Latest research in football - week 17 - 2020

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 The Influence of Match Status on Ball Possession in High Performance Women's Football
Reference: Front Psychol. 2020 Mar 23;11:487. doi: 10.3389/fpsyg.2020.00487. eCollection 2020.
Authors: Maneiro R, Losada JL, Casal CA, Ardá A
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Summary: The objective of this study was to examine the effect of the situational match status variable on the ball possession of the teams that participated in the 2015 FIFA Women's World Cup. The 52 games played during the championship have been collected, and 3,740 ball possessions made by the teams were analyzed. The teams have been divided into successful and unsuccessful. Three types of analysis have been carried out: a univariate analysis for both groups with the categorical and continuous variables selected; a bivariate analysis, using chi-square tests and the exact Fischer test; and finally, a multivariable technique such as the decision trees was incorporated. The available results show significant differences between the two groups considered. Specifically, there are significant differences between winning and losing teams in terms of match status. The results of the post hoc test have shown that unsuccessful teams make few ball possessions with a winning match status, most of the possessions are performed when they are losing. Instead, successful teams make more possessions when they are winning than when they are losing. Also, spend more time keeping the ball in their offensive zone, and completing a greater number of passes in it. The results of the decision tree identified that the unsuccessful teams have more ball possessions in forward and middle lines with a draw during the first half, while in the second, a large percentage of possessions are made with an unfavorable match status. Instead, the successful teams have more ball possessions in the first part with a draw, while in the second it happens with a favorable match status.

#2 Changes of Differential Urinary Metabolites after High-Intensive Training in Teenage Football Players
Reference: Biomed Res Int. 2020 Mar 18;2020:2073803. doi: 10.1155/2020/2073803. eCollection 2020.
Authors: Cao B, Liu S, Yang L, Chi A
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Summary: The mechanism underlying the fatigue of football players is closely related to the energy depletion and accumulation of metabolites; the present study tries to explore the metabolic mechanism in teenage football players during exercise-induced fatigue. 12 teenage football players were subjected to three groups of combined training by using a cycle ergometer, with the subjective Rating of Perceived Exertion (RPE) as a fatigue criterion. The following indicators were measured in each group after training: maximum oxygen uptake (VO2max), anaerobic power, and average anaerobic power. Urine samples were collected before and after the training. Gas chromatography-mass spectrometry (GC-MS) was performed for the metabonomics analysis of the samples. The metabolism data was analyzed by using principal component analysis (PCA) and orthogonal partial least squares analysis (OPLS-DA), through the Kyoto Encyclopedia of Genes and Genomes (KEGG) database to confirm the potential differences between metabolites, and the MetPA database was used to analyze the related metabolic pathways. There was no significant difference between the maximal oxygen uptakes among the three groups. Compared with group 1, the maximum and average anaerobic power in group 3 significantly decreased (p < 0.05) at the end of training. GC-MS detected 635 metabolites in the urine samples. Through PCA, OPLS-DA analysis, and KEGG matching, 25 different metabolites (3↑22↓) that met the conditions were finally selected. These different metabolites belonged to 5 metabolic pathways: glycine-serine-threonine metabolism, citrate cycle, tyrosine metabolism, nitrogen metabolism, and glycerophospholipid metabolism. During the combined exercise of aerobic and anaerobic metabolism, teenage football players show a significant decrease in anaerobic capacity after fatigue. The metabolic mechanism of exercise fatigue was related to disorders in amino acid and energy metabolism.

#3 Long-Term Recreational Football Training and Health in Aging
Reference: Int J Environ Res Public Health. 2020 Mar 21;17(6). pii: E2087. doi: 10.3390/ijerph17062087.
Authors: Imperlini E, Mancini A, Orrù S, Vitucci D, Di Onofrio V, Gallè F, Valerio G, Salvatore G, Liguori G, Buono P, Alfieri A
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Summary: This narrative review aims to critically analyze the effects of exercise on health in aging. Here we discuss the main clinical and biomolecular modifications induced by long-term recreational football training in older subjects. In particular, the effects induced by long-term recreational football training on cardiovascular, metabolic and musculo-skeletal fitness, together with the modifications in the muscle expression of hallmarks related to oxidative metabolism, DNA repair and senescence suppression pathways and protein quality control mechanisms will be provided. All these topics will be debated also in terms of preventing non-communicable metabolic diseases, in order to achieve successful aging over time.

