Latest research in football - week 47 - 2021

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 Examining Internal and External Physical Workloads Between Training and Competitive Matches Within Collegiate Division I Men's Soccer

Reference: J Strength Cond Res. 2021 Sep 29. doi: 10.1519/JSC.0000000000004149. Online ahead of print.

Authors: Travis Anderson, William M Adams, Kerry J Martin, Laurie Wideman

Summary: A direct analysis comparing differences in the demands of competition relative to in-season training in Division I collegiate soccer players has yet to be reported. Thus, the primary purpose of this study was to compare the absolute and relative internal and external workloads measured during training with competitive matches. Twenty-six male college soccer players were monitored over 2 consecutive seasons using a GPS and heart rate (HR) telemetry system. Differences between outdoor training sessions and competitive matches were analyzed for internal and external absolute and relative training workloads. Differences in training workloads between the 3 days before a match were also analyzed. Absolute time in HR zone 4 (80-89% of HRmax) and 5 (90-100% of HRmax); accelerations in zone 1 (0.50-0.99 m·s-2), zone 2 (1.00-1.99 m·s-2), and zone 3 (2.00-2.99 m·s-2); all negative acceleration zones; training load; and estimated energy expenditure were greater in competition than training (p < 0.05). By contrast, when comparing training and competition values using metrics relative to session duration, relative workload in trainings were greater than competition for HR zone 1 (50-59% of HRmax), zone 2 (60-69% of HRmax), zone 3 (70-79% of HRmax), and zone 4 (80-89% of HRmax) and all acceleration and negative acceleration zones. In addition, absolute training workloads were generally greatest 3 days prior (p < 0.01), but not different 2 days before the competitive match. Absolute physical workloads of competition are significantly greater than those achieved during training; however, these differences and impact on the physical condition of players are mitigated by the greater relative workloads achieved during training. These results provide meaningful metrics that may lead to insights into proper conditioning and in-season workload management for Division I collegiate soccer programs.



#2 Prediction of Hamstring Injuries in Australian Football Using Biceps Femoris Architectural Risk Factors Derived From Soccer

Reference: Am J Sports Med. 2021 Sep 30;3635465211041686. doi: 10.1177/03635465211041686.

Authors: Connor Lee Dow, Ryan G Timmins, Joshua D Ruddy, Morgan D Williams, Nirav Maniar, Jack T Hickey, Matthew N Bourne, David A Opar

Summary: Hamstring strain injuries are the most common injuries in team sports. Biceps femoris long head architecture is associated with the risk of hamstring injury in soccer. To assess the overall predictive ability of architectural variables, risk factors need to be applied to and validated across different cohorts. The aim was to assess the generalizability of previously established risk factors for a hamstring strain injury (HSI), including demographics, injury history, and biceps femoris long head (BFlh) architecture to predict HSIs in a cohort of elite Australian football players. Demographic, injury history, and BFlh architectural data were collected from elite soccer (n = 152) and Australian football (n = 169) players at the beginning of the preseason for their respective competitions. Any prospectively occurring HSIs were reported to the research team. Optimal cut points for continuous variables used to determine an association with the HSI risk were established from previously published data in soccer and subsequently applied to the Australian football cohort to derive the relative risk (RR) for these variables. Logistic regression models were built using data from the soccer cohort and utilized to estimate the probability of an injury in the Australian football cohort. The area under the curve (AUC) and Brier score were the primary outcome measures to assess the performance of the logistic regression models. A total of 27 and 30 prospective HSIs occurred in the soccer and Australian football cohorts, respectively. When using cut points derived from the soccer cohort and applying these to the Australian football cohort, only older athletes (aged ≥25.4 years; RR, 2.7 [95% CI, 1.4-5.2]) and those with a prior HSI (RR, 2.5 [95% CI, 1.3-4.8]) were at an increased risk of HSIs. Using the same approach, height, weight, fascicle length, muscle thickness, pennation angle, and relative fascicle length were not significantly associated with an increased risk of HSIs in Australian football players. The logistic regression model constructed using age and prior HSIs performed the best (AUC = 0.67; Brier score = 0.14), with the worst performing model being the one that was constructed using pennation angle (AUC = 0.53; Brier score = 0.18). Applying cut points derived from previously published data in soccer to a dataset from Australian football identified older age and prior HSIs, but none of the modifiable HSI risk factors, to be associated with an injury. The transference of HSI risk factor data between soccer and Australian football appears limited and suggests that cohort-specific cut points must be established.



#3 The knee function of the soccer players after ACLR is comparable with non-injured controls: A case-control study

Reference: J Orthop Surg (Hong Kong). Sep-Dec 2021;29(3):23094990211036101. doi:10.1177/23094990211036101.

Authors: Marcin E Domzalski, Filip Pieta, Katarzyna Przybylak

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Summary: Many studies report a high primary success rate of ACL reconstruction (ACLR), with an increased risk of decline in knee performance correlating with the time passed since surgery. Only one study has compared male soccer players after ACLR to a matched control group of uninjured players in terms of their return to sport and performance. The purpose of this cross-sectional case-control study was to determine the knee performance between soccer players after ACLR and control group matched by age, sex, and professional experience. All the male professional soccer players aged 18-36 years at the time of injury, who sustained an ACL tear while playing league soccer in Poland between January 2008 and December 2011 were contacted and compared with age and experience-matched healthy control group selected from professional football players. KOOS, IKDC-2000, Lysholm and SF-36 scales were used for comparison. The average follow-up was 7.9 years (range 6-9 years). The ACL-injured soccer players scored significantly lower in IKDC and Lysholm scores compared with the reference group but still were classified as normal knee function in both scales. In all five dimensions of the KOOS and subscales of SF-36 no apparent differences were noted. In all scales in the study group, no correlation was observed between the player's age and follow-up time after ACLR. After ACL reconstruction and successful return to professional sport, knee function is as good as uninjured team members in the midterm follow-up.



#4 Avoiding a red card: recommendations for a consistent standard of concussion management in professional football (soccer)

Reference: Br J Sports Med. 2021 Sep 28;bjsports-2021-104796.  doi: 10.1136/bjsports-2021-104796.

