Distribution of muscle fibre types in human skeletal muscle fascicles: an autopsy study of three human muscles.

The predominance of type 2 fibres in the periphery of the muscle fascicle is a phenomenon attributed to local factors or to the adaptation of the muscle to functional needs. As the majority of relevant studies has been performed on quadriceps muscle of males, the purpose of this study was to examine other muscles along with quadriceps, in females as well as in males, with parallel morphometric analysis of fibres, in order to determine whether differences in size exist in addition to differences in proportion. Cryostat sections (ATPase, pH 9.4) were studied from 13 quadriceps femoris, 13 biceps brachii and 11 deltoid muscles taken at autopsy from 11 males and 8 females. The number and smallest diameter of type 1 and 2 fibres were counted and the percentage and mean diameter of the two types of fibres were calculated in the interior and the periphery of randomly selected fascicles. We found that: the predominance of type 2 fibres in the periphery is constant in all muscles studied, regardless of sex and age; there is a progressive age-related reduction in the diameter of type 2 fibres.