Nicole L. Campbell: Core exercises strengthen your core muscles, including the muscles in your abdomen and back. You can do many core exercises with a fitness ball. Let's try a side exercise.

Lie on your right side, with the fitness ball between your legs. Prop yourself up on your right elbow, with the opposite hand in front of you.

To begin the exercise, tighten your abdominal muscles. Keeping the ball between your legs, raise your legs a few inches off of the floor. Hold for three deep breaths. Then return to the starting position. Also try the exercise lying on your left side.

If you're just starting out, repeat the exercise five times on each side. Remember to breathe freely and deeply throughout the exercise, and keep your abdominal muscles nice and tight. As you get stronger, gradually increase to 10 to 15 repetitions on each side.