4 healthy men had biopsies taken from the soleus and the lateral head of the gastrocnemius muscle for determination of capillary supply, fibre type distribution and fibre area.
In serial transverse sections slow twitch (ST) and fast twitch (FT) fibres were identified histochemically by myofibrillar adenosine triphosphatase stains and capillaries visualized by a periodic acid Schiff stain after digestion of glycogen by α-amylase.
In soleus, ST and FT fibre type areas were approximately two times greater than in gastrocnemius. FT fibres (11060 μm2) were 50% greater than ST fibres (7520 μm2) in soleus, whereas no difference between FT and ST fibres was observed in gastrocnemius (4730 μm2 and 4310 μm2, respectively). Both muscles were mixed with respect to fibre types but in all subjects soleus had a higher relative content of ST fibres than gastrocnemius. The area occupied by ST fibres relative to total area was 64% in soleus and 50% in gastrocnemius.
Capillary density was 288 capillaries·mm−2 in soleus and 365 in gastrocnemius. Evaluated on the basis of mean number of capillaries in contact with fibres of each type relative to fibre type area (μm−2·10−3) individual ST fibres had a richer capillary supply than FT fibres in both soleus (0.84 and 0.57, respectively) and gastrocnemius (1.12 and 0.92, respectively).
Differences in organization of the capillary network between soleus and gastrocnemius were observed. Capillaries are running mainly parallel to the muscle fibres in gastrocnemius, but tortuously and/or frequently branching in soleus. Tortuously and/or frequently branching capillaries implies nutritional advantages, which will not be reflected in the quantitative data obtained from counts of capillaries made on transverse sectioned muscle. Therefore the absolute values given for soleus and gastrocnemius, respectively, cannot be directly compared.
Human muscles Soleus Gastrocnemius Capillary density Capillary arrangement Fibre type area