Authors: Vincent Gouttebarge, Edwin A Goedhart, Emmanuel Orhant, Jon Patricios

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#5 Adolescent female handball players present greater bone mass content than soccer players: A cross-sectional study

Reference: Bone. 2021 Sep 25;154:116217.  doi: 10.1016/j.bone.2021.116217. Online ahead of print.

Authors: Ulysses Fagundes, Rodrigo Luiz Vancini, Aldo Seffrin, Alexandre Aparecido de Almeida, Pantelis T Nikolaidis, Thomas Rosemann, Beat Knechtle, Marilia Santos Andrade, Claudio Andre Barbosa de Lira

Summary: Osteoporosis is a systemic disease affecting half of women over the age of 50 years. Considering that almost 90% of peak of bone mass is achieved until the second decade of life, ensuring a maximal bone mineral content acquisition may compensate for age-associated bone loss. Among several other factors, physical activity has been recommended to improve bone mass acquisition. However, it is unknown whether athletes involved with sports with different impact loading characteristics differ in regards to bone mass measurements. The purpose was to compare the bone mass content, bone mass density and lean mass of young female soccer players (odd-impact loading exercise), handball players (high-impact loading exercises) and non-athletes. A total of 115 female handball players (15.5 ± 1.3 years, 165.2 ± 5.6 cm and 61.9 ± 9.3 kg) and 142 soccer players (15.5 ± 1.5 years, 163.7 ± 6.6 cm and 56.5 ± 7.7 kg) were evaluated for body composition using a dual-emission X-ray absorptiometry system, and 136 female non-athletes (data from NHANES) (15.1 ± 1.32 years, 163.5 ± 5.8 cm and 67.2 ± 19.4 kg) were considered as the control. Handball players presented higher bone mass content values than soccer players for upper limbs (294.8 ± 40.2 g and 270.7 ± 45.7 g, p < 0.001), lower limbs (1011.6 ± 145.5 g and 967.7 ± 144.3 g, p = 0.035), trunk (911.1 ± 182.5 g and 841.6 ± 163.7 g, p = 0.001), ribs (312.4 ± 69.9 g and 272.9 ± 58.0 g, p < 0.001), spine (245.1 ± 46.8 g and 222.0 ± 45.1 g, p < 0.001) and total bone mass (2708.7 ± 384.1 g and 2534.8 ± 386.0 g, p < 0.001). Moreover, non-athletes presented lower bone mass content for lower limbs (740.6 ± 132.3 g, p < 0.001), trunk (539.7 ± 98.6 g, p < 0.001), ribs (138.2 ± 29.9 g, p < 0.001), pelvis (238.9 ± 54.6 g, p < 0.001), spine (152.8 ± 26.4 g, p < 0.001) and total bone mass (1987.5 ± 311.3 g, p < 0.001) than both handball and soccer players. Handball players also presented higher bone mass density values than soccer players for trunk, ribs and spine (p < 0.05) and handball and soccer players presented higher bone mass density than non-athletes for all measurements (p < 0.005). Finally, the non-athletes' lower limb lean mass was lower than soccer and handball players values (p < 0.05). Adolescent females engaged in handball training for at least one year present higher bone mass contents than those who are engaged in soccer training, which, in turn, present higher bone mass contents than non-athletes. These results might be used by physicians and healthcare providers to justify the choice of a particular sport to enhance bone mass gain in female adolescents.



#6 Influence of the Area per Player in Non-Professional Soccer Players: A Pilot Study Focused on Positional Roles

Reference: Int J Environ Res Public Health. 2021 Sep 18;18(18):9833.  doi: 10.3390/ijerph18189833.

Authors: Annamaria Mancini, Daniela Vitucci, Pasquale Meo, Adriano Capobianco, Domenico Martone, Francesca Cozzolino, Pasqualina Buono, Esther Imperlini, Stefania Orrù

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Summary: This study analyses the influence of different area per player (AP; 75, 98 and 131 m2) on the average metabolic power (MP) and other soccer-related performance variables in relation to the positional roles. We recruited 19 non-professional male soccer players (25.2 ± 6.3 y; 23.7 ± 2.3 kg/m2; 16.4 ± 6.3 y soccer experience) to play three different small-sided games (SSGs): SSG1 (5 vs. 5; 30 × 30 m; 5 min), SSG2 (5 vs. 5; 35 × 45 m; 5 min) and SSG3 (7 vs. 7; 35 × 45 m; 8 min). Specific playing rules were applied. GPS-assessed soccer-related variables were: average MP (AMP), distance covered in 1 min (DIS); % time spent at high speed (v > 16 km/h; % hst) or MP (>20 W/kg; % hmpt); % distance covered at high positive/negative speed (2 < v < 4 m/s2, % ACC; -6 < v < -2 m/s2, % DEC); and number of actions at high MP (hmpa). All recorded variables differed when each SSG was compared to the others (p < 0.05), but for hmpa for attackers. Most performance variables were positively associated with increasing AP (p < 0.05), but for % ACC and % DEC, and differed among positional roles within the same SSG (p < 0.05). Here the general applicability of SSGs, regardless the physical/technical skills of the group of players, to enhance performance is confirmed; furthermore, quantitative advices on AMP and other performance variables are provided to achieve significant improvements in all soccer players of the team.



#7 Running Performance of High-Level Soccer Player Positions Induces Significant Muscle Damage and Fatigue Up to 24 h Postgame

Reference: Front Psychol. 2021 Sep 14;12:708725. doi: 10.3389/fpsyg.2021.708725. eCollection 2021.

