Muscle Fiber Types: How Many and What Kind?

STUDIES on normal and pathological striated muscle are increasingly clouded by inconsistencies in the definition of fiber types and lack of correlation between different systems of nomenclature. The purpose of the present communication is to point out some of the problems involved in the classification of fibers and to add new information of value in the analysis of human biopsy material. The histochemical reaction for myosin adenosine triphosphatase (ATPase) and the pH lability of this reaction is used to characterize the various types of fibers. Material and Methods Muscle was obtained by biopsy in man, rat, and rabbit. Gastrocnemius and soleus were investigated in the animals. The human biopsies were taken from the biceps. The methods used for histochemical analysis have been given elsewhere. 1 In summary, unfixed frozen material was sectioned at 10μ thickness in the cryostat and the following histochemical reactions were carried out: (1) reduced diphosphopyridine