Latest research in football - week 45 - 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 Distance Between Players During a Soccer Match: The Influence of Player Position

Reference: Front Psychol. 2021 Aug 19;12:723414. doi: 10.3389/fpsyg.2021.723414. eCollection 2021.

Authors: David Garrido, Daniel R Antequera, Roberto López Del Campo, Ricardo Resta, Javier M Buldú

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Summary: In this study, we analyse the proximity between professional players during a soccer match. Specifically, we are concerned about the time a player remains at a distance to a rival that is closer than 2 m, which has a series of consequences, from the risk of contagion during a soccer match to the understanding of the tactical performance of players during the attacking/defensive phases. Departing from a dataset containing the Euclidean positions of all players during 60 matches of the Spanish national league (30 from LaLiga Santander and 30 from LaLiga Smartbank, respectively, the first and second divisions), we analysed 1,670 participations of elite soccer players. Our results show a high heterogeneity of both the player-player interaction time (from 0 to 14 min) and the aggregated time with all opponents (from <1 to 44 min). Furthermore, when the player position is taken into account, we observe that goalkeepers are the players with the lowest exposure (lower than 1 min), while forwards are the players with the highest values of the accumulated time (~21 min). In this regard, defender-forward interactions are the most frequent. To the best of our knowledge, this is the largest dataset describing the proximity between soccer players. Therefore, we believe these results may be crucial to the development of epidemiological models aiming the predict the risk of contagion between players and, furthermore, to understand better the statistics of all actions that involve proximity between players.



#2 Weekly Variations of Short-Duration Maximal Jumping Performance in Soccer Players: Exploring Relationships With Accumulated Training Load and Match Demands

Reference: Front Physiol. 2021 Aug 19;12:690353.  doi: 10.3389/fphys.2021.690353. eCollection 2021.

Authors: Rui Silva, Filipe Manuel Clemente, Francisco Tomás González-Fernández, André Bernardo, Luca Paolo Ardigò

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Summary: The aim of this study was 2-fold: (1) to analyze variations of short-duration maximal jumping performance in players exposed to a match and those who were not and (2) to analyze the relationships between changes in the short-duration maximal jumping performance and different accumulated training load and match demands measures.  Twenty-four professional soccer players (age: 20.3 ± 1.7 years) were monitored daily for their training load and match demands over 6 weeks. In addition, they performed a weekly short-duration maximal jumping performance test (72 h after the last match). Negative moderate correlations were found between percentage of change of countermovement jump (CMJ) height and Acummulated training load (ATL) of total distance (TD), high metabolic load (HML), accelerations (ACC), and decelerations (DEC) (r = -0.38, p = 0.004; r = -0.33, p = 0.013; r = -0.39, p = 0.003; and r = -0.30, p = 0.026). No correlations were found for match load (ML). TD, HML, ACC, and DCC (r = 0.27, r = 0.25, r = 0.31, and r = 0.22, respectively) were used to predict the percentage of change of CMJ height.  Match participation has negative effects on CMJ performance. The ATL of HML, ACC, DCC, and TD have a significant influence on both CMJ measures changes. Also, the ATL values of those metrics are the best predictors of the percentage changes of CMJ performance.



#3 Scoping review of tests to assess tactical knowledge and tactical performance of young soccer players

Reference: J Sports Sci. 2021 Sep 6;1-17. doi: 10.1080/02640414.2021.1916262. Online ahead of print.

Authors: Leandro Rechenchosky, Vanessa Menezes Menegassi, Matheus de Oliveira Jaime, Paulo Henrique Borges, Hugo Sarmento, David Mancha-Triguero, Jaime Serra-Olivares, Wilson Rinaldi

Summary: This scoping review aimed to systematically map studies/tests for assessing the tactical domain of young soccer players. The study followed the PRISMA-ScR and Joanna Briggs Institute guidelines. The databases searched were Scopus, SPORTDiscus, SciELO, LILACS, and BDTD. The eligibility criteria were defined based on the elements of population, context, and concept, without restrictions on the period, language, and type of publication. Twenty-four papers were included, from 1997 to 2020, totalling 29 tests/instruments for the assessment of the tactical domain, with the majority of studies having an European sample. Twelve terms were used to nominate the tactical component, regardless of the assessment method and approach. Six tests met eight or nine criteria in the critical appraisal: TCTOF, TACSIS Spanish version, Semi-Structured Interview, TCTP-OE, GPET, and FUTSAT. Thus, it is concluded that studies and tests for the assessment of the tactical domain of young soccer players are recent and mainly European; there is no consensus about the adopted terminology; and few tests met the majority of the quality criteria. Therefore, we suggest: a) the construction/adaptation of tests with samples from other continents; b) the use of the proposed criteria; and c) that the terms tactical knowledge and tactical performance are adopted.



#4 Oxidative Stress and Abnormal Tendon Sonographic Features in Elite Soccer Players (A Pilot Study)

Reference: Rev Bras Ortop (Sao Paulo). 2021 Aug;56(4):432-437.  doi: 10.1055/s-0040-1721364. Epub 2021 Feb 10.

Authors: Michele Abate, Luigi Di Carlo, Giulio Cocco, Antonino Cocco, Ernesto Sabatini, Vincenzo Salini

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Summary: Sound experimental data suggest that oxidative stress plays an important role in the pathogenesis of tendinopathies. However, this hypothesis in humans remains speculative given that clinical data are lacking to confirm it. Recently, a new methodology has allowed to quantify the oxidative stress in vivo by measuring the concentration of hydroperoxides of organic compounds, which have been utilized as an oxidative stress-related marker in several pathologic and physiologic conditions. Given the reliability of this test and the lack of information in subjects with tendinopathies, the aim of the present study was to assess the oxidative stress status in elite professional soccer players with and without ultrasonographic features of tendon damage.  In 73 elite players, blood metabolic parameters were evaluated and oxidative stress was measured by means of a specific test (expressed as U-Carr units). Therefore, an ultrasonographic evaluation of the Achilles and patellar tendons was performed.  No significant relationships were observed between metabolic parameters and oxidative stress biomarkers. The Achilles and patellar tendons showed a normal echographic pattern in 58 athletes, and sonographic abnormalities in 15. The athletes with ultrasonographic alterations, compared to those with normal US picture, showed significantly higher U-Carr levels ( p = 0.000), body mass index (BMI) values ( p = 0.03) and were older ( p = 0.005). The difference in U-Carr values among the subjects remained significant also after adjustment for age and BMI.  The results of the present study support the hypothesis that oxidative substances, also increased at systemic and not only at local level, may favor tendon damage. 



