The distribution and relative sized of fibre types in the extensor digitorum longus and soleus muscles of the adult rat.

Histochemical fibre types classified in sections stained for succinic dehydrogenase (sdh) and myosin ATPase at pH 9.4, were found to be distributed in a consistent manner within the extensor digitorum longus (EDL) and 4 soleus muscles of the adult rat. Simple morphometric techniques applied to complete transverse sections of both muscles showed that the relative distributions and proportions of fibre types along their deep to superficial, and medial to lateral, axes varied accoording to the histochemical method used for fibre typing. Similar differences occurred when the relative ranges of size exhibited by each fibre type were compared in sections stained for SDH and ATPase, and the discrepancies in fibre classification were confirmed by an analysis of individual fibres in serial sections. The findings are discussed in relation to those previosly reported for the EDL and soleus muscles of the rat.