Latest research in football - week 35 - 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 Energy Requirements of Male Academy Soccer Players from the English Premier League
Reference: Med Sci Sports Exerc. 2020 Jul 21. doi: 10.1249/MSS.0000000000002443. Online ahead of print.
Authors: Marcus P Hannon, Lloyd J F Parker, Daniel J Carney, John McKeown, John R Speakman, Catherine Hambly, Barry Drust, Viswanath B Unnithan, Graeme L Close, James P Morton
Summary: The purpose was to inform the energy requirements of highly trained adolescent soccer players, total energy expenditure (TEE) was quantified in academy soccer players from the English Premier League (EPL). Twenty-four male adolescent soccer players from an EPL academy (n=8 U12/13; n=8 U15; n=8 U18) were assessed for baseline maturity (maturity offset), body composition (DXA) and resting metabolic rate (RMR; indirect calorimetry). Subsequently, TEE, energy intake (EI) and physical loading patterns were assessed over a 14-day in-season period using doubly labelled water, the remote food photographic method and global positioning system technology, respectively. Under-18 players presented with greater RMR (2236±93 kcal⋅day) and TEE (3586±487 kcal⋅day; range: 2542-5172 kcal⋅day) than both U15 (2023±162 and 3029±262 kcal⋅day, respectively; TEE range: 2738-3726 kcal⋅day) and U12/13 players (1892±211 and 2859±265 kcal⋅day, respectively; TEE range: 2275-3903 kcal⋅day) (all P<0.01), though no difference in TEE was apparent between the U12/13 and U15 age-groups. Fat-free mass was significantly different between all comparisons in a hierarchal manner (U18: 57.2±6.1 kg > U15: 42.9±5.8 kg > U12/13: 31.1±3.5 kg; all P<0.01). Within age-groups, no differences were apparent between EI and TEE (U12/13: -29±277 kcal⋅day, P=0.78; U15: -134±327 kcal⋅day, P=0.28; U18: -243±724 kcal⋅day, P=0.37), whilst U18 players (3180±279 kcal⋅day) reported higher EI than both U15 (2821±338 kcal⋅day; P=0.05) and U12/13 players (2659±187 kcal⋅day; P<0.01). The TEE of male academy soccer players progressively increase as players progress through the academy age-groups. In some individuals (evident in all age-groups), TEE was greater than that previously observed in adult EPL soccer players.

#2 Minimal Stabilization Time for Ultra-short Heart Rate Variability Measurements in Professional Soccer
Reference: Int J Sports Med. 2020 Jul 22. doi: 10.1055/a-1186-1316. Online ahead of print.
Authors: Francisco Forner-Llacer, Rodrigo Aranda-Malaves, Rafael Aranda Malavés, Julio Calleja-Gonzalez, Jose Antonio Perez-Turpin, Joaquin Gonzalez-Rodenas
Summary: The main aims of this study were: 1) to compare 1-minute RMSSD measurements using different stabilization times between them and also with the criterion; and 2) to determine the agreement between every 1-minute RMSSD measurement with the criterion in professional soccer players. Seven hundred eighteen HRV measurements from professional soccer players were taken. HRV was calculated from 5 to 10 minutes (criterion) and from 1-minute windows with different pre-stabilization times. Friedman and post-hoc tests were applied to compare 1-minute and criterion measurements. Effect size was considered to describe magnitude of change. To determine agreement, Spearman's correlation was applied, and Bland-Altman analysis was also done between each ultra-short HRV time window and the 5-minute HRV criterion period. The 1-minute HRV without any pre-stabilization time was the only one different from all the other 1-minute measurements that included 1 or more minutes of pre-stabilization (p<0.001). One-minute HRV measurements with 1 or more minutes of pre-stabilisation were highly correlated with those for the criterion period. One-minute HRV without pre-stabilization showed the lowest correlation and the highest bias from the criterion. It is concluded that 1-minute HRV measurements with a prior 1-minute or longer pre-stabilization time are valid to measure HRV in professional male soccer players.

