Exercise induced muscle damage. Anatomopathology and Physiopathology. Exhaustive and unusual physical exercise induces structural and ultra-structural alterations in skeletal muscular whose physiopathology is still unclear. These alterations are described in detail, giving special importance to irregularities of cross striated pattern, paleness with Schiff periodic acid, vacuolization, segmental necrosis, central nuclei, activation of satellite cells and fibroblasts, intra-cellular edema and to the muscular inflammatory reaction with phagocytes infiltration. Their onset times and hypothetical underlying mechanisms are also analyzed. In the origin of these anomalies are metabolic and mechanical factors whose contribution is conditioned by the type of exercise. Experimental data suggests that morphological characteristics of muscle damage induced by exercise are variable according to the metabolic or mechanical stress of exercise.