Yoga compared to other workouts

I don't think yoga should be done for either calorie burning or for relaxation but really for dynamic flexibility and strength improvement. I have done a fair bit of yoga when younger. It can be relaxing but if you do a serious workout with proper form, it is as much about strength as it is about flexibility. For example, some of the back inversions, such as a camel pose (ustrasana), holding it for 1 minute is much tougher for me than doing lat pull downs for the same time. So also for even the upward dog - it can be quite a killer on the arms and wrists and you have to hold the whole pose for a 1 minute. Or take a look at what yoga super gran is doing here - at any age, the peacock pose is very demanding strengthwise.

http://www.dailymail.co.uk/news/article-1172810/The-yoga-supergran-bend-backwards-age-83.html

The thing about yoga, as compared to either a gym workout or cardio, is that you can only measure improvements against yourself - each of us is built differently and if you have, let's say, long legs and a shorter torso, you will find some of the forward bends very challenging ,but you may be much more flexible around the pelvis and find a lotus pose a cinch. Someone else might find the reverse true, so it can be both demoralising and counterproductive to get competitive about it or too regimental. My yoga guru used to say that all of us can (and tend to) monitor how far we could run at what speed or how much weights we pressed in the gym, but no one keeps track of how much you can bend forward (or back) and that's where spinal flexibility starts getting lost

Hope that helps