Latest research in football - week 46 - 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 Multiscale fractal dimension applied to tactical analysis in football: A novel approach to evaluate the shapes of team organization on the pitch

Reference: PLoS One. 2021 Sep 1;16(9):e0256771. doi: 10.1371/journal.pone.0256771. eCollection 2021.

Authors: Murilo José de Oliveira Bueno, Maisa Silva, Sergio Augusto Cunha, Ricardo da Silva Torres, Felipe Arruda Moura

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Summary: The aim of this study was to evaluate different shape descriptors applied to images of polygons that represent the organization of football teams on the pitch. The effectiveness of different shape descriptors (area/perimeter, fractal area, circularity, maximum fractal, rectangularity, multiscale fractal curve-MFC), and the concatenation of all shape descriptors (except MFC), denominated Alldescriptors (AllD)) was evaluated and applied to polygons corresponding to the shapes represented by the convex hull obtained from players' 2D coordinates. A content-based image retrieval system (CBIR) was applied for 25 users (mean age of 31.9 ± 8.4 years) to evaluate the relevant images. Measures of effectiveness were used to evaluate the shape descriptors (P@n and R@n). The MFD (P@5, 0.46±0.37 and P@10, 0.40±0.31, p < 0.001; R@5, 0.14±0.13 and R@10, 0.24±0.19, p < 0.001) and AllD (P@5 = 0.43±0.36 and P@10 = 0.39±0.32, p < 0.001; R@5 = 0.13±0.11 and R@10 = 0.24±0.20, p < 0.001) descriptors presented higher values of effectiveness. As a practical demonstration, the best evaluated shape descriptor (MFC) was applied for tactical analysis of an official match. K-means clustering technique was applied, and different shapes of organization could be identified throughout the match. The MFC was the most effective shape descriptor in relation to all others, making it possible to apply this descriptor in the analysis of professional football matches.



#2 Psychological factors and performance in women's football: A systematic review

Reference: Scand J Med Sci Sports. 2021 Sep 5. doi: 10.1111/sms.14043. Online ahead of print.

Authors: Susann Dahl Pettersen, Frode Adolfsen, Monica Martinussen

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Summary: The amount of research conducted on female football players, compared to male players, is sparce. Even though research on female football players has increased the past decade, there is still a lack of studies of how psychological factors affect their performance. The objective of the current systematic review was therefore to summarize existing quantitative research into the relationship between psychological factors and performance in women's football. Literature was sourced from MEDLINE/PubMed, Embase, and PsychInfo. Two independent reviewers applied the selection criteria and assessed the quality of the studies. A total of 14 studies met the inclusion criteria. The total number of participants was 1449, and 15 psychological factors were examined in relation to football performance. The results revealed a tendency for higher leveled players to score higher on psychological factors like mental toughness, conscientiousness, and executive functions. They also had lower levels of anxiety. Enjoyment and a perceived mastery climate were related to increased levels of performance and perceived competence. Mood was unrelated to performance. Limitations and implications for future research are discussed.



#3 Football and Ice Hockey Fans' Experience of a 12-Week Training and Weight-Loss Pilot Intervention (ViSiT) in Sweden-A Focus Group Study

Reference: Front Sports Act Living. 2021 Aug 18;3:616427. doi: 10.3389/fspor.2021.616427. eCollection 2021.

Authors: Janna Skagerström, Magdalena Hjertstedt, Petra Dannapfel, Ulrika Müssener, Matti Leijon

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Summary: Excess weight is associated with an increased risk of poor health and premature mortality. This is more problematic for men than for women because men have a lower life expectancy and a higher prevalence of several lifestyle-related diseases. A concept whereby overweight male supporters of professional football clubs are recruited and offered a weight-loss intervention has been developed in Scotland. In the present study, we explore participants' experiences of a similar pilot intervention, called ViSiT, conducted with supporters in one ice hockey club and one football club in Sweden to assess the feasibility of using the intervention in a Swedish context. In this user centered evaluation, focus groups were conducted with 12 men who had completed the 12-week ViSiT intervention. Participants discussed reasons for participating in and completing the intervention, effects of the intervention, advantages, and areas of improvement of the intervention, and thoughts on the club's involvement. The material was analyzed using thematic analysis according to Braun and Clarke. The analyses revealed four themes: reasons to participate, motivation and reinforcement, change of habit, and areas for improvement. The intervention was seen as an opportunity to change daily lifestyle behaviors. The group format, as well as the involvement of a prestigious sports club, was important for signing up to the intervention and for motivating continued involvement. The intervention had also resulted in increased knowledge on health and changed mindsets about being more attentive to regulating day-to-day behavior. Although the overall feedback on the intervention was positive, the participants suggested that possibilities to have more individual coaching should be added. The ViSiT weight loss and lifestyle intervention may be feasible in a Swedish context to reach overweight men at risk of poor health. The ice hockey and football club supporters expressed similar experiences from participating in the intervention. ViSiT seem to have a potential to be adopted by many sports clubs for a widespread reach to a group normally considered reluctant to participate in lifestyle change programs.



#4 Influence of the MCT1-T1470A polymorphism (rs1049434) on repeated sprint ability and blood lactate accumulation in elite football players: a pilot study

Reference: Eur J Appl Physiol.2021 Sep 4.doi: 10.1007/s00421-021-04797-z. Online ahead of print.

Authors: M Massidda, L Flore, N Kikuchi, M Scorcu, F Piras, P Cugia, P Cięszczyk, F Tocco, C M Calò

Summary: The aim of this study is to investigate the influence of the MCT1 T1470A polymorphism (rs1049434) on repeated sprint ability (RSA) and lactate accumulation after RSA testing. Twenty-six elite Italian male football players (age: 17.7 ± 0.78 years; height: 179.2 ± 7.40 cm; weight: 72.1 ± 5.38 kg) performed RSA testing (6 × 30-m sprints with an active recovery between sprints), and lactate measurements were obtained at 1, 3, 5, 7, and 10 min post-exercise. Genotyping for the MCT1 T1470A polymorphism was performed using PCR. Genotype distributions were in Hardy-Weinberg equilibrium, being 42% wildtype (A/A), 46% heterozygotes (T/A), and 12% mutated homozygotes (T/T). Significant differences between genotypic groups were found in the two final sprint times of the RSA test. Under a dominant model, carriers of the major A-allele (Glu-490) in the dominant model showed a significantly lower sprint time compared to footballers with the T/T (Asp/Asp) genotype (5th Sprint time: A/A + T/A = 4.60 s vs TT = 4.97 s, 95% CI 0.07-0.67, p = 0.022; 6th Sprint: A/A + T/A = 4.56 s vs T/T = 4.87 s, 95% CI 0.05-0.57, p = 0.033). The T1470A (Glu490Asp) polymorphism of MCT1 was associated with RSA. Our findings suggest that the presence of the major A-allele (Glu-490) is favourable for RSA in football players.



