The routine: "Hatha yoga" traditionally refers to any physical practice of yoga. That is to say that Bikram, Iyengar, and kundalini are all various styles of hatha yoga. However, classes in the U.S. described simply as "hatha yoga" usually refer to a gentle form of yoga that focuses on basic postures and breathing techniques.
The burn: 175 calories per hour
Same as: A slow walk
Bikram and Hot Yoga
The routine: Bikram classes are comprised of 26 postures, each performed twice, in a studio heated to over 100 degrees.
The burn: 636 calories per hour
Same as: An hour of jogging
The routine: It's an Americanized version of ashtanga yoga, similar to vinyasa.
The burn: 300 calories per hour
Same as: A brisk walk
The routine: More intense than hatha, the poses are linked together in a fast, flowing sequence.
The burn: 445 calories per hour
Same as: An hour of moderate bike riding