Latest research in football - week 44 - 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 Effect of skill-based training vs. small-sided games on physical performance improvement in young soccer players
Reference: Biol Sport. 2020 Sep;37(3):305-312. doi: 10.5114/biolsport.2020.96319. Epub 2020 Jun 26.
Authors: Mustafa Karahan
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Summary: Recently, there has been increasing attention to research related to the effect of skill-based or game-based training on soccer players' physical performance. Therefore, this study aimed to compare the effectiveness of skill-based training (SBT) at maximum intensity versus the small-sided game (SSG) on the physical performance characteristics of young soccer players during the pre-season period. Twenty-two male soccer players (mean age 15.3 ± 3 years) were randomly assigned to either an SBT or SSG fully controlled intervention programme, running parallel for eight weeks and held twice a week. On three non-consecutive days before and after training players completed a test battery consisting of the 20 m sprint, T-run, countermovement jump, running anaerobic sprint test (RAST) and 20 m shuttle run. Data were analysed with a two-way ANOVA test for repeated measures. SBT and SSG interventions induced a significant improvement in the anaerobic power (10.9% vs 6.2%), explosive power (8.5% vs 5.6%), VO2max (6.7% vs 6.5%) and vertical jump (5.3% vs 2.9%), respectively. When the improvements in the physical performance variables of both groups are compared, the SBT group achieved greater improvement than the SSG group in anaerobic power (by 4.7%), in explosive power (by 2.8%), in vertical jumping (by 2.3%), in the 20 m sprint (by 2.2%) and T-test scores (by 1.7%). However, improvements in the VO2max were similar in both groups. The results of the present study suggest that SBT at maximum intensity may be more effective than SSG in improving the physical performance characteristics of young soccer players in the pre-competitive season.

#2 Curve sprinting in soccer: relationship with linear sprints and vertical jump performance
Reference: Biol Sport. 2020 Sep;37(3):277-283. doi: 10.5114/biolsport.2020.96271. Epub 2020 Jun 9.
Authors: Irineu Loturco, Lucas A Pereira, Alberto Fílter, Jesús Olivares-Jabalera, Valter P Reis, Victor Fernandes, Tomás T Freitas, Bernardo Requena
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Summary: We examined the relationships among linear speed, vertical jumping ability and curve sprint (CS) performance. Moreover, the correlations between linear and curvilinear sprint velocities and CS deficit were tested. Twenty-eight under-20 soccer players performed squat and countermovement jumps, 17-m linear sprint (with split times at 5 and 10 m), and a CS test for both sides. For the first time, the new proposed CS deficit was calculated as the difference between 17-m velocity and CS test velocity. Pearson's product moment of correlation was performed to determine the relationships among the distinct variables tested. Significance level was set at P < 0.05. Large to very large relationships between linear sprint speed and CS performance were observed, on both the "good" and "weak" sides. In addition, moderate to large correlations between linear and curve sprint abilities and vertical jumps were found. Finally, the CS deficit was negatively associated with the CS good side performance. Linear sprint and CS velocities for both good and weak sides were closely related. The CS deficit was only related to the CS weak side performance, and the vertical jumping ability was significantly associated with both linear and curvilinear sprint velocities. The present results suggest that training methods capable of improving linear sprint and vertical jumping abilities may also improve CS performance.

