THE BLOG
03/21/2013 05:10 pm ET | Updated May 21, 2013

The Yoga Injuries Debate: How 'Dangerous' Is Yoga, Really?

Brace yourself: The debate over yoga injuries has reemerged, and no matter how tired you may be of the prolonged row, there are useful things to pay attention to here.

First came new articles and blog posts from New York Times reporter William Broad, coinciding with the publication of the paperback version of his book, The Science of Yoga. Then followed a rebuttal of some of the claims made by Broad by Yoga Journal's medical editor Timothy McCall, M.D., followed by numerous other articles in the yoga blogosphere.

Why is this debate worth some serious attention? Because Broad offers up some pretty strong claims about a practice otherwise known for its extensive health benefits. In his book and accompanying articles, William Broad argues that yoga comes with a more extensive and severe risk of injury than the yoga community has faced up to.

Leading members of the yoga community, on the other hand, have pointed out that Broad's writings -- while replete with implied connections -- offer no solid evidence to back up the serious claims. Others have pointed to the somewhat suspicious timing of Broad's enthusiastic drumming of the alarm, which coincides with first the hardcover, then the softcover publications of his book.

So what is fact and what is fiction? I caught up with Dr. Timothy McCall to get the details of what caused him to speak up in this debate.

You yourself have been writing about yoga injuries and how to prevent them for years. So why the strong reaction to the claims made in the New York Times articles and the accompanying book?

While the coverage in the New York Times has been overly sensational, all the controversy it generated got the yoga community talking about the risk of injuries and how they can be lessened, and that's a good thing. As with any other serious physical activity yoga, of course, can lead to injuries. But Broad goes out of his way to argue that yoga is a particularly risky -- and even sometimes deadly -- and that this has long been the dirty little secret of the yoga community.

Those are strong contentions, and there's little evidence to support them. Indeed, most of the evidence we do have contradicts them. Further, little differentiation is made between more vigorous and acrobatic yoga classes, in which injuries appear to be more common, and which are clearly not suitable for everyone, and styles that are gentle and restorative. In addition, in yoga therapy tailored to the individual, injuries are very rare.

I've been diplomatic in my responses to these inaccuracies in the past, but the recent claims about yoga being "remarkably dangerous" for men were for me the straw that broke the camel's back. As astronomer Carl Sagan once said "extraordinary claims require extraordinary evidence." These are extraordinary claims about yoga, but they are backed by little if any good evidence.

Can you give an example?

Well, first off, the claims that yoga is dangerous to life and limb strangely omit data on the actual rates of yoga injuries. You can't say that yoga puts people at great risk for injury without comparing it to the injury risk from other physical activities.

Indeed, when you look at the actual injury rates compared to other physical activities, yoga appears to be comparatively low risk. For example, in 2007 numbers, the injury rate for yoga was about 3.5 people out of every 10,000 practitioners. Compare that to the injury rate for weight-training and golf of around 15 and 39 respectively out of every 10,000 practitioners. So compared to other common physical activities, yoga appears to be much safer.

Yes, in a recent New York Times blog post, the author acknowledged that the injury rates are higher for golf and weightlifting than for yoga. But in that same post, it is argued that the injury rates matter less, because the injuries from yoga are far more serious, even life-threatening.

And that of course refers to the most disturbing claim of all: That yoga may cause strokes in some people. You take issue with the science backing up this claim as well?

This is probably the best example of an attention-grabbing claim that is not backed up by any solid scientific evidence. At issue is a relatively rare type of stroke that results from minute tears to the vertebral arteries. The vertebral arteries are linguini-like blood vessels that run along the lateral aspect toward the back of the cervical vertebrae. Strokes due to vertebral artery tears are uncommon, but they are known to occur and sometimes due to trivial trauma, such as when people move their head suddenly and abruptly, e.g. while sneezing, driving a car, or swimming the breast stroke. They can also occur if people lean their head way back, such as when painting a ceiling or when an elderly woman drops her head back into a hairdresser's sink for a shampoo.

These are activities that millions of people do every single day without problems. So it may be that these strokes have more to do with an underlying physiological weakness, such as connective tissue abnormalities in the blood vessels, than with the precipitating event itself. It's similar to someone with osteoporosis incurring a vertebral fracture while sneezing. You can't say that the sneeze itself caused the vertebral fracture so much as it revealed the underlying frailty of the bones.

