The Science of Yoga

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 weightlifting 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