1. In order to make this exercise you have to set on a flat bench holding dumbbell on each hand, and your elbows to your sides.
2. Raise the dumbbell and rotate the forearms until it is horizontal with your palms faces your shoulder.
3. Then slowly begin to bring the dumbbell back to the starting position as your breathe in, and repeat the movement to the other arm.
Tips and Advices:
The key to making this move safe and effective is to Use light weights, and do the movements slowly.