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

Following studies were retrieved for this week:

1 Effects of Short Sprint Interval Training Frequency on Physical and Physiological Performance Adaptations in Male Soccer Players

Reference: J Sports Sci Med. 2024 Dec 1;23(4):707-717. doi: 10.52082/jssm.2024.707. eCollection 2024 Dec.
Authors: Qingwen Liu, Wanglong Wang, Chuan Shu
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11622051/pdf/jssm-23-707.pdf
Summary: The study aimed to evaluate the effects of varying frequencies (1 vs. 2 vs. 3) of short sprint interval training (sSIT) on young male soccer players‘ physical performance and physiological parameters. Forty young male soccer players were randomly assigned to four experimental groups engaging in 36 trials sSIT for a duration of 6 weeks as follows: once weekly (1sSIT = 4 sets of 9 × 5 sec all-out runs), twice weekly (2sSIT = 2 sets of 9 × 5 sec all-out runs), and three times weekly (3sSIT = 2 sets of 6 × 5 sec all-out runs), or an active control group which continued their soccer practice routines. Before and after the 6-week training period, physical performance (countermovement vertical jump, 20-m sprint, Illinois change of direction, Yo-Yo intermittent recovery level 1 [Yo-Yo IR 1] and kicking distance) and physiological parameters (cardiorespiratory fitness, peak and average power output) were evaluated. All sSIT groups demonstrated significant (p < 0.01) and small to very large training effects (i.e., effect size) on measured parameters. More importantly, a comparison of inter-individual variability in the adaptive changes revealed that the 3sSIT group results in lower residuals in changes in cardiorespiratory fitness and anaerobic power, coupled with lower coefficient of variations in the mean group changes and perceived exertion throughout the training period. The findings indicate that incorporating one, two, or three weekly sessions of sSIT into routine soccer training can lead to similar enhancements in soccer players‘ physiological and performance adaptations. More importantly, higher training frequencies result in more homogenized adaptations among team members by reducing inter-individual variability in the magnitude of the adaptive responses.

2 Prediction of Perceived Exertion Ratings in National Level Soccer Players Using Wearable Sensor Data and Machine Learning Techniques

Reference: J Sports Sci Med. 2024 Dec 1;23(4):744-753.  doi: 10.52082/jssm.2024.744. eCollection 2024 Dec.
Authors: Robert Leppich, Philipp Kunz, André Bauer, Samuel Kounev, Billy Sperlich, Peter Düking
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11622056/pdf/jssm-23-744.pdf
Summary: This study aimed to identify relationships between external and internal load parameters with subjective ratings of perceived exertion (RPE). Consecutively, these relationships shall be used to evaluate different machine learning models and design a deep learning architecture to predict RPE in highly trained/national level soccer players. From a dataset comprising 5402 training sessions and 732 match observations, we gathered data on 174 distinct parameters, encompassing heart rate, GPS, accelerometer data and RPE (Borg’s 0-10 scale) of 26 professional male professional soccer players. Nine machine learning algorithms and one deep learning architecture was employed. Rigorous preprocessing protocols were employed to ensure dataset equilibrium and minimize bias. The efficacy and generalizability of these models were evaluated through a systematic 5-fold cross-validation approach. The deep learning model exhibited highest predictive power for RPE (Mean Absolute Error: 1.08 ± 0.07). Tree-based machine learning models demonstrated high-quality predictions (Mean Absolute Error: 1.15 ± 0.03) and a higher robustness against outliers. The strongest contribution to reducing the uncertainty of RPE with the tree-based machine learning models was maximal heart rate (determining 1.81% of RPE), followed by maximal acceleration (determining 1.48%) and total distance covered in speed zone 10-13 km/h (determining 1.44%). A multitude of external and internal parameters rather than a single variable are relevant for RPE prediction in highly trained/national level soccer players, with maximum heart rate having the strongest influence on RPE. The ExtraTree Machine Learning model exhibits the lowest error rates for RPE predictions, demonstrates applicability to players not specifically considered in this investigation, and can be run on nearly any modern computer platform.

3 Effects of Two In-Season Short High-Intensity Interval Training Formats on Aerobic and Neuromuscular Performance in Young Soccer Players

