Well... its not cardio or weight lifting... but man.. it keeps you fit. The dynamic flows or ashtanga sequences are challenging, lots of isometric weight balance in freaky positions, smooth transitions, push ups (chaturanga/plank poses) etc.  Having said all that: puting your foot on your ankle is not yoga. Hanging from a sling is not yoga. Sitting arond doing breathing exercises is in fact part of yoga, but supposed to train you lung capacity for the dynamics and not the whole "exersize". Yoga is also fasting, vegetarianism, living salt and sugar free, controlling impulses and letting go the petty cravings of the matrial world. An aspect of Yoga these fat lazy fucks might want to look in to before posting their stupid tumblr shit