EFFECTS OF PHYSICAL-TRAINING ON THE STRUCTURE AND METABOLISM OF SKELETAL-MUSCLES IN ATHLETES

Biopsy specimens of skeletal muscle tissue were taken from m. vastus l ateralis of cross country skiers in the beginning and at the end of tr aining season. The activities of NADH-tetrazolium reductase, cytochrom e c oxidase, malate dehydrogenase, alpha-glycerophosphate dehydrogenas e, and myoglobin peroxidase were measured by cytophotometry. Mitochond rial respiratory rate was measured in skinned muscular fibers, and the ir dimensions and density of vascularization were estimated. Training did not change NADH-tetrazolium reductase activity, maximum mitochondr ial respiratory rate, capillary density, muscular fiber size, or maxim um oxygen consumption. Increments were found in cytochrome c oxidase a ctivity, respiratory control (by 195%), and creatine-stimulated respir atory rate (p < 0.05). Conversely, the activities of alpha-glycerophos phate dehydrogenase, myoglobin peroxidase (p < 0.05), malate dehydroge nase, and the basal mitochondrial respiratory rate decreased Adaptatio n to endurance training may proceed not only through increases in maxi mal oxygen consumption and muscular fiber oxidative potential with imp roved substrate delivery, but also by optimizing the use of available substrates through qualitative changes in the mitochondrial respirator y chain.