Monday, September 5, 2011

Recent studies with practical applications to football-Part 1

Hamilton (2010). Vitamin D and human skeletal muscle. Scand J Med Sci Sports. 20(2):182-90.


Vitamin D deficiency is an increasingly described phenomenon worldwide, with well-known impacts on calcium metabolism and bone health. Vitamin D has also been associated with chronic health problems such as bowel and colonic cancer, arthritis, diabetes and cardiovascular disease. In the early 20th century, athletes and coaches felt that ultraviolet rays had a positive impact on athletic performance, and increasingly, evidence is accumulating to support this view. Both cross-sectional and longitudinal studies allude to a functional role for vitamin D in muscle and more recently the discovery of the vitamin D receptor in muscle tissue provides a mechanistic understanding of the function of vitamin D within muscle. The identification of broad genomic and non-genomic roles for vitamin D within skeletal muscle has highlighted the potential impact vitamin D deficiency may have on both under-performance and the risk of injury in athletes. This review describes the current understanding of the role vitamin D plays within skeletal muscle tissue.

Papacosta and Nassis  (2011). Saliva as a tool for monitoring steroid, peptide and immune markers in sport and exercise science. J Sci Med Sport. 14(5):424-34.

This paper discusses the use of saliva analysis as a tool for monitoring steroid, peptide, and immune markers of sports training. Salivary gland physiology, regarding the regulation and stimulation of saliva secretion, as well as methodological issues including saliva collection, storage and analysis are addressed in the paper. The effects of exercise on saliva composition are then considered. It is concluded that the measurement of physiological biomarkers in whole saliva can provide an important tool for assessing the immunological and endocrinological status associated with exercise and training.

Chelly et al. (2010). Effects of in-season short-term plyometric training program on leg power, jump- and sprint performance of soccer players J. Strength & Condit. Res., 24 (10), 2670-2676. 
The subjects (23 men, age 19 ± 0.7 years) were randomly assigned to a control (normal training) group (n = 11) and an experimental group (n = 12) that also performed biweekly plyometric training. The results showed that biweekly plyometric training of junior soccer players (including adapted hurdle and depth jumps) improved important components of athletic performance (squat and countermovement jump and sprinting).

Buchheit, et al. (2010). Improving repeated sprint ability in young elite soccer players: repeated shuttle sprints vs. explosive strength training J. Strength & Condit. Res., 24 (10), 2715-2722. 

To compare the effects of explosive strength (ExpS) vs. repeated shuttle sprint (RS) training on repeated sprint ability (RSA) in young elite soccer players, 15 elite male adolescents (14.5 ± 0.5 years) performed, in addition to their soccer training program, RS (n = 7) or ExpS (n = 8) training once a week for a total of 10 weeks. RS training consisted of 2-3 sets of 5-6 × 15- to 20-m repeated shuttle sprints interspersed with 14 seconds of passive or 23 seconds of active recovery (˜2 m/s); ExpS training consisted of 4-6 series of 4-6 exercises (e.g., maximal unilateral countermovement jumps (CMJs), calf and squat plyometric jumps, and short sprints). Before and after training, performance was assessed by 10 and 30 m (10 and 30 m) sprint times, best (RSAbest) and mean (RSAmean) times on a repeated shuttle sprint ability test, a CMJ, and a hopping (Hop) test. After training, except for 10 m (p = 0.22), all performances were significantly improved in both groups (all p's < 0.05). Relative changes in 30 m (-2.1 ± 2.0%) were similar for both groups (p = 0.45). RS training induced greater improvement in RSAbest (-2.90 ± 2.1 vs. -0.08 ± 3.3%, p = 0.04) and tended to enhance RSAmean more (-2.61 ± 2.8 vs. -0.75 ± 2.5%, p = 0.10, effect size [ES] = 0.70) than ExpS. In contrast, ExpS tended to induce greater improvements in CMJ (14.8 ± 7.7 vs. 6.8 ± 3.7%, p = 0.02) and Hop height (27.5 ± 19.2 vs. 13.5 ± 13.2%, p = 0.08, ES = 0.9) compared with RS. Improvements in the repeated shuttle sprint test were only observed after RS training, whereas CMJ height was only increased after ExpS. Because RS and ExpS were equally efficient at enhancing maximal sprinting speed, RS training-induced improvements in RSA were likely more related to progresses in the ability to change direction.

Arnoczky et al. (2011). What Is Platelet-Rich Plasma? Operative Techniques in Sports Medicine 19(3), 142-148

Platelet-rich plasma (PRP) has been advocated as a way to introduce increased concentrations of growth factors and other bioactive molecules to injured tissues in an attempt to optimize the local healing environment. PRP has been used extensively in dental and cosmetic surgery for almost 30 years, and the safety and efficacy of this autologous product in these areas have been well established. Recently, PRP has been increasingly used in the treatment of a variety of sports-related injuries in the hopes that the increased levels of autologous growth factors and secretory proteins provided by the concentrated platelets could enhance the biological processes associated with tissue repair and regeneration. However, all PRP preparations are not the same. Variations in the volume of whole blood taken, the platelet recovery efficacy, the final volume of plasma in which the platelets are suspended, the presence or absence of red and/or white blood cells, the addition of thrombin or calcium chloride to induce fibrin formation, and the addition of pH-altering compounds can all affect the character and potential efficacy of the final PRP product. This article reviews the basic principles involved in creating PRP and examines the potential basic science significance of the individual blood components contained in the various forms of PRP currently used in sports medicine.

Mejia et al. (2011). The Effects of Platelet-Rich Plasma on Muscle: Basic Science and Clinical Application. Operative Techniques in Sports Medicine 19(3), 149-153

Muscle injuries are the most common type of injuries in sports. The natural course in this repair process is often slow, incomplete, and unpredictable. For competitive or professional athletes, this delay or unpredictability in complete healing may be costly or career ending. With the introduction of the potential benefits of platelet-rich plasma (PRP) preparations, our treatment algorithm is changing. Our understanding of growth factors and their roles in the modulation and activation in soft-tissue healing is expanding at a rapid pace. This has led to its clinical use far outpacing clinical trials. Basic science has documented a potential for PRP to regenerate and modulate skeletal muscle and, thus, provides a foundation for clinical treatment and improved patient outcomes. Despite widespread anecdotal use in a variety of musculoskeletal injuries, research investigating its clinical efficacy is still in its infancy. This article addresses the biological effects of PRP on skeletal muscle myogenesis and its potential clinical applications.

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