Doing crunches is one of the most common ways to tone the stomach, and it works! However, if you want to add some intensity or need a variation, doing the crunch on the stability ball is the way to go. Using the ball allows for a better range of motion and challenges other muscles to keep you balanced on the ball. The most important thing to remember is to keep the focus on the abs and not the hip flexors. Squeeze that stomach, look toward the sky and don't forget to breathe!
Beginners - Don't rush it! Take the time to work on balancing on the ball before you crunch.
Advanced - If you need more intensity, work the obliques by twisting (opposite elbow to opposite leg) or add a dumbbell (extended away from your head!) to provide more resistance.
Picture taken of Amy Mac at the Parthenon in Nashville.