The Science of Yoga: The Risks and the Rewards

by William J Broad

  The study came across as strong and authoritative. For instance, the Davis scientists reported that the fledgling yogis racked up solid gains in muscular strength. One test centered on knee extension—the act of straightening out the leg while raising a heavy weight. On average, the students improved 28 percent. They also showed greater flexibility. On average, they increased the amount they could bend forward (as in the Frog) by 14 percent. Their backward stretches (as in the Sun Salutation) improved even more, rising on average nearly 200 percent.

  Unfortunately, the gains in aerobic conditioning—the primary interest of Amsterdam the cardiologist—were quite small. Even so, the Davis scientists judged them to be statistically significant. They reported that VO2 max rose on average 7 percent. Moreover, they judged that the positive finding stood out from all previous studies, marking a milestone in the scientific evaluation of yoga.

  “The present study,” the authors declared, “is the first to show improvements in cardiorespiratory endurance by direct measurements.” The scientists concluded that the overall results of their study indicated that Hatha yoga “would meet the objectives of current recommendations to improve physical fitness and health.”

  That was a big claim for what was indisputably a small investigation—for what its authors conceded was a “pilot study” that amounted to a preliminary look in search of noteworthy trends. The scientists offered no comment on how the small observed gain in aerobic conditioning measured up to the official recommendations of such groups as the American College of Sports Medicine, although their use of the conditional tense, “would meet,” bespoke caution.

  Nor did the authors put the aerobic figure into a wider context. They made no comparison of the 7 percent rise to what a sedentary individual might gain from endurance training, where scientists had found that peak oxygenation could increase up to 50 percent.

  “In summary,” the Davis scientists said, “the results of this investigation indicate that eight weeks of Hatha yoga practice can significantly improve multiple health-related aspects of physical fitness.”

  It was, arguably, a small step for the recognition of yoga as an aerobic activity—a step grounded in the discipline’s growing incorporation of such vigorous poses as the Frog and the Sun Salutation. Or perhaps it was simply a fluke. The lack of experimental controls increased the chance of false readings.

  Whatever the study’s scientific merit, the leaders of the yoga community, long on the defensive when it came to cardiovascular issues, seized on the modest finding as a breakthrough. It was hard proof, they asserted, that yoga is all an individual needs to stay fit. The contention was a bold restatement of Gune’s early claims. Only now—in theory, at least—it had the steel of modern science.

  A portrait of the aerobics research formed the heart of a 2002 article in Yoga Journal. The glossy magazine prides itself on giving readers “the most current scientific information available.” It spread its lengthy cover story on yoga fitness over nine pages and illustrated it with lots of color photographs of yogis in scientific labs undergoing close scrutiny. A main location for the documentary photos was the University of California at Davis. In its article, Yoga Journal reported that it had carefully surveyed the world of science and discovered solid evidence that “optimal fitness” requires no running or swimming to strengthen the heart and no weight lifting to build the muscles.

  “Yoga is all you need,” it declared, “for a fit mind and body.”

  The article said nothing about the downbeat findings of Cooper and the Duke scientists. It did, however, highlight the Davis study, calling the 7 percent rise “a very respectable increase” and hailing the aerobic finding as a breakthrough. Even so, the article, like the Davis authors, provided little context for the figure—making no comparison, for instance, to what endurance training can do for peak oxygenation.

  Reaching further, Yoga Journal filled its article with profiles, testimonials, and anecdotal studies of people who hailed the yoga-alone perspective.

  It quoted Dina Amsterdam. “I haven’t done anything but yoga and some hiking for ten years,” she said. “Yoga completely brought me back to physical and emotional health.”

  The Davis and Yoga Journal articles quickly became the go-to authorities around the globe for demonstrating that yoga alone was vigorous enough to meet the aerobic recommendations. The door had opened a crack, and a blast of aggressive marketing shot through.

  One of the flashiest promoters was YogaFit, a commercial style that originated in Los Angeles. Its founding goal was to make yoga an integral part of the fitness industry. The style combined push-ups, 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 instead on 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 to swing 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 they did yoga but as they walked briskly on treadmills and rested in chairs. That gave the scientists a reasonable basis for comparison. It was an experimental control meant to enhance the reliability and—not inconsequentially—the credibility of their measurements.

