Іvanchenko E. Anticipatory changes of human leg H-reflexes caused by contralateral lower extremity voluntary movements

Anticipatory changes of the soleus and long peroneal H-reflexes and background EMG-activity preceding the contralateral leg voluntary movements were studied in healthy humans. Contralateral plantar flexion and dorsiflexion, as well as the knee joint flexion, were performed at the maximal velocity. The subjects were in the lying prone position with the relaxed legs, or in standing position with the support on both or one foot. While prone all conditioning movements of the contralateral leg evoked anticipatory facilitation of the testing soleus H-reflex. It aroused at 90 - 60 ms and reached the maxi-mum at 30 ms before the conditioning movement. Facilitation of the long peroneal H-reflexes also took place before the contralateral plantar flexion. No considerable changes of the soleus or long peroneus background EMG-activity were observed during the premo-tor period. It is supposed that mechanism leading to the H-reflex facilitation is the de-crease of presynaptic inhibition at 1a. In standing position with support on feet, contralateral plantar flexion and knee joint flexion caused anticipatory inhibition of the soleus H-reflex. Contralateral dorsiflexion was preceded by the H-reflex facilitation. There was also corresponding decrease of the soleus background EMG-activity before the contralateral plantar flexion and its increase before dorsiflexion. The present results indicate the anticipatory changes of muscle tone and suggest participation of postsynaptic mechanism in the facilitation and inhibition of the testing H-reflex. When the moving contralateral extremity has no support, its plantar flexion does not cause anticipatory inhibition but facilitation of the soleus H-reflex. It is supposed that premotor changes of the H-reflexes in standing position reflect the arising of anticipatory postural adjustments. Keywords: H- reflex, voluntary motion, premotor period, contralateral extremity, background EMG-activity, anticipatory postural adjustments.