Latest research in football - week 23 - 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 Sprint Endurance Abilities in Elite Female Soccer Players
Reference: Int J Sports Physiol Perform, 2020 May 29;1-7. doi: 10.1123/ijspp.2019-0526. Online ahead of print.
Authors: Carlo Castagna, Stefano D'Ottavio, Paolo Roberto Gabrielli, Susana Póvoas
Summary: The aim was to profile sprint endurance performance of elite-level female soccer players. Twenty-five female national-team soccer players (age 25.1 [2.7] y, body mass 59.6 [3.6] kg, height 168.5 [4.1] cm) were tested for sprint endurance, performing 5 maximal sprints, interspersed with 30 seconds of active recovery (5 × 30 m) and a 30-second all-out shuttle run in a soccer pitch. The Yo-Yo Intermittent Recovery Test level 1 (YYIR1) evaluated intermittent high-intensity endurance under the same field-testing conditions. Maximal anaerobic capacity was assessed while participants performed three 10-second all-out bouts separated by 20 seconds of passive recovery (3 × 10 s) on a nonmotorized treadmill. Huge interplayer variability was observed for sprint decrements in 3 × 10 seconds (coefficient of variation = 37%) and 5 × 30 m (coefficient of variation = 62%). The 3 × 10 performance was largely associated with 5 × 30-m mean and best time and very largely with 30 seconds. A very large and nearly perfect correlation was observed between 30 seconds and 5 × 30 mMean (r = -.86) and 5 × 30 mBest (r = -.92), respectively. The YYIR1 was moderately to largely associated with 5 × 30-m variables and 30 seconds, respectively. A nearly perfect association was observed between 5 × 30 mBest and 5 × 30 mMean (r = .97). Elite female soccer players' sprint endurance variables are characterized by remarkable variability. Associations between sprint endurance variables suggest physiological interdependence and a likelihood of a general ability in sustaining sprinting in this population.

#2 The Value of Preseason Screening for Injury Prediction: The Development and Internal Validation of a Multivariable Prognostic Model to Predict Indirect Muscle Injury Risk in Elite Football (Soccer) Players
Reference: Sports Med Open, 2020 May 27;6(1):22. doi: 10.1186/s40798-020-00249-8.
Authors: Tom Hughes , Richard D Riley, Michael J Callaghan, Jamie C Sergeant
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Summary: In elite football (soccer), periodic health examination (PHE) could provide prognostic factors to predict injury risk. The aim was to develop and internally validate a prognostic model to predict individualised indirect (non-contact) muscle injury (IMI) risk during a season in elite footballers, only using PHE-derived candidate prognostic factors. Routinely collected preseason PHE and injury data were used from 152 players over 5 seasons (1st July 2013 to 19th May 2018). Ten candidate prognostic factors (12 parameters) were included in model development. Multiple imputation was used to handle missing values. The outcome was any time-loss, index indirect muscle injury (I-IMI) affecting the lower extremity. A full logistic regression model was fitted, and a parsimonious model developed using backward-selection to remove factors that exceeded a threshold that was equivalent to Akaike's Information Criterion (alpha 0.157). Predictive performance was assessed through calibration, discrimination and decision-curve analysis, averaged across all imputed datasets. The model was internally validated using bootstrapping and adjusted for overfitting. During 317 participant-seasons, 138 I-IMIs were recorded. The parsimonious model included only age and frequency of previous IMIs; apparent calibration was perfect, but discrimination was modest (C-index = 0.641, 95% confidence interval (CI) = 0.580 to 0.703), with clinical utility evident between risk thresholds of 37-71%. After validation and overfitting adjustment, performance deteriorated (C-index = 0.589 (95% CI = 0.528 to 0.651); calibration-in-the-large = - 0.009 (95% CI = - 0.239 to 0.239); calibration slope = 0.718 (95% CI = 0.275 to 1.161)). The selected PHE data were insufficient prognostic factors from which to develop a useful model for predicting IMI risk in elite footballers. Further research should prioritise identifying novel prognostic factors to improve future risk prediction models in this field.

