Latest research in football - week 3 - 2022

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


Following studies were retrieved for this week:

#1 Predictive Analytic Techniques to Identify Hidden Relationships between Training Load, Fatigue and Muscle Strains in Young Soccer Players

Reference: Sports (Basel). 2021 Dec 24;10(1):3.  doi: 10.3390/sports10010003.

Authors: Mauro Mandorino, António J Figueiredo, Gianluca Cima, Antonio Tessitore

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Summary: This study aimed to analyze different predictive analytic techniques to forecast the risk of muscle strain injuries (MSI) in youth soccer based on training load data. Twenty-two young soccer players (age: 13.5 ± 0.3 years) were recruited, and an injury surveillance system was applied to record all MSI during the season. Anthropometric data, predicted age at peak height velocity, and skeletal age were collected. The session-RPE method was daily employed to quantify internal training/match load, and monotony, strain, and cumulative load over the weeks were calculated. A countermovement jump (CMJ) test was submitted before and after each training/match to quantify players' neuromuscular fatigue. All these data were used to predict the risk of MSI through different data mining models: Logistic Regression (LR), Random Forest (RF), Support Vector Machine (SVM). Among them, SVM showed the best predictive ability (area under the curve = 0.84 ± 0.05). Then, Decision tree (DT) algorithm was employed to understand the interactions identified by the SVM model. The rules extracted by DT revealed how the risk of injury could change according to players' maturity status, neuromuscular fatigue, anthropometric factors, higher workloads, and low recovery status. This approach allowed to identify MSI and the underlying risk factors.



#2 A Narrative Review for a Machine Learning Application in Sports: An Example Based on Injury Forecasting in Soccer

Reference: Sports (Basel). 2021 Dec 24;10(1):5. doi: 10.3390/sports10010005.

Authors: Alessio Rossi, Luca Pappalardo, Paolo Cintia

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Summary: In the last decade, the number of studies about machine learning algorithms applied to sports, e.g., injury forecasting and athlete performance prediction, have rapidly increased. Due to the number of works and experiments already present in the state-of-the-art regarding machine-learning techniques in sport science, the aim of this narrative review is to provide a guideline describing a correct approach for training, validating, and testing machine learning models to predict events in sports science. The main contribution of this narrative review is to highlight any possible strengths and limitations during all the stages of model development, i.e., training, validation, testing, and interpretation, in order to limit possible errors that could induce misleading results. In particular, this paper shows an example about injury forecaster that provides a description of all the features that could be used to predict injuries, all the possible pre-processing approaches for time series analysis, how to correctly split the dataset to train and test the predictive models, and the importance to explain the decision-making approach of the white and black box models.



#3 Biochemical Markers and Wellness Status During a Congested Match Play Period in Elite Soccer Players

Reference: Int J Sports Physiol Perform. 2022 Jan 17;1-16. doi: 10.1123/ijspp.2020-0914. Online ahead of print.

Authors: Karim Saidi, Hassane Zouhal, Daniel Boullosa, Gregory Dupont, Anthony C Hackney, Benoit Bideau, Urs Granacher, Abderraouf Ben Abderrahman

Summary: The aim was to analyze biochemical markers, wellness status, and physical fitness in elite soccer players in relation to changes in training and match exposure during a congested period of match play. Fourteen elite soccer players were evaluated 3 times (T1, T2, and T3) over 12 weeks (T1-T2: 6-wk regular period of match play and T2-T3: 6-wk congested period of match play). Players performed vertical jump tests, repeated shuttle sprint ability test, and the Yo-Yo Intermittent Recovery Test at T1, T2, and T3. Plasma C-reactive protein, creatinine, and creatine kinase were analyzed at T1, T2, and T3. Wellness status was measured daily using the Hopper questionnaire (delayed onset of muscle soreness, stress, fatigue, and sleep quality). Training session rating of perceived exertion was also recorded on a daily basis. A significant increase was found in stress, fatigue, delayed onset of muscle soreness scores, and Hopper index during the congested period (between T2 and T3) compared with the regular period (between T1 and T2) (.001 < P < .008, 0.8 < ES < 2.3). Between T2 and T3, significant relationships were found between the percentage variations (Δ%) of C-reactive protein, and Δ% of creatine kinase with the Hopper Index, and the Δ% of fatigue score. In addition, the Δ% of fatigue score and Δ% of delayed onset of muscle soreness score correlated with Δ% Yo-Yo Intermittent Recovery Test and Δ% best of repeated shuttle sprint ability test (.49 < r < P < .01). An intensive period of congested match play significantly compromised elite soccer players' physical fitness and wellness status. Elite soccer players' wellness status reflects declines in physical fitness during this period while biochemical changes do not.



#4 Visual search strategy and anticipation in tactical behavior of young soccer players

Reference: Sci Med Footb. 2021 May;5(2):158-164. doi: 10.1080/24733938.2020.1823462. Epub 2020 Sep 29.

Authors: João Vítor de Assis, Varley Costa, Filipe Casanova, Felippe Cardoso, Israel Teoldo

Summary: The aim of the present study was to compare the visual search strategy (VSS) and anticipation between two groups of young players of different efficiencies in tactical behavior (TB). A total of 44 Brazilian male soccer players aged 14.00 (± 1.06) years from three regional clubs participated in the study. TB was assessed using FUT-SAT; anticipation score was obtained by a video-based assessment, while VSS was performed using the Mobile Eye-XG® system. The soccer players were divided into two groups based on their TB results into those more efficient and those less efficient. The results showed that soccer players with higher efficiency in TB were better at anticipating and performed a higher number of shorter visual fixations and a greater average amount of fixations per location. They were also able to adjust their VSS in performing a longer fixation time on the player in possession of the ball. Therefore, there is support for an integration of visual search strategy and anticipation within tactical behavior. Visual search strategy and anticipation seem to contribute to the efficiency of tactical behavior in young soccer players.



#5 The Mézières Method as a Novel Treatment for Elite Spanish Second-Division Soccer League Players With Low Back Pain: A Randomized Controlled Trial

Reference: J Sport Rehabil. 2022 Jan 25;1-16. doi: 10.1123/jsr.2021-0047. Online ahead of print.

