Modulation of H reflexes in the forearm during voluntary teeth clenching in humans.

We investigated whether there is any modulation of the H reflex in the forearm during teeth clenching and how any correlation that may be found is modulated. The H reflexes of the flexor carpi radialis (FCR) and the extensor carpi radialis (ECR) muscles were evoked on the right side in five healthy adult volunteers. The H reflexes of the FCR and ECR muscles were facilitated in association with voluntary teeth clenching in a force-dependent manner ( r=0.46-0.663, P<0.05). The increase in amplitude of the H reflex of the FCR muscle associated with teeth clenching started before the onset of the EMG activity of the masseter muscle. The results of the present study demonstrate that oral motor activity exerts strong influences on the motor activity of the forearm.