Teacher Bill Arce leads a "kick-butt" Ashtanga yoga class in Pacific Grove.

Ashtanga yoga, explains local yoga instructor Bill Arce, is all about generating heat yet staying focused on breathing to keep your heart rate low. "The postures are secondary to breathing," he says. "You hold a pose for a few breaths and then, boom, you''re jumping to another pose. It''s a real kick-butt practice."

It is precisely this "kick-butt" kind of description that had always scared me away from Ashtanga. More than four years ago, I started yoga to gain flexibility and strength, and (hopefully) to improve my rapidly slumping posture. Yoga''s stretches and poses seemed to be a smarter way to improve overall health and muscle tone than, say, weight training or running.

All schools of yoga get into some pretty twisted poses (legs crossed behind the head, handstands with the legs jutting out horizontally to the side) but I''d always had the impression that Ashtanga places undue, almost masochistic, emphasis on these gravity-defying pretzel poses. Between that and what I''d heard of its lung-splitting ("kick-butt") workouts, Ashtanga sounded less like yoga and more like aerobics on steroids.

Learning that Madonna practices Ashtanga as her sole form of exercise didn''t make it seem any more accessible to a mere mortal like myself. And knowing that "Power" yoga was an Ashtanga spin-off didn''t help, either. Some years back, I''d read an article on this American invention and how it was being practiced in glitzy New York City studios. Glossy color pictures portrayed classes filled with beautifully sculpted people in the latest gym fashions; the teacher gave instruction through a headset microphone. It seemed far removed from the meditative, carefully aligned poses I''d studied and come to love and respect through Iyengar-based yoga.

So it was with some trepidation that I attended my first Ashtanga class (going only because I felt I should for this article). I began to gain some confidence when the Pacific Grove class started and instructor Elisabeth McCloud led us through a series of familiar "sun salutation" poses. McCloud not only welcomed me warmly, she helped me figure out what was going on and how to modify poses that were too difficult for me. Even so, I was quickly humbled as the repetition and pace of even the familiar "easy" poses began to take their toll. My arms began to shake, my back began telling me to lighten up. Even in this beginner class--a class that didn''t even do all of the Ashtanga primary series poses--I couldn''t keep up.

Truth be told, I was pleasantly surprised to find myself moving deeper than I normally do into some stretches--probably because of the heat that Arce talks about. And I began to see how Ashtanga would build strength very quickly. I was also surprised to see how Ashtanga can be very meditative despite (or perhaps because of) its emphasis on vigor. Because each of the six levels of Ashtanga follow a set series of movements, explains Arce, you can focus on your breath and not on what is about to happen next. "We already think too much in our society," he says.

Emily Griffith, another local teacher, puts it this way: "When one truly practices Ashtanga, one withdraws his senses from the physical and it becomes a moving meditation."

Griffith is studying yoga in India until February and answered my questions by email. She''s 68-years-old and has been practicing yoga for more than 30 years--Ashtanga for the past 10. She says she finds that Ashtanga''s use of the breath and vinyasas (combining breath with movement) "helps people to advance in yoga more rapidly than other methods."

Both McCloud and Griffith concede that there might be more likelihood of injury with Ashtanga than other forms of yoga and, the day after class, I did find out that I''d stressed my back in a way that it did not appreciate. But McCloud and Griffin attribute this increased risk of injury to a student being overly ambitious, or a teacher pushing too hard. And Arce sees an enormous payoff from Ashtanga. The women in particular, he says, build health and self-esteem as they build strength. Says Arce, women often lack the upper-body strength necessary for lengthening the spine and keeping it healthy.

Arce also boasts somewhat proudly that, although Ashtanga has gained popularity, until about five years ago it was considered to be "the dark side of yoga." Because of Ashtanga''s emphasis on vigorous workouts, he says mischievously, "it was kind of like we were the bad boys of yoga."

Call me boring, but I don''t feel the need to go over to the dark side in my own yoga practice. I can see doing more Ashtanga, which would undoubtedly make me stronger. Ashtanga''s set series of poses and movements might also help me become more regular in my practice.

But I don''t foresee giving up my careful Iyengar-based classes anytime soon. I''ve found plenty of meditation and challenge in learning to hold poses for longer than a few breaths and working with subtle adjustments in the poses (rather than rapid movement and sweat) to make changes in the way I hold my body. As my current teacher Tamara Botkin Siegman says, "There are many paths to yoga, just like there are many paths to God."