Latest research in football - week 16 - 2019

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 Effects of Creatine Supplementation on Athletic Performance in Soccer Players: A Systematic Review and Meta-Analysis
Reference: Nutrients. 2019 Mar 31;11(4). pii: E757. doi: 10.3390/nu11040757.
Authors: Mielgo-Ayuso J, Calleja-Gonzalez J, Marqués-Jiménez D, Caballero-García A, Córdova A, Fernández-Lázaro D
Summary: Studies have shown that creatine supplementation increases intramuscular creatine concentrations, favoring the energy system of phosphagens, which may help explain the observed improvements in high-intensity exercise performance. However, research on physical performance in soccer has shown controversial results, in part because the energy system used is not taken into account. The main aim of this investigation was to perform a systematic review and meta-analysis to determine the efficacy of creatine supplementation for increasing performance in skills related to soccer depending upon the type of metabolism used (aerobic, phosphagen, and anaerobic metabolism). A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in the Medline/PubMed and Web of Science, Cochrane Library, and Scopus databases until January 2019. The search included studies with a double-blind and randomized experimental design in which creatine supplementation was compared to an identical placebo situation (dose, duration, timing, and drug appearance). There were no filters applied to the soccer players' level, gender, or age. A final meta-analysis was performed using the random effects model and pooled standardized mean differences (SMD) (Hedges's g). Nine studies published were included in the meta-analysis. This revealed that creatine supplementation did not present beneficial effects on aerobic performance tests (SMD, -0.05; 95% confidence interval (CI), -0.37 to 0.28; p = 0.78) and phosphagen metabolism performance tests (strength, single jump, single sprint, and agility tests: SMD, 0.21; 95% CI, -0.03 to 0.45; p = 0.08). However, creatine supplementation showed beneficial effects on anaerobic performance tests (SMD, 1.23; 95% CI, 0.55⁻1.91; p <0.001). Concretely, creatine demonstrated a large and significant effect on Wingate test performance (SMD, 2.26; 95% CI, 1.40⁻3.11; p <0.001). In conclusion, creatine supplementation with a loading dose of 20⁻30 g/day, divided 3⁻4 times per day, ingested for 6 to 7 days, and followed by 5 g/day for 9 weeks or with a low dose of 3 mg/kg/day for 14 days presents positive effects on improving physical performance tests related to anaerobic metabolism, especially anaerobic power, in soccer players.

#2 Dietary Intake of Polish Female Soccer Players
Reference: Int J Environ Res Public Health. 2019 Mar 29;16(7). pii: E1134. doi: 10.3390/ijerph16071134.
Authors: Dobrowolski H, Włodarek D
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Summary: The aim of the study was to evaluate the energy expenditure and fulfillment of nutritional needs of female soccer players. Participants in this research were 41 professional soccer players from the three Polish female soccer league levels: Ekstraleague, I League and II League. The participants had their height and body mass measured. Total Energy Expenditure was measured by means of a SenseWear Pro3 Armband device. Data related to the food-intake energy values and the consumption of macro- and micronutrients were obtained through systematic recording of results, which was conducted over a three-day-long period at the start of the competitive season. The average age of the participants was 21 ± 5 years, the average height was 167.5 ± 5 cm, and the average body mass was 62.53 ± 9.8 kg. The average energy expenditure of the participants was 2811 ± 493 kcal/day, and their average energy intake was 1476 ± 434 kcal/day. The average consumption of carbohydrates, fats, and proteins was 199 ± 20.6, 47.3 ± 20.7, and 72.3 ± 24.2 g/day, respectively. There was a prevalence of inadequate intake of potassium, calcium, magnesium, iodine, vitamins D, E and B1, and folate in the diet of the examined group. The remaining micronutrients were consumed in the prescribed amounts by at least 50% of the examined group. The participants demonstrated low energy intakes, and consequently, low consumption of macronutrients and a large number of micronutrients.

#3 Sport-Related Structural Brain Injury in High School Soccer: Epidural Hemorrhage After a "Header"
Reference: World Neurosurg. 2019 Mar 27. pii: S1878-8750(19)30878-2. doi: 10.1016/j.wneu.2019.03.198. [Epub ahead of print]
Authors: Mummareddy N, Legarreta AD, Yengo-Kahn AM, Bow HC, Solomon GS, Naftel RP, Zuckerman SL
Summary: Sport-related structural brain injury (SRSBI) is a rare but potentially catastrophic injury. Limited data exists outlining its epidemiology, pathophysiology, and outcomes. We present the case of an epidural hematoma (EDH) suffered during a high school soccer game. A 16-year-old male experienced a head-to-ball collision and head-to-head collision with another player. He denied loss of consciousness, endorsed retrograde amnesia, and complained of a minor headache. On the sidelines, he subsequently passed brief orientation and physical exertion tests. Upon returning to play, he experienced blurry vision, along with headache and nausea/vomiting. At the local hospital, he was found to have a 2.6cm right frontal EDH. After transfer to our institution, increasing somnolence was noted, prompting emergent evacuation of the EDH. His post-operative course was unremarkable, and he was discharged on post-operative day 2. At the 2-week and 3-month follow up visits, he did not express any complaints or residual deficits and was cleared for full sporting activity. This case highlights one of the few SRSBIs that have occurred in soccer. Due to their rarity and severity, a concerted effort should be made to report these cases of SRSBIs regarding mechanism, post-collision symptoms, and long-term outcomes.

