Latest research in football - week 46 - 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 How to Use Global Positioning Systems (GPS) Data to Monitor Training Load in the "Real World" of Elite Soccer
Reference: Front Physiol. 2020 Aug 20;11:944. doi: 10.3389/fphys.2020.00944. eCollection 2020.
Authors: Guillaume Ravé, Urs Granacher, Daniel Boullosa, Anthony C Hackney, Hassane Zouhal
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#2 Successful return to professional men's football (soccer) competition after the COVID-19 shutdown: a cohort study in the German Bundesliga
Reference: Br J Sports Med. 2020 Sep 24;bjsports-2020-103150. doi: 10.1136/bjsports-2020-103150. Online ahead of print.
Authors: Tim Meyer, Dietrich Mack, Katrin Donde, Oliver Harzer, Werner Krutsch, Annika Rössler, Janine Kimpel, Dorothee von Laer, Barbara C Gärtner
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Summary: The aim was to evaluate the restart of the German Bundesliga (football (soccer)) during the COVID-19 pandemic from a medical perspective. Participants were male professional football players from the two highest German leagues and the officials working closely with them. Our report covers nine match days spread over 9 weeks (May to July 2020). Daily symptom monitoring, PCR testing for SARS-CoV-2 RNA twice weekly, and antibody tests (on two occasions-early during the phase in May 2020 and in the week of the last match) were conducted. Target variables were: (1) onset of typical COVID-19 symptoms, (2) positive PCR results, and (3) IgG seroconversion against SARS-CoV-2. All detected seroconversions were controlled by neutralisation tests. Suspicious symptoms were reported for one player; an immediate additional PCR test as well as all subsequent diagnostic and antibody tests proved negative for coronavirus. Of 1702 regularly tested individuals (1079 players, 623 officials members), 8 players and 4 officials tested positive during one of the first rounds of PCR testing prior to the onset of team training, 2 players during the third round. No further positive results occurred during the remainder of the season. 694 players and 291 officials provided two serum samples for antibody testing. Nine players converted from negative/borderline to positive (without symptoms); two players who initially tested positive tested negative at the end of the season. 22 players remained seropositive throughout the season. None of the seroconversions was confirmed in the neutralisation test. Professional football training and matches can be carried out safely during the COVID-19 pandemic. This requires strict hygiene measures including regular PCR testing.

#3 Characteristics of Soccer Players Undergoing Primary Hip Arthroscopy for Femoroacetabular Impingement: A Sex- and Competitive Level-Specific Analysis
Reference: Am J Sports Med. 2020 Sep 23;363546520958697. doi: 10.1177/0363546520958697. Online ahead of print.
Authors: Niv Marom, Matthew S Dooley, Joost A Burger, Brenda Chang, Struan H Coleman, Anil S Ranawat, Bryan T Kelly, Danyal H Nawabi
Summary: Radiographic features of femoroacetabular impingement (FAI) are prevalent in kicking athletes, especially soccer players. However, there remains a paucity of data on the characteristics of symptomatic soccer players with an established diagnosis of FAI. The purpose was to report on patient demographics, injury, and clinical and radiographic characteristics in a large cohort of soccer players who underwent primary hip arthroscopy for FAI and to perform a sex- and competition level-specific analysis of these data. An institutional hip preservation registry containing 3318 consecutive primary hip arthroscopies for FAI performed between March 2010 and January 2016 was retrospectively reviewed for patients identified as soccer players. Patient demographics, injury characteristics, and clinical and radiographic findings were recorded, and sex- and competition level-specific differences were analyzed. A total of 421 hips (336 soccer players) were identified, including 257 (61.0%) men and 164 (39.0%) women. Of these, 105 (24.9%) were reported as highly competitive, 194 (46.1%) as competitive, 75 (17.8%) as recreational, and 47 (11.2%) did not report a level. The majority of the 336 soccer players (231 hips; 55%) reported chronic hip pain lasting >6 months with no acute injury at the initial visit. Alpha angle, coronal center-edge angle, and femoral version on computed tomography scan measured 64.5°± 12°, 32.3°± 9°, and 13.7°± 10° (mean ± SD), respectively. There were 230 (55%) hips with a type 2 anterior inferior iliac spine (AIIS), 78 (18.5%) with a type 1 AIIS, and 19 (4.5%) with a type 3 AIIS. When compared with male athletes, female athletes had more hip internal rotation on physical examination (14.9° vs 8°; P < .001), lower alpha angles (57.5° vs 68.5°; P < .001), and lower-grade AIIS morphology (P = .003). Acute injury as the reason for hip symptoms was most likely in the highly competitive group (P < .001). Female soccer players were more likely to have less severe clinical and radiographic findings than were male soccer players. Acute injury as the cause of hip symptoms was more common in highly competitive players. Focusing on soccer players with an established FAI diagnosis, the findings of this study suggest that there are sex- and competition level-based differences in the presentation, physical examination, and imaging characteristics among the players. These findings can better guide clinicians in the diagnostic evaluation of symptomatic soccer players with FAI and in tailoring treatment recommendations to specific cohorts.