#3 Changes in γH2AX and H4K16ac levels are involved in the biochemical response to a competitive soccer match in adolescent players
Reference: Sci Rep. 2020 Sep 2;10(1):14481. doi: 10.1038/s41598-020-71436-6.
Authors: Katarzyna Kozioł, Jacek Zebrowski, Gabriela Betlej, Ewelina Bator, Wojciech Czarny, Wojciech Bajorek, Bartłomiej Czarnota, Robert Czaja, Paweł Król, Aleksandra Kwiatkowska
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Summary: The aim of this study was to examine novel putative markers of the response to the competitive soccer match in adolescent players, such as changes in global levels of γH2AX and H4K16ac in the chromatin of peripheral mononuclear blood cells (PMBCs) and a Fourier-transform infrared spectroscopy (FTIR)-based biochemical fingerprint of serum. These characteristics were examined with reference to the physiological and metabolic aspects of this response. Immediately post-match we noticed: (1) a systemic inflammatory response, manifesting as peaks in leukocyte count and changes in concentrations of IL-6, TNFα, and cortisol; (2) a peak in plasma lactate; (3) onset of oxidative stress, manifesting as a decline in GSH/GSSG; (4) onset of muscle injury, reflected in an increase in CK activity. Twenty-four hours post-match the decrease in GSH/GSSG was accompanied by accumulation of MDA and 8-OHdG, macromolecule oxidation end-products, and an increase in CK activity. No changes in SOD1 or GPX1 levels were found. Repeated measures correlation revealed several associations between the investigated biomarkers. The FTIR analysis revealed that the match had the greatest impact on serum lipid profile immediately post-game. In turn, increases in γH2AX and H4K16ac levels at 24 h post-match indicated activation of a DNA repair pathway.

#4 Prospective analysis of craniofacial soccer incidents during FIFA competitions: an observational study
Reference: Braz Oral Res. 2020;34:e106. doi: 10.1590/1807-3107bor-2020.vol34.0106. Epub 2020 Aug 28.
Authors: Mateus de Azevedo Kinalski, Kaue Collares, Marcos Britto Correa
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Summary: The aim of this prospective epidemiological study was to evaluate the occurrence of incidents involving the craniofacial region of soccer players during three official FIFA competitions. The craniofacial incidents were identified by video analysis of all 144 matches of two FIFA World Cups (2014/2018) and the 2017 FIFA Confederations Cup. Data collection included incident type, incident severity, site affected, incident cause and referee decision. The multivariate Poisson regression model was performed to analyze the associations between covariates. A total of 238 incidents were observed in the craniofacial region (1.6 incidents/match), representing a rate of 48.5 incidents per 1000 hours. At least 80.6% of the matches presented at least one incident, and, in more than 60%, the referee's decision was no foul. According to severity, 26.8% of the incidents were classified as having mild or high severity. Incidents involving lacerations or fracture presented higher severity compared with hits (IRR 3.45[95%CI: 1.89-6.30]). Head-to-head impacts showed an incidence of severe incidents twice as high as those involving upper extremities (IRR 2.01[95%CI:1.07-3.76]). A high number of craniofacial incidents were observed in the last FIFA competitions. Head-to-head impacts and lacerations or fractures were associated with higher incident severity.

#5 Can A Superimposed Whole-Body Electromyostimulation Intervention Enhance the Effects of a 10-Week Athletic Strength Training in Youth Elite Soccer Players?
Reference: J Sports Sci Med. 2020 Aug 13;19(3):535-546. eCollection 2020 Sep.
Authors: Oliver Ludwig, Joshua Berger, Torsten Schuh, Marco Backfisch, Stephan Becker, Michael Fröhlich
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Summary: Strength training in youth soccer has both a preventive and a sports-specific component. Whole-body electromyostimulation (WB-EMS) could represent an interesting time-saving add-on to classical strength exercises in performance-oriented soccer. The objective of this study was to find out whether a 10-week superimposed WB-EMS training might have a more positive impact on strength parameters in male youth elite soccer players than regular athletic strength exercises alone. A total of 30 male youth soccer players from a youth academy aged 15 to 17 years participated in the study. Before and after the intervention, the isometric extension and flexion forces of trunk and knee, and the hip abduction and adduction forces were tested. Twelve players (control group) absolved a conventional 20-minute strength training once a week for a period of ten weeks. Eighteen players absolved the same exercises but with superimposed WB-EMS. Blood creatine kinase concentration was measured for training control. ANOVAs, Friedman tests and post hoc t-tests were calculated (p = 0.05) to examine the strength development during the training period between the groups. While we could not find significant strength increases in the leg, hip and trunk muscles in the control group (<4%), the strength of the WB-EMS group improved significantly in 4 of the 6 muscle groups tested. In this group, the strength of knee flexors increased significantly by 20.68 ± 21.55%, knee extensors by 31.43 ± 37.02%, hip adductors by 21.70 ± 12.86% and trunk flexors by 33.72 ± 27.43%. The rates of strength increase are partly in line with other studies, partly clearly higher, which might be explained by the athletically active target group. A 10-week superimposed WB-EMS training improves the strength of certain leg, hip and trunk muscles in male adolescent elite soccer players to a greater extent than a pure athletic strength training of the same duration.

