Latest research in football - week 1 - 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 Visualizing a Team's Goal Chances in Soccer from Attacking Events: A Bayesian Inference Approach
Reference: Big Data. 2018 Dec 1;6(4):271-290. doi: 10.1089/big.2018.0071. Epub 2018 Dec 13.
Authors: Whitaker GA, Silva R, Edwards D
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Summary: We consider the task of determining the number of chances a soccer team creates, along with the composite nature of each chance-the players involved and the locations on the pitch of the assist and the chance. We infer this information using data consisting solely of attacking events, which the authors believe to be the first approach of its kind. We propose an interpretable Bayesian inference approach and implement a Poisson model to capture chance occurrences, from which we infer team abilities. We then use a Gaussian mixture model to capture the areas on the pitch a player makes an assist/takes a chance. This approach allows the visualization of differences between players in the way they approach attacking play (making assists/taking chances). We apply the resulting scheme to the 2016/2017 English Premier League, capturing team abilities to create chances, before highlighting key areas where players have most impact.

#2 Predicting the defensive performance of individual players in one vs. one soccer games
Reference: PLoS One. 2018 Dec 31;13(12):e0209822. doi: 10.1371/journal.pone.0209822. eCollection 2018.
Authors: Wilson RS, Smith NMA, Santiago PRP, Camata T, Ramos SP, Caetano FG, Cunha SA, Sandes de Souza AP, Moura FA
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Summary: The aim of this study was to use technical skill and physical performance and coaches' rankings to predict the defensive performance of junior soccer players. Twenty-one male players (mean age 17.2 years, SD = 1.1) were recruited from the Londrina Junior Team Football Academy in Brazil. Data were collected during regular training sessions. After participants had warmed up, players were asked to either dribble the ball or sprint through five custom circuits that varied in average curvature (0-1.37 radians.m-1). In addition, four coaches were asked to rank the players from best to worst in defensive ability. Dribbling, sprinting, and coaches' rankings were then compared with defending performance as assessed in the one vs. one competitions (N = 1090 paired-trials: 40-65 trials per individual), in which they acted as defender or attacker in turn. When defending, the objective was to steal the ball or prevent the attacker from running around them with the ball into a scoring zone. Testing occurred over three days. Overall, dribbling performance (r = 0.56; P = 0.008) and coaches' ranking (r = 0.59; P = 0.004) were significantly related to defensive ability; sprinting performance was not (r = 0.20; P = 0.38). Though dribbling performance and coaches' ranking each explained 30% and 37% of the variance in defensive performance, respectively, the two predictors were not related (r = 0.27; P = 0.23), so combined these traits explained more than half the variance in defensive performance. In conclusion, the current study demonstrates that including only one metric of closed-skill performance-dribbling speed-doubles the ability of coaches to identify their best defensive players in one vs. one scenarios.

#3 Patellar and Achilles Tendon Stiffness in Elite Soccer Players Assessed Using Myotonometric Measurements
Reference: Sports Health. 2019 Jan 2:1941738118820517. doi: 10.1177/1941738118820517. [Epub ahead of print]
Authors: Cristi-Sánchez I, Danes-Daetz C, Neira A, Ferrada W, Yáñez Díaz R, Silvestre Aguirre R
Summary: Tendon overuse injuries are an issue in elite footballers (soccer players) and may affect tendon function. Achilles and patellar tendinopathy are the most frequent pathologies. Tendon stiffness, the relationship between the force applied to a tendon and the displacement exerted, may help represent tendon function. Stiffness is affected by training and pathology. Nevertheless, information regarding this mechanical property is lacking for elite soccer athletes. Achilles and patellar tendon stiffness assessed using myotonometric measurements will be greater in elite soccer athletes than in control participants. Forty-nine elite soccer athletes and 49 control participants were evaluated during the 2017 preseason. A handheld device was used to measure Achilles and patellar tendon stiffness. Dominant and nondominant limbs were assessed for both groups. A significantly stiffer patellar tendon was found for both the dominant and the nondominant limb in the elite soccer athletes compared with the control group. Nevertheless, no differences were found in Achilles tendon stiffness between groups. When comparing between playing positions in soccer athletes, no significant differences were found for both tendons. Greater patellar tendon stiffness may be related to an improvement in force transmission during muscle contraction. On the other hand, it seems that after years of professional training, Achilles tendon stiffness does not change, conserving the storing-releasing function of elastic energy. The nonsignificant differences between positions may be attributable to the years of homogeneous training that the players underwent. The present study shows another technique for measuring mechanical properties of tendons in soccer athletes that could be used in clinical settings. In the future, this technique may help clinicians choose the best exercise protocol to address impairments in tendon stiffness.

