Latest research in football - week 48 - 2022

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


Following studies were retrieved for this week:

#1 Effects of a 10-Week Combined Coordination and Agility Training Program on Young Male Soccer Players

Reference: Int J Environ Res Public Health. 2021 Sep 26;18(19):10125. doi: 10.3390/ijerph181910125.

Authors: Francisco Tomás González-Fernández, Hugo Sarmento, Alfonso Castillo-Rodríguez, Rui Silva, Filipe Manuel Clemente

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Summary: The current literature has shown how working on coordination and agility produces effects on specific aspects in team sports. The purpose of this study was to examine the effects of a ten-week coordination training program applied to soccer on different tests that evaluate speed (30 m speed test), agility (Illinois Agility Test (IAT)) and lower body strength (countermovement jump (CMJ)). Forty U16 male soccer players from two nonprofessional teams (twenty in the control group (CG) (aged = 14.70 ± 0.47, body weight = 60.15 ± 8.07 kg, height = 1.71 ± 0.06 m) and twenty in the experimental group (EG) (aged = 14.50 ± 0.51, body weight = 58.08 ± 9.78 kg, height = 1.69 ± 0.06 m)) performed a combined coordination and agility program during 10 min every training day (3 days a week) for 10 weeks. The results of this study showed that coordination training produced adaptations in the power (CMJ of EG (p = 0.001)) and agility capacities (IAT of EG (p = 0.002)) of young soccer players, but not on speed performance at longer distances (CG, p = 0.20 and EG, p = 0.09). Despite the benefits of the training program, a combination of training methods that includes power, agility, speed, and strength can enhance such improvements.



#2 Effects of a Specific Core Stability Program on the Sprint and Change-of-Direction Maneuverability Performance in Youth, Male Soccer Players

Reference: Int J Environ Res Public Health. 2021 Sep 26;18(19):10116. doi: 10.3390/ijerph181910116.

Authors: Eric Brull-Muria, Jose Vicente Beltran-Garrido

Summary: Although it is recommended to use sport-specific training programs to optimize performance, studies analyzing the effects of the core stability training with high levels of sport-specificity on athletic performance are insufficient and unclear. The objective of this study was to analyze the effects of the level of specificity of a CORE stability program on specific soccer actions. Fourteen youth players were randomly assigned to the specific core stability group (SCS; n = 7) or the general core stability group (GCS; n = 7). The eight-week intervention consisted of two weekly training sessions added to the usual soccer training. Both groups performed four CORE stability tasks. The SCS group followed the principle of sports specificity, while the GCS group performed CORE stability commons. Ten-meter linear sprinting (Sprint) and change-of-direction maneuverability (V-cut) were evaluated before and after the intervention programs. A statistically significant improvement was obtained in Sprint (d = 0.84 95% CI (0.22, 1.45), p = 0.008) and V-cut (d = 1.24 95% CI (0.52, 1.93), p < 0.001). At posttest, statistically nonsignificant differences were obtained between groups in Sprint (d = 1.03 95% CI (-0.25, 2.30), p = 0.082) and V-cut (d = -0.56 95% CI (-1.89, 0.78), p = 0.370). In conclusion, sprint and change-of-direction maneuverability were improved, but there was no superiority of any type of training.



#3 Sprint Variables Are Associated with the Odds Ratios of Non-Contact Injuries in Professional Soccer Players

Reference: Int J Environ Res Public Health. 2021 Oct 3;18(19):10417. doi: 10.3390/ijerph181910417.

Authors: Hadi Nobari, Elena Mainer-Pardos, Angel Denche Zamorano, Thomas G Bowman, Filipe Manuel Clemente, Jorge Pérez-Gómez

Summary: Significant evidence has emerged that a high volume of sprinting during training is associated with an increased risk of non-contact injuries in professional soccer players. Training load has been reported as a modifiable risk factor for successive injury in soccer. Sprint workload measures and non-contact injuries were recorded weekly in twenty-one professional soccer players over a one season period. Odds ratio (OR) and relative risk (RR) were calculated based on the weeks of high and low load of total distance (TD), high-speed distance (HSD), sprint distance (SPD). and repeated sprints (RS). The Poisson distribution estimated the interval time between the last injury and the new injury. The weeks with high-load levels increased the risk of non-contact injury associated with TD (OR: 4.1; RR: 2.4), HSD (OR: 4.6; RR: 2.6), SPD (OR: 6.9; RR: 3.7), and RS (OR: 4.3; RR: 2.7). The time between injuries was significantly longer in weeks of low-load in TD (rate ratio time (RRT) 1.5 vs. 4.2), HSD (RRT: 1.6 vs. 4.6), and SPD (RRT: 1.7 vs. 7.7) compared to weeks of high-load. The findings highlight an increased risk of non-contact injuries during high weekly sprint workloads. Possibly, TD, HSD, and SPD measured via a wearable inertial measurement unit could be modeled to track training and to reduce non-contact injuries. Finally, the interval time between the last injury and the new injury at the high-load is shorter than the low-load.



#4 An 8-Week Program of Plyometrics and Sprints with Changes of Direction Improved Anaerobic Fitness in Young Male Soccer Players

Reference: Int J Environ Res Public Health. 2021 Oct 4;18(19):10446. doi: 10.3390/ijerph181910446.

