Latest research in football - week 15 - 2017

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 ACTN3/ACE genotypes and mitochondrial genome in professional soccer players’ performance
Reference: J Biol Regul Homeost Agents. 2017 Jan-Mar;31(1):207-213.
Authors: Galeandro V, Notarnicola A, Bianco A, Tafuri S, Russo L, Pesce V, Moretti B, Petruzzella V
Summary: Two nuclear genes, ACTN3, encoding for the α-actinin skeletal muscle isoform 3, and ACE encoding the angiotensin-converting enzyme, have both been associated with quantitative physical performance traits in the general population. The purpose of our study was to assess the association between the two nuclear gene variants, R577X (rs1815739) in ACTN3 and I/D (rs4340) in ACE, with elite athletes’ performance and the effect of training on the mitochondrial DNA (mtDNA) content in peripheral blood. We evaluated the genotypes and frequencies of ACTN3 R577X and ACE I/D polymorphisms between soccer players (n = 43) and healthy non-athletic controls (n = 128). Total DNA was extracted from peripheral blood samples using the standard procedure. The genotypes were assessed by PCR-RFLP analysis and mtDNA cellular content by RT-PCR. The soccer players showed a tendency to a prevalence of ACTN3RR and ACEDD genotypes both independently and in co-occurrence. The effect of physical training on the mitochondrial DNA content in the athletic population was reflected strikingly in its increase in peripheral blood. Based on our results, we suggest that the analysis of ACTN3 and ACE genotypes could predict talent in the soccer field and that knowledge of the genetic variants could determine types and training times for soccer players. In addition, the novelty of this work, never before described in the sports literature, is that the increase of mitochondrial content can be correlated with the training load, suggesting that the mtDNA copy number may be considered a viable bioenergetics biomarker.

#2 Strength and endurance training reduces the loss of eccentric hamstring torque observed after soccer specific fatigue
Reference: Phys Ther Sport. 2017 Feb 2;25:39-46. doi: 10.1016/j.ptsp.2017.01.006. [Epub ahead of print]
Authors: Matthews MJ, Heron K, Todd S, Tomlinson A, Jones P, Delextrat A, Cohen DD
Summary: The purpose was to investigate the effect of two hamstring training protocols on eccentric peak torque before and after soccer specific fatigue. Twenty-two university male soccer players participated in this study. Isokinetic strength tests were performed at 60°/s pre and post fatigue, before and after 2 different training interventions. A 45-min soccer specific fatigue modified BEAST protocol (M-BEAST) was used to induce fatigue. Players were randomly assigned to a 4 week hamstrings conditioning intervention with either a maximum strength (STR) or a muscle endurance (END) emphasis. The following parameters were evaluated: Eccentric peak torque (EccPT), angle of peak torque (APT), and angle specific torques at knee joint angles of 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° and 90°. There was a significant effect of the M-BEAST on the Eccentric torque angle profile before training as well as significant improvements in post-fatigue torque angle profile following the effects of both strength and muscle endurance interventions. Forty-five minutes of simulated soccer activity leads to reduced eccentric hamstring torque at longer muscle lengths. Short-term conditioning programs (4-weeks) with either a maximum strength or a muscular endurance emphasis can equally reduce fatigue induced loss of strength over this time period.

#3 Sport Nutrition Knowledge, Behaviors and Beliefs of High School Soccer Players
Reference: Nutrients. 2017 Apr 1;9(4). pii: E350. doi: 10.3390/nu9040350.
Authors: Manore MM, Patton-Lopez MM, Meng Y, Wong SS
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Summary: For adolescent athletes (14-18 years), data on sport nutrition knowledge, behaviors and beliefs are limited, especially based on sex, race/ethnicity and socioeconomic status. High school soccer players (n = 535; 55% female; 51% White, 41% Latino; 41% National School Lunch Program (NSLP) participants (80% Latino)) completed two questionnaires (demographic/health history and sport nutrition). The sport nutrition knowledge score was 45.6% with higher scores in NSLP-Whites vs. NSLP-Latinos (p < 0.01). Supplement knowledge differed by sex (16% lower in females; p = 0.047) and race/ethnicity (33% lower in Latinos; p < 0.001). Breakfast consumption was 57%; females ate breakfast less (50%) than males (60%; p < 0.001); NSLP-participants ate breakfast less (47%) than non-NSLP (62%; p < 0.001). Supplement use was 46%, with Latinos using more supplements than Whites do (p = 0.016). Overall, 30% used protein shakes, with females using less than males (p = 0.02), while use was twice as likely in Latino vs. White (p = 0.03). Overall, 45% reported their nutrient requirements were different from non-athlete peers. Latinos were less likely (p = 0.03) to report that their diet met nutritional requirements, but more than twice as likely to report that nutritional supplements were necessary for training (p < 0.001). Adolescent athletes, especially females and Latinos, would benefit from sport nutrition education that enhances food selection skills for health and sport performance.

