Latest research in football - week 52 - 2019

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 Comparing the Aerobic Fitness of Professional Male Soccer Players and Soccer Referees
Reference: Curr Sports Med Rep. 2019 Dec;18(12):497-501. doi: 10.1249/JSR.0000000000000668.
Authors: Santos-Silva PR, D'Andrea Greve JM, Pedrinelli A, Almeida AM, Osorio BB, Ferreira M, Ferreira C
Summary: We looked to compare the aerobic performance between professional soccer referees and players. Fifty male soccer referees and 61 male soccer players were tested on a treadmill. The referees and players possessed 15 ± 7 years and 7 ± 3 years of experience in soccer, respectively. Significant differences were observed between the referees and players with regards to: age (34.8 ± 4.6 years vs 20.8 ± 2.7 years; P < 0.001, maximum oxygen uptake (54.7 ± 5.4 mL·kg·min vs 58.8 ± 4.4 mL·kg·min; P < 0.001), and maximal heart rate in peak exercise (184 ± 11 bpm vs 192 ± 9 bpm, P < 0.001). Less significant differences also were observed and included; running speed at the maximum oxygen uptake (16.6 ± 1 km·h vs 16.4 ± 1.1 km·h), running speed at the ventilatory threshold (213.5 ± 1.1 km·h vs 13.2 ± 0.9 km·h), and percentage of maximal oxygen uptake at the ventilatory threshold (285.1% ± 3.2% vs 84.1% ± 6.2%). The effect size of most comparative variables between the two groups was small (<0.6). Older elite-level soccer referees are able to reach and maintain aerobic physical fitness levels similar to professional soccer players. Aerobic physical fitness may be a measurable factor for maintaining elite-level soccer licensure rather than age alone.

#2 Scapula Fractures in Elite Soccer and Rugby Players
Reference: Orthop J Sports Med. 2019 Dec 2;7(12):2325967119887388. doi: 10.1177/2325967119887388. eCollection 2019 Dec.
Authors: McIntosh J, Akhbari P, Malhas A, Funk L
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Summary: Scapula fractures are uncommon in sports and are poorly understood in this patient group. The purpose was to report on scapula fractures in contact and collision athletes and assess the injury patterns of different mechanisms of injury. A retrospective case series was performed of all sports-related scapula fractures treated at a single institution between 2007 and 2015. The mechanisms of injury were divided into direct lateral impact, fall onto an outstretched arm, or abduction/external rotation. A total of 11 patients were identified: 9 professional rugby players, 1 professional soccer player, and 1 amateur soccer player. The mean age was 28 years (range, 18-35 years). The mean return to play was 127 days in those treated nonoperatively and 163 days in those treated operatively. A direct impact mechanism occurred in 7 patients, all of whom sustained glenoid neck and body fractures and were treated nonoperatively. Two rugby players had a concomitant suprascapular nerve injury. An outstretched arm mechanism occurred in 2 cases, leading to posterior and inferior glenoid fractures. Both patients were treated operatively. An abduction/external rotation mechanism occurred in 2 cases, resulting in an anteroinferior and an anterior glenoid rim fracture. One case was treated operatively and the other was treated nonoperatively. Of those with glenoid fractures, 75% were not visible on plain radiographs and required further imaging. Scapula fractures acquired in sports are a serious injury with a prolonged recovery period. The mechanism of injury can help predict the injury pattern and highlight the need for further imaging. There is a high association with suprascapular nerve injuries.

