Just like fashion, fitness trends come and go. Remember the AbFlex? I used to watch that infomercial over and over as a kid as I dreamed of getting a rippled, sizzling six pack. Too bad it was only a fad. However, once in a while, a fitness product comes in the market and actually does make sense. One such product is the exercise ball, also known as a gym ball, Swiss ball, or physio ball. Physiotherapists have been using these balls for years improving the...