#5 Physical activity on mental wellbeing in senior English Premier League soccer players during the COVID-19 pandemic and the lockdown

Reference: Eur J Sport Sci. 2021 Sep 3;1-25. doi: 10.1080/17461391.2021.1976841. Online ahead of print.

Authors: Sophie Grimson, Gary Brickley, Nicholas J Smeeton, Will Abbott, Adam Brett 

Summary: The COVID-19 pandemic and the subsequent lockdown created new stressors that could potentially attenuate mental wellbeing (MW) in athletes, who are already susceptible to poor MW. This study aims to describe fluctuations to MW during 'lockdown' and subsequent 'return to sport' protocols, in comparison to the normal 'in-season' in professional soccer.Twenty-five English Premier League (EPL) soccer players completed the Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS) every two weeks, during the 2019/2020 season, and every week during 'lockdown' and 'return to training' for 28 weeks. The duration of each physical activity (PA) session completed was recorded. No significant differences were found for MW between time points (In-season, lockdown, return to training, and the restart) (51.5±5.6 vs. 50.7±4.8 vs. 50.8±5.7 vs. 50.7±5.6 (p >0.05)) respectively. Individually, differences were identified; in-season weekly session duration (243±38 min) was higher than during lockdown (180±62 min) (p <0.05). During lockdown, weekly MW scores were related to the previous 7-day number of sessions (r = 0.151) and active min (r = 0.142) (p <0.05). Furthermore, participants that exercised >250 min in lockdown, had higher MW scores (52.46 ± 4.65) than <250 min (50.35±6.55) (p <0.05). MW responses to lockdown were best understood on an individual basis. Additionally, PA only had a measurable effect on MW when >250 min. Further, stressors imposed upon players during an EPL season, are potentially greater than those inflicted by the lockdown. Implications for monitoring MW in EPL soccer players and the potential inclusion of an in-season break are discussed.



#6 The dominant leg is more likely to get injured in soccer players: systematic review and meta-analysis

Reference: Biol Sport. 2021 Sep;38(3):397-435.  doi: 10.5114/biolsport.2021.100265. Epub 2020 Oct 28.

Authors: Matthew D DeLang, Paul A Salamh, Abdulaziz Farooq, Montassar Tabben, Rodney Whiteley, Nicol van Dyk, Karim Chamari

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Summary: In soccer (football), dominant limb kicking produces higher ball velocity and is used with greater frequency than the non-dominant limb. It is unclear whether limb dominance has an effect on injury incidence. The purpose of this systematic review with meta-analysis is to examine the relationship between limb dominance and soccer injuries. Studies were identified from four online databases according to PRISMA guidelines to identify studies of soccer players that reported lower extremity injuries by limb dominance. Relevant studies were assessed for inclusion and retained. Data from retained studies underwent meta-analyses to determine relative risk of dominant versus non-dominant limb injuries using random-effects models. Seventy-four studies were included, with 36 of them eligible for meta-analysis. For prospective lower extremity injury studies, soccer players demonstrated a 1.6 times greater risk of injury to the dominant limb (95% CI [1.3-1.8]). Grouped by injury location, hamstring (RR 1.3 [95% CI 1.1-1.4]) and hip/groin (RR 1.9 [95% CI 1.3-2.7]) injuries were more likely to occur to the dominant limb. Greater risk of injury was present in the dominant limb across playing levels (amateurs RR 2.6 [95% CI 2.1-3.2]; youths RR 1.5 [95% CI 1.26-1.67]; professionals RR 1.3 [95% CI 1.14-1.46]). Both males (RR 1.5 [95% CI 1.33-1.68)] and females (RR 1.5 [95% CI 1.14-1.89]) were more likely to sustain injuries to the dominant limb. Future studies investigating soccer injury should adjust for this confounding factor by using consistent methods for assigning limb dominance and tracking use of the dominant versus non-dominant limb.



#7 Differences in worst-case scenarios calculated by fixed length and rolling average methods in professional soccer match-play

Reference: Biol Sport. 2021 Sep;38(3):325-331. doi: 10.5114/biolsport.2021.99706. Epub 2020 Oct 24.

Authors: José M Oliva-Lozano, Isabel Martín-Fuentes, Víctor Fortes, José M Muyor 

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Summary: The aims of this study were to describe the worst-case scenarios (WCS) in professional soccer players calculated by fixed length and rolling average methods with regards to each playing position. This was done, firstly, by comparing total distance (TD covered in the WCS; secondly, by comparing high-speed running distance (HSRD); and thirdly, by comparing sprint distance (SPD). The study was conducted over a three-mesocycle competitive period. The WCS of three distance-related variables (TD, HSRD, SPD) in four time windows (1, 3, 5, 10 minutes) were calculated according to playing position (central defender; full-back; midfielder, wide midfielder, and forward) using fixed length and rolling average methods. A significant effect of the type of method used to calculate the WCS in TD (F(1, 142) = 151.49, p < 0.001, ηp2 = 0.52), HSRD (F(1, 138) = 336.95, p < 0.001, ηp2 = 0.71) and SPD (F(1, 138) = 76.74, p < 0.001, ηp2 = 0.36) was observed. In addition, there was a significant interaction between type of method and WCS duration in TD (F(1.36, 193.53) = 41.95, p < 0.001, ηp2 = 0.23), HSRD (F(2.28, 315.11) = 21.77, p < 0.001, ηp2 = 0.14) and SPD (F(2.59, 358.41) = 6.93, p < 0.001, ηp2 = 0.05). In conclusion, the use of fixed length methods of different durations significantly underestimated the WCS of TD, HSRD and SPD across the most common playing positions in professional soccer players. Therefore, the application of rolling averages is recommended for an appropriate WCS analysis in professional soccer match-play.



