Every exercise fad reflects the values of an era: Aerobics matched the fast-paced mood of the '80s, while yoga and Pilates gave the '90s an inward-looking discipline in line with the approaching millennium.

So what does the current popularity of Muay Thai, a martial art that emphasizes no-holds-barred knockout power, tell us about the new century? It's fast-paced, aggressive and could get brutal.

Muay Thai, commonly referred to as Thai boxing, has its roots in a 3,000-year-old tradition of unarmed combat that developed in Thailand. Sometimes called "the science of the eight limbs," because of its use of devastating elbow and knee strikes, Thai boxing requires extremely rigorous conditioning, so even if you don't want to step in the ring, the training is an effective way to shed extra pounds. Unlike other martial arts that have been popular in America since Bruce Lee's era, Thai boxing classes have only recently become available at New York-area gyms.

But two new schools in Manhattan, and a few celebrity practitioners, are helping make Thai boxing one of the more popular new ways to get in shape - and defend yourself.

For a traditional approach to Thai boxing, students can visit the basement gym at 224 W. 30th St., where Master K, a 65-year-old veteran of the art, now offers classes (you can take up to 12 classes a month for a $180 fee). Master K's gym is slightly more pricey than a typical yoga studio, but it also offers something that could potentially be more valuable than just fitness or serenity: self-defense skills.

"It surprises me how many women have been coming to learn from me," says Master K, "but it's one of the most effective fighting styles. The hips and body are involved in every strike."

At the Wat (Thai for "temple,") a serenely beautiful new training center in lower Manhattan, the sweet air of incense floats past statues of Buddhas, who smile placidly as students go through a grueling series of exercises, from skipping rope and shadowboxing, to grappling, kneeing and performing two-person isometric strength-building techniques. "It's just been getting bigger and bigger," says Phil Nurse, the former professional Thai boxer who opened the Wat last April.

Nurse, whose clients include fashion designer Cynthia Rowley and supermodel Naomi Campbell, says an increasing number of women have been joining his school - including several who continued training up to the seventh month of pregnancy.

"They want something different, something more energetic and challenging than a gym workout," says Nurse. (The chance to glimpse actor Daniel Day-Lewis training alongside them may also be a factor.)

For $150 a month, or $25 a class, the Wat (31 Howard St.) offers not only Thai boxing but meditation, stretching and conditioning classes. But according to Nurse, a former British and European champion, it's not just the killer abs, extreme endurance and sleekly toned muscles of a Thai fighter that attract students: It's the sense of peace and calm that comes from feeling confident.

Angela Castro, 26 a former marathon runner, recently tried Thai boxing for the first time. "Compared to spinning or the treadmill or the elliptical machine, it's a great way to get your aggression out while learning to defend yourself."

The Wat recently added a women-only sparring class, which Nurse says he created "strictly because there was a demand for it. A lot of women want to take the next step and know, 'What would I do in the street? How would I react?' It's not just about losing your temper. It's about keeping control. And Thai boxing can teach you that."

Originally published on April 18, 2004