From tremor to movement: differences in variability and coupling during bilateral finger actions.

This study examined changes in movement variability, coupling, and muscle activity across three different bilateral finger movements (e.g., postural, isometric, and isotonic). It was predicted that movements characterized by increased interlimb coupling would be associated with increased levels of muscle activity and reduced movement variability. The results demonstrated task-specific differences in interlimb relations with coupling being lowest during postural tasks and highest under isotonic conditions. However, a similar pattern was not observed for muscle activity and movement variability. Of the three tasks, postural tremor movements were more variable and had lower levels of muscle activity. Alternatively, increased muscle activity and more regular movement dynamics were seen under isometric conditions. Overall, it would appear that differences in bilateral coupling across tasks are not reflective of a single driving mechanism but rather reflect differential contribution from intrinsic neuromuscular and mechanical sources.