Latest research in football - week 18 - 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 Acute Effects of Match-Play on Neuromuscular and Subjective Recovery and Stress State in Division I Collegiate Female Soccer 

Reference: J Strength Cond Res. 2021 Feb 4. doi: 10.1519/JSC.0000000000003981. Online ahead of print. 

Authors: Ai Ishida, Caleb D Bazyler, Adam L Sayers, Satoshi Mizuguchi, Jeremy A Gentles 

Summary: The purpose of this study was to investigate acute effects of match-play on neuromuscular performance and subjective recovery and stress state and the relationship between training load (TL) and changes in neuromuscular performance in female soccer players. Twelve National Collegiate Athlete Association Division I players participated (20.7 ± 2.3 years; 64.4 ± 7.2 kg; 164.5 ± 6.0 cm) and completed countermovement jump (CMJ) at 0 kg (CMJ0) and 20 kg (CMJ20) and the Short Recovery Stress Scale (SRSS) at 3 hours pre-match (Pre), 12 hours post-match (Post12), and 38 hours post-match (Post38). Countermovement jump variables included body mass, jump height (JH), modified reactive strength index (RSI), peak force (PF), relative PF, eccentric impulse, concentric impulse (CI), peak power (PP), relative PP (RPP), eccentric average PP, and concentric average power (CAP). The SRSS consists of 4 Stress Scales (SSs) and 4 Recovery Scales (RSs). Training loads included total distance, total PlayerLoad, high-speed running, and session ratings of perceived exertion. Significant moderate to large decreases were observed from Pre to Post12 in JH, RSI, CI, PP, RPP, and CAP in CMJ0 and CMJ20 (p < 0.05, effect size [ES] = 0.63-1.35). Significant changes were observed from Pre to Post12 in all RSs (p < 0.05, ES = 0.65-0.79) and 3 SSs (p < 0.05, ES = 0.71-0.77). Significant correlations were observed between CMJ20 PP from Pre to Post12 and all TLs (p < 0.05, r = -0.58 to -0.68). CMJ0 and CMJ20 JH and PP may indicate acute neuromuscular changes after match-play. The magnitude of CMJ20 PP decrements from Pre to Post12 may be affected by soccer match-play volumes. 



#2 Cardiovascular effects of COVID-19 lockdown in professional Football players 

Reference: Panminerva Med. 2021 Feb 10. doi: 10.23736/S0031-0808.21.04340-8. Online ahead of print. 

Authors: Elena Cavarretta, Ilaria D'Angeli, Maura Giammarinaro, Salvatore Gervasi, Maurizio Fanchini, Andrea Causarano, Vincenzo Costa, Massimo Manara, Noemi Terribili, Luigi Sciarra, Leonardo CalÒ, Chiara Fossati, Mariangela Peruzzi, Francesco Versaci, Roberto Carnevale, Giuseppe Biondi-Zoccai, Giacomo Frati 

Summary: The COVID-19 pandemic with the stay-at-home orders and lockdown has dramatically forced athletes to stop team training and competitions, causing deep changes in habits and lifestyle. Aim of this study was to evaluate in a retrospective single center study the cardiovascular (CV) health and fitness of elite football player after COVID-19 lockdown in Italy and to compare such findings with the 2019 off-season period, in order to identify potential differences in the CV features and outcomes. All 29 professional Football players of the first male team were enrolled before resuming training and competition after COVID-19 lockdown and underwent several exams including physical examination, resting and stress electrocardiography (ECG), echocardiography, spirometry and blood tests. Median age was 27 years (23; 31), with no athlete being COVID-19 positive at the time of the evaluation. In comparison with the usual off-season 2-month detraining, significant differences were found for left ventricular (LV) mass (189g [172; 212] vs. 181g [167; 206], p=0.024) and LV mass index for body surface area (94g/m2 [85; 104] vs 88g/m2 [79.5; 101.5], p=0.017), while LV mass/fat free mass remained unchanged (2.8 g/Kg [2.6; 2.9] vs 2.9 g/Kg [2.6; 3.2], p=0.222). Respiratory function and metabolic profile were improved, while no significant changes were found in ECG findings, at rest and during exercise. Prolonged abstinence from training and competitions induced by lockdown elicited significant changes in comparison with off-season in parameters ascribable to detraining, as the changes in LV mass, in respiratory function and in metabolic profile. 



#3 Injuries in youth football and the relationship to player maturation: an analysis of time-loss injuries during four seasons in an English elite male football academy 

Reference: Scand J Med Sci Sports. 2021 Feb 9. doi: 10.1111/sms.13933. Online ahead of print. 

