EFFECTS OF EXERCISE ON STRUCTURE AND METABOLISM OF SKELETAL MUSCLE AT CELL LEVEL

The capacity of the mitochondrial fraction from hind limb muscles to oxidize pyruvate triples in rats subjected to a strenuous program of swimming or treadmill running. Concomitantly the concentrations of cytochromes and the activities of structural bound mitochondrial enzymes (glycerol-1-phosphate-oxidase, succinate-dehydrogenase) expressed per g of muscle increase approximately twofold in response to the training. There is also a significant rise in mitochondrial protein content. Electron micrographs of exercised muscles show a marked hypertrophy and increase in number of mitochondria. These findings suggest that the rise in respiratory enzyme activity is due to de novo-synthesis of enzyme protein. Phosphorylation is not uncoupled from respiration at any stage of the exercise, indicating that the increase in mitochondrial electron transport capacity is associated with a rise in the capacity to produce ATP. Under our conditions anaerobic muscle metabolism (glycolytic enzymes and metabolites) however remains unchanged. Only glycogen increases approximately 50% after five weeks of swimming exercise. © 1969 Springer-Verlag.