Why might antagonist muscles co-contract during a movement?

• A. To stabilize a joint, control motion, and improve precision.
• B. To speed up the movement
• C. To shorten the agonist
• D. To increase fat accumulation

Answer: (A)

Antagonist co-contraction around a joint increases joint stiffness, which helps stabilize the limb and give the nervous system finer control over movement. When both sides of a joint activate together, they resist perturbations and limit unwanted, excess motion. This is especially useful during precise or slow, deliberate actions, or when the limb must hold a position against external forces. The result is steadier, more controlled movement and better accuracy.

Co-contraction tends to slow or stabilize movement rather than speed it up, so it wouldn’t be used to hasten action. It also doesn’t shorten the agonist; both muscles are active, but the opposing activation opposes the net movement to maintain stability. And fat accumulation isn’t related to this motor control mechanism.