Latest research in football - week 44 - 2018

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 Variation in the Correlation Between Heart Rate and Session Rating of Perceived Exertion-Based Estimations of Internal Training Load in Youth Soccer Players
Reference: Pediatr Exerc Sci. 2018 Oct 28:1-8. doi: 10.1123/pes.2018-0033. [Epub ahead of print]
Authors: Vahia D, Kelly A, Knapman H, Williams CA
Summary: When exposed to the same external load, players receive different internal loads, resulting in varied adaptations in fitness. In adult soccer, internal training load is measured using heart rate (HR) and session rating of perceived exertion (sRPE) scales, but these have been underutilized in youth soccer. This study investigated the in-season variation in correlation between HR and sRPE estimations of training load for adolescent soccer players. Fifteen male professional adolescent players were monitored for 7 months. Within-participant correlations and Bland-Altman agreement plots for HR and sRPE were calculated for each month to analyze variation over the season and for individual players to analyze the validity of the scale. The monthly correlations ranged from r = .60 to r = .73 (P < .05) and the overall correlation was r = .64 (95% confidence interval, .60-.68; P < .001). Bland-Altman plots showed an agreement of methods. Results showed consistently large correlations for all months. sRPE is a consistent method of measure of internal training load for the entire season for youth soccer players. Validity analysis found no bias in sRPE measurements when compared with HR for all players in the study.

#2 Mental Fatigue in Football: Is it Time to Shift the Goalposts? An Evaluation of the Current Methodology
Reference: Sports Med. 2018 Nov 2. doi: 10.1007/s40279-018-1016-z. [Epub ahead of print]
Authors: Thompson CJ, Fransen J, Skorski S, Smith MR, Meyer T, Barrett S, Coutts AJ
Summary: Research in football for a long time has focused on the physical nature of fatigue as opposed to its mental aspects. However, since 2016, six original articles have investigated the effects of induced mental fatigue in football on isolated physical, skill and decision-making performance tests, along with physical, technical and tactical performance outcomes in small-sided games. Whilst these studies have overall shown a negative impact of mental fatigue on task performance, this current opinion aims to critically examine the methodological approach to this problem, most notably the lack of ecological validity when inducing mental fatigue and the present approach to measuring mental fatigue using visual analogue scales (VAS). It is suggested that future research on mental fatigue in football may benefit from the use of surveys/interviews to understand the true cognitive demands of elite football players. Additionally, future research should aim to reduce the reliance on using VAS to measure mental fatigue as results from this tool may be confounded by several response biases. In conclusion, this article highlights the need for mentally fatiguing tasks that adequately represent football-associated mental fatigue and assessments of mental fatigue that minimise the confounding effect of response bias.

#3 A systematic review on small-sided games in football players: Acute and chronic adaptations
Reference: J Sports Sci. 2018 Oct 29:1-29. doi: 10.1080/02640414.2018.1535821. [Epub ahead of print]
Authors: Bujalance-Moreno P, Latorre-Román PÁ, García-Pinillos F
Summary: Small-sided games (SSG) are played on a small pitch, often using modified rules and involving a smaller number of players. This article aimed to critically analyse the literature to determine how small-sided games affect the performance of football players in the short- and long term. Electronic databases were searched for literature dating from January 2000 to July 2018. The methodological quality of the studies was evaluated using the modified Downs and Black Quality Index (cross-sectional studies) and the Physiotherapy Evidence Database (PEDro) scale (intervention studies). Fifty-three studies, 44 cross-sectional and 9 intervention studies, met the inclusionary criteria for review. Most of the cross-sectional studies focused on describing the differences between SSG protocols, whereas 4 studies focused on making a comparison between "interval" and "continuous" SSG training regimes. On the other hand, intervention studies focused on making a comparison between SSG-based protocols and high-intensity intermittent training (HIIT)-based running protocols, in addition to determine the effect of a SSG-based training programme alone. SSG-based football plans (2 to 4 SSG sessions per week) show athletic performance improvements in football players by improving sprint, repeated sprint ability (RSA) and change of direction (COD) along with muscular and physiological adaptation.

