To make your forearm muscle bigger, you need to curl with your palm facing inward, not up.
Scientific Claim
The brachioradialis is preferentially activated during elbow flexion when the forearm is in a neutral (hammer) grip position compared to supinated (palms-up) grip.
Original Statement
“the brachioradialis... doesn't cross over the wrist and won't be trained through wrist movements. It instead helps bend your elbows during curls, but so do your biceps. So, to target this muscle more, you want to first rotate your arm into a neutral hammer grip.”
Context Details
Domain
exercise
Population
human
Subject
elbow flexion in neutral grip position
Action
preferentially activates
Target
the brachioradialis muscle
Intervention Details
Evidence from Studies
Supporting (2)
When you lift something with your palm facing sideways (neutral grip), your brachioradialis muscle works harder than when your palm is facing up (supinated grip), and this study proved it by measuring muscle activity.
When people pedal with their arms, their forearm muscle (brachioradialis) works much harder when their hand is in a hammer position than when their palm is facing up — this study measured that difference.
Contradicting (2)
The function of brachioradialis.
The study found that the brachioradialis muscle works just as hard whether your palm is up, down, or sideways during elbow bending — so it doesn’t prefer the hammer grip like the claim says.
Muscular coordination of biceps brachii and brachioradialis in elbow flexion with respect to hand position
The study found that when you hold your hand like you're holding a hammer (neutral), your forearm muscle doesn't work harder than when your palm is facing up — in fact, it works the most when your palm is facing down.