#6 Can Haematological and Hormonal Biomarkers Predict Fitness Parameters in Youth Soccer Players? A Pilot Study
Reference: Int J Environ Res Public Health. 2020 Aug 29;17(17):E6294. doi: 10.3390/ijerph17176294.
Authors: Fabrizio Perroni, Silvia Migliaccio, Paolo Borrione, Mario Vetrano, Stefano Amatori, Davide Sisti, Marco B L Rocchi, Gerardo Salerno, Riccardo Del Vescovo, Elena Cavarretta, Laura Guidetti, Carlo Baldari, Vincenzo Visco
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Summary: The study aimed to investigate the correlations among immune, haematological, endocrinological markers and fitness parameters, and assess if the physiological parameters could be a predictor of fitness values. Anthropometric, physical evaluations (countermovement jump-CMJ, 10 m sprint, VO2max, repeated sprint ability-RSA total time and index) and determination of blood (IL-6, IL-10, IL-17A and tumour necrosis factor) and salivary (testosterone and cortisol) samples parameters in 28 young male soccer players (age: 13.0 ± 0.2 years, body mass index (BMI): 19.5 ± 2.2 kg/m2) were analysed. To evaluate the dependence of the variables related to athletic performance, multiple linear regression with backward stepwise elimination was considered. A significant regression equation was found in CMJ (F(5,16) = 9.86, p < 0.001, R2 adjusted = 0.679) and in the RSA index (F(5,16) = 15.39, p < 0.001, R2 adjusted = 0.774) considering only five variables, in a 10 m sprint (F(4,17) = 20.25, p < 0.001, R2 adjusted = 0.786) and in the RSA total time (F(4,17) = 15.31, p < 0.001, R2 adjusted = 0.732) considering only four variables and in VO2max (F(9,12) = 32.09, p < 0.001, R2 adjusted = 0.930) considering nine variables. Our study suggests the use of regression equations to predict the fitness values of youth soccer players by blood and saliva samples, during different phases of the season, short periods of match congestion or recovery from an injury.

#7 Fair Play as an Injury Prevention Intervention: Do Yellow Card Accumulation Policies Reduce High School Soccer Injuries?
Reference: Clin J Sport Med. 2020 Sep 15. doi: 10.1097/JSM.0000000000000877. Online ahead of print.
Authors: Peter K Kriz, Jingzhen Yang, Alan Arakkal, Timothy Keeley, R Dawn Comstock
Summary: The objective was to Evaluate yellow card policies' (YCPs) effectiveness in reducing competition contact injuries (CCIs). Soccer players from High School (HS) Reporting Information Online participating schools, 2005/06 to 2017/18. Athlete exposure (AE), CCIs from HS competitions collected from states with/without YCPs were used as independent variables. Rate and rate ratio (RR) of athlete-athlete CCIs recorded by athletic trainers were compared between states with/without YCPs and pre-YCPs/post-YCPs among the states with YCPs using Poisson regressions. Proportions of severe athlete-athlete CCIs were also described in states with/without YCPs. Fifteen states implemented YCPs between 2005/06 and 2017/18; 901 athlete-athlete CCIs occurred during 352 775 competition AEs in states with YCPs, and 3525 injuries during 1 459 708 competition AEs in states without YCPs. There was no significant difference in injury rates between schools in states with/without YCPs (RR 1.07; 95% confidence interval [CI]: 0.97-1.17). Among state with YCPs, injury rates were not significantly different between pre-YCP and post-YCP implementation (RR 1.15; 95% CI: 0.98-1.34). Although a significantly lower proportion of injuries resulting in >3 weeks' time loss (TL) occurred in states with YCPs (injury proportion ratio 0.81; 95% CI: 0.66-0.997), no significant differences were observed in proportions of other severe athlete-athlete CCIs between states with/without YCPs. Yellow card policies were ineffective in lowering HS soccer athlete-athlete CCI rates, although injuries resulting in >3 weeks' TL were less prevalent in states with YCPs. Implementation of YCPs alone, without proper enforcement, may not be a sufficient injury prevention strategy.

