Skeletal muscle fiber types and their vascular support.

Different neural and thyroidal influences on mammalian skeletal muscle result in considerable heterogeneity in muscle-fiber characteristics. Muscle fibers can, nonetheless, be grouped into three relatively homogeneous classes, based primarily on their contractile properties. There is a remarkable matching of metabolic support systems to contractile properties and, in turn, appropriate vascular supply for the metabolic systems of each of the three muscle fiber types. The contractile, metabolic, and vascular characteristics of each fiber type are consistent with known patterns of muscle fiber recruitment for the performance of muscular work.