Abnormal muscle tone with a specific motor pattern is observed in the affected side of a hemiplegic patient, who receives motor stress on the unaffected side of the upper limb during therapeutic exercise. In order to clarify the relation between the intensity of motor stress on upper limbs and changes in muscle tonus of lower limbs, we examined the changes in the H-reflex of the bilateral soleus muscle induced by grasping with the left hand, using repetitive evoked electromyograms at a stimulus

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... frequency of 5 Hz. Eight healthy male subjects volunteered for this experiment. Subjects grasped a sphygmomanometer cuff by the left hand at five degrees of load intensity, 0, 20, 40, 60 and 80% of maximum voluntary contraction, and 10 consecutive H waves were recorded from the bilateral soleus for each intensity. The H-reflex of the right soleus increased significantly (p<0.01) with increasing grasping strength of the left hand, but that of the left soleus showed hardly any change. Right hemisphere dominance in the left upper limbs concentrated on grasping with the left hand resulted in disinhibition of the left cerebral hemisphere. The H-reflex from the right soleus was consequently increased.