#5 A 2D qualitative movement assessment of a deceleration task detects football players with high knee joint loading

Reference: Knee Surg Sports Traumatol Arthrosc.2021 Sep 4. doi: 10.1007/s00167-021-06709-2.

Authors: Stefano Di Paolo, Stefano Zaffagnini, Filippo Tosarelli, Fabrizio Aggio, Laura Bragonzoni, Alberto Grassi, Francesco Della Villa

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Summary: The deceleration (pressing) is a common situational pattern leading to anterior cruciate ligament (ACL) injury in football. Although mainly assessed for performance purposes, a stronger focus on movement quality might support the screening of at-risk athletes. The aim of the present study was to describe a 2D scoring system for the assessment of the deceleration task and to associate it with the knee joint loading (knee abduction moment) evaluated through the gold standard 3D motion capture. The hypothesis was that lower 2D scores would be associated with higher knee joint loading. Thirty-four competitive football (soccer) players (age 22.8 ± 4.1, 16 females) performed a series of deceleration tasks. 3D motion analysis was recorded using ten stereophotogrammetric cameras, a force platform, and three high-speed cameras. The 2D qualitative assessment was performed via a scoring system based on the video analysis of frontal and lateral planes joint kinematics for five scoring criteria. The intra- and inter-rater reliabilities were calculated for each 2D scoring criteria. The peak knee abduction moment was extracted and grouped according to the results of the 2D evaluation. An ICC > 0.94 was found for all the 2D scoring criteria, both for intra-rater and inter-rater reliability. The players with low 2D frontal plane scores and low total scores (0-4) showed significantly higher peak knee abduction moment values (p < 0.001). A significant negative rank correlation was found between the total score and the peak knee abduction moment (ρ = - 0.25, p < 0.001). The qualitative 2D scoring system described successfully discerned between athletes with high and low knee joint loading during a deceleration task. The application of this qualitative movement assessment based on a detailed and accurate scoring system is suitable to identify players and patients with high knee joint loading (high knee abduction moments) and target additional training in the scenario of the primary and secondary ACL injury risk reduction.



#6 3-Week passive acclimation to extreme environmental heat (100± 3 °C) in dry sauna increases physical and physiological performance among young semi-professional football players

Reference: J Therm Biol. 2021 Aug;100:103048. doi: 10.1016/j.jtherbio.2021.103048. Epub 2021 Jul 1.

Authors: I Bartolomé, J Siquier-Coll, M Pérez-Quintero, M C Robles-Gil, F J Grijota, D Muñoz, M Maynar-Mariño

Summary: This manuscript aims to evaluate the influence of a novel passive heat acclimation program among human participants in the physical performance, as well as in several physiological parameters. 36 male football players were acclimated using a dry sauna bath to extreme hot (100 ± 3 °C), performing a total of nine sauna sessions with a weekly frequency of three sessions. The players were randomly into the sauna group (SG; n = 18; age: 20.69 ± 2.09 years) and the control group (CG; n = 18; age: 20.23 ± 1.98 years). All participants performed maximal effort test until exhaustion as well as hamstring flexibility test before and after the acclimation program. Anthropometric, respiratory, circulatory, hematological and physiological variables were evaluated at the beginning and at the end of the survey. Statistical analysis consisted of a Mann-Whitney U test to determine differences between groups at the beginning and at the end of the survey and a Wilcoxon test for paired samples to compare the differences for each group separately. Additionally, size effects of the pre-post acclimation changes were calculated. After the acclimation program SG participants experienced a diminution in body weight (p < 0.01), body mass index (p < 0.01), body fat (p < 0.05) and fat percentage (p < 0.05) decreased. Hamstring flexibility (p < 0.05) and work capacity (p < 0.05) increased. External basal temperature decreased (p < 0.05) as well as post-exercise systolic and diastolic blood pressures (p < 0.05). Finally, maximal oxygen uptake (ml Kg-1 min-1) (p < 0.05), maximal minute ventilation (p < 0.05) and maximal breath frequency (p < 0.05) increased at the end of the intervention. There were no significant changes in the CG in any variable. Favorable adaptations have been observed in this survey, suggesting a beneficial effect of extreme heat acclimation on physical performance. Several of the observed responses seem interesting for sport performance and health promotion as well. However, this is a novel, extreme protocol which requires further research.



#7 The Training of Medium- to Long-Distance Sprint Performance in Football Code Athletes: A Systematic Review and Meta-analysis

Reference: Sports Med. 2021 Sep 9. doi: 10.1007/s40279-021-01552-4. Online ahead of print.

