Latest research in football - week 26 - 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 The Evolution of Physical and Technical Performance Parameters in the Chinese Soccer Super League
Reference: Biol Sport. 2020 Jun;37(2):139-145. doi: 10.5114/biolsport.2020.93039. Epub 2020 Feb 11.
Authors: Changjing Zhou, Miguel-Ángel Gómez, Alberto Lorenzo
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Summary: Performance analysis in soccer has attained greater importance for coaching staff in order to gather and manage useful information (i.e., physical, technical, and tactical) of their teams during consecutive seasons. Accordingly, we examined the evolution of physical and technical performance parameters in the Chinese Soccer Super League (CSL). Data were collected from 1,429 CSL matches from the 2012 season to the 2017 season using the Amisco Pro (Amisco, Nice, France) system. Fourteen technical performance-related indicators and 11 physical performance-related indicators were analysed using a mixed linear model for repeated measures. Significant main effects of season were followed up using the Bonferroni correction (multiple comparisons). Although there were some irregularities, performance variables generally showed significant upward trends across the six seasons (p<0.05), resulting in significant increases from the 2012 season to the 2017 season in the total sprint distance (2,069.7±509.3 m vs. 2,272±493.6 m; p<0.001; effect size [ES]: 0.40), number of sprints (100.1±22.8 vs. 104.8±20.8, p<0.001; ES: 0.22), high-speed distance (2568.4±503.5 m vs. 2823.1±479.2 m; (p<0.001; ES: 0.52), and high-speed effort (187.5±36.1 to 204.7±33.7; p<0.001; ES: 0.49). Furthermore, there were ~23% more crosses (p<0.001; ES: 0.45), ~12% more shots on target (p<0.001; ES: 0.22), and ~11% more opponent penalty area entries (p<0.001; ES: 0.20) during the 2017 season than in the 2012 season. Coaches and sports scientists should be mindful of this evolution when preparing training sessions and recruiting new players, and even when predicting future trends in the Chinese Soccer Super League.

#2 The Cumulative and Residual Changes in Eccentric Knee Flexor Strength Indices Following Soccer-Specific Treadmill Running: Novel Considerations of Angle Specific Torque
Reference: J Sports Sci. 2020 Jun 7;1-9. doi: 10.1080/02640414.2020.1763053. Online ahead of print.
Authors: Richard Michael Page, Matt Greig
Summary: With potential implications for recovery and conditioning practices, the aim of this study was to assess the cumulative and residual response of angle specific eccentric knee flexor (eccKF) strength indices following soccer-specific activity. Thirteen semi-professional soccer players were therefore required to complete a 90-minute soccer-specific treadmill running. with eccKF isokinetic strength assessments completed pre-trial, immediately post-trial, and 48 hours post-trial. The strength assessments comprised the completion of 5 repetitions at angular velocities of 60 and 300 deg·s-1. Isokinetic data was analysed for measures of peak torque (PT), angle of peak torque (APT), functional range (FR), and angle specific torque (AST). Significant post-trial impairments were observed for measures of slow velocity PT60 (6.6%) and AST300 (12.5%). Further significant differences were observed 48 hours post-trial for PT300 (10.7%) and PT60 (12.8%) PT, APT60 (~15°), and AST300 (>13.6%). These data have implications for post exercise recovery monitoring and the prescription of recovery modalities and conditioning practices in the 2 days following match-play. The AST and APT responses highlight the importance of analysis of the entire strength-angle curve and at a range of angular velocities.