Authors: Orges Lena, Jasemin Todri, Ardita Todri, Luis Fernández Azorín, Juan Martínez Fuentes, Petraq Papajorgji, Sergio Hernandez Sanchez, Mercedes Castejon Castejon, Martha Cecilia León Garzón, Jose Luis Martínez Gil

Summary: The puspose was to evaluate the efficacy of 24 weeks of treatment with Mézières method in a Spanish elite second-division soccer team with low back pain (LBP), analyzing their state of back health, flexibility, pain, and steps speed. A total of 20 players with LBP from the second soccer division league were allocated equally to the experimental and control groups (n = 10) as per selection criteria and participated in 2 different rehabilitation programs. The postural Mézières method was implemented in the experimental group, whereas the standard European treatment protocol for LBP was implemented in the control group. Both treatments had a twice weekly session of 40 minutes duration for 24 weeks consecutively with a follow-up in the fourth, 12th, and 24th weeks. Multivariate analysis of covariance with the baseline assessment as a covariance showed a significant difference between groups at the 12th and 24th weeks of the treatment for pain and back functionality. A relevant difference between the experimental and control groups was shown only at the 24th week of the treatment (P < .05) for back flexibility. A significant difference between groups was reported for the quality of life scale and steps speed at the 24th week of the treatment (P > .05). The Mézières method showed a positive effect in the elite soccer athletes with nonspecific chronic LBP and can be used as an alternative treatment.



#6 Player Position Affects Relationship Between Internal and External Training Loads During Division I Collegiate Female Soccer Season

Reference: J Strength Cond Res. 2022 Feb 1;36(2):513-517. doi: 10.1519/JSC.0000000000004188.

Authors: Ai Ishida, S Kyle Travis, Garrison Draper, Jason B White, Michael H Stone

Summary: The purpose of this study was to investigate how competition phase and player position affect the relationship between internal and external training loads (ITL and ETL, respectively) in collegiate female soccer. Seventeen players participated (21.8 ± 1.7 years; 165.1 ± 6.2 cm; and 63.7 ± 7.9 kg). Nineteen match-plays (10 nonconference and 9 conference) were completed during the 2019 competitive season, including 270 observations of 17 players (defenders = 5, midfielders = 9, and forwards = 3). Internal training load was assessed using session rating of perceived exertion (sRPE). External training load included total distance and high-speed running (HSR) distance. A linear mixed model was compiled with fixed effects of total distance, HSR, competition phase, and player position (defenders, midfielders, and forwards) and random effects of player. There were statistically significant main effects for total distance (p < 0.001), HSR (p = 0.047) and player position (p = 0.045) on the prediction model of sRPE. However, the main effect of competition phase did not statistically contribute to the prediction model of sRPE (p = 0.38). In the final model, total distance (p < 0.001) and player position for forwards (p = 0.008) were significant predictors of sRPE. However, there was no statistically significant fixed effect of HSR on sRPE (p = 0.15). The final model explained 60.6% of the variance in sRPE (R2 = 0.60), whereas the random effect also explained 6.1% of the variance (R2 = 0.06). Our findings indicated that total distance and player position were strong predictors of sRPE. The relationship between ITL and ETL should be monitored by player position in female soccer players.



#7 Effect of Varying Recovery Duration on Postactivation Potentiation of Explosive Jump and Short Sprint in Elite Young Soccer Players

Reference: J Strength Cond Res. 2022 Feb 1;36(2):534-539. doi: 10.1519/JSC.0000000000003435.

Authors: Yusuf Köklü, Özlem Köklü, Erhan Işıkdemir, Utku Alemdaroğlu

Summary: The purpose of this study was to investigate the effects of postactivation potentiation (PAP) on vertical jump and sprint performances with different recovery durations. Twelve elite young soccer players (average age: 17.0 ± 0.6 years; body mass: 67.0 ± 5.4 kg; height: 175.0 ± 3.5 cm) voluntarily performed countermovement jump (CMJ) and 30-m sprints (with 10-m split times) under unloaded and 4 different recovery duration conditions (R1: 1 minute, R2: 2 minutes, R3: 3 minutes, and R4: 4 minutes) after a set of 3 repetitions of half-squat exercises at 90% of 1-repetition maximum. Electromyographic assessments of both limbs' vastus lateralis (VL) and semitendinosus (ST) muscle activity were also made during the tests. Vertical jump height, sprint time, and VL and ST muscle activity root mean square (RMS) values were analyzed. The results show that players demonstrated significantly better CMJ, 10-, and 30-m sprint performances in the R4 condition compared with the unloaded condition (p < 0.05). The players also showed significantly higher RMS values for VL and ST muscle activity in the CMJ and 30-m test performances for both legs in the R4 condition compared with the unloaded, R1, R2, and R3 conditions (p < 0.05). According to these results, if sports scientists and coaches desire to increase the PAP effect after heavy resistance training, 4 minutes of recovery time instead of 1, 2, or 3 minutes for CMJ, 10-, and 30-m sprint performances is recommended.



#8 Incidence and Severity of Concussions Among Young Soccer Players Based on Age, Sex, and Player Position

Reference: Orthop J Sports Med. 2022 Jan 17;10(1):23259671211059216. doi: 10.1177/23259671211059216. eCollection 2022 Jan.

Authors: Alden R Weiner, John R Durbin, Susie R Lunardi, Adam Y Li, Theodore C Hannah, Alexander J Schupper, Jonathan S Gal, Oranicha Jumreornvong, Zachary Spiera, Muhammad Ali, Naoum Fares Marayati, Alex Gometz, Mark R Lovell, Tanvir F Choudhri

