The Science of Yoga

compression and displacement between the C3 and C6 vertebrae. Health professionals, they wrote in their 2007 report, “need to be aware of this potentially serious complication of a relatively innocuous exercise.”
    In my thirties, I somehow managed to rupture a disk in my lower back. The cause seemed to be the repeated shocks of running on pavement rather than yoga. I looked into surgery, but found I could prevent bouts of pain with a selection of yoga postures and abdominal exercises.
    In 2007, I experienced my own “serious complication” while studying with Robin in Pennsylvania. It happened as I did the Extended Side Angle pose, or Utthita Parsvakonasana. That was the posture that Krishnamacharya praised as a cure for many diseases. I was coming out of the pose and chatting with my partner—instead of paying attention to what I was doing—when my back gave way.
    Blinding pain forced me to ignore everything but the explosion of fire. It was excruciating. My legs failed and the room vanished in tears. My body slammed into a wall.
    Recovery took weeks. But the humbling experience gave me a deeper appreciation for yoga safety.
    The redesign of poses by the yoga community ranged from tweaks to wholesale rearrangements. More drastic, some authorities called for the removal of risky postures from the Hatha corpus entirely or gave them warnings harsh enough to serve as de facto prohibitions, as with Kapalbhati and Bhastrika. The wave of new precautions was different from when medical outsiders drew up lists of X-Rated Exercises. It featured some of yoga’s biggest names, giving it disciplinary cachet. Even Iyengar got involved. Moreover, the stars often made their recommendations in the literature of yoga rather than medicine, meaning the advice tended to receive wide readership among everyday practitioners.
    The Headstand became an early target. In general, teachers advised students to unburden theneck. But they seldom mentioned that such easing contradicted Iyengar. “The whole weight of the body,” the guru wrote in Light on Yoga, “should be borne on the head alone and not on the forearms and hands.”
    Richard Rosen—a teacher in Oakland, California, who had studied at the Iyengar Institute in San Francisco—called for exactly the reverse, with the complete elimination of weight from the head and neck. The idea was to suspend the head off the floor by pressing the forearms down. “If everything feels relatively comfortable,” he wrote in Yoga World, “slowly lower your crown to the floor until it just barely touches. Keep 95 percent of your weight on the forearms and shoulders.” His recommendations seemed to require a level of gymnastic skill and strength that many beginning and intermediate students would find daunting. As for the risks, Rosen never mentioned any specifically by name but simply called the Headstand “dangerous if not practiced intelligently.”
    Robin had us do Headstands in which we transferred body weight from the neck and head to the arms. With practice, it was fairly easy to do. “At this point in the game,” he remarked as we practiced the redesigned pose, “you want a maximum amount of weight on your arms—and a minimum on your head.” Someone asked how much weight should be transferred. “Seventy-two point three percent,” he replied, eliciting howls of laughter.
    Timothy McCall, a physician who became the medical editor of Yoga Journal , advocated a more drastic approach. He called the Headstand too dangerous for general yoga classes unless a teacher had a proven ability to avoid trouble. His warning was based partly on his own injury. Through trial and error, he had found that doing the Headstand had led to a condition known as thoracic outlet syndrome, which arises from the compression of nerves passing from the neck into the arms. As a result, he felt unusual tingling in his right hand as well as sporadic numbness. McCall stopped doing the pose and his symptoms went away. Later, in recommending that general yoga classes avoid the Headstand, he noted how the inversion could produce other injuries, including degenerative arthritis of the cervical spine and retinal tears because the Headstand raises eye pressure. “Unfortunately,” McCall concluded, “the negative effects of Headstand can be insidious.”
    Today, a number of schools avoid teaching the inversion or ban it outright. The cautious stylesinclude Kripalu, Bikram, Viniyoga, and Kundalini. If, as