Hammer curl

Q: What muscles do hammer curls work?

Hammer curls work the three elbow flexors: brachialis, brachioradialis and biceps brachii. All three are involved in every curl grip. The brachialis is a pure flexor that works from any forearm position, the brachioradialis is active whether the forearm is supinated, neutral or pronated, and the biceps brachii contributes to flexion while also being the forearm's main supinator.

Q: Are hammer curls better than regular bicep curls?

Not for biceps activation. In the one study that compared them directly under load, a supinated grip produced higher biceps brachii activation than a neutral grip during the lifting phase. Hammer curls are worth doing because the neutral position does not require holding the forearm in supination under load, and because varying grips lets you train the elbow flexors without repeating the same joint position every session.

Q: Do hammer curls build the brachioradialis?

They train it, but so does every other curl. Three studies bear on the claim and none supports it: one found a supinated grip higher, one found a pronated grip higher, and the one usually cited in favour of hammer curls concluded that all eight variations it tested activated the brachioradialis equally.

Q: Is a 50 lb hammer curl good?

There is no reliable public dataset of hammer curl weights by bodyweight and training age, so anyone giving you a confident number is guessing. What actually determines whether a given weight is appropriate is whether you can complete your target reps with your elbow still and your torso quiet, and whether that weight has moved over the past few months.

Q: Are hammer curls worth doing?

Most regular RepCount users have logged hammer curls at some point, though they appear in only about one in eleven workouts. That is the profile of an accessory, and the logs bear it out: when a hammer curl shows up it is usually the only curl in the session, with no barbell, dumbbell or concentration curl alongside it in 60% of cases. They are accessory work: typically about three sets, in a session of around seven exercises, most often alongside pulldowns, dumbbell curls and cable rows.

Q: Should you straighten your arms at the bottom of a hammer curl?

Yes. A common cue says to stop just short and keep constant tension, but the range you would be giving up is the one that produces the result. In an arm curl study that split the movement in half, training the stretched bottom half produced greater biceps growth and greater full-range strength than training the top half, and a later trial in trained lifters found that lengthened half-reps matched full reps. Straighten the arm; what you lose by stopping short is more than what you gain.

Q: Should I curl both arms at once or alternate?

Either. Nothing in the evidence favours one over the other, so it is a preference rather than a technique point. Curling both at once finishes the set faster; alternating gives each arm a rest between reps. The illustration on this page shows both arms together, which is not a recommendation.

Q: How many sets and reps should I do?

Hammer curls are isolation work for a small muscle group, so they suit being placed at the end of a session and taken close to failure with clean form rather than loaded heavy. The weight matters less than whether the elbow stays put and the arm straightens at the bottom.

Also called neutral grip curl, dumbbell hammer curl.

What is a hammer curl?

A hammer curl is a dumbbell curl performed with a neutral grip: palms facing each other, thumbs up, the dumbbell running front to back. It trains the three elbow flexors — brachialis, brachioradialis and biceps brachii — the same muscles every curl works, in a wrist position many lifters find more comfortable to load.

Anatomical illustration of a standing dumbbell hammer curl, shown at the bottom and top of the rep with the elbow flexors highlighted.

How do you perform a hammer curl?

Set up

Stand with a dumbbell in each hand, arms at your sides, palms facing your thighs.
Set your feet about hip width apart and brace lightly through your midsection.
Let your shoulders sit back and down rather than rolled forward.

Execution

Keep your palms facing each other for the whole rep. The grip never rotates.
Bend at the elbow and lift the dumbbell toward your shoulder.
Keep your upper arm roughly vertical so your elbow stays under your shoulder.
Stop when your forearm runs out of travel, without swinging the weight up.
Lower under control, all the way back to a straight arm.
Alternate arms, or curl both together if you prefer.

