Latest research in football - week 15 - 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 Hypertrophic adaptations to a 6-week in-season barbell vs. flywheel squat added to regular soccer training

Reference: J Sports Med Phys Fitness. 2022 Apr 12. doi: 10.23736/S0022-4707.22.13793-X. Online ahead of print.

Authors: Cristoforo Filetti, Bruno Ruscello, Italo Leo, Marco Porta, Aldo Chiari, Carlos Miranda, Vincenzo Rago

Summary: The aim of this study was to compare the hypertrophic adaptations to barbell or flywheel squat exercise added to regular in-season soccer training. Quadriceps' (rectus femoris [RF], vastus medialis [VM] and vastus lateralis [VL]) cross-sectional area (CSA) in its portions (proximal [PROX], middle [MID], and distal [DIST]) was measured on both legs before and after a 6-week barbell (80 to 90 % one-maximum repetition; n=7) or flywheel (0.0611 to 0.0811 Kg·m2; n=7) in an U19 professional soccer team using a 3T magnetic resonance imagery. Both groups underwent 5 sets × 6 reps per session of squat separated by 3-min rest, while controlling the time under tension (within 0.5 and 0.8 s). The barbell squat group experienced moderate CSA increments in the VMMID and the VLDIST of the right leg (d=0.98-0.99). Additionally, the flywheel group experience large CSA increments in the RFMID, VLPROX and VLMID of the right leg (d=1.00-1.84). On average, flywheel squat training largely produced greater force during exercise compared to the barbell squat training (29.2 vs. 12.2 N·kg-1; d=5.95), whereas the barbell squat training produced moderately greater power output (10.5 vs. 9.7; d=0.52). Barbell squat training seems to be more effective for VM hypertrophy whereas flywheel squat triggers greater RF and VL hypertrophy as complementary to regular field-based soccer practice and competition within a short range of time (6 weeks) during the in-season. These findings can be considered also from either strength or reconditioning perspective based on the increase in the quadriceps muscles' CSA as mechanism underlying strength/power adaptations.



#2 Associations between match participation, maturation, physical fitness, and hormonal levels in elite male soccer player U15: a prospective study with observational cohort

Reference: BMC Pediatr. 2022 Apr 11;22(1):196. doi: 10.1186/s12887-022-03257-7.

Authors: Ebrahim Eskandarifard, Hadi Nobari, Filipe Manuel Clemente, Rui Silva, Ana Filipa Silva, Antonio José Figueiredo

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Summary: The aims of this study were to analyze the relationships between minutes of play (MP) and maturity status, fitness, and hormonal levels and to explain how those measures influence the time of play. Twenty-six youth soccer players U15 participated in this study over a full-season period. Anthropometric measures, maturity status, growth hormone (GH), insulin-like growth factor and physical levels such as maximal oxygen uptake (VO2max), fatigue index, countermovement jump (CMJ) performance were collected. At the end-season, players were assessed in 6 different tests over four days. VO2max largely correlated with GH (r = 0.57) and CMJ (r = 0.51). Also, GH largely correlated with CMJ (r = 0.55). MP had moderate correlations with VO2max (r = 0.44) and CMJ (r = 0.42). Multiple linear regression with maturation, physical fitness and hormonal levels explained R2 of 0.62 of the MP (F (8, 17) = 3.47, p = 0.015). Although each independent variable alone was not able to determine the playing time, when using the interactions, the model significantly explained the MP. The combination of maturity status, physical fitness, and hormonal levels seem to play a determinant role in explaining the match participation in youth soccer players.



#3 COVID-19 Confinement Effects on Game Actions during Competition Restart in Professional Soccer Players

Reference: Int J Environ Res Public Health. 2022 Apr 2;19(7):4252. doi: 10.3390/ijerph19074252.

Authors: Abraham García-Aliaga, Moisés Marquina, Ignacio Refoyo Román, Diego Muriarte Solana, Juan A Piñero Madrona, Roberto López Del Campo, Fabio Nevado Garrosa, Daniel Mon-López

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Summary: The main objective of the present study was to compare high-intensity actions in a week of three matches before and after the COVID-19 lockdown. The observational methodology was used. This study analysed 551 professional soccer players from 22 different Spanish teams (LaLiga Smartbank 2019-2020) by a multi-camera tracking system and associated software (Mediacoach®, Spain). Variables of distances per minute and totals, travelled at High Intensity (HIR), Very High Intensity (VHIR), Sprint (HSR), player's maximum speed, average speed, and the number of efforts in VHIR and HSR were analysed in the first and second half of the games, the full match, as well as in relation to the playing position. Players who participated in the same number of matches pre- and post-COVID-19 showed an increase in the total minutes played, p < 0.05, and small decreases in game actions, p < 0.05, with an effect size between 0.21 and 0.45, while players who participated in different number of matches pre- and post-COVID-19 showed a performance decrease, p < 0.05, with a size effect between 0.13 and 0.51; this was evident, particularly, for midfielders, p < 0.05, with a size effect between 0.39 and 0.75. The results seem to show that the playing intensity after COVID-19 confinement did not lead to large performance losses, except for midfielders who were the most involved players and showed a higher decrease in performance. The main findings of this study could provide insight to football coaches for rotations in starting line-ups and game substitutions, so as not to affect the intensity levels of the competitions.