  Another precaution centered on skill. The scientists recruited volunteers from a university yoga class, and the subjects had practiced for at least a month. The experience factor implied that the moves and postures would be more precise and rigorous than with beginners, in theory strengthening the aerobic stimulus. It bespoke an effort to take the measure of yoga as regular exercise.

  Clay and her team also brought new precision to the measurement of oxygen intake. Unlike the before-and-after methods of the Duke and Davis studies, the Texas researchers fitted their subjects with face masks hooked up to breath analyzers, producing direct readings of respiration. The scientists judged that the gains in accuracy would outweigh any inconvenience.

  The yoga session was shorter than in the Davis study. It lasted just a half hour, compared to an hour and a half. The scientists said they designed it to resemble a routine in a health club. The Texas study, like the Davis investigation, put Sun Salutations at the heart of the session.

  The investigators cited the Davis paper in reviewing prior research. But their findings bore little resemblance. Perhaps most conspicuously, the Texas scientists explicitly addressed how their findings measured up to the official recommendations.

  The team examined a variation of VO2 max known as maximum oxygen uptake reserve. It expresses the difference between oxygen consumption at peak levels of exercise and during rest. Since the resting metabolic rate of individuals can vary, exercise physiologists consider the reserve formula a more accurate way of making comparisons of athletic fitness. (The method is similar to how the vital index took personal factors into account.) The American College of Sports Medicine, in promoting aerobic conditioning, recommends that individuals draw on 50 to 85 percent of their maximum reserve. By contrast, the Texas scientists found that women walking briskly on the treadmill used about 45 percent.

  And yoga? The women, while doing the routine, achieved far less—only 15 percent. The results, the scientists reported, “indicate that the metabolic intensity of hatha yoga is well below that required for improving cardiovascular health.”

  The only encouraging news centered on the Sun Salutation. Clay and her team said the fluid pose turned out to represent the workout’s most aerobic aspect—a wide belief in the yoga community that had previously gone untested. The scientists found that Sun Salutations drew on 34 percent of the maximum reserve—more than twice the overall yoga session. And they suggested that the reading, though “significantly lower” than the 50 percent minimum of the American College of Sports Medicine, was nonetheless high enough for yoga teachers to consider putting more emphasis on the vigorous pose.

  “To increase intensity,” the researchers said, “it appears that the Sun Salutation or similar series of asanas should comprise the greatest portion of a Hatha yoga session.”

  Another downbeat finding emerged in 2005, just a month later. The study was done at the University of Wisconsin. It centered on thirty-four women with no yoga experience and no history of regular exercise. The women were divided into yoga and control groups. The yogis did fifty-five minutes of Hatha three times a week for two months while the non-yoga group did no exercise at all. Compared to the Texas study, the workout was longer and presumably more vigorous.

  The investigators in Wisconsin found gains in strength, endurance, balance, and flexibility. But not in VO2 max. “The intensity just wasn’t there,” noted John Porcari, one of the scientists.

  The Wisconsin team did a companion study to see if Power Yoga—a demanding series of poses based on the Ashtanga system, with emphasis on flowing postures like the Sun Salutation—posed a greater aerobic challenge. The scientists recruited fifteen participants with at least intermediate experience. It turned out that the heightened vigor did make a difference, but only slightly. “You certainly sweat,” Porcari said. “But it’s not an aerobic workout.”

  He disagreed with the Texans on the idea of introducing wide customizations meant to increase yoga’s vigor. Porcari said that adding more energetic postures as a way to boost cardio benefits would, by definition, come at the expense of flexibility, balance, and the other traditional benefits.

  “It’s always a trade-off,” he said. “Yoga was designed for relaxation, primarily. The more aerobic you make yoga, the less improvement you’ll see in those other areas.”

  Many yoga studies go unnoticed. The Wisconsin inquiry made waves, probably because its sponsor was the American Council on Exercise, a nonprofit group that seeks to protect consumers from risky and ineffective fitness programs. That gave the study added authority and exposure. The council, based in San Diego, published a digest of the Wisconsin study in its magazine and sent out a press release. The statement noted that the Wisconsin scientists had found that each Hatha session burned just 144 calories—similar to a slow walk.