Authors: Ben Nicholson, Alex Dinsdale, Ben Jones, Kevin Till

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Summary: Within the football codes, medium-distance (i.e., > 20 m and ≤ 40 m) and long-distance (i.e., > 40 m) sprint performance and maximum velocity sprinting are important capacities for success. Despite this, no research has identified the most effective training methods for enhancing medium- to long-distance sprint outcomes. This systematic review with meta-analysis aimed to (1) analyse the ability of different methods to enhance medium- to long-distance sprint performance outcomes (0-30 m, 0 to > 30 m, and the maximum sprinting velocity phase [Vmax]) within football code athletes and (2) identify how moderator variables (i.e., football code, sex, age, playing standard, phase of season) affected the training response. We conducted a systematic search of electronic databases and performed a random-effects meta-analysis (within-group changes and pairwise between-group differences) to establish standardised mean differences (SMDs) with 95% confidence intervals and 95% prediction intervals. This identified the magnitude and direction of the individual training effects of intervention subgroups (sport only; primary, secondary, tertiary, and combined training methods) on medium- to long-distance sprint performance while considering moderator variables. In total, 60 studies met the inclusion criteria (26 with a sport-only control group), totalling 111 intervention groups and 1500 athletes. The within-group changes design reported significant performance improvements (small-moderate) between pre- and post-training for the combined, secondary (0-30 and 0 to > 30 m), and tertiary training methods (0-30 m). A significant moderate improvement was found in the Vmax phase performance only for tertiary training methods, with no significant effect found for sport only or primary training methods. The pairwise between-group differences design (experimental vs. control) reported favourable performance improvements (large SMD) for the combined (0 to > 30 m), primary (Vmax phase), secondary (0-30 m), and tertiary methods (all outcomes) when compared with the sport-only control groups. Subgroup analysis showed that the significant differences between the meta-analysis designs consistently demonstrated a larger effect in the pairwise between-group differences than the within-group change. No individual training mode was found to be the most effective. Subgroup analysis identified that football code, age, and phase of season moderated the overall magnitude of training effects. This review provides the first systematic review and meta-analysis of all sprint performance development methods exclusively in football code athletes. Secondary, tertiary, and combined training methods appeared to improve medium-long sprint performance of football code athletes. Tertiary training methods should be implemented to enhance Vmax phase performance. Nether sport-only nor primary training methods appeared to enhance medium to long sprint performance. Performance changes may be attributed to either adaptations specific to the acceleration or Vmax phases, or both, but not exclusively Vmax. Regardless of the population characteristics, sprint performance can be enhanced by increasing either the magnitude or the orientation of force an athlete can generate in the sprinting action, or both.



#8 Cardiac magnetic resonance and follow up of professional soccer players recovering from COVID-19

Reference: Medicina (B Aires). 2021;81(4):491-495. [Article in Spanish]

Authors: Roberto Peidro, Rubén Argemi, Jorge Batista, Lucas Logioco, Diego Perez De Arenaza, Guillermo Bortman

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Summary: The incidence of post-COVID-19 cardiac compromise is not well known. The eventual cardiac repercussions on a return to high-performance sport are unclear. A prospective observational study with evaluation by physical examination, electrocardiogram, Doppler echocardiogram and cardiac magnetic resonance imaging (CMR) was carried out in international level professional soccer players recovering from COVID-19 who had the disease asymptomatic or with mild symptoms. Four-month follow-up with participation in national and international competitions. Twenty-four soccer players were included, age 27.13 years (between 20 and 36). Nine (37.5%) had asymptomatic disease and 15 (62.5%) had mild symptoms. No athletes required hospitalization. Physical, electrocardiographic, and echocardiographic examinations did not reveal heart disease. CMRs showed ventricular thicknesses and volumes consistent with high-performance athletes. In T1, T2 and fat saturation signals, no fat infiltration or signs of edema were observed. No late enhancement after gadolinium injection. They began their training between 12 and 14 days after diagnosis. Eleven (45.8%) participated between 4 and 6 international matches of Libertadores de América International Cup. The remaining 13 completed high intensity training sessions and participated in local league competitions. At 4 months after diagnosis, none of the soccer players developed cardiac events and training and competitions were well tolerated. These findings suggest low cardiovascular impact of COVID 19 and excellent tolerance to early post-COVID high intensity exercise of young athletes recovering from the disease with no or mild symptoms.



#9 Estimation of final standings in football competitions with a premature ending: the case of COVID-19

Reference: Adv Stat Anal. 2021 Sep 2;1-18. doi: 10.1007/s10182-021-00415-7. Online ahead of print.

Authors: P Gorgi, S J Koopman, R Lit

Free PMC article

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Summary: We study an alternative approach to determine the final league table in football competitions with a premature ending. For several countries, a premature ending of the 2019/2020 football season has occurred due to the COVID-19 pandemic. We propose a model-based method as a possible alternative to the use of the incomplete standings to determine the final table. This method measures the performance of the teams in the matches of the season that have been played and predicts the remaining non-played matches through a paired-comparison model. The main advantage of the method compared to the incomplete standings is that it takes account of the bias in the performance measure due to the schedule of the matches in a season. Therefore, the resulting ranking of the teams based on our proposed method can be regarded as more fair in this respect. A forecasting study based on historical data of seven of the main European competitions is used to validate the method. The empirical results suggest that the model-based approach produces more accurate predictions of the true final standings than those based on the incomplete standings.



#10 Expert and Novice Goalkeepers' Perceptions of Changes During Open Play Soccer

Reference: Percept Mot Skills. 2021 Aug 29;315125211040750. doi: 10.1177/00315125211040750.

Authors: Jie Li, Jing Yang, Yue Qin, Yu Zhang

Summary: In the present study we investigated expert and novice football (i.e., soccer) goalkeepers' three stages of perceiving changes in open play situations-detection, localization, and identification-with and without time constraints. We adopted the continual cycling flicker paradigm to investigate goalkeepers' perceptions when provided with sufficient time (Experiment 1), and we utilized the limited display one-shot change detection paradigm to study their perceptions under time constraints (Experiment 2). Images of goalkeepers' first-person views of open play soccer scenes were used as stimuli. Semantic or non-semantic changes in these scenes were produced by modifying one element in each image. Separate groups of expert and novice goalkeepers were required to detect, localize, and identify the scene changes. We found that expert goalkeepers detected scene changes more quickly than novices under both time allowances. Furthermore, compared to novices, experts localized the changes more accurately under time constraints and identified the changes more quickly when given sufficient time. Additionally, semantic changes were detected more quickly and localized and identified more accurately than non-semantic changes when there was sufficient time. Under time constraints expert goalkeepers' greater efficiency was likely due to pre-attentive processing; with sufficient time, they were able to focus attention to extracting detailed information for identification.



#11 COVID-19 Outbreak Among a University's Men's and Women's Soccer Teams - Chicago, Illinois, July-August 2020

Reference: MMWR Morb Mortal Wkly Rep. 2020 Oct 30;69(43):1591-1594.  doi: 10.15585/mmwr.mm6943e5.