Reference: J Sports Sci Med. 2024 Dec 1;23(4):812-821. doi: 10.52082/jssm.2024.812. eCollection 2024 Dec.
Authors: Pierros Thomakos, Prokopis Tsekos, Zacharias Tselios, Konstantinos Spyrou, Christos Katsikas, Athanasios Tsoukos, Gregory C Bogdanis
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11622058/pdf/jssm-23-812.pdf
Summary: Supplementary high-intensity interval training (HIIT) programs, focusing on different aspects of fitness, are commonly used in soccer practice. This study examined the impact of two different HIIT formats applied during the competitive season on aerobic and neuromuscular performance. Twenty-six young players from two youth amateur soccer teams (aged 18.1 ± 0.7 and 18.7 ± 1.1 years) participated. In a randomized design, Team A served as an experimental group, performing either a 10s/10s linear running HIIT or a 15s/15s HIIT with changes of direction, both at 100% of maximum aerobic speed, twice per week for six weeks. In that period, team B acted as a control group, maintaining their usual training soccer regimen. Following two weeks of lower volume and frequency training, team B added the two HIIT formats in their training for six weeks, while team A acted as control. Before and after each 6-weeks period, aerobic fitness and neuromuscular performance was evaluated by the countermovement jump (CMJ). The 3-way ANOVA showed that both HIIT formats significantly enhanced Yo-Yo Intermittent Recovery Test Level 1 (Yo-YO IR1) performance compared to the respective control periods. However, the main finding was that the 10s/10s compared with the 15s/15s HIIT format induced 45-50% greater improvements in Yo-YO IR1 (total distance: 18.5 ± 11.7% vs. 9.0 ± 8.5%, V̇O2max: 5.6 ± 3.2% vs. 3.0 ± 2.7%, and vV̇O2max: (3.3 ± 1.9% vs. 1.8 ± 1.7%, all p = 0.39, d = 0.85). Countermovement jump performance remained unchanged across both groups (p > 0.68). During HIIT rating of perceived exertion was higher in the 15s/15s vs. the 10s/10s format (6.4 ± 0.5 vs. 4.7 ± 1.2 a.u., p < 0.001). These findings suggest that while both HIIT formats effectively enhance aerobic performance during the season, the 10s/10s format offers superior benefits with less perceived exertion, while the 15s/15s format induces higher internal load.

4 The Effect of Speed Endurance Versus Core Training on The Repeated Sprint Ability of Youth Male Soccer Players – A Randomized Controlled Trial

Reference: J Sports Sci Med. 2024 Dec 1;23(4):907-915. doi: 10.52082/jssm.2024.907. eCollection 2024 Dec.
Authors: Olavo Maciel, Ricardo Martins, Fábio Y Nakamura, Pedro Figueiredo, José Afonso, Ivan Baptista
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11622046/pdf/jssm-23-907.pdf
Summary: The effects of specific training protocols to improve repeated sprint ability are well known; however, the utility of non-specific training for this purpose is doubtful. Therefore, this study aimed to compare the effects of a specific (sport-related) vs. non-specific (general physical development) eight-week training protocol on developing or maintaining repeated sprint ability in soccer players. Thirty-eight male soccer players (aged 17.1 ± 0.3 years) were randomly divided into a speed endurance group (n = 18) and a core training group (n = 20). The speed endurance group performed 4 sprints lasting 15 seconds with a recovery of 75 seconds, while the core training group performed 2 sets of 4 exercises for 30 seconds with 15 seconds of recovery. Both protocols were performed twice a week. All players performed the Running-Based Anaerobic Sprint Test (6 consecutive 35-meter sprints with 10-seconds recovery intervals). A mixed two-way ANOVA was performed with no significant effects in the interaction term. On average, the speed endurance and the core training groups improved their repeated sprint ability by 7.9% and 8.0%, respectively, from pre- to post-assessment (p < 0.001, η2 p = 0.459). No significant between-group differences were detected for the Running-Based Anaerobic Sprint Test total time or maximum power. In principle, specific and non-specific low-volume training protocols may improve repeated sprint ability over eight weeks in soccer players. However, the improvements may have been derived from the continued soccer-specific training, which is the reason why future studies should include a passive control group and test whether high session volumes produce different results.

5 Elastic Bands During Half-Squats as A Re-Warm-Up Strategy for Youth Soccer Players‘ Performance

Reference: J Sports Sci Med. 2024 Dec 1;23(4):843-851. doi: 10.52082/jssm.2024.843. eCollection 2024 Dec.
Authors: Javier Sanchez-Sanchez, Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Alejandro Rodríguez-Fernández
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11622050/pdf/jssm-23-843.pdf
Summary: The study aimed to assess the immediate effects of re-warm-up strategies using half-squats with elastic looped bands on the performance of youth soccer players. A cross-over study design with repeated measures was implemented in field youth male soccer players (n = 20, age 15.7 ± 0.8 years). Following the first 45-min of match play, players were subjected to one of four re-warm-up (Re-w) interventions of equal duration: no Re-w (PAS), half-squat without elastic looped bands (SQ), half-squat with bands placed on the thighs (SQT), and half-squat with bands placed on the lower legs (SQL). These interventions were compared against a control condition (CON). The Re-w protocols were initiated 10-min after half-time, and players‘ performance was evaluated through vertical and horizontal jump tests, 20-m linear sprint, and T-agility test. Statistical analysis using ANOVA revealed that the SQT and SQL interventions significantly improved (p < 0.001) several performance metrics compared to the PAS and SQ conditions. These improvements were observed in squat jumps, unilateral squat jumps (both dominant and non-dominant legs), countermovement jumps, horizontal jumps, triple horizontal jumps, the 20-m linear sprint, and T-agility performance. In conclusion, SQT and SQL are equally effective to enhance performance as Re-w strategies after the 1st-half of a soccer match. However, the lack of physiological data and 2nd-half assessments suggests the need for further research to confirm the persistence of these effects.

