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Dose-Response Relationships between Training Load Measures and Physical Fitness in Professional Soccer Players

The aim of this cohort study was two-fold: (i) to analyze within-group changes of final velocity in a 30-15 intermittent fitness test (VIFT), final velocity in a Vameval test (Vvameval), 20-m sprint and countermovement jump (CMJ); (ii) to explore the relationships between VIFT and Vvameval outcomes and their changes with internal and external loads.





Acceleration and High-Speed Running Profiles of Women’s International and Domestic Football Matches

The aim of the present study was to compare the acceleration, deceleration, and high-speed running profiles of players during international and domestic matches and to determine if differences were apparent across playing positions (defenders, midfielders, and attackers).





Latest research in football - week 14 - 2021

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 Does Warm-up Type Matter? A Comparison between Traditional and Functional Inertial Warm-up in Young Soccer Players 

Reference: J Funct Morphol Kinesiol. 2020 Nov 19;5(4):84. doi: 10.3390/jfmk5040084. 

Authors: Giovanni Fiorilli, Federico Quinzi, Andrea Buonsenso, Giulia Di Martino, Marco Centorbi, Arrigo Giombini, Giuseppe Calcagno, Alessandra di Cagno 

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Summary: Functional inertial training, a popular high-intensity training mode, provides high neuromuscular activation, developing proprioception, postural control, power, and sprint time. Aim of the study was to assess the acute effects of two types of warm-up (WU), inertial warm-up (IWU) vs. traditional warm-up (TWU), on explosive and reactive strength, sprint, and Change of Directions (COD) in young soccer players. In a randomized cross-over design study, twelve soccer players (aged 13.3 ± 0.7) performed 16 min of IWU and 16 min of TWU. IWU and TWU were spaced two weeks apart. Pre and post intervention tests, aimed at assessing explosive and reactive strength, sprint, and COD ability included: Squat Jump test (SJ), Countermovement Jump test (CMJ), Drop Jump test (DJ), Seven Repetition Hopping test (7R-HOP), 40 m-sprint test (40 m), and Illinois Agility Test (IAT). RM-ANOVA, used to compare differences between IWU and TWU effects (the level of significance set at ρ ≤ 0.05), showed enhanced performance after the IWU compared to the TWU. In addition, the effects of the IWU on performance lasted longer after the IWU than after the TWU. For IAT, the enhanced effects of IWU on performance lasted up to ten minutes after the administration of the IWU. Our results suggest that IWU affects functional changes displaying earlier adaptation in explosive and reactive strength with longer lasting effects compared to TWU and it could be recommended in young soccer athletes as a WU procedure. 



#2 Bioimpedance Vector References Need to Be Period-Specific for Assessing Body Composition and Cellular Health in Elite Soccer Players: A Brief Report 

Reference: J Funct Morphol Kinesiol. 2020 Oct 1;5(4):73. doi: 10.3390/jfmk5040073. 

Authors: Tindaro Bongiovanni, Gabriele Mascherini, Federico Genovesi, Giulio Pasta, Fedon Marcello Iaia, Athos Trecroci, Marco Ventimiglia, Giampietro Alberti, Francesco Campa

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Summary: Bioimpedance data through bioimpedance vector analysis (BIVA) is used to evaluate cellular function and body fluid content. This study aimed to (i) identify whether BIVA patters differ according to the competitive period and (ii) provide specific references for assessing bioelectric properties at the start of the season in male elite soccer players. The study included 131 male soccer players (age: 25.1 ± 4.7 yr, height: 183.4 ± 6.1 cm, weight: 79.3 ± 6.6) registered in the first Italian soccer division (Serie A). Bioimpedance analysis was performed just before the start of the competitive season and BIVA was applied. In order to verify the need for period-specific references, bioelectrical values measured at the start of the season were compared to the reference values for the male elite soccer player population. The results of the two-sample Hotelling T2 tests showed that in the bivariate interpretation of the raw bioimpedance parameters (resistance (R) and reactance (Xc)) the bioelectric properties significantly (T2 = 15.3, F = 7.6, p ≤ 0.001, Mahalanobis D = 0.45) differ between the two phases of the competition analyzed. In particular, the mean impedance vector is more displaced to the left into the R-Xc graph at the beginning of the season than in the first half of the championship. For an accurate evaluation of body composition and cellular health, the tolerance ellipses displayed by BIVA approach into the R-Xc graph must be period-specific. This study provides new specific tolerance ellipses (R/H: 246 ± 32.1, Xc/H: 34.3 ± 5.1, r: 0.7) for performing BIVA at the beginning of the competitive season in male elite soccer players. 



#3 Body Composition Changes over Multiple Academic Years in Female Collegiate Soccer Players

Reference: J Funct Morphol Kinesiol. 2020 Sep 28;5(4):72. doi: 10.3390/jfmk5040072. 

Authors: Austin Katona, Caroline Riewe, Angela Bruzina, Nicholas J Ollberding, Mary Ankrom, Jon Divine, Robert Mangine, Abigail Peairs

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Summary: Body composition plays a key role in overall health and sports performance and its assessment is an important part of many athletic programs. The purpose of this study was to describe longitudinal changes in body composition for collegiate female soccer players in order to provide data to inform future training and nutrition interventions for this population. A linear mixed-model (LMM) approach was used to analyze four years of pre- and post-season body composition data, including total mass, fat-free mass (FFM), fat mass, and body fat percentage (%BF) for 49 athletes. Athletes gained an average of 0.5 kg FFM during the season (p < 0.05) and increased total mass, FFM, fat mass, and %BF (2.5 kg, 1.1 kg, 1.7 kg, and 1.7%, respectively; p < 0.05) over four years. Freshmen experienced a 1.5 kg gain in total mass pre- to post-season (p < 0.05), while no changes in total mass or body composition were seen in other grade levels. Gains in %BF during the off season between Freshman and Sophomore years represented negative changes in body composition that should be addressed further. These results can help interdisciplinary athlete care teams optimize training programs in this population by understanding what changes are expected over multiple years. Normalizing these changes may also help the promotion of realistic body composition goals and the development of positive training and dietary habits. 



#4 Effects of Hoverboard on Balance in Young Soccer Athletes 

Reference: J Funct Morphol Kinesiol. 2020 Aug 6;5(3):60. doi: 10.3390/jfmk5030060. 

Authors: Stefano Moffa, Angelica Perna, Gabriele Candela, Alessandro Cattolico, Carmine Sellitto, Paolo De Blasiis, Germano Guerra, Domenico Tafuri, Angela Lucariello

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Summary: Hoverboards are always more popular among children. Hoverboards are to them like a game or a mean of transport, but they could be used as a valid and useful instrument in children's training programs to improve their performance. In this study, we compared the athletic performance of two groups of 12 children. A total of 24 children aged between 8 and 11 years followed a similar training program for five months, but the first group used a hoverboard (Hb+ group: Age: Standard Deviation (SD) = 1.15 Mean = 9.66; Weight: SD = 5.90 Mean = 32; Height: SD = 7.64 Mean = 135.08) for some of the training time, differently from the second group (Hb- group: Age: SD = 1.15 Mean = 9.66; Weight: SD = 5.82 Mean = 31.16; Height: SD = 7.66 Mean = 136.16), which never used it. All of the children were asked to complete three tests (one leg test, stork test and balance beam walking test) before starting their own training program and after five months, to evaluate how their performances changed in terms of time. Comparing the recorded time difference between T0 and T1 of the Hb+ group with the same difference measured in Hb- group, it was found that there was a statistically significant difference (p value < 0.05) between these data for all three tests. Children who used the hoverboard in their training program achieved better result than children who did not use it. In the future, the hoverboard could help athletes to improve their performances, possibly applying it not only in football training, but even in other sports. 



#5 Body Fat Assessment in International Elite Soccer Referees 

Reference: J Funct Morphol Kinesiol. 2020 Jun 6;5(2):38. doi: 10.3390/jfmk5020038. 

Authors: Cristian Petri, Francesco Campa, Vitor Hugo Teixeira, Pascal Izzicupo, Giorgio Galanti, Angelo Pizzi, Georgian Badicu, Gabriele Mascherini

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Summary: Soccer referees are a specific group in the sports population that are receiving increasing attention from sports scientists. A lower fat mass percentage (FM%) is a useful parameter to monitor fitness status and aerobic performance, while being able to evaluate it with a simple and quick field-based method can allow a regular assessment. The aim of this study was to provide a specific profile for referees based on morphological and body composition features while comparing the accuracy of different skinfold-based equations in estimating FM% in a cohort of soccer referees. Forty-three elite international soccer referees (age 38.8 ± 3.6 years), who participated in the 2018 Russian World Cup, underwent body composition assessments with skinfold thickness and dual-energy X-ray absorptiometry (DXA). Six equations used to derive FM% from skinfold thickness were compared with DXA measurements. The percentage of body fat estimated using DXA was 18.2 ± 4.1%, whereas skinfold-based FM% assessed from the six formulas ranged between 11.0% ± 1.7% to 15.6% ± 2.4%. Among the six equations considered, the Faulkner's formula showed the highest correlation with FM% estimated by DXA (r = 0.77; R2 = 0.59 p < 0.001). Additionally, a new skinfold-based equation was developed: FM% = 8.386 + (0.478 × iliac crest skinfold) + (0.395 × abdominal skinfold, r = 0.78; R2 = 0.61; standard error of the estimate (SEE) = 2.62 %; p < 0.001). Due to these findings, national and international federations will now be able to perform regular body composition assessments using skinfold measurements. 



#6 Injury prevention effects of stretching exercise intervention by physical therapists in male high school soccer players

Reference: Scand J Med Sci Sports. 2020 Nov;30(11):2178-2192. doi: 10.1111/sms.13777. Epub 2020 Aug 2. 

Authors: Nobuhide Azuma, Fujiko Someya

Summary: We aimed to examine the prevalence of injury after physical therapy intervention for muscle tightness and injury prevention in male high school soccer players. A randomized controlled trial was conducted. Participants comprised 124 players from two high schools who competed in national tournament soccer games held from April 2018 to March 2019. Players were randomly divided into intervention (with a 12-week stretching intervention by physical therapists) and control groups (without the intervention). Players and coaches provided written information regarding injuries and daily training and match times; physical therapists visited each team weekly to collect data and review documentation. Muscle tightness and injury incidence, number, type, location, circumstances, situations, severity, and contents during the 12-week intervention period and a subsequent 40-week observation period were compared between groups. Injuries were significantly lower with intervention during the 40-week observation period (P < .01) but not during the 12-week intervention period (P = .44). Injury types mainly included disorder, non-contact, lower-limb/trunk, and muscle/tendon injuries. Significant interactions were observed for all tightness-test measurement items. The intervention group showed significant improvements in heel-buttock distance, and straight leg-raise and hip rotation angles (pre-intervention < 12 weeks < 52 weeks), as well as significant improvements in ankle dorsiflexion angles at 12 and 52 weeks (relative to pre-intervention values). Instructed stretching exercises, personally designed by physical therapists to address muscle tightness, improved the range of motion and trunk flexibility, with a positive effect on the injury rate in male high school soccer players, especially for non-contact disorder injuries during training. 



#7 Associations of Body Composition, Maximum Strength, Power Characteristics with Sprinting, Jumping, and Intermittent Endurance Performance in Male Intercollegiate Soccer Players

Reference: J Funct Morphol Kinesiol. 2021 Jan 7;6(1):E7. doi: 10.3390/jfmk6010007. 

Authors: Ai Ishida, S Kyle Travis, Michael H Stone

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Summary: The purpose of this study was to determine the relationships between body composition, strength, power characteristics, sprinting, jumping, and intermittent endurance performance in collegiate male players. Twenty-three players participated (19.7 ± 1.6 yrs; 71.8 ± 7.1 kg; 176.5 ± 5.1 cm). Measurements of interest in body composition included body fat percentage (BF%), lean body mass (LBM), and body mass (BM). Power characteristics were measured with an unloaded squat jump (SJ0) and loaded SJ at 20 kg (SJ20) and 40 kg (SJ40), and unloaded countermovement jump (CMJ0). Power assessments included peak power (PP) and PP allometrically scaled (PPa). Strength characteristics were assessed using isometric mid-thigh pull. Strength assessment included isometric peak force (IPF) and IPF allometrically scaled (IPFa). Performance measures included 10m and 20 m sprint time, CMJ0 jump-height, and Yo-Yo intermittent endurance test level 1 distance. Significant correlations ranging from moderate to very large were found for LBM and CMJ jump height (CM0 JH) (p = 0.01, r = 0.50); BF% and sprint times at 10 m (p = 0.03, r = 0.44) and 20 m (p = 0.02, r = 0.50). PP and PPa from SJ0 and CMJ0 were significantly correlated to 10m sprint time (p < 0.05, r = -0.45 to -0.53) and 20 m sprint time (p < 0.05, r = -0.40 to -0.49). Our findings agree with previous literature in that body composition and power characteristics are directly related to soccer-related performance. 



#8 Cell integrity indicators in university athletes: comparison among playing positions in indoor football 

Reference: J Sports Med Phys Fitness. 2021 Jan 22. doi: 10.23736/S0022-4707.21.12008-0. Online ahead of print. 

Authors: Priscila C Martins, Paula DA Silva, Diego A Silva

Summary: The aim of this study was to compare cell integrity indicators according to the playing position in university indoor football athletes. The sample consisted of 34 university athletes (20 female and 14 male). Dependent variables were cell integrity indicators: total body water (TBW), intracellular water (ICW), extracellular water (ECW), ECW/ICW ratio, body cell mass (BCM), ECW/BCM ratio, phase angle (PhA), resistance (R), Xc (reactance) and impedance (Z), evaluated by the electrical bioimpedance method. Independent variable was the playing position: goalkeeper (a), defender (a), winger (left and right) and pivot collected through questionnaire. Control variables were age, time of sport practice, participation in competitions per year and training load obtained by applying the anamnesis form, and body fat and fat and bone-free mass were obtained through dual emission X-ray absorptiometry (DXA). Covariance analysis (ANCOVA) was used, with post-roc Tukey's test, to identify difference between groups, with p <0.05. In the adjusted analysis, female athletes in the defense position had BCM values (31.1 ±2.1) higher than those in the wing position (25.8 ±1.1) (p <0.01). In males, pivots showed higher ICW values (31.47 ±0.77) when compared to defenders (25.7 ±0.8) (p = 0.02). In addition, goalkeepers had higher TBW values (52.7 ±2.5) compared to wingers (42.3 ±1.2) (p = 0.03). Cell integrity indicators may vary according to the playing position in indoor football. 



#9 Reopening elite sport during the COVID-19 pandemic: Experiences from a controlled return to elite football in Denmark

Reference: Scand J Med Sci Sports. 2021 Jan 21. doi: 10.1111/sms.13915. Online ahead of print. 

Authors: Lars Pedersen, Jens Lindberg, Rune Rasmussen Lind, Hanne Rasmusen

Summary: As the SARS-CoV-2 infection rate decreased in spring 2020, phased reopening of Danish society began, including a reopening of elite football (soccer), adhering to a strict protocol. In this study, we report the consequences of resumption of competitive play in the two best football (soccer) leagues for men in Denmark measured by number of SARS-CoV-2 positive players. The players were tested weekly for SARS-CoV-2 for 11 consecutive weeks. The test protocol comprised 26 teams with 748 players. In total, 6511 tests were done with a positivity rate of 0.06%. The incidence rate of players testing positive for SARS-CoV-2 was 0.53% (4/748). There were no signs of a chain of infection. We found a low incidence rate of SARS-CoV-2, and based on this, a controlled reopening of professional football strictly following a detailed protocol appears safe for the players. 



#10 The Influence of Child-Related Factors on Caregiver Perceptions of Their Child's Sustained Participation in a Community Football Program: A Study of Children with and without Neurodevelopmental Disorders 

Reference: Int J Environ Res Public Health. 2021 Jan 19;18(2):831. doi: 10.3390/ijerph18020831. 

Authors: Carmel Sivaratnam, Bethany Devenish, Tayla Chellew, Nicole Papadopoulos, Jane McGillivray, Nicole Rinehart

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Summary: This study evaluated the influence of activity preference and involvement on season completion in a community-based football program for children with and without neurodevelopmental disorders. Caregivers (n = 1428) of 1529 children aged 4 to 17 (M = 7.27, SD = 1.85), with (n = 175) and without (n = 1354) neurodevelopmental disorders who were currently participating or had previously participated in a group-based NAB AFL Auskick football program completed an online survey. The survey collected information on their child's completion of any attempted seasons of the football program, level of involvement during the sessions and preference for football over other sports and activities. Eighty percent of children with a neurodevelopmental diagnosis had completed all seasons of Auskick, compared with 93% of children without a neurodevelopmental diagnosis. Results indicated that children with neurodevelopmental disorders (n = 135) were 3.71 times less likely to complete a football season than their typically developing peers (n = 903). Higher levels of involvement during football sessions and greater preference for football were linked to a higher football season completion rate, irrespective of neurodevelopmental disability diagnosis. This study highlights the influence of child-related factors, in particular, preference and involvement, on children's sustained participation in community football programs, regardless of neurodevelopmental disability status. 



#11 The effects of residential environment on the condition and fitness of soccer players in the summer 

Reference: J Exerc Rehabil. 2020 Dec 28;16(6):522-528. doi: 10.12965/jer.2040748.374. eCollection 2020 Dec. 

Authors: Jae-Hoon Jang, Chang-Hwa Joo

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Summary: Exercise performance is reduced in hot environments due to physiological responses caused by increased body temperature. A proper residential environment is important for improving the performance and maintaining physical condition of soccer players in the summer. The purpose of this study was to determine the effect of indoor temperature of the resting space during the summer on the fitness and condition of soccer players. A total of 12 K-3 League semiprofessional players without serious injuries in the last 3 months voluntarily participated in the study. Participants performed speed (10 m, 20 m, and 30 m), soccer-specific coordination skill (dribbling), agility, repeated sprints, Yo-Yo intermittent level 2, vertical jump, and questionnaire (fatigue, sleep quality, muscle soreness, stress, and mood) after staying indoor temperature at 20°C, 26°C, and 30°C for one night, respectively. There was no difference among groups in physical fitness (speed, agility, jump, coordination, Yo-Yo intermittent level 2, and repeated sprints). The differences in fatigue and sleep quality were not statistically significant among groups, but they tended to be different. Muscle soreness was similar among all groups. Significant differences were observed between the 20°C and 30°C groups in stress and mood levels. The present study concluded that, while the physical fitness did not differ among groups, the 30°C residential environment was shown to have a negative psychological effect. Considering that many diseases associated with hot weather occur in low residential temperatures, a room temperature of 26°C is recommended for elite soccer players in hot summer weather. 



#12 Effects of home confinement due to COVID-19 pandemic on eccentric hamstring muscle strength in football players 

Reference: Scand J Med Sci Sports. 2020 Oct;30(10):2010-2012. doi: 10.1111/sms.13768. 

Authors: Victor Moreno-Pérez, Juan Del Coso, Daniel Romero-Rodríguez, Luis Marcé-Hernández, Marcelo Peñaranda, Marc Madruga-Parera

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Influence of Players’ Maximum Running Speed on the Team’s Ranking Position at the End of the Spanish LaLiga

The aim was to determine the influence of a player’s peak/maximum running speed on the team’s final ranking position. A second aim was to investigate differences in maximum running speed among playing positions.





A Preseason Training Program With the Nordic Hamstring Exercise Increases Eccentric Knee Flexor Strength and Fascicle Length

The aim of this study was to investigate the collective and individual responses of professional female soccer players engaged in a preseason training program with the NHE regarding eccentric knee flexor strength and biceps femoris long head fascicle length.





Latest research in football - week 13 - 2021

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 Predictive equations for resting metabolic rate are not appropriate to use in Brazilian male adolescent football athletes 

Reference: PLoS One. 2021 Jan 14;16(1):e0244970. doi: 10.1371/journal.pone.0244970. eCollection 2021. 

Authors: Taillan M Oliveira, Paula A Penna-Franca, Christian H Dias-Silva, Victor Z Bittencourt, Fabio F L C Cahuê, Sidnei J Fonseca-Junior, Anna Paola T R Pierucci

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Summary: High accuracy in estimating energy expenditure is essential for enhancing sports performance. The resting metabolic rate (RMR), as a primary component of total energy expenditure (TEE), is commonly estimated using predictive equations. However, these references may not be applicable to adolescent athletes. The purpose of this cross-sectional study was to analyse the differences between predicted RMR in relation to energy expenditure measured by indirect calorimetry (IC) among 45 Brazilian male adolescent football athletes. Indirect calorimetry (IC) and anthropometric (bioimpedance) measurements were recorded at a single visit to the laboratory after fasting overnight. The mean age was 15.6 ± 1.14 years, body mass was 63.05 ± 7.8 kg, and height was 172 ± 7.5 cm. The RMR values predicted by equations proposed by the Food and Agriculture Organization (FAO) (United Nations), Henry and Rees (HR), Harris Benedict (HB), and Cunningham (CUN) were compared with IC RMR values, by correlation analysis. The FAO and HR predictive equations yielded different values from IC (IC: 1716.26 ± 202.58, HR: 1864.87 ± 147.78, FAO: 1854.28 ± 130.19, p = 0.001). A moderate correlation of 0.504 was found between the results of HB and IC. In the survival-agreement model, the CUN equation showed low disagreement with the IC RMR, with error values between 200 and 300 kcal/day. The results showed that HB and CUN yielded similar values as IC, with the CUN equation showing low disagreement with IC; hence, adolescent athletes should undergo evaluation with precise laboratory methods to ensure that accurate information about RMR is recorded. 



#2 Who Will Score? A Machine Learning Approach to Supporting Football Team Building and Transfers

Reference: Entropy (Basel). 2021 Jan 10;23(1):E90. doi: 10.3390/e23010090. 

Authors: Bartosz Ćwiklinski, Agata Giełczyk, Michał Choraś

Summary: The machine learning (ML) techniques have been implemented in numerous applications, including health-care, security, entertainment, and sports. In this article, we present how the ML can be used for building a professional football team and planning player transfers. In this research, we defined numerous parameters for player assessment, and three definitions of a successful transfer. We used the Random Forest, Naive Bayes, and AdaBoost algorithms in order to predict the player transfer success. We used realistic, publicly available data in order to train and test the classifiers. In the article, we present numerous experiments; they differ in the weights of parameters, the successful transfer definitions, and other factors. We report promising results (accuracy = 0.82, precision = 0.84, recall = 0.82, and F1-score = 0.83). The presented research proves that machine learning can be helpful in professional football team building. The proposed algorithm will be developed in the future and it may be implemented as a professional tool for football talent scouts. 



#3 Injury Profile in Women's Football: A Systematic Review and Meta-Analysis 

Reference: Sports Med. 2021 Jan 12. doi: 10.1007/s40279-020-01401-w. Online ahead of print. 

Authors: Alejandro López-Valenciano, Javier Raya-González, Jose Alberto Garcia-Gómez, Alba Aparicio-Sarmiento, Pilar Sainz de Baranda, Mark De Ste Croix, Francisco Ayala

Summary: Football is the most popular sport among women; however, little is known about the injury profile in this population. This information would help design tailored injury risk mitigation strategies that may make football safer for women. The aim of this study was to perform a systematic review and meta-analysis of epidemiological data of injuries in women´s football. A systematic review following PRISMA guidelines was performed up to January 2020 in PubMed, Web of Science, Sportdiscus and the Cochrane Library databases. Twenty-two studies reporting the incidence of injuries in women football were analysed. Two reviewers independently extracted data (intraclass correlation coefficient [ICC] for inter-reviewer reliability = 0.87) and assessed study quality using the STROBE statement, GRADE approach, Newcastle Ottawa Scale and Downs and Black assessment tools. Studies were combined in pooled analyses (injury incidence and injury proportion) using a Poisson random effects regression model. The overall incidence of injuries in female football players was 6.1 injuries/1000 h of exposure. Match injury incidence (19.2 injuries/1000 h of exposure) was almost six times higher than training injury incidence rate (3.5 injuries/1000 h of exposure). Lower extremity injuries had the highest incidence rates (4.8 injuries/1000 h of exposure). The most common types of injuries were muscle/tendon (1.8 injuries/1000 h of exposure) and joint (non-bone) and ligament (1.5 injuries/1000 h of exposure), which were frequently associated with traumatic incidents. Slight/minimal injuries (1-3 days of time loss) were the most common. The incidence rate of injuries during matches in the top five world ranking leagues was higher than the rest of the leagues (19.3 vs 10.7 injuries/1000 h of exposure, respectively). The weighted injury proportion was 1.1 (95% confidence interval = 0.6-1.7) whereby on average players sustained more than one injury per season. Female football players are exposed to a substantial risk of sustaining injuries, especially during matches that require the highest level of performance. To markedly reduce overall injury burden, efforts should focus on introducing and evaluating preventative measures that target match specific dynamics to make football players more capable of responding to the challenges that they have to deal with during match play. 



#4 Influence of Traditional Sporting Games on the Development of Creative Skills in Team Sports. The Case of Football

Reference: Front Psychol. 2020 Dec 23;11:611803. doi: 10.3389/fpsyg.2020.611803. eCollection 2020. 

Authors: Alexandre Oboeuf , Sylvain Hanneton, Joséphine Buffet, Corinne Fantoni, Lazhar Labiadh

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Summary: The aim of this present study is to investigate the influence of three learning contexts on the development of motor creativity of young footballers (8-9 years old). In team sport, creativity is a fundamental issue because it allows players to adapt in an environment of high social uncertainty. To carry out this work, we suggest a method for assessing motor creativity into ecological situations based on the analysis of praxical communications. Creativity originates from an interaction between divergence and convergence. In our case, the number of communications (fluidity) and the diversity of updated communications (flexibility) are our divergence indicators. Convergence, understood as the ability to make good decisions, is assessed by two expert judges (R > 0.90). Sixty boys' football players (M = 8.67; SD = 0.3) coming from three football clubs participated in this research. The study lasted 2 years. Each year, a team of 10 players from each club participated in the research twice a week for 32 weeks (8 months), these groups attended different training sessions: (a) the control group (n = 20) followed a classical learning; (b) the decoding group (n = 20) attended training focused on learning the praxemes of football; (c) the traditional sporting games group (n = 20) followed a training session that was jointly focused on praxemes and the practice of traditional sporting games. The motor creativity of players and groups was assessed both at the beginning and at the end of the year during football matches. Compared to the control group, in the post-test, the group with the highest fluidity is the decoding group (p < 0.001) and the one with the highest fluidity is the traditional sporting games group. The latter group is also the one with the best convergence (p < 0.001). The results showed that traditional games can help develop players' creative abilities. This research invites us to investigate the complementarity between the different offered training. 



#5 Effect of acute football activity and physical fitness on glycaemic and insulinaemic responses in adolescents

Reference: J Sports Sci. 2021 Jan 11;1-9. doi: 10.1080/02640414.2020.1860362. Online ahead of print. 

Authors: Ryan A Williams, Simon Cooper, Karah J Dring, Lorna Hatch, John G Morris, Caroline Sunderland, Mary E Nevill

Summary: The present study examined the metabolic responses to an acute bout of football and the overall and moderating role of physical fitness on these responses, in adolescents. Thirty-six adolescents (16 girls, 20 boys; 12.6±0.5 y) completed two trials (60-min football and 60-min seated rest) separated by 7-d. Capillary blood samples were taken at baseline (60-min prior to exercise/rest), immediately, 30- and 60-min post-exercise and 30-, 60- and 120-min following a standardised lunch (1.5-, 2- and 3-h post-exercise), for the determination of blood glucose and plasma insulin concentrations. The median split of distance covered on the multi-stage fitness test was used to define high- and low-fit groups. Overall plasma insulin tAUC following lunch was lower in high-fit participants compared to low-fit (high-fit: 3784.2±1653.1 pmol·L-1x120min, low-fit: 6457.3±3290.7 pmol·L-1x120min; p<0.001), although there was no acute effect of the football session (p>0.05). Football reduced blood glucose concentration 1-h post-exercise compared to control (exercise: 3.8±0.6 mmol·L-1, rest: 4.6±0.8 mmol·L-1; p<0.001), but this was similar for the high- and low-fit participants (p>0.05). Blood glucose tAUC was not affected by exercise or physical fitness (p>0.05). These data emphasise the importance of physical fitness for metabolic health in adolescents, as well as the utility of football as a popular form of games-based activity for improving glucose regulation. 



#6 Effects of football fitness training on lymphedema and upper-extremity function in women after treatment for breast cancer: a randomized trial 

Reference: Acta Oncol. 2021 Jan 11;1-9. doi: 10.1080/0284186X.2020.1868570. Online ahead of print. 

Authors: Kira Bloomquist, Peter Krustrup, Bjørn Fristrup, Victor Sørensen, Jørn Wulff Helge, Eva Wulff Helge, Eva Soelberg Vadstrup, Mikael Rørth, Sandra C Hayes, Jacob Uth

Summary: Breast cancer survivors are encouraged to be physically active. A recent review suggests that football training is an effective exercise modality for women across the lifespan, positively influencing health variables such as strength, fitness and social well-being. However, football is a contact sport, potentially posing an increased risk of trauma-related injury. Against this backdrop, breast cancer survivors are advised to avoid trauma or injury to the affected or at-risk arm in order to protect against lymphedema onset or exacerbation. The aim of this study was therefore to evaluate the feasibility and safety of Football Fitness training in relation to lymphedema and upper-extremity function after treatment for breast cancer. Sixty-eight women aged 18-75 years, who had received surgery for stage I-III breast cancer and completed (neo) adjuvant chemotherapy and/or radiotherapy within five years, were randomized (2:1) to a Football Fitness group (FFG, n = 46) or a control group (CON, n = 22) for twelve months. Secondary analyses using linear mixed models were performed to assess changes in upper-body morbidity, specifically arm lymphedema (inter-arm volume % difference, dual energy X-ray absorptiometry; extracellular fluid (L-Dex), bioimpedance spectroscopy), self-reported breast and arm symptoms (EORTC breast cancer-specific questionnaire (BR23) and upper-extremity function (DASH questionnaire) at baseline, six- and twelve-month follow-up. We observed similar point prevalent cases of lymphedema between groups at all time points, irrespective of measurement method. At the six-month post-baseline assessment, reductions in L-Dex (extracellular fluid) were found in FFG versus CON. These significant findings were not maintained at the twelve-month assessment. No difference between groups was observed for inter-limb volume difference %, nor any of the remaining outcomes. While superiority of Football Fitness was not observed, the results support that participation in Football Fitness training is feasible and suggests no negative effects on breast cancer-specific upper-body morbidity, including lymphedema. 



#7 Playing Non-Professional Football in COVID-19 Time: A Narrative Review of Recommendations, Considerations, and Best Practices 

Reference: Int J Environ Res Public Health. 2021 Jan 12;18(2):E568. doi: 10.3390/ijerph18020568. 

Authors: Markel Rico-González, José Pino-Ortega, Luca Paolo Ardigò

Summary: The coronavirus disease (COVID-19) pandemic in 2020 resulted in widespread interruption of team sports training and competitions. Our aim was to review the recommendations and best practices in return to play in non-professional football after activity lockdown. The authors searched two electronic databases (PubMed, Web of Science) to extract studies published before September 15 2020. Twenty studies explained recommendations, considerations, or best practices in return to play in football, and all of them were clustered into three groups: (1) training load management (n = 10), (2) medical recommendations (n = 9), and (3) recovery related issues (n = 5). The way to establish a progression in training process should be based on training load management and managing the number of stimuli per time. Following the studies, this training process should be divided into three phases: phase 1-physical distancing should be maintained; phases 2 and 3-group training should start. Medical considerations were clustered into different groups: general, pre- and post- training, during training, education, planning to return to competition, and suggestions for post confinement weeks. In particular, social issues, strict hygiene questions, and continuous PCR testing should be considered in return to play over football season. Finally, since a correlation has been found between high-intensive training loads and immunoglobulin A, nutritional and lifestyle recovery strategies should be performed. Moreover, since immunosuppression has been related to congested schedules (<72 h between matches), football federations should avoid this situation. 



#8 Nontraumatic Exertional Fatalities in Football Players, Part 1: Letter to the Editor

Reference: Orthop J Sports Med. 2020 Dec 29;8(12):2325967120980395. doi: 10.1177/2325967120980395. eCollection 2020 Dec. 

Authors: William M Adams, Samantha E Scarneo-Miller, Rebecca L Stearns, Douglas J Casa

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#9 Internal and External Training Load in Under-19 versus Professional Soccer Players during the In-Season Period 

Reference: Int J Environ Res Public Health. 2021 Jan 11;18(2):E558. doi: 10.3390/ijerph18020558. 

Authors: Sullivan Coppalle, Guillaume Ravé, Jason Moran, Iyed Salhi, Abderraouf Ben Abderrahman, Sghaeir Zouita, Urs Granacher, Hassane Zouhal 

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Summary: This study aimed to compare the training load of a professional under-19 soccer team (U-19) to that of an elite adult team (EAT), from the same club, during the in-season period. Thirty-nine healthy soccer players were involved (EAT [n = 20]; U-19 [n = 19]) in the study which spanned four weeks. Training load (TL) was monitored as external TL, using a global positioning system (GPS), and internal TL, using a rating of perceived exertion (RPE). TL data were recorded after each training session. During soccer matches, players' RPEs were recorded. The internal TL was quantified daily by means of the session rating of perceived exertion (session-RPE) using Borg's 0-10 scale. For GPS data, the selected running speed intensities (over 0.5 s time intervals) were 12-15.9 km/h; 16-19.9 km/h; 20-24.9 km/h; >25 km/h (sprint). Distances covered between 16 and 19.9 km/h, > 20 km/h and >25 km/h were significantly higher in U-19 compared to EAT over the course of the study (p = 0.023, d = 0.243, small; p = 0.016, d = 0.298, small; and p = 0.001, d = 0.564, small, respectively). EAT players performed significantly fewer sprints per week compared to U-19 players (p = 0.002, d = 0.526, small). RPE was significantly higher in U-19 compared to EAT (p = 0.001, d = 0.188, trivial). The external and internal measures of TL were significantly higher in the U-19 group compared to the EAT soccer players. In conclusion, the results obtained show that the training load is greater in U19 compared to EAT. 



#10 Evaluation of the accuracy of different body composition prediction formulas, compared to Dual Energy X-ray Absorptiometry, in soccer players of Colombian professional teams

Reference: Nutr Hosp. 2021 Jan 15. doi: 10.20960/nh.03206. Online ahead of print. [Article in Spanish] 

Authors: Maximiliano Kammerer López, Natalia Del Carmen Ceballos Feria, Maria Camila Mayor Rengifo, Hugo Hernando Hoyos García, Santiago Gómez Velásquez

Summary: Professional soccer both in the local setting and in other countries is highly competitive, and those who practice it must have specific morphological, anthropometric, and body composition characteristics, in addition to constant monitoring of nutritional and training interventions. Currently, the gold-standard criterion for the evaluation of body composition is Dual Energy X-ray Absorciometry (DXA), which is a costly laboratory method with limited use for many professionals. Knowing which field methods obtain similar results to this would allow a better interdisciplinary approach, which could have a positive impact on sports performance. The objective of this study was to evaluate the accuracy of different formulas for predicting fat percentage and fat mass, as compared to DXA, in Colombian soccer team players. A cross-sectional, analytical study using convenience sampling. A total of 79 professional male soccer players, belonging to 4 Colombian first and second division clubs, were included. Thirty anthropometric variables were measured, wherewith a descriptive analysis was performed using the SPSS v.21 program, and a procedure with analytical scope was carried out to establish concordance indices between different measurements using the Bland and Altman method. This statistical process was performed using the library (BlandAltmanLeh) of the statistical program "R". Average age was 23 ± 4.4 years, and the percentage of body fat was estimated using six equations: Jackson and Pollock (7.20 ± 2.58 %), Yuhasz as modified by Carter (7.52 ± 8.50 %), Reilly (10.04 ± 1.43 %), Faulkner (11.23 ± 11.90 %), Pariskova and Buskova (11.08 ± 16.06 %), and Durnin and Womersley (12.41 ± 20,10 %), in addition to the calculation of fat percentage for fat mass using the five-component method (13.17 ± 2.86 %). The percentage of body fat that showed the lowest intermethod difference was fractionation by five components (0.54 ± 3.56), followed by Durnin and Womersley (0.66 ± 3.52). The calculations of fat percentage using the fractionation of 5 components method and the Durnin and Womersley equation were closest to the results obtained by the gold-standard method (DXA) in soccer players of Colombian professional teams. 



#11 Prevalence of Low Energy Availability in Collegiate Women Soccer Athletes 

Reference:  J Funct Morphol Kinesiol. 2020 Dec 18;5(4):96. doi: 10.3390/jfmk5040096. 

Authors: Meghan K Magee, Brittanie L Lockard, Hannah A Zabriskie, Alexis Q Schaefer, Joel A Luedke, Jacob L Erickson, Margaret T Jones, Andrew R Jagim

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Summary: Limited information exists on the prevalence of low energy availability (LEA) in collegiate team sports. The purpose of this study was to examine the prevalence of LEA in collegiate women soccer players. Collegiate women soccer athletes (n = 18, height: 1.67 ± 0.05 m; body mass: 65.3 ± 7.9 kg; body fat %: 24.9 ± 5.6%) had their body composition and sport nutrition knowledge assessed in the pre-season. Energy availability was assessed mid-season using a 4-day dietary log and activity energy expenditure values from a team-based monitoring system. A validated screening tool was used to screen for LEA. The screening tool classified 56.3% of athletes as at risk of LEA (<30 kcal/kg of FFM); however, the actual dietary intake identified 67% as LEA. Athletes identified as non-LEA consumed significantly more absolute (p = 0.040) and relative (p = 0.004) energy than LEA athletes. There was a high prevalence of LEA among collegiate women soccer athletes. Although previously validated in women endurance athletes, the LEA screening tool was not effective in identifying those at risk of LEA in this sample of athletes. 



#12 Detection Accuracy of Soccer Players in Aerial Images Captured from Several Viewpoints

Reference: J Funct Morphol Kinesiol. 2019 Jan 21;4(1):9. doi: 10.3390/jfmk4010009. 

Authors: Takuro Oki, Ryusuke Miyamoto, Hiroyuki Yomo, Shinsuke Hara

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Summary: In the fields of professional and amateur sports, players' health, physical and physiological conditions during exercise should be properly monitored and managed. The authors of this paper previously proposed a real-time vital-sign monitoring system for players using a wireless multi-hop sensor network that transmits their vital data. However, existing routing schemes based on the received signal strength indicator or global positioning system do not work well, because of the high speeds and the density of sensor nodes attached to players. To solve this problem, we proposed a novel scheme, image-assisted routing (IAR), which estimates the locations of sensor nodes using images captured from cameras mounted on unmanned aerial vehicles. However, it is not clear where the best viewpoints are for aerial player detection. In this study, the authors investigated detection accuracy from several viewpoints using an aerial-image dataset generated with computer graphics. Experimental results show that the detection accuracy was best when the viewpoints were slightly distant from just above the center of the field. In the best case, the detection accuracy was very good: 0.005524 miss rate at 0.01 false positive-per-image. These results are informative for player detection using aerial images and can facilitate to realize IAR. 



#13 The Physical Demands of NCAA Division I Women's College Soccer 

Reference: J Funct Morphol Kinesiol. 2019 Dec 12;4(4):73. doi: 10.3390/jfmk4040073. 

Authors: Robert W Sausaman, Matt L Sams, Satoshi Mizuguchi, Brad H DeWeese, Michael H Stone

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Summary: Extensive research into women's collegiate soccer is scarce, leaving gaps in the literature with little information available detailing the physical demands at different standards of play. Our purpose was to elucidate the physical demands of the Division I collegiate level and identify differences between playing positions. Twenty-three field players were observed during four competitive seasons using 10-Hz GPS units (Catapult Sports, Melbourne, Australia). Descriptive statistics and 95% confidence intervals were used to determine group and position-specific physical demands. Linear mixed modelling (LMM) was used to compare attacker, midfielder, and defender position groups. Total distance, high-speed distance, and sprint distance were 9486 ± 300 m, 1014 ± 118 m, and 428 ± 70 m, respectively. Furthermore, attackers were observed to cover the greatest distance at all speeds compared to midfielders and defenders. Our findings suggest that the physical demands of Division I women's soccer differ by position and appear lower compared to higher standards of play. Therefore, coaches and sports scientists responsible for the physical training of Division I collegiate players should consider the specific physical demands of the collegiate level and playing position when prescribing training, as well as in the development of their annual training programs. 



#14 Lateral Ankle Sprains and Their Association with Physical Function in Young Soccer Players 

Reference: Open Access J Sports Med. 2021 Jan 12;12:1-10. doi: 10.2147/OAJSM.S283421. eCollection 2021. 

Authors: Kenichiro Murata, Tsukasa Kumai, Norikazu Hirose

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Summary: Lateral ankle sprain (LAS) in childhood can result in lateral malleolus avulsion fractures; additionally, bone nonunion may occur. Physical maturity relates to the development of bone morphology and physical functionality. It is unknown how changes in physical functionality attributable to physical maturity affect young soccer players with abnormal lateral malleolus (ALM) morphology. Hence, the present study aimed to investigate the bone morphology of the lateral malleolus in young soccer players and to examine its relationship with physical functionality at different maturity levels. Two hundred and ninety young soccer players aged 6-15 years were included. The presence of ALM was assessed using ultrasonography. The subjects were allocated to three groups based on physical maturity (Pre-, Mid-, and Post-peak height velocity age [PHVA]). The prevalence of ALM and the relationship between ALM and physical maturity were examined for body composition, foot pressure distribution, foot alignment, ankle mobility, and single-leg balance. The prevalence of ALM was 17.6%. For physical maturity, the post-PHVA group showed a decrease in ankle dorsiflexion and eversion and an increase in one-leg hop distance compared to the Pre-PHVA group (P < 0.05). In the ALM group, the center of pressure during heel raising was distributed laterally in the Post-PHVA (P < 0.01), and the weight-bearing dorsiflexion angle was decreased in the Mid- and Post-PHVA (P < 0.05). In the Post-PHVA young soccer players, decreased ankle dorsiflexion and eversion and increased one-leg hop distance were observed. The ALM group exhibited lateral loading during heel raising in the Post-PHVA group and decreased weight-bearing ankle dorsiflexion angle in the Mid- and Post-PHVA groups. The findings indicate the importance of secondary prevention of LAS and ultrasonography. Prospective studies of LAS in young athletes are required in the future. 






Quantification of Training Load Relative to Match Load of Youth National Team

The aims of this study were to (1) quantify the external training load relative to match load in days before a subsequent international game and (2) examine the cumulative training load in relation to match load of U-17 national team soccer players.





A Meta-Analytical Comparison of the Effects of Small-Sided Games vs. Running-Based High-Intensity Interval Training on Soccer Players’ Repeated-Sprint Ability

This systematic review with a meta-analysis was conducted to compare the effects of small-sided games (SSGs)-based interventions with the effects of running-based high-intensity interval training (HIIT) interventions on soccer players’ repeated sprint ability (RSA).





Latest research in football - week 12 - 2021

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 Physical performance development in a female national team soccer program 

Reference: J Sci Med Sport . 2020 Dec 31;S1440-2440(20)30864-1. doi: 10.1016/j.jsams.2020.12.009.

Authors: Robert A Poehling, Ming-Chang Tsai, Sarah A Manson, Michael S Koehle, Cesar M P Meylan

Summary: Significant resources are invested in maximizing player performance without extensive knowledge of the athletic progression of elite female soccer players during their career. The aim of the current study was therefore to investigate the change in physical performance characteristics in 12- to 34-year-old female soccer players in a national team program. Physical performance was assessed across five years and 657 testing occasions (n = 143) using anthropometrics, 40 m sprint (10 m split), broad jump, countermovement jump, squat jump, and 30-15 intermittent fitness test (IFT). Using a Gaussian mixture model, Youth and Senior groups were bifurcated at approximately 23 years old. Subsequent linear mixed models for each group and variable identified significant improvements in the Youth group in maximal speed (30-40 m split), broad jump, countermovement jump, and final velocity30-15IFT (p ≤ 0.002), and a decrease in squat jump height with increasing age (p = 0.04). The Senior group recorded slower 10 m sprint time and a decrease in squat jump height with increasing age (p < 0.001). Body mass increased from 12 to 34 years old (Youth and Senior: p ≤ 0.001). The Youth group significantly differed in the rate of change compared to the Senior group in body mass, 10 m sprint time, countermovement jump, squat jump, and final velocity30-15IFT (p ≤ 0.001). This information can be used to identify average rates of physical performance improvement and decay to help guide optimal physical training and maximize the longevity of a female soccer players' career. 



#2 The Effect of Coach Feedback and Awareness of Head Impact Exposure on Practice Structure in Youth Football

Reference: J Neurotrauma. 2021 Jan 4. doi: 10.1089/neu.2020.7224. Online ahead of print. 

Authors: Daniella M DiGuglielmo, Gabriella M Milef, Justin B Moore, Mireille E Kelley, Alexander K Powers, Joel D Stitzel, Jillian E Urban

Summary: With the concern of concussion risk and repetitive head impacts in youth football, organizations have adopted rules that limit contact during practice. However, rule changes are not ubiquitous among organizations and are challenging to monitor and enforce. Ultimately, football practice activities are determined by coaches, but it is unknown whether providing objective data to coaches relating activities to their athletes' head impact exposure (HIE) would alter practice structure or help reduce HIE. This study evaluated the effect of coach awareness of HIE on practice structure over time. Head impact data from three intervention (56 players) and control (38 players) teams were collected over two youth football seasons. Athletes were instrumented with the Head Impact Telemetry (HIT) System and time-synchronized video was recorded for practices and games. Impact frequencies and head accelerations were compiled into weekly HIE practice and game reports shared with the head coach of each intervention team. Time per drill, impact rate, and impact magnitude were compared among three time frames (pre-season, mid-season, and late-season) using generalized linear models. Control teams had higher impact rates than intervention teams in all drills across time frames. Among all teams, 95th percentile linear and rotational accelerations were highest during mid-season. Among intervention teams, more time was spent on scrimmage and skill development from pre-season to late-season, with less time spent on tackling. This study suggests receiving objective data informing HIE in practice may contribute to changes in practice structure and help inform intervention efforts to improve head impact safety in football. 



#3 Injury and illness epidemiology in professional Asian football: lower general incidence and burden but higher ACL and hamstring injury burden compared with Europe

Reference: Br J Sports Med. 2021 Jan 5;bjsports-2020-102945. doi: 10.1136/bjsports-2020-102945. 

Authors: Montassar Tabben, Cristiano Eirale, Gurcharan Singh, Abdulaziz Al-Kuwari, Jan Ekstrand, Hakim Chalabi, Roald Bahr, Karim Chamari

Summary: While football injury and illness epidemiology surveillance at professional club level in Europe is available, epidemiological data from other continents are lacking. The aim was to investigate injury and illness epidemiology in professional Asian football. Professional teams from the Asian Football Confederation (AFC) league were followed prospectively for three consecutive AFC seasons (2017 through 2019, 13 teams per season, 322 team months). Time-loss injuries and illnesses in addition to individual match and training exposure were recorded using standardised digital tools in accordance with international consensus procedures. In total, 232 665 hours of exposure (88.6% training and 11.4% matches) and 1159 injuries were recorded; 496 (42.8%) occurred during matches, 610 (52.6%) during training; 32 (2.8%) were reported as 'not applicable' and for 21 injuries (1.8%) information was missing. Injury incidence was significantly greater during match play (19.2±8.6 injuries per 1000 hours) than training (2.8±1.4, p<0.0001), resulting in a low overall incidence of 5.1±2.2.The injury burden for match injuries was greater than from training injuries (456±336 days per 1000 hours vs 54±34 days, p<0.0001). The two specific injuries causing the greatest burden were complete ACL ruptures (0.14 injuries (95% CI 0.9 to 0.19) and 29.8 days lost (29.1 to 30.5) per 1000 hours) and hamstring strains (0.86 injuries (0.74 to 0.99) and 17.5 days (17.0 to 18.1) lost per 1000 hours).Reinjuries constituted 9.9% of all injuries. Index injuries caused 22.6±40.8 days of absence compared with 25.1±39 for reinjuries (p=0.62). The 175 illnesses recorded resulted in 1.4±2.9 days of time loss per team per month. Professional Asian football is characterised by an overall injury incidence similar to that reported from Europe, but with a high rate of ACL ruptures and hamstring injury, warranting further investigations. 



#4 Convergent Validity of CR100-Based Session Ratings of Perceived Exertion in Elite Youth Football Players of Different Ages 

Reference: Int J Sports Physiol Perform. 2021 Jan 6;1-5. doi: 10.1123/ijspp.2020-0047. Online ahead of print. 

Authors: Fabio R Serpiello, Will G Hopkins 

Summary: The purpose was to assess the convergent validity of internal load measured with the CR100 scale in youth football players of 3 age groups. A total of 59 players, age 12-17 years, from the youth academy of a professional football club were involved in this study. Convergent validity was examined by calculating the correlation between session ratings of perceived exertion (sRPE) and Edwards load, a commonly used load index derived from the heart rate, with the data originating from 1 competitive season. The magnitude of the relationship between sRPE and Edwards load was obtained with weighted mean correlations and by assessing the effect of the change of the Edwards load on sRPE. Differences between the individuals' intercepts and slopes were assessed by interpreting the SD representing the random effects (player identity and the interaction of player identity and scaled Edwards load). Probabilistic decisions about true (infinite sample) magnitudes accounting for sampling uncertainty were based on 1-sided hypothesis tests of substantial magnitudes, followed by reference Bayesian analysis. Very high relationships exist between the sRPE and Edwards load across all age groups, with no meaningful differences in the magnitudes of the relationships between groups. Moderate to large differences between training sessions and games were found in the slopes of the relationships between the sRPE and Edwards load in all age groups. Finally, mostly small to moderate differences were observed between individuals for the intercepts and slopes of the relationships between the sRPE and Edwards load. Practitioners working in youth team sports can safely use the CR100 scale to track internal load. 



#5 Experiences and Strategies Influencing Older Adults to Continue Playing Walking Football 

Reference: J Aging Phys Act. 2021 Jan 7;1-13. doi: 10.1123/japa.2020-0058. Online ahead of print. 

Authors: Rachel Cholerton, Helen Quirk, Jeff Breckon, Joanne Butt 

Summary: Adults aged 55+ years are most likely to be inactive, despite research suggesting that older adults experience multiple benefits when participating in physical activity and sport. Limited research focuses on long-term continuation of sport participation in this population, especially in "adapted sports" like walking football. This study explored the experiences of walking football maintenance in 55- to 75-year-old players. Semistructured interviews were conducted, with 17 older adults maintaining walking football play over 6 months. The inductive analysis revealed five higher-order themes representing maintenance influences and two higher-order themes relating to maintenance mechanisms (i.e., the conscious process by which players maintain). Influences when maintaining walking football included individual- and culture-level influences (e.g., perceived benefits of maintenance and ability acceptance). Maintenance mechanisms included cognitions and behaviors (e.g., scheduling sessions and redefining physical activity expectations). Findings highlight novel implications for policy and practice, which are important to consider when delivering walking football to older adults. 



#6 Upper-Body Resistance Training Following Soccer Match Play: Compatible, Complementary, or Contraindicated?

Reference: Int J Sports Physiol Perform. 2021 Jan 13;1-11. doi: 10.1123/ijspp.2020-0762. Online ahead of print. 

Authors: Angelo Sabag, Ric Lovell, Neil P Walsh, Nick Grantham, Mathieu Lacome, Martin Buchheit 

Summary: During heavily congested schedules, professional soccer players can experience exacerbated fatigue responses, which are thought to contribute to an increased risk of injury. Given that match-induced residual fatigue can last up to 72 hours, many coaches naturally prioritize recovery in the days immediately following match day. While it is intuitive for coaches and training staff to decrease the amount of auxiliary training practices to focus on recovery, prescribing upper-body resistance training on the day after match play has recently emerged as a specific training modality in this context. While these sessions may be implemented to increase training stimulus, there are limited data available regarding the efficacy of such a practice to improve recovery kinetics. In this narrative review, the authors look at the theoretical implications of performing upper-body resistance training on the day after match play on the status of various physiological and psychological systems, including neuromuscular, metabolic, hormonal, perceptual, and immunological recovery. The available evidence suggests that in most cases this practice, as currently implemented (ie, low volume, low intensity), is unlikely to be complementary (ie, does not accelerate recovery) but is potentially compatible (ie, does not impair recovery). Overall, because the perception of such sessions may be player dependent, their programming requires an individualized approach and should take into account match dynamics (eg, fixture scheduling, playing time, travel). 



#7 The Risk of Knee Osteoarthritis in Professional Soccer Players 

Reference: Dtsch Arztebl Int. 2021 Jan 1;118(1):arztebl.m2021.0007. doi: 10.3238/arztebl.m2021.0007. 

Authors: Alice Freiberg, Ulrich Bolm-Audorff, Andreas Seidler 

Summary: We address the question whether professional soccer players with and without macroinjury of the knee joint are at an elevated risk for knee osteoarthritis. A systematic review with meta-analyses was conducted. The study protocol was prospectively registered (registration number CRD42019137139). The MEDLINE, EMBASE, and Web of Science databases were searched for relevant publications; in addition, forward searching was performed, and the listed references were considered. All steps of the process were undertaken independently by two reviewers, and any discordances were resolved by consensus. For all publications whose full text was included, the methods used were critically evaluated. The quality of the evidence was judged using the GRADE criteria. The pooled odds ratio for objectively ascertained osteoarthrosis of the knee was 2.25 (95% confidence interval [1.41-3.61], I2 = 71%). When only radiologically ascertained knee osteoarthrosis was considered, the odds ratio was 3.98 [1.34; 11.83], I2 = 58%). The pooled risk estimator in studies in which knee joint macroinjury was excluded was 2.81 ([1.25; 6.32], I2 = 71%). A marked association was found between soccer playing and knee osteoarthritis in male professional soccer players. For female professional soccer players, the risk of knee osteoarthritis could not be assessed because of the lack of data. Knee injuries seem to play an important role in the development of knee osteoarthritis in professional soccer players. 



#8 Analyzing the Magnitude of Interlimb Asymmetries in Young Female Soccer Players: A Preliminary Study 

Reference: Int J Environ Res Public Health. 2021 Jan 8;18(2):E475. doi: 10.3390/ijerph18020475. 

Authors: Javier Raya-González, Filipe Manuel Clemente, Daniel Castillo

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Summary: Although asymmetries in lower limbs have been linked with players' performance in male soccer players, literature that has been published addressing female soccer is scarce. Thus, the aim of this study was twofold: (i) describe the asymmetries of women soccer players during jumping, change-of-direction and range-of-motion tests; and (ii) test possible relationships between asymmetries and injury risk in female soccer players. Sixteen female players (15.5 ± 1.5 years) performed a battery of fitness tests (i.e., jump ability, change-of-direction ability and passive range-of-motion) and muscle mass analysis via dual-energy X-ray absorptiometry, through which the specific asymmetry index and the related injury risk were calculated. Significant (p < 0.05) lower asymmetries in the change-of-direction test were observed in comparison to those observed in jumping and range-of-motion tests; significant (p < 0.05) lower asymmetries in muscle mass were also reported compared to those found in the change-of-direction and countermovement jump tests. Additionally, increased injury risk for countermovement jump and hip flexion with extended knee range-of-motion (relating to asymmetry values) and for ankle flexion with flexed knee range-of-motion in both legs (relating to reference range-of-motion values), as well as increased individual injury risk values, were observed across all tests. These findings suggest the necessity to implement individual approaches for asymmetry and injury risk analyses. 



#9 Physical performance and perception of foot discomfort during a soccer-specific match simulation. A comparison of football boots

Reference: J Sports Sci. 2021 Jan 12;1-9. doi: 10.1080/02640414.2020.1856461. Online ahead of print. 

Authors: Katrine Okholm Kryger, Kumbirai Mutamba, Séan Mitchell, Stuart Charles Miller, Steph Forrester

Summary: Football boots are marketed with emphasis on a single key performance characteristic (e.g. speed). Little is known on how design parameters impact players' performance. This study investigated the impact of boot design on performance maintenance and perceived foot comfort during a 90-minute match simulation drill. Eleven male university football players tested two commercially available "sprint boots" known to generate significantly different plantar pressures (high=Boot H and low=Boot L) . Players completed a modified Soccer-specific Aerobic Field Test on a 3G pitch. Heart rate, rated perceived exertion and perceived foot discomfort were assessed for each 15-min interval. Power generation was assessed pre- and post-match simulation. A significantly higher mean heart rate was seen for Boot L in the 60th-75th and 75th-90th minute intervals (P = 0.017, P = 0.012 respectively). Perceived exertion did not differ between boots (P ≥ 0.302). Power generation significantly decreased in Boot H between pre- and post-match (P = 0.042). Both boots increased discomfort with significantly more plantar discomfort felt in the last 30 min in Boot H (75th min: P = 0.037; 90th min: P = 0.048). The results imply that a comfortable boot design may improve maintenance of performance during match-play. 



#10 The Association Between Training Load and Injury Risk in Elite Youth Soccer Players: a Systematic Review and Best Evidence Synthesis 

Reference: Sports Med Open. 2021 Jan 11;7(1):6. doi: 10.1186/s40798-020-00296-1. 

Authors: Sven Verstappen, Rogier M van Rijn, Rick Cost, Janine H Stubbe

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Summary: Injury risk in elite youth soccer players is high. Implementing an optimal training load is of utmost importance to reduce the risk of injuries. The aim was to conduct a systematic review and best evidence synthesis to explore the effects of internal and external training load on injury risk in elite youth soccer players. MEDLINE, Embase, Web of Science, CENTRAL, and CINAHL were searched up until 17 January 2020. Each article had to meet all of the following criteria: (1) the study population consisted of male elite youth soccer players aged between 12 and 21 years; (2) a longitudinal, prospective study design was used; (3) soccer-related injuries were registered (i.e., self-reported or by medical staff); (4) external and/or internal load parameters were described; and (5) the article was published in an English peer-reviewed scientific journal. The quality of the included articles was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS). A best evidence synthesis was performed to rank the level of evidence. Five studies (2 high quality, 3 low quality) were included. Best evidence synthesis highlighted that there was moderate evidence for (1) no association between 2-, 3-, and 4-week cumulative loads for total distance covered; (2) no association between 1-week workloads (sRPE × duration); and (3) no association between A:C workload ratios (4 weeks) and injury risk. For all other comparisons, only insufficient or conflicting evidence was found. There is a paucity of evidence for an association between internal and external training load parameters and injury risk in elite youth soccer players. 



#11 Effects of high-intensity interval training in men soccer player's physical fitness: A systematic review with meta-analysis of randomized-controlled and non-controlled trials

Reference: J Sports Sci. 2021 Jan 11;1-22. doi: 10.1080/02640414.2020.1863644. Online ahead of print. 

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Fábio Yuzo Nakamura, Hugo Sarmento

Summary: This systematic review with meta-analysis (SRMA) was conducted to assess the effects of high-intensity interval training (HIIT) programmes on men soccer players' aerobic fitness (maximal oxygen uptake and aerobic performance), repeated sprint ability (RSA), vertical jump height (VJH), and linear sprinting time (ST). An electronic search yielded 1,714 articles, 33 of which were included in the present study. Meta-analyses revealed significant benefits of HIIT compared to controls in maximal oxygen uptake (p = 0.018), AP (p = 0.041), and RSA (p = 0.049). No significant effects were found in terms of ST (p = 0.080). The meta-analyses of non-controlled studies revealed significant improvements after HIIT in maximal oxygen uptake (p = 0.001), AP (p = 0.007), RSA (p = 0.001), and ST (p < 0.001). However, no significant improvements in VHJ were found (p = 0.063). Furthermore, no significant differences were found in sub-group analysis (comparisons between HIIT types). In conclusion, HIIT is effective for improving maximal oxygen uptake, AP, and RSA regardless of the HIIT type. For VHJ and ST outcomes, it seems reasonable to complement the HIIT since it might not be enough to achieve significant changes. 



#12 The Validity of an Updated Metabolic Power Algorithm Based upon di Prampero's Theoretical Model in Elite Soccer Players

Reference: Int J Environ Res Public Health. 2020 Dec 20;17(24):9554. doi: 10.3390/ijerph17249554. 

Authors: Cristian Savoia, Johnny Padulo, Roberto Colli, Emanuele Marra, Allistair McRobert, Neil Chester, Vito Azzone, Samuel A Pullinger, Dominic A Doran

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Summary: The aim of this study was to update the metabolic power (MP) algorithm (PV˙O2, W·kg-1) related to the kinematics data (PGPS, W·kg-1) in a soccer-specific performance model. For this aim, seventeen professional (Serie A) male soccer players (V˙O2max 55.7 ± 3.4 mL·min-1·kg-1) performed a 6 min run at 10.29 km·h-1 to determine linear-running energy cost (Cr). On a separate day, thirteen also performed an 8 min soccer-specific intermittent exercise protocol. For both procedures, a portable Cosmed K4b2 gas-analyzer and GPS (10 Hz) was used to assess the energy cost above resting (C). From this aim, the MP was estimated through a newly derived C equation (PGPSn) and compared with both the commonly used (PGPSo) equation and direct measurement (PV˙O2). Both PGPSn and PGPSo correlated with PV˙O2 (r = 0.66, p < 0.05). Estimates of fixed bias were negligible (PGPSn = -0.80 W·kg-1 and PGPSo = -1.59 W·kg-1), and the bounds of the 95% CIs show that they were not statistically significant from 0. Proportional bias estimates were negligible (absolute differences from one being 0.03 W·kg-1 for PGPSn and 0.01 W·kg-1 for PGPSo) and not statistically significant as both 95% CIs span 1. All variables were distributed around the line of unity and resulted in an under- or overestimation of PGPSn, while PGPSo routinely underestimated MP across ranges. Repeated-measures ANOVA showed differences over MP conditions (F1,38 = 16.929 and p < 0.001). Following Bonferroni post hoc test significant differences regarding the MP between PGPSo and PV˙O2/PGPSn (p < 0.001) were established, while no differences were found between PV˙O2 and PGPSn (p = 0.853). The new approach showed it can help the coaches and the soccer trainers to better monitor external training load during the training seasons. 



#13 Effects of Strength vs. Plyometric Training Programs on Vertical Jumping, Linear Sprint and Change of Direction Speed Performance in Female Soccer Players: A Systematic Review and Meta-Analysis

Reference: Int J Environ Res Public Health. 2021 Jan 6;18(2):E401. doi: 10.3390/ijerph18020401. 

Authors: Elena Pardos-Mainer, Demetrio Lozano, Marcelino Torrontegui-Duarte, Antonio Cartón-Llorente, Alberto Roso-Moliner

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Summary: The main purpose of this systematic review and meta-analysis was to compare the effects of strength training (ST) and plyometric training (PT) on vertical jump, linear sprint and change of direction (COD) performance in female soccer players. A systematic search of the PubMed, Web of Science, Google Scholar and SportDiscus databases revealed 12 studies satisfying the inclusion criteria. The inverse-variance random-effects model for meta-analyses was used. Effect sizes (ES) were represented by the standardized mean difference and presented alongside 95% confidence intervals (CI). The magnitude of the main effect was small to moderate (vertical jump (ES 0.53 (95% CI-0.11, 0.95), Z = 2.47 (p = 0.01); linear sprint (ES -0.66 (95% CI-2.03, -0.21), Z = 2.20 (p = 0.03); COD (ES -0.36 (95% CI-0.68, -0.03), Z = 2.17 (p = 0.03)). Subgroup analyses were performed (i.e., ST and PT duration, frequency, session duration and total number of sessions), revealing no significant subgroup differences (p = 0.12-0.88). In conclusion, PT provides better benefits than ST to improve vertical jump, linear sprint and COD performance in female soccer players. However, significant limitations in the current literature prevent assured PT and ST prescription recommendations being made. 






Influence of Size and Maturity on Injury in Young Elite Soccer Players

The purpose of this study was to investigate sports injuries in younger (U9–U11) and older (U12–U13) children playing soccer at an elite level, analysing potential anthropometric and maturity risk factors. 





