The brachialis is the often-overlooked muscle between the biceps and triceps. Training your brachialis is a great way to help “project” a massive arm. Why? Because as the brachialis develops, it pushes your biceps and triceps further away from one another, making for a wider-appearing arm.
The standard hammer-grip curl is good, but I prefer the cross-body variation shown here. Grip the dumbbell as hard as you can throughout the rep.