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 homo geneous classes, based primarily on their contractile properties. Ther e is a remarkable matching of metabolic support systems to contractile properties and, in turn, appropriate vascular supply for the metaboli c systems of each of the three muscle fiber types. The contractile, me tabolic, and vascular characteristics of each fiber type are consisten t with known patterns of muscle fiber recruitment for the performance of muscular work.