Latest research in football week - 24 - 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 Regions at Risk in the Knee Joint of Young Professional Soccer Players: Longitudinal Evaluation of Early Cartilage Degeneration by Quantitative T2 Mapping in 3 T MRI
Reference: Cartilage. 2020 May 25;1947603520924773. doi: 10.1177/1947603520924773. Online ahead of print.
Authors: Hanna Schenk, David Simon, Leonie Waldenmeier, Christoph Evers , Rolf Janka, Goetz H Welsch, Milena L Pachowsky
Summary: The study aims to detect regions at risk for (pre-)osteoarthritis in the tibiofemoral joint of young professional soccer players by evaluating cartilage composition by T2 mapping in a 3 T magnetic resonance imaging setting. In this longitudinal study, 20 professional adolescent soccer players were included. Tibiofemoral cartilage was assessed by quantitative T2 mapping and T2 values were evaluated by regions of interest analysis. Statistical evaluation, using Wilcoxon signed-rank tests, was performed to compare global T2 values and subregional T2 values between a baseline and a follow-up investigation 4.3 years later. Based on the average of playing time (15 years) we divided the cohort in 2 groups and differences were evaluated. When comparing baseline and follow-up, our findings showed statistically significant increases of the global medial tibial and femoral T2 values. The most noticeable results of the subregional T2 analysis were statistically significant increases in the medial posterior zones (deep femoral 36.1 vs. 39.5, P = 0.001; superficial femoral 57.0 vs. 62.4, P = 0.034; deep tibial 28.3 vs. 34.1, P = 0.009; superficial tibial 43.2 vs. 55.3, P = 0.002). The elevation of T2 values in the medial, especially medial posterior, compartment of the knee joint indicates that these regions are at risk for early cartilage degeneration already at the time of adolescence. The findings can help individualize and optimize training concepts and to be aware of the chronic stress on these vulnerable areas. Prevention programs should be established in young players to avoid further cartilage damage.

#2 The Demands of the Extra-Time Period of Soccer: A Systematic Review
Reference: J Sport Health Sci. 2020 May 20;S2095-2546(20)30042-9.
doi: 10.1016/j.jshs.2020.03.008. Online ahead of print.
Authors: Adam Field, Robert Joseph Naughton, Matthew Haines, Steve Lui, Liam David Corr, Mark Russell, Richard Michael Page, Liam David Harper 
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Summary: Soccer match-play is typically contested over 90 min; however, in some cup and tournament scenarios, when matches are tied, they proceed to an additional 30 min, which is termed "extra-time" (ET). This systematic review sought to appraise the literature available on 120-min of soccer-specific exercise, with a view to identifying practical recommendations and future research opportunities. The review was conducted according to the PRISMA guidelines. Independent researchers performed a systematic search of PubMed, CINAHL and Psych Info in May 2019, with the following keywords entered in various combinations: "soccer," "football," "extra-time," "extra time," "120 minutes," "120 min, "additional 30 minutes," and "additional 30 min." The search yielded an initial 73 articles. Following the screening process, 11 articles were accepted for analyses. Articles were subsequently organized into the following 5 categories: movement demands of extra-time, performance responses to extra-time, physiologic and neuromuscular response during extra-time, nutritional inventions, and recovery and extra-time. The results highlighted that during competitive match-play, players cover 5%-12% less distance relative to match duration (i.e., meters per minute) during ET compared to the preceding 90 min. Reductions in technical performance (i.e., shot speed, number of passes and dribbles) were also observed during ET. Additionally, carbohydrate provision may attenuate and improve dribbling performance during ET. Moreover, objective and subjective measures of recovery may be further compromised following ET when compared to 90 min. Additional investigations are warranted to further substantiate these findings and identify interventions to improve performance during ET.

