Latest research in football - week 43 - 2023

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 Training Volume and High-Speed Loads Vary Within Microcycle in Elite North American Soccer Players

Reference: J Strength Cond Res. 2023 Nov 1;37(11):2229-2234. doi: 10.1519/JSC.0000000000004522.

Authors: Ai Ishida, Garrison Draper, Matthew Wright, Jonathan Emerson, Michael H Stone

Summary: The purposes of this study were to reduce dimensionality of external training load variables and examine how the selected variables varied within microcycle in elite North American soccer players. Data were collected from 18 players during 2018-2020 in-seasons. Microcycle was categorized as 1, 2, 3, 4, 5 days before match day (MD-1, MD-2, MD-3, MD-4, and MD-5, respectively). Training load variables included total distance, average speed, maximum velocity, high-speed running distance (HSR), average HSR, HSR efforts, average HSR efforts, sprint distance, average sprint distance, sprint efforts, average sprint efforts, total PlayerLoad, and average PlayerLoad. The first principal component (PC) can explain 66.0% of the variances and be represented by "high-speed load" (e.g., HSR and sprint-related variables) with the second PC relating to "volume" (e.g., total distance and PlayerLoad) accounting for 17.9% of the variance. Average sprint distance and total distance were selected for further analysis. Average sprint distance was significantly higher at MD-3 than at MD-2 (p = 0.01, mean difference = 0.36 m•minute-1, 95% confidence intervals [CIs] = 0.07-0.65 m•minute-1) and MD-4 (p = 0.012, mean difference = 0.26 m•minute-1, 95% CIs = 0.10-0.41 m•minute-1). Total distance was significantly higher at MD-3 than at MD-1 (p < 0.001, mean difference = 1,465 m, 95% CIs = 1,003-1926 m), and MD-2 (p < 0.001, mean difference = 941 m, 95% CIs = 523-1,360 m). Principal component analysis may simplify reporting process of external training loads. Practitioners may need to choose "volume" and "high-speed load" variables. Elite North American Soccer players may accumulate higher average sprint distance at MD-3 than at other training days.



#2 Short-Term Effects of Lower-Extremity Heavy Resistance versus High-Impact Plyometric Training on Neuromuscular Functional Performance of Professional Soccer Players

Reference: Sports (Basel). 2023 Oct 4;11(10):193. doi: 10.3390/sports11100193.

Authors: Michał Boraczyński, José Magalhães, Jacek J Nowakowski, James J Laskin

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Summary: The purpose was to compare the effects of short-term 8 week heavy-resistance or plyometric training protocols (HRT or PLY) incorporated into regular soccer practice on measures of neuromuscular functional performance in professional soccer players, a single-blind randomized controlled trial was conducted. Forty-seven participants aged 22.3 ± 3.52 years were assigned to three groups: HRT (n = 15), PLY (n = 15), and control (CON; n = 17). The HRT group performed 3 sets and 10 repetitions twice a week using 80% of their baseline 1-RM (weeks 1-3), followed by 8 repetitions at 85% 1-RM (weeks 4-6), and 6 repetitions at 90% 1-RM (weeks 7-8) of 6 lower-body strength exercises with a 1 min rest period between sets. The PLY protocol involved a preparatory phase (weeks 1-2), followed by two 3-week progressive periods (weeks 3-5 and weeks 6-8). The plyometric sessions consisted of four jump exercises/drills with progressively increasing number of sets and total number of foot contacts. The rest intervals between repetitions and sets were 15 and 90 s, respectively. Outcome measures included tests assessing 10 and 30 m speed (t10m and t30m), one-repetition maximum half-back squat (1-RM squat), isokinetic peak torques for the quadriceps and hamstring muscles (Qcon and Hcon), countermovement jump (CMJ), and squat jump (SJ). Two-way ANOVA detected main effects of time and group×time interactions for all examined variables, except t30m, 1-RM, and relative 1-RM. Post hoc analyses revealed significant increases in the HRT group (t10m: 6.3%, t30m: 7.1%; absolute 1-RM: 29.6%; relative 1-RM: 30.3%, Qcon: 24.5%; Hcon: 14.4%; CMJ: 5.9%; SJ: 7.2%, all p < 0.001) and the PLY group (t10m: 3.1%; t30m: 4.1%; absolute 1-RM:19.1%; relative 1-RM: 20.3%; Qcon: 12.6%; Hcon: 8.7%; CMJ: 3.3%; SJ: 3.5%, all p < 0.001). HRT was superior compared to PLY in relative 1-RM, Qcon and Hcon (all p < 0.001). In addition, we found knee muscular strength imbalance in 70.5% of participants from the total sample (H/Q ratio < 60%). The HRT and PLY protocols resulted in improved neuromuscular functional performance compared to the regular soccer regime. This study showed that during the pre-competitive season, additional HRT and PLY drills/exercises as a substitute for standard soccer training as part of a regular 90 min practice twice a week for 8 weeks, can produce acute physical performance-enhancing effects in professional soccer players.