#4 Effects of a 12-Month Complex Proprioceptive-Coordinative Training Program on Soccer Performance in Prepubertal Boys Aged 10-11 Years
Reference: J Strength Cond Res. 2017 Mar 31. doi: 10.1519/JSC.0000000000001878. [Epub ahead of print]
Authors: Boraczynski M, Sozanski H, Boraczynski T
Summary: The aim was to examine the effects of a series of on-field proprioceptive-coordinative (P-C) exercises on motor performance (MP) in prepubertal soccer players. Fifty-three male soccer players aged 10.1-11.8 years were randomized among two experimental programs receiving P-C training (P-CT; n = 26) or regular training (RT; n = 27). A control group (C; n = 22) consisted of age-matched (10.3-11.9 years) cohorts not involved in any regular physical activity. Both experimental groups completed an identical 12-month comprehensive soccer program except training in P-CT was modified to substitute small-sided conditioning games with 24 multi-mode P-C exercises with modulated exercise intensity (every 8-9 weeks based on predicted HRmax). Pre-, peri-, and post-training measures included anthropometry and five tests assessing soccer-specific MP: movement rhythm (turning the ball backwards - T1), motor adaptation (running with the ball around poles - T2), spatial orientation (running to sequentially numbered balls - T3), balance (single-leg static balance - T4), and kinesthetic differentiation of movement (landing the ball on a 2 × 2 m sector - T5). Repeated measures ANOVA revealed no significant between-group differences for age, anthropometry and BF% at baseline. Significant main effects for group (P-CT vs. RT) were found in all tests (T1-T5) and main effects for time (group P-CT) in T3-T5, while a significant group × time interaction was observed only in T4 (F = 2.98, p = 0.0204). Post-hoc tests indicated that P-CT attained significantly better results than RT at peri-training (by 26.4%; p < 0.01) and post-training (by 31.9%, p < 0.01). Modulated exercise intensity had little effect on soccer performance (T1-T3, T5). Based on the results, it is recommended that the training of young soccer players be supplemented with the bilateral balance exercises and games employed in the study. Furthermore, the suitability of monitoring HR in P-C exercises targeting the analyzed MP skills is questionable.

#5 Cut-offs of isokinetic strength ratio and hamstring strain prediction in professional soccer players
Reference: Scand J Med Sci Sports. 2017 Apr 4. doi: 10.1111/sms.12890. [Epub ahead of print]
Authors: Dauty M, Menu P, Fouasson-Chailloux A
Summary: Hamstring strain injuries frequently occur during professional soccer practice. Low hamstring strength represents an intrinsic modifiable risk factor but cut-offs of isokinetic knee strength ratios are controversial to predict hamstring strain in professional soccer players. We aimed to predict hamstring strain in accordance to cut-offs of isokinetic knee strength ratios. Bilateral, conventional and functional isokinetic strength ratios were calculated in 194 professional soccer players at the beginning of 15 consecutive seasons. 36 soccer players presented a moderate hamstring strain and 158 were not injured. The different calculated isokinetic ratios were compared with the right and left limb of the uninjured population. Different usual cut-offs were tested: at 0.85 and 0.90 for the bilateral concentric and eccentric hamstring-to-hamstring ratio, at 0.60 and 0.47 for the conventional hamstring-to-quadriceps ratio and at 0.80 and 1 for the mixed hamstring-to-quadriceps ratio. The specific ratios for the studied population were also determined by the 10th percentile and then tested. Hamstring strain prediction was established in term of odds ratios. No cut-off with bilateral, conventional or functional isokinetic strength ratio was predictive of hamstring strain after univariate analysis. Specific cut-offs determined from the studied population were not more predictive. Very few injured soccer players presented values under the cut-offs at 0.47 for the conventional ratio and at 0.80 for the mixed ratio. Regardless of their values, cut-offs of isokinetic strength ratios were not predictive of hamstring injuries. The use of isokinetic cut-offs is not recommended to predict hamstring muscle strain in professional soccer players.

