Strain injury is a contraction-induced damage to skeletal muscle, also known as an overstretched or torn muscle. It is a very common and frequently recurring injury in most team sports and sprinting activities and is especially frequent in the hamstrings muscles. A better insight in the predisposing factors would allow to reduce the high incidence of strain injury in sports. The current project investigates whether athletes with a high proportion of fast-twitch muscle fibers are more prone to strain injury than athletes with predominantly slow-twitch fibers. An underlying mechanism could be an accumulation of muscle fatigue in the former as 1) fast-twitch fibers have a markedly delayed recovery from fatigue, and 2) fatigue is a known risk factor for strain injury. A fast muscle typology seems a logic risk factor for strain injury, as has been suggested in vitro experiments. However, it was never tested in the actual sports population, because the only available method to quantify muscle fiber type composition was a histological evaluation of an invasive muscle biopsy. Yet, we have recently developed a non-invasive method in athletes by proton magnetic resonance spectroscopy. This will allow us to investigate, in an elite team sport population, if muscle typology is a risk factor, and importantly, to develop guidelines for adequate recovery times from intensive training in a personalized manner, with the ultimate goal to reduce muscle strain injury incidence in sports.