10 exercise products fitness experts don't recommend

With claims that you can get in shape in just six minutes a day (as advertisement for the Shake Weight states) or tone your abs even while watching TV (the Flex Belt), it's no surprise that the U.S. exercise equipment industry is a $4 billion business. But too often, marketing is triumphing over biology. It takes work, sweat and time to shed those pesky pounds and tone those muscles.

We asked certified fitness trainers and gym owners what they would never use with their clients. Here are the top 10 pieces of equipment they say they wouldn't waste money on: