Latest research in football - week 28 - 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 Biomarkers of insulin action during single soccer sessions before and after a 12-week training period in type 2 diabetes patients on a caloric-restricted diet
Reference: Physiol Behav. 2019 Jul 16:112618. doi: 10.1016/j.physbeh.2019.112618. [Epub ahead of print]
Authors: de Sousa MV, Fukui R, Dagogo-Jack S, Krustrup P, Zouhal H, da Silva MER
Summary: We investigated the biomarkers of insulin action as well as changes in free fatty acids and lactate concentration after an acute soccer session pre and post training with caloric-restricted diet versus diet alone in type 2 diabetes (T2D) patients. Fifty-one middle-aged (61.1 ± 6.4 years) T2D patients were randomly allocated to the soccer+diet group (SDG) or the diet group (DG). The control group comprised T2D patients observing a caloric-restricted diet who did not receive soccer training. Over 12 weeks, SDG performed 3 × 40 min per week of soccer training. The first soccer session for SDG induced acute increases in blood lactate (1.4 ± 0.1-6.0 ± 0.7 mmol/L, P < 0.05) and glucagon levels (112.1 ± 6.2-142.9 ± 8.0 pg/mL, P < 0.05), whereas glucose and insulin levels remained unchanged. Moreover, this session showed suppressed insulin levels as well as higher free fatty acids, lactate levels and glucagon/insulin ratio compared to DG (p < 0.05). After 12 weeks, a baseline decrease was observed in glucagon, leptin and lactate levels in SDG and DG (p < 0.05), whereas HOMA-IR, Adipo-IR and glucose levels were lower only in SDG (p < 0.05). At the last soccer training session, the blood lactate response was significantly lower than for the first session (4.0 ± 0.4 vs 6.0 ± 0.7 mmol/L). At 48 h pre intervention, a decrease was observed in leptin levels (p < 0.05), which remained lower post intervention. The positive correlation between leptin and insulin, and the lower levels after training, could be attributed to the improved insulin sensitivity along with the weight loss observed in both groups (~3.4 kg for DG and 3.7 kg for SDG). Acute soccer sessions markedly improved insulin action markers in T2D patients, while the cumulative effects enhanced insulin sensitivity and decreased risk factors associated with cardiovascular disease after 12 weeks of intervention better than caloric-restricted diet.

#2 "REOFUT" as an Observation Tool for Tactical Analysis on Offensive Performance in Soccer: Mixed Method Perspective
Reference: Front Psychol. 2019 Jun 28;10:1476. doi: 10.3389/fpsyg.2019.01476. eCollection 2019.
Authors: Aranda R, González-Ródenas J, López-Bondia I, Aranda-Malavés R, Tudela-Desantes A, Anguera MT
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Summary: Performance analysis in complex sports like soccer requires the study of the influence of the interaction between both teams during the game on final performance. The mixed methods approach involves the collection, analysis, and interpretation of qualitative and quantitative data for the same purpose and within the framework of the same study. To build certain observation tools, mixed methods are necessary in order to take advantage of integration between qualitative and quantitative elements. The aim of this study was to develop a new no standard observation tool to analyze soccer offensive performance considering not only the observed team but also some aspects of the opponent behavior, as well as to test its reliability. The process consisted in expert meetings and exploratory observations. Experts carried out several design and re-design steps of the observation tool to its final form which includes two macro-criteria and 31 dimensions. The basic unit of analysis was the "team possession" and the main aims of study were: (a) technical, tactical and spatial characteristics of the start, the development and the end of the team possession and its offensive performance, (b) the behavior of the observed team just after losing the ball possession and its defensive performance. Inter-observer and intra-observer analysis were carried out and kappa coefficient was calculated to test the observation tool reliability and improve the quality of data. Results indicate that optimal inter and intra-reliability levels obtained in this work are high enough as for suggesting that the observation tool for offensive performance in soccer (REOFUT) could be an adequate tool for analyzing offensive play actions and their performance in soccer.

#3 Self-Control in Aiming Supports Coping With Psychological Pressure in Soccer Penalty Kicks
Reference: Front Psychol. 2019 Jun 27;10:1438. doi: 10.3389/fpsyg.2019.01438. eCollection 2019.
Authors: Navia JA, van der Kamp J, Avilés C, Aceituno J
Summary: This study addressed the question whether coaches better allow athletes to self-control their decisions when under pressure or whether to impose a decision upon them. To this end, an experiment was conducted that manipulated the soccer kickers' degree of control in decision-making. Two groups of elite under-19 soccer players (n = 18) took penalty kicks in a self-controlled (i.e., kickers themselves decided to which side to direct the ball) and an externally controlled condition (i.e., the decision to which side to direct the ball was imposed upon the kickers). One group performed the penalty kick under psychological pressure (i.e., the present coaching staff assessed their performance), while the second group performed without pressure. Just before and after performing the kicks, CSAI-2 was used to measure cognitive and somatic anxiety and self-confidence. Further, the number of goals scored, ball placement and speed, and the duration of preparatory and performatory behaviors were determined. The results verified increased levels of cognitive and somatic anxiety after performing the kicks in the pressured group compared to the no-pressure group. In addition, degree of self-control affected the participants' performance, particularly in the pressured group. They scored more goals and placed the kicks higher in the self-controlled than in the externally-controlled condition. Participants also took more time preparing and performing the run-up in the self-controlled condition. Findings indicate that increased self-control helps coping with the debilitating effects of pressure and can counter performance deteriorations. The findings are discussed within the framework of self-control theories, and recommendations for practitioners and athletes are made.