#3 Infrared Low-Level Laser Therapy (Photobiomodulation Therapy) before Intense Progressive Running Test of High-Level Soccer Players: Effects on Functional, Muscle Damage, Inflammatory, and Oxidative Stress Markers-A Randomized Controlled Trial
Reference: Oxid Med Cell Longev. 2019 Nov 16;2019:6239058. doi: 10.1155/2019/6239058. eCollection 2019.
Authors: Tomazoni SS, Machado CDSM, De Marchi T, Casalechi HL, Bjordal JM, de Carvalho PTC, Leal-Junior ECP
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Summary: The effects of preexercise photobiomodulation therapy (PBMT) to enhance performance, accelerate recovery, and attenuate exercise-induced oxidative stress were still not fully investigated, especially in high-level athletes. The aim of this study was to evaluate the effects of PBMT (using infrared low-level laser therapy) applied before a progressive running test on functional aspects, muscle damage, and inflammatory and oxidative stress markers in high-level soccer players. A randomized, triple-blind, placebo-controlled crossover trial was performed. Twenty-two high-level male soccer players from the same team were recruited and treated with active PBMT and placebo. The order of interventions was randomized. Immediately after the application of active PBMT or placebo, the volunteers performed a standardized high-intensity progressive running test (ergospirometry test) until exhaustion. We analyzed rates of oxygen uptake (VO2 max), time until exhaustion, and aerobic and anaerobic threshold during the intense progressive running test. Creatine kinase (CK) and lactate dehydrogenase (LDH) activities, levels of interleukin-1β (IL-1-β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α), levels of thiobarbituric acid (TBARS) and carbonylated proteins, and catalase (CAT) and superoxide dismutase (SOD) activities were measured before and five minutes after the end of the test. PBMT increased the VO2 max (both relative and absolute values-p < 0.0467 and p < 0.0013, respectively), time until exhaustion (p < 0.0043), time (p < 0.0007) and volume (p < 0.0355) in which anaerobic threshold happened, and volume in which aerobic threshold happened (p < 0.0068). Moreover, PBMT decreased CK (p < 0.0001) and LDH (p < 0.0001) activities. Regarding the cytokines, PBMT decreased only IL-6 (p < 0.0001). Finally, PBMT decreased TBARS (p < 0.0001) and carbonylated protein levels (p < 0.01) and increased SOD (p < 0.0001)and CAT (p < 0.0001) activities. The findings of this study demonstrate that preexercise PBMT acts on different functional aspects and biochemical markers. Moreover, preexercise PBMT seems to play an important antioxidant effect, decreasing exercise-induced oxidative stress and consequently enhancing athletic performance and improving postexercise recovery.

#4 Effects of a 6-Week Strength Training of the Neck Flexors and Extensors on the Head Acceleration during Headers in Soccer
Reference: J Sports Sci Med. 2019 Nov 19;18(4):729-737. eCollection 2019 Dec.
Authors: Becker S, Berger J, Backfisch M, Ludwig O, Kelm J, Fröhlich M
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Summary: The importance of well trained and stable neck flexors and extensors as well as trunk muscles for intentional headers in soccer is increasingly discussed. The neck flexors and extensors should ensure a coupling of trunk and head at the time of ball contact to increase the physical mass hitting the ball and reduce head acceleration. The aim of the study was to analyze the influence of a 6-week strength training program (neck flexors, neck extensors) on the acceleration of the head during standing, jumping and running headers as well as after fatigue of the trunk muscles on a pendulum header. A total of 33 active male soccer players (20.3 ± 3.6 years, 1.81 ± 0.07 m, 75.5 ± 8.3 kg) participated and formed two training intervention groups (IG1: independent adult team, IG2: independent youth team) and one control group (CG: players from different teams). The training intervention consisted of three exercises for the neck flexors and extensors. The training effects were verified by means of the isometric maximum voluntary contraction (IMVC) measured by a telemetric Noraxon DTS force sensor. The head acceleration during ball contact was determined using a telemetric Noraxon DTS 3D accelerometer. There was no significant change of the IMVC over time between the groups (F=2.265, p=.121). Head acceleration was not reduced significantly for standing (IG1 0.4 ± 2.0, IG2 0.1 ± 1.4, CG -0.4 ± 1.2; F = 0.796, p = 0.460), jumping (IG1-0.7 ± 1.4, IG2-0.2 ± 0.9, CG 0.1 ± 1.2; F = 1.272, p = 0.295) and running (IG1-1.0 ± 1.9, IG2-0.2 ± 1.4, CG -0.1 ± 1.6; F = 1.050, p = 0.362) headers as well as after fatigue of the trunk musculature for post-jumping (IG1-0.2 ± 2.1, IG2-0.6 ± 1.4; CG -0.6 ± 1.3; F = 0.184, p = 0.833) and post-running (IG1-0.3 ± 1.6, IG2-0.7 ± 1.2, CG 0.0 ± 1.4; F = 0.695, p = 0.507) headers over time between IG1, IG2 and CG. A 6-week strength training of the neck flexors and neck extensors could not show the presumed preventive benefit. Both the effects of a training intervention and the consequences of an effective intervention for the acceleration of the head while heading seem to be more complex than previously assumed and presumably only come into effect in case of strong impacts.

