Latest research in football - week 38 - 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 The FIFA 11+ Shoulder Injury Prevention Program Was Effective in Reducing Upper Extremity Injuries Among Soccer Goalkeepers: A Randomized Controlled Trial

Reference: Am J Sports Med. 2021 Jun 17;3635465211021828.  doi: 10.1177/03635465211021828. 

Authors: Wesam Saleh A Al Attar, Oliver Faude, Mario Bizzini, Saud Alarifi, Hosam Alzahrani, Raed S Almalki, Riyadh G Banjar, Ross H Sanders

Summary: Soccer is one of the most popular sports worldwide. Goalkeepers are more likely to injure their upper limbs, particularly their shoulders, than outfield players. To reduce upper extremity injuries, the FIFA 11+ Shoulder Injury Prevention Program (FIFA 11+S) was developed. The purpose of this study was to assess the effectiveness of the FIFA 11+S program in reducing the incidence of upper extremity injuries among amateur soccer goalkeepers. A total of 726 goalkeepers, who were blinded to study intent, were randomly assigned to the experimental group (n = 360) or control group (n = 366). The experimental group was instructed to perform the FIFA 11+S program before all training sessions for 1 season (6 months). The control group was instructed to continue performing their usual routine warm-up program before training sessions for 1 season. Primary outcomes included the incidence of upper extremity injury and incidence of mechanism, type, and severity of injury measured using injury risk ratios (IRR); compliance with the experimental and control interventions was also recorded. A total of 50 injuries (0.62 injuries per 1000 exposure-hours) were reported in the experimental group, and 122 injuries (1.94 injuries/1000 hours) were reported in the control group. The FIFA 11+S program reduced the total number of upper extremity injuries by 68% (IRR = 0.32 [95% CI, 0.27-0.34]) compared with the usual warm-up. The FIFA 11+S program reduced the incidence of contact injury (IRR = 0.30 [95% CI, 0.25-0.31]), noncontact injury (IRR = 0.40 [95% CI, 0.35-0.43]), initial injury (IRR = 0.34 [95% CI, 0.29-0.36]), recurrent injury (IRR = 0.20 [95% CI, 0.17-0.21]), and overuse injury (IRR = 0.40 [95% CI, 0.35-0.43]). Participants in the experimental group demonstrated a significant decrease in injuries of minor (IRR = 0.32 [95% CI, 0.27-0.34]) and moderate severity (IRR = 0.33 [95% CI, 0.29-0.35]) compared with the control group. We noted no difference in compliance between the experimental and control groups (80% vs 73%, respectively; P = .92). The FIFA 11+S program resulted in 50% fewer upper extremity injuries among soccer goalkeepers, compared with a regular warm-up.



#2 Blood and performance adaptations to individual training load in professional soccer: a team study

Reference: J Sports Med Phys Fitness. 2021 Jun 17.  doi: 10.23736/S0022-4707.21.12690-8. Online ahead of print.

Authors: Vincenzo Rago, Italo Leo, Arcano Marrocco, Riccardo Izzo, Cristoforo Filetti

Summary: The aim of this study was to describe seasonal changes in iron storage, hormonal status and functional capacity in relation to accumulated training load in a professional male soccer team. Resting blood samples, countermovement jump (CMJ) and aerobic capacity (45-15 test) were collected over a 6-month period from the start of the preparatory period to the middle-season (E1 to E4) in a professional male soccer team (n=15 outfield players). External training load was regularly quantified using a wearable 10-Hz global positioning system. One player systematically showed reduced iron storage throughout the season (ferritin<110 μg·l-1, hemoglobin<14 g·dl-1). No significant differences in blood and performance parameters were observed throughout the season (P>0.05). However, accumulated total distance and high-intensity distance (above maximal aerobic speed) from E1 to E3 were negatively correlated to changes in haematocrit, hemoglobin and red blood cells (r=-0.85 to -0.67; P<0.05) and positively to changes in ferritin (r=0.63-0.69; P<0.05). Additionally, high-intensity distance covered between E1 and E3 was negatively correlated to changes in testosterone concentrations (r [95%CI]=-0.71 [-0.93; -0.15]; P=0.021). Resting blood parameters and functional capacity of male soccer players appeared to be stable throughout the early competitive period. However, iron storage and hormonal status are likely to be affected by accumulated high-intensity activity performed during practice and competition. Practitioners involved with GPS-based TL monitoring could consider the accumulated amount of high-intensity activity to inform medical staffs about possible changes in oxygen-carrying capacity and anaerobic overtraining.



#3 Pre- and post-match hop test outcomes in soccer players returning to performance after lower extremity injury

Reference: J Sports Med Phys Fitness. 2021 Jun 17.  doi: 10.23736/S0022-4707.21.12576-9. Online ahead of print.

