STARTING POSITION:
Select the appropriate weight of the dumbbell. Sit on a bench. Grab the dumbbell and place your forearm on your leg, letting your hand hang outside the leg. Your palm should face up.
MOVEMENT:
Fully flex your wrist making sure you don't move any other part of your body. Return to the starting position in a smooth movement. Repeat the movement for the specified amount of repetitions, then switch sides and repeat the exercise.
TIPS: The exercise key is quality over quantity. The trick is to perform the exercise using proper form.