Both are elbow-flexion movements. A standard curl turns the forearm toward palms-up; a hammer curl keeps the palms facing each other. Because the biceps brachii flexes the elbow and helps supinate the forearm, the palms-up position gives it the clearer direct biceps role.
Neutral grip does not switch the biceps off. The biceps, brachialis and brachioradialis still share the work. Choose dumbbells, cables or an EZ-bar by wrist stability, available resistance and a controlled elbow range—not by claims that one tool isolates a muscle head.
The direct evidence is useful, but its scope is narrow and should not be turned into a universal growth ranking.
In the 2023 comparison, ten competitive bodybuilders performed non-exhaustive curls with supinated, neutral and pronated grips.
Brachioradialis excitation was slightly greater in the supinated condition in that study; other studies report small or inconsistent grip differences.
Electrical excitation, a small trained sample and one testing protocol cannot establish which exercise produces more muscle growth over months.
The result supports a supinated curl as the clearer primary biceps choice. It does not require deleting hammer curls, which can still add useful neutral-grip volume and individual wrist comfort within a balanced weekly plan.
Neither grip isolates a specific biceps head. Shoulder position and resistance profile create clearer loading changes than grip labels alone.
Hold the dumbbells with palms facing your sides and wrists stacked.
Keep the upper arm calm; stop before the shoulder rolls forward.
Lower until the elbow reaches a comfortable extended position.
A little natural movement is fine; repeated hip drive is not.
Use a supinated grip or rotate toward palms-up as you curl.
Avoid leaning back to manufacture the last repetition.
Do not lift the elbow excessively or fold the wrist backward.
Return through the same controlled path and useful range.
Use the movements on separate days or in the same session after pulling work. Keep the priority curl first and add the second only while technique and elbow comfort remain stable.
Standard palms-up curls are the stronger primary choice for direct biceps-brachii training because supination matches the muscle’s anatomy and produced greater excitation in the best direct grip comparison. That conclusion is narrower than claiming guaranteed long-term growth superiority.
Hammer curls remain useful for neutral-grip variety, added elbow-flexor volume and individual wrist comfort. Use both when your program has room, but describe the difference honestly: it is a change in grip, mechanics and comfort—not a switch that isolates the long head or guarantees greater brachioradialis activation.
