SETUP: Grab a heavy dumbbell by one side so your hands are underneath the plates. Stand up straight, with your elbows pinned tight to your side.
REP: Curl the weight up, making sure your hands stay flat against the surface of the dumbbell. Lower under control.
TIP: The narrow-grip you we use on this exercise prioritizes the long head of the biceps. That makes this a great exercise for adding size to your arms (the long head of the biceps is the bigger of the two), and the flat grip allows us to do this without involving the forearms very much.