1. Sit on a bench, box, or chair with a dumbbell in your left.
2. Extend your arm toward the floor and brace the back of it against the inside of your left thigh. Allow your hand to open and the dumbbell to roll to your fingertips.
3. Now close your hand and perform a wrist curl, squeezing the weight as hard as possible. Choose a weight you could perform 8–12 normal biceps curls with.