Reciprocal inhibition between the forearm muscles in patients with Parkinson's disease.

Reciprocal inhibition of H-reflexes in the forearm flexor muscles was examined in patients with Parkinson's disease (PD). The early disynaptic phase and the later presynaptic phase of reciprocal inhibition were normal in PD patients. The effects of radial nerve stimulation on flexor muscle voluntary contraction was also evaluated. Radial nerve stimulation produced suppression of the ongoing electromyographic activities. The latency and degree of the suppression in PD patients were the same as those in control subjects. The duration of suppression in PD patients was longer than that in control subjects, reflecting the delayed termination of reciprocal inhibition in PD patients. Reciprocal inhibition between the forearm muscles was retained in patients with PD.