Latest research in football - week 16 -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 Effect of two incremental intensity field tests on wellness indices, recovery state, and physical enjoyment in soccer players

Reference: Eur Rev Med Pharmacol Sci. 2022 Apr;26(7):2279-2287. doi: 10.26355/eurrev_202204_28457.

Authors: O Selmi, D E Levitt, A Muscella, N Ouerghi, I Issaoui, W Abassi, L Hill, T Rosemann, A Bouassida, B Knechtle

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Summary: Competitive athletes must undergo fitness testing to monitor athlete progress and to create appropriate, progressive training programs. However, fitness testing adds to training stress; therefore, impacts of testing on wellness and recovery must be considered in test selection. This study investigated the effects of two incremental field tests [VAMEVAL test (T-VAM) and 20-m maximum shuttle test (20-m MST)] on wellness, total quality of recovery (TQR) and physical enjoyment (PE) in competitive soccer players. Twenty-two soccer players (20.9±1.5 years) completed two T-VAM and two 20-m MST in a randomized order on separate days with a 1-week interval between tests. TQR and wellness indices (sleep, fatigue, stress and muscle soreness) measures were collected before and 24 hours after each test. Heart rate (HR) was continuously monitored during each test. Rating of perceived exertion (RPE) and PE were assessed after each test. T-VAM resulted in higher PE, TQR and wellness scores than 20-m MST (p<0.05). T-VAM and 20-m MST resulted in similar HR and maximal aerobic speed. For T-VAM, TQR was correlated (p<0.01) with RPE and wellness indices. For 20-m MST, TQR was correlated (p<0.01) with wellness indices. HRmax and RPE were not correlated with wellness indices, TQR or PE. Overall, T-VAM and 20-m MST produced similar aerobic fitness testing results, but athletes responded more favorably to T-VAM. Coaches can use T-VAM for evaluating aerobic fitness while maximizing well-being and physical enjoyment among soccer players.



#2 Seasonal Variation of Physical Performance, Bilateral Deficit, and Interlimb Asymmetry in Elite Academy Soccer Players: Which Metrics Are Sensitive to Change?

Reference: J Strength Cond Res. 2022 Apr 1. doi: 10.1519/JSC.0000000000004248. Online ahead of print.

Authors: Chris Bishop, Will Abbott, Calum Brashill, Irineu Loturco, Marco Beato, Anthony Turner

Summary: This study aimed to report seasonal variations for (a) physical performance, (b) interlimb asymmetry, and (c) bilateral deficit (BLD) data over the course of a competitive soccer season and determine which metrics are sensitive to change. This study used a repeated-measures observational design for 19 under-20, elite, academy, soccer players (age: 17.58 ± 0.61 years; height: 1.81 ± 0.09 m; body mass: 74.36 ± 7.58 kg), who conducted bilateral and single-leg countermovement jumps (CMJ and SLCMJ), linear speed (5, 10, 20, and 30-m) and 505 change of direction (COD) speed tests, at pre, mid, and end of season time points. For jump tests, jump height, reactive strength index modified, time to takeoff, and countermovement depth metrics were monitored, with interlimb asymmetry and the BLD also calculated for each. Significant improvements (p < 0.05) in performance were evident in all fitness tests: CMJ (effect size [ES]: 0.61 to 1.03), SLCMJ (ES: 0.60 to 2.25), linear speed (ES: -0.54 to -1.96), and COD speed (ES: -0.68 to -1.14). Significant reductions in asymmetry (ES: -0.68 to -1.07) and significant increases in the BLD (ES: 1.15 to 1.57) were also evident throughout the season. Additionally, kappa coefficients were used to determine consistency in limb dominance throughout the season, but only poor to fair levels of agreement (kappa: -0.17 to 0.37) were evident, highlighting the fluctuating nature of limb dominance throughout the season. Despite all tests exhibiting meaningful change, the SLCMJ and linear speed showed the most frequent and largest differences in performance, highlighting their usefulness in the ongoing monitoring process of physical capacities in elite male academy players across a competitive soccer season.



#3 Relative age effect in Italian soccer. A cultural issue in talent management?

Reference: J Sports Med Phys Fitness. 2022 Apr 19. doi: 10.23736/S0022-4707.22.13663-7. Online ahead of print.

