The hammer curl is a dumbbell curl variation performed with a neutral grip, meaning your palms face each other throughout the entire movement. This exercise is an effective addition to any arm training regimen, but it is not intended to target the triceps muscle. The primary focus is entirely on the muscles responsible for elbow flexion, which is the act of bending the arm. The hammer curl is a purposeful change in grip that shifts the emphasis from one set of arm flexors to others, making it a distinct alternative to the standard palms-up curl.
Primary Muscles Activated
The unique neutral grip of the hammer curl is designed to maximize the recruitment of two specific muscles: the brachialis and the brachioradialis. The brachialis is a deep muscle located underneath the biceps brachii, and its primary function is to flex the elbow, regardless of the forearm’s rotational position. Because it does not contribute to forearm rotation, the neutral grip places it in an optimal mechanical position, making it the strongest elbow flexor during this movement. Developing the brachialis is important for overall arm thickness, as its growth effectively pushes the overlying biceps muscle upward.
The exercise also heavily engages the brachioradialis, a prominent muscle that runs along the thumb side of the forearm. This muscle contributes significantly to the visual size and girth of the upper forearm, and the hammer curl is one of the most effective ways to train it.
The biceps brachii is still involved in the movement, but its activation is secondary compared to the brachialis and brachioradialis. In a traditional supinated (palms-up) curl, the biceps is the dominant muscle because it is responsible for both elbow flexion and forearm supination. By removing the element of supination with the neutral grip, the mechanical advantage of the biceps is reduced, allowing the deeper muscles to take on the majority of the load.
Understanding the Neutral Grip
The difference between a hammer curl and a standard bicep curl lies entirely in the biomechanical effect of the hand position. A supinated grip (palms facing up) places the biceps brachii in its strongest line of pull, maximizing its contribution to the curl. This grip also stretches the long head of the biceps, which helps to create the peak of the muscle.
Conversely, the neutral grip reduces the mechanical leverage of the biceps brachii. This position forces the forearm to remain in a neutral rotation, shifting the primary workload to the brachialis and brachioradialis. Since the brachialis only functions to flex the elbow, it maintains a strong pulling angle throughout the entire range of motion.
This strategic change in hand position allows individuals to often lift slightly heavier weights during a hammer curl compared to a strict supinated curl. This is partly because the brachialis is a powerful muscle, and the neutral grip recruits it more fully. The technique provides a distinct stimulus for comprehensive arm development.
Why Triceps Are Not Involved
The triceps brachii muscle is functionally separate from the muscles targeted during any type of curl. The triceps are located on the back of the upper arm and are the primary antagonists to the biceps and other elbow flexors. Their sole function at the elbow is extension, the act of straightening the arm.
The hammer curl, like all curling movements, is an exercise in elbow flexion, which is the opposite action of the triceps. Therefore, the triceps are not the target muscle; they are stretched and relaxed while the flexors contract to lift the weight. The triceps are involved only in a stabilizing capacity or as the opposing muscle group to control the lowering phase.
To effectively target the triceps, one must perform elbow extension movements, such as tricep pushdowns, overhead extensions, or skull crushers. These exercises place the triceps under tension to straighten the arm against resistance. The hammer curl and triceps exercises serve complementary roles in arm training.