The purpose of this study is to investigate and determine the time course and distribution on muscle hyperalgesia and muscle pain in a repeated, low dose NGF model. It is hypothesized that low dosages i.m injections of NGF are able to induce mechanical hyperalgesia and muscle soreness in a same manner (effect of duration) as for dosages previously used in NGF studies. Furthermore, it is also speculated if several injections of low dose NGF into the muscle combined are able to course immediate pain sensation and spreading of muscle hypersensitivity.