Authors: Bruno Ruscello, Gabriele Morganti, Gennaro Apollaro, Antonio Saponara, Mario Esposito, Lorenzo Marcelli, Cristoforo Filetti, Marco Porta, Alberto Grossi, Laura Pantanella

Summary: Relative Age Effect (RAE) is a well-known phenomenon among those involved in youth sports, especially when the sport being investigated is widespread and involves early selection for participation in national and international competitions. The purpose of this study was to verify whether the Italian youth soccer ecosystem has adapted to this issue over the years, comparing players born in 1995 and in 2005 and been playing in Under 16 teams in the appropriate years. The sample included 13 professional Italian soccer teams. The number of players analysed was 260 (1995) and 344 boys (2005), respectively, making a total of 604 players enrolled in this study. Relative age effects were detected by chi-square (χ²) goodness of fit tests both in players born in 1995 (p<0.000;V=0.40) and in 2005 (p<0.0001;V=0.39). χ² test of independence showed no significant difference between the two groups of players (p=0.986;V=0.02), confirming a substantial parity of the phenomenon over the two investigated birth years. Ten years of research and dissemination of RAE did not change the selection policies adopted by coaches and/or scouts, who favor relatively older players during the selection processes. Therefore, RAE appears as the result of the Talent Identification and Development Structures, characterized by early selection and early specialization, and which consider performance as the pre-requisite for gaining access to the next developmental stages. Sport organizations should be aware of this issue and counteract accordingly, since it is important to mitigate the presence of RAE, as it causes inequality of opportunity.



#4 An Assist for Cognitive Diagnostics in Soccer: Two Valid Tasks Measuring Inhibition and Cognitive Flexibility in a Soccer-Specific Setting With a Soccer-Specific Motor Response

Reference: Front Psychol. 2022 Mar 31;13:867849. doi: 10.3389/fpsyg.2022.867849. eCollection 2022.

Authors: Lisa Musculus, Franziska Lautenbach, Simon Knöbel, Martin Leo Reinhard, Peter Weigel, Nils Gatzmaga, Andy Borchert, Maximilian Pelka

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Summary: In professional soccer, players, coaches, and researchers alike recognize the importance of cognitive skills. Research addressing the relevance of cognitive skills has been based on the cognitive component skills approach (i.e., general cognitive processes) or the expert performance approach (i.e., sport-specific cognitive processes). Our project aimed to combine the strengths of both approaches to develop and validate cognitive tasks measuring inhibition and cognitive flexibility in a soccer-specific setting with a soccer-specific motor response. In the main study 77 elite youth soccer players completed a computerized version of the standard flanker and number-letter tasks as well as flanker and number-letter tasks requiring a soccer-specific motor response (i.e., pass) in a soccer-specific setting (i.e., the SoccerBot360). Results show good reliability for both tasks. For the SoccerBot360 number-letter task, switch effects for response times and accuracy and acceptable convergent validity were shown. A flanker effect for response time but not accuracy was apparent. Due to no acceptable convergent validity, the flanker task was revised (i.e., adaptation of stimuli) and 63 adult soccer players participated in a follow-up validation study in the SoccerBot100. The revised flanker task showed the flanker effect for response time, but not for accuracy. However, acceptable convergent validity for response time was present. Thus, the soccer-specific number-letter and to some extent the soccer-specific flanker task show potential to be used as a valid cognitive diagnostic tool by soccer clubs.



#5 Pelvic incidence and osteitis pubis in professional soccer players

Reference: Acta Ortop Bras. 2022 Jan 28;30(1):e244380. doi: 10.1590/1413-785220223001e244380. eCollection 2022.

Authors: Fernando Mansano Rodrigues, Atul Kumar Taneja, Erica Narahashi, Flavio Duarte Silva, Artur Rocha Corrêa Fernandes, Guilherme G Falotico, André Fukunishi Yamada

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Summary: Osteitis pubis is a common inflammatory disease of the pubic symphysis, defined as a chronic pain syndrome caused by repetitive microtrauma. Since adaptative changes are necessary in the pelvis to adjust the equilibrium of the myotendinous structures, the aim of this study was to evaluate the correlation between pelvic incidence and osteitis pubis among professional soccer players. An observational, cross-sectional study was performed with professional soccer players from five teams during pre-season. Athletes with previous congenital pelvic abnormalities or a history of surgery were excluded. Radiographs of the pelvis were analyzed by two radiologists and assessed for findings consistent with osteitis pubis, and the following parameters were measured: pelvic incidence (PI), sacral inclination (SI), and pelvic version (PV). A total of 107 subjects were included in the study, with a mean age of 25.6 ± 3.1 years. Findings compatible with osteitis pubis were present in 74.8% of the subjects (80/107). There was no statistical correlation between osteitis pubis and PI (52.3°±12.7° vs. 48.4°±10.8°; p=0.156), SI (43.1°±9.8° vs. 39.9°±10.1°; p=0.146), or PV (9.2°± 6.3° vs 8.6°± 7.5°; p=0.649). Agreement between readers was excellent (p<0.0001). There was no significant correlation between pelvic parameters and radiographic diagnosis of osteitis pubis. 



#6 Visual strategies of young soccer players during a passing test - A pilot study

Reference: J Eye Mov Res. 2022 Feb 21;15(1):10.16910/jemr.15.1.3. doi: 10.16910/jemr.15.1.3. eCollection 2022.

