Gregg D’Andrea

After teaching spinning at workout meccas like Equinox and Crunch, D’Andrea opened his own 5,000-square-foot fitness studio last year to cater to his considerable following. (He claims a 70 percent retention rate among his clients.) Free advice: “For weight training, dumbbells give far better results than machines. And forget weight belts. Last I heard, cavemen didn’t wear weight belts, and they were in better shape than some of the people working out now.”