#4 A Simple Field Tapping Test for Evaluating Frequency Qualities of the Lower Limb Neuromuscular System in Soccer Players: A Validity and Reliability Study

Reference: Int J Environ Res Public Health. 2022 Mar 23;19(7):3792. doi: 10.3390/ijerph19073792.

Authors: Safouen Chaabouni, Rihab Methnani, Badria Al Hadabi, Majid Al Busafi, Mahfoodha Al Kitani, Khalifa Al Jadidi, Pierre Samozino, Wassim Moalla, Nabil Gmada

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Summary: Over the years, the foot tapping test protocol has been proposed by scientists to identify the capabilities of the lower limb neuromuscular system in the medical context; however, to our knowledge, no studies have established its usefulness and relationship to athletic performance. The aim of the present study was to test the reliability, criterion validity and sensitivity of a new foot tapping (TAP) test, and to examine its relationship with proxies of athletic performance in soccer players. Forty voluntary soccer players of two different levels participated in this study (20 players from the national level: age: 22.6 ± 2.5 years and 20 players from regional level: 25.1 ± 3.6 years). They performed the TAP test on two separate occasions to test its relative and absolute reliability. To examine the criterion validity of the TAP test, all participants performed four types of jumps, sprint tests, agility tests, the Wingate test and the finger tapping test considered a gold standard tapping test. The sensitivity was assessed with national and regional player levels. The TAP test presented a high relative and absolute reliability with intra-class correlation coefficient ICC > 0.90, standard errors of measurement SEM < 5% and mean difference ±95% limits of agreement equal to 0.2 ± 0.8 tap·s-1. National level players showed a higher TAP score (p < 0.001; dz = 1.96, large) compared to regional players (9.68 ± 1.41 tap·s-1 vs. 7.28 ± 1.01 tap·s-1, respectively) and the value of area under curve measured by the receiver operating characteristic curve technique was 0.95 (95% CI: 0.827-0.990). The TAP test showed a significant association with the finger tapping test (r = 0.84, p < 0.001), whereas no correlation was seen between the TAP test and all the other physical tests measured. The TAP test could be considered a valid and reliable test to assess lower limb neuromuscular ability in soccer players.



#5 Sports Performance Tests for Amputee Football Players: A Scoping Review

Reference: Int J Environ Res Public Health. 2022 Apr 6;19(7):4386. doi: 10.3390/ijerph19074386.

Authors: Agnieszka Magdalena Nowak, Jolanta Marszalek, Bartosz Molik

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Summary: This scoping review aims to identify sports performance tests for amputee football players and to critically analyze the methodological quality, validation data, reliability, and standardization of sport-specific tests to indicate the best-fitting tests. Electronic database searches were conducted between January 2019 and October 2021. Twelve articles met the inclusion criteria. Qualitative assessment of each study was conducted by STROBE checklist. Twenty-nine sports performance tests were identified. No sports performance test fully met all three criteria associated with the qualitative assessment of tests. The critical appraisal of the articles demonstrates a gap in study design, settings, and main results description. Some inconsistencies were found in the methodological descriptions of tests assessing the same motor skill. A STROBE score of 13 points was considered a satisfactory score for the article (it was obtained by 8 of the 12 studies). The weakest point of the analyzed studies was the description of how the test group size was accessed and later obtained. No test was found that was simultaneously presented as valid, reliable, and standardized. The authors can recommend the use of the two-sports performance tests that are the closest to ideal: the L test and the YYIRT1.



#6 The Relationship between Different Large-Sided Games and Official Matches on Professional Football Players' Locomotor Intensity

Reference: Int J Environ Res Public Health. 2022 Apr 1;19(7):4214. doi: 10.3390/ijerph19074214.

