DURING THE HAN DYNASTY, Chinese peasants used the ritual of qigong to manage daily stresses such as goiter and invading- barbarians. Two millenniums later, the ancient practice is returning--showing up alongside disco, yoga and aqua aerobics as the hottest trend in stress relief at American spas and health clubs. As the wizened masters cringe, stockbrokers, supermodels and housewives are twisting themselves into poses like "bending bear" and "flying wild goose." The goal is to cultivate "qi" (pronounced "chee"), the Chinese notion of restorative energy that flows through the body.

Posh gyms like the Sports Club/LA are introducing classes such as "SynerChi Sculpt," which "Abs of Steel" guru, Scott Cole, combines qigong, yoga and weightlifting. The Spa at Turnberry Isle, in Aventura, Fla., recently added qigong to its activity schedule, between flamenco dance and Samadhi mud treatments. Employees at companies including Prudential Financial and Mattel have taken qigong workshops, and golf pros are scrambling for private lessons after hearing rumors that Tiger Woods practiced it as a kid.

"We're bringing these beautiful movements to the mainstream," says Scott Cole, the rippled fitness guru of the "Abs of Steel" video series. He has abandoned stomach crunches in favor of qigong and t'ai chi in his latest DVDs. Mr. Cole has added a few of his own moves to the traditional poses, including "Chinese Elvis." Classes at spas typically involve following an instructor in deep breathing exercises mixed with a series of gentle fluid movements, such as knee bends, hip twists and arm motions. The practice also can involve pinching- your ears and slapping yourself. "Consider it an advanced game of 'Simon Says.' " says Ron Navarre, a Manhattan instructor. The booming- interest in Eastern exercise practices is part of a massive shift in the $13 billion health-club industry. "It's not just about the trophy body anymore," says Norris Tomlinson, who oversees exercise programs for the 396 Bally Total Fitness centers around the country. "The baby boomers are realizing- they don't need to bounce around as much to achieve fitness, and they're taking a more holistic approach."

Baby boomers are the fastest growing segment of gym members, joining at more than twice the rate of the overall population. Ten percent of all Americans over age 55 belong to a health club. Many are looking for more than sculpted pecs. They're interested in the secondary benefits of working out, from stress relief to lower blood pressure. The fitness industry is bending over backward to accommodate folks with creaky joints. In addition to stocking up on low-impact equipment such as elliptical trainers and lean-back exercise bikes, they are padding class schedules with activities such as pilates, t'ai chi, yoga and now qigong. Of the new offerings, qigong is particularly accessible to novices. While the true masters study for years, most people can feel tingling sensations in their limbs after a class.

It's so gentle, in fact, that Dino Scopas, a 58-year-old administrator at the Academy of Dramatic Arts, doesn't remove his button-down oxford before classes at Rally's gym in Manhattan. "I go straight from work, take off my shoes, my watch and take the change out of my pockets," he says.

The practice is discreet enough that Anil Singh, a producer at the Web site Space.corn, has tried doing the movements in line at the grocery store and on airplanes during business trips. He now does qigong breathing exercises and arm motions on the subway every morning on the way to work. "I take the local train, so it's not as jarring as the express would be," he says.

While qigong has been pitched to do everything from reversing aging to improving sex, until recently there has been little scientific research into the claims. Last year, the Center for Alternative and Complementary Medicine at the National Institutes of Health earmarked more than $500,000 in grants to study the health benefits of qigong. So far, studies have shown it can help elderly people develop better balance and can lower blood pressure.

Numerous studies also have explored the links between the type of slow, deep breathing involved in practices such as qigong and yoga. "All of these practices set into motion the mechanism that triggers the body's relaxation response, the antithesis of, the body's fight or flight reaction," says Paul Rosch, president of the American Institute of Stress.

While the practice has been a staple of Chinese medicine for centuries, Western doctors are just beginning to look at using medical qigong, a specific from of the practice, to treat patients. Its potential-to relieve stress without exhausting the body has made it an increasingly common recommendation for terminally ill patients. At the Stanford Center for Integrative Medicine, cancer patients are offered weekly qigong classes. Doctors at the University Medical Center in Tucson, Ariz., prescribe qigong to patients with severe heart disease. Just as interest in qigong- blossoms in the U.S., the practice is coming under attack in China, where officials have banned several forms. Qigong- is linked to the spiritual practice of the Falun Gong sect, which blends exercises with Buddhist teachings.

Even in the U.S., the modern appetite for ancient wisdom is encountering skeptics. "First it was hot tubs, then yoga, then massage, then qigong," says Mr. Rosch of the American Stress Institute. "The bottom line is, if there's a way to make money out of it, they'll do it, and they'll call it whatever they want."

And since truly mastering qigong takes decades-there are some 7.000 different exercises-the hyper-simplification and "fusion" classes showing up at gyms and spas has ruffled some purists. "It used to exist as a deep experience for the lucky few who came across it," says Richard Jesaitis of New York, who has studied the discipline for 30 years.

"Now, it's an industry."

Still, some qigong newcomers are happy the practice is catching on. Jill Kreidberg, of Excelsior, Minn., uses the qigong as an instant stress reliever. "It doesn't have to be this major project," she says. Sometimes, running errands at the mall, she ducks into the bathroom to do the "crane breathing" from the "five animal frolics form.