6 Ankle Sprains in Brazilian Professional Soccer: Epidemiological Analysis of 126,357 Match Hours

Reference: Rev Bras Ortop (Sao Paulo). 2024 May 13;59(5):e682-e688. doi: 10.1055/s-0044-1785660. eCollection 2024 Oct.
Authors: Ewerton Borges de Souza Lima, Gabriel de Melo Salgado, Eduardo Patrício Mello, Paulo Henrique Schmidt Lara, Gustavo Gonçalves Arliani, Moisés Cohen
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11624919/pdf/10-1055-s-0044-1785660.pdf
Summary: This study aimed to perform an epidemiological analysis of ankle sprains in professional soccer players in Brazil. This prospective epidemiological study analyzed ankle sprains in professional male soccer athletes during the Brazilian Championship and the Paulista Football Championship from 2016 to 2019. All on-pitch medical care provided in official matches was recorded. The variables evaluated included the age and position of the player, injury diagnosis, pitch site where the injury occurred, playing time, imaging tests performed, surgical treatment, time away from competitions, and injury recurrence. We assessed the incidence of injuries according to the Federation Internationale de Football Association (FIFA) incidence formula. Ankle sprains represented 10.17% of total injuries, with a FIFA index equal to 2,002. Lateral ligament injuries represented 53.75% of all sprains. The forwards were the most injured athletes, with 86 lesions. The midfield had the highest number of sprains (75.50%). Almost half (47.04%) of sprains occurred in the final 15 minutes of each half-time. Injuries recurred in 31.22% of cases, and 7.11% of injuries underwent surgical treatment. The average time away from competitions was 13.95 days. Ankle sprains are common injuries in soccer. Although the average time to return to sport is brief, these injuries have a high recurrence rate and are potentially surgical, leading to a longer time off competitions.

7 Is limb asymmetry an intrinsic risk factor for time-loss groin injury in professional male soccer players?

Reference: Phys Ther Sport. 2024 Nov 26:71:53-60. doi: 10.1016/j.ptsp.2024.11.008. Online ahead of print.
Authors: Aynkaran Vigneswaran, Andreas Serner, Abdulaziz Farooq, Courtney Kipps, Andrea Britt Mosler
Download link: https://pdf.sciencedirectassets.com/272404/1-s2.0-S1466853X24X00073/1-s2.0-S1466853X24001275/main.pdf?X-Amz-Security-Token=IQoJb3JpZ2luX2VjEEcaCXVzLWVhc3QtMSJHMEUCIBDzcqniSTDQQhR9QFYCTEyS2NZpcxaKAzWDOeQxDkDDAiEAmELiAL38D2wIjF72PlvJ74pvln%2BUGFxMv%2BM9YFk8fDAqswUIEBAFGgwwNTkwMDM1NDY4NjUiDMnI4sb5rmd1Yn7XUyqQBSqSlaPGGU3%2FkxgFhnkgZA9iIxlU7sOf9tCZOfkarivBll8lA7SX67dfRNj3VsDR9I0uGquUGQ2bIAAtMFnD4nLpJLj%2Faccqlur8jaGbmTghJtz16W5d1OiUyKfd%2BO5N2bj3HRPZ4VrSiS4mus0iFP74izDOHiJufJD41xSiPrADsJCD28Ua6HusYPu%2FYQMmWIn0MKhMCsMoxI97OpXG22VMpVkUSoAVryh72VDjE6s1ZzzWOo0e4MZHU%2FCIEvZ4Un5NtaXkkJ%2Fj7BIE3NiIKnEBOjCAwt%2FTVs%2F%2BMUm3YXkMGvTb19Z%2BtPC1PfZz5sAZ7IYQz6A13zu1jXcpCfAyAhOOQN%2FhqWKa9YzezQl9iQAXcIMqahVpAKpJVOOPFbHwT7C2yGBtkrkcXIRJPsdo3Lb6HjT9yVeclNICylLF6lh5kC49fxkwwu45O8SpI7v9%2F1lJ75facyjKVHAC2hNFXt30GfS1nhQqDEu1qAnN6ezKSNM6AnQ3rY%2B%2FAJeC4Zxeclv9EoPDIzZHph6363cH8r7i4knCCHcZE9TMzhGjyiffdhOudPlmGOYuWVpfvcBt%2FjFHN8qluevMF2Jiu96emn47SG0qGEDcaWQlm8ziCTjfzK%2FRiDOi%2BrzG9A9YGd92aGYJ8n%2BYljgrS22fGI1hUUTZK10GZsFsob9X6hKoH4W4N5VWKdRdT5PbkdhMqK1Hg1lWFcUCsT0Vckh3eOE%2FcXdtfp%2FDmS5jKsZ43Wrv0udCPIxvLhQ%2BmWEueSeCIfrIG7GNXF0v4tNlkYrrk1r3c5QtOJ5o51ETYAnabpoUqKHWsRLvGxbpMmYkpdW8SYeO%2BWn5VzfVDlTmySHrER2e9xgiURel%2F7joNi4dePf2976cMLPv%2BboGOrEBYnhIvA%2FY%2FRPXnp%2FlQbDRGi85%2BmFTXp28eO%2FnU5paBbXmj8Msyongs46rFcZmka0TgQK6eY6LC2B48QDFds618FerpgXaVKZw9Af6NUatloNaVb6QbhwpIRx%2BKU7ZfckwjTbeeXpxE00CUmLCk5t8NeGF7V%2F%2F1PXsxAut5ex%2Fwn34nGWJr33WyOPxHjEDzsKjSaxGhVaFB2IdSVK6r%2BI0Wz7hY9meKRT7yF%2BZV1LmyklP&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20241215T065843Z&X-Amz-SignedHeaders=host&X-Amz-Expires=300&X-Amz-Credential=ASIAQ3PHCVTYY5XRUN2Z%2F20241215%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=0d0b72119a0f2479fcd374a1e19e5055d2735bf98cc525e37eca809e26ce0230&hash=c94b00b0106b78487faa0efea13c1a9f19945b1a239011b332224e7c8c4d92c3&host=68042c943591013ac2b2430a89b270f6af2c76d8dfd086a07176afe7c76c2c61&pii=S1466853X24001275&tid=spdf-b837340b-a073-4928-8e5b-008b34158d4a&sid=0294b5913d5e9640678b8d42d6cd2ac430e6gxrqb&type=client&tsoh=d3d3LnNjaWVuY2VkaXJlY3QuY29t&ua=1e035d095153570c000d50&rr=8f248bfb5981914a&cc=de
Summary: The aim was to provide normative values for between-limb asymmetry of hip strength and range of motion (ROM) in professional male soccer players and evaluate the relationship between these asymmetries and groin injury. A total of 438 professional male soccer players underwent musculoskeletal screening, injury and exposure surveillance over two consecutive seasons. Between-limb asymmetry for two hip strength (eccentric adduction and abduction) and six ROM measures were calculated, and normal asymmetry considered within 1 standard deviation (SD) of the mean. Cox proportional hazard regression analysis estimated the association between asymmetry and time-loss groin injury. Normal asymmetry ranged between 0.3% and 27.3% across strength and ROM variables. No association was found between groin injuries and asymmetry in eccentric hip adduction (HR = 0.99, 95%CI = 0.98-1.00; p = 0.167) or abduction strength (HR = 1.00, 95%CI = 0.99-1.01; p = 0.745). For five of the six ROM measures, no association with groin injuries were determined. A statistically significant, though likely clinically irrelevant, association was found between groin injury and dominant leg total hip rotation ROM (HR = 1.03, 95% CI = 1.00-1.05; p = 0.040). Normal hip strength and ROM asymmetry ranged between -27 and +20%. No clinically relevant associations were found between asymmetry in hip strength or ROM and time-loss groin injuries.

