MAMMALIAN skeletal muscles are composed of two main types of fibers which differ in metabolic and physiological properties. The type of fiber which predominates in "red" or slow muscles, such as the soleus, is marked by high activities of the enzymes of oxidative and lipid metabolism. By contrast, the fiber type which predominates in "white" or fast muscles, such as the extensor digitorum longus, has greater activity of the enzymes of anaerobic glycolysis.1-3
It has recently been established that the specific motor innervation plays an important role in determining these differences in muscle properties. After sectioning and cross-uniting nerves to red and white muscles, both the histochemical characteristics4,5 and the speeds of contraction of the muscles6,7 become reversed. Denervation results in slowing of both fast and slow muscles8,9 and disappearance of the differences in their enzymatic activities.10,11 influence these properties of muscle has been