Latest research in football - week 43 - 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 Assessment of Body Composition, Lower Limbs Power, and Anaerobic Power of Senior Soccer Players in Portugal: Differences According to the Competitive Level

Reference: Int J Environ Res Public Health. 2021 Jul 30;18(15):8069.10.3390/ijerph18158069.

Authors: Diogo Tereso, Rui Paulo, João Petrica, Pedro Duarte-Mendes, José M Gamonales, Sergio J Ibáñez

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Summary: During a soccer game, the most diversified stimuli occur all the time, the physical condition level plays a determinant role, and there may be variations according to the competitive level. In this sense, the present study aimed to verify differences in body composition, lower limbs power, and anaerobic power, comparing senior soccer players of different competitive levels. Participants were 81 players belonging to six soccer teams, aged between 18 and 35 years, with a mean age of 23.14 ± 4.23 years, who were divided into three distinct competitive levels: Elite, Sub-Elite and Non-Elite. The players performed bioimpedance evaluations on a tetrapolarInbody270 scale (body composition), the Countermovement Jump (CMJ) through the ChronoJump (lower limbs power), and Running Anaerobic Sprint Test (RAST) (anaerobic power). Based on the competitive level analysis, we verified that the players present body composition values similar to each other regardless of the competitive level in which they play. Concerning the performance evaluations, we verified that the elite players present higher values of highest jump (p = 0.012; d = 0.76, moderate; and p = 0.022; d = 0.71, moderate) and maximum force produced (p = 0.05; d = 0.64, moderate; and p = 0.002; d = 1.00, moderate), together with higher values of anaerobic power (p < 0.001; d = 2.43, very large; and p < 0.001; d = 2.22, very large), compared to the others. We can thus conclude that there is a homogeneity regarding the body composition of soccer players, regardless of their competitive level; in turn, elite players show better performance indicators in all variables.



#2 Wearable Inertial Measurement Unit to Accelerometer-Based Training Monotony and Strain during a Soccer Season: A within-Group Study for Starters and Non-Starters

Reference: Int J Environ Res Public Health. 2021 Jul 28;18(15):8007.

 doi: 10.3390/ijerph18158007.

Authors: Hadi Nobari, Mustafa Sögüt, Rafael Oliveira, Jorge Pérez-Gómez, Katsuhiko Suzuki, Hassane Zouhal

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Summary: The purpose of this study was to analyze the intragroup differences in weekly training monotony (TM) and training strain (TS) between starter and non-starter male professional soccer players at accelerometry based variables throughout the periods of a season. TM and TS of different accelerations and decelerations zones for twenty-one players were followed for forty-eight weeks. Regardless of group, players obtained the highest mean TM (starters = 3.3 ± 0.6, non-starters = 2.2 ± 1.1, in arbitrary unit, AU) and TS (starters = 1288.9 ± 265.2, non-starters = 765.4 ± 547.5, AU) scores in the pre-season for accelerations at Zone 1 (<2 m/s2). The results also indicated that both groups exhibited similar TM and TS scores in accelerations at Zones 2 (2 to 4 m/s2) and 3 (>4 m/s2) across the entire season. While the starters showed the highest TM and TS scores at deceleration Zone 1 (<-2 m/s2) in the end-season, the non-starters exhibited the highest scores at the deceleration Zone 1 in pre-season. It seems that in pre-season, coaches applied higher levels of training with greater emphasis on deceleration for non-starters. This tendency was reduced over time for non-starters, while starters presented higher values of deceleration Zone 1. These results highlight the variations in TM and TS across the different periods of a full season according to match starting status among professional soccer players, and the results suggest that non-starter players should receive higher levels of load to compensate for non-participation in matches throughout a soccer season.



#3 Training Load in Different Age Category Soccer Players and Relationship to Different Pitch Size Small-Sided Games

Reference: Sensors (Basel). 2021 Jul 31;21(15):5220.  doi: 10.3390/s21155220.

Authors: Fernando J Santos, Teresa P Figueiredo, Dalton M Pessôa Filho, Carlos E L Verardi, Anderson G Macedo, Cátia C Ferreira, Mário C Espada

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Summary: This study sought to evaluate the training load in different age category soccer players associated with distinct pitch size small-sided games (SSGs). Twenty-four soccer players (eight in each age category: U-12, U-15, and U-23) performed three consecutive 4 vs. 4 ball possession SSGs (SSG1: 16 × 24 m; SSG2: 20 × 30 m; and SSG3: 24 × 36 m) all with 3 min duration and 3 min rest. Subjects carried ultra-wideband-based position-tracking system devices (WIMU PRO, RealTrack System). Total distance covered increased from SSG1 to SSG3 in all age categories and predominantly in running speeds below 12 km·h-1. Moreover, distance covered in 12-18 km·h-1 running speed was different in all performed SSGs and age categories. Residual or null values were observed at 18-21 km·h-1 or above running speed, namely in U-12, the only age category where metabolic power and high metabolic load distance differences occurred throughout the performed SSGs. Edwards' TRIMP differences between age categories was only observed in SSG2 (U-12 < U-15). The design of SSGs must consider that the training load of the players differs according to their age category and metabolic assessment should be considered in parallel to external load evaluation in SSGs. Wearable technology represents a fundamental support in soccer.



