The diagnosis of the muscular injuries sportsmen suffer is carried out through a clinical diagnosis together with confirmation tests through imaging techniques (echography and/or nuclear magnetic resonance) and laboratory techniques through blood testing that detect the presence of non-specific serum markers of muscular injuries. Imaging tests turned out to be excellent for the detection and confirmation of injuries of second-and third-degree. However, first-degree injuries remain, many times, without confirmation through these techniques. The traditional serum markers behave in a similar way, all of them being non-specific of the skeletal muscle. The evaluation of the fast and slow myosin in blood 48 hours after the injury turned out to be a good parameter for the detection of especially type 1 injuries, since fast myosin is an exclusive marker of the skeletal muscle. The correct diagnosis of first-degree injuries can fecilitate the prevention of the injury's progression in sportsmen subjected to continued training and competitions. It can also help the sports doctor to make his decisions.