#4 Player Tracking Data Analytics as a Tool for Physical Performance Management in Football: A Case Study from Chelsea Football Club Academy
Reference: Sports (Basel). 2018 Oct 26;6(4). pii: E130. doi: 10.3390/sports6040130.
Authors: De Silva V, Caine M, Skinner J, Dogan S, Kondoz A, Peter T, Axtell E, Birnie M, Smith B
Summary: Global positioning system (GPS) based player movement tracking data are widely used by professional football (soccer) clubs and academies to provide insight into activity demands during training and competitive matches. However, the use of movement tracking data to inform the design of training programmes is still an open research question. The objective of this study is to analyse player tracking data to understand activity level differences between training and match sessions, with respect to different playing positions. This study analyses the per-session summary of historical movement data collected through GPS tracking to profile high-speed running activity as well as distance covered during training sessions as a whole and competitive matches. We utilise 20,913 data points collected from 53 football players aged between 18 and 23 at an elite football academy across four full seasons (2014⁻2018). Through ANOVA analysis and probability distribution analysis, we compare the activity demands, measured by the number of high-speed runs, the amount of high-speed distance, and distance covered by players in key playing positions, such as Central Midfielders, Full Backs, and Centre Forwards. While there are significant positional differences in physical activity demands during competitive matches, the physical activity levels during training sessions do not show positional variations. In matches, the Centre Forwards face the highest demand for High Speed Runs (HSRs), compared to Central Midfielders and Full Backs. However, on average the Central Midfielders tend to cover more distance than Centre Forwards and Full Backs. An increase in high-speed work demand in matches and training over the past four seasons, also shown by a gradual change in the extreme values of high-speed running activity, was also found. This large-scale, longitudinal study makes an important contribution to the literature, providing novel insights from an elite performance environment about the relationship between player activity levels during training and match play, and how these vary by playing position.

#5 Fitness effects of one year soccer training of 8-10 and 10-12 years old school children
Reference: J Sports Med Phys Fitness. 2018 Oct 31. doi: 10.23736/S0022-4707.18.08612-7. [Epub ahead of print]
Authors: Michailidis Y, Metaxas TI, Stefanidis P, Christoulas K
Summary: The purpose of the study was to investigate the effect of one year soccer training on physical fitness performance, of U10 and U12 youth levels. 28, 10-year-old and 28, 12-year-old children participated in the study. In the U12 group, 19 children participated only in the physical fitness sessions at school (control group - CG) and 9 children in four extra soccer trainings (Soccer group - SG). In the U10 group, 11 children participated only in the physical fitness sessions at school (control group - CG) and 17 children in four extra soccer trainings (Soccer group - SG). Height, body weight, body fat, standing long jump, 30 m sprint, sit and reach test, abdominal test and Yo-Yo IE1 tests were performed at the beginning and at the end of the season. School physical education programs and soccer training cannot affect anthropometric characteristics like body fat and body mass index. Soccer groups improve their performances at all fitness tests (p<0.05). The U10 control group didn't increase its performance in abdominal test and the U12 level control group didn't improve in the abdominal test nor Yo-Yo IE1 test. Soccer groups in all ages indicated greater improvements than control groups (p<0.05). In conclusion soccer training four times per week can improve the physical fitness of U10 and U12 children's.

#6 Prevalence of vitamin D deficiency amongst soccer athletes and effects of 8 weeks supplementation
Reference: J Sports Med Phys Fitness. 2018 Oct 31. doi: 10.23736/S0022-4707.18.08551-1. [Epub ahead of print]
Authors: Teixeira P, Santos AC, Casalta-Lopes J, Almeida M, Loureiro J, Ermida V, Caldas J, Fontes-Ribeiro C
Summary: High prevalence of vitamin D deficiency is well known around the world in risk populations. Although less is known about the athletic population, some studies report vitamin D deficiency amongst athletic population and adequate vitamin D levels are crucial for athletic population as it can prevent injuries such as stress fractures and might even have ergogenic effects for example on muscle function. The main objectives were to evaluate the basal serum levels of 25(OH)D and calcium in professional soccer athletes on the latitude 40 ̊N, to evaluate the effects in 25(OH)D and calcium serum levels following supplementation of 1667 IU/day of cholecalciferol during a period of 8 weeks and evaluate eventual toxicity arising from it. 28 professional athletes were evaluated according to the skin type. Basal serum levels of 25(OH)D and calcium were evaluated during winter months. Athletes were then supplemented with cholecalciferol 25.000 IU every two weeks. Serum levels of 25(OH)D and calcium were evaluated after supplementation. 25(OH)D initially ranged between 9.9 ng/mL and 32.9 ng/mL with a median of 19.2 IQR 7.24 ng/mL. A statistically significant inverse correlation exists between vitamin D deficiency and the Fitzpatrick scale (ρ= - 0,555 p=0.003). After 8 weeks, 25(OH)D ranged between 10.6 ng/mL and 43.4 ng/mL with a median of 33.2 ng/mL IQR 6.1 ng/mL. We verified a statistically significant increase of serum 25(OH) D levels (11.74 ± 5.988; IC95% [9,02; 14,47]; p<0,001. In addition, there was a statistically significant reduction of calcium: -0,36 ± 0,457; IC95% [- 0,57; -0,15]; p=0,002. Professional athletes have a high prevalence of vitamin D. Supplementation with cholecalciferol in winter months during 8 weeks is safe and effective in raising 25(OH)D serum levels. However, it may not be sufficient for athletes to reach adequate vitamin D levels.