#4 Soccer-related head injuries-analysis of sentinel surveillance data collected by the electronic Canadian Hospitals Injury Reporting and Prevention Program
Reference: Paediatr Child Health. 2019 Aug 30;25(6):378-384. doi: 10.1093/pch/pxz116. eCollection 2020 Oct.
Authors: Sarah Zutrauen, Steven McFaull, Minh T Do
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Summary: Participating in sports is a great way to gain physical, psychological, and social benefits. However, it also carries the risk of injury. Soccer is one of the most popular sports worldwide, and in recent years, there have been concerns about potential vulnerabilities to head injuries. The aim was to investigate soccer-related head injuries (SRHIs), using data from the electronic Canadian Hospitals Injury Reporting and Prevention Program (eCHIRPP) surveillance system. Specifically, we aim to compare characteristics of SRHI cases to all head injury cases within the eCHIRPP database. Descriptive analyses of emergency department (ED) injury surveillance data (2011 to 2017) for individuals aged 5 to 29 years from all participating eCHIRPP sites. Computation of proportionate injury ratios (PIR) comparing SRHIs to all head injuries reported to eCHIRPP, and 95% confidence intervals (CI). A total of 3,970 SRHIs were reported to eCHIRPP. Injuries were from contact with another player, the ball, ground, goal-post, and other causes. Of the injuries caused by contact with the ball, 9% were from purposely directing the ball with the head (heading). A higher proportion of concussions (PIR=1.32, 95% confidence interval [CI]: 1.27 to 1.37) and minor closed head injuries (PIR=1.20, 95% CI: 1.15 to 1.26) were observed in soccer players. Higher proportions of head injuries occurred in organized soccer and soccer played outdoors. However, admission to the ED for a SRHI was rare (PIR=0.40, 95% CI: 0.30 to 0.55). Overall, elevated proportions of brain injuries were observed among soccer players, however, these injuries were unlikely to result in a hospital admission. Moreover, purposely heading the ball contributed to few ED visits.

#5 Maturity-associated considerations for training load, injury risk, and physical performance within youth soccer: One size does not fit all
Reference: J Sport Health Sci. 2020 Sep 19;S2095-2546(20)30119-8. doi: 10.1016/j.jshs.2020.09.003. Online ahead of print.
Authors: Chris Towlson, Jamie Salter, Jack D Ade, Kevin Enright, Liam D Harper, Richard M Page, James J Malone
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Summary: Biological maturation can be defined as the timing and tempo of progress to achieve a mature state. The estimation of age of peak height velocity (PHV) or percentage of final estimated adult stature attainment (%EASA) is typically used to inform the training process in young athletes. In youth soccer, maturity-related changes in anthropometric and physical fitness characteristics are diverse among individuals, particularly around PHV. During this time, players are also at an increased risk of sustaining an overuse or growth-related injury. As a result, the implementation of training interventions can be challenging. The purpose of this review is to (1) highlight and discuss many of the methods that can be used to estimate maturation in the applied setting and (2) discuss the implications of manipulating training load around PHV on physical development and injury risk. We also have provided key stakeholders with a practical online tool for estimating player maturation status (see online supplementary maturity estimation tool(s)). Whilst estimating maturity using predictive equations is useful in guiding the training process, practitioners should be aware of its limitations. To increase the accuracy and usefulness of data, it is also vital that sports scientists implement reliable testing protocols at predetermined time-points.