#4 Travel fatigue and sleep/wake behaviors of professional soccer players during international competition
Reference: Sleep Health. 2019 Apr;5(2):141-147. doi: 10.1016/j.sleh.2018.10.013. Epub 2018 Dec 12.
Authors: Lastella M, Roach GD, Sargent C
Summary: The magnitude of travel completed by professional Australian soccer teams during domestic competition is substantial. The inclusion of Australian soccer teams into the Asian Champions league has seen additional stress placed on soccer players' training and competition schedules. For management staff, the complexity of organizing training and travel schedules during domestic competition and the Asian Champions league is challenging. Seven male professional soccer players (mean ± SD: age 25.2 ± 3.2 years, height 182.8 ± 5.2 cm, body mass 84.6 ± 7.4 kg) participated in this study which examined the sleep and fatigue levels of Australian soccer players during an intensive home and away travel schedule during the Asian Champions league. Seven male professional soccer players' (mean ± SD: age 25.2 ± 3.2 years, height 182.8 ± 5.2 cm, body mass 84.6 ± 7.4 kg) sleep/wake behavior was assessed using sleep diaries and wrist activity monitors for 19 days, including 9 days before, 5 days during, and 4 days after a home and away group stage match of the Asian Champions league. Analyses examined differences in sleep/wake behavior and fatigue levels between day type (training day, rest day, pregame, and postgame) and between sleep location (Adelaide, during flight, and Hiroshima). Sleep/wake behavior and fatigue levels were poorest the night immediately after games compared to the night before games, training days, and rest days. Soccer players' sleep/wake behaviors were disrupted during flights such that they obtained 3.6 hours less sleep during flights compared to sleep in Adelaide (7.0 ± 1.6 hours) and Hiroshima (7.0 ± 2.1 hours). The sleep/wake behaviors of professional soccer players are compromised when they are required to travel and compete in multiple matches within a short period of time.

#5 Medial collateral ligament injuries of the knee in male professional football players: a prospective three-season study of 130 cases from the UEFA Elite Club Injury Study
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Apr 4. doi: 10.1007/s00167-019-05491-6. [Epub ahead of print]
Authors: Lundblad M, Hägglund M, Thomeé C, Hamrin Senorski E, Ekstrand J, Karlsson J, Waldén M
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Summary: Medial collateral ligament (MCL) injury is the single most common traumatic knee injury in football. The purpose of this study was to study the epidemiology and mechanisms of MCL injury in men's professional football and to evaluate the diagnostic and treatment methods used. Fifty-one teams were followed prospectively between one and three full seasons (2013/2014-2015/2016). Individual player exposure and time-loss injuries were recorded by the teams' medical staffs. Moreover, details on clinical grading, imaging findings and specific treatments were recorded for all injuries with MCL injury of the knee as the main diagnosis. Agreement between magnetic resonance imaging (MRI) and clinical grading (grades I-III) was described by weighted kappa. One hundred and thirty of 4364 registered injuries (3%) were MCL injuries. Most MCL injuries (98 injuries, 75%) occurred with a contact mechanism, where the two most common playing situations were being tackled (38 injuries, 29%) and tackling (15 injuries, 12%). MRI was used in 88 (68%) of the injuries, while 33 (25%) were diagnosed by clinical examination alone. In the 88 cases in which both MRI and clinical examination were used to evaluate the grading of MCL injury, 80 (92% agreement) were equally evaluated with a weighted kappa of 0.87 (95% CI 0.77-0.96). Using a stabilising knee brace in players who sustained a grade II MCL injury was associated with a longer lay-off period compared with players who did not use a brace (41.5 (SD 13.2) vs. 31.5 (SD 20.3) days, p = 0.010). Three-quarter of the MCL injuries occurred with a contact mechanism. The clinical grading of MCL injuries showed almost perfect agreement with MRI grading, in cases where the MCL injury is the primary diagnosis. Not all grade II MCL injuries were treated with a brace and may thus indicate that routine bracing should not be necessary in milder cases.