#5 Monitoring the Athlete Match Response: Can External Load Variables Predict Post-match Acute and Residual Fatigue in Soccer? A Systematic Review with Meta-analysis
Reference: Sports Med Open. 2019 Dec 9;5(1):48. doi: 10.1186/s40798-019-0219-7.
Authors: Hader K, Rumpf MC, Hertzog M, Kilduff LP, Girard O, Silva JR
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Summary: Monitoring athletes' external load during a soccer match may be useful to predict post-match acute and residual fatigue. This estimation would allow individual adjustments to training programs to minimize injury risk, improve well-being, and restore players' physical performance and inform the recovery process. Using a systematic review and meta-analysis of the literature, the aim is to determine which monitoring variables would be the strongest predictors of acute (immediately) and residual (up to 72 h) fatigue states in soccer. PubMed, SPORTDiscus, and Web of Science databases were searched (until September 2018). Studies concurrently examining soccer match-related external load metrics and subjective and/or objective measures were selected to determine pooled correlations ([Formula: see text]) with confidence intervals (CI). The quality and strength of the findings of each study were evaluated to identify overall levels of evidence. Eleven studies were included (n = 165 athletes). Acute ([Formula: see text] = 0.67; 95% CI = [0.40, 0.94]) and residual (24 h post-match, [Formula: see text] = 0.54; 95% CI = [0.35, 0.65]) changes in muscle damage markers and countermovement jump peak power output (CMJPPO) were, with moderate to strong evidence, largely correlated with running distance above 5.5 m s-1. No other external load metric was largely correlated with both biochemical and neuromuscular markers. For every 100-m run above 5.5 m·s-1, CK activity measured 24 h post-match increased by 30% and CMJPPO decreased by 0.5%. Conversely, the total distance covered did not present any evidence of a clear relationship with any fatigue-related marker at any time-point. Running distance above 5.5 m·s-1 represents the most sensitive monitoring variable characterizing biochemical and neuromuscular responses, at least when assessed during the initial 24 h (not at 48 h/72 h) post-match recovery period. In addition, total distance covered is not sensitive enough to inform decision-making during the fatigue monitoring process.

#6 A bioecological perspective on talent identification in junior-elite soccer: A Pan-European perspective
Reference: J Sports Sci. 2019 Dec 9:1-10. doi: 10.1080/02640414.2019.1702282. [Epub ahead of print]
Authors: Reeves MJ, Roberts SJ
Summary: Elite soccer clubs across Europe spend ever-increasing sums of money on transfers and salaries for world-class players. Consequently, clubs' talent identification and development processes for junior players have become more professionalised. Based on a holistic ecological approach, this study presents an analysis of talent identification practices across some of the most productive soccer academies in Europe (N = 11). Data were collected via semi-structured interviews with 11 heads of academy recruitment from clubs in the "big five" European leagues. Clubs were purposively sampled based on their player productivity ranking. Interviews ranged from 52:26 minutes to 114:06 minutes in length (m = 87:53 ± 20.10 minutes). This study argues that holistic ecological approaches the environments were characterised through the interplay of factors that ranged from high-level internal to international level relationships. This resulted in the identification and recruitment of players from local and international environments. The purpose of recruitment was suggested to have a dual purpose: recruitment of players for the first team; recruitment of players for further development/monitoring and/or selling to another club.

#7 Endocrine Responses to Various 1 × 1 Small-Sided Games in Youth Soccer Players
Reference: Int J Environ Res Public Health. 2019 Dec 6;16(24). pii: E4974. doi: 10.3390/ijerph16244974.
Authors: Chmura P, Podgórski T, Konefał M, Rokita A, Chmura J, Andrzejewski M
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Summary: The aim of this study was to determine relationships between repeated 1 × 1 small-sided games (SSGs) (variable duration, constant work-to-rest ratio) and the concentration of steroid hormones and characteristic fatigue markers in youth soccer players. Eighteen young male soccer players were assigned at random to two experimental groups: E1-undertaking a six 30 s one-on-one SSGs with a 2 min rest period; and E2-playing six 45 s SSGs with a 3 min rest interval. Capillary blood was collected from the players at rest, after the last game, and 15 and 30 min after the exercise protocol. The variables assessed included serum cortisol (C), free testosterone (FT) and total testosterone (TT). An effect was observed between the measurement times (TT (F = 15.26, p ≤ 0.0001), FT (F = 6.86, p = 0.0006)). In terms of cortisol (C) levels, no interactions or effect between the studied groups were revealed, but an interaction was found (F = 4.01, p = 0.0126) and the effect appeared between the measurement times (F = 11.16, p ≤ 0.0001). The study results show that in all likelihood, longer rest intervals in repeated 30 s 1 × 1 SSGs can reduce catabolic reactions and hence the risk of overtraining in youth soccer players.