#4 Variation of aerobic performance indices of professional elite soccer players during the annual macrocycle
Reference: J Sports Med Phys Fitness. 2019 Jul 15. doi: 10.23736/S0022-4707.19.09800-1. [Epub ahead of print]
Authors: Bekris E, Mylonis E, Gissis I, Katis A, Metaxas T, Komsis S, Kombotieta N
Summary: The purpose of the present study was to examine the variation of aerobic performance parameters of elite Greek soccer players. In the study participated twenty-four (24) male professional soccer players (age: 24.3±4.3 years, height: 180.3±3.8 cm and mass: 77.4±6.1 kg), who competed at the top level of the Greek National Championship. Four measurements regarding aerobic parameters were conducted during the annual training cycle (preseason, start of the season, end of the first championship round and end of the season). The ANOVA analysis showed that maximum oxygen uptake (VO2max) was significantly increased after the completion of the preseason and continued to increase until the end of the first round of the Championship. In contrast, a decline was observed towards the end of the season. The velocity to maximum oxygen uptake (vVO2max) and the velocity parameter in respiratory threshold were significantly increased at the end of the preseason and the end of the first round, while the parameters were differentiated at the end of the season. The lactate concentration showed no significant changes during the four measurements. A systematic observation of players' performance, especially recording parameters such as VO2max, during the annual training cycle, could provide the necessary feedback for both trainers and players in order to increase team performance.

#5 Knee isokinetic muscle strength and balance ratio in female soccer players of different age groups: a cross-sectional study
Reference: Phys Sportsmed. 2019 Jul 16. doi: 10.1080/00913847.2019.1642808. [Epub ahead of print]
Authors: Vargas VZ, Motta C, Peres B, Vancini RL, Andre Barbosa de Lira C, Andrade MS
Summary: As a consequence of years of soccer training and sexual maturation, there is an increase in lower body muscle mass and strength especially in the knee extensors and flexors muscles. In this context, the lack of knee joint stability, resulting from strength imbalance between knee extensor and flexors muscles, has been associated with knee injuries. The aim of this study was to compare the knee flexor and extensor muscle peak torque, average power, contralateral deficit, conventional and functional balance ratios of female soccer players from different age groups.  Sixty-six female soccer players were divided into four groups: under 13 (U13), under 15 (U15), under 17 (U17) years old and professional (PRO). Flexor and extensor knee muscle strength in concentric and eccentric actions of both limbs were assessed using isokinetic dynamometer. For the dominant limb, the knee concentric extensor muscles peak torques, assessed at 60 and at 240 deg/sec, and average power of U15 group were significantly higher than U13 group. Extensor muscles average power of PRO group was higher than U17. Dominant knee flexor average power of U15 was significant higher than U13 group. Peak torque at 60 deg/sec and 240 deg/sec and average power of PRO group were higher than U17 group. No differences were found regarding the eccentric action for flexor and extensor muscles. Conventional and functional balance ratios were similar among all age group, except for U13, which presented higher values than U15 group for dominant limb. The greatest increases in muscular performance occur when the athlete starts practicing soccer (after U13) and when they become professional (after U17) and the balance ratios, and muscle balance ratios remain stable in all age groups, although they are below the recommended level in the literature, which may increase the risk for lower limb injury

#6 The influence of youth soccer players' sprint performance on the different sided games' external load using GPS devices
Reference: Res Sports Med. 2019 Jul 15:1-12. doi: 10.1080/15438627.2019.1643726. [Epub ahead of print]
Authors: Castillo D, Raya-González J, Manuel Clemente F, Yanci J
Summary: The aims of this study are 1) to compare sided games' (SGs) external responses encountered by players according to pitch size and to 2) examine the relationships between sprint performance and SGs' external physical responses. Twenty soccer players under 15 years of age (U-15) participated in this study. Each player performed a sprinting test (10 m and 30 m sprints) and played a SG on two different pitch sizes (small at 100 [SSG] and large at 200 [LSG] m2 per player). Higher external responses (p < 0.01, ES = -6.41-1.22) were found in LSG in comparison to SSG, except to distance accelerating and decelerating (p > 0.05, ES = -0.26-0.27). Players who were faster over 10 and 30 m covered higher distances cruising and sprinting (r = -0.47/-0.66; ± 0.23/± 0.30, respectively, p < 0.05), performed a greater number of sprints, achieved higher maximum velocity (Velmax) during LSG and covered a greater distance at high-intensity accelerating (r = -0.50/-0.70; ±0.21/±0.29, respectively, p < 0.05) during both SG. LSG demanded a higher external load in comparison with SSG. In addition, the improved sprint capacity could allow players to perform greater running activities and short-term actions at high-intensities during SG.

