The purpose of this investigation is to determine to what extent and in what manner selected types, intensities, and duration of specific chronic exercise regimens, initiated prior to the onset of clinical symptoms, affect the onset and future course of muscular dystrophy. Specific histological, histochemical and biochemical alterations, mediated by the defined chronic exercise regimens will be studied in skeletal and cardiac muscle of the BIO 14.6 line of dystrophic hamsters. A range of parameters has been selected to identify how the muscle physiology and biochemistry change and to attempt to determine the sources for the beneficial effects observed in our previous investigation. Oxidative and glycolytic enzymes and substrates will be measured and some determinations of lipid metabolism will be made. Ribonucleic acid distribution will be studied to determine the amount of regeneration. Capillary counts and capillary-to-fiber ratios will be determined, where possible, to reflect grossly the circulation to muscle fibers. The serum enzymes SALD, SGOT, LDH, and CPK, will be used to aid in the differentiation of normal adaptive changes from pathological effects. Collateral axonal nerve sprouting and motor end-plate cholinesterase activity are included to reflect neural adaptations. The cellular and biochemical measures will be related to qualitative histopathological assessment, in vitro quantified measures of the contractile characteristics of skeletal muscle, and to serial clinical evaluations. Some animals will be maintained on the exercise regimens to determine if length of life is altered by physical activity.