#3 Costs Resulting From Nonprofessional Soccer Injuries in Switzerland: A Detailed Analysis
Reference: J Sport Health Sci. 2020 May;9(3):240-247.
doi: 10.1016/j.jshs.2018.08.001. Epub 2018 Aug 23.
Authors: Angela Gebert, Markus Gerber, Uwe Pühse, Philippe Gassmann, Hanspeter Stamm, Markus Lamprecht
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Summary: Soccer injuries constitute an important public health problem and cause a high economic burden. Nevertheless, comprehensive data regarding injury costs in nonprofessional soccer are missing. The aim of this study was to determine which groups of nonprofessional soccer athletes, injury types, and injury situations caused high injury costs. A cross-sectional, retrospective telephone survey was carried out with a random sample of persons who had sustained a soccer injury between July 2013 and June 2014 and who had reported this accident to the Swiss National Accident Insurance Fund (Suva). One year after the corresponding accident, every injury was linked to its costs and to the answers obtained in the interview about injury setting, injury characteristics, and injury causes. Finally, the costs of 702 injuries were analyzed. The average cost of an injury in nonprofessional soccer amounted to €4030 (bias-corrected and accelerated 95% confidence interval (BCa 95%CI): 3427-4719). Persons aged 30 years and older experienced 35% of soccer injuries but accounted for 49% of all costs. A total of 58% of all costs were the result of injuries that occurred during amateur games. In particular, game injuries sustained by players in separate leagues for players aged 30+/40+ years led to high average costs of €8190 (BCa 95%CI: 5036-11,645). Knee injuries accounted for 25% of all injuries and were responsible for 53% of all costs. Although contact and foul play did not lead to above-average costs, twisting or turning situations were highly cost relevant, leading to an average sum of €7710 (BCa 95%CI: 5376-10,466) per injury. Nonprofessional soccer players aged 30 years and older and particularly players in 30+/40+ leagues had above-average injury costs. Furthermore, the prevention of knee injuries, noncontact and nonfoul play injuries, and injuries caused by twisting and turning should be of highest priority in decreasing health care costs.

#4 Physical and Physiological Responses of U-14, U-16, and U-18 Soccer Players on Different Small-Sided Games
Reference: Sports (Basel). 2020 May 18;8(5):E66.
doi: 10.3390/sports8050066.
Authors: Jorge López-Fernández, Javier Sánchez-Sánchez, Jorge García-Unanue, Enrique Hernando, Leonor Gallardo
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Summary: As most existing studies in youth academies are focused on top players, the objective of this research is to analyze the physical and physiological demands of various small-sided games (SSGs) on different age categories within a sub-elite soccer academy. We evaluated 63 young players from a Spanish sub-elite academy (under 14 = 21; under 16 = 21; under 18 = 21). Players performed four different small-side games focused on possession game (3-a-side; 4-a-side; 5-a-side; 6-a-side). The global indicators of performance and high-intensity actions were recorded through global positioning systems, whereas the heart rate responses were measured using heart rate monitors. Results: Under 16 ran a greater distance at high-intensity velocity than under 14 in the small side games 3v3 and 6v6. Furthermore, under 16 also ran a greater distance at high-intensity velocity than under 18 in the small side game 3v3 (p < 0.01). Under 14 showed greater acceleration at the highest intensity (> 2.75 m/s2) than the other age groups, under 16 and U18 (p < 0.01; ES (effect size) > 1). According to the physiological load, SSG 3v3 presented lower outcomes in Zone 6 (> 95% HRmax) than the small side game 4v4 and the small side game 5v5, in both under 14 and under 16. The workload of SSGs varies depending on the number of players, but also depending on the players' ages. Therefore, when designing the SSGs it is important to consider both the players' ages and the workload that want to be achieved.

#5 The Intermittent Nature of Player Physical Output in Professional Football Matches: An Analysis of Sequences of Peak Intensity and Associated Fatigue Responses
Reference: Eur J Sport Sci. 2020 May 28;1-21. doi: 10.1080/17461391.2020.1776400. Online ahead of print.
Authors: Jan Schimpchen, Sudarshan Gopaladesikan, Tim Meyer
Summary: Professional footballers experience transient periods of in-game fatigue which might affect match outcomes. Further information regarding the degree of fatigue elicited by periods of peak physical intensity across different movement metrics is needed to allow for a more informed design of targeted training interventions. To that end, the purpose of this study was to identify sequences of player peak physical output in-game for three different rolling time windows (1-, 5-, 10-minutes) across three movement categories (total distance, high-intensity distance, average acceleration/deceleration) for 29 players during a full season of professional football matches. Physical performance was also assessed for the 5-minutes after peak intensity to identify possible signs of acute fatigue, while goal differential and match time were registered as contextual variables to analyze whether peak physical output fluctuations were game-state dependent. Total distance and average acceleration/deceleration were reduced by 11-18% in the first minute after peak intensity but returned to match average within the third minute. High-intensity distance remained reduced by 64-89% from the first minute after peak intensity to 6-31% at the fifth minute after. Both contextual factors had an influence on players' ability to perform at peak intensity, but only when considering total distance and average acceleration/deceleration. In contrast, high-intensity distance peak performance remained unaffected by contextual factors. These findings indicate that player in-game fatigue is most pronounced after periods of peak high-intensity running, highlighting the need for targeted training interventions to minimize subsequent reductions in players' physical output capabilities.

