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Heredity differentiates the percentage and amount of the two markedly different fiber types. In humans the cardiovascular-type fibers have at different times been called red, tonic, type I, slow-twitch or slow-oxidative fibers. By contrast, the anaerobic-type fibers have been called white, phasic, type II, fast-twitch or fastglycolytic fibers. Further subdivisions of type II fibers are the IIa (fast-oxidativeglycolytic) and IIb (fast-glycolytic) fibers. It is noteworthy that the soleus, a muscle involved in standing posture and gait, generally contains 25%–40% more type I fibers, while the triceps has 10%–30% more type II fibers than the other arm muscles (Foss & Keteyian 1998). The proportions and types of muscle fibers vary greatly between adults. It is suggested that the new, popular periodization models of exercise training, which include light, moderate and high-intensity training phases, satisfactorily overload the different muscle …