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'The Science of Yoga' by William J. Broad

25 yoga poses.

25 yoga poses. Credit: Fotolia

THE SCIENCE OF YOGA: The Risks and the Rewards, by William J. Broad. Simon & Schuster, 298 pp., $26.


Who knew yoga could be so dangerous? Or is the risk overblown?

A man sits on his heels for hours (over a period of days or weeks) and deadens nerves in his lower legs. A woman practices Kapalbhati -- forceful exhaling -- and collapses a lung. A woman attempting the wheel -- making the body arc like a croquet wicket -- balances on her head, bends her neck backward and suffers a stroke.

Author William J. Broad, a yogi since 1970 and the chief science writer for The New York Times, remains devoted to the practice. He has much to say about yoga's benefits to the mind and body. But his chapter on bizarre injuries will get the most attention. His six examples from medical journals include three strokes: yoga postures that include "extreme bending of the neck" can cause a clot in the vertebral arteries, triggering a rare type of stroke that tends to strike young, healthy people.

When the author tries to quantify yoga injuries, however, the most common seem to be orthopedic: lower back, shoulder, knee and neck. Not that those aren't painful, as Broad can attest.

"My research has prompted me to change my own routine," he writes. "I have de-emphasized or dropped certain poses, added others, and in general now handle yoga with much greater care."

Forget freaky injuries, however: Modern urbanites' true terror is gaining weight. Broad finds that yoga does not raise metabolism; in fact, it lowers it. Nor does yoga improve physical conditioning like aerobic exercise does. (More vigorous forms of yoga, such as vinyasa flow, might do better. Yoga studies are rare, since drug companies have no reason to pay for them.)

Lowering metabolism sounds like a bad thing, but it contributes toward a major benefit of yoga: boosting moods. An experiment at Duke University Medical Center, published in 1989, included about 100 people: a control group, another that used stationary bicycles and a group of yogis. After four months, the bicyclists had improved their conditioning and the yogis had not -- but they believed they had.

The yogis "reported enhanced sleep, energy, health, endurance and flexibility," Broad writes. "They described how they experienced a wide range of social benefits, including better sex lives, social lives and family relationships. . . . They had better moods, self-confidence and life satisfaction."

As for sex, Broad finds that yoga raises testosterone levels and lowers the level of cortisol, a stress hormone. Another yoga practice, rapid breathing, can boost arousal. You don't need pills or twin bathtubs.

Some practitioners think of yoga as a path to enlightenment. This book can be enlightening for yogis and non-yogis alike.

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