Which statement best defines the antagonist muscle during a stretch?

• A. The muscle that is being stretched
• B. The muscle that actively contracts to produce movement
• C. The muscle that stabilizes the joint
• D. The muscle that fatigues first during exercise

Answer: (A)

The key idea is that an antagonist is the muscle whose action would oppose the movement produced by the opposing muscle (the agonist). In a stretch, you lengthen the muscle, which means it would oppose the movement if it were to contract. So the muscle you’re stretching is functioning as the antagonist in that context. The other options describe roles that aren’t about opposing movement: the muscle that actively contracts to move is the agonist; the one that stabilizes a joint is a stabilizer; and fatigue timing isn’t about defining antagonists.