#4 Muscle Damage Biomarkers in Congestion Weeks in English Premier League Soccer Players: A Prospective Study for Two Consecutive Seasons

Reference: Int J Environ Res Public Health. 2021 Jul 28;18(15):7960.  doi: 10.3390/ijerph18157960.

Authors: Álvaro García-Romero-Pérez, Francisco Javier Ordonez, Fernando Reyes-Gil, Elena Sonsoles Rodríguez-López, Ángel Oliva-Pascual-Vaca

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Summary: The current study was conducted to compare muscle damage biomarkers in single- vs. multi-match weeks in elite soccer players for two consecutive seasons. A secondary objective was to analyze the influence of playing position and exposure time on muscle damage in single- vs. multi-match weeks. This is a prospective cohort study performed in a professional elite soccer club in the English Premier League during the 2018-2019 and 2019-2020 seasons up until the lockdown due to the COVID-19 pandemic. Data were collected in the Medical Department Room of an English Premier League Club before and after the soccer game from a total of 29 elite soccer players (mean ± S.D.; age = 27.59 ± 3.83 years; height = 1.83 ± 0.05 m; body mass = 80.16 ± 7.45 kg) who were enrolled in the club during both seasons. The main outcome measurements were creatine kinase (CK), weight, lean mass, % fat DEXA, high speed running, total distance, density of total distance and high-speed running and wellbeing questionnaires. Significance was set at p < 0.05. Players who completed more than 60 min in the previous game had significantly increased pregame CK levels and fatigue in multi-match weeks. Midfielders had both significantly increased pregame CK and muscle soreness in multi-match weeks. Midfielders and players with an exposure time of at least 60 min showed higher pregame CK values that should play a key role for deciding substitutions.



#5 Low Horizontal Force Production Capacity during Sprinting as a Potential Risk Factor of Hamstring Injury in Football

Reference: Int J Environ Res Public Health. 2021 Jul 23;18(15):7827.  doi: 10.3390/ijerph18157827.

Authors: Pascal Edouard, Johan Lahti, Ryu Nagahara, Pierre Samozino, Laurent Navarro, Kenny Guex, Jérémy Rossi, Matt Brughelli, Jurdan Mendiguchia, Jean-Benoît Morin

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Summary: Clear decreases in horizontal force production capacity during sprint acceleration have been reported after hamstring injuries (HI) in football players. We hypothesized that lower FH0 is associated with a higher HI occurrence in football players. We aimed to analyze the association between sprint running horizontal force production capacities at low (FH0) and high (V0) velocities, and HI occurrence in football. This prospective cohort study included 284 football players over one season. All players performed 30 m field sprints at the beginning and different times during the season. Sprint velocity data were used to compute sprint mechanical properties. Players' injury data were prospectively collected during the entire season. Cox regression analyses were performed using new HI as the outcome, and horizontal force production capacity (FH0 and V0) was used at the start of the season (model 1) and at each measurement time point within the season (model 2) as explanatory variables, adjusted for individual players' (model 2) age, geographical group of players, height, body mass, and previous HI, with cumulative hours of football practice as the time scale. A total of 47 new HI (20% of all injuries) were observed in 38 out of 284 players (13%). There were no associations between FH0 and/or V0 values at the start of the season and new HI occurrence during the season (model 1). During the season, a total of 801 measurements were performed, from one to six per player. Lower measured FH0 values were significantly associated with a higher risk of sustaining HI within the weeks following sprint measurement (HR = 2.67 (95% CI: 1.51 to 4.73), p < 0.001) (model 2). In conclusion, low horizontal force production capacities at low velocity during early sprint acceleration (FH0) may be considered as a potential additional factor associated with HI risk in a comprehensive, multifactorial, and individualized approach.



#6 Virtual reality promotes greater improvements than video-stimulation screen on perceptual-cognitive skills in young soccer athletes

Reference: Hum Mov Sci. 2021 Aug 11;79:102856. doi: 10.1016/j.humov.2021.102856. Online ahead of print.