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Summary: Previously studied risk factors for sports-related concussion in soccer players include sex, age, and player position. However, prior studies were limited in number, they reported conflicting results, and most did not assess initial concussion severity. The purpose of this study was to conduct an in-depth analysis of soccer players across key demographic groups (sex, age, position) for both concussion incidence and severity. It was hypothesized that concussion incidence and severity would be higher among male players, players aged ≥17 years, and goalkeepers. The authors analyzed baseline and postinjury ImPACT (Immediate Post-Concussion Assessment and Cognitive Testing) scores for athletes aged 12 to 22 years between July 2009 and June 2019. Players were assigned to an age group based on when they had their most recent baseline test. Concussion incidence and concussion severity index were compared using t tests and multivariate logistic regression. For 1189 individuals who reported soccer as their primary sport, 1032 contributed 1754 baseline ImPACT tests (some individuals had multiple baseline tests), whereas 445 individuals were suspected of sustaining a concussion and then referred for a postinjury 1 test. Of these players, 254 (24.6%) had both a baseline and a postinjury test and were analyzed for concussion severity. Linear regression showed that forwards had a lower incidence of ImPACT-proxied concussions than goalkeepers had (P = .008). Female players had a significantly higher incidence of ImPACT concussions compared with male players (mean, 0.07 [female] vs 0.04 [male] concussions per person-year; P = .05). Players in the ≥17-year age group had a higher incidence of ImPACT concussions than players in the 15- to 16-year age group (P = .04), although the 15- to 16-year age group had more severe concussions than the ≥17-year age group (mean severity index, 2.91 [age 15-16 years] vs 1.73 [age ≥17 years]; P = .001). Female soccer players experienced a higher incidence of concussion than did male players, and goalkeepers experienced a greater incidence of ImPACT concussions than did forwards. Players of both sexes and all positions in the 15- to 16-year age group showed increased initial concussion severity compared with the ≥17-year age group, despite a lower comparative incidence of ImPACT concussions. Further study is needed to understand whether sex and player position affect concussion severity.



#9 Improving Soccer Players' Memorization of Soccer Tactics: Effects of Visual Realism, Soccer Expertise and Visuospatial Abilities

Reference: Percept Mot Skills. 2022 Jan 27;315125221076448. doi: 10.1177/00315125221076448.

Authors: Hatem Ben Mahfoudh, Bachir Zoudji

Summary: In this study we aimed to examine the effect of visual realism on soccer players' memorization of soccer tactics according to their level of expertise and visuospatial abilities. We divided 48 volunteers into novice and expert soccer players and had them first perform a multitask visuospatial abilities (VSA) test and then undergo training with three dynamic soccer scenes, each presented with varied levels of realism (schematic, moderately realistic and highly realistic). We then tested players' memorization and reproduction of the soccer scenes and measured their visual processing with eye-tracking glasses to identify their cognitive processes during memorization. We found that reducing visual realism improved visual processing and memorization when compared to higher realism (p < .001). Second, both higher (versus lower) player expertise and higher (versus lower) VSA influenced visual processing and enhanced memorization efficiency (p < .001). Third, there were significant interaction effects between visual realism, player expertise, and player VSA (p < .001) such that players with high VSA benefited more from reduced (versus accentuated) visual realism than did players with low-VSA. Thus, increasing visual realism can hinder tactical learning effectiveness, especially for learners who lack domain expertise and visuospatial abilities. Practically speaking, coaches and educators might improve their communications by tailoring tactical instructions to learners' cognitive skills.



#10 Practical Applications for Designing Soccer´ Training Tasks from Multivariate Data Analysis: A Systematic Review Emhasizing Tactical Training

Reference: Percept Mot Skills. 2022 Jan 27;315125211073404. doi: 10.1177/00315125211073404. 

Authors: Markel Rico-González, José Pino-Ortega, Gibson Moreira Praça, Filipe Manuel Manuel Clemente

Summary: Novel viewpoints have led to an understanding that good soccer performers are capable of continuous decision-making and performing excellent motor skills in a well conditioned mental state. Our aims in this review were to: (a) summarize the effects of different conditions and constraints on a soccer player's response and (b) identify potential training designs for varied soccer tasks from a multivariate perspective, emphasizing tactical training. We performed a systematic literature review according to PRISMA guidelines and identified multiple different player constraints, including model strategies for play, drills designed for varied conditions, and training regimens for the dimensions of the physical demands soccer players will face. The use of match-sized training spaces may improve physical fitness and collective tactical behavior, while smaller spaces may contribute to improving tactical behavior from micro-structures (e.g., 1 vs. 1). Pre-session exercises that accelerate the appearance of fatigue during training may help delay the onset of match fatigue and boost players´ creativity. Pitch modifications (dimensions or boundary modifications), modification of game principles (defending strategies or team formations), and altering the number of players involved or coach instructions may contribute to different players improvements. Differential learning, as a non-linear pedagogy, may induce improvements in all dimensions, but especially in creative thinking.



#11 Evaluation of soccer team defense based on prediction models of ball recovery and being attacked: A pilot study

Reference: PLoS One. 2022 Jan 27;17(1):e0263051. doi: 10.1371/journal.pone.0263051. eCollection 2022.

Authors: Kosuke Toda, Masakiyo Teranishi, Keisuke Kushiro, Keisuke Fujii

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Summary: With the development of measurement technology, data on the movements of actual games in various sports can be obtained and used for planning and evaluating the tactics and strategy. Defense in team sports is generally difficult to be evaluated because of the lack of statistical data. Conventional evaluation methods based on predictions of scores are considered unreliable because they predict rare events throughout the game. Besides, it is difficult to evaluate various plays leading up to a score. In this study, we propose a method to evaluate team defense from a comprehensive perspective related to team performance by predicting ball recovery and being attacked, which occur more frequently than goals, using player actions and positional data of all players and the ball. Using data from 45 soccer matches, we examined the relationship between the proposed index and team performance in actual matches and throughout a season. Results show that the proposed classifiers predicted the true events (mean F1 score > 0.483) better than the existing classifiers which were based on rare events or goals (mean F1 score < 0.201). Also, the proposed index had a moderate correlation with the long-term outcomes of the season (r = 0.397). These results suggest that the proposed index might be a more reliable indicator rather than winning or losing with the inclusion of accidental factors.



#12 The relationship between running distance and coaches' perception of team performance in professional soccer player during multiple seasons

Reference: Sci Rep. 2022 Jan 27;12(1):1454. doi: 10.1038/s41598-022-05519-x.