Authors: Astrid Vereijken, Inne Aerts, Emiel van Trijffel, Bruno Tassignon, Jo Verschueren, Romain Meeusen 

Summary: Most soccer injuries concern the lower extremity with a higher injury rate during the second half of matches. In advising safe return to sport, hop tests are usually assessed at the point of return to sport under non-fatigued conditions. No studies exist investigating hop test outcomes before and after a match in soccer players returning to performance after lower extremity injury and non-injured teammates. The objective is to assess differences in hop test outcomes before and after a match in and between soccer players returning to performance after lower extremity injury and their non-injured teammates. A repeated-measures design was used to measure outcomes on five hop tests before and after a soccer match. For analyzing differences in hop tests before and after a match, paired sample t-tests were used. Independent t-tests were used to analyze differences between soccer players after injury and non-injured teammates. Effect sizes were calculated using Cohen's d. Hop tests were completed by 61 amateur soccer players after injury and 121 non-injured teammates. Differences in hop tests before and after the match within both groups had negligible to small effect sizes (d=0.00-0.49), except for the figure of 8 and 30 seconds side hop in the injured leg of RTPf soccer players (d=0.56 and d=0.71 respectively). Differences between both groups were negligible to small (d=0.00-0.36). Soccer players returning to performance after a lower extremity injury showed similar scores on hop tests than their non-injured teammates. More demanding sport-specific performance test and measurement of quality of movement are additionally recommended for safe return to sport decision-making.



#4 A Novel Approach to Training Monotony and Acute-Chronic Workload Index: A Comparative Study in Soccer

Reference: Front Sports Act Living. 2021 May 31;3:661200.  doi: 10.3389/fspor.2021.661200. eCollection 2021.

Authors: José Afonso, Fábio Yuzo Nakamura, Rui Canário-Lemos, Rafael Peixoto, Cátia Fernandes, Tomás Mota, Miguel Ferreira, Rafaela Silva, Armando Teixeira, Filipe Manuel Clemente 

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Summary: Load is a multifactorial construct, but usually reduced to parameters of volume and intensity. In the last decades, other constructs have been proposed for assessing load, but also relying on relationships between volume and intensity. For example, Foster's Training Monotony has been used in athletes' load management simply by computing mean weekly load divided by its standard deviation, often multiplied by session rate of perceived exertion. Meanwhile, the Acute to Chronic Workload Ratio (ACWR) has been debated by the sport scientists as a useful monitoring metric and related to so-called injury prevention. None of these models includes parameters that are representative of training specificity, namely load orientation. The aim of this study is to present broader conceptual approaches translated by new indices for assessing Intraweek Training Monotony (ITM) and Acute to Chronic Workload Index (ACWI) while incorporating load orientation, session duration and weekly density (frequency normalized) in addition to parameters related to proxies of external and/or internal load. Our ITM and Foster's Training Monotony were similar in terms of average values, but very different for individualized analysis, illustrating how average values may be deceiving. While Foster's model provided clusters of values, ITM provided more scattered, individualized data. ACWI and ACWR provided very distinct qualitative information, and the two models were uncorrelated. Therefore, the models incorporating training load orientation presented in this study provide distinct and not redundant information when compared to previous models. More importantly, ITM and ACWI are metrics that are compatible to each other and might fit to coaches' monitoring targets in the short and medium terms, respectively. Because our models include several parameters, including load orientation, we contend that might provide a more complete monitoring tool. However, we suggest they are used for intraindividual comparisons and not so strongly for interindividual comparisons.



#5 Premature Professionalisation or Early Engagement? Examining Practise in Football Player Pathways

Reference: Front Sports Act Living. 2021 Jun 7;3:660167.  doi: 10.3389/fspor.2021.660167. eCollection 2021.

Authors: Liam Sweeney, Dan Horan, Áine MacNamara

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Summary: There is a growing debate, both in the academic and sporting worlds, about the most appropriate pathway for high potential young players in sport. In this regard, there has been a considerable focus on the age of selection into structured talent development pathways and the nature of the experience once players have been recruited. Given the economic and reputational currency associated with developing professional footballers in particular, it is unsurprising that professional football clubs continue to invest significant financial resources into their academy structures. Understandably, this recruitment policy has attracted substantial attention within the media and research community, with ethical concerns arising surrounding the impact early selection may have on the welfare and the experiences of the young players within the pathway. The aim of this perspective article was to critically consider the research underpinning the early engagement practises of football clubs and the extent to which, and how, the pathway can provide players with the most appropriate starting point for their development. This evidence points to the need to look beyond the prevalent 'early specialisation vs. diversification' debate in youth sport towards a consideration of an early engagement perspective that reflects the biopsychosocial influences on talent development and the socio-political environment that influences decisions. We provide practical recommendations focused on the quality of the early engagement experience.



#6 What Will We Do? The Action Plan From a Brazilian Professional Football Club Youth Academy Facing the COVID-19 Pandemic

Reference: Front Sports Act Living. 2021 Jun 7;3:589459.  doi: 10.3389/fspor.2021.589459. eCollection 2021.

