Hammer Curl vs Bicep Curl: Which Builds Bigger Arms?

Hammer curl vs bicep curl isn't a contest you need to settle: do both. The standard palms-up bicep curl puts more of the work on the biceps brachii, because that muscle both bends the elbow and rotates the palm upwards. The neutral-grip hammer curl shares the load more with the brachialis and brachioradialis, and most lifters can use a bit more weight on it. If you want bigger biceps, make the supinated curl your main lift and add hammer curls for thickness. If grip, forearms or cranky elbows are your priority, flip that.

Below is how each curl works, what the research actually shows (it's less dramatic than social media suggests), and how to put them together in a training week.

The short answer in one table

	Bicep curl (supinated)	Hammer curl (neutral)
Grip	Palms facing up	Palms facing each other
Main bias	Biceps brachii (both heads)	Brachialis and brachioradialis
Biceps involvement	High	Moderate to high
Forearm involvement	Lower	Higher, especially brachioradialis
Load you can handle	Moderate	Usually a little heavier
Elbow and wrist comfort	Can bother people with tight forearm rotation	Usually more forgiving
Best for	Biceps size and the classic peak	Arm thickness, forearms, grip carryover
Kit needed	Dumbbells, barbell, EZ bar or cable	Dumbbells, rope cable or a neutral-grip bar

What actually changes when you turn your hand

Three muscles bend your elbow, and forearm position changes how much each one contributes.

Biceps brachii

The biceps has two heads (long and short) that start at the shoulder blade and attach to the radius, the forearm bone on the thumb side. Because it wraps around the radius, the biceps doesn't just bend the elbow; it also turns your palm up. That second job, supination, is why a palms-up grip lets it work from its strongest position. Turn the hand to neutral and the biceps is still very active, but it's no longer doing everything it was built to do.

The long head crosses the shoulder joint, so arm position matters too. Curls with your elbows behind your body, like the incline dumbbell curl, stretch the long head more. Curls with the elbows in front, like preacher curls, bias the short head. Grip changes the biceps-versus-forearm balance; shoulder angle changes the long-head-versus-short-head balance. Two separate dials.

Brachialis

The brachialis sits underneath the biceps on the lower half of the upper arm and attaches to the ulna, the forearm bone that doesn't rotate. That means forearm position barely changes its leverage: it bends the elbow whether your palm faces up, in or down. It's a pure elbow flexor and does a big share of the work on every curl.

Why care? A well-developed brachialis pushes the biceps up and out and fills the gap between biceps and triceps when you look at the arm from the side. Plenty of lifters with "flat" arms have decent biceps and an undertrained brachialis.

Brachioradialis

The brachioradialis runs from the outside of the lower upper arm down to the wrist on the thumb side. It's the meaty muscle at the top of your forearm, and it has its best line of pull with the hand in neutral or turned slightly down. Hammer curls and reverse curls train it hard; palms-up curls train it less.

What the research shows (and what it doesn't)

Most "hammer curl vs bicep curl" posts quote EMG percentages with no source. Here's what two real studies found.

A 2015 study in Frontiers in Physiology had 16 healthy adults perform slow elbow flexion with the hand pronated, neutral and supinated while recording surface EMG from the biceps and brachioradialis (Kleiber et al., 2015). The brachioradialis contributed significantly more with the palm facing down than in the neutral or supinated positions. Biceps activity, normalised to maximum, didn't change significantly across hand positions. So in that setup, the clearest effect of grip was on the forearm muscle, not the biceps.

A larger 2025 study tested 36 healthy men holding a light 1kg load at five elbow angles in each forearm position (BMC Sports Science, Medicine and Rehabilitation, 2025). Between 30 and 90 degrees of elbow bend, biceps EMG was higher with the palm up than with it neutral or down, and neutral beat pronated. The brachioradialis showed the opposite tendency in that mid range: its activity was lower in supination than in neutral or pronation.

Put together, the direction is consistent with the anatomy. Palms up nudges work towards the biceps; neutral and palms down nudge it towards the brachioradialis. Be honest about the limits, though. Both studies used light loads or isometric holds, surface EMG can't see the brachialis well because it's buried under the biceps, and EMG amplitude isn't the same thing as muscle growth. Nobody has run a long training study pitting hammer curls against supinated curls for arm size. The evidence supports "different emphasis", not "one is useless".

Which should you prioritise?

For bigger biceps

Lead with a supinated curl. Barbell, EZ bar, dumbbell or cable bicep curls all work. Do them first in your arm work while you're fresh, then add one or two sets of hammer curls for the brachialis. If you specifically want the long head, rotate in incline curls.

For thicker arms overall

Split it roughly evenly. Arm size from the side comes from the brachialis as much as the biceps, so give hammer curls equal billing: alternate which one you do first each session.

