Yoga on the Subcontinent once meant only soulful swamis and asceticism. No longer. Embraced—and reinvented—by the West, it's now more about slick mat work and toned muscles than spiritual searching. Justine Hardy has it both ways

It is 6:30 a.m. and I have my leg somewhere faintly unsavory. I am taking the morning yoga class at Goa's Bhakti Kutir, an eco-resort of bamboo-and-wood cabins set under a canopy of palms a little back from the heat of the beach. Beside me, a woman with an Italian accent is grunting from the effort, and a Japanese woman is simply being a pretzel. A saffron-robed and bearded swami—a smooth, elastic-skinned young man with wise old eyes—is teaching us in the dirt round under the palm trees. He has come down from his ashram in the Himalayas at the invitation of the resort's owners. He is gentle but tough, and he will not let us give up.

Goa, on India's southwest coast, is a former Portuguese colony, a place of whitewashed churches, elegant broad-balconied houses, and a Catholic tradition layered on top of Hinduism and Sunni Islam. It has long been a destination beloved by hippies, ravers, beach bunnies, and yoga seekers alike, and we have all of them here today. There are boho-chic types, loosely hung in floppy cotton, and also some serious yoga aficionados. For decades, foreign yoga teachers have been bringing their devotees to places such as this to take classes on the beach. Yoga lovers are pouring into India in record numbers, especially to the south, for a bit of yoga-by-the-sea. At Bhakti Kutir, one of these imported yoga retreats is in progress. A British teacher has come with a group of lean-limbed Londoners who seem happy to be here for mornings of hard-core mat work followed by lazy afternoons of beach life.

At the end of my Indian-led class, the swami quietly slips away. The atmosphere shifts when the group from London show up at breakfast, after their morning session. The teacher is what's known in the trade as a yoga-diva: lithe, tanned, underdressed, and smoking with a frenzied intensity. In contrast to the swami from the hills, she demands constant attention from her paid-up acolytes. Each day, the swami disappears after class, smiling and nodding, so light in his presence that he hardly seems to be there at all. Every day at mealtimes, we are subjected to the noisy politics of the Londoners—discussions of one another's postures and where to go next for the post-practice afternoon buzz. "They are doing something, but I'm not sure if it's any kind of yoga I recognize," says Panta Ferrao, the Goan co-owner of the resort, as the diva stomps off, miniskirt so tiny that you can see her buttocks. No knickers either. Panta rolls his eyes. Not surprisingly, many Indians think the yoga practiced by Westerners is too sexy to be considered spiritual. But that doesn't mean they don't like to watch. And they do, lined up along the Goan shore, when the whiteys strip down for a bit of sunset asana with a bit of yoga beach flirtation on the side.

Yoga, which of course originated in India, is an Eastern philosophy aimed at achieving union of the human soul and the divine. Its teachings are, above all, spiritual, guardedly passed along within the elite Brahman caste. The physical practice, which now enjoys international stardom, is just one aspect of an eight-part discipline that draws together moral codes of behavior and balanced ways of living and moving in the world, with the ultimate goal of reaching inner liberation. In the 1960s, the West latched on to the ancient philosophy and discipline at a time when our sense of spirituality was being challenged by rapid-fire commercialism. Since then, Westerners have been traveling to India to learn from the masters. Today, however, as a result of India's new posture as a modern power, yoga is being repackaged in the West and exported back to its homeland—this time as a lifestyle option for a generation of ambitious Indians eager to have it all. But instead of the purist version, which prescribes hour-long headstands and such austere practices as standing waist-deep in an icy Himalayan river, the new yoga is more about having a well-toned behind and a bit of breathing space between the last high-octane meeting and the next decaffeinated latte.