#8 Acute Effects of Foam Rolling on Blood Flow Measured by Ultrasonography in Soccer Players

Reference: J Strength Cond Res. 2021 Sep 1. doi: 10.1519/JSC.0000000000004125. Online ahead of print.

Authors: Alejandra Alonso-Calvete, Alexis Padrón-Cabo, Miguel Lorenzo-Martínez, Ezequiel Rey

Summary: In recent years, foam rolling (FR) has become a popular device for recovery to increase range of motion and decrease pain after sport practice and competition. However, there is little evidence about the underlying physiological effects of FR, specifically in blood flow parameters. Thus, the aim of this study was to analyze acute effects of FR on blood flow parameters (maximal velocity and maximal volume) measured by Doppler ultrasonography in soccer players. Twelve soccer players were assessed in 3 different situations: pre-FR intervention, immediately after FR intervention, and 30 minutes after FR intervention. The femoral artery was measured in the dominant leg with subjects in horizontal lying position. Before the intervention, subjects completed one familiarization session with FR. The FR intervention consisted of 2 sets, each with 45 seconds of FR and 15 seconds of rest between sets with a high-density foam roller in quadriceps, hamstrings, and iliotibial band. Results showed a significant increase in both maximal velocity (p < 0.001; effect size [ES] = 0.81) and maximal volume (p = 0.001; ES = 1.73) after intervention in comparison with pretest, but after 30 minutes, there were no significant differences. Therefore, this increase of the blood flow could promote important advantages for postexercise recovery, suggesting an acute effect that may contribute to the understanding of local physiological mechanism of FR.



#9 The Influence of Environmental Constraints in 360° Videos on Decision Making in Soccer

Reference: J Sport Exerc Psychol. 2021 Sep 1;1-10. doi: 10.1123/jsep.2020-0166. Online ahead of print.

Authors: Lisa Musculus, Jurek Bäder, Lukas Sander, Tobias Vogt 

Summary: Decision making is an important prerequisite of soccer expertise. Beyond expertise, considering the effects of environmental constraints on decision-making processes could help specify existing theories. To address this gap, expert and nonexpert soccer players were enrolled to test how environmental constraints affect decision-making processes. Environmental constraints were experimentally manipulated: Opponent pressure was implemented by presenting a close opponent player in soccer scenes, time constraint was implemented by providing short time intervals for making the decision, and first-person perspective was implemented by using 360° videos. The experts outperformed the nonexperts, and the results showed significant main effects of time constraint and opponent pressure, but not perspective. The players' option and decision quality improved under the time constraint but were negatively affected by opponent pressure. The negative effects of opponent pressure were especially true under limited time and in third-person perspective. The results, alternative manipulations, and implications of environmental effects are discussed for decision-making research.



#10 Moving Beyond One-Size-Fits-All Approaches to Injury Prevention: Evaluating How Tailored Injury Prevention Programs Are Developed and Implemented in Academy Soccer

Reference: J Orthop Sports Phys Ther. 2021 Sep;51(9):432-439. doi: 10.2519/jospt.2021.10513.

Authors: James O'Brien, Emanuel Santner, Josef Kröll

Summary: The aim was to evaluate the real-world development and implementation of tailored injury prevention exercise programs (IPEPs) in academy soccer players. The participants were 38 players and staff members (eg, coaches, physical therapists) from 4 male teams in 1 European soccer academy. The content and nature of the 4 teams' IPEPs and the degree of implementation across 1 playing season were evaluated. Additionally, participants took part in semi-structured interviews and focus groups, focusing on the development of tailored IPEPs and implementation barriers and facilitators. Teams employed multiple IPEPs, developed by the team physical therapists and strength and conditioning coaches. A range of sources, including scientific literature, guidelines, individual player screening data, and previous experience, influenced IPEP development. Across all teams, 76% of IPEP sessions were completed as originally planned and a further 11% were completed in modified form. The key barriers to implementation during the season were related to scheduling changes and managing player workload. Thematic coding of interviews and focus groups identified 25 IPEP implementation barriers (eg, time and scheduling, player workload) and 41 facilitators (eg, program adaptability, facilities and equipment). In a male soccer academy setting, physical therapists and strength and conditioning coaches played the key role in IPEP development. Teams employed a range of different, internally developed programs. The key implementation factors were related to time and scheduling and managing player workload. 



#11 Association between offensive and defensive playing style variables and ranking position in a national football league

Reference: J Sports Sci. 2021 Sep 9;1-9. doi: 10.1080/02640414.2021.1976488. Online ahead of print.

Authors: Alejandro Lopez-Valenciano, Jose Alberto Garcia-Gómez, Roberto López-Del Campo, Ricardo Resta, Victor Moreno-Perez, Hugo Blanco-Pita, Ángel Valés-Vázquez, Juan Del Coso

Summary: The aim of this study was to determine the association of playing style and efficacy variables with football success in a professional football league. Match statistics were obtained from 23 football teams competing in the 2017-2018 and 2018-2019 seasons of the Spanish national league(LaLiga). Offensive and defensive playing style and efficacy variables were calculated. Pearson's correlation coefficient tests and principal component analysis (PCA) were applied to establish the influence of these variables on the number of points obtained at the end of the season and on the ranking position. In isolation, the efficacy of completion showed the highest association with ranking points and position. A two-dimension PCA explained 77.8% of the variance in the ranking position. In dimension-1 (58.5%), game initiative and attack building, and in dimension-2 (19.3%), efficacy of defensive containment and a lower rate of long passes were within the variables that explained more variance in the ranking position. Success in football, measured by ranking position at the end of the Spanish national league, was associated with several playing style and efficacy variables. Overall, a dominant game style with high efficacy to finish attacking plays, and an offensive game initiative, are most associated with successful football.



