamburger SV - 53.763
#10: Borussia Mönchengladbach - 51.393
#11: Benfica Lissabon - 50.322
#12: VfB Stuttgart - 50.031
#13: Newcastle United - 49.754
#14: Ajax Amsterdam - 49.206
#15: 1. FC Köln - 48.322
#16: Feyenoord Rotterdam - 47.412
#17: Hertha BSC - 46.846
#18: Eintracht Frankfurt - 46.650
#19: Atletico Madrid - 46.624
#20: PSG – 46.160






Latest research in football - week 31 - 2016

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 Motor Subsystem as a Predictor of Success in Young Football Talents: A Person-Oriented Study
Reference: PLoS One. 2016 Aug 10;11(8):e0161049. doi: 10.1371/journal.pone.0161049. eCollection 2016.
Authors: Zibung M, Zuber C, Conzelmann A
Download link:
Summary: Motor tests play a key role in talent selection in football. However, individual motor tests only focus on specific areas of a player's complex performance. To evaluate his or her overall performance during a game, the current study takes a holistic perspective and uses a person-oriented approach. In this approach, several factors are viewed together as a system, whose state is analysed longitudinally. Based on this idea, six motor tests were aggregated to form the Motor Function subsystem. 104 young, top-level, male football talents were tested three times (2011, 2012, 2013; Mage, t2011 = 12.26, SD = 0.29), and their overall level of performance was determined one year later (2014). The data were analysed using the LICUR method, a pattern-analytical procedure for person-oriented approaches. At all three measuring points, four patterns could be identified, which remained stable over time. One of the patterns found at the third measuring point identified more subsequently successful players than random selection would. This pattern is characterised by above-average, but not necessarily the best, performance on the tests. Developmental paths along structurally stable patterns that occur more often than predicted by chance indicate that the Motor Function subsystem is a viable means of forecasting in the age range of 12-15 years. Above-average, though not necessary outstanding, performance both on fitness and technical tests appears to be particularly promising. These findings underscore the view that a holistic perspective may be profitable in talent selection.

#2 Extra-articular tenodesis combined with an anterior cruciate ligament reconstruction in acute anterior cruciate ligament tear in elite female football players
Reference: Int Orthop. 2016 Aug 10. [Epub ahead of print]
Authors: Guzzini M, Mazza D, Fabbri M, Lanzetti R, Redler A, Iorio C, Monaco E, Ferretti A
Summary: The growing popularity of elite soccer among female participants has led to increased incidents of anterior cruciate ligament (ACL) ruptures. Many authors underline a positive glide after ACL reconstruction (ACLR), especially in women. In fact, an isolated intra-articular ACLR may be inadequate to control rotational instability after a combined injury of the ACL and the peripheral structures of the knee. Extra-articular procedures are sometimes used in primary cases displaying excessive antero-lateral rotatory instability. The purpose of this case series was to report subjective and objective outcomes after combined ACL and lateral extra-articular tenodesis (LET) with a minimum 4-year follow-up in a selected high-risk population of elite female football players. Between January 2007 and December 2010, 16 elite Italian female football players were included in the study. All patients underwent the same surgical technique: anatomical ACLR with autogenous semitendinosus and gracilis tendons. After the intra-articular reconstruction was performed, an additional extra-articular MacIntosh modified Coker-Arnold procedure was carried out. Patients were assessed pre- and post-operatively with the subjective and objective International Knee Documentation Committee (IKDC) evaluation form, Tegner activity scale (TAS) and Lysholm score. Joint laxity was assessed with KT-1000 by measuring the side-to-side (S/S) differences in displacement at manual maximum (mm) testing. At a mean follow-up of 72.6 ± 8.1 months, two independent examiners reviewed all players. All of the patients had a fully recovered range of motion. Lachman test was negative in all patients (100 %). The evaluation of joint laxity and clinical evaluation showed a statistically significant improvement. No patients experienced complication or a re-rupture. The rationale of combining extra-articular procedures with ACLR is to restrict the internal rotation of the reconstructed knee, taking advantage of its long lever arm and thus providing more stability in the rotational axis and preventing the ACL graft from undergoing further excessive strain. The combination of an LET with ACLR in elite female football players demonstrated excellent results in terms of subjective scales, post-operative residual laxity and re-rupture rate with no complication, and a complete return to sport activity.