Authors: Richard A Teran, Isaac Ghinai, Stephanie Gretsch, Tracy Cable, Stephanie R Black, Stefan J Green, Omar Perez, George E Chlipala, Mark Maienschein-Cline, Kevin J Kunstman, Susan C Bleasdale, Marielle J Fricchione

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Summary: Data on transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), among college athletes are limited. In August 2020, the Chicago Department of Public Health (CDPH) was notified of a cluster of COVID-19 cases among a university's men's and women's soccer teams. CDPH initiated an investigation, interviewed members of both teams, and collated laboratory data to understand transmission of SARS-CoV-2 within the teams. Numerous social gatherings with limited mask use or social distancing preceded the outbreak. Transmission resulted in 17 laboratory-confirmed COVID-19 cases across both teams (n = 45), likely from a single source introduction of SARS-CoV-2 (based on whole genome sequencing) and subsequent transmission during multiple gatherings. Colleges and universities are at risk for COVID-19 outbreaks because of shared housing and social gatherings where recommended prevention guidance is not followed. Improved strategies to promote mask use and social distancing among college-aged adults need to be implemented, as well as periodic repeat testing to identify asymptomatic infections and prevent outbreaks among groups at increased risk for infection because of frequent exposure to close contacts in congregate settings on and off campus.



#12 Contemporary practices of strength and conditioning coaches in professional soccer

Reference: Biol Sport. 2021 Sep;38(3):377-390. doi: 10.5114/biolsport.2021.99328. Epub 2020 Oct 24.

Authors: Anthony Weldon, Michael J Duncan, Anthony Turner, Jaime Sampaio, Mark Noon, Del P Wong, Vivian W Lai

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Summary: This study describes the contemporary practices of strength and conditioning coaches in professional soccer. Fifty-two strength and conditioning coaches from professional leagues across 18 countries completed an online survey, consisting of 45 questions, with eight sections: (a) background information, (b) muscular strength and power development, (c) speed development, (d) plyometrics, (e) flexibility development, (f) physical testing, (g) technology use, and (h) programing. A frequency analysis was used to assess and report responses to fixed response questions, and thematic-analysis used for open-ended questions to create clear, identifiable and distinct themes. All strength and conditioning coaches were educated to degree level or higher, 65% held strength and conditioning certifications and 54% held soccer coaching certifications. Concentric (100%) and eccentric (98%) modes of resistance were the most commonly prescribed, whereas the squat (including variations) (52%) was deemed the most important exercise for soccer players. Hang clean (33%) and multiple hops/lunges (89%) were the most programed Olympic weightlifting and plyometric exercises. Global Positioning Systems (94%) were the most utilized technology-based equipment. Time, scheduling and fixtures were the biggest issues faced, which made it difficult to periodize training programs and apply appropriate training loads. Furthermore, strength and conditioning coaches would like to further integrate technology to comprehensively monitor and test players, while also believing that technology will continue to be developed and integrated in the future. Strength and conditioning coaches from professional soccer can use the information from this study to review current practices and also provide ideas for diversifying or modifying future practices.



#13 Effects of 30 days of ketogenic diet on body composition, muscle strength, muscle area, metabolism, and performance in semi-professional soccer players

Reference: Randomized Controlled TrialJ Int Soc Sports Nutr. 2021 Sep 16;18(1):62.  doi: 10.1186/s12970-021-00459-9.

Authors: A Antonio Paoli, Laura Mancin, Massimiliano Caprio, Elena Monti, Marco V Narici, Lorenzo Cenci, Fabio Piccini, Matteo Pincella, Davide Grigoletto, Giuseppe Marcolin

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Summary: A ketogenic diet (KD) is a nutritional approach, usually adopted for weight loss, that restricts daily carbohydrates under 30 g/day. KD showed contradictory results on sport performance, whilst no data are available on team sports. We sought to investigate the influence of a KD on different parameters in semi-professional soccer players. Subjects were randomly assigned to a iso-protein (1.8 g/Kg body weight/day) ketogenic diet (KD) or western diet (WD) for 30 days. Body weight and body composition, resting energy expenditure (REE), respiratory exchange ratio (RER), cross sectional area (CSA) and isometric muscle strength of quadriceps, counter movement jump (CMJ) and yoyo intermittent recovery test time were measured. There was a significantly higher decrease of body fat (p = 0.0359), visceral adipose tissue (VAT) (p = 0.0018), waist circumference (p = 0.0185) and extra-cellular water (p = 0.0060) in KD compared to WD group. Lean soft tissue, quadriceps muscle area, maximal strength and REE showed no changes in both groups. RER decreased significantly in KD (p = 0.0008). Yo-yo intermittent test improved significantly (p < 0.0001) in both groups without significant differences between groups. CMJ significantly improved (p = 0.0021) only in KD. This is the first study investigating the effects of a KD on semi-professional soccer players. In our study KD athletes lost fat mass without any detrimental effects on strength, power and muscle mass. When the goal is a rapid weight reduction in such athletes, the use of a KD should be taken into account.



#14 Association Between Endocrine Markers, Accumulated Workload, and Fitness Parameters During a Season in Elite Young Soccer Players

Reference: Front Psychol. 2021 Aug 31;12:702454. doi: 10.3389/fpsyg.2021.702454. eCollection 2021.

Authors: Hadi Nobari, Elena Mainer-Pardos, José Carmelo Adsuar, Juan Manuel Franco-García, Jorge Rojo-Ramos, Marco Antonio Cossio-Bolaños, Luis Urzua Alul, Jorge Pérez-Gómez2

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Summary: The purpose of this study was to analyze differences between endocrine markers in soccer players, based on playing positions, and correlations between endocrine markers (testosterone, cortisol, growth hormone, and insulin-like growth factor-1), with accumulated workload training and fitness parameters [maximal oxygen uptake (VO2max), countermovement jump (CMJ), and isometric maximal strength (1-RM) of the knee for hamstring (ISH) and quadriceps (ISQ) muscles] during early-, mid-, and end-seasons. Twenty-four elite soccer players under 17 participated in this study. The results showed that there was no difference between levels of the endocrine markers among the different positions of the players. Significant correlations were observed between endocrines parameters and fitness performance (ISQ, ISH, VO2max, and CMJ). Regression analysis showed that 1-RM and VO2max were the best predictors of endocrine markers. These findings demonstrated that the activity profiles of youth soccer players were not influenced by endocrine markers. Also, it may be assumed that endocrines levels can be used to better explain the physical capacities of this population. Finally, endocrines markers may help to predict changes in 1-RM and VO2max.