8 Women football observers‘ experiences: a perspective from system justification and glass ceiling

Reference: Front Psychol. 2024 Nov 28:15:1495843. doi: 10.3389/fpsyg.2024.1495843. eCollection 2024.
Authors: Yeliz Eratli Şirin, Günseli Öz
Summary: The legitimization theory of the system explains that despite people’s inherent drive towards personal and group interests, they tend to support social systems. Understanding the sources of social pressure and the glass ceiling perceptions of female football observers is the main aim of this study in terms of examining attitudes within the legitimized system. To this end, the study sought to answer how female football observers are constructed in a marginalized position within the male-dominated football culture through sources of social pressure, and how they accommodate the acceptance of legitimizing the system despite encountering glass ceiling barriers in the context of Turkey. Data for the research were collected through in-depth individual interviews (9 female observers) using qualitative research methods. The collected data were analyzed using thematic analysis. After a comprehensive analysis of the interview transcripts, four themes emerged. Gender-based positive and negative experiences; Glass Ceiling: Organizational Factors; Legitimization of Hierarchy-Reducing Myths; and Hope for Future Intragroup Progress within the Current System. Our analysis reveals that female football observers, identified as match officials, indicate changes in authoritarian attitudes within recent institutional policies during their stadium experiences, characterized towards a more rational, female observer, and referee-focused stance. Additionally, entrenched stereotypes and legitimizing myths reducing hierarchy appear to generally establish legitimacy for female match officiating within the legitimization process. The research results suggest the importance for policymakers in the central referee committee in Turkey to consider the dimensions of legitimization both verbally and in writing when creating policies regarding women.

9 Return-to-play criteria following a hamstring injury in professional football: a scoping review

Reference: Res Sports Med. 2024 Dec 12:1-20. doi: 10.1080/15438627.2024.2439274. Online ahead of print.
Authors: Paolo Perna, Fearghal Kerin, Neil Greig, Marco Beato
Summary: The present scoping review aims to describe the available criteria to determine Return-To-Play (RTP), propose methodological considerations and new research questions, and provide information to help practitioners in professional football make informed decisions regarding RTP following a hamstring strain injury (HSI) in professional male football. The following electronic databases were searched: PubMed, MEDLINE, web of science and SPORTDiscus using keywords related to HSI in elite football. All types of studies in English reporting at least one RTP criterion for professional football players who sustained an HSI were included. In total, 19 studies met the inclusion criteria. RTP criteria were divided into three categories: clinical, strength and performance criteria. Clinical criteria were also divided into sub-categories: absence of pain, hamstring flexibility, medical staff clearance, psychological readiness, surgeon’s opinion and imaging. Practitioners working in professional male football could benefit from using a combination of criteria in their RTP battery of tests.

