The Science of Yoga

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 enoughfor 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 VO 2 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 scientistshad 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 VO 2 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