#7 Changes in Transcranial Sonographic Measurement of the Optic Nerve Sheath Diameter in Non-concussed Collegiate Soccer Players Across a Single Season
Reference: Cureus. 2018 Aug 3;10(8):e3090. doi: 10.7759/cureus.3090.
Authors: Sadrameli SS, Wong MS, Kabir R, Wiese JR, Podell K, Volpi JJ, Gadhia RR
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Summary: Introduction Bedside ultrasound measurement of the optic nerve sheath diameter (ONSD) is emerging as a non-invasive technique to evaluate and predict raised intracranial pressure (ICP) in both children and adults. The prognostic value of increased ONSD on brain computed tomography (CT) scan has previously been correlated with increased intensive care unit (ICU) mortality in patients with severe traumatic brain injury (TBI). Previous studies have also evaluated the association between high-contact sports, such as soccer, and TBI; however, the related changes in ONSD are still unknown. The aim of this study was to evaluate for the natural evolution of changes in ONSD in athletes who participate in high-contact sports. Methods In this prospective observational study, volunteers from a collegiate women's soccer team underwent the measurement of ONSD with transcranial Doppler (TCD). ONSDs were measured during the initial visit during the pre-season period and again at the three-month follow-up. A single experienced neuro-sonographer performed all measurements to eliminate any operator bias. Results Twenty-four female college soccer players between the ages of 18 and 23 were included in this analysis. Mean ONSD during the initial pre-season clinic visit and the three-month follow-up were 4.14±0.6 mm and 5.02±0.72 mm, respectively (P < 0.0001). A two-tailed t-test analysis was performed, which resulted in a t-value of 4.76 and P < 0.00001. The average ONSD measured during the post-season follow-up showed a 21.3% increase compared to the baseline. Conclusion The evaluation of high-contact sports athletes is limited due to the lack of objective radiologic and diagnostic tools. Moreover, in an athlete suffering a concussion, return-to-play decisions are heavily dependent on the symptoms reported by the athletes. In our analysis of collegiate women's soccer players, active participation in soccer competitions and practice may be associated with an increase in ONSD, independent of concussions. Further studies are underway to evaluate the clinical significance of these findings as well as possible correlations between concussions and changes in ONSD.

#8 Changes in Sport Nutrition Knowledge, Attitudes/Beliefs and Behaviors Following a Two-Year Sport Nutrition Education and Life-Skills Intervention among High School Soccer Players
Reference: Nutrients. 2018 Nov 2;10(11). pii: E1636. doi: 10.3390/nu10111636.
Authors: Patton-Lopez MM, Manore MM, Branscum A, Meng Y, Wong SS
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Summary: The purpose of this study was to examine the impact of a sport nutrition education and life-skills intervention on sport nutrition knowledge (SNK), attitudes/beliefs and dietary behaviors relevant to sport nutrition among high school (HS) soccer players. Three assessments were done over the 2-year intervention (baseline = time 1, end year 1 = time 2, end year 2 = time 3). Participants (n = 217; females = 64%; Latino = 47.5%; 14.9 ± 0.9-year; 46.5% National School Breakfast/Lunch Program) were assigned to an intervention group (IG, n = 153; 9 schools) or comparison group (CG, n = 64; 4 schools) based on geographical location. Differences over time were examined based on group, sex, socioeconomic status (SES) and race/ethnicity. The IG increased SNK scores by ~10% (time 1 = 51.6%; time 3 = 60.9%; p ≤ 0.001), with the greatest change in the female IG vs. CG and no differences in male IG vs. CG. Daily breakfast consumption was 53.7% in both groups. IG players were 3 times more likely (95%CI = 2.59, 7.77) to report trying to eat for performance (IG = 48.7% vs. CG = 30.2%). By time 3, IG players were less likely to report that 'diet met nutritional requirements' (31.6%) compared to CG (47.6%). For IG, the consumption of lunch (≥5-days/week) did not change (92.2⁻93.4%), but declined in the CG (90.6%) (p = 0.04). No other differences by sub-population (race/ethnicity, SES) were observed. Our findings indicate that HS athletes are motivated to learn and improve diet behaviors, and benefit from team-based nutrition interventions. Future interventions should consider delivery of curriculum/experiential learning during a defined training period, with messages reinforced with supports at home, school and athletic settings.