10 An Educational Review on Machine Learning: A SWOT Analysis for Implementing Machine Learning Techniques in Football

Reference: Int J Sports Physiol Perform. 2024 Dec 11:1-9. doi: 10.1123/ijspp.2024-0247. Online ahead of print.
Authors: Marco Beato, Mohamed Hisham Jaward, George P Nassis, Pedro Figueiredo, Filipe Manuel Clemente, Peter Krustrup
Download link: https://journals.humankinetics.com/view/journals/ijspp/aop/article-10.1123-ijspp.2024-0247/article-10.1123-ijspp.2024-0247.xml
Summary: The abundance of data in football presents both opportunities and challenges for decision making. Consequently, this review has 2 primary objectives: first, to provide practitioners with a concise overview of the characteristics of machine-learning (ML) analysis, and, second, to conduct a strengths, weaknesses, opportunities, and threats (SWOT) analysis regarding the implementation of ML techniques in professional football clubs. This review explains the difference between artificial intelligence and ML and the difference between ML and statistical analysis. Moreover, we summarize and explain the characteristics of ML learning approaches, such as supervised learning, unsupervised learning, and reinforcement learning. Finally, we present an example of a SWOT analysis that suggests some actions to be considered in applying ML techniques by medical and sport science staff working in football. Specifically, 4 dimensions are presented: the use of strengths to create opportunities and make the most of them, the use of strengths to avoid threats, working on weaknesses to take advantage of opportunities, and upgrading weaknesses to avoid threats. ML analysis can be an invaluable tool for football clubs and sport-science and medical departments due to its ability to analyze vast amounts of data and extract meaningful insights. Moreover, ML can enhance performance by assessing the risk of injury, physiological parameters, and physical fitness, as well as optimizing training, recommending strategies based on opponent analysis, and identifying talent and assessing player suitability.

11 Linear and Multidirectional Speed Testing (On-Field and Off-Field) Protocols in Senior and Elite Female Football

Reference: J Strength Cond Res. 2025 Jan 1;39(1):e70-e84. doi: 10.1519/JSC.0000000000004990.
Authors: Marco Beato, Naomi Datson, Filipe Manuel Clemente, Damian James Harper, Alberto Fílter, Stacey Emmonds, Thomas Dos‘ Santos, Paul A Jones
Summary: Female football has had a considerable rise in popularity with millions of fans after matches during the recent Women’s World Cup. Despite this, the football scientific literature is still biased toward male footballers; therefore, this review aims to present the most recent literature and best practices for assessing linear and multidirectional speed and underpinning physical qualities, and to offer practical recommendations based on the most recent evidence and authors‘ expertise for practitioners working with female football players. This review categorizes tests as on-field and off-field, highlighting common protocols, their advantages, and the existing limitations. Among the most common on-field tests, we found the change of direction speed, horizontal deceleration, linear sprinting, and curved sprinting; although the suggested off-field tests are multi-joint isometric, single-joint isometric, isokinetic dynamometry, Nordic hamstring, and vertical jumps. These tests are valuable tools for assessing players‘ physical abilities, serving as a benchmark for tracking physical changes throughout the season, and aiding practitioners in individualizing and optimizing training protocols. This review highlights that strength (eccentric, isometric, concentric, and reactive) and rapid force production are crucial for generating braking and propulsive forces, which underpin linear and multidirectional motion. In conclusion, the evidence and practical suggestions reported in this review will improve the practitioners‘ knowledge of which tests and the consequent training protocols can be used in senior and elite female football players. But practitioners need to be aware about the scarcity of comprehensive studies on female soccer that hinders a complete understanding of the reliability of all assessment protocols used.

12 Critical Fluctuations as an Early Warning Signal of Sports Injuries? A Proof of Concept Using Football Monitoring Data

Reference: Sports Med Open. 2024 Dec 16;10(1):129. doi: 10.1186/s40798-024-00787-5.
Authors: Niklas D Neumann, Jur J Brauers, Nico W van Yperen, Mees van der Linde, Koen A P M Lemmink, Michel S Brink, Fred Hasselman, Ruud J R den Hartigh
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11649608/pdf/40798_2024_Article_787.pdf
Summary: There has been an increasing interest in the development and prevention of sports injuries from a complex dynamic systems perspective. From this perspective, injuries may occur following critical fluctuations in the psychophysiological state of an athlete. Our objective was to quantify these so-called Early Warning Signals (EWS) as a proof of concept to determine their explanatory performance for injuries. The sample consisted of 23 professional youth football (soccer) players. Self-reports of psychological and physiological factors as well as data from heart rate and GPS sensors were gathered on every training and match day over two competitive seasons, which resulted in an average of 339 observations per player (range = 155-430). We calculated the Dynamic Complexity (DC) index of these data, representing a metric of critical fluctuations. Next, we used this EWS to predict injuries (traumatic and overuse). Results showed a significant peak of DC in 30% of the incurred injuries, in the six data points (roughly one and a half weeks) before the injury. The warning signal exhibited a specificity of 95%, that is, correctly classifying non-injury instances. We followed up on this promising result with additional calculations to account for the naturally imbalanced data (fewer injuries than non-injuries). The relatively low F1 we obtained (0.08) suggests that the model’s overall ability to discriminate between injuries and non-injuries is rather poor, due to the high false positive rate. By detecting critical fluctuations preceding one-third of the injuries, this study provided support for the complex systems theory of injuries. Furthermore, it suggests that increasing critical fluctuations may be seen as an EWS on which practitioners can intervene. Yet, the relatively high false positive rate on the entire data set, including periods without injuries, suggests critical fluctuations may also precede transitions to other (e.g., stronger) states. Future research should therefore dig deeper into the meaning of critical fluctuations in the psychophysiological states of athletes. Complex Systems Theory suggests that sports injuries may be preceded by a warning signal characterized by a short window of increased critical fluctuations. Results of the current study showed such increased critical fluctuations before 30% of the injuries. Across the entire data set, we also found a considerable number of critical fluctuations that were not followed by an injury, suggesting that the warning signal may also precede transitions to other (e.g., healthier) states. Increased critical fluctuations may be interpreted as a window of opportunity for the practitioner to launch timely and targeted interventions, and researchers should dig deeper into the meaning of such fluctuations.