Authors: J C Ponce-Bordón, T García-Calvo, J M Candela-Guardiola, F R Serpiello, R López Del Campo, R Resta, J J Pulido

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Summary: This study analyzed how the physical movement profile of soccer matches evolved throughout a season by assessing the variability of different metrics depending on the season phase. In addition, the evolution of running distances was investigated in the relation to the team performance based on the coaches' perception. Games from four consecutives Spanish LaLiga seasons (n = 1520) were recorded using an optical tracking system (i.e., ChyronHego). Total distance (TD), distance covered between 14 and 21 km h-1 (MIRD), 21-24 km h-1 (HIRD), and > 24 km h-1 (VHIRD) were analyzed, as well as the number of efforts between 21 and 24 km h-1 (Sp21) and > 24 km h-1 (Sp24). Seasons were divided into four phases (P): P1 (matches 1-10), P2 (11-19), P3 (20-29), and P4 (30-38). Linear mixed models revealed that soccer players covered significantly greater distances and completed a higher number of sprints in P2 and P3. Also, team performance evaluated by soccer coaches was positively related to TD, HIRD, VHIRD and Sp21 in P1. A negative relationship was observed between team performance and distance covered at speeds below 21 km h-1 in P2 and P3. Team performance was negatively related to TD, MIRD, and HIRD, and Sp21 in P4. As conclusion, the team performance perceived by coaches is related to the movement profile throughout a season, and it significantly influences the evolution of soccer players' movement profiles. Specifically, it seems that the players of the best teams have the best physical performance at the beginning of the season with respect to the rest of the phases.



#13 Isokinetic hamstring and quadriceps strength interpretation guideline for football (soccer) players with ACL reconstruction: a Delphi consensus study in the Netherlands

Reference: Sci Med Footb. 2022 Jan 11;1-12. doi: 10.1080/24733938.2021.2024592. Online ahead of print.

Authors: Nick van der Horst, Remy van Denderen

Summary: Strength testing is a key part of rehabilitation and return to sport (RTS) decision making for football players after anterior cruciate ligament reconstruction (ACLR). Isokinetic testing has been the gold standard for strength measurement for decades, but a uniform protocol and clinical implications of test results are lacking. Therefore, this study aimed to 1) develop a uniform protocol for football players based on knowledge and experience from experts in the field of ACL rehabilitation and 2) clarify the clinical interpretation of different isokinetic test outcomes. In a structured Delphi consensus procedure 42 experts (98% full response rate) fulfilled three rounds that involved a survey, content analysis and anonymised feedback report for each round. Surveys addressed the isokinetic protocol, evaluation report and torque-angle curve of the isokinetic test for strength evaluation in football players after ACLR. The final protocol consisted of concentric knee flexion and extension isokinetic testing with 5 repetitions at 60°/sec, 20 repetitions at 180°/sec and 15 repetitions at 300°/sec and 60 seconds rest between sets. All parameters were deemed valuable, with Peak Torque, Max Rep Total Work, Total Work, Range of Motion and Agonist to Antagonist ratio being considered key for clinical interpretation. For qualitative assessment, it was advised to assess the shape, course, volume, potential dips, peak, and build-up to the peak of the parabola. This Delphi consensus study provided a guideline for data collection and clinical interpretation of isokinetic strength testing in football players after ACLR.



#14 Menstrual cycle phase and elite female soccer match-play: influence on various physical performance outputs

Reference: Sci Med Footb. 2021 May;5(2):97-104. doi: 10.1080/24733938.2020.1802057. Epub 2020 Aug 12.

Authors: Ross Julian, Sabrina Skorski, Anne Hecksteden, Christina Pfeifer, Paul S Bradley, Emiel Schulze, Tim Meyer

Summary: The aim of the study was to investigate whether menstrual cycle phases influence the physical performance during soccer match-play. Fifteen elite female soccer players, with physiologically normal menstrual cycles, competed in matches over a four-month period. Physical performance was assessed via GPS and expressed as meters per minute, and separated into four individualised thresholds (low, high, very high and sprinting). Seventy-six complete individual match observations, 36 from the follicular and 40 from the luteal phase were recorded. The differences in physical match performance parameters between the cycle phases were evaluated using a mixed linear model. The results of the current study indicate that very high-intensity running distance was significantly greater during the luteal phase compared to the follicular phase (5.90 ± 2.16 m.min-1 vs. 6.64 ± 2.72 m.min-1; p = 0.02). However, this finding was accompanied by large variations across matches (CV = 39.5%). Overall, the results suggest that the menstrual cycle phase does not influence match physical performance of female soccer players to a significant degree. Therefore, at present, interventions or other methods of coping with menstrual cycle phase do not seem necessary on a group/team level to maximise competitive physical performance.



#15 Occurrences of near-to-maximal speed-running bouts in elite soccer: insights for training prescription and injury mitigation

Reference: Sci Med Footb. 2021 May;5(2):105-110. doi: 10.1080/24733938.2020.1802058. Epub 2020 Aug 5.

Authors: Martin Buchheit, Ben M Simpson, Karim Hader, Mathieu Lacome

Summary: The aim was to quantify the occurrence of near-to-maximal speed-running bouts in elite soccer players. Tracking match data from 35 professional players (23 ± 3 yrs) were analysed over four seasons (2015-2019). The number of runs reaching >80, >85 and >90% of players' individual maximal sprinting speed (MSS) was computed. Differences in peak speed occurrences between halves and positions were analysed. Occurrences were not different between halves, but slightly-to-moderately position-dependent, with wingers (3.5 ± 2.0 runs >80% per half) and central midfielders (1.6 ± 1.5 runs >80% per half) performing the most and the least number of near-to-maximal speed-running bouts. Players did not reach >90% of MSS at all in 35% (Attackers) to 65% (Midfielders) of their matches; they reached ≥3 times >90% MSS per match in 2% (Midfielders) to 11% (Attackers) of their matches only. The maximal number of cumulated match occurrences during congested periods was observed in acentral defender (2 runs >90% of MSS every 4 days for 31 days) and a winger (1 run every 4 days for 52 days). The occurrence of near-to-maximal speed-running bouts is low in elite soccer. Match context, playing position and individual player profile are the main determinants of those occurrences.



#16 Impact of COVID-19 lockdown on professional soccer players' match physical activities

Reference: Sci Med Footb. 2021 Nov;5(sup1):44-52. doi: 10.1080/24733938.2021.1995033. Epub 2021 Oct 31.