#6 The brains of elite soccer players are subject to experience-dependent alterations in white matter connectivity
Reference: Cortex. 2020 Sep 1;132:79-91. doi: 10.1016/j.cortex.2020.07.016. Online ahead of print.
Authors: Zai-Fu Yao, Ilja G Sligte, David Moreau, Shulan Hsieh, Cheng-Ta Yang, K Richard Ridderinkhof, Neil G Muggleton, Chun-Hao Wang
Summary: Soccer is the only major sport with voluntary unprotected head-to-ball contact. It is crucial to determine if head impact through long-term soccer training is manifested in brain structure and connectivity, and whether such alterations are due to sustained training per se. Using diffusion tensor imaging, we documented a comprehensive view of soccer players' brains in a sample of twenty-five right-handed male elite soccer players aged from 18 to 22 years and twenty-five non-athletic controls aged 19-24 years. Importantly, none had recalled a history of concussion. We performed a whole-brain tract-based spatial statistical analysis, and a tract-specific probabilistic tractography method to measure the differences of white matter properties between groups. Whole-brain integrity analysis showed stronger microstructural integrity within the corpus callosum tract in soccer players compared to controls. Further, tract-specific probabilistic tractography revealed that the anterior part of corpus callosum may be the brain structure most relevant to training experience, which may put into perspective prior evidence showing corpus callosum alteration in retired or concussed athletes practicing contact sports. Intriguingly, experience-related alterations showed left hemispheric lateralization of potential early signs of concussion-like effects. In sum, we concluded that the observed gains and losses may be due to a consequence of engagement in protracted soccer training that incurs prognostic hallmarks associated with minor injury-induced neural inflammation.

#7 Player load in male elite soccer: Comparisons of patterns between matches and positions
Reference: PLoS One. 2020 Sep 21;15(9):e0239162. doi: 10.1371/journal.pone.0239162. eCollection 2020.
Authors: Terje Dalen, Tore Kristian Aune, Geir Håvard Hjelde, Gertjan Ettema, Øyvind Sandbakk, David McGhie
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Summary: Our primary aim was to explore the development of player load throughout match time (i.e., the pattern) using moving 5-min windows in an elite soccer team and our secondary aim was to compare player load patterns between different positions within the same team. The dataset included domestic home matches (n = 34) over three seasons for a Norwegian Elite League team. Player movements (mean ± SD age 25.5 ± 4.2 years, height 183.6 ± 6.6 cm, body mass 78.9 ± 7.4 kg) were recorded at 20 Hz using body-worn sensors. Data for each variable (player load, player load per meter, total distance, accelerations, decelerations, sprint distance, high-intensity running distance) were averaged within positions in each match, converted to z-scores and averaged across all matches, yielding one time series for each variable for each position. Pattern similarity between positions was assessed with cross-correlations. Overall, we observed a distinct pattern in player load throughout match time, which also occurred in the majority of individual matches. The pattern shows peaks at regular intervals (~15 min), each followed by a period of lower load, declining until the next peak. The same pattern was evident in player load per meter. The cross-correlation analyses support the visual evidence, with correlations ranging 0.88-0.97 (p < .001) in all position pairs. In contrast, no specific patterns were discernible in total distance, accelerations, decelerations, sprint distance and high-intensity running distance, with cross-correlations ranging 0.65-0.89 (p < .001), 0.32-0.64 (p < .005), 0.18-0.65 (p < .005 in nine position pairs), 0.02-0.38 (p < .05 in three pairs) and 0.01-0.52 (p < .05 in three pairs), respectively. This study demonstrated similarity in player load patterns between both matches and positions in elite soccer competition, which could indicate a physical "pacing pattern" employed by the team.