#4 Examination of Physical Characteristics and Positional Differences in Professional Soccer Players in Qatar
Reference: Sports (Basel). 2018 Dec 31;7(1). pii: E9. doi: 10.3390/sports7010009.
Authors: Wik EH, Auliffe SM, Read PJ
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Summary: Physical characteristics in professional soccer differ between competition levels and playing positions, and normative data aid practitioners in profiling their players to optimize performance and reduce injury risk. Given the paucity of research in Arabic soccer populations, the purpose of this study was to provide position-specific normative values for professional players competing in the Qatar Stars League. One hundred and ninety-five players completed a musculoskeletal assessment as part of an annual periodic health examination. Tests included measures of range of motion (hip, ankle, and hamstring), bilateral and unilateral jump performance, and quadriceps/hamstring (isokinetic/NordBord), hip adduction/abduction (eccentric), and groin (isometric) strength. Descriptive data were examined, and positional differences were analyzed using a one-way analysis of variance (ANOVA). Goalkeepers were significantly heavier (p < 0.01), had a higher body mass index (p < 0.05) than outfield positions and demonstrated greater absolute strength. Defenders were the strongest relative to body mass, and these differences were significant (p < 0.05) versus goalkeepers and strikers. No meaningful between-group comparisons were apparent for jumping or range of motion tests. Compared to mean values from other professional leagues, soccer players in Qatar appear to be shorter, lighter and display inferior strength and jump capacities. These data can be used to tailor training and rehabilitation programs to the specifics of the league and position in which the athletes compete.

#5 Photobiomodulation therapy as a tool to prevent hamstring strain injuries by reducing soccer-induced fatigue on hamstring muscles
Reference: Lasers Med Sci. 2019 Jan 3. doi: 10.1007/s10103-018-02709-w. [Epub ahead of print]
Authors: Dornelles MP, Fritsch CG, Sonda FC, Johnson DS, Leal-Junior ECP, Vaz MA, Baroni BM
Summary: Muscle fatigue is a potential risk factor for hamstring strain injuries in soccer players. The aim of this study was to verify the effect of photobiomodulation therapy (PBMT) on the hamstrings' muscle fatigue of soccer players during a simulated match. Twelve male amateur soccer players (~ 25 years) participated in this randomized, crossover, double-blinded, placebo-controlled trial. The volunteers were evaluated in two sessions, with a minimum 7-day interval. At each session, volunteers received either PBMT (300 J per thigh) or placebo treatment on the hamstrings prior to the simulated soccer match. Muscle strength and functional capacity were evaluated through isokinetic dynamometry and countermovement jump (CMJ) tests, respectively, before and immediately after the simulated soccer match. Players had lower reductions on hamstring eccentric peak torque [4.85% (ES = 0.31) vs. 8.72% (ES = 0.50)], hamstring-to-quadriceps torque ratio [3.60% (ES = 0.24) vs. 7.75% (ES = 0.50)], and CMJ height [1.77% (ES = 0.09) vs. 5.47% (ES = 0.32)] when treated with PBMT compared to placebo. Magnitude-based inference supports that PBMT promoted 75%, 69%, and 53% chances for beneficial effects on hamstring eccentric peak torque, hamstring-to-quadriceps torque ratio, and CMJ height, respectively, compared to placebo treatment. In conclusion, PBMT applied before a simulated soccer match proved to be effective in attenuating the hamstrings' muscle fatigue. These findings support PBMT as a promising tool to prevent hamstring strain injury in soccer players.

