Hammer curls are a staple in the training regimens of athletes, bodybuilders, and fitness enthusiasts who prioritize functional arm development. Unlike standard bicep curls, this exercise involves a neutral wrist position—palms facing each other throughout the movement—which creates a unique demand on the musculoskeletal system. Understanding which muscles do hammer curls target is essential for designing a balanced program that improves strength, hypertrophy, and joint stability.
The Primary Muscle: The Brachialis
The most significant muscle activated during a hammer curl is the brachialis, a flat muscle located beneath the biceps brachii. This muscle acts as the primary flexor of the elbow joint, and its position deep to the biceps makes it a powerful force in lifting the forearm. Because the hammer curl’s grip minimizes the biceps' ability to supinate the wrist, the brachialis is forced to do the majority of the work. For individuals seeking to increase arm circumference at the elbow level, targeting this muscle is paramount.
Synergists and Secondary Movers
While the brachialis is the star of the show, several other muscles contribute to the success of the lift. The brachioradialis, a muscle of the forearm, plays a crucial role, particularly as the grip transitions or the elbow angle changes. The flexor carpi radialis and other wrist flexors are also engaged to stabilize the wrist joint in the neutral position. Additionally, the anterior fibers of the deltoid and the trapezius may provide slight stabilization to the shoulder girdle, ensuring the movement remains focused on the elbow.
Biceps Brachii Involvement
Although the hammer curl is not the optimal movement for maximizing bicep size, the biceps brachii is still involved in the exercise. Its role, however, is primarily isometric, acting as a stabilizer rather than the prime mover. The neutral grip significantly reduces the strain on the biceps tendon compared to a supinated curl, which is beneficial for those recovering from tendonitis or elbow pain. This makes the exercise a smart accessory movement for maintaining arm size without excessive joint stress.
Functional Strength and Athletic Carryover
Beyond aesthetics, hammer curls offer significant functional benefits. The neutral grip mimics the natural alignment of the arm when performing pulling or lifting tasks in daily life or sports. This exercise helps fortify the tendons and ligaments around the elbow, improving resilience against the strains common in throwing, racket sports, and weight training. By developing the brachialis and brachioradialis, athletes often see improvements in their overall pressing and pulling strength, as a stronger elbow joint allows for more aggressive training.