Authors: Ermanno Rampinini, Marco Martin, Andrea Bosio, Federico Donghi, Domenico Carlomagno, Marco Riggio, Aaron J Coutts

Summary: The COVID-19 pandemic forced the 2019-20 Italian Serie A competition to stop and players went into lockdown. During lockdown, players only trained at home, likely having a detrimental effect on players' physical fitness and capacity. This study investigated the effect of the COVID-19 lockdown on professional soccer players' match physical activities. Match activities of 265 male professional soccer players were assessed in two periods prior to (PRE1 and PRE2) and one period following the lockdown (POST) using a video tracking system. Linear mixed models were used to examine differences between-periods in total (TD), very high-speed (VHS), sprint (SPR), high-acceleration (ACC) and high-deceleration (DEC) distances, considering full match data and data from six 15-min intervals. TD and VHS during POST were lower than the two other competitive periods (p < 0.001, d small-moderate). SPR did not show differences between periods (p > 0.636). ACC and DEC during POST were lower than PRE2 (p < 0.015, d small). Declines in most 15-min intervals after lockdown were observed in TD and VHS. There were small differences in the temporal distribution of SPR, ACC and DEC at POST. After the COVID-19 lockdown, soccer players' higher-intensity running activities were similar to those of games played before the lockdown, but TD and VHS decreased, both considering the entire match and 15-min intervals. The temporal distribution of running activities was mostly stable throughout the season.



#17 Does playing football (soccer) lead to SARS-CoV-2 transmission? - A case study of 3 matches with 18 infected football players

Reference: Sci Med Footb. 2021 Nov;5(sup1):2-7. doi: 10.1080/24733938.2021.1895442. Epub 2021 Mar 18.

Authors: Florian Egger, Oliver Faude, Sebastian Schreiber, Barbara C Gärtner, Tim Meyer

Summary: The risk of viral transmission of SARS-CoV-2 associated with football (soccer) training and match play is unknown. Therefore, studies on infection-relevant contacts in football are of utmost importance.A retrospective video-based analysis was performed over 3 matches with 18 SARS-CoV-2 positive players (age: 17.6 ± 3.1 years; 2 professional, 2 semi-professional and 14 youth academy players) during the pre-season in August and September 2020 in Germany. Repeated RT-PCR tests were performed in 5 of 6 teams and pre-match RT-PCR tests in 4 of 6 teams. The last RT-PCR test ranged between 5 - 14 days post-match. The most important result was that no case of virus transmission was found as documented by RT-PCR tests (and symptom monitoring up to 14 days post-match). Physical contact between contagious and non-infected players never lasted longer than 3 seconds each and the position of players during duels was almost exclusively laterally or behind each other.In conclusion, very low risk of SARS-CoV-2 transmission during football match play has been documented. Nevertheless, due to the observational retrospective design of the study, which was based on ethical reasons, inconsistent RT-PCR testing should be regarded as limitation and larger studies are needed to confirm a low probability of virus transmission.



#18 Physical match performance and injuries in professional soccer before and after the COVID-19 break

Reference: Sci Med Footb. 2021 Nov;5(sup1):31-34. doi: 10.1080/24733938.2021.1955955. Epub 2021 Jul 19.

Authors: Maximiliane Thron, Sascha Härtel, Alexander Woll, Ludwig Ruf, Timo Gross , Stefan Altmann

Summary: The aim was to examine possible differences in physical match performance and the injury occurrence before and after the COVID-19 induced interruption of the 2019/2020 season of the German Bundesliga. Due to the interruption, matches and soccer-specific training were suspended for nine weeks, matches after the resumption of play occurred congested, and the playing situation changed, regarding, e.g., an increase to five substitutions. For this purpose, the 25 match-days before (pre) and the 9 match-days after (post) the COVID-19 induced interruption were examined regarding total distance, sprinting distance, average peak velocity, high-intensity distance, and injury occurrence. Average peak velocity increased slightly for the comparison of pre and post with a small effect size (MD = 0.28 km/h, 95% CI: 0.11-0.45, p < 0.01, ES = 0.30, 95% CI: 0.12-0.48). There were no relevant differences in total distance, sprinting distance, high-intensity distance, and injury occurrence (0.11 ≤ p ≤ 0.82; 0.02≤ ES≤0.15). In terms of physical match performance and injury occurence results suggest the opportunity to recover and work on individual physical weaknesses during the interruption alongside with an increased number of substitutions was sufficient to compensate for the short soccer-specific preparation phase before the commencement of matches and the congested match schedule after the COVID-19 break.



#19 The influence of the offside rule on players' positional dynamics in soccer small-sided games

Reference: Sci Med Footb. 2021 May;5(2):144-149. doi: 10.1080/24733938.2020.1819559. Epub 2020 Sep 9.

Authors: Gibson Moreira Praça, Mauro Heleno Chagas, Sarah Glória Teles Bredt, André Gustavo Pereira Andrade, Igor Junio Oliveira Custódio, Marcelo Rochael

Summary: Previous studies on soccer small-sided games (SSGs) chose between with and without offside rule conditions without evidence-based criteria. The current study aimed to compare the positional dynamics of 3v3 SSGs with and without the offside rule. Twenty-four Brazilian U-17 national-level soccer players were recruited. They were split into eight teams and played SSGs with and without the offside rule . Positional data were gathered by a Global Positioning System, and teams' length, width, the length per width ratio (LPWratio), stretch index and players' spatial exploration index were calculated. Data were compared between the experimental conditions by a paired t-test. Results showed that SSGs with the offside rule presented lower values of length (~16.63%, large effect), the LPWratio (~19.74%, large effect), and players' spatial exploration (~4.13%, small-to-moderate effect). We conclude that the offside rule impacts players' positional behavior in SSGs, inducing a less exploratory behavior mainly in the width axis. For this reason, we recommend caution when interpreting previous results on SSG when the offside rule was not applied since adopting this rule might elicit different responses to the players . Coaches can manipulate this rule aiming to achieve specific tactical goals for the training session.



#20 The dose-response relationship between training-load measures and aerobic fitness in elite academy soccer players

Reference: Sci Med Footb. 2021 May;5(2):128-136. doi: 10.1080/24733938.2020.1817536. Epub 2020 Sep 9.