Authors: Lucas Albuquerque Freire, Michele Andrade de Brito, Natã Sant'anna Esteves, Márcio Tannure, Maamer Slimani, Hela Znazen, Nicola Luigi Bragazzi, Ciro José Brito, Dany Alexis Sobarzo Soto, Daniel Gonçalves, Bianca Miarka

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Summary: This study aimed to determine the impact of a soccer game on the creatine kinase (Ck) response and recovery and the specific Global Positioning System (GPS)-accelerometry-derived performance analysis during matches and comparing playing positions. A sample composed of 118 observations of 24 professional soccer teams of the Brazil League Serie A was recruited and classified according to playing positions, i.e., Left/Right Defenders (D = 30, age: 25.2 ± 5.8 years, height: 187 ± 5.5 cm, weight: 80 ± 5.8 kg), Offensive Midfielders (OM = 44, age: 25.1 ± 0.2 years, height: 177 ± 0.3 cm, weight: 73 ± 1.2 kg), Forwards (F = 9, age: 25.1 ± 0.2 years, height: 176.9 ± 4.3 cm, weight: 74.5 ± 2.1 kg), Left/Right Wingers (M = 23, age: 24.5 ± 0.5 years, height: 175 ± 1.1 cm, weight: 74 ± 4.4 kg), and Strikers (S = 12, age: 28 ± 0.2 years, height: 184 ± 1.0 cm, weight: 80 ± 1.4 kg). Blood Ck concentration was measured pre-, immediately post-, and 24 h postgame, and the GPS-accelerometry parameters were assessed during games. Findings demonstrated that Ck concentrations were higher at all postgame moments when compared with pregame, with incomplete recovery markers being identified up to 24 h after the game (range: 402-835 U/L). Moreover, Midfielders (108.6 ± 5.6 m/min) and Forwards (109.1 ± 8.3 m/min) had a higher relative distance vs. other positions (100.9 ± 10.1 m/min). Strikers [8.2 (8.1, 9.05) load/min] and Defenders [8.45 (8, 8.8) load/min] demonstrated lower load/min than Wingers [9.5 (9.2, 9.8) load/min], Midfielders [10.6 (9.9, 11.67) load/min], and Forwards [11 (10.65, 11, 15) load/min]. These results could be used to adopt specific training programs and recovery strategies after match according to the playing positions.



#8 A new peak-power estimation equations in 12 to 14 years-old soccer players

Reference: Medicine (Baltimore). 2021 Oct 1;100(39):e27383. doi: 10.1097/MD.0000000000027383.

Authors: Mehmet Gülü, Cengiz Akalan

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Summary: The aim of this study was to develop an age and soccer-specific regression equation to estimate the peak power of children aged 12-14 from the height of their vertical jumps using a large sample (n = 188). This study included 188 male soccer players (age, 12.6 ± 0.55; height, 153.31 ± 8.38 cm; and body weight, 43.65 ± 7.58 kg). Their actual peak power values obtained from vertical jumps were recorded using a force platform. The body weights of the participants were measured using Tanita. A regression model was developed using body weight and vertical jump values. All data were analyzed with the IBM SPSS (version 21) statistical analysis program. A multiple linear regression model was used to generate the best estimation of peak power. In this regression model, Power = -1714,116 + [(47.788 ∗ body weight (kg)] + [(58,976 ∗ Countermovement jump height (cm)]. Actual peak power is highly predictable for 12-14-year-old football players. In line with the new model, the actual peak power values obtained in this study were close to the estimated peak power values obtained with the Tufano formula. This may be because of the larger sample size and the same branch used for both equation models.



#9 The Impact of COVID-19 Lockdown on Agility, Explosive Power, and Speed-Endurance Capacity in Youth Soccer Players

Reference: Int J Environ Res Public Health. 2021 Sep 12;18(18):9604. doi: 10.3390/ijerph18189604.

Authors: József Márton Pucsok, Miklós Kovács, Gergely Ráthonyi, Balázs Pocsai, László Balogh

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Summary: Our goal was to assess agility, explosive power, and speed-endurance capacity by implementing noninvasive procedures and sport-specific tests. We hypothesized that agility, speed, explosive power, and speed-endurance capacity might be maintained or increased by an individualized home-based training program. Eleven adolescent athletes participated in our study; they executed three tests before the coronavirus outbreak and 13 weeks later, after the pandemic curfew. We used the SpeedCourt System to assess the sport-specific speed and agility parameters and monitor speed-endurance capacity. We conducted the first measurement at the end of the preparatory period, on 28 February 2020. The second session consisted of 4 weeks of regular training and 9 weeks of individual, home-based activities. Compared to the first (pre-pandemic) testing session, our participants demonstrated a significantly improved capacity of the lower limbs' explosive strength after completing the home-based exercise routine, compared to the first (pre-pandemic) testing session. We found that agility, speed, and explosive power might be maintained at the same level under home-based conditions. We found that it was challenging for the participants to increase their "pre-pandemic" endurance capacities.



#10 The Effects of Exercise Difficulty and Time-of-Day on the Perception of the Task and Soccer Performance in Child Soccer Players

Reference: Children (Basel). 2021 Sep 10;8(9):793. doi: 10.3390/children8090793.

Authors: Liwa Masmoudi, Adnene Gharbi, Cyrine H'Mida, Khaled Trabelsi, Omar Boukhris, Hamdi Chtourou, Mohamed Amine Bouzid, Cain C T Clark, Nizar Souissi, Thomas Rosemann, Beat Knechtle

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Summary: In soccer, accurate kicking skills are important determinants of successful performance. A successful kick must meet several criteria, including speed, accuracy, and timing. In fact, players who are able to kick the ball more accurately under various difficulties, such as time pressure, space constraints, the opponent's pressure, and the distance between the kicking point and the goal, have a clear advantage during soccer games. The aim of the present study was to investigate the effect of exercise difficulty and time-of-day on perceived task difficulty and kicking performance. Accordingly, 32 boys (age: 11 ± 0.7 years; height: 1.45 ± 0.07 m; body-mass: 38.9 ± 7.8 kg) performed shooting accuracy tests under two difficulty levels (distance (long-distance (LD) vs. short-distance (SD)) and time pressure (Without-time-pressure (WTP) vs. With-time-pressure (TP)) at 08:00 h and 17:00 h. Absolute-error, variable-error, and constant-error were evaluated during the kicking tasks, in addition to ball velocity and shooting quality. Moreover, rating-of-perceived-exertion score (RPE), feeling-scale (FS), and perceived difficulty were completed immediately at the end of each test. The results showed that shooting quality was not affected by the time-of-day, but it was better in WTP vs. TP (p < 0.05), and in SD vs. LD (p < 0.05), respectively. Higher values for FS and lower values for RPE were observed in the morning compared to the afternoon (p < 0.05) and in WTP vs. TP (p < 0.05). In conclusion, specific soccer skills of boys were not time-of-day dependent, but they may be associated with time pressure and task difficulty.



