Contralateral inhibition of soleus H reflexes with different velocities of passive movement of the opposite leg.

The research question was, do events arising from rhythmic passive movement of the human leg lead to inhibition of the H reflex pathway in the stationary leg contralateral to that movement? Further, as the angular velocity of the passive movement increases, does the contralateral reflex inhibition also increase? Stable stimulation of the tibial nerve elicited H reflexes in the EMG of soleus. Trials involved the stimulated or the contralateral leg being rotated passively in a pedalling motion, at various velocities. The controls were made with the subjects seated and relaxed. The results showed that reflex magnitudes were significantly depressed when the test limb was passively rotated at 60 rpm. in comparison to the seated control trials. Rotation of the opposite limb depressed reflex magnitudes in the test limb, which was stationary. This contralateral inhibition increased, (mean reflex magnitudes of 62.68%, 41.04%, 16.65% and 9.58% of peak-to-peak Mmax), as the velocity of rotation of the opposite limb increased (10, 30, 60, 90 rpm, respectively) (P < 0.01). The effect of movement velocity was interpreted as the result of altered sensory receptor discharge arising from the passive movement. It is concluded that contralateral sensory activity contributes to the movement-elicited afferent discharge which tunes the spinal somatosensory-motor mechanisms for human locomotion.