#6 Case Study: Hydration Intervention Improves Pre-game Hydration Status in Female Collegiate Soccer Players
Reference: Int J Sport Nutr Exerc Metab. 2017 Apr 7:1-18. doi: 10.1123/ijsnem.2016-0209. [Epub ahead of print]
Authors: Hoerner NR, Domnik K, Koehler K, Schaenzer W, Braun H
Summary: Little is known about whether athletes follow hydration guidelines. The objective of the present study was to assess fluid status in female soccer players in a hot and humid environment, and to assess the effect of an intervention aimed at preventing players from exercising in a dehydrated state. We hypothesized that following the intervention, players would exhibit improved hydration status, as indicated by greater voluntary fluid intake and improved hydration markers. Ten female collegiate soccer players (20±1yrs., 64±9kg) participated in this seven-week study. Changes in body weight (BW), fluid intake, urine color (UC), and urine specific gravity (USG) were measured periodically over three days. Dehydration was classified as USG ≥1.020g/ml and UC >3. Following a 7- week intervention (to individualize hydration strategies), BW, fluid intake, UC, and USG were again measured on two game days to evaluate the impact of the intervention. Pre-test: five players started exercising dehydrated (USG 1.029g/ml; UC 6). Seven players were dehydrated before the next morning practice session (USG 1.029g/ml; UC 5). Five players had a mean BW loss of 2.5%.Post-test: four players were dehydrated before game 1. Despite hydration guidelines, two players experienced tiredness and cramps during the second half. Six players were dehydrated 4h before game 2 and subsequently received individual rehydration instructions. 2h before game 2, none of the players were dehydrated. No symptoms of tiredness or cramps were reported. Hydration status assessment coupled with an intervention of individualized drinking strategies, can prevent female soccer players from exercising in a dehydrated state.

#7 n-3 Fatty Acid Supplementation During 4 Weeks of Training Leads to Improved Anaerobic Endurance Capacity, But Not Maximal Strength, Speed, or Power in Soccer Players
Reference: Int J Sport Nutr Exerc Metab. 2017 Apr 7:1-25. doi: 10.1123/ijsnem.2016-0325. [Epub ahead of print]
Authors: Gravina L, Brown FF, Alexander L, Dick J, Bell G, Witard OC, Galloway SD
Summary: Omega-3 fatty acid (n-3 FA) supplementation could promote adaptation to soccer-specific training. We examined the impact of a 4 wk period of n-3 FA supplementation during training on adaptations in 1RM knee extensor strength, 20m sprint speed, vertical jump power, and anaerobic endurance capacity (Yo-Yo test) in competitive soccer players. Twenty six soccer players were randomly assigned to one of two groups: n-3 FA supplementation (n-3 FA; n=13) or placebo (n=13). Both groups performed two experimental trial days. Assessments of physical function and respiratory function were conducted pre (PRE) and post (POST) supplementation. Training session intensity, competitive games and nutritional intake were monitored during the 4 wk period. No differences were observed in respiratory measurements (FEV1, FVC) between groups. No main effect of treatment was observed for 1RM knee extensor strength, explosive leg power, or 20 m sprint performance, but strength improved as a result of the training period in both groups (p<0.05). Yo-Yo test distance improved with training in the n-3 FA group only (p<0.01). The mean difference (95% CI) in Yo-Yo test distance completed from PRE to POST was 203 (66 to 340) m for n-3 FA, and 62 (-94 to 217) m for placebo, with a moderate effect size (Cohen's d of 0.52). We conclude that 4 wk of n-3 FA supplementation does not improve strength, power or speed assessments in competitive soccer players. However, the increase in anaerobic endurance capacity evident only in the n-3 FA treatment group suggests an interaction that requires further study.