#3 Comparisons and associations among anthropometric indices of first and second division and assistant soccer referees

Reference: Front Psychol. 2023 Oct 10:14:1149779. doi: 10.3389/fpsyg.2023.1149779. eCollection 2023.

Authors: Meysam Rostamzadeh Samarein, Mohammad Hossein Samanipour, Foad Asjodi, Pooya Shokati, Zanyar Fallahi, Thomas E Brownlee, João Paulo Brito, Nicola Luigi Bragazzi, Rafael Oliveira

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Summary: Body composition is an important predictor of performance and a key component of health and physical fitness. Therefore, the purposes of this study were to compare soccer referees of the first and second divisions and field assistant referees from Iran and to analyze associations of a body shape index (ABSI), body adiposity index (BAI), abdominal volume index (AVI), body roundness index (BRI), conicity index (ConI), and body mass index (BMI) with body fat percentage (%BF). A total of 270 male soccer referees from the first (n = 124) and second (n = 72) divisions and assistant referees (n = 74) participated in this study. Skinfold thickness (measured at the chest, biceps, triceps, subscapular, abdominal, iliac crest, and front thigh), height, weight, hip circumference, and waist circumference were assessed to evaluate waist-to-height ratio (WHtR), %BF, and also ABSI, BRI, BAI, ConI, and AVI according to the ISAK protocol. The main results indicated differences in WHR, WHtR, ABSI, BRI, AVI, ConI, and BF% with the assistant referees presenting higher values (p < 0.05). When considering the backward selection model, there were some associations with %BF in each group, specifically BMI, BAI, and ABSI in the first division; BMI, WHR, and ABSI in the second division; and BMI in the assistant referee group (all p < 0.05). The present study did not confirm the hypothesis that the first-division referees presented better body composition-related variables than the second division or assistant referees. Instead, it showed that the assistant referees that participated in both divisions showed a tendency to higher values which suggests that the level of division is not a major factor when analyzing body composition.



#4 Average demands and most demanding passages of national-level female soccer matches: do small- and large-sided games replicate match demands?

Reference: Front Sports Act Living. 2023 Oct 11:5:1236112. doi: 10.3389/fspor.2023.1236112. eCollection 2023.

Authors: E H J Savolainen, T Vänttinen, J Peltonen, J K Ihalainen, S Walker

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Summary: This study aims to (1) determine the average and most demanding passage (MDP) load of national-level female soccer matches and (2) evaluate the relationship between average and MDP load during small-sided games (SSGs), large-sided games (LSGs), and matches. A total of 37 national-level female soccer players from a single club senior team and the U18 team participated. The average and 1-, 3-, and 5-min MDP external (total, high-speed, and very-high-speed running distances, acceleration and deceleration distances, average metabolic power, and high-metabolic load distance) and internal loads (average heart rate, rate of perceived exertion) of the 29 league matches, ten 4 vs. 4 + goalkeepers SSGs, and six 8 vs. 8 + goalkeepers LSGs were analyzed by the Polar Team Pro player tracking system. In matches, the external load variables during 1-, 3-, and 5-min MDPs were 167%-1,165%, 135%-504%, and 126%-359%, of match average values, respectively. In LSGs, all external load variables reached higher average values compared with those during matches, except for the very-high-speed running distance; however, no variable reached higher values of 1-min MDP compared with those during the matches. In SSGs, the average acceleration and deceleration distances were higher compared with those during the matches. The findings from the present study suggest that LSGs and SSGs can be used to overload the average values of the selected external load variables compared with those during the matches; however, other training options must be explored to overload 1-min match MDPs.