Authors: Neil Light, Adam Johnson, Stuart Williams, Neal Smith, Beverley Hale, Kristian Thorborg

Summary: A better insight into injuries in elite youth football may inform prevention strategies. The purpose of this prospective cohort study was to investigate the frequency, incidence and pattern of time-loss injuries in an elite male football academy, exploring injuries in relation to age and maturation status. Across four consecutive playing seasons, playing exposure and injuries to all academy players (U'9 to U'21) were recorded by club medical staff. Maturation status at the time of injury was also calculated for players competing in U'13 to U'16 aged squads. Time-loss injury occurrence and maturation status at time of injury were the main outcome measures. A total of 603 time-loss injuries were recorded, from 190 different players. Playing exposure was 229,317 hours resulting in an overall injury rate of 2.4 p/1000h, ranging from 0.7 p/1000h (U'11) to 4.8 p/1000h (u'21). Most injuries were traumatic in mechanism (73%). The most common injury location was the thigh (23%) and the most common injury type was muscle injury (29%) combining to provide the most common injury diagnosis; thigh muscle injury (17%). In U'13-U'16 players, a higher number of injuries to early-maturing players were observed in U'13-U'14 players, whilst more injuries to U'15-U'16 players occurred when classed as 'on-time' in maturity status. Maturation status did not statistically relate to injury pattern, however knee bone (not-fracture) injuries peaked in U'13 players whilst hip/groin muscle injuries peaked in U'15 players. 



#4 Effect of tDCS on well-being and autonomic function in professional male players after official soccer matches 

Reference: Physiol Behav. 2021 Feb 6;233:113351. doi: 10.1016/j.physbeh.2021.113351. Online ahead of print. 

Authors: Alexandre Moreira, Daniel Gomes da Silva Machado, Luciane Moscaleski, Marom Bikson, Gozde Unal, Paul S Bradley, Abrahão F Baptista, Edgard Morya, Thais Cevada, Lucas Marques, Vinicius Zanetti, Alexandre Hideki Okano

Summary: This study aimed to examine the effect of transcranial direct current stimulation (tDCS) used as a recovery strategy, on heart rate (HR) measures and perceived well-being in 12 male professional soccer players. tDCS was applied in the days after official matches targeting the left dorsolateral prefrontal cortex (DLPFC) with 2 mA for 20 min (F3-F4 montage). Participants were randomly assigned to anodal tDCS (a-tDCS) or sham tDCS sessions. Players completed the Well-Being Questionnaire (WBQ) and performed the Submaximal Running Test (SRT) before and after tDCS. HR during exercise (HRex) was determined during the last 30 s of SRT. HR recovery (HRR) was recorded at 60 s after SRT. The HRR index was calculated from the absolute difference between HRex and HRR. A significant increase was observed for WBQ (effect of time; p<0.001; ηp2=0.417) with no effect for condition or interaction. A decrease in HRR (p = 0.014; ηp2=0.241), and an increase in HRR index were observed (p = 0.045; ηp2=0.168), with no effect for condition or interaction. No change for HRex was evident (p>0.05). These results suggest that a-tDCS over the DLPFC may have a positive effect on enhancing well-being and parasympathetic autonomic markers, which opens up a possibility for testing tDCS as a promising recovery-enhancing strategy targeting the brain in soccer players. The findings suggest that brain areas related to emotional and autonomic control might be involved in these changes with a possible interaction effect of tDCS by placebo-related effects, but more research is needed to verify this effect. 



#5 Growth and Maturity Status of Female Soccer Players: A Narrative Review 

Reference: Int J Environ Res Public Health. 2021 Feb 4;18(4):1448. doi: 10.3390/ijerph18041448. 

Authors: Robert M Malina, Diogo V Martinho, João Valente-Dos-Santos, Manuel J Coelho-E-Silva, Sławomir M Kozieł

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Summary: Reported mean ages, heights and weights of female soccer players aged <19 years in 161 studies spanning the years 1992-2020 were extracted from the literature or calculated from data available to the authors; 35 studies spanning the years 1981-2020 also included an indicator of biological maturation. Heights and weights were plotted relative to U.S. reference data. Preece-Baines Model 1 was fitted to moving averages to estimate ages at peak velocity. Maturity indicators included skeletal age, pubertal status, age at menarche, percentage of predicted adult height and predicted maturity offset. Heights and weights showed negligible secular variation across the time interval. Heights were slightly above or approximated the reference medians through 14 years old and then varied between the medians and 75th percentiles through 18 years old. Weights were above the reference medians from 9 to 18 years old. Mean ages at menarche ranged from 12.7 to 13.0 years. The trend in heights and weights suggested the persistence and/or selection of taller and heavier players during adolescence, while estimated age at peak height velocity (PHV) and ages at menarche were within the range of mean ages in European and North American samples. Data for skeletal and sexual maturity status were limited; predicted maturity offset increased linearly with mean ages and heights at prediction. 