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

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Summary: This study examined the effects of 8 weeks of twice-weekly combined plyometric and sprint with change-of-direction (CPSCoD) training into habitual training regimes of young male soccer players. Participants were randomly allocated to an experimental group (n = 17, age: 14.6 ± 0.44 years, body mass: 61.2 ± 7.34 kg, height: 1.67 ± 0.09 m, body fat: 11.2 ± 1.56%) and a control group (n = 16, age: 14.6 ± 0.39 years, body mass: 61.1 ± 3.96 kg, height: 1.67 ± 0.05 m, body fat: 11.8 ± 1.47%). Measures obtained pre- and post intervention included vertical and horizontal jump performance (i.e., squat jump (SJ), countermovement jump (CMJ), and standing long jump (SLJ)), and sprint performance (i.e., 5 m and 20 m sprint). In addition, Measures obtained pre- and post-intervention included 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 performance (stork balance test). The training group experienced superior jump (all p < 0.05; d ≥ 0.61), sprint (all p < 0.05; d ≥ 0.58), change-of-direction (CoD) ability (all p < 0.05; d ≥ 0.58), RCoD (all parameters except the fatigue index p < 0.01; effect size (d) ≥ 0.71), and static balance (all p < 0.05; d ≥ 0.66) improvement. Adding twice-weekly CPSCoD training to standard training improves the anaerobic performance of U15 male soccer players.



#5 Different Pitch Configurations Constrain the Playing Tactics and the Creation of Goal Scoring Opportunities during Small Sided Games in Youth Soccer Players

Reference: Int J Environ Res Public Health. 2021 Oct 6;18(19):10500. doi: 10.3390/ijerph181910500.

Authors: Joaquín González-Rodenas, Rodrigo Aranda-Malavés, Andrés Tudela-Desantes, Pedro de Matías-Cid, Rafael Aranda

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Summary: The aim of this study was to explore the tactical effects of different pitch configurations on the collective playing tactics and the creation of goal scoring opportunities (GSO) during small sided soccer games (SSG) in youth players. A total of 22 players performed a 7 vs. 7 + 1 floater (including goalkeepers) under three different pitch configurations ("Standard", 53 × 38 m; "Long", 63 × 32 m; and "Wide", 43 × 47 m). Eleven tactical indicators related to the development and the end of the team possessions were evaluated by systematic observation. Friedman tests (non-parametric ANOVA for repeated measures) revealed that the long and wide configurations produced more counterattacks (p = 0.0028; ES = 0.3), higher offensive penetration (p = 0.007; ES = 0.41), and more GSO (p = 0.018; ES = 0.30) than the standard format. Regarding the creation of GSO, the wide configuration produced more assists in the form of crosses than the long and standard formats (p = 0.025; ES = 0.31), more utilization of wide subspaces to assist the final player (p = 0.022; ES = 0.35), more number of headers as the final action (p = 0.022; ES = 0.32), and less assists in the form of passes in behind the defense (p = 0.034; ES = 0.28), than the long configuration. The modulation of the pitch configuration during SSG produced different tactical demands, requiring players to implement different tactical solutions to create GSO.



#6 In-season monotony, strain and acute/chronic workload of perceived exertion, global positioning system running based variables between player positions of a top elite soccer team

Reference: BMC Sports Sci Med Rehabil. 2021 Oct 12;13(1):126. doi: 10.1186/s13102-021-00356-3.

Authors: Rafael Oliveira, Alexandre Martins, Hadi Nobari, Matilde Nalha, Bruno Mendes, Filipe Manuel Clemente, João Paulo Brito

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Summary: The interpretation of the load variations across a period seems important to control the weekly progression or variation of the load, or to identify within- micro and mesocycle variations. Thus, the aim of this study was to describe the in-season variations of training monotony, training strain, and acute: chronic workload ratio (ACWR) through session rating of perceived exertion (s-RPE), total distance and high-speed running (HSR) according to playing positions in an elite soccer team. Seventeen professional players from an European First League team participated in this study. They were divided four central defenders (CD), three wide defenders (WD), four central midfielders (CM), three wide midfielders (WM) and three strikers (ST). The players were monitored daily over a 41-week period of competition where 52 matches occurred during the 2015-2016 in-season. Through the collection of s-RPE, total distance and HSR, training monotony, training strain and ACWR were calculated for each measure, respectively. Data were analysed across ten mesocycles (M: 1-10). The main results showed significant differences (p < 0.05) for TMs-RPE between CD vs. ST (moderate effect) in M2; between CD vs. CM (moderate effect) for TS of s-RPE; between CD vs. ST moderate effect) in M6 for ACWR of s-RPE. In addition, there was significant difference between CM vs. ST (moderate effect) in M2 for TS of TD; between WD vs. ST (moderate effect) in M3 for ACWR of TD. Moreover, there were significant differences for TM of HSR between CD vs. WD (very large effect); CD vs. WD (moderate effect) in M4 for TS of HSR. The present study presents new insights to coaches and technical staff about the variation profiling of TM, TS, and ACWR calculated with internal and external load measures, between player positions during 10 mesocycles.



#7 Tanner-Whitehouse and Modified Bayley-Pinneau Adult Height Predictions in Elite Youth Soccer Players from the Middle East

Reference: Med Sci Sports Exerc. 2021 Jul 7. doi: 10.1249/MSS.0000000000002740. Online ahead of print.