Authors: Leonardo S Fortes, Sebastião S Almeida, Gibson M Praça, José R A Nascimento-Júnior, Dalton Lima-Junior, Bruno Teixeira Barbosa, Maria E C Ferreira

Summary: The literature has shown the positive effect of virtual reality (VR) in percepto-cognitive skills. However, the literature lacks findings about at what extent VR would be better than video. Purpose This study aimed to analyze the chronic effect of VR and video-stimulation screen training on passing decision-making, visual search behavior, and inhibitory control performance in young soccer athletes. Method A total of 26 young soccer players underwent an 8-week training protocol after being randomly assigned to the VR (n = 13) or video-screen (VID, n = 13) group. Passing decision-making, visual search behavior, and inhibitory control performance were measured before and after both interventions. Results A group x time interaction was found for decision-making performance (p < 0.01) and visual search behavior (p < 0.01). Both groups improved both decision-making performance (p < 0.01) and visual search behavior (p < 0.01); however, greater improvements were verified in VR (p < 0.01). Both VR and VID improved inhibitory control (p < 0.01), but no group interaction effect was observed (p > 0.05). Conclusion Our results suggest that VR leads to greater improvements in decision-making and visual search behavior in young soccer athletes than VID.



#7 Analysis of Selected Lymphocyte (CD45+) Subset Distribution in Capillary Blood of Young Soccer Players

Reference: J Strength Cond Res. 2021 Aug 1;35(8):2279-2286. doi: 10.1519/JSC.0000000000003105.

Authors: Robert Nowak, Dorota Kostrzewa-Nowak, Rafał Buryta

Summary: Mechanisms responsible for increasing athletes' physical capacity and induction of exercise-induced immunosuppression processes are not fully understood. The aim of the study was to monitor changes in percentages of lymphocyte subsets: T, Th, Tc, B, and NK cells in capillary blood of junior soccer players. Ten subjects median aged 18 years (range 17-19 years) were recruited form young soccer players. Capillary blood was collected 24 hours after each soccer match during the 8 weeks of the final phase of Central Junior League competition, and white blood cell (WBC) phenotyping was performed to determine the percentages of B lymphocytes, NK cells, and T-lymphocyte subsets. Cumulative match-time (a sum of time spend playing the game by each athlete during the observation period) was also calculated. Significant changes in the percentage of total lymphocytes (p = 0.00005) and T cells (p = 0.00006) were observed. The slight increases in lymphocytes' and Th cells' median percentages correlated with increasing cumulative match-time of studied subjects, although the correlation was not strong (R = 0.24; p = 0.0205 and R = 0.30; p = 0.0035, for lymphocytes and Th cells, respectively). It seems that the exercise bouts are among considerable factors influencing the changes in WBC subsets, especially in CD3+ cells, among young soccer players. Regarding the number of games played and training loads, they are more susceptible to immunosuppression and subsequent infections and thus should be monitored regarding WBC phenotype assessment.



#8 Effects of a Neuromuscular Warm-Up Program in Youth Female Soccer Players

Reference: J Hum Kinet. 2021 Jul 28;79:29-40. doi: 10.2478/hukin-2021-0080. eCollection 2021 Jul.

Authors: Elena Isla, Blanca Romero-Moraleda, José María Moya, Francisco Esparza-Ros, Javier Mallo

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Summary: The protective effects of different warm-up injury prevention routines in youth female soccer players have been demonstrated in the literature, however, there is a paucity of information regarding the effects that these kinds of programs have on soccer-specific physical performance variables. The purpose of this study was to assess the effectiveness of a 12-week neuromuscular warm-up program on physical performance in youth female soccer players. Players (age: 13.94 ± 0.82 years) were divided into two groups. One group performed a neuromuscular activation program (n = 21) twice per week whereas the other group (control, n = 17) continued with their habitual warm-up routine for the same duration. Both groups of players performed strength, jumping and balance tests before and after the intervention period. Substantially greater improvements were detected in the mean velocity for the squat (p < 0.001; Effect Size = 0.95) and the hip thrust (p < 0.001; Effect Size = 0.51) in the experimental group in comparison to the control group. In addition, after the intervention period players in the experimental group showed an increase in the jumping height in the unloaded double-leg and single-leg counter-movement jumps (p = 0.003-0.012; Effect Size = 0.42-0.46). The results of this study provide evidence that a 12-week neuromuscular warm-up program can be effective to improve different physical performance variables in youth female soccer players.



#9 The Fifth Metatarsal Bone Fracture in Athletes - Modalities of Treatment Related to Agility in Soccer Players

Reference: J Hum Kinet. 2021 Jul 28;79:101-110. doi: 10.2478/hukin-2020-0059. eCollection 2021 Jul.