Authors: Pieter Vansteenkiste, Matthieu Lenoir, Izabela Krejtz, Krzysztof Krejtz

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Summary: In sports, studies on visual behavior have mostly focused on expert-novice differences during decision making tasks and during aiming tasks. How visual behavior changes during the early stages of skill acquisition however, has hardly been documented. The current study investigated gaze behavior of young soccer players during the execution of a soccer passing task. Gaze behavior of eleven 8- to 10-year-old soccer players was recorded while they performed the Loughborough Soccer Passing Test. Based on their score, participants were then divided into a high performance group (N=5), and a low performance group (N=6). Results showed that the low performance group tended to look more at the ball while they were handling it. These findings suggest that gaze strategies develop alongside technical skills. More insights in the interplay between technical skills and gaze strategies during skill acquisition could lead to improved training methods for young soccer players.



#7 Is There a Sex Difference in Technical Skills among Youth Soccer Players in Norway?

Reference: Sports (Basel). 2022 Mar 29;10(4):50. doi: 10.3390/sports10040050.

Authors: Arne Sørensen, Emma C Haugen, Roland van den Tillaar

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Summary: Female soccer has recently experienced an impressive increase in the number of players, and an impressive improvement in the quality of elite matches. Still, studies show sex differences in match statistics on passing accuracy and the ability to control the ball in international matches, which is explained by a lower skill of level in female soccer players as compared to male players. Therefore, the aim of this study was to evaluate if female youth soccer players had bridged the gap in technical skills to reach the level that boys have traditionally attained. Sixteen male and 17 female youth soccer players of the same age and experience level took part in technical skill tests of reception of the ball on the ground and long passes. The results show a significant difference between the sexes in reception performance in favour of the male players (p &lt; 0.05, ES = 1.09), but no significant difference in the long pass test (p = 0.11, ES = 0.43). This leads to the conclusion that the lower score on ball reception is probably the result of experience in small-sided self-organised soccer games during childhood among the male players, which influences reception skills but not the ability to make accurate long passes.



#8 An Examination of the Experiences of Practitioners Delivering Sport Psychology Services within English Premier League Soccer Academies

Reference: Sports (Basel). 2022 Apr 13;10(4):60. doi: 10.3390/sports10040060.

Authors: Francesca Dean, Emma Kavanagh, Amanda Wilding, Tim Rees

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Summary: Sport psychology has become increasingly recognized and accepted within professional sports, including soccer. To date, there is a lack of research that examines the provision of sport psychology within elite soccer, particularly from the experience of applied practitioners working within the field. The current study adopted a qualitative, inductive approach, to examine the experiences of practitioners responsible for sport psychology delivery within elite soccer academies in England. Seven participants (four females; three males), working within academies in the English Premier League, took part in semi-structured interviews about their experience of delivering sport psychology services within elite soccer academies. Results demonstrated that the provision of sport psychology is continually evolving, yet there are a number of factors that appear to inhibit the full integration of the discipline into academy soccer. Six key themes were identified: The breadth of sport psychology provision; what is sport psychology; the stigma surrounding sport psychology services; psychological literacy; the elite youth soccer environment; and the delivery of sport psychology under the Elite Player Performance Plan. Participants identified a lack of psychological literacy among coaches and academy staff, as well as a low level of guidance regarding the provision of psychology within the England Football Association's guiding document-the Elite Player Performance Plan-leading to considerable variation in the nature of the sport psychology provision. Future research would do well to also sample from a range of staff working within English soccer academies, in order to assess their perception of the level of provision and understanding of psychology.



#9 Relationships between Fitness Status and Blood Biomarkers in Professional Soccer Players

Reference: J Healthc Eng. 2022 Apr 11;2022:5135817. doi: 10.1155/2022/5135817. eCollection 2022.

Authors: Ana Filipa Silva, Francisco Tomás González-Fernández, Halil Ibrahim Ceylan, Rui Silva, Saeid Younesi, Yung-Sheng Chen, Georgian Badicu, Paweł Wolański, Eugenia Murawska-Ciałowicz, Filipe Manuel Clemente

