Yoga is not just for recovery or working on flexibility. Many women see yoga as a softer fitness option, but depending on the format (and there are many out there with more and more hybrids popping up), yoga can provide both a vigorous workout and much sought after weight loss. If you are a yoga purist and dislike when weights/plyo elements are added into your flows, you can still find the challenge you need in Vinyasa or power, terms often used interchangeably. The key factor here is pace: each asana (pose) typically matches with one breath resulting in a quick pace.
The other major factor in these classes is the serious strength element that comes from asanas that require lots of muscular engagements: push-ups, lunges, squats, single leg and arm balances, and lots of transition work in the form of a traditional Vinyasa (high plank to low plank [Chaturanga], to Upward Facing Dog, Downward Facing Dog, and back to a Standing or Seated Pose). Over and over again. Add in the very popular element of a heated classroom, and you'll get the even more challenging option of hot yoga. In these classes, you may actually feel the fat melting away (along with lots of sweat) as you lengthen, strengthen, and find some Zen.