#6 Accelerations - a new approach to quantify physical performance decline in male elite soccer?
Reference: Eur J Sport Sci. 2019 Jan 11:1-9. doi: 10.1080/17461391.2019.1566403. [Epub ahead of print]
Authors: Dalen T, Lorås H, Hjelde GH, Kjøsnes TN, Wisløff U
Summary: The aim of the current study was (1) to investigate whether the number of accelerations is a more precise estimate of performance decline in soccer compared to distances with high-speed running (HSR) and (2) to compare changes in the number of accelerations and HSR distances across playing positions in order to examine whether the match profiles of the physical measures are consistent or demonstrate high interposition variability. The dataset includes domestic home games (N = 34) over three full seasons (2012-2014) for a team in the Norwegian Elite League. The change in the number of accelerations throughout the match demonstrates a more clear pattern compared to the distance covered by HSR. In numbers of accelerations, a systematic and linear decrease can be observed throughout the match, with 34% less accelerations from the first to the last 5-minute period of the game (6.7 vs. 4.4 accelerations). This pattern of results captures the change in the number of accelerations across all positions. HSR distance had more variability during the match. All five positions investigated displayed a similar trend in accelerations and HSR profiles after the peak periods in each half. In contrast to the absolute number of accelerations, there were major positional differences in the mean HSR distance during the match. Our data suggest a more visible performance decline in the number of accelerations from the start to the end of the game, than the decline in the distance covered by HSR distance.

#7 A Nationwide Follow-up Survey on the Effectiveness of an Implemented Neuromuscular Training Program to Reduce Acute Knee Injuries in Soccer Players
Reference: Orthop J Sports Med. 2018 Dec 21;6(12):2325967118813841. doi: 10.1177/2325967118813841. eCollection 2018 Dec.
Authors: Åman M, Larsén K, Forssblad M, Näsmark A, Waldén M, Hägglund M
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Summary: A cruciate ligament (CL) injury is a severe injury in soccer. Neuromuscular training programs have a well-documented preventive effect, but there are few studies on the effectiveness of such a program at a national level. The Swedish Knee Control Program (KCP) was found to be effective in preventing CL injuries in youth female soccer players. The KCP was implemented nationwide in Sweden in 2010. The purpose was to evaluate the effectiveness of the Swedish KCP in reducing acute knee injuries in soccer players at a nationwide level. All licensed soccer players in Sweden are covered by the same insurance company. Using this insurance database, around 17,500 acute knee injuries that were reported to the insurance company between 2006 and 2015 were included in the study. By matching the number of licensed soccer players with the number of reported injuries each year, the annual incidence of knee and CL injuries was able to be calculated. To evaluate the spread of the KCP nationally, a questionnaire was sent to all 24 Swedish district football associations (FAs) with questions regarding KCP education. The number of downloads of the KCP mobile application (app) was obtained. The incidence of CL injuries decreased during the study period for both male (from 2.9 to 2.4 per 1000 player-years) and female players (from 4.9 to 3.9 per 1000 player-years). The overall incidence of knee injuries decreased in both male (from 5.6 to 4.6 per 1000 player-years) and female players (from 8.7 to 6.4 per 1000 player-years). Comparing before and after the nationwide implementation of the KCP, there was a decrease in the incidence of CL injuries by 6% (rate ratio [RR], 0.94 [95% CI, 0.89-0.98]) in male players and 13% (RR, 0.87 [95% CI, 0.81-0.92]) in female players and a decrease in the incidence of knee injuries by 8% (RR, 0.92 [95% CI, 0.89-0.96]) and 21% (RR, 0.79 [95% CI, 0.75-0.83]), respectively (P < .01 for all). This trend corresponded to a reduction of approximately 100 CL injuries each year in Sweden. A total of 21 of 24 district FAs held organized KCP educational courses during the study period. The percentage of district FAs holding KCP courses was between 46% and 79% each year. There were 101,236 downloads of the KCP app. The KCP can be considered partially implemented nationwide, and the incidence of knee and CL injuries has decreased in both sexes at a nationwide level.