Authors: Murilo Dos Reis Morbi, Annie Rangel Kopanakis, Pau Mateu, Billy Graeff, Renato Francisco Rodrigues Marques

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Summary: In 2020, the world was affected by the COVID-19 pandemic, which remains a major challenge for most countries today. In Brazil, football clubs' youth academies have faced a disruption of their regular activities. In order to study how the learning cultures of a Brazilian professional football club youth academy have been changed, and the alternatives created by the club's staff within this context, this perspective article aims to analyze how they have structured the Under-15 (U15) team learning culture during social isolation due to the COVID-19 pandemic. Through document and thematic analysis on a Brazilian professional football club's youth academy program, we promoted a dialogue between the process of adaptation to remote theoretical-tactical teaching with the learning theory proposed by Hodkinson and collaborators. The main theme of analysis of this study was the remote structure of the theoretical-tactical learning and physical training. Challenged with the need to transpose face-to-face activities into a learning culture based on remote communication, the U15 team coaching staff created a process to prescribe physical training, and to teach and discuss football tactical issues with young players during the period of social isolation. This perspective article shows that it is possible for sports institutions to create programs for the development of young athletes within the social isolation/distancing context, considering both theoretical-tactical learning and physical training processes. The adaptation to remote environments as structures for the learning culture seems a challenge, but is also a good alternative for young players to develop their interpretation and perception of football theoretical-tactical issues.



#7 Decision-making to stop or continue playing after football injuries - A systematic video analysis of 711 injury situations in amateur football

Reference: Eur J Sport Sci. 2021 Jun 23;1-17.  doi: 10.1080/17461391.2021.1943717. Online ahead of print.

Authors: Krutsch Volker, Oberhauser Julia, Krutsch Werner, Loose Oliver, Weber Johannes, Kerschbaum Maximilian, Lang Siegmund, Koch Matthias, Alt Volker, Worlicek Michael

Summary: Scientific injury registration via video analysis is lacking in amateur football. The purpose of this study was to analyse match injury situations with a focus on the decisions made by players and referees after sustaining a football trauma. In a retrospective cohort study, traumatic injuries sustained in any of the 305 matches of the highest amateur level (4th league) in Germany in the 2015-16 season were assessed by means of video analysis and a standardised video protocol. In total, 711 traumatic incidents at 919 different body regions had been recorded. The three most frequently injured body regions were the ankles (34.1%), the head (17.5%) and the knees (17.0%). 90% (n=156) of head injuries were direct contact injuries, this percentage was significantly higher than that of contact injuries on ankle (68.4%; p<0.001) or knee (52.6%; p=0.001). Referees decided on foul play significantly more often in case of knee injuries (57.1%; p=0.002) or ankle injuries (64.5%; p<0.001) than in head injuries (39.8%). Only 26.1% of players with a head injury opted for substitution, which was lower than after ankle (27.8%; p=0.78) and knee injuries (34.0%; p=0.13). In conclusion, amateur football is associated with a considerable number of injury situations that are followed by match interruptions and the substitution of players. Players and referees decided to continue playing more often after a head injury than after an injury to other body regions. An advanced education programme on the risks and management of head injuries in football is required to prevent long-term health consequences.



#8 Fitness assessment in talented football referees: an academy based longitudinal field-study

Reference: J Sports Med Phys Fitness. 2021 Jun 22.  doi: 10.23736/S0022-4707.21.12293-5. Online ahead of print.

Authors: Carlo Castagna, Alejo P Leguizamón, Susana C Póvoas

Summary: This study aim was to profile physical fitness in talented football referees (FR) with performance relevant field-tests across time. Thirty-eight male FR (age 28±1.5 years, height 178±5.1 cm, body mass 69.0±7.34 kg, body fat 17.2±2.87%) were observed for 15 months. Endurance was assessed with the Yo-Yo Intermittent Recovery Test level 1 (YYIR1) and repeated sprint ability (RSA) with 5x30m line-sprints with 30s recovery (5x30m). Long sprint endurance (LSA) and change of direction ability (COD) evaluated with novel field-tests. FR was tested six times (every three months) during the study. YYIR1 performance showed large increments across testing occasions. Sprint time in the COD largely and significantly decreased across the testing occasions. Very large associations were reported between 5x30m and LSA tests grand mean (r=0.89, 0.78-0.94, P<0.0001). A nearly perfect (r=0.97, 0.94-0.99, P<0.0001) association was observed between 5x30m best sprint and 5x30m grand means. The results of this study revealed ability-related variations in performance across time. The effect of training and competitions on the determinism of physical fitness in refereeing seem plausible. Interestingly, sprint endurance tests shared a very large variance proposing tests interchangeability and mutual physiological demands. This study information provides useful information for the development of sound field-tests batteries in talented FR.



#9 Concussion in European professional football: a view of team physicians

Reference: BMJ Open Sport Exerc Med. 2021 Jun 3;7(2):e001086.  doi: 10.1136/bmjsem-2021-001086. eCollection 2021.

