Why your hammer grip feels harder than palms-up curl
Muscular coordination of biceps brachii and brachioradialis in elbow flexion with respect to hand position
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When you curl with your palm facing inward (hammer grip), your forearm muscle (brachioradialis) works harder to bend your elbow, while your bicep doesn't change effort — your body just uses the forearm more to make up for the bicep's awkward angle.
Surprising Findings
Biceps activation didn’t change across hand positions — even though biomechanics suggest it should be weaker in pronation.
Common belief is that supinated grips maximize bicep recruitment. This study shows the bicep is surprisingly consistent — it doesn’t adapt to grip, the body just shifts work to another muscle.
Practical Takeaways
If you want to target your forearm, use hammer curls. If you want to focus on biceps, supinated curls are fine — but don’t assume hammer curls are ‘better’ for biceps.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When you curl with your palm facing inward (hammer grip), your forearm muscle (brachioradialis) works harder to bend your elbow, while your bicep doesn't change effort — your body just uses the forearm more to make up for the bicep's awkward angle.
Surprising Findings
Biceps activation didn’t change across hand positions — even though biomechanics suggest it should be weaker in pronation.
Common belief is that supinated grips maximize bicep recruitment. This study shows the bicep is surprisingly consistent — it doesn’t adapt to grip, the body just shifts work to another muscle.
Practical Takeaways
If you want to target your forearm, use hammer curls. If you want to focus on biceps, supinated curls are fine — but don’t assume hammer curls are ‘better’ for biceps.
Publication
Journal
Frontiers in Physiology
Year
2015
Authors
T. Kleiber, Leonie Kunz, C. Disselhorst-Klug
Related Content
Claims (6)
The brachioradialis is preferentially activated during elbow flexion when the forearm is in a neutral (hammer) grip position compared to supinated (palms-up) grip.
Elbow flexion performed in a stretched position (e.g., incline or preacher curl) increases relative activation of the brachioradialis by limiting biceps mechanical advantage.
When your palm is down, your bicep can’t pull as well because its tendon gets twisted — so your body makes your other forearm muscle work harder to bend your elbow.
Your body switches which forearm muscle does most of the work when bending your elbow — your bicep stays steady, but your other muscle steps up when your palm is down.
When your palm faces down and you bend your elbow, your forearm muscle (brachioradialis) works harder than when your palm faces up or straight ahead — but your bicep works the same no matter how your hand is turned.