#3 Preseason Assessment of Anaerobic Performance in Elite Soccer Players: Comparison of Isokinetic and Functional Tests
Reference: Sports Biomech, 2020 May 28;1-15. doi: 10.1080/14763141.2020.1750681.
Authors: François Delvaux, Cédric Schwartz, Carlos Rodriguez, Bénédicte Forthomme, Jean-François Kaux, Jean-Louis Croisier
Summary: Isokinetic and functional jump tests are frequently performed for assessing the physical qualities of soccer players during preseason. The purpose of this investigation was to explore, in an elite soccer players population, the relationships between isokinetic strength and functional jump performances. Thirty-eight professional soccer players were evaluated as follows: isokinetic knee assessment in concentric (CON) mode (60, 240°/s) for quadriceps and hamstrings, and in eccentric (ECC) mode for the hamstrings only (30°/s); one-leg hop tests for distance (single hop (SH), triple hop (TH) and triple crossover hop (TCH)); one-leg vertical jump tests (countermovement jump, drop jump). Players with a low bodyweight normalised (BWN) quadriceps (Q) strength (<2.71 Nm/kg) performed, for a majority of the measured variables, significantly reduced jump performances compared to the players with high BWN Q strength (>3.14 Nm/kg; p < 0.05). Greater bilateral differences between uninjured and past injured lower limbs were found with isokinetics (Q CON 60°/s (mean bilateral difference (MBD): 10.3%; p < 0.01), Q CON 240°/s (MBD: 9.9%; p < 0.05), H ECC 30°/s (MBD: 16.1%; p < 0.001) than with functional tests (MBD: 2 to 9%; p > 0.05. In conclusion, due to their complementary role and implications for performance, functional and isokinetic tests should be associated in a preseason soccer players assessment.

#4 Eccentric-Overload Production During the Flywheel Squat Exercise in Young Soccer Players: Implications for Injury Prevention
Reference: Int J Environ Res Public Health. 2020 May 22;17(10):E3671. doi: 10.3390/ijerph17103671.
Authors: Javier Raya-González, Daniel Castillo, Marta Domínguez-Díez, José Luis Hernández-Davó
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Summary: This study aimed to evaluate the differences in power production between movement phases (i.e., concentric and eccentric) during the execution of resistance exercises with a flywheel device, differentiating between execution regimes (i.e., bilateral, unilateral dominant leg and unilateral non-dominant leg). Twenty young elite soccer players (U-17) performed two sets of six repetitions of the bilateral half-squat (inertia 0.025 kg·m-2) and the lateral-squat exercise (inertia 0.010 kg·m-2) on a flywheel device. During the testing sessions, mean and peak power in concentric (MPcon) and eccentric (MPecc) phases were recorded. The non-dominant leg showed higher values in all power variables measured, although substantial differences were only found in MPecc (ES = 0.40, likely) and PPcon (ES = 0.36, possibly). On the other hand, for both exercises, MPcon was higher than MPecc (ES = -0.57 to -0.31, possibly/likely greater), while only PPecc was higher than PPcon in the dominant lateral-squat (ES = 0.44, likely). These findings suggest that young soccer players have difficulty in reaching eccentric-overload during flywheel exercises, achieving it only with the dominant leg. Therefore, coaches should propose precise preventive programs based on flywheel devices, attending to the specific characteristics of each limb, as well as managing other variables to elicit eccentric-overload.

#5 Workload Monitoring in Top-level Soccer Players During Congested Fixture Periods
Reference: Int J Sports Med. 2020 May 26. doi: 10.1055/a-1171-1865. Online ahead of print.
Authors: Antonio Gualtieri, Ermanno Rampinini, Roberto Sassi, Marco Beato
Summary: This study assessed the internal and external workload of starters and non-starters in a professional top-level soccer team during a congested fixture period. Twenty Serie A soccer players were monitored in this study during two mesocycles of 21 days each. Starters and non-starters were divided based on the match time played in each mesocycle. The following metrics were recorded: exposure time, total distance, relative total distance, high-speed running distance over 20 km·h-1, very high-speed running distance over 25 km·h-1, individual very high-speed distance over 80% of maximum peak speed, and rating of perceived exertion. Differences between starters and non-starters were found for: exposure time (effect size=large to very large), rating of perceived exertion (large to very large), total distance (large to very large), and individual very high-speed distance over 80% of maximum peak speed (moderate to large). Furthermore, differences for relative total distance, high-speed running distance over 20 km·h-1 and very high-speed running distance over 25 km·h-1 were small to moderate, but not significant. This study reports that during congested fixture periods, starters had higher exposure time, rating of perceived exertion, total distance, and individual very high-speed distance over 80% of maximum peak speed than non-starters.