#8 Cardio respiratory response: Validation of new modifications of Bruce protocol for exercise testing and training in elite Saudi triathlon and soccer players
Reference: Saudi J Biol Sci. 2019 Jan;26(1):105-111. doi: 10.1016/j.sjbs.2017.05.009. Epub 2017 May 19.
Authors: Badawy MM, Muaidi QI
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Summary: The Bruce protocol is the traditional method used to assess maximal fitness level, although it may have limitations, such as its short duration and large work rate increases, with very high levels of exertion that consist of speed/incline combinations. Modifications have been added to elicit similar maximal fitness achievements. The authors of this experimental trial have proposed a new treadmill protocol that allows optimal test duration in conjunction with peak oxygen consumption 'VO2max', and with appropriate patient comfort and safety during both exercise testing and training. Twenty-two elite Saudi players, comprising eleven Saudi triathlon athletes, and eleven Saudi elite soccer players, BMI, body fat mass percentage, body fat free mass percentage. cardiovascular parameter; including, absolute and relative "VO2max" as well as maximal heart rate "HR max", were assessed during a graded treadmill running modified protocol, using a Quark Cardio Pulmonary Exercise Testing Unit (CPET). Descriptive statistics were used to obtain the anthropometric characteristics, including comparisons between the means, independent sample T-test and a regression analysis, to test the association of the protocol duration and the corresponding, dependent variables. It is often difficult to achieve a high cardiorespiratory response, VO2max, without an association to high values of HR max, and peak perceived exertion. This may lead to cardiovascular risk. Our new modifications can provide a practical, valid alternative protocol to be used comfortably both during exercise testing and training, rather than performance testing only, to achieve high VO2max with minimal cardiovascular stress.

#9 Knee Angle Affects Posterior Chain Muscle Activation During an Isometric Test Used in Soccer Players
Reference: Sports (Basel). 2019 Jan 4;7(1). pii: E13. doi: 10.3390/sports7010013.
Authors: Read PJ, Turner AN, Clarke R, Applebee S, Hughes J
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Summary: It has been suggested that altering the knee flexion angle during a commonly used supine isometric strength test developed with professional soccer players changes preferential hamstring muscle recruitment. The aim of this study was to examine the electromyography (EMG) knee joint-angle relationship during this test, as these data are currently unknown. Ten recreational male soccer athletes (age: 28 ± 2.4 years) were recruited and performed a supine isometric strength test on their dominant leg with the knee placed at two pre-selected flexion angles (30° and 90°). The surface EMG of the gluteus maximus, biceps femoris, semitendinosus, and medial gastrocnemius was measured, in addition to the within-session reliability (intraclass correlation coefficient (ICC) and coefficient of variation (CV)). Within-session reliability showed large variation dependent upon the test position and muscle measured (CV% = 8.8⁻36.1) Absolute mean EMG activity and percentage of maximum voluntary isometric contraction (MVIC) indicated different magnitudes of activation between the two test positions; however, significant mean differences were present for the biceps femoris only with greater activation recorded at the 30° knee angle (% MVIC: 31 ± 9 vs. 22 ± 7; p = 0.002). These differences (30% mean difference) were greater than the observed typical measurement error (CV% = 13.1⁻14.3 for the 90° and 30° test positions, respectively). Furthermore, the percentage MVIC showed a trend of heightened activation of all muscles with the knee positioned at 30°, but there was also more within-subject variation, and this was more pronounced for the gluteus maximus (CV% = 36.1 vs. 19.8) and medial gastrocnemius (CV% 31 vs. 22.6). These results indicate that biceps femoris and overall posterior chain muscle activation is increased with the knee positioned at 30° of flexion; however, the 90° angle displayed less variation in performance within individual participants, especially in the gluteus maximus and medial gastrocnemius. Thus, practitioners using this test to assess hamstring muscle strength should ensure appropriate familiarisation is afforded, and then may wish to prioritise the 30° knee position.