#8 Interactive Improvements of Visual and Auditory Function for Enhancing Performance in Youth Soccer Players
Reference: Int J Environ Res Public Health. 2019 Dec 5;16(24). pii: E4909. doi: 10.3390/ijerph16244909.
Authors: Song YH, Ha SM, Yook JS, Ha MS
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Summary: We analyzed the effects of a regular training program on the health- and skill-related physical fitness (PF) of talented soccer players aged < 12 years; visual reaction time (VRT) and auditory reaction time (ART) were also assessed. In this single-group interventional study, 78 talented male youth soccer players (mean age, 9.54 years) were critically selected by the Korean Educational Development Institute and underwent a 22-week training program consisting of 16 weeks of PF and basic skill training (90 min/week) and 6 weeks of intensive training (3, 150-min sessions/week). We assessed the pre- and post-training body composition, cardiovascular endurance, muscle strength and endurance, and flexibility. We also measured power, agility, coordination and speed, passing ability, VRT, and ART. All variables improved after training. Post-training VRT correlated with ART, muscle mass, power, cardiovascular endurance, 10-m dribble time, 10-m ball touch count, and 10-m successful pass count. ART only correlated with muscle mass. ART and 10-m ball-touch count influenced VRT, and VRT influenced ART. In conclusion, the training program enhanced the PF and visual- and auditory-related reactions in talented youth soccer players. This study suggests the importance of the assessed relationships, indicating that a training program that improves these parameters enhances the players' performance.

#9 Effect of Training Load on Post-Exercise Cardiac Troponin T Elevations in Young Soccer Players
Reference: Int J Environ Res Public Health. 2019 Dec 2;16(23). pii: E4853. doi: 10.3390/ijerph16234853.
Authors: Cirer-Sastre R, Legaz-Arrese A, Corbi F, López-Laval I, Puente-Lanzarote J, Hernández-González V, Reverter-Masià J
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Summary: Training load (TL) metrics are usually assessed to estimate the individual, physiological and psychological, acute, and adaptive responses to training. Cardiac troponins (cTn) reflect myocardial damage and are routinely analyzed for the clinical diagnosis of myocardial injury. The association between TL and post-exercise cTn elevations is scarcely investigated in young athletes, especially after playing common team sports such as soccer. The objective of this study was to assess the relationship between TL measurements during a small-sided soccer game and the subsequent increase in cTn in young players. Twenty male soccer players (age 11.9 ± 2 years, height 151 ± 13 cm, weight 43 ± 13 kg) were monitored during a 5 × 5 small-sided game and had blood samples drawn before, immediately after, and 3 h after exercise for a posterior analysis of high-sensitivity cardiac troponin T (hs-cTnT). Internal, external, and mixed metrics of TL were obtained from the rating of perceived exertion (RPE), heart rate (HR), and GPS player tracking. The results show that the concentration of hs-cTnT peaked at 3 h post-exercise in all participants. The magnitude of hs-cTnT elevation was mainly explained by the exercise duration in the maximal heart rate zone (Maximum Probability of Effect (MPE) = 92.5%), time in the high-speed zone (MPE = 90.4 %), and distance in the high-speed zone (MPE = 90.45%). Our results support the idea that common metrics of TL in soccer, easily obtained using player tracking systems, are strongly associated with the release of hs-cTnT in children and adolescents.

#10 Recreational Football is Medicine against Non-Communicable Diseases: A systematic Review
Reference: Scand J Med Sci Sports. 2019 Dec 13. doi: 10.1111/sms.13611. [Epub ahead of print]
Authors: Sarmento H, Manuel Clemente F, Marques A, Milanovic Z, David Harper L, Figueiredo A
Summary: The purpose of this research was to conduct a systematic review of published articles related to the effect of recreational football on non-communicable diseases. A systematic review of Web of Science, SPORTdiscus, MEDLINE and PubMed databases was performed according PRISMA guidelines. Only empirical studies were included. There were no restrictions on the types of study design eligible for inclusion. The primary outcome measures result from the potential effects of recreational football on non-communicable diseases (e.g., blood pressure, bone density, LDL-Cholesterol, fat mass, etc.). A total of 44 articles met the inclusion criteria and were included. Recreational football is shown to: (1) decrease blood pressure and resting heart rate, improve cardiac structure and functioning, as well as increase maximal oxygen uptake in both sexes; (2) reduce cholesterol and triglycerides levels, increase insulin sensitivity, and have a positive impact on glycaemic control; (3) improve bone mineralization, increase both bone mineral density and content, as well as acting as a stimulus for osteogenesis; (4) be clearly beneficial for bone health, whilst slightly beneficial for body composition, muscle strength and maximal oxygen uptake in adults with prostate cancer. The present systematic review demonstrated the benefits of recreational football practice on non-communicable diseases related to cardiovascular and bone health, body composition, type 2 diabetes and prostate cancer. The effectiveness of recreational football on the aforementioned diseases may be related to age and gender; however, further research is required.

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