Which term defines the muscle that contracts and causes movement?

• A. Agonist Muscle
• B. Antagonist Muscle
• C. Stabilizer
• D. Synergist

Answer: (A)

The main idea is identifying the muscle that contracts to produce the movement at a joint—the primary mover. That muscle is called the agonist. It shortens and generates the force that creates the action. For example, during elbow flexion the biceps brachii is the agonist because it contracts to pull the forearm toward the shoulder. The antagonist opposes that movement and helps control it, a stabilizer fixes a joint to allow the movement to occur smoothly, and a synergist assists the agonist by adding extra force or guiding the motion to reduce unwanted movements. So, the term for the muscle that contracts and causes movement is the agonist.