#7 Injury Surveillance in Major League Soccer: A 4-Year Comparison of Injury on Natural Grass Versus Artificial Turf Field
Reference: Am J Sports Med. 2019 Jul 15:363546519860522. doi: 10.1177/0363546519860522. [Epub ahead of print]
Authors: Calloway SP, Hardin DM, Crawford MD, Hardin JM, Lemak LJ, Giza E, Forsythe B, Lu Y, Patel BH, Osbahr DC, Gerhardt MB, Mandelbaum BR, Baldwin WW
Summary: Artificial playing surfaces are becoming more common due to decreased cost of maintenance and increased field usability across different environmental conditions. The Fédération Internationale de Football Association (FIFA) has approved newer generation artificial turf for soccer competition at the elite level, but many elite-level athletes prefer to play on natural grass surfaces due to a perceived increase in injury rate, discomfort, and fatigability on artificial turf. Injury rates and rates of individually categorized types of injury experienced on artificial turf are noninferior to rates of injury on the standard comparator, natural grass, in elite-level Major League Soccer athletes. Over the course of 4 Major League Soccer seasons (2013-2016), athlete injury data were recorded electronically. Injury data recorded in matches between 2 Major League Soccer teams were then analyzed. Playing surface was known for each venue, and all artificial turf surfaces were rated as 2-star according to FIFA criteria. Incidence rate ratios (Artificial Turf ÷ Natural Grass) were calculated with a 95% CI (α = .05) for both overall injury incidence and individual injury subgroups. A noninferiority margin (δ) of 0.15 was used to determine noninferiority of injury incidence rates. A total of 2174 in-game injuries were recorded during the study period, with 1.54 injuries per game on artificial turf and 1.49 injuries per game on natural grass (incidence rate ratio, 1.033; 95% CI, 0.937-1.139). Within injury subgroups, overall ankle injury, Achilles injury, and ankle fracture were found to have a statistically higher incidence on artificial turf. Artificial turf was found to be noninferior to natural grass for overall foot injury and forefoot injury. No statistically significant differences were found in knee injuries between the 2 surfaces. The overall rate of injury on artificial turf was noninferior to that on natural grass. Within individual injury categories, a higher rate of ankle injury was found on artificial turf. No other injury subgroup demonstrated statistically significant differences between surfaces. FIFA 2-star rated artificial turf is a viable alternative to natural grass in elite-level soccer competition. Innovative research methods for comparing artificial turf versus natural grass may elucidate relative advantages with respect to player safety.

#8 Orthopedic injuries in a formation of a soccer club
Reference: Rev Bras Ortop. 2013 Jun 11;48(1):41-45. doi: 10.1016/j.rboe.2011.12.001. eCollection 2013 Jan-Feb.
Authors: Carvalho DA
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Summary: Football is one of the most popular sports in the world with approximately 400 million practitioners. All physical activity generates an overload somewhere in the locomotor system, above all, in young athletes. The purpose was to conduct the epidemiological survey of orthopedic injuries in a medical department of the categories of junior soccer a football club in Curitiba. Epidemiological survey of injuries in 310 different athletes during the 2009 and 2010 seasons were analysed. The number of recorded visits was 3.64 per athlete orthopedic complaints in two years. Furthermore, we find 2.88 injuries/1,000 hours of play, and the junior (under 20 and under 18) with the highest rate (3.05). The most frequent injury was contusion (32.15%), lower limbs, especially the thigh (3.94%). The higher incidence of injuries occurred in the Middle - campers (30.65%), being the training responsible for 88.31% of the complaints. The epidemiological survey of medical care is a medical department is an important tool for analysis of the main complaints, as well as the primary means of prevention and maintaining the health of athletes.