#15 The influence of playing surface on external demands and physiological responses during a soccer match simulation

Reference: J Sports Sci. 2021 Sep 17;1-9. doi: 10.1080/02640414.2021.1976472. Online ahead of print.

Authors: Daniel Wt Wundersitz, Craig A Staunton, Brett A Gordon, Michael Ic Kingsley

Summary: We investigated the effects of playing surfaces with different impact absorption characteristics on external demand and physiological responses. Fifteen participants completed a soccer match simulation on natural grass, synthetic turf and concrete surfaces. Accelerometry-derived PlayerLoadTM per minute (PL·min-1) and average net force (AvFNet) were used to quantify external demands at the centre of mass (CoM), upper-back, mid-back and hip. Heart rate, oxygen uptake, energy expenditure and RPE quantified physiological responses. The concrete surface exhibited the least impact absorption, with peak decelerations ~3.5x synthetic turf and ~10x natural grass (p < 0.001). Despite this, there was no differences in external demand between surfaces (surface: p ≥ 0.194; η2p≤0.092). Both AvFNet and PL·min-1 (location: p < 0.001; η2p≥0.859) were higher at the hip (613(91)N; 12.5(1.2)arb.u), reduced at the mid-back (521(67)N; 8.8(0.7)arb.u) and upper-back (502(60)N; 8.8(0.7)arb.u) when compared to CoM (576(78)N; 10.7(1.0)arb.u). Although playing surface did not influence the external demands, heart rate or oxygen uptake (p > 0.05), energy expenditure was highest on natural grass compared to synthetic turf (P = 0.034) and RPE was highest on synthetic turf compared to concrete (p = 0.026). Different playing surfaces can alter physiological responses to soccer-specific activity even when the external demands are similar.



#16 Muscle Fibre Typology as a Novel Risk Factor for Hamstring Strain Injuries in Professional Football (Soccer): A Prospective Cohort Study

Reference: Sports Med. 2021 Sep 13. doi: 10.1007/s40279-021-01538-2. Online ahead of print.

Authors: E Lievens, K Van Vossel, F Van de Casteele, E Wezenbeek, D Deprez, S Matthys, B De Winne, S McNally, W De Graaf, J B Murdoch, J G Bourgois, E Witvrouw, Wim Derave

Summary: Hamstring strain injuries (HSI) are prevalent in team sports and occur frequently in the later phase of matches. In the search for interindividual factors that determine muscle fatigue and possibly injury risk, muscle fibre typology is a likely candidate. The aim of the study was to determine whether muscle fibre typology is a risk factor for HSI. A prospective cohort study was conducted over three seasons in professional football players competing in the Belgian Jupiler Pro League (n = 118) and in the English Premier League (n = 47). A total of 27 HSI were sustained during this period. Muscle fibre typology was non-invasively estimated using proton magnetic resonance spectroscopy and was characterized as a fast, slow, or intermediate typology based on the carnosine concentration in the soleus. A multivariate Cox model was used to identify risk factors for HSI. Football players exhibited a wide variety of muscle typologies (slow 44.9%, intermediate 39.8%, fast 15.3%). In the combined cohort, players with a fast typology displayed a 5.3-fold (95% confidence interval [CI] 1.92-14.8; P = 0.001) higher risk of sustaining an index HSI than slow typology players. This was also independently observed in both leagues separately as, respectively, a 6.7-fold (95% CI 1.3-34.1; P = 0.023) and a 5.1-fold (95% CI 1.2-20.4; P = 0.023) higher chance was found in fast typology players than in slow typology players of the Jupiler Pro League and the Premier League cohort.



#17 Mind your step: predicting maximum ankle inversion during cutting movements in soccer

Reference: Sports Biomech. 2021 Sep 13;1-15. doi: 10.1080/14763141.2021.1974533. Online ahead of print.

Authors: Paul Miller, Daniel J Brinkmann, Christina Ramsenthaler, Albert Gollhofer, Dominic Gehring

Summary: The objective of this investigation was to identify parameters at initial contact that would predict the subsequent maximum ankle inversion angle during cutting movements. We conducted a secondary data analysis and calculated kinematics of 1,400 cuttings performed by 46 male soccer athletes. The movement task consisted of an approach run, followed by a pre-planned cutting movement. A linear mixed regression model was applied to predict the maximum ankle inversion angle during the first 100 ms of ground contact. The prediction was made based on six predictors that describe change-of-direction intensity and foot placement as found to be relevant in the literature. The model explained 62% of the variance of maximum ankle inversion angles. A change of the main predictors (foot rotation, cutting angle and initial ankle inversion) by 1 SD caused a reduction of the subsequent maximum ankle inversion angle by 2.6-4.4°. Regarding the intensity of a change-of-direction movement, cutting angle seems to have a higher influence on maximum ankle inversion angle than approach velocity. With respect to the individual foot positioning, the maximum ankle inversion angle can be reduced by increasing exorotation and eversion of the foot while shifting towards forefoot landing.



#18 Variations in Elite Female Soccer Players' Sleep, and Associations With Perceived Fatigue and Soccer Games

Reference: Front Sports Act Living. 2021 Aug 25;3:694537. doi: 10.3389/fspor.2021.694537. eCollection 2021.