Authors: Lorenzo Lolli, Amanda Johnson, Mauricio Monaco, Marco Cardinale, Valter Di Salvo, Warren Gregson

Summary: The aim was to provide the first scrutiny of adult height prediction protocols based on automated Greulich-Pyle and Tanner-Whitehouse (TW) skeletal ages applied to elite youth soccer players from the Middle East. We examined the application of modified Bayley-Pinneau (BoneXpert®), TW-II, and TW-III protocols using mixed-longitudinal data available for 103 subjects (chronological age range: 19.4 to 27.9 years) previously enrolled as academy student-athletes (annual screening range: 1 to 6 visits). Random-effects generalized additive models quantified the presence of systematic mean differences between actual versus predicted adult height. Effects were deemed practically equivalent based on the location of the confidence interval (95%CI) against a realistic difference value of [INCREMENT] = ± 1 cm. Each model pooled residual standard deviation (SD) described the actual precision of height predictions and was used to calculate a 95% prediction interval (95%PI). The BoneXpert® method over-predicted adult height systematically at chronological ages in the range of approximately 13.5 to 14.5 years (95%CI range: -1.9 to -1 cm) and Greulich-Pyle skeletal ages between 13.5 and 15 years (95%CI range: -3.1 to -1 cm). Effects based on TW-II were practically equivalent across the chronological and skeletal age measurement ranges, with this protocol yielding adult height predictions with a precision (SD) of approximately ±2.6 cm. The mean TW-III effects indicated systematic adult height over-predictions until the attainment of 14.5 and 15 years of chronological age (95%CI range: -3.8 to -1.1 cm) and TW-III skeletal age (95%CI range: -5.2 to -2.3 cm), respectively. TW-II adult height prediction method provided more consistent estimates and can be considered the method of choice for talent development purposes in youth soccer players from the Middle East.



#8 Soccer-related injuries utilization of U.S. emergency departments for concussions, intracranial injuries, and other-injuries in a national representative probability sample: Nationwide Emergency Department Sample, 2010 to 2013

Reference: PLoS One. 2021 Oct 12;16(10):e0258345. doi: 10.1371/journal.pone.0258345. eCollection 2021.

Authors: Gerardo Flores, Christopher C Giza, Barbara Bates-Jensen, Mary-Lynn Brecht, Dorothy Wiley

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Summary: Soccer participation in the United States (U.S.) has increased over time, and injuries as well as interest to prevent injuries has become more common. This study described Emergency Department (ED) visits related to concussions, intracranial injuries (ICI), and all-other injuries attributed to soccer play; described healthcare cost and length of hospital stay of soccer-related injuries; and determined independent predictors of concussions, ICI, and all-other soccer injuries leading to ED visits. The study examined soccer-related weighted discharge data from the Nationwide Emergency Department Sample, Healthcare Cost and Utilization Project, Agency for Healthcare Research and Quality. Weighted tabular analysis of univariate and bivariate analyses and weighted and adjusted logistic regression models were conducted. A total of 480,580 of U.S. ED visits related to soccer injuries were available for analysis between 2010 to 2013. Generally, 98% of soccer-related ED visits resulted in routine (treat-and-release) visits. However, the odds of transfer to a short-term hospital following ED evaluation and treatment was more than 37-fold higher for soccer-injured youth and adults diagnosed with ICI when compared to all-other soccer injuries; additionally, these patients showed 28-fold higher odds of being admitted for inpatient care at the ED-affiliated hospital. For concussion, soccer-injured patients with concussion showed nearly 1.5-fold higher odds of being transferred to a short-term hospital than did those with any other soccer injury. Soccer-related ED visits cost more than 700 million in U.S. dollars from 2010 to 2013. Notable differences were noted between concussions, ICI, and all-other soccer injuries presenting to U.S. ED. Albeit underestimated given that this study excludes other forms of health care and treatment for injuries, such as outpatient clinics, over the counter medications and treatment, and rehabilitation, healthcare cost associated with soccer-related injuries presenting to ED is high, and remarkably costly in those with an ICI diagnosis.



#9 Influence of 2D:4D ratio on fitness parameters and accumulated training load in elite youth soccer players

Reference: BMC Sports Sci Med Rehabil. 2021 Oct 11;13(1):125. doi: 10.1186/s13102-021-00354-5.

Authors: Hadi Nobari, Ana Ruivo Alves, Filipe Manuel Clemente, Jorge Pérez-Gómez

Summary: Digit ratio (2D:4D) characterized by the length of the second digit (2D) divided by the length of the fourth digit (4D), is a powerful marker of athletic performance. Some studies showed a negative correlation between 2D:4D ratio and sports performances. The purpose of the present study was three-fold: (1) to analyze the influence of anthropometric and 2D:4D ratio on variations of accumulated training load (ATL) and fitness parameters: maximal oxygen uptake (V̇O2max), countermovement jump (CMJ), isometric muscular strength of the knee extensor for hamstring (ISH) and flexor for quadriceps (ISQ) muscles; along three stages of evaluation of soccer players based on playing positions; (2) to analyze the correlations between 2D:4D ratio and aforementioned parameters; and (3) to investigate if variance in fitness levels and ATL can explain the 2D:4D ratio. Twenty-four elite players under 17 years were daily monitored for their rating perceived exertion and ATL across 24 weeks over the season. Soccer players have also measured in three stages for anthropometric traits and fitness parameters. Significant differences were observed between playing positions for body mass, goalkeepers had higher body mass compared to centre-midfielder and winger players. Moreover, there were significant differences in ATL between early-season to mid-season in goalkeepers (P = 0.032). The 2D:4D ratio (left and right) shown largely and negatively association with muscular strength (ISQ: r = - 0.80; r = - 0.78, P ≤ 0.001, ISH: r = - 0.63; r = - 0.62, P = 0.001, respectively) and VO2max changes (r = - 0.55, P = 0.005; r = - 0.50, P = 0.013, respectively); lastly, both 2D:4D ratio significantly predicted changes in muscular strength and VO2max in young soccer players. Goalkeepers tended to have higher body mass compared to centre-midfielder and winger players; and 2D:4D ratio revealed a mighty predictor of physical fitness changes in soccer players. Evidence should be helpful to professionals to highlight the usefulness of the 2D:4D into the identification of talent, but also to optimize young players' performance.



#10 Associations between Physical Status and Training Load in Women Soccer Players

Reference: Int J Environ Res Public Health. 2021 Sep 23;18(19):10015. doi: 10.3390/ijerph181910015.