13 Adaptations to Change of Direction Ability After Eight Weeks of Strength or Plyometric Training in Elite Youth Football Players

Reference: Res Q Exerc Sport. 2024 Dec 17:1-8. doi: 10.1080/02701367.2024.2433454. Online ahead of print.
Authors: Mads Lerche, Anders Borup, Samuel J Callaghan, Matthew Buckthorpe
Summary: This study aimed to investigate the effects of plyometric (PT) or strength (ST) training on change of direction (COD) performance at two differing angles among highly trained youth footballers. Seventy-one national-level youth football players (14.6 ± 1.8 years) were randomly allocated to either an 8-week, twice weekly, plyometric (PT) or strength training (ST) group. Pre- and post-intervention testing consisted of measures of COD performance at 45 and 180º, as well as maximal strength assessed via Trap Bar Deadlift 5RM (TBD5RM) and reactive strength index (RSI) from a 40 cm drop jump, respectively. Changes from pre- to post-testing were assessed via mixed ANOVAs (p ≤ .05) and effect sizes. Both training groups improved TBD5RM (PT = 7.8%, p < .001, ES = 0.32. ST = 6.9%, p < .001, ES = 0.28) and RSI (PT = 15.9%, p < .001, ES = 0.59. ST = 15.6%, p < .001, ES = 0.64) measures. Significant improvement in 45° COD performance was found for both training groups (PT = 4.0%, p < .001, ES = -0.68. ST = 3.6%, p < .001, ES = -0.61), whilst neither group improved at 180° (PT = 0.8%, p = .192, ES = -0.17. ST = 0.8%, p = .282, ES = -0.23). No significant differences in changes were found between training groups. Both PT and ST were effective at enhancing maximal and explosive strength as well as COD performance measured at shallow angles. Neither method enhanced the sharp angle COD performance.

14 Fresh osteochondral allograft transplantation of the medial femoral condyle in an elite football player

Reference: BMJ Case Rep. 2024 Dec 18;17(12):e262374. doi: 10.1136/bcr-2024-262374.
Authors: João Pedro Oliveira, João Castro Mendes, Fernando Fonseca
Summary: We present an elite footballer in his 20s with a large and symptomatic osteochondral lesion of the weight-bearing area of the medial femoral condyle, who was proposed for a single plug fresh osteochondral allograft transplantation. The lesion was due to repetitive micro traumas and had become highly symptomatic being responsible for making the football practice at a professional level almost impossible, reaching a point that keeping an elite sports career was compromised. Six months after surgery, the athlete returned to sports and, at a 3-year follow-up, still participated in elite high-level football, with a Tegner Activity Scale 10/10, IKDC 93.1, KOOS 97 and Lysholm Scoring 100.

15 Frequency and intensity of change of directions in German Bundesliga soccer

Reference: Sci Med Footb. 2024 Dec 14:1-13. doi: 10.1080/24733938.2024.2439859. Online ahead of print.
Authors: Jan-Philip Deutsch, Lars Donath, Bjoern Braunstein, Robert Rein
Summary: The aim of this study was to investigate the change of direction (COD) frequencies and intensities of high-performance soccer players of the German Bundesliga independent of tactical and match context. COD data were collected from 18 German Bundesliga soccer teams (season 2016-2017; 308 fixtures) by an optical tracking system (OTS) (TRACAB). CODs were tracked using a modified algorithm and were sub-categorized by entry velocity (<3.0 m⋅s-1, 3.0-5.5 m⋅s-1, 5.5-7.0 m⋅s-1 and >7.0 m⋅s-1) and COD angle (20-59°, 60-119° and 120-180°). COD metric frequencies were compared between playing positions (goalkeepers, centre backs, full-backs, central midfielders, wide midfielders, and strikers). In general, regardless of entry velocity or COD angle, central midfielders consistently executed the highest number of COD actions during matches compared to the other playing positions. About ≈ 55% and ≈ 38% of CODs were <3.0 m⋅s-1 and <5.5 m⋅s-1, whereas ≈ 7% were >5.5 m⋅s-1. The distribution of COD angle types was ≈ 5% for 20-59°, ≈25% 60-119° and ≈ 70% for 120-180° COD angles. Our data provide insights into the COD demands of high-performance soccer in the German Bundesliga in terms of entry velocity and COD angles and their combination based on a large dataset of OTS data, which provides insights to facilitate the development of physical conditioning strategies, position-specific external load management, and multidirectional speed training with adequate test battery selection and return-to-play protocols for soccer players.

