H-reflex modulation in the human medial and lateral gastrocnemii during standing and walking.

INTRODUCTION The soleus H-reflex is dynamically modulated during walking. However, modulation of the gastrocnemii H-reflexes has not been studied systematically. METHODS The medial and lateral gastrocnemii (MG and LG) and soleus H-reflexes were measured during standing and walking in humans. RESULTS Maximum H-reflex amplitude was significantly smaller in MG (mean 1.1 mV) or LG (1.1 mV) than in soleus (3.3 mV). Despite these size differences, the reflex amplitudes of the three muscles were positively correlated. The MG and LG H-reflexes were phase- and task-dependently modulated in ways similar to the soleus H-reflex. CONCLUSIONS Although there are anatomical and physiological differences between the soleus and gastrocnemii muscles, the reflexes of the three muscles are similarly modulated during walking and between standing and walking. Our findings support the hypothesis that these reflexes are synergistically modulated during walking to facilitate ongoing movement.