#4 Changes in countermovement jump performance and subjective readiness-to-train scores following a simulated soccer match
Reference: Eur J Sport Sci. 2020 Apr 17:1-25. doi: 10.1080/17461391.2020.1757764. [Epub ahead of print]
Authors: Lombard W, Starling L, Wewege L, Lambert M
Summary: The study investigated whether countermovement jump (CMJ) metrics and subjective responses to a readiness-to-train questionnaire (RTT-Q) tracked simulated match-induced acute fatigue. This was a randomized cross-over repeated measures study. Participants were assigned into one of two groups; CONTROL or LIST. The LIST group performed the Loughborough Intermittent Shuttle Run (LIST), which was designed to simulate the demands of a soccer match. The CONTROL performed light physical activity at an intensity of <65% of maximal heart rate. Each group performed three CMJ's and completed an RTT-Q before (PRE), and again at 24 h and 48 h after the LIST and/or CONTROL interventions. At 24 h there were significant differences in RTT-Q answers between the Pre and 24 h for the LIST group for questions; "Do you feel physically strong today?" and "Do you have muscle soreness today?" (p = 0.02 and 0.0008, respectively). The questions "Do you feel mentally strong today?" and "Do you have muscle soreness today?" (p=0.02 and p = 0.0001 respectively) were the only questions that had a significant difference between Pre and 48 h for the LIST group. None of the CMJ metrics (LIST or CONTROL) changed significantly at any stage of the experiment. Although fatigue was detected by changes in the RTT-Q at 24 h and 48 h after the LIST, none of the CMJ metrics changed. These findings suggest that subjective measures are more sensitive to low-level fatigue than objective measures, thus effective monitoring should include both.

#5 Unlocking the potential of big data to support tactical performance analysis in professional soccer: A systematic review
Reference: Eur J Sport Sci. 2020 Apr 16:1-16. doi: 10.1080/17461391.2020.1747552. [Epub ahead of print]
Authors: Goes FR, Meerhoff LA, Bueno MJO, Rodrigues DM, Moura FA, Brink MS, Elferink-Gemser MT, Knobbe AJ, Cunha SA, Torres RS, Lemmink KAPM
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Summary: In professional soccer, increasing amounts of data are collected that harness great potential when it comes to analysing tactical behaviour. Unlocking this potential is difficult as big data challenges the data management and analytics methods commonly employed in sports. By joining forces with computer science, solutions to these challenges could be achieved, helping sports science to find new insights, as is happening in other scientific domains. We aim to bring multiple domains together in the context of analysing tactical behaviour in soccer using position tracking data. A systematic literature search for studies employing position tracking data to study tactical behaviour in soccer was conducted in seven electronic databases, resulting in 2338 identified studies and finally the inclusion of 73 papers. Each domain clearly contributes to the analysis of tactical behaviour, albeit in - sometimes radically - different ways. Accordingly, we present a multidisciplinary framework where each domain's contributions to feature construction, modelling and interpretation can be situated. We discuss a set of key challenges concerning the data analytics process, specifically feature construction, spatial and temporal aggregation. Moreover, we discuss how these challenges could be resolved through multidisciplinary collaboration, which is pivotal in unlocking the potential of position tracking data in sports analytics. Over the recent years, there has been a considerable growth in studies on tactical behaviour using position tracking data, especially in the domains of sports science and computer science. Yet both domains have contributed distinctly different studies, with the first being more focused on developing theories and practical implications, and the latter more on developing techniques. Considerable opportunities exist for collaboration between sports science and computer science in the study of tactics in soccer, especially when using position tracking data. Collaborations between the domains of sports science and computer science benefit from a stronger dialogue yielding a cyclical collaboration. We have proposed a framework that could serve as the foundation for the combination of sports science and computer science expertise in tactical analysis in soccer.

#6 The Federated Practice of Soccer Influences Hamstring Flexibility in Healthy Adolescents: Role of Age and Weight Status
Reference: Sports (Basel). 2020 Apr 13;8(4). pii: E49. doi: 10.3390/sports8040049.
Authors: Ponce-González JG, Gutiérrez-Manzanedo JV, De Castro-Maqueda G, Fernández-Torres VJ, Fernández-Santos JR
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Summary: The aim of this study was to compare the hamstring flexibility between federated soccer and non-federated adolescents, and also to evaluate the effect of age and weight status on hamstring flexibility. The participants were 234 students (11-18 years old) divided into: (i) G1: non-federated (n = 127), and (ii) G2: federated in soccer (n = 107). The deep flexion of the trunk (DF) test and the sit and reach test (SRT) were performed. G2 showed higher values for the DF and SRT compared to G1 (p < 0.05). Both flexibility tests correlated positively (r = 0.4, p < 0.001). Body mass index (BMI) was negatively correlated with the DF test (r = -0.3, p < 0.001), but not with the SRT. Divided by BMI, the underweight and normal weight groups had higher scores in the DF test compared with the overweight and obese groups (p < 0.001). BMI was negatively correlated with hamstring flexibility. Federated soccer students present higher scores of hamstring flexibility.