Effect of a Shock Micro-Cycle on Biochemical Markers in University Soccer Players

This study aimed to examine various biochemical biomarkers changes during a shock micro-cycle in soccer players from a university team.





Latest research in football - week 11 - 2021

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 Ordering sequential competitions to reduce order relevance: Soccer penalty shootouts

Reference: PLoS One. 2020 Dec 30;15(12):e0243786. doi: 10.1371/journal.pone.0243786. eCollection 2020. 

Authors: Nils Rudi, Marcelo Olivares, Aditya Shetty

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Summary: In sequential competitions, the order in which teams take turns may have an impact on performance and the outcome. Previous studies with penalty shootouts have shown mixed evidence of a possible advantage for the first shooting team. This has led to some debate on whether a change in the rules of the game is needed. This work contributes to the debate by collecting an extensive dataset of shootouts which corroborates an advantage for the first shooter, albeit with a smaller effect than what has been documented in previous research. To evaluate the impact of alternative ordering of shots, we model shootouts as a probability network, calibrate it using the data from the traditional ordering, and use the model to conduct counterfactual analysis. Our results show that alternating the team that shoots first in each round would reduce the impact of ordering. These results were in part developed as supplement to field studies to support the International Football Association Board's (IFAB) consideration of changing the shooting order. 



#2 Defining the Normal Spectrum of Electrocardiographic and Left Ventricular Adaptations in Mixed-Race Male Adolescent Soccer Players 

Reference: Circulation. 2021 Jan 5;143(1):94-96. doi: 10.1161/CIRCULATIONAHA.120.049740. Epub 2020 Dec 30. 

Authors: Aneil Malhotra, David Oxborough, Prashant Rao, Gherardo Finocchiaro, Harshil Dhutia, Vivek Prasad, Chris Miller, Bernard Keavney, Michael Papadakis, Sanjay Sharma

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#3 Putting the player first: A method to analyse and develop expert players performance in professional soccer

Reference: J Sports Sci. 2020 Dec 31;1-13. doi: 10.1080/02640414.2020.1864103. Online ahead of print. 

Authors: Eileen Gleeson, Seamus Kelly

Summary: The purpose of this paper is to present a player-centred performance analysis method as an effective mechanism to enhance expert players' performance in professional soccer. Data were collected through an application of a developed performance analysis method and subsequent unstructured interviews to explore participants' experience of the applied methodology. Grounded by an enactive perspective of human activity, the applied methodology foregrounds the player's intrinsic experience and places the player at the centre of the analysis and interpretation process. The sample included thirty professional soccer players with professional playing experience ranging from 2 years to 19 years and representing three professional teams. Using an interpretive data analysis approach results were considered from a methodological perspective concerning the core functions of a performance analysis method. Categories regarding performance analysis and performance development were highlighted. Findings demonstrate that adopting a player-centred approach to performance analysis in professional soccer provides advancement of the understanding of the collective performance of the expert player and may increase the opportunity for sustained learning. 



#4 Salivary Immunoendocrine and Self-report Monitoring Profiles across an Elite-Level Professional Football Season 

Reference: Med Sci Sports Exerc. 2020 Dec 23;Publish Ahead of Print. doi: 10.1249/MSS.0000000000002553.

Authors: Matthew Springham, Sean Williams, Mark Waldron, Anthony J Strudwick, Chris Mclellan, Robert U Newton 

Summary: This investigation examined the longitudinal changes and inter-relationships of salivary and self-report monitoring measures across a professional football season. Measures were collected bi-weekly from 18 senior professional male players across a six-week pre-season and eight five-week in-season mesocycles and analysed using a linear mixed-effects model. Analysis identified a small (P=0.003) cross-season suppression of salivary immunoglobulin-A, small reductions to salivary α-amylase (P=0.047) and salivary cortisol (P=0.007), and trivial changes to salivary testosterone (P>0.05). The testosterone:cortisol ratio typically responded inversely to changes in player workload. Self-report measures of fatigue (P=0.030), sleep quality (P=0.003) and muscle soreness (P=0.005) improved (ES=small) across the first half of the season. Fatigue and sleep measures were most consistently related to hormonal measures (R2 = 0.43 to 0.45). For these relationships, increases in cortisol were associated with compromised self-report responses, whereas increases in testosterone:cortisol were associated with improved responses. Non-linear relationships were identified for fatigue with immunoglobulin-A (P=0.017; ES=trivial) and testosterone (P=0.012; ES=trivial); for sleep quality with testosterone (P<0.001; ES=trivial); for muscle soreness with testosterone (P=0.012; ES=trivial) and for the self-report inventory sum with testosterone (P=0.027; ES=trivial). For these relationships, self-report responses were optimal at mean immunoglobulin-A and testosterone levels and very low levels (-2 SD) exerted the most compromising effects. Players can experience a chronic cross-season suppression of mucosal immunity. Salivary immunoglobulin-A, testosterone, cortisol and testosterone:cortisol measures relate to self-report measures of fatigue, sleep quality and muscle soreness. In-season reductions in testosterone, cortisol and testosterone:cortisol or increases in cortisol among elite football players could be used to indicate the need for reduced workload, which might lead to improved wellbeing. 



#5 The incidence and characteristics of purposeful heading in male and female youth football (soccer) within Australia

Reference: J Sci Med Sport. 2020 Dec 26;S1440-2440(20)30865-3. doi: 10.1016/j.jsams.2020.12.010.

Authors: Kerry Peek, Teale Vella, Tim Meyer, Florian Beaudouin, Marnee McKay

Summary: The aim was too quantify the incidence and characteristics of purposeful headers and unintentional head impacts during male and female youth football (soccer) games in Australia. Ten match-videos (total n=110) per playing age (under 13-20 males; under 13-17 females) from the 2019 National Premier League season were coded for purposeful headers and unintentional head impacts. Total headers and head impacts as well as incidence rate (IR) per 1000 match-hours for different match characteristics were calculated. Purposeful headers accounted for 99% (n=4615, IR:1618) of total head impacts. The IR of purposeful headers per 1000 match-hours was highest for under-15 males (IR:2117) and under-17 females (IR:2090) followed by under-20 males (IR:1761). Midfielders completed the most headers in all female age groups (mean IR:713) and under 13-14 males (mean IR:891), with defenders completing the most headers in under 15-20 males (mean IR:760). Heading duels accounted for 16% of total headers with most headers performed during free play (68%), throw-ins (15%), free kicks (12%) and corner kicks (5%). Only 57 head impacts (IR:20) were coded as unintentional head impacts resulting from being struck by the ball or opponent body part with 4 (IR:1.4) requiring medical attention. Heading is a complex skill. Given the propensity of youth players of all ages to purposefully head the ball, consideration should be given to coaching heading technique based on specific game scenarios for their playing position and age group. The findings of this study can be used to inform heading guidelines. 



#6 Comparison of multidirectional jump performance and lower limb passive range of motion profile between soccer and basketball young players 

Reference: PLoS One. 2021 Jan 7;16(1):e0245277. doi: 10.1371/journal.pone.0245277. eCollection 2021. 

Authors: Marta Domínguez-Díez, Daniel Castillo, Javier Raya-González, Silvia Sánchez-Díaz, María Soto-Célix, Tara Rendo-Urteaga, Ángel Lago-Rodríguez

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Summary: This study was performed aimed at comparing multidirectional bilateral and unilateral jump performance and passive range of motion (ROM) of lower limbs between soccer and basketball young players and evaluating associations between inter-limb ROM asymmetry and bilateral jump performance. A total of 67 young male athletes participated in this study, who were classified as soccer (n = 40; 15.55 ± 1.5 y; 1.76 ± 0.12 m; 58.15 ± 10.82 kg; 19.84 ± 2.98 kg·m2) and basketball (n = 27; 15.7 ± 1.66 y; 1.76 ± 0.12 m; 62.33 ± 16.57 kg; 19.84 ± 2.98 kg·m2) players. Participants were asked to perform bilateral and unilateral multidirectional jumps, and passive ROM of hip (flexion, extension and abduction), knee (flexion) and ankle (dorsiflexion) joints was also assessed. Significant between-group differences were observed for hip extension with flexed knee ROM in dominant (soccer: 142.43 ± 7.74°; basketball: 148.63 ± 8.10°) and non-dominant (soccer: 144.38 ± 8.36°; basketball: 148.63 ± 6.45°) legs; hip flexion with flexed knee ROM in dominant (soccer: 13.26 ± 4.71°; basketball: 9.96 ± 3.42°) and non-dominant (soccer: 12.86 ± 4.55°; basketball: 9.70 ± 3.62°) legs; and for the ratio of hip abduction (soccer: 1.02 ± 0.08; basketball: 0.97 ± 0.11). However, no significant between-group differences were observed for bilateral and unilateral jump capacity, or for inter-limb asymmetries (dominant vs. non-dominant leg). Finally, no associations were observed between ROM ratio (dominant vs. non-dominant leg) and bilateral jump performance. These findings lead to the suggestion that differences on passive ROM values in young male athletes may be sport-specific. Additionally, there seems to be need for the implementation of training strategies specifically aimed at improving bilateral or unilateral jump ability, or at diminishing inter limb passive ROM differences in order to improve multidirectional jump performance for neither soccer nor basketball youth male players. 



#7 Improving Soccer Knowledge From Computerized Game Diagrams: Benefits of Sequential Instructional Arrows 

Reference: Percept Mot Skills. 2021 Jan 5;31512520983083. doi: 10.1177/0031512520983083.

Authors: Ghazi Rekik, Yosra Belkhir, Mohamed Jarraya

Summary: In this study, we used Cognitive Load Theory to examine the role of a sequential versus simultaneous presentation technique for learning tactical skills from computerized diagrams of soccer scenes with two levels of complexity. Young soccer players learned the evolution of soccer game systems from computer-based diagrams with three types of instructional arrows: simultaneous, sequential-without-tracing, and sequential-with-tracing. We randomly assigned participants to one of six experimental conditions (three arrow presentation methods by two levels of soccer scene complexity) and asked them to rate their invested mental efforts, complete a recall-reconstruction test, and indicate their attitudes, immediately after the learning phase. When diagram content complexity was low, the three types of arrow presentations had similar learning effects. However, when diagram content complexity was high, the two sequential means of presenting instructional arrows produced better learning outcomes (with a clear relative advantage for the sequential-with-tracing presentation). We also found that the sequential presentation of arrows elicited more positive player attitudes whatever the level of content complexity. Considering the better learning outcomes and improved player attitudes from sequential diagram presentations, soccer coaches should present computer-based instructional diagram arrows sequentially, rather than simultaneously. A sequential-with-tracing arrow presentation was particularly beneficial for learning complex team sport scenes. 



#8 The effect of a weekly flywheel resistance training session on elite U-16 soccer players' physical performance during the competitive season. A randomized controlled trial 

Reference: Res Sports Med. 2021 Jan 5;1-15. doi: 10.1080/15438627.2020.1870978. Online ahead of print. 

Authors: Javier Raya-González, Daniel Castillo, Kevin L de Keijzer, Marco Beato

Summary: This study investigated the effects of a weekly flywheel resistance training session over a 10-week period on U16 soccer players' physical performance with special attention to change of direction ability (e.g., deficit [CODdef]). Twenty elite young soccer players were assigned to an experimental (EG, n = 10) or control (CG, n = 10) group. Unilateral countermovement jumps with dominant (CMJd) and non-dominant (CMJnd) leg, 10, 20, and 30-m linear sprint test and change of direction sprint test in 5 + 5 (COD10) and 10 + 10 m (COD20) were performed before and after flywheel training period. Significant within-group differences were found in CG in COD10 (p = 0.01; effect size [ES] = large) and CODdef10 (p = 0.03; ES = small) with dominant leg, while differences in EG were observed in CMJ (p = 0.001-0.01; ES = moderate-large) and in all COD and CODdef variables (p = 0.001-0.04; ES = large). Between-groups analysis revealed differences in favour of the EG in CMJ (p = 0.03-0.05) and COD and CODdef variables (p = 0.001-0.05). These findings suggest a weekly flywheel training session is suitable for improving jumping and COD abilities in U16 elite soccer players in season. 



#9 Effectiveness of Plyometric and Eccentric Exercise for Jumping and Stability in Female Soccer Players-A Single-Blind, Randomized Controlled Pilot Study 

Reference: Int J Environ Res Public Health. 2021 Jan 3;18(1):294. doi: 10.3390/ijerph18010294. 

Authors: Guillermo Porrati-Paladino, Rubén Cuesta-Barriuso

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Summary: Hamstring muscle injury is common in female soccer players. Changes affecting eccentric strength, flexibility, and the quadriceps-hamstring contraction cycle are risk factors associated with this type of injury. Seventeen soccer players were randomized to two groups: experimental (plyometric and eccentric exercises without external loads) and control (eccentric exercises without external loads). Eighteen sessions were scheduled over 6 weeks. The exercise program included three plyometric exercises (single-leg squat and lunge, 180 jump, and broad jump stick landing) and three eccentric exercises (Nordic hamstring exercise, diver, and glider). Dependent variables were jumping height (My Jump 2.0 App) and anterior, posteromedial, and posterolateral lower limb stability (Y-Balance test). Following intervention, improvements were found in anterior and posteromedial stability (p = 0.04) in the experimental group. Posterolateral stability improved in athletes included in the control group (p = 0.02). There were differences in the repeated measures analysis for all variables, with no changes in group interaction (p > 0.05). Eccentric exercises, either combined with plyometric exercises or alone, can improve lower limb stability. No changes in jump height were noted in either group. There were no differences between the two groups in the variables studied. Future studies should analyze the effect of external loads on jumping stability and height in the performance of plyometric exercises. 



#10 Sustained Passing Performance of Elite and Subelite Female Soccer Players Following a Female Match-Specific Exercise Protocol

Reference: Int J Sports Physiol Perform. 2021 Jan 4;1-7. doi: 10.1123/ijspp.2020-0082. Online ahead of print. 

Authors: Mikayla J Lyons, Jennifer Conlon, Amy Perejmibida, Paola Chivers, Christopher Joyce 

Summary: This study examined the maintenance of passing performance following soccer-specific high-intensity intermittent exercise in elite (n = 9) and subelite (n = 11) Western Australian female soccer players (19.5 [2.5] y). A total of 20 participants completed the Loughborough Soccer Passing Test (LSPT) prior to, during, and following 90 minutes of a modified, female-specific, individualized exercise protocol (Loughborough Intermittent Shuttle Test [LIST]) to simulate 2 halves of a soccer match. Performance in the LSPT was calculated by adding "raw time" to the accumulated "penalty time" for each test. Elite players recorded greater distances (t58 = 4.671, P < .001, effect size [ES] = 1.21) and higher derived VO2max values (t58 = 4.715, P < .001, ES = 1.20) for the LIST exercise protocol over the subelite players. The total performance times for each LSPT were longer in the subelites in comparison with the elites, with a very large ES difference seen in post-LIST1 (t18 = -6.64, P < .001, ES = 2.99) and post-LIST2 (t18 = -9.143, P < .001, ES = 4.12). No between-groups differences were identified for "raw time" at any time point. Hence, all reported LSPT performance differences are attributed to "penalty time." These data suggest that elite players can sustain their passing performance more efficiently throughout match play that can subelite female soccer players. These findings may contribute to future talent-identification testing by helping to distinguish between elite- and subelite-level players through sustained passing performance. Coaches may also use this information to better inform best-practice training methods through modification of male soccer-specific high-intensity intermittent exercise to a female cohort. 



#11 Morning Priming Exercise Strategy to Enhance Afternoon Performance in Young Elite Soccer Players

Reference: Int J Sports Physiol Perform. 2021 Jan 5;1-8. doi: 10.1123/ijspp.2020-0094. Online ahead of print. 

Authors: Federico Donghi, Ermanno Rampinini, Andrea Bosio, Maurizio Fanchini, Domenico Carlomagno, Nicola A Maffiuletti 

Summary: The purpose was to compare the effects of different modalities of morning priming exercise on afternoon physical performance with the associated hormonal and psychophysiological responses in young soccer players. In a randomized counterbalanced crossover design, 12 young soccer players completed 3 different morning conditions on 3 different days: repeated-sprint running (6 × 40 m), easy exercise (4 × 12 fast half squats, 6 speed ladder drills, and 20-m sprints), and control (no exercise). Blood testosterone and cortisol concentrations were assessed upon arrival (approximately 8:30AM) and approximately 5 hours and 30 minutes later. Body temperature, self-reported mood, quadriceps neuromuscular function (maximal voluntary contraction, voluntary activation, rate of torque development, and twitch contractile properties), jump, and sprint performance were evaluated twice per day, while rating of perceived exertion, motivation, and the Yo-Yo Intermittent Recovery level 2 (IR2) tests were assessed once per day. Compared with the control, repeated-sprint running induced a possible positive effect on testosterone (+11.6%) but a possible to very likely negative effect on twitch contractile properties (-13.0%), jump height (-1.4%), and Yo-Yo IR2 (-7.1%). On the other hand, easy exercise had an unclear effect on testosterone (-3.3%), resulted in lower self-reported fatigue (-31.0%) and cortisol (-12.9%), and had a possible positive effect on the rate of torque development (+4.3%) and Yo-Yo IR2 (+6.5%) compared with the control. Players' testosterone levels were positively influenced by repeated-sprint running, but this did not translate into better physical function, as both muscular and endurance performance were reduced. Easy exercise seemed to be suitable to optimize the physical performance and psychophysiological state of young soccer players. 



#12 Monitoring Practices of Training Load and Biological Maturity in UK Soccer Academies 

Reference: Int J Sports Physiol Perform. 2021 Jan 5;1-12. doi: 10.1123/ijspp.2019-0624. Online ahead of print. 

Authors: Jamie Salter, Mark B A De Ste Croix, Jonathan D Hughes, Matthew Weston, Christopher Towlson 

Summary: Overuse injury risk increases during periods of accelerated growth, which can subsequently impact development in academy soccer, suggesting a need to quantify training exposure. Nonprescriptive development scheme legislation could lead to inconsistent approaches to monitoring maturity and training load. Therefore, this study aimed to communicate current practices of UK soccer academies toward biological maturity and training load. Forty-nine respondents completed an online survey representing support staff from male Premier League academies (n = 38) and female Regional Talent Clubs (n = 11). The survey included 16 questions covering maturity and training-load monitoring. Questions were multiple-choice or unipolar scaled (agreement 0-100) with a magnitude-based decision approach used for interpretation. Injury prevention was deemed highest importance for maturity (83.0 [5.3], mean [SD]) and training-load monitoring (80.0 [2.8]). There were large differences in methods adopted for maturity estimation and moderate differences for training-load monitoring between academies. Predictions of maturity were deemed comparatively low in importance for bio-banded (biological classification) training (61.0 [3.3]) and low for bio-banded competition (56.0 [1.8]) across academies. Few respondents reported maturity (42%) and training load (16%) to parent/guardians, and only 9% of medical staff were routinely provided this data. Although consistencies between academies exist, disparities in monitoring approaches are likely reflective of environment-specific resource and logistical constraints. Designating consistent and qualified responsibility to staff will help promote fidelity, feedback, and transparency to advise stakeholders of maturity-load relationships. Practitioners should consider biological categorization to manage load prescription to promote maturity-appropriate dose-responses and to help reduce the risk of noncontact injury. 



#13 Detrimental Effects of the Off-Season in Soccer Players: A Systematic Review and Meta-analysis 

Reference: Sports Med. 2021 Jan 5. doi: 10.1007/s40279-020-01407-4. Online ahead of print. 

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Hugo Sarmento

Summary: The off-season period in soccer leads necessarily to changes in fitness status. However, there is a lack of systematization that allows identifying the magnitude of these changes in groups participating in off-season training programs compared with those subjected to training cessation. This systematic review with meta-analysis was conducted to assess the effects of training cessation in off-season training programs on men soccer players' body fat, maximal oxygen uptake (VO2max), yo-yo intermittent recovery test (YYIRT), vertical jump, sprinting time, and repeated-sprint ability. To qualify for inclusion in the systematic review, studies must have included: (1) a detraining period of ≥ 2 weeks; (2) controlled trials or cohorts of healthy men soccer players with no restriction on age; and (3) a pre-post training cessation or off-season training programs measure of body fat (%), VO2max (mL kg-1 min-1), YYIRT performance (meters), vertical jump (height), sprinting (time), and repeated-sprint ability (total time). The electronic search yielded 563 articles, and 12 were subsequently included. Significant (all p < 0.05) detrimental training cessation effects were noted for body fat (ES = 0.26), VO2max (ES = - 1.48), YYIRT (ES = - 0.46), vertical jump (ES = - 0.81), and repeated-sprint ability (ES = 0.68). Similarly, significant (all p < 0.05) detrimental off-season training programs effects were noted for body fat (ES = 0.26), VO2max (ES = - 0.48), vertical jump (ES = - 0.51), and sprinting time (ES = 0.86). When training cessation and off-season training programs effects were compared, greater detrimental effects were noted after training cessation for VO2max (p = 0.002) and repeated-sprint ability (p < 0.001). Detrimental effects on body composition and physical fitness were observed after both training cessation and off-season training programs. However, off-season training programs seem to ameliorate such detrimental effects on VO2max and repeated-sprint ability to some extent. The results presented here call for the implementation of more effective off-season training programs among male soccer players. 



#14 COVID-19-Related Restrictions and Quarantine COVID-19: Effects on Cardiovascular and Yo-Yo Test Performance in Professional Soccer Players 

Reference: Front Psychol. 2020 Dec 18;11:589543. doi: 10.3389/fpsyg.2020.589543. eCollection 2020. 

Authors: Lucas de Albuquerque Freire, Márcio Tannure, Márcio Sampaio, Maamer Slimani, Hela Znazen, Nicola Luigi Bragazzi, Esteban Aedo-Muñoz, Dany Alexis Sobarzo Soto, Ciro José Brito, Bianca Miarka 

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Summary: The present study aimed to verify the quarantine's effects during a serious viral outbreak on the cardiovascular and performance associated with the Yo-Yo test in a sample of professional soccer players. 20 high-level soccer players (n = 20; age: 26 ± 4 years-old; weight: 76.85 ± 6.7 kg; height: 179 ± 6 cm) participated in this study. The intermittent Yo-Yo test was performed pre- and post- COVID-19 quarantine in a random order. During each test, the soccer players' running performance outcomes were monitored using a portable 5-Hz GPS with a 100 Hz accelerometer and a paired t-test was conducted at a p-value of ≤ 0.05. The main results demonstrated significant differences between pre- versus post-COVID-19 quarantine in the following variables: relative distance (161.7 ± 5.9 > 141.1 ± 33.8 m/min), maximal speed (18.7 ± 0.9 > 18.2 ± 0.6 km/h), acceleration (60 ± 20 frequency > 52 ± 16 frequency), deceleration (34 ± 13 frequency > 27 ± 6 frequency), sprints > 19 km/h [0.8 (0.2;3)% >0.5 (0;0.5)%], and in high intensity running distance [16.48 (2.68;41.64)m > 0.827 (0.164;3.0)m]. We concluded that COVID-19-related restrictions and quarantine COVID-19 demonstrated adverse effects on professional soccer players' Yo-Yo tests performance. 






Effects of Mental Fatigue in Total Running Distance and Tactical Behaviour During Small-Sided Games

Mental fatigue can impact physical demands and tactical behaviour in sport-related contexts. Small-sided games (SSGs) are often used to develop a specific sport-related context. This systematic review (with a meta-analysis) was conducted to compare the effects of mental fatigue vs. control conditions in terms of the total running distance and tactical behaviour of soccer players during SSGs.





Selected, Deselected and Reselected: A Case Study Analysis of Attributes Associated With Player Reselection Following Closure of a Youth Soccer Academy

Considering the perceived benefit of early recruitment and the time and resources spent developing youth players, individuals released from talent development programmes are often re-recruited by rival academies. Limited data exists on players deselected from (or reselected to) youth soccer academies.





Latest research in football - week 10 - 2021

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 Intra and inter-tester reliability of a novel device to assess gluteal muscle strength in professional football players

Reference: Res Sports Med. 2020 Dec 30;1-13. doi: 10.1080/15438627.2020.1868466. Online ahead of print. 

Authors: V Moreno-Pérez, M Beato, J Del Coso, J L Hernández-Davó, A Sole, M Peñaranda-Moraga, M Madruga-Parera, D Romero-Rodríguez

Summary: The aim of this study is to investigate inter-tester and intra-tester reliability of a novel clam test (CLAMT) for the measurement of gluteal muscle strength and to detect possible differences between CLAMT values in football players with and without a history of groin injuries. Twenty male football players participated in the test-retest and sixty-two male professional football players participated in the case-control study. Hip abductor maximal muscle strength was evaluated either using CLAMT or in a supine position with the hip in a neutral pose. For CLAMT, intraclass correlation coefficient (ICC) for inter-tester-intra-day reliability was 0.80 (95% CI: 0.60-0.90), with a standard error of measurement of 34.2 N. The intra-tester-intra-day ICC was 0.92 (95% CI: 0.87-0.95), with a standard error of measurement of 23.6 N. The inter-week ICC was 0.96 (95% CI: 0.92-0.98), with a standard error of measurement of 18.9 N. CLAMT showed lower (but not significant) strength values in football players with a history of groin injuries to non-injured players. CLAMT showed good to excellent levels of reliability, intraday and inter-week, with low standard errors of measurement while it was effective (possible) to identify residual weakness in players with previous groin injuries. 



#2 Assessment of Biomechanical Response to Fatigue through Wearable Sensors in Semi-Professional Football Referees 

Reference: Sensors (Basel). 2020 Dec 24;21(1):E66. doi: 10.3390/s21010066. 

Authors: Luigi Truppa, Michelangelo Guaitolini, Pietro Garofalo, Carlo Castagna, Andrea Mannini

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Summary: Quantifying muscle fatigue is a key aspect of everyday sport practice. A reliable and objective solution that can fulfil this task would be deeply important for two main reasons: (i) it would grant an objective indicator to adjust the daily training load for each player and (ii) it would provide an innovative tool to reduce the risk of fatigue-related injuries. Available solutions for objectively quantifying the fatigue level of fatigue can be invasive for the athlete; they could alter the performance or they are not compatible with daily practice on the playground. Building on previous findings that identified fatigue-related parameters in the kinematic of the counter-movement jump (CMJ), this study evaluates the physical response to a fatigue protocol (i.e., Yo-Yo Intermittent Recovery Test Level 1) in 16 football referees, by monitoring CMJ performance with wearable magneto-inertial measurement units (MIMU). Nineteen kinematic parameters were selected as suitable indicators for fatigue detection. The analysis of their variations allowed us to distinguish two opposites but coherent responses to the fatigue protocol. Indeed, eight out of sixteen athletes showed reduced performance (e.g., an effective fatigue condition), while the other eight athletes experienced an improvement of the execution likely due to the so-called Post-Activation Potentiation. In both cases, the above parameters were significantly influenced by the fatigue protocol (p < 0.05), confirming their validity for fatigue monitoring. Interesting correlations between several kinematic parameters and muscular mass were highlighted in the fatigued group. Finally, a "fatigue approximation index" was proposed and validated as fatigue quantifier. 



#3 Technical match actions and plasma stress markers in elite female football players during an official FIFA Tournament 

Reference: Scand J Med Sci Sports. 2020 Dec 29. doi: 10.1111/sms.13878. Online ahead of print. 

Authors: Susana Póvoas, António Ascensão, Josė Magalhães, Pedro Silva , Håvard Wiig, Truls Raastad, Carlo Castagna, Helena Andersson 

Summary: This study analyzed the impact of performing four consecutive football matches separated by 48-72 hours during a FIFA tournament on physical load, technical performance and plasma markers of redox state, muscle damage and inflammation in elite female players. Forty-eight players from three national teams were evaluated at seven time points: before (baseline) and throughout the tournament (after each match and before two training sessions). Only data from players who played all matches were included in the analyses (N = 13). The players were divided into high-rank (N = 6) and low-rank (N = 7) team players according to FIFA standards. Plasma creatine kinase (CK), C-reactive protein (CRP), total antioxidant status (TAS), and uric acid (UA) were analyzed at the selected time points. Technical performance and physical load were also quantified according to team rank. Players from low-rank teams played significantly more time than high-rank players (85 ± 10 vs 67 ± 15 minutes; P = .02; d = 1.51). Low-rank team players presented higher values in technical performance actions than the high-rank team players, but most of the differences were explained by the longer match time played. UA content differed across the matches, increasing from baseline (F(4,40) = 3.90; P = .01) and more in the high-rank team players (F(1,10) = 20.46; P = .001), while CRP only differed across the matches (F(4,36) = 2.66; P = .05), also increasing from baseline. A large time effect was shown for UA only in the high-rank players (η2 p = 0.50; P = .02). Four consecutive matches did not result in considerable alterations in plasma stress markers, physical load, and technical performance in elite female football players from distinct rank levels. 



#4 Delayed peroneal muscle reaction time in male amateur footballers during a simulated prolonged football protocol 

Reference: Res Sports Med. 2020 Dec 29;1-9. doi: 10.1080/15438627.2020.1868467. Online ahead of print. 

Authors: Wei Sun, Edwin C H Chan, Daniel T P Fong

Summary: Peroneal muscle fatigue could result in ankle inversion sprain injuries. This study investigated the peroneal muscle reaction time during a simulated prolonged football protocol. Nine male footballers completed a 105-minute simulated prolonged football protocol. The peroneal muscle reaction time to an ankle inversion perturbation was measured every 15 minutes by a surface electromyography system sampling at 1000 Hz. One-way repeated ANOVA with post-hoc paired t-test showed a steady upward trend starting from 48.9 ms at baseline to 57.1 ms at the end of the first half, followed by a recovery back to 50.9 ms at the start of the second half and a further delay in the last 30 minutes to 60.2 ms at the end of the protocol. Delayed peroneal muscle reaction was found after 30 minutes of the first half and 15 minutes of the second half of a football match. The risk of ankle sprain could increase in the latter minutes in each half protocol. Thus, prevention injury training strategies should focus on these specific durations in football matches. 



#5 The Football Association Injury and Illness Surveillance Study: The Incidence, Burden and Severity of Injuries and Illness in Men's and Women's International Football 

Reference: Sports Med. 2020 Dec 28;1-20. doi: 10.1007/s40279-020-01411-8. Online ahead of print. 

Authors: Bradley Sprouse, Jon Alty, Steve Kemp, Charlotte Cowie, Ritan Mehta, Alicia Tang, John Morris, Simon Cooper, Ian Varley  

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Summary: The aim was to determine the incidence and characteristics of injury and illness in English men's and women's senior and youth international football. Time-loss injuries and illnesses, alongside match and training exposure, were collected across 8 seasons (2012-2020) in youth (U15, U16, U17, U18, U19) and senior (U20, U21, U23, senior) English men's and women's international teams. Analysis of incidence, burden, and severity of injury and illness was completed. Sex-specific comparisons were made between the senior and youth groups, and across the 8 seasons of data collection. In men's international football, 535 injuries were recorded (216 senior; 319 youth) during 73,326 h of exposure. Overall, match injury incidence (31.1 ± 10.8 injuries/1000 h) and burden (454.0 ± 195.9 d absent/1000 h) were greater than training injury incidence (4.0 ± 1.0 injuries/1000 h) and burden (51.0 ± 21.8 d absent/1000 h) (both P < 0.001). In women's international football, 503 injuries were recorded (senior: 177; youth: 326) during 80,766 h of exposure and match injury incidence (27.6 ± 11.3 injuries/1000 h) and burden (506.7 ± 350.2 days absent/1000 h) were greater than training injury incidence (5.1 ± 1.8 injuries/1000 h) and burden (87.6 ± 32.8 days absent/1000 h) (both P < 0.001). In women's international football, a group × season interaction was observed for training injury incidence (P = 0.021), with the senior group recording a greater training injury incidence during the 2015-2016 season compared to the youth group (14.4 vs 5.7 injuries/1000 h; P = 0.022). There was no difference in injury severity between match and training for men's (P = 0.965) and women's (P = 0.064) international football. The findings provide a comprehensive examination of injury and illness in English men's and women's senior and youth international football. Practitioners will be able to benchmark their team's injury and illness incidence and characteristics to the match-play and training information provided in the present study. 



#6 Prospective Study of Muscle Injuries in Three Consecutive Seasons of the Brazilian Football Championship 

Reference: Rev Bras Ortop (Sao Paulo). 2020 Dec;55(6):687-694. doi: 10.1055/s-0040-1712988. Epub 2020 Sep 24. 

Authors: Gabriel Furlan Margato, Edilson Ferreira Andrade Júnior, Paulo Henrique Schmidt Lara, Jorge Roberto Pagura, Moisés Cohen, Gustavo Gonçalves Arliani

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Summary: The aim was to perform a prospective evaluation of muscle injuries that occurred during the matches of series A and B of the Brazilian Men's Football Championship from 2016 to 2018. A prospective-cohort study with data collection regarding muscle injuries that occurred during the official matches of the first and second divisions of the Brazilian Men's Soccer Championship in the 2016, 2017 and 2018 seasons. The total number of muscle injuries was of 577 throughout the 3 seasons, with a gradual and annual reduction in the incidence of injuries (219 injuries in 2016, 195 in 2017, and 163 in 2018), with a statistically significant difference between the 2016 and 2018 seasons. Muscle injuries represented approximately 35% of the total lesions. The incidence of muscle injuries was of 7.66 per 1,000 hours of play. During the 3 seasons (2016 to 2018), the most common injury was of the hamstring muscle (41.1%, 40.5%, and 33.7% respectively). Wingers were the most affected players, and the most common injury severity scale was moderate (8 to 28 days). The moment of the match with the highest incidence of injuries was in the period between 61 and 75 minutes, with an index of 19.9%, with no statistical difference in relation to the other periods of the match. There was an incidence of muscle injuries of 7.7 /1,000 h, and they occurred predominantly in home games, in defenders (wingers and centre-backs), with an average age of 28 years, mainly involving the hamstring muscles, with a moderate mean time of absence (8 to 28 days). 



#7 FIFA Sudden Death Registry (FIFA-SDR): a prospective, observational study of sudden death in worldwide football from 2014 to 2018

Reference: Br J Sports Med. 2020 Dec 23;bjsports-2020-102368. doi: 10.1136/bjsports-2020-102368.

Authors: Florian Egger, Jürgen Scharhag, Andreas Kästner, Jiří Dvořák, Philipp Bohm, Tim Meyer

Summary: The aim was to investigate the underlying causes and regional patterns of sudden death in football (soccer) players worldwide to inform and improve existing screening and prevention measures. From 2014 to 2018 cases of sudden cardiac death (SCD), survived sudden cardiac arrest (SCA) and traumatic sudden death were recorded by media monitoring (Meltwater), a confidential web-based data platform and data synchronisation with existing national Sudden Death Registries (n=16). Inclusion criteria were met when sudden death occurred during football-specific activity or up to 1 hour afterwards. Death during other activities was excluded. A total of 617 players (mean age 34±16 years, 96% men) with sudden death were reported from 67 countries; 142 players (23%) survived. A diagnosis by autopsy or definite medical reports was established in 211 cases (34%). The leading cause in players >35 years was coronary artery disease (76%) and in players ≤35 years was sudden unexplained death (SUD, 22%). In players ≤35 years the leading cause of SCD varied by region: cardiomyopathy in South America (42%), coronary artery anomaly in North America (33%) and SUD in Europe (26%). Traumatic sudden death including commotio cordis occurred infrequently (6%). Cardiopulmonary resuscitation (CPR) resulted in a survival rate of 85% with the use of an automated external defibrillator (AED) compared with 35% without. Regional variation in SCD aetiology should be verified by expansion of national registries and uniform autopsy protocols. Immediate access to an AED at training and competition sites, as well as CPR training for players, coaches and staff members, is needed to improve survival from SCA. 



#8 Injury patterns differ with age in male youth football: a four-season prospective study of 1111 time-loss injuries in an elite national academy 

Reference: Br J Sports Med. 2020 Dec 23;bjsports-2020-103430. doi: 10.1136/bjsports-2020-103430. 

Authors: Eirik Halvorsen Wik, Lorenzo Lolli, Karim Chamari, Olivier Materne, Valter Di Salvo, Warren Gregson, Roald Bahr

Summary: The purpose was to describe age group patterns for injury incidence, severity and burden in elite male youth football. Prospective cohort study capturing data on individual exposure and time-loss injuries from training and matches over four seasons (2016/2017 through 2019/2020) at a national football academy (U13-U18; age range: 11-18 years). Injury incidence was calculated as the number of injuries per 1000 hours, injury severity as the median number of days lost and injury burden as the number of days lost per 1000 hours. We included 301 players (591 player-seasons) and recorded 1111 time-loss injuries. Overall incidence was 12.0 per 1000 hours (95% CI 11.3 to 12.7) and burden was 255 days lost per 1000 hours (252 to 259). The mean incidence for overall injuries was higher in the older age groups (7.8 to 18.6 injuries per 1000 hours), while the greatest burden was observed in the U16 age group (425 days; 415 to 435). In older age groups, incidence and burden were higher for muscle injuries and lower for physis injuries. Incidence of joint sprains and bone stress injuries was greatest for players in the U16, U17 and U18 age groups, with the largest burden observed for U16 players. No clear age group trend was observed for fractures. Injury patterns differed with age; tailoring prevention programmes may be possible. 



#9 The Size and Prevalence of Bony Hip Morphology Does Not Differ Between Football Players With and Without Hip and/or Groin Pain: Findings From the FORCe Cohort 

Reference: J Orthop Sports Phys Ther. 2020 Dec 25;1-43. doi: 10.2519/jospt.2021.9622. Online ahead of print. 

Authors: Joshua Heerey, Rintje Agricola, Anne Smith, Joanne Kemp, Tania Pizzari, Matthew King, Peter Lawrenson, Mark Scholes, Kay Crossley

Summary: The aim was to compare the size and prevalence of bony hip morphology in football players' hips with and without hip and/or groin pain. 184 (290 hips; 20% women) football players (soccer and Australian football) with self-reported hip and/or groin pain (>6 months duration) and a positive FADIR test and 55 (110 hips; 25% women) control football players (no pain, negative FADIR) were recruited. For bony hip morphology, alpha angle and lateral-center-edge-angle (LCEA) were determined from anteroposterior pelvis and Dunn 45° radiographs. The alpha angle and LCEA were analyzed as continuous measures (size) and dichotomised using threshold values to determine the prevalence of bony hip morphology (cam, large cam, pincer and acetabular dysplasia). Regression analyses estimated differences in the size and prevalence of bony hip morphology between football players with and without pain. In all football players and in men, the size and prevalence of bony hip morphology did not differ between hips with and without hip and/or groin pain. In football players, cam morphology was evident in 63% hips without pain and 71% of hips with hip and/or groin pain. Women with hip and/or groin pain had larger alpha angle values than women without on the Dunn 45° view (5.9°; 95% CI: 1.2°, 10.6°, P = .014). The size and prevalence bony hip morphology appears similar in football players with and without hip and/or groin pain.



#10 Applying a holistic hamstring injury prevention approach in elite football: 12 seasons, single club study

Reference: Scand J Med Sci Sports. 2020 Dec 31. doi: 10.1111/sms.13913. Online ahead of print. 

Authors: Luis Suarez-Arrones, Fábio Yuzo Nakamura, Rafael A Maldonado, Nacho Torreno, Valter Di Salvo, Alberto Mendez-Villanueva

Summary: The aim was to investigate the preventive effect of a complex training program based on holistic hamstring health understanding in elite professional soccer players. This study involved an elite club in Europe and was conducted over 12 seasons. The last 2 seasons were the intervention period and the others were the control seasons. During the intervention period, players performed a complex program organized into different interventions throughout the week having as a priority the player health. Hamstring injuries, absenteeism, injury rates, and injury burden between the control and intervention seasons were compared using a rate ratio (RR) with 95% CI. Players had a mean exposure of 333.5±18.6 hours per season with no significant differences between the intervention and control seasons. The overall injury rate was 3 times lower during the two intervention seasons than during the previous seasons (p<0.01); the match injury rate was 2.7 times lower (p<0.01) and the training rate 4.3 times (p<0.01). Injury burden was almost 4 times lower during the two intervention seasons than during the previous seasons (p<0.01) and recurrences in the control group were 10% vs. 0% in the intervention group. Hamstring injuries were reduced ~3 times during the seasons in which elite football players were exposed to multicomponent, complex prevention training with individual approaches based on player needs, management of training load, individualized physiotherapy treatment, and planned staff communication, in comparison to the control seasons without a clearly defined and structured injury prevention intervention. 



#11 A four-week training program with the Nordic hamstring exercise during preseason increases eccentric strength of male soccer player

Reference: Int J Sports Phys Ther. 2020 Aug;15(4):571-578. 

Authors: Nathalia Trevisol de Oliveira, Thales Menezes Medeiros, Karoline Baptista Vianna, Gabriel Dos Santos Oliveira, João Breno de Araujo Ribeiro-Alvares, Bruno Manfredini Baroni

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Summary: The Nordic hamstring exercise (NHE) is an effective strategy to prevent hamstring strain injuries in soccer players. The current literature recommends a 10-week training program with three sessions per week, but the short preseason period and the congested schedule make difficult for high-performance soccer teams to apply the NHE as recommended. The purpose of this study was to examine the effect of a pragmatic NHE training program during a four-week preseason period on eccentric knee flexor strength of high-performance soccer players. This study included 25 under-20 male soccer players from a premier league club. They performed eight sessions of NHE (3 sets of 6-10 repetitions, twice a week) during the four-week preseason period. The eccentric knee flexor strength was evaluated during the NHE execution on a custom-made device, before and after the training program. The NHE training program significantly increased the players' eccentric knee flexor strength in both right (Δ = 13%; p<0.001; effect size = 0.97) and left limbs (Δ = 13%; p<0.001; effect size = 0.92). Individual analysis identified 76% of the players as responders to the NHE training program (Δ = 16%; effect size = 1.60), and 24% as non-responders (Δ = 3%; effect size = 0.24). A four-week training program with NHE performed twice a week is feasible in the real-world of high-performance soccer clubs and increases the eccentric knee flexor strength of male soccer players. 



#12 Association of Low Energy Availability and Suppressed Metabolic Status in Korean Male Collegiate Soccer Players: A Pilot Study

Reference: Am J Mens Health. Nov-Dec 2020;14(6):1557988320982186. doi: 10.1177/1557988320982186. 

Authors: Sihyung Lee, Moto Kuniko, Seungah Han, Taewoong Oh, Motoko Taguchi

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Summary: Low energy availability (EA) can impair physiological function in athletes. The purpose of this study was to investigate EA status, metabolic status, and bone metabolism with biochemical analysis in Korean male soccer players. Twelve male athletes (18-20 years) completed the study. Body composition and bone mineral density were measured using dual energy X-ray absorptiometry (DXA), while VO2 max was determined by an incremental exercise test. Blood samples were taken for bone marker and hormone analyses. Resting energy expenditure (REE) was measured using the Douglas bag method and predicted using the DXA method. Food diaries and heart rates (HR) during training were recorded, and the Profile of Mood States 2 and Eating Attitude Test 26 were completed. Group differences between low EA (LEA <30 kcal/kg FFM/d, n = 5) and high EA (HEA ≥30 kcal/kg FFM/d, n = 7) were evaluated. The mean EA of the all participants was 31.9 ± 9.8 kcal/kg FFM/d with only two participants having an EA above 45 kcal/kg FFM/d. LEA showed suppressed REE (LEA: 26.0 ± 1.7 kcal/kg/d, HEA: 28.8 ± 1.4 kcal/kg/d, p = .011) with a lower REEratio (LEA: 0.91 ± 0.06, HEA: 1.01 ± 0.05, p = .008) as well as a lower insulin-like growth factor 1 (IGF-1) level (LEA: 248.6 ± 51.2 ng/mL, HEA: 318.9 ± 43.4 ng/mL, p = .028) compared to HEA. There were no group differences in bone markers or other hormone levels. Korean male athletes exhibited low EA status with suppressed metabolism, but there was limited evidence on the effect of EA on bone metabolism, endocrine system, and psychological parameters. 



#13 Systematic review and meta-analysis of sex-based differences for concussion incidence in soccer 

Reference: Phys Sportsmed. 2021 Jan 7;1-9. doi: 10.1080/00913847.2020.1868955. Online ahead of print. 

Authors: Udit Dave, James Kinderknecht, Jennifer Cheng, Kristen Santiago, Bridget Jivanelli, Daphne I Ling

Summary: The purpose was to compare concussion incidence in male and female soccer players due to the specific concussion-causing activity. PubMed, EMBASE, and Cochrane Library were searched for studies published between January 2000 and February 2020. Search terms included 'sex,' 'gender,' 'sex differences,' 'brain injury,' 'sports,' 'athletes,' 'incidence,' 'epidemiology,' 'symptoms,' and 'injury rate.' Studies that contained data on concussion incidence in soccer and featured comparisons by sex and soccer activity were included. Studies that were not written in English, contained data on non-sports-related concussions, or were conference abstracts were excluded. Six studies were included in this meta-analysis, each of which contributed the number of concussions in males and females for a specific soccer activity. Concussion incidence rates were calculated using athlete-exposures as the denominator and a rate ratio was measured by dividing the concussion rate among female soccer players by the rate among male soccer players. Female soccer players were shown to have a greater rate of concussions from heading [1.65 (95% CI: 1.35, 2.03, p < 0.001)] and goalkeeping [1.63 (95% CI: 1.22, 2.17, p = 0.001)]. There were 3 studies comparing sex differences for general play. While the pooled rate ratio was statistically significant [1.51 (95% CI: 1.12, 2.04), p = 0.007], this result was largely driven by 1 study. Concussion incidence rates were significantly higher in female soccer players compared to male players while heading. There is also some evidence to suggest that the incidence is higher for female goalkeepers. Soccer coaches and health care providers need to recognize this sex difference when coaching or treating players. 



#14 Magnetic resonance imaging of midtarsal sprain: Prevalence and impact on the time of return to play in professional soccer players 

Reference: Eur J Radiol. 2020 Dec 24;135:109491. doi: 10.1016/j.ejrad.2020.109491. Online ahead of print. 

Authors: Miriam T Leiderer, Goetz H Welsch, Isabel Molwitz, Kai-Jonathan Maas, Gerhard Adam, Peter Bannas, Frank Oliver Henes 

Summary: Ankle sprain is a common injury in professional soccer, but to date midtarsal sprain has not been investigated in this context. The purpose of this study was to determine the prevalence of midtarsal sprain by MRI and to assess its impact on the time of return to play in professional soccer players. We included 52 professional soccer players who underwent 59 MRI examinations after acute ankle trauma between January 2012 and September 2019. Images were retrospectively reviewed in consensus by two radiologists for assessment of midtarsal sprain and ankle sprain. Ligaments were graded as i) normal, ii) partial tear, or iii) complete tear. Time to return to play (RTP) for each athlete was retrieved from team medical records. A Kruskal-Wallis test and Dunn's pairwise tests were used to calculate differences in RTP time between groups with i) isolated midtarsal sprain, ii) isolated lateral ankle sprain, and iii) combined midtarsal and lateral ankle sprain. MRI revealed isolated ankle sprain in 24 of 59 MRI examinations (40.6 %). Acute midtarsal ligament injury was present in 15 examinations (25.4 %). Four of the 15 examinations (26.7 %) had isolated midtarsal injuries and eleven of the 15 examinations (73.3 %) had concomitant ankle sprain. RTP time was 39 days (range 9-70 days) for isolated midtarsal sprain. RTP time was significantly higher for athletes with combined ankle and midtarsal sprain (47 days, range 15-74 days) when compared to athletes with isolated ankle sprain (24 days, range 2-59 days) (p = .019). Our MRI study reveals that midtarsal sprain is a frequent injury in professional soccer players with ankle sprain. Midtarsal ligament findings on MRI combined with evidence of lateral ankle sprain is associated with a longer time of return to play compared to isolated lateral ligament injuries. 



#15 Whole and peak physical characteristics of elite youth female soccer match-play 

Reference: J Sports Sci. 2020 Dec 30;1-10. doi: 10.1080/02640414.2020.1868669. Online ahead of print. 

Authors: Alice Harkness-Armstrong, Kevin Till, Naomi Datson, Stacey Emmonds

Summary: This study quantified whole and peak physical characteristics of Under (U)14 and U16 elite youth female soccer, and compared by position and age-group. Data was collected using 10 Hz GPS units from 431 match observations, during 50 matches involving 201 players (U14 n = 93; U16 n = 108) representing Regional Talent Centres in The Football Association's Girl's England Talent Pathway League. Whole match data were reported as absolute and relative; total (TD), high-speed running (HSR; ≥3.46 m·s-1), very high-speed running (VHSR; ≥5.29 m·s-1), and sprinting (SPR; ≥6.26 m·s-1) distance, and maximum velocity. Moving average analysis determined peak data (1-10 minute durations). Linear mixed models established position-specific differences. U16s covered greater; absolute distance at all speeds (small-moderate ESs; p < 0.001); relative VHSR and SPR m·min-1 (small-moderate ESs; p < 0.001); peak TD and HSR m·min-1 (small ESs) across several peak-durations, and VHSR m·min-1 (small ESs; p < 0.001) across all peak-durations compared to U14s. Position-specific differences were observed across all positions between and within both age-groups, identifying whole and peak physical characteristics are age- and position-dependent within elite youth female soccer match-play. Findings may facilitate informed coaching practices and training programme design, talent identification and development processes. 



#16 Concurrent validity, inter-unit reliability and biological variability of a low-cost pocket radar for ball velocity measurement in soccer and tennis 

Reference: J Sports Sci. 2020 Dec 30;1-8. doi: 10.1080/02640414.2020.1868090. Online ahead of print. 

Authors: Alejandro Hernández-Belmonte, Alejandro Sánchez-Pay

Summary: This study aimed to analyse the (i) concurrent validity, (ii) inter-unit reliability, and (iii) biological variability of a low-cost device called Pocket radar. Eleven men recreational soccer players performed 6 kicks to a soccer ball, whereas 13 men recreational tennis players conducted 10 shots to a tennis ball. All executions were simultaneously measured by two Pocket units and the Stalker radar (reference criterion). The within-subject variation among the executions was used for the biological variability analysis. The level of agreement and magnitude of errors included the intraclass correlation coefficient (ICC), Pearson's correlation coefficient (r), bias, and the smallest detectable change (SDC). A good agreement (ICC ≥ 0.98, r ≥ 0.98) and very low magnitude of error (SDC ≤ 7.70 km·h-1, bias ≤ 3.19 km·h-1) were found between both Pocket units and the Stalker, in soccer and tennis. Inter-unit analysis found limited technical errors (SDC ≤ 5.49 km·h-1, bias ≤ -0.93 km·h-1) and nearly perfect agreement (ICC = 0.99, r ≥ 0.98) in both sessions. These technical errors were lower than the variations due to the biological variability, in soccer (SDC = 2.47 km·h-1 vs. SDC ≥ 8.6 km·h-1) and tennis (SDC = 5.49 km·h-1 vs. SDC ≥ 21.95 km·h-1). These findings suggest the Pocket radar as a valid and highly sensitive tool for BV measurement. 






Associations Between Variations in Accumulated Workload and Physiological Variables in Young Footballers Over the Season

This study sought to analyse the relationship between in-season training workload with changes in aerobic power (VO2max), maximum and resting heart rate (HRmax and HRrest), linear sprint medium (LSM) and short test (LSS) in U16 soccer players. An additional aim was to explain changes in fitness levels during the in-season through regression models, considering accumulated load, baseline levels, and peak height velocity (PHV) as predictors.





How did three consecutive matches with extra time affect physical performance? A case study of the 2018 football Men’s World Cup

How did three consecutive matches with extra time affect physical performance? A case study of the 2018 football Men’s World Cup





Latest research in football - week 9 - 2021

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 Effect of Preparatory Posture on Goalkeeper's Diving Save Performance in Football 

Reference: Front Sports Act Living. 2019 Aug 21;1:15. doi: 10.3389/fspor.2019.00015. eCollection 2019. 

Authors: Rony Ibrahim, Idsart Kingma, Vosse de Boode, Gert S Faber, Jaap H van Dieën

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Summary: Identifying the optimal preparatory posture of football goalkeepers can be very relevant for improving goalkeepers' diving save performance, and coaching practices of technical and strength and conditioning coaches. This study aimed to analyse the effect of different starting stance widths and knee flexion angles on movement time, center of mass (CoM) trajectory and velocity in goalkeepers' diving saves. Ten elite goalkeepers performed dives from preferred (PT) and imposed postures, by altering knee angle (45, 75, and 90°) and stance width (50, 75, and 100% of leg length) independently, at the starting position. Repeated measures ANOVA showed a main effect of preparatory posture on dive time (p < 0.01). Pairwise comparisons showed that the fastest dive movement time was observed when goalkeepers started from a stance width of 75% (SW75). CoM traveled a larger distance between contralateral and ipsilateral peak ground reaction forces in SW75 than PT (p < 0.05). The goalkeepers were also more efficient in SW75, as a smaller countermovement and vertical velocity range were observed during high and low dives, respectively, from SW75 than PT (p < 0.05). Thus, diving from a position with wider stance width than the preferred one leads to shorter movement time, and a faster and more direct CoM trajectory toward the ball. 



#2 Role of tattoos in football: Behavioral patterns and success-analysis of the FIFA World Cup 2018

Reference: Clin Dermatol. Nov-Dec 2020;38(6):788-792. doi: 10.1016/j.clindermatol.2020.04.006.

Authors: Simon M Mueller, Michael Bayer, Mattia Antenna, Stefan Gysin

Summary: Epidemiologic studies suggest that individuals with tattoos are more extroverted, aggressive, and more likely to take risks than individuals with no tattoos. Whether these personality traits affect athletic performance is uncertain. We compared behavioral patterns and rates of success of football players at the International Federation of Association Football (FIFA) World Cup 2018 by tattoo status. In this cross-sectional study, 32.7% of football players had visible tattoos (241 of 736), mostly on their arms (97.1%). Footballers with tattoos played longer on average (208 versus 160 minutes; P < .001), received more cards (.38 versus .27; P < .001), and committed more fouls per player (2.64 versus 2.2; P < .001). Players with tattoos attempted more shots at goal (P = .016), but without higher goal success (P = .204). The higher number of disciplinary events (being whistled for fouls and given yellow or red cards) and longer playing time of football players with tattoos may reflect personality traits reported in nonathletic individuals with tattoos, such as dominance, extroversion, aggressiveness, and willingness to take risks. 



#3 Angular Velocity, Moment, and Power Analysis of the Ankle, Knee, and Hip Joints in the Goalkeeper's Diving Save in Football

Reference: Front Sports Act Living. 2020 Feb 28;2:13. doi: 10.3389/fspor.2020.00013. eCollection 2020. 

Authors: Rony Ibrahim, Idsart Kingma, Vosse de Boode, Gert S Faber, Jaap H van Dieën 

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Summary: The aim of this study was to identify biomechanical characteristics of goalkeeper's diving performance in football. Lower extremity joints powers, moments, and angular velocities, were investigated in seven elite goalkeepers diving to save balls, shot from a ball canon to unanticipated heights (high and low) and sides (right and left). Our result showed that there was a proximal-to-distal sequence for each leg in timing of peak joints powers (p < 0.05). Hip extensors produced the largest (p < 0.05) peak moment, the contralateral (relative to dive side) peak was significantly larger than the ipsilateral one for high (4.56 ± 1.02 N·m·kg-1, and 3.52 ± 0.79 N·m·kg-1) and low dives (3.52 ± 0.79 N·m·kg-1, and 2.52 ± 0.56 N·m·kg-1). The ankle plantar flexors produced the second largest peak moment (p < 0.05), and the peak ipsilateral ankle power and angular velocity were the largest (p < 0.05) of all joints, during high (1,502 ± 338 W, and 14.73 ± 1.36 rad·s-1) and low dives (868 ± 263 W, and 14.14 ± 3.09 rad·s-1). Strength and conditioning coaches need to focus on hip extensors and ankle plantar flexors, and for specificity in power training that should elicit triple extension of the lower limbs' joints in a proximal-to-distal sequence. 



#4 Referee Bias in Professional Football: Favoritism Toward Successful Teams in Potential Penalty Situations 

Reference: Front Sports Act Living. 2020 Feb 27;2:19. doi: 10.3389/fspor.2020.00019. eCollection 2020. 

Authors: Martin Kjeøen Erikstad, Bjørn Tore Johansen

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Summary: Past studies have indicated that multiple factors may influence sport referees' decisions, such as pressure from spectators and athletes' reputation. Grounded in the social impact theory framework, this study examined whether Norwegian Premier League (NPL) referees are biased by a team's success when awarding penalties. Using video footage (similar to video assistant referees), an expert panel (EP) of four NPL referees evaluated all potential penalty situations (N = 43) involving either of two successful teams during an entire NPL season. Fifty-five potential penalty situations from matches without successful teams were also rated. Overall, the match referees identified 73.3% (22 of 30) of the EP-identified penalties during matches without successful teams. Successful teams were awarded 110% (11 of 10) of the EP-identified penalties, while their opponents were awarded 12.5% (1 of 8). Chi square statistic revealed that successful teams were more likely to receive an incorrect penalty compared with their opponents, and less likely to be denied a penalty they should have been awarded. These findings indicate that referees' decisions may be unintentionally biased by a team's success, extending our knowledge about how football referees may be influenced by social forces. 



#5 Large Reductions in Match Play Physical Performance Variables Across a Professional Football Season With Control for Situational and Contextual Variables

Reference: Front Sports Act Living. 2020 Oct 15;2:570937. doi: 10.3389/fspor.2020.570937. eCollection 2020. 

Authors: Matthew Springham, Sean Williams, Mark Waldron, Darren Burgess, Robert Usher Newton

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Summary: This investigation examined match play physical performance across a professional football season using a multicamera computerized tracking system. A linear mixed-effects model, controlling for situational and contextual variables, identified decreases in team average total distance (TD): season quarter 1 (Q1) (11,047 m) > season quarter 2 (Q2) (10,473 m) (P = 0.002; ES = Small), season quarter 3 (Q3) (10,449 m) (P < 0.001; ES = Moderate), and season quarter 4 (Q4) (10,385 m) (P < 0.001; ES = Moderate); work rate (WR): Q1 (115 m/min) > Q3 (108 m/min) (P < 0.001; ES = Moderate), Q4 (107 m/min) (P < 0.001; ES = Moderate); Q2 (109 m/min) > Q4 (107 m/min) (P = 0.003; ES = Small); high-speed running distance (HSR): Q1 (1,051 m) > Q2 (813 m) (P = 0.006; ES = Small); number of high-speed runs (NHSR): Q1 (87) > Q2 (65) (P < 0.001; ES = Small), Q3 (64) (P = 0.002; ES = Small); sprint distance (SD): Q1 (202 m) > Q4 (130 m) (P < 0.001; ES = Moderate), Q2 (179 m) > Q3 (165 m) (P = 0.035; ES = Small), Q4 (130 m) (P < 0.001; ES = Moderate) and number of sprints (NS): Q1 (20.4) > Q3 (10.2) (P < 0.001; ES = Moderate), Q4 (8.3) (P < 0.001; ES = Large); Q2 (14.9) > Q3 (10.2) (P < 0.001; ES = Moderate), Q4 (8.3) (P < 0.001; ES = Large). Within-position changes were observed for WR: Q1 (122 m/min) > Q4 (113 m/min) (P = 0.002; ES = Large) in central midfielders and for NS: Q1 > Q3 in wide defenders (21.7 vs. 10.8) (P = 0.044; ES = Large) and central midfielders (18.1 vs. 8.3) (P = 0.002; ES = Large); Q1 > Q4 in central defenders (13.1 vs. 5.3) (P = 0.014; ES = Large), wide defenders (21.6 vs. 7.1) (P < 0.001; ES = Very Large), central midfielders (18.1 vs. 8.5) (P = 0.005; ES = Large), and wide midfielders (20.8 vs. 12.2) (P = 0.012; ES = Large); Q2 > Q3 in central midfielders (16.9 vs. 8.3) (P = 0.002; ES = Large) and Q2 > Q4 in wide defenders (16.3 vs. 7.1) (P = 0.005; ES = Very Large), central midfielders (16.9 vs. 8.5) (P = 0.004; ES = Large), and wide midfielders (20.8 vs. 12.2) (P = 0.007; ES = Large). The match-play physical performance was reduced across the competitive season. The most notable reductions were observed in wide defenders, central midfielders, and wide midfielders in sprint performance indices. 



#6 Origins of Relative Age Effects in Youth Football-A Nationwide Analysis 

Reference: Front Sports Act Living. 2020 Dec 3;2:591072. doi: 10.3389/fspor.2020.591072. eCollection 2020. 

Authors: Michael Romann, Eva Rüeger, Mirjam Hintermann, Raphael Kern, Oliver Faude 

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Summary: Relative age effects (RAEs) refer to the overrepresentation of players born earlier in the selection year compared to late-born players within the same age category. To date, the origins and mechanisms of RAEs are still unclear. To evaluate the development of RAEs in terms of age group and selection level, we analyzed data of all registered child and adolescent football players in Switzerland. Age category, selection level, and birthdate from all licensed 101,991 Swiss child and youth football players assigned to a specific team [9,149 girls (9.0%) and 92,842 boys (91.0%); age range: 4.6-19.6 years] were analyzed. Additionally, out of 1,128 clubs, 54 clubs provided their documented waiting lists (1,224 players). Birthdate distributions were split by age category, sex, and birth quarter (Q1 = January to March, Q4 = October to December). RAEs were calculated using odds ratios (Q1 vs. Q4) with 95% confidence intervals (95% CI). We found small RAEs among U8 players (OR 1.44 [95% CI 1.31, 1.59]) and U10 (OR 1.24 [95% CI 1.16, 1.32]). The RAE was negligible in all other age categories, independent of gender. In children's football, 5,584 (71.3%) teams performed selections. In teams without selection, there were no obvious RAEs. However, teams with selections for the same age category showed small RAEs with an overrepresentation of Q1 athletes in the first team (OR = 1.29 [95% CI 1.24, 1.35]) and inverse RAEs with an underrepresentation of Q1 athletes in the last team (OR = 0.85 [95% CI 0.82, 0.89]). Only small RAEs were observed on the waiting lists for the U8 (OR = 1.48 [1.13, 1.95]). RAEs have a small, but consistent effect on participation in Swiss children's football at the grassroots level. Contrary to expectations, no inverse RAEs were found on the waiting lists. Nonetheless, first time coach selections seem to be the origin of RAEs. To protect young athletes from discrimination, RAE biases should be analyzed and eliminated at all stages of sport participation, selection, and dropout situations. Modifications to the organizational structure of sport and athlete development systems are recommended to prevent RAE-related discrimination in youth sports. 



#7 Asymptomatic Degenerative Changes in the Lumbar Spine Among Professional Soccer Players 

Reference: Spine (Phila Pa 1976). 2021 Jan 15;46(2):122-128. doi: 10.1097/BRS.0000000000003726. 

Authors: Eduard Bezuglov, Artemii Lazarev, Arseniy Petrov, Alesia Brodskaia, Anastasiya Lyubushkina, Kamila Kubacheva, Evgeny Achkasov, Vladimir Nikolenko

Summary: The aim of this study was to evaluate the actual prevalence of degenerative spinal changes and their association with age in a cohort of professional soccer players. Presently, there are data that athletes have more degenerative changes than nonathletes; however, the research examining the prevalence of degenerative spinal conditions among professional elite soccer players is scarce. Professional male soccer players were included in the study (n = 40, average age 26,6 ± 4,5 years, average height 18 ± 0.07 m, weight 76.7 ± 7.1 kg). Lumbosacral spine MRI scanning at the L1-S1 level has been performed. Two radiologists with at least 7 years of experience of working with athletes evaluated all images independently of each other. 92.5% (n = 37) of soccer players had ≥1 spinal degenerative condition. Thirty-five percent (n = 14) of players had three to five, and 50% (n = 20) had six or more conditions. The average age of players who had six or more conditions was significantly higher than those who had zero to five or three to five conditions-28.1 ± 4.8 years versus 25.1 ± 3.6 years (P = 0.029), and 24.8 ± 3.6 years, respectively.Kruskal-Wallis test has shown no association between the number of degenerative conditions and weight (P = 0.98) as well as body mass index (P = 0.99). The age was associated with degenerative changes (P = 0.008).Disc desiccation was the most common pathologic condition, which was found in 82.5% of athletes. Facet joint arthropathy and spondylosis were present in 70, and 50% of the studied lumbar spine MRI scans, respectively. The spondylolysis prevalence of 20% was noted. Elite professional soccer players demonstrate a high prevalence of asymptomatic degenerative lumbar spinal degenerative changes, which are significantly associated with age. These conditions might lead to the development of symptomatic lower back pain, given the high-intensity exercise required in professional soccer. It is presently unclear what measures might be applied for the primary prevention of these degenerative spinal conditions.Level of Evidence: 4. 



