Celebrity trainer Tracy Anderson told Redbook magazine that those trendy, expensive spinning classes can actually make you gain weight — particularly in your thighs, and particularly if all you're doing for exercise is spinning.
She's on to something, agrees fitness expert Michael Mantell.
"People do cardio as a main way that they're trying to lose weight, and the problem with this is 60 percent of the weight they lose is fat, and 40 percent is muscle," says Mantell, who's the senior fitness consultant for behavioral sciences for the American Council on Exercise.
"And we don't want to lose lean muscle, because lean muscle burns more calories per pound, per day, than fat does."
Read more: For weight loss, HOW you exercise is more important than how much
Spin class can indeed add bulk to your thighs — but keep in mind that it's muscle, of course, not fat. The other reason spinning — or any exercise program — can lead to weight gain: It makes you super hungry, and gives you a handy way to justify post-class beers, or fries, or whatever your personal caloric Kryptonite may be.
If you love SoulCycle and the like, don't stop going. The high-intensity cardio is an effective, efficient way to burn calories, and the pedaling gives you some resistance training, too.
But if your only exercise, ever, is spinning, you'll need to add more resistance training, two or three times a week, if weight loss is your goal. That means lifting weights (free weights or machines), programs like P90X, or the classics: push-ups, pull-ups, squats, lunges.
Read more: Is diet or exercise best for weight loss?
Actually, "more resistance training" is solid advice for anyone trying to lose weight, whether or not spinning is your thing, Mantell says.
"Most people say if you want to lose weight, you cut down on the cardio and you add the resistance training," he says.