ABSTRACT
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.
