Human plantar flexion strength and structure.

Plantar flexion strengths were studied in 30 right-handed males. Static and dynamic maximum plantar flexion torques were recorded, knees fully extended (0 degrees) and in 90 degrees flexion. In five of the subjects the soleus and gastrocnemius muscle structure were studied by light microscopy and enzyme histochemistry. Specimens were obtained by needle biopsy, usually bilaterally. Intraindividual declines of force were found to be a function of angular motion velocity. Static and dynamic torques correlated significantly. Peak torques were significantly greater (mean 15%) at the 0 degrees than at the 90 degrees knee angle and left maximum plantar flexion torques at 0 degrees were greater (mean 10%) than right. Mean morphometric data on the m. soleus suggested right-left symmetry, which could not be demonstrated for the m. gastrocnemius. Fibres with low stainability for myofibrillar ATPase (Type 1 fibres) had smaller diameters, but constituted the major part of the cross-sectional areas. In these five non-athletes no significant correlation between data on plantar flexion strength and morphometric data on triceps surae structure could be demonstrated. On the other hand, strength covariated with calf circumference.