What is an antagonist?

• A. Muscle that Creates Opposing Movement
• B. Main Mover
• C. Stabilizing Muscle
• D. Muscle That Shortens During Movement

Answer: (A)

An antagonist is the muscle whose action opposes the main mover at a joint. It helps control and smooth the movement by braking or opposing the force of the agonist. For example, when you bend the elbow, the biceps acts as the primary mover (agonist) and shortens to flex the elbow, while the triceps serves as the antagonist, lengthening to oppose that flexion and prevent the motion from happening too quickly or overshooting. Stabilizing muscles exist to hold joints steady, but the antagonist specifically describes the muscle that produces the opposite movement. The idea that a muscle shortens during movement describes the agonist, not the antagonist, though antagonists can co-contract to stabilize in some tasks.