Authors: Romualdo Caldeira, Élvio Rúbio Gouveia, Andreas Ihle, Adilson Marques, Filipe Manuel Clemente, Helder Lopes, Ricardo Henriques , Hugo Sarmento

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Summary: Large-sided games (LSG) are commonly used in the training contexts for providing either technical/tactical or locomotor/physiological stimuli. Despite natural similarities with the official match, the locomotor profile seems to be different, which must be considered by the coaches to identify compensatory strategies for achieving the ideal dose of training. The aim of this study was two-fold: (1) to investigate the locomotor demands imposed by LSGs and the official matches; and (2) to compare the effect of different pitch sizes' LSG conditions in the locomotor demands. This study followed an observational design. Sixteen professional football players from the same team (26.3 ± 3.0 years old) were included. The study was conducted over four weeks. The same GK + 10 × 10 + GK play format with different pitch sizes (i.e., area per player ranging between 195 m2 to 291 m2) was analyzed. Three official matches were also collected in which the 10 most demanding minutes were considered for further comparisons. Only the same players who participated in matches were considered in comparison with the LSG. The data were obtained using a 10-Hz global positioning system technology. Total distance (TD) and mechanical work (MW) scores increased 20% and 23%, respectively, between the smallest and biggest pitch sizes (p < 0.001). There was a significant difference in locomotor intensity metrics between opponents from different positions on the table (p = 0.001). The biggest LSG (i.e., 291 m2 per player) was the only one that required similar levels of locomotor intensity as required in the official full match. The present study demonstrates that LSG pitch size variation requires different locomotor intensities. Bigger pitch sizes cause an increase in TD and MW. In addition, considering the position on the table, the level of opponents induces different TD covered. Finally, the largest LSG simulates the official match more accurately.



#7 Reliability of a Qualitative Instrument to Assess High-Risk Mechanisms during a 90° Change of Direction in Female Football Players

Reference: Int J Environ Res Public Health. 2022 Mar 31;19(7):4143. doi: 10.3390/ijerph19074143.

Authors: Alba Aparicio-Sarmiento, Raquel Hernández-García, Antonio Cejudo, José Manuel Palao, Pilar Sainz de Baranda

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Summary: Sidestep cuts between 60° and 180° and one-leg landings have been identified as the main mechanisms of ACL injuries in several sports. This study sought to determine intra- and inter-rater reliability of a qualitative tool to assess high-risk movements in a 90° change of direction when the test is applied in a real framework of sport practice. Female footballers from two teams (n = 38) participated in this study and were asked to perform 90° cutting trials to each side, which were simultaneously filmed from a frontal and a sagittal view. A total of 61 cases were selected for 2D qualitative observational analysis by three raters. Poor reliability was found among each pair of raters as well as moderate reliability when the Cutting Movement Assessment Score (CMAS) was given by the same rater at different moments, but with too high a minimum detectable change. On the other hand, raters presented a significant, as well as moderate-to-good intra-rater reliability for most items of the CMAS tool. There was, however, non-significant reliability between observers in rating most check-points of the tool. For these reasons, more objective guidelines and clearer definitions for each criterion within the CMAS, as well as a longer, standardised training period for novel observers, would be highly recommended to improve the reliability of this tool in an applied context with female footballers.



#8 Intra and Inter-Observer Reliability and Repeatability of Metatarsus Adductus Angle in Recreational Football Players: A Concordance Study

Reference: J Clin Med. 2022 Apr 6;11(7):2043. doi: 10.3390/jcm11072043.

Authors: Eduardo Pérez Boal, Carlos Martin-Villa, Ricardo Becerro de Bengoa Vallejo, Marta Elena Losa Iglesias, Bibiana Trevissón Redondo, Israel Casado Hernández, César Calvo Lobo, David Rodríguez Sanz

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Summary: Metatarsus adductus (MA) is a congenital foot deformity often unrecognized at birth. There is adduction of the metatarsals, supination of the subtalar joint, and plantarflexion of the first ray. The aims of this study were to assess the intra and inter-reader reliability of the radiographic MA measurement angles used in the literature. All consecutive recreational football players who practice activity more than 5 h/week over 21 years of age with MA by roentgenographic evaluation on weight-bearing dorsoplantar images were included in a cross-sectional study. Controls were matched to cases according to age and gender. We assess all radiographic measurements to evaluate metatarsus adductus with the different measurements frequently used in the literature: Sgarlato, modified Sgarlato, Rearfoot, Root, Engel, modified Engel, Kite, Kilmartin, modified Kilmartin, Simons, and Laaveg & Ponseti. The variables measured in 80 weight-bearing dorsoplantar foot radiographs show excellent reliability ranging p > 0.900 in Sgarlato and modified Sgarlato with low SEM, CV, and MCD. Rearfoot, Root, Engel, modified Engel, Kite, Kilmartin, Simons, Laaveg & Ponseti, and modified Kilmartin's angles showed intra or inter reliability with ICC lower than <0.900, systematic differences between intersession or inter observers, or high MCD value. It is more suitable to measure the MA angle with the Sgarlato and modified Sgarlato techniques to show higher reliability and repeatability for intra and inter-observer.