#11 Effects of the COVID-19 confinement period on hip strength, flexibility and muscle injury rate in professional soccer players

Reference: Phys Sportsmed. 2021 Oct 6;1-8.  doi: 10.1080/00913847.2021.1985384. Online ahead of print.

Authors: Cigdem Demir, Burak Subasi, Gulcan Harput

Summary: This study aimed to examine the effects of COVID-19 confinement on hamstring eccentric strength, hip adduction-abduction strength, and posterior chain flexibility in professional male soccer players. We also aimed to investigate whether muscle strength and flexibility would change when the players returned to play after COVID-19 confinement. Thirty professional male soccer (Age; 24.9 ± 4.8 yrs, BMI; 22.7 ± 1.4 kg/m2) players participated in this study. Hamstring eccentric strength, hip abduction-adduction strength and posterior chain flexibility (PCF) were measured before (time 1) and after the home confinement period (time 2) and after return to play (time 3). Repeated measures of ANOVA was used for statistical analysis. PCF decreased from time 1 to time 2 (p = 0.005) but it increased from time 2 to time 3 (p = 0.03). Hamstring eccentric strength decreased from time 1 to time 2 for both dominant (p = 0.002) and non-dominant (p = 0.04) limbs and no difference was observed between time 2 and time 3 (p > 0.05). Hip abductor and adductor strength did not change between time 1 and time 2 (p > 0.05) but they increased from time 2 and time 3 in the dominant limb (p < 0.05). Five players (16%) had muscle injuries including hamstrings and adductors when they returned to play. This study showed that 8-week COVID-19 confinement had an adverse effect on hamstring eccentric strength and PCF and 3 players had hamstring muscle injuries when they returned to play. Therefore, soccer players can be at risk of hamstring muscle injuries due to long-term detraining. Hip abductor and adductor strength seem not to be negatively affected by 8-week COVID-19 confinement. However, 2 players had adductor strain when they returned to play.



#12 Reduced Injury Prevalence in Soccer Athletes Following GPS Guided Acclimatization

Reference: Int J Exerc Sci. 2021 Aug 1;14(7):1070-1077. eCollection 2021.

Authors: Montgomery Bertschy, Jeffrey T Howard, Sakiko Oyama, Kelly Cheever

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Summary: GPS technology has been used to retrospectively correlate injury risk to changes in training load, however the use of GPS technology to plan and monitor training load over an acclimatization period to prevent musculoskeletal injury remains unexplored. This article reports the utility of GPS technology to help develop and monitor incremental increases in training load while transitioning from off-season to in season to reduce musculoskeletal injury. A series of daily minimum standards were established based on observed training loads in year 1 to gradually acclimate soccer athletes over a 5-week period prior to competition season in year 2. Daily check-ins with GPS data were used to ensure athletes met the standards to safely reach the expected training load of a competitive season. Following the 5-week GPS guided training program a lower overall prevalence of injury (Year 1: 92.6% (95%CI = 75.7-100) vs. Year 2: 55.2% (95%CI = 35.7-73.6)) (p = .002) and overall injury rate (Year 1: 8.1/1000 exposure hours (95%CI = 5.2-12) vs 4.6/1000 exposure hours (95%CI = 2.7-7.5) in year 2 (p = .08)) was observed. The observed reduction in injury prevalence and incidence demonstrates how GPS data can be used to proactively design and monitor preventative chronic training load acclimatization programs.



#13 Intra- and Inter-Limb Strength Asymmetry in Soccer: A Comparison of Professional and Under-18 Players

Reference: Sports (Basel). 2021 Sep 13;9(9):129. doi: 10.3390/sports9090129.

Authors: Chris Bishop, Giuseppe Coratella, Marco Beato

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Summary: The present study examined the isokinetic peak torque exerted by both knee extensors and flexors, anterior-posterior imbalance and the magnitude and direction of inter-limb asymmetry in professional and academy soccer players. (2) Methods: one hundred soccer players (professional = 50, elite academy = 50) volunteered to take part in this investigation. An isokinetic dynamometer was used to measure the knee extensor (quadriceps) and flexors muscle (hamstrings) torques of the limbs as well as inter-limb asymmetries-using a standard percentage difference equation. (3) Results: professional players exhibited significantly greater (effect size [ES] = large) strength levels in the quadriceps and hamstrings under both testing conditions, significantly higher (small to moderate) intra-limb ratio values for 60°·s-1 but not for the 300°·s-1 test condition, significantly (small to moderate) lower inter-limb asymmetry values for all test conditions, with the exception of the hamstrings at 60°·s-1 and the direction of asymmetry was poor to slight, indicating that limb dominance was rarely the same between groups. (4) Conclusions: this study shows that isokinetic assessments, i.e., peak torque exerted by both knee extensors and flexors and intra-limb ratio, and the subsequent inter-limb asymmetry, i.e., magnitude and direction, can differentiate between professional and academy soccer players.



#14 Association between Change in Regional Phase Angle and Jump Performance: A Pilot Study in Serie A Soccer Players

Reference: Eur J Investig Health Psychol Educ. 2021 Aug 15;11(3):860-865.  doi: 10.3390/ejihpe11030063.

