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.
Therefore, before we conclude that any relaxation has specific benefits we need to demonstrate that it has benefits above and beyond those for the relaxation itself. The same is true of any form of exercise, any form of mental activity for cognition, and any form of massage for muscle relaxation. It is therefore misleading to say that “Yoga works for X, or has these benefits” when the evidence only shows that exercise has those benefit, and there is nothing special about yoga as a form of exercise.
In addition to marketing generic benefits as if they were specific to yoga, proponents often mix in a liberal dose of pure pseudoscience and mysticism. Most yoga practitioners I know expect at least a casual mention of “energy” or some similar reference from their yoga instructors and are content to just ignore it. Some instructors, however, go way beyond a little mystical window dressing. The following e-mail I received from one skeptical yoga practitioner is typical:
I have recently been trying to lose weight, in addition to dietary changes, I have been exercising more, along with a normal gym routine I have decided to try yoga. I did quick a PubMed search and there did seem to be some evidence that yoga is effective for losing weight. During the classes the teacher stands at the front and gives a bit of dialogue to accompany the instructions on how to do the poses. Some of the things they say in these dialogues picked my skeptical ears and are the reason for this email. Along with the obligatory ”shared energy” and ”shared spirit” type of comments, which I fully expected, they made some other claims which have a pseudo sciencey twinge and I was hoping you guys could clear them up for me. Here are some of the more memorable ones in no particular order; during one bent over pose they say you are squeezing the pancreas/liver this apparently pushes toxin out and they also say you can taste the toxins coming out in your mouth (taste described as chloriney), during reverse back bending pose they say if you look back as far as you can you can stretch your optic nerve, in one pose where you bend your arms awkwardly they say that you build up blood pressure and when this pressure is released the blood will move so intensely through you arteries it will blast away plaque build up, near the end they have a breathing exercise which they claim is pushing out all the toxins the stretching has apparently pushed into your lungs, throughout they talk about the increasing of bone density and of joint strength, finally that stretching your lower back calms you because personal stress building up in your lower back muscles/tissues. Are any of these thing possible or is it all pure pseudo science?
None of those specific claims is based in reality. I certainly hope that yoga practitioners are not squeezing their liver or pancreas, or that they are stretching their optic nerve. Nerves don’t like to be stretched – that causes damage. It also would not be safe to perform a maneuver that backs up your blood flow and then releases it in a powerful blast. This has a much greater chance of causing a brain hemorrhage than scouring plaque off your arteries. In other words, the yoga instructor better hope that everything they are claiming is a lie, or else they are likely to find themselves liable for very real medical harm.
This brings up a very important question about yoga – how safe is it? All interventions should be considered on a risk vs benefit basis. While it seems that yoga carries with it the generic benefits of exercise, how does it rate in terms of risk? Not very well, it turns out – but of course, it depends on exactly how it is practiced. There is risk of injury from yoga, as there is with any sport or significant exercise. But yoga often involves poses that push the practitioner to extremes. There are reports, for example, of vertebral artery dissection and subsequent stroke from excessive neck extension or rotation.
In a telling New York Times article, yoga teacher Glenn Black warns that yoga is not for most people, but rather should be reserved for people who are already in good physical condition. For the general public the risk of injury is high, and they should be given either very basic routines, or targeted exercises for their specific issues. This would be more in line with what a physical therapist would do for a client – assess their needs and vulnerabilities, then target exercises that will be safe and effective for them. Other risks include overstretching ligaments, herniated discs, and neck or back strain.
Yoga is also susceptible to evidence-free marketing fads. I recently learned about so-called “hot yoga,” which is essentially yoga in a hot and humid environment. Such an environment might be conducive to dehydration and becoming overheated, but there is no evidence that it enhances the exercise or has any health benefits.
Yoga, if practiced responsibly, seems to be a reasonably effective form of stretching and exercise. There is insufficient evidence, however, to conclude that it is any superior to any other form of exercise of the same duration and intensity. There are concerns about the safety of yoga, as it often involves extreme stretching or poses that the average person might find not only difficult but physically harmful. I would therefore recommend caution before starting a yoga routine. If you have any physical limitations or medical conditions, consult your physician and consider a physical therapy assessment first. Find an instructor who seems reasonable and evidence-based. And do not feel pressured to try poses that are painful or seem to push you beyond reasonable physical limits.
Further – all of the mystical and pseudoscientific woo that often accompanies yoga is counterproductive. It may be useful for marketing to the gullible, but it taints the entire practice with pseudoscience. I would also find it difficult to trust in the competence of an instructor who thinks a yoga pose will squeeze toxins out of my liver.
It would be nice, but perhaps too much to hope for, to have a science-based yoga movement – yoga-based exercises minus the woo, and evidence-based to maximize safety and effectiveness.