Lysosomal changes related to exercise injuries and training-induced protection in mouse skeletal muscle

Three experiments were designed to study the lysosomal changes associated with the development and maintenance of the endurance training induced resistance against exercise injuries in mouse skeletal muscles. The activities of arylsulphatase, cathepsin C, cathepsin D, and beta-glucuronidase were assayed from the red part of mouse quadriceps femoris muscle 4 days after prolonged strenuous running of 4-9 h duration. Exercise injuries were characterized by necrotic fibers and focal inflammation. Strenuous running of untrained mice induced necrotic lesions and a 4-5 fold increase in the activities of lysosomal enzymes. This lysosomal response was considerably reduced already by daily training bouts on the 3 days preceding the strenuous exertion. Simultaneously exercise injuries were markedly reduced. Extending the endurance training program increased the running ability of mice and further reduced the necrotic lesions and lysosomal changes induced by the strenuous exercise. The detraining of 1 week after the termination of regular endurance training considerably increased the degree of exercise induced lysosomal response. The detraining of longer durations further increased the lysosomal response and no effect of prior endurance training existed after 1 month detraining. Our observations suggest that the severity of exercise injuries is related to the strength of the exercise stimulus and the level of preceding physical activity and can be characterized by the lysosomal changes.