Add Yahoo as a preferred source to see more of our stories on Google. Your favorite ab-building machine at the gym may be causing you more harm than good. That's right—we're talking about the torso ...

With each year that passes, I really don't notice any "noticeable" decline in my movement efficiency or strength. I cruise through most weeks with three or four workouts and pretty much keep trucking.

Even after three months at the Port Charlotte YMCA, Cara McCarthy hesitates at the torso-rotation machine. "I'm still figuring this one out," she said. "Adjust it and lean back, I'm thinking." ...