#3 Mental health and suicide in former professional soccer players
Reference: J Neurol Neurosurg Psychiatry. 2020 Jul 21;jnnp-2020-323315. doi: 10.1136/jnnp-2020-323315. Online ahead of print.
Authors: Emma R Russell , Thomas McCabe, Daniel F Mackay, Katy Stewart, John A MacLean, Jill P Pell , William Stewart
Summary: There is growing recognition of an association between contact sports participation and increased risk of neurodegenerative disease, including Alzheimer's disease and chronic traumatic encephalopathy. In addition to cognitive impairment, a range of mental health disorders and suicidality are proposed as diagnostic features of traumatic encephalopathy syndrome, the putative clinical syndrome associated with chronic traumatic encephalopathy. However, to date, epidemiological data on contact sport participation and mental health outcomes are limited. For a cohort of former professional soccer players (n=7676) with known high neurodegenerative mortality and their matched general population controls (n=23 028), data on mental health outcomes were obtained by individual-level record linkage to national electronic records of hospital admissions and death certification. Compared with matched population controls, former professional soccer players showed lower risk of hospital admission for anxiety and stress related disorders, depression, drug use disorders, alcohol use disorders and bipolar and affective mood disorders. Among soccer players, there was no significant difference in risk of hospitalisation for mental health disorders between outfield players and goalkeepers. There was no significant difference in rate of death by suicide between soccer players and controls. Among a population of former professional soccer players with known high neurodegenerative disease mortality, hospital admissions for common mental health disorders were lower than population controls, with no difference in suicide. Our data provide support for the reappraisal of currently proposed diagnostic clinical criteria for traumatic encephalopathy syndrome, in particular the inclusion of mental health outcomes.

#4 Groin injury risk of pubertal soccer players increases during peak height velocity due to changes in movement techniques
Reference: J Sports Sci. 2020 Jul 21;1-9. doi: 10.1080/02640414.2020.1794769. Online ahead of print.
Authors: Thomas Dupré , Wolfgang Potthast
Summary: Adolescent athletes experience an increase in injury incidence when they undergo peak height velocity (PHV). To find the reason behind this increase, the present study investigated if PHV influences hip joint kinematics, kinetics and adductor muscle forces in two groups of adolescent soccer players performing 90°-cutting manoeuvres and inside passing. One group was estimated to be more than half a year before PHV (PRE, N = 12). The second group was estimated to be less than half a year before or after PHV (MID, N = 10). Maximum static gripping and adductor forces were measured. Motion capturing and inverse dynamics were used to calculate kinematics and kinetics. The MID group was significantly taller and heavier compared to PRE while the force measurements showed no differences. Statistics showed a higher hip abduction moment for MID during the cutting manoeuvre. Results from the anthropometrics and force measurements suggest that the moments of inertia of the participants' extremities increase faster than the muscles can adapt. A higher abduction moment of MID likely increases the load on the adductor muscles through a change of technique. Combining both findings, it is likely that the risk of suffering a groin injury is increased in the MID group.

#5 Landing Evaluation in Soccer Players with or without Anterior Cruciate Ligament Reconstruction
Reference: Int J Sports Med. 2020 Jul 20. doi: 10.1055/a-1171-1900. Online ahead of print.
Authors: Ahmad Alanazi, Katy Mitchell, Toni Roddey, Aqeel Alenazi, Msaad Alzhrani, Alexis Ortiz 
Summary: The purpose of this study was to evaluate landing biomechanics in soccer players following ACLR during two landing tasks. Eighteen soccer players with an ACLR and 18 sex-matched healthy control soccer players participated in the study. Planned landing included jumping forward and landing on the force-plates, whereas unplanned landing included jumping forward to head a soccer ball and landing on the force-plates. A significant landing×group interaction was found only for knee flexion angles (p=0.002). Follow-up comparisons showed that the ACL group landed with greater knee flexion during planned landing compared with unplanned landing (p<0.001). Significant main effects of landing were found. The unplanned landing showed reduction in hip flexion (p<0.001), hip extension moments (p<0.013), knee extension moments (p<0.001), and peak pressure (p<0.001). A significant main effect for group for gastrocnemius muscle was found showing that the ACL group landed with reduced gastrocnemius activity (p=0.002). Unplanned landing showed greater injury predisposing factors compared with planned landing. The ACL group showed nearly similar landing biomechanics to the control group during both landing tasks. However, the ACL group used a protective landing strategy by reducing gastrocnemius activity.