#12 Acceleration profile of high-impact movements during young football games: a cross-sectional study involving healthy children

Reference: Sports Biomech. 2021 Sep 7;1-15. doi: 10.1080/14763141.2021.1970796. Online ahead of print.

Authors: Shogo Sasaki, Yasuharu Nagano, Yusaku Suganuma, Takeshi Koyama, Hiroshi Ichikawa

Summary: Repetitive high-impact movements cause growth-related injuries in children. This study aimed to identify which movements during junior football games require >6 G and >8 G acceleration and the frequency at which they occur. Additionally, we compared the components of acceleration among movements with >8 G resultant acceleration. Eleven young male footballers (10.7 ± 0.4 years) played 8-a-side games while wearing a tri-axial accelerometer on their upper back. The number and frequency of the movements that generated >6 G and >8 G were calculated, and each directive acceleration of the top five items was compared using two-way ANOVA to examine the effect of movements. The frequency of movements that generated >6 G and >8 G acceleration during junior football games was 8.70 case/min and 2.62 case/min, respectively. The top five >8 G movements were braking and pre-braking in shuffle, slowdown, stop, and run/jog items. The vertical acceleration was significantly greater during braking in shuffle than during slowdown, stop, and run/jog and also greater during stop and pre-braking in shuffle than during run/jog movement. This pilot study suggests that decelerated movements mainly provoked high-impact situations and may be key actions for preventing overuse injury in young footballers.



#13 No Fans-No Pressure: Referees in Professional Football During the COVID-19 Pandemic

Reference: Front Sports Act Living. 2021 Aug 19;3:720488. doi: 10.3389/fspor.2021.720488. eCollection 2021.

Authors: Michael Christian Leitner, Fabio Richlan 

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Summary: Due to the COVID-19 pandemic, European elite football (a.k.a. soccer) leagues played the remaining season 2019/20 without or strongly limited attendance of supporters (i.e., "ghost games"). From a sport psychological perspective this situation poses a unique opportunity to investigate the crowd's influence on referee decisions and the associated effect of "home advantage." A total of 1286 matches-played in the top leagues of Spain, England, Germany, Italy, Russia, Turkey, Austria and the Czech Republic-were analyzed for results, fouls, bookings and reasons for bookings and contrasted between respective matchdays of season 2018/19 (regular attendance) and season 2019/20 (ghost games). Following recent methodological developments in the research on the home advantage effect, four different statistical analyses-including Pollard's traditional method-were used for the assessment of the home advantage effect. There are two main findings. First, home teams were booked significantly more often with yellow cards for committing fouls in ghost games. Most importantly, this effect was independent of the course of the games. In contrast, bookings for other reasons (criticism and unfair sportsmanship) changed similarly for both home and away teams in ghost games. Second, the overall home performance and home advantage effect in the respective elite leagues-identified in the respective matches of the regular 2018/19 season-vanished in the ghost games of the 2019/20 season. We conclude that the lack of supporters in top European football during the COVID-19 pandemic led to decreased social pressure from the ranks on referees, which also had a potential impact on the home advantage. Referees assessed the play of home teams more objectively, leading to increased yellow cards awarded for fouls committed by the home teams. Since there were no significant changes in referee decisions against the away teams, we argue that our observations reflect a reduction of unconscious favoritism of referees for the home teams.



#14 Perceived load, fatigue and recovery responses during congested and non-congested micro-cycles in international football tournaments

Reference: J Sci Med Sport. 2021 Jul 9;S1440-2440(21)00177-8.  doi: 10.1016/j.jsams.2021.07.001. 

Authors: Denny Noor, Alan McCall, Mark Jones, Craig Duncan, Fabian Ehrmann, Tim Meyer, Rob Duffield

Summary: The aim was to describe the perceived load, fatigue and recovery profiles during congested and non-congested schedules in international football tournaments. Internal load (session-rating of perceived exertion [s-RPE]) and perceived ratings of fatigue, muscle soreness, psychological status, sleep quality, and sleep duration were recorded daily from 37 national team footballers during the competition phase of 3 international tournaments. ANOVA and Effect Size (ES) analyses compared individualised internal load and perceived response profiles between congested and non-congested acute 2-match schedules. Conditions included Acute Congestion (≤4 days between two matches), Non-Congestion (>4 days between two matches), Single-Match, and No-Match. Significantly higher s-RPE match loads (p < 0.001) within the single- and multi-match conditions resulted in significantly worsened (p < 0.05) subjective ratings of perceived fatigue, muscle soreness and sleep duration in the 24-48 h post-match. Internal load profiles were not different between the Acute-Congestion or Non-congestion conditions (p > 0.05); though Acute-Congestion had significantly worsened pre-match subjective ratings compared to Non-Congestion on both MD1 (p = 0.040; ES = 0.94) and MD2 (p = 0.033; ES = 0.94). However, between-match differences in Acute-Congestion showed no further impairments in perceived response between the first and second matches (p > 0.05). During international tournaments, internal load and perceived fatigue/recovery profiles are largely determined by their exposure (or lack thereof) to match-play. Periods of acute match congestion impaired players pre-match perceived status when compared to non-congested microcycles. However, acute match congestion does not appear to exacerbate players post-match fatigue/recovery response within the context of international football tournaments.



#15 The effect of the adapted soccer programme on motor learning and psychosocial behaviour in adolescents with Down syndrome

Reference: J Intellect Disabil Res. 2021 Sep 9. doi: 10.1111/jir.12881. Online ahead of print.