Authors: Lillian Gonçalves, Filipe Manuel Clemente, Joel Ignacio Barrera, Hugo Sarmento, Gibson Moreira Praça, André Gustavo Pereira de Andrade, António José Figueiredo, Rui Silva, Ana Filipa Silva, José María Cancela Carral

Summary: This study aimed to analyze the variations of fitness status, as well as test the relationships between accumulated training load and fitness changes in women soccer players. This study followed an observational analytic cohort design. Observations were conducted over 23 consecutive weeks (from the preseason to the midseason). Twenty-two women soccer players from the same first Portuguese league team (22.7 ± 5.21 years old) took part in the study. The fitness assessment included anthropometry, hip adductor and abductor strength, vertical jump, change of direction, linear speed, repeated sprint ability, and the Yo-Yo intermittent recovery test. The training load was monitored daily using session rating of perceived exertion (s-RPE). A one-way repeated ANOVA revealed no significant differences for any of the variables analyzed across the three moments of fitness assessments (p > 0.05). The t-test also revealed no differences in the training load across the moments of the season (t = 1.216; p = 0.235). No significant correlations were found between fitness levels and accumulated training load (range: r = 0.023 to -0.447; p > 0.05). This study revealed no differences in the fitness status during the analyzed season, and the fitness status had no significant relationship with accumulated training load.



#11 External Loads of Elite Soccer Referees: A Systematic Review with meta-analysis

Reference: Res Sports Med. 2021 Oct 11;1-15. doi: 10.1080/15438627.2021.1988948. Online ahead of print.

Authors: Artur Avelino Birk Preissler, Thaís Reichert, Pedro Schons, Rochelle Rocha Costa, Rodrigo Sudatti Delevatti, Benedito Sérgio Denadai, Luiz Fernando Martins Kruel

Summary: The objective of the present study was to describe the total and fragmented external loads, at different intensities, of soccer referees in European and South American competitions during official matches through a systematic review and meta-analysis of cross-sectional studies. A systematic review was conducted in April, 2020. In all, 32 studies were included, incorporating 578 referees evaluated in 3170 games through video analysis or a global positioning system. Regarding external loads, it was observed that the total average distance covered by the referees was 10,461.74 m, with running speeds predominantly below 13 km.h-1. The total distance covered by the referees in the European competitions was higher and more intense than that of the referees in the South American tournaments, being 11,187.02 m and 9319.61 m, respectively. We suggest that referees' training can be organized according to the distances found at different intensities, in which low-intensity races can be performed below 13 km.h-1 with distances of approximately 4500 m, while high-intensity training can be developed with speeds from 18 to 24 km.h-1 for approximately 800 m. In addition, planning must consider the competition characteristics.



#12 Inhabiting the Body(ies) in Female Soccer Players: The Protective Role of Positive Body Image

Reference: Front Psychol. 2021 Sep 24;12:718836. doi: 10.3389/fpsyg.2021.718836. eCollection 2021.

Authors: Débora Godoy-Izquierdo, Isabel Díaz

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Summary: In a social and sports world dominated by weight-centred beliefs and highly exigent and gendered athletic and beauty body standards, the vulnerability for eating pathology, i.e., disordered eating and eating disorders (EDs), is elevated among women athletes. The aim of this study was to explore body image facets and ED risk among female athletes in masculinised sports such as soccer. Forty-five federated amateur female soccer players from Spain participated in this study, voluntarily complying with an extensive evaluation protocol on attitudes towards body and appearance and eating practises. The participants overall reported self-representations of their bodies that corresponded to their reality as athletes, but their body ideals were also more demanding in terms of low fat and muscularity, in association with the functionality of their body and the physical demands of their athletic activity. Despite having a fairly high positive body image and body satisfaction, they also expressed negative attitudes towards their bodies. Around 2 out of 10 players were at risk of suffering from an ED. Players with negative attitudes towards their bodies had an odd 12 times likely to develop an ED compared to those with lower self-devaluation, after adjusting for BMI and body perceptions (OR = 12.3, p < 0.01). On the contrary, players who appreciate their bodies and hold a positive body image had an odd 83% lower to suffer from eating pathology, after adjusting for BMI and body satisfaction (OR = 0.17, p < 0.05). Our findings support the healthy and protective role of positive body image in sports contexts. Body attitudes should be addressed in preventive and therapeutic efforts for reducing the prevalence of EDs in women's sports, within both a "negative" and a "positive" paradigm of body image.



#13 From Garrincha’s legs to Neymar’s legs: The genu varum and valgum in soccer. Historical overview and update

Reference: Acta Ortop Bras. Sep-Oct 2021;29(5):277-282. doi: 10.1590/1413-785220212905242471.

Authors: Fabrício Luz Cardoso, Enrico DE Losso Seneme, Marcos Vinícius Muriano DA Silva, Marcos Henrique Ferreira Laraya, José Antonio Galbiatti, Ricardo Hideki Yanasse

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Summary: The presence of abnormalities in knee alignment (genu varum and genu valgum) is extremely common in soccer. It can occur in the junior league / youth academy and perpetuate itself throughout the professional career. The consequences of years of high-level sports practice in players with genu varum / genu valgum can be harmful to the knees. By observing football matches of the present and the past, the authors of the article noted that great Brazilian soccer players were, or are, affected by the malalignment of the knees: Garrincha (the most famous), Leandro, Dunga, Romário, Rivaldo and Neymar. This study aims to discuss the relationship between high-performance sport and the development of these orthopedic deformities, serving as a tool for updating the trauma-orthopedic knee subspecialty. 



#14 Football Match Dynamics Explored by Recurrence Analysis

Reference: Front Psychol. 2021 Sep 24;12:747058. doi: 10.3389/fpsyg.2021.747058. eCollection 2021.