For forearms and grip

Prioritise hammer curls and add reverse curls. You'll load the brachioradialis directly, and holding a heavier dumbbell in a neutral grip for 8 to 12 reps gives your grip a decent workout as a side effect. They won't replace deadlifts or carries for grip strength, but they help.

For sore elbows or wrists

Start with hammer curls. People who can't comfortably rotate their forearm all the way to palms-up often feel straight-bar curls in the wrist or the inner elbow. The neutral grip skips that end range. An EZ bar or a rope attachment on a cable is a halfway house worth trying before you drop supinated curls entirely. If curling of any kind causes sharp pain rather than muscle burn, stop and get it checked.

How to do each one well

You can find step-by-step technique in our full hammer curl guide and bicep curl guide, so here are the cues that matter most for the comparison.

Bicep curl. Start with your arms long and palms facing forward. Keep your elbows pinned just in front of your ribs and curl until your forearm is near vertical; going higher just lets the biceps rest. With dumbbells, you can start with palms in and rotate up as you lift, which uses the biceps' supination role fully. Squeeze at the top, then lower over 2 to 3 seconds.

Hammer curl. Palms face each other the whole way, thumbs pointing up. Curl straight up in front of you or slightly across your body towards the opposite shoulder (the cross-body version tends to light up the brachialis and lets many people move a touch more weight). Don't let your wrist flop back; keep it in line with your forearm.

Common mistakes with both

Swinging the weight up. Hammer curls invite this because you can handle more load. If your hips move or your shoulders roll forward to start the rep, the weight is too heavy. Drop 2kg and own every rep.

Cutting the bottom short. The stretched position at the bottom is where a lot of the growth stimulus lives. Straighten your arm fully (without locking hard) before the next rep.

Elbows drifting forward. Letting the elbows travel up turns the end of the curl into a front raise and takes tension off the arm. Keep them roughly under your shoulders.

Treating the hammer curl as a "heavy day" ego lift. A little more weight than your bicep curl is normal. Twice as much usually means momentum is doing the work.

Doing ten sets of each. Rows, pull-ups and chin-ups already hammer your elbow flexors. Huge curl volumes on top often just leave your elbows achy.

How to program both in a week

For most lifters, 6 to 12 hard sets of direct curling a week is a solid range, split across two sessions. Here's a simple template that covers both goals.

Day	Exercise	Sets x reps	Rest
Session A	Dumbbell or EZ bar bicep curl	3 x 8 to 10	90 seconds
Session A	Hammer curl	2 x 10 to 12	60 to 90 seconds
Session B	Incline dumbbell curl or cable curl	3 x 10 to 12	60 to 90 seconds
Session B	Cross-body hammer curl	3 x 8 to 12	60 to 90 seconds

Take most sets to within one or two reps of failure. When you hit the top of the rep range on every set with clean form, add the smallest jump you can. That's where curls get awkward on fixed dumbbells: going from 10kg to 12.5kg is a 25% jump, which is big for a small muscle. Adjustable dumbbells with 2kg steps make steady progression much easier, and a single pair covers both curls plus all your pressing and rowing. Our top pick in the best adjustable dumbbells UK roundup is the NÜOBELL 232, which runs from 2kg to 32kg per dumbbell in 2kg increments.

Check NÜOBELL 232 price on Amazon

If you're newer to lifting, a single session of 2 sets of each curl, twice a week, is enough to start. Combined with the NHS recommendation of muscle-strengthening work on at least two days a week, that's an easy habit to fit around a full-body plan.

Rep ranges that suit each curl

Both curls respond well to 8 to 15 reps. Bicep curls can go a little lower (6 to 10) on a barbell or EZ bar if you like heavier work. Hammer curls often feel best at 10 to 15, because grip can give out before the arm does at very heavy loads. If your grip is the weak link, that's useful information: keep going, and it'll catch up.

Variations worth knowing

• Zottman curl: curl up palms-up, rotate to palms-down at the top, lower slowly. Biceps on the way up, brachioradialis on the way down, in one rep.
• Rope cable hammer curl: constant tension through the whole range and kind on the wrists.
• Reverse curl (palms down): the strongest brachioradialis bias of the lot, as the 2015 study found. Use about half to two-thirds of your bicep curl weight.
• Spider or preacher curl: short-head bias and almost impossible to cheat.

Our verdict

The hammer curl vs bicep curl debate has a boring but useful answer. The supinated bicep curl is the better choice when biceps size is the goal, and the hammer curl is better for brachialis, forearm and grip work, plus it's often the comfier option for elbows and wrists. Since a full arm needs all three elbow flexors, run both, adjust the ratio to your priorities, and spend your effort on progressive overload and clean reps rather than hunting for the one perfect curl.

Recommended reads

• Hammer curls: how to do them and muscles worked
• Bicep curl: technique, benefits and variations
• Cable bicep curl guide
• Incline dumbbell curl guide
• The best adjustable dumbbells in the UK