#6 Individual Response to External Training Load in Elite Football Players
Reference: Int J Sports Physiol Perform. 2020 Jan 30;15(5):696-704. doi: 10.1123/ijspp.2019-0453.
Authors: Håvard Wiig, Thor Einar Andersen, Live S Luteberget, Matt Spencer
Summary: The purpose was to investigate within-player effect, between-player effect, and individual response of external training load from player tracking devices on session rating of perceived exertion training load (sRPE-TL) in elite football players. The authors collected sRPE-TL from 18 outfield players in 21 training sessions. Total distance, high-speed running distance (>14.4 m/s), very high-speed running distance (>19.8 m/s), PlayerLoad™, PlayerLoad2D™, and high-intensity events (HIE > 1.5, HIE > 2.5, and HIE > 3.5 m/s) were extracted from the tracking devices. The authors modeled within-player and between-player effects of single external load variables on sRPE-TL, and multiple levels of variability, using a linear mixed model. The effect of 2 SDs of external load on sRPE-TL was evaluated with magnitude-based inferences. Total distance, PlayerLoad™, PlayerLoad2D™, and HIE > 1.5 had most likely substantial within-player effects on sRPE-TL (100%-106%, very large effect sizes). Moreover, the authors observed likely substantial between-player effects (12%-19%, small to moderate effect sizes) from the majority of the external load variables and likely to very likely substantial individual responses of PlayerLoad™, high-speed running distance, very high-speed running distance, and HIE > 1.5 (19%-30% coefficient of variation, moderate to large effect sizes). Finally, sRPE-TL showed large to very large between-session variability with all external load variables. External load variables with low intensity-thresholds had the strongest relationship with sRPE-TL. Furthermore, the between-player effect of external load and the individual response to external load advocate for monitoring sRPE-TL in addition to external load. Finally, the large between-session variability in sRPE-TL demonstrates that substantial amounts of sRPE-TL in training sessions are not explained by single external load variables.

#7 Females Sustain more Ankle Injuries than Males in Youth Football
Reference: Int J Sports Med. 2020 Jul 20. doi: 10.1055/a-1192-5399. Online ahead of print.
Authors: Taru Sokka, Matias Hilska, Tommi Vasankari, Mari Leppänen, Pekka Kannus, Jari Parkkari, Heidi Haapasalo, Hannele Forsman, Jani Raitanen, Kati Pasanen
Summary: This prospective study evaluated the incidence and pattern of acute injuries in youth (9- to 14-year- old) football players. Ten football clubs [n=730 players (567 males, 163 females)] participated in the 20-week follow-up study (January-June 2015). Data was collected by sending a standardized weekly SMS to players' parents/guardians with follow-up interviews for injured players. During the study period, 278 players (38%) sustained 410 acute injuries. The overall injury incidence for males and females was 6.47 (95% CI, 5.84-7.09) injuries per 1000 h of football exposure. Most injuries (40%) caused minimal absence from sports. Eighty-four percent of the injuries affected the lower extremities, with the ankle (30%), knee (17%), and thigh (16%) being the most commonly injured body sites. Females had significantly higher ankle injury rate (IRR) 1.85 (95% CI, 1.18-2.91, p=0.007) and non-contact ankle injury rate IRR 2.78 (95% CI, 1.91-4.02, p<0.001) than males. In conclusion, our results showed that the acute injury incidence among youth football is moderately high, and females are at higher risk for ankle injuries. Injury prevention programs aimed at preventing ankle injuries should be considered in the future.

#8 Homogeneous Distribution of Passing between Players of a Team Predicts Attempts to Shoot at Goal in Association Football: A Case Study with 10 Matches
Reference: Nonlinear Dynamics Psychol Life Sci. 2020 Jul;24(3):353-365.
Authors: Jose Gama , Goncalo Dias, Pedro Passos, Micael Couceiro, Keith Davids 
Summary: This paper presents a case study which aims to establish a relationship between the homogeneity of passing distribution between players of a team and goal attempts in the team sport of association football. We observed data from 10 competitive football matches, involving 10 different professional football teams of different performance levels, competing in the Portuguese League during the 2010/2011 season. Performance data were analysed using the Match Analysis Software Amisco. Shannon's entropy measure was used to quantify the homogeneity of passing distribution within each team. Results suggested the existence of a pattern between an increase in the homogeneity of passing distributions and the attempts to scoring goals in the sample of competitive matches studied. A homogeneous distribution of passes can moderately predict (approximately 45% of accuracy) when a goal attempt will occur within the following minute of an entropy assessment.