Authors: Vincent Gouttebarge, Imtiaz Ahmad, Zafar Iqbal, Emmanuel Orhant, Craig Rosenbloom, Kristof Sas, Gino M M J Kerkhoffs

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Summary: The objective was to explore the view and thoughts of physicians working in professional football about several aspects (eg, education and use of video footages) likely to enhance concussions' recognition and on-field management. An observational study based on a cross-sectional design by means of an electronic survey was conducted among physicians working for a professional football club in Belgium, England or France. A total of 96 physicians (95% male; mean age: 44 years) completed the survey. Nearly all participants (95%) were in favour of informational sessions about concussion for players or technical staff. Only 5%-10% of the participants mentioned that they had felt pressured by the technical staff or players not to substitute a player with a (potential) concussion. Most participants were in favour of an additional permanent concussion substitution and a temporary concussion substitution. Four out of five participants reported that the availability of instant video footages (side-line) would ease the recognition of concussion. A better recognition and on-field management of concussions in professional football can only be achieved with a holistic approach, including adequate laws of the football game and protocols. Especially, regular education of players and technical staff should be made mandatory while the medical teams should be provided side-line with instant video footages.



#10 Conservative Treatment of the Fifth Metatarsal Bone Fractures in Professional Football Players Using Platelet-Rich Plasma

Reference: Foot Ankle Spec. 2021 Jun 18;19386400211017368. doi: 10.1177/19386400211017368.

Authors: Eduard Bezuglov, Andrey Zholinsky, Gleb Chernov, Vladimir Khaitin, Evgeniy Goncharov, Zbigniew Waśkiewicz, Ekaterina Barskova, Artemii Lazarev

Summary: Injuries of the metatarsal bones in football are relatively rare and in most cases are localized in the fifth metatarsal. The gold standard of the diagnosis of fractures in this area can be X-rays, which in most cases allows verifying the diagnosis. The treatment tactics depend on the localization of the fracture according to Lawrence and Botte's classification: 3 zones of localization are distinguished. Fractures located in zones 2 and 3 belong to a high-risk group due to delayed consolidation and nonunion and therefore athletes are most often treated with osteosynthesis using intramedullary screws. The minimal recovery time for this type of treatment is at least 8 weeks. This report describes 7 cases of the fifth metatarsal bone fractures, located in zones 2 and 3 in professional football players who were treated with an immobilization boot, cryotherapy, nutritional supplements of calcium and vitamin D, and local injections of platelet-rich plasma, which contains numerous growth factors. The deadline for returning to regular training activities was 43 to 50 days, and there was no relapse of damage within 6 months of follow-up. 



#11 Covid-19: Deaths in Brazil near half a million as controversial football tournament gets under way

Reference: BMJ. 2021 Jun 15;373:n1539.  doi: 10.1136/bmj.n1539.

Authors: Luke Taylor

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#12 External Training Load Monitoring and the Impact on Training Load Management in Collegiate Male Soccer Players

Reference: J Strength Cond Res. 2021 Jun 17.  doi: 10.1519/JSC.0000000000004080. Online ahead of print.

Authors: Jacob R Gdovin, Riley Galloway, Lorenzo S Tomasiello, Michael Seabolt, Robert Booker

Summary: Soccer is a physically demanding sport within the National Collegiate Athletic Association and continuously increases in popularity. To ensure athletes are adequately prepared for weekly physical stressors, coaches can use global positioning system technology to monitor external workloads and exercise intensity. These data can subsequently help coaches and practitioners better implement individualized training programs to ensure athletes are properly balancing the overreaching and overtraining paradigm. Therefore, the purpose of this observational study was to retrospectively analyze 3 consecutive seasons of external workload (total and high intensity distance) and injury data, which were derived from all training sessions and matches in 46 Division-I collegiate male soccer players. A coach's interpretation sought to provide practical insight into the functionality behind load management and how it prepares athletes for the physical stressors placed on them throughout a season. Two separate 3 × 3 repeated measures ANOVAs were conducted to determine differences between total distance and distance at high-intensity with an alpha level set at 0.05. Total distance between preseason and in-season (p = 0.003), acute high-intensity distance (p < 0.001), and chronic high-intensity distance (p < 0.001) yielded significant differences. These results conclude the demands of each athlete change weekly and between seasons. It is recommended that sport coaches and practitioners develop individualized training programs by workload monitoring while considering variables such as a team's style of play, experience, position, role within a program, training intensity, and the length of time between conditioning sessions, practices, and matches.



#13 Talent Identification in Youth Soccer: Prognosis of U17 Soccer Performance on the Basis of General Athleticism and Talent Promotion Interventions in Second-Grade Children

Reference: Front Sports Act Living. 2021 Jun 4;3:625645.  doi: 10.3389/fspor.2021.625645. eCollection 2021.

