Patients with Parkinson's disease have a less differentiated muscle activation pattern than healthy controls during manual circle movement

To investigate changes in modulation of agonist and antagonist activity in patients with Parkinson’s disease (PD) during execution of continuous circle movement. PD patients experience changes in the organization of motor execution inducing problems with initiation and inhibition of movement. This leads to impaired starting and stopping of (purposeful) movement. On the other hand, purposeful movement requires a motor system in which initiation and inhibition of successive movements are adequately organized; the continuous modulation of agonist and antagonist activity. Yet, it is not clear how changes in initiation and inhibition, regarding the agonist-antagonist adjustment, in PD patients cause a decline in the ability to execute purposeful movement. A continuous circle task could provide further insight in specific changes in modulated muscle activity in PD patients. We employed a two-directional, continuous circle task (clockwise and counter clockwise) using a manipulandum with visual feedback. Kinematic and electromyographic (EMG) parameters of 4 lower arm muscles were used to compare (ant)agonist activity between a group of mildly affected PD patients (N515, stage 1-2 Hoehn Yahr) and 2 groups of healthy subjects (elderly, N516 and young subjects, N516). Comparison of kinematic parameters showed that PD patients perform circle movements significantly slower, make more errors and show more variability in task execution compared to both young and elderly subjects. The EMG data showed that PD patients use a less differentiated muscle-activation pattern than young subjects, when executing circle movements. The muscle activation pattern
of elderly was found to be slightly less differentiated than in young subjects, but still substantially better than in PD patients. We conclude that PD patients, compared to healthy subjects, show changes in kinematics and muscle activation patterns during execution of a continuous circle task. These changes in execution of continuous movement might provide an objective measure of both bradykinesia and rigidity, potentially useful for diagnosis, follow-up of disease progression and further fundamental investigations into these phenomena.