Authors: D B Perić, B Milićević-Marinković, D Djurović

Summary: Numerous studies have proven the significant positive impact of the regular physical activity on general health conditions and quality of life of people with intellectual disability. In practice, various adapted sports activities are used. The current study deals with the effects of the soccer programme. The purpose of the study is to evaluate the effects of adapted soccer on the motor learning and some psychosocial characteristics in adolescents with Down syndrome. Twenty-five participants were recruited and randomised into two groups (exercise and control). Adolescents placed in the exercise group carried out a special soccer programme twice a week during 16 weeks, while adolescents placed in the control group continued with their usual daily regime. Specific motor coordination, level of aggression, attention disorders, level of anxiety and depression, and social problems were measured before and after the training period. Mixed ANOVA were used to evaluate the effects of the experimental treatment. The exercise group had significant improvements (P < 0.05) in one of three motor variables (only in the easiest task) and in all psychosocial variables. There are no one significant change in the control group. The adapted soccer programme influenced more seriously on psychosocial characteristics than on motor learning of adolescent with DS. The results suggest that adapted soccer training can decrease aggression, anxiety and depression levels, and improve attention, social behaviour and simple motor skills in adolescents with Down syndrome.



#16  Ankle Injuries in Soccer Players: A Narrative Review

Reference: Cureus. 2021 Aug 16;13(8):e17228. doi: 10.7759/cureus.17228. eCollection 2021 Aug.

Authors: Spyridon Kolokotsios, Gianna Drousia, Ioannis Koukoulithras, Minas Plexousakis

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Summary: Soccer is one of the most popular sport, with many describing it as the "king of sports." In recent years, increased global participation in soccer has led to an inevitable increase in injury rates, especially in the lower extremities. Consequently, there is an increase in the epidemiology of soccer injuries, both in professionals and amateur athletes. The cause of an injury is multifactorial and depends on psychosocial, predisposing, intrinsic, and extrinsic factors. Also, contact with another player and non-contact injuries seem to be the most widespread mechanisms of injuries. The most common injuries recorded in soccer are ankle sprains and hamstrings injuries. More specifically, many studies have shown a correlation between the previous injury in lower extremities, weakness of abductors muscle, and psychosocial factors with the ankle sprain. Additionally, according to study results, injuries in adult men, adolescent men, and women during a match are higher than injuries during training. This narrative review aims to record the epidemiology of ankle injuries, risk factors, and the relationship between circadian rhythm, sleep, and injuries.



#17 Ball heading and subclinical concussion in soccer as a risk factor for anterior cruciate ligament injury

Reference: J Orthop Surg Res. 2021 Sep 19;16(1):566.: 10.1186/s13018-021-02711-z.

Authors: George Kakavas, Nikolaos Malliaropoulos, Wieslaw Blach, Georgios Bikos, Filippo Migliorini, Nicola Maffulli 

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Summary: Soccer players have a high risk of anterior cruciate ligament (ACL) injury, a potentially career-ending event. ACL rupture has been linked with abnormal neuromuscular control in the lower limb. Additionally, heading the ball with the unprotected head during game play is increasingly recognized as a major source of exposure to concussive and sub-concussive repetitive head impacts. This article provides a hypothesis of potential connection of ACL injury with ball heading in soccer players. The study reviews literature sources regarding the impact of neurocognitive alterations after ball headings in ACL injuries. Poor baseline neurocognitive performance or impairments in neurocognitive performance via sleep deprivation, psychological stress, or concussion can increase the risk for subsequent musculoskeletal injury.



#18 The LEAF questionnaire is a good screening tool for the identification of the Female Athlete Triad/Relative Energy Deficiency in Sport among young football players

Reference: PeerJ. 2021 Sep 3;9:e12118.  doi: 10.7717/peerj.12118. eCollection 2021.

Authors: Edyta Łuszczki, Pawel Jagielski, Anna Bartosiewicz, Maciej Kuchciak, Katarzyna Dereń, Artur Stolarczyk, Paweł Pakosz, Lukasz Oleksy

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Summary: It has been noticed that Female Athlete Triad (Fat) and Relative Energy Deficiency (Red-S) in Sport are characterized by the symptoms of impaired endocrine-metabolic function and bone health in female athletes. In addition, it may be evaluated with a qualitative tool, such as Low Energy Availability in Females questionnaire (LEAF-Q) and quantitative measurements: bone mineral density (BMD), resting energy expenditure (REE), body composition, 24-hour dietary recall. The aim of this study was to assess the prevalence of Triad and Red-S using the LEAF-Q in youth female football players. Additionally, the difference in the BMD, body composition, REE and energy intake (EI) were assessed between the Triad/Red-S risk and not at-risk groups. Almost two thirds (64.7%) of participants are classified as being at-risk for the triad according to their LEAF-Q scores. There were no statistically significant differences (p > 0.05) between most of the values among children from the analyzed groups. There was a statistically significant difference (p < 0.001) between the EI values among girls from the two analyzed groups: at-risk (1,773.18 kcal ± 232.57) and not at-risk (2,054.00 kcal ± 191.39). Girls who did not meet the energy intake recommendations were 10.00 as likely to be in the Triad/Red-S risk group. Early identification of Fat/Red-S symptoms by screening tools such as the LEAF questionnaire is important in protecting young athletes from long-term damage due to the progression of the risk factors associated with the Fat/Red-S.



#19 Perceptions of Football Analysts Goal-Scoring Opportunity Predictions: A Qualitative Case Study

Reference: Front Psychol. 2021 Sep 6;12:735167. doi: 10.3389/fpsyg.2021.735167. eCollection 2021.