#6 Involving research-invested clinicians in data collection affects injury incidence in youth football
Reference: Scand J Med Sci Sports. 2019 Apr 2. doi: 10.1111/sms.13427. [Epub ahead of print]
Authors: Wik EH, Materne O, Chamari K, Duque JDP, Horobeanu C, Salcinovic B, Bahr R, Johnson A
Summary: It is well established that differences in injury definition and recording methodology restrict comparisons between injury surveillance programmes. There is, however, little documentation of the variation that can exist between data recorders. The aim of this study was therefore to explore the effect on reported injuries when team recorders or supervisors are involved in research. Injury data collected prospectively over five seasons for the U16, U17 and U18 age groups in a youth football (soccer) academy were used to compare different recording settings based on the research involvement of the clinicians. A research-invested team physiotherapist reported an 8.8 times greater incidence (p<0.001) of non-time-loss injuries and a 2.5 times greater incidence (p<0.001) of minimal injuries (1-3 days lost) compared to a setting where neither the team physiotherapists or the supervisor relied on the collected data for research purposes. When team physiotherapists were not invested in research themselves but were supervised by a researcher, the incidence of non-time-loss injuries and minimal injuries was 2.5 times (p<0.001) and 2.0 times greater (p<0.01) than in the non-invested setting, respectively. However, there were no differences between recording settings for overall incidence of time-loss injuries. The results from this study demonstrate that involving clinicians that are relying on the collected data for research purposes can significantly affect the reported rates of non-time-loss and minimal injuries. Time-loss injuries overall were not affected by research investment, and should therefore be preferred for comparisons between teams and seasons. This article is protected by copyright. All rights reserved.

#7 Possession in Football: More Than a Quantitative Aspect - A Mixed Method Study
Reference: Front Psychol. 2019 Mar 18;10:501. doi: 10.3389/fpsyg.2019.00501. eCollection 2019.
Authors: Casal CA, Anguera MT, Maneiro R, Losada JL
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Summary: The aim of the present study was to identify and differentiate the factors that determine the possession times of successful and unsuccessful elite football teams, with the purpose of identifying a more effective possession model. For this, match corresponding to the round of eighth-finals, quarter-finals, semi-finals and final of the 2016 UEFA Euro France in which 2,636 offensive sequences occurred, were analyzed. Video recordings of matches were analyzed and coded post-event using systematic observation. The performance indicators recorded and analyzed were: phase; match period; type of start-up; interaction context; intention; field zone; possession time, passes, attack outcome; match status and final outcome. An ANOVA was performed to analyze data in order to study the influence of a set of variables. A Box-Cox transformation was applied on the variable explained to achieve normal conditions. A study of the main effects and significant interactions was also carried out, complemented with a set of predictions with the variables that were more significant. It is hypothesized that possession analysis from a mixed methods perspective will identify a more effective offensive playstyle. Results show how, in successful teams, possession time is influenced by: Type of start-up, intention and field zone. On the other hand, in unsuccessful teams, possession time is determined fundamentally by intention and match status. In terms of the results of the predictive models, in the case of successful teams, they will have longer possessions in the offensive zone with the score in favor and, in the defensive zone with a draw score, in both situations, initiated with the intention of progressing by means of a transition. For unsuccessful teams, possessions will be of longer duration in the defensive zone with a draw score, regardless of the type of start-up and, in the offensive zone, losing and initiating the play by means of a set ball action and winning by means of a transition. Results obtained in this work identify key factors that determine possession time in teams and allow to differentiate the possessions of successful and unsuccessful teams, identifying a more effective ball possession model. This information can be used to design a possession model with greater probabilities of success and increase the offensive performance of teams.

#8 Influence of Aerobic Power on Youth Players' Tactical Behavior and Network Properties during Football Small-Sided Games
Reference: Sports (Basel). 2019 Mar 25;7(3). pii: E73. doi: 10.3390/sports7030073.
Authors: Praça GM, Sousa RBE, Greco PJ
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Summary: This study aimed to compare the incidence of tactical principles, the percentage of successful tactical principles, and the network properties between higher and lower aerobic power in young football players during small-sided games. Eighteen Under-17 Brazilian players were recruited. Firstly, they performed the Yo-Yo Intermittent Recovery Test Level 2, which was used to split them into two groups with higher and lower aerobic power. In the sequence, they played three vs three small-sided games within each group. The System of Tactical Assessment in Soccer was used to analyze the tactical behavior demonstrated by measuring the incidence of tactical principles and the percentage of successful principles, while the macro variables, density and clustering coefficient from social network analysis for team sports was used to analyze players' interactions. No differences were reported for the incidence of tactical principles (p > 0.05, small or small-to-moderate effect sizes), the percentage of successful offensive principles (p = 0.122, small-to-moderate effect size), or the network variables (p > 0.05; small effect sizes). The lower aerobic power group demonstrated a higher percentage of successful defensive tactical principles (p = 0.043; small-to-moderate effect size). We concluded that aerobic power has a limited impact on player behavior, indicating that players' actions within a small-sided game are mostly constrained by other parameters.