#6 Genetic Association Research in Football: A Systematic Review
Reference: Eur J Sport Sci. 2020 May 28;1-52. doi: 10.1080/17461391.2020.1776401. Online ahead of print.
Authors: Alexander B T McAuley, David C Hughes, Loukia G Tsaprouni, Ian Varley, Bruce Suraci, Thomas R Roos, Adam J Herbert, Adam L Kelly 
Summary: Genetic variation is responsible for a large amount of the inter-individual performance disparities seen in sport. As such, in the last ten years genetic association studies have become more common; with one of the most frequently researched sports being football. However, the progress and methodological rigor of genetic association research in football is yet to be evaluated. Therefore, the aim of this paper was to identify and evaluate all genetic association studies involving football players and outline where and how future research should be directed. Firstly, a systematic search was conducted in the Pubmed and SPORTDiscus databases, which identified 80 eligible studies. Progression analysis revealed that 103 distinct genes have been investigated across multiple disciplines; however, research has predominately focused on the association of the ACTN3 or ACE gene. Furthermore, 55% of the total studies have been published within the last four years; showcasing that genetic association research in football is increasing at a substantial rate. However, there are several methodological inconsistencies which hinder research implications, such as; inadequate description or omission of ethnicity and on-field positions. Furthermore, there is a limited amount of research on several key areas crucial to footballing performance, in particular; psychological related traits. Moving forward, improved research designs, larger sample sizes, and the utilisation of genome-wide and polygenic profiling approaches are recommended. Finally, we introduce the Football Gene Project, which aims to address several of these limitations and ultimately facilitate greater individualised athlete development within football.

#7 Erythrasma in Athletes and Football Players
Reference: Wien Med Wochenschr. 2020 May 26. doi: 10.1007/s10354-020-00753-2. Online ahead of print.
Authors: Lilia Zisova, Valentin Valchev, Georgi Kasabov
Summary: Erythrasma is a superficial skin infection that presents with red-brown, flaky macules. It is caused by the Gram-positive bacteria Corynebacterium minutissimum. The purpose of our study is to investigate the prevalence and incidence of erythrasma in active sportsmen, i.e., athletes and football players, comparing the results with the incidence of the disease in the general population. A total of 140 sportsmen, 110 male athletes and 30 football players, were examined by clinical examination, microscopic examination (Gram staining), and Wood's lamp examination. Erythrasma was diagnosed in 39% (43) of the athletes and in 40% (12) of the football players studied. Inguinal folds were found to be most commonly affected. The disease was often localized to more than one area. This erythrasma study conducted in Bulgaria is the first in active athletes. The worldwide prevalence of erythrasma in the general population varies from 4 to 15%. It was found that the incidence of erythrasma is high in men actively involved in sports. The results obtained are explained by the presence of many factors predisposing for the development of this disease in the athletes.

#8 Epidemiologic Assessment of Concussions in an NCAA Division I Women's Soccer Team
Reference: Orthop J Sports Med. 2020 May 15;8(5):2325967120921746. doi: 10.1177/2325967120921746. eCollection 2020 May.
Authors: Alexander E Weber, Nicholas A Trasolini, Ioanna K Bolia, Santano Rosario, John P Prodromo, Catherine Hill, Russ Romano, Charles Y Liu, James E Tibone, Seth C Gamradt
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Summary: Among collegiate sports, ice hockey and wrestling have been reported to have the highest rates of concussion injury. Recent literature has shown that among all sports, female soccer players had the highest rate of concussion injury at the high school level. Sport-specific analysis will increase our knowledge of epidemiologic characteristics of this serious injury in young soccer players, where "heading" is commonly involved during participation. Our hypothesis was that heading during soccer will be associated with increased frequency of concussion injury in collegiate female players compared with other mechanisms of injury, and concussion injury mechanism and rates will differ by setting of injury (practice or match) and player position. This was a retrospective review and epidemiologic analysis of all concussions documented from a single National Collegiate Athletic Association (NCAA) Division I female collegiate soccer team between 2004 and 2017. A total of 381 participants were reviewed, and concussion injury mechanism, setting (practice or match), player position, and number of games and practices missed due to injury were analyzed. Overall, 25 concussions in 22 players from the 2004 to 2017 seasons were identified, for an annual rate of 1.79 concussions per year. Collisions (36%) followed by headers (20%) were the most common mechanisms. Forwards sustained the most concussions (32%). Injuries were more common in games (56%) than practice (40%). Of note, the most common cause of concussion during practice was headers (40%). Of the concussions documented, 20 (91%) were the player's first concussion. On average, each concussion resulted in a player missing 3.96 games and 12.46 practices. Our results demonstrate that concussion rates in female NCAA soccer players vary by position and occur with different frequencies and mechanisms in practice and games. Interventions for concussion avoidance should aim to limit exposure to high-risk activity, including player-to-player contact in games and headers in practice. Although gameplay and collisions can be unpredictable and difficult to control, practice settings can be modified in an attempt to decrease risk.