Authors: Rubén D Aguado-Méndez, José Antonio González-Jurado, Álvaro Reina-Gómez, Fernando Manuel Otero-Saborido

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Summary: This study aimed to understand the way tactical football analysts perceive the general match analysis issues and to analyze their tactical interpretation of the predictive models of conceded goal-scoring opportunities. Nine tactical analysts responded to the semi-structured interviews that included a general section on the match analysis and a specific one on the results of a study on goal-scoring opportunities conceded by a Spanish La Liga team. Following their transcription, the interviews were codified into categories by the two researchers using Atlas Ti® software. Subsequently, frequency count and co-occurrence analysis were performed based on the encodings. The content analysis reflected that analysts play a crucial role in the analysis of their own team and that of the opponent, the essential skills to exercise as a tactical analyst being "understanding of the game" and "clear observation methodology." Based on the case study of the conceded goal-scoring opportunities, the major causes and/or solutions attributed by analysts in some of the predictive models were the adaptability of the "style of play" itself according to the "opponent" and "pressure after losing."



#20 Shedding Light on Incidence and Burden of Physeal Injuries in Youth Elite Football Academy: A 4-Season Prospective Study

Reference: Scand J Med Sci Sports. 2021 Sep 22.  doi: 10.1111/sms.14059. Online ahead of print.

Authors: Olivier Materne, Karim Chamari, Abdulaziz Farooq, Montassar Tabben, Adam Weir, Per Holmich, Roald Bahr, Matt Greig, Lars R McNaughton

Summary: Physeal injuries have been overlooked in epidemiological research in youth sports. Our prospective study investigated the incidence, severity, and burden of physeal injuries in a youth elite football academy. 551 youth male football players from Under-9 to Under-19 were included and observed over four consecutive seasons. Injuries involving the physis were diagnosed and recorded according to type, location, and diagnosis. Injury incidence (II), severity (days lost), and injury burden (IB) were calculated per squad per season (25 players/squad). There were 307 physeal injuries: 262 apophyseal- (85%), 26 physeal- (9%), 2 epiphyseal- (1%) and 17 other physeal-injuries (5%) with 80% (n=245) causing time-loss. The overall mean incidence of time-loss physeal injuries was 6 injuries/squad-season leading to a total of 157 days lost/squad-season. The U-16s had the highest burden with 444 days lost per squad-season [Median: 20 (95%CI:12-30) days; II: 10 (95%CI:7.3.1-13.4)]. Apophyseal injuries of the hip-pelvis resulted in the greatest burden [Median: 13 (95%CI: 10-17); II: 2.5 (95%CI: 2.1-3.0)]. Peak apophyseal injury incidence per body parts occurred in U-11 for foot-ankle (II: 2.4; 95% CI: 1.0-4.9), U-14 for knee (II: 4.5; 95% CI: 2.7-7.1), and in U-17 for hip-pelvis (II: 6.4; 95% CI: 4.2-9.3). Physeal injuries accounted for a quarter of all-time loss with the largest injury burden in U-16. Most physeal injuries involved the lower limb and affected the apophysis. Physeal and apophyseal injuries incidence, burden and pattern vary substantially depending on age. Hip-pelvic apophyseal injuries accounted for the largest injury burden.



#21 Integrating video tracking and GPS to quantify accelerations and decelerations in elite soccer

Reference: Sci Rep. 2021 Sep 17;11(1):18531. doi: 10.1038/s41598-021-97903-2.

Authors: Eduard Pons, Tomás García-Calvo, Francesc Cos, Ricardo Resta, Hugo Blanco, Roberto López Del Campo, Jesús Díaz-García, Juan José Pulido-González

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Summary: The aim of this study was to analyze the degree of agreement comparing number and distance covered in different acceleration and deceleration sections registered by a video tracking system (MEDIACOACH) and a GPS device (WIMU PRO) during official competition. Data from a Spanish professional club were registered over the course of a season. First, the descriptive statistics presented more bursts of accelerations and decelerations in WIMU PRO than in MEDIACOACH, whereas the distances covered recorded by both systems were similar. Second, negative relationships were found (i.e., negative bias) comparing WIMU PRO to MEDIACOACH in the number of accelerations and decelerations between 0/1 m/s2 and ½ m/s2 (p < 0.05), and in the distances covered in accelerations and decelerations (p < 0.05) between 0/1 m/s2 and in accelerations and decelerations registered between 2/3 m/s2 and more than 3 m/s2. Moreover, the differences in means (i.e., standardized mean bias) across the two devices were trivial (> 0.19) and small (0.2-0.59) for most variables. The standardized typical errors in the estimate (TEE) were moderate (0.3-0.59) and small to moderate (0.1-0.29 to 0.3-0.59), respectively. Also, the Intra class Correlation Coefficients (ICCs) for agreement and consistency between systems showed good and excellent values (> 0.90). The magnitude of change in means (%) between systems, defined as the percentage change between the numbers or values, was below 14% and 7% for number and distances covered, respectively. All scores in the smallest worthwhile change were lower than 9% and in the coefficients of variation were lower than 95% and 15%, respectively. Thus, both systems demonstrated an acceptable degree of agreement and could be useful in analyzing players' acceleration demands in professional soccer. However, caution is required when interpreting the results and a comparison with a gold standard is required in order to validate both systems.



#22 Effect of bio-banding on physiological and technical-tactical key performance indicators in youth elite soccer

Reference: Eur J Sport Sci. 2021 Sep 19;1-9. doi: 10.1080/17461391.2021.1974100. Online ahead of print.