#9 Effects of the pitch configuration design on players' physical performance and movement behaviour during soccer small-sided games
Reference: Res Sports Med. 2018 Nov 5:1-16. doi: 10.1080/15438627.2018.1544133. [Epub ahead of print]
Authors: Coutinho D, Gonçalves B, Santos S, Travassos B, Wong DP, Sampaio J
Summary: This study aimed to identify the effects of different pitch configurations on youth players positional and physical performances. Forty players participated in a Gk + 5vs5 + Gk small-sided game under four conditions: regular condition (regular), pitch with the direction of competitive matches; sided condition (sided), goals were changed to width; different pitch orientation (≠orientation), performed in side-to-side line compared to competitive matches; dynamic pitch (dynamic), boundaries were randomly changed every minute by: regular pitch; decrease 6 m width; diamond shape. The following variables were considered: players' effective playing space, distance between teammates' dyads time spent synchronized, average speed and a ratio between the distance covered at different intensities and distance covered while recovering. Overall, players exhibited better performances in pitches that are more representative of the environmental information seen during competitive matches (regular and ≠orientation). However, coaches may also use different boundary conditions to promote the players' ability to adapt to different context information.

#10 Chronic Ingestion of Sodium and Potassium Bicarbonate, with Potassium, Magnesium and Calcium Citrate Improves Anaerobic Performance in Elite Soccer Players
Reference: Nutrients. 2018 Nov 1;10(11). pii: E1610. doi: 10.3390/nu10111610.
Authors: Chycki J, Golas A, Halz M, Maszczyk A, Toborek M, Zajac A
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Summary: Anaerobic power and anaerobic capacity significantly influence performance in many sport disciplines. These include prolonged sprints in athletics, swimming, or cycling, and other high intensity intermittent sports, such as soccer or basketball. Considering the association of exercise-induced acidosis and fatigue, the ingestion of potential buffering agents such as sodium bicarbonate, has been suggested to attenuate metabolic acidosis and improve anaerobic performance. Since elite soccer players cover from 200 to 350 m while sprinting, performing 40⁻60 all out sprints during a game, it seems that repeated sprint ability in soccer players is among the key components of success. In our experiment, we evaluated the effectiveness of chronic supplementation with sodium and potassium bicarbonate, fortified with minerals, on speed and speed endurance in elite soccer players. Twenty-six soccer players participated in the study. The subjects were randomly divided into two groups. The experimental group was supplemented with sodium bi-carbonate and potassium di-carbonate fortified with minerals, while the control group received a placebo. The athletes were tested at baseline and after nine days of supplementation. Anaerobic performance was evaluated by the Repeated Anaerobic Sprint Test (RAST) protocol which involved 6 × 30 m max sprints, separated by 10 s of active recovery. Resting, post ingestion and post exercise concentrations of HCO₃- and blood pH were measured as well as lactate concentration. The current investigation demonstrated a significant increase in RAST performance of elite soccer players supplemented with sodium and potassium bicarbonate along with calcium phosphate, potassium citrate, and magnesium citrate ingested twice a day over a nine-day training period. The improvements in anaerobic performance were caused by increased resting blood pH and bicarbonate levels.

