The effect of isometric contraction on the regulation of force tremor in the contralateral limb

This study examined how regulating force tremor in a single limb is altered when the opposite limb is actively engaged in a force generating task. Index finger abduction force and first dorsal interosseous (FDI) activity were assessed in thirteen healthy subjects, at target forces from 5% to 60% MVC for the non-dominant limb (unilateral task), and again when the dominant limb simultaneously generated a submaximal abduction force (bilateral task). When the non-dominant limb generated force at 20% MVC, tremor was greater during the bilateral task compared with the unilateral task; a finding reflected in the amplitude of peak power of force. Bilateral responses were also examined during a prolonged 60% MVC unilateral contraction. Force tremor and muscle activity amplitude increased while the frequency of activity decreased for the contracting limb. Additionally, force tremor significantly decreased towards the end of the prolonged contraction in the contralateral limb. Overall, it appears that the process of performing isometric contractions invokes tremor-related changes in the opposite limb at selective force targets, and performing prolonged unilateral contractions invokes tremor-related changes in the opposite limb when it is at rest.