  “Aerobics?” The Washington Post asked in its headline. “Not Among Yoga’s Strengths.”

  Yoga Journal took notice—defensively, acting like a true believer in denial. Its headline said it all: “Flexible and Fit.”

  The magazine faulted the Wisconsin study, as well as the reaction of the news media, and went on to cite new evidence of yoga’s aerobic benefits. Once again, it found support at the University of California at Davis—the main source of its original good news on VO2 max some four years earlier. A Davis researcher, Yoga Journal reported, had studied four yoga instructors who displayed levels of fitness comparable to someone who jogged three or four times a week. The news media, the article insisted, had fallen for a misleading story and had missed an inspiring one.

  But the new evidence was thin. Yoga Journal gave no details about the new Davis study, just the claims. And, as it turns out, the study was never published. Its existence amounted to a rumor, although the readers of Yoga Journal could be forgiven for thinking otherwise.

  The more obvious problem was that the Davis scientist had drawn a comparison between extensive and small efforts—comparing teachers who did “several hours of yoga a day” to joggers who ran as little as three times a week. The finding implied that running was far more aerobic—just what an impartial observer might conclude.

  “I think you just proved the point,” a reader wrote Yoga Journal in noting the lopsided comparison.

  A final study, published in 2007, sought to settle the debate once and for all. It fairly breathed thoroughness and rigor. For instance, it did its recruiting in the studios of Manhattan, where youth, fierce competition, and starry clientele had resulted in challenging routines and gifted students—some of the best the planet had to offer. The sites ranged from downtown, to Midtown, to the Upper West Side. They included the torture chambers of Bikram Yoga (“we forge bodies and minds of steel”), the stylish removes of Levitate Yoga (“be free to wear the latest Louis Vuitton or Prada items”), and the sunny halls of the World Yoga Center (“created with a pioneering and idealistic spirit”).

  The researchers came from the Brooklyn campus of Long Island Uni
versity as well as the Mailman School of Public Health of Columbia University, a star of the biological sciences. They knew their stuff. The lead scientist, Marshall Hagins, had a doctorate in biomechanics and ergonomics and a clinical doctorate in physical therapy, and had practiced yoga for a decade.

  The study’s funding signaled its gravitas. Often, yoga investigators list no source of financial backing in their published work, implying that they undertook it on their own or with the aid of anonymous colleagues. That was the case with the Davis study. Such research tends to be modest in scope because the funding tends to be modest. Not so mainstream science. There, investigators typically go out of their way to thank their patrons—in the life sciences, often federal agencies. So it was with the New York study. The team in its published report said it had received support from the National Institutes of Health, the world’s premier organization for health-care research.

  The New York team recruited twenty subjects who had practiced yoga for at least one year, felt comfortable doing Sun Salutations, and could perform such advanced poses as the Headstand. The group consisted of two men and eighteen women.

  The scientists judged that some of the previous studies had significant flaws. For instance, subjects were inexperienced or had been forced to wear clumsy masks and mouthpieces. “Such techniques,” the scientists noted, “may alter the performance of the yoga activities and therefore provide invalid estimates.” Invalid estimates. In the polite world of scientific discourse, that was tantamount to ridicule.

  Seeking better results, the scientists made their measurements while the subjects did yoga in a special chamber that could track overall changes in respiratory activity. It let the yogis move about freely even while being scrutinized intimately. Known as a metabolic chamber, the rare and costly piece of scientific equipment was located at Saint Luke’s–Roosevelt Hospital on the city’s Upper West Side, near the Columbia campus. It was, in effect, an airtight cell. Machines linked to the metabolic chamber could measure a subject’s exact consumption of oxygen, exhalation of carbon dioxide, and radiation of metabolic heat. Columbia scientists often used the chamber to study obesity. They would examine a subject’s metabolic rate during meals, sleep, and light activities. But now they lent their apparatus to the scrutiny of yoga. The aim was not to track the addition of layers of fat but to see how efficiently yoga burned calories by fanning the body’s metabolic flames. In terms of sophistication and accuracy, the chamber was light-years away from the rough bags that Hill had strapped on his runners, and from the traditional sets of before-and-after measurements that some modern scientists had used to track VO2 max. It was cutting-edge.