Upper frequency limits of bilateral coordination patterns

This study examined what changes occur in upper-limb bilateral coordination during clapping as the movement frequency requirements were increased to the maximum. Subjects were required to begin the clapping action at approximately 1 Hz and gradually increase the movement speed until their maximal frequency was achieved. Hand and finger displacement and surface electromyograms (EMG) from finger flexor/extensor muscles were recorded. The results showed that the maximal attainable movement frequency was between 7 and 8 Hz. As the action approached the ceiling frequency (>5 Hz), there was a significant reduction in movement amplitude of the non-preferred limb accompanied by increased co-activation of the muscles within this limb. The movement amplitude of preferred limb was maintained. Subsequently, there was a decrease in coupling between the two limbs with the bilateral coordination pattern transitioning from an in-phase pattern to an asymmetric mode, where only the preferred limb was moving. These findings reveal that there is a frequency induced transition to single-limb motion that reflects a stability boundary at the upper frequency limits of bimanual coordination.