#10 Interpersonal Coordination in Soccer: Interpreting Literature to Enhance the Representativeness of Task Design, From Dyads to Teams
Reference: Front Psychol. 2018 Dec 11;9:2550. doi: 10.3389/fpsyg.2018.02550. eCollection 2018.
Authors: Santos R, Duarte R, Davids K, Teoldo I
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Summary: Interpersonal coordination in soccer has become a trending topic in sports sciences, and several studies have examined how interpersonal coordination unfolds at different levels (i.e., dyads, sub-groups, teams). Investigations have largely focused on interactional behaviors at micro and macro levels through tasks from dyadic (i.e., 1 vs. 1) to team (i.e., 11 vs. 11) levels. However, as the degree of representativeness of a task depends on the magnitude of the relationship between simulated and intended environments, it is necessary to address a discussion on the correspondence between competitive and practice/experimental settings in soccer. The aims of this paper are to: (i) provide a brief description of the main concepts underlying the subject of interpersonal coordination in sports teams; (ii) demonstrate, through exemplar research findings, how interpersonal coordination in soccer unfolds at different scales; and (iii), discuss how coaches and researchers may ensure representativeness for practice and experimental tasks. We observed that papers addressing the analysis of interpersonal coordination tendencies in soccer often resort to dyadic (one vs. one) or sub-group (many vs. many) experimental tasks, instead of full-sized (11 vs. 11) games. Consequently, the extent to which such patterns reflect those observed in competition is somewhat uncertain. The design of practice and/or experimental tasks that rely on sub-phases of the game (e.g., 1 vs. 1, 4 vs. 4) should ensure the preservation of players' behavior patterns in intended match conditions (11 vs. 11). This can be accomplished by measuring the level of action fidelity of the task, ensuring correspondence and successful transfer across contexts.

#12 Use of Saliva in Alternative to Serum Sampling to Monitor Biomarkers Modifications in Professional Soccer Players
Reference: Front Physiol. 2018 Dec 20;9:1828. doi: 10.3389/fphys.2018.01828. eCollection 2018.
Authors: Francavilla VC, Vitale F, Ciaccio M, Bongiovanni T, Marotta C, Caldarella R, Todaro L, Zarcone M, Muratore R, Bellia C, Francavilla G, Mazzucco W
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Summary: We aimed to investigate the correlation between serum and salivary concentrations of steroid hormones and IgA, and the variation in concentrations of these biomarkers, across a soccer competitive season in a sample of players playing for an Italian major League team. Thirty-five elite male soccer players were recruited and assessed for salivary hormones (cortisol, testosterone, T/C‰ and DHEA-S) and IgA at three different time-points: (t1) after the pre-season period and 16 official matches played; (t2) after a winter break and three official matches played; (t3) 2 days after the final match of the championship and 19 matches played. Players were also tested for blood biomarkers (ser-C, ser-T, ser-T/C‰, ser-IgA, ACTH) at two detection times (t1 and t3). Blood samples were collected immediately after saliva sampling. The Spearman's rank correlation was used to explore the correlation between blood and salivary concentrations of cortisol, free testosterone and IgA in the different time points. One-way ANOVA and permutation test were performed to explore changes by time of hormones and IgA concentrations over the competitive season. We documented a positive correlation between serum and saliva concentrations for Cortisol at t1 (+58.2%; p-value = 0.002) and t3 (+54.2%; p-value = 0.018) and for Testosterone at t1 (+42.0%; p-value = 0.033). Moreover, a positive variation was documented across the season (D = t3-t1) for Cortisol (D = +6.83; SEM = ±2.70; Var% = +37.6; p-value = 0.032), Testosterone (D = +0.33; SEM = ±0.07; Var% = +27.3; p-value = 0.002) and DHEA-S (D = +44.48; SEM = ±18.54; Var% = +82.0; p-value = 0.042), while a decrease of sal-T/C ratio and no variation in salivary IgA concentrations were reported. In conclusion, our findings support for experimental use of saliva samples to monitor steroid hormones modifications in professional soccer players across a competitive season.

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