The key to a working wrist curl is full range of motion — your wrist should flex fully at the top and extend fully at the bottom. Hold a dumbbell in each hand with your forearms resting on a table or your thighs, palms facing up. Curl your wrists upward and squeeze, then lower all the way until your wrists extend backward and the dumbbell is held mostly by your fingertips. That full bottom position is what activates the forearm. Do not bounce or use momentum; the slower you move, the more tension you maintain through the full range of motion.