#8 Covid-19 Has Turned Home Advantage Into Home Disadvantage in the German Soccer Bundesliga 

Reference: Front Sports Act Living. 2020 Nov 5;2:593499. doi: 10.3389/fspor.2020.593499. eCollection 2020. 

Authors: Markus Tilp, Sigrid Thaller

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Summary: The main factors for home advantage (HA), quantified by the number of points won at home expressed as a percentage of all points, are believed to be crowd support, territoriality, familiarity, and travel fatigue. In 2020, the German Soccer Bundesliga interrupted its championship due to the Covid-19 pandemic after 25 rounds and the last nine rounds were played without audience. This unique situation allowed studying the effect of spectators on the team's performance and the referee's decisions. We hypothesized a decrease in HA and a more balanced distribution of fouls and disciplinary cards in the games without audience (GWOA) compared to the games with audience (GWA). We evaluated n = 223 GWA and n = 83 GWOA of the season 2019/20 and all games of the preceding season 2018/19 to analyze the distribution of game outcomes (wins, losses, and draws) and HA. We analyzed the number of fouls, disciplinary cards, and penalty kicks. We found significant differences in HA between GWA (HA = 54.35%) and GWOA (HA = 44.1%) as well as GWOA and games of 2018/19 (HA = 57.63%). The distribution of game outcomes in GWOA did not differ from GWA but differed significantly from 2018/19 (p = 0.031). The distribution of fouls showed a significant difference to equal distribution in GWA [home: 2,595 (48.56%); away: 2,749 (51.44%)] but not in GWOA [home: 1,067 (50.54%); away: 1,044 (49.46%)]. In the GWOA, we counted 178 (51.1%, home) and 170 (48.9%, away) cards, representing a significant difference in the distribution to GWA [home: 405 (44.85%); away: 498 (55.15%)]. The number of red cards differed significantly from an equal distribution for GWA (14 home and 28 away) but not for GWOA (eight home and seven away). In the last nine rounds without audience, we observed more home losses (36) than home wins (27). Hence, the Covid-19 lock-down led to a home disadvantage. One reason for this surprising result could be that the home team is missing an important familiar aspect when playing in their empty stadium without social support from their home audience. Furthermore, both teams know about the HA thus the away team could be more motivated in this unusual situation. 



#9 Effect of Practicing Soccer Juggling With Different Sized Balls Upon Performance, Retention, and Transfer to Ball Reception 

Reference: Motor Control. 2016 Oct;20(4):337-49. doi: 10.1123/mc.2015-0026. Epub 2016 Aug 19. 

Authors: Olav Raastad, Tore Kristian Aune, Roland van den Tillaar

Summary: The aim of this study was to investigate if making the skill acquisition phase more difficult or easier would enhance performance in soccer juggling, and if this practice has a positive intertask transfer effect to ball reception performance. Twenty-two adolescent soccer players were tested in juggling a soccer ball and in the control of an approaching ball at a pre, post and retention test. The participants were randomly divided in a small ball size and bigger ball size training group that both trained four times per week for 6 weeks. At the post and retention test both groups enhanced performance in soccer juggling test with no difference between groups and no increase in ball reception performance at these tests. It was concluded that about intra task transfer and retention of soccer juggling skills, it does not matter if you increase (small balls) or decrease the difficulty (larger balls) when using the same amount of practice time within the skill acquisition phase in soccer juggling. In addition that for ball juggling and ball reception (inter task) these two tasks differ too much in afferent information and movement characteristics that no positive transfer between these two skills no positive intertask transfer can be expected. 



#10 Acute effects of small-sided games combined with running drills on internal and external loads in young soccer players 

Reference: Biol Sport. 2020 Dec;37(4):375-381. doi: 10.5114/biolsport.2020.96943. Epub 2020 Jul 5. 

Authors: Yusuf Köklü, Hamit Cihan, Utku Alemdaroğlu, Alexandre Dellal, Del P Wong

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Summary: The purpose of this study was to compare the effects of regular small-sided games (SSGreg) and SSGs combined with running drills (SSGcom) on players' internal and external loads. Eighteen young male soccer players (average age: 18.2 ± 0.5 years) participated in 3 vs. 3 and 4 vs. 4 games, under both SSGreg and SSGcom conditions. SSGreg bouts were played for 4 minutes without additional running drills, while SSGcom bouts consisted of 3 min 30 s SSG and 15 s running before and after the bout, making the duration of each bout 4 minutes. During all SSGs, measurements of heart rate (HR) responses as well as distances covered in four different speed zones - walking (WLK), low-intensity (LIR), moderate-intensity (MIR) and high-intensity running (HIR) - were recorded. Technical characteristics were monitored during the SSGs, and the rating of perceived exertion (RPE) and blood lactate (La-) responses were determined at the end of each SSG condition. Compared to the SSGreg in both 3 vs. 3 and 4 vs. 4 formats, the SSGcom condition resulted in higher La- and RPE responses (p < 0.05), greater distance covered at MIR and HIR speeds and greater total distance (p < 0.05). The results of this study show that replacing 30 s within the 4-min bouts of SSGs (both 3- and 4-a-side) by 2 x 15 s of running drills is effective in increasing internal (La- and RPE) and external loads (MIR and HIR) without a significant decrease in total passes and successful passes in young soccer players. 



#11 Are There Differences in Concentric Isokinetic Strength Performance Profiles between International and Non-International Elite Soccer Players? 

Reference: Int J Environ Res Public Health. 2020 Dec 23;18(1):E35. 

doi: 10.3390/ijerph18010035. 

Authors: Robert Śliwowski, Jakub Marynowicz, Monika Grygorowicz, Andrzej Wieczorek, Łukasz Jadczak

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Summary: The purpose of this study is to evaluate the differences in concentric isokinetic strength characteristics of the knee extensor and knee flexor musculature between international (IL) and non-international level (N-IL) soccer players. The second aim is to establish strength symmetry status in knee muscles for dominant (DL) and non-dominant (NDL) legs for both within and between groups. 100 male top elite soccer players (IL: n = 36, age = 27.5 ± 3.4 years and N-IL: n = 64, age = 27.7 ± 6.4 years) underwent concentric isokinetic strength tests, using a Biodex System 3 dynamometer. Results indicate that statistically significant differences between groups were noted for peak torque of hamstrings (PT-H), hamstrings/quadriceps (H/Q) ratio, and total work of hamstrings (TW-H), where mean values for the IL were similarly higher than for the N-IL group (p = 0.006, p < 0.001, and p = 0.012, respectively). Our results also showed statistically significant differences for peak torque of quadriceps (PT-Q), PT-H, total work of quadriceps (TW-Q) and TW-H between legs, where mean values noted for the DL were higher than for the NDL for both groups (p = 0.021, p < 0.001, p = 0.006, and p = 0.004, respectively). Additional results show that IL players presented more symmetrical strength between legs than N-IL. The results of this study indicate that that the greatest differences in isokinetic strength performance across players at different soccer levels relate to the hamstring muscle. As a result, systematic strength training of these muscle groups is strongly recommended. 



#12 Internal (Factorial) Validity of the ANAM using a Cohort of Woman High-School Soccer Players 

Reference: Arch Clin Neuropsychol. 2020 Dec 29;acaa120. doi: 10.1093/arclin/acaa120. Online ahead of print. 

Authors: Joseph J Glutting, Adam Davey, Victoria E Wahlquist, Marley Watkins, Thomas W Kaminski

Summary: Computerized neuropsychological testing is a cornerstone of sport-related concussion assessment. Female soccer players are at an increased risk for concussion as well as exposures to repetitive head impacts from heading a soccer ball. Our primary aim was to examine factorial validity of the Automated Neuropsychological Assessment Metrics (ANAM) neuropsychological test battery in computing the multiple neurocognitive constructs it purports to measure in a large cohort of interscholastic female soccer players. Study participants included 218 interscholastic female soccer players (age = 17.0±0.7 year; mass = 55.5±6.8 kg; height = 164.7±6.6 cm) drawn from a large (850+) prospective database examining purposeful heading from four area high schools over a 10-year period. The ANAM-2001 measured neurocognitive performance. Three methods were used to identify integral constructs underlying the ANAM: (a) exploratory factor analysis (EFA), (b) first-order confirmatory factor analysis (CFA), and (c) hierarchical CFA. Neuropsychological phenomena measured by the ANAM-2001 were best reproduced by a hierarchical CFA organization, composed of two lower level factors (Simple Reaction Time, Mental Efficiency) and a single, general composite. Although the ANAM was multidimensional, only the composite was found to possess sufficient construct dimensionality and reliability for clinical score interpretation. Findings failed to uphold suppositions that the ANAM measures seven distinct constructs, or that any of its seven tests provide unique information independent of other constructs, or the composite, to support individual interpretation. Outcomes infer the ANAM possesses factorial-validity evidence, but only scores from the composite appear to sufficiently internally valid, and reliable, to support applied use by practitioners. 



#13 SOS to the Soccer World. Each Time the Preseason Games Are Less Friendly 

Reference: Front Sports Act Living. 2020 Dec 18;2:559539. doi: 10.3389/fspor.2020.559539. eCollection 2020. 

Authors: Julio Calleja-Gonzalez, Carlos Lalín, Francesc Cos, Diego Marques-Jimenez, Pedro E Alcaraz, Antonio José Gómez-Díaz, Tomás T Freitas, Juan Mielgo Ayuso, Irineu Loturco, Xavi Peirau, Ignacio Refoyo, Nicolas Terrados, Jaime E Sampaio 

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#14 Changes in sprint performance and sagittal plane kinematics after heavy resisted sprint training in professional soccer players

Reference: PeerJ. 2020 Dec 15;8:e10507. doi: 10.7717/peerj.10507. eCollection 2020. 

Authors: Johan Lahti, Toni Huuhka, Valentin Romero, Ian Bezodis, Jean-Benoit Morin, Keijo Häkkinen 

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Summary: Sprint performance is an essential skill to target within soccer, which can be likely achieved with a variety of methods, including different on-field training options. One such method could be heavy resisted sprint training. However, the effects of such overload on sprint performance and the related kinetic changes are unknown in a professional setting. Another unknown factor is whether violating kinematic specificity via heavy resistance will lead to changes in unloaded sprinting kinematics. We investigated whether heavy resisted sled training (HS) affects sprint performance, kinetics, sagittal plane kinematics, and spatiotemporal parameters in professional male soccer players. After familiarization, a nine-week training protocol and a two-week taper was completed with sprint performance and force-velocity (FV) profiles compared before and after. Out of the two recruited homogenous soccer teams (N = 32, age: 24.1 ± 5.1 years: height: 180 ± 10 cm; body-mass: 76.7 ± 7.7 kg, 30-m split-time: 4.63 ± 0.13 s), one was used as a control group continuing training as normal with no systematic acceleration training (CON, N = 13), while the intervention team was matched into two HS subgroups based on their sprint performance. Subgroup one trained with a resistance that induced a 60% velocity decrement from maximal velocity (N = 10, HS60%) and subgroup two used a 50% velocity decrement resistance (N = 9, HS50%) based on individual load-velocity profiles. Both heavy resistance subgroups improved significantly all 10-30-m split times (p < 0.05, d = - 1.25; -0.62). Post-hoc analysis showed that HS50% improved significantly more compared to CON in 0-10-m split-time (d = 1.03) and peak power (d = 1.16). Initial maximal theoretical horizontal force capacity (F0) and sprint FV-sprint profile properties showed a significant moderate relationship with F0 adaptation potential (p < 0.05). No significant differences in sprinting kinematics or spatiotemporal variables were observed that remained under the between-session minimal detectable change. With appropriate coaching, heavy resisted sprint training could be one pragmatic option to assist improvements in sprint performance without adverse changes in sprinting kinematics in professional soccer players. Assessing each player's initial individual sprint FV-profile may assist in predicting adaptation potential. More studies are needed that compare heavy resisted sprinting in randomized conditions. 



#15 Reliability assessment of the functional movement screen for predicting injury risk in Japanese college soccer players 

Reference: J Phys Ther Sci. 2020 Dec;32(12):850-855. doi: 10.1589/jpts.32.850. Epub 2020 Dec 11. 

Authors: Takayuki Miyamori, Masashi Nagao, Yu Shimasaki, Takayuki Okazaki, Naoki Akiyoshi, Hirofumi Nishio, Yuji Takazawa, Masafumi Yoshimura

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Summary: This study aimed to assess the reliability of the Functional Movement Screen and explore whether this evaluation tool can predict the risks of personal injuries in Japanese soccer players. Seventy-five Japanese college soccer players who participated in our 1 year prospective cohort study underwent a Functional Movement Screen assessment. Demographic data, athletic characteristics, and types and frequency of injuries sustained, were analyzed with the assessment results. There was no significant difference in the mean Functional Movement Screen composite scores between genders. Although the Functional Movement Screen showed excellent inter-rater reliability (0.92), low overall internal consistency (0.35) was observed. A maximum score of 3 in straight leg raise occurred in 94% of the females and was considered a ceiling effect. None of the cut-off point scores of the Functional Movement Screen were associated with the number of overall injuries, lower limb injuries, and traumatic injuries, or time to return to play. The Functional Movement Screen composite score of ≤15 represented the maximum sensitivity of 76.92% and specificity of 34.78% with 0.56 in the area under the curve. Functional Movement Screen composite scores do not have sufficient sensitivity and specificity for predicting injuries in Japanese college soccer players. 






Optimal Pretaper Phase on Physical Match Performance in Professional Soccer

The aim was to investigate the optimal pretaper duration on match running performance in a professional soccer team.






Eyes-Open Versus Eyes-Closed Somatosensory Motor Balance in Professional Soccer Players With Chronic Ankle Instability

The aim was to compare an eyes-open versus an eyes-closed balance training protocol in professional soccer players with chronic ankle instability





Latest research in football - week 8 - 2021

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 Lack of Abdominal Stability and Control as a Possible Contributor to Rectus Femoris Avulsion Fracture in the Adolescent Soccer Player: A Case Report 

Reference: Pediatr Phys Ther. 2021 Jan 1;33(1):E15-E22. doi: 10.1097/PEP.0000000000000773. 

Authors: Chelsea Lasky-McFarlin, Mae Thomas, Jennifer Newman, Deborah Thorpe 

Summary: The purpose was to describe evaluation and physical therapy treatment for an athlete who is male and 13 years old with healing bilateral rectus femoris avulsion fractures. Fractures of the anterior inferior iliac spine may be linked to poor abdominal stability in soccer athletes who are male and an adolescent. The development and use of an abdominal stability screening tool could be an efficient and effective way to determine fracture risk and guide prevention programs. Following 8 weeks of conservative physical therapy treatment, the athlete met all goals and returned to pain-free soccer activities without residual impairments. Four months following discharge, he reported full participation in soccer competition without complications. This case illustrates that abdominal weakness is a potential risk factor for anterior inferior iliac spine avulsion fracture. Screening for abdominal weakness and incorporating preventative programs into training regimens is recommended to prevent anterior inferior iliac spine injuries in this population. 



#2 Urinary N-Terminal Fragment of Titin Reflects Muscle Damage After a Soccer Match in Male Collegiate Soccer Players 

Reference: J Strength Cond Res. 2020 Dec 17;Publish Ahead of Print. doi: 10.1519/JSC.0000000000003923.

Authors: Yoko Tanabe, Kazuhiro Shimizu, Emi Kondo, Mikinobu Yasumatsu, Daisuke Nakamura, Hiroyuki Sagayama, Hideyuki Takahashi 

Summary: Previous studies have demonstrated that noninvasive urinary N-terminal fragment of titin (U-titin) concentration highly correlates with serum creatine kinase (CK) activity, a classic invasive muscle damage marker. This finding indicates that U-titin could be used to estimate muscle damage. However, these results were achieved using a laboratory-based eccentric exercise model. Therefore, it remains unclear whether U-titin is useful for evaluating muscle damage occurring in field sports events. As a result, we evaluated whether U-titin concentration closely relates to serum CK activity after a soccer match. Seventeen collegiate soccer players (age: 20 ± 1 year; height: 172 ± 6 cm; body mass: 65 ± 5 kg; Yo-Yo intermittent recovery test level 2, 1,135 ± 196 m) completed a test match (2 halves of 45 minutes separated by 15 minutes of normal half-time). U-titin concentration, serum CK activity, countermovement jump performance, and muscle soreness were assessed 2 hours before the match and 30 minutes, 24 hours, and 48 hours after the match. U-titin concentrations and CK activity similarly increased at 24 hours and returned to the baseline value at 48 hours after the match. Moreover, the percentage of changes in U-titin concentration from baseline after the match significantly and positively correlated with serum CK activity (r = 0.82, p < 0.05). These results suggest that the noninvasive marker U-titin can be used to assess muscle damage conditions in field sports events, such as soccer matches. 



#3 Elite Soccer Players do Not Cover Less Distance in the Second Half of the Matches When Game Interruptions Are Considered 

Reference: J Strength Cond Res. 2020 Dec 17;Publish Ahead of Print. doi: 10.1519/JSC.0000000000003935.

Authors: Ezequiel Rey, Anton Kalén, Miguel Lorenzo-Martínez, Roberto López-Del Campo, Fabio Nevado-Garrosa, Carlos Lago-Peñas 

Summary: This study aimed to analyze quantitative differences in the physical demands of male elite soccer players between the first and second halves during official matches, accounting for effective playing time (the duration of play after subtracting the game interruptions) and playing positions. A total of 4,249 individual match observations of 412 outfield players competing in the Spanish first division league (LaLiga) were undertaken during the 2018-2019 season, using a computerized tracking system (TRACAB, Chyronhego, New York, NY). The players were classified into 5 positional roles: central defenders (CD), external defenders (ED), central midfielders (CM), external midfielders (EM), and forwards (F). The main results showed that in contrast to those observed when total playing time was considered, independent of playing position, there were no significant differences on high-speed running (HSR) (5.5 ± 2.4 vs. 5.5 ± 2.4 m·min-1) and sprint (5.3 ± 3.3 vs. 5.4 ± 3.3 m·min-1) distances between the first and second halves in professional soccer players when the effective playing time was considered. However, differences in match running performance at HSR and sprint distances between the first and second halves were dependent on players' playing position. Whereas ED and EM maintained HSR and sprint efforts during the second half, CD and CM significantly increased (p < 0.001) the distance covered at sprint during the second period of the match. Contrarily, F were unable to maintain their HSR (6.2 ± 2.3 vs. 5.9 ± 3.3 m·min-1) and sprint (7.0 ± 3.5 vs. 6.5 ± 3.4 m·min-1) match running performances during the second half. Such findings demonstrate that total playing time could overestimate fatigue-induced performance declines. Thus, effective playing time and playing position should be taken into account when interpreting the match running performance of professional soccer players. 



#4 Sprint and jump performances in highly trained young soccer players of different chronological age: Effects of linear vs. change-of-direction sprint training 

Reference: J Exerc Sci Fit . 2021 Apr;19(2):81-90. doi: 10.1016/j.jesf.2020.10.003. Epub 2020 Nov 13. 

Authors: Thomas Pavillon, Claire Tourny, Abderraouf Ben Aabderrahman, Iyed Salhi, Sghaeir Zouita, Mehdi Rouissi, Anthony C Hackney, Urs Granacher, Hassane Zouhal

Summary: The aim of this study was to examine the effects of two different sprint-training regimes on sprint and jump performances according to age in elite young male soccer players over the course of one soccer season. Players were randomly assigned to two training groups. Group 1 performed systematic change-of-direction sprints (CODST, U19 [n = 9], U17 [n = 9], U15 [n = 10]) while group 2 conducted systematic linear sprints (LST, U19 [n = 9], U17 [n = 9], U15 [n = 9]). Training volumes were similar between groups (40 sprints per week x 30 weeks = 1200 sprints per season). Pre and post training, all players performed tests for the assessment of linear and slalom sprint speed (5-m and 10-m), countermovement jump, and maximal aerobic speed performance. For all physical fitness measures, the baseline-adjusted means data (ANCOVA) across the age groups showed no significant differences between LST and CODST at post (0.061 < p < 0.995; 0.0017 < d < 1.01). The analyses of baseline-adjusted means for all physical fitness measures for U15, U17, and U19 (LST vs. CODST) revealed no significant differences between LST and CODST for U15 (0.213 < p < 0.917; 0.001 < d < 0.087), U17 (0.132 < p < 0.976; 0.001 < d < 0.310), and U19 (0.300 < p < 0.999; 0.001 < d < 0.049) at post. The results from this study showed that both, LST and CODST induced significant changes in the sprint, lower limbs power, and aerobic performances in young elite soccer players. Since no significant differences were observed between LST and CODST, the observed changes are most likely due to training and/or maturation. Therefore, more research is needed to elucidate whether CODST, LST or a combination of both is beneficial for youth soccer athletes' performance development. 



#5 Biological Maturity Status in Elite Youth Soccer Players: A Comparison of Pragmatic Diagnostics With Magnetic Resonance Imaging 

Reference: Front Sports Act Living. 2020 Dec 15;2:587861. doi: 10.3389/fspor.2020.587861. eCollection 2020. 

Authors: Daniel Leyhr, Dennis Murr, Lajos Basten, Katrin Eichler, Thomas Hauser, Dennis Lüdin, Michael Romann, Giuseppe Sardo, Oliver Höner

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Summary: The influence of biological maturity status (BMS) on talent identification and development within elite youth soccer is critically debated. During adolescence, maturity-related performance differences within the same age group may cause greater chances of being selected for early maturing players. Therefore, coaches need to consider players' BMS. While standard methods for assessing BMS in adolescents are expensive and time-consuming imaging techniques (i.e., X-ray and MRI), there also exist more pragmatic procedures. This study aimed to evaluate commonly used methods to assess BMS within a highly selected sample of youth soccer players. A total of N = 63 elite male soccer players (U12 and U14) within the German Soccer Association's talent promotion program completed a test battery assessing BMS outcomes. Utilizing MRI diagnostics, players' skeletal age (SAMRI) was determined by radiologists and served as the reference method. Further commonly used methods included skeletal age measured by an ultrasound device (SAUS), the maturity offset (MOMIR), and the percentage of adult height (PAHKR). The relation of these alternative BMS outcomes to SAMRI was examined using different perspectives: performing bivariate correlation analyses (1), modeling BMS as a latent variable (BMSlat) based on the multiple alternative diagnostics (2), and investigating individual differences in agreement (3). (1) Correlations of SAMRI and the further BMS variables ranked from r = 0.80 to r = 0.84 for the total sample and were lower for U12 (0.56 ≤ r ≤ 0.66), and U14 (0.61 ≤ r ≤ 0.74) (2). The latent structural equation modeling (SEM) (R 2 = 51%) revealed a significant influence on BMSlat for MOMIR (? = 0.51, p <0.05). The additional contribution of PAHKR (? = 0.27, p = 0.06) and SAUS (? = -0.03, p = 0.90) was rather small (3). The investigation of individual differences between the reference method and alternative diagnostics indicated a significant bias for MOMIR (p <0.01). The results support the use of economical and time-efficient methods for assessing BMS within elite youth soccer. Bivariate correlation analyses as well as the multivariate latent variable approach highlight the measures' usefulness. However, the observed individual level differences for some of the utilized procedures led to the recommendation for practitioners to use at least two alternative assessment methods in order to receive more reliable information about players' BMS within the talent promotion process. 



#6 Longitudinal Physical Development of Future Professional Male Soccer Players: Implications for Talent Identification and Development? 

Reference: Front Sports Act Living . 2020 Oct 21;2:578203. doi: 10.3389/fspor.2020.578203. eCollection 2020. 

Authors: Chris Saward, Mark Hulse, John G Morris, Heita Goto, Caroline Sunderland, Mary E Nevill

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Summary: The present study examined if elite youth male association football (soccer) players aged 8-19 y (n = 2,875) from the English talent development system, who ultimately achieved professional status differed in stature, body mass, and physical performance (20-m sprint speed, slalom agility speed, vertical counter-movement jump with arm swing jump height, multistage fitness test distance) compared with their non-professional peers. The study also examined the longitudinal pattern of development of stature, body mass, and physical performance, and if this was different between future professionals and non-professionals, while considering the effects of playing position. Multilevel modeling of the 8,898 individual (player-occasion) data points suggested that from age 12.0, the future professionals performed better in a vertical counter-movement jump with arm swing test and slalom agility test than future non-professionals, and improved at a faster rate, so that by age 18.0 the differences in vertical counter-movement jump with arm swing and slalom agility performance were 1.7 cm (p < 0.001, d = 0.3) and 0.14 s (p < 0.001, d = 0.5), respectively. In addition, future professionals were faster (by 0.02-0.04 s on the 20-m sprint, p < 0.001, d = 0.2) and ran further in the multistage fitness test (by 47 m, p = 0.014, d = 0.2) than future non-professionals throughout their development, but there were no differences in stature or body mass during development between the groups. Whereas, multistage fitness test performance improved linearly with age, the development of all other physical characteristics was non-linear. There were inter-individual differences in the development of all characteristics, and there were differences between playing positions in the development of all characteristics. Thus, in summary, future professionals jump higher, are more agile, faster, and more endurance fit than future non-professionals as they age, and the pattern of development is different in professionals and non-professionals for vertical jumping and slalom agility performance. 



#7 Female Youth Soccer Participation and Continued Engagement: Associations With Community Size, Community Density, and Relative Age 

Reference: Front Sports Act Living. 2020 Sep 18;2:552597. doi: 10.3389/fspor.2020.552597. eCollection 2020. 

Authors: Kristy L Smith, Patricia L Weir 

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Summary: Environmental context can impact youth engagement in sport and athlete development. Previous work has examined the population size of the birthplace of elite athletes; commonly known as the birthplace or community size effect. Community density has also been recognized as an important variable. Exact estimates for the ideal community characteristics and a thorough understanding of the underlying mechanisms has been somewhat elusive. Existing studies are cross-sectional in nature and there is evidence to suggest that significant variation exists within imposed categories. An athlete's birthdate position in a similar-age cohort can also impact development and has been associated with (dis)advantages resulting from subtle age differences (i.e., the relative age effect); it remains unknown if this variable is associated with population density. The objective of this study was to establish longitudinal participation trends among female youth soccer players in Ontario Canada, with consideration of community size, community density, and relative age. Within-category variation and associations between the variables were assessed. Registration entries at age 10 years (n = 9,826) and 16 years (n = 2,305) were isolated for analysis. Odds ratio analyses were conducted within each community size and density category for all 10 year old registrants; 95% confidence intervals were obtained. This procedure was repeated for all registrants at 16 years of age using the expected distribution at age 10 years to examine continued engagement. Findings suggest medium-sized communities (i.e., 10,000-249,999 inhabitants) provide the best odds of participation and continued engagement. Less densely populated communities (i.e., 50-<400 population/km2) appeared to be ideal for facilitating participation at age 10 years, but not for engagement at age 16 years. However, within-category variation was evident when each community was inspected individually. Consistent with previous attempts to find an association between community size and the relative age effect, there did not appear to be an association between community density and birth quartile distribution. Observations from this study show that community size and community density are truly unique and separate variables. Future studies should consider the underlying contributions to both low and high participation and continued engagement, while being mindful of within-category variation. 



#8 Endurance Capacities in Professional Soccer Players: Are Performance Profiles Position Specific? 

Reference: Front Sports Act Living. 2020 Sep 18;2:549897. doi: 10.3389/fspor.2020.549897. eCollection 2020. 

Authors: Stefan Altmann, Rainer Neumann, Alexander Woll , Sascha Härtel

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Summary: The aim of this study was to investigate position-specific endurance performance of soccer players. 136 professional players competing in the 1st and 2nd division in Germany were divided into the positional groups goalkeepers (GK), central defenders (CD), wingers (WI), central midfielders (CM), and forwards (FW). All players performed an incremental treadmill test with blood lactate sampling until exhaustion with the following endurance parameters being obtained: Fixed aerobic threshold (v2mmol/l), fixed anaerobic threshold (v4mmol/l), individual aerobic threshold (vLT), individual anaerobic threshold (vIAT), and maximum velocity (vmax). Results revealed significant differences between GK and all outfield playing positions for all endurance parameters (p ≤ 0.03; ES 0.87-2.19). No significant differences among outfield playing positions were evident for any of the parameters. However, trends were found in favor of the CM compared to the WI (p = 0.11; ES = 0.68) and the FW (p = 0.06; ES = 0.47) relating to vLT as well as in favor of the CM compared to the WI (p = 0.10; ES = 0.56) relating to vIAT. Findings suggest that goalkeepers possess the lowest endurance capacity compared to other playing positions. While outfield players in general showed similar endurance performance, CM seem to possess the highest aerobic capacity of all positions as indicated by all lactate-based thresholds, however, with only small to moderate ES. These findings could lead one to question the appropriateness of current endurance training regimes to prepare all players adequately for their positional match-running demands. Indeed, endurance training of players should be specific to their match-running demands. However, it remains unknown to what extent these demands are position or player specific. 



#9 Player Monitoring in Professional Soccer: Spikes in Acute:Chronic Workload Are Dissociated From Injury Occurrence 

Reference: Front Sports Act Living. 2020 Jul 8;2:75. doi: 10.3389/fspor.2020.00075. eCollection 2020. 

Authors: Luis Suarez-Arrones, Borja De Alba, Mareike Röll, Ignacio Torreno, Sarah Strütt, Kathrin Freyler, Ramona Ritzmann

Summary: This study aimed to determine whether spikes in acute:chronic workload ratio (ACWR) are associated with injury incidence, and to examine the differences in external load due to greater or lesser exposure to matches and the long-term effects of the load during a chronic seasonal period. Fifteen professional soccer players belonging to the squad of a European Champions League club were enrolled in this study. External training and match load were assessed from all athletes using a global positioning system (GPS). We calculated the uncoupled ACWR for 10 consecutive competitive microcycles. Injuries were identified and determined by the days of absence. The differences in external load were determined using a linear mixed-model approach. In addition to the null hypothesis testing, the effect size was calculated. Thirteen athletes who did not suffer an injury exceeded several times the critical threshold of an ACWR > 1.5. This is equivalent to 1 player exceeding the critical threshold for ACWR in total distance (TD), 2 players for ACWR at distance covered above moderate speed (MSD), 2 players for ACWR at distance covered above high speed (HSD), 2 players for ACWR at distance covered above very high speed (VHSD), and 2 players for ACWR in DC at sprint per week. One athlete experienced a non-contact muscle strain injury and another a contact -injury manifested as a concussion; both athletes document an ACWR <1.5 within the 4 weeks prior to the injury event. Players with lesser participation in official games covered lower TD (-19.6%, very-large ES), MSD (-24.8%, very-large ES), HSD (-25.1%, moderate ES), VHSD (-25.5%, moderate ES), and DC at sprint (-30.6%, moderate ES) over the course of the 10-weeks period in comparison with the players with greater participation in official games. The present study demonstrated that spikes in the ACWR were not related to a subsequent injury occurrence in professional soccer players. Differences in participation in official games caused significant imbalances in the chronic external loads between players in a squad, which should be minimized in training sessions in order to prevent substantial changes in workload for those who usually do not play. 



#10 Biomarkers Correlate With Body Composition and Performance Changes Throughout the Season in Women's Division I Collegiate Soccer Players 

Reference: Front Sports Act Living. 2020 Jul 2;2:74. doi: 10.3389/fspor.2020.00074. eCollection 2020. 

Authors: Bridget A McFadden, Alan J Walker, Michelle A Arent, Brittany N Bozzini, David J Sanders, Harry P Cintineo, Marissa L Bello, Shawn M Arent

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Summary: The purpose of this study was to evaluate the effects of a competitive soccer season on biomarkers and performance metrics in order to determine the correlation between changes in biomarkers, body composition, and performance outcomes. Twenty-one Division 1 female collegiate soccer players were monitored throughout the 16-week season. Player workload was measured using heart rate and Global Position Satellite systems at all practices and games. Performance testing, including vertical jump, VO2max, and 3-repetition maximum testing for bench press, squat and deadlift, occurred prior to pre-season and immediately post-season. Blood draws occurred prior to preseason and every 4-weeks thereafter, following a game. Body composition was assessed prior to the start of season (week 0) and weeks 6, 10, 14, and 17 (post-season). Delta area under the curve was calculated for biomarkers and body composition variables to account for seasonal changes adjusted for baseline. Pearson-product moment correlations were used to assess relationships with significance set at p < 0.05. Trends were considered p ≤ 0.10. No significant time main effects were seen for anabolic biomarkers (p > 0.05). Significant time effects were seen for catabolic biomarkers throughout the season (p = 0.001). No changes in body weight, VO2max, vertical jump, and deadlift occurred. Squat and bench press improved (p = 0.01 and p = 0.02, respectively) with a decline in percent body fat (p = 0.03) and a trend for increased fat free mass (p = 0.09). Additionally, total cortisol (TCORT) negatively correlated with fat free mass (r = -0.48; p = 0.03) and positively correlated with VO2max (r = 0.47; p = 0.04). A trend was shown for a positive correlation between both TCORT and free cortisol (FCORT) and percent body fat (r = 0.39; r = 0.40; p = 0.08, respectively). IGF-1 and growth hormone positively correlated to deadlift (r = 0.57; P = 0.02 and r = 0.59; p = 0.03), whereas creatine kinase showed a trend for a positive correlation with deadlift (r = 0.49; p = 0.06). IL-6 negatively correlated with bench press (r = -0.53; p = 0.03). These findings support a relationship between biomarkers, performance outcomes, and body composition. Biomarker monitoring may be useful to detect individual player's physiological response to an athletic season and may help provide insights in efforts to optimize performance outcomes. 



#11 The Effects of Cold Water Immersion on the Recovery of Drop Jump Performance and Mechanics: A Pilot Study in Under-20 Soccer Players 

Reference: Front Sports Act Living. 2020 Mar 31;2:17. doi: 10.3389/fspor.2020.00017. eCollection 2020. 

Authors: Adam Kositsky, Janne Avela

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Summary: Cold water immersion (CWI) is a popular method used for enhancing recovery from exercise. However, the efficacy of this approach is inconclusive and studies investigating variables contributing to overall performance are scarce. Additionally, few studies have investigated the recovery of stretch-shortening cycle (SSC) performance after a fatiguing SSC task. The SSC occurs naturally in human locomotion and induces a recovery pattern different from isolated muscle contractions (e.g., pure eccentric exercise). Therefore, the main aim of this study was to investigate the effects of a single CWI on jumping performance and mechanics after exhaustive SSC exercise. On a sledge apparatus, 10 male under-20 soccer players (age 18-20 years) performed five sets of 20 maximal drop jumps (DJ) followed by continuous submaximal rebounding. Subjects were equally randomized into a passive recovery control (CON) or CWI group (10 ± 0.5°C for 20 min). Prior to, upon completion of, and at 24 and 48 h follow-ups, subjects performed maximal DJs recorded with a high-speed video camera. Blood samples were taken and subjective muscle soreness was measured. Rebound jump height was impaired immediately after exercise, although significant only for CWI (CON: -12.4 cm, p = 0.083; CWI: -9.9 cm, p = 0.009). The CWI group demonstrated significant recovery of jump height at 24 h (+6.3 cm, p = 0.031) and 48 h (+8.9 cm, p = 0.002) compared to post-exercise. Ankle joint stiffness was decreased for CWI (-2.1 to -2.5 Nm/°, p = 0.005-0.041). Creatine kinase activity was similarly increased for both groups at 24 and 48 h, while there was also no group effect in muscle soreness (p ≥ 0.056). This pilot study demonstrates the potential for CWI to slightly enhance the recovery of DJ performance. However, this occurred in parallel with reduced ankle joint stiffness, signifying that jumps were performed with less efficiency, which would not be favorable for repeated SSC actions. While this should be confirmed with a larger sample size, this highlights the potential for CWI to be detrimental to the mechanical properties of the ankle joint. Therefore, future recovery intervention studies should concomitantly investigate variables contributing to performance, rather than just overall performance itself. 



#12 Moving Advertisements Systematically Affect Gaze Behavior and Performance in the Soccer Penalty Kick 

Reference: Front Sports Act Living. 2020 Jan 14;1:69. doi: 10.3389/fspor.2019.00069. eCollection 2019. 

Authors: Gareth Paterson, John van der Kamp, Geert Savelsbergh

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Summary: The aim of the current study was to investigate whether a moving advertisement positioned behind the goal area would influence the visual attention of participants performing a soccer penalty kick, and, whether this would an effect on subsequent motor performance. It was hypothesized that if the (moving) advertisement would function as a distractor, then this would result in non-specific disruptions in penalty performance measures, especially affecting aiming location and precision. Alternatively, it was reasoned that, in line with the Dunker illusion, the moving advertisement would systematically affect perception of target location, resulting in changes in penalty performance and aiming that are specific for the direction of motion of the advertisement. To test these hypotheses, we investigated the gaze behavior and kicking performance of intermediate skilled soccer players taking penalty kicks in three differing advertisement conditions, namely no advertisement, a stationary advertisement, and a moving advertisement. The latter condition consisted of an advertisement moving from left to right and an advertisement moving from right to left. Results showed that a moving advertisement placed behind the goal area indeed caught the visual attention of soccer penalty kickers using a goalkeeper-dependent kicking strategy. Participants kicking performance tended to be less variable within the no advertisement condition compared to the moving advertisement condition. In addition, systematic, direction-specific effects on aiming were found when comparing conditions in which the advertisement moved in opposite directions. This pattern of findings indicate that the accuracy of the penalty kick is impacted by task-irrelevant contextual information. 



#13 Sprint performance in football (soccer) players with and without a previous hamstring strain injury: An explorative  cross-sectional study

Reference: Int J Sports Phys Ther. 2020 Dec;15(6):947-957. doi: 10.26603/ijspt20200947. 

Authors: Lasse Ishøi, Kristian Thorborg, Per Hölmich, Kasper Krommes 

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Summary: Hamstring strain injuries are common in many sports. Following a hamstring injury, deficits in peak and explosive strength may persist after return to sport potentially affecting sprint performance. Assessment of repeated-sprint ability is recognized as an important part of the return to sport evaluation after a hamstring injury.Purpose: This purpose of this exploratory cross-sectional study was to compare sprinting performance obtained during a repeated-sprint test between football players with and without a previous hamstring strain injury. Forty-four fully active sub-elite football players, 11 with a previous hamstring strain injury during the preceding 12 months (cases; mean age, SD: 25.6 ± 4.4) and 33 demographically similar controls (mean age, SD: 23.2 ± 3.7), were included from six clubs. All players underwent a repeated-sprint test, consisting of six 30-meter maximal sprints with 90 seconds of recovery between sprints. Sprint performance was captured using high-speed video-recording and subsequently assessed by a blinded tester to calculate maximal sprint velocity, maximal horizontal force, maximal horizontal power, and mechanical effectiveness. A significant between-group difference was seen in favor of players having a previous hamstring injury over 6 sprints for maximal velocity (mean difference: 0.457 m/s, 95% CI: 0.059-0.849, p = 0.025) and mechanical effectiveness (mean difference: 0.009, 95% CI: 0.001-0.016, p = 0.020). Repeated-sprint performance was not impaired in football players with a previous hamstring strain injury; in fact, higher mean maximal sprinting velocity and better mechanical effectiveness were found in players with compared to without a previous hamstring injury. The higher sprinting velocity, which likely increases biomechanical load on the hamstring muscles, in previously injured players may increase the risk of recurrent injuries. 



#14 Worst case scenario match analysis and contextual variables in professional soccer players: a longitudinal study 

Reference: Biol Sport. 2020 Dec;37(4):429-436. doi: 10.5114/biolsport.2020.97067. Epub 2020 Jul 10. 

Authors: José M Oliva-Lozano, Daniel Rojas-Valverde, Carlos D Gómez-Carmona, Víctor Fortes, José Pino-Ortega

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Summary: This study aimed to describe the worst-case scenarios (WCS) of professional soccer players by playing position in different durations and analyse WCS considering different contextual variables (match half, match location and match outcome). A longitudinal study was conducted in a professional soccer team. Data were collected from different WCS durations in the total distance (TD), high-speed running distance (HSRD), and sprinting distance (SPD). A mixed analysis of variance was performed to compare different WCS durations between playing positions and contextual variables, making pairwise comparisons by Bonferroni post hoc test. Positional differences were found for TD (p < 0.01, ? p 2 = 0.02), HSRD (p < 0.01, ? p 2 = 0.01) and SPD (p < 0.01, ? p 2 = 0.02). There was a significant interaction when comparing WCS by match half in TD (F = 6.1, p < 0.01, ? p 2 = 0.07) but no significant differences in HSRD (p = 0.403, ? p 2 = 0) or SPD (p = 0.376, ? p 2 = 0). A significant interaction was identified when comparing WCS by match location in TD (F = 51.5, p < 0.01, ? p 2 = 0.14), HSRD (F = 19.15, p < 0.01, ? p 2 = 0.05) and SPD (F = 8.95, p < 0.01, ? p 2 = 0.01) as well as WCS by match outcome in TD (F = 36.4, p < 0.01, ? p 2 = 0.08), HSRD (F = 13.6, p < 0.01, ? p 2 = 0.04) and SPD (F = 7.4, p < 0.01, ? p 2 = 0.02). Positional differences exist in TD, HSRD, and SPD in match-play WCS, and contextual variables such as match half, match location and match outcome have a significant impact on the WCS of professional soccer players. 



#15 Accelerometry-based variables in professional soccer players: comparisons between periods of the season and playing positions 

Reference: Biol Sport. 2020 Dec;37(4):389-403. doi: 10.5114/biolsport.2020.96852. Epub 2020 Jul 10. 

Authors: Filipe Manuel Clemente, Rui Silva, Rodrigo Ramirez-Campillo, José Afonso, Bruno Mendes, Yung-Sheng Chen

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Summary: The aim of this study was to provide reference data of variation in external training loads for weekly periods within the annual season. Specifically, we aimed to compare the weekly acute load, monotony, and training strain of accelerometry-based measures across a professional soccer season (pre-season, first and second halves of the season) according to players' positions. Nineteen professional players were monitored daily for 45 weeks using an 18-Hz global positioning system to obtain measures of high metabolic load distance (HMLD), impacts, and high intensity accelerations and decelerations. Workload indices of acute load, training monotony, and training strain were calculated weekly for each of the measures. The HMLD had greater training strain values in the pre-season than in the first (p ≤ 0.001; d = 0.793) and second halves of the season (p ≤ 0.001; d = 0.858). Comparisons between playing positions showed that midfielders had the highest weekly acute load of HMLD (6901 arbitrary units [AU]), while central defenders had the lowest (4986 AU). The pre-season period was associated with the highest acute and strain load of HMLD and number of impacts, with a progressive decrease seen during the season. In conclusion, coaches should consider paying greater attention to variations in HMLD and impacts between periods of the season and between players to individualize training accordingly. 



#16 Biomechanical measures during two sport-specific tasks differentiate between soccer players who go on to anterior cruciate ligament injury and those who do not – a prospective cohort analysis

Reference: Int J Sports Phys Ther. 2020 Dec;15(6):928-935. doi: 10.26603/ijspt20200928. 

Authors: Celeste Dix, Amelia Arundale, Holly Silvers-Granelli, Adam Marmon, Ryan Zarzycki, Lynn Snyder-Mackler 

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Summary: Decelerating and cutting are two common movements during which non-contact anterior cruciate ligament (ACL) injuries occur in soccer players. Retrospective video analysis of ACL injuries has demonstrated that players are often in knee valgus at the time of injury. The purpose was too determine whether prospectively measured components of valgus collapse during a deceleration and 90 ° cut can differentiate between collegiate women's soccer players who go on to non-contact ACL injury. 51 NCAA women's soccer players completed motion analysis of a deceleration and 90 ° before the competitive season. Players were classified as Injured (noncontact ACL injury during the season) or Uninjured at the end of the season. Differences between groups for peak hip adduction, internal rotation, and knee abduction angles, and knee valgus collapse were analyzed with a MANOVA. Four non-contact ACL injuries were reported at the end of the season. There was a significant difference between groups for hip adduction angle during the 90 ° cut (p = 0.02) and deceleration (p = 0.03). Players who went on to ACL injury were in more hip adduction. Hip adduction angle is larger in players who go on to ACL injury than those who do not during two sport-specific tasks. The components of knee injury prevention programs that address proximal control and strength are likely crucial for preventing ACL injuries. 






Seasonal training and match load and micro-cycle periodization in male Premier League academy soccer players

The aim was to assess on pitch external loading of English Premier League (EPL) academy soccer players (U12-U18 age groups) over an entire competitive season.





The World’s Most Valuable Soccer Teams

Forbes has released its bi-annual list of the 20 most valued soccer teams.


The list includes nine teams from the English Premier League, four from the Italian Serie A, three from the Spanish La Liga, two from the German Bundesliga and one from each the Netherlands and France.

There is no real surprise inside the top ten, as the “usual” big teams are present. Ajax and Leicester premiered inside the top 20.


The revenues and operating income listed are for the 2019-2020 season in US dollar.


1. Barcelona

Value: $4.76 billion

Revenue (2020): $792 million

Operating Income (2020): $62.2 million

Debt Value: 6%


2. Real Madrid

Value: $4.75 billion

Revenue (2020): $792 million

Operating Income (2020): $92 million

Debt Value: 6%


3. Bayern Munich

Value: $4.215 billion

Revenue (2020): $703 million

Operating Income (2020): $49.2 million

Debt Value: 0%


4. Manchester United

Value: $4.2 billion

Revenue (2020): $643 million

Operating Income (2020): $166.6 million

Debt Value: 16%


5. Liverpool

Value: $4.1 billion

Revenue (2020): $619 million

Operating Income (2020): $61.9 million

Debt Value: 2%


6. Manchester City

Value: $4 billion

Revenue (2020): $609 million

Operating Income (2020): -$2 million

Debt Value: 0%


7. Chelsea

Value: $3.2 billion

Revenue (2020): $520 million

Operating Income (2020): $34.7 million

Debt Value: 0%


8. Arsenal

Value: $2.8 billion

Revenue (2020): $430 million

Operating Income (2020): $47.3 million

Debt Value: 7%


9. Paris Saint-Germain

Value: $2.5 billion

Revenue (2020): $599 million

Operating Income (2020): -$4.5 million

Debt Value: 0%


10. Tottenham Hotspur

Value: $2.3 billion

Revenue (2020): $494 million

Operating Income: $134.2 million

Debt Value: 39%


11. Juventus

Value: $1.95 billion

Revenue (2020): $441 million

Operating Income: -$14 million

Debt Value: 16%


12. Borussia Dortmund

Value: $1.9 billion

Revenue (2020): $405 million

Operating Income: $15.1 million

Debt Value: 0%


13. Atlético de Madrid

Value: $1 billion

Revenue (2020): $368 million

Operating Income: $61.7 million

Debt Value: 26%


14. Inter Milan

Value: $743 million

Revenue (2020): $323 million

Operating Income: $13.1 million

Debt Value: 8%


15. Everton

Value: $658 million

Revenue (2020): $235 million

Operating Income: $15 million

Debt Value: 0%


16. AC Milan

Value: $559 million

Revenue (2020): $165 million

Operating Income: -$92.4 million

Debt Value: 4%


17. AS Roma

Value: $548 million

Revenue (2020): $156 million

Operating Income: -$108.4 million

Debt Value: 56%


18. West Ham United

Value: $508 million

Revenue (2020): $175 million

Operating Income: -$24.2 million

Debt Value: 18%


19. Leicester City

Value: $455 million

Revenue (2020): $189 million

Operating Income: -$49.3 million

Debt Value: 17%


20. Ajax

Value: $413 million

Revenue (2020): $172 million

Operating Income: $1.7 million

Debt Value: 11%



Team values are enterprise values (equity plus net debt) and include the economics of the team's stadium but exclude the value of the real estate. Operating income is earnings before interest, taxes, depreciation and amortization, player trading and disposal of player registrations. Debt is interest-bearing borrowings (including stadium debt)








Motor performance is not related to injury risk in growing elite-level male youth football players

The aim was to identify the relationship between growth velocity and injury in elite-level youth footballers.





Latest research in football - week 7 - 2021

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 Shared Situational Awareness in a Professional Soccer Team: An Explorative Analysis of Post-Performance Interviews 

Reference: Int J Environ Res Public Health. 2020 Dec 9;17(24):E9203. doi: 10.3390/ijerph17249203. 

Authors: Gaute S Schei, Rune Giske

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Summary: Sport science research has done little to elaborate on the cognitive factors that turn a collection of individual players into a coordinated elite team. The purpose of this paper is to clarify if the players and coach of an elite soccer team express shared situational awareness. Ten players and one coach were exposed to twelve video pictures from a previous soccer match, and their statements for each picture were recorded and analyzed using a qualitative approach. Two of five game situations were with ball possession and three out of seven were without ball possession; the player statements are contradictory, with a high threat for inadequate coordination. In seven of the twelve game situations, the players' statements coincided and expressed a shared situational awareness, with good opportunities for adequate defensive and offensive coordination. In two of the game situations, there was a high threat for inadequate coordination. There was consensus among 9 out of 10 players, but the player with the divergent statement was central in the situation. The procedure followed in the study could be used to elucidate if a team has shared situational awareness and clarify in which situations there exists discrepancies and data that can be used to improve team coordination on and off the field. 



#2 The moderating impact of maturation on acute neuromuscular and psycho-physiological responses to simulated soccer activity in academy soccer players

Reference: Eur J Sport Sci. 2020 Dec 14;1-11. doi: 10.1080/17461391.2020.1851775. Online ahead of print. 

Authors: Jamie Salter, Mark B A De Ste Croix, Jonathan D Hughes

Summary: Resource constraints complicate load monitoring practices in some academies, which is problematic based on load-injury associations surrounding periods of rapid non-linear growth. Limited research has explored relationships between maturation and perceived psycho-physiological response to activity and associated neuromuscular performance changes. This study aimed to quantify neuromuscular and psycho-physiological responses to standardised activity and analyse whether dose-responses were moderated by maturation. Fifty-seven male soccer players (age: 14.1 ± 0.9 years; stature: 165 ± 10 cm; body mass, 57 ± 9 kg; percentage of predicted adult height 92.7 ± 5%) from two Elite Player Performance Plan (EPPP) academies completed the youth soccer-specific aerobic fitness test (Y-SAFT60). Countermovement jump (CMJ), reactive strength index (RSI), absolute (ABS) and relative leg stiffness (REL) were measured pre-post the Y-SAFT60 with playerload (PL), heart rate (HR), total distance (TDist) and differential ratings of perceived exertion (dRPE) used as markers of load and intensity. A moderation model was employed to analyse interactions of maturation as a continuous variable. Analysis indicated no significant interaction (p <0.05) between maturation and neuromuscular performance but RPE-Technical demonstrated significant interactions (p = 0.01). Slope analysis indicated four variables (PL, RSI, ABS and REL) that demonstrated significance at various stages of maturation, most notably aligning with peak height velocity (87-96% PAH). Tentatively, we propose that maturational developments in the neuromuscular system offer some mechanistic explanation to the varied dose-responses observed. It is therefore important that maturation is habitually considered within prescription of training programmes and that further empirical studies are completed to determine maturity specific dose-responses. Components of both neuromuscular performance and psycho-physiological response to simulated soccer was influenced by maturity status. Individuals more biologically developed are more capable of 'coping' with the biomechanical load of simulated soccer activity resulting in more favourable neuromuscular responses. The period surrounding peak height velocity appears to influence whole body load-response pathways resulting in altered movement patterns during this period. To minimise the impact of maturity status, practitioners can restrict activities that elicit high biomechanical load and introduce biologically categorised training activities. 



#3 Effects of soccer training in muscular strength: a comparative study in trained youth soccer players and untrained boys of the same biological age 

Reference: J Sports Med Phys Fitness. 2020 Dec 14. doi: 10.23736/S0022-4707.20.11822-X. 

Authors: Athanasios Mandroukas, Thomas I Metaxas, Yiannis Michailidis, Kosmas Christoulas, Jan Heller

Summary: It is not clear if soccer training affected the development of muscle strength positively in children. We hypothesize that soccer training could positively affect the isokinetic concentric muscle strength and anthropometric characteristics in different ages of adolescents of the same biological age. A total of one-hundred and twenty-six (n=126) young soccer players (n=66) and untrained boys (n=60) throughout the developmental ages of 12, 14 and 16 years volunteered to participate in the study. Sexual maturation was classified according to Tanner's stages. Soccer players, except from their school's physical education program, participate also in a soccer training program. All participants underwent anthropometric measurements. The isokinetic-concentric peak torque values of the hamstrings (H) and quadriceps (Q), as well as the conventional strength ratios of H:Q, were measured on an isokinetic dynamometer at angular velocities of 60, 180, and 300°·s-1. Anthropometric differences in the same age group, between trained and untrained, were presented only for 12 year-olds (height, p<0.001 and BMI, p<0.01). Between groups, differences were observed in almost all anthropometric measurements, probably as result of development. The absolute isokinetic-concentric muscle strength was significantly higher (p<0.001) in the 12 and 16 years old trained group, compared to untrained, for the knee-flexors and knee-extensors. However, no significant differences were found between the 14 years old trained and untrained, for the muscle groups of Q and H. The H:Q strength ratios did not differ between groups at all angular velocities. The results of this study showed that systematic soccer training has a positive effect in the peripheral system, expressed as an increased lower limb muscle strength; specifically, Q and H. 



#4 Rethinking training in elite soccer players: comparative evidence of small sided games and official match play in kinematic parameters

Reference: J Sports Med Phys Fitness. 2020 Dec 14. doi: 10.23736/S0022-4707.20.11400-2. 

Authors: Cristian Savoia, Ferdinando Iellamo, Giuseppe Caminiti, Dominic A Doran, Samuel Pullinger, Mario Innaurato, Giuseppe Annino, Vincenzo Manzi  

Summary: The aim of this study was to compare kinematics parameters among official matches and SSGs of an Italian premier league soccer team. Eighteen elite professional male soccer players (4 central defenders, 4 wide defenders, 3 central midfielders, 3 box-to-box midfielders, 2 wingers and 2 strikers) took part in the study. Players were monitored during four months of full training (including pre-season and in-season) and over 26 matches (14 Serie A matches, 9 Europa League matches, and 3 friendly matches), from July 2017 until November 2017. The kinematic parameters during official matches and SSGs were evaluated through Video Match Analysis. The kinematic data analysis shows that the metabolic power, that constitutes an integrated measure of acceleration and velocity, fails to reflect what occurs during actual matchplay. An increased attention should be place in planning SSGs during training to better reproduce actual match situations. 



#5 Muscle Activity Asymmetry of The Lower Limbs During Sprinting in Elite Soccer Players

Reference: J Hum Kinet. 2020 Oct 31;75:239-245. doi: 10.2478/hukin-2020-0049. eCollection 2020 Oct. 

Authors: Przemysław Pietraszewski, Artur Gołaś, Aleksander Matusiński, Sylwia Mrzygłód, Aleksandra Mostowik, Adam Maszczyk

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Summary: The analysis of movement patterns through EMG activity provides the opportunity to identify the muscle groups most involved in a particular exercise, and to determine the scope of inter-limb deficiencies. The aim of the present study was to investigate the effects of a side-to-side muscle activity asymmetry between the left and the right lower limb during sprinting in soccer players. Sixteen professional soccer players took part in the study. Their age, body mass and body height equaled 23.7 ± 7.6 years, 81.2 ± 10.8 kg and 179.3 ± 12.2 cm, respectively. The sprint test consisted of two maximal sprints over 30 m with a 5-min rest interval between each sprint. EMG was recorded bilaterally from the quadriceps, hamstrings and gluteal muscles. Regression analysis revealed a significant effect of a side-to-side average muscle activity asymmetry between the left and right hamstring (LH/RH) muscles during the speed tests at 5 m (p = 0.044), and 30 m (p = 0.045), as well as the left and right glutes (LG/RG) at 5 m (p = 0.044) and 30 m (p = 0.043). Our results indicate that hamstring and glute muscles should be selectively and additionally activated during resistance training in soccer players to prevent injuries and improve sprint performance. 



#6 Tactical Behaviour of Youth Soccer Players: Differences Depending on Task Constraint Modification, Age and Skill Level

Reference: J Hum Kinet. 2020 Oct 31;75:225-238. doi: 10.2478/hukin-2020-0051. eCollection 2020 Oct. 

Authors: João Cláudio Machado, Daniel Barreira, Israel Teoldo, Jaime Serra-Olivares, Alberto Góes, Alcides José Scaglia

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Summary: This study aimed to investigate: i) how Small-Sided and Conditioned Games based on different representation and exaggeration modification strategies, from the Teaching Games for Understanding pedagogical principles, affected team performance and exploratory behaviour; and ii) how teams and players of different ages and skill levels were affected by the use of these different modification strategies. In total, forty-eight youth male soccer players participated in the study (U15, n = 24 mean age = 13.06 ± 1.53 years; U17, n = 24 mean age = 16.89 ± 0.11 years). In both categories, players were organized into three groups according to their tactical efficiency level (Group 01 = High Skilled Players (HSP), Group 02 = Intermediate Skilled Players (ISP), and Group 03 = Low Skilled Players (LSP)). The HSP and LSP groups performed two types of Gk+4vs4+Gk Small-Sided and Conditioned Games (SSCGs) based on different representation and exaggeration modification strategies. The first type of SSCGs was modified by structural constraints (Structural SSCG) and the second type was modified by rule manipulation (Manipulation SSCG). Team performance and exploratory behaviour were analysed through the Offensive Sequences Characterization System and Lag Sequential Analysis, respectively. SSCG modification strategies affected differently tactical performance and exploratory behaviour of teams composed of players of different skill levels. It was found that SSCG modification strategy through rule manipulation provided players and teams with a higher level of difficulty, compromising their performance and inhibiting exploratory behaviour. This information is crucial to practitioners wishing to apply more appropriate pedagogical strategies to improve a specific tactical problem using a player-centred and game-based approach. 



#7 Match and Training High Intensity Activity-Demands Profile During a Competitive Mesocycle in Youth Elite Soccer Players

Reference: J Hum Kinet. 2020 Oct 31;75:195-205. doi: 10.2478/hukin-2020-0050. eCollection 2020 Oct. 

Authors: José María Oliva-Lozano, Carlos David Gómez-Carmona, José Pino-Ortega, Víctor Moreno-Pérez, Manuel Antonio Rodríguez-Pérez

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Summary: The monitoring of the high intensity activity-demands profile during official matches (OMs) and training sessions (TSs) provides a deeper understanding of the relationship between training and competition loads as well as players' fitness characteristics. The aims of this study were to: 1) describe the training and match high intensity activity-demands profile in U-19 soccer players; 2) compare the profile depending on the type of session (OM or TS) throughout match-weeks; and 3) differentiate between profiles depending on the match location (home or away). Twenty-five U-19 Spanish soccer players were monitored during TSs and OMs for a one-month competitive period using a WIMU PROTM wearable inertial device. The variables of the study were: high speed running distance (HSRD), total sprints (SPs), maximum speed (MS) and player load (PL). OMs required higher demands than TSs in HSRD (460.99 ± 206.18 vs. 315.45 ± 180.12 m; p < 0.01; d = 0.75), SPs (10.86 ± 6.64 vs. 7.23 ± 4.82; p < 0.01; d = 0.69), MS (29.99 ± 2.54 vs. 28.50 ± 2.4 km/h; p < 0.01; d = 0.59) and PL (103.08 ± 24.15 vs. 83.18 ± 17.96 a.u.; p < 0.01; d = 0.94). The interaction between the type of session and mean week's demands presented differences with medium effect size in MS (p < 0.01; ωp 2 = 0.06) and small effect size in HSRD (p = 0.04; ωp 2 = 0.03), and SP (p = 0.05; ωp 2 = 0.03), but there were no differences in PL (p = 0.18; ωp 2 = 0). Finally, no differences were found in the match location comparison (p > 0.33; d = 0.22-0.33). Therefore, the profiles presented could be useful for future scientific purposes and serve as valid information for coaches trying to optimize performance. 



#8 Relationships Between Measures of Functional and Isometric Lower Body Strength, Aerobic Capacity, Anaerobic Power, Sprint and Countermovement Jump Performance in Professional Soccer Players

Reference: J Hum Kinet. 2020 Oct 31;75:161-175. doi: 10.2478/hukin-2020-0045. eCollection 2020 Oct. 

Authors: Michał Boraczyński, Tomasz Boraczyński, Robert Podstawski, Zbigniew Wójcik, Piotr Gronek

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Summary: The purpose of this study was to assess a wide range of physiological and performance variables and investigate whether and to what extent these variables are associated with each other in soccer. Twenty-five male soccer players (25.1 ± 4.56 years; body mass, 75.2 ± 5.92 kg; body height, 180.6 ± 5.45 cm) performed: 5- and 30-m sprints (T5m and T30m, respectively), 1-repetition-maximum (1RM) half squat, maximal voluntary isometric contraction (MVIC) of the knee extensors, countermovement jump (CMJ) to obtain vertical jump height (CMJheight) and power output (CMJpower), the 10-s Wingate Anaerobic Test (WAnT) to obtain peak power (Pmax), and the 20-m multi-stage shuttle run test (MST) to evaluate aerobic capacity. 1RM, MVIC, and Pmax were normalized to body mass. Large negative correlations were found between sprint times and 1RM half back squat/BM (r = -0.510 to -0.570, r2 = 0.260-0.325, both p < 0.01) and Pmax/BM (r = -0.501, r2 = 0.251, p < 0.01). T30m most strongly and negatively correlated with CMJheight (r = -0.744, r2 = 0.554, p < 0.001). WAnT-determined Pmax showed a very large correlation between absolute Pmax and knee-extensor MVIC (r = 0.827, r2 = 0.684, p < 0.001) and large correlations between absolute Pmax and 1RM half squat (r = 0.674, r2 = 0.454, p < 0.001) and CMJpower (r = 0.579, r2 = 0.335, p < 0.01). We also identified a large inverse relationship between CMJheight and T30m (r = -0.744, r2 = 0.554, p < 0.001) and large positive correlation between CMJheight and MVIC/BM (r = 0.702, p < 0.001). The results demonstrate that elite soccer players with greater lower body strength (quantified by the MVIC of the knee extensor and the 1RM half squat) show better sprint and CMJ performance, suggesting the incorporation of soccer-specific resistance training to develop lower body musculature and therefore maximize sprinting ability. The higher correlation coefficients found between T30m and the physiological and athletic measures compared with T5m promote the use of this sprint distance when assessing performance. The use of relative measures (normalized to body mass) is advisable when comparing strength variables with sprint and CMJ performance or anaerobic power. Considering the correlations of WAnT-determined Pmax versus CMJpower, coaches should administer tests that assess jumping and linear sprint performance rather than the cycling-specific WAnT. 



#9 The Relationship Between Repeated-Sprint Ability, Aerobic Capacity, and Oxygen Uptake Recovery Kinetics in Female Soccer Athletes 

Reference: J Hum Kinet. 2020 Oct 31;75:115-126. doi: 10.2478/hukin-2020-0042. eCollection 2020 Oct. 