Authors: Andreas Hohmann, Maximilian Siener

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Summary: Several talent identification programs in elementary school have implemented motor diagnostics to introduce children to groups of sports, like game sports, or even to particular sports like soccer. However, as in most other sports, in youth soccer, the predictive value of such early testing is still unclear. This prospective study evaluated the midterm prognostic validity of generic motor performance tests. The sample consisted of male second-grade children, which had received a recommendation to participate in soccer. The talent screening campaign was a basic check comprising two anthropometric parameters, five physical fitness, and three motor competence diagnostics of the German Motor Test 6-18. The test data were collected from the participating elementary school classes of the years 2010 to 2014. The soccer competition performance of those children having completed the age of at least 15 years (n = 502) up to the end of the season 2019/2020 (2020, September 30) was recorded. This group of U17 players was then assigned individually to five different competition levels. The prognostic validity of the physical and physiological tests was determined using ANOVAs, odds ratios, and a regression path analysis. All diagnostic methods exhibited medium-to-high prognostic validity over the 8 year time span from the talent screening to the later soccer competitions in the adolescent age groups. For later success in soccer on the province level, the 6-min run (OR = 4.28), dynamic balance (OR = 4.04), and 20-m sprint (OR = 2.46), as well as the participation in the training center of the German Soccer Federation (OR = 5.67) and the diversity of club sport activities (OR = 3.56), were of particular importance.



#14 Acute effects of whole-body vibrations on the fatigue induced by multiple repeated sprint ability test in soccer players

Reference: J Sports Med Phys Fitness. 2021 Jun 22.  doi: 10.23736/S0022-4707.21.12349-7. Online ahead of print.

Authors: Giuseppe Annino, Vincenzo Manzi, Paolo Buselli, Bruno Ruscello, Fabrizio Franceschetti, Cristian Romagnoli, Franco Cotelli, Maurizio Casasco, Elvira Padua, Ferdinando Iellamo

Summary: We tested the hypothesis that Whole Body Vibration (WBV) positively affects the fatigue process ensuing from repeated bouts of maximal efforts, as induced by repeated sprints ability (RSA). Eleven male soccer players performed three sets of six repeated shuttle sprints (40 metres). Eleven male soccer players (age 23,6±4,5 years) were cross-randomized to perform WBW before RSA and during the recovery between sets (WBV-with) or to warm-up and passive recovery between sets (WBV-without). The effects of WBV were quantified by sprint time (ST) and blood lactate concentration (LA), collected up to 15th min after completion of tests. ST during RSA showed a better maintenance of performance in the WBV-with compared to WBV-without condition in all three sets, reaching a statistical significance between-groups during the 2nd and 3rd set (P< 0.05). No significant differences in ST over the sets were detected in WBVwith, whereas a significant decrease was observed in the WBV-without condition (P<0.001). LA recovered significantly faster from the 9th to 15th minute of recovery in WBV-with as compared to WBV-without (P<0.05). These findings would indicate that WBV performed during recovery between RSA sets is capable of delaying the onset of muscle fatigue resulting in a better maintenance of sprint performance.



#15 Goal Side Selection of Penalty Shots in Soccer: A Laboratory Study and Analyses of Men's World Cup Shoot-Outs

Reference: Percept Mot Skills. 2021 Jun 23;315125211025412.  doi: 10.1177/00315125211025412. 

Authors: Mauro R Pereira, Geoffrey R Patching

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Summary: Penalty kicks in soccer provide a unique scenario in which to examine human choice behavior under competitive conditions. Here, we report two studies examining the tendency for soccer kickers to select the goal side with the largest area to the left or right of the goalkeeper's veridical midline, when the goalkeeper stands marginally off-center. In Study I participants viewed realistic images of a soccer goal and goalkeeper with instructions to choose the left or right side of the goalmouth to best score a goal. We systematically displaced the goalkeeper's position along the goal line; and, to simulate changes in the kicker's viewing position, we systematically displaced the lateral position of the goalmouth in each image. While, overall, participants tended to choose the left over the right goal side, this preference was modulated by the goalkeeper's position relative to the center of the goal and jointly on the lateral position of the goalmouth relative to the participants' body midline. In Study II we analyzed 100 penalty shots from men's world cup shoot-outs between the years 1982 to 2018. Again, we found a small tendency for kickers to aim the ball to the left goal side, but with barely any modulating effect of changes in the goalkeeper's position and no effect of changes in the kicker's position. In contrast to earlier claims that a goalkeeper may benefit by standing marginally to the left or right of the center of the goal to influence the direction of the kicker's shot, our findings suggest that this is probably not a good strategy in elite football competitions.



#16 When do soccer players experience the most demanding passages of match play? A longitudinal study in a professional team

Reference: Res Sports Med. 2021 Jun 23;1-11.  doi: 10.1080/15438627.2021.1943390. Online ahead of print.