#7 Lower Limb Kinetic Asymmetries in Professional Soccer Players With and Without Anterior Cruciate Ligament Reconstruction: Nine Months Is Not Enough Time to Restore "Functional" Symmetry or Return to Performance
Reference: Am J Sports Med. 2020 Apr 15:363546520912218. doi: 10.1177/0363546520912218. [Epub ahead of print]
Authors: Read PJ, Michael Auliffe S, Wilson MG, Graham-Smith P
Summary: Residual between-limb deficits are a possible contributing factor to poor outcomes in athletic populations after anterior cruciate ligament reconstruction (ACLR). Comprehensive appraisals of movement strategies utilized by athletes at key clinical milestones during rehabilitation are warranted. The purpose was to examine kinetic parameters recorded during a countermovement jump with a force platform in healthy professional soccer players and to compare their performance with those who had undergone ACLR at different stages of their rehabilitation. A total of 370 male professional soccer players attended a physical screening assessment where they performed at counter jump movement protocol on dual force plates and were divided into 4 groups: group 1 (<6 months post-ACLR), group 2 (6-9 months post-ACLR), group 3 (>9 months post-ACLR), and group 4 (healthy matched controls). Players in the later phases of rehabilitation increased their jump performance; however, values were significantly lower than those of healthy matched controls (P > .05). Significant between-limb differences were present for both eccentric- and concentric-phase variables (P < .05), with effect sizes ranging from moderate to very large (d = 0.42-1.35). Asymmetries were lower in players who were further away from surgery; however, between-limb differences remained significantly greater in players >9 months after ACLR versus matched controls-specifically, for concentric impulse, concentric peak force, eccentric deceleration impulse, and eccentric deceleration rate of force development asymmetry (P < .05). Logistic regression identified concentric impulse asymmetry as being most strongly associated with a history of ACLR when group prediction analysis was performed (ACLR group 1, 2, or 3 vs matched controls), with odds ratios ranging from 1.50 to 1.91. Between-limb deficits in key eccentric and concentric loading parameters remain >9 months after ACLR, indicating a compensatory offloading strategy to protect the involved limb during an athletic performance task. Concentric impulse asymmetry could be considered an important variable to monitor during rehabilitation.

#8 Timing and Reasons Behind Single-Sport Specialization in Soccer: A Survey of 64 Major League Soccer Athletes
Reference: Sports Health. 2020 Apr 14:1941738120911373. doi: 10.1177/1941738120911373. [Epub ahead of print]
Authors: Knapik DM, Rizzone KH, Voos JE
Summary: Single-sport specialization at the exclusion of other sports has become increasingly popular in youth sporting culture. The purpose of this study was to survey Major League Soccer (MLS) athletes to examine factors influencing the timing of single-sport specialization in soccer. The hypothesis is that the majority of surveyed athletes will have participated in multiple sports prior to specialization and specialized primarily as a result of a coach's recommendation, with no significant impact on specialization timing stemming from birth or high school location, obtaining a collegiate scholarship, MLS experience, or position. Anonymous surveys were distributed to 3 MLS organizations and completed by MLS athletes during preseason physicals. Surveys evaluated the age and reason(s) behind an athlete's decision to specialize in soccer, birth location, geographic high school location for US-born athletes, participation in a developmental league, college scholarship, years in the MLS, and position played. Approximately 74% (64/86) of athletes returned completed surveys. Athletes reported beginning soccer at a mean age of 5.1 ± 2.1 years and specializing at age 12.6 ± 4.3 years. Athletes who participated in no other sports prior to specialization (P < 0.001), athletes reporting soccer to be their first sport played at an advanced level (P < 0.001), and athletes receiving a college scholarship (P = 0.02) specialized at a significantly younger age. Internationally born athletes specialized at significantly younger ages when compared with US-born athletes (P < 0.001). The majority of athletes participated in multiple sports prior to specialization and eventually specialized to focus exclusively on soccer. The timing of sport specialization in professional MLS athletes was not associated with multisport participation prior to specialization, playing soccer at an advanced level prior to other sports, receiving a college scholarship, or being born outside the United States. Timing of sport specialization is associated with multiple factors prior to athlete promotion to the MLS that warrant further investigation to better understand the impact of specialization on injury incidence, performance, and career length.