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Summary: Physical conditions are recognized to be optimal after the pre-season (PS) phase in professional sports. Given that blood measures may also reveal variations, which in turn, may present associations with fitness changes. The aim of this study is to test the changes of blood markers and physical fitness outcomes at the beginning and following the PS phase. Additionally, we aimed also to analyze the associations of training adaptations between blood markers and the physical fitness measures.  25 professional male soccer players (28.1 ± 4.6 years old, 2.0 ± 7.8 kg, and 176.7 ± 4.9 cm) were assessed for hematological and biochemical parameters, and physical fitness measures in the baseline and after the phase of PS. Increases in platelets were observed after the PS phase (p = 0.001, η2 = 0.39). Regarding the biochemical parameters, significant increases between PS were found for creatinine (Cre) (p = 0.001, η2 = 0.66), alkaline phosphatase (ALP) (p = 0.001, η2 = 0.79), C-Reactive Protein (CRP) (p = 0.001, η2 = 0.74), cortisol (C) (p = 0.001, η2 = 0.63), and testosterone (T) (p = 0.001, η2 = 0.76), whereas significant decreases were found for albumin (Alb) (p = 0.004, η2 = 0.29), and calcium corrected (Ca Corr.) (p = 0.002, η2 = 0.32). Moderate correlations were found between albumin and the 5-meter linear sprint split (r = -0.44 (95%CI: -0.71; -0.05)) and CRP (r = -0.48 (95%CI: -0.74; -0.10)). Moderate correlations were found between VAMEVAL and hemoglobin (r = 0.44 (95%CI: 0.05; 0.71)). The overall physical fitness measures improved after the PS phase. Also, significant variations (decreases/increases) were observed for the case of biomchemical and hematological outcomes. Coaches should carefully consider the adaptative changes observed in blood parameters as the changes in whole organism and metabolism after specific critical phases as the PS in professional players. Thus, optimal management of stimulus/recovery can be warranted to minimize illness and injury rate and to follow the direction and dynamics of adaptative changes.



#10 Physiological and Sprint Kinetics Associated With the Yo-Yo Intermittent Recovery Test Level 1 Performances in Soccer Players

Reference: Int J Sports Physiol Perform. 2022 Apr 22;1-9. doi: 10.1123/ijspp.2021-0483. Online ahead of print.

Authors: Mark Kramer, Martinique Sparks, Ben Coetzee

Summary: The Yo-Yo Intermittent Recovery Test Level 1 (YYIR1) is often utilized to indirectly assess the cardiorespiratory fitness of team-sport athletes due to its proposed association with match-play high-speed running performance and predicted maximal oxygen uptake. No previous research has investigated the relationships between YYIR1 performances, actual oxygen uptake recorded during the YYIR1, and true all-out sprint kinetics (eg, maximal sprint speed, maximal force capacity, and maximal power output), which therefore served as the primary objective of this study. The aim was to assess the true physiological kinetics (V˙O2 and heart-rate responses) during the YYIR1 and to evaluate the correlations between the physiological kinetics, sprint kinetics, and YYIR1 performance parameters. A total of 23 amateur male soccer players were recruited for the study (age 22.52 [2.86] y; height 1.75 [0.06] m; body mass 65.61 [8.43] kg). Each participant completed a YYIR1 and 2 all-out sprint tests. Significant differences were observed between actual and predicted maximal oxygen-uptake values (Mdiff = 17.57 mL·kg-1·min-1, P < .001, r = .63). Shuttle distances showed statistically significant correlations with maximal sprint speed (r = .42, P = .044) and theoretic maximal speed (r = .44, P = .035). However, no other correlations with sprint kinetic parameters (eg, maximal force or power output) were observed. Practitioners should carefully consider the outcomes and utilities of the parameters derived from the YYIR1. The estimations of maximal oxygen uptake from shuttle performances as a proxy for cardiorespiratory fitness are not adequate. However, shuttle distances appear to be positively associated with all-out sprinting capacities.



#11 Management of FAIS in professional soccer athletes and return to sports

Reference: Orthopade. 2022 Apr 28. doi: 10.1007/s00132-022-04257-2. 

Authors: Stefan Budde, Marco Ezechieli

Summary: The prevalence of femoroacetabular impingement syndrome in professional soccer athletes is high. Professional training and treatment conditions ensure an effective conservative therapy focusing on dynamic stability, motion control, muscle balance and core stability. In the case of persistent limitations, indication for surgery has to be considered carefully. The probability is high that return to a professional level of soccer is feasible. However, the period of rehabilitation is long, leading to a potential conflict area between economic and medical interests. Good communication and intensive patient education are essential.



#12 Quantifying technical actions in professional soccer using foot-mounted inertial measurement units

Reference: Sci Med Footb. 2022 May;6(2):203-214. doi: 10.1080/24733938.2021.1910333. Epub 2021 Apr 22.

Authors: Joshua Marris, Steve Barrett, Grant Abt, Chris Towlson

Summary: This study aimed to (i) establish the concurrent validity and intra-unit reliability of a foot-mounted inertial measurement unit for monitoring soccer technical actions, (ii) quantify the within-microcycle inter-positional differences in the technical actions of professional soccer training, and (iii) determine the influence of drill category on the technical actions of professional soccer training. Twenty-one professional soccer players' technical performance data (ball touches, releases, ball touches per minute, releases per minute), collected during training sessions throughout twenty-four weekly microcycles, were analysed using general linear modelling. The inertial measurement unit exhibited good concurrent validity (PA = 95.1% - 100.0%) and intra-unit reliability (PA = 95.9% - 96.9%, CV = 1.4% - 2.9%) when compared with retrospective video analyses. The most ball touches and releases were observed on MD - 1, with MD - 5 eliciting the highest frequency of ball touches and releases per minute. Central midfielders performed the most ball touches, releases, ball touches per minute and releases per minute. Small-sided games evoked more ball touches and releases per minute than previously reported in match-play. The fewest ball touches and releases per minute were observed during tactical drills. The results of this study provide a novel understanding of the within-microcycle, inter-positional and drill category differences in the technical actions performed by professional players during training.