Authors: Bruno Archiza, Daniela K Andaku, Thomas Beltrame, Cleiton A Libardi, Audrey Borghi-Silva

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Summary: This study investigated the relationship between repeated-sprint ability, aerobic capacity, and oxygen uptake kinetics during the transition between exercise and recovery (off-transient) in female athletes of an intermittent sport modality. Eighteen professional soccer players completed three tests: 1) a maximal incremental exercise test; 2) a constant speed time-to-exhaustion test; and 3) a repeated-sprint ability test consisting of six 40-m sprints with 20 s of passive recovery in-between. Correlations between time-to-exhaustion, repeated-sprint ability, and oxygen uptake kinetics were calculated afterwards. The level of significance was set at p < 0.05. A performance decrement during repeated-sprint ability was found to be related to: 1) time-to-exhaustion (e.g., exercise tolerance; r = -0.773, p < 0.001); 2) oxygen uptake recovery time (r = 0.601, p = 0.008); and 3) oxygen uptake mean response time of recovery (r = 0.722, p < 0.001). Moreover, the best sprint time (r = -0.601, p = 0.008) and the mean sprint time (r = -0.608, p = 0.007) were found to be related to maximal oxygen uptake. Collectively, these results reinforce the relation between oxygen uptake kinetics and the ability to maintain sprint performance in female athletes. These results may contribute to coaches and training staff of female soccer teams to focus on training and improve their athletes' aerobic capacity and recovery capacity to improve intermittent exercise performance. 



#10 Unilateral Plyometric Training is Superior to Volume-Matched Bilateral Training for Improving Strength, Speed and Power of Lower Limbs in Preadolescent Soccer Athletes

Reference: J Hum Kinet. 2020 Aug 31;74:161-176. doi: 10.2478/hukin-2020-0022. eCollection 2020 Aug. 

Authors: Vasileios Drouzas, Christos Katsikas, Andreas Zafeiridis, Athanasios Z Jamurtas, Gregory C Bogdanis

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Summary: This study compared the effects of unilateral and bilateral plyometric training on strength, sprint performance and lower limb power. Sixty-eight preadolescent soccer athletes were randomly assigned to a unilateral plyometric training group (n=23), a bilateral plyometric training group (n=23) and a control group (n=22). Both plyometric training groups trained with equal volumes of unilateral or bilateral exercises for 15 minutes in each session, at which time the control group performed soccer-specific drills. Plyometric exercises were executed twice weekly for 10 weeks during the competitive season. The following tests were performed before and after the intervention: single-leg and double-leg countermovement jump, squat jump, horizontal jumps in different directions, maximal isometric strength of quadriceps and hamstrings, sprint performance, agility and balance. Unilateral plyometric training resulted in greater improvements compared to the control group in the following variables: hamstrings strength (ES: 0.91, p=0.037), 5m sprint time (ES: 0.93, p=0.004), single-leg countermovement jump (ES: 0.90, p=0.006), single- and double-leg squat jump (ES: 0.87, p=0.030 and ES: 0.73, p=0.067, respectively) and single-leg hop performance (ES: 1.01, p=0.004). The only tests where there was an improvement of BPT compared with the CG were the single-leg and double leg SJ (ES: 0.76, p=0.026; ES: 0.70, p=0.050). Quadriceps strength, side hop test, double-leg horizontal jump test, flamingo balance test and modified agility T-test were equally improved in all three groups (p<0.001). In conclusion, unilateral lower-limb plyometric training is more effective in increasing muscle strength and power in preadolescent soccer players when compared to bilateral training or soccer training alone. 



#11 Effectiveness and time-course adaptation of resistance training vs. plyometric training in prepubertal soccer players

Reference: J Sport Health Sci. 2020 Dec;9(6):620-627. doi: 10.1016/j.jshs.2016.07.008. Epub 2016 Jul 16. 

Authors: Yassine Negra, Helmi Chaabene, Thomas Stöggl, Mehréz Hammami, Mohamed Souhaiel Chelly, Younés Hachana

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Summary: This study aimed to assess the effectiveness and time course for improvements in explosive actions through resistance training (RT) vs. plyometric training (PT) in prepubertal soccer players. Thirty-four male subjects were assigned to: a control group (n = 11); an RT group (5 regular soccer training sessions per week, n = 12); a PT group (3 soccer training sessions and 2 RT sessions per week, n = 11). The outcome measures included tests for the assessment of muscle strength (e.g., 1 repetition maximum half-squat test), jump ability (e.g., countermovement jump, squat jump, standing long jump, and multiple 5 bounds test), linear speed (e.g., 20 m sprint test), and change of direction (e.g., Illinois change of direction test). The RTG showed an improvement in the half-squat (Δ = 13.2%; d = 1.3, p< 0.001) and countermovement jump (Δ = 9.4%; d = 2.4, p< 0.001) at Week 4, whereas improvements in the 20-m sprint (Δ = 4.2%; d = 1.1, p < 0.01); change of direction (CoD) (Δ = 3.8%; d = 2.1, p < 0.01); multiple 5 bounds (Δ = 5.1%; d = 1.5, p < 0.05); standing long jump (Δ = 7.2%; d = 1.2, p < 0.01); squat jump (Δ = 19.6%; d = 1.5, p < 0.01); were evident at Week 8. The PTG showed improvements in CoD (Δ = 2.1%; d = 1.3, p< 0.05); standing long jump (Δ = 9.3%; d = 1.1, p< 0.01); countermovement jump (Δ = 16.1%; d = 1.2, p< 0.01); and squat jump (Δ = 16.7%; d = 1.4, p< 0.01); at Week 8 whereas improvements in the 20-m sprint (Δ = 4.1%; d = 1.3, p < 0.01); and multiple 5 bounds (Δ = 7.4%; d = 2.4, p< 0.001); were evident only after Week. The RT and PT groups showed improvements in all sprint, CoD, and jump tests (p< 0.05) and in half-squat performance, for which improvement was only shown within the RTG (p< 0.001). RT and PT conducted in combination with regular soccer training are safe and feasible interventions for prepubertal soccer players. In addition, these interventions were shown to be effective training tools to improve explosive actions with different time courses of improvements, which manifested earlier in the RTG than in the PTG. These outcomes may help coaches and fitness trainers set out clear and concise goals of training according to the specific time course of improvement difference between RT and PT on proxies of athletic performance of prepubertal soccer players. 



#12 Morphological changes of the lateral abdominal muscles in adolescent soccer players with low back pain: A prospective cohort study 

Reference: J Sport Health Sci. 2020 Dec;9(6):614-619. doi: 10.1016/j.jshs.2018.02.002. Epub 2018 Mar 7. 

Authors: Pawel Linek, Pardis Noormohammadpour, Mohammad Ali Mansournia, Tomasz Wolny, Damian Sikora

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Summary: Most papers examining the lateral abdominal muscles (LAMs) and low back pain (LBP) are cross-sectional, with groups of participants being divided into a control and an LBP group. We hypothesized that morphological measurements of the LAMs in adolescent soccer players may predict future LBP incidence. The aim of this study was to examine the associations between the morphology of LAMs and LBP incidence rate among adolescent soccer players. Ninety-seven adolescent male soccer players with no LBP at baseline were recruited into the prospective cohort study. The thickness of the LAMs was measured at baseline by ultrasound imaging in a supine rest position. Nine cases of LBP occurred during the follow-up 6-month observation. An obliquus internus (OI) asymmetry was related to increasing LBP risk (odds ratio = 19.99; 95%CI: 2.4-167.9). Spearman correlation also showed a linear relationship between OI asymmetry value and duration of LBP (R = 0.75, p = 0.02). An OI side-to-side difference greater than 1.25 mm suggests possible LBP incidence in the 6-month observation among adolescent soccer players. The morphological changes of the OI may be related to LBP's incidence in adolescent soccer players. The presence of OI asymmetry increases the odds of LBP by at least 2.4 times. Hypertrophy of the OI on one side of the body may contribute to trunk muscle imbalance. 



#13 The professional contribution of chiropractors to Danish elite football clubs: a qualitative exploration of role and perceived value in an interprofessional service provision context

Reference: Chiropr Man Therap. 2020 Dec 18;28(1):69. doi: 10.1186/s12998-020-00358-x. 

Authors: Joachim Hostrup, Anders Koza, Corrie Myburgh

Summary: Interprofessional team-based care has been widely adopted in elite level athletic health and performance practice. Chiropractors can claim some penetration as health care service providers in high level sport. However, their position as valued members of interprofessional health care teams, especially those built around traditional medical organisational structures, is unclear. This investigation sought to explore the perceived role and value of chiropractors as service providers in elite Danish football clubs. A comparative qualitative case study was conducted. Six Danish premiere league (Superliga) clubs were purposively sampled to compare and contrast instances where chiropractors were both present and absent from the health care team. Triangulated responses were solicited from healthcare coordinators, chiropractors and athletes within each club's organization through semi-structured individual interviews. The audio-recorded responses were transcribed verbatim and thematically analyzed using a framework approach. Data were collected September and November 2019. A coding framework of 14 codes and 4 code families emerged, centering around the role of chiropractors, benefits of utilizing chiropractic care and facilitators and barriers to interprofessional practice. From this framework, three themes were abstracted, these being: "Broadening horizons", "In-house preferred to take-away" and "Already covered, or even necessary?" In this practice context, chiropractors fill the role of musculoskeletal health care service providers. Their perceived value stems from additional expert disciplinary knowledge, improved diagnostic triage and increased treatment flexibility. However, where not utilized, the role of a spinal health expert is questioned and when acknowledged, is limited to that of a technician/therapist. It is unclear from this investigation whether chiropractors can claim core provider status. Further exploration of this interesting context of interprofessional practice is warranted. 



#14 The Relationships between Internal and External Load Measures for Division I College Football Practice

Reference: Sports (Basel). 2020 Dec 15;8(12):E165. doi: 10.3390/sports8120165. 

Authors: Eric J Sobolewski

Summary: The aim of this study is to explore the relationships between internal and external load measures in American football. Thirty football players wore a portable integrated monitor unit for 10 weeks during the fall football season. Relationships between internal and external load measurements were determined. Internal load consisted of heart rate zones and heart rate-derived measures and session Ratings of Perceived Exertion (sRPE). External load consisted of distance in different speed zones, total distance traveled, and accelerations. There were many significant positive relationships, but the meaningful relationships (r > 0.5) were between heart rate-derived measures of load (Training Impulse and heart rate reserve) and low-intensity movement and total distance. Only accelerations between 1 and 1.99 m·s-2 were moderately correlated to heart rate-derived internal load. RPE values alone did not correlate strong enough with any of the measure but sRPE training load (sRPE-TL) correlated to most external values. Overall, moderate correlations were present between heart rate-derived internal load to total distance and lower intensity movement. sRPE-TL values had high correlations but were highly dependent on duration, not perceived exertion. When addressing load in American football, duration of the session is a key component in determining internal load as HR data and sRPE alone do not correlate highly with external loads. 



#15 Association of high profile football matches in Europe with traffic accidents in Asia: archival study

Reference: BMJ. 2020 Dec 16;371:m4465. doi: 10.1136/bmj.m4465. 

Authors: Kai Chi Yam, Joshua Conrad Jackson, Jenson Lau, Xin Qin, Christopher M Barnes, Juin-Kuan Chong

Summary: The aim was to investigate the association between popular football games played in Europe and the incidence of traffic accidents in Asia. Study based on 41 538 traffic accidents involving taxis in Singapore and 1 814 320 traffic accidents in Taiwan, combined with 12 788 European club football games over a seven year period. The largest taxi company in Singapore, with fine grained traffic accident records in a three year span; all traffic accident records in Taiwan in a six year span. Days when high profile football games were played or not played. Number of traffic accidents was choosen as the main outcome measure. Regression based and time series models suggest that days with high profile European football matches were more positively associated with traffic accidents than days with less popular European football matches. For an approximate €134.74m (£120.25m; $159.76m) increase in average market value for matches played on a given day, approximately one extra accident would occur among Singapore taxi drivers, and for an approximate €7.99m increase in average market value of matches, approximately one extra accident would occur among all drivers in Taiwan. This association remained after control for weather conditions, time of the year, weekend versus weekday effects, driver demographics, and underlying temporal trends. It was also stronger for daytime traffic accidents than for night time traffic accidents, suggesting that the association between high profile football matches and traffic accidents cannot be attributed to night time celebration or attention deficits while watching and driving. Annually, this increased rate of traffic accidents may translate to approximately 371 accidents among taxi drivers in Singapore and approximately 41 079 accidents among the Taiwanese public, as well as economic losses of approximately €821 448 among Singapore taxi drivers and approximately €13 994 409 among Taiwanese drivers and insurers. The total health and economic impact of this finding is likely to be much higher because GMT+8 is the most populous time zone, encompassing 24% of the world's population. 

Conclusions: Days featuring high profile football matches in Europe were associated with more traffic accidents in Taiwan and Singapore than were days with lower profile football matches. A potential causal mechanism may be Asian drivers losing sleep by watching high profile European matches, which are often played in the middle of the night in Asia. 



#16 Neurocognitive performance and mental health of retired female football players compared to non-contact sport athletes 

Reference: BMJ Open Sport Exerc Med. 2020 Dec 3;6(1):e000952. doi: 10.1136/bmjsem-2020-000952. eCollection 2020. 

Authors: Annika Prien, Nina Feddermann-Demont, Evert Verhagen, Jos Twisk, Astrid Junge

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Summary: Adverse long-term effects of playing football due to repetitive head impact exposure on neurocognition and mental health are controversial. To date, no studies have evaluated such effects in women. The aim was to (1) compare neurocognitive performance, cognitive symptoms and mental health in retired elite female football players (FB) with retired elite female non-contact sport athletes (CON), and to (2) assess whether findings are related to history of concussion and/or heading exposure in FB. Neurocognitive performance, mental health and cognitive symptoms were assessed using computerised tests (CNS-vital signs), paper pen tests (Category fluency, Trail-Making Test, Digit Span, Paced Auditory Serial Addition Test), questionnaires (Hospital Anxiety and Depression Scale, SF-36v2 Health Survey) and a symptom checklist. Heading exposure and concussion history were self-reported in an online survey and in a clinical interview, respectively. Linear regression was used to analyse the effect of football, concussion and heading exposure on outcomes adjusted for confounders. FB (n=66) performed similar to CON (n=45) on neurocognitive tests, except for significantly lower scores on verbal memory (mean difference (MD)=-7.038, 95% CI -12.98 to -0.08, p=0.038) and verbal fluency tests (MD=-7.534, 95% CI -13.75 to -0.46, p=0.016). Among FB weaker verbal fluency performance was significantly associated with ≥2 concussions (MD=-10.36, 95% CI -18.48 to -2.83, p=0.017), and weaker verbal memory performance with frequent heading (MD=-9.166, 95% CI -17.59 to -0.123, p=0.041). The depression score differed significantly between study populations, and was significantly associated with frequent heading but not with history of concussion in FB. 

Conclusion: Further studies should investigate the clinical relevance of our findings and whether the observed associations point to a causal link between repetitive head impacts and verbal memory/fluency or mental health. 






Recovery Kinetics Following Small-Sided Games in Competitive Soccer Players: Does Player Density Size Matter?

The aim was to examine the recovery kinetics of exercise-induced muscle damage, neuromuscular fatigue and performance following small-sided games of different densities in football.





Effects of Plyometric Training with Agility Ladder on Physical Fitness in Youth Soccer Players

The aim was to assess the effects of plyometric training with an agility ladder on components of physical fitness in youth footballers.





Latest research in football - week 6 - 2021

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 Physical Demands of U10 Players in a 7-a-Side Soccer Tournament Depending on the Playing Position and Level of Opponents in Consecutive Matches Using Global Positioning Systems (GPS)

Reference: Sensors (Basel). 2020 Dec 6;20(23):6968. doi: 10.3390/s20236968. 

Authors: Antonio Hernandez-Martin, Javier Sanchez-Sanchez, Jose Luis Felipe, Samuel Manzano-Carrasco, Carlos Majano, Leonor Gallardo, Jorge Garcia-Unanue 

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Summary: The aim of this study was to analyse the physical demands of U10 players in a 7-a-side-soccer tournament based on the playing positions in 6 consecutive matches by global positioning systems (GPS). Variables of total distance, relative distance in different speed zones, maximum speed, time interval between accelerations, maximum speed acceleration, maximum acceleration, acceleration distance and the number of high-intensity accelerations were analysed. Differences between playing positions were found in the total distance covered by the midfielders. They covered higher total distances than the defenders (+1167 m; 95% CI: 411 to 1922 m; effect size (ES) = 1.41; p < 0.05) and forwards (+1388 m; CI 95%: 712 a 2063 m; TE = 0.85; p < 0.05). The total covered distance increased in the final rounds with respect to the group stage (p < 0.05; ES: 0.44 to 1.62), and high-intensity actions, such as the number of accelerations, were greater in the final rounds compared to the group stage (p < 0.05; ES: 0.44 to 1.62). The physical performance of young football players in a tournament with consecutive matches on a 40 × 62 m football field on the same day is influenced by the playing position and dependent on the level difference between opponents. 



#2 Evaluating the validity of self-report as a method for quantifying heading exposure in male youth soccer 

Reference: Res Sports Med. 2020 Dec 6;1-13. doi: 10.1080/15438627.2020.1853541. Online ahead of print. 

Authors: Stian B Sandmo, Jolien Gooijers, Caroline Seer, David Kaufmann, Roald Bahr, Ofer Pasternak, Michael L Lipton, Yorghos Tripodis , Inga K Koerte

Summary: Assessing heading exposure in football is important when exploring the association between heading and brain alterations. To this end, questionnaires have been developed for use in adult populations. However, the validity of self-report in adolescents remains to be elucidated. Male youth soccer players (n = 34) completed a questionnaire on heading exposure after a two-week period, which included matches and training sessions. Self-reported numbers were compared to observation (considered reference). In total, we observed 157 training sessions and 64 matches. Self-reported heading exposure correlated with observed heading exposure (Spearman's rho 0.68; p < 0.001). Players systematically overestimated their heading exposure by a factor of 3 with the random error of 46%. Area under the curve was 0.87 (95% CI 0.67-1) utilizing self-report for identifying players from high- and low-exposure groups. Thus, in this study, self-reported data could be used to group youth players into high and low heading exposure groups, but not to quantify individual heading exposure. 



#3 Prevalence of SARS-CoV-2 IgG antibodies in a large prospective cohort study of elite football players in Germany (May-June 2020): implications for a testing protocol in asymptomatic individuals and estimation of the rate of undetected cases

Reference: Clin Microbiol Infect. 2020 Dec 4;S1198-743X(20)30729-1. doi: 10.1016/j.cmi.2020.11.033.

Authors: Dietrich Mack, Barbara Christine Gärtner, Annika Rössler, Janine Kimpel, Katrin Donde, Oliver Harzer, Werner Krutsch, Dorothee von Laer, Tim Meyer

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Summary: Elite professional football players and staff are a unique group that might give insight into the epidemiology of SARS-CoV-2 infections in Germany and thus can serve as a model for a geographical distribution and an estimation of undetected infections. In this prospective cohort study seroprevalence was determined twice in May and June 2020 in players and staff from German Bundesliga. As screening assays a commercial ELISA (Euroimmun) and a CLIA (Roche) was used and an in-house neutralisation assay (NT) as gold standard. Participants were tested twice weekly using PCR from nasopharyngeal and/or oropharyngeal swabs. Seroprevalence (NT used as confirmation) in 2,164 samples from 1,184 players and staff was rather similar in May (23/1157 (1.99%)) and in June (21/1007 (2.09%)). All participants were PCR negative during the study period. Significant regional differences in seroprevalence were not observed. When comparing seroprevalence with the cumulative incidence of infections derived from the German notification system (subgroup matching to cohort; men, age: 20-69), IgG was found 8-10 times more frequently, pointing to a high rate of undetected infections. ELISA and CLIA correlated only moderately (Kappa 0.52). Seroprevalence with high quality diagnostic in Germany seemed to be around 2%. The number of undetected infections seems to be 8-10 times higher than notification data. Quality of antibody assays is rather variable, thus results should ideally be confirmed at least by a second assay to prove IgG positivity. 



#4 Are Die-Hard Football or Other Sports Fans at Risk of Cardiovascular Events? 

Reference: Curr Probl Cardiol. 2020 Nov 2;100743. doi: 10.1016/j.cpcardiol.2020.100743. Online ahead of print. 

Authors: Miguel A Maturana, Elizabeth A Glover, Joel Raja, Sean R Dornbush, John Alexander, Courtland Blount, Nadim R Khouzam, Amir R Khouzam, Rami N Khouzam

Summary: Trigger factors such as earthquakes, war, and terrorism have been shown to increase the risk of cardiovascular events in different studies. Similarly, strong emotions and psychological stress have been associated with myocardial infarction, symptomatic arrhythmias, and sudden cardiac death. Die-hard soccer, rugby, football, and baseball fans seem to be at risk of cardiac events, particularly in individuals with prior history of coronary artery disease. Transient hemodynamic changes, endothelial dysfunction, and an overwhelming sympathetic nervous system stimulation appear to affect cardiac hemostasis creating a procoagulant and arrhythmogenic environment. High-risk behaviors such as tobacco abuse and binge drinking appear to contribute to this risk generating a proinflammatory state characterized by elevated levels of endothelin-1 and overexpression of sCD40L, sVCAM-1, MCP-1, and TNF-alpha. The outcome of the game and unexpected results, especially among fans of the defeated team, seem to further correlate with adverse cardiovascular effects. 



#5 The incidence and mechanism of heading in European professional football players over three seasons

Reference: Scand J Med Sci Sports. 2020 Dec 6. doi: 10.1111/sms.13900. Online ahead of print. 

Authors: Gregory J Tierney, Barry Higgins

Summary: There are concerns surrounding the risk of neurodegenerative diseases associated with football (soccer) heading. The aim of this study was to conduct analysis on the incidence and mechanism of heading in the "Big 5" professional European football leagues (Bundesliga, Ligue 1, Premier League, La Liga and Serie A) and one lower tier professional league (English Championship) from 2016/17-2018/19. Match event data from 7147 matches were obtained from Opta Sports data feed. The data were parsed to extract header event details including player position, coordinates on the field, header type and preceding match event (including distance football travelled). Incidence data were reported as headers per match or match headers per player. Medians and interquartile ranges (IQR) were reported and either the Mann-Whitney U-Test or Kruskal-Wallis test were conducted for comparisons between positions and leagues. In the "Big 5" leagues, the most headers per match occurred during the Premier League (111.2 headers per match). However, the lower tier English Championship had the highest number of headers per match overall (139.0 headers per match). In all leagues, defenders had the greatest median number of match headers per player (p<0.001). The highest median distance travelled by the football during a preceding match event was for goal kicks (57.5 m; IQR 53.7-61.1). The findings add necessary information for current longitudinal studies aiming to understand the potential link between football heading and neurodegenerative diseases. These studies should account for league, playing position and level of play. 



#6 Post-match recovery of eccentric knee flexor strength in male professional football players

Reference: Phys Ther Sport. 2020 Nov 25;47:140-146. doi: 10.1016/j.ptsp.2020.11.032. Online ahead of print. 

Authors: César Augusto Bueno, João Breno de Araujo Ribeiro-Alvares, Gabriel Dos Santos Oliveira, Rafael Grazioli, Filipe Veeck, Ronei Silveira Pinto, Eduardo Lusa Cadore, Bruno Manfredini Baroni

Summary: This study aimed at verifying the effect of a football match on the eccentric knee flexor strength of male professional players along a 72-h period. Fifteen players were assessed in four timepoints: 24 h before, immediately after, 48 h and 72 h after the match. The eccentric knee flexor strength was assessed during the Nordic hamstring exercise execution. Players presented a significant strength reduction immediately after match (Δ = 12%; p = 0.001; large effect size, d = 1.10), and did not recover their strength capacity within a 48 h-period (Δ = 6%; p = 0.011; moderate effect size, d = 0.57). At 72 h after the match, strength was similar to baseline levels (Δ = 3.5%; p = 0.122; small effect size, d = 0.34). Secondarily, individual response analysis considered a player 'fully recovered' when his strength deficit compared to the baseline measure was lower than the measurement coefficient of variation (i.e., <5%). Only 6 (40%) and 9 (60%) players were 'fully recovered' at 48 h and 72 h after the match, respectively. Professional football players experienced an immediately post-match drop on the eccentric knee flexor strength, and significant strength deficits persisted for a 48-h period. Some players were not recovered at 72 h after the match. 



#7 Radiological (Magnetic Resonance Image and Ultrasound) and biochemical effects of virtual reality training on balance training in football players with chronic low back pain: A randomized controlled study

Reference: J Back Musculoskelet Rehabil. 2020 Nov 27. doi: 10.3233/BMR-191657. Online ahead of print. 

Authors: Gopal Nambi, Walid Kamal Abdelbasset, Bader A Alqahatani 

Summary: Virtual reality training is commonly used for balance problems in neurological conditions with the use of visual and auditory biofeedback. The knowledge about the effective implementation of this training in chronic low back pain is lacking. The objective of this study is to find the radiological and biochemical effects of virtual reality training in football players with chronic low back pain. A randomized, single-blinded controlled study was conducted on 36 participants. The first group received virtual reality training (VRT; n= 12), the second group received combined physical rehabilitation (CPR; n= 12), and the third group (control group; n= 12) received conventional training exercises for four weeks. Radiological (muscle cross-sectional area and muscle thickness) and biochemical (CRP, TNF-α, IL-2, IL-4, IL-6) values were measured at baseline and after four weeks. Four weeks following training, the VRT group showed more significant changes in the muscle cross-sectional area than the CPR and control groups (p 0.001). Biochemical measures such as CRP, TNF-α, IL-2, IL-4, and IL-6 also showed significant improvement in the VRT group compared to the other two groups (p 0.001). The results show that virtual reality training has positive effects on the radiological and biochemical aspects in university football players with chronic low back pain. 



#8 What Is the Relevance in the Passing Action between the Passer and the Receiver in Soccer? Study of Elite Soccer in La Liga

Reference: Int J Environ Res Public Health. 2020 Dec 15;17(24):E9396. doi: 10.3390/ijerph17249396. 

Authors: Antonio Cordón-Carmona, Abraham García-Aliaga, Moisés Marquina, Jorge Lorenzo Calvo, Daniel Mon-López, Ignacio Refoyo Roman 

Summary: Soccer is a high-complexity sport in which 22 players interact simultaneously in a common space. The ball-holder interacts with their teammates by passing actions, establishing a unique communication among them in the development of the game in its offensive phase. The main aim of the present study was to analyze the pass action according to the trajectory of the ball receiver and the space for receiving the ball in terms of success at the end of play. Twenty La Liga 2018/2019 matches of two elite teams were analyzed. A system of notational analysis was used to create 11 categories based on context, timing and pass analysis. The data were analyzed using chi-squared analysis. The results showed that the main performance indicators were the efficiency of the pass, the zone of the field, the trajectory of the receiver and the reception space of the ball, which presented a moderate association with the end of play (p < 0.001). We concluded that receiving the ball on approach and in separation increased the probability of success by 5% and 7%, respectively, and a diagonal run increased the probability by 7%. Moreover, the combined analysis of these variables would improve the team performance. 



#9 Can Talented Youth Soccer Players Who Have Undergone Anterior Cruciate Ligament Reconstruction Reach the Elite Level?

Reference: Am J Sports Med. 2020 Dec 17;363546520976651. doi: 10.1177/0363546520976651. 

Authors: Alexander Sandon, Tor Söderström, Andreas Stenling, Magnus Forssbla

Summary: Anterior cruciate ligament (ACL) ruptures are common in soccer players, and reconstructive surgery is often performed to restore knee stability and enable a return to play. The purpose was to investigate whether an ACL reconstruction for talented youth soccer players affects their potential to become elite players at the senior level. All soccer players who participated in the Swedish National Elite Camp for 15-year-old players between 2005 and 2011 (N = 5285 players; 2631 boys and 2654 girls) were matched with the Swedish National Knee Ligament Registry to identify the players who had undergone ACL reconstruction. Information on player participation in Swedish league games and level of play was collected from the Swedish Football Association's administrative data system. The players with an ACL reconstruction who were injured at the ages of 15 to 19 years were compared with the rest of the players who participated in the National Elite Camp to see whether an early ACL reconstruction affected whether they remained active as soccer players and their chance to play at the elite level as seniors. A total of 524 (9.9%) players had undergone an ACL reconstruction, and 292 (5.5%; 75 male and 217 female) had sustained their injury at age 15 to 19 years. During the follow-up period, 122 (23.3%) players underwent ACL reconstruction: revision (11.5%; n = 60) or contralateral (11.8%; n = 62). Male and female soccer players undergoing an ACL reconstruction at age 15 to 19 years experienced no significant effect on being active or playing at the elite level in the season that they turned 21 years old. Of the youth players who underwent ACL reconstruction, 12% of the male players and 11.5% of the female players progressed to the elite level at the age of 21 years compared with 10.3% of the men and 11.1% of the women among the uninjured players. ACL reconstructive surgery in talented youth soccer players offers them the opportunity to become elite players as seniors and permits an activity level on a par with that of their uninjured peers. However, almost 1 in 4 requires further ACL surgery, so the players' future knee health should be considered when deciding on a return to play. 



#10 Acute Effects of Warm-Up, Exercise and Recovery-Related Strategies on Assessments of Soccer Kicking Performance: A Critical and Systematic Review 

Reference: Sports Med. 2020 Dec 17. doi: 10.1007/s40279-020-01391-9. Online ahead of print. 

Authors: Luiz H Palucci Vieira, Felipe B Santinelli, Christopher Carling, Eleftherios Kellis, Paulo R P Santiago, Fabio A Barbieri

Summary: A number of reviews have collated information on the impact of warming-up, physical exertion and recovery strategies on physical, subjective and physiological markers in soccer players yet none have solely analyzed their potential effects on components of kicking performance. The purpose was to systematically analyse the influence of warm-up, exercise and/or recovery-related strategies on kicking performance in male soccer players and provide a critical appraisal on research paradigm related to kicking testing constraints and data acquisition methods. A systematic literature search was performed (until July 2020) in PubMed, Web of Science, SPORTDiscus, Scopus and ProQuest. Studies in male soccer populations, which included the effects of warm-up routines, physical exercise and/or recovery-related interventions, reported on comparisons pre-post or between experimental conditions and that computed at least one measure of kicking kinematics and/or performance were considered. Methodological quality and risk of bias were determined for the included studies. Constraints related to kicking testing and data acquisition methods were also summarized and discussed. Altogether, 52 studies were included. Of these, 10 examined the respective effects of a warm-up, 34 physical exercise, and 21 recovery-related strategies. The results of eight studies showed that lower limb kinematics, kicking accuracy or ball velocity were improved following warm-ups involving dynamic but not static stretching. Declines in ball velocity occurred notably following intermittent endurance or graded until exhaustion exercise (three studies in both cases) without inclusion of any ball skills. In contrast, conflicting evidence in five studies was observed regarding ball velocity following intermittent endurance exercise interspersed with execution of ball skills. Kicking accuracy was less frequently affected by physical exercise (remained stable across 14 of 19 studies). One investigation indicated that consumption of a carbohydrate beverage pre- and mid-exercise demonstrated benefits in counteracting the potentially deleterious consequences of exercise on ball velocity, while four studies reported conflicting results regarding kicking accuracy. Most evidence synthesized for the interventions demonstrated moderate level (77%) and unclear-to-high risk of bias in at least one item evaluated (98%). The main limitations identified across studies were kicks generally performed over short distances (50%), in the absence of opposition (96%), and following experimental instructions which did not concomitantly consider velocity and accuracy (62%). Also, notational-based metrics were predominantly used to obtain accuracy outcomes (54%). The results from this review can help inform future research and practical interventions in an attempt to measure and optimise soccer kicking performance. However, given the risk of bias and a relative lack of strong evidence, caution is required when applying some of the current findings in practice. 



#11 Running patterns and force-velocity sprinting profiles in elite training young soccer players: A Cross-Sectional Study

Reference: Eur J Sport Sci. 2020 Dec 17;1-25. doi: 10.1080/17461391.2020.1866078. Online ahead of print. 

Authors: Qingshan Zhang, Félicie Pommerell, Adam Owen, Robin Trama, Cyril Martin, Christophe A Hautier

Summary: The Volodalen® field method permits to classify runners into aerial or terrestrial, based on vertical oscillation, upper-body motion, pelvis and foot position at ground contact, and foot strike pattern. The present study aimed to compare the sprint running force-velocity profiles between aerial and terrestrial runners. Sixty-Four French National-Level young soccer players (28 females, 36 males) performed three trials of unloaded maximal 40m sprints. External horizontal power-force-velocity relationships were computed using a validated biomechanical model and based on the velocity-time curve. Accordingly, the participants were classified into patterns in aerial and terrestrial runners. Terrestrial runners showed a higher maximal horizontal force (F 0) (6.73 ± 1.03 vs 6.01 ± 0.94 N·kg-1), maximal horizontal power (P max) (14.04 ± 3.24 vs 12.51 ± 3.31), maximal acceleration (Acc) (6.83 ± 0.85 vs 6.26 ± 0.89 m·s-2), and maximal rate of horizontal force (RF max) (57.41 ± 4.64 vs 52.81 ± 5.69 %) compared to aerial runners. In contrast, terrestrial runners displayed a more negative rate of decrease of RF (D RF) (-11.65 ± 1.71 vs -10.23 ± 1.66 %) and slope of the Force-Velocity relationship (F-V slope) (-0.83 ± 0.11 vs -0.77 ± 0.10 N·s·m-1·kg-1) than aerial runners. The results indicate that terrestrial runners displayed more efficient force production in the forward direction and displayed more "force-oriented" F-V profiles. Nevertheless, aerial runners were more effective in maintaining a net horizontal force production with increasing speed. Our results suggest that terrestrial runners could be more adapted to the specific short distance and high acceleration sprints running. 



#12 Variability of professional soccer players' perceived match load after successive matches 

Reference: Res Sports Med. 2020 Dec 17;1-15. doi: 10.1080/15438627.2020.1856104. Online ahead of print. 

Authors: Unai Azcárate, Asier Los Arcos, Javier Yanci

Summary: This study analyses the differential perceived match load accumulated by professional soccer players depending on their: (a) participation in several consecutive official matches within the same week (Pre_Cup, Cup, and Post_Cup), and (b) total match participation time (i.e. 90 min, 70-90 min and < 70 min). Participants were 21 Spanish Second Division professional soccer players (M age = 27.1, SD = 3.3 years; M body height = 182.1, SD = 3.9 cm; M body mass = 75.8, SD = 5.14 kg). There were no significant differences (p > 0.05) in dRPE-ML among Pre_Cup, Cup and Post_Cup matches or in dRPE-ML between teams that took part in two or three official matches within the same week or three official matches in 2-4 consecutive weeks. The results suggest that participating in several matches in the same week does not increase accumulated perceived exertion for professional soccer players. 



#13 The Relationship between Motivational Climate and Personal Treatment Satisfaction among Young Soccer Players in Norway: The Moderating Role of Supportive Coach-Behaviour

Reference: Sports (Basel). 2020 Dec 12;8(12):E162. doi: 10.3390/sports8120162. 

Authors: Tommy Haugen, Jan F Riesen, Ketil Østrem, Rune Høigaard, Martin K Erikstad

Summary: Motivational climate and coach-behaviour seem important to understand sport involvement and participation. However, less is known about the potential interaction between these facets, and how it relates to athlete satisfaction. This study's purpose is to examine the relationship between the perceived motivational climate, supportive coach-behaviour, and athletes' personal treatment satisfaction among young soccer players. More specifically, we investigated the moderating effect of supportive coach-behaviour on the relationship between motivational climate and personal treatment satisfaction. Five hundred and thirty-two players (Mean age = 15.4 years, SD = 1.2) attending a Norwegian national soccer tournament participated in the study. Self-completion questionnaires were used to attain data. A linear regression analysis revealed that mastery of climate and supportive coach-behaviour were positively associated with personal treatment satisfaction. A negative association was found between performance climate and personal treatment satisfaction. Further, moderation analyses revealed that supportive coach-behaviour moderated the relationship between performance climate and personal treatment satisfaction. The findings indicate that a performance climate may not be as maladaptive when coaches provide supportive behaviour. The findings highlight the value of a further examination of the interaction between motivational climate and coaching behaviours, and its potential relations to young athlete's sport experience. 



#14 Position Specific Running Performances in Professional Football (Soccer): Influence of Different Tactical Formations

Reference: Sports (Basel). 2020 Dec 10;8(12):E161. doi: 10.3390/sports8120161. 

Authors: Toni Modric, Sime Versic, Damir Sekulic 

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Summary: Running performances (RPs) are known to be important parameters of success in football (soccer), but there is a lack of studies where RPs are contextualized regarding applied tactical solutions. This study aims to quantify and analyze the differences in position-specific RPs in professional football, when games are played with three defensive players (3DP) and four defensive players (4DP). The participants here include professional football players (M ± SD, age 23.57 ± 2.84 years, body height 181.9 ± 5.17 cm, body mass 78.36 ± 4.18 kg) playing at the highest competitive level in Croatia. RPs were measured by global positioning system and classified into four groups based on playing positions: central defenders (CD; n = 47), wide defenders (WD; n = 24), midfielders (MF; n = 48), or forwards (FW; n = 19). Analysis of variance and discriminant canonical analysis are used to identify differences between 3DP and 4DP tactical solutions in terms of the RPs for each playing position. The number of accelerations and decelerations most significantly contributed to the differentiation of 3DP and 4DP among MFs (Wilks λ = 0.31, p < 0.001), with higher occurrences with 3DP. For CDs, total distance, and high-intensity running were higher in 3DP (Wilks λ = 0.66, p < 0.001). No multivariate differences were found for FW and WD players in terms of the RPs between 3DP and 4DP tactical formations. The characteristics and differences shown in this study may provide useful information for coaching staff regarding changing in-season tactical formations. Additionally, the results are useful for optimizing training programs for football players with different playing positions. When changing from 4DP to 3DP tactical formations, WDs training programs should include more of high-intensity running, while MFs training programs should be more based on short intensity activities (accelerations and decelerations). 



#15 A New Approach for Training-load Quantification in Elite-level Soccer: Contextual Factors

Reference: Int J Sports Med. 2020 Dec 15. doi: 10.1055/a-1289-9059. Online ahead of print. 

Authors: Berni Guerrero-Calderón, Maximilian Klemp, Alfonso Castillo-Rodriguez, José Alfonso Morcillo, Daniel Memmert

Summary: The aims of this study were to analyse the physical responses of professional soccer players during training considering the contextual factors of match location, season period, and quality of the opposition; and to establish prediction models of physical responses during training sessions. Training data was obtained from 30 professional soccer players from Spanish La Liga using global positioning technology (N=1365 performances). A decreased workload was showed during training weeks prior to home matches, showing large effects in power events, equivalent distance, total distance, walk distance and low-speed running distance. Also, the quality of the opposition also affected the training workload (p<0.05). All regression-models showed moderate effects, with an adjusted R2 of 0.37 for metabolic-work, 0.34 for total distance covered, 0.25 for high-speed running distance (18-21 km·h-1), 0.29 for very high-speed running distance (21-24 km·h-1), 0.22 for sprint running distance (>24 km·h-1) and 0.34 for equivalent distance. The main finding of this study was the great association of match location, season period and quality of opposition on the workload performed by players in the training week before the match; and the development of workload prediction-models considering these contextual factors, thus proposing a new and innovative approach to quantify the workload in soccer. 



#16 Body temperature and physical performance responses are not maintained at the time of pitch-entry when typical substitute-specific match-day practices are adopted before simulated soccer match-play

Reference: J Sci Med Sport. 2020 Nov 30;S1440-2440(20)30835-5. doi: 10.1016/j.jsams.2020.11.013. 

Authors: Samuel P Hills, Hendrickus G J Aben, David P Starr, Liam P Kilduff, Shawn M Arent, Martin J Barwood, Jon N Radcliffe, Carlton B Cooke, Mark Russell

Summary: The purpose was to profile performance and physiological responses to typical patterns of match-day activity for second-half soccer substitutes. Following a warm-up, 13 male team sports players underwent 85min of rest, punctuated with five min rewarm-ups at 25, 50, and 70min, before 30min of simulated soccer match-play. Countermovement jump performance (jump height, peak power output), alongside 15m sprints, were assessed post-warm-up, and pre- and post-simulated match-play. Core temperature, heart rate, ratings of perceived exertion, and blood glucose and lactate concentrations were measured throughout. Warm-up-induced core temperature elevations (2.3%, +0.85°C; p<0.001) were maintained until after the first rewarm-up. Thereafter, core temperature was reduced from post-warm-up values until pre-simulated match-play (1.6%, -0.60°C; p<0.001), where values were similar to pre-warm-up (37.07±0.24°C, p=0.981). Simulated match-play increased core temperature progressively (p≤0.05) but values remained lower than post-warm-up (5min; p=0.002) until 10min into exercise. From post-warm-up to pre-simulated match-play, sprint times (3.9%, +0.10s, p=0.003), jump height (9.4%, -3.1cm; p=0.017), and peak power output (7.2%, -296W; p<0.001) worsened. Despite increased ratings of perceived exertion and elevated blood lactate concentrations (p≤0.05), sprint times were maintained throughout exercise, whereas peak power increased (7.8%, +294W; p=0.006) pre- to post-exercise. At the point of simulated pitch-entry, body temperature and physical performance responses were not maintained from warm-up cessation despite typical substitute-specific match-day practices being employed in thermoneutral conditions. Evidence of performance-limiting fatigue was absent during 30min of simulated match-play. These data question the efficacy of practices typically implemented by substitutes before pitch-entry. 






Processing visual information in elite junior soccer players: Effects of age and training experience on visual perception, attention and decision making

The aim was to examine the effects of chronological age and training experience on perception, attention and decision making in young footballer.





Session-to-session variations of internal load during different small-sided games: a study in professional soccer players

The aim was to analyse variations of internal load across small sided games in professional soccer. 





Latest research in football - week 5 - 2021

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 Implementing High-speed Running and Sprinting Training in Professional Soccer

Reference: Int J Sports Med. 2020 Dec 8. doi: 10.1055/a-1302-7968. Online ahead of print. 

Authors: Marco Beato, Barry Drust, Antonio Dello Iacono

Summary: High-speed running and sprinting training play an important role in the development of physical capabilities, sport-specific performance and injury prevention among soccer players. This commentary aims to summarize the current evidence regarding high-speed running and sprinting training in professional soccer and to inform its implementation in research and applied settings. It is structured into four sections: 1) Evidence-based high-speed running and sprinting conditioning methodologies; 2) Monitoring of high-speed running and sprinting performance in soccer 3) Recommendations for effective implementation of high-speed running and sprinting training in applied soccer settings; 4) Limitations and future directions. The contemporary literature provides preliminary methodological guidelines for coaches and practitioners. The recommended methods to ensure high-speed running and sprinting exposure for both conditioning purposes and injury prevention strategies among soccer players are: high-intensity running training, field-based drills and ball-drills in the form of medium- and large-sided games. Global navigation satellite systems are valid and reliable technologies for high-speed running and sprinting monitoring practice. Future research is required to refine, and advance training practices aimed at optimizing individual high-speed running and sprinting training responses and associated long-term effects. 



#2 The association between perceptual-cognitive processes and response time in decision making in young soccer players

Reference: J Sports Sci. 2020 Dec 7;1-10. doi: 10.1080/02640414.2020.1851901. 

Authors: Felippe da Silva Leite Cardoso, José Afonso Neves, André Roca, Israel Teoldo

Summary: In soccer, it is relevant to understand the roles of Systems 1 (intuitive) and 2 (deliberative) in perceptual-cognitive processes and how they influence response time when making decisions. The aim of this study was to analyse how response time in decision making managed by Systems 1 and 2 is associated to the perceptual-cognitive processes of young soccer players. Ninety young soccer players participated. Perceptual-cognitive processes were assessed through visual search strategies, cognitive effort, and verbal reports. Participants wore a mobile-eye tracking system while viewing 11-a-side match play video-based soccer simulations. Response time in decision making was used to create two sub-groups: faster and slower decision-makers. Results indicated that players with faster response time in decision making employed more fixations of shorter duration, displayed less cognitive effort, as well as a greater number of thought processes associated with planning. These results reinforce that there are differences in the way of using the perceptive-cognitive processes from the priority system in the decision-making process. It is concluded that faster decision making, managed by System 1, implies greater ability to employ visual search strategies and to process information, thus enabling increased cognitive efficiency. 



#3 Long-term Stress Distribution Patterns Across the Ankle Joint in Soccer Players: A Computed Tomography Osteoabsorptiometry Study 

Reference: Orthop J Sports Med. 2020 Nov 19;8(11):2325967120963085. doi: 10.1177/2325967120963085. eCollection 2020 Nov. 

Authors: Junki Shiota, Daisuke Momma, Takayoshi Yamaguchi, Norimasa Iwasaki

Summary: The distribution pattern of subchondral bone density is considered to accurately reflect the stress distribution over a joint under long-term physiologic loading. The biomechanical characteristics of the surface of the ankle joint in soccer players can be determined by measuring this distribution pattern under long-term loading. The purpose was to evaluate the distribution of subchondral bone density across the ankle joint in soccer players and to determine the effects of soccer activities, including kicking motion, on the ankle joint surface under long-term loading conditions by computed tomography (CT) osteoabsorptiometry (CTOAM). CT imaging data were obtained from both ankles of 10 soccer players (soccer group) and 10 nonathletic volunteers (control group). The distribution patterns of subchondral bone density across the articular surface of the ankle joints were assessed by CTOAM. Quantitative analysis was performed of the locations and percentages of high-density areas on the articular surface. Stress distribution patterns over the ankle joint differed between the soccer players and controls. In the soccer players, the high-density areas were found in the anterior part of the distal tibia and proximal talus as well as the distal fibula. The percentages of high-density areas were greater in the soccer players compared with controls (P < .0001). Stress distribution over the articular surface of the ankle joint was affected by soccer activities. A high stress concentration was seen in soccer players in the anterior part of the tibia and talus and in the fibula; such excessive stress may lead to anterior impingement. 



#4 The financial and performance cost of injuries to teams in Australian professional soccer

Reference: J Sci Med Sport. 2020 Nov 26;S1440-2440(20)30813-6. doi: 10.1016/j.jsams.2020.11.004. 

Authors: Donna Lu, Alan McCall, Mark Jones, Jeff Steinweg, Les Gelis, Job Fransen, Rob Duffield

Summary: The aim was to determine the relationship between injury incidence, player-salary cost and team performance in the professional Australian soccer league. Injury incidence, player-salary cost and team performance data were collected from the 10-club A-League competition (n=27 matches/season) over 6 seasons from 2012/13. Player-salary cost of injury was calculated from the salary cap, injury-induced missed matches and player exposure, and trends were reported from Poisson regressions. Team performance was determined from ranking, points, goals (scored, conceded and difference) and match outcome (win, loss or draw) per season and analysed via a mixed-effects Poisson models to estimate association with injury. Nine-hundred-and-sixteen injuries resulted in 3148 missed matches. Injury incidence remained stable apart from a decrease in 2015/16 (p=0.01). Missed matches were significantly higher in season 2013/14 (55.1 [50.7-59.9]; p<0.01) and 2014/15 (71.4 [66.4-76.8]; p<0.001) compared to 2012/13, without differences between other seasons. Player-salary cost ranged between AUD$187,990-AUD$332,680/team, peaking in 2014/15 (p<0.01). Multi-collinearity was detected for team performance variables except for matches lost. Teams who finished the season with greater positive goal differences were associated with 1% less injuries (p=0.003). Similarly, more missed matches were associated with 1% less league points and losses (p<0.001). Player-salary costs remained stable, concomitant with stable injury rates and missed matches. Despite injury being associated with goals difference, points and match losses; the magnitude of these relationships are small and team performance is more complex than injury occurrence alone. Injury prevention remains necessary for reducing injury-induced player-salary costs; however, additional services are required to improve team performance. 



#5 A Novel Method to Categorize Stretch-Shortening Cycle Performance Across Maturity in Youth Soccer Players

Reference: J Strength Cond Res. 2020 Dec 3. doi: 10.1519/JSC.0000000000003900. Online ahead of print. 

Authors: Jason S Pedley, Rhodri S Lloyd, Paul J Read, Isabel S Moore, Gregory D Myer, Jon L Oliver

Summary: This study used a novel method to categorize stretch-shortening cycle (SSC) function during a drop jump (DJ) using the force-time curve. This method was then used to determine the effect of maturity status upon SSC function and effect of SSC function on DJ performance. Prepeak, circa-peak, and postpeak height velocity male youth soccer players completed a preseason 30-cm DJ onto a force plate. Stretch-shortening cycle function was categorized as poor (impact peak and not spring-like), moderate (impact peak and spring-like), or good (no impact peak and spring-like). Interactions between SSC function and maturity status, and SSC function and kinetic variables were explored. Youth soccer players displaying good SSC function were older and more mature than those with poor SSC function; however, 9.9% of post peak height velocity still displayed poor SSC function. Players with good SSC function recorded significantly shorter ground contact times, reduced time between peak landing and takeoff force, reduced center of mass displacement, and significantly greater takeoff forces than players with moderate and poor SSC function (all p < 0.05). SSC function during a standardized DJ improves with maturation, but a portion of mature players still demonstrate poor SSC function. Good SSC function was associated with improved DJ outcome measures except jump height. Tailored training interventions based on SSC competency may be required to optimally enhance SSC function. 



#6 Inspiratory Muscle Training Improves Aerobic Capacity in Amateur Indoor Football Players

Reference: Int J Sports Med. 2020 Dec 11. doi: 10.1055/a-1255-3256. 

Authors: Matheus Martins de Sousa, Matheus Dos Santos Pimentel, Isabela de Andrade Sobreira, Rondineli de Jesus Barros, Audrey Borghi-Silva, Flavia Mazzoli-Rocha

Summary: Inspiratory muscle training represents a recommended clinical practice to improve physical performance of healthy individuals, athletes, and those with chronic diseases. This study aimed to evaluate whether high- and low-intensity inspiratory muscle training interferes with the aerobic capacity of indoor soccer players. Volunteers were equally and randomly divided into CON (control group, no inspiratory muscle training); HIG (high-intensity group, inspiratory muscle training at 80% of maximal inspiratory pressure, 3 sets of 12 repetitions); and LIG (low-intensity group, inspiratory muscle training at 50% of maximal inspiratory pressure, 2 sets of 20 repetitions). Before and after inspiratory muscle training, maximal inspiratory and expiratory pressures, the incremental shuttle run test, and the 3-min step test were evaluated. Both inspiratory muscle training protocols improved maximal inspiratory and expiratory pressures, and indirect maximal oxygen consumption and distance traveled in the shuttle test compared to CON. However, only HIG achieved significant increases of indirect oxygen consumption and frequency of step rise in the 3-min step test (p<0.05). Inspiratory muscle training is an important tool to enhance maximal inspiratory pressure and exercise tolerance with potential benefits on submaximal aerobic capacity. However, high-intensity inspiratory muscle training improved aerobic capacity in amateur indoor soccer players in both submaximal tests. 



#7 Association Between Proteomic Blood Biomarkers and DTI/NODDI Metrics in Adolescent Football Players: A Pilot Study

Reference: Front Neurol. 2020 Nov 16;11:581781. doi: 10.3389/fneur.2020.581781. eCollection 2020. 

Authors: Keisuke Kawata, Jesse A Steinfeldt, Megan E Huibregtse, Madeleine K Nowak, Jonathan T Macy, Kyle Kercher, Devin J Rettke, Andrea Shin, Zhongxue Chen, Keisuke Ejima, Sharlene D Newman, Hu Cheng 

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Summary: While neuroimaging and blood biomarker have been two of the most active areas of research in the neurotrauma community, these fields rarely intersect to delineate subconcussive brain injury. The aim of the study was to examine the association between diffusion MRI techniques [diffusion tensor imaging (DTI) and neurite orientation/dispersion density imaging (NODDI)] and brain-injury blood biomarker levels [tau, neurofilament-light (NfL), glial-fibrillary-acidic-protein (GFAP)] in high-school football players at their baseline, aiming to detect cumulative neuronal damage from prior seasons. Twenty-five football players were enrolled in the study. MRI measures and blood samples were obtained during preseason data collection. The whole-brain, tract-based spatial statistics was conducted for six diffusion metrics: fractional anisotropy (FA), mean diffusivity (MD), axial/radial diffusivity (AD, RD), neurite density index (NDI), and orientation dispersion index (ODI). Five players were ineligible for MRIs, and three serum samples were excluded due to hemolysis, resulting in 17 completed set of diffusion metrics and blood biomarker levels for association analysis. Our permutation-based regression model revealed that serum tau levels were significantly associated with MD and NDI in various axonal tracts; specifically, elevated serum tau levels correlated to elevated MD (p = 0.0044) and reduced NDI (p = 0.016) in the corpus callosum and surrounding white matter tracts (e.g., longitudinal fasciculus). Additionally, there was a negative association between NfL and ODI in the focal area of the longitudinal fasciculus. Our data suggest that high school football players may develop axonal microstructural abnormality in the corpus callosum and surrounding white matter tracts, such as longitudinal fasciculus. A future study is warranted to determine the longitudinal multimodal relationship in response to repetitive exposure to sports-related head impacts. 



#8 The Influence of Basic Psychological Needs and Passion in Promoting Elite Young Football Players' Development

Reference: Front Psychol. 2020 Nov 16;11:570584. doi: 10.3389/fpsyg.2020.570584. eCollection 2020. 

Authors: José L Chamorro, Rubén Moreno, Tomás García-Calvo, Miquel Torregrossa

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Summary: Motivational variables and cognitive skills have been identified as important in an athlete's development. The aim of this study is to explore the influence of each basic psychological needs satisfaction on player's development regarding reflection and concentration disruption with the mediation of types of passion in Spanish young elite football players. A total of 487 elite U18 male football players (Mage = 17.43, SD = 0.71) completed measures of basic psychological needs satisfaction, passion for football, reflective thinking, and concentration disruption. Measurement models were defined using exploratory structural equation models. The results provide support for the model, where each psychological needs satisfaction prompted reflection and had a negative influence on concentration disruption with the mediation of harmonious passion. In addition, obsessive passion mediated the positive relationship between competence satisfaction and concentration disruption. Finally, competence and relatedness satisfaction influenced the development of reflection directly and positively and, exclusively, relatedness satisfaction had a negative influence in a direct way on concentration disruption. In sum, our results highlight that (a) the environment of young footballers through psychological needs satisfaction has a positive (i.e., reflection) or negative (i.e., concentration disruption) influence on the field, but only with the mediation of harmonious passion, (b) in a competitive environment, the perception of competence can have a positive influence on concentration disruption, but only with the development of obsessive passion as a mediator, and (c) relatedness satisfaction plays a key role in distinguishing between reflection and concentration disruption. 



#9 Outbreak of community-acquired Staphylococcus aureus skin infections in an Australian professional football team

Reference: J Sci Med Sport. 2020 Nov 20;S1440-2440(20)30815-X. doi: 10.1016/j.jsams.2020.11.006.

Authors: Ramon Z Shaban, Cecilia Li, Matthew V N O'Sullivan, Jen Kok, Kathy Dempsey, Marc Ramsperger, Mitchell Brown, Shizar Nahidi, Cristina Sotomayor-Castillo

Summary: Skin and soft tissue infections commonly affect athletes and can lead to cluster outbreaks if not managed appropriately. We report the findings of an investigation into an outbreak of community-acquired Staphylococcus aureus infection in an Australian professional football team. Nose, axilla, groin and throat swab were collected from 47 participants. MRSA and MSSA isolates underwent antibiotic susceptibility testing, binary typing and whole genome sequencing. Infection control practitioners (ICPs) investigated the training grounds for risk factors in the transmission of S. aureus. Almost half of the participants (n=23, 48.9%) were found to be colonised with MSSA. An outbreak cluster of MRSA ST5 closely related to the fusidic acid-resistant New Zealand NZAK3 clone was identified in a group of four players. MSSA ST15 and MSSA ST291 strains were found to have colonised and spread between two and five players, respectively. All participants were advised to undergo decolonisation treatment consisting of 4% chlorhexidine body wash and mupirocin nasal ointment for ten days. The ICP team identified several unhygienic practices within the club's shared facilities that may have played a role in the transmission of S. aureus. We report for the first time a community-associated S. aureus outbreak involving the highly successful fusidic acid-resistant MRSA ST5 clone in a professional football club associated with inadequate hygiene procedures. Management and prevention of S. aureus relies heavily on hygiene education and adherence to personal and environmental hygiene practices and policies. 



#10 Illness and infection in elite full-contact football-code sports: A systematic review

Reference: J Sci Med Sport. 2020 Nov 10;S1440-2440(20)30810-0. doi: 10.1016/j.jsams.2020.11.001. 

Authors: Lucy Chesson, Sarah Whitehead, Kirsten Flanagan, Kevin Deighton, Jamie Matu, Susan H Backhouse, Ben Jones

Summary: Full-contact football-code team sports offer a unique environment for illness risk. During training and match-play, players are exposed to high-intensity collisions which may result in skin-on-skin abrasions and transfer of bodily fluids. Understanding the incidence of all illnesses and infections and what impact they cause to time-loss from training and competition is important to improve athlete care within these sports. This review aimed to systematically report, quantify and compare the type, incidence, prevalence and count of illnesses across full-contact football-code team sports. A systematic search of Cochrane Library, MEDLINE, SPORTDiscus, PsycINFO and CINAHL electronic databases was performed from inception to October 2019; keywords relating to illness, athletes and epidemiology were used. Studies were excluded if they did not quantify illness or infection, involve elite athletes, investigate full-contact football-code sports or were review articles. Twenty-eight studies met the eligibility criteria. Five different football-codes were reported: American football (n=10), Australian rules football (n=3), rugby league (n=2), rugby sevens (n=3) and rugby union (n=9). One multi-sport study included both American football and rugby union. Full-contact football-code athletes are most commonly affected by respiratory system illnesses. There is a distinct lack of consensus of illness monitoring methodology. Full-contact football-code team sport athletes are most commonly affected by respiratory system illnesses. Due to various monitoring methodologies, illness incidence could only be compared between studies that used matching incidence exposure measures. High-quality illness surveillance data collection is an essential component to undertake effective and targeted illness prevention in athletes. 



#11 Factors influencing optimum countermovement jump performance and movement strategy in Championship professional football players: implications for player profiling

Reference: Res Sports Med. 2020 Dec 10;1-11. doi: 10.1080/15438627.2020.1860049. Online ahead of print. 

Authors: Andy Mitchell, Craig Holding, Matt Greig

Summary: Single leg countermovement jump (CMJ) is a common profiling test influenced by sport, age, sex and playing level. Controlling for these confounding variables, outfield players from an English Championship squad (n = 36) were retrospectively categorized as best (n = 10) or worst (n = 10), based on mean single leg CMJ height and flight time:contraction time ratio. Movement strategy was quantified as force-time history metrics differentiating eccentric and concentric phases. Jump height revealed that best performers elicited greater rate of force development in both phases (P ≤ 0.033), with concentric impulse the strongest predictor of performance. Time ratio also differentiated best performers as utilizing a shallower (P = 0.002) countermovement, with concentric rate of force development the strongest predictor of good performance. Successful jump height performance can mask ineffectual eccentric and stretch shortening cycle neuromuscular characteristics. Time ratio is therefore advocated as the key performance indicator, with movement strategy prioritized over gross outcome measures. 



#12 Effects of football versus aerobic exercise training on muscle architecture in healthy men adults: a study protocol of a two-armed randomized controlled trial 

Reference: Trials. 2020 Dec 9;21(1):1007. doi: 10.1186/s13063-020-04797-y. 

Authors: Guevar Alkhateeb, Lars Donath

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Summary: Sports and exercise training can attenuate age-related declines in physical function. As people age, they suffer a progressive deterioration of overall muscle structure and function, such as muscle diameter, strength, mass, and power. Therefore, supporting older adults-aged 50 years and above-to continue being physically active is a very important factor. Several forms of exercise (strength, agility, endurance, balance, and flexibility) are recommended. In this regard, football has been repeatedly shown to be an integrative approach to promote measures of strength, endurance, and agility. However, there has been no previous randomized controlled trial that comparatively investigates the effects of football training versus traditional aerobic exercise training on muscle architecture and patella tendon properties in healthy community dwellers. The study protocol is designed to examine whether football differentially affects muscle thickness, muscle length, fascicle length, pennation angle, patella tendon length, and thickness compared to a workload matched traditional aerobic exercise training regimen. The study sample consists of 60 untrained but healthy men (50-60 years old), who will be randomly assigned (strata: age, activate) to two groups: football group (n = 30) and aerobic group (n = 30). The intervention will take place within 12 consecutive weeks, two times a week for 60 min each session. The football group will perform recreational football training as a large-sided game, whereas the aerobic group undergoes a running exercise. Both groups have the same external workload ranging between moderate and high exercise intensity. The outcome measure will be collected before and after the intervention period. Findings of this study will provide insight into the effects of 24 sessions of both football and aerobic training program on the selected groups of men adults, including detecting their effects on the thigh muscle architecture. 



#13 Financial Performance Analysis in European Football Clubs

Reference: Entropy (Basel). 2020 Sep 21;22(9):1056. doi: 10.3390/e22091056. 

Authors: David Alaminos, Ignacio Esteban, Manuel A Fernández-Gámez

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Summary: The financial performance of football clubs has become an essential element to ensure the solvency and viability of the club over time. For this, both the theory and the practical and regulatory evidence show the need to study financial factors, as well as sports and corporate factors to analyze the possible flow of income and for good management of the club's accounts, respectively. Through these factors, the present study analyzes the financial performance of European football clubs using neural networks as a methodology, where the popular multilayer perceptron and the novel quantum neural network are applied. The results show the financial performance of the club is determined by liquidity, leverage, and sporting performance. Additionally, the quantum network as the most accurate variant. These conclusions can be useful for football clubs and interest groups, as well as for regulatory bodies that try to make the best recommendations and conditions for the football industry. 



#14 Spatial and Temporal Entropies in the Spanish Football League: A Network Science Perspective

Reference: Entropy (Basel). 2020 Feb 2;22(2):172. doi: 10.3390/e22020172. 

Authors: Johann H Martínez, David Garrido, José L Herrera-Diestra, Javier Busquets, Ricardo Sevilla-Escoboza, Javier M Buldú

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Summary: We quantified the spatial and temporal entropy related to football teams and their players by means of a pass-based interaction. First, we calculated the spatial entropy associated to the positions of all passes made by a football team during a match, obtaining a spatial entropy ranking of Spanish teams during the 2017/2018 season. Second, we investigated how the player's average location in the field is related to the amount of entropy of his passes. Next, we constructed the temporal passing networks of each team and computed the deviation of their network parameters along the match. For each network parameter, we obtained the permutation entropy and the statistical complexity of its temporal fluctuations. Finally, we investigated how the permutation entropy (and statistical complexity) of the network parameters was related to the total number of passes made by a football team. Our results show that (i) spatial entropy changes according to the position of players in the field, and (ii) the organization of passing networks change during a match and its evolution can be captured measuring the permutation entropy and statistical complexity of the network parameters, allowing to identify what parameters evolve more randomly. 






Markers of muscle damage and strength performance in professional football players during the competitive period

The study investigated the impact of competitive soccer on the short-term changes in isometric strength of the adductor muscle group.





Effectiveness of Abdominal and Gluteus Medius Training in Lumbo-Pelvic Stability and Adductor Strength in Female Footballers

The purpose was to establish if the inclusion of gluteus medius-specific exercises in an abdominal training program is more effective for improving lumbo-pelvic stability and adductor muscle strength.





Latest research in football - week 4 - 2021

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 combination of physical and mental load exacerbates the negative effect of each on the capability of skilled soccer players to anticipate action 

Reference: J Sports Sci. 2020 Dec 4;1-9. doi: 10.1080/02640414.2020.1855747.

Authors: David Alder, David P Broadbent, Jamie Poolton

Summary: This study examined the impact of combining physical and mental load on the anticipatory judgements of skilled soccer players. Sixteen players completed an 11vs11 video anticipation test in four counterbalanced conditions, each separated by 7 days. The baseline condition consisted of only the anticipation test. A physical load condition required participants to complete a simulated soccer protocol on a treadmill followed by the anticipation test. A mental load condition required participants to complete a 30-min Stroop test followed by the anticipation test. Finally, in the combined load condition, participants completed the physical load protocol alongside the mentally loading Stroop task followed by the anticipation test. Response accuracy, visual search behaviour and measures of effort were assessed throughout. Response accuracy decreased in the separate physical load and mental load conditions when compared to baseline and worsened further in the combined load condition. The reduction in response accuracy across experimental conditions coincided with an increase in the number of fixations when compared to the baseline condition. It is suggested that the separate sources of load impaired the players ability to allocate sufficient resources to task-relevant information leading to a reduction in anticipatory accuracy, and this was exacerbated in the combined load condition. 



