Latest research in football - week 1 - 2021

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

Following studies were retrieved for this week:

#1 History of ankle sprain affect the star excursion balance test among youth football players
Reference: Foot Ankle Surg. 2020 Oct 21;S1268-7731(20)30219-8. doi: 10.1016/j.fas.2020.10.004. Online ahead of print.
Authors: Hideaki Nagamoto, Haruki Yaguchi, Hiroyuki Takahashi
Summary: The relationship between the results of the Star Excursion Balance Test (SEBT) and lateral ankle sprain (LAS) among youth football players was investigated. The dominant leg and history of LASs were asked from 33 male youth football players. The SEBT in the anterior, posterolateral, and posteromedial directions were measured for both limbs. The relationship between the history of LAS and reach difference over 4 cm between the dominant and nondominant legs in each direction was statistically analyzed. The number of players with the history of LAS, whose dominant/nondominant reach difference was over 4 cm in the anterior direction, was significantly higher to that in players without a history of LAS in both the dominant (94% vs. 63%, p = 0.02) and nondominant (100% vs. 25%, p = 0.02) legs. Youth football players with a history of LAS showed reach deficit in the anterior direction in the SEBT.

#2 COVID-19, indications for professional football teams and referees training resumption
Reference: J Infect Dev Ctries. 2020 Oct 31;14(10):1084-1089. doi: 10.3855/jidc.13436.
Authors: Matthew Gavino Donadu, Angelo Renato Pizzi, Paolo Zeppilli
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Summary: These indications were drawn up by the Federal Medical-Scientific Commission (FIGC Commission), supplemented for the necessary time by some experts on the subject; currently they are intended to grant the highest achievable guarantee level to protect the health of players, referees and all professionals involved in case of resumption of collective training (Document dated 18 April 2020). They were designed to minimize the risk of contagion were thus based on the fact that during that phase of SARS-COV-2 virus pandemic (COVID-19) and in the absence of an effective vaccine, the zero-contagion risk did not exist and does not exist to date. Those guidelines have been updated on the basis of ongoing medical-scientific evidence, taking into account the indications given by the Technical-Scientific Committee and the opinion of the Italian Football Federation representatives, during a meeting that took place on May 7 and was transmitted to FIGC on May 11, 2020; these indications are to be considered stringent and binding for the purposes of sport training resumption.

#3 Multiple athletic performances, maturation, and Functional Movement Screen total and individual scores across different age categories in young soccer players
Reference: J Exerc Rehabil. 2020 Oct 27;16(5):432-441. doi: 10.12965/jer.2040546.273. eCollection 2020 Oct.
Authors: Igor Bakalľár, Jaromír Šimonek, Janka Kanásová, Bohumila Krčmárová, Matúš Krčmár
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Summary: The purpose of this study was to evaluate differences in multiple athletic performances, and to examine associations between athletic performance and Functional Movement Screen (FMS) in young soccer players. Forty-one soccer players were tested on peak height velocity (PHV), 5-, 10-, and 30-m sprint times, 505 change of direction (505 COD), Y-reactive agility tests, countermovement jump (CMJ), and squat jump (SJ) height. Significant main effects (P<0.01) were recorded in all tests except FMS total score whereas the U16 group outperformed U12 and U14 in almost each test. However, when the results were adjusted to the PHV 7 of 11 tests were nonsignificant. Significant associations were recorded between trunk stability push-up (TSPU) and 5 m (P=0.04) and 505 COD (preferred) times (P=0.01), and SJ height (P=0.03) in the U12. In the U14, significant associations were recoded between TSPU and SJ (P<0.01) and CMJ height (P=0.03). In the U16, significant associations were recorded between deep overhead squat and 5-m sprint time (P=0.02) and CMJ height (P=0.04). Results of this study indicate that athletic performance in young soccer players is multidimensional in nature, and it is a consequence of several factors including maturation, different training strategies, and movement proficiency.