Authors: Tindaro Bongiovanni, Athos Trecroci, Alessio Rossi, Fedon Marcello Iaia, Giulio Pasta, Francesco Campa

Summary: This observational longitudinal investigation aimed to investigate whether change in bioelectrical regional phase angle (PhA) is a predictor of change in vertical jump performance in elite soccer players. Fifteen soccer players (age: 28.7 ± 5.0 years, body weight: 82.4 ± 6.8 kg, height: 186.0 ± 0.1 cm, body mass index: 23.8 ± 1.2 kg/m2) competing in the first Italian division (Serie A) were included in this study and tested before the pre-season period and after the first half of the championship. Whole body and lower hemisoma PhA were obtained with a phase-sensitive 50 kHz bioelectrical impedance analyzer and legs lean soft tissue was estimated using specific bioimpedance-based equation developed for athletes. Vertical jump performance was assessed using the countermovement jump (CMJ). The major findings of the study are that changes in lower hemisoma PhA are more strongly related with changes in jump performance (r2 = 0.617, p = 0.001) than changes in whole-body PhA (r2 = 0.270, p = 0.047), even after adjusting for legs lean soft tissue and for body mass index (β = 5.17, p = 0.004). These data suggest that changes in lower hemisoma PhA might be used as a tool for evaluating performance related parameters in sports where specific body segments are involved, in preference to the whole-body measured value.



#15 The Effect of High-Intensity Accelerations and Decelerations on Match Outcome of an Elite English League Two Football Team

Reference: Int J Environ Res Public Health. 2021 Sep 21;18(18):9913.  doi: 10.3390/ijerph18189913.

Authors: David Rhodes, Stephen Valassakis, Lukasz Bortnik, Richard Eaves, Damian Harper, Jill Alexander

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Summary: Previous research has highlighted the frequency of high-intensity accelerations and decelerations in elite football. The influence of these actions on match performance outcomes has not been established. The aim of the present study was to identify the influence of high-intensity accelerations and decelerations on match performance outcomes (i.e., win, draw, lost). Comparisons were also made between team and positional high-intensity accelerations and decelerations recorded within the games. 26 elite outfield footballers from an elite English Football League (EFL) Two team completed the present study. Global Positioning System (GPS) technology was utilised to quantify high-intensity accelerations and decelerations during 45 games in a competitive season. Magnitude analysis and the effects of results, positions and fixture periods were observed. Significant effects of results, periods and positions were observed (p ≤ 0.05), with the highest outputs observed in games won. Positionally, fullbacks and centre forwards in a 4-3-3 formation exhibited the greatest frequency of high-intensity accelerations and decelerations. Very large differences were observed between the frequency of high-intensity decelerations compared to accelerations in games won (g = 2.37), drawn (g = 2.99) and lost (g = 3.59). The highest team frequencies of high-intensity accelerations (n = 3330) and decelerations (n = 6482) were completed in games won. The frequency of high-intensity accelerations and decelerations has a significant impact on match performance outcomes in an elite English League Two football team. Consideration needs to be given to specific conditioning and recovery strategies to optimise high-intensity acceleration and deceleration performance in games. Caution should be taken as these findings are representative of one team within the EFL.



#16 Eccentric Hamstring Muscle Strength during Home Confinement Due to the COVID-19 Pandemic, and Football Competition Resumption in Professional Football Referees: A Prospective Observational Study

Reference: Int J Environ Res Public Health. 2021 Sep 15;18(18):9737.  doi: 10.3390/ijerph18189737.

Authors: Víctor Moreno-Pérez, Marc Madruga-Parera, Daniel Romero-Rodríguez, Javier Sanchéz-Sanchéz, José Luis Felipe, Lluis Marcè-Hernández, Eudald Recasens-Sarrà, Juan Del Coso

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#17 High Risk of New Knee Injuries in Female Soccer Players After Primary Anterior Cruciate Ligament Reconstruction at 5- to 10-Year Follow-up

Reference: Am J Sports Med. 2021 Oct 8;3635465211044458.  doi: 10.1177/03635465211044458.

Authors: Anne Fältström, Joanna Kvist, Martin Hägglund

Summary: A new anterior cruciate ligament (ACL) injury after ACL reconstruction is a feared outcome. The purpose was to study the risk of new knee injuries in female soccer players 5 to 10 years after primary unilateral ACL reconstruction and to compare players who returned to soccer with (1) players who did not return and (2) knee-healthy soccer players (controls). Demographic, soccer-specific, and surgical data were recorded at baseline for 317 female soccer players (mean ± SD age, 20.1 ± 2.7 years) 1.6 ± 0.7 years after ACL reconstruction and for 119 matched controls (mean age, 19.5 ± 2.5 years). Data on new knee injuries and soccer-playing status were collected 5 to 10 years after ACL reconstruction via a questionnaire. Among players with ACL reconstruction, 222 (70%) responded at a mean 6.5 ± 1.0 years after primary ACL reconstruction. We compared 3 cohorts: (1) among 163 players with ACL reconstruction who returned to soccer, 68 (42%) sustained 44 reruptures and 29 contralateral ruptures; (2) among 59 players with ACL reconstruction who did not return to soccer, 11 (19%) sustained 9 reruptures and 2 contralateral ruptures; and (3) among 113 knee-healthy controls, 12 (11%) sustained 13 ACL injuries. Players who returned had a >2-fold higher risk of a new ACL injury than players who did not return (risk ratio, 2.24; 95% CI, 1.27-3.93; P = .005) and a 4-fold higher risk than controls (risk ratio, 3.93; 95% CI, 2.23-6.91; P <.001). A new ACL, meniscal, or cartilage injury was the most frequent new knee injury. Among players who returned to soccer, 68% reported a new knee injury, and they had a 2- to 5-times higher risk of any new knee injury and knee surgery than players who did not return and controls. Two-thirds of female soccer players with ACL reconstruction who returned to soccer sustained a new knee injury within 5 to 10 years; 42% had a new ACL injury. Their risk of a new knee injury and knee surgery was 2 to 5 times greater than that for players who did not return and for knee-healthy controls. New injury may have negative consequences for long-term knee health and should be a critical consideration in the decision to return to play.



#18 Diagnostic Musculoskeletal Ultrasound for the Acute Evaluation and Management of Soccer Players

Reference: Curr Sports Med Rep. 2021 Oct 1;20(10):525-530. doi: 10.1249/JSR.0000000000000890.

