Biceps curl

Barbell or dumbbells

Bending the elbow with the palm up trains all three elbow flexors, with the biceps doing the most work.

What each muscle does in the biceps curl

Muscle	Role	Action
Biceps brachii	Primary	Flexes the elbow and supinates the forearm
Brachialis	Secondary	Flexes the elbow in any forearm position
Brachioradialis	Secondary	Flexes the elbow, especially with a neutral grip

Primary muscles are the prime movers; secondary muscles assist or stabilise. The balance shifts with grip, stance, range of motion and technique.