Slow and Fast Muscles After Cross Innervation: Enzymatic and Physiological Changes

MAMMALIAN skeletal muscles have been shown histochemically to consist of fibers with different enzymatic characteristics within the same muscle, indicating differences in energy metabolism. 1-3 Muscles with fast speeds of contraction are composed predominantly of fibers with high activities of enzymes of anaerobic glycolysis, while slow muscles consist almost entirely of fibers with high activities of enzymes of oxidative and lipid metabolism. 2,3 These enzymatic differences disappear following denervation, suggesting that the preferential energy metabolism of muscle fibers is determined by the nerve supply. 4,5 After sectioning and cross-uniting nerve to "fast" and "slow" muscles, the speeds of contraction of the muscles become reversed. 6,7 The present study was undertaken to determine whether these physiological changes in cross-innervated muscles are accompanied by corresponding changes in preferential energy metabolism. Preliminary observations have been presented. 8 Material and Methods Surgical section and cross union or reunion of the nerves to soleus