Authors: Zachary Bailowitz, Christopher J Visco, Kevin Christen, Christopher S Ahmad

Summary: Musculoskeletal ultrasound (US) has many applications in the care of athletes. This article reviews the current literature and identifies research gaps regarding musculoskeletal US in the athletic training room setting to evaluate and manage soccer players. The best evidence for US in the training room setting is for diagnosis and prognosis of muscle injuries, where studies show that it is equivalent to other imaging modalities. US also has been used for injury risk prediction, although the data are mixed. Many applications of US are described in other sport settings and may have crossover applications to soccer.



#19 Return-to-Play Times and Player Performance After Medial Collateral Ligament Injury in Elite-Level European Soccer Players

Reference: Orthop J Sports Med. 2021 Sep 28;9(9):23259671211033904. doi: 10.1177/23259671211033904. eCollection 2021 Sep.

Authors: Ophelie Z Lavoie-Gagne, Julia Retzky, Connor C Diaz, Nabil Mehta, Avinaash Korrapati, Enrico M Forlenza, Derrick M Knapik, Brian Forsythe

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Summary: Participation in elite-level soccer predisposes athletes to injuries of the medial collateral ligament (MCL), resulting in variable durations of time lost from sport. The purpose was to (1) determine the rate of return to play (RTP) and timing after MCL injuries, (2) investigate MCL reinjury incidence after RTP, and (3) evaluate the long-term effects of MCL injury on future performance. Using publicly available records, we identified athletes who had sustained MCL injury between 2000 and 2016 across the 5 major European soccer leagues (English Premier League, Bundesliga, La Liga, Ligue 1, and Serie A). Injured athletes were matched to controls using demographic characteristics and performance metrics from the season before injury. We recorded injury severity, RTP rate, reinjury incidence, player characteristics associated with RTP within 2 seasons of injury, player availability, field time, and performance metrics during the 4 seasons after injury. A total of 59 athletes sustained 61 MCL injuries, with 86% (51/59) of injuries classified as moderate to severe and surgical intervention performed in 14% (8/59) of athletes. After injury, athletes missed a median of 33 days (range, 3-259 days) and 4 games (range, 1-30 games). Overall, 71% (42/59) of athletes returned successfully at the same level, with multivariable regression demonstrating no athlete characteristic predictive of RTP. MCL reinjury was reported in 3% (2/59) of athletes. Midfielders demonstrated decreased field time after RTP when compared with controls (P < .05). No significant differences in player performance for any position were identified out to 4 seasons after injury. Injured athletes had a significantly higher rate of long-term retention (P < .001). MCL injuries resulted in a median loss of 33 days in elite European soccer athletes, with the majority of injuries treated nonoperatively. RTP remained high, and few athletes experienced reinjury. While midfielders demonstrated a significant decrease in field time after RTP, player performance and long-term retention were not compromised. Future studies are warranted to better understand athlete-specific and external variables predictive of MCL injury and reinjury, while evaluating treatment and rehabilitation protocols to minimize time lost and to optimize athlete safety and health.



#20 Prospective and Randomized Clinical Evaluation of Hamstring Versus Patellar Tendon Autograft for Anterior Cruciate Ligament Reconstruction in Soccer Players

Reference: Orthop J Sports Med. 2021 Sep 24;9(9):23259671211028168.  doi: 10.1177/23259671211028168. eCollection 2021 Sep.

Authors: Luiz Gabriel Betoni Guglielmetti, Victor Eduardo Roman Salas, Pedro Baches Jorge, Fabrício Roberto Severino, Aires Duarte, Victor Marques de Oliveira, Ricardo de Paula Leite Cury

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Summary: Anterior cruciate ligament (ACL) reconstruction is usually performed with autologous bone-patellar tendon-bone (PT) or hamstring tendon (HT) graft. There has been only 1 randomized clinical trial examining ACL reconstruction with these grafts specifically in soccer players, and more studies comparing these graft types within a homogenous cohort such as soccer athletes may better highlight differences in outcomes. The aim was to compare the results of ACL reconstruction with PT versus HT autograft in soccer players and to evaluate objective and subjective outcomes. A total of 62 professional or semiprofessional soccer players (mean age, 25.1 years) with ACL injury were randomized to undergo reconstruction with PT or HT autograft by a single orthopaedic surgeon (n = 31 in each group). Outcome measures were recorded preoperatively and at 2 years postoperatively. The primary outcome was the modified Cincinnati Knee Rating System, and secondary outcomes were the objective and subjective International Knee Documentation Committee scores, Lachman test, pivot-shift test, anterior drawer test, and Lysholm score. The following variables were also evaluated postoperatively: return to soccer, level at return, graft rerupture, postoperative complications, anterior knee pain, patellar tendinitis, difficulty sprinting, and loss of kicking power. The PT and HT groups were homogenous in terms of age, sex distribution, injured side, and time from injury to surgery, and there was no difference between them on any preoperative outcome score. At 2 years postoperatively, there were no differences between the groups on any outcome score; however, there were significantly fewer patients with anterior knee pain in the HT group compared with the PT group (7 [22.6%] vs 15 [48.4%], respectively; P = .03). Two patients from each group (2/31; 6.5%) sustained rerupture. There were no differences between soccer players who underwent different types of ACL reconstruction with the exception of anterior knee pain, which was more frequent in players who underwent reconstruction with PT graft.



#21 Quantitative evaluation of bone marrow fat content and unsaturated fatty index in young male soccer players using proton magnetic resonance spectroscopy ( 1 H-MRS): a preliminary study

Reference: Quant Imaging Med Surg. 2021 Oct;11(10):4275-4286. doi: 10.21037/qims-21-64.

