The relative importance of the gastrocnemius and soleus muscles in the ankle jerk of man

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Abstract
The electromyographic responses were recorded from the soleus and gastrocnemius muscles of man during the ankle jerk. This study was made on 12 normal subjects and in each case both legs were tested and potentials recorded by means of skin electrodes. It was found that during a reflex contraction the composite action potential was greater over the soleus than the gastronemius. On the basis of animal experimentation the soleus has a greater density of muscle spindles and therefore, may be expected to be more sensitive to stretch. It is also assumed that a greater contraction occurs in the soleus. The results are consistent with the reported greater activity of the soleus in standing. Normal posture must be based on the stretch reflex.