Bogutska G. The influence of the upper extremity movements on the H-reflex of the human soleus muscle

The influence of short-time voluntary movements of the human upper extremity on the soleus muscle H-reflex was examined, using the method of pair stimuli. The effect of flexion and extension of the ipsilateral elbow, flexion of fingers into fist, flexion of contralateral elbow was studied. The size of H-reflex found changes which had two-phase character. In the first phase during the horizontal position of the body all the conditioning movements of the upper extremity caused the relief of the tested H-reflex. Increasing of its amplitude appeared in 30-40 msec before the beginning of the movement and thus it can be considered as anticipatory postural changes that regulate muscular tone and body position in the space. Its duration was 100-300 msec. In the vertical body position of the subject during the ipsilateral elbow flexion the inhibition of H-reflex appeared instead of the relief. In the later phase of voluntary movements of the upper extremity, regardless of the position of subject's body in the space, the long-time inhibition of H-reflex appeared. It reached the maximum depth at the test-interval 700 msec. Inhibition during the voluntary movement of the contralateral upper extremity appeared earlier and was deeper than the analogous movement of the ipsilateral upper extremity. Inhibition duration, which was calculated with the help of the regression equation, was 6,6 sec. after the ipsilateral forearm flexion and 8,5 sec. after the contralateral forearm flexion. Long-time inhibition of H-reflex does not subside during the moderate tonic excitement of the tested muscle motoneurons in the conditions of the voluntary sole of the foot flexion. The phenomenon of occlusion is observed during the interaction of the inhibition with the inhibiting effect of the common peroneus nerve, which causes depolarization of primary afferents of the arch of the soleus muscle H-reflex. These conditions point at the localization of the studied long-time inhibition in the presynaptic part of the H-reflex arch. This inhibition appears reflexively as a result of the afferent activity of the upper extremity muscles. It can be caused not only by voluntary hand movements, but also by the biceps muscle of arm traction under the influence of electric stimulation. Key words: H-reflex, voluntary movements, interaction of upper and lower extremities, anticipatory postural rearrangements, presynaptic inhibition.