Alongside the biceps brachii, the brachialis (the primary forearm flexor) and brachioradialis (another forearm muscle), also form the active muscle groups during these exercises.

To fully develop your arms, you need to target the entire muscle group: the long and short heads of the biceps brachii, the brachialis (your elbow flexor), and the brachioradialis (forearm muscles).

To sculpt sleeve-busting muscle, you need to focus on the brachialis—the muscle that lies under the biceps brachii—too, he says. So what's the best way to do that?

Flex your elbows to bring the dumbbells towards your shoulders. Key muscles: Biceps brachii, brachialis (muscle beneath the biceps), forearms.

Bicep-focused exercises don’t only work the biceps, by the way. We also have a muscle called the brachialis that lies underneath the bicep and also helps to bend the elbow.

However, hammer curls also emphasize two other arm muscles: the brachialis, a muscle beneath the biceps brachii that helps support the elbow joint, and the brachioradialis, a forearm muscle that ...