#13 Endoscopic curettage and allografting of simple bone cysts of the calcaneus in young soccer players: Report of three cases

Reference: Foot (Edinb). 2021 Sep 25;51:101868. doi: 10.1016/j.foot.2021.101868. Online ahead of print.

Authors: Ioannis Terzidis, Theodorakys Marín Fermín, Efthymios Papasoulis, Trifon Totlis, Emmanouil Papakostas, Aristotelis Sideridis

Summary: Open curettage with bone graft has been the traditionally suggested surgical treatment for the symptomatic simple (or unicameral as they used to be called) calcaneal bone cyst. Less invasive endoscopically assisted treatment with curettage and bone grafting with allograft have recently provided less postoperative morbidity. The aim of the present study is to present our experience with this method in young soccer athletes. Between April 2014 and May 2016 three consecutive young soccer players with symptomatic calcaneal bone cysts underwent endoscopic curettage, and percutaneous injection of demineralized bone matrix allograft. The mean age was 17.3 (16, 17 and 19 years old), and the mean follow-up was 32.1 (range 24-47) months. Both radiographic and functional follow-up, using the AOFAS score, showed good to excellent results. All lesions were radiographically healed. Preoperative AOFAS score (max. 100 pts) was 78.6 ± 4.7, improving to 98.0 ± 4.1. The patients returned to their initial level of sports activities within 18.3 (range 17-19) weeks after surgery. Evidence suggests an earlier return to sports using bone substitutes. However, the present study showed that endoscopic curettage and percutaneous injection of bone allograft is also an excellent treatment option for young athletes with a symptomatic calcaneal bone cyst.



#14 Inter-methodological quantification of the target change for performance test outcomes relevant to elite female soccer players

Reference: Sci Med Footb. 2022 May;6(2):248-261. doi: 10.1080/24733938.2021.1942538. Epub 2021 Jun 27.

Authors: Naomi Datson, Lorenzo Lolli, Barry Drust, Greg Atkinson, Matthew Weston, Warren Gregson

Summary: Valid and informed interpretations of changes in physical performance test data are important within athletic development programmes. At present, there is a lack of consensus regarding a suitable method for deeming whether a change in physical performance is practically relevant or not. We compared true population variance in mean test scores between those derived from evidence synthesis of observational studies to those derived from practioner opinion (n = 30), and to those derived from a measurement error (minimal detectable change) quantification (n = 140). All these methods can help to obtain 'target' change score values for performance variables. We found that the conventional 'blanket' target change of 0.2 (between-subjects SD) systematically underestimated practically relevant and more informed changes derived for 5-m sprinting, 30-m sprinting, CMJ, and Yo-Yo Intermittent Recovery Level 1 (IR1) tests in elite female soccer players. For the first time in the field of sport and exercise sciences, we have illustrated the use of a principled approach for comparing different methods for the definition of changes in physical performance test variables that are practically relevant. Our between-method comparison approach provides preliminary guidance for arriving at target change values that may be useful for research purposes and tracking of individual female soccer player's physical performance.



#15 An audit of hormonal contraceptive use in Women's Super League soccer players; implications on symptomology

Reference: Sci Med Footb. 2022 May;6(2):153-158. doi: 10.1080/24733938.2021.1921248. Epub 2021 May 16.

Authors: Lloyd J Parker, Kirsty J Elliott-Sale, Marcus P Hannon, James P Morton, Graeme L Close

Summary: The aim was to audit hormonal contraceptive use and associated symptomology in elite women's soccer in England. Seventy-five elite women's soccer players from the Women's Super League (WSL) completed a questionnaire to assess: hormonal contraceptive (HC) use or non-use, reasons for initiation and discontinuation and the symptoms experienced by HC and non-HC users. Twenty-eight per cent reported current HC use, with 43% having used HCs previously. Combined HCs accounted for 62% of total usage, with progestin-only HCs making up the remainder. Eighty-six per cent pre-empted negative symptoms before commencing HCs, with 38% experiencing adverse symptoms. Negative symptoms were most common in progestin-only HC users (63%). Eighty-six per cent reported benefits associated with HC usage include pain management and the ability to predict or control their cycles. Six non-HC users reported amenorrhea, with one medically diagnosed. Negative MC-related symptoms were reported by 74%, with 4% unable to train due to these symptoms. Unfavorable symptoms typically occurred during the first days of menstruation (59%). Most WSL players do not currently use HCs (72%). Most HC users reported benefits of HC usage, whilst most non-HC users reported negative symptoms especially around menstruation. Practitioners should track players' MCs to help minimise discomfort and maximise performance.