#6 Abdominal Organ Injuries in Youth Soccer: A Case Series and Review of Literature

Reference: Curr Sports Med Rep. 2021 Feb 1;20(2):69-75. doi: 10.1249/JSR.0000000000000785. 

Authors: Sayyar Khakimov, Peter Zaki, Joseph Hess, William Hennrikus

Summary: We describe 13 children who presented to the Penn State Health Milton S. Hershey Medical Center (HMC) with pediatric soccer-related abdominal organ injuries. A review of the Pennsylvania Trauma System Foundation's Trauma Registry was performed between 2001 and 2015 for children with soccer injuries hospitalized at trauma centers across Pennsylvania. Out of 52 children at Hershey Medical Center, 13 suffered abdominal organ injuries. Injuries included the spleen [5], kidney [4], liver [2], and combined organ involvement [2]. All patients presented with abdominal and/or flank pain. All patients with kidney injuries presented with hematuria. All patients presented after a player-to-player (P2P) contact. Nearly all patients (12/13) were treated nonsurgically. Our findings showed that abdominal organ injuries constitute a substantial portion of pediatric soccer injuries requiring hospitalization, with spleen being the organ injured most frequently. Soccer-related abdominal organ injuries should be suspected in players who suffer abdominal and/or flank pain, and/or hematuria after a P2P contact. 



#7 Relationship Between Wellness Index and Internal Training Load in Soccer: Application of a Machine Learning Model

Reference: Int J Sports Physiol Perform. 2021 Feb 9;1-9. doi: 10.1123/ijspp.2020-0093. Online ahead of print. 

Authors: Enrico Perri, Carlo Simonelli, Alessio Rossi, Athos Trecroci, Giampietro Alberti, F Marcello Iaia 

Summary: The aim was to investigate the relationship between the training load (TL = rate of perceived exertion × training time) and wellness index (WI) in soccer. The WI and TL data were recorded from 28 subelite players (age = 20.9 [2.4] y; height = 181.0 [5.8] cm; body mass = 72.0 [4.4] kg) throughout the 2017/2018 season. Predictive models were constructed using a supervised machine learning method that predicts the WI according to the planned TL. The validity of our predictive model was assessed by comparing the classification's accuracy with the one computed from a baseline that randomly assigns a class to an example by respecting the distribution of classes (B1). A higher TL was reported after the games and during match day (MD)-5 and MD-4, while a higher WI was recorded on the following days (MD-6, MD-4, and MD-3, respectively). A significant correlation was reported between daily TL (TLMDi) and WI measured the day after (WIMDi+1) (r = .72, P < .001). Additionally, a similar weekly pattern seems to be repeating itself throughout the season in both TL and WI. Nevertheless, the higher accuracy of ordinal regression (39% [2%]) compared with the results obtained by baseline B1 (21% [1%]) demonstrated that the machine learning approach used in this study can predict the WI according to the TL performed the day before (MD<i). The machine learning technique can be used to predict the WI based on a targeted weekly TL. Such an approach may contribute to enhancing the training-induced adaptations, maximizing the players' readiness and reducing the potential drops in performance associated with poor wellness scores. 



#8 Effectiveness of Abdominal and Gluteus Medius Training in Lumbo-Pelvic Stability and Adductor Strength in Female Soccer Players. A Randomized Controlled Study 

Reference: Int J Environ Res Public Health. 2021 Feb 5;18(4):1528. doi: 10.3390/ijerph18041528. 

Authors: Héctor Guerrero-Tapia, Rodrigo Martín-Baeza, Rubén Cuesta-Barriuso

Summary: Abdominal and lumbo-pelvic stability alterations may be the origin of lower limb injuries, such as adductor pathology in soccer players. Imbalance can be caused by both intrinsic and extrinsic factors. In this randomized controlled trial over 8 weeks, 25 female footballers were randomly allocated to an experimental group (isometric abdominal training and gluteus medius-specific training) or a control group (isometric abdominal training). Evaluations were performed at baseline, at the end of the intervention and after a 4-week follow-up period. The exercise protocol in common for both groups included three exercises: Plank, Lateral plank and Bird dog. Specific exercises for the gluteus medius were: Pelvic drop and Stabilization of the gluteus medius in knee valgus. Outcome measures were lumbar-pelvic stability and adductor strength. After the intervention, there was an increase in lumbo-pelvic stability in both groups, being greater in the control group than in the experimental group (mean differences [MD]: 4.84 vs. MD: 9.58; p < 0.01) with differences in the analysis of repeated measures (p < 0.001), but not in group interaction (p = 0.26). Changes were found in adductor strength in the experimental group (MD: -2.48; p < 0.001 in the left adductor; MD: -1.48; p < 0.01 in right adductor) and control group (MD: -1.68; p < 0.001 in the left adductor; MD: -2.05; p < 0.001 in the right adductor) after the intervention, with differences in the analysis of repeated measures in left (p < 0.001) and right (p < 0.001) adductor strength. An abdominal and gluteal training protocol shows no advantage over a protocol of abdominal training alone for lumbo-pelvic stability and adductor strength, while improvements in both variables are maintained at four weeks follow-up. 