#9 Concussion in American Versus European Professional Soccer: A Decade-Long Comparative Analysis of Incidence, Return to Play, Performance, and Longevity
Reference: Am J Sports Med. 2019 Jul 15:363546519859542. doi: 10.1177/0363546519859542. [Epub ahead of print]
Authors: Ramkumar PN, Navarro SM, Haeberle HS, Luu BC, Jang A, Frangiamore SJ, Farrow LD, Schickendantz MS, Williams RJ 3rd
Summary: The incidence and effect of sports-related concussions (SRCs) within the global sport of professional soccer is poorly described. The purpose was to comparatively examine the effects of SRC on athletes in Major League Soccer (MLS) and the English Premier League (EPL) in terms of incidence, return to play (RTP), performance, and career longevity. Contracts, transactions, injury reports, and performance statistics from 2008 to 2017 were obtained and cross-referenced across 6 publicly available websites detailing MLS and EPL data, including official league publications. For each league, players who sustained a concussion were compared with the 2008-2017 uninjured player pool. RTP and games missed were analyzed and compared. Career length was analyzed with Kaplan-Meier survival curves. Player performance changes were evaluated before and after concussion. Of the 1784 eligible MLS and 2001 eligible EPL players evaluated over the 10-year period, the incidence of publicly reported concussions per 1000 athlete-exposures was 20.22 and 18.68, respectively (P = .53). The incidence of reported concussions steadily increased in both leagues. MLS players missed a mean 7.3 games after concussion (37.0 days missed); EPL players missed a mean 0.6 games after concussion (10.9 days missed) (P < .0001, P < .0001). Statistical performance in terms of games started, assists, shots on goal, and total shots after concussion was significantly reduced at all nongoalie positions for players in the EPL; however, MLS nongoalie positions with concussion had no significant decreases in these categories. Goalies in both leagues had no significant change in performance or games started. The probability of playing a full season after concussion was not significantly decreased when compared with the uninjured pool in both leagues. This study established the SRC incidence among elite soccer players in 2 international professional leagues and identified major RTP and performance differences between EPL and MLS players. While career longevity was unaffected, the approach to managing concussion as in MLS may better promote player safety and preserve on-field performance.

#10 How does the modern football goalkeeper train? - An exploration of expert goalkeeper coaches' skill training approaches
Reference: J Sports Sci. 2019 Jul 16:1-9. doi: 10.1080/02640414.2019.1643202. [Epub ahead of print]
Authors: Otte FW, Millar SK, Hüttermann S
Summary: The football goalkeeper position arguably represents a unique role within the team sport. Despite its highly complex skill demands, research on football goalkeeping has only sporadically examined the position within isolated and limited parameters. In particular, there is limited literature on "modern" skill acquisition training methods and approaches within the field of goalkeeper training. In a cross-cultural study with fifteen expert goalkeeper coaches, researchers here examined the overarching research question of "how does the modern football goalkeeper train?". Semi-structured interviews explored expert coaches' views on critical skills for performance in goalkeeping and the training approaches used to develop these critical skills. Results indicate that four skill sets are considered essential by goalkeeper coaches, these are: decision-making skills, athleticism, mentality, and technical skills. In terms of developing these skills in goalkeeper-specific training, the majority of expert coaches apply a similar microstructure to training sessions. This structure involves a steady progression from simple to complex training tasks, where for large parts, isolated technical training appears to be prioritised over a holistic training approach that integrates technical skills and perceptual-cognitive components (e.g., decision making). Scientific and practical recommendations for researchers and practitioners in the field of football goalkeeper coaching are provided.

#11 A Decision-Analytic Approach to Addressing the Evidence About Football and Chronic Traumatic Encephalopathy
Reference: Semin Neurol. 2019 Jul 16. doi: 10.1055/s-0039-1688484. [Epub ahead of print]
Authors: Brand KP, Finkel AM
Summary: Doubts can be raised about almost any assertion that a particular exposure can lead to an increase in a given adverse health effect. Even some of the most well-accepted causal associations in public health, such as that linking cigarette smoking to increased lung cancer risk, have intriguing research questions remaining to be answered. The inquiry whether an exposure causes a disease is never wholly a yes/no question but ought to follow from an appraisal of the weight of evidence supporting the positive conclusion in light of any coherent theories casting doubt on this evidence and the data supporting these. More importantly, such an appraisal cannot be made sensibly without considering the relative consequences to public health and economic welfare of specific actions based on unwarranted credulity (false positives) versus unwarranted skepticism (false negatives). Here we appraise the weight of evidence for the premise that repeated head impacts (RHIs) in professional football can increase the incidence of chronic traumatic encephalopathy (CTE) and, in turn, cause a variety of cognitive and behavioral symptoms. We first dismiss four logical fallacies that should not affect the appraisal of the weight of evidence. We then examine four alternative hypotheses in which RHI is not associated with CTE or symptoms (or both), and we conclude that the chances are small that the RHI→ CTE→ symptoms link is coincidental or artifactual. In particular, we observe that there are many specific interventions for which, even under a skeptical appraisal of the weight of evidence, the costs of a false positive are smaller than the false negative costs of refusing to intervene.

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