A muscle acting in opposition to the action produced by the prime mover or agonist, and which is responsible for returning a limb to its initial position. The biceps and the triceps muscles are, for example, antagonist muscles. Thus, when bending the elbow, an action of the biceps, the triceps is the antagonist. In healthy people, the antagonist is inhibited when the agonist is active, a process known as reciprocal innervation. In the cerebral palsies, both can be activated, a process known as co-activation. An important change in motor development is that from co-activation to reciprocal innervation in carrying out movements such as reaching and walking.
See Agonist muscle, Central pattern generator, Cerebral palsy, Dynamics, Isotonic contraction, Monosynaptic and polysynaptic reflexes, Motor development, Primary motor cortex, Reflex