The Science of Yoga

sit-ups, squats, and other repetitive exercises with traditional yoga postures in a flowing kind of Vinyasa format. A centerpiece was the Sun Salutation. Seeking a wide audience, the style hailed sweat over what it characterized as yogic mumbo-jumbo, focusing insteadon earthy rewards. For instance, its YogaButt program claimed to “totally transform your thighs and glutes,” resulting in a bottom that is “sleek and sexy.” YogaFit sold. Starting in the 1990s, its fast workouts spread through gyms, spas, and health clubs, with thousands of women taking up the contemporary hybrid. Its big hit was YogaButt. To satisfy demand, the company developed a course of training that could certify instructors in four hours.
    YogaFit presented itself as a plunge into extreme fitness. Beth Shaw, its founder, claimed that the vigorous style focused minds, trimmed fat, toned bodies, and provided “a tough cardiovascular workout.” Her promotional literature, when enumerating the fitness benefits of the style, cited the number one payoff as “cardiovascular endurance.”
    In 2003, the company sought to substantiate her cardio declarations. The sixteen-page paper, “Health Benefits of Hatha Yoga,” cited no lab studies that YogaFit had sponsored. Instead, it reviewed the existing research. The paper cited the Davis study, the Yoga Journal article, and other inquiries as demonstrating that the style offered a serious path to the heights of cardiovascular fitness.
    As usual in such tellings, the paper ignored the negative findings and the context. Still, it made the best of a tenuous situation and called YogaFit and other energetic styles of yoga “aerobically challenging.”
    The good news spread. It traveled far beyond the insular world of yoga into mainstream culture. There, amid the blur of health and beauty tips, it got promoted as a scientific insight—with all the weightiness that such a discovery implied.
    In 2004, Shape , which calls itself the lifestyle magazine for the active woman, hailed the Davis findings as proving that yoga provided all the cardiovascular benefits that anyone could want. “You don’t need traditional cardio,” it assured its readers, which it put at more than six million. The attainment of this most challenging of fitness goals, the magazine added, requires “nothing more than a yoga mat.”
    A principal dynamic in the psychology of scientific advance is the action–reaction cycle. Its workings are often on public display in the case of big claims, especially when the perception arises that the claimants have offered inadequate evidence to back up their declarations. At that point, the pendulum starts toswing in the opposite direction and the organized skepticism of science takes over. Rivals seek to poke holes in the original claim and try to discredit the original arguments. At times, the resulting disputes get settled quickly. But sometimes they drag on for decades as each side seeks to assemble evidence weighty enough to settle the argument once and for all.
    Yoga’s claims of aerobic excellence got caught up in that kind of reactive cycle. A large assertion had been made and had received considerable public notice—that yoga alone is sufficient to achieve cardiovascular fitness.
    The claim was big and so were the stakes. If true, yoga could enter the pantheon of activities that global authorities had identified as vigorous enough to produce the array of cardio benefits—to raise stamina and lower the risk of heart disease, diabetes, cancer, and many other diseases.
    From a business angle, the claim was pure gold. It could turn a simple form of exercise requiring no costly equipment or investment into a dazzling profit center. The pronouncement caught the attention not only of supporters but, increasingly, of skeptics.
    The wave of scientific reaction started in 2005 even as the aerobic claims continued to echo and multiply through yogic and popular culture. It began at Texas State University. Carolyn C. Clay, a young scientist who practiced yoga, talked four colleagues into joining the investigation. Their study appeared in The Journal of Strength and Conditioning Research , the scientific forum of the National Strength and Conditioning Association, a nonprofit group of scientists and athletic professionals. The researchers looked at twenty-six women. That was more than twice as many subjects as in the Davis investigation. Moreover, the scientists examined the women not only as