Synergists: Biceps Brachii (especially the long head), Brachialis
Stand with a dumbbell in each hand, with each dumbbell resting on the front of a thigh [waiting for illustration to be corrected].
Keeping your upper arm fixed, exhale as you curl the left dumbbell upward, across your body, and toward your left shoulder.
Hold for a count of two and squeeze your biceps.
Inhale as you reverse the motion and return the dumbbell to the starting position.
Repeat with your right arm.
Keep alternating arms.
Comments and tips
Keep your body and upper arms still; only your forearms should move.
You can alternate your arms, as described above, or do one arm at a time (as demonstrated in the video).
The standard hammer curl works the same muscles (i.e. your brachioradialis, in your forearm, and your brachialis and biceps brachii, both in your upper arm). However, compared with the standard hammer curl, the cross-body hammer curl puts a bit more emphasis on your brachialis and the long (outer) head of your biceps brachii. Therefore, the standard hammer curl is a little better for building big forearms, whereas the cross-body hammer curl is a little better for building a big biceps peak.