The Science of Yoga

gentle on the heart. By contrast, the newer styles tend to be hyperkinetic, some done to the beat of rock music. The objective is to get the heart pounding and the body exhausted. That makes them more aerobic (“requiring air”)—in other words, more focused on reinvigorating the blood. Incontrast to Gune’s style of yoga, the new goal is to maximize rather than minimize the energetic costs.
    Brands that focus on aerobics include YogaFit and Power Yoga. To a lesser extent, the vigor extends to older styles such as Ashtanga and Vinyasa. And then there is Bikram. “My classes are so hard,” Choudhury boasts, “you use your heart more than if you run a marathon.”
    Fortunately, that kind of pronouncement is open to investigation.
    The analytic lens of the sports establishment began to form in the nineteenth century as health authorities struggled to identify universal factors that determine the origins of human fitness. The question was seen as urgent. Around the globe, waves of people were leaving farms and giving up agrarian lifestyles that had kept them physically active from dawn to dusk. Medical experts agreed that the new sedentary lifestyles of the cities were often unhealthy but could achieve no consensus on what forms of exercise to recommend—even as entrepreneurs and hucksters got rich promoting their own methods. It was an age of dumbbells and medicine balls, of weighted clubs and chest expanders, of gimmicks and gadgets. The scientific goal was to develop objective standards that would let investigators cut through the competing claims and document what was truly beneficial. The resulting programs of exercise were seen as important to help city dwellers improve their health, avoid fatigue, and better enjoy their lives and leisure time.
    By 1900, investigators had identified a factor that they called vital capacity. It measured a person’s ability to breathe deeply—seemingly a good measure of fitness because breathing is considered a foundation of the metabolism and, in earlier days, was viewed as an expression of the human spirit and soul. Science saw deep breathing as similar to blowing on a fire—in theory it fanned the body’s metabolic flames.
    Seeking precision, scientists defined vital capacity as the maximum volume of air that an individual could exhale after a deep inhalation. A sedentary life was found to reduce vital capacity, and an active life to increase it. Scientists quickly developed a refinement known as the vital index, which sought to eliminate differences due to age, size, sex, and other individual factors. It consisted of the ratio of vital capacity to weight. Early in the twentieth century, athletes aspired to a high vital index as an indication of competitive excellence.
    Gune became an enthusiasticfan of the vital index and cited yoga’s impact on the physiologic measure as evidence of the discipline’s power to raise human vitality. Viewed narrowly, his claims were exactly right. Pranayama gave the lungs, the chest, and the abdominal muscles a comprehensive workout and improved the flexibility of the rib cage. The natural result was an aptitude for deep breathing. The big question was whether the pulmonary skills translated into heightened fitness.
    Gune had no doubts. In his estimation, yoga, with its proven ability to expand the lungs, outshone all other sports and systems of exercise. And he said so bluntly. Shortly after starting his ashram, he declared that the discipline excels at “increasing the vital index” and improving all aspects of life. Yoga, Gune insisted, let students attain the “physiological perfection of the human body”—not improvement or development but perfection. “There can be no other system more suitable.”
    Unfortunately, just as the guru was seizing on the vital index as evidence of yoga’s superiority, scientists in Europe and the United States were abandoning the measure as deceptive and potentially meaningless. For instance, they noted that the vital index of a growing child usually fell steadily between the ages of, say, ten and twenty, since body weight during those years increases faster than lung size. Yet common sense suggested that those same years saw great rises in athletic prowess.
    So the question arose with new urgency: What did, in fact, define the human capacity for physical vigor and, if such a factor existed, could science find a way to measure its development?
    In the 1920s, as Gune was beginning his program