#5 Normative reference and cut-offs values of maximal aerobic speed-20 m shuttle run test and maximal oxygen uptake for Tunisian adolescent (elite) soccer players

Reference: Heliyon. 2023 Oct 10;9(10):e20842. doi: 10.1016/j.heliyon.2023.e20842. eCollection 2023 Oct.

Authors: Hatem Ghouili, Amel Dridi, Nejmeddine Ouerghi, Mohamed Ben Aissa, Anissa Bouassida, Noomen Guelmami, Andrew Sortwell, Luís Branquinho, Pedro Forte, Ismail Dergaa

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Summary: This study aimed to develop reference curves of aerobic parameters of 20 m shuttle run test for Tunisian soccer players. The study was conducted in the 2022/2023 pre-season. The reference curves of the maximal aerobic speed (MAS) and the maximal oxygen uptake (VO2max) were developed according to the Lambda, Mu and Sigma (LMS) method, using data from 742 Tunisian premier league soccer players aged 11-18 years. Measured variables included: weight, height, body mass index and maximal heart rate (HRmax). HRmax was measured when the participants completed the maximal aerobic speed. VO2max was estimated using the 20 m shuttle run test protocol (speed increment every minute). Our results presented the smoothed percentiles (3rd, 10th, 25th, 50th, 75th, 90th and 97th) of MAS (km/h) and VO2max (ml/kg•min⁻1) according to age. In addition, raw data showed that VO2 max was positively correlated with age (r = 0.333; P < 0.001), height (cm) (r = 0.279; P < 0.001), weight (kg) (r = 0.266; P < 0.001), practice period (years) (r = 0.324; P < 0.001) and BMI (kg/m2) (r = 0.10; P < 0.05). However, it was negatively correlated to HRmax (bpm) (r = -0.247; P < 0.001). Only the measurements within the age group [12-12.99] are significantly higher (p < 0.001; ES = 0.63) compared with the previous age group [11-11.99]. Finally, regarding prevalence, our findings showed that 15.5 % of the players in our sample had VO2max values above the 87.7th percentile cut-off, while only 0.3 % exceeded the 99.18th percentile. The development of normative curves could help coaches and physical trainers to more accurately detect weaknesses in the aerobic performance of their players in order to sustain high-intensity repetitive actions during a soccer match.



#6 Data Analysis of Psychological Approaches to Soccer Research: Using LDA Topic Modeling

Reference: Behav Sci (Basel). 2023 Sep 22;13(10):787. doi: 10.3390/bs13100787.

Authors: Jea Woog Lee, Doug Hyun Han

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Summary: This study identifies the topical areas of research that have attempted a psychological approach to soccer research over the last 33 years (1990-2022) and explored the growth and stagnation of the topic as well as research contributions to soccer development. Data were obtained from 1863 papers from the Web of Science database. The data were collected through keyword text mining and data preprocessing to determine the keywords needed for analysis. Based on the keywords, latent Dirichlet allocation-based topic modeling analysis was performed to analyze the topic distribution of papers and explore research trends by topic area. The topic modeling process included four topic area and fifty topics. The "Coaching Essentials in Football" topic area had the highest frequency, but it was not statistically identified as a trend. However, coaching, including training, is expected to continue to be an important research topic, as it is a key requirement for success in the highly competitive elite football world. Interest in the research field of "Psychological Skills for Performance Development" has waned in recent years. This may be due to the predominance of other subject areas rather than a lack of interest. Various high-tech interventions and problem-solving attempts are being made in this field, providing opportunities for qualitative and quantitative expansion. "Motivation, cognition, and emotion" is a largely underrated subject area in soccer psychology. This could be because survey-based psychological evaluation attempts have decreased as the importance of rapid field application has been emphasized in recent soccer-related studies. However, measuring psychological factors contributes to the study of football psychology through a new methodology and theoretical background. Recognizing the important role of psychological factors in player performance and mental management, as well as presenting new research directions and approaches that can be directly applied to the field, will advance soccer psychology research.



