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This study identified small absolute strength differences and a wide overlap of the absolute strength measurements at the group level. The small associations between lower hamstring eccentric strength and lower quadriceps concentric strength with HSIs can only be considered as weak risk factors. The identification of these risk factors still does not allow the identification of individual players at risk. The use of isokinetic testing to determine the association between strength differences and HSIs is not supported.

In recent years there have been rapid developments in the use of growth factors for accelerated healing of injury. Growth factors have been used in maxillo-facial and plastic surgery with success and the technology is now being developed for orthopaedics and sports medicine applications. Growth factors mediate the biological processes necessary for repair of soft tissues such as muscle, tendon and ligament following acute traumatic or overuse injury, and animal studies have demonstrated clear benefits in terms of accelerated healing. There are various ways of delivering higher doses of growth factors to injured tissue, but each has in common a reliance on release of growth factors from blood platelets. Platelets contain growth factors in their alpha-granules (insulin-like growth factor-1, basic fibroblast growth factor, platelet-derived growth factor, epidermal growth factor, vascular endothelial growth factor, transforming growth factor-beta(1)) and these are released upon injection at the site of an injury. Three commonly utilised techniques are known as platelet-rich plasma, autologous blood injections and autologous conditioned serum. Each of these techniques has been studied clinically in humans to a very limited degree so far, but results are promising in terms of earlier return to play following muscle and particularly tendon injury. The use of growth factors in sports medicine is restricted under the terms of the World Anti-Doping Agency (WADA) anti-doping code, particularly because of concerns regarding the insulin-like growth factor-1 content of such preparations, and the potential for abuse as performance-enhancing agents. The basic science and clinical trials related to the technology are reviewed, and the use of such agents in relation to the WADA code is discussed.

BackgroundTo evaluate the efficacy of a single platelet-rich plasma (PRP) injection in reducing the return to sport duration in male athletes, following an acute hamstring injury.MethodsA randomised, three-arm (double-blind for the injection arms), parallel-group trial, in which 90 professional athletes with MRI positive hamstring injuries were randomised to injection with PRP-intervention, platelet-poor plasma (PPP-control) or no injection. All received an intensive standardised rehabilitation programme. The primary outcome measure was time to return to play, with secondary measures including reinjury rate after 2 and 6 months.ResultsThe adjusted HR for the PRP group compared with the PPP group was 2.29 (95% CI 1.30 to 4.04) p=0.004; for the PRP group compared with the no injection group 1.48 (95% CI 0.869 to 2.520) p=0.15, and for the PPP group compared with the no injection group 1.57 (95% CI 0.88 to −2.80) p=0.13. The adjusted difference for time to return to sports between the PRP and PPP groups was −5.7 days (95% CI −10.1 to −1.4) p=0.01; between the PRP and no injection groups −2.9 days (95% CI −7.2 to 1.4) p=0.189 and between the PPP and no injection groups 2.8 days (95% CI −1.6 to 7.2) p=0.210. There was no significant difference for the secondary outcome measures. No adverse effects were reported.ConclusionsOur findings indicate that there is no benefit of a single PRP injection over intensive rehabilitation in athletes who have sustained acute, MRI positive hamstring injuries. Intensive physiotherapy led rehabilitation remains the primary means of ensuring an optimal return to sport following muscle injury.Trial registration numberClinicalTrials.gov Identifier:NCT01812564.

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 recent decades, there has been increased awareness of the impact of vitamin D on muscle morphology and function, but this is not well recognized in the Sports Medicine literature. 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 underperformance and the risk of injury in athletes. This review describes the current understanding of the role vitamin D plays within skeletal muscle tissue.