Friday, September 21, 2012

Interventions to prevent ACL injuries-Recent studies in football (Part III)

Recent studies in football –Part III
Abstracts modified from PubMed
Gagnier JJ, Morgenstern H, Chess L. Interventions Designed to Prevent Anterior Cruciate Ligament Injuries in Adolescents and Adults: A Systematic Review and Meta-analysis. Am J Sports Med. 2012 Sep 12. [Epub ahead of print]
Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan.
Anterior cruciate ligament (ACL) injuries are common, result in significant morbidity, and are expensive to repair surgically and to rehabilitate. Several randomized and observational studies have tested neuromuscular interventions as preventive measures for these injuries. The aim of this study was to conduct a systematic review and meta-analysis of all known comparative studies for estimating and testing the effect of neuromuscular and educational interventions on the incidence of ACL injuries in adolescents and adults, both male and female. Several databases were used to identify eligible studies through July 4, 2011: MEDLINE, EMBASE, SPORTDiscus, Cumulative Index to Nursing and Allied Health Literature, the Cochrane Central Register of Controlled Trials, and Health Technology Assessment. Eligible studies were assessed for risk of bias, and meta-analyses were performed on the estimated intervention effect (log incidence rate ratio) using inverse-variance weighting, subgroup analysis, and random-effects meta-regression to estimate the overall (pooled) effect and explore heterogeneity of effect across studies (measured by I(2) and tested with the Q statistic). Eight cohort (observational) studies and 6 randomized trials were included, involving a total of approximately 27,000 participants. The random-effects meta-analysis yielded a pooled rate-ratio estimate of 0.485 (95% confidence interval [CI], 0.299-0.788; P = .003), indicating a lower ACL rate in the intervention groups, but there was appreciable heterogeneity of the estimated effect across studies (I(2) = 64%; P = .001). In the meta-regressions, the estimated effect was stronger for studies that were not randomized, performed in the United States, conducted in soccer players, had a longer duration of follow-up (more than 1 season), and had more hours of training per week in the intervention group, better compliance, and no dropouts. Nevertheless, residual heterogeneity was still observed within subgroups of those variables (I(2) > 50%; P < .10).

Conclusion: Various types of neuromuscular and educational interventions appear to reduce the incidence rate of ACL injuries by approximately 50%, but the estimated effect varied appreciably among studies and was not able to explain most of that variability.

Hoier B, Nordsborg N, Andersen S, Jensen L, Nybo L, Bangsbo J, Hellsten Y. Pro- and anti-angiogenic factors in human skeletal muscle in response to acute exercise and training. J Physiol. 2012 Feb 1;590(Pt 3):595-606. Epub 2011 Dec 12.
Department of Exercise and Sport Sciences, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen, Denmark.
This study examined the effect of acute exercise and 4 weeks of aerobic training on skeletal muscle gene and protein expression of pro- and anti-angiogenic factors in 14 young male subjects. Training consisted of 60 min of cycling (60% of ), 3 times/week. Biopsies were obtained from vastus lateralis muscle before and after training. Muscle interstitial fluid was collected during cycling at weeks 0 and 4. Training increased (P < 0.05) the capillary: fibre ratio and capillary density by 23% and 12%, respectively. The concentration of interstitial vascular endothelial growth factor (VEGF) in response to acute exercise increased similarly (>6-fold; P < 0.05) before and after training. Resting protein levels of soluble VEGF receptor-1 in interstitial fluid, and of VEGF, thrombospondin-1 (TSP-1) and tissue inhibitor of matrix metalloproteinase-1 (TIMP1) in muscle were unaffected by training, whereas endothelial nitric oxide synthase protein levels in muscle increased by 50% (P < 0.05). Before and after training, acute exercise induced a similar increase (P < 0.05) in the mRNA level of angiopoietin 2, matrix metalloproteinase 9 and TSP-1. After training, TIMP1 mRNA content increased with exercise (P < 0.05).

Conclusions: Acute exercise induced a similar increase in the gene-expression of both pro- and anti-angiogenic factors in untrained and trained muscle. We propose that the increase in anti-angiogenic factors with exercise is important for modulation of angiogenesis. The lack of effect of training on basal muscle VEGF protein levels and VEGF secretion during exercise suggests that increased VEGF levels are not a prerequisite for exercise-induced capillary growth in healthy muscle.

