Lie on an exercise ball with your hips lower than your shoulder. Reach back and grab something that won't move. Lift and ben your legs so your thighs point up and your lower legs point ahead. Do a standard reverse crunch, using your abs and hip flexors to curl your legs toward your chest.
Lie on the floor or a mat with your arms at your sides. Hold your legs off the floor with your knees bent at a 90-degree angle so your thighs point straight up and your lower legs point straight, parallel to the floor.
Procedure: Crunch your pelvis toward your rib cage. Your tailbone should rise a few inches off the floor as your knees move toward your chin. Pause, then slowly return to the starting position.