#6 Role of Basal Hormones on Sweat Rate and Sweat Na+ Loss in Elite Women Soccer Players
Reference: Int J Sports Med. 2020 May 26. doi: 10.1055/a-1165-2072. Online ahead of print.
Authors: Mauricio Castro-Sepulveda, Jorge Cancino, Sebastian Jannas-Vela, Francisca Jesam, Casandra Lobos, Juan Del Coso, Hermann Zbinden-Foncea
Summary: We aimed to determine whether basal concentrations of testosterone, cortisol or the ratio testosterone/cortisol were related to sweat Na+ loss, sweat Na+ concentration ([Na+]) and sweat rate during exercise. Twenty-two female elite soccer players participated in the study. Testosterone and cortisol were measured in blood samples before exercise. Sweat samples were collected during a training session (~20°C, ~30% RH, and ~0.55 m/s of wind speed) to measure sweat [Na+]. Sweat rate was determined by considering the difference between post-and pre-body weight, along with the amount of liquid consumed. During exercise, sweat Na+ loss (0.33[0.19] g/h) and sweat rate (0.49[0.20] L/h) were related to basal testosterone concentration (1.4[0.4] pg/mL) (r=0.54; r=0.55, respectively; p<0.05), but not with basal cortisol concentration (119.2[24.2] ng/mL) nor testosterone/cortisol ratio (0.012[0.003]) (p>0.05). However, when Na+ loss was adjusted to sweat rate, no association was found between Na+ loss and testosterone (p>0.05). In addition, no differences were found between players with high vs. low Na+ loss adjusted to sweat loss in menstrual phase or intensity during exercise (p>0.05). In conclusion, these results suggest that in these specific environmental conditions, basal levels of testosterone might increase sweat rate and therefore, the amount of Na+ lost during exercise in elite women soccer players.

#7 Comparison of Lipid and Lipoprotein Values of Wrestlers and Soccer Players
Reference: Turk J Pharm Sci. 2020 Apr;17(2):172-176. doi: 10.4274/tjps.galenos.2018.66934. Epub 2020 Apr 24.
Authors: Semra Çetin, Cuma Ece, Meltem Paksoy, Hasan Nedim Çetin
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Summary: The aim of this study was to compare the lipid and lipoprotein values of wrestlers and soccer players. A total of 35 subjects, 17 male wrestlers who are sporting for 11.5 years and 18 male soccer player students who are sporting for 11.9 years, participated in this study. Triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) levels were determined by Hitachi 717 autoanalyzer. To determine the differences between the wrestlers and the soccer players the independent t-test was performed. There was a significant difference in body weight and body mass index between the wrestlers and the soccer players (p<0.05). Moreover, there were significant differences in plasma TC, LDL-C, and HDL-C values between the wrestlers and soccer players (all, p<0.05). However, there was no significant difference in plasma TG values between the wrestlers and the soccer players (p>0.05). On the other hand, TC and LDL-C values of the wrestlers were significantly higher than soccer players (p<0.05). The HDL-C values of the soccer players were significantly higher the wrestlers (p<0.05). The ratio TC/HDL-C of the wrestlers was markedly higher than soccer players (p<0.05). TC, TG, HDL-C, and LDL-C values of the soccer players were in better ranges than wrestlers. This situation can be caused by the effect of different sports branches as well as the training differences. The lipid and lipoprotein values of the wrestlers and soccer players showed that they do not carry a risk of cardiovascular disease. In addition, it can be recommended that wrestlers should do jogging or aerobic training in their daily regular training.

