Which muscle is the primary mover when performing a bicep curl?

The biceps brachii is the primary mover when performing a biceps curl.

A biceps curl mainly involves elbow flexion: the forearm bends toward the upper arm while the weight is raised. The biceps brachii is a major contributor to that action and also helps supinate the forearm, turning the palm upward. It has two heads, the long head and short head, which join into a muscle on the front of the upper arm.

The answer does not mean the biceps works alone. The brachialis lies beneath it and is a powerful elbow flexor, while the brachioradialis assists with elbow flexion, particularly when the forearm is in a neutral or thumb-up position. The triceps performs the opposing action—elbow extension—so it is not the prime mover during the lifting phase of a standard curl.

Grip and shoulder position can change how much different muscles contribute. A supinated dumbbell curl emphasizes the biceps brachii, whereas a hammer curl gives the brachialis and brachioradialis a larger role. Even so, “biceps” remains the canonical quiz answer for the standard curl.