The Science of Yoga

in its fifth edition. In 2010, it advised readers that vigorous styles such as Ashtanga were ideal for getting a “cardio workout.” The language wasn’t as strong as Beth Shaw’s “tough cardiovascular workout.” But it nonetheless put the practice right up there with the sweaty rigors of fast treadmills.
    The Davis and Yoga Journal articles kept getting cited, their claims immortalized on the Internet. The Huffington Post ran a link to Yoga Journal ’s glowing tribute.
    The aerobic mythology sped across cyberspace until it found its way to HealthCentral.com, a flourishing commercial site that sells drugs and gives away medical advice. The site claims more than seventeen million readers a month and, on its home page, proudly declares that it features material from Harvard Health Publications, the arm of the Harvard Medical School that seeksto publicize the most authoritative health information. The site’s reference to Harvard included a picture of the school’s crest—a shield bearing three open books, their pages spelling out veritas —”truth” in Latin.
    “Does Yoga Provide Enough of a Cardio Workout?” HealthCentral .com asked its readers in 2010.
    The answer came from never-never land, despite the implication that the Harvard Medical School had somehow been involved in producing or vetting the information. It came from a place where the ancient practice had somehow morphed into a modern fitness machine.
    “Rest assured,” the site told its readers. “Yoga is all you need.”
    In recent years, many people have learned to ignore the exaggerated claims and the unabashed gurus (with or without fleets of Rolls-Royces). They lift weights to build muscles and run to challenge their hearts, even while pursuing yoga for flexibility and its other rewards. They are known as cross trainers. Their diverse workouts complement one another to produce a balance of benefits.
    Cross training has no gurus, no schools, no fees, and no advocacy groups. Even so, it has a growing number of adherents, including top athletes. For instance, Alan Jaeger, a baseball pro with a passion for yoga, runs a school in Los Angeles for big-league pitchers. His stars run, stretch, meditate, listen to music, do yoga poses, and meditate again—doing that kind of routine for hours before getting around to throwing a ball.
    The popularity of cross training serves as an instructive counterpoint to yoga’s overstated fitness claims. It speaks to the wisdom of people who pay close attention to what their bodies tell them tell them—and to the recommendations of public health officials.
    The guidelines for aerobic exercise developed slowly over the course of the twentieth century, as we have seen. Ultimately, the enterprise drew on the work of hundreds of scientists. A less conspicuous effort got under way during the same period. It focused not on the straightforward goal of quantifying oxygen uptake and determining its role in physical fitness but on the more difficult and amorphous problem of understanding how changing situations can shape human emotion.
    By nature, the moodquestion was far more challenging than studying the ups and downs of VO 2 max. An added complication was that the investigation of human feeling had less political traction because it involved fewer scientists, received less funding, and had less institutional support than was the case with research into sports and physical training. The pool of candidates shrank further still when the focus was on such curiosities as yoga. The discoveries in that case could be quite serendipitous in nature, as with the Duke investigators.
    Scattered groups of scientists nonetheless made notable progress in the course of the twentieth century. In recent years, their work has become more abundant and substantial. The field—after an early history of false starts and digressions—now appears to be coming into its own.
    The trend is significant. In the end, it may elucidate one of yoga’s most important benefits.

III
MOODS
    S at Bir Khalsa chatted amiably as we walked down the street. His beard was long and gray, his turban white, and his bracelet made of steel—all signs of his Sikh religion. He was not, however, Indian. Born in Toronto of European stock, he had converted to Sikhism decades ago upon taking up Kundalini Yoga, an energetic form that emphasizes rapid breathing and deep meditation.
    No one on Longwood Avenue seemed to give the turbaned Sikh a second look. Boston