#8 Effects of Maturation on Knee Biomechanics During Cutting and Landing in Young Female Soccer Players
Reference: PLoS One. 2020 May 26;15(5):e0233701. doi: 10.1371/journal.pone.0233701. eCollection 2020.
Authors: Audrey E Westbrook, Jeffrey B Taylor, Anh-Dung Nguyen, Mark V Paterno, Kevin R Ford 
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Summary: Young female soccer players are at high risk of anterior cruciate ligament injury due to the fast-paced nature of the sport and surplus of unplanned movements during play. Neuromuscular training programs that aim to reduce this injury by targeting the associated biomechanical movements are a potential solution. While previous studies have examined the lack of dynamic knee control during landing, there are few that outline the role that maturation can play during unanticipated cutting. Therefore, the purpose of this study was to determine if young female soccer players across multiple phases of maturation exhibited the before seen differences in knee control during a drop landing as well as an unanticipated cutting task. 139 female soccer players volunteered to participate in this study and were classified in three maturational groups based on percent adult stature: prepubertal (PRE), pubertal (PUB), and post-pubertal (POST). Each group performed a drop vertical jump (DVJ) and an unanticipated cutting task (CUT). Standard 3D motion capture techniques were used to determine peak knee flexion/abduction angles and moments during each task. Within tasks, POST exhibited significantly greater peak abduction angles and moments compared to PUB/PRE. While each maturational group exhibited greater peak knee abduction angles during the DVJ compared to the CUT, peak knee abduction moments during the CUT were greater compared to the DVJ. Participants within each maturational group exhibited greater knee flexion during the DVJ compared to the CUT, however there were no differences identified between groups. During both tasks, POST/PUB exhibited greater peak knee flexion moments compared to PRE, as well as POST compared to PUB. Overall, each group exhibited significantly greater peak knee flexion moments during the CUT compared to the DVJ. These observed differences indicate the need for neuromuscular training programs that target both jumping and cutting techniques to reduce ACL injuries.

#9 Effects of Different Plyometric Training Frequencies on Measures of Athletic Performance in Prepuberal Male Soccer Players
Reference: J Strength Cond Res. 2020 Jun;34(6):1609-1617. doi: 10.1519/JSC.0000000000002486.
Authors: Raja Bouguezzi, Helmi Chaabene, Yassine Negra, Rodrigo Ramirez-Campillo, Zied Jlalia, Bessem Mkaouer, Younés Hachana
Summary: This study aimed to compare the effects of 1 vs. 2 sessions of equal-weekly volume plyometric training (PT) across 8 weeks on measures of athletic performance (i.e., sprint time, change of direction [CoD], jumping ability, and muscle strength) in prepuberal male soccer players. Thirty participants were randomly assigned either to 1 session PT group (1SPT [n = 15]) or 2 sessions PT group (2SPT [n = 15]). Plyometric training was integrated into their regular soccer training routine. Pretraining and posttraining tests for the assessment of sprint time (e.g., 5, 10, 20, and 30-m), CoD (e.g., T-test and modified Illinois change of direction test [MICODT]), jumping ability (e.g., standing long jump [SLJ], countermovement jump [CMJ], and squat jump [SJ]), muscle strength (reactive strength index [RSI]), and kicking distance were conducted. Results showed a main effect of time for 5-m sprint-time performance (F(1,56) = 4.00, effect size [ES] = 0.53 [medium], p = 0.05), T-test (F(1,56) = 23.19, ES = 1.28 [large], p < 0.001), MICODT (F(1,56) = 5.72, ES = 0.94 [large], p = 0.02), SLJ (F(1,56) = 16.63, ES = 1.09 [large], p < 0.001), CMJ (F(1,56) = 15.43, ES = 1.04 [large], p < 0.001), SJ (F(1,56) = 20.27, ES = 1.20 [large], p < 0.001), RSI (F(1,56) = 26.26, ES = 1.36 [large], p < 0.001), and kicking distance (F(1,56) = 47.19, ES = 1.83 [large], p < 0.001). There were no training group × time interactions in all the measured outcomes. In conclusion, when an equated moderate volume of jumps is performed, higher PT frequency across 8 weeks has no extra effects on prepuberal male soccer players' measures of athletic performance. The present findings may help optimizing PT interventions dedicated to prepuberal male soccer players.