Authors: Dennis Lüdin, Lars Donath, Stephen Cobley, Michael Romann

Summary: Bio-banding has been introduced to reduce the impact of inter-individual differences due to biological maturation among youth athletes. Existing studies in youth soccer have generally examined the pilot-testing application of bio-banding. This is the first study that investigated whether bio-banded (BB) versus chronological age (CA) competition affects reliable physiological and technical-tactical in-game key performance indicators (KPIs) using a randomized cross-over repeated measures design. Sixty-five youth elite soccer players from the under-13 (U13) and under-14 (U14) age category and with maturity offsets (MO) between -2.5 and 0.5 years, competed in both a BB and CA game. For statistical analysis, players were divided into four sub-groups according to CA and MO: U13MOlow (CA ≤ 12.7, MO ≤ -1.4), U13MOhigh (CA ≤ 12.7, MO > -1.4), U14MOlow (CA > 12.7, MO ≤ -1.4), U14MOhigh (CA > 12.7, MO > -1.4). The two-factor mixed ANOVA revealed significant (p < .05) interactions between competition format and sub-group for the KPIs high accelerations (η2pηp2 = .176), conquered balls (η2pηp2 = .227) and attack balls (η2pηp2 = .146). Especially, U13MOhigh (i.e. early maturing players) faced a higher physiological challenge by having more high accelerations (|d| = 0.6) in BB games. Notably, U14MOlow (i.e. late maturing players) had more opportunities to show their technical-tactical abilities during BB games with more conquered balls (|d| = 1.1) and attack balls (|d| = 1.6). Affected KPIs indicate new challenges and learning opportunities during BB competition depending on a player's individual maturity status. Bio-banding can beneficially be applied to enhance the talent development of youth elite soccer players.



#23 Comparison of Immediate Effects of Foam Rolling and Dynamic Stretching to Only Dynamic Stretching on Flexibility, Balance, and Agility in Male Soccer Players

Reference: J Sport Rehabil. 2021 Sep 20;1-7. doi: 10.1123/jsr.2021-0017. Online ahead of print.

Authors: Erhan Seçer, Derya Özer Kaya

Summary: Dynamic stretching (DS) is typically suggested during warm-up protocols. Also, foam rolling (FR), which is applied with a foam cylinder, has increased popularity in recent years. However, the combined effects of DS and FR in improving flexibility, dynamic balance, and agility performance are unclear in current literature. Therefore, this study aim to evaluate and compare the acute effects of DS as well as DS followed by FR (DS + FR) on flexibility, dynamic balance, and agility in male soccer players. Thirty volunteer male soccer players (mean age 18.80 [0.66] y) were included in the study. Each participant performed the 2 sessions (DS and DS + FR) on separate occasions in a randomized order, with an interval of 72 hours. All sessions were performed in the indoor gym at the sports club. Flexibility was assessed by sit-and-reach test, dynamic balance was assessed by Y balance test, and agility was assessed by t test. Compared with the pretest results, significant improvement in flexibility was observed in both groups (change = 0.55, percentage change = 2.05, effect size [ES] = 0.15, P = .041; change = 0.64, percentage change = 2.36, ES = 0.20, P = .025; respectively). Balance scores did not significantly improve in either group (change = 0.40, percentage change = 0.45, ES = 0.09, P = .342; change = 0.93, percentage change = 1.02, ES = 0.23, P = .103; respectively). Agility performance significantly improved in both groups (change = -0.12, percentage change = -1.18, ES = 0.19, P = .021; change = -0.21, percentage change = -2.18, ES = 0.38, P = .005; respectively). Both DS and DS + FR improved flexibility and agility and did not affect balance. DS + FR was not superior to DS at improving flexibility and agility as compared only with DS. Both methods are effective warm-up protocols to augment factors related to injury risk and performance. It seems that further studies that investigate the combined effects of FR and DS are needed.



#24 Impact of COVID-19 lockdown on the epidemiology of soccer muscle injuries in Italian Serie A professional football players

Reference: J Sports Med Phys Fitness. 2021 Sep 21. doi: 10.23736/S0022-4707.21.12903-2. Online ahead of print.

Authors: Nicola Marotta, Alessandro DE Sire, Alessandra Gimigliano, Andrea Demeco, Lucrezia Moggio, Andrea Vescio, Teresa Iona, Antonio Ammendolia

Summary: The aim was to evaluate the influence that COVID-19 lockdown had on the epidemiology of soccer musculoskeletal injuries during 2019/2020 Italian First Football League Serie A in professional football players. In this retrospective study we analyzed records from media-based platform (Trasfermarkt,, describing the epidemiology of muscle injuries before and after the first COVID-19 lockdown phases in Italian professional football players. We also classified the severity of the injury as the number of missing days from participation. We assessed a lower prevalence of post-lockdown injuries, albeit showing a similar injury rate at 1000 game-hours (pre-lockdown: 16.9 [13.0-20.7], post-lockdown: 15.5 [9.9-21.1]; RR: 0.92 [0.46-1.8]). All risk ratios for injury rate were not significantly different (p> .05) between pre- and post-lockdown. The incidence of muscle injuries has not significantly changed after the first COVID-19 lockdown in Italian professional soccer players. Recognizing injury rates might be crucial for physician to evaluate adequate preventive measures.



#25 Association of phase angle and appendicular upper and lower body lean soft tissue with physical performance in young elite soccer players: a pilot study

Reference: J Sports Med Phys Fitness. 2021 Sep 21. doi: 10.23736/S0022-4707.21.12911-1. Online ahead of print.