#2 Differential Change in Oculomotor Performance among Female Collegiate Soccer Players versus Non-Contact Athletes from Pre- to Post-Season 

Reference: Neurotrauma Rep. 2020 Nov 10;1(1):169-180. doi: 10.1089/neur.2020.0051. eCollection 2020. 

Authors: Virginia T Gallagher, Prianka Murthy, Jane Stocks, Brian Vesci, Danielle Colegrove, Jeffrey Mjaanes, Yufen Chen, Hans Breiter, Cynthia LaBella, Amy A Herrold, James L Reilly

Summary: Sensitive and reliable tools are needed to evaluate potential behavioral and cognitive changes following head impact exposure in contact and collision sport participation. We evaluated change in oculomotor testing performance among female, varsity, collegiate athletes following variable exposure to head impacts across a season. Female, collegiate, contact sport (soccer, CONT) and non-contact sport (NON-CONT) athletes were assessed pre-season and post-season. Soccer athletes were grouped according to total season game headers into low dose (≤40 headers; CONT-Low Dose) or high dose (>40 headers; CONT-High Dose) groups. Performance on pro-saccade (reflexive visual response), anti-saccade (executive inhibition), and memory-guided saccade (MGS, spatial working memory) computer-based laboratory tasks were assessed. Primary saccade measures included latency/reaction time, inhibition error rate (anti-saccade only), and spatial accuracy (MGS only). NON-CONT (n = 20), CONT-Low Dose (n = 17), and CONT-High Dose (n = 7) groups significantly differed on pre-season versus post-season latency on tasks with executive functioning demands (anti-saccade and MGS, p ≤ 0.001). Specifically, NON-CONT and CONT-Low Dose demonstrated shorter (i.e., faster) anti-saccade (1.84% and 2.68%, respectively) and MGS (5.74% and 2.76%, respectively) latencies from pre-season to post-season, whereas CONT-High Dose showed 1.40% average longer anti-saccade, and 0.74% shorter MGS, latencies. NON-CONT and CONT-Low Dose demonstrated reduced (i.e., improved) inhibition error rate on the anti-saccade task at post-season versus pre-season, whereas CONT-High Dose demonstrated relative stability (p = 0.021). The results of this study suggest differential exposure to subconcussive head impacts in collegiate female athletes is associated with differential change in reaction time and inhibitory control performances on executive saccadic oculomotor testing. 



#3 Effects of the COVID-19 confinement period on physical conditions in young elite soccer players 

Reference: J Sports Med Phys Fitness. 2020 Dec 3. doi: 10.23736/S0022-4707.20.11669-4. Online ahead of print. 

Authors: Marc Dauty, Pierre Menu, Alban Fouasson-Chailloux

Summary: The rapid spread of the SARS-CoV-2 infection required general confinement measures reducing or even preventing sport practice, which was a risk of detraining in athletes. In adolescents, detraining is poorly known as well as its prevention by homeexercises. This article aimed to assess the effects of Covid-19 confinement on detraining in young high-level soccer players despite a multimodal training program conducted at home. Twenty-five elite soccer players, aged 14, were included to perform physical exercises at home during the Covid-19 confinement. Two cardio-training sessions and two upper and lower limb muscle strengthening sessions were performed per week. The exercise program was monitored remotely via the web. Hooper, training and mental indexes allowed a psychological follow-up. The effect of Covid-19 confinement on aerobic capacity was measured using a pre- and post-confinement Yo-Yo test. Out of the 25 adolescences who completed the exercises program, 19 performed the post-confinement Yo-Yo test. The running distance decreased by 614 +/- 630 m (-25%) (p = 0001) and the maximal running speed by 0.97 +/- 1 km/h (-5%) (p=0.001), confirming detraining. Hooper, training and mental indexes remained stable showing a well-supported home Covid-19 confinement. The 2-month period of strict home confinement due to the SARS-CoV-2 pandemic was responsible for a decrease of aerobic abilities in adolescent soccer players, despite a remotely monitored multimodal exercises program. 



#4 Relationships Between Training Load Variables in Professional Youth Football Players 

Reference: Int J Sports Med. 2020 Dec 1. doi: 10.1055/a-1300-2959. Online ahead of print. 

Authors: Patrick Maughan, Paul Swinton, Niall MacFarlane

Summary: This study aims to investigate the relationship between subjective and external measures of load in professional youth football players whilst accounting for the effect of training theme or competition. Data from ratings of perceived exertion and global positioning system-derived measures of external training load were collected from 20 professional youth players (age=17.4±1.3 yrs) across a 46-week season. General characteristics of training sessions were categorised based on their proximity to match day. The underlying structure of the data was investigated with principal component analysis. An extraction criterion comprising eigenvalues >1 was used to identify which components to retain. Three components were retained for training performed three days prior to match day (80.2% of variance), with two components (72.9-89.7% of variance) retained for all other modes. Generally, the first component was represented by measures of volume (Total Distance, PlayerLoad and low intensity running) whilst the second and third components were characterised by measures of intensity. Identification of multiple components indicates that load monitoring should comprise multiple variables. Additionally, differences in the underlying structure across training days that reflected different goals suggest that effective monitoring should be specific to the demands of different session types. 



#5 High-intensity Interval Training Shock Microcycle Improves Running Performance but not Economy in Female Soccer Players 

Reference: Int J Sports Med. 2020 Dec 11. doi: 10.1055/a-1302-8002. Online ahead of print. 

Authors: Filippo Dolci, Andrew E Kilding, Tania Spiteri, Paola Chivers, Benjamin Piggott, Andrew Maiorana, Nicolas Hart

Summary: This study aimed to evaluate the effect of high-intensity interval training shock microcycles (HIITSM) on endurance, running economy and change of direction economy in female soccer players. Nineteen sub-elite female soccer players were randomised to two groups: HIITSM (10 HIIT sessions over 13 days) or HIITTRAD (4 HIIT sessions over 13 days) interventions. Endurance performance was evaluated through the 30-15 intermittent fitness test (30-15IFT); running economy over a 5-min treadmill run; and change of direction economy over two conditions: (1) 5-min 20m shuttle run, and (2) 5-min 10m shuttle run. HIITSM significantly improved 30-15IFT scores compared to baseline (+4.4%, p=0.009; d=0.96) and 30-15IFT scores relative to HIITTRAD (p=0.002; d=2.01). There was no significant interaction (group×time) for running economy and change of direction economy. Pre- to post- intervention there was a significant main time effect for blood lactate over 20m and 10m shuttle runs (p<0.001 and p=0.037, respectively), with large (d=0.93) and moderate (d=0.53) changes observed for the HIITSM over the two distances, respectively. HIITSM may be more effective than HIITTRAD to improve 30-15IFT over shorter training periods but may not affect running economy and change of direction economy. 



#6 Lower-Limb Muscle Excitation, Peak Torque, and External Load Responses to a 120-Minute Treadmill-Based Soccer-Specific Simulation 

Reference: Res Q Exerc Sport. 2020 Dec 11;1-11. doi: 10.1080/02701367.2020.1844858. Online ahead of print. 

Authors: Adam Field, Richard Michael Page, Liam Corr, Robert Naughton, Matthew Haines, Liam David Harper, Sean Hudson

Summary: The aim of this study was to investigate thigh musculature excitation and torque generation in response to soccer-specific exercise incorporating an extra-time (ET) period. Twelve semiprofessional soccer players performed 120-min treadmill-based soccer-specific exercise. Surface electromyography (EMG) signals for the rectus femoris (EMGRF) and biceps femoris (EMGBF) were measured as the mean response across a pre-determined 10-second sprint bout during each 15-min block of exercise. Peak eccentric torque of the knee flexors (eccKF) and concentric torque of the knee extensors (conKE) were recorded across angular velocities of 60, 180, and 270 degs-1 immediately pre- and post-exercise. Tri-axial PlayerLoad™ (PL-T) was monitored throughout exercise and defined across vertical (PL-V), anterior-posterior (PL-AP), and medial-lateral (PL-ML) planes of motion. A reduction in normalized EMGRF amplitude was evident at 105‒120 min, versus 0‒15 min (-12.5%; p = .037), 15‒30 min (-12.5%; p = .047), and 45‒60 min (-14%; p = .030). Peak torque of the eccKF was significantly reduced from pre- to post-exercise at 60 (-7.7%; p = .018), 180 (-10.5%; p = .042), and 270 degs-1 (-7.5%; p = .034). A main effect for time was identified for PL-T (p < .010), PL-V (p = .033), and PL-AP (p < .010). These findings suggest that muscle excitation of the rectus femoris is reduced during ET, accompanied with a deficit in the torque generation of the knee flexors following 120 min of soccer-specific activity. Practitioners should adequately condition players for the additional ET period by incorporating exercises into training schedules that develop fatigue-resistant eccentric hamstring strength to minimize injury risk. 



#7 Incidence of Acute Hamstring Injuries in Soccer: A Systematic Review of 13 Studies Involving More Than 3800 Athletes With 2 Million Sport Exposure Hours 

Reference: J Orthop Sports Phys Ther. 2020 Dec 11;1-34. doi: 10.2519/jospt.2021.9305. Online ahead of print. 

Authors: Willemijn M Diemer, Marinus Winters, Johannes L Tol, Haiko I M F L Pas, Maarten H Moen

Summary: The aim was to estimate the incidence and recurrence rate of acute hamstring injuries in all levels of soccer. We included prospective studies of all levels of adult soccer players that registered acute hamstring injuries and provided a description of incidence of acute hamstring injuries in n/1000 playing hours (or available data to calculate this). Due to heterogeneity, we synthesised the data descriptively. Thirteen studies including 3868 players met the inclusion criteria. Two of thirteen included studies reported on hamstring injuries in women and thirteen on men. The incidence of acute hamstring injury ranged from 0.3 to 0.5 per 1000 exposure hours in women and 0.3 to 1.9 per 1000 exposure hours in men. Hamstring injuries accounted for 5% to 15% of all soccer-related injuries. Hamstring injury recurrence rates ranged from 4% to 68%, depending on the injury definition. Certainty of the evidence ranged from moderate to very low. The incidence of acute hamstring injury in soccer was 0.3 to 1.9 per 1000 exposure hours. The recurrence rate was 4-68%. Certainty of the evidence ranged from moderate to very low. 



#8 Concentric and eccentric isokinetic hamstring injury risk among 582 professional elite soccer players: a 10-years retrospective cohort study 

Reference: BMJ Open Sport Exerc Med. 2020 Nov 23;6(1):e000868. 

doi: 10.1136/bmjsem-2020-000868. eCollection 2020. 

Authors: Ricardo Lima Burigo, Robson Dias Scoz, Bruno Mazziotti de Oliveira Alves, Rubens Alexandre da Silva, Cesar Augusto Melo-Silva, Edgar Ramos Vieira, Rogerio Pessoto Hirata, Cesar Ferreira Amorim

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Summary: Different authors have tried to correlate the peak isokinetic torque values with the incidence of soccer match injuries. However, due to the wide variety of assessment testing protocols, such an inference becomes difficult. This study aimed to verify the capacity of an isokinetic test to establish injury risk reference values for hamstring strain injuries. A retrospective cohort study based on isokinetic data and clinical records from the last 10 years was conducted in 582 Brazilian elite-professional soccer players, who were subjected to the same isokinetic test protocol, machine, and tester. A Multivariate Logistic Regression Analysis for Complex Data Sampling was used to generate injury risk statistical indexes. Multivariate regression analysis of both legs provided important data to identify the cut-off values of Concentric Peak Torque (181.82 Newton/*metres), Concentric Work (236.23 watts) and Concentric Power (130.11 joules). The injury risk indexes indicate that an increase of just one Newton unit in CPT (Concentric Peak Torque) and CJ (Concentric Power) above those cut-off values, can reduce the risk of future injuries by 2% and 2.7%, respectively. 



#9 Traditional Free-Weight Vs. Variable Resistance Training Applied to Elite Young Soccer Players During a Short Preseason: Effects on Strength, Speed, and Power Performance 

Reference: J Strength Cond Res. 2020 Dec 4. doi: 10.1519/JSC.0000000000003899. Online ahead of print. 

Authors: Irineu Loturco, Lucas A Pereira, Valter P Reis, Vinicius Zanetti, Chris Bishop, Michael R Mcguigan

Summary: Maximizing the neuromuscular capacities of players is a critical challenge during short soccer preseasons. This study compared the effects of 2 strength-power training regimes, on the strength, speed, and power performance of elite young soccer players during a 4-week preseason. Twenty-five under-20 players from the same club were pair matched in 2 training groups as follows: traditional training group (TTG) (n = 13), athletes performed half-squat (HS) and jump-squat (JS) exercises as traditionally prescribed, and elastic band (EB) group (EBG) (n = 12), athletes performed HS and JS with EB attached to the barbell. Vertical jump height, 20-m sprint velocity, change of direction (COD) speed, HS and JS power, and 1 repetition maximum (1RM) in the HS were assessed before, after 2-week, and after 4-week of training. A two-way analysis of variance with repeated measures was used to assess the effects of both training protocols over the experimental period. Both strategies were effective for significantly improving HS and JS power (effect sizes [ESs] = 1.00-1.77), HS 1RM (ES = 1.68 and 1.51 for TTG and EBG, respectively), vertical jumping ability (ES = 0.37-0.65), and COD speed (ES = 0.81 and 0.39 for TTG and EBG, respectively), when comparing premeasures and postmeasures. By contrast, both TTG and EBG failed to increase 20-m sprint velocity (ES ranging between -0.54 and 0.23). In conclusion, both training schemes were able to improve the strength and power performance but not the sprint capacity of young soccer players. To accelerate strength gains over very-short time periods (i.e., 2 weeks), variable resistance training may be advantageous. Conversely, to optimize power adaptations in ballistic exercises across a similar time period, traditional free-weight training may be preferred. 



#10 The Association Between Training Load Indices and Injuries in Elite Soccer Players 

Reference: J Strength Cond Res. 2020 Dec 4. doi: 10.1519/JSC.0000000000003914. Online ahead of print. 

Authors: Caoimhe Tiernan, Tom Comyns, Mark Lyons, Alan M Nevill, Giles Warrington

Summary: The purpose was to investigate the association between contact injuries, noncontact injuries, and training load indices, across different lag periods in elite soccer players. Internal load (session rate of perceived exertion) was collected from 15 elite soccer players over 1 season (40-weeks). Acute (7 days), chronic (28 days), acute:chronic workload ratio (ACWR) (uncoupled), exponentially weighted moving averages (EWMA) ACWR, and 2-, 3-, and 4-week cumulative load were calculated on a rolling weekly basis. Multilevel logistic regression was used to analyze the associations between contact, noncontact injuries, and training load indices, across different lag periods (5 and 7 days). A player was at a significantly higher risk of a noncontact injury 5 days later, if week-to-week acute load changes increased (odds ratio [OR] = 1.97). An increase in EWMA ACWR was associated with an increased risk of both a contact (OR = 1.30) and noncontact injury (OR = 1.35), 5 days later. An increase in 2-week cumulative load (OR = 1.77) was associated with an increased risk of a contact injury 7 days later and 3-week cumulative load (OR = 1.55) 5 days later. These findings suggest that to reduce the potential risk of a noncontact injury, training load should be gradually increased, avoiding an increase in week-to-week acute load change (≥9%) or EWMA ACWR (>1.20). Findings indicated that EWMA ACWR may be a more sensitive measure for detecting a player at a higher risk of an injury than ACWR. Furthermore, a high 2- and 3-week cumulative load was associated with an increased risk of a contact injury, which may indicate accumulated fatigue. Practitioners must note that this study investigated associations with injury risk and not injury prediction. 



#11 Warm-up durations in a hot-dry climate affect thermoregulation, mean power-output and fatigue, but not peak power in specific soccer repeated-sprint ability 

Reference: BMC Sports Sci Med Rehabil. 2020 Dec 9;12(1):76. doi: 10.1186/s13102-020-00221-9. 

Authors: Mohamed Frikha, Nesrine Chaâri, Noureddine Ben Said, Mohammed Shaab Alibrahim

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Summary: This study addressed the lack of data on the effect of warm-up (WU) duration in hot-dry climate (~ 30 °C; ~ 18% RH), on thermoregulation, muscular power-output, and fatigue after specific soccer repeated-sprint test (RSA). Eleven amateur soccer players participated in a cross-over randomized study and they underwent the Bangsbo repeated-sprint test, after three WU durations (i.e. WU10, WU15 and WU20 min) at 70% of MAV, and on different days. Peak power (PP), mean power (MP) and the fatigue index (FI) were recorded and analyzed. Likewise, heart rate (HR), tympanic temperature (Ttym), mean body temperature (MBT) and rating of perceived exertion (RPE) were recorded during each session. The repeated measure ANOVA showed that MP improved after WU15 in comparison to WU10 and WU20 (p = 0.04 and p = 0.001; respectively). Nonetheless, no significant effect on PP was recorded after all WU durations. FI during RSA increased after WU20 in comparison to WU15 and WU10 (p < 0.001 and p = 0.003; respectively). Higher RPE values (p < 0.001) were recorded after WU15 and WU20 in comparison to WU10 duration. The two-way ANOVA showed higher ΔTtym and ΔMBT values after WU15 and WU20 compared to WU10 (p = 0.039 and p < 0.001for Ttym; p = 0.005 and p < 0.001 for MBT, respectively). The WU15 at 70% of MAV better assists mean power-output during soccer RSA in hot-dry (~ 30 °C; 18% RH) climate, but not peak power. Reducing WU duration up to 10 min seems to be insufficient to induce beneficial physiological changes necessary for optimizing repeated-sprint performance, while its extension up to 20 min remains detrimental for muscular power and induces higher fatigue. 



#12 Retirement of professional soccer players - A systematic review from social sciences perspectives 

Reference: J Sports Sci. 2020 Dec 9;1-12. doi: 10.1080/02640414.2020.1851449. Online ahead of print. 

Authors: Michael Barth, Arne Güllich, Carina Andrea Forstinger, Torsten Schlesinger, Frank Schröder, Eike Emrich

Summary: Retiring professional athletes face multifaceted changes and potential issues of adjustment, occupational development, and well-being, which raises concerns around the world. The study systematically reviewed the available research investigating professional soccer players' sport retirement from social sciences perspectives. The literature search in electronic databases and a "snowballing" procedure yielded 17 eligible studies investigating > 2,200 retired professional soccer players. The review followed the PRISMA statement. Nine studies focused on an early transition phase to retirement period; four studies investigated later periods of ten years or longer after retirement. Around half of the players reported involuntary retirement, often associated with declining performance and/or injury. Studies suggest issues of adjustment and mental health during early years after retirement, while psychological issues had apparently declined around 1-2 decades after retirement. However, available studies had notable limitations including lack of evidenced representative samples, report of measures' reliability, and control for confounders. Furthermore, while theoretical models emphasise a holistic perspective, quantitative research often took a narrow rather than holistic perspective. In summary, available knowledge is fraught with some uncertainty regarding reliability and representativeness of the population of retired professional soccer players. We offer future directions to advance the development of a theory of sport retirement. 



#13 The Challenges of Treating Female Soccer Players With ACL Injuries: Hamstring Versus Bone-Patellar Tendon-Bone Autograft 

Reference: Orthop J Sports Med. 2020 Nov 30;8(11):2325967120964884. 

doi: 10.1177/2325967120964884. eCollection 2020 Nov. 

Authors: Elise Britt, Ryan Ouillette, Eric Edmonds, Henry Chambers, Kristina Johnson, Tracey Bastrom, Andrew Pennock

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Summary: Although anterior cruciate ligament (ACL) injuries are common in female soccer players, the optimal graft option for ACL reconstruction is currently unclear. The hypothesis was to compare the outcomes of female soccer players after ACL reconstruction using either hamstring tendon autograft or bone-patellar tendon-bone (BTB) autograft. We hypothesized that there would be no difference in clinical outcome scores, return to sport, or retear rates between BTB and hamstring grafts in our study cohort. We performed a retrospective review of all skeletally mature adolescent female soccer players who underwent primary ACL reconstruction using either hamstring tendon or BTB autograft between 2013 and 2016. Demographic, injury, and surgical variables were documented. Outcome measures included the Lysholm score, Single Assessment Numeric Evaluation, Tegner activity score, and visual analog scales for pain and for satisfaction, as well as ability to return to sport. Overall, 90 female soccer players met the inclusion criteria, of whom 79% (41 BTB and 30 hamstring) were available for a minimum 2-year follow-up or had a graft failure before the follow-up. The BTB group had a lower body mass index (mean ± SD, 23 ± 3 vs 25 ± 4; P = .02) and shorter postoperative follow-up time in months (mean ± SD, 37.4 vs 46.1; P ≤ .001); otherwise, no differences in demographic, injury, or surgical variables between groups were noted. Regarding outcome measures, the BTB group achieved a higher Tegner score (6.0 vs 4.2; P = .004), and there was no other difference between groups. Of the patients who did not return to soccer, 44.7% reported fear as the reason. Of the patients who did return to soccer, 31.9% sustained another ACL injury (retear or contralateral tear), with no differences in reinjury rates based on graft selection. Adolescent female soccer players undergoing ACL reconstruction had relatively high satisfaction and outcome scores independent of autograft choice. Notwithstanding, patients and families need to be counseled that less than half of patients will return to their preinjury level of sport and, if an athlete attempts to return, there is a high risk of further ACL injury. 



#14 Acute Effects of Brief Mindfulness Intervention Coupled with Carbohydrate Ingestion to Re-Energize Soccer Players: A Randomized Crossover Trial 

Reference: Int J Environ Res Public Health. 2020 Dec 4;17(23):9037. doi: 10.3390/ijerph17239037. 

Authors: Yuxin Zhu, Fenghua Sun, Chunxiao Li, Daniel Hung Kay Chow

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Summary: This field experiment investigated the acute effects of brief mindfulness-based intervention (MBI) coupled with carbohydrate (CHO) intake on players' recovery from half-time break in a simulated soccer competition. In a single-blinded randomized crossover experiment, 14 male players received 3 treatments (Control: non-carbohydrate solution + travelling introduction audio; CHO: CHO-electrolyte solution + travelling introduction audio; and CHO_M: CHO-electrolyte solution + MBI) during simulated half-time breaks. Vertical jump, sprint performance, mindfulness level, rate of perceived exertion, muscle pain, mental fatigue, blood glucose, and lactate were measured immediately before, during, and after the exercise. (1) MBI significantly increased participants' mindfulness level (Control vs. CHO_M, p < 0.01; CHO vs. CHO_M, p < 0.01) and decreased mental fatigue for CHO_M condition (pre vs. post, p < 0.01); (2) participants in the CHO_M condition performed better in the repeated sprint tests than in the Control and CHO condition (Control vs. CHO_M, p = 0.02; CHO vs. CHO_M, p = 0.02). Findings of this study provide preliminary evidence of the positive effect of MBI coupled with CHO ingestion on athletes' recovery from fatigue in the early stage of the second half of a game. 






Assessment of External Load during Matches in Two Consecutive Seasons Using the Mediacoach® Video Analysis System

The aim was to describe the training and match injury incidence and physical demands variables observed during a competition using a multi-camera video analysis. 





Game Insight Skills as a Predictor of Talent for Youth Soccer Players

The aim was to find within-group differences for game insight in an elite group of youth footballers by means of Game Insight inDicator (GID).





Latest research in football - week 3 - 2021

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 Global Positioning System Analysis of Physical Demands in Small and Large-Sided Games with Floaters and Official Matches in the Process of Return to Play in High Level Soccer Players

Reference: Sensors (Basel). 2020 Nov 18;20(22):6605. doi: 10.3390/s20226605. 

Authors: Demetrio Lozano, Miguel Lampre, Adrián Díez, Oliver Gonzalo-Skok , Diego Jaén-Carrillo, Daniel Castillo, José Luis Arjol 

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Summary: The aim of this study was twofold: (i) to analyze the physical demands in the return to play (RTP) process of high-level soccer players in the role of floater in different soccer sided games (SGs) formats (i.e., 4vs4 + 2 and 8vs8 + 1); and (ii) to analyze the differences in physical demands encountered by regular and floater players among the SGs formats and official matches by means of global positioning system technology (GPS APEX pod, North Ireland) was used. Twenty-six highly trained, male soccer players (U16 years) participated in this investigation. Players were classified into two groups: 23 regular and 3 floater players, a total of eight SGs were analyzed, which involved the recording of 80 observations of regular and floater players. Match-play players showed most likely-probable differences in distance covered at high-intensity per minute (D > 14.4/min), at high-speed running per minute (D > 21/min), and peak velocity (Vpeak) in comparison to floaters in the 8vs8 + 1 LSG (large-side-games), and presented most likely differences in accelerations >2/min in comparison to match-play players. Therefore, the use of floaters during the last phase of the RTP (return to play) seems to be a useful strategy for progressive reintroduction into specific training (1) floater in the 4vs4 + 2 SSG; (2) floater in the 8vs8 + 1 LSG; (3) regular player in the 4vs4 + 2 SSG; and (4) regular player in the 8vs8 + 1 LSG before starting full trainings and returning to competition. 



#2 The Training of Short Distance Sprint Performance in Football Code Athletes: A Systematic Review and Meta-Analysis 

Reference: Sports Med. 2020 Nov 27. doi: 10.1007/s40279-020-01372-y. Online ahead of print. 

Authors: Ben Nicholson, Alex Dinsdale, Ben Jones, Kevin Till

Summary: Short-sprint (≤ 20 m) performance is an important quality for success in the football codes. Therefore, developing an evidence base for understanding training methods to enhance short-sprint performance is key for practitioners. However, current systematic reviews are limited by (1) a lack of focus on football code athletes, (2) a lack of consideration of all training modalities and (3) a failure to account for the normal training practices undertaken by intervention groups within their analysis. Therefore, this review aimed to (1) conduct a systematic review of the scientific literature evaluating training interventions upon short-sprint performance within football code athletes, (2) undertake a meta-analysis to assess the magnitude of change of sport-sprint performance following training interventions and (3) identify how moderator variables affect the training response. A systematic search of electronic databases was conducted. A random-effects meta-analysis was performed to establish standardised mean difference with 95% confidence intervals. This identified the magnitude and direction of the individual training effects of intervention subgroups (primary, secondary, combined-specific, tertiary and combined training methods) on short-sprint performance while considering moderator variables (i.e., football code, sex, age, playing standard, phase of season). 121 studies met the inclusion criteria, totalling 3419 athletes. Significant improvements (small-large) were found between pre- and post-training in short-sprint performance for the combined, secondary, tertiary and combined-specific training methods. No significant effect was found for primary or sport only training. No individual mode was found to be the most effective. Between-subgroup analysis identified that football code, age, playing standard and phase of season all moderated the overall magnitude of training effects. This review provides the largest systematic review and meta-analysis of short-sprint performance development methods and the only one to assess football code athletes exclusively. Practitioners can apply combined, secondary and tertiary training methods to improve short-sprint performance within football code athletes. The application of sport only and primary methods does not appear to improve short-sprint performance. Regardless of the population characteristics, short-sprint performance can be enhanced by increasing either or both the magnitude and the orientation of force an athlete can generate in the sprinting action. 



#3 Youth Football Players' Psychological Well-Being: The Key Role of Relationships

Reference: Front Psychol. 2020 Nov 10;11:567776. doi: 10.3389/fpsyg.2020.567776. eCollection 2020. 

Authors: Eleonora Reverberi, Chiara D'Angelo, Martin A Littlewood, Caterina Francesca Gozzoli  1 

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Summary: Well-being in youth sport is a growing topic in literature. Practicing sports at a youth level is recognized as an important opportunity for growth and development but also an experience that conversely can prove to be tiring and cause discomfort. Sometimes expectations and pressures make it a risky experience. This is emphasized even more when looking at very popular and spectacular sports, such as football in some European Countries; practicing football often solicits the hope of becoming champions one day and thus being able living thanks to the beloved sport. How do young Italian football practitioners feel? What role do relationships with significant others belonging to the world of sport and extra-sport play on the well-being of young athletes? On which specific aspects of psychological well-being (PWB) are these relationships based? Are there any differences between elite and amateurs levels? These are the questions upon which this paper focuses, considering a sample of young Italian football practitioners. Analysis reveals a strong and positive influence of some dimensions of the relationships with significant others on PWB, specifically team effort, coach closeness, and parental learning climate. Moreover, elite players perceive significantly better relationships than sub-elite and amateurs and have significantly higher levels of PWB. Those results provide a first evidence for the importance of good relationships within and outside sport for an effective development of youth football players since they positively influence players' PWB, which is higher in elite players. It emerges the necessity to further investigate different aspects of PWB and to deepen the knowledge about the meaning of relationship in developmental athletes according to a psychosocial approach. 



#4 Performance Effects with Injury Prevention Exercise Programmes in Male Youth Football Players: A Randomised Trial Comparing Two Interventions 

Reference: Sports Med Open. 2020 Nov 23;6(1):56. doi: 10.1186/s40798-020-00282-7. 

Authors: Hanna Lindblom, Markus Waldén, Martin Hägglund

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Summary: Increased performance from injury prevention exercise programmes (IPEPs) may affect injury risks positively and support the implementation of IPEPs. The primary aim was to study the performance effects of injury prevention exercises from two different IPEPs, the Knee Control IPEP and the further developed Knee Control+ IPEP, in youth male football players, and the secondary aim was to compare potential differences in performance effects between the IPEPs. Four male youth football teams were tested for agility, hop and sprint performance at the start of the second half of the competitive season and after the end of the 8-week season. Per randomisation, two teams used Knee Control and two teams Knee Control+. In total, 47 players executed a median of 13 IPEP sessions (range 11-21 sessions). No improvements in performance were seen in the group as a whole. The intervention groups showed small declines in sprint and agility performance. There was a significant between-group difference in change for the 505 agility test, with improved performance in the Knee Control and worse performance in the Knee Control+ group, ΔKC vs KC+ = - 0.012 (95% CI - 0.19 to -0.04), d = 0.98. No clinically meaningful performance effects were seen from the Knee Control or Knee Control+ IPEP in youth male athletes and no meaningful differences were seen between Knee Control and Knee Control+ regarding effects on performance tests. 



#5 Assessment of the Dietary Intake of High-Rank Professional Male Football Players during a Preseason Training Week 

Reference: Int J Environ Res Public Health. 2020 Nov 18;17(22):8567. doi: 10.3390/ijerph17228567. 

Authors: Anna Książek, Aleksandra Zagrodna, Małgorzata Słowińska-Lisowska 

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Summary: A well-balanced diet is one of the main factors that may play a supportive role in enhancing acute training stimuli in optimal training adaptation. The aim of the present study was to examine the energy and macro- and micronutrient intake including and excluding supplements among top-level Polish football players during one week of the general preparatory period. In addition, the study looked at whether athletes consume carbohydrates in recommended amounts, depending on the completed training sessions. A total of 26 professional football players were included in the study. The preseason dietary intake was assessed using a 7-day estimated food record. The energy value of the diet and the amounts of the dietary ingredients were assessed using the software Dieta 6.0. The average consumption of energy, vitamin B2, vitamin C, vitamin E, folate, and calcium was lower than recommendations, and average intake of sodium and potassium was higher than the norm in the diets of the athletes. The results of this study do not confirm the justification for adding protein preparations to diets of the studied players. Furthermore, football players dietary carbohydrate intake was relatively low in comparison to requirements based on training loads. Based on our results we conclude that further work is necessary to reinforce education about nutritional habits and adjust nutritional strategies to individual needs to enhance athletic performance. 



#6 Interpretation of elevated high-sensitivity cardiac troponin I in elite soccer players previously infected by severe acute respiratory syndrome coronavirus 2 

Reference: Int J Cardiol. 2020 Nov 23;S0167-5273(20)34162-0. doi: 10.1016/j.ijcard.2020.11.039. Online ahead of print. 

Authors: Giuseppe Mascia, Fabio Pescetelli, Amedeo Baldari, Piero Gatto, Sara Seitun, Paolo Sartori, Maurizio Pieroni, Leonardo Calò, Roberta Della Bona, Italo Porto

Summary: The aim was to clarify the meaning of elevated cardiac troponin in elite football athletes previously infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and screened for cardiovascular involvement in the wake of competitive sport resumption. We designed a retrospective cohort study with the collaboration of two Italian Serie A teams. Football players from both rosters (58 athletes) were systematically analysed. For every SARS-CoV-2 positive athlete, the Italian Football Federation protocol requested full blood tests including high-sensitivity cardiac troponin I (hscTnI), along with a complete cardiovascular examination. We extended the analysis to SARS-CoV-2 negative athletes. A total of 13/58 players (22.4%) suffered from SARS-CoV-2infection: all had a negative cardiovascular examination and 2/13 (15%) showed increased hs-cTnI values (120,8 pg/ml and 72,6 pg/ml, respectively; upper reference level 39,2 pg/ml), which did not track with inflammatory biomarkers. Regarding the 45/58 (77,6%) non infected athletes, a slight increase in hs-cTnI was observed in 2 (4.5%) subjects (values: 61 pg/ml and 75 pg/ml respectively). All hs-cTnI positive athletes (4/58, 7%) underwent cardiac magnetic resonance (CMR), that excluded any cardiac injury. In our retrospective study, SARS-CoV-2 infection in elite football athletes was not associated to clinical or biomarkers abnormalities. Increased hs-cTnI was rare and not significantly associated with previous SARS-COV2 infection nor with pathological findings at CMR, albeit elevated hs-cTnI was numerically more prevalent in the infected group. 



#7 Using Behavioral Skills Training With Video Feedback to Prevent Risk of Injury in Youth Female Soccer Athletes 

Reference: Behav Anal Pract. 2020 Aug 17;13(4):811-819. doi: 10.1007/s40617-020-00473-4. eCollection 2020 Dec. 

Authors: Marrissa Harris, Laura Baylot Casey, James N Meindl, Douglas Powell, William C Hunter, Diana Delgado 

Summary: Female athletes are at a greater risk for anterior cruciate ligament (ACL) injuries than males. Current training programs for ACL injury reduction focus on muscle strengthening, appropriate movement patterns, and balance training. However, there is limited research on effective strategies to teach youth female soccer athletes how to properly perform desired movements associated with a decreased risk of ACL injuries. Behavioral skills training (BST) programs have been shown to be effective in teaching a wide variety of skills, but research on applications to sports is limited. This study evaluated a BST package for teaching a stepwise agility program to 3 youth female soccer athletes that consisted of verbal instructions, modeling, rehearsal, and feedback, which included video replay. Results showed a significant improvement in the number of steps the participants performed correctly relative to baseline, as well as maintenance of skills at follow-up. Implications for coaches and athletes, as well as limitations and directions for future research, are discussed. 



#8 Entropy Analysis of Soccer Dynamics 

Reference: Entropy (Basel). 2019 Feb 16;21(2):187. doi: 10.3390/e21020187. 

Authors: António M Lopes, J A Tenreiro Machado

Summary: This paper adopts the information and fractional calculus tools for studying the dynamics of a national soccer league. A soccer league season is treated as a complex system (CS) with a state observable at discrete time instants, that is, at the time of rounds. The CS state, consisting of the goals scored by the teams, is processed by means of different tools, namely entropy, mutual information and Jensen-Shannon divergence. The CS behavior is visualized in 3-D maps generated by multidimensional scaling. The points on the maps represent rounds and their relative positioning allows for a direct interpretation of the results. 



#9 Effects of Plyometric Jump Training in Female Soccer Player's Physical Fitness: A Systematic Review with Meta-Analysis 

Reference: Int J Environ Res Public Health. 2020 Nov 30;17(23):E8911. doi: 10.3390/ijerph17238911. 

Authors: Mario Sánchez, Javier Sanchez-Sanchez, Fabio Y Nakamura, Filipe M Clemente, Blanca Romero-Moraleda, Rodrigo Ramirez-Campillo

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Summary: We aimed to assess the effects of plyometric jump training (PJT) on female soccer player's physical fitness. To this aim, a systematic review with meta-analysis (SRMA) was conducted. The electronic databases PubMed, MEDLINE, Web of Science, and SCOPUS were used. To qualify for inclusion, peer-reviewed studies must have included (i) a PJT programme of ≥2 weeks, (ii) healthy athletes, (iii) a control group, and (iv) physical fitness outcomes (e.g., jump; sprint). Studies were excluded if (i) they incorporated injuried female soccer players, (ii) did not involve PJT or an active control group, (iv) lack of baseline and/or follow-up data. Data was meta-analyzed using the inverse variance random-effects model. Ten moderate-to-high quality studies were included in the analyses, comprising 13 training groups (n = 140) and 10 control groups (n = 110). Small to large (ES = 0.60-2.24; p = 0.040 to <0.001) effects were noted for countermovement jump, drop jump, kicking performance, linear sprint, change of direction speed, and endurance. The moderator analyses (i.e., PJT duration, age groups, competitive level, and soccer experience) revealed no significant differences between groups. In conclusion, PJT may improve the physical fitness of female soccer players. Such improvements might be expected after PJT interventions with six or more weeks of duration, and in players with different chronological ages, competitive levels and soccer experience. 



#10 The Adaptive Behavior of a Soccer Team: An Entropy-Based Analysis 

Reference: Entropy (Basel). 2018 Oct 2;20(10):758. doi: 10.3390/e20100758. 

Authors: Yair Neuman , Navot Israeli, Dan Vilenchik, Yochai Cohen

Summary: To optimize its performance, a competitive team, such as a soccer team, must maintain a delicate balance between organization and disorganization. On the one hand, the team should maintain organized patterns of behavior to maximize the cooperation between its members. On the other hand, the team's behavior should be disordered enough to mislead its opponent and to maintain enough degrees of freedom. In this paper, we have analyzed this dynamic in the context of soccer games and examined whether it is correlated with the team's performance. We measured the organization associated with the behavior of a soccer team through the Tsallis entropy of ball passes between the players. Analyzing data taken from the English Premier League (2015/2016), we show that the team's position at the end of the season is correlated with the team's entropy as measured with a super-additive entropy index. Moreover, the entropy score of a team significantly contributes to the prediction of the team's position at the end of the season beyond the prediction gained by the team's position at the end of the previous season. 



#11 Effect of Training and Match Loads on Hamstring Passive Stiffness in Professional Soccer Players 

Reference: J Musculoskelet Neuronal Interact. 2020 Dec 1;20(4):488-497. 

Authors: Danguole Satkunskiene, Tiago M da Silva, Sigitas Kamandulis, Nuno M C Leite, Aurelijus Domeika, Mantas Mickevicius, Audrius Snieckus

Summary: The purpose of this study was to identify differences in hamstring passive stiffness between the pre-season and in-season periods. Hamstring strength and passive stiffness were measured in professional male soccer players before and after the pre-season (4 weeks), and after the in-season (6 weeks) periods using an isokinetic dynamometer. Muscle passive stiffness was determined from the slope of the passive torque-angle relationship. External loads (acceleration and jumps) were monitored by GPS and internal loads by questionnaire. Hamstring passive stiffness increased after 10 weeks of training and matches, without changes in passive peak torque and range of motion. The hamstring passive stiffness modifications were associated with the volume and intensity of accelerations and jumps. The individual data analysis also provided some support for the suppression of the biomechanical adaptation in the subjects with relatively large external load. Regular training and match workouts increase hamstring passive stiffness in professional soccer players but the adaptation of muscle-tendon unit passive elements might not occur if players experience excessive mechanical stress. 



#12 Asymmetry Thresholds for Common Screening Tests and Their Effects on Jump Performance in Professional Soccer Players 

Reference: J Athl Train. 2020 Dec 2. doi: 10.4085/1062-6050-0013.20. Online ahead of print. 

Authors: Paul J Read, Seán McAuliffe, Chris Bishop, Jon L Oliver, Phil Graham-Smith, Mohammed Abdulaziz Farooq

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Summary: Arbitrary asymmetry thresholds are regularly used in professional soccer athletes, notwithstanding the sparse literature available to examine their prevalence. The aim was to establish normative and positional asymmetry values for commonly used screening tests and investigate their relationships with jumping performance. A total of 203 professional male soccer players participated in this study. Bilateral and unilateral jumping; range of motion; and hamstrings (HAM), quadriceps (QUAD), and hip-adductor and -abductor strength tests were used to quantify asymmetry. Players were divided into 4 quartiles (Q1-Q4) based on the magnitude of their asymmetry for each test. Single composite scores were also developed to group tests by range of motion and HAM, QUAD, hip-adduction, and hip-abduction strength, and differences in jump performance were examined among players in each quartile. Large variability (range = 5.2%-14.5%) was evident in asymmetry scores across the different tests and physical qualities. Forwards displayed greater asymmetry in concentric quadriceps and eccentric hip-abduction strength (P < .05). The HAM and QUAD composite scores indicated that Q4 players jumps were shorter than than in other quartiles during a single-legged countermovement jump and 10-second hop (P < .05). No decrements in unilateral jump performance were shown among players in each quartile for range of motion or hip-adduction and -abduction strength, and no composite measures of asymmetry affected bilateral jump performance. No single asymmetry threshold was present for all tests; the outcomes were task, variable, and population specific. Larger asymmetries in HAM and QUAD strength appeared to be detrimental to unilateral jump performance. 



#13 Cardiac Structure and Function in Elite Female and Male Soccer Players 

Reference: JAMA Cardiol. 2020 Dec 2;e206088. doi: 10.1001/jamacardio.2020.6088. Online ahead of print. 

Authors: Timothy W Churchill, Bradley J Petek, Meagan M Wasfy, James S Guseh, Rory B Weiner, Tamanna K Singh, Christian Schmied, Hughie O'Malley, George Chiampas, Aaron L Baggish

Summary: Population-specific normative data are essential for the evaluation of competitive athletes. At present, there are limited data defining normal electrocardiographic (ECG) and echocardiographic values among elite US soccer players. The objective was to describe ECG and echocardiographic findings in healthy elite US soccer players. This cross-sectional study analyzed Fédération Internationale de Football Association-mandated screening sessions performed at US Soccer National Team training locations from January 2015 to December 2019. US women's and men's national team soccer players undergoing mandated cardiovascular screening were included. Normal training-related and abnormal ECG findings were reported using the International Recommendations for Electrocardiographic Interpretation in Athletes. Echocardiographic measurements of structural and functional parameters relevant to cardiovascular remodeling were assessed relative to American Society of Echocardiography guideline-defined normal ranges. A total of 238 athletes (122 [51%] female; mean [SD] age, 20 [4] years; age range, 15-40 years) were included. Male athletes demonstrated a higher prevalence of normal training-related ECG findings, while female athletes were more likely to have abnormal ECG patterns (14 [11%] vs 0 in male cohort), largely accounted for by abnormal T-wave inversions. Echocardiography revealed no pathologic findings meeting criteria for sport restriction, but athletes frequently exceeded normal ranges for structural cardiac parameters responsive to exercise-induced remodeling including body surface area-indexed left ventricular (LV) mass (58 of 113 female athletes [51%] and 67 of 114 male athletes [59%]), indexed LV volume (89 of 115 female athletes [77%] and 76 of 111 male athletes [68%]), and LV wall thickness (37 of 122 female athletes [30%] and 47 of 116 male athletes [41%]). Age-stratified analysis revealed age-dependent increases in LV wall thickness, mass, and volumes among female athletes and LV wall thickness and mass among male athletes. These data represent the first set of comprehensive normative values for elite US soccer players and one of the largest sport-specific echocardiographic remodeling studies in female athletes. Abnormal ECG findings were more common in female athletes, while both female and male athletes frequently exceeded clinical normality cut points for remodeling-associated echocardiographic parameters. 



#14 Football (soccer)-related spinal cord injury-reported cases from 1976 to 2020 

Reference: Spinal Cord Ser Cases. 2020 Nov 30;6(1):106. doi: 10.1038/s41394-020-00360-8. 

Authors: Manoj K Poudel, Andrew L Sherman

Summary: The aim was to analyze the existing data on soccer (international football)-related spinal cord injury (SCI). Cases of soccer (international football)-related SCI that were reported globally. Fourteen cases of football-related SCI that occurred between 1976 and 2020 were found. Average age at the time of injury was 19 and 86% of individuals were males. Eight of 14 individuals had vertebral fracture/dislocation, whereas two individuals had concomitant traumatic brain injury. Neurologically, 54% had tetraplegia, 39% had paraplegia, and 8% each suffered from hemiplegia and sensory deficit. Two cases could regain ability to walk with orthosis and four had full mobility with "Return to Play" (RTP). The mortality was 14%. Younger males were most commonly affected. The most common etiology, vertebral level of injury, and neurological manifestation was fall, cervical spine, and tetraplegia respectively. More than 50% of the individuals with football-related SCI were able to walk or RTP after rehabilitation. Further studies are required to establish universal RTP criteria and formulate preventive measures. 



#15 The road from the 2018 FIFA World Cup to UEFA EURO 2020 Direction of travel of time zones crossed and results achieved by soccer players

Reference: Res Sports Med. 2020 Nov 29;1-11. doi: 10.1080/15438627.2020.1853545. Online ahead of print. 

Authors: Michał Zacharko, Marek Konefał, Łukasz Radzimiński, Paweł Chmura, Krzysztof Błażejczyk, Jan Chmura, Marcin Andrzejewski 

Summary: The study detailed here has sought to assess the physical and technical activity engaged in by football players in the light of the direction of travel in which time zones were crossed as players transferred from training centres to match venues, in the context of matches played at the 2018 FIFA World Cup in Russia. The material consisted of 945 observations of 340 players. Analysed: total distances covered [km], distances covered with high-intensity running (20-25 km/h) [m], numbers of sprints, numbers of shots, numbers of passes, pass accuracy [%] and the official ranking of national teams. Three categories of time-zone shift (training centre match venue) were taken account of, i.e. (1) WestEast (WE), (2) Same Zone (SZ) and (3) EastWest (EW). Analysis of results revealed that players in the EW and SZ categories were able to achieve results significantly better than those moving WE (total distances covered H = 11.815(2); p = 0.003; numbers of passes H = 7.630(2); p = 0.022), and this in relation to team placings in the end-of-tournament ranking (H = 18.099(2); p = 0.001). The results will be valuable in searching places for training centres during future FIFA World Cup and UEFA European Championship competitions. 






Acceleration intensity is an important contributor to the external and internal training load demands of repeated sprint exercises in soccer

The aim was to evaluate the effect of acceleration on the external and internal load during repeated sprint exercise.





Testing protocol affects the velocity at VO2max in semi-professional soccer players

The aim was to compare three different protocols to assess the velocity associated with the maximal oxygen uptake in footballers.





Latest research in football - week 2 - 2021

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 Change of direction asymmetry across different age categories in youth soccer

Reference: PeerJ. 2020 Jul 27;8:e9486. doi: 10.7717/peerj.9486. eCollection 2020. 

Authors: Athos Trecroci, Alessio Rossi, Thomas Dos'Santos, Damiano Formenti, Luca Cavaggioni, Stefano Longo, F Marcello Iaia, Giampietro Alberti  

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Summary: In youth, the development of change of direction (COD) and sprint performance is a key component for successfully competing in soccer across age. During a COD, the presence of directional asymmetries may be detrimental due to the unpredictable nature of the sport. Therefore, the aims of the study were to investigate asymmetries in COD ability and to examine the differences in COD and sprint performance across age in young soccer players. Sixty-eight sub-elite soccer players of different age categories (U18, U17, U16, U15) were tested on a 10-m linear sprint test and 90°COD (5-m entry and exit) test in both directions. Asymmetric index (AI) of COD deficit was obtained for dominant (fastest) and non-dominant directions (slowest). The results showed that U16 were more asymmetrical than U18, U17, and U15 from large to moderate effects. The sprint time improved linearly across age with U18 and U15 displaying the fastest and slowest 10-m sprint performance (p < 0.01), respectively. Moreover, COD ability measured by COD deficit did not change across age (p > 0.05). Given the results of this study, practitioners are encouraged to assess asymmetries between dominant and non-dominant directions rather than solely players' COD ability in young soccer players. 



#2 Normative data for hip strength, flexibility and stiffness in male soccer athletes and effect of age and limb dominance

Reference: Phys Ther Sport. 2020 Nov 5;47:53-58. doi: 10.1016/j.ptsp.2020.11.022. Online ahead of print. 

Authors: Juliana M Ocarino, Renan A Resende, Natalia F N Bittencourt, Ricardo V A Correa, Luciana M Mendonça, Guilherme F Reis, Thales R Souza, Sergio T Fonseca

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Summary: The objective was to establish normative data for hip strength, flexibility, and stiffness in male soccer athletes and to investigate the effect of age and limb dominance on these variables. A total of 293 asymptomatic male soccer athletes were assessed. Elite youth players aged 15-17 years and professional adult players aged 18-29 years old. Rectus femoris, iliopsoas, hamstring muscle flexibility, passive hip stiffness, and isometric hip strength were measured using a goniometer, inclinometer, and handheld dynamometer, respectively. escriptive and mixed analyses of variance were used as statistical procedures. The dominant limb had lower iliopsoas (P = 0.010) and rectus femoris (P = 0.003) flexibility and higher external rotators torque compared to the non-dominant limb (P = 0.006) in both age groups. In adult athletes, the dominant limb had lower hip stiffness than the non-dominant limb (P = 0.002). Adults had higher hip external rotator torque than younger athletes (P < 0.0001). No differences were observed for hamstrings flexibility and hip extensors torque. This study provided normative data of hip strength, flexibility, and stiffness for youth and adult male soccer athletes. In addition, there were no clinically relevant inter-limb differences. 



#3 Change-of-Direction Performance in Elite Soccer Players: Preliminary Analysis According to Their Playing Positions

Reference: Int J Environ Res Public Health. 2020 Nov 12;17(22):E8360. doi: 10.3390/ijerph17228360. 

Authors: Dorsaf Sariati, Raouf Hammami, Mokhtar Chtara, Alessandro Zagatto, Daniel Boullosa, Cain C T Clark, Anthony C Hackney, Urs Granacher, Nizar Souissi, Hassane Zouhal 

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Summary: Our objective was to examine the relationship between change of direction (CoD) performance, with (CoDb), and without the ball (CoDwb), and selected measures of physical fitness (jump performance, speed, balance) in elite soccer players, according to players' positions. Forty elite male soccer players performed the change-of-direction and acceleration test (CODAT) with (CODATb), and without the ball (CODATwb), 5- and 20-m sprint tests, the 5-jump test (5JT), and the Y-balance test (YBT). Analyses of the whole sample showed significant correlations between all CODAT measures (CODATwb and CODATb, respectively) and sprint 5-m (r = 0.72, p < 0.001; r = 0.52, p < 0.01), sprint 20-m (r = 0.54, p < 0.03; r = 0.45, p < 0.05), jump (r = -0.62, p < 0.01; r = -0.64, p < 0.01) and balance (r = -0.50, p < 0.01; r = -0.83, p < 0.001) performances. Correlations were significantly different between player positions (defender, midfielder and striker). When examining the entire sample, the single best predictor of CODATwb was performance in the 5-m test with an explained variance of 52% (p < 0.001). For CODATb, the Y-balance performance explained 68% of the variance of performance (p < 0.001). In conclusion, soccer coaches and fitness trainers are advised to improve players' CoD using neuromuscular training that mimic crucial match actions. Meanwhile, CoD testing and training should be designed in line with the demands of playing position. 



#4 Correlation between Pupilometer and the Vestibular/Ocular Motor Screening in Division I Female Collegiate Soccer Athletes 

Reference: Neurology. 2020 Nov 17;95(20 Supplement 1):S2-S3. doi: 10.1212/01.wnl.0000719880.39493.e2. 

Authors: John Heick, Lauren Entsler 

Summary: The objective of this study was to explore the correlation between pupilometer and Vestibular Ocular Motor Screening on Division 1 female collegiate soccer players. Concussions are one of the most prevalent acquired neurologic conditions occurring in young adults with an estimated 1.6 to 3.8 million head injuries. Concussions are assessed with a variety of measures such as the Vestibular/Ocular Motor Screen (VOMS). Visual disruptions are frequently observed following concussion with an estimated 65%-90% of patients complaining of visual disruption. A pupilometer measures objective pupillary activity such as pupil constriction latency, diameter, speed of constriction and dilation, and reflex recovery time. This prospective study recruited Division I female soccer athletes aged 18 to 28. Athletes were excluded if they had a lower extremity injury in the past 3 months that caused the athlete to miss more than 1 day of practice, had a history of a head injury in the past 6 months, or were diagnosed with a visual, vestibular, or balance disorder. Twenty-six female Division I collegiate soccer athletes (mean age of 20.46 ± 2.36 years) completed baseline pupilometer and VOMS testing. Three of the twenty-six had borderline pupillary index scores and five had abnormal VOMS scores at baseline. One athlete had a concussion during the 2019 season and at retest, pupilometer results were normal but two VOMS components were abnormal. The pupilometer and VOMS were poorly correlated. While the neurocognitive consequences of participation in soccer is becoming uncertain, the current study suggests that 11% of female soccer athletes without a diagnosis of a concussion had abnormal pupilometer results and 19% had abnormal VOMS scores. Evidence is mounting that repetitive hits to the head can lead to potential neurocognitive impairments. Future studies are warranted to examine baseline measures across age in female soccer athletes. 



#5 Characteristics of Potential Concussive Events in Three Elite Soccer Tournaments

Reference: Neurology. 2020 Nov 17;95(20 Supplement 1):S10. doi: 10.1212/01.wnl.0000719960.65926.65. 

Author: Nicholas Charles Armstrong 

Summary: The aim was to determine the characteristics of potential concussive events (PCEs) in professional soccer. Soccer players are at risk of sustaining sport-related concussions. The acute and chronic effects of concussive and sub-concussive impacts to the head are potentially detrimental to both players and healthcare systems worldwide. Identifying patterns in the nature and characteristics of these injuries may help sporting organizations understand how to reduce the burden of sport-related brain injuries. The present study analyzed the 2014 and 2018 FIFA World Cups (WC), and the 2016 Euro Cup (EC). Between the three tournaments, a total of 179 professional international matches were played. The researchers collected data pertaining to PCEs including mechanism of injury, location on the head, and number of concussion symptoms. A total of 237 PCEs were identified over 179 matches (1.32 per match, 40.12 per 1,000 hours of exposure). The most common mechanism of injury was elbow-to-head (n = 68, 28.7%), followed by head-to-head (n = 55, 23.2%) and hand/fist-to-head (n = 36, 15.2%). The impact locations most frequently affected were the frontal region (n = 54, 22.8%), followed by the parietal and occipital regions (n = 47, 19.8%), temporal region (n = 46, 19.4%), anterior surface of the mandible (n = 43, 18.1%), and nasal/maxilla region (n = 39, 16.5%). Most players (n = 210, 88.6%) showed two or more signs of concussion. Our study intended to investigate the prevalence, identification and nature of PCEs in professional soccer tournaments. Our findings indicate that different contexts and mechanisms of head contact and contact to different regions of the head can be associated with varying signs of concussion. Ultimately, promoting and enforcing enhanced concussion prevention initiatives in elite soccer can have an impact at all levels of the game. These findings may assist physicians, athletes, soccer organizations and other stakeholders worldwide with the care of injured players and the implementation of new rules and regulations to better protect their players. 



#6 Concussion among soccer players in the 2017 Brazilian championship - the gap between protocol and medical practice 

Reference: Concussion. 2020 Oct 28;5(4):CNC83. doi: 10.2217/cnc-2020-0015. 

Authors: Cármine Porcelli Salvarani, Lucas Ribeiro de Medeiros, Fernando Henrique Sapatero, Diego Ciotta de Castro, Vinícius Simon Tomazini, Leonardo Henrique Micheletti Sotocorno, Paulo Sérgio Teixeira da Costa, Bruno Bueno Pimenta, Diego Almeida de Oliveira, Eduardo Almeida Dias, Eduardo Vinícius Colman da Silva

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Summary: The present study aims to report traumatic brain injury (TBI) among soccer players in the 2017 Brazilian Soccer Championship and discuss the protocols for concussion evaluation. This is an observational study utilizing video analysis of 380 matches. TBI was considered as any event in which one or more soccer player(s) had a head trauma. For potential concussion diagnosis, we analyzed players with one of the following signs: slowness to get up, disorientation, motor incoordination, loss of consciousness, head clutching and impact seizure. There were 374 TBIs in total. The average time for medical assessment was 1'35". 13 players had concussion with an average time of 3'19″ for medical evaluation. Four players were replaced after having a concussion. There is a gap between concussion protocols and medical practices in Brazilian elite soccer. Further discussion about soccer replacement rules are imperative. 



#7 The acute effect of wearable resistance load and placement upon change of direction performance in soccer players

Reference: PLoS One. 2020 Nov 18;15(11):e0242493. doi: 10.1371/journal.pone.0242493. eCollection 2020. 

Authors: Johannes Istvan Rydså, Roland van den Tillaar

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Summary: The aim of the study was to examine the acute effect of different lower limb wearable resistance on placement (shank vs thigh) and various loads (1-5% of body mass) upon change of direction (COD) ability. Twelve male soccer players (age: 23.3 ± 2.5 years; height: 179.2 ± 7.4 cm; body mass: 78.3 ± 7.1 kg) performed a change of direction test with different additional loads fixed on either the shank or thigh. Measurement consisted of total time, 90° and 45° split times. large effects of the different wearable resistance placement (p<0.05) and load (p<0.001) were found for total and split change of direction time performance. Change of direction times were higher with shank loading compared with thigh loading. It was concluded that lower limb wearable resistance loading with different loads had an acute effect upon change of direction performance in male soccer players. Furthermore, that distal placement (shank vs thigh) with similar body mass load had a larger effect upon COD performance. 



#8 The Effects of a Soccer-Specific Fitness Test on Eccentric Knee Flexor Strength

Reference: J Sport Rehabil. 2020 Nov 20;1-5. doi: 10.1123/jsr.2019-0532. Online ahead of print. 

Authors: Christopher Michael Brogden, Lewis Gough, Adam Kelly 

Summary: Physiological fitness testing, such as the Yo-Yo Intermittent Recovery Test (YYIR) is a key requirement of the Elite Player Performance Plan, introduced by the English Premier League. Eccentric hamstring strength has been identified as a risk factor for hamstring injuries in soccer players, with fatigue highlighted to further exasperate this issue. The aim of the current study was to examine the effect of the YYIR level 1 (YYIR1) on eccentric knee flexor strength assessed using the NordBord in youth soccer players. A total of 67 male academy soccer players (age = 16.58 [0.57] y; height = 175.45 [5.85] cm; mass = 66.30 [8.21] kg) volunteered to participate in the current study during the English competitive soccer season. Participants conducted eccentric hamstring strength assessments using the NordBord prior to and immediately postcompletion of the YYIR1, with outcome measures of peak force and peak force relative to body mass recorded. Paired t tests highlighted increased absolute eccentric knee flexor strength values (P < .001) immediately post-YYIR1 for both the dominant and nondominant limbs, with the same trend (P < .001) observed for eccentric strength relative to body mass. The results of this study indicate that the YYIR1 does not induce eccentric knee flexor fatigue and as such is not a valid assessment method to assess the effects of fatigue on hamstring function. However, results do suggest that the NordBord may be considered a viable and more accessible alternative to detect pre-post fitness test/fatigue protocol differences in eccentric knee flexor peak strength while working in the field. 



#9 Relative age-related differences between different competitive levels and field positions in young soccer players

Reference: Res Sports Med. 2020 Nov 26;1-11. doi: 10.1080/15438627.2020.1853540. Online ahead of print. 

Authors: I Peña-González, A Javaloyes, J M Sarabia, M Moya-Ramón

Summary: The aims of this study were to report the relative age effect in different competitive levels and field positions and to analyse the differences within and between different competitive levels and field positions. Data for 203 young soccer players (14.2 ± 1.1 years) included anthropometrics and physical performance (Countermovement jump [CMJ], 30-m sprint, T-test and Yo-Yo IR1). Their competitive level and their field position were registered. The percentage of relative older players (1stHY) was higher in the better competitive levels (L1: 80.6%, p <.001; L2: 68.2%, p <.001 and L3: 58.5%, p <.01), but it was similar between field positions (DF: 68.1%, p <.001; MF: 69.6%, p <.001 and FW: 67.2%, p <.001). Anthropometrical and physical performance differences were found between players of different competitive levels but not between relative older and younger players in each competitive level and field position. The relative age effect is higher in the better competitive levels. Anthropometrical and physical performance differences between players are not due to the relative age but to the level of competition. Relatively older players do not seem to be more likely to be selected for specific field positions. The causes of relative age effect need more research. 



#10 Lower Extremity Movement Quality Does Not Moderate Internal Training Load Response of Male Collegiate Soccer Athletes

Reference: J Athl Train. 2020 Nov 25. doi: 10.4085/1062-6050-0322.20. Online ahead of print. 

Authors: Tara A Condon Ms Atc, Timothy Eckard, Alain J Aguilar, Barnett S Frank, Darin A Padua, Erik A Wikstrom

Summary: Training load and movement quality are associated with injury risk in athletes. Given these associations, it is important to understand how movement quality may moderate training load so that appropriate prevention strategies be employed. The aim was to determine how absolute and relative internal training load change over the course of a men's NCAA soccer season, and determine how movement quality, assessed using the Landing Error Scoring System (LESS), moderates relative internal training load. One NCAA Division I male collegiate soccer team was recruited and followed over two consecutive seasons. Fifty-two athletes (height = 1.81 ± .06 m, mass = 75.74 ± 6.64 kg, age = 19.71 ± 1.30 years) consented to participate and forty six met the criteria to be included in the final statistical analysis. Daily absolute internal training load was tracked over the course of two seasons using a rated perceived exertion scale and time which were subsequently used to calculate absolute and relative internal training loads. Movement quality was assessed using the LESS and categorized participants as poor movers (LESS >5) and good movers (LESS <4). The 46 athletes included in the final analysis included 29 poor movers and 17good movers. Absolute (p < 0.001) and relative (p<0.001) internal training load differed across weeks of the season. However, movement quality did not moderate relative (p=0.264) internal training load. Absolute and relative training load changed across weeks of a male collegiate soccer season. Movement quality did not impact relative training load but further research with larger sample sizes are needed to confirm this result. 



#11 Soccer-Specific Reactive Repeated-Sprint Ability in Elite Youth Soccer Players: Maturation Trends and Association With Various Physical Performance Tests 

Reference: J Strength Cond Res. 2020 Dec;34(12):3538-3545. doi: 10.1519/JSC.0000000000002362. 

Authors: Michele Di Mascio, Jack Ade, Craig Musham, Olivier Girard, Paul S Bradley 

Summary: Repeated-sprint ability is an important physical prerequisite for competitive soccer and deviates for players in various stages of growth and development. Thus, this study investigated reactive repeated-sprint ability in elite youth soccer players in relation to maturation (age at peak height velocity) and its association with performance of other physical tests. Elite male youth players from an English Premier League academy (U12, n = 8; U13, n = 11; U14, n = 15; U15, n = 6; U16, n = 10; and U18, n = 13) completed the reactive repeated-sprint test (RRST; 8 × 30-m sprints with 30-second active recovery), and other physical tests including the Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2), arrowhead agility test, countermovement jump test with arms (CMJA), in addition to 10- and 20-m straight-line sprints. Reactive repeated-sprint test (RRST) performance (total time across 8 sprints) progressively improved from U12 to U16 (p < 0.01; effect size [ES]: 1.0-1.9), yet with no differences found between U16 and U18. No between-group differences in RRST performance were evident after accounting for age at peak height velocity (p > 0.05; ES: <0.3). Correlation magnitudes between performance on the RRST and other tests were trivial to moderate for the Yo-Yo IR2 (r = -0.15 to 0.42), moderate to very large for the arrowhead agility test (r = 0.48-0.90), moderate to large for CMJA (r = -0.43 to 0.66), and trivial to large for 10- and 20-m sprints (r = 0.05-0.61). The RRST was sensitive at tracking maturation trends in elite youth players, although performance improvements were not as marked from 15 to 16 years of age. RRST performance correlates with several physical qualities decisive for competitive soccer (agility, speed, power, and aerobic endurance). 