#9 Nutrition for Female Soccer Players-Recommendations
Reference: Medicina (Kaunas). 2020 Jan 10;56(1). pii: E28. doi: 10.3390/medicina56010028.
Authors: Dobrowolski H, Karczemna A, Włodarek D
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Summary: Soccer is one of the most popular sports in the world. As its number of players is increasing, the number of female players is also on the rise. However, there are limited data about how the diets of female soccer players should be designed. Thus, the aim of our work is to deliver concise nutritional recommendations for women practicing this sport. Based on a literature review, we emphasize that individual adjustment of the energy value of the diet is the key factor for the physical performance of female soccer players. Appropriate macronutrient intake makes it possible to achieve the proper energy value of the diet (5-10 g/kg body mass/day carbohydrates; 1.2-1.7 g/kg body mass/day proteins; <30% fats from energy). The micronutrients should be consumed in amounts corresponding to individual values recommended in national standards. Soccer players should pay special attention to the proper consumption of such micronutrients, as well as vitamins such as iron, calcium, and vitamin D. The right amount of fluid intake, consistent with the player's needs, is crucial in maximizing exercise performance. The diet of a female practicing soccer is usually characterized with low energy values, which increases the risk of various health consequences related to low energy availability. Monitoring the diets of female soccer players is, therefore, necessary.

#10 Scaling left ventricular mass in adolescent female soccer players
Reference: BMC Pediatr. 2020 Apr 13;20(1):157. doi: 10.1186/s12887-020-02043-7.
Authors: V Martinho D, Valente-Dos-Santos J, Coelho-E-Silva MJ, Gutiérrez AO, Duarte JP, Lourenço-Farinha P, Luz LGO, Gonçalves-Santos J, Machado DRL, Leite N, Conde J, Castanheira JM, Cumming SP, Sherar LB, Malina RM
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Summary: The aim of the study was to examine the contribution of chronological age (CA), skeletal maturation, training experience and concurrent body size descriptors, to inter-individual variance in left ventricular mass (LVM) among female adolescent soccer players. The sample included 228 female soccer players 11.8-17.1 years. Training experience defined as years of participation in competitive soccer (range 2-9 years), was obtained by interview. Stature, body mass and skinfolds (triceps, medial calf) were measured. Fat mass was estimated; Fat-free mass was derived. LVM was assessed by echocardiography. Skeletal maturity status was as the difference of skeletal age (SA, Fels method) minus CA. Fat-free mass was the most prominent single predictor of LVM (R2 = 36.6%). It was associated with an allometric coefficient close to linearity (k = 0.924, 95%CI: 0.737 to 1.112). A significant multiplicative allometric model including body mass, fat-free mass, CA, training experience and skeletal maturity status was also obtained (R = 0.684; R2 = 46.2%). Stature has limitations as a valid size descriptor of LVM. Body mass, fat-free mass, training experience, CA, body mass and skeletal maturity status were relevant factors contributing to inter-individual variability in LVM.

#11 Internal jugular vein compression applied during competitive female soccer season preserves functional and structural connectome organization
Reference: Brain Connect. 2020 Apr 13. doi: 10.1089/brain.2019.0729. [Epub ahead of print]
Authors: Dudley J, Yuan W, Diekfuss J, Barber Foss KD, DiCesare CA, Altaye M, Logan K, Leach J, Myer G
Summary: Characterization of, and evaluation of strategies to mitigate, the effects of sub-concussive impacts (SCI) on brain structure and function are crucial to understand potential long-term neurological risks associated with sports participation. In this study, we applied a graph theoretical framework to resting state functional magnetic resonance imaging (rs-fMRI) and diffusion tensor imaging (DTI) data to evaluate the efficacy of a jugular vein compression collar for preserving functional and structural measures of brain network organization in a cohort of female high school soccer players throughout a season of competitive play. Athletes were assigned to a collar (N = 72) or non-collar (N = 56) group before engaging in a season of play, during which head impact data were recorded via accelerometer for every practice and competition. Participants completed neuroimaging sessions before and following the season. Non-collar-wearing athletes exhibited significantly increased rs-fMRI-derived global clustering coefficients (p = 0.032) and DTI-derived modularity (p = 0.042), compared to collar-wearing athletes. No longitudinal changes in any graph measures were observed for the collar group (p > 0.05). The observed increase in graph measures in the non-collar group is congruent with previous studies of SCI and is similar to graph theoretical studies of traumatic brain injury. The absence of alterations in graph metrics in the collar group indicates a potential ameliorating effect of the collar device against network reorganization, in line with previous literature.

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