The Science of Yoga: The Risks and the Rewards (12 page)

Careful measurements showed that the runners—once achieving a certain intensity of effort—could increase their oxygen uptake no more. The situation held steady no matter how much they sped up their pace or how hard they pushed themselves. It was a hidden barrier. Like a bellows blowing air, the heart and lungs turned out to work beautifully at fanning the body’s inner fire but had intrinsic limits that no level of effort could overcome.

In pioneering reports of 1923 and 1924, Hill and his colleagues coined the term “maximal oxygen uptake,” defining it as the peak consumption of oxygen during exercise that got incrementally harder. It soon became the gold standard of physical fitness and exercise physiology—the single most important factor in determining what made for athletic excellence. The vital index, meanwhile, was cast onto the scrap heap of history.

What determined the maximum uptake? Amazingly, peak oxygenation of the body was found to have little or nothing to do with lung size, lung elasticity, the depth of breathing, eating habits, vitamins, the amount of sleep, good posture, body weight, or whether an individual possessed an unusually potent form of hemoglobin or some other energizing factor in the bloodstream. No. The scientists concluded that it rested on one main factor—the size of an individual’s heart and its ability to send blood rushing through the lungs and blood vessels to the muscles. In short, the secret of athletes who drove themselves to heights of physical performance centered on a big heart.

A central myth of Hatha yoga—one Gune had identified—held that deep breathing increased the blood’s oxygenation despite the relative stillness of the body and the modest use of the muscles during yogic practice. Hill ignored that misunderstanding. His discovery centered on the
quantity
of blood oxygenation rather than mythic attributes of
quality.
It bespoke huge volumes of rushing blood. Peak oxygen consumption was typically expressed in
liters of oxygen—with top athletes each minute drawing in six, seven, or even eight liters—in other words, up to two gallons.
Two gallons.
It was a flood compared to a phantom trickle. With great elegance, Hill and his colleagues overturned the misconceptions of the vital index to show that the central element of peak oxygenation rested on the workings of the heart rather than the lungs.

Today in sports medicine and exercise physiology, peak oxygen consumption is known by the ubiquitous acronym VO
₂
max. In the argot of science, the
V
stands for volume, the
O
₂
for oxygen in its usual chemical notation, and “max” for maximum. VO
₂
max is accepted around the globe as the best single measure of cardiovascular fitness and aerobic power.

In the early days, the question was whether coaches and individuals could raise the maximum uptake so as to increase athletic performance. The answer emerged quickly: very much so. Regular aerobic training turned out to increase the size of the heart, most especially its left ventricle—the heart’s largest chamber, which pumps oxygenated blood into the arteries and body. A bigger left ventricle sent out more blood per beat and more oxygen to the tissues and muscles. Scientists sought to measure the rise. It turned out that the cardiac output of elite athletes was about twice that of untrained individuals.

The benefits extended to most anyone who took up vigorous exercise. In time, scientists found that three months of endurance training could raise VO
₂
max between 15 and 30 percent. Two years raised it as much as 50 percent.

The new perspective was a breakthrough. At last, after many decades of mistakes and misapprehensions, scientists had uncovered what seemed like a dependable guide to human fitness.

The topic was long obscure. Then Kenneth H. Cooper came along. A track star in his native Oklahoma, the physician worked for the Air Force and early in his career devised a simple test that provided a good estimate of an individual’s VO
₂
max. The test measured how far a person could run in twelve minutes. Cooper’s rule of thumb let the Air Force quickly assess the fitness of new recruits. Eager to popularize his insights, he invented a new word, “aerobics,” and in 1968 authored a book by the same name. It drew on his years of research to show what kinds of exercise produced the best cardiovascular workout. Cooper found that such muscular activities as calisthenics and weight
lifting were the least effective. Participant sports like golf and tennis came in second. And the big winners? Challenging sports like running, swimming, and cycling, as well as vigorous participant sports such as handball, squash, and basketball. His analyses caught on rapidly and helped get millions of people off their chairs and into the streets. Starting in the 1970s, jogging became fashionable.

The surge of activity resulted in a number of scientific inquiries that examined what aerobic exercise could do not only for athletics but health. The results were dramatic. Perhaps most important, the studies showed that aerobic exercise lowered an individual’s risk of heart attack and heart disease—
the
leading cause of death in the developed world. It also reduced the prevalence of diabetes, stroke, obesity, depression, dementia, osteoporosis, hypertension, gallstones, diverticulitis, and a dozen forms of cancer. Finally, it helped patients cope with all kinds of chronic health problems. Frank Hu, an epidemiologist at the Harvard School of Public Health, praised the benefits as exceptional. For general health, he called vigorous exercise “the single thing that comes close to a magic bullet.”

Why did it do so much good? Scientists found that forceful exercise improved the performance of virtually every tissue in the human body. For instance, it produced new capillaries in skeletal muscles, the heart, and the brain, increasing the flow of nutrients and the removal of toxins. Scientists also discovered that it raised the number of circulating red blood cells, improving the transport of oxygen. Still another repercussion centered on blood vessels. It caused their walls to produce nitric oxide, a relaxant that increases blood flow.