#8 Sportomics in professional soccer players: metabolomics results during preseason
Reference: J Sports Med Phys Fitness. 2020 Sep 16. doi: 10.23736/S0022-4707.20.11200-3. Online ahead of print.
Authors: Roberta Pintus, Tindaro Bongiovanni, Sara Corbu, Vincenzo C Francavilla, Angelica Dessí, Antonio Noto, Giovanni Corsello, Gabriele Finco, Vassilios Fanos, Flaminia C Marincola
Summary: Sportomics is the application of metabolomics to study the metabolism shifts of individuals that practice sports or do physical exercise. This aim is reached by the analysis of low molecular weight metabolites (< 1.5 kDa) present in biological fluids such as blood, saliva or urine. In this study, authors performed a 1H-NMR analysis of urine from 21 professional soccer players collected at 3 different time points during the pre-season preparation period before the beginning of Serie A Championship (First Division) in Italy. Urine profile changed during the observational period. In particular, significant variations were observed for trimethylamine-N-oxide, dimethylamine, hippuric acid, hypoxantine, guanidoacetic acid, 3-hydroxybutyric acid, citric acid and creatine. These modifications could be related to the diet, training and microbiota. For instance, trimethylamine-N-oxide and hippuric acid are both of dietary origins but are also related to the microbiota, while 3-hydroxy-butyric acid is associated with the type of physical exercise. This is the first sportomics study ever performed on professional soccer players, according to authors' knowledge. In the future, sportomics could be applied in a tailored way to choose the best diet and training program in the single individual to obtain the best possible performances and to prevent injuries of athletes.

#9 Incidence of injuries in young soccer players: epidemiological study in an Italian elite club
Reference: J Sports Med Phys Fitness. 2020 Sep 16. doi: 10.23736/S0022-4707.20.11157-5. Online ahead of print.
Authors: Gabriele Thiebat, Andrea Spreafico, Stefano Mazzoni, Giovanni Ravasio, Laura De Girolamo, Herbert Schoenhuber
Summary: Football is the most popular sport in the world, increasingly played by the youngsters. However, little epidemiological data exists regarding injuries in young players. The aim of this study was to describe the most common types and sites of injury among the different classes of a single professional football club. The present perspective study covered a three-season period, including 679 children divided in 9 age classes. All the athletes were managed by the same staff and for each injury, onset date, date of return to training, anatomic site and type of injury were recorded. The mean age of the population was 12.7 years old (Range 7.4- 16.9). A total 975 injuries were recorded without significant differences among seasons (p=0.682). The most affected classes were U17 and U16, while the lowest rate of injury was in U11. The most common injury in U9 and U10 affected foot & ankle, while in all the other classes thigh was the most frequently site involved. Focusing on the type of injury, the most common cause was traumatic (40.9%), followed by muscular diseases. The mean value of absence from soccer was 19.7 days (± 1.2). The highest rate of injuries occurred in September and August. In January and February, injuries were more frequent during competitions, whereas in the other months the rate was inverted. This study highlights that pre-season and the final phase of the season are more at risk of injury and the type of injury differs between classes.

#10 Morphology of possible regions in elite soccer players
Reference: Sports Biomech. 2020 Sep 16;1-14. doi: 10.1080/14763141.2020.1797862. Online ahead of print.
Authors: Nikolas Sten Knudsen, Thomas Bull Andersen
Summary: The popularity of spatio-temporal analyses in soccer is increasing. As many of these analyses depend on the regions a player can occupy in a certain amount of time (the possible regions), the understanding of this concepts is important for analyses to produce usable results. This study investigated how possible regions of soccer morph with varying times and running speeds. Twenty-four players from the Danish Superliga participated, and 13 players were analysed. The possible regions were analysed with times from 0.5 to 4 s (0.5 s increments) and initial velocities from 1 to 7 m/s (1 m/s increments). In this study, we showed that the possible regions can be described by ellipses (eccentricity of 0.5348 ± 0.1912). When comparing the possible region ellipses at every time and velocity pair, 1.95 % of the ellipses were not significantly different from the others. In conclusion, possible regions are unique in shape and size depending on player running speed and time available. However, as only few strikers participated, the results for this group should be interpreted with caution. Coaches can predict possible regions based on these parameters increasing precision of post-game analyses.

