Anticipatory changes of soleus H-reflex amplitude during execution process for heel raise from standing position

Soleus (SOL) H-reflex amplitude changes before the EMG onset of that muscle were compared between simple plantar flexion (SPF) and heel raise from standing position (STM). Results indicated that (1) the SOL H-reflex amplitude decreased during the STM but not the SPF, (2) in the STM, anticipatory EMG activity in the antagonist tibialis anterior (TA) appeared before the EMG onset of the agonist (SOL) and the onset corresponded to the initiation of the decreasing SOL H-reflex, and (3) EMG reaction time of the SOL in the STM was significantly longer than in the SPF. These results suggest that the decreasing SOL H-reflex amplitude is caused by the reciprocal inhibition originating from the postural synergy, the TA. The functional significance of the decreased SOL H-reflex amplitude might lead to a delay in the activation of focal musculature.