#9 The Effect of Acute Caffeine Ingestion on Tactical Performance of Professional Soccer Players

Reference: Nutrients. 2022 Mar 31;14(7):1466. doi: 10.3390/nu14071466.

Authors: Rodrigo Freire de Almeida, Israel Teoldo da Costa, Guilherme Machado, Natalia Madalena Rinaldi, Rodrigo Aquino, Jason Tallis, Neil David Clarke, Lucas Guimaraes-Ferreira

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Summary: In soccer, physical, tactical, and decision-making processes are highly important facets of successful performance. Caffeine has well established effects for promoting both physical and cognitive performance, but the translation of such benefits specifically for soccer match play is not well established. This study examined the effects of acute caffeine ingestion on tactical performance during small-sided games (SSG) in professional soccer players. Nineteen soccer players (22 ± 4 years) underwent a randomized, counterbalanced, crossover, double-blind placebo-controlled trial. The protocol consisted of 5 bouts of 5-min SSG with 3 players plus a goalkeeper in each team (3 + GK × 3 + GK) with each SSG separated by 1 min rest intervals. Tactical performance was assessed using the system of tactical assessment in soccer (FUT-SAT). Prior to each experimental trial, participants ingested caffeine (5 mg·kg-1) or a placebo 60 min before the protocol. Overall, caffeine ingestion resulted in an increased ball possession time when compared to the placebo. When the offensive and defensive core principles were analyzed, the results were equivocal. Caffeine resulted in positive effects on some tactical decisions during the protocol, but it was deleterious or promoted no observed effect on other of the core tactical principles. Caffeine ingestion resulted in less offensive (during SSG3) and defensive (SSG 2, SSG3, and SSG4) errors. Caffeine ingestion also resulted in higher total offensive success during SSG 1 and SSG2, but it was detrimental during SSG3. Additionally, total defensive success was lower for the caffeine conditions during SSG 2 and SSG5 when compared to the placebo. In conclusion, caffeine influenced aspects of tactical decisions in soccer, resulting in fewer offensive and defensive errors, although it may be deleterious considering other tactical parameters. Future studies may clarify the effects of caffeine ingestion on specific decision-making parameters in soccer.



#10 Perceived Social Support, Reinjury Anxiety, and Psychological Readiness to Return to Sport in Soccer Players

Reference: J Sport Rehabil. 2022 Apr 11;1-7. doi: 10.1123/jsr.2021-0181. Online ahead of print.

Authors: Dale Forsdyke, Daniel Madigan, Adam Gledhill, Andy Smith

Summary: The burden of sports injury in soccer is high, and return to sport outcomes following injury are often poor. This is compounded by a current lack of understanding surrounding the factors that may optimize psychological readiness to return to sport. Consequently, in the present study, we aim to further our understanding of these issues by examining the role of perceived social support in predicting psychological readiness to return to sport. In doing so, we extend previous research by examining whether reinjury anxiety is a mediating factor in this relationship. A sample of 150 previously injured soccer players (mean age = 25.32 y) completed measures of perceived social support, reinjury anxiety during rehabilitation, and psychological readiness to return to sport. Mediation analyses showed that reinjury anxiety partly accounted for the positive relationship between perceived social support and psychological readiness to return to sport. These findings suggest that injured soccer players with higher perceptions of social support will experience less reinjury anxiety during rehabilitation and, as a consequence, will be more psychologically ready upon return to sport.



#11 Discovering Oculometric Patterns to Detect Cognitive Performance Changes in Healthy Youth Football Athletes

Reference: J Healthc Inform Res. 2019 Feb 8;3(4):371-392. doi: 10.1007/s41666-019-00045-4. eCollection 2019 Dec.

Authors: Gaurav N Pradhan, Jamie M Bogle, Michael J Cevette, Jan Stepanek

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Summary: In this paper, we focus on the application of oculometric patterns extracted from raw eye movements during a mental workload task to assess changes in cognitive performance in healthy youth athletes over the course of a typical sport season. Oculometric features pertaining to fixations and saccades were measured on 116 athletes in pre- and post-season testing. Participants were between 7 and 14 years of age at pre-season testing. Due to varied developmental rates, there were large interindividual performance differences during a mental workload task consisting of reading numbers. Based on different reading speeds, we classified three profiles (slow, moderate, and fast) and established their corresponding baselines for oculometric data. Within each profile, we describe changes in oculomotor function based on changes in cognitive performance during the season. To visualize these changes in multidimensional oculometric data, we also present a multidimensional visualization tool named DiViTo (diagnostic visualization tool). These experimental, computational informatics and visualization methodologies may serve to utilize oculometric information to detect changes in cognitive performance due to mild or severe cognitive impairment such as concussion/mild traumatic brain injury, as well as possibly other disorders such as attention deficit hyperactivity disorders, learning/reading disabilities, impairment of alertness, and neurocognitive function.