Authors: Krzysztof Ficek, Natalia Kędra, Radosław Skowronek, Kamila Kluczniok, Magdalena Strózik, Paweł Gwiazdoń, Grzegorz Hajduk

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Summary: The 5th metatarsal fracture is a common foot fracture which could exclude a player from competition for several months and significantly affect his or her career. This manuscript presents the treatment and rehabilitation of professional soccer players who had acute fractures of the 5th metatarsal bone and a cannulated screw fixation. The main purpose of the analysis was to determine the minimum time necessary for a permanent return to the sport after a 5th metatarsal fracture among professional soccer players. We followed the surgical and rehabilitation path of 21 professional soccer players from the Polish League (Ist and IInd divisions) who suffered from the 5th metatarsal bone fracture. All players underwent standard percutaneous internal fixation with the use of cannulated screws. The total inability to play lasted for 9.2 (± 1.86) weeks among players treated only surgically (n = 10), 17.5 (± 2.5) weeks in the conservative and later surgery group, excluding players with nonunion (n = 6), and 24.5 (± 10.5) weeks for nonunion and switch treatment (n = 4) players. Prompt fracture stabilization surgery is recommended for athletes, enabling the implementation of an aggressive rehabilitation protocol as soon as possible. Early limb loading after surgery (from week 2) does not delay fracture healing or hinder the bone union, thus rehabilitation plays a crucial role in shortening the time of RTP (return to play) and is obligatory for each athlete who undergoes surgical treatment.



#10 Long-Term Trend Analysis of Playing Styles in the Chinese Soccer Super League

Reference: J Hum Kinet. 2021 Jul 28;79:237-247. doi: 10.2478/hukin-2021-0077. eCollection 2021 Jul.

Authors: Changjing Zhou, Carlos Lago-Peñas, Alberto Lorenzo, Miguel-Ángel Gómez

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Summary: The aim of this study was to identify playing styles adopted by teams in the Chinese Soccer Super League (CSL) and to investigate their evolution across a 6-season period. Data were collected from 1,429 CSL matches from 2012 to 2017 seasons using the Amisco system. Seventeen technical performance-related indicators and eleven physical performance-related indicators were included in the factor analysis (PCA: principal components analysis) in order to group them into performance factors (styles of play). Seven factors were obtained (eigenvalues greater than 1) and explained 74.44% of the total variance. Multivariate analyses of covariance (MANCOVA) were used to check differences among seven styles of play (team's ranking was used as a covariate) during the six seasons under study. The main findings showed that Factor 1 (high intensity play) and factor 3 (offensive actions) of CSL soccer increased substantially along the seasons. Coaches and sports scientists should take into consideration these performance trends when preparing training and controlling for matches.



#11 Coach Encouragement During Soccer Practices Can Influence Players' Mental and Physical Loads

Reference: J Hum Kinet. 2021 Jul 28;79:277-288. doi: 10.2478/hukin-2021-0079. eCollection 2021 Jul.

Authors: Jesús Díaz-García, Juan José Pulido, José Carlos Ponce-Bordón, Carlos Cano-Prado, Miguel Ángel López-Gajardo, Tomás García-Calvo

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Summary: This study analyzed the influence of the coaches' encouragement on the mental and physical load in soccer practices. The participants were 36 semiprofessional Spanish soccer players (Mage = 22.40; SD = 2.25) belonging to two male teams and one female team. Following the same practices' design and order, two training sessions of each team were completed. In one session, coaches maintained a passive verbal attitude, whereas in the other session, coaches intervened with an active attitude through continuous general encouragement. The mental load and fatigue were measured using self-reported questionnaires (Likert scales), and internal and external physical loads were quantified using the rating of perceived exertion and the Global Position System. A t-test for related samples and magnitude based on an inference spreadsheet was performed. The results demonstrated that mental and internal physical loads increased when coaches participated with active verbal encouragement. Especially, increases in performance satisfaction, mental effort, and RPE values, and decreases in unsafety values were detected due to encouragement interventions. Nevertheless, the external physical load did not show a clear trend. Based on these findings, coaches can use this information to manipulate their verbal encouragement during practices according to their physical and mental objectives with specific soccer strategies.



#12 The Coaches' Efficacy Expectations of Youth Soccer Players with Different Maturity Status and Physical Performance

Reference: J Hum Kinet. 2021 Jul 28;79:289-299. doi: 10.2478/hukin-2021-0083. eCollection 2021 Jul.

Authors: Iván Peña-González, Tomas García-Calvo, Eduardo M Cervelló, Manuel Moya-Ramón

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Summary: This study aimed to report possible anthropometrical and physical performance differences between youth soccer players with different maturity status and to report the coaches' expectations, hypothesizing that coaches would expect more from players with advanced maturity. One hundred twenty-two (122) players completed a physical performance battery. Their maturity status was estimated and the coaches' efficacy expectations (CEEs) were assessed. Players with advanced maturation had better physical performance (F = 26.5-73.4; p < 0.01) and their CEEs for strength-related tasks were different according to the maturity status (F = 8.3-10.9; p < 0.01), but not for speed-related tests, nor for their general ability to play soccer. Normalized data showed significant differences between physical performance tests and their respective CEEs within each maturity group, especially in the Post-PHV group. This study confirms the physical advantages of players with advanced maturity while it shows controversial results of how maturation affects the coaches' perceptions and, indirectly, the coaches' identification and selection of talented players.



#13 Neuromuscular Performance and Training Workload Over an In-Season Mesocycle in Elite Young Soccer Players

Reference: Int J Sports Physiol Perform. 2021 Aug 17;1-7. doi: 10.1123/ijspp.2020-0834. Online ahead of print.