#11 Developmental differences of kinematic and muscular activation patterns in instep soccer kick
Reference: Sports Biomech. 2020 Sep 15;1-16. doi: 10.1080/14763141.2020.1815827. Online ahead of print.
Authors: Ali Onur Cerrah, Deniz Şimsek, Abdullah Ruhi Soylu, Hiroyuki Nunome, Hayri Ertan
Summary: Kinematic and neuromuscular activity differences amongst soccer players in different age groups were examined in this study. Thirty male soccer players evenly divided into three age groups (Group 1: age 12-13; Group 2: age 14-15; Group 3: age 16-17) were asked to perform instep kicks towards a target 11 m away. Their anthropometrics, instep kick kinematics, resultant ball velocities, both legs isokinetic strength, and electromyography (EMG) during kicking were compared amongst the three age groups. There were significant differences in height, body mass, body mass index, ball velocities, and isokinetic strength values amongst three age groups. Also, kicking kinematics including angular and linear velocities of hip, knee, ankle, and toe were significantly different (p < 0.05) amongst groups in several kicking phases. Furthermore, the activities of m. rectus femoris, m. vastus medialis, m. biceps femoris were significantly different amongst groups (p < 0.05). The ball velocities and leg strength parameters increased with age, neuromuscular activations, and kinematic parameters differed especially in leg-coking and forward swing phase of instep soccer kick. It should be concluded that an increase of resultant ball velocity of the instep kick is closely associated with chronical age, the development of leg muscle strength, and the neuromuscular activity of the kicking leg.

#12 Body Water Content and Morphological Characteristics Modify Bioimpedance Vector Patterns in Volleyball, Soccer, and Rugby Players
Reference: Int J Environ Res Public Health. 2020 Sep 10;17(18):E6604. doi: 10.3390/ijerph17186604.
Authors: Francesco Campa, Analiza M Silva, Catarina N Matias, Cristina P Monteiro, Antonio Paoli, João Pedro Nunes, Jacopo Talluri, Henry Lukaski, Stefania Toselli
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Summary: Bioimpedance vector analysis (BIVA) is a widely used method based on the interpretation of raw bioimpedance parameters to evaluate body composition and cellular health in athletes. However, several variables contribute to influencing BIVA patterns by militating against an optimal interpretation of the data. This study aims to explore the association of morphological characteristics with bioelectrical properties in volleyball, soccer, and rugby players. 164 athletes belonging to professional teams (age 26.2 ± 4.4 yrs; body mass index (BMI) 25.4 ± 2.4 kg/m2) underwent bioimpedance and anthropometric measurements. Bioelectric resistance (R) and reactance (Xc) were standardized for the athlete's height and used to plot the vector in the R-Xc graph according to the BIVA approach. Total body water (TBW), phase angle (PhA), and somatotype were determined from bioelectrical and anthropometric data. No significant difference (p > 0.05) for age and for age at the start of competition among the athletes was found. Athletes divided into groups of TBW limited by quartiles showed significant differences in the mean vector position in the R-Xc graph (p < 0.001), where a higher content of body fluids resulted in a shorter vector and lower positioning in the graph. Furthermore, six categories of somatotypes were identified, and the results of bivariate and partial correlation analysis highlighted a direct association between PhA and mesomorphy (r = 0.401, p < 0.001) while showing an inverse correlation with ectomorphy (r = -0.416, p < 0.001), even adjusted for age. On the contrary, no association was observed between PhA and endomorphy (r = 0.100, p = 0.471). Body fluid content affects the vector length in the R-Xc graph. In addition, the lateral displacement of the vector, which determines the PhA, can be modified by the morphological characteristics of the athlete. In particular, higher PhA values are observed in subjects with a high mesomorphic component, whereas lower values are found when ectomorphy is dominant.

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