Hoier B, Passos M, Bangsbo J, Hellsten Y. Intense intermittent exercise provides weak stimulus for VEGF secretion and capillary growth in skeletal muscle. Exp Physiol. 2012 Sep 7. [Epub ahead of print]

University of Copenhagen, Copenhagen, Denmark;
The effect of acute intense intermittent exercise compared to moderate intensity exercise, on angiogenic factors and the effect of four weeks of intense intermittent training on capillary growth were examined in nine young healthy males, pre-conditioned by moderate intensity endurance training. The intense training consisted of 24 one-min cycling bouts at an initial work rate of 316 ± 19W (~117% of pre VO2 max), performed 3 times/week. Skeletal muscle biopsies and muscle microdialysates were otained from m.v. lateralis before, during, and after acute exercise performed at either moderate or high intensity. Comparison of the response in angiogenic factors to acute moderate versus high intensity exercise, performed prior to the intense training intervention, revealed that intense exercise resulted in a markedly lower (~60%; P < 0.05) increase in interstitial VEGF than did moderate intensity exercise. Muscle interstitial fluid obtained during moderate intensity exercise increased endothelial cell proliferation in vitro more than interstitial fluid obtained during intense exercise (6-fold vs. 2.5-fold, respectively; P < 0.05). The four weeks of high intensity training did not lead to an increased capillarization in the muscle but abolished the exercise induced increase in mRNA for several angiogenic factors, increased the eNOS protein levels, lowered TSP-1 protein levels in muscle but increased interstitial TSP-1 protein levels.
Conclusions: Intense intermittent exercise provides a weak stimulus for VEGF secretion and endothelial cell proliferation and that intense intermittent training does not induce a sufficient angiogenic stimulus to induce capillary growth in muscle previously conditioned by moderate intensity exercise.

Gunnarsson TP, Christensen PM, Holse K, Christiansen D, Bangsbo J. Effect of additional speed endurance training on performance and muscle adaptations. Med Sci Sports Exerc. 2012 Oct;44(10):1942-8.
Department of Exercise and Sport Sciences, Section of Human Physiology, University of Copenhagen, DENMARK.
The present study examined the effect of additional speed endurance training (SET) during the season on muscle adaptations and performance of trained soccer players. Eighteen sub-elite soccer players performed one session with six to nine 30-s intervals at an intensity of 90%-95% of maximal intensity (SET) a week for 5 wk (SET intervention). Before and after the SET intervention, the players carried out the Yo-Yo intermittent recovery level 2 (Yo-Yo IR2) test, a sprint test (10 and 30 m), and an agility test. In addition, seven of the players had a resting muscle biopsy specimen taken and they carried out a running protocol on a motorized treadmill before and after the SET intervention. After the SET intervention, the Yo-Yo IR2 test (n = 13) performance was 11% better (P < 0.05), whereas sprint (n = 15) and agility (n = 13) performances were unchanged. The expression of the monocarboxylate transporter 1 (n = 6) was 9% higher (P < 0.05). and the expression of the Na/K pump subunit β1 (n = 6) was 13% lower (P < 0.05) after the SET intervention. The Na/K pump subunits α1, α2, as well as the monocarboxylate transporter 4 and the Na/H exchanger 1 (n = 6) were unchanged. After the SET intervention, the relative number of Type IIx fibers and oxygen consumption at 10 km·h were lower (P < 0.05), whereas V˙O2max was unchanged.
Conclusions:  Adding 30 min of SET once a week during the season for trained soccer players did lead to an improved ability to perform repeated high-intensity exercise, with a concomitant increase in the expression of monocarboxylate transporter 1 and an improved running economy.

Scott BR, Lockie RG, Knight TJ, Clark AC, Janse de Jonge X AK. A Comparison of Methods to Quantify the In-Season Training Load of Professional Soccer Players. Int J Sports Physiol Perform. 2012 Sep 5. [Epub ahead of print]
Exercise and Sport Science, Faculty of Science and Information Technology, University of Newcastle, Ourimbah, New South Wales, Australia.
The aim of the study was to compare various measures of training load (TL), derived from physiological (heart rate [HR]), perceptual (rating of perceived exertion [RPE]) and physical (global positioning system [GPS] and accelerometer) data, during in-season field-based training for professional soccer. Fifteen professional male soccer players (age: 24.9 ± 5.4 yr, body mass: 77.6 ± 7.5 kg, height: 181.1 ± 6.9 cm) were assessed in-season, across 97 individual training sessions. Measures of external-TL (total distance [TD], the volume of low-speed activity [LSA; <14.4km·h-1], high-speed running [HSR; >14.4 km·h-1] and very high-speed running [VHSR; >19.8 km·h-1], and Player Load™), HR and session-RPE (sRPE) scores were recorded. Internal-TL scores (HR-based and sRPE-based) were calculated, and their relationships with measures of external-TL were quantified using Pearson's product moment correlations. Physical measures of TD, LSA volume and Player Load™ provided large, significant (r = 0.71-0.84; P < 0.01) correlations with the HR-based and sRPE-based methods. Volume of HSR and VHSR provided moderate to large, significant (r = 0.40-0.67; P < 0.01) correlations with measures of internal-TL.
Conclusions:  Whilst the volume of HSR and VHSR provided significant relationships with internal-TL, physical performance measures of TD, LSA volume and Player Load™ appear to be more acceptable indicators of external-TL, due to the greater magnitude of their correlations with measures of internal-TL.