#12 Intracranial bleeding following soccer-related head trauma in a young student with occult factor VII deficiency 

Reference: Clin Case Rep. 2020 Oct 3;8(11):2148-2151. doi: 10.1002/ccr3.3094. eCollection 2020 Nov. 

Authors: Nerea Lopetegui Lia, Abigael Luke, Syed Daniyal Asad, Shashank Sama, Leo J Wolansky, Upendra P Hegde 


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Summary: It is important to obtain coagulation tests to assess bleeding risk in trauma patients undergoing emergency surgery when a bleeding disorder may be obscured. Identifying specific clotting factor defects is critical in successful patient management. 



#13 Coronary artery z-score values in adolescent elite male soccer players 

Reference: Cardiol Young. 2020 Nov 24;1-5. doi: 10.1017/S1047951120004011. Online ahead of print. 

Authors: Stephan Gerling, Tobias Pollinger, Markus Johann Dechant, Michael Melter, Werner Krutsch, Holger Michel

Summary: With the increased training loads at very early ages in European elite youth soccer, there is an interest to analyse coronary artery remodelling due to high-intensity exercise. Prospective echocardiographic study in 259 adolescent elite male soccer players and 48 matched controls. The mean age was 12.7 ± 0.63 years in soccer players and 12.6 ± 0.7 years in controls (p > 0.05). Soccer players had significant greater indexed left ventricular mass (93 ± 13 g/m2 versus 79 ± 12 g/m2, p = 0.001). Both coronary arteries origin could be identified in every participant. In soccer players, the mean diameter of the left main coronary artery was 3.67 mm (SD ± 0.59) and 2.61 mm (SD ± 0.48) for right main coronary artery. Controls showed smaller mean luminal diameter (left main coronary artery, p = 0.01; right main coronary artery, p = 0.025). In soccer players, a total of 91% (n = 196) and in controls a total of 94% (n = 45) showed left main coronary artery z scores within the normal range: -2.0 to 2.0. In right main coronary artery, a pattern of z score values distribution was comparable (soccer players 94%, n = 202 vs. controls 84%, n = 40). A subgroup of soccer players had supernormal z score values (>2.0 to 2.5) for left main coronary artery (9%, n = 19, p = 0.01) and right main coronary artery (6%, n = 10, p = 0.025), respectively. Elite soccer training in early adolescence may be a stimulus strong enough to develop increased coronary arteries diameters. In soccer players, a coronary artery z score >2.0-2.5 might reflect a physiologic response induced by multiannual high-intensity training. 



#14 Relationships between Training Loads and Selected Blood Parameters in Professional Soccer Players during a 12-Day Sports Camp 

Reference: Int J Environ Res Public Health. 2020 Nov 19;17(22):8580. doi: 10.3390/ijerph17228580. 

Authors: Łukasz Radzimiński, Zbigniew Jastrzębski, Guillermo F López-Sánchez, Andrzej Szwarc, Henryk Duda, Aleksander Stuła, Jacek Paszulewicz, Paul Dragos

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Summary: The main purpose of this study is to assess the relations between training loads and selected blood parameters in professional soccer players during a preseason sports camp. Fifteen professional soccer players (age: 24.3 ± 5.25 year; height: 182.6 ± 6.75 cm; weight: 76.4 ± 6.72 kg) participated in the 12-day training camp. All the training sessions and friendly games were accurately analyzed with a GPS system. Blood samples were taken from the players and analyzed before the camp (PRE), in the middle (MID), and one day after the camp (POST). Mean total distance covered by the players during the camp was 85,205 ± 2685 m, high-intensity running 12,454 ± 1873 m, and sprinting 639 ± 219 m. The highest aspartate transaminase (AST), lactate dehydrogenase (LDH), creatine kinase (CK), and C-reactive protein (CRP) values were observed after six days of the camp. The application of intensive training during a 12-day sports camp can be associated with chronic muscle pain with high activity of some blood enzymes (CK, AST) and a high concentration of myoglobin (Mb). During training camps longer than 10 days, it would be necessary to apply, every second or third day, one day of rest, and the training load should not exceed two units every day. 






The Goal Scale: A New Instrument to Measure the Perceived Exertion in Soccer Players


The aim of the study was to develop and validate a specific pictorial perceived exertion scale for soccer players called GOAL scale.





The 2015 U.S. Soccer Federation header ban and its effect on emergency room concussion rates in soccer players aged 10-13

The aim was to assess the change in proportion of children aged 10-13 playing soccer in the US presenting to an Emergency Department (ED) with a concussion in relation to any other injury before and after the ban.





Latest research in football - week 1 - 2021

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 History of ankle sprain affect the star excursion balance test among youth football players
Reference: Foot Ankle Surg. 2020 Oct 21;S1268-7731(20)30219-8. doi: 10.1016/j.fas.2020.10.004. Online ahead of print.
Authors: Hideaki Nagamoto, Haruki Yaguchi, Hiroyuki Takahashi
Summary: The relationship between the results of the Star Excursion Balance Test (SEBT) and lateral ankle sprain (LAS) among youth football players was investigated. The dominant leg and history of LASs were asked from 33 male youth football players. The SEBT in the anterior, posterolateral, and posteromedial directions were measured for both limbs. The relationship between the history of LAS and reach difference over 4 cm between the dominant and nondominant legs in each direction was statistically analyzed. The number of players with the history of LAS, whose dominant/nondominant reach difference was over 4 cm in the anterior direction, was significantly higher to that in players without a history of LAS in both the dominant (94% vs. 63%, p = 0.02) and nondominant (100% vs. 25%, p = 0.02) legs. Youth football players with a history of LAS showed reach deficit in the anterior direction in the SEBT.

#2 COVID-19, indications for professional football teams and referees training resumption
Reference: J Infect Dev Ctries. 2020 Oct 31;14(10):1084-1089. doi: 10.3855/jidc.13436.
Authors: Matthew Gavino Donadu, Angelo Renato Pizzi, Paolo Zeppilli
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Summary: These indications were drawn up by the Federal Medical-Scientific Commission (FIGC Commission), supplemented for the necessary time by some experts on the subject; currently they are intended to grant the highest achievable guarantee level to protect the health of players, referees and all professionals involved in case of resumption of collective training (Document dated 18 April 2020). They were designed to minimize the risk of contagion were thus based on the fact that during that phase of SARS-COV-2 virus pandemic (COVID-19) and in the absence of an effective vaccine, the zero-contagion risk did not exist and does not exist to date. Those guidelines have been updated on the basis of ongoing medical-scientific evidence, taking into account the indications given by the Technical-Scientific Committee and the opinion of the Italian Football Federation representatives, during a meeting that took place on May 7 and was transmitted to FIGC on May 11, 2020; these indications are to be considered stringent and binding for the purposes of sport training resumption.

#3 Multiple athletic performances, maturation, and Functional Movement Screen total and individual scores across different age categories in young soccer players
Reference: J Exerc Rehabil. 2020 Oct 27;16(5):432-441. doi: 10.12965/jer.2040546.273. eCollection 2020 Oct.
Authors: Igor Bakalľár, Jaromír Šimonek, Janka Kanásová, Bohumila Krčmárová, Matúš Krčmár
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Summary: The purpose of this study was to evaluate differences in multiple athletic performances, and to examine associations between athletic performance and Functional Movement Screen (FMS) in young soccer players. Forty-one soccer players were tested on peak height velocity (PHV), 5-, 10-, and 30-m sprint times, 505 change of direction (505 COD), Y-reactive agility tests, countermovement jump (CMJ), and squat jump (SJ) height. Significant main effects (P<0.01) were recorded in all tests except FMS total score whereas the U16 group outperformed U12 and U14 in almost each test. However, when the results were adjusted to the PHV 7 of 11 tests were nonsignificant. Significant associations were recorded between trunk stability push-up (TSPU) and 5 m (P=0.04) and 505 COD (preferred) times (P=0.01), and SJ height (P=0.03) in the U12. In the U14, significant associations were recoded between TSPU and SJ (P<0.01) and CMJ height (P=0.03). In the U16, significant associations were recorded between deep overhead squat and 5-m sprint time (P=0.02) and CMJ height (P=0.04). Results of this study indicate that athletic performance in young soccer players is multidimensional in nature, and it is a consequence of several factors including maturation, different training strategies, and movement proficiency.

#4 Effects of purposeful soccer heading on circulating small extracellular vesicle concentration and cargo
Reference: J Sport Health Sci. 2020 Nov 12;S2095-2546(20)30155-1. doi: 10.1016/j.jshs.2020.11.006. Online ahead of print.
Authors: Eric R Muñoz, Jaclyn B Caccese, Brittany E Wilson, Kyle T Shuler, Fernando V Santos, Carolina T Cabán, John J Jeka, Dianne Langford, Matthew B Hudson
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Summary: Considering the potential cumulative effects of repetitive head impact (HI) exposure, we need sensitive biomarkers to track short- and long-term effects. Circulating small extracellular vesicles (sEVs) (<200 nm) traffic biological molecules throughout the body and may have diagnostic value as biomarkers for disease. The purpose of this study was to identify the microRNA (miRNA) profile in circulating sEVs derived from human plasma following repetitive HI exposure. Healthy adult (ages 18-35 years) soccer players were randomly assigned to 1 of 3 groups: the HI group performed 10 standing headers, the leg impact group performed 10 soccer ball trapping maneuvers over 10 min, and the control group did not participate in any soccer drills. Plasma was collected before testing and 24 h afterward, and sEVs were isolated and characterized via nanoparticle tracking analysis. Next-generation sequencing was utilized to identify candidate microRNAs isolated from sEVs, and candidate microRNAs were analyzed via quantitative polymerase chain reaction. In silico target prediction was performed using TargetScan and miRWalk programs, and target validation was performed using luciferase reporter vectors with a miR-7844-5p mimic in HEK293 cells. Plasma sEV concentration and size were not affected across time and group following repetitive HI exposure. After 24 h, the HI read count from next-generation sequencing showed a 4-fold or greater increase in miR-92b-5p, miR-423-5p, and miR-24-3p and a 3-fold or greater decrease in miR-7844-5p, miR-144-5p, miR-221-5p, and miR-22-3p. Analysis of quantitative polymerase chain reaction revealed that leg impact did not alter the candidate miRNA levels. To our knowledge, miR-7844-5p is a previously unknown miRNA. We identified 8 miR-7844-5p mRNA targets: PPP1R1B, LIMS1, ATG12, MAP1LC3B, ITGA1, MAPK1, GSK3B, and MAPK8. Collectively, these data indicate repetitive HI exposure alters plasma sEV miRNA content, but not sEV size or number. Furthermore, for the first time we demonstrate that previously unknown miR-7844-5p targets mRNAs known to be involved in mitochondrial apoptosis, autophagy regulation, mood disorders, and neurodegenerative disease.

#5 Modeling ball possession dynamics in the game of football
Reference: Phys Rev E. 2020 Oct;102(4-1):042120. doi: 10.1103/PhysRevE.102.042120.
Authors: A Chacoma, N Almeira, J I Perotti, O V Billoni
Summary: In this paper, we study interaction dynamics in the game of football-soccer in the context of ball possession intervals. To do so, we analyze a database comprising one season of the five major football leagues of Europe. Using this input, we developed a stochastic model based on three agents: two teammates and one defender. Despite its simplicity, the model is able to capture, in good approximation, the statistical behavior of possession times, pass lengths, and number of passes performed. In the last section, we show that the model's dynamics can be mapped into a Wiener process with drift and an absorbing barrier.

#6 A multidisciplinary investigation into "playing-up" in academy football according to age phase
Reference: J Sports Sci. 2020 Nov 17;1-11. doi: 10.1080/02640414.2020.1848117. Online ahead of print.
Authors: Adam Kelly, Mark R Wilson, Daniel T Jackson, Daniel E Goldman, Jennifer Turnnidge, Jean Côté, Craig A Williams
Summary: In an attempt to facilitate more appropriate levels of challenge, a common practice in academy football is to play-up talented youth players with chronologically older peers. However, the context of playing-up in academy football is yet to be empirically explored. Thus, the purpose of this study was to examine the multidimensional factors that differentiated players who play-up from those who do not. Ninety-eight participants from a single football academy were examined within their age phase: Foundation Development Phase (FDP; under-9 to under-11; n = 40) and Youth Development Phase (YDP; under-12 to under-16; n = 58). Drawing upon the FA Four Corner Model, 27 factors relating to Technical/Tactical, Physical, Psychological, and Social development were assessed. Following MANOVA analysis within both the FDP and YDP, significant differences were observed for Technical/Tactical and Social sub-components (P < 0.05). Further differences were observed for Physical and Psychological sub-components (P < 0.05) within the YDP. In sum, Technical/Tactical and Social characteristics appeared to differentiate those who play-up compared to those who do not within the FDP. In the YDP however, there were measures representing all sub-components from the FA Four Corner Model. Subsequently, it is suggested coaches and practitioners consider these holistic factors when playing-up youth football players within relevant age-phases.

#7 Can psychological characteristics, football experience, and player status predict state anxiety before important matches in Danish elite-level female football players?
Reference: Scand J Med Sci Sports. 2020 Nov 17. doi: 10.1111/sms.13881. Online ahead of print.
Authors: Esben Elholm Madsen, Tina Hansen, Sidsel Damsgaard Thomsen, Jeppe Panduro, Georgios Ermidis, Peter Krustrup, Morten B Randers, Carsten Hvid Larsen, Anne-Marie Elbe, Johan Wikman
Summary: Elite football can make players' feel nervous, and personality characteristics, as well as experience, affect how well pressure is handled before important games. Studying the psychological characteristics of female football players can provide information on how well psychological pressure is handled and provide knowledge on how to support players in order to improve performance. Based on a sample of 128 female elite football players from 8 top-level teams, the present study investigates whether psychological characteristics, football experience / player status in elite female football players can predict state anxiety before important matches. Our results outline that high age and national team experience negatively predicted most of the trait anxiety subscales. In line with previous research no psychological differences were found between goalkeepers, defenders, midfielders, and strikers while starting players revealed to have significantly lower trait anxiety. When measuring before important matches we found that somatic state anxiety was negatively associated with senior national team experience, and positively associated with worry trait anxiety and fear of failure. Cognitive state anxiety was negatively associated with hope for success and positively associated with somatic and worry trait anxiety. Self-confidence was positively associated with youth national team experience and negatively associated with worry trait anxiety. It can be concluded that psychological characteristics and national team experience are both important for optimal state anxiety before important matches in elite-level women's football. Implications for practice and future research are discussed.

#8 A Review of On-Field Investigations into the Biomechanics of Concussion in Football and Translation to Head Injury Mitigation Strategies
Reference: Ann Biomed Eng. 2020 Nov 16. doi: 10.1007/s10439-020-02684-w. Online ahead of print.
Authors: Bethany Rowson, Stefan M Duma
Summary: This review paper summarizes the scientific advancements in the field of concussion biomechanics in American football throughout the past five decades. The focus is on-field biomechanical data collection, and the translation of that data to injury metrics and helmet evaluation. On-field data has been collected with video analysis for laboratory reconstructions or wearable head impact sensors. Concussion biomechanics have been studied across all levels of play, from youth to professional, which has allowed for comparison of head impact exposure and injury tolerance between different age groups. In general, head impact exposure and injury tolerance increase with increasing age. Average values for concussive head impact kinematics are lower for youth players in both linear and rotational acceleration. Head impact data from concussive and non-concussive events have been used to develop injury metrics and risk functions for use in protective equipment evaluation. These risk functions have been used to evaluate helmet performance for each level of play, showing substantial differences in the ability of different helmet models to reduce concussion risk. New advances in head impact sensor technology allow for biomechanical measurements in helmeted and non-helmeted sports for a more complete understanding of concussion tolerance in different demographics. These sensors along with advances in finite element modeling will lead to a better understanding of the mechanisms of injury and human tolerance to head impact.

#9 Injury incidence and burden in a youth elite football academy: a four-season prospective study of 551 players aged from under 9 to under 19 years
Reference: Br J Sports Med. 2020 Nov 16;bjsports-2020-102859. doi: 10.1136/bjsports-2020-102859. Online ahead of print.
Authors: Olivier Materne, Karim Chamari, Abdulaziz Farooq, Adam Weir, Per Hölmich, Roald Bahr, Matt Greig, Lars R McNaughton
Summary: The objective was to investigate the incidence and burden of injuries by age group in youth football (soccer) academy players during four consecutive seasons. All injuries that caused time-loss or required medical attention (as per consensus definitions) were prospectively recorded in 551 youth football players from under 9 years to under 19 years. Injury incidence (II) and burden (IB) were calculated as number of injuries per squad season (s-s), as well as for type, location and age groups. A total of 2204 injuries were recorded. 40% (n=882) required medical attention and 60% (n=1322) caused time-loss. The total time-loss was 25 034 days. A squad of 25 players sustained an average of 30 time-loss injuries (TLI) per s-s with an IB of 574 days lost per s-s. Compared with the other age groups, U-16 players had the highest TLI incidence per s-s (95% CI lower-upper): II= 59 (52 to 67); IB=992 days; (963 to 1022) and U-18 players had the greatest burden per s-s: II= 42.1 (36.1 to 49.1); IB= 1408 days (1373 to 1444). Across the cohort of players, contusions (II=7.7/s-s), sprains (II=4.9/s-s) and growth-related injuries (II=4.3/s-s) were the most common TLI. Meniscus/cartilage injuries had the greatest injury severity (95% CI lower-upper): II= 0.4 (0.3 to 0.7), IB= 73 days (22 to 181). The burden (95% CI lower-upper) of physeal fractures (II= 0.8; 0.6 to 1.2; IB= 58 days; 33 to 78) was double than non-physeal fractures. At this youth football academy, each squad of 25 players averaged 30 injuries per season which resulted in 574 days lost. The highest incidence of TLI occurred in under-16 players, while the highest IB occurred in under-18 players.

#10 Genu varum and football participation: Does football participation affect lower extremity alignment in adolescents?
Reference: Knee. 2020 Nov 13;27(6):1801-1810. doi: 10.1016/j.knee.2020.10.007. Online ahead of print.
Authors: A Isın, T Melekoğlu
Summary: Genu varum is one of the most common anatomical variations of knee alignment which is considered a risk factor for anterior knee pain and anterior cruciate ligament injury among football players. Considering that millions of children participate in high-level football training, the purpose of this study was to determine the genu varum development in adolescent football players and non-athlete peers. The hypothesis of this study was that genu varum incidence was higher in adolescent football players compared with non-athletic peers. The design was a cross-sectional study. Two-hundred and thirty-seven male football players (FG) and aged-matched and anthropometrically similar non-athletes (CG) were recruited into the study. The quadriceps angle and intercondylar-intermalleolar distance were measured to evaluate the leg alignment. The distance between the medial edges of the condyles and malleoli was measured in millimeters using a digital caliper while angle measurements were performed using a photographic technique in a standing position. To analyze the variables, comparison, correlation and regression statistical tests were performed. The intercondylar-intermalleolar distance and quadriceps angle values were significantly higher in FG than CG in all ages. In FG, a very strong correlation was found between number of training years and the intercondylar-intermalleolar distance. The prevalence of genu varum was markedly higher in FG than CG (~37% vs. 2%, respectively) based on intercondylar-intermalleolar distance. This study determined that the prevalence of genu varum and abnormal quadriceps angles in adolescent football players is significantly higher compared with their non-athletic peers.

#11 Aerobic fitness and game performance indicators in professional football players; playing position specifics and associations
Reference: Heliyon. 2020 Nov 3;6(11):e05427. doi: 10.1016/j.heliyon.2020.e05427. eCollection 2020 Nov.
Authors: Toni Modric, Sime Versic, Damir Sekulic
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Summary: The aim of this study was to identify associations between aerobic fitness (AF) and game performance indicator (GPI) in elite football. Participants were professional football players (males, n = 16; age: 23.76 ± 2.64; body height: 181.62 ± 7.09 cm; body mass: 77.01 ± 6.34 kg). AF testing was conducted by direct measurement and included VO2max, running speed at aerobic threshold (AeT), and running speed at anaerobic threshold (AT). The GPI were collected by the position-specific performance statistics index (InStat index). The players were observed over one competitive half-season, resulting in 82 game performances, grouped according to the positions in game: defenders (n = 39), midfielders (n = 32) and forwards (n = 11). VO2max was not found to be a good discriminator of AF among different playing positions. AeT (F-test = 26.36. p = 0.01) and AT (F-test = 7.25, p = 0.01) were highest among midfielders, and lowest among forwards. No correlations were found between AF and GPI. This study confirmed that AeT and AT are better indicators of AF than VO2max in football players at different playing positions. The lack of associations between AF and GPI was discussed with regard to calculation of InStat as a GPI.

#12 Physical exercises for preventing injuries among adult male football players: A systematic review
Reference: J Sport Health Sci. 2020 Nov 11;S2095-2546(20)30152-6. doi: 10.1016/j.jshs.2020.11.003. Online ahead of print.
Authors: Jorge Pérez-Gómez, José Carmelo Adsuar, Pedro E Alcaraz, Jorge Carlos-Vivas
Free article
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Summary: Football is the most practised sport in the world and is associated with the risk of injuries in the players. Some studies have been published that identify injury prevention programmes, but there is no review of the full body of evidence on injury prevention programmes for use by football coaches. The aim of this article was to carry out a systematic review of published studies on injury prevention programmes for adult male footballers, identify points of common understanding and establish recommendations that should be considered in the design of injury prevention strategies. PubMed and EMBASE databases were used to identify relevant published articles using the following keywords: 'soccer', 'injury', and 'prevention'. A total of 2512 studies were identified initially, but only 11 studies met the inclusion criteria, and their outcomes are presented. Results revealed that injury prevention programmes in football have focused on strength training, proprioceptive training, multicomponent programmes (balance, core stability, functional strength and mobility) and warm-up programmes. Based on results from the studies analysed, football players can lower the incidence of match and training injuries by participating in dynamic warm-up programmes that include preventive exercises before games or during training sessions, and by adding strength, balance and mobility training to the training sessions.

#13 Structure, Intensity and Player Duels in Under-13 Football Training in Switzerland
Reference: Int J Environ Res Public Health. 2020 Nov 11;17(22):E8351. doi: 10.3390/ijerph17228351.
Authors: Jonas Uebersax, Ralf Roth, Tobias Bächle, Oliver Faude
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Summary: We evaluated the structure (i.e., the different training parts), contents (i.e., the various activities used), intensity and occurrence of contact situations and headers during training sessions in under-13 football in Switzerland. A total of 242 players from 20 different teams on average aged 11.4 (SD 0.7) years participated. The participants were filmed during a typical training session while they were equipped with a heart rate sensor. The sessions were systematically recorded to allow for detailed analyses. Furthermore, a preliminary and explorative analysis of the influence of the level of play on these results was conducted. The overall findings indicated that training included 33.4% playing forms, 29.5% training forms, 28.4% inactivity time and 8.7% athletics. The highest heart rates were achieved in the playing forms (166 min-1, 83% HRmax) compared to the other two activities (training forms 154 min-1, 77% HRmax; athletics 150 min-1, 75% HRmax). Each player had 12.8 duels and 0.6 headers per training. Overall, most duels were conducted from the anterior direction. Playing forms induce higher cardio-circulatory load as well as a better learning environment. Potentially dangerous situations like contact with other players or headers occurred in a single player on average every six min during a training session.

#14 Consistency and identifiability of football teams: a network science perspective
Reference: Sci Rep. 2020 Nov 12;10(1):19735. doi: 10.1038/s41598-020-76835-3.
Authors: D Garrido, D R Antequera, J Busquets, R López Del Campo, R Resta Serra, S Jos Vielcazat, J M Buldú
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Summary: We investigated the ability of football teams to develop a particular playing style by looking at their passing patterns. Using the information contained in the pass sequences during matches, we constructed the pitch passing networks of teams, whose nodes are the divisions of the pitch for a given spatial scale and links account for the number of passes from region to region. We translated football passings networks into their corresponding adjacency matrices. We calculated the correlations between matrices of the same team to quantify how consistent the passing patterns of a given team are. Next, we quantified the differences with other teams' matrices and obtained an identifiability parameter that indicates how unique are the passing patterns of a given team. Consistency and identifiability rankings were calculated during a whole season, allowing to detect those teams of a league whose passing patterns are different from the rest. Furthermore, we found differences between teams playing at home or away. Finally, we used the identifiability parameter to investigate what teams imposed their passing patterns over the rivals during a given match.

#15 Metabolomics profiling of plasma, urine and saliva after short term training in young professional football players in Saudi Arabia
Reference: Sci Rep. 2020 Nov 12;10(1):19759. doi: 10.1038/s41598-020-75755-6.
Authors: Mansour A Alzharani, Ghareeb O Alshuwaier, Khalid S Aljaloud, Naser F Al-Tannak, David G Watson
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Summary: Metabolomics profiling was carried out to observe the effect of short-term intensive physical activity on the metabolome of young Saudi professional football players. Urine, plasma and saliva were collected on 2 days pre- and post-training. An Orbitrap Exactive mass spectrometer was used to analyze the samples. A reversed-phase (RP) column was used for the analysis of non-polar plasma metabolites, and a ZIC-pHILIC column was used for the analysis of plasma, saliva and urine. mzMine was used to extract the data, and the results were modelled using Simca-P 14.1 software. There was no marked variation in the metabolite profiles between pre day 1 and 2 or between post day 1 and 2 according to principal components analysis (PCA). When orthogonal partial least squares (OPLSDA) modelling was also used, and then models could be fitted based on a total number of metabolites of 75, 16 and 32 for urine, plasma and saliva using hydrophilic interaction chromatography (HILIC) and 6 for analysis of plasma with reversed-phase (RP) chromatography respectively. The present study concludes that acylcarnitine may increase post-exercise in football players suggesting that they may burn fat rather than glucose. The levels of carnitine metabolites in plasma post-exercise could provide an important indicator of fitness.





How does the mid-season coach change affect physical performance on top soccer players?


The aim was to analyze the locomtion and metabolic responses of professional players in the top three competitive standards of Spanish soccer during the four weeks before and after dismissal of the coach.





Worst case scenario match analysis and contextual variables in professional soccer players: a longitudinal study

This study aimed to describe the worst-case scenarios (WCS) of professional soccer players by playing position in different durations and analyse WCS considering different contextual variables (match half, -location and outcome)





Latest research in football - week 53 - 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 Relationship between movement dysfunctions and sports injuries according to gender of youth soccer player
Reference: J Exerc Rehabil. 2020 Oct 27;16(5):427-431. doi: 10.12965/jer.2040650.325. eCollection 2020 Oct.
Authors: Ki-Hoon Lim, Tae-Beom Seo, Young-Pyo Kim
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Summary: The purpose of this study is to investigate relationship between movement dysfunctions and sports injuries according to gender of youth soccer player. Thirty-eight middle school soccer players participated in this study and they were divided into male (n=19) and female (n=19) groups. The Functional Movement Screen (FMS) and the Quadriceps-angle (Q-angle) during single-leg squat were analyzed for identifying imbalance and asymmetry of the body, and sports injury questionnaire was examined for 6 months after FMS test. The number of sports injuries did not show significant difference between youth male and female soccer athletes. In FMS results, the scores of overhead squat, hurdle step, in-line lunge, shoulder mobility, active straight leg raise, and rotary stability and the total scores were no significant differences between gender, but the score for the trunk stability push-up was significantly higher in male group than female group. There was no significant difference of Q-angle values between the left and right legs, but Q-angle value between youth male and female groups significantly showed interaction. Therefore, the present data suggested that FMS and Q-angle during single-leg squat might be indicators to predict and/or prevent sports injury in youth male and female soccer players.

#2 Can Small-side Games Provide Adequate High-speed Training in Professional Soccer?
Reference: Int J Sports Med. 2020 Nov 11. doi: 10.1055/a-1293-8471. Online ahead of print.
Authors: Jose Asian-Clemente, Alberto Rabano-Muñoz, Borja Muñoz, Jesus Franco, Luis Suarez-Arrones
Summary: The aim was to compare the running activity in official matches with that achieved in two small-sided games, designed with the same relative area per player but with different constraints and field dimensions, aiming to stimulate high-speed and very-high-speed running. Seventeen young professional players played one 5 vs. 5+5 with 2 floaters, varying in terms of whether there was a change of playing area (SSGCA) or not change (SSGNC). Running activity was monitored using GPS and the following variables were recorded: total distance covered; high-speed distance (18-21 km·h-1); very high-speed distance (>21 km·h-1); peak speed; accelerations and decelerations between 2-3 m·s-2 and above 3 m·s-2. SSGCA achieved statistically higher total distance, high-speed, peak speed and number of accelerations and decelerations than SSGNC (large to small magnitude). Both drills showed statistically greater high speed, number of accelerations and decelerations than official matches (large to small magnitude). Moreover, SSGCA exhibited statistically more total distance and distance at higher speed than official matches (moderate and small magnitude, respectively). In contrast, official matches showed statistically higher peak speeds than both training tasks and more very high speed than SSGNC (large and moderate magnitude, respectively). Coaches could use SSGCA to promote greater running activity in soccer players.

#3 Concussions in Soccer: An Epidemiological Analysis in the Pediatric Population
Reference: Orthop J Sports Med. 2020 Oct 21;8(10):2325967120951077. doi: 10.1177/2325967120951077. eCollection 2020 Oct.
Authors: Kiran Chatha, Taylor Pruis, Carlos Fernandez Peaguda, Eric Guo, Sandra Koen, Danielle Malone, Vani Sabesan
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Summary: As the popularity of youth soccer has increased in the United States, more attention has been focused on the effect of concussion injuries, with recent debate on whether heading should be disallowed. There is little evidence examining the epidemiology of these injuries. The purpose of this study was to examine the prevalence and incidence of youth soccer-related concussions. We hypothesized that concussion rates will correlate with increased participation in youth soccer. The National Electronic Injury Surveillance System was used to collect data on concussion injuries that occurred during soccer in pediatric patients from 2008 through 2016. Soccer-related concussion injuries were identified using specific codes and were analyzed for variation in disposition. The types of contact were categorized into player-to-player, head-to-ball, player-to-post, and player-to-ground contacts. Contact types related to hospitalization were subanalyzed. A weighted total of 3285 concussion injuries were identified during the study period, with an average of 386 concussions each year. The average age was 13.5 years, and there were no differences seen in incidence between the sexes. The overall incidence of concussion injuries increased (r = 0.789), while hospitalizations decreased (r = -0.574). The most common cause of concussion was found to be player-to-player contact, followed by head-to-ground contact and then head-to-ball contact. Subanalysis showed that 13% of hospitalizations were due to head-to-ball contact, compared with 39% and 44% due to player-to-player contact and head-to-ground contact, respectively. The relative risk of hospitalization from a concussion due to head-to-ball contact was 7.06 compared with 22.60 due to head-to-ground contact. The incidence of concussion in youth soccer has been increasing over the past decade as predicted, given the growing participation rates in both male and female soccer players. The most common cause of concussion was player-to-player contact, and the majority of concussions resulting in hospitalization occurred because of head-to-ground contact.

#4 Acute Physiological Responses to High-Intensity Resistance Circuit Training vs. Traditional Strength Training in Soccer Players
Reference: Biology (Basel). 2020 Nov 7;9(11):E383. doi: 10.3390/biology9110383.
Authors: Cristian Marín-Pagán, Anthony J Blazevich, Linda H Chung, Salvador Romero-Arenas, Tomás T Freitas, Pedro E Alcaraz
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Summary: The aim of this study was to evaluate and compare the cardiorespiratory and metabolic responses induced by high-intensity resistance circuit-based (HRC) and traditional strength (TS) training protocols. Ten amateur soccer players reported to the laboratory on four occasions: (1) protocol familiarization and load determination; (2) maximal oxygen consumption test; (3) and (4) resistance training protocols (HRC and TS), completed in a cross-over randomized order. In both protocols, the same structure was used (two blocks of 3 sets × 3 exercises, separated by a 5-min rest), with only the time between consecutive exercises differing: TS (3 min) and HRC (~35 s, allowing 3 min of local recovery). To test for between-protocol differences, paired t-tests were applied. Results showed that oxygen consumption and heart rate during HRC were 75% and 39% higher than TS, respectively (p < 0.001). After the training sessions, blood lactate concentration at 1.5, 5 and 7 min and excess post-exercise oxygen consumption were higher in HRC. The respiratory exchange ratio was 6.7% greater during HRC, with no between-group differences found post-exercise. The energy cost of HRC was ~66% higher than TS. In conclusion, HRC training induces greater cardiorespiratory and metabolic responses in soccer players and thus may be a time-effective training strategy.

#5 Exploring the Relationship Between Participation in an Adult-women's Soccer League and Intimate Partner Violence in Rural Kenya
Reference: J Interpers Violence. 2020 Nov 1;886260520969241. doi: 10.1177/0886260520969241. Online ahead of print.
Authors: Francis Barchi, Samantha C Winter, Daniel Mbogo, Bendettah Thomas, Brittany Ammerman
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Summary: Rates of intimate partner violence (IPV) against women in Sub-Saharan Africa are among the highest of any region in the world. Empirical studies on the effectiveness of IPV-prevention programs in Africa, though few, suggest that successful programs have emphasized community-level engagement and attitudinal change around gender roles. This study explored the relationship between adult women's participation in an all-women's soccer league and IPV in rural Kenya. Nikumbuke Project is a health- and literacy-based program for 702 women in Kwale County, Kenya, that also hosts a women's soccer league. A total of 684 Nikumbuke members completed surveys for this study, 543 of whom identified as having had a partner in the preceding 12 months and were included in this analysis. Participants in the study were, on average, in their late 30s, married with 4-6 children, a primary education or less, and no source of formal employment. Logistic regression models examined the association between a woman's participation in the soccer league and the odds that she would have experienced recent IPV, controlling for other covariates. Women who played on soccer teams had 59% lower odds of reporting physical IPV in the preceding 12 months and approximately 43% lower odds of reporting any form of IPV during the same period compared to women who did not play soccer. Support of more gender-equitable norms was associated with lower odds of all forms of recent violence. More research is needed to identify the underlying reasons for these observed effects and to determine the presence of a causal or temporal relationship between adult women's sports and IPV-risk reduction. Nonetheless, findings from this study point to a novel IPV intervention in communities that might otherwise be resistant to more overt attempts to address gender-based violence (GBV) or where social service agencies with the capacity for IPV-prevention programming may be limited.

#6 The Acute Effects of Cognitive-Based Neuromuscular Training and Game-Based Training on the Dynamic Balance and Speed Performance of Healthy Young Soccer Players: A Randomized Controlled Trial
Reference: Games Health J. 2020 Nov 9. doi: 10.1089/g4h.2020.0051. Online ahead of print.
Authors: Murat Emirzeoğlu, Özlem Ülger
Summary: The aim of this study was to investigate the acute effects of cognitive and game-based trainings (GBT) on dynamic balance (DB) and speed performance (SP) in healthy young soccer players. Forty-nine male soccer players were divided into three groups: cognitive-based neuromuscular training (CBNT; n = 16; age = 16.93 ± 1.18 years; body mass index [BMI] = 21.37 ± 1.57 kg/m2) group, GBT (n = 17; age = 17.05 ± 1.39 years; BMI = 21.10 ± 0.97 kg/m2) group, and control group (n = 16; age = 16.75 ± 1.12 years; BMI = 21.95 ± 1.36 kg/m2). The athletes in CBNT and GBT groups took part in one session lasting 1 hour. The Star Excursion Balance Test and the Speed Dribbling Test were used to evaluate DB and SP, respectively. The measurements were taken just before and after the trainings. Statistical analysis of the study was performed using SPSS 22.0 software (Statistical Package for Social Sciences, Inc., Chicago, IL). The Paired Student's t-test and Wilcoxon test were used. For in-group evaluation the ANOVA test was used for comparisons between the three groups. The Tukey's test was used for post hoc analysis. DB significantly improved in all directions in the GBT group (P < 0.05). Also, significant improvements were observed in DB in all directions except anterior, anterolateral, and anteromedial in the CBNT group, and except anterior, medial, and anteromedial directons in the control group (P < 0.05). SP significantly developed just in the CBNT and GBT groups (P = 0.001, P = 0.003, respectively). CBNT and GBT improved the DB of soccer players by 9.6% and 9.5%, respectively. Also, trainings improved the SP by 3.1% and 2.6%, respectively. CBNT and GBT are promising trainings that can improve DB and SP of healthy young soccer players.

#7 Characterization of On-Field Head Impact Exposure in Youth Soccer
Reference: J Appl Biomech. 2020 Nov 3;1-7. doi: 10.1123/jab.2020-0071. Online ahead of print.
Autors: Brian T Tomblin, N Stewart Pritchard, Tanner M Filben, Logan E Miller, Christopher M Miles, Jillian E Urban, Joel D Stitzel
Summary: The objective of this research was to characterize head impacts with a validated mouthpiece sensor in competitive youth female soccer players during a single season with a validated mouthpiece sensor. Participants included 14 youth female soccer athletes across 2 club-level teams at different age levels (team 1, ages 12-13 y; team 2, ages 14-15 y). Head impact and time-synchronized video data were collected for 66 practices and games. Video data were reviewed to characterize the type and frequency of contact experienced by each athlete. A total of 2216 contact scenarios were observed; heading the ball (n = 681, 30.7%) was most common. Other observed contact scenarios included collisions, dives, falls, and unintentional ball contact. Team 1 experienced a higher rate of headers per player per hour of play than team 2, while team 2 experienced a higher rate of collisions and dives. A total of 935 video-verified contact scenarios were concurrent with recorded head kinematics. While headers resulted in a maximum linear acceleration of 56.1g, the less frequent head-to-head collisions (n = 6) resulted in a maximum of 113.5g. The results of this study improve the understanding of head impact exposure in youth female soccer players and inform head impact exposure reduction in youth soccer.

#8 Residual deficits in reactive strength indicate incomplete restoration of athletic qualities following anterior cruciate ligament reconstruction in professional soccer players
Reference: J Athl Train. 2020 Nov 5. doi: 10.4085/169-20. Online ahead of print.
Authors: Paul J Read, William T Davies, Chris Bishop, Sean Mc Auliffe, Mathew G Wilson, Anthony N Turner
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#9 Prediction of Somatotype from Bioimpedance Analysis in Elite Youth Soccer Players
Reference: Int J Environ Res Public Health. 2020 Nov 5;17(21):8176. doi: 10.3390/ijerph17218176.
Authors: Francesco Campa, Catarina N Matias, Pantelis T Nikolaidis, Henry Lukaski, Jacopo Talluri, Stefania Toselli
Summary: The accurate body composition assessment comprises several variables, causing it to be a time consuming evaluation as well as requiring different and sometimes costly measurement instruments. The aim of this study was to develop new equations for the somatotype prediction, reducing the number of normal measurements required by the Heath and Carter approach. A group of 173 male soccer players (age, 13.6 ± 2.2 years, mean ± standard deviation; body mass index, BMI, 19.9 ± 2.5 kg/m2), members of the academy of a professional Italian soccer team participating in the first division (Serie A), participated in this study. Bioelectrical impedance analysis (BIA) was performed using the single frequency of 50 kHz and fat-free mass (FFM) was calculated using a BIA specific, impedance based equation. Somatotype components were estimated according to the Heath-Carter method. The participants were randomly split into development (n = 117) and validation groups (n = 56). New anthropometric and BIA based models were developed (endomorphy = -1.953 - 0.011 × stature2/resistance + 0.135 × BMI + 0.232 × triceps skinfold, R2 = 0.86, SEE = 0.28; mesomorphy = 6.848 + 0.138 × phase angle + 0.232 × contracted arm circumference + 0.166 × calf circumference - 0.093 × stature, R2 = 0.87, SEE = 0.40; ectomorphy = -5.592 - 38.237 × FFM/stature + 0.123 × stature, R2 = 0.86, SEE = 0.37). Cross validation revealed R2 of 0.84, 0.80, and 0.87 for endomorphy, mesomorphy, and ectomorphy, respectively. The new proposed equations allow for the integration of the somatotype assessment into BIA, reducing the number of collected measurements, the instruments used, and the time normally required to obtain a complete body composition analysis.

#10 Potential prognostic factors for hamstring muscle injury in elite male soccer players: A prospective study
Reference: PLoS One. 2020 Nov 9;15(11):e0241127. doi: 10.1371/journal.pone.0241127. eCollection 2020.
Authors: Ismet Shalaj, Masar Gjaka, Norbert Bachl, Barbara Wessner, Harald Tschan, Faton Tishukaj
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Summary: Hamstring injuries remain the most common injury type across many professional sports. Despite a variety of intervention strategies, its incidence in soccer players playing in the UEFA Champions League has increased by 4% per year over the last decade. Test batteries trying to identify potential risk factors have produced inconclusive results. The purpose of the current study was to prospectively record hamstring injuries, to investigate the incidence and characteristics of the injuries, and to identify possible risk factors in elite male soccer players, playing in the Kosovo national premier league. A total of 143 soccer players from 11 teams in Kosovo were recruited. To identify possible prevalent musculoskeletal or medical conditions a widespread health and fitness assessment was performed including isokinetic strength testing, Nordic hamstring strength test, functional tests, and a comprehensive anamnesis surveying previous hamstring injuries. On average 27.9% of the players sustained at least one hamstring injury with three players suffering bilateral strains with the re-injury rate being 23%. Injured players were significantly older and heavier and had a higher body mass index compared to non-injured ones (p < 0.05). There was a lower passing rate in the Nordic hamstring strength test and a higher injury incidence among the previously injured players compared to non-injured ones (p < 0.05). Except for hamstring/quadriceps ratio and relative torque at 60°/sec (p < 0.05) for dominant and non-dominant leg, there were no other significant differences in isokinetic strength regardless of the angular velocity. No differences were observed for functional tests between cohorts. Regression analysis revealed that age, Nordic hamstring strength test, previous injury history, and isokinetic concentric torque at 240°/sec could determine hamstring injuries by 25.9%, with no other significant predicting risk factors. The battery of laboratory and field-based tests performed during preseason to determine performance related skills showed limited diagnostic conclusiveness, making it difficult to detect players at risk for future hamstring injuries.

#11 Perceptions of Stress of Swedish Volunteer Youth Soccer Coaches
Reference: Sports (Basel). 2020 Nov 3;8(11):E146. doi: 10.3390/sports8110146.
Authors: Krister Hertting, Stefan Wagnsson, Karin Grahn
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Summary: The work of a coach can be stressful, and little is known about how volunteer coaches in child and youth soccer perceive stress. Therefore, the overall aim of this study was to explore perceptions of stress among Swedish volunteer youth soccer coaches. An online questionnaire was distributed to 1514 soccer coaches of which 688 (78% men and 22% women; 4% < 30 years, 34% 31-40 years; 57% 41-50 years and 5% > 51 years) with non-profit positions responded. Findings indicate that participants in general do not feel excessively stressed by being a volunteer youth soccer coach (M = 2.20; SD = 0.93; Min = 1; Max = 5), and no significant differences in perceived stress level were found based on gender, age, ethnicity, educational level or occupation. Multiple regression analysis showed that demands from employment (β = 0.24, p < 0.001), difficulty catching up with the family (β = 0.22, p < 0.001), not having enough time to plan activities (β = 0.13, p < 0.001), feeling pressured when selecting the team (β = 0.09, p = 0.013) and own demands to achieve good results (β = 0.07, p = 0.045), significantly contributed to perceptions of stress among the investigated youth sport coaches. The results shed light on the important aim that sport clubs develop holistic strategies when recruiting and retaining coaches and for other functions concerning child and youth soccer teams.

#12 Differences in physical fitness after an 8-week preseason training among elite football players aged 17-19 years
Reference: J Exerc Rehabil. 2020 Oct 27;16(5):442-449. doi: 10.12965/jer.2040598.299. eCollection 2020 Oct.
Authors: Hojun Lee, Chang-Hwa Joo
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Summary: There may be an optimal period of time to maximize the improvement of physical fitness during adolescence. The aim of this study was to examine the magnitude of changes in physical fitness after 8 weeks of preseason training according to chronological ages after the age at peak high velocity. Thirty male young football players from an elite football team (U-16, n=10; U-17, n=10; U-18, n=10) participated in the study. The players completed an 8-week general preseason football training and participated in the pre- and posttests to measure physical fitness. The 8-week preseason training improved the power of all young players (P<0.05). The 20-m sprint performance was improved by training in U-16 and U-18 (P<0.05), but no changes were found in the U-17 group (P>0.05). Significant differences were found in the arrowhead left in U-16 and U-18 (P<0.05) after training; however, no difference was observed in U-17 (P>0.05). Coordination was enhanced further in U-16 and U-17 (P<0.05) compared with that in U-18 (P>0.05). The performance of repeated sprints and Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) were similar between pre- and posttraining in all age groups (P>0.05). Collectively, the results emphasized the importance of systematic and scientific training methods to improve the fitness levels of young football players in the preseason training period. Moreover, training to improve coordination in young football players is effective at younger ages.

#13 What Do Football Players Look at? An Eye-Tracking Analysis of the Visual Fixations of Players in 11 v 11 Elite Football Match Play
Reference: Front Psychol. 2020 Oct 16;11:562995. doi: 10.3389/fpsyg.2020.562995. eCollection 2020.
Authors: Karl Marius Aksum, Lukas Magnaguagno, Christian Thue Bjørndal, Geir Jordet
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Summary: Current knowledge of gaze behavior in football has primarily originated from eye-tracking research in laboratory settings. Using eye-tracking with elite players in a real-world 11 v 11 football game, this exploratory case study examined the visual fixations of midfield players in the Norwegian premier league. A total of 2,832 fixations by five players, aged 17-23 years (M = 19.84), were analyzed. Our results show that elite football midfielders increased their fixation duration when more information sources became available to them. Additionally, participants used shorter fixation durations than previously reported in laboratory studies. Furthermore, significant differences in gaze behavior between the attack and defense phases were found for both areas of interest and fixation location. Lastly, fixation locations were mainly on the ball, opponent, and teammate category and the player in possession of the ball. Combined, the results of this study enhance the knowledge of how elite footballers use their vision when playing under actual match-play conditions. They also suggest that laboratory designs may not be able to capture the dynamic environment that footballers experience in competition.

#14 Effects of a 10 vs. 20-Min Injury Prevention Program on Neuromuscular and Functional Performance in Adolescent Football Players
Reference: Front Physiol. 2020 Oct 15;11:578866. doi: 10.3389/fphys.2020.578866. eCollection 2020.
Authors: Anna Lina Rahlf, Cornelius John, Daniel Hamacher, Astrid Zech
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Summary: Regular injury prevention training is not only effective in reducing sports injury rates, but also in improving neuromuscular and performance-related variables. However, it is currently unknown if this effect can be modified by varying the training dosage. The objective was t compare the effects of two injury prevention programmes with a different training duration on neuromuscular control and functional performance in adolescent football players. 342 (15.4 ± 1.7 years) male football players from 18 teams were initially included. The teams were cluster-randomized into two intervention groups. Both groups performed an injury prevention program twice a week during one football season (10 months) using the same exercises but a different duration. One intervention group (INT10, n = 175) performed the program for 10 min, while the other intervention group (INT20, n = 167) for 20 min. At the beginning and end of the season, balance control (Balance Error Scoring System = BESS), jump performance (Squat Jump, Countermovement Jump) and flexibility (Sit and Reach Test, ankle flexibility, hip flexibility) tests were performed. For the final analysis, nine teams with 104 players were considered. Significant group by time interactions were found for the sit and reach test (p < 0.001) and ankle flexibility (p < 0.001) with higher improvements in the INT20 group. Improvements over the period of one season but no group differences were found for the BESS, Squat Jump and hip flexibility. Within a single training session, performing structured neuromuscular training with a longer duration is more effective than a shorter duration for improving lower extremity flexibility.





Biological Maturity Status in Elite Youth Soccer Players: A Comparison of Pragmatic Diagnostics With Magnetic Resonance Imaging

This study aimed to evaluate commonly used methods to assess BMS within a highly selected sample of youth soccer players.





Endurance Capacities in Professional Soccer Players: Are Performance Profiles Position Specific?

The aim of this study was to investigate position-specific endurance performance of soccer players.





Latest research in football - week 52 - 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 Playing Position, Match Half, and Match Day on the Trunk Inclination, G-Forces, and Locomotor Efficiency Experienced by Elite Soccer Players in Match Play
Reference: Sensors (Basel). 2020 Oct 14;20(20):E5814. doi: 10.3390/s20205814.
Authors: José M Oliva-Lozano, Elisa F Maraver, Víctor Fortes, José M Muyor
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Summary: The rapid growth of wearable sensors has allowed the analysis of trunk kinematics during the match, which is necessary for having a better understanding of the postural demands of soccer players. However, some contextual variables may have an impact on the physical demands of the players. This study aimed to analyze the effect of three contextual variables (playing position, match half, and match day) on the sagittal trunk inclination, G-forces, and locomotor efficiency experienced by soccer players in match play. Then, wearable sensors were used to collect the trunk kinematics during 13 matches. Firstly, positional differences were found on the trunk inclination (p = 0.01) and the G-forces experienced by the players (p < 0.001). For example, the greatest and lowest trunk inclination was found for FW (~34.01°) and FB (~28.85°) while the greatest and lowest G-forces were found for WMF (1.16 G) and CD (1.12 G), respectively. However, there were no positional differences in the locomotor efficiency (p = 0.10). Secondly, the match half had a significant effect on the trunk inclination (p = 0.01) and the G-forces experienced by the players (p < 0.001) with significantly lower values observed during the second half. No differences between halves were found on the locomotor efficiency for any playing position (p = 0.41). Finally, no significant effect of match day on any variable was observed. This investigation is one of the first steps towards enhancing the understanding of trunk kinematics from elite soccer players. The positional differences found on the trunk inclination and G-forces imply that the development of position-specific training drills considering the postural demands is necessary to prepare the players not only for the physical demands but also for successful performance in the field of regard. The resistance to fatigue needs to be trained given the differences between halves.

#2 The use of a running power-meter for performance analysis in five-a-side football
Reference: Gait Posture. 2020 Sep 30;83:35-43. doi: 10.1016/j.gaitpost.2020.09.028. Online ahead of print.
Authors: Paul W Macdermid, Tom Pearce, Andrew Foskett
Summary: Power output considers all movement aspects of the game of football and could have meaningful impact for teams. The aim was to assess inter-reliability of ten power meters designed for running; and as a descriptor of individual and team performance during a five-a-side football match. The work aimed to assess inter-device reliability of running power-meters combined with data analysis from intermittent running, along with descriptives of player work rate, gait and team performance during a small-sided game of football. 10 different running power meters inter-reliability were on a treadmill at 8, 10, 12, and 16 km h-1 for 60 s in a random order. Football players (N = 10) performed the Yo-Yo ET1 with the running power meters to determine participants' endurance capability, while assessing the ability to record metrics of gait and power output during intermittent running. Following a period of 7-days participants took part in a 20 min small-sided game of football wearing the running power meters to provide descriptors of work and gait. Good inter-device reliability for the power meters (CV 1.67, range 1.51-1.94 %) during continuous treadmill running were found. Overall mean ± SD results for Yo-Yo ET1 power output 263 ± 36W, power:weight 3.59 ± 0.34W∙kg-1 significantly (p < 0.05) increased with successive stages, while ground-contact time 234 ± 17 ms, and vertical oscillation 90.7 ± 27 mm did not change (p > 0.05). Descriptive analysis of the small-sided game presented mean ± SD absolute and relative power outputs of 148 ± 44W and 1.98 ± 0.53W∙kg-1, equating to 54 ± 21 %Wmax and 74 ± 5%HRmax. Characteristics of gait included cadence 125 ± 22 rpm, ground contact time 266 ± 19 ms, and vertical oscillation 76.7 ± 7 mm. The winning team worked relatively harder than the losing team (53.3 ± 0.7 %Wmax vs 46.7 ± 0.4 %Wmax, p < 0.0001) with more time (398 s vs 141 s) spent above 70 %Wmax.

#3 Attitudes, beliefs and factors influencing football coaches' adherence to the 11+ injury prevention programme
Reference: BMJ Open Sport Exerc Med. 2020 Sep 24;6(1):e000830. doi: 10.1136/bmjsem-2020-000830. eCollection 2020.
Authors: Julie Shamlaye, Luboš Tomšovský, Mark L Fulcher
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Summary: The purpose was to explore football coaches' beliefs and attitudes about injury prevention and the 11+ injury prevention programme, and to investigate factors that may influence adherence to the 11+ injury prevention programme. A total of 538 football coaches who had completed an injury prevention education workshop were invited to participate in a web-based nationwide survey. The survey questions explored beliefs and attitudes about injury prevention and the 11+ injury prevention programme, self-reported adherence to the 11+ programme, as well as perceived barriers and facilitators to the use of the 11+ programme. There were 158 respondents. The majority believe that injury prevention is part of their coaching role (94%) that a structured warm-up is an important part of their team's preparation for training and games (96%), and that the 11+ is effective (92%). While most respondents (95%) use the 11+, modifications are common. Participants with greater coaching experience are more likely to use the programme. Time constraints are the main barriers to adherence, while knowing that the programme enhances performance is seen as a major facilitator. Coaches who attended an injury prevention workshop have positive attitudes towards injury prevention and the 11+ programme. However, coaches with less coaching experience may be less likely to use the 11+ and could therefore be the target population for future education workshops. Promoting the performance enhancing effects of the 11+ and encouraging modifications could improve acceptability and adherence.

#4 Mechanisms explaining the birthplace effect for male elite football players
Reference: J Sports Sci. 2020 Oct 21;1-7. doi: 10.1080/02640414.2020.1835237. Online ahead of print.
Authors: Michiel H H van Nieuwstadt, Marjolijn Das, Marije T Elferink-Gemser
Summary: Earlier research shows that wide regional variations exist in the success of athletes' talent development but is divided with respect to the role of urbanity: both low and high urbanity have been identified as settings that contribute to the presence of talent hotspots. In this article, we intend to provide more insight into the role of urbanity in talent development in Dutch football. We used public data on the regional background of male elite players (N = 825) and combined this with public data on municipal characteristics from Statistics Netherlands and other sources: urbanity, football participation, instructional resources and population composition effects (migration background and income of inhabitants). Linear regression analysis showed that football participation, the proportion of non-western migrants and median income predict "talent yield", i.e., the proportion of young people that reach an elite level in a municipality. Urbanity does not have an independent influence when the proportion of non-western migrants in the municipality is taken into account. The presence of instructional resources does not have an independent influence. The results suggest that characteristics of the built environment, such as indoor and outdoor play opportunities, may be less influential in talent development than previously assumed.

#5 Short-Term Effect of Ankle Eversion Taping on Bilateral Acute Ankle Inversion Sprains in an Amateur College Football Goalkeeper: A Case Report
Reference: Healthcare (Basel). 2020 Oct 15;8(4):E403. doi: 10.3390/healthcare8040403.
Authors: Jung-Hoon Lee
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Summary: This case study aimed to investigate the short-term effects of ankle eversion taping (AET) using kinesiology tape on bilateral acute ankle inversion sprains in an amateur college soccer goalkeeper. Ankle eversion taping was applied for two weeks (average 16 h/day) on a 24-year-old goalkeeper with bilateral grade 2 acute ankle inversion sprain with swelling (left ankle more severe) during a soccer match. The subject had a foot ankle outcome score (FAOS) of 41%; visual analog scale (VAS) scores of 5/10 and 7/10 for the right and left ankles, respectively; patient-specific functional and pain scale (PSFS) score of 12/50; and limited range of motion of the ankle. The swelling disappeared after AET in both ankles. In the weight-bearing lunge test, the right and left ankle distances increased from 2 cm to 12 cm, and from 0 cm to 12 cm, respectively. The FAOS improved from 20% to 97%, while the PSFS score improved from 12/50 to 50/50. The VAS scores decreased to 0/10 for both ankles. AET is a potential clinical treatment method for acute ankle inversion sprain with swelling.

#6 How Successful Are the Teams of the European Football Elite off the Field?-CSR Activities of the Premier League and the Primera División
Reference: Int J Environ Res Public Health. 2020 Oct 16;17(20):7534. doi: 10.3390/ijerph17207534.
Authors: Kinga Ráthonyi-Ódor, Éva Bácsné Bába, Anetta Müller, Zoltán Bács, Gergely Ráthonyi
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Summary: In the past two decades the sports sector has turned its attention to understanding the idea of sustainability, particularly to the practical steps related to this. The purpose of this study is to investigate the nature of CSR (corporate social responsibility) activities carried out by teams playing in the Premier League and the Primera División in the 2018/2019 season, and how these CSR actions serve environmental protection and society, manifesting the concept of sustainable development. We applied comparative analysis based on secondary databases. We examined the available reports regarding all the 40 teams, focusing on information about their CSR aspirations and related academic research results, and we worked out specific criteria to evaluate environmentally and socially related CSR activities. Arsenal and Real Madrid were chosen to show good practices that can serve as examples for the other members of the sports sector. At Premier League clubs, the practical application of the CSR activities has been intensively developed. Clubs share detailed statistical information about their actions, while some of the clubs even publish their future plans. The quantity and detail of the information found with Primera División clubs is rather varied. Some clubs introduce their CSR activities in full detail; however, in the case of most clubs, the accessible information is rather superficial and lacks any exact descriptions. The findings clearly show that the sports world is consciously shifting towards the realization of sustainable development, which requires a comprehensive reconnection of sporting society and an increase in awareness in order to achieve the efficient and successful integration of CSR activities into sport.

#8 The sound of silence in association football: Home advantage and referee bias decrease in matches played without spectators
Reference: Eur J Sport Sci. 2020 Nov 1;1-21. doi: 10.1080/17461391.2020.1845814. Online ahead of print.
Authors: Fabrizio Sors, Michele Grassi, Tiziano Agostini, Mauro Murgia
Summary: Home advantage and referee bias are two well-documented phenomena in professional sports, especially in association football. Among the various factors determining them, the crowd noise is considered as one of the most relevant; yet, the majority of previous studies could not isolate its contribution. The possibility to study the effects of crowd noise - or, better, of its absence - in an ecological context was given by the matches played behind closed doors due to the COVID-19 pandemic. The aim of the present study was to investigate whether home advantage and referee bias still occur (and to what extent) during matches played in absence of spectators. In particular, the focus was on the first and second divisions of the top four countries in the UEFA ranking, for a total of 841 matches behind closed doors. The hypothesis was that, if these phenomena are largely due to the effect of crowd noise, the absence of spectators should reduce their occurrence. Various parameters for each of the two phenomena were considered, and the analyses revealed a reduction of home advantage and the absence of referee bias. The results bring further support to the claim that, among all the factors contributing to home advantage and referee bias, crowd noise has a relevant role. Thus, spectators can significantly contribute to determine the dynamics and the outcomes of professional football matches.

#9 Special Issue on Concussion Biomechanics in Football
Reference: Ann Biomed Eng. 2020 Nov 3. doi: 10.1007/s10439-020-02653-3. Online ahead of print.
Authors: Bethany Rowson, Stefan M Duma
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#10 Athlete workloads during collegiate women's soccer practice: Implications for return-to-play
Reference: J Athl Train. 2020 Nov 5. doi: 10.4085/205-20. Online ahead of print.
Authors: Natalie Kupperman, Alexandra F DeJong, Peter Alston, Jay Hertel, Susan A Saliba
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Summary: Athlete monitoring using wearable technology is often incorporated with soccer athletes. While evaluations have tracked global outcomes across soccer seasons, there is little information on athlete loads during individual practice drills. Understanding these demands is important for athletic trainers for return-to-play decision-making. The objective was to provide descriptive information on total distance, total playerload (PL), distance per minute, and PL per minute for practice drill structures and game-play by player position among female soccer athletes across a competitive season. Thirty-two female college soccer players (20±1 years) participated in this study. Athletes wore a single GPS and triaxial accelerometer unit during all practices and games in a single soccer season. Individual practice drills were labeled by the team's strength and conditioning coach, and binned into physical, technical and tactical skills, and small- and large-sided competition drill structures. Descriptive analyses were used to assess the median total distance, total PL, distance per minute, and PL per minute by drill structure and player position (defenders, midfielders, forwards/strikers) during practices and games. Small- and large-sided competitive drills imposed the greatest percentage of workload across all measures for each position (~20% of total practice), followed by physical drills. When comparing technical and tactical, technical skills required athletes to cover the greatest distance (technical: ~17%; tactical: ~15%), tactical skills required higher play intensity during practices across all positions (technical: ~18%; tactical: ~13%). Defenders had the highest median PL outcomes of all positions during practices. Different practice drill types imposed varying levels of demands on female soccer athletes, which simulated game play. Athletic trainers and other clinicians may use this information for formulating objective return-to-play guidelines for injured collegiate women's soccer players.

#11 The relationship between Isometric Mid-Thigh Pull variables and athletic performance measures: empirical study of english professional soccer players and meta-analysis of extant literature
Reference: J Sports Med Phys Fitness. 2020 Nov 4. doi: 10.23736/S0022-4707.20.11205-2. Online ahead of print.
Authors: Liam Mason, Andrew Kirkland, James Steele, James Wright
Summary: There is currently limited evidence available to support the use of the isometric mid thigh pull (IMTP) within professional soccer. The aim of this study was to analyse the association between IMTP variables, with common markers of athletic performance capability. Eleven professional development soccer players (age: 20 ± 2 years, stature: 1.82 ± 0.10 m, mass: 76.4 ± 12.8 kg) performed IMTP, 5 m and 10 m accelerations, maximal sprint speed (MSS), countermovement jump (CMJ), and the 505 change of direction test (COD). Relative and absolute Peak force (PF) and force at 50, 100, 150 and 200 ms values were measured during the IMTP. Relative F150, F200, PF displayed large to very large correlations with MSS (r = 0.51, r = 0.66, and r = 0.76 respectively), while absolute PF also displayed a large correlation with MSS (r = 0.57). Relative and absolute PF showed large correlations with CMJ height (r = 0.54 and r = 0.55 respectively). Relative F150 and F200 highlighted large correlations with COD ability (r = -0.68 and r = -0.60 respectively). Relative F200 and PF had a large negative correlation with 10m acceleration (r = -0.55 and r = -0.53 respectively). This study provides an important contribution to knowledge within the area of IMTP testing in professional soccer by evidencing the prominence of the isometric force generating capacity as an underpinning factor in relation to athletic capability.

#12 Effects of Strength vs. Plyometric Training on Change of Direction Performance in Experienced Soccer Players
Reference: Sports (Basel). 2020 Oct 30;8(11):E144. doi: 10.3390/sports8110144.
Authors: Håvard Guldteig Rædergård, Hallvard Nygaard Falch, Roland van den Tillaar
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Summary: The purpose of this study was to compare how 6 weeks of strength- vs. plyometric training, which were matched upon direction of motion and workload, influences change of direction (COD) performance. Twenty-one experienced male soccer players (age: 22.2 ± 2.7) were pair-matched into a strength- (n = 10) and a plyometric (n = 11) training group. CODs of 45°, 90°, 135° and 180° performed from either a 4 m or 20 m approach distance were compared before and after intervention. Results showed no significant difference between groups. Significant effects were only found within the plyometric training group (-3.2% to -4.6%) in 90°, 135° and 180° CODs from 4 m and a 180° COD from a 20 m approach distance. Individual changes in COD performances showed that with the 4 m approach at least 55% and 81% of the strength and plyometric training group, respectively, improved COD performance, while with the 20 m approach at least 66% of both groups improved performance. This study showed that the plyometric training program can improve most CODs, with angles over 90°, although this is dependent on the distance approaching the COD. Considering the limited time of implementing physical conditioning, in addition to regular soccer practice in most soccer environments, the current plyometric training program can be advantageous in improving CODs at maximal intensity.

