How the Body Works : Muscles move joints
Muscles move joints
Movement at joints is effected by the action of muscles that are generally arranged in opposing pairs. As one muscle contracts and shortens, the other relaxes and becomes longer. For example, the biceps and triceps. The biceps and triceps control movement of the forearm, the biceps contract and act as the prime mover, while triceps, the antagonist, relaxes. When the elbow is straightened the reverse occurs.