#16 Collective behaviour in high and low-level youth soccer teams

Reference: Sci Med Footb. 2022 May;6(2):164-171. doi: 10.1080/24733938.2021.1917774. Epub 2021 Jul 22.

Authors: Jade O'Brien-Smith, Job Fransen, William B Sheehan, Matthieu Lenoir, Kyle Bennett, Mitchell R Smith

Summary: An expert/non-expert paradigm often helps understand the underpinnings of sports expertise; however, this method is scarcely extended to the complexities of collective behaviour in youth soccer. Therefore, the objectives of the current study are to investigate differences in the collective behaviour of youth soccer teams by expertise level. Soccer players aged 15 to 20 years from high (n = 35) and low (n = 40) playing levels competed in two age-matched 5v5 small-sided games. For each game, teams' skill involvement (shot, pass, dribble, touch), passing networks (closeness, density, betweenness), and spatiotemporal characteristics (stretch index, effective area, length (L) & width (W), LpW ratio, synchrony) were measured using video footage and GPS coordinates. High level teams had more attempted (p = .009), and completed skills (p = .003), particularly for the number of passes (p = .001) and shots (p = .012-.045). However, there were no significant between-group differences for either the passing networks or spatiotemporal characteristics. The findings from the current research suggest that the high-level teams can quickly and effectively move the ball within existing team structures and may better optimise their afforded space to execute desired skills when compared to the low-level teams.



#17 Quantifying change of direction load using positional data from small-sided games in soccer

Reference: Sci Med Footb. 2022 May;6(2):234-240. doi: 10.1080/24733938.2021.1912382. Epub 2021 Apr 15.

Authors: Brenda M T Merks, Wouter G P Frencken, A R Den Otter, Michel S Brink

Summary: Quantifying change of direction (COD) load through positional data from small-sided games (SSG) and assess its criterion and construct validity. Elite male youth soccer players (n = 25, 16.8 ± 1.3 years) played three SSG (5v5, 5×4 min) with different field dimensions (small [40×30 m], medium [55×38 m], large [70×45 m]). Positional data of the players was obtained with a Local Position Measurement system. COD load (AU) was quantified based on the combination of velocity and change in heading direction. Additionally, total distance covered, running distance, acceleration count, deceleration count, and Rating of Perceived Exertion were measured. Criterion validity was assessed by correlating COD load and the load indicators. Construct validity was determined by testing the differences between the SSG field dimensions. Strong correlations were determined between COD load and total distance covered (r = 0.74, p < .01) and running distance (r = 0.84, p < .01). Middle and large field size resulted in highest COD load (p < .05). These results suggest that the COD load measure shows sufficient criterion and construct validity.



#18 Fundamental movement skills and perceived competence, but not fitness, are the key factors associated with technical skill performance in boys who play grassroots soccer

Reference: Sci Med Footb. 2022 May;6(2):215-220. doi: 10.1080/24733938.2021.1910332. Epub 2021 Apr 7.

Authors: Michael Duncan, Emma L J Eyre, Mark Noon, Rhys Morris, Doug Thake, Neil Clarke

Summary: This study examined the association between fitness, fundamental movement skills (FMS) and perceived competence on technical skills in boys engaged in grassroots soccer. Methods: Sixty boys (8-12 years of age, Mean ± SD = 10 ± 1 years) undertook assessment of FMS, perceived competence, physical fitness (15m sprint speed, standing long jump distance and seated 1kg medicine ball throw as a composite z-score) and technical skills (dribbling, passing and shooting as a composite z-score). Multiple backwards linear regression was used to determine to amount of variance in technical skill explained by FMS, perceived competence and fitness. Results indicated a significant model (F 3,58= 42.04, P = .0001, Adj R2 = .680) which explained 68% of the variance in technical skills. Perceived competence (β=.316, P =.001), Total FMS (β=.140, P =.002), and chronological age (β=.863), P =.001) significantly contributed to the model. This study demonstrates that better technical skills (passing, dribbling, shooting) in youth soccer are explained, alongside age, by being competent in FMS and having a more positive perception of competence. Coaches should therefore seek to encourage development of these factors during childhood for the benefit of technical skill performance.



#19 The influence of relative playing area and player numerical imbalance on physical and perceptual demands in soccer small-sided game formats

Reference: Sci Med Footb. 2022 May;6(2):221-227. doi: 10.1080/24733938.2021.1939408. Epub 2021 Jun 11.