16 Metabolomics analyses and physical interventions in soccer: a systematic review

Reference: Metabolomics. 2024 Dec 15;21(1):7. doi: 10.1007/s11306-024-02202-2.
Authors: Larissa Castro Pedroso, Gabriel Chabaribery Bedore, João Pedro da Cruz, Filipe Antônio Barros Sousa, Pedro Paulo Menezes Scariot, Ivan Gustavo Masselli Dos Reis, Álex Ap Rosini Silva, Andreia M Porcari, Leonardo Henrique Dalcheco Messias
Download link: https://link.springer.com/content/pdf/10.1007/s11306-024-02202-2.pdf
Summary: Soccer is the most recognized sports worldwide. It is a fertile ground for the use of metabolomics analyses, considering the multifactorial nature of soccer’s physical demands on the body. Although scientific studies have tried using it to better understand the impacts of soccer into different contexts of the sport, no systematic review is available on metabolomics analyses in soccer athletes subjected to physical exertion interventions. Retrieve scientific articles that conducted metabolomics analyses on soccer athletes subjected to physical exertion interventions. Initially, 271 studies were screened, and 48 were retrieved for abstract analysis. Of these, 26 met the eligibility criteria, but 5 failed to meet inclusion criteria. The 21 studies included in this systematic review demonstrate that responses from physical training or acute exercise sessions, followed by the effects of soccer matches, have been the primary focus of researchers to date, highlighting alterations on metabolites from the energy metabolism, immunological pathway, purines, tryptophan/phenylalanine metabolism, as well as oxidative species and antioxidant capacity. Other studies suggest, albeit preliminarily, that organic metabolites have the potential to distinguish soccer players‘ performance and physical fitness, as well as provide valuable insights into diet, physical condition, training load, and recovery throughout the season. Despite metabolomics great potential to understand physiological alterations provoked by soccer as shown by the included studies, future studies should consider female athletes, explore the cause-and-effect relationship between metabolites and soccer performance more deeply, and examine the effects of different training periodizations on these markers.

17 Did social isolation affect anxiety and sleep quality of elite soccer players during the COVID-19 lockdown? Comparisons to training before distancing in the pandemic and outlook for mental health

Reference: Front Psychol. 2024 Nov 29:15:1490862. doi: 10.3389/fpsyg.2024.1490862. eCollection 2024.
Authors: Whyllerton Mayron da Cruz, Danilo Reis Coimbra, Guilherme Torres Vilarino, Amândio Manuel Cupido Dos Santos, Vernon Furtado da Silva, Stefania Mancone, Lavinia Falese, Pierluigi Diotaiuti, Alexandro Andrade
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11641121/pdf/fpsyg-15-1490862.pdf
Summary: The aim was to analyze the anxiety levels and sleep quality of elite soccer athletes in training pre-pandemic and during the lockdown caused by COVID-19. This is an exploratory study with a longitudinal design carried out with elite soccer athletes from two Brazilian soccer clubs. Data collection took place in person pre-pandemic (training) and online (during lockdown) between February and May 2020. The instruments used to assess sleep, daytime sleepiness, and anxiety were the Pittsburgh Sleep Quality Index (PSQI), Epworth Daytime Sleepiness Scale-(ESS-BR), and Competitive Anxiety Scale (SCAT). For data analysis, descriptive statistics (frequencies, percentages, maximum and minimum) and non-parametric inferential statistics were used, establishing a significance of p < 0.05. In total, 76 male soccer athletes participated in the study. A significant increase was observed in anxiety levels in confinement compared to pre-pandemic training (p = 0.017; g = 0.83), and sleepiness significantly reduced in training compared to baseline levels (p = 0.007; g = 0.48). The athletes demonstrated good sleep quality and the pandemic did not significantly alter daytime sleepiness compared to training and baseline. From the results it can be concluded that elite soccer athletes presented alterations in anxiety levels compared to training during confinement, however, no effects of confinement were observed on sleep quality and sleepiness. New studies are needed to analyze the long-term consequences of the pandemic and the relationships between anxiety and sleep in training and competition in athletes.

