Hammer Curl

What the hammer curl actually trains

Three muscles do elbow flexion, and the grip decides which of them takes the lead.

The biceps brachii is the visible one with two heads, and it both flexes the elbow and supinates the forearm. It works hardest with the palm up.

The brachialis sits underneath the biceps, crosses only the elbow, and does not care about forearm rotation. It is a strong elbow flexor in any grip, and because it sits beneath the biceps, developing it pushes the biceps up and adds thickness to the arm viewed from the side.

The brachioradialis runs along the top of the forearm and contributes most in a neutral or overhand grip.

A hammer curl, with the palms facing each other, removes the biceps' supination advantage and shifts more of the work to the brachialis and brachioradialis. Coratella and colleagues examined biceps curl variations and found the way a curl is performed changes the muscle activity involved, which is the mechanism behind rotating between grips rather than repeating one.

Setting up and curling

Stand tall with a dumbbell in each hand, palms facing your thighs. Feet hip width, abs braced, elbows pinned at your sides.

Let the arms hang completely straight so the muscles start from a stretch. Wrists straight, grip firm.

Curl up towards the shoulder without rotating the wrist. Keep the elbow still so the upper arm does not swing forward. Stop close to the shoulder and hold for a beat.

Lower over about two seconds to completely straight arms, and pause briefly before the next rep.

Both arms at once or alternating both work. Alternating lets you use slightly more weight per arm and takes longer; simultaneous is more time-efficient and slightly harder to cheat.

The mistakes that cost you the most

Swinging is the universal curl error. The hips generate the rep, the arm goes along for the ride, and the set looks productive while doing very little. The test is whether you can stop the dumbbell dead at any point in the range.

Elbows drifting forward brings the front delt in and shortens the range at the same time. Pin them.

Rotating the wrist on the way up turns a hammer curl into a normal curl, which defeats the point of selecting it.

Cutting the bottom of the range is the quiet one. Straight arms on every rep. Pallares and colleagues found longer ranges of motion produced at least as good adaptations as shorter ones, and the bottom of a curl is where the elbow flexors are longest.

And the programming error: doing only hammer curls, or only supinated curls. They are complementary, not interchangeable.

How to programme the hammer curl

Three to four sets of eight to fifteen with 90 seconds of rest. Arms are small muscles with short movements, so higher reps and shorter rest suit them, and very heavy low-rep curling tends to become a swinging contest.

This is one of the best places in the gym to train to failure. Nothing to drop, no spotter, no risk. Refalo and colleagues found the difference from training closer to failure was modest once volume was equated, so it is a choice, but if any set in your session is going to the end, a curl is a sensible candidate.

Remember that every pulling exercise you do trains the elbow flexors as well. Chin-ups in particular load the biceps heavily. Schoenfeld and colleagues found weekly sets per muscle related to hypertrophy in a dose-response way, but the count for biceps should include the rows and chin-ups, not just the curls.

Two sessions a week of three or four sets, split between a hammer and a supinated variation, covers the arm properly for most people.

Where the hammer curl sits in your week

At the end of a pull session, in the arm block. On an upper/lower split, in the upper accessory block. On a bro split, on arm day or after back work.

Never before your rows or chin-ups. Pre-fatiguing the elbow flexors makes every pulling exercise worse and gains you nothing.

If arms are a priority, the useful structure is one supinated curl and one neutral or reverse-grip curl in the same block, two or three sets each. That covers the biceps, brachialis and brachioradialis in about eight minutes.

Variations and swaps

Cross-body hammer curls, curling towards the opposite shoulder, are often felt more strongly in the brachialis and are worth trying if the standard version does not.

Rope hammer curls on a low cable give constant tension through the range, including at the top where dumbbells get easy.

Incline hammer curls, seated with the arms hanging back, lengthen the position at the shoulder and make the bottom of the range considerably harder.

Reverse curls, with an overhand grip, take the emphasis further towards the brachioradialis and the forearm extensors. They also build grip, which the hammer curl does modestly and which Lee and colleagues and others have associated with broader strength measures.

Zottman curls cover both directions in one exercise: palms up on the way, rotate at the top, palms down on the way down.

What the evidence does and does not say

It says curl variations differ in the muscle activity they produce, and that grip position changes which elbow flexors contribute most. That is the basis for including more than one grip.

It does not say hammer curls build bigger arms than supinated curls, or that the brachialis can be isolated. Most of that argument comes from electromyography, and Vigotsky and colleagues have made the case that EMG amplitude measures electrical activity at a moment rather than predicting growth over months.

The practical summary is simpler than the debate: curl with your palms up sometimes and facing each other other times, use a full range, do not swing, and do enough of it. The muscle underneath does not need to be isolated to grow, only trained.

Hammer curl: common questions

What is the difference between hammer curls and normal curls?

Grip. A hammer curl keeps the palms facing each other, which removes the biceps' supination advantage and shifts more work to the brachialis and brachioradialis. A supinated curl loads the biceps brachii more directly. Both are worth doing.

Do hammer curls make your arms bigger?

They build the brachialis, which sits beneath the biceps, and developing it adds thickness to the arm and pushes the biceps up. They are a genuine addition rather than a substitute for supinated curls.

Should I curl both arms at once or alternate?

Either. Alternating lets you use slightly more weight per arm and takes longer. Curling both at once is more time-efficient and slightly harder to cheat on.

How heavy should hammer curls be?

Light enough that you can stop the dumbbell dead at any point in the range without swinging. If finishing the set requires leaning back, the weight is too heavy.

Do I need curls if I do chin-ups and rows?

Pulling exercises load the elbow flexors substantially, so some arm growth comes for free. If arms are a priority, direct curl work adds volume cheaply, and the neutral grip covers muscles that pulling alone trains less directly.