National Academy of Sports Medicine (NASM) Certified Personal Trainer (CPT) Practice Exam

Which term defines muscles that act as the prime mover in an exercise?

1. Antagonists

2. Synergists

3. Agonists

4. Stabilizers

The correct answer is: Agonists

The term that defines muscles acting as the prime mover in an exercise is "agonists." Agonist muscles are those that contract to produce the primary movement during an exercise. For example, during a bicep curl, the biceps brachii acts as the agonist since it is the main muscle responsible for flexing the elbow and lifting the weight. In contrast, antagonist muscles are those that oppose the action of the agonists; they provide balance and stability during movement but do not perform the primary action. Synergists assist the agonists by stabilizing joints or enhancing the movement, but they are not the main movers. Stabilizers help maintain posture and stabilize a body segment during movement but do not contribute to the action of the exercise itself. Thus, "agonists" accurately captures the role of the muscles that are directly responsible for executing a particular movement.