Abs seem to be the common target area that people struggle toning. It doesn't help that abdominal exercises are usually done on the floor which can be hard. Not only do you have to deal with the hard surfaces but the crunching motion can cause lower back problems. Prevent any further damage to you back by working out abs on an exercise ball. The exercise ball relieves back pressure by strengthening and developing the core body muscles that help stabilize your spine.
The fitness ball has multiple uses other than just being a workout ball for abs. The fitness ball can also act as a yoga ball by incorporating exercise ball workouts into the routine. Work on your balance by using the ball as a stability ball, using the muscles in your core to keep you from falling off the ball. Balance ball workouts have unlimited amount of different exercises you could do, get creative with it!