Authors: Colin Clancy, Nigel Gleeson, Tom Mercer

Summary: The purpose of this study was to assess neuromuscular performance capabilities over an in-season mesocycle in early-career professional soccer players and examine the relationship with training workload. Neuromuscular performance capabilities (isometric knee extensor: peak force, rate of force development, and peak twitch force) of 12 professional soccer players were assessed weekly over a 6-week period. Training and match workload were also recorded over the same period for each player (high-intensity running distance). Changes in neuromuscular performance and workload variables were analyzed. There was evidence of fluctuations in neuromuscular performance capability over the mesocycle that reached statistical (P < .05) and practical (13.3% [peak-to-peak]) significance alongside interweek heterogeneity in training and match workload (∼17.5% [coefficient of variation], P < .05). Congruence among fluctuating patterns of intramesocycle training load and concomitant neuromuscular performance responses was noted over time for acute training load and acute:chronic workload ratio with peak force and rate of force development. Neuromuscular performance capabilities fluctuate over an in-season mesocycle and are influenced by high-intensity running workload, emphasizing the need for acute monitoring in elite soccer players.



#14 The Influence of Menstrual Cycle on Bioimpedance Vector Patterns, Performance, and Flexibility in Elite Soccer Players

Reference: Int J Sports Physiol Perform. 2021 Aug 17;1-9. doi: 10.1123/ijspp.2021-0135. Online ahead of print.

Authors: Francesco Campa, Matteo Levi Micheli, Matilde Pompignoli, Roberto Cannataro, Massimo Gulisano, Stefania Toselli, Gianpiero Greco, Giuseppe Coratella

Summary: The aim was to examine whether menstrual cycle affects body composition and bioimpedance vector analysis (BIVA) patterns, jumping and sprinting ability, and flexibility in elite soccer players. A total of 20 elite female soccer players (age: 23.8 [3.4] y, height: 1.63 [0.04] m, body mass: 61.4 [5.9] kg, and body mass index: 22.5 [2.4] kg/m2) were monitored during the early follicular and ovulatory phase across 2 consecutive menstrual cycles. Bioimpedance analysis was performed using foot-to-hand technology, and total body water and fat mass were determined by specific equations developed for athletes. Bioelectrical resistance and reactance were adjusted according to the BIVA procedures and plotted as a vector within the resistance-reactance graph. In addition, countermovement jump, 20-m sprint, and sit and reach were assessed. A time effect (P < .05) was found for body mass, total body water, bioelectrical resistance and reactance, and flexibility. Specifically, body mass increased (P = .021) along with a gain in total body water (P = .001) from the ovulatory to the early follicular phase, while it decreased from the early follicular to the ovulatory phase during the second menstrual cycle. The BIVA vector shortened during the early follicular phases (P < .001). No change in jumping and sprinting capacity was observed (P > .05). Flexibility was impaired during the early follicular phases (P < .05). Specific bioelectrical impedance analysis and BIVA procedures are able to detect menstrual cycle-induced changes in body composition in elite soccer players. The early follicular phase resulted in fluid accumulations and BIVA vector shortening. In addition, while menstrual cycle did not affect performance, a fluctuation in flexibility was observed.



#15 Screening Youth Soccer Players by Means of Cognitive Function and Agility Testing

Reference: Percept Mot Skills. 2021 Aug 17;315125211040283. doi: 10.1177/00315125211040283. 

Authors: Nicola Lovecchio, Gianluca Manes, Luca Filipas, Matteo Giuriato, Antonio La Torre, F Marcello Iaia, Roberto Codella

Summary: Talent identification in sports is a heavily debated topic. Previous studies have separately explored either executive functions or gross motor skills to predict the success of top-level soccer players or, more generally, to characterize elite performance in soccer. However, at mid-childhood, the possibility to scope sport-specific requirements remains elusive. We aimed in this study to investigate a valid and simple method of testing for a unique combination of cognitive and speed abilities for identifying promising soccer players at mid-childhood. We measured cognitive functions by means of a Stroop smartphone application and agility with a T-Drill Ball-success test, in two groups of (a) elite- (n = 31) and (b) low-division (n = 37) Italian 7-year-old male soccer players. We administered the tests in a randomized order to both groups. We found better inhibitory control, cognitive flexibility and soccer-specific agility in high-division versus low-division players (p < .001). Inhibitory response and agility were positively associated with the augmented quality of the performance from low-division players to high-division players (r = .55; p = .0001). These results suggest that, even at an early age, cognitive control together with soccer-specific skills is associated with better performance.



#16 Hamstring Strain Injury (HSI) Prevention in Professional and Semi-Professional Football Teams: A Systematic Review and Meta-Analysis

Reference: Int J Environ Res Public Health. 2021 Aug 4;18(16):8272. doi: 10.3390/ijerph18168272.

