Premovement silence of EMG activity prior to movement in Parkinson patients.

Premovement silence (PMS) of tonic agonist electromyographic activity (EMG) preceding a maximum effort elbow extension was studied in eight bradykinetic Parkinson patients. The occurrence and duration of PMS have been shown to be significantly correlated with peak acceleration of movement in normal subjects. To determine if inability to silence the EMG prior to the initial agonist burst may contribute to bradykinesia of Parkinson's disease, patients maintained elbow extension against a tonic load on triceps, and in response to a tone performed a maximum effort elbow extension. All eight patients showed some trials (mean = 30%) with PMS. However, neither the incidence of PMS nor its duration were significantly correlated with mean peak acceleration. A significant correlation was found between the incidence of abnormal initial agonist bursts, called "segmented bursts," and mean peak acceleration. We conclude that ability to silence the agonist muscle prior to movement is not strongly associated with bradykinesia in Parkinson's disease.