#4 Effects of purposeful soccer heading on circulating small extracellular vesicle concentration and cargo
Reference: J Sport Health Sci. 2020 Nov 12;S2095-2546(20)30155-1. doi: 10.1016/j.jshs.2020.11.006. Online ahead of print.
Authors: Eric R Muñoz, Jaclyn B Caccese, Brittany E Wilson, Kyle T Shuler, Fernando V Santos, Carolina T Cabán, John J Jeka, Dianne Langford, Matthew B Hudson
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Summary: Considering the potential cumulative effects of repetitive head impact (HI) exposure, we need sensitive biomarkers to track short- and long-term effects. Circulating small extracellular vesicles (sEVs) (<200 nm) traffic biological molecules throughout the body and may have diagnostic value as biomarkers for disease. The purpose of this study was to identify the microRNA (miRNA) profile in circulating sEVs derived from human plasma following repetitive HI exposure. Healthy adult (ages 18-35 years) soccer players were randomly assigned to 1 of 3 groups: the HI group performed 10 standing headers, the leg impact group performed 10 soccer ball trapping maneuvers over 10 min, and the control group did not participate in any soccer drills. Plasma was collected before testing and 24 h afterward, and sEVs were isolated and characterized via nanoparticle tracking analysis. Next-generation sequencing was utilized to identify candidate microRNAs isolated from sEVs, and candidate microRNAs were analyzed via quantitative polymerase chain reaction. In silico target prediction was performed using TargetScan and miRWalk programs, and target validation was performed using luciferase reporter vectors with a miR-7844-5p mimic in HEK293 cells. Plasma sEV concentration and size were not affected across time and group following repetitive HI exposure. After 24 h, the HI read count from next-generation sequencing showed a 4-fold or greater increase in miR-92b-5p, miR-423-5p, and miR-24-3p and a 3-fold or greater decrease in miR-7844-5p, miR-144-5p, miR-221-5p, and miR-22-3p. Analysis of quantitative polymerase chain reaction revealed that leg impact did not alter the candidate miRNA levels. To our knowledge, miR-7844-5p is a previously unknown miRNA. We identified 8 miR-7844-5p mRNA targets: PPP1R1B, LIMS1, ATG12, MAP1LC3B, ITGA1, MAPK1, GSK3B, and MAPK8. Collectively, these data indicate repetitive HI exposure alters plasma sEV miRNA content, but not sEV size or number. Furthermore, for the first time we demonstrate that previously unknown miR-7844-5p targets mRNAs known to be involved in mitochondrial apoptosis, autophagy regulation, mood disorders, and neurodegenerative disease.

#5 Modeling ball possession dynamics in the game of football
Reference: Phys Rev E. 2020 Oct;102(4-1):042120. doi: 10.1103/PhysRevE.102.042120.
Authors: A Chacoma, N Almeira, J I Perotti, O V Billoni
Summary: In this paper, we study interaction dynamics in the game of football-soccer in the context of ball possession intervals. To do so, we analyze a database comprising one season of the five major football leagues of Europe. Using this input, we developed a stochastic model based on three agents: two teammates and one defender. Despite its simplicity, the model is able to capture, in good approximation, the statistical behavior of possession times, pass lengths, and number of passes performed. In the last section, we show that the model's dynamics can be mapped into a Wiener process with drift and an absorbing barrier.

#6 A multidisciplinary investigation into "playing-up" in academy football according to age phase
Reference: J Sports Sci. 2020 Nov 17;1-11. doi: 10.1080/02640414.2020.1848117. Online ahead of print.
Authors: Adam Kelly, Mark R Wilson, Daniel T Jackson, Daniel E Goldman, Jennifer Turnnidge, Jean Côté, Craig A Williams
Summary: In an attempt to facilitate more appropriate levels of challenge, a common practice in academy football is to play-up talented youth players with chronologically older peers. However, the context of playing-up in academy football is yet to be empirically explored. Thus, the purpose of this study was to examine the multidimensional factors that differentiated players who play-up from those who do not. Ninety-eight participants from a single football academy were examined within their age phase: Foundation Development Phase (FDP; under-9 to under-11; n = 40) and Youth Development Phase (YDP; under-12 to under-16; n = 58). Drawing upon the FA Four Corner Model, 27 factors relating to Technical/Tactical, Physical, Psychological, and Social development were assessed. Following MANOVA analysis within both the FDP and YDP, significant differences were observed for Technical/Tactical and Social sub-components (P < 0.05). Further differences were observed for Physical and Psychological sub-components (P < 0.05) within the YDP. In sum, Technical/Tactical and Social characteristics appeared to differentiate those who play-up compared to those who do not within the FDP. In the YDP however, there were measures representing all sub-components from the FA Four Corner Model. Subsequently, it is suggested coaches and practitioners consider these holistic factors when playing-up youth football players within relevant age-phases.