Authors: Martin Lames, Sebastian Hermann, René Prüßner, Hendrik Meth

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Summary: A widely accepted notion of football matches in performance analysis (PA) is to consider them as dynamic interaction processes with emerging behaviors. The description and analysis of these processes requires specific methods. Recurrence analysis is a technique for analyzing complex systems in many domains like astrophysics, earth sciences, engineering, biology, cardiology, and neuroscience. Its general concept is to examine the recurrence behavior of a system, as in when, how often and how close its trajectory in a phase space returns to a previous state. The aim of the study is to apply recurrence analysis to football matches. Positional data from 21 football matches of a German Bundesliga team were examined. The phase space was made up of the field players' x,y-positions at each second of the match. For each pair of seconds, the average distance of all the players between their positions at these two time points was calculated. Recurrence plots (RPs) were obtained by color-coding these distances. With a recurrence threshold of rt = 9 m and a minimum line length of lmin = 3 s, general recurrence parameters were calculated to characterize the individual recurrence behaviors of each match. Three football-specific recurrence parameters were defined to represent recurrence properties of open play. RPs showed commonalities (typical features indicating set plays and continuous gameplay) as well as unique structures during each match (number, distribution, and sequence of typical features). The recurrence parameters showed several significant correlations with traditional performance indicators like number of goals and passes completed, e.g., the correlation between number of goals and recurrence rate is r = -0.622 (p = 0.003). By extending the sample and design of recurrence studies, there is great potential for recurrence analysis to improve both the practical and theoretical potential of performance analysis.



#15 Sharp pain in a normal Achilles tendon of a professional female football player was related to a plantaris tendon in a rare position: a case report

Reference: J Med Case Rep. 2021 Oct 18;15(1):513. doi: 10.1186/s13256-021-03131-7.

Authors: Håkan Alfredson, Lorenzo Masci, Christoph Spang

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Summary: Plantaris tendinopathy and plantaris-associated Achilles tendinopathy can be responsible for chronic pain in the Achilles tendon midportion, often accompanied by medial tenderness. As conservative treatments are less successful for this patient group, proper diagnosis is important for decision making. This report presents a case with plantaris tendinopathy in a rare (superficial) location. This article describes a pain history and treatment timeline of a professional Swedish female soccer player (32 years old, Northern European ethnicity, white) who suffered from sharp pain in the Achilles tendon midportion and tenderness on the medial and superficial side for about 2 years. Conservative treatments, including eccentric exercises, were not successful and, to some extent, even caused additional irritation in that region. Ultrasound showed a wide and thick plantaris tendon located on the superficial side of the Achilles tendon midportion. The patient was surgically treated with local removal of the plantaris tendon. After surgery there was a relatively quick (4-6 weeks) rehabilitation, with immediate weight bearing, gradual increased loading, and return to running activities after 4 weeks. At follow-up at 8 weeks, the patient was running and had not experienced any further episodes of sharp pain during change of direction or sprinting. The plantaris tendon should be considered as a possible source of Achilles tendon pain. This case study demonstrates that the plantaris tendon can be found in unexpected (superficial) positions and needs to be carefully visualized during clinical and imaging examinations.



#16 High injury rates and weak injury prevention strategies in football referees at all levels of play

Reference: Scand J Med Sci Sports. 2021 Oct 17. doi: 10.1111/sms.14083. Online ahead of print.

Authors: Dominik Szymski, Sabine Opitz, Christian Pfeifer, Markus Rupp, Peter Angele, Volker Alt, Werner Krutsch, Volker Krutsch

Summary: Football referees need other physiological requirements on field than football players and are affected by different types of injury. The absence of referees may result in cancelled matches, so special focus should be placed on injury prevention through specific training programmes for referees. This study retrospectively analysed injury occurrence and prevention strategies for German football referees at the different levels of play over one season. Data were collected by means of seasonal injury reports based on the consensus statement of injury definition and data collection. Of the 923 participating referees, 91 (9.9%) played at the professional level, 151 (16.3%) at the semi-professional, 681 (73.8%) at the amateur level. 86.2% (n=796) were men and 13.8% (n=127) women. Referees at the amateur level showed the highest injury incidence (3.14/1000h football) compared to referees at the semi-professional (1.92/1000h; p<0.001) and professional level (1.01/1000h; p<0.001). Most referees at the amateur (n=372; 56.4%) and semi-professional level (n=46; 31.3%) conducted warm-up programmes of <10 minutes, whereas the mean warm-up duration of professional referees was >11 minutes (n=75; 82.4%). Although running and stretching exercises were common among referees during warm-up, preventive exercises focusing on coordination and trunk muscles were less frequent, especially among amateur referees (jumping: 15.9%; strengthening: 9.7%; balance exercises: 7.9%). Injury incidence was highest at lower amateur levels, which thus has specific need for injury prevention. Appropriate training exercises to prevent injuries of referees were weak at all levels of play, especially the lack of strength, plyometric and balance exercises in training and warm-up programmes.



#17 Understanding the Presence of Mental Fatigue in Elite Female Football

Reference: Res Q Exerc Sport. 2021 Oct 15;1-12. doi: 10.1080/02701367.2021.1873224. Online ahead of print.