#3 Poor Hamstrings-To-Quadriceps Torque Ratios in Male Soccer Players: Weak Hamstrings, Strong Quadriceps, or Both?
Reference: Sports Biomech. 2020 Jun 8;1-11. doi: 10.1080/14763141.2020.1766100. Online ahead of print.
Authors: Carolina G Fritsch, Maurício P Dornelles, Gabriel Dos S Oliveira, Bruno M Baroni
Summary: This study aimed to evaluate the influence of hamstrings and quadriceps strength on the hamstrings-to-quadriceps conventional (H:Qcon) and functional (H:Qfun) ratios in male soccer players. Quadriceps concentric peak torque (PT) and hamstrings concentric and eccentric PT were assessed with isokinetic dynamometry at 60°/s in 101 players (202 legs). The cut-points of 0.50, 0.55 and 0.60 were used to assess muscle imbalance through the H:Qcon ratio, while 0.80, 0.85 and 0.90 were used for H:Qfun ratio. Legs with lower H:Qcon ratio had decreased hamstrings concentric PT (p < 0.01; moderate and large effect sizes) and increased quadriceps concentric PT (p < 0.01; moderate effect sizes) in all cut-points. Legs with lower H:Qfun ratio had decreased hamstrings eccentric PT (p < 0.01; large effect sizes) for all cut-points, and controversial results for quadriceps concentric PT (p < 0.01 only for 0.80 cut-point; small effect sizes). H:Qcon ratio presented only weak correlations with quadriceps (r = -0.37) and hamstrings (r = 0.45) concentric PT, while H:Qfun ratio had a negligible correlation with quadriceps concentric PT (r = -0.30) and a moderate correlation with hamstrings eccentric PT (r = 0.66). In conclusion, our findings support that hamstrings strength deficit is the key factor for low H:Q ratios in male soccer players, especially those with poor H:Qfun ratio.

#4 Bilateral Deficit and Bilateral Performance: Relationship With Sprinting and Change of Direction in Elite Youth Soccer Players
Reference: Sports (Basel). 2020 Jun 3;8(6):E82. doi: 10.3390/sports8060082.
Authors: Giampiero Ascenzi, Bruno Ruscello, Cristoforo Filetti, Daniele Bonanno, Valter Di Salvo, F Javier Nuñez, Alberto Mendez-Villanueva, Luis Suarez-Arrones
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Summary: The purpose of the study was to examine the differences in bilateral deficit (BLD) at different loadings during the half-squat jump (SJ) and horizontal countermovement jump (HCMJ) to determine if there is a relationship with linear sprint or change of direction (COD). The second goal was to check if fast players were more powerful in SJ and HCMJ than slow players in bilateral performance (BP). Twenty-seven male youth soccer players participated in the study. Players were divided in two groups, faster and slower, according to their sprint performance (10 and 40 m). BLD average power with body weight (BW) and 25%BW were significantly higher than 50%BW (p < 0.01). BLD during HCMJ was significantly higher than BLD during SJ with BW, 25%BW and 50%BW (p < 0.01). There were no statistical relationships between BLD and sprint or COD performance (p > 0.05). Fast players showed significantly higher SJ power with all the different loads and HCMJ than slow players (p < 0.01), and fast players lost more time executing COD-90° than slow players (p < 0.01). There were no statistical differences between fast and slow players in BLD. BLD seems to be dependent on motor task, contraction type and load and could not be a proper measure to estimate sprint and COD performance. Faster players are confirmed to be more powerful players than slow players, and decrements in COD could be a key benchmark to identify deficit between linear and COD performance.

#5 Comparison of 10 vs. 20 Min Neuromuscular Training for the Prevention of Lower Extremity Injuries in Male Youth Football: A Cluster Randomised Controlled Trial
Reference: J Sports Sci. 2020 Jun 10;1-9. doi: 10.1080/02640414.2020.1776459. Online ahead of print.
Authors: Anna Lina Rahlf, Astrid Zech
Summary: The aim of this study was to compare the effects of 20 min neuromuscular training with a programme of 10 min in youth football players. 342 (15.4 ± 1.7 years) male football players from 18 teams were included, and cluster-randomized by team into two intervention groups. Both groups performed an injury prevention programme twice a week over five months using the same exercises but a different duration. The first intervention group (INT10, n = 175) performed the programme for 10 min, the second intervention group (INT20, n = 167) for 20 min. Primary outcomes were lower extremity (LE) injuries. Secondary outcomes were injury type, severity, mechanism and compliance to the intervention. 13 teams with 185 players were included for final analysis. No significant group difference was found between INT10 (6.37 per 1000 h) and INT20 (7.20 per 1000 h) for the incidence rate ratio of the lower extremities (IRR = 1.03, 95% confidence interval 0.59, 1.79), nor for the distribution of injury location, type, severity or mechanism. The results show that performing preventive exercises for 10 min is no less effective than 20 min in youth football players. Shorter training sessions can, therefore, be effectively used for injury prevention.