#3 Dietary intake according to hydration status in 9-10 year-old soccer players
Reference: Nutr Hosp. 2016 Jul 13;33 Suppl 3:315. doi: 10.20960/nh.315.
Authors: Rodriguez L, Azevedp AR, Seabra A, Padrao P, Moreira P
Summary: Children have an increased risk of voluntary dehydration especially during physical activity which may increase the risk of non-compensating water losses. The aim of this study was to assess the hydration status and its relation to food intake in a children group of soccer players. A sample of 36 boys aged 9-10 years was included in this study; 30 completed a 24 h urine collection. Participants completed a 24 h urine collection; a 24 hours food recall corresponding to the day of urine collection was applied, weight and height were measured and parents/caregivers fi lled a lifestyle and socio-demographic questionnaire. The free water reserve (FWR [ml/24 h] = urine volume [ml/24 h] - obligatory urine volume [ml/24 h]) was used to assess the hydration status. Food and beverage groups were created and models of unconditional logistic regression were fi tted in order to estimate the magnitude of the association between the hydration status and diet. Forty three per cent of participants were classifi ed as at risk of hypohydration. Children who reported a high fruit and vegetables intake (above the median) were at decreased risk of hypohydration (OR = 0.19, 95% CI 0.04-0.94, p = 0.041), compared to children who reported a low fruit and vegetables intake. Almost half of the children were at risk of hypohydration. Our results suggested that water food sources such as fruit and vegetables may contribute to euhydration.

#4 Ethnic Differences in Bony Hip Morphology in a Cohort of 445 Professional Male Soccer Players
Reference: Am J Sports Med. 2016 Aug 4. pii: 0363546516656163. [Epub ahead of print]
Authors: Mosler AB, Crossley KM, Waarsing JH, Jomaah N, Weir A, Hölmich P, Agricola R
Summary: Participation in high-impact athletic activities has recently been associated with a higher prevalence of cam deformity. Bony hip morphology has also emerged as an important factor in the development of hip osteoarthritis. However, it is unknown whether bony morphology differs between ethnicities in athletes participating in high-impact sports. The purpose was to investigate whether the prevalence of specific bony hip morphological abnormalities differed between professional male soccer players of diverse ethnic backgrounds. Professional male soccer players from an entire league attending preparticipation screening were invited to participate in this study. Ethnicity was registered, and standardized radiographs of anteroposterior pelvic and Dunn views were obtained. Cam and pincer deformity, and acetabular dysplasia were quantified using the alpha angle, triangular index, and lateral center-edge angle (LCEA). Regression analyses with generalized estimating equations were used to determine prevalence differences in bony hip morphology. A total of 445 male soccer players (890 hips; mean age ± SD, 25 ± 4.9 years) participated in the study, representing the following ethnic groups: Arabic (59%), black (24%), Persian (7%), white (6%), East Asian (2%), and other (2%). The prevalence of cam deformity (alpha angle >60°) ranged from 57.5% to 71.7% across 4 of the groups, but East Asians had a significantly lower prevalence (18.8%; P ≤ .032). A large cam deformity (alpha angle >78°) was more prevalent in white (33.3%) compared with black soccer players (17.8%; P = .041) and was absent in East Asian players. Pincer deformity (LCEA >40°) was uncommon (3%) in all ethnicities. The prevalence of acetabular dysplasia (LCEA <20°) ranged from 8.0% to 16.7%, apart from the white group, in which prevalence was only 1.9% (P = .03). The prevalence of a cam deformity and acetabular dysplasia differed between ethnicities in this cohort of professional male soccer players. These findings suggest that there may be ethnic differences in both acetabular morphology and femoral bony response to athletic load

#5 Holistic Patterns as an Instrument for Predicting the Performance of Promising Young Soccer Players - A 3-Years Longitudinal Study
Reference: Front Psychol. 2016 Jul 27;7:1088. doi: 10.3389/fpsyg.2016.01088. eCollection 2016.
Authors: Zuber C, Zibung M, Conzelmann A
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Summary: Multidimensional and dynamic talent models represent the current state of the art, but these demands have hardly ever been implemented so far. One reason for this could be the methodological problems associated with these requirements. This paper will present a proposal for dealing with this, namely for examining the development of young soccer players holistically. The patterns formed by the constructs net hope, motor abilities, technical skills and biological maturity were examined, as well as the way in which these holistic patterns are related to subsequent sporting success. 119 young elite soccer players were questioned and tested three times at intervals of 1 year, beginning at the age of 12. At the age of 15, the level of performance reached by the players was determined. At all three measuring points, four patterns were identified, which displayed partial structural and high individual stability. The highly skilled players, scoring above average on all factors - but not necessarily those having the highest overall scores - were significantly more likely to advance to the highest level of performance. Failure-fearing fit players, i.e., physically strong, early developed players but with some technical weaknesses, have good chances of reaching the middle performance level. In contrast, none of the achievement-oriented, highly skilled, late-matured or late-matured, low skilled players reached the highest performance level. The results indicate the importance of holistic approaches for predicting performance among promising soccer talents in the medium-term and thus provide valuable clues for their selection and promotion.

