Hammer curls do work the long head of the biceps, but they’re not the most efficient exercise for it. The neutral (palms-facing-in) grip reduces overall biceps activation by about 12% compared to a standard supinated (palms-up) curl. That said, the long head still contributes meaningfully to every hammer curl rep, and the exercise offers unique benefits for arm development that supinated curls don’t.
Why the Neutral Grip Reduces Biceps Activation
The biceps brachii isn’t just an elbow flexor. It’s also a forearm supinator, meaning it actively rotates your palm upward. When you curl with a supinated grip, the biceps is working double duty: bending the elbow and holding the forearm in that turned-up position. A hammer curl removes the supination demand entirely because your palm stays neutral throughout the movement.
EMG research published in Sports measured muscle excitation across three grip positions and found that biceps activation during the lifting phase was 12% higher with a supinated grip than a neutral one. The study also noted that this difference disappeared during the lowering phase, where all three grips produced similar biceps activity. One important limitation: the electrode placement used in this research couldn’t separate the long head from the short head, so the 12% figure reflects the biceps as a whole.
Researchers did observe that when biceps activation dropped during neutral and pronated grips, the front deltoid picked up the slack, increasing its activity by 6 to 9% to stabilize the shoulder joint. The study specifically noted this appeared to compensate for lower excitation of the long head in particular, since the long head’s tendon originates inside the shoulder joint and plays a role in stabilizing it.
What the Long Head Actually Does
The long head of the biceps starts at a bony ridge on the shoulder blade called the supraglenoid tubercle, runs through the shoulder joint capsule, and merges with the short head before attaching near the elbow. Because it crosses both the shoulder and elbow joints, its activation depends on two factors: elbow flexion angle and shoulder position.
During any curl, including hammer curls, the long head contributes to bending the elbow. It never shuts off completely regardless of grip. But its recruitment increases when two conditions are met: the forearm is supinated, and the arm is positioned behind the torso (which stretches the long head). A hammer curl meets neither of these conditions in its standard form, which is why it’s a decent long head exercise but not an optimal one.
Where Hammer Curls Excel
The real value of hammer curls is what happens beneath and alongside the biceps. The brachialis, a thick muscle that sits under the biceps, is a pure elbow flexor with no role in supination. It works hard during every grip position, but it gets relatively more of the total workload during hammer curls because the biceps contribution drops. A well-developed brachialis pushes the biceps up from underneath, adding width to the upper arm and making the biceps appear taller when flexed.
The brachioradialis, the prominent muscle on the thumb side of your forearm, also works during hammer curls. Its natural resting position is a neutral grip, so it functions efficiently during the movement. Building this muscle improves forearm size and grip strength, both of which support heavier lifting on other exercises.
Better Exercises for the Long Head
If your primary goal is long head development, exercises that combine supination with shoulder extension will outperform hammer curls. The incline dumbbell curl is the most commonly recommended option. Setting a bench to 45 to 60 degrees and curling with palms up places your arms behind your torso, stretching the long head at the bottom of each rep. Research from the Journal of Sports Science and Medicine found that both incline curls and standard standing curls produced consistent biceps long head activation throughout the full range of motion, making them preferable for overall biceps development.
That same study found something worth noting about the incline position: the shoulder hyperextension stretches the long head beyond its optimal length at the bottom of the rep, which can reduce force production in that range. This isn’t a problem in practice since it simply means the bottom portion of an incline curl is harder, which is exactly the kind of stimulus that drives muscle growth in the stretched position.
Concentration curls also deserve mention. Bracing your elbow against your thigh eliminates momentum and keeps tension on the biceps through the full contraction, which helps develop peak shape. Standard supinated curls, whether with a barbell or dumbbells, remain a reliable staple for both heads.
How to Use Hammer Curls in Your Program
Hammer curls work best as a complement to supinated curls, not a replacement. A practical approach is to include one supinated curl variation (incline curls, barbell curls, or concentration curls) as your primary biceps exercise for long head emphasis, then follow it with hammer curls to target the brachialis and brachioradialis. Three to four sets of 10 to 12 reps is a standard range for hammer curls.
You can also modify hammer curls to shift more work toward the long head. Performing them on an incline bench, with your arms hanging behind your torso, combines the neutral grip’s brachialis emphasis with a stretched shoulder position that increases long head involvement. This hybrid won’t fully replicate the activation of a supinated incline curl, but it’s a reasonable way to get more long head work from a single exercise while still building forearm and brachialis size.
Keeping your elbows pinned to your sides during hammer curls also matters. When the elbows drift forward, the shoulder flexes and the long head shortens, reducing its contribution. A strict elbow position maintains tension on the long head throughout the rep.