18 Assessing maximal sprinting speed in soccer – criterion validity of commonly used devices

Reference: Sci Med Footb. 2024 Dec 16:1-6. doi: 10.1080/24733938.2024.2441321. Online ahead of print.
Authors: Stefan Altmann, Ludwig Ruf, Marco Backfisch, Maximiliane Thron, Alexander Woll, Linus Walter, Damon Kaul, Luca Bergdolt, Sascha Härtel
Summary: This study aimed to investigate the criterion validity of commonly used devices to assess maximal sprinting speed (MSS) in soccer. Thirty elite youth soccer players completed three trials of a 30-m sprint test to assess MSS. All sprints were simultaneously captured via a radar gun (Stalker ATS II), timing gates (Smartspeed Pro, Fusion Sport), a magnetic timing system (Humotion SmarTracks) and a global navigation satellite system (GNSS) (Kinexon Perform GPS Pro). The radar gun and the GNSS recorded sprinting speed continuously, while the fastest 5-m split during the 30-m sprint was used for the timing gates and the magnetic system. The best trial of the radar gun (i.e. criterion measure) and corresponding values of the other devices were analyzed. Equivalence testing was performed to assess the statistical equivalence of MSS between the radar gun and the three other devices against a difference value of ± 0.36 km/h and Bland & Altman’s 95% limits of agreement (LoA) were computed to investigate the agreement between MSS results. Differences between GNSS versus radar gun suggested a lack of systematic bias (-0.01 km/h, 95% confidence interval [CI] -0.15 to 0.15 km/h), whereas timing gates-based MSS assessments were prone to larger uncertainty compared to the criterion method (-0.19 km/h, 95% CI: -0.37 to 0.00 km/h) given the pre-defined region of equivalence. The magnetic system (-0.54 km/h; -0.71 to -0.37 km/h) overestimated MSS compared to the radar gun with mean differences being non-equivalent. Based on the practically important difference bounds of ± 0.36 km/h, the width of the 95% LoA was broad enough to suggest a lack of reasonable agreement for MSS assessment regardless of device of interest (GNSS: -0.79 to 0.78 km/h, timing gates: -0.79 to 1.16 km/h, magnetic system: -0.24 to 1.32 km/h). While our results suggested a lack of systematic bias for the investigated GNSS and the timing gates when compared against the radar gun for MSS assessment over 30 m in elite youth soccer players on a team level, the width of the 95% LoAs did not indicate reasonable measurement interchangeability on an individual level. Based on the present results, we do not recommend using the magnetic system for both group and individual analyses in this population.

19 Prevalence of Urinary Incontinence in Female Professional Soccer Players by Category and Specific Position: A Comparative Study with a Control Group

Reference: Healthcare (Basel). 2024 Dec 7;12(23):2478. doi: 10.3390/healthcare12232478.
Authors: Julia M Sebastian-Rico, María Jesús Muñoz-Fernández, Luis Manuel Martínez-Aranda, África Calvo-Lluch, Manuel Ortega-Becerra
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11641451/pdf/healthcare-12-02478.pdf
Summary: Urinary incontinence (UI) significantly impacts quality of life, with varying prevalence in women depending on factors such as age, childbirth, and type of sport practiced. This study compared the prevalence, types, and severity of urinary incontinence (UI) between professional female soccer players and sedentary students, analyzing its relation to playing position and competitive level. A descriptive, observational, and analytical cross-sectional study was conducted, assessing the prevalence, severity, and types of UI among 235 nulliparous professional female soccer players (experimental group, EG) and 252 sedentary female students (control group, CG). Data were collected using the short version of the International Consultation on Incontinence Questionnaire (ICIQ-SF). Statistical analyses included Fisher’s exact test to compare prevalence rates. The findings revealed that 35% of soccer players and 31% of sedentary students reported experiencing UI. Stress urinary incontinence (SUI) was the most prevalent type in both groups, affecting 26% of soccer players and 14% of sedentary students, while mixed UI was more frequent among sedentary women (17%) (p < 0.05). No significant differences were observed in UI prevalence based on playing position or competitive level (p ≥ 0.05). However, female soccer players exhibited a significantly higher prevalence of UI during physical exertion or exercise compared to the control group (p ≤ 0.001), suggesting that high-impact sports may contribute to pelvic floor dysfunction. Additionally, 23.8% of soccer players reported mild-to-moderate UI severity. Female soccer players showed higher UI prevalence during exercise, underscoring the need for targeted interventions like pelvic floor training.

20 Developing a New Expected Goals Metric to Quantify Performance in a Virtual Reality Soccer Goalkeeping App Called CleanSheet

Reference: Sensors (Basel). 2024 Nov 25;24(23):7527. doi: 10.3390/s24237527.
Authors: Matthew Simpson, Cathy Craig
Download link: https://pmc.ncbi.nlm.nih.gov/articles/PMC11644063/pdf/sensors-24-07527.pdf
Summary: As virtual reality (VR) sports training apps start to become more mainstream, it is important that human performance is measured from VR gameplay interaction data in a more meaningful way. CleanSheet is a VR training app that is played by over 100,000 users around the world. Many of those players are aspiring goalkeepers who want to use the app as a new way to train and improve their general goalkeeping performance. Whilst the leaderboards display how many shots players saved, these data do not take into account the difficulty of the shot faced. This study presents a regression model developed from a combination of existing expected goals (xG) models, goalkeeper performance metrics, and psychological research to produce a new shot difficulty metric called CSxG. Utilizing user save rate data as the target variable, a model was developed that incorporated three input variables relating to ball flight and in-goal positioning. Our analysis showed that the required rate of closure (RROC), adapted from Tau theory, was the most significant predictor of the proportion of goals conceded. A validation process evaluated the new xG model for CleanSheet by comparing its difficulty predictions against user performance data across players of varying skill levels. CSxG effectively predicted shot difficulty at the extremes but showed less accuracy for mid-range scores (0.4 to 0.8). Additional variables influencing shot difficulty, such as build-up play and goalpost size, were identified for future model enhancements. This research contributes to the advancement of predictive modeling in sports performance analysis, highlighting the potential for improved goalkeeper training and strategy development using VR technology.