#12 Professional football training strategies during home confinement in the COVID-19 pandemic

Reference: J Sports Med Phys Fitness. 2022 Apr 12. doi: 10.23736/S0022-4707.22.13143-9. Online ahead of print.

Authors: Paolo Albino, Antonio Ponzo, Stefano D'Ottavio, Gioacchino Pollara, Angelo Ventura, F Rodia

Summary: SARS-COVID-19 emergency forced athletes to train at home on their own and mostly unsupervised, making it difficult to provide training solutions. The aims of the study were 1) to collect data and experiences from a Serie A male football team, a top-level female football team and a male young elite football team; 2) to compare data from lockdown and pre-lockdown period; 3) to report changes in training strategies adopted to overcome logistical constraints and 4) to evaluate their congruence to cardio, strength and stretching recommendation mentioned above; 5) to report compliance through player daily feedback. Three different professional football teams were enrolled. From March 16, 2020 to April 13, 2020, data for each team were recorded weekly and compared to a standard training period (October 15-November 15, 2019) from the same groups. The Rate of Perceived Exertion (RPE), Visual Analogue Scale (VAS) and Total Quality of Recovery (TQR) values were used to compare the two periods using The Student t-test and Pearson test. Each group chose a different training approach. Between the pre-lockdown and the lockdown period, there was no significant difference in the VAS, TQR and RPE indexes. Other else players' compliance differed between the groups during the lockdown period. Most athletes maintained a high level of training during the COVID-19 forced isolation, thanks to the help of team athletic trainers who provide functional tools and indications customized for each differ. Athletes' feedback and compliance differed according to their gender and age. Monitoring with live video sessions and social group sharing among younger players improved compliance and aggregation.



#13 The relationship between team-level and league-level injury rate, type and location in a professional football league

Reference: J Sci Med Sport. 2022 Mar 30;S1440-2440(22)00080-9. doi: 10.1016/j.jsams.2022.03.017.

Authors: Donna Lu, Alan McCall, Mark Jones, Rob Duffield

Summary: The aim was to describe the relationship between team- and league-level variability of injury rate, type, and location over 6 seasons in professional Australian football (A-League). Injury incidence, type and location were collected from all A-League teams (n = 10) for 6 consecutive seasons (2012/13 to 2017/18) via a standardised injury surveillance system. Intra-class correlation and coefficient of variation were calculated to assess the between-season variability of injury measures for each team. To determine the relationship between team-level injury variability on league-level injury rates, Marginal Coefficient of Determination to Coefficient of Determination were then calculated from generalised linear mixed models. This allowed determination between season trends, where league-level injury incidence, type- and location rates as the response variables, season as the predictor variable and teams as random intercepts. The majority of teams showed poor to moderate correlations for between-season injury rates (intra-class correlation: r = 0.319-0.831), but also showed low-moderate variability between-seasons for injury rate (coefficient of variation 34 ± 22%). League injury rates were stable, though were reduced in 2015/16 compared to 2012/13 (β = 0.738; p = 0.011). Joint/Ligament injuries had coinciding significant reduction in 2015/16 (p = 0.001). The model variance showed the reduction of Joint/Ligament injuries was league-wide rather than team-specific (Marginal Coefficient of Determintion = 0.23; Coefficient of Determination = 0.23). In the A-League, low between-season injury rate variability from teams contributed to a stable league-level injury trend over seasons. A reduction in league injury rate in 2015/16 was mirrored by league-wide Joint/Ligament injury rates, without specific effect by team.



#14 Knee and hip agonist-antagonist relationship in male under-19 soccer players

Reference: PLoS One. 2022 Apr 15;17(4):e0266881. doi: 10.1371/journal.pone.0266881. eCollection 2022.