#10 GreenSea: Visual Soccer Analysis Using Broad Learning System
Reference: IEEE Trans Cybern. 2020 May 21;PP.  doi: 10.1109/TCYB.2020.2988792. Online ahead of print.
Authors: Bin Sheng, Ping Li, Yuhan Zhang, Lijuan Mao, C L Philip Chen
Summary: Modern soccer increasingly places trust in visual analysis and statistics rather than only relying on the human experience. However, soccer is an extraordinarily complex game that no widely accepted quantitative analysis methods exist. The statistics collection and visualization are time consuming which result in numerous adjustments. To tackle this issue, we developed GreenSea, a visual-based assessment system designed for soccer game analysis, tactics, and training. The system uses a broad learning system (BLS) to train the model in order to avoid the time-consuming issue that traditional deep learning may suffer. Users are able to apply multiple views of a soccer game, and visual summarization of essential statistics using advanced visualization and animation that are available. A marking system trained by BLS is designed to perform quantitative analysis. A novel recurrent discriminative BLS (RDBLS) is proposed to carry out long-term tracking. In our RDBLS, the structure is adjusted to have better performance on the binary classification problem of the discriminative model. Several experiments are carried out to verify that our proposed RDBLS model can outperform the standard BLS and other methods. Two studies were conducted to verify the effectiveness of our GreenSea. The first study was on how GreenSea assists a youth training coach to assess each trainee's performance for selecting most potential players. The second study was on how GreenSea was used to help the U20 Shanghai soccer team coaching staff analyze games and make tactics during the 13th National Games. Our studies have shown the usability of GreenSea and the values of our system to both amateur and expert users.

#11 How Manipulation of Playing Area Dimensions in Ball Possession Games Constrains Physical Effort and Technical Actions in under-11, under-15 and under-23 Soccer Players
Referernce: Res Sports Med. 2020 May 26;1-15. doi: 10.1080/15438627.2020.1770760.

Authors: Nuno André Nunes, Bruno Gonçalves, Keith Davids, Pedro Esteves, Bruno Travassos
Summary: The aim of this study was to investigate the effects of playing area manipulation (20 × 15 m, 25 × 20 m and 30 × 25 m) on external workloads (total distance covered, distance covered while walking, running and sprinting, number of sprints, maximum sprint speed), internal load perceptions (rating of perceived exertion) and technical actions of passing (number of passes with dominant and non-dominant foot, and maximum passing speed) during 4v4 ball possession small-sided and conditioned games in under-11, under-15 and under-23 soccer players. Results showed higher values in the large playing area for under-11 in the distance covered in different speed zones, sprint number and RPE (all p <.001) for under-15 in sprints number (p <.01) and maximum sprint speed (p =.02), and for under-23 in both RPE and sprint numbers (p <.01). Although no significant differences were found on technical actions, it was still possible to notice some effects through pairwise comparison. High-intensity running was promoted on larger playing areas, where under-11 s were also able to perform more technical actions of passing. Opposite, under-23s were able to perform more passing on smaller playing areas, where under-11 s perceived the exercise more intense. The impact of different playing areas was reduced for the under-15.

#12 Transformational Parenting and Coaching on Mental Toughness and Physical Performance in Adolescent Soccer Players: The Moderating Effect of Athlete Age
Reference: Eur J Sport Sci. 2020 May 25;1-10. doi: 10.1080/17461391.2020.1765027.
Authors: Ross M Murray, James H Dugdale, Christine M Habeeb, Calum A Arthur 
Summary: Both parent and coach leadership behaviours are instrumental to adolescent athlete development. Researchers, however, are yet to examine parent and coach leadership influences simultaneously, and at different stages of adolescents' psychological and physical development. Therefore, the purpose of this study was to understand if the effects of transformational parenting, and transformational coaching on mental toughness and performance varied at different ages during adolescence. Early adolescent (ages 10-14) and late adolescent (ages 15-18) soccer players (n = 334) completed questionnaires assessing their perceptions of their mother's, father's, and coach's transformational leadership, as well as a questionnaire assessing mental toughness. Participants also completed a comprehensive battery of physical fitness tests relevant to soccer. Results indicated that transformational fathering was more strongly associated with levels of mental toughness for early adolescent athletes than it was for later adolescent athletes. Results also indicated that transformational coaching was more strongly associated with physical performance for later adolescent athletes than it was for early adolescents. Overall, these results can inform development models and provide support for future longitudinal studies to assess the impact of parent and coach transformational leadership across different stages of athlete development.

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