Respiratory capacity of white, red, and intermediate muscle: adaptative response to exercise.

BALDWIN, K. M., G. H. KLINKERFUSS, R. L. TERJUNG, P. A MOLI?, AND J. 0. HOLLOSZY. Respiratory capacity of white, red, and intermediate muscle: adaptive response to exercise. Am. J. Physiol. 222(2): 373-378. 1972.-A program of running can result in a twofold increase in the respiratory capacity of mixed muscles such as the gastrocnemius and quadriceps in the rat. This study was undertaken to determine which fiber type or types participate in the increase in oxidative capacity. The soleus muscle, and the superficial, white and deep, red portions of the quadriceps were used to determine the responses of intermediate, white and red muscle to endurance exercise. The capacity to oxidize pyruvate-Z14C and palmitate-U-14C, the levels of activity of cytochrome oxidase, carnitine palmityltransferase, and citrate synthase, and the concentration of cytochrome c increased to approximately the same extent in all three muscle types in rats subjected to a program of running. These results are not compatible with the interpretation that the exercise-induced increase in oxidative capacity of muscle is due to transformation of white into red fibers as appears to be the case by histochemical appearance. Since the respiratory capacity of all three muscle types increased approximately twofold, the approximately fivefold difference in capacity for oxidative metabolism between red and white muscle was maintained in the trained animals.