“…The altered function of the muscles of the larynx is presented in various diseases of the voice, these changes have expression in the metabolism of muscle fibers in its organization and morphological appearance, as histochemical and immunohistochemical study of muscle fibers is a valuable tool for evaluation. The histochemical differentiation of muscle fibers supports the diagnosis of many myopathies (Hebling & Esquisatto, 2005). The preferred method for the differentiation of muscle fibers is based on the histochemical reaction for the identification of the enzyme nicotinamide dinucleotides tetrazolium reductase (NADH-TR) (Dubowitz et al, 1985), which can be classified into Type I (slow, fatigue-resistant); and Type II, subclassified as Type IIa (fast, fatigue-resistant) and Type IIb (fast, fatigable) (López-Chicharro, 2006), in the human vocal muscle a higher frequency of fibers Type I and Type II that characterizes the muscle as having aerobic metabolism, resistance to fatigue, and fast contraction has been reported (Guida & Zorzetto, 2000).…”