#7 Artificial Turf Increases the Physical Demand of Soccer by Heightening Match Running Performance Compared with Natural Grass

Reference: J Strength Cond Res. 2023 Nov 1;37(11):2222-2228. doi: 10.1519/JSC.0000000000004539.

Authors: Toni Modric, Michael Esco, Sandro Perkovic, Zlatko Basic, Sime Versic, Ryland Morgans, Damir Sekulic

Summary: This study aimed to determine differences in match running performance (MRP) of elite soccer players (n = 31) during matches played on artificial turf (AT) and natural grass (NG). The players' MRP (AT; 131 observations, NG; 135 observations) were collected during official matches (n = 32) using global positioning system and classified according to their playing positions as central defenders, central midfielders, fullbacks, forwards, and wingers. The MRP variables included total distance covered (TD), low-intensity running (LIR), moderate-intensity running (MIR), high-intensity running (HIR), total (Tacc) and high-intensity accelerations (Hacc), and total (Tdec) and high-intensity decelerations (Hdec). The influence of match outcome, location, and opponent quality was controlled for as contextual factors. Playing matches on AT resulted in (a) increased TD (Cohen's d (d) = 0.55, 0.61, and 0.28, respectively), MIR (d = 0.91, 0.79, and 0.49, respectively), and HIR (d = 0.67, 0.44, and 0.38, respectively) for central defenders, central midfielders, fullbacks; (b) increased Tacc (d = 0.38, 0.37, and 0.4, respectively) and Tdec (d = 0.31, 0.34, and 0.31, respectively) for central defenders, central midfielders, and wingers; and (c) decreased Hdec (d = -1.5) for forwards. These results show that playing on AT is more physically demanding for defensive and midfield players than playing on NG. Soccer coaches should consider implementing preparatory strategies that mitigate the increased demands of playing on AT for these players, especially before a competitive period when transitions between pitch surfaces routinely occur.



#8 Application of a Custom Device to Measure Isometric Knee Strength: Possible Injury Correlation in Professional Soccer (Football) Players

Reference: J Funct Morphol Kinesiol. 2023 Oct 5;8(4):141. doi: 10.3390/jfmk8040141.

Authors: Paolo Cigni, Tommaso Minuti, Andrea Mannini, Alessandro Cucini, Michele Costagli, Stefano Rapetti, Luca Alimonta, Erika Cione, Roberto Cannataro, Leonardo Ricotti

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Summary: Injury in sports is an occurrence that prevents athletes from participating in training and competitions and has an incidence of 8.1 injuries/1000 h of practice. This translates into a cost and also into danger, especially if the event is repeated, for the health of the athlete; the injury certainly has a multifactorial causality. On the other hand, having instruments that can represent an alarm could be helpful for those involved in sports science. We used a specifically designed instrument, presented in a previous work, which shows excellent reliability and repeatability in measuring the strength of the knee flexors and extensors to test 107 players belonging to three different teams playing in the Italian Serie A. We took three measurements, beginning of the season, mid-season, and close to the end of the season. This retrospective study on 107 professional soccer players demonstrates that isometric force-related parameters of the knee extensors and flexors are associated with the risk of injury to lower limbs. Logistic regression evidenced a significant correlation between the parameter indicating the imbalance of the force between the flexors of the two limbs (p≤0.05, OR = 1.089) and the occurrence of injuries. Survival analyses (p≤0.001) evidenced a correlation between the population survival time and the injury incidence. We demonstrated that the analysis of the strength imbalance is correlated with injury occurrence, but it is well known that sports injuries are a multifactorial event; so, they cannot be predicted by only one parameter. However, the method proposed in this paper could represent a useful tool for sport scientists.



#9 The Reliability of Linear Speed with and without Ball Possession of Pubertal Soccer Players

Reference: J Funct Morphol Kinesiol. 2023 Oct 16;8(4):147. doi: 10.3390/jfmk8040147.

