Size and proportion of fiber types in human muscle fascicles.

Size and distribution of 2 histochemical types of muscle fibers within the human muscle fascicle were investigated. Cryostat sections (ATPase, pH 9.4) were studied from 15 quadriceps femoris, 15 biceps brachii and 15 deltoid muscles taken at autopsy from 12 males and 9 females who had no history of neuromuscular disease. The number and the lesser diameter of type 1 and type 2 fibers were counted and percentage and mean diameter of the 2 types of fibers were calculated separately for periphery and interior of randomly selected fascicles. The results showed that a progressive age-related reduction of the diameter of type 2 fibers is observed and the predominance of type 2 fibers in the periphery is a constant finding in all muscles studied, regardless of sex and age.