This exercise works the flexor muscles located on the back or underside of your forearm. Forearm workout with dumbbells. Dumbbell exercises for forearms target the inner and outer forearm muscles. Browse through the various dumbbell exercises for forearms below: Palms-Up Wrist Curl One-Arm Palm-Up Wrist Curl Palms-Down Wrist Curl One-Arm Palm-Down Wrist Curl Palms-Up Wrist Curl Sit on one end of a bench and hold one dumbbell on each hand, wrists against your knees, […] To do this exercise: Start with 5- or 10-pound dumbbells, or a lighter weight if needed. But before we get into the workout, let us look at some important pointers that we must remember: a) Do not work on your forearms every day.