What best describes a synergist muscle?

• A. A muscle that resists the movement
• B. A muscle that assists an agonist to produce a movement
• C. A muscle that stabilizes joints passively
• D. A muscle that acts as a prime mover

Answer: (B)

Synergist muscles help the main mover by adding force and guiding the movement, making the action smooth and efficient. They assist the agonist in producing the movement, providing extra leverage and helping to stabilize the joint so the motion happens with less extraneous movement. For example, during elbow flexion the biceps brachii acts as the main mover, while synergists like the brachialis and brachioradialis contribute additional force and help stabilize the forearm. In contrast, a muscle that resists the movement is the antagonist, a muscle that stabilizes joints passively is a stabilizer, and the prime mover is the agonist.