Is yoga really exercise? - from the Guardian

The trend towards high-intensity workouts has reinforced the notion, held by some, that yoga doesn’t really count because most of its forms don’t make the heart pound. It does, however, lower blood pressure and the risk of heart disease. A review of 17 studies published in 2013 found yoga reduced blood pressure and therefore the risks of heart disease and stroke.

Another study found that overweight, middle-aged individuals who had done yoga for at least four of the previous 10 years had, on average, lost 5lbs. This compared to an average weight gain of 13.5lbs for those who hadn’t done yoga. The ancient Indian practice has been linked to hormonal changes that improve mood and boost sleep.
“During yoga, core muscles are required to generate more force than they ordinarily would, which causes an adaption response that strengthens those muscles,” says Dr McGuigan. “So yes, it is exercise. It is also complementary to other activities that require joint control, which is pretty much every sport.”