#13 Purposeful Heading in Youth Soccer: A Review
Reference: Sports Med. 2020 Nov 3. doi: 10.1007/s40279-020-01376-8. Online ahead of print.
Authors: Victoria E Wahlquist, Thomas W Kaminski
Summary: Recent public concern over the short- and long-term effects of repetitive head impacts (RHI) associated with purposeful heading in soccer has led researchers to study a multitude of variables related to this important aspect of the game. Of particular interests are the effects of soccer heading in the youth population (≤ 13 years old) whose brains are undergoing rapid development. We conducted a review on youth soccer heading that includes purposeful heading frequency, head impact biomechanics, head injuries, clinical outcomes, and modifying factors. We have concluded that youth soccer players head the ball at a low frequency that typically increases with age and with a finding that boys head the ball more often than girls do. Interestingly, although girls head the ball less frequently than boys do, they tend to sustain higher head impact magnitudes. Head injuries are more likely to occur in girls versus boys and during games because of contact with another player. Clinical outcome measures of concussion are often utilized to study the effects of soccer heading, in both field and laboratory environments. Immediately following soccer heading, youth often report having a headache and demonstrate some deficits in balance measures. Modifying factors that may benefit soccer players participating in purposeful heading activities include stronger neck musculature, wearing headgear, and the use of mouthguards. Research involving youth soccer players needs to be expanded and funded appropriately to better understand the consequences of RHI in both the short and long term.

#14 Relationships Between Training Workload Parameters with Variations in Anaerobic Power and Change of Direction Status in Elite Youth Soccer Players
Reference: Int J Environ Res Public Health. 2020 Oct 29;17(21):E7934. doi: 10.3390/ijerph17217934.
Authors: Hadi Nobari, Luis Felipe Tubagi Polito, Filipe Manuel Clemente, Jorge Pérez-Gómez, Mina Ahmadi, Miguel Ángel Garcia-Gordillo, Ana Filipa Silva, Jose Carmelo Adsuar
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Summary: The purpose of this study was to test the relationships between training workload (WL) parameters with variations in anaerobic power and change of direction (COD) in under-16 soccer players. Twenty-three elite players under 16 years were daily monitored for their WL across 20 weeks during the competition soccer season. Additionally, players were assessed three times for anthropometric, body composition, COD, and anaerobic power. A correlational analysis between the mean differences between assessments and accumulated WL parameters were conducted. Moreover, a regression analysis was executed to explain the variations in the percentage of change in fitness levels considering the accumulated WL parameters and peak height velocity. The accumulated daily loads during one week showed a large and a moderate correlation with peak power and COD at different periods of the season. Regression analysis showed no significant predictions for COD (F(12, 10) = 1.2, p = 0.41) prediction, acute load (F(12, 10) = 0.63, p = 0.78), or chronic load (F(12, 10) = 0.59, p = 0.81). In conclusion, it may be assumed that the values of the chronic workload and the accumulated training monotony can be used to better explain the physical capacities of young soccer players, suggesting the importance of psychophysiological instruments to identify the effects of the training process in this population.

#15 Coronavirus Disease-19 Quarantine Is More Detrimental Than Traditional Off-Season on Physical Conditioning of Professional Soccer Players
Reference: J Strength Cond Res. 2020 Oct 30. doi: 10.1519/JSC.0000000000003890. Online ahead of print.
Authors: Rafael Grazioli, Irineu Loturco, Bruno M Baroni, Gabriel S Oliveira, Vasyl Saciura, Everton Vanoni, Rafael Dias, Filipe Veeck, Ronei S Pinto, Eduardo L Cadore
Summary: Beyond the severe health crisis, the coronavirus disease 2019 has also affected the high-performance sports scenario. In soccer, practitioners are concerned about the effects of long-term detraining on players' conditioning, and caution is required when activities return. This study assessed body composition, jump and sprint performance, hamstring eccentric strength, and intermittent cardiorespiratory fitness of 23 male professional soccer players who returned to training activities after 63 days of quarantine. The results were compared with their physical condition assessed before a pre-season phase as soon as they returned to training after a regular 24-day off-season period. In comparison with after off-season assessments, the quarantine induced significant increases in body mass, body fat mass, 10- and 20-m sprint times as well as decreases in countermovement jump height (p < 0.05). There were no significant changes in hamstring eccentric strength, squat jump height, and cardiorespiratory fitness (p > 0.05). In summary, we showed that 63 days of quarantine impaired several physical performance measures compared with regular off-season in soccer players. Given the present results, special attention should be given to body composition-related and speed power-related capabilities after long-term detraining in professional soccer.

#16 Monitoring Training Load in Soccer: The ROMEI Model
Reference: J Strength Cond Res. 2020 Oct 30. doi: 10.1519/JSC.0000000000003875. Online ahead of print.
Authors: Marco Montini, Jacopo E Rocchi
Summary: For a training organization, monitoring training load (TL) is of paramount importance. Despite this, a conclusive response on such topic is yet to be reported. The aims of this study were to investigate the relationship between TL indicators and to propose a new method for monitoring TL response and physical fitness. Twenty professional soccer players were retrospectively evaluated. The first phase of data analysis included 34 in-season training sessions. Subsequently, three microcycles (T1-T2-T3) of pre-season training were processed. A regression model was used to examine the relationships between internal TL (session rating of perceived exertion [s-RPE]) and external TL (energy expenditure, EE). The standard error of the regression equation was used to propose a new model called "ROMEI" (Relation of Ongoing Monitored Exercise in Individual). The level of statistical significance was set at p < 0.05. During the competitive season and the pre-season training camp, the average TL values were 65.8 ± 22 and 58.2 ± 22 minutes; 336 ± 204 and 228 ± 101 AU of s-RPE; and 29 ± 13 and 25 ± 9 kJ kJ of EE, respectively. In the competitive season, the collective and average individual correlation coefficients between s-RPE and EE were r = 0.888 and r = 0.892 ± 0.05, respectively. Considering slope values (m) of the regression line, data highlighted a significant increase of +34.4 ± 15.9% in T2 vs. T3 (p < 0.001) and +38.2 ± 15.2% in T1 vs. T3 (p < 0.001). Data shown in this investigation support the use of an individualized analysis to better understand the TL administered to soccer players rather than a collective analysis. This may be accomplished with the proposed ROMEI model.





Player Monitoring in Professional Soccer: Spikes in Acute:Chronic Workload Are Dissociated From Injury Occurrence

This study aimed to determine whether spikes in acute:chronic workload ratio (ACWR) are associated with injury incidence and to examine the differences in external load due to greater or lesser exposure to matches and the long-term effects of the load during a chronic seasonal period.





Biomechanical measures during two sport-specific tasks differentiate between footballers with and without future ACL injury


The aim was to determine whether prospectively measured components of valgus collapse during a deceleration cut can differentiate between female footballers who go on to non-contact ACL injury





Latest research in football - week 51 - 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 Are goals scored just before halftime worth more? An old soccer wisdom statistically tested
Reference: PloSONE. 2020 Oct 20;15(10):e0240438. doi: 10.1371/journal.pone.0240438.
Authors: Henrich R Greve, Jo Nesbø, Nils Rudi, Marat Salikhov
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Summary: There is an old soccer wisdom that a goal scored just before halftime has greater value than other goals. Many dismiss this old wisdom as just another myth waiting to be busted. To test which is right we have analysed the final score difference through linear regression and outcome (win, draw, loss) through logistic regression. We use games from many leagues, control for the halftime score, comparing games in which a goal was scored after 1 minute remained of regulation time with games in which it was scored before the 44th minute. Our main finding is that the home team scoring just before halftime influence these outcomes to its advantage, compared with scoring earlier with the same halftime score. We conclude that a goal scored just before halftime has greater value than other goals provided it is scored by the home team. In other words; the wisdom may be old, but it's still wise.

#2 Assessing Interlimb Jump Asymmetry in Young Soccer Players: The My Jump 2 App
Reference: Int J Sports Physiol Perform. 2020 Oct 19;1-9. doi: 10.1123/ijspp.2019-0981. Online ahead of print.
Authors: Matheus Barbalho, Ana Francisca Rozin Kleiner, Bianca Callegari, Ramon Costa de Lima, Givago da Silva Souza, Anselmo de Athayde Costa E Silva, Victor Silveira Coswig
Summary: Jumps are important evaluation tools for muscle strength and power and for interlimb asymmetries. Different jump tests are well related to athletic performance, prediction of injury risk, and common motor gestures of several sports such as soccer. Low-cost mobile applications (apps) have gained popularity for this measure. The authors hypothesized that the My Jump 2 app would be a valid tool to assess drop-jump performance and interlimb asymmetry in soccer players. Eleven male soccer players took part in this study (18.2 [1.3] y, 69.9 [9.5] kg, 174 [6.6] cm). The athletes performed each test twice on a force plate (gold-standard method), while the jumps were recorded through the mobile app. Measures with the My Jump 2 app were applied by 2 evaluators, independently and in duplicate (interrater and intrarater reliability). The agreement analysis between both evaluations was done using an intraclass correlation coefficient and Bland-Altman plots. Compared with the force platform, the app tested showed excellent reliability for the drop jump's flight time and interlimb asymmetry (intraclass correlation coefficient > .98). For interlimb contact-time asymmetry, the values were 18.4 (9.9) and 19.1 (9.9) milliseconds for the My Jump 2 app and the force platform, respectively (P = .88). For flight-time asymmetries, the values were 389.7 (114.3) and 396.8 (112.5) milliseconds for the My Jump 2 app and the force platform, respectively (P = .88). The My Jump 2 app is a valid tool to assess drop-jump and interlimb asymmetry in soccer players.

#3 Soccer-Related Concussions Among Swedish Elite Soccer Players: A Descriptive Study of 1,030 Players
Reference: Front Neurol. 2020 Sep 23;11:510800. doi: 10.3389/fneur.2020.510800. eCollection 2020.
Authors: Sofie Hänni, Fredrik Vedung , Yelverton Tegner, Niklas Marklund, Jakob Johansson
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Summary: There are growing concerns about the short- and long-term consequences of sports-related concussion, which account for about 5-9% of all sports injuries. We hypothesized there may be sex differences in concussion history and concussion-related symptoms, evaluated among elite soccer players in Sweden. Soccer players (n = 1,030) from 55 Swedish elite soccer teams participated in this study. Questionnaires were completed prior to the start of the 2017 season. Player history of soccer-related concussion (SoRC), symptoms and management following a SoRC were evaluated. Before the start of the season the players completed a baseline questionnaire assessing previous concussions. The Sports Concussion Assessment Tool 3 was included with regard to symptom evaluation. Out of 993 responding players 334 (34.6%) reported a previous SoRC and 103 players (10.4%) reported a SoRC during the past year. After sustaining a SoRC, 114 players (34.2%) reported that they continued their ongoing activity without a period of rest, more commonly female (44.9%) than male players (27.7%; P = 0.002). Symptom resolution time was 1 week or less for 61.3% of the players that reported having persisting symptoms. A positive correlation was observed between number of previous concussions and prevalence of three persisting symptoms: fatigue (P < 0.001), concentration/memory issues (P = 0.002) and headache (P = 0.047). About 35% of male and female elite soccer players in Sweden have experienced a previous SoRC, and about 10% experienced a SoRC during the last year. Female players continued to play after a SoRC, without a period of rest, more often than males. A higher risk of persisting symptoms was observed in players with a history of multiple concussions.

#4 The Academic Background of Youth Soccer Coaches Modulates Their Behavior During Training
Reference: Front Psychol. 2020 Sep 24;11:582209. doi: 10.3389/fpsyg.2020.582209. eCollection 2020.
Authors: David Agustí, Rafael Ballester, Jordi Juan-Blay, William G Taylor, Florentino Huertas
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Summary: This investigation aims to explore the relationship between the academic backgrounds of youth soccer coaches (U10 and U12 age groups) in Spain and the type of verbal behavior used during training sessions. The sample consisted of 70 coaches divided into two groups, depending on whether or not they had engaged with a university-level academic studies related to Physical Education and or Sport Sciences. A modified version of the "Coach Analysis and Intervention System" (CAIS), developed by Cushion et al. (2012), was used to collect data. A total of 32,886 verbal behaviors were noted and analyzed. Our results suggest that the coaches with university academic backgrounds frequently use more verbal behaviors and that these could be associated with positive effects on the players' learning and development processes. We suggest it is important to develop specific training programs aimed at optimizing the coaches' communicative and socio-affective skills in order to maximize their impact in youth athletes' learning process.

#5 Perceived barriers to implementation of injury prevention programs among collegiate women's soccer coaches
Reference: J Sci Med Sport. 2020 Sep 29;S1440-2440(20)30775-1. doi: 10.1016/j.jsams.2020.09.016.
Authors: Celeste Dix, David Logerstedt, Amelia Arundale, Lynn Snyder-Mackler
Summary: Knee injury prevention programs (IPPs) reduce knee and anterior cruciate ligament (ACL) injury rates in female athletes, however, implementation of IPPs is low. The purpose of this study was to identify barriers to implementation of IPPs among collegiate women's soccer coaches. A custom survey based on the RE-AIM (reach, effectiveness, adoption, implementation, maintenance) framework and existing literature was sent to 151 out of 153 women's National Collegiate Athletic Association (NCAA) soccer coaches in the NCAA's Eastern Region. Ten respondents reported that they did not use an IPP (Non-users), and nineteen respondents reported that they did use an IPP (Users). "Cost" was the most highly ranked barrier (median rank: 2) to implementing an IPP among Non-users. For the statement, "Who should be responsible for completing an IPP," Users said "Coaches" (47%) and "Other" (21%), while Non-users said "Strength and conditioning" (50%) and "Athletic trainers" (30%). Respondents who marked "Other", elaborated that it was the responsibility of coaches, athletes, and additional staff members. Cost was the primary barrier to implementation of an IPP. Since the majority of Non-users indicated that implementation of an IPP was the responsibility of a non-coaching staff member, cost may be a surrogate for the expense of hiring an additional staff member rather than the cost of performing the IPP itself. Additionally, using a team-based approach that encompasses athletes, coaches, and non-coaching staff members may support long-term implementation of IPPs.

#6 Head impacts in semiprofessional male Soccer players: a prospective video analysis over one season of competitive games
Reference: Brain Inj. 2020 Oct 18;1-6. doi: 10.1080/02699052.2020.1831067. Online ahead of print.
Authors: Hélène Cassoudesalle, Maxime Bildet, Hervé Petit, Patrick Dehail
Summary: Soccer exposes players to head injuries and involves repeated intentional head impacts through heading the ball. Our objective was to investigate the rate of both intentional headers and involuntary head impacts in semiprofessional male soccer players during one season. In this prospective cohort study, we followed 54 men (16-35 years) playing in two soccer clubs participating in the same regional French championship throughout the 2017-2018 season. All head impacts that occurred in competitive games were analyzed using video recordings. Player position, game exposure, referee's decision were also reported. Head impact incidence rate (IR) per 1000 player-hours, with the 95% confidence intervals (CIs) were calculated. Results: Headers IR was 3584.7 per 1000 player-hours (95% CI = 3431.9, 3737.5). Forwards and center-backs performed a higher number of headers. Involuntary head impacts IR was 44.1/1000 player-hours (95% CI = 27.1, 60.9). Just under half led the referee to stop playing time for a caregiver examination. Three concussions with a loss of consciousness after a head-to-head impact in a heading duel were recorded. Conclusions: Intentional headers were relatively common, contrary to involuntary head impacts that were however mainly due to heading duels. Head-to-head impact should lead to a systematic exit from the game for suspicion of concussion.

#7 The Effect of Fixture Congestion on Performance During Professional Male Soccer Match-Play: A Systematic Critical Review with Meta-Analysis
Reference: Sports Med. 2020 Oct 17. doi: 10.1007/s40279-020-01359-9. Online ahead of print.
Authors: Ross Julian, Richard Michael Page, Liam David Harper
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Summary: Fixture congestion (defined as a minimum of two successive bouts of match-play, with an inter-match recovery period of < 96 h) is a frequent and contemporary issue in professional soccer due to increased commercialisation of the sport and a rise in the number of domestic and international cup competitions. To date, there is no published systematic review or meta-analysis on the impact of fixture congestion on performance during soccer match play. We sought to conduct a systematic review and meta-analysis of the literature related to the effects of fixture congestion on physical, technical, and tactical performance in professional soccer match-play. Adhering to PRISMA guidelines and following pre-registration with the Open Science Framework ( ), a comprehensive and systematic search of three research databases was conducted to identify articles related to soccer fixture congestion. For inclusion in the systematic review and meta-analysis, studies had to include male professional soccer players, a congestion period that contained two matches ≤ 96 h, and have outcome measures related to physical, technical or tactical performance. Exclusion criteria comprised non-male and/or youth players, data that only assessed impact of congestion on injury, used simulated protocols, or were grey literature, such as theses or dissertations. Out of sixteen articles included in the systematic review, only five were eligible for the meta-analysis, and the only variable that was measured consistently across studies was total distance covered. Fixture congestion had no impact on total distance covered [p = 0.134; pooled standardized mean difference; Hedge's G = 0.12 (- 0.04, 0.28)]. Between-study variance, heterogeneity, and inconsistency across studies were moderate [Cochrane's Q = 6.7, p = 0.150, I2 = 40.7% (CI 0.00, 93.34)]. Data from articles included in the systematic review suggest fixture congestion has equivocal effects on physical performance, with variation between studies and low quality of research design in some instances. Tactical performance may be negatively impacted by fixture congestion; however, only one article was identified that measured this element. Technical performance is unchanged during fixture congestion; however, again, research design and the sensitivity and relevance of methods and variables require improvement. Total distance covered is not impacted by fixture congestion. However, some studies observed a negative effect of fixture congestion on variables such as low- and moderate-intensity distance covered, perhaps suggesting that players employ pacing strategies to maintain high-intensity actions. There is a lack of data on changes in tactical performance during fixture congestion. With ever increasing numbers of competitive matches scheduled, more research needs to be conducted using consistent measures of performance (e.g., movement thresholds) with an integration of physical, technical and tactical aspects.

#8 Effect of Playing Position, Match Half, and Match Day on the Trunk Inclination, G-Forces, and Locomotor Efficiency Experienced by Elite Soccer Players in Match Play
Reference: Sensors (Basel). 2020 Oct 14;20(20):E5814. doi: 10.3390/s20205814.
Authors: José M Oliva-Lozano, Elisa F Maraver, Víctor Fortes, José M Muyor
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Summary: The rapid growth of wearable sensors has allowed the analysis of trunk kinematics during the match, which is necessary for having a better understanding of the postural demands of soccer players. However, some contextual variables may have an impact on the physical demands of the players. This study aimed to analyze the effect of three contextual variables (playing position, match half, and match day) on the sagittal trunk inclination, G-forces, and locomotor efficiency experienced by soccer players in match play. Then, wearable sensors were used to collect the trunk kinematics during 13 matches. Firstly, positional differences were found on the trunk inclination (p = 0.01) and the G-forces experienced by the players (p < 0.001). For example, the greatest and lowest trunk inclination was found for FW (~34.01°) and FB (~28.85°) while the greatest and lowest G-forces were found for WMF (1.16 G) and CD (1.12 G), respectively. However, there were no positional differences in the locomotor efficiency (p = 0.10). Secondly, the match half had a significant effect on the trunk inclination (p = 0.01) and the G-forces experienced by the players (p < 0.001) with significantly lower values observed during the second half. No differences between halves were found on the locomotor efficiency for any playing position (p = 0.41). Finally, no significant effect of match day on any variable was observed. This investigation is one of the first steps towards enhancing the understanding of trunk kinematics from elite soccer players. The positional differences found on the trunk inclination and G-forces imply that the development of position-specific training drills considering the postural demands is necessary to prepare the players not only for the physical demands but also for successful performance in the field of regard. The resistance to fatigue needs to be trained given the differences between halves.

#9 Effects of Combined Strength and Resisted Sprint Training on Physical Performance in U-19 Elite Soccer Players
Reference: J Strength Cond Res. 2020 Oct 15. doi: 10.1519/JSC.0000000000003829. Online ahead of print.
Authors: Mehdi Ben Brahim, Rim Bougatfa, Emna Makni, Pablo Prieto Gonzalez, Hussain Yasin, Raghad Tarwneh, Wassim Moalla, Mohamed Elloumi
Summary: This study assessed the effects of combined muscular strength and resisted sprint training using both sled and weight vest compared with regular soccer training on physical fitness of lower limbs in U-19 elite soccer players. Thirty-four male soccer players (age: 18.8 ± 0.8 years, height: 1.81 ± 0.05 m, body mass: 76.4 ± 4.9 kg, and body fat mass: 11.3 ± 4.2%) were randomly assigned into a resisted sprint training group (RSTG, n = 20), using both weight vest and sled, and a control group (CONTG, n = 14). Sprinting ability (5 m and 20 m), squat jump (SJ) and counter-movement jump (CMJ) tests, 1 repetition maximum of half-back squat (1RM half-back squat), and soccer ball-shooting speed were assessed before and after a 6-week training program. Within-group interactions showed significant combined muscular strength and resisted sprint training effects were observed for all the tests' measurements (effect sizes = 0.97 and 3.69 for 20-m sprint and SJ, respectively). However, significant increases of performances were observed for 5-m and 20-m sprinting time ( = 0.25, p < 0.01 and = 0.22, p < 0.01, respectively), SJ and CMJ ( = 0.78, p < 0.0001 and = 0.34, p < 0.001, respectively), 1 repetition maximum (1-RM) half-back squat ( = 0.45, p < 0.0001), and soccer ball-shooting speed ( = 0.41, p < 0.0001) in RSTG with large effect size, whereas the CONTG showed significant performances increase only for CMJ (p < 0.05), 1RM half-back squat (p < 0.01), and soccer ball-shooting speed (p < 0.05). We conclude that combined strength and both horizontal (weighted sled) and vertical (weighted vest) resisted sprint training are more effective than regular soccer training for enhancing sprinting and jumping abilities as well as ball-shooting speed in soccer.

#10 Neck and Trunk Strength Training to Mitigate Head Acceleration in Youth Soccer Players
Reference: J Strength Cond Res. 2020 Oct 15. doi: 10.1519/JSC.0000000000003822. Online ahead of print.
Authors: Carsten Müller, Karen Zentgraf
Summary: Heading in soccer involves repetitive head accelerations that may be detrimental for brain health. One way to mitigate adverse effects may be to increase head-neck stabilization and thus reduce the kinematic response after intentional headers. This study aimed to (a) assess associations between neck strength and head kinematics and (b) evaluate an exercise intervention designed to increase strength and attenuate head acceleration during intentional heading in youth soccer players. In 22 athletes, we used accelerometers to assess associations between neck strength and peak linear acceleration (PLA). We attached the accelerometers to the occiput and sternum, allowing us to differentiate between total, trunk, and head PLA. Longitudinally, we evaluated the effects of a 14-week twice-weekly resistance training in a subsample of 14 athletes compared with regular soccer training (N = 13). Results showed that female athletes had lower isolated neck strength (p ≤ 0.004), lower functional neck strength (p ≤ 0.017), and higher total PLA during purposeful headers compared with males (17.2 ± 3.5 g and 13.0 ± 2.3 g, respectively, at 9.6 m·s ball velocity during impact; p = 0.003). The intervention group showed moderate to large strength gains ( = 0.16-0.42), resulting in lower PLA (total -2.4 g, trunk -0.8 g, and head -1.5 g) during headers. We conclude that a resistance training focusing on cervical and trunk musculature is practicable in youth soccer, elicits strength gains, and helps to mitigate PLA during purposeful heading. Results should encourage youth strength and conditioning professionals to incorporate neck exercises as a risk reduction strategy into their training routine.

#11 Factors affecting peak impact force during soccer headers and implications for the mitigation of head injuries
Reference: PLoS One. 2020 Oct 16;15(10):e0240162. doi: 10.1371/journal.pone.0240162. eCollection 2020.
Authors: Joshua Auger, Justin Markel, Dimitri D Pecoski, Nicolas Leiva-Molano, Thomas M Talavage, Larry Leverenz, Francis Shen, Eric A Nauman
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Summary: It has been documented that up to 22% of all soccer injuries are concussions. This is in part due to players purposely using their head to direct the ball during play. To provide a more complete understanding of head trauma in soccer athletes, this study characterized the effects of four soccer ball characteristics (size, inflation pressure, mass, velocity) on the resulting peak impact force as it relates to the potential for incurring neurophysiological changes. A total of six hundred trials were performed on size 4 and 5 soccer balls as well as a novel lightweight soccer ball. Impact force was measured with a force plate and ball velocity was determined using motion capture. These data were used, in conjunction with dimensional analysis to relate impact force to ball size, mass, velocity, and pressure. Reasonable reductions in allowable ball parameters resulted in a 19.7% decrease in peak impact force. Adjustments to ball parameters could reduce a high cumulative peak translational acceleration soccer athlete down into a previously defined safer low loading range. In addition, it was noted that water absorption by soccer balls can result in masses that substantially increase impact force and quickly surpass the NCAA weight limit for game play. Additional research is required to determine whether varying soccer ball characteristics will enable soccer players to avoid persistent neurophysiological deficits or what additional interventions may be necessary and the legal implications of these data are discussed.

#12 Sex and Sport Differences in College Lacrosse and Soccer Head Impact Biomechanics
Reference: Med Sci Sports Exerc . 2020 Nov;52(11):2349-2356. doi: 10.1249/MSS.0000000000002382.
Authors: Jason P Mihalik, Stephanie A Amalfe, Patricia R Roby, Cassie B Ford, Robert C Lynall, Kaitlin E Riegler, Elizabeth F Teel, Erin B Wasserman, Margot Putukian
Summary: Sport-related head impact biomechanics research has been male-centric and focused primarily on American football and ice hockey, which do not address popular sports in which both sexes participate. The purpose of this study was to quantify college female and male lacrosse and soccer head impact biomechanics. Head impact biomechanics were collected from college lacrosse and soccer players across two Division 1 college athletic programs (96 female athletes, 141 male athletes; age, 19.8 ± 1.3 yr; height, 174.8 ± 9.2 cm; mass, 72.4 ± 11.7 kg). We deployed helmetless head impact measurement devices (X2 Biosystems xPatch) before each event. Peak linear and rotational accelerations were log-transformed for random intercepts general linear mixed models, and subsequently categorized based on impact magnitude for additional categorical analyses. Most linear (69.4%) and rotational (72.3%) head impact accelerations sustained by our study cohort were categorized as mild. On average, male athletes sustained impacts with higher linear accelerations than females (P = 0.04), and lacrosse athletes sustained higher linear acceleration impacts than soccer athletes (P = 0.023). Soccer athletes sustained significantly higher-magnitude impacts during competitions versus practices (linear, P < 0.001, rotational, P < 0.001), whereas lacrosse athletes sustained higher-magnitude impacts during practices versus competition (linear, P < 0.001; rotational, P < 0.001). Male athletes sustained higher accelerations in competitions versus practice (linear, P = 0.004; rotational, P < 0.001), whereas female athletes sustained higher accelerations in practice versus competitions (linear, P < 0.001; rotational, P = 0.02). There were no interactions between sex and sport on impact magnitude. Male athletes and lacrosse athletes experience higher-magnitude head impacts. Given the limited literature in this area, future research should continue characterizing head impact biomechanics in women's and nonhelmeted sports as well as validate nonhelmeted head impact technologies.

#13 Will the real leaders please stand up? The emergence of shared leadership in semi-professional soccer teams
Reference: J Sci Med Sport. 2020 Sep 17;S1440-2440(20)30753-2. doi: 10.1016/j.jsams.2020.09.007.
Authors: Niels Mertens, Filip Boen, Niklas K Steffens, S Alexander Haslam, Katrien Fransen
Summary: High-quality leadership is often regarded as one of the main sources of competitive advantage. Especially within sport teams, a team's leadership structure has historically been considered to be stable across the season, with the coach and team captain as the formal, and often sole, leaders. In line with recent organizational research, the present study aims to broaden this perspective by also taking informal leaders into account and exploring how leadership structures among athletes within sport teams evolve over the course of a season. Using social network analysis, we analyzed the leadership structure of 20 semi-professional soccer teams (N=460 players, Mage=23.50 years; SD=4.55) at the start of the season and then again halfway through the season. More specifically, for each team we constructed a leadership network for four leadership roles (task, motivational, social, and external leadership) at these two time points. Findings suggest that leadership structures in sport teams can change considerably over the course of the competitive season, thereby challenging the classic view of stable, vertical leadership structures. The transition to more shared forms of leadership can be attributed to the emergence of informal leaders over time as players engage more strongly in leadership roles. Furthermore, our results suggest that as teams evolve towards shared leadership their functioning and performance benefits from these changes.
Conclusions: Based on these findings, we recommend that coaches actively implement a structure of shared leadership and seek to develop the leadership qualities of formal and informal athlete leaders.

#14 "All My Problems Go Away for 90 Minutes": How Football and Psychotherapy Improves Young Men's Mental Health
Reference: Am J Mens Health. Sep-Oct 2020;14(5):1557988320959992. doi: 10.1177/1557988320959992.
Authors: Amy McGrane , Niamh Bird, Chelsea Arten, Katriona O'Sullivan
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Summary: This qualitative research sought to establish the impact of an 8-week program combining football and one-to-one psychotherapy on young males' mental health, determining the factors that predict help-seeking behaviors in this group of men. Pre- and post-participation focus groups were used as the method of data collection. Six males (19-35 years old; M = 25.5) completed both pre-intervention and follow-up focus groups. Help-seeking behaviors were influenced by the appeal of football and the perception of the counselor being accessible. Barriers included gender norms, socialization, financial difficulties, and challenging social landscapes. Post-participation focus groups revealed that positive social and counseling relationships facilitated improved mental health. Sport was deemed an acceptable medium to deliver a mental health intervention as it increased social connections and facilitated help-seeking. Findings support previous research indicating that combining sports and psychotherapy positively impacts young males' mental health.





Moving Advertisements Systematically Affect Gaze Behavior and Performance in the Soccer Penalty Kick

The aim of the current study was to investigate whether a moving advertisement positioned behind the goal area would influence the visual attention of participants performing a soccer penalty kick, and, whether this would an effect on subsequent motor performance.





Worst case scenario match analysis and contextual variables in professional soccer players: a longitudinal study


This study aimed to describe the worst-case scenarios of professional soccer players by playing position in different durations and analyse WCS considering different contextual variables (match half and location)





Latest research in football - week 50 - 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 Regulatory Fit: Impact on Anxiety, Arousal, and Performance in College-Level Soccer Players
Reference:  Int J Exerc Sci. 2020 Sep 1;13(5):1430-1447. eCollection 2020.
Authors: Brianna N Leitzelar, Lindsey C Blom, Justin Guilkey, Jocelyn Bolin, Anthony Mahon
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Summary: Sport performance may be facilitated using regulatory fit, which is a match between individuals' situational strategy and their chronic self-regulatory strategy. However, researchers have not examined the impact of regulatory fit on psychological and physiological components of sport performance, such as anxiety and arousal. Therefore, the purpose of this study was to evaluate the psychophysiological reactions to regulatory fit by examining anxiety, arousal, and sport performance. Female college-level soccer players (n = 25) were randomly assigned to the regulatory match or regulatory mismatch conditions and completed anxiety (Competitive Sport Anxiety Inventory-2R, CSAI-2R) and underwent arousal (heart rate variability, HRV; pre-ejection period, PEP) measures pre- and post-regulatory focus manipulation. Subsequently, participants completed a sport performance task (10 penalty kicks). The impact of regulatory fit on the dependent variables was explored through repeated measures ANOVAs. Results revealed a significant time effect for cognitive anxiety and self-confidence subscales of the CSAI-2R, suggesting the penalty kicking task increased cognitive anxiety and reduced self-confidence in all participants. In addition, there was a significant interaction effect of condition on pre-ejection period (PEP), with a greater increase in PEP for those experiencing regulatory fit compared to those who were not. There were non-significant interaction and main effects for all other variables. Since PEP is an inverse measure of sympathetic (SNS) modulation, experiencing regulatory fit may reduce SNS involvement in the heartbeat. Thus, the current results indicate experiencing regulatory fit may influence arousal prior to athletic competition.

#2 Video analysis of concussion mechanisms and immediate management in French men's professional football (soccer) from 2015 to 2019
Reference: Scand J Med Sci Sports. 2020 Oct 10. doi: 10.1111/sms.13852. Online ahead of print.
Authors: Hélène Cassoudesalle, Bertrand Laborde, Emmanuel Orhant, Patrick Dehail
Summary: In this study, the concussion mechanisms were analysed in male professional competition football, with the main objective to specify the frequency of head-to-head impact, and immediate management of the concussed players was described in order to check its compliance with the recommendations of football's governing bodies. Based on continuously recorded data from the French Football Federation (FFF), a retrospective database of all reported concussions during matches in the 1st and 2nd French Male leagues was generated comprising seasons 2015/16-2018/19. Injury mechanisms, playing action, immediate medical assessment and management of concussed players, foul play-referee's decision were analysed from video recordings. In total, 41 concussions were reported (incidence rate of 0.44/1000 hours of match exposure [95% CI: 0.40 to 0.49]) of which 36 were identified and analysed on video sequences. The commonest playing action leading to concussion was aerial challenge (61%) and the main mechanism was head-to-head impact (47%). Following the head impact, 28% of concussed players were not medically assessed on-pitch and 53% returned to play the same match. Head-to-head impact was not associated with systematic medical assessment, nor with foul play. In conclusion, the main cause of concussions involved head-to-head impact occurring when two players challenge for heading the ball in the air. The detection of potential concussive head impacts and the immediate management of players possibly concussed during matches remain insufficient according to the international recommendations. Some rules changes, with particular vigilance in case of head-to-head impact, should be discussed.

#3 Behind the mask: demedicalising race and mental health in professional football
Reference: Lancet Psychiatry. 2020 Oct 9;S2215-0366(20)30418-1. doi: 10.1016/S2215-0366(20)30418-1. Online ahead of print.
Authors: Michael Bennett
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#4 Evaluation of a Reactive Agility Assessment Device in Youth Football Players
Reference: J Strength Cond Res. 2020 Oct 9. doi: 10.1519/JSC.0000000000003867. Online ahead of print.
Authors: Jay R Hoffman
Summary: The purpose of this study was to examine the reliability and validity of the Blazepod reactive agility device on sport-specific movements in competitive youth football players. Thirty-one male athletes (16.7 ± 1.5 years; 179.4 ± 7.0 cm; 75.0 ± 21.0 kg), all members of a youth tackle football team, volunteered to participate in this study. Subjects performed 3 reactive agility drills (side shuffle reactive agility, 1-m reactive agility, and 3-m reactive agility) at least 72 hours apart. In addition, all subjects also performed 3 traditional agility exercises: proagility, T drill, and L drill. These sessions were part of the offseason conditioning program for the football team that involved sport-specific drills. All assessments occurred following a warm-up and conducted in the same order on each occasion. To assess the validity of the reactive agility drills, the head coach was asked to rank the football playing and agility ability of the players participating in the study. The intraclass correlation coefficient values indicated that all 3 reactive agility drills displayed excellent reliability (r's ranging from 0.833 to 0.884). The measurement error was smaller than the individual variability, indicating that measurement error had a very limited effect on the results. Subjective rankings for agility significantly correlated with each of the agility and reactive agility measurements. Results of this study indicate that the Blazepod reactive agility device is a reliable measure of reactive agility performance and are consistent with the coach's perception of the athlete's agility performance, thus demonstrating construct validity.

#5 Explicit and implicit activation of gender stereotypes additively impair soccer performance and learning in women
Reference: Eur J Sport Sci. 2020 Oct 13;1-21. doi: 10.1080/17461391.2020.1833087. Online ahead of print.
Authors: Priscila Lopes Cardozo, Leon Flôres Cibeira, Luiz Carlos Rigo, Suzete Chiviacowsky
Summary: Studies involving the manipulation of instructions regarding the negative characteristics of a group or comparisons with members of another group (explicit activation of stereotypes) have shown that age, weight, and gender stereotypes can be harmful to motor performance and learning. To date, however, no study has observed whether implicit stereotype threats, such as the sex of the coach or experimenter, can also influence the acquisition of motor skills. In the present study, the individual and combined impact of implicit and explicit influences of gender stereotype on women's soccer performance and learning was examined. In a 2 × 2 design, 60 women were divided into four groups according to the presence or absence of explicit (ES) and implicit (IS) stereotypes: ES/IS, ES, IS, and control. The groups with implicit activation practiced in the presence of a male experimenter. The groups with explicit activation received instructions activating the gender negative stereotype. The control group practiced without stereotype activations. The results showed that both explicit and implicit activation additively impaired soccer performance and learning, with both main effects being significant for practice and retention. The ES/IS group showed lower scores on the task relative to the other groups, while the ES and IS groups showed worse scores compared with the control group. The findings suggest that stigmatized populations may be forced to cope with more than one social identity threat while learning sport motor skills and indicate the importance of further studies testing strategies to minimize the deleterious effects of negative stereotypes.

#6 PassVizor: Toward Better Understanding of the Dynamics of Soccer Passes
References: IEEE Trans Vis Comput Graph. 2020 Oct 13;PP. doi: 10.1109/TVCG.2020.3030359.
Authors: Xiao Xie, Jiachen Wang, Hongye Liang, Dazhen Deng, Shoubin Cheng, Hui Zhang, Wei Chen, Yingcai Wu
Summary: In soccer, passing is the most frequent interaction between players and plays a significant role in creating scoring chances. Experts are interested in analyzing players' passing behavior to learn passing tactics, i.e., how players build up an attack with passing. Various approaches have been proposed to facilitate the analysis of passing tactics. However, the dynamic changes of a team's employed tactics over a match have not been comprehensively investigated. To address the problem, we closely collaborate with domain experts and characterize requirements to analyze the dynamic changes of a team's passing tactics. To characterize the passing tactic employed for each attack, we propose a topic-based approach that provides a high-level abstraction of complex passing behaviors. Based on the model, we propose a glyph-based design to reveal the multi-variate information of passing tactics within different phases of attacks, including player identity, spatial context, and formation. We further design and develop PassVizor, a visual analytics system, to support the comprehensive analysis of passing dynamics. With the system, users can detect the changing patterns of passing tactics and examine the detailed passing process for evaluating passing tactics. We invite experts to conduct analysis with PassVizor and demonstrate the usability of the system through an expert interview.

#7 Does acute soccer heading cause an increase in plasma S100B? A randomized controlled trial
Reference: PLoS One. 2020 Oct 23;15(10):e0239507. doi: 10.1371/journal.pone.0239507. eCollection 2020.
Authors: Megan E Huibregtse, Madeleine K Nowak, Joseph E Kim, Rachel M Kalbfell, Alekhya Koppineni, Keisuke Ejima, Keisuke Kawata
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Summary: The purpose of this study was to test the effect of subconcussive head impacts on acute changes in plasma S100B. In this randomized controlled trial, 79 healthy adult soccer players were randomly assigned to either the heading (n = 41) or kicking-control groups (n = 38). The heading group executed 10 headers with soccer balls projected at a speed of 25 mph, whereas the kicking-control group performed 10 kicks. Plasma samples were obtained at pre-, 0h post-, 2h post- and 24h post-intervention and measured for S100B. The primary hypothesis was that there would be a significant group difference (group-by-time interaction) in plasma S100B at 2h post-intervention. Secondary hypotheses included (1) no significant group differences in plasma S100B concentrations at 0h post- and 24h post-intervention; (2) a significant within-group increase in S100B concentrations in the heading group at 2h post-intervention compared to pre-intervention; and (3) no significant within-group changes in plasma S100B in the kicking-control group. Data from 68 subjects were available for analysis (heading n = 37, kicking n = 31). There were no differences in S100B concentrations between heading and kicking groups over time, as evidenced by nonsignificant group-by-time interaction at 2h post-intervention (B = 2.20, 95%CI [-22.22, 26.63], p = 0.86) and at all the other time points (0h post: B = -11.05, 95%CI [-35.37, 13.28], p = 0.38; 24h post: B = 16.11, 95%CI [-8.29, 40.51], p = 0.20). Part of the secondary outcome, the heading group showed elevation in plasma S100B concentrations at 24h post-intervention compared to pre-heading baseline (B = 19.57, 95%CI [3.13, 36.02], p = 0.02), whereas all other within-group comparisons in both remained nonsignificant. The data suggest that 10 bouts of acute controlled soccer headings do not elevate S100B concentrations up to 24-hour post-heading. Further dose-response studies with longer follow-up time points may help determine thresholds of acute soccer heading exposure that are related to astrocyte activation.

#8 The impact of team preferences on soccer offside judgments in laypersons: a quasi-experimental study
Reference: Cogn Res Princ Implic. 2020 Oct 23;5(1):50. doi: 10.1186/s41235-020-00253-2.
Authors: Peter Wühr, Frowin Fasold, Daniel Memmert
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Summary: The present study uses a quasi-experimental design to investigate the impact of team preferences on the accuracy of offside judgments. In Experiments 1 and 2, supporters of two German soccer clubs (i.e., Borussia Dortmund and FC Schalke 04) judged offsides in artificial scenes from a match between the clubs. We expected that supporters of both clubs would less frequently report the offside position of a forward from the preferred team. The results of Experiment 1 partly confirmed the predictions. Both groups reported the offside position of a yellow forward less frequently than that of a blue forward, and this effect was much larger for supporters of Borussia Dortmund than for supporters of Schalke 04. The difference between groups could be attributed to team preferences. The weaker effect of team preference in supporters of Schalke 04 was attributed to an unexpected perceptual effect that increased the accuracy of offside judgments for blue forwards in both groups. Experiments 2 and 3 showed the presumed effect of team preferences and the perceptual effect, respectively, in isolation. In summary, the results of our experiments provide evidence for (a) an effect of team preferences and (b) an effect of shirt-background contrast on offside judgments in soccer.

#9 Neural correlates of cognitive processing capacity in elite soccer players
Reference: Biol Psychol. 2020 Oct 19;107971. doi: 10.1016/j.biopsycho.2020.107971. Online ahead of print.
Authors: Chun-Hao Wang, Chih-Chun Lin, David Moreau, Cheng-Ta Yang, Wei-Kuang Liang
Summary: Although great progress has been made in our understanding of perceptual-cognitive expertise in team sports, the neurocognitive mechanisms underlying such cognitive advantage in the face of multiple, sometimes conflicting, channels of information are not well understood. Two electroencephalographic indices associated with perceptual decisions, the P3 component of event-related potential and alpha inter-trial phase coherence (ITPC), were measured and compared across elite soccer players and non-athletic controls while performing a redundant-target task. Specifically, we adopted an effective diagnostic tool, Systems Factorial Technology, to assess participants' workload capacity. Soccer players exhibited larger workload capacity while making faster decisions compared with controls. Moreover, this larger workload capacity was associated with modulations of P3 and alpha ITPC when processing two targets relative to one target and one distractor, an effect that was not observed in controls. Together, the present findings offer a possible mechanistic explanation of perceptual-cognitive expertise in the context of team sports.

#10 Technical determinants of success in professional women's soccer: A wider range of variables reveals new insights
Reference: PLoS One. 2020 Oct 22;15(10):e0240992. doi: 10.1371/journal.pone.0240992. eCollection 2020.
Authors: Laura M S de Jong, Paul B Gastin, Maia Angelova, Lyndell Bruce, Dan B Dwyer
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Summary: Knowledge of optimal technical performance is used to determine match strategy and the design of training programs. Previous studies in men's soccer have identified certain technical characteristics that are related to success. These studies however, have relative limited sample sizes or limited ranges of performance indicators, which may have limited the analytical approaches that were used. Research in women's soccer and our understanding of optimal technical performance, is even more limited (n = 3). Therefore, the aim of this study was to identify technical determinants of match outcome in the women's game and to compare analytical approaches using a large sample size (n = 1390 team performances) and range of variables (n = 450). Three different analytical approaches (i.e. combinations of technical performance variables) were used, a data-driven approach, a rational approach and an approach based on the literature in men's soccer. Match outcome was modelled using variables from each analytical approach, using generalised linear modelling and decision trees. It was found that the rational and data-driven approaches outperformed the literature-driven approach in predicting match outcome. The strongest determinants of match outcome were; scoring first, intentional assists relative to the opponent, the percentage of shots on goal saved by the goalkeeper relative to the opponent, shots on goal relative to the opponent and the percentage of duels that are successful. Moreover the rational and data-driven approach achieved higher prediction accuracies than comparable studies about men's soccer.

#11 Changes in resting-state functional brain connectivity associated with head impacts over one men's semi-professional soccer season
Reference: J Neurosci Res. 2020 Oct 21. doi: 10.1002/jnr.24742. Online ahead of print.
Authors: Hélène Cassoudesalle, Adrien Petit, Sandra Chanraud, Hervé Petit, Jérôme Badaut, Igor Sibon, Patrick Dehail
Summary: Soccer, as a contact sport, exposes players to repetitive head impacts, especially through heading the ball. The question of a long-term brain cumulative effect remains. Our objective was to determine whether exposure to head impacts over one soccer season was associated with changes in functional brain connectivity at rest, using magnetic resonance imaging (MRI). In this prospective cohort study, 10 semi-professional men soccer players, aged 18-25 years, and 20 age-matched men athletes without a concussion history and who do not practice any contact sport were recruited in Bordeaux (France). Exposure to head impacts per soccer player during competitive games over one season was measured using video analysis. Resting-state functional magnetic resonance imaging data were acquired for both groups at two times, before and after the season. With a seed-based analysis, resting-state networks that have been intimately associated with aspects of cognitive functioning were investigated. The results showed a mean head impacts of 42 (±33) per soccer player over the season, mainly intentional head-to-ball impacts and no concussion. No head impact was found among the other athletes. The number of head impacts between the two MRI acquisitions before and after the season was associated with increased connectivity within the default mode network and the cortico-cerebellar network. In conclusion, our findings suggest that the brain functioning changes over one soccer season in association with exposure to repetitive head impacts.

#12 Sleep Restriction in Elite Soccer Players: Effects on Explosive Power, Wellbeing, and Cognitive Function
Reference: Res Q Exerc Sport. 2020 Oct 21;1-8. doi: 10.1080/02701367.2020.1834071. Online ahead of print.
Authors: W Abbott, A Brett, A W Watson, H Brooker, T Clifford
Summary: The aim was to investigate the cognitive, physical, and perceptual effects of sleep restriction (SR) in soccer players following a night match. In a crossover design, nine male soccer players from the English Premier League 2 (age, 21 ± 5 years; height, 1.80 ± 0.75 m; body mass, 74.2 ± 6.8 kg) recorded their sleep quality and quantity with sleep logs and a subjective survey after two night matches (19:00); one where sleep duration was not altered (CON) and one where sleep was restricted by a later bed-time (SR). Countermovement jump height (CMJ), subjective wellbeing (1-5 likert scale for mood, stress, fatigue, sleep, and soreness), and cognitive function were measured at baseline and the morning following the match (+12 h; M + 1). Bed-time was later in SR than CON (02:36 ± 0.17 vs. 22:43 ± 29; P = .0001; ηp2 = 0.999) and sleep duration was shorter in SR than CON (5.37 ± 0.16 vs. 8.59 h ± 0.36; P = .0001; ηp2 = 0.926). CMJ decreased by ~8% after the match in both SR and CON (P = .0001; ηp2 = 0.915) but there were no differences between the conditions (P > .05; ηp2 = 0.041-0.139). Wellbeing was rated worse after both matches (P = .0001; ηp2 = 0.949) but there were no differences between the trials (P > .05; ηp2 = 0.172-257). SR did not influence cognitive function (P > .05; interaction effects, ηp2 = 0.172-257). SR following a nighttime soccer match does not impair CMJ performance, subjective wellbeing, or cognitive function the following morning.

#13 Reliability of Change-of-Direction Economy in Soccer Players
Reference: Int J Sports Physiol Perform. 2020 Oct 28;1-7. doi: 10.1123/ijspp.2019-0877. Online ahead of print.
Authors: Filippo Dolci, Andrew E Kilding, Tania Spiteri, Paola Chivers, Ben Piggott, Andrew Maiorana, Nicolas H Hart
Summary: The purpose was to evaluate the reliability of new change-of-direction-economy tests (assessing energetic efficiency when performing continuous shuttle runs) compared with common running-economy tests in soccer players Methods: Sixteen subelite, male soccer players were recruited to perform a testing battery involving running economy (RE), 10-m shuttle-running economy (SRE10), and 20-m shuttle-running economy (SRE20) at 8.4 km·h-1 mean speed on 2 different days within 48 hours. SRE10 and SRE20 consisted of continuous shuttle runs interspersed with 180° directional changes. During the RE, SRE20, and SRE10 tests, respiratory exchange ratio and oxygen uptake were collected and used to calculate the movement-economy values over any running condition as oxygen cost and energetic cost. The secondary variables (carbon dioxide production, heart rate, minute ventilation, and blood lactate) were also monitored during all tests. Depending on expression (oxygen cost or energetic cost), reliability was established for RE (CV: 5.5%-5.8%; ICC = .77-.88), SRE10 (CV: 3.5%-3.8%; ICC = .78-.96), and SRE20 (CV: 3.5%-3.8%; ICC = .66-.94). All secondary physiological variables reported good reliability (CV < 10%), except for blood lactate (CV < 35.8). The RE, SRE10, and SRE20 tests show good reliability in soccer players, whereas blood lactate has the highest variability among physiological variables during the economy tests. The assessment of change-of-direction economy through performing 20- and 10-m shuttle runs is reliable and can be applied to evaluate soccer players' energetic movement efficiency under more soccer-specific running conditions.

#14 Male and female soccer players exhibit different knee joint mechanics during pre-planned change of direction
Reference: Sports Biomech. 2020 Oct 29;1-14. doi: 10.1080/14763141.2020.1830160. Online ahead of print.
Authors: Christopher Thomas, Thomas Dos'Santos, Paul Comfort, Paul A Jones
Summary: Change of direction manoeuvres is important in soccer and associated with non-contact anterior cruciate ligament injury, yet it is not known how the mechanics differentiate between males and females during 180° turns. Twenty-eight soccer players (14 males and 14 females) performed 180° turns with ground reaction forces collected over penultimate and final contacts. A two-way (contact × limb) multivariate analysis of variance (MANOVA) were run to examine differences between contact (penultimate and final) or limb (dominant and non-dominant) for sagittal plane hip, knee and ankle peak angles and moments, and frontal plane knee abduction moments and angles between sexes. Average horizontal GRF was increased on the dominant limb, compared to non-dominant and for the final contact compared to the penultimate contact. Knee abduction angles were increased in females compared to males, while the opposite was true for knee abduction moments. Statistically significant differences were evident, with increases in peak vertical GRF, peak hip flexion angle, peak knee flexion angle, peak knee extensor moment, and peak ankle dorsiflexion angle observed in the penultimate contact compared to final contact. The results indicate the penultimate contact during turns helps reduce loading on the final contact, yet male and female soccer players exhibit different knee joint mechanics during pre-planned change of direction.

#15 Short-Term Detraining Does Not Impair Strength, Speed, and Power Performance in Elite Young Soccer Players
Reference: Sports (Basel). 2020 Oct 25;8(11):E141. doi: 10.3390/sports8110141.
Authors: Lucas A Pereira, Tomás T Freitas, Bruno Pivetti, Pedro E Alcaraz, Ian Jeffreys, Irineu Loturco
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Summary: This study aimed to examine the effects of short-term detraining on the strength, speed, and jump capacities of under-20 soccer players. Twenty-four elite under-20 soccer players from the same professional club were assessed pre and post 26 days of detraining. The measurements were performed in the following order: countermovement jump (CMJ); 10 m linear sprint velocity; and one-repetition maximum test (1RM) in the horizontal leg-press exercise. To analyze the differences between pre- and post-tests, a paired T-test was applied. The significance level was set as p < 0.05. Soccer players exhibited a significant increase in CMJ performance (p = 0.02) and no significant differences in 10 m sprint velocity and 1RM leg-press were found after the short-term training cessation (p = 0.61; p = 0.55, respectively). We demonstrated that a short-term detraining period was capable of promoting a significant increase in the vertical jump height without inducing negative effects on the strength and speed capabilities of elite under-20 soccer players. Practitioners and sport scientists should be aware of these findings to program more effective training strategies at the beginning of the subsequent training cycle.

#16 Reproducibility and inter-observer agreement of Greulich-Pyle protocol to estimate skeletal age among female adolescent soccer players
Reference: BMC Pediatr. 2020 Oct 26;20(1):494. doi: 10.1186/s12887-020-02383-4.
Authors: Yuri V Faustino-da-Silva, Diogo V Martinho, Manuel J Coelho-E-Silva, João Valente-Dos-Santos, Jorge Conde, Tomás G Oliveira, Enio R V Ronque, Ricardo R Agostinete, Rômulo A Fernandes, Lauren B Sherar
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Summary: Skeletal age (SA) is considered the best method of assessing biological maturation. The aim of this study was to determine intra-observer (reproducibility) and inter-observer agreement of SA values obtained via the Greulich-Pyle (GP) method. In addition, the variation in calculated SAs by alternative GP protocols was examined. The sample was composed of 100 Portuguese female soccer players aged 12.0-16.7 years. SAs were determined using the GP method by two observers (OB1: experience < 100 exams using GP; OB2: experience > 2000 exams using several methods). The radiographs were examined using alternative GP protocols: (wholeGP) the plate was matched to the atlas as an overall approach; (30-boneGP) bone-by-bone inspections of 30-bones; (GPpmb) bone-by-bone inspections of the pre-mature bones only. For the 30-boneGP and GPpmb approaches, SA was calculated via the mean (M) and the median (Md). Reproducibility ranged 82-100% and 88-100% for OB1 and OB2, respectively. Inter-observer agreement (100 participants multiplied by 30 bones) was 92.1%. For specific bones, agreement rates less than 90% were found for scaphoid (81%), medial phalange V (83%), trapezium (84%) and metacarpal V (87%). Differences in wholeGP SAs obtained by the two observers were moderate (d-cohen was 0.79). Mean differences between observers when using bone-by bone SAs were trivial (30-boneGP: d-cohen less than 0.05; GPpmb: d-cohen less than 0.10). The impact of using the mean or the median was negligible, particularly when analyses did not include bones scored as mature. The GP appeared to be a reasonably reproducible method to assess SA and inter-observer agreement was acceptable. There is evidence to support a recommendation of only scoring pre-mature bones during later adolescence. Further research is required to examine whether these findings are consistent in younger girls and in boys.





Accelerometry-based variables in professional soccer players: comparisons between periods of the season and playing positions

The aim of this study was to provide reference data of variation in external training loads for weekly periods within annual season.





Most running demand passages of match play in youth soccer congestion period

The objective of this study was to determine whether there is a decrease in the physical performance of the players in the most demanding passages (MDP) during periods of competition congestion.





Latest research in football - week 49 - 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 Capturing and Quantifying Tactical Behaviors in Small-Sided and Conditioned Games in Soccer: A Systematic Review
Reference: Res Q Exerc Sport. 2020 Oct 8;1-15. doi: 10.1080/02701367.2020.1823307. Online ahead of print.
Authors: Nuno Coito , Keith Davids, Hugo Folgado , Teresa Bento, Bruno Travassos
Summary: The aim was to systematically describe and analyze the tracking systems, the variables, and the statistical methods used to evaluate the players and teams' tactical behavior in small-sided and conditioned games (SSCGs). A search was done in Web of Science, PubMed, Science Direct, and Scielo databases to identify manuscripts published between 2008 and 2019 that manipulated small-sided and conditioned games (SSCGs) and analyzed tactical behaviors of players and teams. rom 349 articles identified, 31 were selected for review. To collect positional data, the global positioning system (GPS), the local position measurement (LPM) system, and TACTO were identified as reliable tracking systems. Twenty-one positional variables were identified to evaluate tactical behaviors, grouped into five main categories: team balance, playing space, width and length of playing space, and interpersonal distance. Tactical behavior patterns were analyzed using approximate entropy, sample entropy, Shannon entropy, and patterns of coordination between players and teams were analyzed using relative phase and running correlation. The tracking systems analyzed were reliable but revealed different advantages and disadvantages of their use. Authors should define the use of each tracking system based on their purpose and level of precision required for analysis. A great duplication was observed on the variables used with similar purposes of tactical analysis. The identification of the variables according to their purpose of analysis will allow a better understanding of their use in the future.

#2 Quantifying the Peak Physical Match-Play Demands of Professional Soccer Substitutes Following Pitch-Entry: Assessing Contextual Influences
Reference: Res Q Exerc Sport. 2020 Oct 8;1-12.
Authors: Samuel P Hills, Stephen Barrett, Bradley Thoseby , Liam P Kilduff , Martin J Barwood, Jon N Radcliffe, Carlton B Cooke, Mark Russell
Summary: The purpose was to quantify the peak post-pitch-entry physical responses of soccer substitutes while assessing contextual influences. Peak responses may be important performance indicators for substitutes introduced to provide a physical impact. Thirty-three professional substitutes wore Microelectromechanical Systems during 44 matches (4 ± 3 observations·player-1). Post-pitch-entry relative peak values for total and high-speed (> 5.5 m·s-1) distances, average acceleration, and PlayerLoad™ were calculated using rolling averages over 60-s to 600-s. Linear mixed models assessed contextual influences (position, substitution timing, scoreline, and location). Substitutes introduced during the final ~15 min of match-play covered less high-speed distance than first-half substitutes (~2.8-3.1 m·min-1) over 480-s to 600-s epochs, and less than 60:00-74:59 min substitutes (~1.7-1.8 m·min-1) during 540-s and 600-s epochs. Average acceleration during all except 180-s epochs was lower for 75:00+ min substitutes compared with first-half replacements (~0.27-0.43 m·s-2), and lower than 60:00-74:59 min substitutes during 60-s (~0.13 m·s-2). Substitutes introduced when their team was winning recorded greater distances over 120-s to 600-s (~6.2-7.7 m·min-1), and higher PlayerLoad™ values during 120-s, 180-s, 300-s, and 480-s epochs (~2.7-3.6 arbitrary units·min-1), compared with when scores were level at pitch-entry. Irrespective of substitution timing, substitute midfielders exceeded the total distance of substitute attackers (~5.9-16.2 m·min-1) for all except 360-s and 600-s epochs, and defenders (~13.3-26.7 m·min-1) during epochs < 300-s. This study provides benchmark data for practitioners tailoring training and recovery protocols, particularly "top-up" conditioning, to the competitive demands of soccer substitutes. Knowing how contextual factors influence substitutes' peak match-play responses may help managers/coaches assess the efficacy of substitution strategies.

#3 Varying Demands and Quality of Play Between In-Conference and Out-of-Conference Games in Division I Collegiate Women's Soccer
Reference: J Strength Cond Res. 2020 Oct 5. doi: 10.1519/JSC.0000000000003841. Online ahead of print.
Authors: Brittany N Bozzini, Bridget A McFadden, Alan J Walker , Shawn M Arent
Summary: The purpose of this study was to assess differences in physical workloads, physiological responses, and performance variables between in-conference (IC) and out-of-conference (OC) games during a collegiate women's soccer season. Female field players (N = 11), who played a minimum of 45 minutes for >50% of games, were evaluated using an integrative GPS and HR monitoring system to determine training load (TL), exercise energy expenditure (EEE), total distance covered (DIS), sprints, time spent in HR zones 4 and 5 (HRZ4 = 80-89% HRmax; HRZ5 = 90-100% HRmax), and distance covered in speed zones 4 and 5 (DISZ4 = 15.0-19.9 km·h; DISZ5 = ≥20 km·h). In addition, percent passing accuracy (PA%), dribbling success (DS%), tackling success (TS%), and challenges won (CW%) were generated for all games. Workload data were analyzed as a rate per minute playing time (PT) per game to account for differences in game duration and PT between OC (n = 7) and IC games (n = 11). Repeated-measures multivariate analyses of variance with univariate follow-ups and effect sizes (Hedges' g) were conducted to compare conditions (OC vs. CON) (p < 0.05). There were significantly greater TL, DIS, EEE, and HRZ5 per minute PT in OC versus IC games (Hedges' g: TL = 0.48; DIS = 0.20, EEE = 0.55; HRZ5 = 0.83; p < 0.05). Further analysis found significant differences in first half play favoring OC games (p < 0.05), but not second half play (p > 0.05). Based on these findings, OC games seem to be more demanding compared to IC, particularly during first half play. Emphasis should be placed on tailoring TL to the accumulating in-season demands through athlete-monitoring technology to prevent declines in performance in the latter half of the season.

#4 Effects of Moderate-to-Heavy Sled Training Using Different Magnitudes of Velocity Loss in Professional Soccer Players
Reference: J Strength Cond Res. 2020 Oct 1. doi: 10.1519/JSC.0000000000003813. Online ahead of print.
Authors: Rafael Grazioli, Irineu Loturco, Pedro Lopez, Igor Setuain, Jean Goulart, Filipe Veeck, Martinho Inácio, Mikel Izquierdo, Ronei S Pinto, Eduardo L Cadore 
Summary: This study investigated the effects of a 11-week moderate-to-heavy sled training intervention with different magnitudes of velocity loss on sprint and jump performance, mechanical muscle function, and body composition in professional soccer players. Seventeen players (age 25.8 ± 4.3 years; height 180.0 ± 8.6 cm; weight 77.7 ± 9.7 kg) were randomly allocated into 2 groups, based on different magnitudes of velocity loss: 10% of velocity decrease (G10, n = 8) and 20% of velocity decrease (G20, n = 9). The velocity-based sled training consisted of 20-m resisted sprints with a progressive loading increase from 45 to 65% of body-mass throughout the intervention. Pre-intervention and postintervention sprint and jump performance, hamstring and quadriceps peak torque and isometric rate of torque development, and lower-limb lean mass measured by dual X-ray absorptiometry were assessed and compared. Two-way repeated measures analysis of variance revealed a significant time-effect for decreases in 10- and 20-m sprint times (p = 0.018 and p = 0.033, respectively), but without a time-group interaction. The G10 showed greater beneficial effects than G20 for both 10-m (-5.5 ± 3.3%, magnitude-based inference [MBI]: possibly vs. -1.7 ± 5.9%, MBI: possibly trivial) and 20-m (-2.5 ± 2.1%, MBI: possibly vs. -1.4 ± 3.7%, MBI: likely trivial) sprint times. Moreover, there was a significant time effect for countermovement jump height and quadriceps isometric peak torque, which decreased significantly after training (p = 0.019 and p = 0.010, respectively), with no within-group effect of time vs. group interaction for these respective outcomes. The novel velocity-based sled model proposed here, especially under lower magnitudes of velocity loss, was able to significantly improve linear sprint performance in professional soccer players.

#5 Performance on sprint, agility and jump tests have moderate to strong correlations in youth football players but performance tests are weakly correlated to neuromuscular control tests
Reference: Knee Surg Sports Traumatol Arthrosc. 2020 Oct 8. doi: 10.1007/s00167-020-06302-z.
Authors: Sofi Sonesson, Hanna Lindblom, Martin Hägglund
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Summary: This study aimed at evaluating the correlation between seven different performance tests and two neuromuscular control tests in youth football players and to evaluate the influence of sex and age groups on test results. One-hundred and fifteen football players (66 boys, 49 girls) mean age 14 ± 0.7 (range 13-16) years from youth teams were tested at the start of the second half of the competitive season. A test battery including agility t-test, 505 agility test, single-leg hop for distance test, side-hop test, countermovement jump test, 10-m sprint test, 20-m sprint test, tuck jump assessment (TJA) and drop vertical jump (DVJ) was completed. Correlations between the seven different performance tests of agility, jump and sprint ability were generally moderate to strong (r = 0.534-0.971). DVJ did not correlate with the performance tests (rho = 0.004 to - 0.101) or with TJA total score (rho = 0.127). There were weak to moderate correlations between TJA total score and the performance tests (r = - 0.323-0.523). Boys performed better than girls in all performance tests (p < 0.001) and in TJA total score (p = 0.002). In boys, older players performed better than younger players in the majority of the tests, while there was no clear age influence among girls. Sprint performance was moderately to strongly correlated with agility and jump performance, and performance tests were weakly to moderately correlated to TJA, while DVJ did not correlate with the other tests. Boys performed better than girls on performance tests and TJA. An age effect on performance was evident in boys but not in girls.