Authors: Filipe Rosa, Hugo Sarmento, João Pedro Duarte, Joel Barrera, Francisco Loureiro, Vasco Vaz, Nestor Saavedra, António José Figueiredo

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Summary: The purpose of this study was to evaluate the strength of the knee flexors and extensors and hip abductor and adductor muscles in young soccer players. Twenty-three male under-19 soccer players participated in this study (age: 17.7 ± 0.2 years; height: 173.0 ± 1.1 cm; body mass: 66.1 ± 1.3 kg). Body composition was measured using a bioelectrical impedance (InBody770), and the dynamometry was performed by an isokinetic dynamometer (Biodex System 3) for knee flexion and extension, and by an isometric dynamometer (Smart Groin Trainer), for hip adduction and abduction. Comparisons were made between dominant members (D) vs. non-dominant members (ND) and adductors vs. abductors (ADD:ABD) using the Wilcoxon test. There were statistically significant differences in the peak torques between the dominant and non-dominant members in the flexion function (Z = -4.198, p < 0.01) and in the extension function (Z = -4.197, p < 0.01) of the knee in concentric muscular action, and the flexion (Z = -4.198, p < 0.01) and in the extension (Z = -4.198, p < 0.01) of the knee in eccentric muscular action. No statistically significant differences were obtained in the conventional ratio (Z = -0.456, p = 0.648) nor the functional ratio (Z = -0.335, p = 0.738) between D and ND members. There were no statistically significant differences between adductors and abductors at the moment of strength for absolute values (N). The reference absolute and normalized to the weight values and the ADD:ABD can be used as a guideline for classifying players in screening and comparison in return tests to sports practice after an injury.



#15 Facilitating national football teams return to training and competition during the COVID-19 pandemic

Reference: BMJ Open Sport Exerc Med. 2022 Apr 10;8(2):e001295. doi: 10.1136/bmjsem-2021-001295. eCollection 2022.

Authors: Andrew Guard, Anne Brenneman, Matt Bradley, George T Chiampas

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Summary: Provide a robust framework to provide a safe environment for return to training and competition of the US national soccer teams following domestic and international travel. US Soccer COVID-19 working group created a return to play manual for its national teams, prescribing discrete phases to return to training and competition. This was underpinned by strict health and safety and travel protocols for specific venues and persons. This was complemented by an aggressive testing cadence and isolation policies for delegations (players, internal and external support staff). Between September 2020 and April 2021, there were nine events for males and females at the youth, senior and Paralympic level, with international opponents hosted domestically. In total, 6590 point of care (POC) (n=1810) and PCR (n=4780) tests combined were run. Overall positivity rate for players and staff in male events of 0.10% (n=2) and 0.00% (n=0) for females were recorded. Staff positivity rate was 0.14% overall, and external vendors 0.10%. Total POC and PCR positives in male events (n=2) occurred either the day of arrival or the following day. The implementation of strictly adhered to protocols and testing cadences yielded low positivity rates within team delegations. By comparison, initial league-wide COVID-19 testing in mid-2020 in other sports reported league-wide positivity rates of 2.9% (National Football League), 2.7% (Major League Soccer) and 5.3% (National Basketball Association). The English Premier League reported an increase in positivity rate in early 2021 from 1.22% to 1.74%.With the implementation of regimented protocols and stringent testing, it is possible to hold elite-level international sporting competitions involving long-haul travel while ensuring continued safety during a global pandemic.



#16 A Longitudinal Study on the Evolution of the Four Main Football Leagues Using Artificial Intelligence: Analysis of the Differences in English Premier League Teams

Reference: Res Q Exerc Sport. 2022 Apr 19;1-9. doi: 10.1080/02701367.2021.2019661. Online ahead of print.

Authors: Abraham García-Aliaga, Moisés Marquina Nieto, Javier Coterón, Asier Rodríguez-González, Javier Gil Ares, Ignacio Refoyo Román

Summary: The aim of this study was to analyze the evolution of the four most important leagues and to identify if there are differences between the English Premier League and the rest of the European leagues.  Each team was characterized according to a set of 52 variables including offensive, defensive, and buildup 10 variables that were computed from OPTA's on-ball event records of the matches for main national leagues between the 2014 and 2018 seasons. To test the evolution of leagues, the t-SNE dimensionality reduction technique was used. To better understand the differences between leagues and teams, the most discriminating variables were obtained as a set of rules discovered by RIPPER, a machine learning algorithm.  The evolution of playing styles has meant that teams in the major European leagues seem to 15 be approaching homogeneity of technical-tactical behavior. Despite this, a distinction can be seen between the English teams concerning the rest of the teams in the other leagues, determined by fewer free kicks, fewer long passes but more vertical, more errors in ball control but greater success in dribbling.  These results provide important knowledge and practical applications because of the study of the different variables and performance indicators among the best football championships.



#17 There's No Sport Without Spectators - Viewing Football Games Without Spectators During the COVID-19 Pandemic

Reference: Front Psychol. 2022 Mar 31;13:860747. doi: 10.3389/fpsyg.2022.860747. eCollection 2022.