#7 Can psychological characteristics, football experience, and player status predict state anxiety before important matches in Danish elite-level female football players?
Reference: Scand J Med Sci Sports. 2020 Nov 17. doi: 10.1111/sms.13881. Online ahead of print.
Authors: Esben Elholm Madsen, Tina Hansen, Sidsel Damsgaard Thomsen, Jeppe Panduro, Georgios Ermidis, Peter Krustrup, Morten B Randers, Carsten Hvid Larsen, Anne-Marie Elbe, Johan Wikman
Summary: Elite football can make players' feel nervous, and personality characteristics, as well as experience, affect how well pressure is handled before important games. Studying the psychological characteristics of female football players can provide information on how well psychological pressure is handled and provide knowledge on how to support players in order to improve performance. Based on a sample of 128 female elite football players from 8 top-level teams, the present study investigates whether psychological characteristics, football experience / player status in elite female football players can predict state anxiety before important matches. Our results outline that high age and national team experience negatively predicted most of the trait anxiety subscales. In line with previous research no psychological differences were found between goalkeepers, defenders, midfielders, and strikers while starting players revealed to have significantly lower trait anxiety. When measuring before important matches we found that somatic state anxiety was negatively associated with senior national team experience, and positively associated with worry trait anxiety and fear of failure. Cognitive state anxiety was negatively associated with hope for success and positively associated with somatic and worry trait anxiety. Self-confidence was positively associated with youth national team experience and negatively associated with worry trait anxiety. It can be concluded that psychological characteristics and national team experience are both important for optimal state anxiety before important matches in elite-level women's football. Implications for practice and future research are discussed.

#8 A Review of On-Field Investigations into the Biomechanics of Concussion in Football and Translation to Head Injury Mitigation Strategies
Reference: Ann Biomed Eng. 2020 Nov 16. doi: 10.1007/s10439-020-02684-w. Online ahead of print.
Authors: Bethany Rowson, Stefan M Duma
Summary: This review paper summarizes the scientific advancements in the field of concussion biomechanics in American football throughout the past five decades. The focus is on-field biomechanical data collection, and the translation of that data to injury metrics and helmet evaluation. On-field data has been collected with video analysis for laboratory reconstructions or wearable head impact sensors. Concussion biomechanics have been studied across all levels of play, from youth to professional, which has allowed for comparison of head impact exposure and injury tolerance between different age groups. In general, head impact exposure and injury tolerance increase with increasing age. Average values for concussive head impact kinematics are lower for youth players in both linear and rotational acceleration. Head impact data from concussive and non-concussive events have been used to develop injury metrics and risk functions for use in protective equipment evaluation. These risk functions have been used to evaluate helmet performance for each level of play, showing substantial differences in the ability of different helmet models to reduce concussion risk. New advances in head impact sensor technology allow for biomechanical measurements in helmeted and non-helmeted sports for a more complete understanding of concussion tolerance in different demographics. These sensors along with advances in finite element modeling will lead to a better understanding of the mechanisms of injury and human tolerance to head impact.

#9 Injury incidence and burden in a youth elite football academy: a four-season prospective study of 551 players aged from under 9 to under 19 years
Reference: Br J Sports Med. 2020 Nov 16;bjsports-2020-102859. doi: 10.1136/bjsports-2020-102859. Online ahead of print.
Authors: Olivier Materne, Karim Chamari, Abdulaziz Farooq, Adam Weir, Per Hölmich, Roald Bahr, Matt Greig, Lars R McNaughton
Summary: The objective was to investigate the incidence and burden of injuries by age group in youth football (soccer) academy players during four consecutive seasons. All injuries that caused time-loss or required medical attention (as per consensus definitions) were prospectively recorded in 551 youth football players from under 9 years to under 19 years. Injury incidence (II) and burden (IB) were calculated as number of injuries per squad season (s-s), as well as for type, location and age groups. A total of 2204 injuries were recorded. 40% (n=882) required medical attention and 60% (n=1322) caused time-loss. The total time-loss was 25 034 days. A squad of 25 players sustained an average of 30 time-loss injuries (TLI) per s-s with an IB of 574 days lost per s-s. Compared with the other age groups, U-16 players had the highest TLI incidence per s-s (95% CI lower-upper): II= 59 (52 to 67); IB=992 days; (963 to 1022) and U-18 players had the greatest burden per s-s: II= 42.1 (36.1 to 49.1); IB= 1408 days (1373 to 1444). Across the cohort of players, contusions (II=7.7/s-s), sprains (II=4.9/s-s) and growth-related injuries (II=4.3/s-s) were the most common TLI. Meniscus/cartilage injuries had the greatest injury severity (95% CI lower-upper): II= 0.4 (0.3 to 0.7), IB= 73 days (22 to 181). The burden (95% CI lower-upper) of physeal fractures (II= 0.8; 0.6 to 1.2; IB= 58 days; 33 to 78) was double than non-physeal fractures. At this youth football academy, each squad of 25 players averaged 30 injuries per season which resulted in 574 days lost. The highest incidence of TLI occurred in under-16 players, while the highest IB occurred in under-18 players.

