Platelet-Rich Plasma (PRP) has been banned in competitive athletes because some people think it may enhance athletic performance. However, there is very little published research to support or undermine this point of view. The purposes of this study are: (1) To assess the effects of local platelet-rich plasma (PRP) therapy on systemic levels of growth factors with suspected or known performance-enhancing effects; and (2) To understand whether the effect of PRP therapy on these growth factors differs between intramuscular and intratendinous PRP injections.