Authors: Ilan Tamir

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Summary: The presence of sports fans in the stands is considered a natural and essential element of sporting events. Beyond the atmosphere fans create and the color they add to the game, their presence reflects the idea that the game is more than a competition between two teams -it is a grand battle between communities and identities, which is also the reason that fans are willing to sacrifice so much on behalf of their team. As is other areas of life, the COVID-19 pandemic created an unusual situation, in which sporting events were held without spectators in the stadium stands. In many places around the world, professional sporting activities were permitted but spectators were not allowed into the stadiums due to social distancing restrictions. The current study examines this unique situation and through it, gains an understanding of fans' beliefs concerning the significance of spectators and their presence in the stadium. Through in-depth interviews with football fans who regularly attend games (in the pre-pandemic period), the current study explores football fans' experiences as they viewed "ghost games" (where teams played to empty stadiums). Findings show that this unique situation, caused by the global pandemic, heightened fans' deep-rooted connection to sports and to their favorite team, and also exacerbated the social, emotional, and professional implications of viewing football games with no spectators.



#18 Effect of 2002 FIFA World Cup: Point of Attachment That Promotes Mass Football Participation

Reference: Front Psychol. 2022 Mar 30;13:857323. doi: 10.3389/fpsyg.2022.857323. eCollection 2022.

Authors: Taeahn Kang, Jeongbeom Hahm, Hirotaka Matsuoka

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Summary: The 2002 FIFA World Cup Korea/Japan significantly promoted football in the host countries. However, it remains unclear how the event has changed mass football (soccer in North America) participation. This study applies points of attachment (POA)-a well-developed concept in the field of sport management-to the 2002 FIFA World Cup and aims to examine which specific POA promoted football participation frequency immediately after the event and the present frequency of football participation in the host countries. An online questionnaire survey was conducted in South Korea (n = 405) and Japan (n = 398). The samples included adults aged > 19 as of the hosting date of the 2002 World Cup. Hierarchical regression analyses were performed to test all the datasets by employing four POAs (players, coaches, national teams, and football) as independent variables. Multiple control variables (e.g., nationality and age) and two dependent variables (football participation frequency immediately after the event and the present frequency of football participation) were included in the model. Correspondingly, those who had a higher attachment to each point during the event showed a higher frequency of football participation immediately after the event. In contrast, only two POAs (players and coaches) led to a higher frequency of present football participation. These findings provide the first empirical evidence highlighting the influence of the 2002 FIFA World Cup on mass football participation depending on the POA.



#19 Effects of Chronological Age, Relative Age, and Maturation Status on Accumulated Training Load and Perceived Exertion in Young Sub-Elite Football Players

Reference: Front Physiol. 2022 Mar 31;13:832202. doi: 10.3389/fphys.2022.832202. eCollection 2022.

Authors: José Eduardo Teixeira, Ana Ruivo Alves, Ricardo Ferraz, Pedro Forte, Miguel Leal, Joana Ribeiro, António J Silva, Tiago M Barbosa, António M Monteiro

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Summary: The aims of this study were 1) to analyze the influence of chronological age, relative age, and biological maturation on accumulated training load and perceived exertion in young sub-elite football players and 2) to understand the interaction effects amongst age grouping, maturation status, and birth quartiles on accumulated training load and perceived exertion in this target population. A 6-week period (18 training sessions and 324 observation cases) concerning 60 young male sub-elite football players grouped into relative age (Q1 to Q4), age group (U15, U17, and U19), and maturation status (Pre-peak height velocity (PHV), Mid-PHV, and Post-PHV) was established. External training load data were collected using 18 Hz global positioning system technology (GPS), heart-rate measures by a 1 Hz short-range telemetry system, and perceived exertion with total quality recovery (TQR) and rating of perceived exertion (RPE). U17 players and U15 players were 2.35 (95% CI: 1.25-4.51) and 1.60 (95% CI: 0.19-4.33) times more likely to pertain to Q1 and Q3, respectively. A negative magnitude for odds ratio was found in all four quartile comparisons within maturation status (95% CI: 6.72-0.64), except for Mid-PHV on Q2 (95% CI: 0.19-4.33). Between- and within-subject analysis reported significant differences in all variables on age group comparison measures (F = 0.439 to 26.636, p = 0.000 to 0.019, η2 = 0.003-0.037), except for dynamic stress load (DSL). Between-subject analysis on maturity status comparison demonstrated significant differences for all training load measures (F = 6.593 to 14.424, p = 0.000 to 0.037, η2 = 0.020-0.092). Interaction effects were found for age group x maturity band x relative age (Λ Pillai's = 0.391, Λ Wilk's = 0.609, F = 11.385, p = 0.000, η2 = 0.391) and maturity band x relative age (Λ Pillai's = 0.252, Λ Wilk's = 0.769, F = 0.955, p = 0.004, η2 = 0.112). Current research has confirmed the effects of chronological age, relative age, and biological maturation on accumulated training load. Perceived exertion does not seem to show any differences concerning age group or maturity status. Evidence should be helpful for professionals to optimize the training process and young football players' performance.