#9 Effects of two exercise programmes on joint position sense, dynamic balance and countermovement jump in male amateur football players. A randomised controlled trial
Reference: J Sports Sci. 2020 Jul 20;1-11. doi: 10.1080/02640414.2020.1794472. Online ahead of print.
Authors: Marcos J Navarro-Santana, Iván Asín-Izquierdo, Guido F Gómez-Chiguano, Daniel Albert-Lucena, Gustavo Plaza-Manzano, Ángel Pérez-Silvestre
Summary: The injury prevention and warm-up exercises programmes improve physical performance and injury ratio, but it is poorly investigated in amateur football. The aim was to assess the effects of two warm-up multi-station programmes (IAI-Programme and FIFA11+) through JPS, LSDT and CMJ. Study design: Randomised controlled trial. 36 football players were randomised into 2 groups: IAI-Programme (n = 18) and FIFA11+ (n = 18) and performed the intervention protocol for 6 weeks. JPS, LSDT and CMJ were measured at baseline, after 6, 10 and 18 weeks (from baseline). The inter-group and intra-group differences were assessed by repeated-measures analysis of variance test (ANOVA). Significant differences between groups were found after 18 weeks in the absolute angular error (-2.18[-4.33,-0.047], d = 0.69, p < 0.05) of the JPS and in the CMJ (p = 0.001, ŋ2p=,0.298) in favour of IAI-Programme when compared to FIFA11 +. No significant differences between groups were found in the LSDT. There were also intra-group differences observed in the LSDT in both groups. IAI-Programme can provide sensitive benefits with respect to the proprioceptive ability of knee flexion and CMJ than FIFA11 +. Both IAI-Programme and FIFA11+ present improvements in the dynamic postural control measured by the LSDT.

#10 Performing Soccer-Specific Training With Blood Flow Restriction Enhances Physical Capacities in Youth Soccer Players
Reference: J Strength Cond Res. 2020 Jul 23. doi: 10.1519/JSC.0000000000003737. Online ahead of print.
Authors: Seyed A Hosseini Kakhak, Mojtaba Kianigul, Amir-Hossein Haghighi, Mehdi Jabbari Nooghabi, Brendan R Scott
Summary: This study investigated the effect of soccer training with blood flow restriction (BFR) on physical performance in youth athletes. Nineteen semiprofessional soccer players were randomly assigned to either normal soccer training (ST; n = 9) or soccer training with BFR (STBFR; n = 10). Both groups performed identical activities during a 6-week preseason training phase, either with or without lower limb BFR. Training included soccer-specific drills, small-sided games, plyometrics, and continuous running. Before and after the intervention, players were assessed for leg extension strength and endurance, countermovement jump performance, 40-yd sprint time, change-of-direction (COD) ability, aerobic endurance, and soccer-specific endurance (while dribbling a ball). Significantly larger improvements were observed in the STBFR compared with the ST group for tests of muscular endurance (74.8 ± 34.1% vs. 4.0 ± 14.6%), COD (8.1 ± 3.7% vs. 2.8 ± 4.7%), and aerobic (54.1 ± 19.6% vs. 24.7 ± 27.2%) and soccer-specific endurance (58.4 ± 19.6% vs. 22.7 ± 10.2%). Main effects for time were observed for maximal strength, jumping, and sprinting performance (p < 0.001) but with no group and time interaction. These findings demonstrate that team sport training with BFR can enhance physical qualities that are related to performance in youth soccer players. This application of BFR may improve the adaptive responses of muscles, without having to dedicate additional training time to muscular qualities.

#11 Assessing the Anthropometric Profile of Spanish Elite Reserve Soccer Players by Playing Position over a Decade
Reference: Int J Environ Res Public Health. 2020 Jul 28;17(15):E5446. doi: 10.3390/ijerph17155446.
Authors: Jon Manuel Vega, Asier Gonzalez-Artetxe, Jon Ander Aguinaco, Asier Los Arcos
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Summary: The aims of this study were to describe the evolution of the anthropometric profile of soccer players over a decade and to compare the anthropometric profiles of players promoted from an elite reserve team to high-level soccer with those players who were not promoted. We examined the body mass, height, body-mass index, and body fat of 98 players enrolled in the reserve team from 2008 to 2018. The players were classified in terms of (a) the highest competitive level they achieved up to the 2019/2020 season (i.e., Spanish 1st-2nd divisions or semi-professional); (b) the period in which they played their last season on the team; and (c) their playing position. Over time, the height of goalkeepers, lateral midfielders, and attackers has increased (effect size = 0.66 ± 1.13) but has decreased in central midfielders (effect size = 0.83). The body fat of defenders has also fallen (effect size = 0.55 ± 0.95). Spanish high-level goalkeepers, lateral midfielders, and attackers were taller than their semi-professional player counterparts (effect size = 1.20 ± 1.98). Body fat did not determine promotion from a reserve team to high-level soccer, but height may be an advantage for several playing positions. The assessment of the anthropometric profile and the application of interventions should be designed according to the playing position.

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