It has taken a century and a half to discover the secret to its appeal.

Bernard's fortunes failed in the Depression, and the center of American yoga migrated to Hollywood. Stars including Greta Garbo, Gloria Swanson, Marilyn Monroe, and Ruth St. Denis were committed to a physical culture routine that kept them in tip-top shape. When Indra Devi (née Eugenie Peterson of Latvia) arrived in town in 1947, she had the good sense to open a hatha yoga school. It was a sensation, and Devi's take on yoga was enormously influential.

Six years later in a book that proved a hit, Forever Young, Forever Healthy, Devi brought about perhaps the most important refinement in the history of yoga in America. She made it all about the poses. Syman writes that when Devi uses the word yoga, she is "referring to only the asanas." This is a turning point in the history of American yoga, which in Devi's classroom and writing made its sharpest turn yet from esoteric pursuit to health-giving practice available to all.

But for yoga to survive in the 1960s, it had to adapt to the new transcendentalists, also known as the hippies, and their obsession with altering consciousness. Syman deftly shows how these yogis turned to chanting and breathing to produce the same mind-blowing effects they had previously obtained through pot and hallucinogens. The emblematic image of the era is the moment that the Beatles met the Maharishi. Yoga was high profile, high stakes, and sometimes just plain high, as gurus debated whether or not LSD was a real help with god-consciousness.

Soon enough the pendulum swung away from what Syman calls the "psychedelic sages," with their rigorous programs and their sometimes corrupt ways. Yoga's final simplification was under way, as it became a practice that helped you overcome aches and pains. Yoga Journalmagazine was born. Eventually, yoga classes became more prevalent. "To imagine yoga ameliorated pain but didn't overwhelm your entire consciousness or dictate much else about your life was to wrest it back from the swamis," Syman writes. Yoga has continued on this path up to the present time, though Syman includes a final chapter called "The New Penitents," chronicling the devotees of Bikram and Ashtanga yoga, who seek a profound intensity in their practice.

Syman does a wonderful job of showing how yoga, like a virus, has kept evolving in order to survive. Yet I wonder if she works a little too hard, missing a core truth in her emphasis on how control of the subtle body helps yoga students "turn mere human flesh into a vehicle for the divine." Her twisting story suggests that she may be straining in her claim that the story of yoga in America is driven by "this possibility—of turning yourself into the very thing you worship, call it God, superconsciousness, Brahman Krishna, Kali, Siva, the Self." This is certainly one of the projects of yoga, but if superconsciousness was what Americans were after, why wouldn't we simply devote ourselves to meditation?

I think the most useful clue to the real secret of yoga's allure in the United States can be found instead in Awakening the Spine, an eccentric yet necessary little book published in 1991 by Vanda Scaravelli, a revered Italian-born yoga teacher who practiced well into her 80s and wrote about yoga with wisdom and rare clarity. In her book, she posed the question: Why do we do yoga? And then she offered an answer: "We do it for the fun of it. To twist, stretch, and move around, is pleasant and enjoyable, a body holiday."

Pierre Bernard understood the fun of yoga. In 1931 the Great Oom put it this way to a reporter: "I'm a curious combination of the business man and the religious scholar ... a man of common sense in love with beauty." He was onto an astonishingly modern idea of how we do yoga in America. With the yoga hoopla of half a decade ago behind us and studios nestled inconspicuously in all kinds of neighborhoods, this simple secret is much easier to see: We are people of common sense, in love with beauty. We do yoga because we feel good when we fit our bodies into these odd shapes and our breath into these odd patterns. It took us a century and a half to learn this particular kind of fun, and we're not giving it up anytime soon.

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