#6 The Resumption of Sports Competitions After COVID-19 Lockdown: The Case of the Spanish Football League
Reference: Chaos Solitons Fractals. 2020 Sep;138:109964. doi: 10.1016/j.chaos.2020.109964. Epub 2020 Jun 4.
Authors: Javier M Buldú, Daniel R Antequera, Jacobo Aguirre
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Summary: In this work, we present a stochastic discrete-time SEIR Susceptible-Exposed-Infectious-Recovered model adapted to describe the propagation of COVID-19 during a football tournament. Specifically, we are concerned about the re-start of the Spanish national football league, La Liga, which is currently -May 2020- stopped with 11 fixtures remaining. Our model includes two additional states of an individual, confined and quarantined, which are reached when an individual presents COVID-19 symptoms or has undergone a virus test with a positive result. The model also accounts for the interaction dynamics of players, considering three different sources of infection: the player social circle, the contact with his/her team colleagues during training sessions, and the interaction with rivals during a match. Our results highlight the influence of the days between matches, the frequency of virus tests and their sensitivity on the number of players infected at the end of the season. Following our findings, we finally propose a variety of strategies to minimise the probability that COVID-19 propagates in case the season of La Liga was re-started after the current lockdown.

#7 Monitoring Matches and Small-sided Games in Elite Young Soccer Players
Reference: Int J Sports Med. 2020 Jun 26. doi: 10.1055/a-1165-1916. Online ahead of print.
Authors: Jonas Darbellay, Davide Malatesta, César Marius Philippe Meylan
Summary: The aim of this study was to compare the distances at various intensity in matches and small-sided games in elite-young soccer players using the metabolic power approach and running speed methods through fixed and individual speed zones. The second aim was to investigate the difference in high intensity external workload (% of total distances covered > 16 km/h or > 20 W/kg) between matches and small-sided games. Global positioning system data from 14 elite-youth players were analyzed during 13 matches and two types of small sided-games. Five intensity zones were used to compare the running distances between the metabolic power approach and the classic performance analysis. Metabolic power recorded more distances covered at high intensity than the running speed methods for every playing situations, except for the zone 5 of fixed speed (> 19 km/h) in matches (P<0.05). Smaller differences of external workload at high intensity were found when using the metabolic power approach compared to the traditional performance analysis. Our results highlight that the traditional analysis underestimates the athlete's high intensity efforts. The metabolic power approach seems more relevant to monitor matches and training situations but also to compare matches to small-sided games in elite-young soccer players.

#8 Level of Play and Coach-Rated Game Intelligence Are Related to Performance on Design Fluency in Elite Soccer Players
Reference: Sci Rep. 2020 Jun 25;10(1):9852. doi: 10.1038/s41598-020-66180-w.
Authors: T Vestberg, R Jafari, R Almeida, L Maurex, M Ingvar, P Petrovic 
Summary: Executive brain functions are innate mechanisms for regulating behavior. While the impact of suboptimal executive functions has been characterized in patients, their contribution to individual success has not been elucidated. We set out to understand how executive functions relate to successful human behavior by examining their relation to game intelligence in sport - the ability to read a game and quickly adapt the behavior. In elite soccer players (n = 51), those playing in national teams (national team players) significantly outperformed those only playing at premier league level (premier league players) in Design Fluency (DF), a complex visuo-spatial executive function test that includes measures of creativity and cognitive flexibility. Their result showed a moderate correlation with coach rated game intelligence, remained also when correcting for low level cognitive capacity and was most evident when considering cognitive flexibility. DF capacity also correlated with number of assists made during the season but not with number of made goals during the same period, linking the fast planning of several steps in DF to fast planning of several steps in the soccer game. Altogether, our data suggests that DF capacity relates to success in soccer both on a subjective and on an objective level.