Authors: Nikolaos Manouras, Christos Batatolis, Panagiotis Ioakimidis, Konstantina Karatrantou, Vassilis Gerodimos

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Summary: Reliable fitness tests with low day-to-day and trial-to-trial variation are a prerequisite for tracking a player's performance or for identifying meaningful changes in training interventions. The present study examined the inter- and intra-session reliability of 30 m linear speed with and without ball possession as well as the reliability of a specific performance index of pubertal soccer players. A total of 40 pubertal (14.87 ± 1.23 years old) male soccer players performed two testing sessions (test-retest) separated by 72 h. Both testing sessions included a protocol consisting of two maximal trials of 30 m linear speed with and without ball possession. A performance index, indicating the difference between the two speed tests, was also calculated using two different equations (delta value and percentage value). The relative and absolute inter-session reliabilities were good/high for all testing variables (ICC = 0.957-0.995; SEM% = 0.62-8.83). There were also good/high relative and absolute intra-session reliabilities observed for all testing variables (ICC = 0.974-0.987; SEM% = 1.26-6.70%). According to the Bland-Altman plots, the differences between test-retest and trials for all observations were within the defined 95% limits of agreement. The reliable testing protocols and performance index for the evaluation of linear speed with and without ball possession, observed in this study, may be used in speed monitoring and training planning of pubertal soccer players.



#10 Action-Evaluator: A Visualization Approach for Player Action Evaluation in Soccer

Reference: IEEE Trans Vis Comput Graph. 2023 Oct 25:PP. doi: 10.1109/TVCG.2023.3326524.

Authors: Anqi Cao, Xiao Xie, Mingxu Zhou, Hui Zhang, Mingliang Xu, Yingcai Wu

Summary: In soccer, player action evaluation provides a fine-grained method to analyze player performance and plays an important role in improving winning chances in future matches. However, previous studies on action evaluation only provide a score for each action, and hardly support inspecting and comparing player actions integrated with complex match context information such as team tactics and player locations. In this work, we collaborate with soccer analysts and coaches to characterize the domain problems of evaluating player performance based on action scores. We design a tailored visualization of soccer player actions that places the action choice together with the tactic it belongs to as well as the player locations in the same view. Based on the design, we introduce a visual analytics system, Action-Evaluator, to facilitate a comprehensive player action evaluation through player navigation, action investigation, and action explanation. With the system, analysts can find players to be analyzed efficiently, learn how they performed under various match situations, and obtain valuable insights to improve their action choices. The usefulness and effectiveness of this work are demonstrated by two case studies on a real-world dataset and an expert interview.



#11 Contemporary reflection on the educational levels of high-performance soccer players in Brazil

Reference: Einstein (Sao Paulo). 2023 Oct 23:21:eAO0269. doi: 10.31744/einstein_journal/2023AO0269. eCollection 2023.

Authors: Paulo Roberto Santos-Silva, Júlia Maria D Andrea Greve, Renato Luis da Silva, Marcelo Mesquita Spinola

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Summary:  Santos-Silva et al. demonstrated that, for Brazilian soccer players, pursuing higher education is still a distant reality. This is because, in relative numbers, only 2.5% of the athletes have completed elementary school, whereas 67% and 5.5% completed high school and higher education, respectively. The mean initial professionalization age is 17.5 years, indicating that soccer players take on a crucial responsibility in a very early stage of life. However, they are still immature in terms of dealing with money,contractual relations with the club, and decision-making. Only 5.5% of Brazilian soccer players surveyed completed higher education. Of these 179 athletes, 67% completed high school. The most educated were goalkeepers and defenders at 37% (66/179). Physical education for sports is different from educating the mind in terms of brain plasticity. As the soccer culture in Brazil is more popular than schooling, this study reflected on the formal education levels of soccer (football) players through descriptive and quantitative analyses. We evaluated 179 national soccer players playing various positions on different teams across six seasons (2012, 2013, 2014, 2015, 2016, and 2022). Data were collected using a questionnaire comprising the following variables: age, position in the pitch, age of professionalization, and education (years of study). The data were distributed according to the pitch position. The mean age, length of professional career, and professionalization age were 23±6 years, 7±5 years, and 17±2 years, respectively. In terms of education, 121 athletes (67%) completed high school, equivalent to 11 years of study. Only 5.5% completed higher education, with defensive players (goalkeepers and defenders) being the most educated at 37% (66/179). According to 2017 figures from the Pesquisa Nacional por Amostra de Domicílios Contínua of the Federal Government of Brazil, the schooling rate is 31.7%, wherein 46.1% of Brazilians aged 25 years or over have completed education. In this study of 179 athletes, 67% had completed high school. Thus, players outrank the Brazilian population in terms of achieving a high school education. There were marked disparities in the relative proportions of goalkeepers (85%), defensive players (68%), midfielders (63%), and forward players (64%) in terms of their education. Our survey revealed that attending higher education remains a distant reality in Brazil.