#20 Prevalence and burden of health problems in top-level football referees

Reference: Sci Med Footb. 2022 Apr 18;1-8. doi: 10.1080/24733938.2022.2055782. Online ahead of print.

Authors: Christian Moen, Thor Einar Andersen, Ben Clarsen, Gitte Madsen-Kaarød, Torstein Dalen-Lorentsen

Summary: Top-level football referees take decisions during strenuous physical activity, and often under great mental pressure. Despite their central role in a football match, little is known about referees' health problems, particularly in female referees. The aim was to investigate the prevalence and burden of health problems in female and male top-level referees. Fifty-five Norwegian male and female top-level referees reported health problems (injuries and illnesses) in pre-season and during the 2020 competitive season, using the Oslo Sports Trauma Research Center Questionnaire on Health Problems (OSTRC-H2). We recorded data for 49 weeks with a compliance of 98%. On average, 34% (95% CI 31-36%) of referees reported at least one health problem each week, and 20% (95% CI 19-22%) reported substantial health problems. Female referees reported more health problems than male referees, and on-field referees reported more health problems than assistant referees. Gradual-onset injuries were most prevalent and caused the greatest absence from training and matches, whereas illnesses represented only a small portion to the overall burden of health problems. The injury incidence was three injuries per athlete-year (95% CI 2.5-3.5) and 11 injuries per 1000 match hours (95% CI 7-18). The illness incidence was 1.4 illnesses per athlete-year (95% CI 1.1-1.8). Injuries to the lower legs and feet represented the highest burden of health problems. Top-level referees, especially females, reported a high prevalence of health problems. Gradual-onset injuries to the lower leg and foot represented the highest injury burden.



#21 Incidence and Clinical Relevance of COVID-19 in a Population of Young Competitive and Elite Football Players: A Retrospective Observational Study

Reference: Sports Med Open. 2022 Apr 15;8(1):54. doi: 10.1186/s40798-022-00442-x.

Authors: Lidia Colangelo, Alessandra Volpe, Elisabetta Toso, Massimo Magnano, Mario Matta, Chiara Vignati, Andrea Marchini, Luca Semperboni, Luca Stefanini, Fiorenzo Gaita

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Summary: The COVID-19 pandemic dramatically changed lifestyle worldwide, including sport. A comprehensive evaluation of the prevalence of cardiac involvement in COVID-19 is essential to finalize a safe protocol for resuming elite sport. The aim of this study is to evaluate incidence of cardiac involvement and COVID-19 impact on athletic performance. This retrospective observational study analysed the data collected from consecutive competitive athletes who performed medical-sports examinations at the J Medical Center from March 2020 to March 2021. All athletes periodically performed a molecular test using a nasopharyngeal swab to detect COVID-19 infection. Positive athletes performed laboratory (cardiac troponin T-cTnT) and instrumental (echocardiography, stress test, Holter ECG) investigations following recovery to identify any cardiac involvement. Cardiac magnetic resonance imaging (MRI) was performed in case of abnormal findings at first-level evaluation. Among 238 athletes (median age 20 years), 77 contracted COVID-19, mainly males (79%) with a median age of 16 years. Fifty-one athletes (66%) presented mild symptoms, and none required hospitalization. Evaluation for resuming sport was performed after a median of 30 days from the first positive test. Abnormal findings were obtained in 13 cases (5 athletes [6%] with elevated cTnT values; 13 athletes [17%] with arrhythmias on Holter ECG and/or during stress test; 2 athletes [3%] anomalies at echocardiography). Cardiac MRI discovered abnormalities in 9 cases, but none of these was clearly related to COVID-19 and none fulfilled acute myocarditis criteria. No negative impact on athletic performance was observed, and none of the athletes developed persistent COVID-related symptoms. Our registry confirms the predominantly self-limiting illness in young athlete population. The incidence of clear COVID-19-related structural myocardial injury was very low, but transient exertional ventricular arrhythmias or pericardial effusion was observed without significant impact on athletic performance. Implemented screening for return to activity is likely reasonable only in moderate-to-severe symptomatic athletes.


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