Authors: Frode Moen, Maja Olsen, Gunvor Halmøy, Maria Hrozanova

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Summary: The current study investigated the associations between female perceived fatigue of elite soccer players and their sleep, and the associations between the sleep of players and soccer games. The sample included 29 female elite soccer players from the Norwegian national soccer team with a mean age of ~26 years. Perceived fatigue and sleep were monitored over a period of 124 consecutive days. In this period, 12.8 ± 3.9 soccer games per player took place. Sleep was monitored with an unobtrusive impulse radio ultra-wideband Doppler radar (Somnofy). Perceived fatigue was based on a self-report mobile phone application that detected daily experienced fatigue. Multilevel analyses of day-to-day associations showed that, first, increased perceived fatigue was associated with increased time in bed (3.6 ± 1.8 min, p = 0.037) and deep sleep (1.2 ± 0.6 min, p = 0.007). Increased rapid eye movement (REM) sleep was associated with subsequently decreased perceived fatigue (-0.21 ± 0.08 arbitrary units [AU], p = 0.008), and increased respiration rate in non-REM sleep was associated with subsequently increased fatigue (0.27 ± 0.09 AU, p = 0.002). Second, game night was associated with reduced time in bed (-1.0 h ± 8.4 min, p = <0.001), total sleep time (-55.2 ± 6.6 min, p = <0.001), time in sleep stages (light: -27.0 ± 5.4 min, p = <0.001; deep: -3.6 ± 1.2 min, p = 0.001; REM: -21.0 ± 3.0 min, p = <0.001), longer sleep-onset latency (3.0 ± 1.2 min, p = 0.013), and increased respiration rate in non-REM sleep (0.32 ± 0.08 respirations per min, p = <0.001), compared to the night before the game. The present findings show that deep and REM sleep and respiration rate in non-REM sleep are the key indicators of perceived fatigue in female elite soccer players. Moreover, sleep is disrupted during game night, likely due to the high physical and mental loads experienced during soccer games. Sleep normalizes during the first and second night after soccer games, likely preventing further negative performance-related consequences.



#19 Vestibular performance in high-level soccer and ice hockey players: Sport-specific norm values and implications

Reference: J Sci Med Sport. 2021 Aug 13;S1440-2440(21)00198-5. doi: 10.1016/j.jsams.2021.08.003. Online ahead of print.

Authors: Alexander Andrea Tarnutzer, Konrad Peter Weber, Christopher J Bockisch, Dominik Straumann, Nina Feddermann-Demont

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Summary: Quantitative vestibular testing in athletes after sports-related concussion (SRC) has become more popular due to accompanying injuries of the peripheral-vestibular organs that require targeted treatment. Sports-specific normative values are currently not available. Taking into account potential adaptational mechanisms, we obtained sports-specific, age- and peak-head-velocity-corrected normative values of peripheral-vestibular function and postural-stability in football (soccer, FB) and ice-hockey (IH) players. Pre-seasonal angular vestibulo-ocular reflex (aVOR) gains and cumulative-saccadic-amplitudes were obtained using the video-head-impulse test and performance in the balance-error-scoring-system (BESS) was recorded and compared in high-level FB-players (n = 510, 197 females) and IH-players (n = 210, males only) (age-range = 13-39y) and in healthy normals (n = 49, 22 females). Statistical analysis was performed using a generalized linear model. aVOR-gain values were significantly higher for FB-players than for IH-players (1.07 ± 0.21 vs. 0.98 ± 0.13, p < 0.001) and controls (1.07 ± 0.21 vs. 0.97 ± 0.17, p < 0.001). Significant age-related changes in aVOR-gains were only observed for the anterior and posterior canals in the IH-players. Cumulative-saccadic-amplitudes were clearly below established cut-off values (0.73°/trial). BESS scores were significantly higher in IH-players than in FB-players (15.4 ± 5.1 vs. 11.2 ± 4.9, p < 0.001). The significantly better performance of the FB players in the vertical aVOR-gains and the BESS compared to the IH-players could be related to sports-specific differences influencing visuo-vestibular and balance performance. Therefore, we recommend using the established normative aVOR-gain values for high-level FB-players, whereas in IH obtaining individual pre-seasonal (baseline) aVOR-gain values is proposed. Further studies should add sports-specific normative aVOR-gain values for IH and other sports.



#20 Traumatic Leg Fractures in UEFA Football Athletes: A Matched-Cohort Analysis of Return to Play, Reinjury, Player Retention, and Performance Outcomes

Reference: Orthop J Sports Med. 2021 Sep 8;9(9):23259671211024218. doi: 10.1177/23259671211024218. eCollection 2021 Sep.

Authors: Ophelie Lavoie-Gagne, Matthew F Gong, Sumit Patel, Matthew R Cohn, Avinaash Korrapati, Enrico M Forlenza, Moses Barmonyallah, Kevin C Parvaresh, Theodore S Wolfson, Brian Forsythe

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Summary: The average professional soccer team experiences 1 to 2 traumatic leg fractures per season, with unknown effects on player performance. The purpose was to (1) determine the rate and time to return to play (RTP) following leg fracture, (2) investigate the rate of reinjury following RTP, and (3) investigate long-term effects that lower extremity (LE) fracture may have on elite soccer player performance. Using publicly available records, we identified athletes sustaining a traumatic leg fracture across the 5 major European soccer leagues (English Premier League, Bundesliga, La Liga, Ligue 1, and Serie A) between 2000 and 2016. Athletes with leg fracture (femur, tibia, and/or fibula) were matched 1:2 to controls by demographic characteristics and performance metrics 1 season before the index timepoint. Investigations included the RTP rate, reinjury rate, player characteristics associated with RTP within 2 seasons, long-term player retention, performance metrics during the 4 following seasons, and subgroup analysis by player position. A total of 112 players with LE fracture and 224 controls were identified. Players with LE fractures were absent for a mean of 157 days (range, 24-601 days) and 21 games (range, 2-68 games). The rate of RTP within 1 season was 80%, with 4% experiencing subsequent refracture. Injured players remained active in the league at a higher rate than their uninjured counterparts. As compared with controls, injured athletes played 309 fewer total minutes (P < .05), scored 0.09 more assists per game (P < .01) 1 season after injury, and scored 0.12 more points per game 4 seasons after injury (P < .01). Defenders were most affected by an LE fracture, playing 5.24 fewer games (P < .05), 603 fewer total minutes (P < .01), and recording 0.19 more assists per 90 minutes of play as compared with controls 1 season after injury (P < .001). Attackers and midfielders demonstrated no significant difference in metrics after RTP when compared with controls. Most players sustaining an LE fracture returned to elite soccer at the same level after a significant loss of playing time, with a 4% rate of refracture. Player retention was higher for those sustaining an LE fracture versus uninjured controls. Overall, injured players did not experience a decline in performance after recovery from an LE fracture.