Authors: José M Oliva-Lozano, Helena Martínez-Puertas, Víctor Fortes, José M Muyor

Summary: This study analysed the periods in which the most demanding passages (MDP) of play occurred during professional soccer matches, considering different criterion variables and investigating the effect that the playing position had on the MDP-of-play occurrence for each criterion variable. The MDP of play were calculated based on five criterion variables: distance covered (DIS), sprinting distance (SPD), high-metabolic load distance (HMLD), and the total of high-intensity accelerations and decelerations (ACCHIGH and DECHIGH). The results showed that the first period of the match (0'-15') was the interval with the highest frequency (i.e., the greatest % of cases) in which the players achieved the MDP of play for all the variables (DIS= 38.9%; SPD= 28.4%; HMLD= 37.7%; ACCHIGH= 54.3%; DECHIGH= 48.8%). The playing position had no significant effect on MDP-of-play occurrence in any variable (likelihood ratio, LR= 15.88-32.05; p > 0.05; effect size, ES= 0.01-0.04), except for the DIS covered (LR= 32.05; p= 0.04; ES= 0.05), in which the most frequent MDP for the full backs occurred within the second period of the match (15'-30'). In conclusion, the first periods of the matches usually elicited the MDP of play and these periods need to be trained to prevent injuries and optimize performance.



#17 Agility testing in amateur soccer: A pilot study of selected physical and perceptual-cognitive contributions

Reference: PLoS One. 2021 Jun 24;16(6):e0253819.  doi: 10.1371/journal.pone.0253819. eCollection 2021.

Authors: Stefan Altmann, Rainer Neumann, Sascha Härtel, Gunther Kurz, Thorsten Stein, Alexander Woll

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Summary: The purpose of this study was to examine the relationships of physical and perceptual-cognitive factors with agility performance in amateur soccer players. Fifteen male amateur soccer players (age, 24.5 ± 1.9 years) completed a linear-sprint test with splits at 5 m, 10 m, and 30 m, a change-of-direction test of 12 m with 2 pre-planned directional changes of 45° at 2 m and 7 m, and a soccer-specific agility test with same movement pattern as the change-of-direction test but with the inclusion of a human stimulus performing passing movements. Additionally, the perceptual-cognitive deficit (agility performance minus change-of-direction performance) was calculated. In relation to agility performance, linear-sprint performance showed large relationships, which were higher with increasing sprint distance (5 m, r = 0.57; 10 m, r = 0.59; 30 m, r = 0.69), change-of-direction performance a very large relationship (r = 0.77), and the perceptual-cognitive deficit a large relationship (r = 0.55). The findings of this study highlight the relatively high contribution of both physical (i.e., linear-sprint and change-of-direction performance) and perceptual-cognitive factors (i.e., perceptual-cognitive deficit) in relation to soccer-specific agility performance at an amateur level. Consequently, such elements might be recommended to be included in training programs aimed at improving agility performance at this playing level. Moreover, the here introduced perceptual-cognitive deficit allows for a convenient and likewise thorough analysis of agility performance. Future studies should investigate the effects of both physically and perceptual-cognitive oriented training interventions on agility performance, which is considered a key element for success in soccer.



#18 Using multiple machine learning algorithms to classify elite and sub-elite goalkeepers in professional men's football

Reference: Sci Rep. 2021 Nov 22;11(1):22703. doi: 10.1038/s41598-021-01187-5.

Authors: Mikael Jamil, Ashwin Phatak, Saumya Mehta, Marco Beato, Daniel Memmert, Mark Connor

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Summary: This study applied multiple machine learning algorithms to classify the performance levels of professional goalkeepers (GK). Technical performances of GK's competing in the elite divisions of England, Spain, Germany, and France were analysed in order to determine which factors distinguish elite GK's from sub-elite GK's. A total of (n = 14,671) player-match observations were analysed via multiple machine learning algorithms (MLA); Logistic Regressions (LR), Gradient Boosting Classifiers (GBC) and Random Forest Classifiers (RFC). The results revealed 15 common features across the three MLA's pertaining to the actions of passing and distribution, distinguished goalkeepers performing at the elite level from those that do not. Specifically, short distribution, passing the ball successfully, receiving passes successfully, and keeping clean sheets were all revealed to be common traits of GK's performing at the elite level. Moderate to high accuracy was reported across all the MLA's for the training data, LR (0.7), RFC (0.82) and GBC (0.71) and testing data, LR (0.67), RFC (0.66) and GBC (0.66). Ultimately, the results discovered in this study suggest that a GK's ability with their feet and not necessarily their hands are what distinguishes the elite GK's from the sub-elite.



#19 Position specific physical performance and running intensity fluctuations in elite women's football

Reference: Scand J Med Sci Sports. 2021 Nov 26.  doi: 10.1111/sms.14105. Online ahead of print.

