The Science of Yoga

peace. Soon he was experiencing difficulty walking, running, and climbing stairs.

    Thunderbolt, Vajrasana
    In Manhattan, an examination showed that both of his feet drooped because of a lack of leg control, and doctors traced the problem to an unresponsive nerve. It was a peripheral branch of the sciatic, the longest nerve of the body, which runs from the lower spine, through the buttocks, and down the legs. The damaged branch ran below the knee, normally providing the lower leg, foot, and toes with sensation and movement. Apparently, the young man’s kneeling in Vajrasana had clamped his knees tight enough and long enough to cut the flow of blood to the lower leg,depriving the nerve of oxygen. The result was nerve deadening.
    It was suggested that the young man simply give up the pose. Reluctantly he did so, opting instead to do his chanting while standing. He improved rapidly, and a checkup two months after the initial visit showed no lingering problems. In describing the case, the attending physician called the condition “yoga foot drop.” The name stuck. In time, a number of similar cases emerged.
    One of the worst featured a woman of forty-two. She fell asleep in Paschimottanasana—the Seated Forward Bend, its Sanskrit name meaning “stretch of the West.” Upon awaking, she found her legs numb and weak. A medical team at the University of Washington, writing in The Neurologist, told of finding injuries to both her sciatic nerves that had crippled her legs. The scientists reported that the woman regained “some sensation” after three months of therapy but still displayed persistent foot drop.

    Seated Forward Bend, Paschimottanasana
    A half year after the mishap, the woman was still unable to walk without assistance. Her doctors said evidence of permanent nerve damage left them doubtful that she would ever recover full use of her legs.
    If the first reported cases were relatively minor, a second wave soon emerged in which the consequences were little short of devastating. The reason was that the damage centered on the brain itself—not some peripheral organ or physiological subsystem. The news got worse. The blows to the body’s most important organ arose not from stretching too much or holding postures too long but from the skilled practice of poses that practitioners did routinely and tended to see as completely safe.
    The situation was so ominous that a leading British physician issued a public alert. Inthe conservative world of medicine, it is a rare day when abstract theorization comes ahead of clinical reports. Usually it is the other way around—first observation, then efforts at explanation and generalization. But the physician had the requisite stature to issue a sharp warning even before his peers had published any reports that described particular cases.
    At the time, in 1972, W. Ritchie Russell was an elder statesman of British medicine. The string of acronyms after his name bespoke his status: M.D. (Medical Doctor), C.B.E. (Commander of the British Empire), F.R.C.P. (Fellow of the Royal College of Physicians), and D.Sc. (Doctor of Science). A neurophysiologist, he had distinguished himself in a long career at Oxford University that showed, among other things, that brain injuries could arise not only from direct impacts to the head but from quick movements of the neck as well, including whiplash. He published his pioneering research in the early 1940s as war swept Europe and neck injuries grew rapidly in number.
    His new warning centered on how some yoga postures threatened to reduce the blood flow to the brain and cause the cerebral disasters known as strokes. The second most important cause of death in the Western world, right after heart disease, strokes often strike older people whose arteries get clogged with fatty deposits. The risk of dying from them rises with age. In addition, Russell worried about a fairly rare type of stroke that tended to strike relatively young, healthy people.
    The word “stroke” is a euphemism for a range of destructive nastiness that develops when the regular flow of blood to the human brain gets interrupted. In many cases, the symptoms arise on just one side of the body because the brain’s functional areas mirror the body’s bilateral symmetry. Most strokes start as simple blockages. The flow of blood through an artery gets reduced or blocked entirely by deposits of fat, clots of coagulated blood, or the swollen linings of torn or damaged vessels,