Effects of movement frequency and joint kinetics on the joint coordination underlying bimanual circle drawing.

Ten healthy participants performed bimanual symmetric and asymmetric circle drawing at 4 frequencies. The authors partitioned the variance of the joint configuration across repetitions into 1 component representing equivalent joint configurations with respect to achieving stability of the mean hand path (i.e., goal-equivalent variance, GEV) and 1 component leading to a variable hand path (non-goal-equivalent variance, NGEV) across cycles. Higher frequencies led to increased NGEV related to control of the nondominant hand and to the relative position and orientation between the hands during asymmetric drawing. The results were related to differences in muscle and interaction moments between the arms, and they suggest a possible relationship between the ability to use intersegmental forces and the stability of interlimb synergy.