Authors: Matthew Ellis, Ryan Penny, Ben Wright, Mark Noon, Tony Myers, Ibrahim Akubat

Summary: The aim of the current study is to examine the dose-response relationships between training load (TL) measures and the consequent changes in aerobic fitness. Data were collected over the 6-week pre-season period in elite youth soccer players. Participants completed a lactate threshold test to identify changes in treadmill speed at 2 mmol · l-1 (S2) and 4 mmol · l-1 (S4). Internal TL was quantified with the following training impulse (TRIMP) methods: Banister TRIMP, Edwards TRIMP, Lucia TRIMP, individual TRIMP (iTRIMP) and rate of perceived exertion was also collected. External TL measures were total distance, PlayerLoad, high speed running (14.4-19.8 km · h-1), very high-speed running (19.8-25.2 km · h-1) and maximal sprint distance (>25.2 km · h-1). Individual high-speed distance was derived from each participants treadmill speed at S4. Different Bayesian regression models were run with different likelihood functions. The best-fitting models with both the lowest out-of-sample prediction error and the highest variance explained (R2) were used. iTRIMP had the strongest relationships with changes in S2 (r = 0.93, R2 = 0.90) and S4 (r = 0.88, R2 = 0.82). Explained variance ranged from 10%-69% and 11%-38% for all other internal TL measures and external measures, respectively. In summary, the iTRIMP method demonstrates a dose-response relationship with changes in aerobic fitness in elite youth soccer players.



#21 Organisation of instep kicking in young U11 to U20 soccer players

Reference: Sci Med Footb. 2021 May;5(2):111-120. doi: 10.1080/24733938.2020.1807043. Epub 2020 Aug 17.

Authors: Luiz H Palucci Vieira, Fabio A Barbieri, Eleftherios Kellis, Lucas Oliveira, Rodrigo Aquino, Sérgio Cunha, Bruno Bedo, João Manechini, Paulo Santiago

Summary: The main purpose of the study was to investigate kicking kinematics and performance in young-trained soccer players according to age, playing status, and biological maturity. Youth male soccer players (N = 105) from five age groups (under-11, under-13, under-15, under-17, and under-20) were evaluated. Four digital video cameras (300 Hz) captured the participants' lower extremity and ball kinematics during penalty kick trials using dominant limb. It was possible to identify non-linear differences in angular joint kinematics (displacement and velocity) of hip, knee and ankle across age-groups. Kicked ball speed and lower extremity mechanical factors discriminated among under-15 players with distinct status (e.g., ball speed and foot-to-ball speed ratio: starters > non-starters and non-participating substitutes; effect size = 1.05 to 1.49 [large]). Estimated maturity offset was not correlated with performance outputs in any age-group (r = -0.28 to 0.39; P > 0.05). We conclude that from ages ~10 to 19 years, differences in kicking kinematics and performance vary across time in youth players. Transition phase between under-13 to under-15 appears the most sensible period for powerful instep kick performance development. Kicking speed in youth soccer is discriminated according to player status, but not estimated biological maturity.



#22 Do elite soccer players cover less distance when their team spent more time in possession of the ball?

Reference: Sci Med Footb. 2021 Nov;5(4):310-316. doi: 10.1080/24733938.2020.1853211. Epub 2020 Dec 2.

Authors: Miguel Lorenzo-Martinez, Anton Kalén, Ezequiel Rey, Roberto López-Del Campo, Ricardo Resta, Carlos Lago-Peñas

Summary: The aim of this study was to examine the association between the time spent in possession by teams and the match-running performance in elite soccer matches. Match performance data were collected from players in Spanish LaLiga (8,468 individual match observations of 412 outfield players) using a multiple-camera computerised tracking system. A k-means cluster analyses classified teams depending on time spent in possession of the ball: very high-percentage ball possession teams (VHPBPT), high-percentage ball possession teams (HPBPT), low-percentage ball possession teams (LPBPT) and very low-percentage ball possession teams (VLPBPT). Overall, physical indicators were highly associated with ball possession. Distances covered in VHPBPT were lower than HPBPT, LPBPT and VLPBPT, especially at low and medium speed. Position-specific changes were also evident for physical profiles. Attackers (central midfielders, external midfielders and forwards) in VHPBPT covered fewer meters per minute at any speed than their counterparts in HPBPT, LPBPT or VLPBPT. However, defenders (Central defenders and External defenders) in VLPBPT covered lower distances. These findings may have a great deal of practical implications and may help coaches to better understand match-running variations according to ball possession strategies and could be used to develop a model for predicting the physical activity profile in competition.



#23 Talent map: how demographic rate, human development index and birthdate can be decisive for the identification and development of soccer players in Brazil

Reference: Sci Med Footb. 2021 Nov;5(4):293-300. doi: 10.1080/24733938.2020.1868559. Epub 2021 Feb 22.

Authors: Israel Teoldo, Felippe Cardoso

Summary: The aim of this paper is to verify how cities' demographic rates and Human Development Index (HDI), as well as the birthdate of Brazilian elite soccer players influenced their identification and development. The sample was comprised of 5,359 players from the Brazilian Serie A Soccer Championship between 2003 and 2019. Players' birthdate and birthplace data were collected, as well as the HDI from their hometowns. Descriptive statistics, chi-square, Pearson correlation and linear regression tests were performed. Results indicated that players born in the first semester of the year, in cities with a demographic rate of up to 100,000 inhabitants and HDI above 0.501, are more likely to play at the highest level (Serie A) of Brazilian soccer. Correlations were observed between birth quartile and HDI (r = -.059; se = 0.04; p < 0.001), birth quartile and demographic rates (r = -063, se = 0.03; p < 0.001), and between HDI and demographic rates (r = 0.458; se = 0.02; p < 0.001). The linear regression method yielded a valid model that included all three variables in this study (F(2) = 9.512; p < 0.001). Based on these findings, it is possible to conclude that birthdate, demographic rate and HDI are important factors in the identification and development of soccer players in Brazil.



#24 Immediate effects of an acute bout of repeated soccer heading on cognitive performance

Reference: Sci Med Footb. 2021 Aug;5(3):181-187. doi: 10.1080/24733938.2020.1846769. Epub 2020 Nov 15.

