Set a bench to about a 90-degree or vertical incline position, grab a pair of dumbbells, and sit down. Sit back on the bench and let your arms hang at your sides with your palms facing each other.
Curl both dumbbells simultaneously, keeping your palms facing each other and your elbows behind your body.
Lower the dumbbells under control, palms still facing each other, until your arms are fully extended once again.
Pause and repeat.