Authors: Andrew N Guard, Kenneth McMillan, Niall G MacFarlane

Summary: This study aimed to examine physiological, mechanical and perceptual loading in small-sided games using different relative playing areas with balanced and unbalanced player numbers. Data were collected in twelve elite youth male soccer players and included heart rate and standard time-motion outputs using commercial GPS. The data demonstrated higher cardiovascular, physical and perceptual demands with increasing pitch size (e.g. average HR was 88.7 vs. 86.7% HRmax with 8 vs. 2 high-intensity acceleration in medium vs. small pitch formats. The largest pitch format resulted in a greater accumulation of high-intensity distance (47 ± 30 m), higher peak velocity (25.2 ± 1.6 km.h-1) and a higher distance and frequency of accelerations (35 ± 9 m and 8 ± 3) compared with the smallest pitch (all p < 0.01). In unbalanced games, there was significantly greater average heart rate in the overloaded team (84.4 ± 4.9 vs. 80.4 ± 4.8% HRmax in 4 v. 6). These data suggest that different game formats including numerical imbalance could be prescribed for squad management to target conditioning stimuli for specific players (e.g. to target a higher training load for players that do not get consistent match exposure).



#20 Variations in the relative age effect with age and sex, and over time-Elite-level data from international soccer world cups

Reference: PLoS One. 2022 Apr 28;17(4):e0264813. doi: 10.1371/journal.pone.0264813. eCollection 2022.

Authors: Arve Vorland Pedersen, Tore Kristian Aune, Terje Dalen, Håvard Lorås

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Summary: The relative age effect (RAE) is a statistical bias observed across sport contexts and consists of a systematic skewness in birth date distribution within an annual-age cohort. In soccer, January 1st is the common cut-off date when categorizing players in competitions according to their chronological age, which potentially disadvantages those within the cohort who were born later in the year. Thus, relatively older soccer players in their cohort can be favored in talent identification, selection, and development. The aim of the current study was to investigate the variations in RAE in male and female international youth world-cup tournaments (U17 and U20) in the period from 1997-2019 and in international senior world-cup-tournaments from 2006-2019. A total of 20,401 soccer players participating in 47 different tournaments were analyzed. The birthdate distributions were categorized into four quartiles (January-March, Q1; April-June, Q2; July-September, Q3; October-December, Q4) and compared to a uniform distribution using Chi-square analysis with Cramer's V (Vc) as a measure of effect size. Based on the existing data concerning RAE in elite junior and senior soccer, it was hypothesized that: (I) the RAE is present in youth soccer world cup tournaments but is stronger in male players than in female players; (II) the younger the soccer players, the stronger the RAE; and (III) the RAE in world cup soccer tournaments has strengthened over time. All these hypotheses were supported by the data; novel findings included that the effect has now entered women's soccer, and in men's soccer it persists into senior world cup tournaments. Thus, a strong RAE bias occurs in selection among elite soccer players competing in international world cup tournaments.



#21 Heading Exposure in Elite Football (Soccer): A Study in Adolescent, Young Adult, and Adult Male and Female Players

Reference: Med Sci Sports Exerc. 2022 Apr 25. doi: 10.1249/MSS.0000000000002945. Online ahead of print.

Authors: Shari Langdon, Edwin Goedhart, Jaap Oosterlaan, Marsh Königs

Summary: This study aims to quantify heading exposure in real-life elite football at the level of individual male and female adolescents, young adults and adults. Heading exposure was determined by video analysis in combination with a structured electronic registration tool and observation training, to comprehensively register heading characteristics. Characteristics of heading events were registered in 116 official matches (96 male, 20 female) of Dutch national teams. Mean exposure for male players based on full match participation was 4.2 headers, with maximum heading exposure at 10.6 headers. Mean heading exposure was higher in adult than adolescent players (p = .049), while maximum heading exposure was higher for adult than for young adult players (p = .045). Maximum heading exposure was higher in male than in female players (p = .015). Defenders had the greatest mean and maximum heading exposure (ps < .001). Longer flight courses of the ball had greater contribution to expected and maximum heading exposure than shorter courses (ps < .01). Frontal headers had greater contribution to exposure than other points of contact on player's head (ps < .001), while linear headers had greater contribution than rotational headers (p = .016). Defensive headers had greater contribution to exposure than other heading types (ps < .014). Unintentional head contacts in elite football players were in most cases (80%) not related to heading situations. This study provides real-life quantifications of expected and maximum heading exposure in elite football, with strong relevance for policy makers and researchers. The results highlight the roles of player and heading characteristics in heading exposure, informing current discussions on the role of heading in football.



#22 Relationships Between Internal and External Load Measures and Fitness Level Changes in Professional Soccer Players

Reference: Res Q Exerc Sport. 2022 Apr 29;1-13. doi: 10.1080/02701367.2022.2053646. Online ahead of print.