#12 Sports, health, and banking: soccer in the lives of bank workers in São Paulo, 1929-1932

Reference: Hist Cienc Saude Manguinhos. 2023 Oct 23:30:e2023054. doi: 10.1590/S0104-59702023000100054. eCollection 2023. [Article in Portuguese]

Authors: Gabriela Marta Marques de Oliveira, Edivaldo Góis Junior

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Summary: This study investigates how soccer was part of the lives of bank workers in the city of São Paulo between 1929 and 1932, looking at who these workers were and the meaning they attributed to sports in the Banking Athletic Sports League (Liga Bancária de Esportes Atléticos). Sources included reports, documents, and publications of the São Paulo State Bank Employees' Association. Reflections on "class" and "class culture," the concept of "experience," and the notion of "middle class" were all utilized in analyzing the sources, and revealed variations in representations of sports and soccer among these employees.



#13 Soccer's Transition

Reference: Sports Health. 2023 Nov-Dec;15(6):779-780. doi: 10.1177/19417381231204483.

Authors: Edward M Wojtys

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#14 Association between sports expertise and visual attention in male and female soccer players

Reference: PeerJ. 2023 Oct 19:11:e16286. doi: 10.7717/peerj.16286. eCollection 2023.

Authors: Peng Jin, Zheqi Ji, Tianyi Wang, Xiaomin Zhu

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Summary: Visual attention plays a crucial role in daily living and in sports, affecting an athlete's performance and thus, potentially, the outcome of a match. However, studies assessing the association between the level of sports expertise and visual attention have yielded mixed results. This study was conducted to examine whether visual attention could be developed with increased sports expertise, and whether visual attention differed between male athletes and female athletes. A total of 128 participants were included in this study: 64 first-level national soccer athletes recruited from college soccer teams (considered elite athletes; 32 men and 32 women with similar soccer performance requirements and training experience), and 64 physical education college students with limited soccer experience (considered novice athletes; 32 men and 32 women with matched soccer experience). To assess visual attention, we used a multiple object tracking (MOT) task with four targets among a total of 10 objects moving at a fixed speed of 10°/s in random directions across a computer monitor screen. Tracking accuracy on the MOT task was calculated for each participant as the proportion of correctly selected targets. A univariate analysis of variance was performed, with group (expert, novice) and sex (male, female) as independent variables, and tracking accuracy on the MOT task as the dependent variable to assess whether sports expertise or sex influenced visual attention. Simple effects tests followed by comparisons with Bonferroni corrections were used, and effect size calculations were performed using Cohen's f statistic. Tracking accuracy on the MOT task was significantly affected by sports expertise (F(1,124) = 91.732, p < 0.001, ηP2 = 0.425), with accuracy among expert soccer athletes superior to that among novice soccer athletes. Moreover, a statistically significant interaction between sports expertise and sex was detected (F(1,124) = 7.046, p = 0.009, η P2= 0.054). Better tracking performance was observed for male soccer players (mean [SD], 0.39 [0.12]) than for female soccer players (mean [SD], 0.27 [0.08]); p < 0.01; d=1.17; r = 0.51) but only in the novice group. No significant sex difference was detected in tracking performance between elite male soccer athletes (mean [SD], 0.51 [0.09]) and elite female soccer athletes (mean [SD], 0.49 [0.11]). These findings confirm previous results indicating that long-term extensive sports training develops visual attention as assessed by MOT performance and extend previous findings to include soccer athletes. The findings of a sex difference in visual attention among novice soccer players but not among elite soccer athletes who had similar performance requirements and training experience suggest that long-term extensive training may minimize the sex difference in visual attention.



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