Authors: Carlo Biz, Pietro Nicoletti, Giovanni Baldin, Nicola Luigi Bragazzi, Alberto Crimì, Pietro Ruggieri

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Summary: Hamstring Strain Injuries (HSIs) are the most common type of lesion in professional footballers and the leading cause of absence days from sports. However, recent studies have shown that high-level football teams apparently do not apply any HSI prevention protocol. The aim of the study was to determine the effect of preventive strategies and protocols in reducing the incidence of hamstring muscle injuries in professional and semi-professional football teams. A literature search of PubMed/MEDLINE, ISI/Web of Science and Scopus databases was conducted with the keywords "hamstring* and (injury* or strain) and prevent* and (soccer or football)". Quality and bias assessment was completed through the Kennelly modified scale. The Injury Incidence Rate (IIR) and the Incidence Rate Ratio (IRR) were assessed in the statistical analysis. In the meta-analysis, data were extracted, pooled and analysed with "Comprehensive Meta-Analysis Version 3.3.070" software. In total, 8 of the 1017 original search studies met the inclusion criteria of this review. The total exposure of the studies was 170,221.8 h, while the number of HSIs recorded was 165 in the intervention groups and 224 in the control groups. The average score of the quality assessment was 23.6/34. The meta-analysis of six of the eight included studies provided strong evidence that interventions are effective in reducing hamstring injuries. The IRR of the effect size was 0.443, with p-value = 0.001. The studies analysed applied different preventive strategies: the Nordic hamstring exercise, the FIFA 11+ programme and exercises for core stability or balance training. All these interventions proved to have a successful effect on prevention of hamstring injuries.



#17 Effects of Match Location, Quality of Opposition and Match Outcome on Match Running Performance in a Portuguese Professional Football Team

Reference: Entropy (Basel). 2021 Jul 29;23(8):973. doi: 10.3390/e23080973.

Authors: José E Teixeira, Miguel Leal, Ricardo Ferraz, Joana Ribeiro, José M Cachada, Tiago M Barbosa, António M Monteiro, Pedro Forte 

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Summary: The aim of this study was to analyze the effects of match location, quality of opposition and match outcome on match running performance according to playing position in a Portuguese professional football team. Twenty-three male professional football players were monitored from eighteen Portuguese Football League matches during the 2019-2020 season. Global positioning system technology (GPS) was used to collect time-motion data. The match running performance was obtained from five playing positions: central defenders (CD), fullbacks (FB), central midfielders (CM), wide midfielders (WM) and forwards (FW). Match running performance was analyzed within specific position and contextual factors using one-way analysis of variance (ANOVA) for repeated measures, standardized (Cohen) differences and smallest worthwhile change. CM and WM players covered significantly greater total distance (F = 15.45, p = 0.000, η2 = 0.334) and average speed (F = 12.79, p < 0.001, η2 = 0.294). WM and FB players covered higher distances at high-speed running (F = 16.93, p = 0.000, η2 = 0.355) and sprinting (F = 13.49; p < 0.001, η2 = 0.305). WM players covered the highest number of accelerations (F = 4.69, p < 0.001, η2 = 0.132) and decelerations (F = 12.21, p < 0.001, η2 = 0.284). The match running performance was influenced by match location (d = 0.06-2.04; CI: -0.42-2.31; SWC = 0.01-1.10), quality of opposition (d = 0.13-2.14; CI: -0.02-2.60; SWC = 0.01-1.55) and match outcome (d = 0.01-2.49; CI: -0.01-2.31; SWC = 0.01-0.35). Contextual factors influenced the match running performance with differential effects between playing positions. This study provides the first report about the contextual influence on match running performance in a Portuguese professional football team. Future research should also integrate tactical and technical key indicators when analyzing the match-related contextual influence on match running performance.



#18 Skeletal muscle phenotype and game performance in elite women football players

Reference: Scand J Med Sci Sports. 2021 Aug 24. doi: 10.1111/sms.14022. 

Authors: Magni Mohr, Ioannis G Fatouros, Athanasios Z Jamurtas, Dimitrios Draganidis, Martin Thomassen, Christina Ørntoft, Georgios Ermidis, Georgios Loules, Dimitrios Batsilas, Athanasios Poulios, Konstantinos Papanikolaou, Morten B Randers, Peter Krustrup, Lars Nybo

