During a bicep curl, which muscle acts as the agonist?

In a bicep curl, the bicep muscle is the agonist because it is the primary muscle responsible for the movement of flexing the elbow joint. As the individual lifts the weight by bending the elbow, the bicep contracts, shortening its muscle fibers to create the force needed for this action.

The other muscles mentioned play different roles during the exercise. The tricep, for example, acts as the antagonist during a bicep curl; it provides resistance and controls the movement as the bicep contracts. The forearm is not a specific muscle but rather a section of the upper limb that includes various muscles, any of which may assist in stabilizing the movement. The deltoid is primarily involved in shoulder movements and does not significantly contribute to the elbow flexion that occurs during a bicep curl. Therefore, the bicep is definitively the agonist in this context.