Authors: Chris J Thompson, Andy Smith, Aaron J Coutts, Sabrina Skorski, Naomi Datson, Mitchell R Smith, Tim Meyer

Summary: Previous research investigating the impact of induced mental fatigue in football (soccer) has demonstrated associated performance decrements in physical, technical, tactical and decision-making performance. A common limitation amongst this research is the protocols used to induce mental fatigue which provides low ecological validity, and the inclusion of recreational or sub-elite players. Therefore, understanding the presence of mental fatigue in elite football can provide insight into protocols with greater ecological validity. The current study used focus groups with 10 elite female football players, focusing on five topics (travel, fixture congestion, receiving tactical information, pre-match routine and pressure to win) related to the perceived causes of mental fatigue in elite football (directed by anecdotal quotes in elite football and research-based theories). Several themes emerged from the data; travel fatigue, inability to switch off from football, fatigue experienced following team meetings, use of pre-match music and internal pressure to succeed. These findings present practical recommendations to reduce mental fatigue in elite football settings, such as considering the timing, content and duration of team meetings, providing players with free time/rest where possible, and considering the modality of coaching instructions during matches.



#18 Body composition changes during the lockdown-restart transition due to the SARS-CoV-2 pandemic in a group of professional football players

Reference: J Sports Med Phys Fitness. 2021 Oct 15. doi: 10.23736/S0022-4707.21.12894-4. Online ahead of print.

Authors: Giovanna Ghiani, Silvana Roberto, Roberto Mura, Francesco Fois, Marco Scorcu, Antonio Crisafulli

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Summary: At the beginning of March 2020, because of the ongoing pandemic, all sport events were suspended in Italy. The Italian Serie A league abruptly interrupted all competitions and teams could not train in a group anymore. These containment measures were gradually eased in May. The aim of this study was to ascertain the impact of the lockdown-restart transition on the body composition of a group of Italian footballers of a Serie A team during the pandemic. The body composition of 18 male football players (age27.6 ± 4.5 yr.) from an Italian Serie A team was studied by bioelectrical impedance (BIA). Measures were conducted after lockdown, when they restarted to train in group with the ball (T0), and after the first regular match (T1). Results show that there were no changes in body mass, body mass index, fat mass, fat-free mass, and total body water between T0 and T1. Differently, intracellular water, extracellular water, and phase angle were changed. We concluded that the lockdown did not have any impact in athletes' body composition as they kept training at home. Moreover, the BIA method was able to detect subtle signals of shift in body water compartments (intra cellular and extra cellular water) likely due to the different kind of training conducted during and after the lockdown.



#19 The Incompatibility of Motherhood and Professional Women's Football in England

Reference: Front Sports Act Living. 2021 Sep 30;3:730151. doi: 10.3389/fspor.2021.730151. eCollection 2021.

Authors: Alex Culvin, Ali Bowes

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Summary: There has been an advancement of professionalisation of women's football globally. Professional women's football in England has grown exponentially since the inception of the Football Association (FA) Women's Super League in 2011. This article offers an examination of the gender-specific needs of women as professional footballers, focusing specifically on the distinctive aspect of maternity policy. Sportswomen often feel compelled to make the difficult decision between motherhood and an athletic career. Contracts have become an essential component of the work-life of professional women footballers. However, these contracts pose questions regarding organisational intentions and motivations. This study draws on 30 semi-structured interviews with professional women footballers in England. Our key considerations include contracts, employment, motherhood, and athletes' bodies. This examination will develop our understanding of the complexities associated with professional football as a career choice for women.



#20 Design and Validation of the Tactical Assessment Instrument in Football (TAIS)

Reference: Res Q Exerc Sport. 2021 Oct 19;1-18. doi: 10.1080/02701367.2021.1889457. Online ahead of print.

Authors: Carmen Barquero-Ruiz, David Kirk, José L Arias-Estero

Summary: The focus on tactics has made assessment more difficult due to the lack of knowledge in the topic and the limitations of current tactical assessment instruments. The purpose was to design and validate a tactical assessment instrument in youth football (TAIS) following an exhaustive, ecological and meticulous process and dealing with the limitations found in the literature. The design was divided in two stages related to its development and validation. During the development stage: (a) a preliminary list of criteria was determined through a literature review; (b) the criteria were delimited through an exploratory observation; and (c) the adequacy of the criteria was determined by consulting experts. In the validation stage: (a) content and comprehension validity were obtained by consulting experts and through a systematic game observation; (b) construct validity was obtained by comparing the tactical outcomes from two groups with different skill levels; (c) criterion validity was established by comparing the tactical outcome using Game Performance Assessment Instrument and the present instrument, and (d) the reliability was obtained through inter-rater reliability. The research process showed that the instrument is a valid and reliable tool comprised of 22 criteria to assess tactical outcomes in 8-12 years old youth football. The TAIS presents several advantages in practical terms with respect to assessment. First, it allows assessment of the three tactical levels nested in the unit of observation. Second, it considers all the player roles. Third, results are presented without general indexes. Fourth, it can be used to assess participants from all the institutional contexts. Finally, it includes contextual variables.



#21 The influence of the grass mixture composition on the quality and suitability for football pitches

Reference: Sci Rep. 2021 Oct 18;11(1):20592. doi: 10.1038/s41598-021-99859-9.

Authors: Karol Wolski, Joanna Markowska, Adam Radkowski, Marek Brennensthul, Łukasz Sobol, Grzegorz Pęczkowski, Henryk Bujak, Wiktoria Grzebieniarz, Iwona Radkowska, Karen Khachatryan

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Summary: The selection of grass mixtures with appropriate visual and functional parameters for sowing football fields is a key element in shaping the sports infrastructure, ensuring the spectacularity of a match and comfort for players. The aim of the research was to investigate the properties of lawn grass mixtures and their suitability for football pitches. The experiment was conducted at the Toya Golf & Country Club (51° 20' E, 17° 07' N), Wrocław, Poland, between 2007 and 2009. 12 grass mixtures were selected, mainly based on red fescue, Kentucky bluegrass, and perennial ryegrass. The assessment was carried out using a nine-point scale, according to the Plant Variety Office methodology for crops and turf grass. Six features of sports turf were studied: appearance, density, colour, leaf fineness, overwintering, and susceptibility to disease and they significantly varied, depending on the grass mixture and the year of research. Our study showed that mixtures based on the dominance of meadow grass were characterized by higher values of the general visual aspect, colour and slenderness of the leaf blade and these based on the dominance of perennial ryegrass and co-dominance of perennial ryegrass and meadow grass were the most useful in terms of wintering, resistance to diseases and sodding.