#8 The validity of small-sided games in predicting 11-vs-11 soccer game performance
Reference: PLoS One. 2020 Sep 21;15(9):e0239448. doi: 10.1371/journal.pone.0239448. eCollection 2020.
Authors: Tom L G Bergkamp, Ruud J R den Hartigh, Wouter G P Frencken, A Susan M Niessen, Rob R Meijer
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Summary: Predicting performance in soccer games has been a major focus within talent identification and development. Past research has mainly used performance levels, such as elite vs. non-elite players, as the performance to predict (i.e. the criterion). Moreover, these studies have mainly focused on isolated performance attributes as predictors of soccer performance levels. However, there has been an increasing interest in finer grained criterion measures of soccer performance, as well as representative assessments at the level of performance predictors. In this study, we first determined the degree to which 7-vs-7 small-sided games can be considered as representative of 11-vs-11 games. Second, we assessed the validity of individual players' small-sided game performance in predicting their 11-vs-11 game performance on a continuous scale. Moreover, we explored the predictive validity for 11-vs-11 game performance of several physiological and motor tests in isolation. Sixty-three elite youth players of a professional soccer academy participated in 11 to 17 small-sided games and six 11-vs-11 soccer games. In-game performance indicators were assessed through notational analysis and combined into an overall offensive and defensive performance measure, based on their relationship with game success. Physiological and motor abilities were assessed using a sprint, endurance, and agility test. Results showed that the small-sided games were faster paced, but representative of 11-vs-11 games, with the exception of aerial duels. Furthermore, individual small-sided game performance yielded moderate predictive validities with 11-vs-11 game performance. In contrast, the physiological and motor tests yielded small to trivial relations with game performance. Altogether, this study provides novel insights into the application of representative soccer assessments and the use of continuous criterion measures of soccer performance.

#9 Match metabolic power over different playing phases in a young professional soccer team
Reference: J Sports Med Phys Fitness. 2020 Aug;60(8):1170-1171. doi: 10.23736/S0022-4707.20.10879-X.
Authors: Andrea Licciardi, Gabriele Grassadonia, Andrea Monte, Luca P Ardigò

Summary: To fully describe soccer match-play metabolic demands, we must consider the different playing phases and namely ball possession (Wp), non-possession (Wnp), and inactive (Bi). Therefore, we aimed at estimating metabolic expenditure featuring the different playing phases by using GPS devices on 21 young players. Metabolic powers and playing phases collection was carried out by using GPS receivers and applying the “metabolic-GPS” approach. Match average metabolic powers resulted significantly different over different playing phases (p=0.008 and d=0.67, moderate). In particular match metabolic powers resulted higher during Wp and Wnp compared with Bi. During victories (V) compared with losses (L), Wp match average metabolic power resulted lower, while Bi power resulted higher. Our measured total distances covered per match (TD) resulted lower during Vs – significantly compared with draws and not significantly compared with Ls. We can hypothesize that 1) Wp is a team’s very demanding task and V can be achieved by limiting it as much as possible and 2) V can be achieved by limiting TDs as much as possible. Accurate soccer workload assessment over both training and matches confirms to be relevant for players physical performance assessment and physical preparation optimization.

