Yoga is an increasingly popular form of exercise in the US. According to Yoga Journal more than 20 million Americans use yoga as their form of exercise. As a form of exercise yoga is fairly straightforward, involving stretching and holding poses that strengthen muscles. It also carries the generic benefits of any exercise in terms of calorie-burning and cardiovascular health.
Yoga, however, is more than exercise – it also comes with a “spiritual” angle. The term itself refers to a number of practices originating in ancient India meant to strength mind, body, and spirit. For this reason it has become a popular target for marketing the latest health pseudoscience. You will be hard pressed, in fact, to find a yoga class that does not incorporate some degree of outright woo, the only question really is not if, but how much. This is unfortunate because yoga may be an effective alternative for low-impact exercise.
There is some evidence that yoga, for example, is effective in relieving low back pain, although it may not be more effective than usual care. There is a lack of quality studies comparing yoga to other forms of exercise, and so we may just be seeing the generic benefits of exercise. Still, if the classes are fun and they keep people motivated to continue their exercise regimen, that is useful.
Yoga, therefore, fits into a more general phenomenon of marketing a specific intervention as if it has specific benefits, when in fact it only has generic benefits. For example, there are many studies showing that transcendental meditation is effective for lowering blood pressure. However, studies generally compare TM to no intervention, not to other forms of relaxation. The parsimonious interpretation is that TM confers the generic benefits of relaxation, but there is no evidence to suggest it confers any specific benefits.