#22 Injury epidemiology in professional football in South America compared with Europe

Reference: BMJ Open Sport Exerc Med. 2021 Oct 1;7(4):e001172. doi: 10.1136/bmjsem-2021-001172. eCollection 2021.

Authors: Håkan Bengtsson, Pablo Alfredo Ortega Gallo, Jan Ekstrand

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Summary: The aim was to describe the injury epidemiology in professional football in South America and compare it with European professional football. Data about football exposures and injury occurrences were registered in Six teams participating in Copa Libertadores in 2016. These teams' exposure and injury data were compared with teams participating in the UEFA Elite Club Injury Study during the 2015/2016 and 2016/2017 seasons. A total of 271 injuries were reported in the South American cohort representing a training injury incidence of 3.2 (95% CI=2.7 to 3.7) injuries/1000 hours of training exposure and 20.9 (95% CI=17.3 to 25.1) injuries/1000 hours of match exposure. While no differences in muscle injury incidence were observed between South American and European teams, the ligament injury incidence in training among South American teams was significantly higher than European teams (0.6 vs 0.3, RR 1.87, 95% CI 1.21 to 2.87). In addition, a significantly higher proportion of all reported injuries among South American teams than European teams occurred in training. A larger proportion of injuries occur in training in South American compared with European professional football. Specifically, ligament injuries in training were more frequent among South American teams.



#23 Incidence of injuries in semi-professional soccer: a six-month retrospective study in the Italian fourth division

Reference: J Sports Med Phys Fitness. 2021 Oct 15. doi: 10.23736/S0022-4707.21.12392-8. Online ahead of print.

Authors: Ennio Belli, Luca Filipas, Antonio LA Torre, Jacopo A Vitale

Summary: Soccer is one of the most popular sports in the world involving about 200 million athletes. Injury management in soccer is crucial for performance and for the costs related to rehabilitation and absence from official matches. While there is quite an exhaustive literature regarding injuries in professional soccer, for amateur soccer the incidence of injuries remains unknown. The purpose of this study was to analyse the prevalence of injuries in the fourth Italian soccer division during the competitive season. Medical staff completed an injury report every two months during the competitive season of the fourth Italian soccer division (14 teams, n = 278). The specific description of the problem, player field-position, number of training losses and number of match losses were collected for each player. The time periods were September/October (T1) November/December (T2), January/February (T3). A significant association between injury type and the period of the season was observed: muscle and tendon injuries were the most prevalent injury type (48.9 %) in all three periods (χ2 (10) = 33.86, p < 0.001). Overall, 108 (39.7 %) injuries occurred at T1, 90 (33.1 %) at T2 and 74 (27.2 %) at T3 (χ2 (12) = 20.32, p = 0.071). Coaches and athletic trainers should be aware of this greater injury risk when preparing a training program for the season, to implement injury prevention protocols for the most prevalent injury types.



#24 Impact of Possession and Player Position on Physical and Technical-Tactical Performance Indicators in the Chinese Football Super League

Reference: Front Psychol. 2021 Sep 29;12:722200. doi: 10.3389/fpsyg.2021.722200. eCollection 2021.

Authors: Tianbiao Liu, Lang Yang, Huimin Chen, Antonio García-de-Alcaraz

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Summary: The purpose of this study was to investigate the impact of high (HPBPT) and low percentage ball possession teams (LPBPT) on physical and technical-tactical performance indicators in the Chinese Football Super League (CSL). Eight physical performance indicators and 26 technical-tactical performance indicators from all 240 matches from season 2018 were analyzed, as well as three contextual variables (team strength, quality of opposition, and match location). Players were divided according to five positions: fullbacks, central defenders, wide midfielders, central midfielders, and attackers. A k-means cluster analysis was conducted to classify all match observations into two groups: HPBPT (n = 229) and LPBPT (n = 251). A mixed linear model was fitted with contextual variables as covariates. When significant interactions or main effects were detected, a post hoc comparison was used to compare physical and technical/tactical differences between HPBPT and LPBPT. Results showed that central defenders and fullbacks covered more high-intensity and sprint running distance in the high possession teams, while wide midfielders and forward covered more high-intensity and sprint running distance in the low possession teams. Meanwhile, players from high ball possession teams were strong in technical indicators, especially in attacking organization. These results may help coaches to understand current football development trends and develop suitable training plans and tests for elite football players.



#25 Header biomechanics in youth and collegiate female soccer

Reference: J Biomech. 2021 Oct 2;128:110782. doi: 10.1016/j.jbiomech.2021.110782. Online ahead of print.