Authors: Marco Martin, Ermanno Rampinini, Andrea Bosio, Andrea Azzalin, Alan McCall, Patrick Ward

Summary: Understanding the dose-response relationship between internal and external training load with changes in aerobic fitness and intermittent running capacity, during different periods of the season, may help in optimizing training process. The aim of the present study was to investigate the dose-response relationships between load measures and changes in aerobic fitness and intermittent running capacity among a large cohort of professional soccer players.  Training load, aerobic fitness and intermittent running capacity of 52 male adult professional players from 3 elite teams were monitored across an entire season and analyzed employing linear mixed models, with a significance level set at p≤0.05.  Relationships between load measures (training and match duration, sRPE-TL, total distance, high and very high-speed running distances) and changes in physical qualities were stronger during the preparation period (PREP) for both aerobic fitness (d= 0.48 to 0.76, p<0.031) and intermittent running capacity (d= 0.46 to 1.89, p<0.046). The magnitude of the relationships reduced during the first competitive period (d= 0.43 to 0.56) and the relationships became trivial in the second competitive period (d= 0.06 to 0.41, p= 0.063 to 0.846).  The moderate to large relationships found between all measures of load and changes in physical capacities suggest that training prescription during the PREP was effective in improving players' fitness. During the competitive phase small changes in aerobic and intermittent running capacities were found, highlighting that coaching staff pursue different aims during the competitive period, such as technical and tactical training and recovery. .



#23 Accuracy of Tracking Devices' Ability to Assess Exercise Energy Expenditure in Professional Female Soccer Players: Implications for Quantifying Energy Availability

Reference: Int J Environ Res Public Health. 2022 Apr 14;19(8):4770. doi: 10.3390/ijerph19084770. 

Authors: Marcus S Dasa, Oddgeir Friborg, Morten Kristoffersen, Gunn Pettersen, Jorunn Sundgot-Borgen, Jan H Rosenvinge

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Summary: The purpose of the study was to assess the accuracy of commonly used GPS/accelerometer-based tracking devices in the estimation of exercise energy expenditure (EEE) during high-intensity intermittent exercise. A total of 13 female soccer players competing at the highest level in Norway (age 20.5 ± 4.3 years; height 168.4 ± 5.1 cm; weight 64.1 ± 5.3 kg; fat free mass 49.7 ± 4.2 kg) completed a single visit test protocol on an artificial grass surface. The test course consisted of walking, jogging, high-speed running, and sprinting, mimicking the physical requirements in soccer. Three commonly used tracking devices were compared against indirect calorimetry as the criterion measure to determine their accuracy in estimating the total energy expenditure. The anaerobic energy consumption (i.e., excess post-exercise oxygen consumption, EPOC) and resting time were examined as adjustment factors possibly improving accuracy. All three devices significantly underestimated the total energy consumption, as compared to the criterion measure (p = 0.022, p = 0.002, p = 0.017; absolute ICC = 0.39, 0.24 and 0.30, respectively), and showed a systematic pattern with increasing underestimation for higher energy consumption. Excluding EPOC from EEE reduced the bias substantially (all p's becoming non-significant; absolute ICC = 0.49, 0.54 and 0.49, respectively); however, bias was still present for all tracking devices. All GPS trackers were biased by showing a general tendency to underestimate the exercise energy consumption during high intensity intermittent exercising, which in addition showed a systematic pattern by over- or underestimation during lower or higher exercising intensity. Adjusting for EPOC reduced the bias and provided a more acceptable accuracy. For a more correct EEE estimation further calibration of these devices by the manufacturers is strongly advised by possibly addressing biases caused by EPOC.



#24 Individualized Analysis of Lateral Asymmetry Using Hip-Knee Angular Measures in Soccer Players: A New Methodological Perspective of Assessment for Lower Limb Asymmetry

Reference: Int J Environ Res Public Health. 2022 Apr 13;19(8):4672. doi: 10.3390/ijerph19084672.

Authors: Oscar García-García, Ángela Molina-Cárdenas, Tania Álvarez-Yates, Mario Iglesias-Caamaño, Virginia Serrano-Gómez

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Summary: This study aimed to: (1) determine the magnitude and direction of lateral asymmetry in well-trained soccer players using hip and knee ROM tests; (2) inquire if asymmetry relies on the ROM test performed and/or gender; and (3) establish asymmetry thresholds for each ROM test to individualize lower-limbs asymmetry. One hundred amateur soccer players were assessed using hip-knee ROM tests: Straight Leg Raise, modified Thomas Test, hip internal rotation and external rotation, hip abduction (ABD) and adduction (ADD), Nachlas Test and Rigde Test. There are significant differences between tests when determining the magnitude of lateral asymmetry (F = 3.451; p = 0.001; ηp2 = 0.031) without significant differences between gender (F = 0.204; p = 0.651; ηp2 = 0.001). Asymmetry threshold results differ significantly between using a fixed or a specific threshold (F = 65.966; p = 0.001; ηp2 = 0.985). All tests indicate that the direction of asymmetry is towards the dominant limb. In conclusion, the ROM test used determines the magnitude and direction of the lateral asymmetry of the amateur soccer players. The ABD and ADD are the ROM tests that showed higher percentages of asymmetry, without differences between female and male soccer players. Using a specific asymmetry threshold formula can classify more players as asymmetrical than with a fixed threshold.


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