#6 Shoulder injuries in soccer goalkeepers: review and development of a FIFA 11+ shoulder injury prevention program
Reference: Open Access J Sports Med. 2016 Aug 8;7:75-80. doi: 10.2147/OAJSM.S97917. eCollection 2016.
Authors: Ejnisman B, Barbosa G, Andreoli CV, de Castro Pochini A, Lobo T, Zogaib R, Cohen M, Bizzini M, Dvorak J
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Summary: In the last years, shoulder injuries have represented an increasing health problem in soccer players. The goalkeepers are more exposed to shoulder disorders than other field players. Injury prevention exercises for upper limbs were cited in few studies involving throwing athletes, but we know that goalkeepers need a specific program. The purpose of this study is to describe the development of an adapted Fédération Internationale de Football Association (FIFA) 11+ program, namely the FIFA 11+ shoulder, which targets the prevention of shoulder injuries in soccer goalkeepers. The FIFA 11+ shoulder program is structured into three parts: general warming-up exercises, exercises to improve strength and balance of the shoulder, elbow, wrist, and finger muscles, and advanced exercises for core stability and muscle control. The exercises were selected based on recommendations from studies demonstrating high electromyographic activity.

#7 Jump Training in Youth Soccer Players: Effects of Haltere Type Handheld Loading
Reference: Int J Sports Med. 2016 Aug 24. [Epub ahead of print]
Authors: Rosas F, Ramirez-Campillo R, Diaz D, Abad-Colil F, Martinez-Salazar C, Caniuqueo A, Cañas-Jamet R, Loturco I, Nakamura FY, McKenzie C, Gonzalez-Rivera J, Sanchez-Sanchez J, Izquierdo M
Summary: The aim of this study was to compare the effects of a jump training program, with or without haltere type handheld loading, on maximal intensity exercise performance. Youth soccer players (12.1±2.2 y) were assigned to either a jump training group (JG, n=21), a jump training group plus haltere type handheld loading (LJG, n=21), or a control group following only soccer training (CG, n=21). Athletes were evaluated for maximal-intensity performance measures before and after 6 weeks of training, during an in-season training period. The CG achieved a significant change in maximal kicking velocity only (ES=0.11-0.20). Both jump training groups improved in right leg (ES=0.28-0.45) and left leg horizontal countermovement jump with arms (ES=0.32-0.47), horizontal countermovement jump with arms (ES=0.28-0.37), vertical countermovement jump with arms (ES=0.26), 20-cm drop jump reactive strength index (ES=0.20-0.37), and maximal kicking velocity (ES=0.27-0.34). Nevertheless, compared to the CG, only the LJG exhibited greater improvements in all performance tests. Therefore, haltere type handheld loading further enhances performance adaptations during jump training in youth soccer players.

#8 Gaze Control in One Versus One Defensive Situations in Soccer Players With Various Levels of Expertise
Reference: Percept Mot Skills. 2016 Aug 23. pii: 0031512516664903. [Epub ahead of print]
Authors: Krzepota J, Stępiński M, Zwierko T
Summary: Experienced and less experienced soccer players were compared in terms of their gaze behavior (number of fixations, fixation duration, number of fixation regions, and distribution of fixations across specific regions) during frontal 1 vs. 1 defensive situations. Twenty-four men (eight experienced soccer players, eight less experienced players and eight non-players) watched 20 video clips. Gaze behavior was registered with an Eye Tracking System. The video scenes were analyzed frame-by-frame. Significant main effect of the group (experience) was observed for the number of fixation regions. Experienced soccer players had a lower number of fixation regions than the non-soccer players. Moreover, the former group presented with significantly larger percentage of fixations in the ball/foot region. These findings suggest that experienced players may use a more efficient search strategy than novices, involving fixation on a lesser number of areas in specific locations.

