Captain's Chair Sit up straight on a sturdy, armless chair or weight bench and grip the sides to stabilize your upper body. Slowly draw your knees up toward your chest. Hold for a moment, then lower slowly. Repeat 10-12 times; rest briefly and repeat. Keep the motion of raising and lowering your legs very controlled. Concentrate on using the strength of your abdominal muscles to push through the exercise, or else you could place too much stress on your lower back.