Authors: A K Winther, I Baptista, S Pedersen, M B Randers, D Johansen, P Krustrup, S A Pettersen

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Summary: The purpose of the present study was to investigate the physical performance of elite female football players during match play along with transient alterations in running performance following 1- and 5-min univariate peak periods. 54 elite female players from four top-level Norwegian teams were monitored for one season (n = 393 match observations), and physical performance data collected using STATSport GPS APEX. Results revealed significant differences in physical performance between the positions during full match play, particularly between wide and central players. Both full backs (FBs) and wide midfielders (WMs) covered more total distance (TD), high-speed running distance (HSRD), and sprint distance (SpD) than center backs (CBs) (p < 0.05-0.001), while WMs also covered more HSRD than both central midfielders (CMs) (p < 0.01) and forwards (FWs) (p < 0.05), and more acceleration -and deceleration distance (Accdist and Decdist ) than both CBs and CMs (p < 0.01-0.001). A similar pattern was observed for the peak period analysis, with FBs and WMs covering more SpD in peak 1 min than CBs and CM (p < 0.001) and more SpD in peak 5-min than CBs, CMs, and FWs (p < 0.001). Irrespective of the variable analyzed, greater distances were covered during the peak 5-min period than in the next-5 and mean 5-min periods (p < 0.001). Significant (p < 0.001), but small to trivial (Cohen's Dz : 0.07-0.20), decreases in distance covered were also observed for each variable following each univariate peak 5-min period. In conclusion, practitioners should account for differences in physical performance when developing training programs for female football players and be aware of transient reductions in physical performance following univariate peak 1- and 5-min periods. Specifically, the very high intensity in 1-min peak periods adds support to the principal of executing speed endurance activities during training to mirror and be prepared for the physical demands of match play.



#20 The Differentiate Effects of Resistance Training With or Without External Load on Young Soccer Players' Performance and Body Composition

Reference: Front Physiol. 2021 Nov 5;12:771684.  doi: 10.3389/fphys.2021.771684. eCollection 2021.

Authors: Moisés Falces-Prieto, Eduardo Sáez de Villarreal-Sáez, Javier Raya-González, Francisco Tomás González-Fernández, Filipe Manuel Clemente, Georgian Badicu, Eugenia Murawska-Ciałowicz

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Summary: The purpose of this study was to examine the effects of 15 weeks (2/week) of two different resistance training (RT) programs [the self-load group (SG) vs. the overload group (OG)] on selected measures of physical performance in young male soccer players.  The countermovement jump (CMJ), aerobic endurance (VO2 max), and body composition [body mass (BM), height (H), body fat percentage (% BF), and lean mass (LM)] were measured before and after the 15-week RT interventions. Subjects were randomized to treatments: 1. SG [age = 15.34 ± 1.34 years]; 2. OG [age = 16.28 ± 1.21 years].  The level of significance set for the study (p ≤ 0.05). Within-group analysis did report significant differences in all variables for the SG (p = 0.008 to 0.001; ES = -0.33 to 1.41, small to large) as in the OG (p = 0.001; ES = 0.82 to 1.30, large). Between-groups analysis reported differences in CMJ (F = 4.32; p = 0.004) for the OG. The main findings of this study indicated that RT with and without external load was effective in improving the measures of physical performance in young soccer players, with special attention to jumping ability, where the OG group was more effective. Furthermore, there is no interference to aerobic endurance. It is recommended that soccer coaches implement RT without external load in the early stages of training or in players with late maturation development and in those soccer clubs with limited material resources.



#21 Toward Automatically Labeling Situations in Soccer

Reference: Front Sports Act Living. 2021 Nov 3;3:725431.  doi: 10.3389/fspor.2021.725431. eCollection 2021.

Authors: Dennis Fassmeyer, Gabriel Anzer, Pascal Bauer, Ulf Brefeld

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Summary: We study the automatic annotation of situations in soccer games. At first sight, this translates nicely into a standard supervised learning problem. However, in a fully supervised setting, predictive accuracies are supposed to correlate positively with the amount of labeled situations: more labeled training data simply promise better performance. Unfortunately, non-trivially annotated situations in soccer games are scarce, expensive and almost always require human experts; a fully supervised approach appears infeasible. Hence, we split the problem into two parts and learn (i) a meaningful feature representation using variational autoencoders on unlabeled data at large scales and (ii) a large-margin classifier acting in this feature space but utilize only a few (manually) annotated examples of the situation of interest. We propose four different architectures of the variational autoencoder and empirically study the detection of corner kicks, crosses and counterattacks. We observe high predictive accuracies above 90% AUC irrespectively of the task.



#22 The relationships between knee extensors/ flexors strength and balance control in elite male soccer players

Reference: PeerJ. 2021 Nov 16;9:e12461. doi: 10.7717/peerj.12461. eCollection 2021.

