The American Council on Exercise reports that most people are unable to work the lower and upper abs independently, but Dr. Len Kravitz from the University of New Mexico indicates that some exercises engage lower abdominal muscles more than upper muscles. The stability ball is an effective tool for toning the lower abs, as the instability of the ball requires your lower abdominal muscles to engage to keep your balance. The instability also makes the ball more dangerous, increasing your risk of falling and poor body alignment during exercises. Follow all instructions for inflating, using and caring for your stability ball.
Choose a ball that fits your height. Ideally, your knees should bend at a 90-degree angle when you sit on the ball.
Perform stability ball crunches. Sit on the ball with your feet slightly wider than hip width and flat on the floor. Walk your feet forward until your thighs are parallel to the floor and your lower back rests on the ball. Cross your arms over your chest and lie back on the ball without arching. Contract your abs to sit up 45 degrees, then recline back. Repeat 12 to 15 times.
Do stability ball knee tucks, which require greater core stability, making it an advanced exercise. Lie on the ball in a plank position, with your hands on the floor and your lower thighs or knees on the ball. Pull your knees to the chest, rolling the ball with you until your knees are directly under your hips. Slowly return the ball to the start position without letting your back arch. Repeat 8 to 15 repetitions.
Do supine reverse crunches. The reverse crunch, sometimes called the reverse curl, can be performed without a ball, but by placing the ball between your legs, you add resistance and inner thigh work. Lie on your back on the floor. Lift your legs toward the ceiling and place the ball between your feet or legs at shin level. Rest your hands at your side. Contract your lower abdominal muscles, lifting your hips and legs up toward the ceiling. Release and repeat 12 to 15 repetitions.