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Ashtanga and Power Yoga

Good for: Weight loss

These two combine the regular benefits of yoga with a killer cardio session. Both styles focus on flowing from one pose to the next without rest—making for a terrific calorie burn (about 500 per hour). "The practice is meant to generate heat in your body," says Mandy Ingber, the yoga instructor behind Jennifer Aniston's ageless body. So, yes, you will sweat. A lot.

In Ashtanga, the more traditional of the two, you'll begin with chanting, then follow a sequence of poses ("asanas") that never changes. In a Power yoga class, the poses vary each time and there's usually none of the spiritual aspect.

Next: Yin Yoga