#8 Left ventricular biomechanics in professional football players
Reference: Scand J Med Sci Sports. 2017 Apr 4. doi: 10.1111/sms.12893. [Epub ahead of print]
Authors: von Lueder TG, Hodt A, Gjerdalen GF, Steine K
Summary: Chronic exercise induces adaptive changes of left ventricular (LV) ejection and filling capacities which may be detected by novel speckle-tracking echocardiography (STE) and tissue Doppler imaging (TDI)-based techniques. 103 consecutive male elite Norwegian soccer players and 46 age-matched healthy controls underwent echocardiography at rest. STE was used to assess LV torsional mechanics and LV systolic longitudinal strain (LS). Diastolic function was evaluated by trans-mitral blood flow, mitral annular velocities by TDI, and LV inflow propagation velocity by colour M-mode. Despite similar global LS, players displayed lower basal wall and higher apical wall LS values vs controls, resulting in an incremental base-to-apex gradient of LS. Colour M-mode and TDI-derived data were similar in both groups. Peak systolic twist rate (TWR) was significantly lower in players (86.4 ± 2.8 vs controls 101.9 ± 5.2 deg/s, P<0.01). Diastolic untwisting rate (UTWR) was higher in players (-124.5 ± 4.2 vs -106.9 ± 6.7 deg/s) and peaked earlier during the cardiac cycle (112.7 ± 0.8 vs 117.4 ± 2.4% of systole duration, both P<0.05). Untwisting/twisting ratio (-1.48 ± 0.05 vs -1.11 ± 0.08; P <0.001) and untwisting performance (=UTR/TW; -9.25 ± 0.34 vs -7.38 ± 0.40 s-1 , P<0.01) were increased in players. Augmented diastolic wall strain (DWS), a novel measure of LV compliance in players was associated with improved myocardial mechanical efficiency. The described myocardial biomechanics may underlie augmented exertional cardiac function in athletes and may have a potential role to characterize athlete's heart by itself or to distinguish it from hypertensive or hypertrophic cardiomyopathy.

#9 Isolated HAGL lesion after arthroscopic Bankart repair in a professional soccer player
Reference: Phys Sportsmed. 2017 Mar 29:1-4. doi: 10.1080/00913847.2017.1309955. [Epub ahead of print]
Authors: Celik H, Seckin MF, Kara A, Akman S
Summary: Post-traumatic anterior shoulder instability commonly occurs following an avulsion of capsulolabral complex from glenoid (Bankart lesion) or rarely after humeral avulsion of the glenohumeral ligaments (HAGL lesion). Arthroscopic Bankart repair offers high success rates of healing. However, trauma following the treatment may cause implant failure or re-avulsion of the treated tissue. We aim to present the diagnosis and treatment of an isolated HAGL lesion in a professional soccer player who had previously undergone arthroscopic Bankart repair.

#10 Daily Distribution of Carbohydrate, Protein and Fat Intake in Elite Youth Academy Soccer Players Over a 7-Day Training Period
Reference: Int J Sport Nutr Exerc Metab. 2016 Oct;26(5):473-480. Epub 2016 Aug 24.
Authors: Naughton RJ, Drust B, O'Boyle A, Morgans R, Abayomi J, Davies IG, Morton JP, Mahon E.
Summary: While traditional approaches to dietary analysis in athletes have focused on total daily energy and macronutrient intake, it is now thought that daily distribution of these parameters can also influence training adaptations. Using 7-day food diaries, we quantified the total daily macronutrient intake and distribution in elite youth soccer players from the English Premier League in U18 (n = 13), U15/16 (n = 25) and U13/14 squads (n = 21). Total energy (43.1 ± 10.3, 32.6 ± 7.9, 28.1 ± 6.8 kcal·kg-1·day-1), CHO (6 ± 1.2, 4.7 ± 1.4, 3.2 ± 1.3 g·kg-1·day-1) and fat (1.3 ± 0.5, 0.9 ± 0.3, 0.9 ± 0.3 g·kg-1·day-1) intake exhibited hierarchical differences (p < .05) such that U13/14 > U15/16 > U18. In addition, CHO intake in U18s was lower (p < .05) at breakfast, dinner and snacks when compared with both squads but no differences were apparent at lunch. Furthermore, the U15/16s reported lower relative daily protein intake than the U13/14s and U18s (1.6 ± 0.3 vs. 2.2 ± 0.5, 2.0 ± 0.3 g·kg-1). A skewed distribution (p < .05) of daily protein intake was observed in all squads, with a hierarchical order of dinner (~0.6 g·kg-1) > lunch (~0.5 g·kg-1) > breakfast (~0.3 g·kg-1). We conclude elite youth soccer players do not meet current CHO guidelines. Although daily protein targets are achieved, we report a skewed daily distribution in all ages such that dinner > lunch > breakfast. Our data suggest that dietary advice for elite youth players should focus on both total daily macronutrient intake and optimal daily distribution patterns.

American Football
#1 Epidemiology of Sport-Related Concussions in High School Athletes: National Athletic Treatment, Injury and Outcomes Network (NATION), 2011-2012 Through 2013-2014

Reference: J Athl Train. 2017 Mar;52(3):175-185. doi: 10.4085/1062-6050-52.1.15.

