Metabolic heterogeneity of muscle fibers classified by myosin ATPase.

Muscle fibers are commonly classified histochemically into three types by the staining intensity for myosin ATPase combined with those for metabolic enzymes. Preincubation at pH 4.6 gives rise to three staining intensities of myosin ATPase which are also used for fiber typing. The two classification systems were compared by computer analysis of the individual staining profiles of over 2,500 fibers, and found not to be equivalent. The analysis showed metabolic heterogeneity among the fiber groups distinguished according to their differences in myosin ATPase.