Authors: Tindaro Bongiovanni, Alessio Rossi, F Marcello Iaia, Giampietro Alberti, Giulio Pasta, Athos Trecroci

Summary: In soccer, a better understanding of the bioimpedance parameters with physical performance may be useful to efficiently monitor and interpret players' performance variation throughout a certain period of the season. Therefore, this study aimed to examine the association between phase angle (PhA) and arms and legs lean soft tissue (ALST and LLST) with physical performance in young elite soccer players. Fifteen young male elite soccer players (age = 14.2±1.2 years, BMI = 20.51±1.38 kg/m2) participated in this investigation. Raw bioimpedance parameters (reactance, resistance, and phase angle) were obtained by a bioelectrical impedance analysis (BIA) device. Then, ALST and LLST were estimated. All players underwent a physical testing battery including countermovement jump (CMJ), 10-m and 20-m sprint, and Yo-Yo Intermittent Recovery Test level 1 (YoYo IRTL1) in the domains of anaerobic and aerobic performance, respectively. The results showed that LST (total, arms and legs) positively correlated with CMJ (0.64 < r < 0.69; p < 0.001) and negatively correlated with 10-m (-0.59 < r < -0.63; p < 0.05) and 20-m sprint (-0.67 < r < -0.73; p < 0.001), while PhA positively correlated with CMJ (r = 0.57; p < 0.05) and negatively correlated (r = -0.54; p < 0.05) only with 20-m sprint. No significant association was found between the BIA-related parameters (PhA and LST) and Yo- Yo IRT level 1. The present findings highlight the existing association of PhA and LST with jumping and sprinting performance in young elite soccer players. This result supports the use of BIA-related measures as a simple and practical approach to monitoring anaerobic performance changes, rather than aerobic, over time throughout the season.



#26 Predicting Cardiorespiratory Fitness in Female Soccer Players: The Basque Female Football Cohort Study

Reference: Int J Sports Physiol Perform. 2021 Sep 21;1-8. doi: 10.1123/ijspp.2020-0848. Online ahead of print.

Authors: Ibai Garcia-Tabar, Aitor Iturricastillo, Julen Castellano, Eduardo L Cadore, Mikel Izquierdo, Igor Setuain

Summary: The purpose was to develop gender-specific operational equations for prediction of cardiorespiratory fitness in female footballers. Forty-eight semiprofessional female footballers performed an intermittent progressive maximal running test for determination of fixed blood lactate concentration (FBLC) thresholds. Relationships between FBLC thresholds and the physiological responses to submaximal running were examined. Developed equations (n = 48) were compared with equations previously obtained in another investigation performed in males (n = 100). Submaximal velocity associated with 90% maximal heart rate was related to FBLC thresholds (r = .76 to .79; P < .001). Predictive power (R2 = .82 to .94) of a single blood lactate concentration (BLC) sample measured at 10 or 11.5 km·h-1 was very high. A single BLC sample taken after a 5-minute running bout at 8.5 km·h-1 was related to FBLC thresholds (r = -.71; P < .001). No difference (P = .15) in the regression lines predicting FBLC thresholds from velocity associated with 90% maximal heart rate was observed between the female and male cohorts. However, regressions estimating FBLC thresholds by a single BLC sample were different (P = .002). Velocity associated with 90% maximal heart rate was robustly related to FBLC thresholds and might serve for mass field testing independently of sex. BLC equations accurately predicted FBLC thresholds. However, these equations are gender-specific. This is the first study reporting operational equations to estimate the FBLC thresholds in female footballers. The use of these equations reduces the burden associated with cardiorespiratory testing. Further cross-validation studies are warranted to validate the proposed equations and establish them for mass field testing.



#26 Endoscopic Flexor Hallucis Longus Transfer for the Management of Acute Achilles Tendon Ruptures in Professional Soccer Players Foot

Reference: Ankle Int. 2021 Sep 24;10711007211036439.  doi: 10.1177/10711007211036439. Online ahead of print.

Authors: Nasef Mohamed N Abdelatif, Jorge Pablo Batista 

Summary: Acute Achilles tendon ruptures (AATRs) that occur in athletes can be a career-ending injury. The aim of this study was to describe return to play and clinical outcomes of isolated endoscopic flexor hallucis longus (FHL) transfer in active soccer players with AATR. Twenty-seven active male soccer players who underwent endoscopically assisted FHL tendon transfer for acute Achilles tendon ruptures were included in this study. Follow up was 46.2 (±10.9) months after surgery. Return to play criteria and clinical outcome measures were evaluated. All players returned to playing professional competitive soccer games. Return to active team training was at a mean of 5.8 (±1.1) months postoperatively. However, return to active competitive match play occurred at a mean of 8.3 (±1.4) months. Twenty-two players (82%) were able to return to their preinjury levels and performances and resumed their professional careers at the same soccer club as their preinjury state. One player (3.7%) shifted his career to professional indoor soccer. At 26 months postoperatively, the mean Tegner activity scale score was 9.7 (±0.4), the mean Achilles tendon total rupture score was 99 (±2), and the mean American Orthopaedic Foot & Ankle Society ankle-hindfoot score was 99 (±3). No patients reported any great toe complaints or symptomatic deficits of flexion strength. The current study demonstrated satisfactory and comparable return to play criteria and clinical results with minimal complications when using an advanced endoscopically assisted technique involving FHL tendon transfer to treat acute Achilles tendon ruptures in this specific subset of patient cohort.



#27 Strength training in professional soccer: effects on short-sprint and jump performance

Reference: Int J Sports Med. 2021 Sep 24. doi: 10.1055/a-1653-7350. Online ahead of print.

Authors: Javier Nuñez, Luis Suarez-Arrones, Moisés de Hoyo, Irineu Loturco

Summary: Several studies have confirmed the efficacy of strength training to maximize soccer player performance during competition. The aim of this meta-analysis was to determine the effects of different strength training protocols on short-sprint and vertical jump performance of professional soccer players from the first division of their countries. The following inclusion criteria were employed for the analysis: (a) randomized studies; (b) high validity and reliability instruments; (c) studies published in a high-quality peer-reviewed journal; (d) studies involving professional soccer players from the first division; (e) studies with descriptions of strength training programs; and (f) studies where countermovement jump and 10-m sprint time were measured pre and post training. Overall, the different strength-oriented training schemes produced similar performance improvements, which seem not to depend on the training strategy. Strength training appears to have a lower effect when applied during in-season than when applied in pre-season periods in first division soccer players. In this meta-analysis it is not possible to confirm that strength training in isolation is capable of improving the short-sprint and jump performance of elite soccer players. The congested fixture schedule and, thus, the limited time to perform complementary (non-specific) training sessions, may contribute to these reduced effects.



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