#9 Antioxidant vitamin supplementation prevents oxidative stress but does not enhance performance in young football athletes
Reference: Nutrition. 2019 Jan 24;63-64:29-35. doi: 10.1016/j.nut.2019.01.007. [Epub ahead of print]
Authors: de Oliveira DCX, Rosa FT, Simões-Ambrósio L, Jordao AA, Deminice R
Summary: The aim of this study was to verify the effects of supplementation with antioxidants (vitamins C and E) on oxidative stress, delayed-onset muscle soreness (DOMS), and performance in football players during a recovery period after an exercise-induced oxidative stress protocol. Twenty-one football athletes were randomly assigned to two groups: placebo and antioxidant-supplemented. Supplementation was performed in a double-blind, controlled manner using vitamin C (500 mg/d) and E (400 UI/d) for 15 d. After 7 d of supplementation, athletes were submitted to an exercise-induced oxidative stress protocol consisting of plyometric jumping and strength resistance sets to exhaustion. Blood samples, performance tests, and DOMS were determined before and 24, 48, and 72 h after exercise. Antioxidant supplementation was continued during the recuperation week and for a total of 15 d. Antioxidant supplementation caused a significant increase in plasma vitamins C and E. The antioxidant supplementation could inhibit oxidative stress characterized by elevated lipid peroxidation markers malondialdehyde and total lipid peroxidation as well as reduced ratio of glutathione to oxidized glutathione promoted by exercise. Antioxidant supplementation, however, did not significantly reduce the plasma creatine kinesis concentration or DOMS during the recovery days. Likewise, supplementation with vitamin C and E did not improve lower body power, agility, or anaerobic power, nor did it provide any indication of faster muscle recovery. Antioxidant supplementation does not attenuate elevated markers of muscle damage or muscle soreness promoted by acute exercise and do not exert any ergogenic effect on football performance of young athletes, although it reduced oxidative stress.

#10 The Effects of a Physically Active Lifestyle on the Health of Former Professional Football Players
Reference: Sports (Basel). 2019 Mar 28;7(4). pii: E75. doi: 10.3390/sports7040075.
Authors: Melekoğlu T, Sezgin E, Işın A, Türk A
Summary: The purpose of this investigation was to determine if a physically active lifestyle affects the health of former football players. Sixty former professional football players aged 40⁻50 years and who ended their sports career at least ten years ago were recruited for the study and grouped into two groups based on their physical activity habits after their retirement. Health and lifestyle characteristics were collected through a questionnaire to obtain information about recreational physical activity levels, diseases, family medical history, smoking, alcohol intake and dietary habits. Furthermore, lung functions, blood parameters and cardiovascular health were evaluated. Our results showed that body weight and body fat percentage were significantly higher in retired footballers who had a sedentary lifestyle compared to those who were physically active. The absolute and predicted values for forced expiratory volume in one-second values were higher in the active group. Twelve retired athletes were found to have intraventricular conduction delay. The findings suggest that former footballers who have higher levels of physical activity have advanced body composition, respiratory functions and serum lipids compared to former footballers with less active lifestyles. It is recommended that former elite athletes should maintain physically active lifestyles to sustain their health and reduce the risk of disease and disability in the later years of life.

#11 Scaling Demands of Soccer According to Anthropometric and Physiological Sex Differences: A Fairer Comparison of Men's and Women's Soccer
Reference: Front Psychol. 2019 Apr 9;10:762. doi: 10.3389/fpsyg.2019.00762. eCollection 2019.
Authors: Pedersen AV, Aksdal IM, Stalsberg R
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Summary: Spectators frequently harass female soccer players, and women's soccer is frequently compared negatively to men's soccer by writers who make the comparison without the backing of any data and without taking into account anthropometric and physiological differences between the sexes. This affects female soccer players' self-confidence negatively and contributes to an undeservedly negative image of women's soccer. In the present paper, we argue that most differences between men's and women's soccer can be explained by women having to adapt to rules and regulations that are suited for men and their physical attributes. Thus, games are much more demanding for women. Furthermore, we argue that if men had to play with a degree of adaptation similar to that which women do today, they would have to alter their style of play radically. As support for our argument, we scale game demands for male and female soccer players according to anthropometric and physiological differences in order to highlight the differences, and use these to predict what would be the most appropriate adaptations. Finally, we show that our predictions are largely supported by the scarce pool of comparable data across the sexes.

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