#11 Epidemiology of injury in English Professional Football players: A cohort study
Reference: Phys Ther Sport. 2018 Oct 29;35:18-22. doi: 10.1016/j.ptsp.2018.10.011. [Epub ahead of print]
Authors: Jones A, Jones G, Greig N, Bower P, Brown J, Hind K, Francis P
Summary: The purpose was to estimate the current incidence and location of injury in English professional football. Professional football players (243 players from 10 squads (24.3 ± 4.21 per squad)) competing in the English Football League and National Conference took part in this study. Injury incidence, training and match exposure were collected in accordance with the international consensus statement on football injury epidemiology. 473 injuries were reported. The estimated incidence of injury was, 9.11 injuries/1000 h of football related activity. There was a higher incidence of injury during match play (24.29/1000 h) compared to training (6.84/1000 h). The thigh was the most common site of injury (31.7%), muscle strains accounted for 41.2% of all injuries. The hamstrings were the most frequently strained muscle group, accounting for 39.5% of all muscle strains and 16.3% of all injuries. Moderate severity injuries (8-28 days) were the most common (44.2%). Incidence of injury has increased over the last 16 years with muscle strains remaining the most prevalent injury. The hamstrings remain the most commonly injured muscle group.

#12 Evidence for a Role of ACTN3 R577X Polymorphism in Football Player's Career Progression
Reference: Int J Sports Med. 2018 Nov 6. doi: 10.1055/a-0753-4973. [Epub ahead of print]
Authors: Coelho DB, Pimenta EM, Rosse IC, de Castro BM, Becker LK, de Oliveira EC, Carvalho MRS, Garcia ES
Summary: The aim was to investigate a possible role of the ACTN3 R577X polymorphism in a Brazilian football player's career progression. 2 questions were formulated: 1. Does ACTN3 polymorphism affect the probability of an individual being a professional football player? 2. Does this polymorphism affect the progression of the athlete throughout his career? The study included 353 players from first division Brazilian football clubs in the following categories: under-14 (U-14), U-15, U-17, U-20, and professional (PRO). The control group (CON) was composed of 100 healthy non-athletes. The chi-squared test was used to assess differences between the allele and genotype frequencies. Comparing football categories, the XX genotype was less frequent among professional players than in the U-20 (p<0.05) or the U-15 category (p<0.05). The RX genotype also presented more frequently in the PRO category than the U-14 category (p<0.05). Moreover, a trend towards a higher frequency of the RX genotype and a lower frequency of the XX genotype was observed in the professional category compared to U-20. These results suggest that the genotype in the ACTN3 polymorphism affects the probability of a football player progressing throughout his career and becoming professional, meaning that playing football selects against the ACTN3 XX genotype.

#13 MRI characteristics of adductor longus lesions in professional football players and prognostic factors for return to play
Reference: Eur J Radiol. 2018 Nov;108:52-58. doi: 10.1016/j.ejrad.2018.09.018. Epub 2018 Sep 17.
Authors: Pezzotta G, Pecorelli A, Querques G, Biancardi S, Morzenti C, Sironi S
Summary: The purpose was to correctly define through Magnetic Resonance Imaging (MRI), diagnosis, staging and prognosis of the adductor longus (AL) acute lesions and to identify a correlation between Return to Play (RTP) and sport-related injury predisposing conditions and complications. Twenty professional football players with acute groin pain and clinical suspicion of AL injury subsequent to sport's activity were evaluated. MRI examinations were performed by one and reviewed by other two radiologists with more than 10 years of experience. Lesions were stratified according to both Munich consensus statement and British Athletics Muscle Injury Classification (BAMIC). Patients were monitored until clinical recovery occurred. According to the Munich consensus statement, 75% of lesions were defined as type 3 and 25%as type 4; while according to the BAMIC, 45% were considered as Grade 1, 20% as Grade 2, 10% as Grade 3, and 25% as Grade 4. RTP was 1-2 weeks for minor lesions (45%), 4-6 weeks for moderate lesions (30%), and more than 6 weeks for complete lesions (25%). Both BAMIC and Munich consensus significantly correlated with RTP (R = 0.958 and 0.974, respectively). The extent of gap was the only independent prognosticator of RTP always present in all three different models of multivariate analysis (p < 0.006, p < 0.002, and p < 0.001, respectively). MRI represents the gold standard imaging technique for the evaluation of AL due to its ability not only to recognize but also to classify acute lesions and define patient's prognosis. MRI is also useful to detect potential predisposing conditions and complications, which may correlate with RTP.

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