[Types of fibers in skeletal muscles of mammals: histochemical and ultrastructural characteristics in relation to their contractile properties].

A tentative correlation of histochemical and ultrastructural features with physiological properties in mammalian skeletal muscle fibers is presented. In particular, the characteristic metabolic and structural profile of fast-twitch red fibers is described and evidence is presented for the presence of such fibers in limb muscles and masticatory muscles of the rat. The existence of interspecies and even intraspecies variation in the histochemical correlates of the different fiber categories is emphasized and the significance of intermediate fiber types is discussed.