Hammer curls: what the neutral grip does not change

Turn your palms inward and you are supposed to switch from the biceps to the brachioradialis. Electromyography finds no such switch.

In the gym, the hammer curl earns its place with one sentence: the neutral grip targets the brachioradialis, the thick muscle along the forearm. Three studies measured what forearm rotation actually moves, and Overload's usage data says which of the six variants members really do.

The brachioradialis does not switch on with the grip

Caufriez et al. (2018) had fifteen young men flex the elbow at maximal effort, with surface electrodes on the biceps, the brachialis and the brachioradialis. Each man repeated the movement in three forearm positions: neutral, full pronation, full supination, with torque measured isokinetically at 60°/s over a 120° range.

All three muscles are highly active in all three positions. For the brachioradialis, activity rises slowly through the first part of the flexion and peaks at end range in 73.3% of subjects. And activity is slightly higher in supination.

The brachioradialis is a full elbow flexor, which the study establishes across the three positions at once. It does not turn on through wrist rotation.

What the implement moves is measurable

Marcolin et al. (2018) compared three curls in twelve trained men: dumbbells, straight bar, EZ bar, one set of ten repetitions at 65% of 1RM each, with biceps and brachioradialis EMG synchronised to an electrogoniometer.

The EZ bar produces higher activation than the dumbbells, for the biceps (p < 0.05) and for the brachioradialis (p < 0.01). The gap between the straight bar and the EZ bar stays small on both muscles, to the point that the authors write that choosing between them is a matter of subjective comfort.

So the difference sits with the implement, worth a few percentage points, not with the rotation of the hand. Two hands on an EZ bar already sit in semi-pronation, which makes the comparison with the hammer grip less clear-cut than it looks.

Arm position outweighs hand position

Oliveira et al. (2009) compared three dumbbell curls in 22 subjects at 40% of maximal isometric contraction: standing, inclined on a bench, and preacher. The incline curl and the standing curl drive the long head of the biceps up to 95% of maximal RMS, and across the whole range. The preacher curl tops out at 80%, over a short arc at the start of the movement.

Kassiano et al. (2025) took the comparison as far as growth. Sixty-three young women did either preacher curls (n = 30) or incline curls (n = 33), twice a week for eight weeks, with elbow flexor thickness measured at three points.

The incline curl grows the proximal region more (mean difference 0.08 cm, 95% CI 0.02-0.13). The preacher curl grows the distal region more (0.10 cm, 95% CI 0.04-0.15). Each group gained more strength on its own exercise at the 3RM test, which the authors put down to specificity.

The six hammer curls in the Overload library

The Overload exercise library holds 897 movements. Six are hammer curl variants. Members spread across them very unevenly.

Variant	Implement	Member uses
Hammer Curls	Dumbbells	636
Cable Hammer Curls - Rope Attachment	Cable	488
Alternate Hammer Curl	Dumbbells	354
Incline Hammer Curls	Dumbbells + bench	24
Preacher Hammer Dumbbell Curl	Dumbbells + preacher bench	11
Cross Body Hammer Curl	Dumbbells	1

One point of method, because it changes how the table reads: this counter adds up how often the movement appears in recorded sessions, not sets and not distinct members. An exercise that sits high in the app's search starts with an advantage.

Two numbers still stand out. The cable rope version takes 488 of the 1,514 uses, nearly a third of the family, for the reason that holds across isolation work: tension stays constant through the whole range, which the guide on cable versus free weights covers in detail. And the cross body hammer curl, often presented as the most effective version for the forearm, has 1.

The two variants the studies separate, incline and preacher, account for 35 uses between them. So the proximal versus distal debate from Kassiano et al. plays out over 2% of the family.

Practical recommendations

• Pick the hammer grip for wrist comfort and load, not to recruit the brachioradialis. Caufriez et al. find it active in neutral, pronation and supination.
• Vary arm position rather than hand position if you want a different distribution. That is the axis on which Kassiano et al. measure a growth difference, 0.08 to 0.10 cm in eight weeks.
• Keep the incline or standing curl for work across the whole range. Oliveira et al. measure up to 95% of maximal RMS there, against 80% over a short arc on the preacher bench.
• Take the EZ bar when dumbbells are free but you want slightly more activation. Marcolin et al. place it above dumbbells on both muscles.
• To target the forearm itself, direct wrist work does a different job from the hammer curl. The guide on wrist curls covers what it adds.

Conclusion

The neutral grip is no switch to the brachioradialis: that muscle flexes the elbow in all three forearm positions, and slightly more in supination. What does move something is the implement, worth a few points of activation, and arm position, worth 0.08 to 0.10 cm of thickness in eight weeks. Take the hammer grip when your wrist asks for it or when you want to load, and leave the incline and preacher curls to distribute the growth.

This article presents the current scientific evidence. For a personalised program, consult a health professional.