#21 Portuguese Football Federation consensus statement 2020: nutrition and performance in football

Reference: BMJ Open Sport Exerc Med. 2021 Aug 26;7(3):e001082.  doi: 10.1136/bmjsem-2021-001082. eCollection 2021.

Authors: Rodrigo Abreu, Pedro Figueiredo, Paulo Beckert, José P Marques, Samuel Amorim, Carlos Caetano, Pedro Carvalho, Carla Sá , Ricardo Cotovio, Joana Cruz , Tiago Dias , Gonçalo Fernandes, Elton Gonçalves , César Leão , Alexandre Leitão, João Lopes, Eduardo Machado, Mónica Neves , André Oliveira , Ana I Pereira , Bruno Pereira , Fernando Ribeiro , Luis M Silva, Filipe Sousa , Tânia Tinoco, Vitor H Teixeira, Monica Sousa, João Brito

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Summary: Nutrition is an undeniable part of promoting health and performance among football (soccer) players. Nevertheless, nutritional strategies adopted in elite football can vary significantly depending on culture, habit and practical constraints and might not always be supported by scientific evidence. Therefore, a group of 28 Portuguese experts on sports nutrition, sports science and sports medicine sought to discuss current practices in the elite football landscape and review the existing evidence on nutritional strategies to be applied when supporting football players. Starting from understanding football's physical and physiological demands, five different moments were identified: preparing to play, match-day, recovery after matches, between matches and during injury or rehabilitation periods. When applicable, specificities of nutritional support to young athletes and female players were also addressed. The result is a set of practical recommendations that gathered consensus among involved experts, highlighting carbohydrates periodisation, hydration and conscious use of dietary supplements.



#22 Higher risk of ACL rupture in amateur football compared to professional football: 5-year results of the 'Anterior cruciate ligament-registry in German football'

Reference: Knee Surg Sports Traumatol Arthrosc. 2021 Sep 15. doi: 10.1007/s00167-021-06737-y.

Authors: Dominik Szymski, Leonard Achenbach, Johannes Zellner, Johannes Weber, Matthias Koch, Florian Zeman, Gunnar Huppertz, Christian Pfeifer, Volker Alt, Werner Krutsch

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Summary: Anterior cruciate ligament (ACL) injuries are a common severe type of football injury at all levels of play. A football-specific ACL registry providing both prospective ACL injury data according to the skill level and risk factors for ACL injury is lacking in the literature. This study is based on the prospective 'ACL registry in German Football' implemented in the 2014-15 season. Professional (1st-3rd league), semi-professional (4th-6th league) and amateur leagues (7th league) were analysed regarding the incidence and risk factors for ACL injuries. Injuries were registered according to the direct reports of the injured players to the study office and double-checked via media analysis. After injury registration, the players received a standardised questionnaire. Data were analysed from the 2014-15 to the 2018-19 football season. Overall, 958 ACL injuries were registered during the 5-year study period. The incidence of ACL injuries was highest in amateur football (0.074/1000 h football exposure) compared to professional (0.058/1000 h; p < 0.0001) and semi-professional football (0.043/1000 h; p < 0.0001). At all skill levels, match incidence (professional: 0.343; semi-professional: 0.249; amateur: 0.319) was significantly higher than training incidence (professional: 0.015; semi-professional: 0.004; amateur: 0.005). Major risk factors were previous ACL injury (mean: 23.3%), other knee injuries (mean: 19.3%) and move to a higher league (mean: 24.2%). This sports-specific ACL registry provides detailed information on the incidence and risk factors for ACL injuries in football over five years. Risk factors are skill level, match exposure, move to a higher league and previous knee injury. These factors offer potential starting points for screening at-risk players and applying targeted prevention.



#23 Football player dominant region determined by a novel model based on instantaneous kinematics variables

Reference: Sci Rep. 2021 Sep 14;11(1):18209. doi: 10.1038/s41598-021-97537-4.

Authors: Fabio Giuliano Caetano, Sylvio Barbon Junior, Ricardo da Silva Torres, Sergio Augusto Cunha, Paulo Régis Caron Ruffino, Luiz Eduardo Barreto Martins, Felipe Arruda Moura

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Summary: Dominant regions are defined as regions of the pitch where a player can reach before any other and are commonly determined without considering the free-spaces in the pitch. We presented an approach to football players' dominant regions analysis, based on movement models created from players' positions, displacement, velocity, and acceleration vectors. 109 Brazilian male professional football players were analysed during official matches, computing over 15 million positional data obtained by video-based tracking system. Movement models were created based on players' instantaneous vectorial kinematics variables, then probabilities models and dominant regions were determined. Accuracy in determining dominant regions by the proposed model was tested for different time-lag windows. We calculated the areas of dominant, free-spaces, and Voronoi regions. Mean correct predictions of dominant region were 96.56%, 88.64%, and 72.31% for one, two, and three seconds, respectively. Dominant regions areas were lower than the ones computed by Voronoi, with median values of 73 and 171 m2, respectively. A median value of 5537 m2 was presented for free-space regions, representing a large part of the pitch. The proposed movement model proved to be more realistic, representing the match dynamics and can be a useful method to evaluate the players' tactical behaviours during matches.



#24 Load Monitoring Practice in Elite Women Association Football

Reference: Front Sports Act Living. 2021 Aug 27;3:715122. doi: 10.3389/fspor.2021.715122. eCollection 2021.