Authors: Jake Ashton, Ginny Coyles, James J Malone, James W Roberts

Summary: There is growing concern surrounding the harmful effects of soccer heading on cognitive function. The present study aims to examine the immediate effects of heading. 30 recreational male soccer players were divided into three groups that undertook 20 consecutive headers with a soft (8.8 psi), hard (16.2 psi), or no (control) ball. A battery of neuropsychological tests was completed before and after heading: King-Devick, trail-making (TM) (A, B), digit span (DS) and spatial span (SS) (forward, backward). Significant increase in the time (M = 4.44 s) and errors (M = 1.45) for the King-Devick test within the hard and soft groups, although there was no significant difference for TM-A and TM-B. Significant decline for SS forward within the hard and soft groups (M= -16%), although the declines for SS backward (M = -16%), DS forward (M= -23%) and DS backward (M = -25%) were present only for the hard group (ps <.05). While outside of regular match-play, this study showed that heading negatively influenced one indicator of a suspected concussion (King-Devick), as well as working memory (DS, SS) that is essential for daily life. These findings contribute to the growing debate surrounding heading safety.



#25 The effect of pre-exercise Nordic hamstring exercise on hamstring neuromuscular response during soccer-specific activity

Reference: Sci Med Footb. 2021 Aug;5(3):242-249. doi: 10.1080/24733938.2020.1837923. Epub 2020 Nov 8.

Authors: Michael O'Boyle, Christopher Michael Brogden, Matt Greig

Summary: The Nordic hamstring exercise (NHE) has emerged as a popular intervention for improving eccentric hamstring strength, however recent literature suggests there is a potential for an increase in injury risk during subsequent exercise. To quantify the influence of pre-exercise NHE on the electromyographical response of the hamstrings, 10 male soccer players completed an experimental trial comprising 6 sets x 5 repetitions of NHE prior to the completion of a 45 minute soccer-specific protocol. Post-exercise NHE were performed in the experimental and control (no pre-exercise NHE) trials. Electromyographic (EMG) response (integrated, mean and peak amplitude) of the biceps femoris to the pre- and post-exercise NHE and the soccer-specific exercise protocol was quantified. Integrated (P= 0.025) and mean (P= 0.020) EMG elicited a significant main effect for time in the soccer-specific protocol with higher values during the first 15 mins indicative of a fatigue effect. However, there was no trial x time interaction (P ≥ 0.78). There was no difference between trials in the EMG response to pre-exercise (P≥ 0.30) or post-exercise (P≥ 0.16) NHE trials. Therefore, although previous studies suggest performing pre-exercise NHE might impair maximal strength metrics, the current study's results suggest that it does not impair the electromyographical response to subsequent soccer-specific exercise or NHE repetitions.



#26 Full duodenal rupture after direct abdominal trauma in soccer: a case report of an elite soccer player with follow up and return to play protocol

Reference: Sci Med Footb. 2021 Aug;5(3):254-260. doi: 10.1080/24733938.2020.1853804. Epub 2020 Dec 14.

Authors: Bahar Hassanmirzaei, Farinaz Fahimipour, Afifeh Khosravi, Tohid Seif Barghi

Summary: Severe traumatic abdominal injuries and duodenal ruptures are relatively rare in soccer and can be easily missed and turn into a life-threatening condition. All team physicians need to be familiar with the warning sign in these situations. This report aims to report a case, discuss the diagnostic and treatment process and the return to play protocol.During a professional female soccer team training session, the injury occurred while the player's epigastrium was hit hardly by the opponent's knee. In the first evaluation, there was only mild epigastrium pain without any other sign. Eventually, pain exacerbated, nausea and vomiting were added. All the initial evaluation (Physical examination, abdominal X-ray, ultrasonography, blood tests) were normal. Eventually, she developed abdominal guarding and underwent abdominopelvic computed tomography with intravenous contrast where Duodenal rupture becomes evident. She underwent laparotomy and full duodenal repair and discharged from the hospital in good health.For the return to play determination in such injuries, the abdomen should not be imposed on any trauma for about 6 months, so while the player can start a self-training session firstly without a ball and then with a ball, she is not allowed to play or train with others for 6 months.



#27 Negative Effects of Mental Fatigue on Performance in the Yo-Yo Test, Loughborough Soccer Passing and Shooting Tests: A Meta-Analysis

Reference: J Funct Morphol Kinesiol. 2022 Jan 13;7(1):10. doi: 10.3390/jfmk7010010.

Authors: Jozo Grgic, Ivan Mikulic, Pavle Mikulic

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Summary: We aimed to examine the effects of mental fatigue on the Yo-Yo test and Loughborough soccer passing and shooting tests performance using a meta-analysis. The search for studies was performed through eight bibliographic databases (Academic Search Elite, AUSPORT, Cochrane Library, PsycInfo, PubMed/MEDLINE, Scopus, SPORTDiscus, and Web of Science). The methodological quality of the included studies was assessed using the PEDro checklist. A random-effects meta-analysis was performed for data analysis. After reviewing 599 search results, seven studies with a total of ten groups were included in the review. All studies were classified as being of good methodological quality. Mental fatigue reduced the distance covered in the Yo-Yo test (Cohen's d: -0.49; 95% confidence interval [CI]: -0.66, -0.32). In the Loughborough soccer passing test, mental fatigue increased the original time needed to complete the test (Cohen's d: -0.24; 95% CI: -0.46, -0.03), increased penalty time (Cohen's d: -0.39; 95% CI: -0.46, -0.31), and decreased performance time (Cohen's d: -0.52; 95% CI: -0.80, -0.24). In the Loughborough soccer shooting test, mental fatigue decreased points per shot (Cohen's d: -0.37; 95% CI: -0.70, -0.04) and shot speed (Cohen's d: -0.35; 95% CI: -0.64, -0.06). Overall, the findings presented in this review demonstrated that mental fatigue negatively impacts endurance-based running performance as well as soccer passing and shooting skills.



#28 Maturation, signal detection, and tactical behavior of young soccer players in the game context

Reference: Sci Med Footb. 2021 Nov;5(4):272-279. doi: 10.1080/24733938.2020.1851043. Epub 2020 Dec 6.