Bradley PS, Bendiksen M, Dellal A, Mohr M, Wilkie A, Datson N, Orntoft C, Zebis M, Gomez-Diaz A, Bangsbo J, Krustrup P. The Application of the Yo-Yo Intermittent Endurance Level 2 Test to Elite Female Soccer Populations. Scand J Med Sci Sports. 2012 Jun 19. doi: 10.1111/j.1600-0838.2012.01483.x. [Epub ahead of print]

Department of Sport and Exercise, University of Sunderland, Sunderland, UK.
The aim of this study was to evaluate the application of the Yo-Yo intermittent endurance test level 2 (Yo-Yo IE2) to elite female soccer populations. Elite senior (n = 92), youth (n = 42), domestic (n = 46) and sub-elite female soccer players (n = 19) carried out the Yo-Yo IE2 test on numerous occasions across the season. Test-retest coefficient of variation (CV) in Yo-Yo IE2 test performance in domestic female players was 4.5%. Elite senior female players' Yo-Yo IE2 test performances were better (P < 0.01) than elite youth, domestic and sub-elite players (mean ± standard deviation; 1774 ± 532 vs 1490 ± 447, 1261 ± 449, and 994 ± 373 m). For elite senior female players, wide midfielders (2057 ± 550 m) had a higher Yo-Yo IE2 test performance (P < 0.05) than central defenders (1588 ± 534 m) and attackers (1516 ± 401 m), but not central midfielders (1764 ± 473 m) or full-backs (1964 ± 522 m). Large correlations were observed between Yo-Yo IE2 test performance and the total and high-intensity distance covered (r = 0.55; P < 0.05) during elite senior soccer matches (r = 0.70; P < 0.01). A large correlation was also obtained between Yo-Yo IE2 test performance and (r = 0.68; P < 0.01). Performances in the Yo-Yo IE2 test were greater (P < 0.05) in the middle and the end of the season compared with the preparation period for elite youth female players (1767 ± 539 and 1742 ± 503 vs 1564 ± 504 m) and in elite senior female players, Yo-Yo IE2 test performance increased by 14% (P < 0.01) after completing 4 weeks of intense training prior to the FIFA Women's World Cup Finals (2049 ± 283 vs 1803 ± 342 m).
Conclusions: The Yo-Yo IE2 test is reproducible and is an indicator of the match-specific physical capacity of female soccer players. Furthermore, the Yo-Yo IE2 test illustrates sensitivity by differentiating intermittent exercise performance of female players in various competitive levels, stages of the season and playing positions.

Hulton AT, Edwards JP, Gregson W, Maclaren D, Doran DA. Effect of Fat and CHO Meals on Intermittent Exercise in Soccer Players. Int J Sports Med. 2012 Sep 12. [Epub ahead of print]
Research Institute for Sport & Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom.
Pre-exercise meals containing carbohydrates (CHO) are recommended to athletes, although there is evidence to suggest that a high fat meal prior to exercise increases utilisation of fats yet may not adversely affect performance. This study investigated the effect of a high fat and high CHO pre-exercise meal prior to high intensity intermittent exercise. Ten male recreational soccer players performed a soccer specific protocol followed by a 1 km time trial 3 ½ h after ingesting one of 2 test meals, high fat meal (HFM) or a high CHO meal (HCM). Blood glucose, fatty acids (FA), glycerol, β-hydroxybutyrate, lactate and insulin were assessed prior to the meal, pre-exercise, half-time, and post-exercise, whilst rates of CHO and fat oxidation were determined at 4 time points during the exercise as well as heart rate (HR) and rating of perceived exertion (RPE). Significant increases in FA, glycerol, β-hydroxybutyrate and fat oxidation after the HFM were observed, while CHO oxidation was significantly higher following the HCM (P<0.05). No performance effect was found for the 1 km time trial (HFM: 228.6+14.4 s; HCM: 229.4+26.5 s) (mean+SD).
Conclusions: The type of meal ingested prior to soccer simulated exercise has an impact on metabolism, but not on the subsequent performance.

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