Is there data indicating that this type of stroke is more common among yoga practitioners?

Not at all. The book cites estimates that among the general public there are 1.5 vertebral artery strokes per year per 100,000 people. The author assumes that yoga practitioners would have the same 1.5 per 100,000 rate of such injuries as the general population. So, with 20 million practitioners in the U.S., the author calculates, 300 yoga practitioners per year suffer this type of stroke, and with the prevailing mortality rate, 5 percent of these would die.

But let's examine those assumptions. If yoga practitioners have the same stroke rate as people who don't do yoga, that means that on net yoga caused zero strokes. Yet, by implying a connection to yoga, the book is pretty much inventing hundreds of yoga-induced strokes and many deaths out of whole cloth.

Using the same logic, if there are 16,000 cases of food poisoning per 100,000 people, every year yoga would be tied to 320,000 episodes of this potentially deadly intestinal infection.

But there are also apparent examples of people who have had a stroke while practicing yoga?

There are some stories, as we would expect given how common strokes are. Each year, 700,000 people in the U.S. suffer from a stroke, one person every 45 seconds. Strokes from dissection of the arteries make up a very small percentage of all strokes.

According to recent statistics, about 1.1-1.5 in 100,000 people suffer from this type of stroke every year. With 20 million yoga practitioners, statistically speaking there ought to be a lot more of the people who suffer from this type of stroke, who also just happen to practice yoga. But we are not seeing anything like the kind of large numbers you would expect.

With all due compassion for the victims of injuries, as my fellow physicians sometimes say: No number of anecdotes equals data. My colleague Dr. Loren Fishman notes that people have to be doing something when they're having a stroke -- they could be eating, watching TV, driving a car, or practicing yoga. With so few cases, you can't infer causality. That kind of premature conclusion is what the whole enterprise of scientific inquiry is set up to avoid.

What about the claim, also made in the book, that a survey -- in which yoga teachers reported on yoga injuries they had witnessed -- documented the stroke threat?

Well, the actual scientific article reporting the survey's results, published in the International Journal of Yoga Therapy, tells a different story than what was reported in the book. The authors, Dr. Loren Fishman of New York's Columbia College of Physicians and Surgeons, as well as yoga teachers Ellen Saltonstall and Susan Genis, note in the article that many answers described conditions that prompted people to take yoga, rather than yoga injuries. They note that "often it was unclear whether injuries cited had resulted from yoga or from some other source."

To resolve the ambiguity, my colleague Roger Cole, Ph.D., contacted study co-author Susan Genis, RYT, Esq., who did the data analysis. Here's how she responded:

William Broad misstates the information we presented. None of the survey responses gave a specific instance of having experienced or having seen a student experience a stroke as a result of yoga practice.

You have argued that yoga might actually help prevent stroke?

Yes, if you have a stiff artery, it's more likely to tear if you move it suddenly or have a traumatic injury, but if you've slowly made that artery more pliable by gently stretching it over years of practice, it might actually be less likely to tear. That's speculation, of course, but there is scientific evidence that people with stiff muscles are more likely to have inflexible arteries.

The bigger picture is that yoga's documented effects of reducing stress and stress hormones, lowering blood pressure, reducing inflammation and the tendency of blood to clot, likely means the practice prevents far more strokes, heart attacks and other serious ailments than it causes.

Despite his allegations, the author says he sees the rewards of practicing yoga as outweighing the risks, and that he is only bringing this out to spark a discussion about how to improve the safety of yoga.

That's a laudable goal, and the yoga community is responding to the challenge. But while we strive to prevent yoga injuries, we should also acknowledge that millions of lives have been made better and healthier by the practice of yoga.

However worthy the aim of improving safety, it doesn't justify making extreme claims on weak evidence. And unfortunately, those claims have already scared away people who could benefit enormously from yoga. And that's a shame.

In response to the controversy, YogaUOnline, an online educational resource, will broadcast free of charge from April 10-14, 2013 a telesummit on Yoga Injuries -- Facts and Fiction, featuring Dr. Timothy McCall, Judith Hanson Lasater, Dr. Loren Fishman, Roger Cole, Jason Crandell, Leslie Kaminoff, Ellen Saltonstall, Dr. Baxter Bell, and other leading yoga teachers.

For more by Eva Norlyk Smith, Ph.D., click here.

For more on yoga, click here.