Muscles' Co-activation in a Stationary Limb Alteres According to the Movement of other Limb

This paper reports an interesting phenomenon of observable muscle co-contraction in stationary limbs according to the movement pattern in an oscillating limb. In the experiments the subject's electromyography signals of biceps and triceps of both left and right arm are recorded. Two experiments were conducted which are different in the posture of left and right arm. The first experiment is conducted when both forearms are in upright posture. In the second experiment though, the right forearm is moving. It was observed that the EMG of both biceps and triceps (i.e. co-activation) of the stationary limb follow that of the opposite moving limb. The reason can be addressed by the necessity of stabilizing the stationary limb when one executes motion in the counter limb. Moreover it can possibly be due to post-intention, pre-motion brain activities that may fire the muscles of both limbs similarly.