#9 Deliberate Soccer Practice Modulates Attentional Functioning in Children
Reference: Front Psychol. 2020 May 12;11:761. doi: 10.3389/fpsyg.2020.00761. eCollection 2020.
Authors: Consuelo Moratal, Juan Lupiáñez, Rafael Ballester, Florentino Huertas
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Summary: The main purpose of this study was to explore the association between the regular practice of open-skill sports (i.e., soccer) and executive control, along with other attentional functions (i.e., alerting and orienting) during preadolescence. The study was conducted on 131 participants (70 non-athletes and 61 soccer players). To measure cognitive performance, participants performed the Attentional Network Test-Interactions (ANT-I) task. Compared to non-athletes, soccer players showed overall faster responses and better executive control (e.g., reduced interference from distractors). Overall, our results provide new empirical evidence supporting the positive association between regular sports practice and cognitive performance, and more specifically executive functions. However, is important to note that the relationship between regular sport practice and cognition is complex and multifactorial. Our findings can be partly explained by the "cardiovascular fitness hypothesis" and the "cognitive component skills approach," suggesting that an externally paced sport environment with high physical fitness and perceptual-cognitive demands may be an appropriate setting to optimize the development of cognitive functioning during early adolescence.

#10 The Importance of Reactive Agility Tests in Differentiating Adolescent Soccer Players
Reference: Int J Environ Res Public Health. 2020 May 28;17(11):E3839. doi: 10.3390/ijerph17113839.
Authors: Nebojša Trajković, Goran Sporiš, Tomislav Krističević, Dejan M Madić, Špela Bogataj
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Summary: The ability to differentiate the elite from nonelite athletes is not clearly defined. We investigated level differences in speed, change of direction speed (CODS), and reactive agility in a group of trained adolescent soccer players. A total of 75 adolescent male soccer players (aged 14-19 years) were recruited. The players were grouped based on the level of play to elite, sub-elite, and amateur players. Players were tested for 5-, 10- and 20-m sprints, CODS, and reactive agility tests (RAT). Elite players had faster reaction movement time during RAT with live opponent stimuli (p ≤ 0.01) compared to sub-elite and amateur players. Moreover, elite players showed a faster time during light stimuli (p ≤ 0.01) but only compared to amateur players. The times for 5-m and 10-m sprint groups did not differ (p > 0.05). The results demonstrated that the skilled players (elite and sub-elite) performed better in reactive agility tests, speed, and COD speed compared to amateur players. Additionally, we can conclude that total and reaction time in the agility test with live opponent stimuli can be a significant factor that differentiates between adolescent soccer players considering their level.

#11 Effects of Knowing the Task's Duration on Soccer Players' Positioning and Pacing Behaviour During Small-Sided Games
Reference: Int J Environ Res Public Health. 2020 May 28;17(11):E3843. doi: 10.3390/ijerph17113843.
Authors: Ricardo Ferraz, Bruno Gonçalves, Diogo Coutinho, Rafael Oliveira, Bruno Travassos, Jaime Sampaio, Mário C Marques
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Summary: The study aimed to identify how the manipulation of knowledge regarding a training task duration constrains the pacing and tactical behaviour of soccer players when playing small-sided games (SSG). Twenty professional and experienced soccer players participated in a cross-sectional field study using three conditions: not informed on the duration of the SSG, which ended after 20 min (Unknown Condition); briefed about playing the SSG for 10 min, but after they completed the 10-min game, they were requested to complete another 10 min (Partial Condition) and informed before that they would play for 20 min (Known Condition). A global positioning system was used to measure the total distance covered and distances of different exercise training zones (walking to sprinting) and to access the dynamic players positioning through the distance from each player to all the teammates and opponents. Additionally, approximate entropy was measured to identify the regularity pattern of each gathered individual variable. The results indicate that the first 10 min of each scenario presented a higher physical impact independently of the initial information. During this time, the tactical behaviour also revealed higher variability. An increase in the distance of the teammates during the second period of 10-min for the Known scenario was also found, which may result from a lower pacing strategy. This study showed that the prior knowledge of the task duration led to different physical and tactical behaviours of the players. Furthermore, the relationship between the physical impact and the regularity of team game patterns should be well analysed by the coach, because the physical impact may be harmful to the development of the collective organization of the team.

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