#10 Short-term effects of maximal dynamic exercise on flow-mediated dilation in professional female soccer players
Reference: J Sports Med Phys Fitness. 2020 Aug;60(8):1159-1166. doi: 10.23736/S0022-4707.20.10681-9.
Authors: Daniela K Andaku, Bruno Archiza, Flávia R Caruso, Renata Trimer, André C Amaral, José C Bonjorno Jr, Claudio R de Oliveira, Shane A Phillips, Ross Arena, Audrey Borghi-Silva
Summary: Endothelial function assessment may provide important insights into the cardiovascular function and long-term effects of exercise training. Many studies have investigated the possible negative effects on cardiovascular function due to extreme athletic performance, leading to undesirable effects. The purposes of this study were to investigate the acute effects of maximal intensity exercise on endothelium-dependent vasodilation, and to understand the patterns of flow-mediated dilation (FMD) change following maximal exercise in elite female athletes with a high-volume training history. Twenty-six elite female soccer players (mean age, 22±4 years; BMI, 21±2 kg/m<sup>2</sup>; VO<inf>2max</inf>, 41±4 mL/kg/min) were evaluated. Brachial artery FMD was determined using high-resolution ultrasound at rest, and after 15 and 60 min of maximal cardiopulmonary exercise (CPX) testing on a treadmill. Flow velocity was measured at baseline and during reactive hyperemia at the same periods. Rest FMD was 12.4±5.5%. Peak diameter in response to reactive hyperemia was augmented after 15 min of CPX (3.5±0.4 vs. 3.6±0.4 mm, P<0.05), returning to resting values after 60 min. However, %FMD did not change among time periods. There were two characteristic patterns of FMD response following CPX. Compared to FMD at rest, half of the subjects responded with an increased FMD following maximum exercise (10.5±6.1 vs. 17.8±7.5%, P<0.05). The other subjects demonstrated a reduced FMD response following maximum exercise (14.2±4.3 vs. 10.9±3.2%, P<0.01). These results indicate that elite female soccer players presented robust brachial artery FMD at rest, with a heterogeneous FMD response to acute exercise with a 50% FMD improvement rate.

#11 Gender differences in instep soccer kicking biomechanics, investigated through a 3D human motion tracker system
Reference: J Sports Med Phys Fitness. 2020 Aug;60(8):1072-1080. doi: 10.23736/S0022-4707.20.10676-5.
Authors: Bruno Ruscello, Mario Esposito, Gianmarco Siligato, Laura Lunetta, Lorenzo Marcelli, Laura Pantanella, Paolo R Gabrielli, Stefano D'ottavio
Summary: This study aims at describing and comparing each other male and female soccer players kicking instep a stationary ball. The different measures we collected by the 3D motion capture system Movit G1 and the High-Speed Camera (240 fps) were considered as dependent variables, whereas the gender was considered as the independent one. Twenty soccer well trained non-professional players: 10 men (age: 25.3±6.5 yrs; height 1.80±0.07 m; body mass 76.9±13.2 kg) and 10 women (age: 19±3.34 yrs; height 1.64±0.07 m; body mass 58.2±7.2 kg) volunteered to participate in the study. Gender differences were found, with a statistical significance (P<0.05) or interesting magnitude (Cohen d>0.5). The most relevant ones were the differences in hip extension of the kicking leg when the foot of the supporting one touches the ground, just before the impact on the ball (independent sample t-Test; P=0.03; Cohen d=1.64) and the speed of the ball, reached immediately after kicking (P<0.001;d=1.23). These results, together with the greater pelvic acceleration shown by men compared to women, highlight the need to develop a gender-differentiated training model, in order to customize the kicking technique in women and to reduce the likelihood, currently higher than for men, of kicking related injuries.

#12 Reducing Injuries in Soccer (Football): an Umbrella Review of Best Evidence Across the Epidemiological Framework for Prevention
Reference: Sports Med Open. 2020 Sep 21;6(1):46. doi: 10.1186/s40798-020-00274-7.
Authors: Oluwatoyosi B A Owoeye, Mitchell J VanderWey, Ian Pike
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Summary: Soccer is the most popular sport in the world. Expectedly, the incidence of soccer-related injuries is high and these injuries exert a significant burden on individuals and families, including health and financial burdens, and on the socioeconomic and healthcare systems. Using established injury prevention frameworks, we present a concise synthesis of the most recent scientific evidence regarding injury rates, characteristics, mechanisms, risk and protective factors, interventions for prevention, and implementation of interventions in soccer. In this umbrella review, we elucidate the most recent available evidence gleaned primarily from systematic reviews and meta-analyses. Further, we express the exigent need to move current soccer injury prevention research evidence into action for improved player outcomes and widespread impact through increased attention to dissemination and implementation research. Additionally, we highlight the importance of an enabling context and effective implementation strategies for the successful integration of evidence-based injury prevention programs into real-world soccer settings. This narrative umbrella review provides guidance to inform future research, practice, and policy towards reducing injuries among soccer players.

