Rest your forearm on a bench with your wrist at the end of it so that your hand can freely move all the way up or down, palm facing up. Hold the dumbbell in the hand resting on the bench. Using your other hand, hold your forearm down so that the weight does not force it upward. Let your weighted hand fall below the bench. Bending only at the wrist, pull your hand as far up as you can, lower it back down, and repeat.

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