Summary: We combined game activity analyses with skeletal muscle phenotypes and comprehensive physiological testing to elucidate factors of importance for physical performance in elite women's football. GPS-data from an experimental game, sprint and endurance testing, and muscle tissue analysis of metabolic enzyme activity, protein expression and fiber type composition were completed for international top-level women players (n = 20; age; 23 ± 4 yrs, height; 166 ± 10 cm, weight; 60 ± 8 kg; VO2max ; 51 ± 6 ml/min/kg). Muscle monocarboxylate transporter 4 (MCT4) protein expression explained 46% of the variance in total game distance, while the ability to maintain high-intensity running (HIR) during the final 15 min of the game correlated to myosin heavy chain 1 (MHCI) and Na+ -K+ ATPase β1, FXYD1 (phospholemman) and superoxide dismutase 2 (SOD2) protein expression (range: r = 0.51-0.71; all p < 0.05). Total HIR distance correlated with (MHCIIa) protein expression (r = 0.51; p < 0.05), while muscle Na+ /H+ exchanger 1 (NHE1) protein explained 36% of the variance in game sprint distance (p < 0.05). Total game accelerations (actions >4 m/s2 ) correlated with platelet endothelial cell adhesion molecule (PECAM-1) protein expression (r = 0.51; p < 0.05), while concentric knee flexor strength explained 42-62% of the variance in intense decelerations (>4 m/s2 ). In conclusion, for elite women players' game endurance performance and resistance to end-game fatigue were affected by monocarboxylate transporter expression and myosin heavy chain profile. HIR was also correlated to ion transporter expression and muscle antioxidative capacity. Finally, the importance of functional strength and measures of muscle vascularization in relation to total game decelerations and accelerations, respectively, illustrates the complex physiological demands in elite women's football.



#19 Evaluation of the effect of high-intensity interval training on macular microcirculation via swept-source optical coherence tomography angiography in young football players

Reference: Indian J Ophthalmol. 2021 Sep;69(9):2334-2339. doi: 10.4103/ijo.IJO_3079_20.

Authors: Yalçın Karaküçük, Nilsel Okudan, Banu Bozkurt, Muaz Belviranlı, Fatih Tobakçal

Summary: This study was conducted to evaluate the effect of high intensity interval training (HIIT) on macular microcirculation, measured by swept source optical coherence tomography angiography (ss OCTA) in young football players. Football players between 18-20 years old were included. After a detailed ophthalmological examination, physiological parameters, including height, body weight, body fat, systemic blood pressure, hematocrit values, oxygen saturation, and heart rate, were recorded. Intraocular pressure and ss OCTA parameters were measured one day before and the day after the high intensity interval training program using DRI OCT Triton (Topcon, Tokyo, Japan) between 11:00 am and 1:00 pm. Fifteen participants completed the study. All were males with a mean age of 18.1 ± 0.4 years. Systolic and diastolic blood pressure and oxygen saturation did not change significantly (P > 0.05), while hematocrit levels increased remarkably (P = 0.049) after the HIIT program. Heart rates and intraocular pressure decreased (P = 0.003, P = 0.017, respectively). There was a significant increase in the central vessel density in deep capillary plexus (before: 18.7 ± 3.8%, after: 21.1 ± 4.5%) and central vessel density in choriocapillaris (before: 54.5 ± 2.8%, after 56.9 ± 2.2%) (P = 0.02, P = 0.02, respectively), although no changes were observed in other ss OCTA or in the central macular thickness and subfoveal choroidal thickness. A 6 week, high intensity interval training program with three exercise sessions per week seems not to alter mean superficial vascular densities, deep foveal avascular zone, and superficial foveal avascular zones, central macular thickness, or subfoveal choroidal thickness, while the central deep vascular density and central choriocapillaris vascular density increased remarkably among ss OCTA parameters.



#20 Incidence of injury in adult elite women's football: a systematic review and meta-analysis

Reference: BMJ Open Sport Exerc Med. 2021 Jul 13;7(3):e001094. doi: 10.1136/bmjsem-2021-001094. eCollection 2021.

Authors: Lawrence Mayhew, Mark I Johnson, Peter Francis, Christoph Lutter, Ali Alali, Gareth Jones

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Summary: The aim was to estimate the incidence of injury in adult elite women's football and to characterise the nature and anatomical location of injuries. Combinations of the key terms were entered into the following electronic databases (PubMed, SPORTDiscus, Science Direct and Discover) from inception to May 2021. (1) Used a prospective cohort design; (2) captured data on elite adult women players; (3) reported injury incidence by anatomical site; (4) captured data of at least one season or national team tournament; (5) included a definition of injury; and (6) written in English. The search identified 1378 records. Twelve studies published between 1991 and 2018 were included in our review and sampled 129 teams. In domestic club football, injury incidence rate was estimated to be 5.7/1000 hours (total), 19.5/1000 hours (match) and 3.1/1000 hours (training). In tournament, football match incidence was estimated to be 55.7/1000 hours. The knee (22.8%; 368/1822) was the most common site of injury in domestic club football. The ankle (23.7%, 105/443) was the most common site of injury in tournament football. Ligament sprains were the most common type of injury (27.8%), followed by muscle strains (19.1%). Severn studies (58%) had a high risk of bias associated with exposure definition and measurement and considerable heterogeneity exists between the included studies (I2=49.7%-95%). Ligament sprains occur more frequently in adult elite women football players. We advise caution in interpretating point estimates of the incidence of injury due to high statistical heterogeneity. Standardising injury reporting and the accurate recording of match and training exposure will overcome such limitations.