#9 Effects Of Different Combinations Of Strength, Power, And Plyometric Training On The Physical Performance Of Elite Young Soccer Players
Reference: J Strength Cond Res. 2016 Aug 18. [Epub ahead of print]
Authors: Kobal R, Loturco I, Barroso R, Gil S, Cuniyochi R, Ugrinowitsch C, Roschel H, Tricoli V.
Summary: The combination of strength (ST) and plyometric training (PT) has been shown to be effective for improving sport specific performance. However, there is no consensus about the most effective way to combine these methods in the same training session, in order to produce greater improvements in neuromuscular performance of soccer players. Thus, the purpose of this study was to compare the effects of different combinations of ST and PT sequences on strength, jump, speed, and agility capacities of elite young soccer players. Twenty-seven soccer players (age: 18.9±0.6 years) participated in an 8-week resistance training program and were divided into three groups: complex training-CP (ST before PT), traditional training-TD (PT before ST), and contrast training-CT (ST and PT performed alternately, set-by-set). The experimental design took place during the competitive period of the season. The ST was composed of half-squat exercises performed at from 60 to 80% of 1RM; the PT was composed of drop jump exercises executed in a range from 30 to 45 cm. After the experimental period, the maximum dynamic strength (Half-squat 1RM) and vertical jump ability (countermovement jump height) increased similarly and significantly in the CP, TD, and CT (48.6, 46.3, and 53% and 13, 14.2 and 14.7%, respectively). Importantly, whereas the TD group presented a significant decrease in sprinting speed in 10- (7%) and 20-m (6%), the other groups did not show this response. Furthermore, no significant alterations were observed in agility performance in any experimental group. In conclusion, in young soccer players, different combinations/sequences of ST and PT sets result in similar performance improvements in muscle strength and jump ability. However, it is suggested that the use of the CP and CT methods are more indicated to maintain/maximize the sprint performance of these athletes.

#10 Exercise intensity and technical demands of small-sided soccer games for under-12 and under-14 players: effect of area per player
Reference: J Strength Cond Res. 2016 Aug 18. [Epub ahead of print]
Authors: Martone D, Giacobbe M, Capobianco A, Imperlini E, Mancini A, Capasso M, Buono P, Orrù S.
Summary: The aim of the present study was to evaluate the effects of six different area per player (AP) on Exercise Intensity (EI)-measured during SSGs and expressed as percentage of maximal heart rate (%MHR)-and Technical Actions (TAs)-involvement with the ball, crosses, headers, tackles, shots on goal, dribbling, passing, and target passing-in U-12 and U-14 soccer players during Small-Sided Games (SSGs). Seventeen male U-12 soccer players (age 10.0±0.5yrs, body mass 39.3±5.3kg, and height 143.8±4.6cm) and sixteen male U-14 soccer players (age 13.2±0.3yrs, body mass 46.6±11.9kg, and height 154.8±8.5cm) performed SSGs with different AP: 40, 50, 66.7, 90, 112.5 and 150m2. Our results indicate that at larger AP the U-12 group's mean EI values were significantly higher than those at smaller AP (p<0.05); in addition inter-group comparison showed that EI was higher in U-12 than in U-14 players when AP of 112.5 and 150m2 were considered (p<0.05). TA analysis evidenced that, moving from smaller to larger AP, U-14 players adapted better to AP changes. In conclusion, these results suggest that AP influences differently EI and TAs in U-12 and U-14 players. Our results could be taken in to account by conditioning coaches in order to better tailor the physiological and/or technical training in young players through the modulation of AP.

#11 Who runs the fastest? Anthropometric and physiological correlates of 20 m sprint performance in male soccer players
Reference: Res Sports Med. 2016 Aug 22:1-11. [Epub ahead of print]
Authors: Nikolaidis PT, Ruano MA, de Oliveira NC, Portes LA, Freiwald J, Leprêtre PM, Knechtle B
Summary: The aim of the present study was to examine the relationship of 20 m sprint performance with anthropometrical and physiological parameters in male soccer players. A hundred and 81 soccer players from the region of Athens (age 23.4 ± 5.0 yrs, body mass 73.4 ± 7.7 kg, height 180.0 ± 5.9 cm, body fat (BF) 14.4 ± 3.6%), classified into quartiles according to 20 m sprint time (group A, 2.84-3.03 s; group B, 3.04-3.09 s; group C, 3.10-3.18 s; group D, 3.19-3.61 s), participated. Soccer players in group A were younger and had better performance in vertical jumps and in the Wingate anaerobic test (WAnT, p < 0.05). Sprint time correlated to age (r = 0.27), body mass (r = 0.23), body height (r = 0.20), BF (r = 0.23), vertical jumps (-0.58 ≤ r ≤ -0.50) and the WAnT (-0.45 ≤ r ≤ -0.30, p < 0.05). In summary, the magnitude of correlations of sprint time with measures of lower limbs muscle strength and power (WAnT and jumps) was larger than with anthropometric measures (body mass and BF).