Sit at the end of a flat bench with your legs in front of you and feet flat on the floor, spaced hip-width apart. While holding a barbell with a shoulder-width, overhand grip, rest your forearms on the tops of your thighs so that your wrists and hands hang off your knees. Flex your wrists so that your hands hang down from your wrists at about a 90 degree angle. Extend your wrist to lift the weight up as high as you can. Hold this position for a second while forcefully contracting your forearm muscles, then slowly return the bar back to the start position.