Authors: Tanner M Filben, N Stewart Pritchard, Logan E Miller, Christopher M Miles, Jillian E Urban, Joel D Stitzel

Summary: Concerns about the effects of intentional heading in soccer have led to regulatory restrictions on headers for youth players. However, there is limited data describing how header exposure varies across age levels, and few studies have attempted to compare head impact exposure across different levels of play with the same sensor. Additionally, little is known about the biomechanical response of the brain to header impacts. The objective of this study was to evaluate head kinematics and the resulting tissue-level brain strain associated with intentional headers among youth and collegiate female soccer players. Six youth and 13 collegiate participants were instrumented with custom mouthpiece-based sensors measuring six-degree-of-freedom head kinematics of headers during practices and games. Kinematics of film-verified headers were used to drive impact simulations with a detailed brain finite element model to estimate tissue-level strain. Linear and rotational head kinematics and strain metrics, specifically 95th percentile maximum principal strain (ε1,95) and the area under the cumulative strain damage measure curve (VSM1), were compared across levels of play (i.e., youth vs. collegiate) while adjusting for session type and ball delivery method. A total of 483 headers (n = 227 youth, n = 256 collegiate) were analyzed. Level of play was significantly associated with linear acceleration, rotational acceleration, rotational velocity, ε1,95, and VSM1. Headers performed by collegiate players had significantly greater mean head kinematics and strain metrics compared to those performed by youth players (all p < .001). Targeted interventions aiming to reduce head impact magnitude in soccer should consider factors associated with the level of play.



#26 Progressive Rehabilitation of a Professional Soccer Player After an Anterior Cruciate Ligament Reconstruction in Phase 1: Clinical Perspective with Video Demonstration

Reference: J Athl Train. 2021 Oct 1;56(10):1132-1136. doi: 10.4085/1062-6050-164-21.

Authors: Francisco Javier Núñez Sánchez, Francisco Ignacio Martínez Cabrera, Fernando Hernandez Abad, Luis Suarez-Arrones

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Summary: We outline a case of success in the rehabilitation of a Romanian first-division soccer player who sustained an anterior cruciate ligament (ACL) rupture with a meniscal tear during competition in the 2012-2013 season. The ligament was reconstructed with an autologous hamstrings graft and partial meniscectomy was performed. The player returned to same-level competition in 7 months and has remained at that level, free of knee injury, to the present (6 years later). Based on postoperative phase 1 as proposed by the Royal Dutch Society for Physical Therapy, we proposed a clinical progression of exercises with video demonstrations to address body functions and structures and the level of activities and participation. All phase 1 objectives were achieved, and all criteria needed to advance to phase 2 of the ACL rehabilitation process were attained.



#27 Effects of chronic betaine supplementation on performance in professional young soccer players during a competitive season: a double blind, randomized, placebo-controlled trial

Reference: J Int Soc Sports Nutr. 2021 Oct 18;18(1):67. doi: 10.1186/s12970-021-00464-y.

Authors: Hadi Nobari, Jason M Cholewa, Alfonso Castillo-Rodríguez, Mehdi Kargarfard, Jorge Pérez-Gómez

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Summary: Various nutritional strategies are adopted for athletes to maintain and to improve performance during the competition season. Betaine may enhance performance during a competitive season by increasing the testosterone to cortisol ratio and reducing systemic inflammation. The aim of this study was to investigate the effect of betaine supplementation on the bio-motor abilities in young professional soccer players. Twenty-nine young professional soccer players (age, 15.5±0.3 years) were matched by position and randomly assigned to one of two groups for 14 weeks: betaine (BG, 2 g/day; n=14) or placebo (PG n=15). Diet was standardized by a nutritionist, and measures of muscular power (countermovement jump: CMJ), change of direction: modified 5-0-5), acceleration (10 m sprint), sprint performance (30 m sprint time: SpT), muscular strength (leg press and bench press one repetition maximum: 1-RM), repeated sprint ability (running-based anaerobic sprint test: RAST), and aerobic capacity (30-15 intermittent fitness test) were assessed in the pre (P1), mid (P2) and post (P3) season over the course of 5 days. All subjects participated in one soccer match and five training sessions per week. Significant (p < 0.05) group x time interactions were found for maximal oxygen uptake (VO2max), anaerobic peak power, and muscular strength favoring BG at P2 and P3 compared to P1. There were meaningful (p < 0.05) group x time interactions for CMJ, SpT, and peak power during the RAST that favored the BG. 14-week of betaine supplementation increased predicted 1-RM, VO2max, and repeated sprint ability performance in youth professional soccer players. Betaine supplementation seems to be a useful nutritional strategy to improve and to maintain performance during a competitive soccer season.



#28 Risk of SARS-CoV-2 transmission from on-field player contacts in amateur, youth and professional football (soccer)

Reference: Br J Sports Med. 2021 Oct 18;bjsports-2021-104441. doi: 10.1136/bjsports-2021-104441. 

Authors: Sebastian Schreiber, Oliver Faude, Barbara Gärtner, Tim Meyer, Florian Egger

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Summary: The objective was to investigate the risk of transmission among potentially infectious SARS-CoV-2-positive football players while participating in training or matches at amateur, youth and professional levels. Between August 2020 and March 2021, football players who tested positive for SARS-CoV-2 and participated in matches or training during the period of potential contagiousness were identified through media search (professional level) and a nationwide registry in Germany (amateur and youth level) to determine symptoms, source of infection and hygiene measures adopted. The definition of potentially infectious players was based on the time of a positive PCR testing and symptom onset. Transmission-relevant contacts on the pitch were evaluated through doubly reviewed video analysis. Out of 1247 identified football matches and training sessions (1071 amateur and youth level, 176 professional level), 104 cases (38 training sessions, 66 matches) with 165 potentially infectious players were detected. Follow-up PCR testing at the professional level (44 cases) revealed no transmission. At the amateur and youth level, the combination of partial PCR testing (31 of 60 cases) and symptom monitoring within 14 days post-exposure (46 of 60 cases) identified 2 of 60 matches in which follow-up infections occurred that were attributed to non-football activities. This is consistent with the video analysis of 21 matches demonstrating frontal contacts were <1 per player-hour (88%, 30 of 34 players), each lasting no longer than 3 s. On-field transmission risk of SARS-CoV-2 in football is very low. Sources of infections in football players are most likely not related to activities on the pitch.


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