Authors: Jian Wang, Peiwei Yi, Yaobin Huang, Qinqin Yu, Yingjie Mei, Jialing Chen, Yanqiu Feng, Xiaodong Zhang

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Summary: Marrow fat exists as a distinct adipose tissue and plays a critical role in affecting both the quantity and quality of bone. However, the effect of soccer training on marrow fat has been rarely reported. This study aims to evaluate and characterize the marrow fat content and composition in different bone areas of soccer players and age-matched healthy subjects using proton magnetic resonance spectroscopy (1H-MRS). Between May 2020 and June 2020, 20 professional soccer players (20.7±0.9 years) and 20 age-matched healthy subjects (21.2±0.8 years) were enrolled in this cross-sectional study. The 1H-MRS were acquired from the 3rd lumbar vertebrae, bilateral femoral necks, and distal tibias of all subjects using a single-voxel point-resolved spatially localized spectroscopy (PRESS) sequence. Four soccer players underwent a second magnetic resonance (MR) examination within a 30-minute interval after the initial scan to evaluate test-retest reproducibility. Inter- and intra-observer measurement reliabilities were assessed using 10 randomly selected spectra from the soccer players group. All spectra were processed using the jMRUI software package ( Quantified water and lipid signals were used to calculate fat content (FC) and the unsaturated fatty index (UI). Compared with healthy subjects, we found that soccer players had a lower FC in L3 and bilateral femoral necks and higher UI in the left femoral neck (P<0.05). All FC and UI values of the bilateral distal tibias showed no significant differences between the two groups (P>0.05). The UI values of the right femoral neck or distal tibia were markedly higher than the left side in both inactive subjects and soccer players (P<0.05, except for the femoral neck in players), and there were notable ΔUI differences in the lower limbs between the soccer players and the healthy subjects (P<0.05). Soccer practice can be considered a positive sport that contributes to decreasing FC in lumbar vertebrae and femoral necks and increasing the UI in femoral necks. Quantitative MRS provides an ideal modality to predict marrow fat metabolism caused by mechanical stimulation.



#22 Effects of Combined Plyometric and Short Sprints Training on Athletic Performance of Male U19 Soccer Players

Reference: Front Psychol. 2021 Sep 15;12:714016.  doi: 10.3389/fpsyg.2021.714016. eCollection 2021.

Authors: Ghaith Aloui, Hermassi Souhail, Lawrence D Hayes, El Ghali Bouhafs, Mohamed Souhaiel Chelly, René Schwesig

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Summary: This project investigated adding 8 weeks of biweekly plyometric and short sprints training into standard training in elite youth soccer players. An experimental group (EG, n = 18, age: 17.6 ± 0.6 years, body mass: 67.6 ± 5.8 kg, height: 1.75 ± 0.06 m, and body fat: 11.5 ± 1.6%) and control group (CG, n = 18, age: 17.5 ± 0.6 years, body mass: 68.8 ± 3.6 kg, height: 1.77 ± 0.04 m, and body fat: 11.7 ± 1.2%) participated. Pre-intervention and post-intervention measures were squat-jump (SJ), countermovement-jump (CMJ), standing long jump (SLJ), 5 and 20 m sprints, change-of-direction ability (4 × 5 m sprint test [S 4 × 5 m] and sprint 9-3-6-3-9 m with backward and forward running [SBF]), repeated change of direction (RCOD), and static balance (the stork balance test). For all parameters, significant (p < 0.001, η2pηp2 > 0.10) time and interaction (group × time) effects were observed. For three parameters (SBF, RCOD fastest time, and SLJ) no significant group effects were observed. The EG consistently showed a significantly higher performance level than the CG and a higher amount of effect sizes d (EG: d range: 1.27-2.61; CG: d range: 0.13-0.79) as an indicator for the development of performance between pre-intervention and post-intervention measures. Adding biweekly plyometric and short sprint training to standard training improves the athletic performance of young soccer players. Such plyometric and short sprint training conditioning can be highly recommended as part of the annual short training program for male elite under-19 (U19) soccer players.



#23 Effects of Three Preseason Training Programs on Speed, Change-of-Direction, and Endurance in Recreationally Trained Soccer Players

Reference: Front Physiol. 2021 Sep 17;12:719580. doi: 10.3389/fphys.2021.719580. eCollection 2021.

Authors: Jérôme Koral, Jaume Lloria Varella, Fernando Lazaro Romero, Clément Foschia

Summary: Modern coaches experience a drastic reduction of the available training time with an increasingly large number of competitions during the competitive season. Thus, they must choose wisely the most efficient methods to improve the physical fitness of their players during the preseason. Among all the methods, this study compared the effects of plyometric training (PT), sprint interval training (SIT), and small-sided games (SSGs) on the performance of recreationally trained soccer players. Seventy-three participants were randomly assigned in one of the three experimental groups (i.e., PT [n = 23], SIT [n = 26] or SSGs [n = 24]) and completed two sessions per week for a total of 3 weeks. Meanwhile, the whole group maintained their habitual soccer-specific training program who do not interfere in the preparation of the season. Repeated sprint ability (RSA), maximal aerobic speed (MAS), and a 30-m sprint were assessed at baseline (PRE) and post-training (POST). Performance in SSGs decreased for the average speed from 0 to 10 m (V 0-10m; -0.84 km h-1, -4 ± 5%, p < 0.001), the maximal distance (D max) covered in the 30-s RSA test (-3.65 m, -3 ± 6%, p < 0.01) and MAS (-0.52 km h-1, -3 ± 6%, p < 0.01). PT increased the mean distance (D mean) covered in the 30-s RSA test (+5.98 m, 5 ± 4%, p < 0.001) and MAS (+0.58 km h-1, 7 ± 5%, p < 0.01) while an improvement of all parameters but the maximal sprint speed reached during the 30-m trip (V max) was found in the SIT group (V 0-10m: +1.462 km h-1, 8 ± 5%, p < 0.001; D max: +7.89 m, 6 ± 5%, p < 0.001; D mean: +8.69 m, 7 ± 5%, p < 0.001 and MAS: +1.74 km h-1, 12 ± 8%, p < 0.001). All SSG POST values were significantly lower than PT and SIT (p < 0.01). D mean and MAS in POST were also significantly higher in SIT than in the PT group (p < 0.001). This study suggests that both PT and SIT could be a better alternative to SSGs to boost performances during preseason. Moreover, SIT seems to produce higher improvements in physical performances than PT.



#24 Downtrends in Offside Offenses Among 'The Big Five' European Football Leagues

Reference: Front Psychol. 2021 Sep 20;12:719270. doi: 10.3389/fpsyg.2021.719270. eCollection 2021.