#21 Physical preparation and return to performance of an elite female football player following ACL reconstruction: a journey to the FIFA Women's World Cup

Reference: BMJ Open Sport Exerc Med. 2020 Dec 1;6(1):e000843. doi: 10.1136/bmjsem-2020-000843. eCollection 2020.

Authors: Matt Taberner, Nicol van Dyk, Tom Allen, Neil Jain, Chris Richter, Barry Drust, Esteban Betancur, Daniel D Cohen

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Summary: ACL injuries are among the most severe knee injuries in elite sport, with a high injury burden and re-injury risk. Despite extensive literature on the injury and the higher incidence of injury and re-injury in female athletes, there is limited evidence on the return to sport (RTS) of elite female football players following ACL reconstruction (ACLR). RTS is best viewed on a continuum aligning the recovery and rehabilitation process with the ultimate aim - a return to performance (RTPerf). We outline the RTS and RTPerf of an elite female football player following ACLR and her journey to the FIFA Women's World Cup, including the gym-based physical preparation and the on-pitch/sports-specific reconditioning. We used the 'control-chaos continuum' as a framework for RTS, guiding a return above pre-injury training load demands while considering the qualitative nature of movement in competition. We then implemented the 'RTPerf pathway' to facilitate a return to team training, competitive match play and a RTPerf. Objective information, clinical reasoning and shared decision-making contributed to this process and helped the player to reach her goal of representing her country at the FIFA Women's World Cup.



#22 Effects of Postoperative Rehabilitation on Gait Parameters and Electromyography Variables in Acute and Chronic Anterior Cruciate Ligament Reconstruction Surgery in Football Players

Reference: Evid Based Complement Alternat Med. 2021 Aug 13;2021:9912795. doi: 10.1155/2021/9912795. eCollection 2021.

Authors: Gopal Nambi, Walid Kamal Abdelbasset, Anju Verma, Shereen H Elsayed, Osama R Aldhafian, Naif Bin Nwihadh, Mohamed A Omar, Tohamy G T Hassan, Ayman K Saleh

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Summary: The results of the a-ACLR, c-ACLR, and control groups were compared. At 8 weeks following postoperative rehabilitation, the a-ACLR group shows more significant changes than the c-ACLR group (p < 0.001). At 6 and 12 months, there are normal values of kinematic and kinetic values in a-ACLR compared with the results of the control group (p < 0.001). The study showed that postoperative rehabilitation provides significant effects in the kinematic, kinetic, and EMG gait parameters in acute ACLR than chronic ACLR subjects. Early surgical intervention and postrehabilitation are mandatory to get the significant effects in the clinical parameters in acute and chronic ACL injury.



#23 Methodological Characteristics, Physiological and Physical Effects, and Future Directions for Combined Training in Soccer: A Systematic Review

Reference: Healthcare (Basel). 2021 Aug 20;9(8):1075. doi: 10.3390/healthcare9081075.

Authors: Jorge Ribeiro, José Afonso, Miguel Camões, Hugo Sarmento, Mário Sá, Ricardo Lima, Rafael Oliveira, Filipe Manuel Clemente

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Summary: Combined training (CT) may combine strength and endurance training within a given time period, but it can also encompass additional protocols consisting of velocity, balance, or mobility as part of the same intervention. These combined approaches have become more common in soccer. This systematic review was conducted to (1) characterize the training protocols used in CT studies in soccer, (2) summarize the main physiological and physical effects of CT on soccer players, and (3) provide future directions for research. Methods: A systematic review of Cochrane Library, PubMed, Scopus, SPORTDiscus, and Web of Science databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The PICOS were defined as follows: P (soccer players of any age or sex); I (CT combining strength and endurance or sprinting or balance or mobility training); C (the control group (whenever applicable), with or without comparative interventions in addition to usual soccer training); O (acute and/or chronic responses: biochemical, physiological and physical); S (must have at least two groups, either randomized or non-randomized). The database search initially identified 79 titles. From those, eight articles were deemed eligible for the systematic review. Three studies analyzed acute responses to concurrent training, while the remaining five analyzed adaptations to CT. In those tested for acute responses, physiological (hormonal) and physical (strength and power external load, internal load) parameters were observed. Adaptations were mainly focused on physical parameters (strength and power, sprints, jumps, repeated sprint ability, aerobic, change-of-direction), with relatively little focus on physiological parameters (muscle architecture). Short-term responses to CT can affect hormonal responses of testosterone after resistance training with internal and external load. In turn, these responses' effects on strength and power have produced mixed results, as have adaptations. Specifically, strength and hypertrophy are affected to a lesser extent than speed/power movements. Nevertheless, it is preferable to perform CT before endurance exercises since it is a limiting factor for interference. Volume, intensity, rest between sessions, and athletes' fitness levels and nutrition dictate the degree of interference.


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