In a hammer curl exercise, which muscle acts as the agonist?

In a hammer curl exercise, the brachioradialis acts as the agonist muscle. The primary function of this muscle is to flex the elbow, particularly in a neutral grip position, as seen in the hammer curl. While the biceps brachii does assist in elbow flexion and contributes to the movement, the brachioradialis is more actively engaged when the hand is positioned in a hammer grip, making it the primary muscle responsible for the action during this specific exercise.

The triceps brachii is involved in elbow extension, not flexion, and therefore does not act as the agonist in this movement. The deltoid, while important for shoulder movements, is not primarily involved in the elbow flexion that characterizes the hammer curl. Thus, focusing on how the hammer curl specifically utilizes the brachioradialis clarifies its role as the primary muscle acting during this exercise.