Muscles that oppose the action of the primary mover are called what?

• A. Agonists
• B. Antagonists
• C. Stabilizers
• D. Synergists

Answer: (B)

Muscles that oppose the action of the primary mover are antagonists. When a muscle contracts to create a motion, the opponent of that movement serves to control, slow, or reverse the action, helping to stabilize the joint and produce smooth, coordinated movement. For example, in elbow flexion, the biceps brachii acts as the primary mover, while the triceps brachii serves as the antagonist that opposes that flexion. Similarly, during knee extension, the quadriceps are the agonists, and the hamstrings act as antagonists. Remember, a muscle can play different roles depending on the direction of the movement and joint position, but the term antagonist specifically refers to those that oppose the primary mover. Synergists assist the agonist, and stabilizers help keep a body part steady during the action.