The Science of Yoga

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, robbing the brain of oxygen. By definition, strokes traumatize and kill brain cells, which are known as neurons. A renewed flow of blood can sometimes mend beleaguered cells. And over time, nearby neurons can sometimes replace the function of dead cells. But damage can also be permanent. Stroke victims thus experience disabilities that range from passing weakness to lasting neurologic damage to death if the destruction involves vitalbrain centers. (Fast treatment can limit the damage, which is why health professionals urge speedy evaluations of suspected stroke victims, preferably within sixty minutes.) The symptoms of stroke vary widely because of the brain’s highly specialized anatomy. For instance, conscious thought and intelligence arise in the outer layers of the brain, so strokes in those areas can affect speech and critical thinking.
    Russell’s concern went deeper. He worried about the inner brain, in particular a functionally diverse region toward the rear. His concern was that yoga postures that involved extreme bending of the neck might compromise the region’s blood supply, destroying parts of the brain rich in primal responsibilities.
    The human neck is made of seven cervical vertebrae that anatomists have numbered, top to bottom, C1 through C7. Their special shapes and compliant disks make the neck the most flexible part of the spinal column. Scientists have measured the neck’s normal range of motion and found the movements to be extraordinarily wide. The neck can stretch backward 75 degrees, forward 40 degrees, and sideways 45 degrees,