Muscle coactivation

Coactivation of biceps and triceps. The biceps’ EMG is on top, while the triceps’ EMG is on the bottom.

Muscle coactivation is a phenomenon in which a muscle is activated coordinately with another muscle. The EMG shown demonstrates the antagonistic muscle activity in the biceps and triceps of a relaxed and seated subject, with the elbow bent at 90 degrees and palm facing up, who alternately activates the biceps and triceps muscles while resisting the movement with the other hand. The muscles work together and there is a large-scale alteration of activity in the biceps and in the triceps. The graph also shows how the process of coactivation works; when the biceps muscle is activated forcefully, it causes a minor increase in the activity of the triceps. Likewise, there is a minor increase of activity in the biceps trace when the triceps is activated. Coactivation of the muscles stabilizes a joint, although the mechanism is not well understood. Muscular coactivation is thought to be required for fine movements.