#13 Correlation of T2* relaxation times of the retropatellar cartilage with tibial tuberosity-trochlea groove distance in professional soccer players
Reference: Sci Rep. 2020 Sep 18;10(1):15355. doi: 10.1038/s41598-020-72299-7.
Authors: Kai-Jonathan Maas, M Warncke, C Behzadi, G H Welsch, G Schoen, M G Kaul, G Adam, P Bannas, F O Henes
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Summary: The tibial tuberosity-trochlear groove (TT-TG) distance is a radiographic measurement that is used to quantify malalignment of the patellofemoral joint (PFJ) in cross-sectional imaging. There is an ongoing debate about the impact of the TT-TG-distance on lateral patellar instability and the initiating of cartilage degeneration. In this prospective study, the association of T2* relaxation times and TT-TG distances in professional soccer players was analyzed. 36 knees of 18 professional soccer players (age: 21 ± 2.8 years) were evaluated. Participants underwent knee MRI at 3 T. For qualitative image analysis, fat-saturated 2D PD-weighted Fast Spin Echo (FSE) and T1-weighted FSE sequences were used. For quantitative analysis, T2* measurements in 3D data acquisitions were performed. In a qualitative analysis there was no structural cartilage damage and no abnormalities of the patellar and trochlea shape. The highest T2* values (26.7 ± 5.9 ms) were observed in the central compartment of the patella. The mean TT-TG distance was 10 ± 4 mm (range 3-20 mm). There was no significant correlation between TT-TG distance and T2* relaxation times in all three compartments of the retropatellar cartilage. Our study shows that so long as patellar and trochlear morphology is normal, TT-TG distance alone does not affect the tissue structure of the retropatellar cartilage in professional soccer players.

#14 Differential Ratings of Perceived Match and Training Exertion in Girls' Soccer
Reference: Int J Sports Physiol Perform. 2020 Sep 18;1-9. doi: 10.1123/ijspp.2019-0595. Online ahead of print.
Authors: Matthew D Wright, Francisco Songane, Stacey Emmonds, Paul Chesterton, Matthew Weston, Shaun J Mclaren
Summary: The aim was to understand the validity of differential ratings of perceived exertion (dRPE) as a measure of girls’ training and match internal loads. Using the centiMax scale (CR100), session dRPE for breathlessness (sRPE-B) and leg muscle exertion (sRPE-L) were collected across a season of training (soccer, resistance, and fitness) and matches from 33 players (15 [1] y). Differences and associations between dRPE were examined using mixed and general linear models. The authors’ minimal practical important difference was 8 arbitrary units (AU). Mean (AU [SD] ∼16) sRPE-B and sRPE-L were 66 and 61 for matches, 51 and 49 for soccer, 86 and 67 for fitness, and 45 and 58 for resistance, respectively. Session RPE-B was rated most likely harder than sRPE-L for fitness (19 AU; 90% confidence limits: ±7) and most likely easier for resistance (−13; ±2). Match (5; ±4) and soccer (−3; ±2) differences were likely to most likely trivial. The within-player relationships between sRPE-B and sRPE-L were very likely moderate for matches (r = .44; 90% confidence limits: ±.12) and resistance training (.38; ±.06), likely large for fitness training (.51; ±.22), and most likely large for soccer training (.56; ±.03). Shared variance ranged from 14% to 35%. Practically meaningful differences between dRPE following physical training sessions coupled with low shared variance in all training types and matches suggest that sRPE-B and sRPE-L represent unique sensory inputs in girls’ soccer players. The data provide evidence for the face and construct validity of dRPE as a measure of internal load in this population.


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