#9 Quantifying and modelling the game speed outputs of English Championship soccer players 

Reference: Res Sports Med. 2021 Feb 10;1-13. doi: 10.1080/15438627.2021.1888108. Online ahead of print. 

Authors: Mark Connor, Dylan Mernagh, Marco Beato

Summary: This study aims to quantify and model the game-speed demands of professional soccer players competing in the English Championship league, to compare the effect of match location and to examine the effect of playing position on game-speed outputs across the season. Twenty-eight male professional soccer players were enrolled. Moving average calculations were applied to the raw GNSS (STATSports) speed data of each player's duration matches (home = 14 and away = 9). Positional groups were centre-back (CB), full-back (FB), centre-midfield (CM), wing-midfield (WM) and centre-forward (CF). The maximum value across each of the moving average window durations was extracted and converted to units of metres per minute. Power-law models were fitted to all observations (R2 = 0.64), home only (R2 = 0.98), and away only (R2 = 0.98). No significant effects are observed in game-speed outputs when home and away games are analysed. Significant differences were seen between the following positional groups; CBvs.CF (d = -0.323), CM (d = -0.530) and FB (d = -0.350). CM displayed positive difference compared to WM (d = 0.614). This study reported power-law model fitted game speed. Players' positional groups have significantly different game-speed demands, which should be considered during match analysis and training periodization. This study found that game speed is not affected by the location of the match. 



#10 Markers of muscle damage and strength performance in professional football (soccer) players during the competitive period 

Reference: Ann Transl Med. 2021 Jan;9(2):113. doi: 10.21037/atm-20-2923. 

Authors: Vladimir Khaitin, Eduard Bezuglov, Artemii Lazarev, Sergey Matveev, Olga Ivanova, Nicola Maffulli, Evgeny Achkasov 

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Summary: The present study investigated the impact of competitive soccer on the short-term changes in isometric strength of the adductor muscle group during the competitive season. In this cohort study we evaluated the association between a serum marker of muscle damage [creatine phosphokinase (CPK)] and isometric strength of the adductor muscles of the hip in 30 professional football players (age: 26.7±2.9 years) during two seasons of the national top-level championship. Serum CPK level was determined the day before the match, 12-20, 36-48, 60-72 h after the match. The maximum voluntary isometric contraction force of the adductor muscles complex was determined immediately after having taken blood samples. There was evidence of a statistically significant positive association between age, body mass index (BMI), percentage of body fat, and muscle strength, and between weight and muscle strength. There was evidence of a statistically significant negative association between the level of CPK and the maximum isometric strength of the adductors of soccer players. Changes in CPK levels were associated with the muscle strength recovery trend (P<0.001). The strength/CPK ratio at different time points had a U-shaped curve. Exercise induced muscle damage significantly affects the strength of the adductor muscle group of professional soccer players during the competitive period. The lower the CPK level, the greater the athletes' strength at a given time point. Also, the greater the decrease in CPK level, the greater the rate of strength restoration. 



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

Reference: Res Sports Med. 2021 Feb 11;1-13. doi: 10.1080/15438627.2021.1888103. Online ahead of print. 

Authors: Saeid Younesi, Alireza Rabbani, Filipe Manuel Clemente, Hugo Sarmento, António Figueiredo

Summary: The aim of this study was to analyse variations of internal load across small-sided games (SSG) in professional soccer. Twenty players (mean ± SD; age 28.1 ± 4.6 yo, height 176.7 ± 4.9 cm, weight 72.0 ± 7.8 kg) performed 3v3, 4v4, and 6v6 formats with/without goalkeeper and touch limitations. Each condition was repeated over three sessions and heart rate (HR) measures including average HR (HRavg), Edwards' training impulse (Edwards' TRIMP) and time in red zone (>80% of maximal HR) were recorded. All measures had trivial-to-moderate typical error (TE) and trivial differences were observed within intervals. The HRavg showed less coefficient of variations (0.9% to 1.7%) compared to Edwards'TRIMP . min-1 and red zone.min-1 (2% to 9.7%). A reduction trend in TE was observed when touching limitations or using goalkeepers. Practitioners can use different SSG formats but if the aim is to have less noise at higher intensities, more controlled drills are recommended. 


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