The secret to honing a set of killer abs is functional training. For men, that means working the rectus abdominus with crunches to get that "six pack," for women it's working the transverse abdominus to tighten the pooch. Having tighter abs also lessens the chance of lower back pain and leads to overall body balance and core strength. One great piece of equipment is an exercise ball, which you can purchase at any sporting goods store at prices starting at $20. The diameter of the ball you will need is based on your height. One place to purchase this ball is GoFit.net.