#9 Understanding the Underlying Mechanisms of Quiet Eye: The Role of Microsaccades, Small Saccades and Pupil-Size Before Final Movement Initiation in a Soccer Penalty Kick
Reference: Eur J Sport Sci. 2020 Jun 25;1-27. doi: 10.1080/17461391.2020.1788648. Online ahead of print.
Authors: Piras Alessandro, Timmis Matthew, Trofè Aurelio, Raffi Milena
Summary: Experts keep a steady final fixation at a specific location just before final movement initiation, the so-called "quiet eye" (QE). However, the eyes are rarely "quiet", and small eye movements occur during visual fixation. The current research investigated the subtle eye movements and underlying mechanisms immediately prior to and during QE. The gaze behaviour of 8 intermediate-level goalkeepers was recorded as they moved (either left or right) in an attempt to predict the future direction of the ball during a soccer penalty kick. Goalkeepers were more likely to predict the direction of the penalty, which was coupled with delaying movement initiation. The temporal sequence of microsaccade rates dropped ∼1000 ms before goalkeepers' final movement initiation. Saccade rates increased, reaching a peak ∼500 ms before final movement initiation, concomitant with microsaccades reduction. Microsaccades predicted the goalkeepers' direction, oriented to the right when goalkeepers moved to the right, and conversely to the left when they moved to the left. Microsaccades may be modulated by attention and appear functionally related to saccadic intrusions. Pupil-size increased proportionally with the lead up to the instance of the penalty being kicked, reaching a plateau at final movement initiation. In conclusion, microsaccades and small saccades could improve the perception of the soccer penalty kick, helping athletes during the period that precedes the critical movement initiation, shifting from covert to overt attention for identifying the useful cues necessary to guide the action.

#10 Basic Cognitive Abilities Relevant to Male Adolescents' Soccer Performance
Reference: Percept Mot Skills. 2020 Jun 23;31512520930158. doi: 10.1177/0031512520930158. Online ahead of print.
Authors: Dragan Glavaš
Summary: While there is a theoretical and empirical consensus that specific cognitive abilities gained through deliberate sports practice influence sports performance, it is less clear whether basic cognitive abilities that are not specifically related to sports practice are relevant to sports performance. Accordingly, this research examined the roles of basic concentration and visuospatial ability in adolescent soccer performance. Participants were 46 adolescent male soccer players (Mage = 16.15 years, standard deviation = 1.13) who averaged 7.21 years (standard deviation = 2.2) of prior soccer training. We measured participant's basic cognitive abilities with the Corsi block and the concentration grid tasks, and we measured their soccer performance through five soccer skills. Concentration had no predictive role in elements of soccer performance, but visuospatial ability was significantly related to tactical abilities, technical skills, mental toughness, and situational awareness and thus, to overall soccer performance. These findings provided support for the importance of visuospatial ability but not concentration (as measured by the concentration grid) in young males' soccer performance.

#11 Sensory Reweighting for Upright Stance in Soccer Players: A Comparison of High and Low Exposure to Soccer Heading
Reference: J Neurotrauma. 2020 Jun 22. doi: 10.1089/neu.2020.7001. Online ahead of print.
Authors: Jaclyn B Caccese, Fernando V Santos, Felipe Yamaguchi, John J Jeka
Summary: The purpose of this study was to compare sensory reweighting for upright stance between soccer players who report higher soccer heading exposure to those who report lower soccer heading exposure. Thirty participants completed a self-reported questionnaire to estimate the number of soccer headers experienced over the prior year and were divided into "low exposure" and "high exposure" groups based on their responses. Sensory reweighting for upright stance was assessed by simultaneously perturbing visual, vestibular, and proprioceptive systems. The visual stimulus was a sinuosoidal translation of the visual scene at 0.2Hz, the vestibular stimulus was ±1mA binaural monopolar galvanic vestibular stimulation (GVS) at 0.36Hz, and the proprioceptive stimulus was Achilles tendon vibration at 0.28Hz. The visual stimulus was presented at two amplitudes (0.2m, 0.8m). Center of mass (COM) gain/phase to each modality, total power, 95% area and velocity were compared between "low exposure" (N=15, 6 males, 21.5±1.9years, 27.7±31.6headers) and "high exposure" groups (N=15, 10 males, 22.1±3.5years, 734.9±877.7headers). Without vibration, COM 95% area (F=5.861, p=.022*, partial η²=.173), velocity (F=14.198, p=.001, partial η²=.336), and total power (F=13.491, p=.001, partial η²=.325) for the "high exposure" group were higher than for the "low exposure" group and postural sway lagged the vestibular stimulus in the "high exposure" group rather than leading it as in the "low exposure" group (F=4.765, p=.038, partial η²=.145). There were no differences in sensory reweighting and no differences in COM gain/phase between groups. These findings lend empirical evidence to a detrimental effect of soccer heading exposure on balance control during upright stance.

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