[A physiological study on instability in Parkinson's disease].

To clarify roles of impairment of proprioceptive reflexes in instability of parkinsonian gait, delta EMG/delta angle of the gastrocnemius and tibialis anterior muscles was measured during the stance phase on patients with Parkinson's disease and normal controls. This ratio decreased in the gastrocnemius muscle, while it was unchanged in the tibialis anterior muscle. delta EMG/delta angle is likely to be correlated with muscle stiffness(delta muscle force/delta muscle length) that reflects from stretch reflexes. Thus our results suggest an impairment of stretch reflexes of the extensor muscle during parkinsonian gait.