Authors: Eder Gonçalves, Franco Noce, Márcio Assis Marques Barbosa, António José Figueiredo, Israel Teoldo

Summary: This study examined the relationship between maturation and signal detection skills, as well as the effect of signal detection on the tactical behavior efficiency of young soccer players. Fifty-four male soccer players participated in the study (U-11, U-13, and U-15). Maturation was evaluated by the Khamis-Roche method, and peak height velocity was estimated. A computer-based test in the Vienna Test System® was used to assess signal detection skills, whereas tactical behavior efficiency was assessed using the System of Tactical Assessment in Soccer. Descriptive analysis, the Kolmogorov-Smirnov test, the Spearman bivariate correlation and the univariate analysis of variance (one-way ANOVA) were performed. Effect sizes were reported as Cohen's d, and the significance level was set at p < .05. Relationships were observed between the percentage of predicted adult height and signal detection performance. Also, signal detection skills were found to affect the tactical behavior efficiency of young soccer players. It is concluded that the players, as seen more mature, can perceive the game faster and more effectively, and are able to provide quicker responses in the game context.



#29 Research in Another un-Examined (RAE) context. A chronology of 35 years of relative age effect research in soccer: is it time to move on?

Reference: Sci Med Footb. 2021 Nov;5(4):301-309. doi: 10.1080/24733938.2020.1841278. Epub 2020 Nov 9.

Authors: Simon J Roberts, Allistair P McRobert, James Rudd, Kevin Enright, Matthew J Reeves

Summary: It is approximately 35 years since the publication of the first relative age effect paper in sport and despite the volume of empirical studies, book chapters, conference presentations, and column inches dedicated to this topic we appear to be no further on in eliminating or attenuating this discriminatory practice. This commentary argues that the ongoing use of univariate methods, focusing on primary or secondary analyses of birth-date data, unearthed from previously un-examined contexts is not conducive to stimulating discussion or providing empirical solutions to relative age effects. This paper concludes by suggesting a departure from the traditionally narrow view of relative age inquiry and instead consider the role of transdisciplinary research.



#30 Part 2 of the 11+ as an effective home-based exercise programme in elite academy football (soccer) players: a one-club matched-paired randomised controlled trial

Reference: Sci Med Footb. 2021 Nov;5(4):339-346. doi: 10.1080/24733938.2021.1874616. Epub 2021 Jan 25.

Authors: Stella Veith, Matthew Whalan, Sean Williams, Steffi Colyer, John A Sampson

Summary: Although the 11+ is known to reduce injuries and improve performance in adolescent footballers, its duration presents a notable barrier to implementation. Hence, this study investigated injury and performance outcomes when 65 elite male academy footballers either performed Part 2 3x/week at training (TG) or at home (HG). Time to stabilisation (TTS), eccentric hamstring strength (EH-S) and countermovement jump height (CMJ-H) were collected 4 times during the 2019 football season. Linear mixed models were used to evaluate main and interaction effects of group and time. Bonferroni post-hoc tests were used to account for multiple comparisons. Differences in time loss and medical attention injuries were determined using a two-tailed Z test for a comparison of rates. Relative to baseline, EH-S (HG 4.3 kg, 95% CI 3 to 5.7, p < 0.001; TG 5.5 kg, 95% CI 4.3 to 6.6, p < 0.001) and CMJ-H (HG 3.5 cm, 95% CI 2.2 to 4.7, p < 0.001; TG 3.2 cm, 95% CI 2.2 to 4.3, p < 0.001) increased, with no difference between groups observed at the end of the season. All injury outcomes were similar. Rescheduling Part 2 did not affect performance or increased injury risks in academy footballers.



#31 The effect of bio-banding on physical and psychological indicators of talent identification in academy soccer players

Reference: Sci Med Footb. 2021 Nov;5(4):280-292. doi: 10.1080/24733938.2020.1862419. Epub 2021 Jan 19.

Authors: Christopher Towlson, Calum MacMaster, Bruno Gonçalves, Jaime Sampaio, John Toner, Niall MacFarlane, Steve Barrett, Ally Hamilton, Rory Jack, Frances Hunter, Tony Myers, Grant Abt

Summary: The aim of this study was to examine the effect of bio-banding on indicators of talent identification in academy soccer players. Seventy-two 11 to 14-year-old soccer players were bio-banded using percentage of estimated adult stature attainment (week 1), maturity-offset (week 2) or a mixed-maturity method (week 3). Players contested five maturity (mis)matched small-sided games with physical and psychological determinants measured. Data were analysed using a series of Bayesian hierarchical models, fitted with different response distributions and different random and fixed effect structures. Few between-maturity differences existed for physical measures. Pre-peak height velocity (PHV) and post-PHV players differed in PlayerLoadTM (anterior-posterior and medial-lateral) having effect sizes above our criterion value. Estimated adult stature attainment explained more of the variance in eight of the physical variables and showed the greatest individual differences between maturity groups across all psychological variables. Pre-PHV and post-PHV players differed in positive attitude, confidence, competitiveness, total psychological score (effect sizes = 0.43-0.69), and session rating of perceived exertion. The maturity-offset method outperformed the estimated adult stature attainment method in all psychological variables. Maturity-matched bio-banding had limited effect on physical variables across all players while enhancing a number of psychological variables considered key for talent identification in pre-PHV players.



#32 Linear Advancing Actions Followed by Deceleration and Turn Are the Most Common Movements Preceding Goals in Male Professional Soccer

Reference: Sci Med Footb. 2022 Jan 21. doi: 10.1080/24733938.2022.2030064. Online ahead of print.

Authors: David Martínez Hernández, Mark Quinn, Paul Jones

Summary: Data were collected through time-motion analysis from soccer players participating in the English Premier League using a modified version of the Bloomfield Movement Classification with differences analysed through chi-square.The most common individual movement preceding a goal was a linear advancing motion (32.4 ± 1%), followed by deceleration (20.2 ± 0.9%) and turn (19.8 ± 0.9%). Actions also involved were change in angle run (cut and arc run), ball blocking, lateral advancing motion (crossover and shuffle) and jumps. Although players followed similar trends there were dissimilarities based on the role, with attackers (assistant and scorer) performing more linear actions, subtle turns and cuts and defenders (defender of assistant and defender of scorer) more ball blockings, lateral movements and arc runs. In 82.9 ± 1.5% of player involvements there was at least 1 high intensity (HI) movement with assistant showing the lowest percentage and defender of scorer the highest.This study shows the multidirectional nature and context specificity of soccer during goal scoring situations, with linear actions such as sprints being the most common movements, followed by decelerations and turns. Moreover, it highlights the recurrent application of these at HI, and so, training strategies should prioritize the development of player's explosiveness.


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