Distribution of fibre sizes in human skeletal muscle. An enzyme histochemical study in m tibialis anterior.

The aim of the study was to determine the fibre size distribution within the human m tibialis anterior. Ten-micron thick cross-sections of the whole muscle were enzyme histochemically stained for myofibrillar ATPase at pH 9.4. The cross-sectional area of 100 fibres with low (type 1) ATPase and high (type 2) ATPase activity was measured in three different regions (superficial, central and deep). Both the type 1 and type 2 fibres were found to be larger in the deep region than in the central or superficial regions. The variation in fibre size could not be explained by the cryofixation or cryo-embedding techniques used. The data suggest that muscle adaptation to physical demands may not only occur by means of variation in types and number of muscle fibres, but also by variation in fibre size over the muscle cross-section.