#10 Genu varum and football participation: Does football participation affect lower extremity alignment in adolescents?
Reference: Knee. 2020 Nov 13;27(6):1801-1810. doi: 10.1016/j.knee.2020.10.007. Online ahead of print.
Authors: A Isın, T Melekoğlu
Summary: Genu varum is one of the most common anatomical variations of knee alignment which is considered a risk factor for anterior knee pain and anterior cruciate ligament injury among football players. Considering that millions of children participate in high-level football training, the purpose of this study was to determine the genu varum development in adolescent football players and non-athlete peers. The hypothesis of this study was that genu varum incidence was higher in adolescent football players compared with non-athletic peers. The design was a cross-sectional study. Two-hundred and thirty-seven male football players (FG) and aged-matched and anthropometrically similar non-athletes (CG) were recruited into the study. The quadriceps angle and intercondylar-intermalleolar distance were measured to evaluate the leg alignment. The distance between the medial edges of the condyles and malleoli was measured in millimeters using a digital caliper while angle measurements were performed using a photographic technique in a standing position. To analyze the variables, comparison, correlation and regression statistical tests were performed. The intercondylar-intermalleolar distance and quadriceps angle values were significantly higher in FG than CG in all ages. In FG, a very strong correlation was found between number of training years and the intercondylar-intermalleolar distance. The prevalence of genu varum was markedly higher in FG than CG (~37% vs. 2%, respectively) based on intercondylar-intermalleolar distance. This study determined that the prevalence of genu varum and abnormal quadriceps angles in adolescent football players is significantly higher compared with their non-athletic peers.

#11 Aerobic fitness and game performance indicators in professional football players; playing position specifics and associations
Reference: Heliyon. 2020 Nov 3;6(11):e05427. doi: 10.1016/j.heliyon.2020.e05427. eCollection 2020 Nov.
Authors: Toni Modric, Sime Versic, Damir Sekulic
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Summary: The aim of this study was to identify associations between aerobic fitness (AF) and game performance indicator (GPI) in elite football. Participants were professional football players (males, n = 16; age: 23.76 ± 2.64; body height: 181.62 ± 7.09 cm; body mass: 77.01 ± 6.34 kg). AF testing was conducted by direct measurement and included VO2max, running speed at aerobic threshold (AeT), and running speed at anaerobic threshold (AT). The GPI were collected by the position-specific performance statistics index (InStat index). The players were observed over one competitive half-season, resulting in 82 game performances, grouped according to the positions in game: defenders (n = 39), midfielders (n = 32) and forwards (n = 11). VO2max was not found to be a good discriminator of AF among different playing positions. AeT (F-test = 26.36. p = 0.01) and AT (F-test = 7.25, p = 0.01) were highest among midfielders, and lowest among forwards. No correlations were found between AF and GPI. This study confirmed that AeT and AT are better indicators of AF than VO2max in football players at different playing positions. The lack of associations between AF and GPI was discussed with regard to calculation of InStat as a GPI.

#12 Physical exercises for preventing injuries among adult male football players: A systematic review
Reference: J Sport Health Sci. 2020 Nov 11;S2095-2546(20)30152-6. doi: 10.1016/j.jshs.2020.11.003. Online ahead of print.
Authors: Jorge Pérez-Gómez, José Carmelo Adsuar, Pedro E Alcaraz, Jorge Carlos-Vivas
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Summary: Football is the most practised sport in the world and is associated with the risk of injuries in the players. Some studies have been published that identify injury prevention programmes, but there is no review of the full body of evidence on injury prevention programmes for use by football coaches. The aim of this article was to carry out a systematic review of published studies on injury prevention programmes for adult male footballers, identify points of common understanding and establish recommendations that should be considered in the design of injury prevention strategies. PubMed and EMBASE databases were used to identify relevant published articles using the following keywords: 'soccer', 'injury', and 'prevention'. A total of 2512 studies were identified initially, but only 11 studies met the inclusion criteria, and their outcomes are presented. Results revealed that injury prevention programmes in football have focused on strength training, proprioceptive training, multicomponent programmes (balance, core stability, functional strength and mobility) and warm-up programmes. Based on results from the studies analysed, football players can lower the incidence of match and training injuries by participating in dynamic warm-up programmes that include preventive exercises before games or during training sessions, and by adding strength, balance and mobility training to the training sessions.