#6 Football - Novel Approaches to Tackle Diabetes
Reference: Exp Clin Endocrinol Diabetes. 2020 Oct 7. doi: 10.1055/a-1262-6352. Online ahead of print.
Authors: Karsten Müssig, Henning E Adamek
Summary: Balanced diet and regular physical activity are of key importance to the prevention of the development and progression of non-communicable diseases. In 2050, 50% of the European population is expected to be obese. Cardiovascular diseases, diabetes mellitus, cancer, as well as joint impairments, will further increase. Therefore, programmes are critical to the improvement of the population's health status in the long run. New ways have to be found that allow addressing more people than with the current approaches. Football has a great potential to attract people at risk for or with already existing non-communicable diseases, such as type 2 diabetes, to participate in health-promoting programmes. The novel football version, walking football was developed for elderly players, aiming at avoiding injuries and physical overload. The present article gives a brief overview on the metabolic effects of recreational football, particularly walking football, as well as health-promoting programmes offered by professional football clubs in humans at risk for or with already existing non-communicable diseases.

#7 Flywheel squats versus free weight high load squats for improving high velocity movements in football. A randomized controlled trial
Reference: BMC Sports Sci Med Rehabil. 2020 Oct 2;12:61. doi: 10.1186/s13102-020-00210-y. eCollection 2020.
Authors: Edvard H Sagelv, Sigurd Pedersen, Lars Petter R Nilsen, Andrea Casolo, Boye Welde, Morten B Randers, Svein Arne Pettersen 
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Summary: High load (HL: > 85% of one repetition maximum (1RM)) squats with maximal intended velocity contractions (MIVC) combined with football sessions can be considered a relevant and time-efficient practice for maintaining and improving high velocity movements in football. Flywheel (FW) resistance exercise (RE) have recently emerged with promising results on physical parameters associated with football performance. In this randomized controlled trial over 6 weeks, 38 recreationally active male football players randomly performed RE with MIVCs two times per week as either 1) FW squats (n = 13) or 2) barbell free weight (BFW) HL squats (n = 13), where a third group served as controls (n = 12). All three groups conducted 2-3 football sessions and one friendly match a week during the intervention period. Pre- to post changes in 10-m sprint, countermovement jump (CMJ) and 1RM partial squat were assessed with univariate analyses of variance. The FW and BFW group equally improved their 10-m sprint time (2 and 2%, respectively, within group: both p < 0.001) and jump height (9 and 8%, respectively, within group: both p < 0.001), which was superior to the control group's change (between groups: both p < 0.001). The BFW group experienced a larger increase (46%) in maximal squat strength than the FW group (17%, between groups: p < 0.001), which both were higher than the control group's change (both p < 0.001). Squats carried out with FWs or BFWs where both are performed with MIVCs and combined with football sessions, were equally effective in improving sprint time and jump height in football players. The BFW group experienced a more than two-fold larger increase in maximal partial squat strength than the FW group in maximal partial squat strength. This presents FW RE as an alternative to BFW HL RE for improving high velocity movements in football.

#8 Mass Gathering Emergency Medicine Organization for the Union of European Football Associations' Under-21 Championship 2019 in Bologna, Italy
Reference: Disaster Med Public Health Prep. 2020 Oct 7;1-4. doi: 10.1017/dmp.2020.291. Online ahead of print.
Authors: Guglielmo Imbriaco, Alfonso Flauto, Tiziano Bussolari, Fiorella Cordenons, Giovanni Gordini 
Summary: Football events represent a type of Mass Gathering Events (MGE) where crowd behavior, temperature and Heat Index, absence of free water, and alcohol consumption can lead to an increased need for medical assistance in participants. This report describes the environmental issues, organization, and healthcare assistance provided during the four matches of the Union of European Football Associations' (UEFA) Under-21 tournament held in Bologna in June, 2019. The four matches had a total of 72655 spectators; 31 patients required medical assistance with a mean Patient Presentation Rate (PPR) of 0.41; Mean Transport To Hospital Rate (TTHR) of 0.04; with PPR and TTHR comparable with literature findings. Majority of patients suffered from minor injuries and illnesses, and were treated directly in stadium medical sites. Medical assistance involved volunteer rescuers, emergency nurses, and physicians; resources were efficiently allocated and provided effective care to every patient.Climate factors, heat and humidity, the absence of free water, and increased alcohol consumption appear to be associated with increased requests for medical assistance. The retrospective analysis of a wider range of environmental factors, and the historical experience developed during similar MGEs suggest the need for a more comprehensive, improved approach for adequately assessing risk and planning the necessary healthcare resources.

#9 Does Distance Produce Beauty? The Influence of COVID-19 Lockdown on the Coach-Athlete Relationship in a Chinese Football School
Reference: Front Psychol. 2020 Sep 11;11:560638. doi: 10.3389/fpsyg.2020.560638. eCollection 2020.
Authors: Juan Li, Hongyan Gao, Pan Liu, Caixia Zhong
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Summary:  This paper examined the relationship between coaches and youth athletes in China by comparing data collected before and after the lockdown. A total of 221 youth athletes aged 13-19 years in one professional football school completed coach-athlete relationship questionnaires. The rank-sum test was used to verify the differences in the data. The results of the Mann-Whitney U test showed that mean value of the three dimensions of the coach-athlete relationship (closeness, commitment, and complementarity) increased after the COVID-19 lockdown. The results also showed that athletes of different age categories showed different changes in the coach-athlete relationship after the lockdown, and the changes were not significantly related to the severity of the COVID-19 epidemic. The theoretical and practical implications are discussed.

#10 The Influence of Emotion in the Management of Amateur Football Organizations
Reference: Front Psychol. 2020 Sep 4;11:2218. doi: 10.3389/fpsyg.2020.02218. eCollection 2020.
Authors: Melany Hebles , Vicente Javier Prado-Gascó, Orlando Llanos-Contreras, Mario Alguacil
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Summary: This article is oriented to the analysis of organizational and emotional variables in amateur sporting organizations. The general objective is to analyze the influence of organizational variables such as service quality, transactional leadership, and transformational leadership and emotional variables such as affective commitment, emotional attachment investment, and emotional attachment dividend to predict the credibility that members of amateur sporting organizations perceive, as well as their degree of identification and loyalty. The opinions of 203 members of Chilean amateur football teams [169 men and 34 women, with ages between 18 and 68 years (mean = 32.75 years, DT = 9.92)] have been analyzed through a self-completed questionnaire. To reach the objectives, two types of differential but complementary analyses, in the form of hierarchical regression models (from hereon, HRMs) and qualitative comparative analysis (from hereon, QCA), were performed. The results obtained suggest that the organizational variables are better predictors than the emotional variables in all of the cases. In the same way, the inclusion of the emotional variables improves the predictive capacity of the proposed models to explain identification and loyalty, but not in the case of credibility. In general, the variables considered seem to explain 37% of the credibility, 56% of loyalty, and 65% of identification. On the other hand, considering the results of the QCA, no variable turned out to be necessary. However, different combinations of variables (conditions) were observed that were able to explain between 47 and 91% of the cases of the variables analyzed. In general, based on these results, it was observed that the emotional variables were important in interaction with other organizational ones since they are present in the three combinations that most explain identification and loyalty and are also present in the three combinations that most explain credibility. This study contributes to the literature by supporting the importance of managing emotions in order for sporting organizations to be more successful.

#11 Differentiation Between Tendinous, Myotendinous and Myofascial Injuries by L-BIA in Professional Football Players
Reference: Front Physiol. 2020 Sep 4;11:574124. doi: 10.3389/fphys.2020.574124. eCollection 2020.
Authors: Lexa Nescolarde, Joaquim Terricabras, Sandra Mechó, Gil Rodas, Javier Yanguas
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Summary: The aim was to differentiate by localized bioimpedance (L-BIA) measurements 24 h after injury, between tendinous, myotendinous junction (MTJ), and myofascial junction (MFJ) injuries, previously diagnosed by MRI exam. To evaluate by L-BIA, the severity of MTJ injuries graded from 1 to 3, and to determine the relationship between days to return to play (RTP) and L-BIA measurements. 3T MRI and tetra polar L-BIA was used to analyzed 37 muscle injuries 24 h after injury in 32 male professional football players, (23.5 ± 1.5 kg m-2; 1.8 ± 0.1 m; 20-30 year.) between the 2016-2017 and 2017-2018 seasons. Muscle injuries were classified by The British Athletics Muscle Injury Classification (BAMIC). Percentage difference of L-BIA parameters [resistance (R), reactance (Xc), and phase angle (PA)] of the injured side were calculated considering contralateral non-injured side as the reference value. According to BAMIC classification and by MRI exam, we found tendinous (n = 4), MTJ (n = 26), and MFJ (n = 7) muscle injuries. In addition, MTJ injuries were grouped according to the severity of injury in grade 1 (n = 11), grade 2 (n = 8), and grade 3 (n = 7). Significant decrease (P < 0.01) was found in the L-BIA parameters R, Xc, and PA, in both MTJ and MFJ as well as in the different grades of MTJ injuries. In particular, in Xc (P < 0.001), which is related to muscle cell disruption. Regarding days to RTP, there was statistical significance among the three different grades of MTJ injuries (P < 0.001), especially when grade 1 was compared to grade 3 and grade 2 compared to 3. L-BIA is a complementary method to imaging diagnostic techniques, such as MRI and US, to quantify MTJ and MFJ injuries. In addition, the increase in the severity of the MTJ injury resulted in higher changes of the Xc parameter and longer time to RTP.

#12 Short and long lever adductor squeeze strength values in 100 elite youth soccer players: Does age and previous groin pain matter?
Reference: Phys Ther Sport. 2020 Oct 6;46:243-248. doi: 10.1016/j.ptsp.2020.10.001. Online ahead of print.
Authors: Matthew D DeLang, J Craig Garrison, Joseph P Hannon, Ryan P McGovern, John Christoforetti, Kristian Thorborg
Summary: The purpose was to examine adductor squeeze strength in elite youth soccer players by investigating the relationship of age and previous one-year groin pain on adductor squeeze force outputs, and to provide reference values for youth players. Elite youth soccer players (n = 100; age 14.5 ± 1.9 years; height 168.0 ± 10.7 cm; mass 60.7 ± 13.0 kg) participated. Adductor squeeze tests were captured in short and long lever positions, and groin pain assessed via subjective retrospective questionnaire. Multiple linear regressions were computed to compare the effects of age and previous one-year groin pain on adductor squeeze strength. Raw adductor squeeze force values (N) had a moderate positive relationship with age (short r = 0.517, p < 0.001; long r = 0.457, p < 0.001), but not when force is normalized to body mass (N/kg; short r = 0.014, p = 0.444; long r = -0.173, p = 0.043). Previous groin pain did not have an effect on short or long lever squeeze strength. Reference values for long lever adductor squeeze strength (3.59 ± 0.77 Nm/kg) are provided. Age and previous groin pain do not have an effect on adductor squeeze strength values in elite youth soccer players, so comparing values to the present adolescent cohort can be quickly interpreted without adjustment for age or previous injury.

#13 The role of alcohol in the link between national football (soccer) tournaments and domestic abuse - Evidence from England
Reference: Soc Sci Med. 2020 Oct 22;268:113457. doi: 10.1016/j.socscimed.2020.113457. Online ahead of print.
Authors: Anna Trendl, Neil Stewart, Timothy L Mullett
Summary: Domestic abuse is increasingly recognised as a serious public health concern worldwide. Previous research has suggested a link between national football (soccer) tournaments and domestic abuse. While hypothesized to be a significant factor, the role alcohol plays in this relationship has not yet been explored quantitatively. In this study, using 10 years' worth of crime data (from 2010 to 2019) from the second largest police force in England (West Midlands Police), we explored the effect of England draws, losses, and wins in national football tournaments on the number of alcohol and non-alcohol-related domestic abuse cases reported to the police. Results from a series of negative binomial regression analyses show that the number of reported alcohol-related domestic abuse cases increases by 47%, 95% confidence interval [26%-71%], following an England football victory. This effect is limited to alcohol-related cases. The estimate translates into a 0.53, 95% CI [0.3-0.8], increase in the daily rate of alcohol-related cases per 100,000 individuals. The England win effect survives various robustness checks (including the re-analysis of a dataset from another geographical area in England), and its time course is strongly consistent with a causal link between England's football victories and an increase in alcohol-related domestic abuse. We also found a comparable increase in the number of other (not classified as domestic abuse) alcohol-related violent crimes on England win days. Further research is required to understand the exact causal pathway between national football tournaments, alcohol consumption, and violent behaviours in domestic settings.

#14 A New Strategy to Integrate Heath-Carter Somatotype Assessment with Bioelectrical Impedance Analysis in Elite Soccer Player
Reference: Sports (Basel). 2020 Oct 27;8(11):E142. doi: 10.3390/sports8110142.
Authors: Francesco Campa, Tindaro Bongiovanni, Catarina N Matias, Federico Genovesi, Athos Trecroci, Alessio Rossi, F Marcello Iaia, Giampietro Alberti, Giulio Pasta, Stefania Toselli
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Summary: Easy-to-apply and quick methods for evaluate body composition are often preferred when assessing soccer teams. This study aimed to develop new equations for the somatotype quantification that would reduce the anthropometric measurements required by the Heath and Carter method, integrating the somatotype assessment to the bioelectrical impedance analysis (BIA). One hundred and seventy-six male elite soccer players (age 26.9 ± 4.5 years), registered in the Italian first division (Serie A), underwent anthropometric measurements and BIA. Endomorphy, mesomorphy, and ectomorphy were obtained according to the Heath and Carter method, while fat mass (FM) and fat free mass (FFM) estimated using a BIA-derived equation specific for athletes. The participants were randomly split into development (n = 117) and validation groups (n = 59, 1/3 of sample). The developed models including resistance2/stature, FM%, FFM, contracted arm and calf circumference, triceps, and supraspinal skinfolds had high predictive ability for endomorphy (R2 = 0.83, Standard Error of Estimate (SEE) = 0.16) mesomorphy (R2 = 0.80, SEE = 0.36), and ectomorphy (endomorphy (R2 = 0.87, SEE = 0.22). Cross validation revealed R2 of 0.80, 0.84, 0.87 for endomorphy, mesomorphy, and ectomorphy, respectively. The proposed strategy allows the integration of somatotype assessment to BIA in soccer players, reducing the number of instruments and measurements required by the Heath and Carter approach.

#15 Effects of Unloaded vs. Ankle-Loaded Plyometric Training on the Physical Fitness of U-17 Male Soccer Players
Reference: Int J Environ Res Public Health. 2020 Oct 27;17(21):E7877. doi: 10.3390/ijerph17217877.
Authors: Mehrez Hammami, Nawel Gaamouri, Katsuhiko Suzuki, Ridha Aouadi, Roy J Shephard, Mohamed Souhaiel Chelly
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Summary: The aim of this study was to compare the impact of two differing plyometric training programs (loaded plyometrics (with 2.5% of body mass placed above the ankle joint) vs. unloaded plyometrics), performed biweekly for 10 weeks, on the physical fitness of elite junior male soccer players. Participants aged 16.0 ± 0.5 years were randomly assigned between unloaded plyometrics (UP; n = 12), loaded plyometrics (LP; n = 14) and control (C; n = 12) groups. Two-way analyses of performance (group x time) were assessed by 40-m sprint times; 9-3-6-3-9 m sprints with 180° turns (S180°); 9-3-6-3-9 m sprints with backward and forward running (SBF); and 4 × 5 m sprints (S4 × 5 m); four jump tests; measures of static and dynamic balance; repeated change of direction tests and the Yo-Yo intermittent recovery test. Both LP and UP enhanced sprinting performance relative to C (p < 0.05) but performance increased more in LP relative to UP (p < 0.05) in all sprints except 40 m. Change of direction times were also significantly shortened by LP relative to UP (p < 0.05) and C (p < 0.01) in all tests, with no significant differences between UP and C. Jumps heights increased similarly in both LP and UP relative to C (p < 0.05), with no significance between LP and UP. LP and UP also enhanced repeated change of direction scores relative to C (p < 0.01) with greater changes in LP than in UP (p < 0.01). Finally, LP enhanced some balance scores relative to UP (p < 0.05) and C (p < 0.05). We conclude that the introduction of 10 weeks of in-season loaded plyometrics into the regimen of U17 male soccer players yields gains in several physical performance scores relative to either unloaded plyometrics or the control training regimen.





Running technique is more effective than soccer-specific training for improving the sprint and agility performances with ball possession

The study aimed at comparing the effects of two training approaches on prepubescent soccer players' sprint performance.





Effect of Practicing Soccer Juggling With Different Sized Balls Upon Performance, Retention and Transfer to Ball Reception

The aim was to investigate if making the skill aquisition phase more difficult or easier would enhance performance in soccer juggling and if this practice has a positive intertask transfer effect to ball reception performance.





Latest research in football - week 48 - 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 Concussion in soccer: a comprehensive review of the literature
Reference: Concussion. 2020 Jul 1;5(3):CNC76. doi: 10.2217/cnc-2020-0004.
Authors: James Mooney, Mitchell Self, Karim ReFaey, Galal Elsayed, Gustavo Chagoya, Joshua D Bernstock, James M Johnston
Summary: Sports-related concussion has been examined extensively in collision sports such as football and hockey. However, historically, lower-risk contact sports such as soccer have only more recently garnered increased attention. Here, we review articles examining the epidemiology, injury mechanisms, sex differences, as well as the neurochemical, neurostructural and neurocognitive changes associated with soccer-related concussion. From 436 titles and abstracts, 121 full texts were reviewed with a total of 64 articles identified for inclusion. Concussion rates are higher during competitions and in female athletes with purposeful heading rarely resulting in concussion. Given a lack of high-level studies examining sports-related concussion in soccer, clinicians and scientists must focus research efforts on large-scale data gathering and development of improved technologies to better detect and understand concussion.

#2 The Effects of Long-Term Magnesium Creatine Chelate Supplementation on Repeated Sprint Ability (RAST) in Elite Soccer Players
Reference: Nutrients. 2020 Sep 28;12(10):E2961. doi: 10.3390/nu12102961.
Authors: Adam Zajac, Artur Golas, Jakub Chycki, Mateusz Halz, Małgorzata Magdalena Michalczyk
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Summary: The aim of the study was to evaluate the effects of 16 weeks of a low dose of magnesium creatine chelate supplementation on repeated sprint ability test (RAST) results in elite soccer players. Twenty well-trained soccer players participated in the study. The players were divided randomly into two groups: the supplemented group (SG = 10) and placebo group (PG = 10). Out of the 20 subjects selected for the study, 16 (SG = 8, PG = 8) completed the entire experiment. The SG ingested a single dose of 5500 mg of magnesium creatine chelate (MgCr-C), in 4 capsules per day, which was 0.07 g/kg/d. The PG received an identical 4 capsules containing corn starch. Before and after the study, the RAST was performed. In the RAST, total time (TT), first and sixth 35 m sprint length (s), average power (AP) and max power (MP) were measured. Additionally, before and after the test, lactate LA (mmol/L) and acid-base equilibrium pH (-log(H+)), bicarbonates HCO3- (mmol/L) were evaluated. Also, in serum at rest, creatinine (mg/dL) concentration was measured. After the study, significantly better results in TT, AP and MP were observed in the SG. No significant changes in the RAST results were observed in the PG. After the study, significant changes in the first 35 m sprint, as well as the sixth 35 m sprint results were registered in the SG, while insignificant changes occurred in the PG. A significantly higher creatinine concentration was observed. Also, a higher post-RAST concentration of LA, HCO3- and lower values of pH were observed in April, May and June compared with baseline values. The long timeframe, i.e., 16 weeks, of the low dose of magnesium creatine chelate supplementation improved the RAST results in the SG. Despite the long period of MgCr-C supplementation, in the end of the study, the creatinine level in the SG reached higher but still reference values.

#3 Is It High Time to Increase Elite Soccer Substitutions Permanently?
Reference: Int J Environ Res Public Health. 2020 Sep 25;17(19):E7008. doi: 10.3390/ijerph17197008.
Authors: Gustavo R Mota, Izabela Aparecida Dos Santos, Rhaí André Arriel, Moacir Marocolo
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Summary: Rules determine how team sport matches occur. Match-induced fatigue is specific to each sport, and may be associated with injury incidence. For example, the injury rate in soccer is distinctly higher during matches than in training sessions. Understanding the differences between team sports rules might be useful for enhancing rules (e.g., safer sport). Therefore, this study aimed to evaluate the impact of the rule-induced physical demands between soccer, futsal, basketball, and handball, focusing on substitution rules. Data from the elite team sports' rules (e.g., absolute and relative court dimensions; the number of players, substitutions allowed, total game time, time-outs) were collected, including the changes due to the coronavirus disease (COVID-19) pandemic in soccer substitutions, and comparisons were performed. The data showed that soccer has higher rule-induced physical demands: e.g., substantially lower substitution rate, higher dimensions in absolute (eight to fifteen times), and relative (four to eight times) values. Simulations also showed that soccer has extremely large differences, even considering COVID-19 substitution changes (from three to up to five). We conclude that elite soccer has remarkably higher overall rule-induced physical demands than elite futsal, basketball and handball, and increasing soccer substitutions permanently (e.g., unlimited) might mitigate overall soccer demands.

#4 Diagnostic performance of the Strength and Pain Assessment (SPA) score for non-contact muscle injury screening in male soccer players
Reference: Phys Sportsmed. 2020 Sep 29;1-7. doi: 10.1080/00913847.2020.1824986. Online ahead of print.
Authors: Luca Semperboni, Chiara Vignati, Maria Giulia Ballatore, Anita Tabacco, Chiara Busso, Marco A Minetto
Summary: The aims of this study were to develop a clinical-feature based scoring system for muscle injury screening and to assess its diagnostic accuracy when large number of injuries are suspected. A prospective diagnostic accuracy study was performed according to the Standards for Reporting of Diagnostic Accuracy (STARD) criteria. The diagnostic accuracy of the Strength and Pain Assessment (SPA) score (index test) was assessed in relation to muscle ultrasonography (reference standard). A large (n = 175) number of male soccer players met the inclusion/exclusion criteria: clinical assessment (i.e., evaluation of pain onset modality, location, distribution, impact on performance, and manual muscle strength testing) and ultrasonography were performed in all players after 48 hours from the sudden or progressive onset of muscle pain during or after a soccer competition. 91 of 175 cases (52%) were classified as functional muscle disorders, while signs of muscle tear were observed in the remaining 84 of 175 (48%) cases that were classified as structural muscle injuries. The median (1st - 3rd quartile) value of the SPA score was significantly (P < 0.001) lower in the functional disorder group [9 (9-10)] compared to the structural injury group [12 (12-13)]. The area under the Receiver Operating Characteristic curve for different cutoff points of the SPA score was 0.977 (95% confidence intervals: 0.957-0.998) and the optimal cutoff value of the SPA score providing the greatest sensitivity and specificity (respectively, 99% and 89%) was 11. This study found that the SPA score has high diagnostic accuracy for structural muscle injuries and could be used as a valid screening tool in soccer players presenting with sudden or progressive onset of muscle pain during or after a competition.

#5 Effects of Field Position on Fluid Balance and Electrolyte Losses in Collegiate Women's Soccer Players
Reference: Medicina (Kaunas). 2020 Sep 24;56(10):E502. doi: 10.3390/medicina56100502.
Authors: Haoyan Wang, Kate S Early, Bailey M Theall, Adam C Lowe, Nathan P Lemoine Jr, Jack Marucci, Shelly Mullenix, Neil M Johannsen
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Summary: Research investigating hydration strategies specialized for women's soccer players is limited, despite the growth in the sport. The purpose of this study was to determine the effects of fluid balance and electrolyte losses in collegiate women's soccer players. Eighteen NCAA Division I women's soccer players were recruited (age: 19.2 ± 1.0 yr; weight: 68.5 ± 9.0 kg, and height: 168.4 ± 6.7 cm; mean ± SD), including: 3 forwards (FW), 7 mid-fielders (MD), 5 defenders (DF), and 3 goalkeepers (GK). Players practiced outdoor during spring off-season training camp for a total 14 practices (WBGT: 18.3 ± 3.1 °C). The main outcome measures included body mass change (BMC), sweat rate, urine and sweat electrolyte concentrations, and fluid intake. Results were analyzed for comparison between low (LOW; 16.2 ± 2.6° C, n = 7) and moderate risk environments for hyperthermia (MOD; 20.5 ± 1.5 °C, n = 7) as well as by field position. The majority (54%) of players were in a hypohydrated state prior to practice. Overall, 26.7% of players had a %BMC greater than 0%, 71.4% of players had a %BMC less than -2%, and 1.9% of players had a %BMC greater than -2% (all MD position). Mean %BMC and sweat rate in all environmental conditions were -0.4 ± 0.4 kg (-0.5 ± 0.6% body mass) and 1.03 ± 0.21 mg·cm-2·min-1, respectively. In the MOD environment, players exhibited a greater sweat rate (1.07 ± 0.22 mg·cm-2·min-1) compared to LOW (0.99 ± 0.22 mg·cm-2·min-1; p = 0.02). By position, DF had a greater total fluid intake and a lower %BMC compared to FW, MD, and GK (all p < 0.001). FW had a greater sweat sodium (Na+) (51.4 ± 9.8 mmol·L-1), whereas GK had the lowest sweat sodium (Na+) (30.9 ± 3.9 mmol·L-1). Hydration strategies should target pre-practice to ensure players are adequately hydrated. Environments deemed to be of moderate risk of hyperthermia significantly elevated the sweat rate but did not influence fluid intake and hydration status compared to low-risk environments. Given the differences in fluid balance and sweat responses, recommendations should be issued relative to soccer position.

#6 Use of Numerically Blinded Ratings of Perceived Exertion in Soccer: Assessing Concurrent and Construct Validity
Reference: Int J Sports Physiol Perform. 2020 Sep 28;1-7. doi: 10.1123/ijspp.2019-0740. Online ahead of print.
Authors: Ric Lovell, Sam Halley, Jason Siegler, Tony Wignell, Aaron J Coutts, Tim Massard
Summary: The purpose was to examine the concurrent and construct validity of numerically blinded ratings of perceived exertion (RPEs). A total of 30 elite male youth soccer players (age 16.7 [0.5] y) were monitored during training and matches over a 17-wk in-season period. The players' external loads were determined via raw 10-Hz global positioning system. Heart rate (HR) was collected continuously and expressed as Bannister and Edwards training impulses, and minutes >80% of the players predetermined the maximum HR by the Yo-Yo Intermittent Recovery Test Level 1. RPE was collected confidentially 10 to 15 min after training/matches using 2 methods: (1) a traditional verbal response to the 0 to 100 category-ratio "centiMax" scale (RPE) and (2) numerically blinded RPE centiMax scale (RPEblind) with the response selected manually via a 5 × 7-in tablet "slider." The RPE and RPEblind were divided by 10 and multiplied by the duration to derive the sessional RPE. Linear mixed models compared ratings, and within-subject repeated-measures correlations assessed the sessional RPE versus HR and external load associations. There were no differences between the RPE and RPEblind (0.19; 95% confidence intervals, -0.59 to 0.20 au, P = .326) or their session values (13.5; 95% confidence intervals, -17.0 to 44.0 au, P = .386), and the ratings were nearly perfectly correlated (r = .96). The associations between the sessional RPE versus HR and external load metrics were large to very large (r = .65-.81), with no differences between the RPE methods (P ≥ .50). The RPEblind also reduced verbal anchor clustering and integer bias by 11% and 50%, respectively. RPEblind demonstrated concurrent and construct validity versus the traditional method, and may be used in situations where practitioners have concerns regarding the authenticity of athlete ratings.

#7 Profiling the Post-match Top-up Conditioning Practices of Professional Soccer Substitutes: An Analysis of Contextual Influences
Reference: J Strength Cond Res. 2020 Oct;34(10):2805-2814. doi: 10.1519/JSC.0000000000003721.
Authors: Samuel P Hills, Stephen Barrett, Matt Busby, Liam P Kilduff, Martin J Barwood, Jon N Radcliffe, Carlton B Cooke, Mark Russell
Summary: Soccer practitioners implement "top-up" conditioning sessions to compensate for substitutes' limited match-play exposure. Although perceived to be valuable for reducing injury risk and augmenting positive physical adaptations, little research has considered the demands of post-match top-up training. To quantify post-match top-up responses, 31 professional soccer players wore 10 Hz microelectromechanical systems after 37 matches whereby they were selected in the match-day squad as substitutes (184 observations; 6 ± 5 observations·player). Linear mixed models and effect sizes (ES) assessed the influence of contextual factors on 23 physical performance variables. Top-ups lasted 17.13 ± 7.44 minutes, eliciting total and high-speed distances of 1.7 ± 6.2 km and 0.4 ± 1.7 km, respectively. Each contextual factor (i.e., position, substitution timing, match location, result, time of day, stage of the season, and fixture density) influenced at least 4 of the dependent variables profiled (p ≤ 0.05). Top-up duration; total, moderate-speed, and low-speed distance; and the number of repeated high-intensity efforts were greater for unused vs. used substitutes (ES: 0.38-0.73, small to moderate). Relative to away matches, home top-ups elicited heightened total, low-speed, and high-speed distances, alongside more moderate-speed accelerations and decelerations, and repeated high-intensity efforts (ES: 0.25-0.89, small to moderate). Although absolute and relative running distances were generally the highest when the fixture density was low, the greatest acceleration and deceleration demands were observed during the most congested fixture periods. Late-season top-ups typically elicited lower absolute physical responses than early and mid-season sessions. These data provide important information for practitioners when considering the aims and design of substitute top-up conditioning sessions, particularly with reference to contextual influences.

#8 Effects of Maturation on Physical Fitness Adaptations to Plyometric Drop Jump Training in Male Youth Soccer Players
Reference: J Strength Cond Res. 2020 Oct;34(10):2760-2768. doi: 10.1519/JSC.0000000000003151.
Authors: Tiago Vera-Assaoka, Rodrigo Ramirez-Campillo, Cristian Alvarez, Felipe Garcia-Pinillos, Jason Moran, Paulo Gentil, David Behm
Summary: Effects of maturation on physical fitness adaptations to plyometric drop jump training in male youth soccer players. J Strength Cond Res 34(10): 2760-2768, 2020-The objective of this study was to compare the effects of maturation on physical fitness adaptations to a twice weekly, 7-week plyometric drop jump training program. Seventy-six young male soccer players (aged 10-16 years) participated in this randomized controlled trial. Before and after the intervention, a physical fitness test battery was applied (countermovement jump; drop jump from 20 to 40 cm; 5 multiple bounds test; 20-m sprint time; change of direction speed; 2.4-km running time-trial; 5 repetition maximum [RM] squat; and maximal kicking distance). Participants were randomly divided into an active soccer-control group (CG) with Tanner stage maturation of 1-3 (CG-early; n = 16) or Tanner stage 4-5 (CG-late; n = 22), and to plyometric drop jump training groups with Tanner stage 1-3 (plyometric jump training [PJT]-early; n = 16) or 4-5 (PJT-late; n = 22). The analysis of variance and effect size (ES) measures revealed that when compared with their age-matched controls, the PJT-early (ES = 0.39-1.58) and PJT-late (ES = 0.21-0.65) groups showed greater improvements (p < 0.05) in sprint time, 2.4-km running time-trial, change of direction speed, 5RM squat, jumping, and kicking distance. The PJT-early exceeded the PJT-late group with greater (p < 0.05) improvements in drop jump from 20 cm (ES = 1.58 vs. 0.51) and 40 cm (ES = 0.71 vs. 0.4) and kicking distance (ES = 0.95 vs. 0.65). Therefore, a 7-week plyometric drop jump training program was effective in improving physical fitness traits in both younger and older male youth soccer players, with greater jumping and kicking adaptations in the less-mature athletes.

#9 Does an Optimal Relationship Between Injury Risk and Workload Represented by the "Sweet Spot" Really Exist? An Example From Elite French Soccer Players and Pentathletes
Reference: Front Physiol. 2020 Aug 28;11:1034. doi: 10.3389/fphys.2020.01034. eCollection 2020.
Authors: Adrien Sedeaud, Quentin De Larochelambert, Issa Moussa, Didier Brasse , Jean-Maxence Berrou, Stephanie Duncombe, Juliana Antero, Emmanuel Orhant, Christopher Carling, Jean-Francois Toussaint
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Summary: The aim was to examine the relationships between the occurrence and severity of injuries using three workload ratios (ACWR, EWMA, REDI) in elite female soccer players and international male and female pentathletes. Female soccer players in the U16 to U18 national French teams (n = 24) and international athletes (n = 12, 4 women and 8 men) in the French modern pentathlon team were monitored throughout an entire season. The Acute Chronic Workload Ratio (ACWR), the Exponentially Weighted Moving Averages (EWMA), and the Robust Exponential Decreasing Index (REDI) were calculated for internal load by the ROE method in soccer and external load in pentathlon. The occurrence and severity of injuries (determined according to time-loss) were quantified in the sweet spot zone [0.8; 1.3] and compared to the other zones of load variation: [0; 0.8], [1.3; 1.5], [1.5; +8], using the three ratios. Over the study period, a total of sixty-six injuries (2.75 per athlete) were reported in the soccer players and twelve in pentathletes (1 per athlete). The cumulative severity of all injuries was 788 days lost in soccer and 36 in pentathlon: respectively, 11.9 days lost per injury in soccer player and 3.0 per pentathlete. The mean values across the three methods in soccer showed a higher number of injuries detected in the [0; 0.8] workload ratio zone: 22.3 ± 6.4. They were 17.3 ± 3.5 in the sweet spot ([0.8-1.3] zone) and 17.6 ± 5.5 in the [1.5; +8] zone. In comparison to the [1.5; +8] zone, soccer players reported a higher number of days lost to injuries in the presumed sweet spot and in the [0-0.8] zone: 204.7 ± 28.7 and 275.0 ± 120.7 days, respectively. In pentathletes, ten of the twelve injuries (83.3%) occurred in the presumed sweet spot. REDI was the only method capable of tracking workloads over all-time series. In the present cohort of elite soccer players and pentathletes, acute chronic workload calculations showed an association with injury occurrence and severity but did not provide evidence supporting existence of a sweet spot diminishing injury risk.

#10 Factors Associated with Ball Velocity and Low Back Pain During Kicking in Adolescent Soccer Players
Reference: Open Access J Sports Med. 2020 Sep 7;11:133-143. doi: 10.2147/OAJSM.S262990. eCollection 2020.
Authors: Michio Tojima, Seira Takei , Suguru Torii
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Summary: The factors associated with low back pain (LBP) and the relationship between LBP and ball velocity during kicking motion of adolescent soccer players remain largely unknown. This study aims to clarify the relationship between increasing ball velocity and LBP in adolescent soccer players. Adolescent soccer players were divided into two groups according to the presence and absence of LBP (LBP group, n=38 and NBP (no back pain) group, n=29, respectively). Real-time kick motion was measured using a three-dimensional motion analysis system and the angle of the lumbar spine, hip, and center of mass (COM) were calculated. Regression analysis was used to identify factors associated with ball velocity and LBP. In addition, Pearson's correlation coefficients were determined between the angle of the lumbar spine and hip, and ball velocity and position of COM in the extracted phase from regression analysis. The major factor associated with increasing ball velocity was the rotation angle of both hips (Adjusted R2=0.244) and vertical position of COM during kicking (Adjusted R2=0.262). Furthermore, the factors associated with LBP were the flexion angle of kick-side hip (OR=1.126) and abduction angle of both hips (kick-side OR=1.124; support-side OR=0.872). The factors for ball velocity and LBP were related to the maximum hip extension phase. In the hip extension phase of kicking, compared with the NBP group, the LBP group showed lesser extension and external rotation of the kick-side hip angle. In the hip flexion phase of kicking, the ball velocity was correlated with vertical (r=0.56)/anterior (r=0.46) position of COM in the NBP group. To compensate for this restricted hip motion, the LBP group could extend and rotate their lumbar spine, which may likely cause stress to this region.

#11 Impact of football matches on number of visits to an emergency department

Reference: Emergencias. 2020 Sep;32(5):345-348.
Authors: Sendoa Ballesteros Peña, Irrintzi Fernández Aedo, Gorka Vallejo de la Hoz
Summary: The purpose was to analyze the impact of a local football team's matches on patient demand for hospital emergency department care in Bilbao, in the Spanish province of Biscay. We retrieved the number of patients coming to the emergency department on the days and hours of matches played by Bilbao's Athletic Club during the 2017-2019 and 2018-2019 seasons and compared the caseloads with those on the same days of the weeks before and after the matches (control days). Ninety-five match days were studied. Nineteen of the matches were considered key events. Visits by adults to the emergency department fell by a statistically significant 7.5% (95% CI, 4.6%-11.6%) when matches were being played in Bilbao. The decrease was 8.4% (95% CI, 5.3%-12.6%) when matches were played away. The decrease in pediatric emergencies was 32.7% (95% CI, 7.4%-68.3%) in the hours while important matches were played outside the city. The impact of football on the number of visits to our hospital emergency department was modest, except during important away matches.

#12 Kinematic Analysis of the Postural Demands in Professional Soccer Match Play Using Inertial Measurement Units
Reference: Sensors (Basel). 2020 Oct 22;20(21):E5971. doi: 10.3390/s20215971.
Authors: José M Oliva-Lozano, Elisa F Maraver, Víctor Fortes, José M Muyor
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Summary: The development of wearable sensors has allowed the analysis of trunk kinematics in match play, which is necessary for a better understanding of the postural demands of the players. The aims of this study were to analyze the postural demands of professional soccer players by playing position. A longitudinal study for 13 consecutive microcycles, which included one match per microcycle, was conducted. Wearable sensors with inertial measurement units were used to collect the percentage (%) of playing time spent and G-forces experienced in different trunk inclinations and the inclination required for different speeds thresholds. The inclination zone had a significant effect on the time percentage spent on each zone (p < 0.001, partial eta-squared (ηp2 = 0.85) and the G-forces experienced by the players (p < 0.001, ηp2 = 0.24). Additionally, a significant effect of the speed variable on the trunk inclination zones was found, since trunk flexion increased with greater speeds (p < 0.001; ηp2 = 0.73), except for midfielders. The players spent most of the time in trunk flexion between 20° and 40°; the greatest G-forces were observed in trunk extension zones between 0° and 30°, and a linear relationship between trunk inclination and speed was found. This study presents a new approach for the analysis of players' performance. Given the large volumes of trunk flexion and the interaction of playing position, coaches are recommended to incorporate position-specific training drills aimed to properly prepare the players for the perception-action demands (i.e., visual exploration and decision-making) of the match, as well as trunk strength exercises and other compensatory strategies before and after the match.

#13 Long-term influence of technical, physical performance indicators and situational variables on match outcome in male professional Chinese soccer
Reference: J Sports Sci. 2020 Oct 27;1-11. doi: 10.1080/02640414.2020.1836793. Online ahead of print.
Authors: Changjing Zhou, Alberto Lorenzo Calvo, Sam Robertson, Miguel-Ángel Gómez
Summary: This study aimed to determine whether the role of technical, physical performance indicators and situational variables in determining match outcome has varied from a long-term analysis (seasons 2012 to 2017) of the Chinese Soccer Super League (CSL). The sample included 1,429 matches where 17 technical performance-related indicators, 11 physical performance-related indicators and two situational variables (match location and quality of opposition) were analysed. Three binary logistic regression models (inclusion of different variables) were used to measure the level of association between factors and match outcome over the six seasons studied. Results of models 1 and 2 revealed that shots on target, possession, total distance in ball possession, total distance out of ball possession, and match location exerted a decreased influence on winning the matches from 2012 to 2014 seasons. However, these indicators play a more important role in winning matches from 2014 to 2017 seasons. Additionally, the quality of opposition has a continuously increased negative effect on the match outcome. In model 3, more variables, such as high-speed distance, high-speed out of ball possession, had a meaningful influence on winning the match. These results provide valuable information about performance indicators and situational variables on winning the matches from a long-term approach.

#14 Electromyographic Comparison of Flywheel Inertial Leg Curl and Nordic Hamstring Exercise Among Soccer Players
Reference: Int J Sports Physiol Perform. 2020 Oct 28;1-6. doi: 10.1123/ijspp.2019-0921. Online ahead of print.
Authors: Helene Pedersen, Atle Hole Saeterbakken, Markus Vagle, Marius Steiro Fimland, Vidar Andersen
Summary: The Nordic hamstring exercise (NHE) has been shown to considerably reduce hamstring injuries among soccer players. However, as the load in the NHE is the person's own bodyweight, it is a very heavy exercise and difficult to individualize. The flywheel inertial leg curl (FLC) could be an alternative since the eccentric overload is based on the amount of work produced in the concentric movement. Therefore, the primary aim of this study was to compare the activation in the hamstrings at long muscle lengths in the NHE and the FLC in amateur soccer players. Fifteen male amateur soccer players performed 5 repetitions in each exercise in a randomized and counterbalanced order. The concentric and eccentric movements were divided into lower and upper phases. Surface EMG was measured distally, proximally, and in the middle, at both muscles. In the lower phase in the eccentric movement, there were no significant differences between the 2 exercises (P = .101-.826). In the lower concentric movement, the FLC led to higher activation in all parts of both the biceps femoris (31%-52%, P < .001) and the semitendinosus (20%-35%, P = .001-.023). Both exercises activated the hamstrings similarly at long muscle lengths during eccentric contractions (Nordic hamstring, nonsignificantly higher). However, when performing concentric contractions, the FLC induced higher activations. Therefore, the FLC could be a useful alternative to the NHE and particularly suitable for weaker athletes before progressing to NHE.





Large Reductions in Match Play Physical Performance Across a Football Season Positional Performances

The aims of this investigation were to report team average and positional changes to match play physical performance across an European Championsleague season while statistically controlling for situational and contextual variables.





The Effect of Preparatory Posture on Goalkeeper’s Diving Save performance in Football

This study aimed to analyse the effect of different starting stance widths and knee flexion angles on movement time, center of mass trajectory and velocity in goalkeepers' diving saves.





Latest research in football - week 47 - 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 Monitoring Cardiorespiratory Fitness in Professional Soccer Players: Is It Worth the Prick?
Reference: Int J Sports Physiol Perform. 2020 Oct 1;1-5. doi: 10.1123/ijspp.2019-0911. Online ahead of print.
Authors: Martin Buchheit, Ben M Simpson, Mathieu Lacome
Summary: The aim was to compare between-tests changes in submaximal exercise heart rate (HRex, 3 min, 12 km/h) and the speed associated with 4 mmol/L of blood lactate (V4mmol) in soccer players to get insight into their level of agreement and respective sensitivity to changes in players' fitness. A total of 19 elite professional players (23 [3] y) performed 2 to 3 graded incremental treadmill tests (3-min stages interspersed with 1 min of passive recovery, starting speed 8 km/h, increment 2 km/h until exhaustion or 18 km/h if exhaustion was not reached before) over 1.5 seasons. The correlation between the changes in HRex and V4mmol was examined. Individual changes in the 2 variables were compared (>2 × typical error considered "clear"). The changes in HRex and V4mmol were largely correlated (r = .82; 90% confidence interval, .65-.91). In more than 90% of the cases, when a clear individual change in HRex was observed, it was associated with a similar clear change in V4mmol (the same direction, improvement, or impairment of fitness) and conversely. When it comes to testing players submaximally, the present results suggest that practitioners can use HRex or V4mmol interchangeably with confidence. However, in comparison with a field-based standardized warm-up run (3-4 min, all players together), the value of a multistage incremental test with repeated blood lactate samplings is questionable for a monitoring purpose given its time, labor, cost, and poorer player buy-in.

#2 Birth sex ratio in the offspring of professional male soccer players: influence of exercise training load
Reference: Hum Reprod. 2020 Oct 2;deaa225. doi: 10.1093/humrep/deaa225. Online ahead of print.
Authors: D Vaamonde, A C Hackney, J M Garcia Manso, E Arriaza Ardiles, M Vaquero
Summary: This is the first study assessing the influence of exercise training load on the offspring sex ratio of children from male professional athletes, observing a bias toward more females being born as a result of both high-intensity and high-volume loads, with intensity having the greatest effect. There is a relatively constant population sex ratio of males to females among various species; however, certain events and circumstances may alter this population sex ratio favoring one sex over the other. Seventy-five male professional soccer players from First Division soccer teams. Offspring variables were sex of the offspring, number of children and order of birth. Exercise training variables were volume and intensity. Total offspring was 122 children (52 males (42.6%), 70 females (57.4%)). Analysis revealed that increase in either the volume (P < 0.001) or intensity (P < 0.001) of training by the players shifted the birth offspring ratio more toward females. Within the sample of females born, more births (i.e. number) were observed as a consequence of training at the highest intensity (45 out of 70; P < 0.001), no such pattern occurred within males (P > 0.05). When female versus male births were compared within each intensity, only the high-intensity comparison was significant (45 (75%) females vs 15 (25%) males, P < 0.001). While this is the first study assessing differences in the sex ratio of the offspring of male athletes (i.e. soccer players), we acknowledge there are limitations and confounders within our approach; e.g. small sample size, ethnic background and variations in the timing of intercourse relative to ovulation as well as in sex hormone levels. As such, we propose that future research is needed to confirm or refute our findings. It is recommended that such work expand on the measurements obtained and conduct direct assessment of sperm characteristics. The findings of the study support the fact that different stressors on the body may alter the sex of the offspring. While in the present study the stressor is the excessive training load of soccer players, other events may lead to similar results. The bias in offspring sex ratio may have important implications for demography and population dynamics, as well as genetic trait inheritance.

#3 Myositis Ossificans of the Adductor Longus in a Soccer Player
Reference: J Orthop Sports Phys Ther. 2020 Oct;50(10):586. doi: 10.2519/jospt.2020.9573.
Authors: Michael Zarro, Kathleen Tamberrino, E McKenzie Bane
Summary: A 20-year-old male collegiate soccer goalkeeper presented to an athletic trainer during the season complaining of right (dominant kicking leg) groin pain. The athletic trainer identified a mass and hematoma and suspected myositis ossificans. The patient was referred to the team physician, who ordered radiographs and magnetic resonance imaging to confirm the diagnosis and rule out other injuries. Imaging demonstrated an adductor longus muscle strain with myositis ossificans.

#4 Prevalence of concomitant knee injuries associated with anterior cruciate ligament tear in kabaddi and football players
Reference: J Clin Orthop Trauma. 2020 Oct;11(Suppl 5):S784-S788. doi: 10.1016/j.jcot.2020.05.037. Epub 2020 Jun 6.
Authors: Ravi Gupta, Anil Kapoor, Gladson DavidMasih
Summary: There is little literature available about the type of sports and concomitant knee injury. The aim was to help in better prediction of concomitant knee injuries in football and kabaddi players. Five hundred and seventeen male athletes [Football (n = 226) and Kabaddi players (n = 291)] aged between 16 and 35 years were enrolled in the study. These were categorized into five groups depending upon the time interval between injury and surgery (0-3 months, 3-6 months, 6-9 months, 9-12 months, 12-18 months and 18-24 months). Meniscal and chondral damage present at the time of ACL reconstruction was documented. The overall incidence of meniscal tear was more in kabaddi players (220/291) as compared to football players (144/226; p = 0.003). The incidence of both menisci tear was more in kabaddi as compared to football (p = 0.02). Incidence of lateral meniscus tear (147/291) in kabaddi was more as compared to football (84/226; p = 0.002). The incidence of condylar damage was comparable in both groups. Medial femoral condyle was more commonly injured in both the sports irrespective of time frame. The chances of meniscus injuries were more in kabaddi players compared to football players in ACL deficient knee. The time interval between injury and surgery had a direct correlation with meniscus and chondral injuries.

#5 Accuracy of maturity prediction equations in individual elite male football players
Reference: Ann Hum Biol. 2020 Jun;47(4):409-416. doi: 10.1080/03014460.2020.1783360.
Authors: Jan Willem Ajw Teunissen, Nikki Rommers, Johan Pion, Sean P Cumming, Roland Rössler, Eva D'Hondt, Matthieu Lenoir, Geert J P Savelsbergh, Robert M Malina
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Summary: Equations predicting age at peak height velocity (APHV) are often used to assess somatic maturity and to adjust training load accordingly. However, information on the intra-individual accuracy of APHV in youth athletes is not available. The purpose of this study is to assess the accuracy of predication equations for the estimation of APHV in individual youth male football players. Body dimensions were measured at least every three months in 17 elite youth male football players (11.9 ± 0.8 years at baseline) from the 2008-2009 through the 2011-2012 seasons. APHV was predicted at each observation with four suggested equations. Predicted APHV was compared to the player's observed APHV using one-sample-t-tests and equivalence-tests. Longitudinal stability was assessed by comparing the linear coefficient of the deviation to zero. Predicted APHV was equivalent to the observed APHV in none of the players. A difference with a large effect size (Cohen's d > 0.8) was noted in 87% of the predictions. Moreover, predictions were not stable over time in 71% of the cases. None of the evaluated prediction equations is accurate for estimating APHV in individual players nor are predictions stable over time, which limits their utility for adjusting training programmes.

#6 The Influence of Recruitment Age and Anthropometric and Physical Characteristics on the Development Pathway of English Academy Football Players
Reference: Int J Sports Physiol Perform. 2020 Sep 29;1-9. doi: 10.1123/ijspp.2019-0534. Online ahead of print.
Authors: Mark R Noon, Emma L J Eyre, Matthew Ellis, Tony D Myers, Rhys O Morris, Peter D Mundy, Ryan Penny, Neil D Clarke
Summary: The purpose was to investigate the influence of recruitment age on retention and release across the development pathway and to explore the influence of anthropometric and physical characteristics on retention and release at different ages throughout the development pathway and the likelihood of obtaining a professional contract. Following receipt of ethics approval, a cross-sectional study tracking 4 cohorts of players over 5 years assessed 76 male youth football players (11-16 y) from an English football academy on 3 occasions annually in anthropometry, countermovement jump height, and linear (30 and 15 m) and multidirectional sprint time. Players were categorized based on their start and release date. Starting early (ie, before U12) in an academy was a key indicator of obtaining a professional contract, representing 87% of the players signed. Bayesian regression models suggest that the majority of differences in physical characteristics between players that were released and retained are trivial, small, and/or uncertain. Players who attained a professional contract at 18 had slower 15- and 30-m sprint times at U13 to U15 (P > 0 = .87-.99), slower multidirectional sprint times at U14 (P > 0 = .99), and lower countermovement jump height at U13 to U16 (P > 0 = .88-.99) compared with players who did not gain a contract. Players recruited early have an increased likelihood of gaining a professional contract. Physical assessments lack utility when used in isolation as a talent-identification tool.

#7 Football spectatorship and selected acute cardiovascular events: lack of a population-scale association in Poland
Reference: Kardiol Pol. 2020 Sep 21. doi: 10.33963/KP.15606. Online ahead of print.
Authors: Jenny E Simon, Łukasz A Małek, Andrzej Śliwczyński, Witold Śmigielski, Karol Korczak, Wojciech Drygas
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Summary: The status of football spectatorship-induced emotional stress as a risk factor for acute cardiovascular (CV) events remains in dispute. Aims: To examine the relation between football spectatorship and the incidence of selected acute CV events across the Polish male population. Events occurring in male patients aged 35 and older across Poland during three tournaments (the 2012 and 2016 European Championships - EC and the 2018 World Cup - WC) were retrospectively analysed through hospital admission codes obtained from the National Health Fund. Of interest were the following primary diagnoses: acute myocardial infarction (AMI, I21), sudden cardiac arrest (SCA, I46), sudden arrhythmias (SA, I47 - I49). The same dates in the years before and after the tournaments constituted the reference periods. A total of 255,383 patients were included in this study. There were no significant differences in the incidence of events between the combined exposure and reference periods: RR = 1.05 (95% CI 0.97 to 1.14, P = 0.20) for AMI, RR = 1.08 (95% CI 0.87 to 1.35, P = 0.47) for SCA, and RR = 1.02 (95% CI 0.98 to 1.06, P = 0.32) for SA. Individual tournament analyses revealed a higher incidence of AMI (RR = 1.20, 95% CI 1.12 - 1.30, P < 0.001) during WC. However, day-by-day analysis of WC did not find a higher incidence of AMI on match vs. match-free days. The emotional stress evoked by football spectatorship is insufficiently potent to precipitate a population-scale increase in selected acute CV events.

#8 Comparing football bettors' response to social media marketing differing in bet complexity and account type - An experimental study
Reference: J Behav Addict. 2020 Sep 26. doi: 10.1556/2006.2020.00056. Online ahead of print.
Authors: Scott Houghton, Mark Moss
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Summary: The current study aimed to assess how sports bettors respond to advertised bets on social media and whether this differs dependent upon bet complexity and social media account type. Employing a 3 × 2 repeated measures design, 145 regular football bettors were recruited to take part in an online study requiring them to rate bets advertised upon social media, providing indications of their likelihood to bet, confidence in the bet and how much they would stake on the bet. Advertised bets differed in terms of complexity (low, medium and high) and each bet was presented separately on both an operator account and an affiliate account. Data analysis highlighted a significant interaction between bet complexity and account type, with bettors rating themselves as being more likely to bet and more confident in bets which were presented on an affiliate account for medium complexity bets but not for low or high complexity bets. This study provides initial evidence that affiliate marketing of sports betting increases bettor's confidence in certain types of bets. This heightens previously addressed concerns around affiliate marketing, given that affiliates are financially incentivised to attract custom toward gambling operators. Future research should explore risk factors for increased uptake of affiliate marketing, and the impact on gambling behaviour.

#9 Inertial flywheel knee- and hip-dominant hamstring strength exercises in professional soccer players: Muscle use and velocity-based (mechanical) eccentric overload
Reference: PLoS One. 2020 Oct 2;15(10):e0239977. doi: 10.1371/journal.pone.0239977. eCollection 2020.
Authors: Luis Suarez-Arrones, F Javier Núñez, Pilar Lara-Lopez, Valter Di Salvo, Alberto Méndez-Villanueva
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Summary: The primary aim of the present study was to analyze mechanical responses during inertial knee- and hip-dominant hamstring strengthening exercises (flywheel leg-curl and hip-extension in conic-pulley), and the secondary aim was to measure and compare regional muscle use using functional magnetic resonance imaging. Mean power, peak power, mean velocity, peak velocity and time in the concentric (CON) and eccentric (ECC) phases were measured. The transverse relaxation time (T2) shift from pre- to post-exercise were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. Peak and mean power in flywheel leg-curl were higher during the CON than the ECC phase (p<0.01). ECC peak power was higher than CON phase (p<0.01) in conic-pulley hip-extension exercise, while mean power was higher during the CON than ECC phase (p<0.01). Flywheel leg-curl showed a higher T2 values in ST and BFs and BFl (p<0.05), while the conic-pulley hip-extension had a higher T2 values in the proximal region of the ST and BFl (p<0.05). In conclusion, ECC overload was only observed in peak power during the conic-pulley hip-extension exercise. Flywheel leg-curl involved a greater overall use of the 4 muscle bellies, more specifically in the ST and BFs, with a selective augmented activity (compared with the conic-pulley) in the 3 regions of the BFs, while conic-pulley hip-extension exercise selectively targeted the proximal and medial regions of the BFl. Physiotherapists and strength and conditioning coaches should consider this when optimizing the training and recovery process for hamstring muscles, especially after injury.

#10 Post-competition recovery strategies in elite male soccer players. Effects on performance: A systematic review and meta-analysis
Reference: PLoS One. 2020 Oct 2;15(10):e0240135. doi: 10.1371/journal.pone.0240135. eCollection 2020.
Authors: Albert Altarriba-Bartes, Javier Peña, Jordi Vicens-Bordas, Raimon Milà-Villaroel, Julio Calleja-González
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Summary: The main aim of the present review was to update the available evidence on the value interest of post-competition recovery strategies in male professional or semi-professional soccer players to determine its effect on post-game performance outcomes, physiological markers, and wellness indicators. A structured search was carried out following the PRISMA guidelines using six online databases: Pubmed, Scopus, SPORTDiscus, Web of Science, CINAHL and Cochrane Central Register of Controlled Trials. The risk of bias was completed following the Cochrane Collaboration Guidelines. Meta-analyses of randomized controlled trials were conducted to determine the between and within-group effects of different recovery strategies on performance, physiological markers and wellness data. Final meta-analyses were performed using the random-effects model and pooled standardized mean differences (SMD). Five randomized controlled trials that used Compression Garments (n = 3), Cold Water Immersion (n = 1), and acute Sleep Hygiene Strategy (n = 1) were included. Greater CMJ values at 48h for the intervention group (SMD = 0.70; 95% CI 0.14 to 1.25; p = 0.001; I2 = 10.4%) were found. For the 20-m sprint and MVC, the results showed no difference either at 24h or 48h. For physiological markers (CK and CRP) and wellness data (DOMS), small to large SMD were present in favor of the intervention group both at 24h (-0.12 to -1.86) and 48h (-0.21 to -0.85). No heterogeneity was present, except for MVC at 24h (I2 = 90.4%; p = 0.0012) and CALF DOMS at 48h (I2 = 93.7%; p = 0.013). The use of recovery strategies offers significant positive effects only in jumping performance (CMJ), with no effects on the 20-m sprint or MVC. Also, the use of recovery strategies offers greater positive effects on muscle damage (physiological markers and wellness data), highlighting the importance of post-match recovery strategies in soccer.





A New Approach for Training-load Quantification in Elite-level Soccer: Contextual Factors


The aims were to analyse the physical response of professional soccer players during training considering the contextual factors of match location, season period and quality of opposition.





Long corner kicks in the English Premier League: Deliveries into the goal area and critical area


The purpose was to investigate long corner kicks within the English Premier League that entered the goal area (6-yard box) or the critical are (6-12 yards from the goal-line in the width of the goal area) with the defining outcome occurring after the first contact.





Latest research in football - week 46 - 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 How to Use Global Positioning Systems (GPS) Data to Monitor Training Load in the "Real World" of Elite Soccer
Reference: Front Physiol. 2020 Aug 20;11:944. doi: 10.3389/fphys.2020.00944. eCollection 2020.
Authors: Guillaume Ravé, Urs Granacher, Daniel Boullosa, Anthony C Hackney, Hassane Zouhal
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#2 Successful return to professional men's football (soccer) competition after the COVID-19 shutdown: a cohort study in the German Bundesliga
Reference: Br J Sports Med. 2020 Sep 24;bjsports-2020-103150. doi: 10.1136/bjsports-2020-103150. Online ahead of print.
Authors: Tim Meyer, Dietrich Mack, Katrin Donde, Oliver Harzer, Werner Krutsch, Annika Rössler, Janine Kimpel, Dorothee von Laer, Barbara C Gärtner
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Summary: The aim was to evaluate the restart of the German Bundesliga (football (soccer)) during the COVID-19 pandemic from a medical perspective. Participants were male professional football players from the two highest German leagues and the officials working closely with them. Our report covers nine match days spread over 9 weeks (May to July 2020). Daily symptom monitoring, PCR testing for SARS-CoV-2 RNA twice weekly, and antibody tests (on two occasions-early during the phase in May 2020 and in the week of the last match) were conducted. Target variables were: (1) onset of typical COVID-19 symptoms, (2) positive PCR results, and (3) IgG seroconversion against SARS-CoV-2. All detected seroconversions were controlled by neutralisation tests. Suspicious symptoms were reported for one player; an immediate additional PCR test as well as all subsequent diagnostic and antibody tests proved negative for coronavirus. Of 1702 regularly tested individuals (1079 players, 623 officials members), 8 players and 4 officials tested positive during one of the first rounds of PCR testing prior to the onset of team training, 2 players during the third round. No further positive results occurred during the remainder of the season. 694 players and 291 officials provided two serum samples for antibody testing. Nine players converted from negative/borderline to positive (without symptoms); two players who initially tested positive tested negative at the end of the season. 22 players remained seropositive throughout the season. None of the seroconversions was confirmed in the neutralisation test. Professional football training and matches can be carried out safely during the COVID-19 pandemic. This requires strict hygiene measures including regular PCR testing.

#3 Characteristics of Soccer Players Undergoing Primary Hip Arthroscopy for Femoroacetabular Impingement: A Sex- and Competitive Level-Specific Analysis
Reference: Am J Sports Med. 2020 Sep 23;363546520958697. doi: 10.1177/0363546520958697. Online ahead of print.
Authors: Niv Marom, Matthew S Dooley, Joost A Burger, Brenda Chang, Struan H Coleman, Anil S Ranawat, Bryan T Kelly, Danyal H Nawabi
Summary: Radiographic features of femoroacetabular impingement (FAI) are prevalent in kicking athletes, especially soccer players. However, there remains a paucity of data on the characteristics of symptomatic soccer players with an established diagnosis of FAI. The purpose was to report on patient demographics, injury, and clinical and radiographic characteristics in a large cohort of soccer players who underwent primary hip arthroscopy for FAI and to perform a sex- and competition level-specific analysis of these data. An institutional hip preservation registry containing 3318 consecutive primary hip arthroscopies for FAI performed between March 2010 and January 2016 was retrospectively reviewed for patients identified as soccer players. Patient demographics, injury characteristics, and clinical and radiographic findings were recorded, and sex- and competition level-specific differences were analyzed. A total of 421 hips (336 soccer players) were identified, including 257 (61.0%) men and 164 (39.0%) women. Of these, 105 (24.9%) were reported as highly competitive, 194 (46.1%) as competitive, 75 (17.8%) as recreational, and 47 (11.2%) did not report a level. The majority of the 336 soccer players (231 hips; 55%) reported chronic hip pain lasting >6 months with no acute injury at the initial visit. Alpha angle, coronal center-edge angle, and femoral version on computed tomography scan measured 64.5°± 12°, 32.3°± 9°, and 13.7°± 10° (mean ± SD), respectively. There were 230 (55%) hips with a type 2 anterior inferior iliac spine (AIIS), 78 (18.5%) with a type 1 AIIS, and 19 (4.5%) with a type 3 AIIS. When compared with male athletes, female athletes had more hip internal rotation on physical examination (14.9° vs 8°; P < .001), lower alpha angles (57.5° vs 68.5°; P < .001), and lower-grade AIIS morphology (P = .003). Acute injury as the reason for hip symptoms was most likely in the highly competitive group (P < .001). Female soccer players were more likely to have less severe clinical and radiographic findings than were male soccer players. Acute injury as the cause of hip symptoms was more common in highly competitive players. Focusing on soccer players with an established FAI diagnosis, the findings of this study suggest that there are sex- and competition level-based differences in the presentation, physical examination, and imaging characteristics among the players. These findings can better guide clinicians in the diagnostic evaluation of symptomatic soccer players with FAI and in tailoring treatment recommendations to specific cohorts.

#4 Soccer-related head injuries-analysis of sentinel surveillance data collected by the electronic Canadian Hospitals Injury Reporting and Prevention Program
Reference: Paediatr Child Health. 2019 Aug 30;25(6):378-384. doi: 10.1093/pch/pxz116. eCollection 2020 Oct.
Authors: Sarah Zutrauen, Steven McFaull, Minh T Do
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Summary: Participating in sports is a great way to gain physical, psychological, and social benefits. However, it also carries the risk of injury. Soccer is one of the most popular sports worldwide, and in recent years, there have been concerns about potential vulnerabilities to head injuries. The aim was to investigate soccer-related head injuries (SRHIs), using data from the electronic Canadian Hospitals Injury Reporting and Prevention Program (eCHIRPP) surveillance system. Specifically, we aim to compare characteristics of SRHI cases to all head injury cases within the eCHIRPP database. Descriptive analyses of emergency department (ED) injury surveillance data (2011 to 2017) for individuals aged 5 to 29 years from all participating eCHIRPP sites. Computation of proportionate injury ratios (PIR) comparing SRHIs to all head injuries reported to eCHIRPP, and 95% confidence intervals (CI). A total of 3,970 SRHIs were reported to eCHIRPP. Injuries were from contact with another player, the ball, ground, goal-post, and other causes. Of the injuries caused by contact with the ball, 9% were from purposely directing the ball with the head (heading). A higher proportion of concussions (PIR=1.32, 95% confidence interval [CI]: 1.27 to 1.37) and minor closed head injuries (PIR=1.20, 95% CI: 1.15 to 1.26) were observed in soccer players. Higher proportions of head injuries occurred in organized soccer and soccer played outdoors. However, admission to the ED for a SRHI was rare (PIR=0.40, 95% CI: 0.30 to 0.55). Overall, elevated proportions of brain injuries were observed among soccer players, however, these injuries were unlikely to result in a hospital admission. Moreover, purposely heading the ball contributed to few ED visits.