Antagonist muscle action is defined as which of the following?

• A. Prime mover
• B. Antagonist muscle action
• C. Stabilizer
• D. Synergist

Answer: (B)

Antagonist muscle action refers to the muscle that opposes the movement produced by the prime mover, controlling and slowing the motion so it occurs smoothly. When a joint bends, the muscle that initiates the bend (the prime mover) works, while its opposite partner lengthens or relaxes to allow that movement. Sometimes the antagonist may also contract slightly to help stabilize the joint or to decelerate the limb, providing control. For example, in elbow flexion the biceps brachii acts as the prime mover, while the triceps brachii serves as the antagonist, lengthening to permit the elbow to bend and sometimes contracting eccentrically to control the speed of the bend. This contrasts with a stabilizer, which holds a body part steady, and a synergist, which assists the prime mover.