Phase-dependent modulation of the soleus H-reflex during rhythmical arm swing in humans

The purpose of this study is to investigate modulation of the soleus H-reflex during rhythmic arm swing in humans. Significant depression of the soleus H-reflex was observed when subjects swung their ipsilateral arms or both arms reciprocally during testing. The degree of soleus H-reflex depression appeared directly proportional to the speed of the arm swing. This depression was observed in the conditioning-testing intervals of 400, 500, and 600 msec during the ipsilateral backward arm swing and at the onset of the ipsilateral arm forward swing. This phase of depression partially overlapped the phase of depression of the soleus H-reflex during walking. However, the pattern of modulation during arm swing was not exactly the same as that during walking. Therefore, we concluded that the ipsilateral arm swing may partially affect the depression of the soleus H-reflex during the arm swing phase of walking but is not responsible for depression of the soleus H-reflex throughout the entire walking cycle.