The wide health benefits prompted medical groups to call for regular exercise and public institutions to set recommended levels. The American College of Sports Medicine said healthy adults should engage weekly in at least three vigorous exercise sessions, each twenty to sixty minutes long. The American Heart Association called for at least five sessions. Many other groups, including the President’s Council on Physical Fitness, made similar recommendations. The push was global. In Geneva, the World Health Organization said regular aerobic exercise held out the promise of “reducing cardiovascular diseases and overall mortality,” the rate at which people die.

In short, vigorous exercise for health maintenance and enhancement became a modern credo. The message was etched in stone. Experts might quibble over the amounts.
But they agreed on the principle and did whatever they could to promote its public acceptance.

It took decades for scientists to consider how yoga measured up. Part of the problem was the relatively small size of the yoga community and its limited ability to win scientific attention. Another was the difficulty of monitoring the aerobic status of practicing yogis. It was easy for investigators to study how yoga could increase an individual’s flexibility and muscular strength—fair measures of fitness. But gauging the flow of invisible gases was a different story. That kind of information was hard enough to get with athletes working out on treadmills. The investigators had to fit their subjects with clumsy face masks and tubes that delivered the gaseous flows to measuring devices. But with yoga—given its range of motions and its series of rather profound rearrangements of the human body—the challenge was far greater. Even so, a number of scientific teams made headway over the years.

Cooper, the VO
₂
max popularizer, did no direct investigations of yoga but carefully examined several activities that were similar, including isometrics and calisthenics. His verdict? They did little or nothing to strengthen the heart and raise oxygen consumption.

“Is your chest heaving?” he asked of the person doing the muscular tensing of isometrics. “Is your heart pounding? Is the blood racing around your system trying to deliver more and more oxygen? Nonsense. None of these beneficial things is going on, nothing that anyone can measure, anyway. We tried it and failed.”

Yoga’s social rise in the 1970s and 1980s led scientists to start assessing how it measured up against aerobic sports. As fate would have it, one of the first investigations was also one of the best. It was done by scientists at the Duke University Medical Center, in Chapel Hill, North Carolina, a top institution for biomedical research. The team studied nearly one hundred older adults—forty-eight men and forty-nine women. A third did Hatha yoga, a third exercised on stationary bicycles, and a third did nothing out of the ordinary.

The team’s use of experimental controls set the study apart from what specialists consider an underworld of shoddy research. Controls let scientists zero in on a single variable and avoid subtle misunderstandings. They try to eliminate the complexities of nature and human interaction to ensure that any
observed changes are the result of the examined factor rather than some extraneous influence. With the Duke study, for instance, the experimental controls let the scientists make sure that the process of simply gathering the subjects to the site of the investigation played no role in the results. What if some walked there? What if some bicycled? What if some ran? Would that affect the fitness measurements? The changes observed in a control group could alert scientists to the existence of an unintended influence and help them eliminate it from their findings. The big challenge for a scientist designing a study with human subjects is to make the experiences of the experimental and control groups as similar as possible—with the exception of the issue under examination. Without such precautions, researchers have no way of knowing whether the changes observed in an experiment would have happened anyway. The practical difficulty of such precautions is their added expense. The recruitment of more subjects—and their subdivision into different kinds of activities—can result in the need for more money, more personnel, more data analysis, and more administrative burdens. But the scientific benefits are usually seen as worth the costs.

In the Duke study, the hundred or so subjects, including the control group, did their designated activities for a total of four months. To get around the measurement dilemma, the team made no readings during the months of assigned activities and instead opted for detailed assessments before and after the training.

The results, published in 1989, were unambiguous. The aerobics group improved its VO
₂
max significantly, raising peak oxygen consumption by 12 percent. But the yogis showed no increase whatsoever and in fact registered a bit of a decline, though it was judged to be statistically insignificant.

A surprise also emerged.
The scientists were intrigued to discover that the yogis, despite their poor showing in terms of aerobic conditioning, nonetheless felt better about themselves. The subjects reported enhanced sleep, energy, health, endurance, and flexibility. They described how they experienced a wide range of social benefits, including better sex lives, social lives, and family relationships. Psychologically, the scientists said, the yogis reported a number of improvements. They had better moods, self-confidence, and life satisfaction. With few exceptions, they said they looked better.

The Duke findings hinted at a fascinating split. It was one thing to
do
good for the hidden intricacies of human physiology and quite another for an individual to
feel
good about themselves. It was the difference between improved fitness and outlook. The subjects who did yoga
felt
they had received a wealth of benefits even though the Duke scientists found no indication whatsoever of aerobic gains. Their discussion of the research findings hinted at their fascination. The improvements in attitude, the scientists said, “are worth noting.”

The Duke team—unknowingly—had stumbled on one of yoga’s secrets. The next chapter will explore the science of how the discipline lifts the human spirit.

Yoga fared slightly better in subsequent studies of aerobic conditioning. One reason was a subtle change in the discipline that put growing emphasis on energetic poses and styles. The new forms downplayed stationary postures for ones that required a much greater level of movement and physical activity, creating
a more athletic experience and increasing the aerobic challenge.