#13 Structure, Intensity and Player Duels in Under-13 Football Training in Switzerland
Reference: Int J Environ Res Public Health. 2020 Nov 11;17(22):E8351. doi: 10.3390/ijerph17228351.
Authors: Jonas Uebersax, Ralf Roth, Tobias Bächle, Oliver Faude
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Summary: We evaluated the structure (i.e., the different training parts), contents (i.e., the various activities used), intensity and occurrence of contact situations and headers during training sessions in under-13 football in Switzerland. A total of 242 players from 20 different teams on average aged 11.4 (SD 0.7) years participated. The participants were filmed during a typical training session while they were equipped with a heart rate sensor. The sessions were systematically recorded to allow for detailed analyses. Furthermore, a preliminary and explorative analysis of the influence of the level of play on these results was conducted. The overall findings indicated that training included 33.4% playing forms, 29.5% training forms, 28.4% inactivity time and 8.7% athletics. The highest heart rates were achieved in the playing forms (166 min-1, 83% HRmax) compared to the other two activities (training forms 154 min-1, 77% HRmax; athletics 150 min-1, 75% HRmax). Each player had 12.8 duels and 0.6 headers per training. Overall, most duels were conducted from the anterior direction. Playing forms induce higher cardio-circulatory load as well as a better learning environment. Potentially dangerous situations like contact with other players or headers occurred in a single player on average every six min during a training session.

#14 Consistency and identifiability of football teams: a network science perspective
Reference: Sci Rep. 2020 Nov 12;10(1):19735. doi: 10.1038/s41598-020-76835-3.
Authors: D Garrido, D R Antequera, J Busquets, R López Del Campo, R Resta Serra, S Jos Vielcazat, J M Buldú
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Summary: We investigated the ability of football teams to develop a particular playing style by looking at their passing patterns. Using the information contained in the pass sequences during matches, we constructed the pitch passing networks of teams, whose nodes are the divisions of the pitch for a given spatial scale and links account for the number of passes from region to region. We translated football passings networks into their corresponding adjacency matrices. We calculated the correlations between matrices of the same team to quantify how consistent the passing patterns of a given team are. Next, we quantified the differences with other teams' matrices and obtained an identifiability parameter that indicates how unique are the passing patterns of a given team. Consistency and identifiability rankings were calculated during a whole season, allowing to detect those teams of a league whose passing patterns are different from the rest. Furthermore, we found differences between teams playing at home or away. Finally, we used the identifiability parameter to investigate what teams imposed their passing patterns over the rivals during a given match.

#15 Metabolomics profiling of plasma, urine and saliva after short term training in young professional football players in Saudi Arabia
Reference: Sci Rep. 2020 Nov 12;10(1):19759. doi: 10.1038/s41598-020-75755-6.
Authors: Mansour A Alzharani, Ghareeb O Alshuwaier, Khalid S Aljaloud, Naser F Al-Tannak, David G Watson
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Summary: Metabolomics profiling was carried out to observe the effect of short-term intensive physical activity on the metabolome of young Saudi professional football players. Urine, plasma and saliva were collected on 2 days pre- and post-training. An Orbitrap Exactive mass spectrometer was used to analyze the samples. A reversed-phase (RP) column was used for the analysis of non-polar plasma metabolites, and a ZIC-pHILIC column was used for the analysis of plasma, saliva and urine. mzMine was used to extract the data, and the results were modelled using Simca-P 14.1 software. There was no marked variation in the metabolite profiles between pre day 1 and 2 or between post day 1 and 2 according to principal components analysis (PCA). When orthogonal partial least squares (OPLSDA) modelling was also used, and then models could be fitted based on a total number of metabolites of 75, 16 and 32 for urine, plasma and saliva using hydrophilic interaction chromatography (HILIC) and 6 for analysis of plasma with reversed-phase (RP) chromatography respectively. The present study concludes that acylcarnitine may increase post-exercise in football players suggesting that they may burn fat rather than glucose. The levels of carnitine metabolites in plasma post-exercise could provide an important indicator of fitness.

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