Common mistakes

Swinging the torso to start the rep
Momentum moves the dumbbell without asking much more of the elbow flexors. If you need body English to finish a set, the weight is doing your programming for you.
Letting the elbow drift forward
Once the elbow travels forward, the front delt takes over the top of the movement and the elbow flexors do less as the range increases.
Choosing hammer curls to hit a specific muscle
No curl grip singles out one elbow flexor; grip changes emphasis modestly at most. Pick the grip that lets you load the movement comfortably and progress it. See what the evidence says ↓

Where it fits in a session

After compound pressing and pulling work, near the end of a session.

Hammer curls are an isolation exercise for a small muscle group, so they do not need to be heavy to be useful, and they respond to being taken close to failure with clean form.

Muscles worked

brachialis
brachioradialis
biceps brachii

Listed as co-actors rather than ranked: the evidence does not support ranking these for a neutral grip, and every curl grip works all three.

What the evidence says

Three studies bear on this, and none of them supports the claim. Coratella and colleagues (2023, ten competitive male bodybuilders) found brachioradialis activation higher with a supinated grip than a neutral one during the lifting phase (+6%, p = 0.004), with no difference between neutral and pronated. Kleiber and colleagues (2015, sixteen participants) found brachioradialis highest in pronation, with supinated and neutral not significantly different from each other (p = 0.67). The first two disagree about which grip is highest, and agree that neutral is not it.

The third is the one usually cited in support of hammer curls. Bagchi and Raizada (2019) compared eight curl variations at 70% of one rep max, and hammer curls did come out numerically highest for brachioradialis. But the paper's own conclusion is that "no statistical difference was observed when comparing the muscle activation of Brachioradialis muscle in the eight different biceps curl exercises", and that all eight had the same effect on the brachioradialis. A ranking inside a non-significant comparison is not a finding. The study most often used to prove hammer curls target the brachioradialis concluded that curl variation does not change brachioradialis activation at all.

One point favours the hammer curl over a reverse grip curl: Coratella found biceps brachii activation higher with a neutral grip than a pronated one (+7%, p < 0.001), while supinated was higher still (+12% over neutral, p = 0.006).

Read these carefully. Both samples are small. Neither study measured brachialis, so claims about hammer curls and the brachialis are untested here in either direction. And EMG amplitude during a set is not the same question as which grip builds more muscle over months, which these studies did not ask.

A plausible reading of why anatomy and EMG seem to disagree, offered as reasoning rather than as a finding from these papers: better leverage can mean a muscle needs less activation to produce the same torque, so the position where a muscle works best is not automatically the position where it shows the most electrical activity.

What lifters actually do

Most regular RepCount users have logged hammer curls at some point, but they appear in only about one in eleven workouts, which is exactly the profile of an accessory: widely tried, modestly used. When they do show up, they are usually the only curl in the session: of the sessions that contain a hammer curl, 60% contain no barbell, dumbbell or concentration curl at all, and the other 40% pair one with it. Those are full sessions of about seven exercises, and the movements the hammer curl most often sits beside are pulldowns, dumbbell curls and cable rows. Lifters treat it as arm work at the end of a pull day.

61.5%

of regular lifters have logged it

8.9%

of workouts include it

2.96

sets per session, on average

7.3

exercises in those sessions

Most often trained alongside

Share of hammer curl sessions that also include each exercise.

Pulldowns26.7%
Dumbbell bicep curl23.2%
Cable row19.9%
Barbell bicep curl16.4%
Pull up14.2%

Figures come from workouts tracked in RepCount.

Variations

Cable hammer curl — Keeps tension more even through the range than a dumbbell does at the top.
Rope hammer curl — Cable variant using a rope attachment, which lets the hands sit naturally neutral.
Seated hammer curl — Removes the option to swing the torso, which is the most common fault standing.
Incline hammer curl — Upper arm sits behind the torso, lengthening the elbow flexors at the bottom.
Preacher hammer curl — Pad fixes the upper arm, so the elbow cannot drift forward.
Cross body hammer curl — Curls the dumbbell across toward the opposite shoulder.

Related tools

Frequently asked questions

What muscles do hammer curls work?