Sit on a bench and rest a barbell in your lap. With an underhand grip on a barbell, rest your wrists on your knees so your hands extend beyond your knees. Allow the weight of the bar to force your wrist toward the floor. Use your forearm muscles to power the weight back up. Perform one set of eight reps, rest 30 seconds then increase the weight 10% and perform as many reps as you can.