In the mind of the public (and unfortunately sometimes in that of the physician also) muscular lesions are too often attributed to pulled or torn muscles. Experience and new theoretical knowledge (particularly microscopic studies) have made it possible to pinpoint the two concepts of microruptures and of true muscular stiffness, which already corresponds to a microscopic lesion of the muscular tissue. An attempt is made to define these two types of lesion, relate them to the "classical" muscular lesions, analyze the pathogenesis and outline their treatment.