Question

when flexing the elbow, the triceps is the ____ and the biceps is the ____. prime mover, flexor antagonist, flexor/prime mover extensor, antagonist protagonist, extensor antagonist

Explanation:

When the elbow flexes, the biceps is the muscle that contracts to cause the movement (prime - mover or flexor), and the triceps relaxes and acts as the antagonist to the biceps' action.

Answer:

antagonist, flexor/prime mover