Authors: Robert Śliwowski, Jakub Marynowicz, Łukasz Jadczak, Monika Grygorowicz, Paweł Kalinowski, Thierry Paillard

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Summary: Strength and balance are important factors for soccer players to be successful. This study's aim was to determine the relationship between lower-limb muscle strength and balance control in elite male soccer players (n = 77). Concentric isokinetic strength (peak torque of quadriceps (PT-Q) and hamstrings (PT-H), hamstrings/quadriceps (H/Q) ratio) was measured for the dominant and non-dominant leg at angular velocities of 60°s-1and 240°s-1, as well as the total work for extensors (TW-Q) and flexors (TW-H) for both legs (at an angular velocity of 240°s-1only). Balance score (BAL score) was used for unilateral assessment of balance control using a Delos Postural System Test measurement tool. Hierarchical multiple regression analyses were performed to predict balance control using isokinetic knee strength performance for dominant and non-dominant legs. Final modelling included peak torque of hamstrings at 240°s-1 and peak torque of the quadriceps at 240°s-1 for the non-dominant leg (R 2 = 19.6%; p ≤ 0.001) and only peak hamstring torque at 240°s-1 for the dominant leg (R 2 = 11.3%; p = 0.003) as significant predictors of balance score. Findings indicate that balance control is widely influenced by peak hamstring torque and peak quadriceps torque at high angular velocity particularly in the non-dominant leg i.e., the supporting leg in soccer players.



#23 Elite Youth Soccer Players' Sources and Types of Soccer Confidence

Reference: Sports (Basel). 2021 Oct 22;9(11):146.  doi: 10.3390/sports9110146.

Authors: Iain Greenlees, Aimee Parr, Sarah Murray, Esther Burkitt

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Summary: Sport confidence is a psychological characteristic considered vital for youth soccer players to possess. However, only limited research has explored the types and sources of sport confidence important to elite youth performers in professional soccer academies. Semi-structured interviews were conducted with 11 academy footballers (aged 10 or 11). Abductive hierarchical content analysis identified types of confidence to include achievement, skill execution, psychological factors, superiority to opposition and tactical awareness. Key sources of confidence identified by players were performance accomplishments, coaching, social support, and preparation. Even though the dimensions reported were similar to previous research, a number of unique sub-themes of confidence sources emerged, including pre-training/competition emotions, coach and team-mate feedback. The results demonstrate the importance of considering maturation levels and context when seeking to understand and develop confidence in youth performers.



#24 Is the Integration of Additional Eccentric, Balance and Core Muscles Exercises into a Typical Soccer Program Effective in Improving Strength and Postural Stability?

Reference: Sports (Basel). 2021 Oct 25;9(11):147.  doi: 10.3390/sports9110147.

Authors: Konstantinos Dafkou, Chrysostomos Sahinis, Athanasios Ellinoudis, Eleftherios Kellis

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Summary: Soccer teams integrate specific exercises into their typical workout programs for injury prevention. The purpose of this study was to investigate whether the incorporation of a brief and supplementary training program that involves eccentric, balance, and core exercises into the weekly soccer schedule can cause positive neuromuscular adaptations. Twenty-one soccer players were randomly allocated to either a training (n = 11) or a control group (n = 10). All players followed their teams' typical program, consisting of 4-5 soccer-specific sessions plus 1 match, weekly. Training group players additionally performed biweekly, hamstring eccentric, balance, and core stability exercises for 8 weeks. Isokinetic concentric and eccentric peak torque (PT) of the hamstrings and quadriceps, changes in the center of pressure (COP) during a 30 s single-leg stance, and a supine bridge (trunk stability) test were assessed before and after the intervention. After the intervention, a 27% increase in hamstring concentric PT and a 33% reduction in COP sway in the stance test, were observed for the training group only (p < 0.05). These improvements were significant only for the non-dominant leg. Furthermore, the control group displayed an increase in COP sway during the bridge test compared to baseline values (p < 0.05), which reflects a deterioration in postural balance over time. Consequently, incorporating small doses of hamstring eccentric, proprioception, and core stability exercises into a typical training program of youth soccer players improves strength and postural balance in the non-dominant leg, as well as core muscle performance.



#25 Differences in Squat Jump, Linear Sprint, and Change-of-Direction Performance among Youth Soccer Players According to Competitive Level

Reference: Sports (Basel). 2021 Oct 27;9(11):149.  doi: 10.3390/sports9110149.

Authors: Michael Keiner, Andreas Kapsecker, Tobias Stefer, Björn Kadlubowski, Klaus Wirth

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Summary: The aim of this investigation was to analyze significant differences in performance depending on the level of play (elite vs. amateur) in youth soccer players (under 17 years. old (U17) and U19). A cross-sectional study was conducted, and 45 elite and amateur male youth soccer players (16.56 ± 0.9 years old) were evaluated in their performances in squat jump (SJ), 10 m linear sprint (LS), 20 m LS, 505 agility test (505) and Illinois agility test (IAT). Differences in performances were analyzed with a 2 × 2 MANOVA, post-hoc ANOVAs, and Hedges' g (g) for pairwise comparisons of subgroups (level of play and age group). This investigation showed that the elite player performance was significantly (p < 0.05) better in all performance tests than amateur players in both age groups. Interestingly, this investigation showed that the more complex the target exercise, the larger the effect sizes for group differences (SJ: g = 0.64-1.18, LS: g = 0.05-2.23, change-of-direction (COD): g = 3.01-6.84). The SJ, LS, 505, and IAT may prove useful in talent selection test batteries to separate between competitive levels in youth soccer players.


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