Authors: O'Connor KL, Baker MM, Dalton SL, Dompier TP, Broglio SP, Kerr ZY

Summary: Sports participation is one of the leading causes of concussions among nearly 8 million US high school student-athletes. The objective was to describe the epidemiology of sport-related concussion (SRC) in 27 high school sports during the 2011-2012 through 2013-2014 academic years. Aggregate injury and exposure data from 27 sports in 147 high schools in the National Athletic Treatment, Injury and Outcomes Network (NATION). Boy and girl high school athletes during the 2011-2012 through 2013-2014 academic years were analyzed. Sport-related concussion counts, percentages, rates per 10 000 athlete-exposures (AEs), rate ratios (RRs), and injury proportion ratios (IPRs) were reported with 95% confidence intervals (CIs). Rate ratios and IPRs with 95% CIs not containing 1.0 were considered significant. Overall, 2004 SRCs were reported among 27 high school sports, for a rate of 3.89 per 10 000 AEs. Football had the highest SRC rate (9.21/10 000 AEs), followed by boys' lacrosse (6.65/10 000 AEs) and girls' soccer (6.11/10 000 AEs). The SRC rate was higher in competition than in practice (RR = 3.30; 95% CI = 3.02, 3.60). Among sex-comparable sports, the SRC rate was higher in girls than in boys (RR = 1.56; 95% CI = 1.34, 1.81); however, the proportion of SRCs due to player-to-player contact was higher in boys than in girls (IPR = 1.48; 95% CI = 1.27, 1.73). Common symptoms reported among all athletes with SRCs were headache (94.7%), dizziness (74.8%), and difficulty concentrating (61.0%). Only 0.8% of players with SRCs returned to play within 24 hours. The majority of athletes with SRCs (65.8%) returned to play between 7 and 28 days. More players had symptoms resolve after 7 days (48.8%) than less than a week (40.7%). Our findings provide updated high school SRC incidence estimates and further evidence of sex differences in reported SRCs. Few athletes with SRCs returned to play within 24 hours or a week. Most injured players returned after 7 days, despite a smaller proportion having symptoms resolve within a week.

#2 Head-Impact-Measurement Devices: A Systematic Review

Reference: J Athl Train. 2017 Mar;52(3):206-227. doi: 10.4085/1062-6050.52.2.05.

Authors: O'Connor KL, Rowson S, Duma SM, Broglio SP

Summary: With an estimated 3.8 million sport- and recreation-related concussions occurring annually, targeted prevention and diagnostic methods are needed. Biomechanical analysis of head impacts may provide quantitative information that can inform both prevention and diagnostic strategies. The objective of the study was to assess available head-impact devices and their clinical utility. We performed a systematic search of the electronic database PubMed for peer-reviewed publications, using the following phrases: accelerometer and concussion, head impact telemetry, head impacts and concussion and sensor, head impacts and sensor, impact sensor and concussion, linear acceleration and concussion, rotational acceleration and concussion, and xpatch concussion. In addition to the literature review, a Google search for head impact monitor and concussion monitor yielded 15 more devices. Included studies were performed in vivo, used commercially available devices, and focused on sport-related concussion. One author reviewed the title and abstract of each study for inclusion and exclusion criteria and then reviewed each full-text article to confirm inclusion criteria. Controversial articles were reviewed by all authors to reach consensus. In total, 61 peer-reviewed articles involving 4 head-impact devices were included. Participants in boxing, football, ice hockey, soccer, or snow sports ranged in age from 6 to 24 years; 18% (n = 11) of the studies included female athletes. The Head Impact Telemetry System was the most widely used device (n = 53). Fourteen additional commercially available devices were presented. Measurements collected by impact monitors provided real-time data to estimate player exposure but did not have the requisite sensitivity to concussion. Proper interpretation of previously reported head-impact kinematics across age, sport, and position may inform future research and enable staff clinicians working on the sidelines to monitor athletes. However, head-impact-monitoring systems have limited clinical utility due to error rates, designs, and low specificity in predicting concussive injury.

#3 American-Style Football Players as Modern Gladiators: Could Heart Rate Provide All Answers?

Reference: JACC Cardiovasc Imaging. 2017 Apr;10(4):495-496. doi: 10.1016/j.jcmg.2016.12.015.

Authors: Tadic M, Cuspidi C, Ivanovic B.

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