Arms, Forearms, Shoulders
1. Attach a rope handle to a low cable pulley, and get into a shoulder-width stance facing the cable stack. Squat down, and, keeping your chest up, grip the rope with your thumbs up.
2. Explosively straighten your hips and lift the cable up, extending your arms as you rotate your body and shoulders to your right side. Quickly drop to the starting position, and explode up to the left side. That's one rep.