Authors: Live S Luteberget, Kobe C Houtmeyers, Jos Vanrenterghem, Arne Jaspers, Michel S Brink, Werner F Helsen

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Summary: The description of current load monitoring practices may serve to highlight developmental needs for both the training ground, academia and related industries. While previous studies described these practices in elite men's football, no study has provided an overview of load monitoring practices in elite women's football. Given the clear organizational differences (i.e., professionalization and infrastructure) between men's and women's clubs, making inferences based on men's data is not appropriate. Therefore, this study aims to provide a first overview of the current load monitoring practices in elite women's football. Twenty-two elite European women's football clubs participated in a closed online survey (40% response rate). The survey consisted of 33 questions using multiple choice or Likert scales. The questions covered three topics; type of data collected and collection purpose, analysis methods, and staff member involvement. All 22 clubs collected data related to different load monitoring purposes, with 18 (82%), 21 (95%), and 22 (100%) clubs collecting external load, internal load, and training outcome data, respectively. Most respondents indicated that their club use training models and take into account multiple indicators to analyse and interpret the data. While sports-science staff members were most involved in the monitoring process, coaching, and sports-medicine staff members also contributed to the discussion of the data. Overall, the results of this study show that most elite women's clubs apply load monitoring practices extensively. Despite the organizational challenges compared to men's football, these observations indicate that women's clubs have a vested interest in load monitoring. We hope these findings encourage future developments within women's football.



#25 Home advantage during the COVID-19 pandemic: Analyses of European football leagues

Reference: Psychol Sport Exerc. 2021 Sep;56:102013. doi: 10.1016/j.psychsport.2021.102013. Epub 2021 Jul 6.

Authors: Dane McCarrick, Merim Bilalic, Nick Neave, Sandy Wolfson

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Summary: The home advantage (HA) is a robust phenomenon in football whereby the home team wins more games and scores more goals than the away team. One explanation is that the home crowd spurs on home team performance and causes the referee to unconsciously favour the home team. The Covid-19 (COVID) pandemic provided a unique opportunity to assess this explanation for HA, as European football leagues played part of the 2019/2020 season with crowds present and concluded with crowds absent. Using multi-level modelling we compared team performance and referee decisions pre-COVID (crowd present) and during-COVID (crowd absent) across 4844 games from 15 leagues in 11 countries. HA (goals scored and points gained) was significantly reduced during-COVID, which reflected the inferior performance of the home team. In games without fans, home teams created significantly fewer attacking opportunities and referee-bias was diluted when controlling for the attacking dominance of teams; such that the number of fouls and yellow cards ruled against away sides, while still significant, was reduced and no effects were observed for red cards. Implications for sporting practice and directions for future research are discussed.



#26 Muscle Fibre Typology as a Novel Risk Factor for Hamstring Strain Injuries in Professional Football (Soccer): A Prospective Cohort Study

Reference: Sports Med. 2021 Sep 13. doi: 10.1007/s40279-021-01538-2. Online ahead of print.

Authors: E Lievens, K Van Vossel, F Van de Casteele, E Wezenbeek, D Deprez, S Matthys, B De Winne, S McNally, W De Graaf, J B Murdoch, J G Bourgois, E Witvrouw, Wim Derave

Summary: Hamstring strain injuries (HSI) are prevalent in team sports and occur frequently in the later phase of matches. In the search for interindividual factors that determine muscle fatigue and possibly injury risk, muscle fibre typology is a likely candidate. The aim of the study was to determine whether muscle fibre typology is a risk factor for HSI. A prospective cohort study was conducted over three seasons in professional football players competing in the Belgian Jupiler Pro League (n = 118) and in the English Premier League (n = 47). A total of 27 HSI were sustained during this period. Muscle fibre typology was non-invasively estimated using proton magnetic resonance spectroscopy and was characterized as a fast, slow, or intermediate typology based on the carnosine concentration in the soleus. A multivariate Cox model was used to identify risk factors for HSI. Football players exhibited a wide variety of muscle typologies (slow 44.9%, intermediate 39.8%, fast 15.3%). In the combined cohort, players with a fast typology displayed a 5.3-fold (95% confidence interval [CI] 1.92-14.8; P = 0.001) higher risk of sustaining an index HSI than slow typology players. This was also independently observed in both leagues separately as, respectively, a 6.7-fold (95% CI 1.3-34.1; P = 0.023) and a 5.1-fold (95% CI 1.2-20.4; P = 0.023) higher chance was found in fast typology players than in slow typology players of the Jupiler Pro League and the Premier League cohort. We identified muscle fibre typology as a novel and potent risk factor for HSI in team sports.



#27 Monitoring post-match fatigue during a competitive season in elite youth soccer players

Reference: J Athl Train. 2021 Sep 20. doi: 10.4085/1062-6050-0245.21. Online ahead of print.

Authors: Daniel A Evans, Daniel T Jackson, Adam L Kelly, Craig A Williams, Alexander B T McAuley, Harry Knapman, Paul T Morgan

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Summary: Countermovement jump (CMJ) and perceived wellness measures are useful for monitoring fatigue. Fatigue indicators should simultaneously show sensitivity to previous load and demonstrate influence on subsequent physical output; however, this has not been examined. This study examined the efficacy of CMJ and wellness measures to both detect post-match fatigue and predict subsequent physical match output in elite youth soccer. Sixteen soccer players (18 ± 1 years) participated in 36 English Football League Youth Alliance League fixtures. Physical match outputs (total distance, high-speed running, very high-speed running, and accelerations and decelerations) were recorded using a 10 Hz global positioning system and 200 Hz accelerometer device during competitive match play. CMJ height and perceived wellness were assessed weekly and daily, respectively, as indirect indicators of fatigue. Four sub-units of wellness (perceived soreness, energy, general stress, and sleep) were measured using customised psychometric questionnaires. Simple linear regression showed that match accelerations and decelerations (AD) were predictive of energy (R2 = 0.08, P = 0.001), stress (R2 = 0.09, P < 0.001), and total wellness (R2 = 0.06, P = 0.002) 2 days post-match. CMJ (R2 = 0.05, P = 0.002), stress (R2 = 0.08, P < 0.001), sleep (R2 = 0.03, P = 0.034), and total wellness (R2 = 0.05, P = 0.006) 5 days pre-match (MD-5) were predictive of AD during the subsequent match. CMJ and wellness may be useful in detecting post-match fatigue. Wellness scores, but not CMJ, on MD-5 influence subsequent match output and therefore may be used to plan and periodise training for the upcoming microcycle.


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