How To Do the Hammer Curl

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The hammer curl exists in most programmes for one stated reason: the neutral grip hits the brachioradialis and brachialis rather than the biceps, so it builds the forearm and the thickness under the bicep.

That reason is repeated everywhere and it is worth checking, because somebody measured it.

What came back does not support the standard claim. The exercise is still worth doing. The justification people give for it is not the one the data supports.

The three-grip comparison

This is the study that matters here.

Ten competitive bodybuilders performed bilateral biceps curls in non-exhaustive six-rep sets using an eight-repetition-maximum load, with the forearm in three positions: supinated, palms up; pronated, palms down; and neutral, the hammer position. Surface electromyography recorded biceps brachii, brachioradialis and anterior deltoid, and the ascending and descending phases of each variation were analysed separately.

During the ascending phase, biceps brachii excitation was greater with the supinated grip than with the pronated grip, by 19 percent with an effect size of 2.60, and greater than the neutral grip by 12 percent with an effect size of 1.24.

That part is expected. Palms up recruits the biceps most, because supination is one of the biceps' jobs.

Here is the part that is not expected.

The brachioradialis also showed greater excitation with the supinated grip than with the pronated grip, by 5 percent with an effect size of 1.01, and greater than the neutral grip by 6 percent with an effect size of 1.10.

The supinated grip beat the hammer grip for brachioradialis activity. The muscle the hammer curl is supposedly for was more excited by the standard curl.

And the anterior deltoid was more excited by the pronated and neutral grips than the supinated one, by 6 and 9 percent, with effect sizes of 2.07 and 3.18.

Read that last one carefully. The neutral grip's largest effect size in this study was on the front of the shoulder, not the forearm.

Ten competitive bodybuilders in a single session, six reps per set, measuring muscle excitation rather than growth over time. Small, specialised sample, and EMG amplitude is not hypertrophy. But it is a direct test of the exact claim, and the claim did not survive it.

So why do hammer curls at all

Three honest reasons, none of which is the one you usually hear.

The neutral grip is the strongest wrist position for most people. You can typically handle more load in a hammer curl than a supinated curl, and load is the variable that drives progression.

It is kinder on the wrist and elbow. If supinated curling with a straight bar aggravates your wrist, the neutral grip removes the rotation that causes it.

And it is a different position, which has value on its own. Training a movement pattern through more than one joint configuration is reasonable practice even without an activation advantage.

What the evidence above does not support is doing hammer curls specifically to target the brachioradialis, since the supinated grip out-excited it on that measure.

These three reasons are practical reasoning, not findings from any source cited here.

The setup and the movement

Stand tall, dumbbells at your sides, palms facing your thighs. That neutral position is held for the entire rep. If your wrist rotates as you curl, you have drifted into a standard curl.

Elbows pinned at your sides. Your upper arm does not travel. This is the same instruction as every curl and it is broken as often here as anywhere.

Curl up without letting your elbow come forward. If the elbow moves toward the front of your body, you have added a front raise to the top of the rep, which the study above suggests is already happening more than you think in this grip.

Stop when your forearm is around vertical or slightly past. Going higher usually means the elbow travelled.

Control the way down across two to three seconds and go to full extension at the bottom. Cutting the bottom short is how people convert a curl into a half-range shrug of the arm.

One arm at a time or both together both work. Alternating lets you handle more load per arm and takes twice as long.

Standard coaching practice rather than findings from the sources cited here.

Which curl implement, and does it matter

There is a comparison of the common bar options.

Twelve participants performed one set of ten repetitions at 65 percent of their one repetition maximum for each of three curl variants: dumbbell curl, straight barbell curl, and EZ or undulated bar curl. Electrodes were placed on biceps brachii and brachioradialis, with an electrical goniometer recorded alongside the EMG to separate the concentric and eccentric phases of each variant.

The discussion states the practical conclusion directly. The EZ variant may be preferred over the dumbbell variant, as it enhances biceps brachii and brachioradialis activity during the whole range of motion, and only in the eccentric phase for the dumbbell comparison.

And on the two bars: the small difference between straight barbell and EZ bar for both muscles makes the choice between these two exercises a matter of subjective comfort.

Subjective comfort. Stated by the researchers, not by me.

That is a useful licence. If your wrists prefer the EZ bar, use it. If the straight bar feels better, use that. This is not a decision worth agonising over.

Twelve participants, one set each, single session, measuring activation rather than growth. And this compared bar and dumbbell curls in a supinated position rather than testing hammer curls.

One more claim that did not hold

While we are checking assumptions, here is a rigorous test of another popular one, on this exact muscle group.

A randomised within-subject trial recruited 21 resistance-trained men averaging 25 years old. Each performed unilateral elbow flexion with one shoulder extended, which lengthens the elbow flexors, and the other shoulder flexed, which shortens them. Both arms used a low-load vascular occlusion regimen at 30 percent of one repetition maximum, 15 repetitions per set, 4 sets per session, 4 sessions per week for 3 weeks, at 80 percent of vascular occlusion pressure. Magnetic resonance imaging measured elbow flexor cross-sectional area before and after.

The stated hypothesis was that hypertrophy would be greater in the extended shoulder position, the long muscle length.

The paper's own title reports the result: similar regional hypertrophy of the elbow flexor muscles at short versus long muscle lengths.

Similar. The long-muscle-length advantage that gets asserted constantly did not appear in this trial, on the arms, measured by MRI, with each participant serving as their own control.

That does not overturn the wider long-length literature, which points the other way in several studies. It does mean the picture is less settled than the confident version you hear, and on the elbow flexors specifically one well-controlled trial found no difference.

Twenty-one men over three weeks using low-load occlusion training, which is a specific and unusual training regimen. Results under occlusion at 30 percent of 1RM may not transfer to normal loading.

Why any of this is worth your time

The hammer curl is a good exercise held up by a bad reason.

What the evidence supports: the supinated grip produced more brachioradialis excitation than the neutral grip, not less, so the standard justification for hammer curls is backwards. The neutral and pronated grips recruited more anterior deltoid, with the largest effect sizes in the study. Bar choice between straight and EZ is explicitly described by researchers as subjective comfort. And the long-muscle-length advantage did not appear for elbow flexors in one MRI-measured within-subject trial.

What that leaves you: do hammer curls because you can load them heavier and they are easier on your wrist, hold the neutral position for the whole rep, keep the elbow still so the front delt does not take over, use full range, and control the descent.

This is a training article, not medical advice. Elbow or wrist pain during curls is a reason to see a qualified professional, not a reason to change your grip and push on.