Author: Yangqing Zhao

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Summary: This study examined the evolution of offside offenses and pass performance across a 10-season period in the top five European soccer leagues. Match performance observations (n = 18 259) were analysed for emergent trends. Two-way ANOVA analyses revealed significant league and seasonal differences among the five leagues (medium effect size). The total offside offenses committed during a match experienced a clear decline during the 10 seasons. In contrast, moderate increases were evident for all passing differential variables. Offside offenses per match were higher in the German Bundesliga and Spanish La Liga than in the English Premier League and France Ligue 1. However, the English Premier League had the greatest value in the touch differential, pass differential, successful pass differential, and key pass differential among all leagues. It is important to note that the number of offside offenses fell after the implementation of VAR.



#25 Hip muscle activity in male football players with hip-related pain; a comparison with asymptomatic controls during walking

Reference: Phys Ther Sport. 2021 Sep 27;52:209-216. doi: 10.1016/j.ptsp.2021.09.008. Online ahead of print.

Authors: Peter R Lawrenson, Kay M Crossley, Paul W Hodges, Bill T Vicenzino, Matthew G King, Joshua J Heerey, Adam I Semciw

Summary: Compare muscle activity between male football players with and without hip-related pain. Morphological and intra-articular features of hip-related pain are proposed pre-cursors to hip osteoarthritis. Altered muscle activity is a feature of severe hip osteoarthritis, but it is not known whether differences exist earlier in the pathological spectrum. Forty-two male football players with hip-related pain; and 19 asymptomatic controls participated in this study. Hip muscle activity (Gluteus maximus, gluteus medius, tensor facia latae, adductor longus and rectus femoris) was recorded during walking using surface electromyography (EMG). Men with hip-related pain had sustained rectus femoris activity prior to toe-off (47-51% of the gait cycle) (p = 0.01, ES = 0.51) unlike controls who had reduced activity. In men with severe hip-related pain, gluteus maximus EMG was sustained into mid-stance (12-20% of the gait cycle) (F = 6.15, p < 0.01) compared to controls. Differences in rectus femoris and gluteus maximus activity were identified between male footballers with and without hip-related pain. The pattern of gluteus maximus EMG relative to peak, approaching mid-stance in severe hip-related pain, is consistent with observations in severe hip osteoarthritis. This supports the hypothesis that symptom severity may influence muscle activity across the spectrum of hip degeneration.



#26 The genetic association with injury risk in male academy soccer players depends on maturity status

Reference: Scand J Med Sci Sports. 2021 Oct 11. doi: 10.1111/sms.14077. Online ahead of print.

Authors: Elliott Cr Hall, Philipp Baumert, Jon Larruskain, Susana M Gil, Josean A Lekue, Edgardo Rienzi, Sacha Moreno, Marcio Tannure, Conall F Murtagh, Jack D Ade, Paul Squires, Patrick Orme, Liam Anderson, Thomas E Brownlee, Craig M Whitworth-Turner, James P Morton, Barry Drust, Alun G Williams, Robert M Erskine

Summary: It is currently unknown if injury risk is associated with genetic variation in academy soccer players (ASP). We investigated whether nine candidate single nucleotide polymorphisms were associated (individually and in combination) with injury in ASP at different stages of maturation. Saliva samples and one season's injury records were collected from 402 Caucasian male ASP from England, Spain, Uruguay and Brazil, whose maturity status was defined as pre- or post-peak height velocity (PHV). Pre-PHV COL5A1 rs12722 CC homozygotes had relatively higher prevalence of any musculoskeletal soft-tissue (22.4% vs. 3.0%, P=0.018) and ligament (18.8% vs. 11.8%, P=0.029) injury than T-allele carriers, while VEGFA rs2010963 CC homozygotes had greater risk of ligament/tendon injury than G-allele carriers. Post-PHV IL6 rs1800795 CC homozygotes had a relatively higher prevalence of any (67.6% vs. 40.6%, P=0.003) and muscle (38.2% vs. 19.2%, P=0.013) injuries than G-allele carriers. Relatively more post-PHV EMILIN1 rs2289360 CC homozygotes suffered any injury than CT and TT genotypes (56.4% vs. 40.3% and 32.8%, P=0.007), while the 'protective' EMILIN1 TT genotype was more frequent in post- than pre-PHV ASP (22.3 vs. 10.0%, P=0.008). Regardless of maturity status, T-alleles of ACTN3 rs1815739 and EMILIN1 rs2289360 were associated with greater absence following ankle injury, while the MMP3 rs679620 T-allele and MYLK rs28497577 GT genotype were associated with greater absence following knee injury. The combination of injury-associated genotypes was greater in injured vs. non-injured ASP. This study is the first to demonstrate that a genetic association exists with injury prevalence in ASP, which differs according to maturity status.



#27 Mass Gathering Medicine in Soccer Leagues: A Review and Creation of the SALEM Tool

Reference: Int J Environ Res Public Health. 2021 Sep 22;18(19):9973. doi: 10.3390/ijerph18199973.

Authors: Anas A Khan, Abdulrahman Y Sabbagh, Jamie Ranse, Michael S Molloy, Gregory R Ciottone

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Summary: Potential risks for public health incidents, outbreaks, and casualties are inferred at association football events, especially if event organizers have not taken appropriate preventative measures. This review explores the potential risks imposed by mass gathering (MG) football events, with particular emphasis on tools and methodologies to manage the risks of football MG events. Effective planning and implementation of MGs along with the mitigation of risks related to people's health require special attention to all potential threats, especially in frequent and recurring MG events such as football leagues. The well-being of all participants can be compromised by ignoring a single risk. Healthcare systems should cooperate with all stakeholders and organizations who are involved in MG management and response. Provision of services during MG or a disaster must be performed by trained personnel or entities that have full access to available resources in accessible publicly known locations at the MG event site. Several MG assessment tools were developed worldwide; however, to adapt to the Saudi context, SALEM tool was developed to provide a guide for MG planning and assessment. SALEM assesses the risks of MG events with scores that help to categorize the risk of MG events by offering recommendations for required resources.



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