Here's a fun way to strengthen your abdominal muscles and train them to stay "pulled in" when you sit and stand up. The transverse abdominus acts as a girdle to compress your front abdominal wall. When it's strong, it will help your midsection remain slim and firm. As an added bonus to this exercise, hugging a stability ball works your inner thigh muscles.
1 Lie on a mat or a padded surface. Hold a stability ball between your calves and ankles. Rest your head on the floor. Inhale and relax your arms on the floor below shoulder level.
2 On an exhale, pull your navel down toward your spine and tighten the muscles in your midsection. Slowly lower your legs as you continue to squeeze the ball with your legs. Do not let your neck or lower back begin to arch away from the floor. (Stop moving your legs before you get to that point.) Pause with your legs at about a 45-degree angle. Inhale and slowly bring your legs up to the starting position. Repeat 12 times.