A class at Bend and Bloom in Brooklyn using foam blocks. Credit: Andrea Morales/The New York Times

ANA FORREST is an itinerant yoga teacher riding the circuit, selling out workshops in South Africa and conducting training sessions in Houston. She is to Yoga Journal as Angelina Jolie is to Us Magazine: a mainstay.

Say “Forrest Yoga” to a yogi, and the first word that comes to mind is “intense.” It is known for its long holding of positions, emphasis on abdominal core work and standing series that can go on for 20 poses on each side. Ms. Forrest, 53, based in Orcas Island, devised her rigorous style with no less a goal than curing the ails of the modern world, including computer roadkill bodies (lower back tightness, shoulder pains and neck aches) and spiritual malaises that lead to destructive behaviors like addictions. The classes attract N.F.L. players, recovering addicts, dancers and cancer patients.

Ms. Forrest is as fierce about hands-on coaching of instructors in her style as she is about her workouts. While Bikram yoga, for instance, has thousands of certified teachers, and studios like YogaWorks have multiple training sessions in multiple locations, Ms. Forrest has so far conducted all her own 200-hour teacher trainings. She has also anointed a relatively tiny group of über-instructors known as ‘Forrest Yoga Guardians’ to aid in maintaining standards.

To reach her goals, she had to create “a circle of people to help,” Ms. Forrest said in a phone interview, admitting to a messianic mission to heal. “My death will be whatever it is, but there will be all these people who can continue this wave to transform.”

In New York two years ago, Ms. Forrest handpicked Erica Mather, 35, who lives in Harlem, to become one of 20 Forrest Yoga Guardians worldwide — a combination of custodian, missionary and mentor. A recent class that Ms. Mather taught at the Pure Yoga studio on the Upper West Side demonstrated the importance of core strength to Forrest Yoga.

INTENSE: Ana Forrest, the creator of Forrest Yoga, in Central Park. Credit: Federica Villabrega 

Students lay on their backs, legs extended into the air, purple yoga blocks squeezed between upper thighs, hands clasped behind the head.

“Active feet,” Ms. Mather said. We flexed our feet, Barbie doll style. We inhaled, pressed down lower backs, held our breath, lifted tailbones, squeezed blocks. The squeeze lasted through eternity. We exhaled, lifted heads, then shoulders. We kept squeezing. Legs were quivering; minds were shrieking, “Get me out of here!” Inhale. Head down. Repeat.

Ms. Mather, who was previously enrolled in a doctoral program at Columbia, sees her practice as offering more than six-pack abs. “The thing that spoke to me about Forrest Yoga was the invitation to feel your body deeply and befriend your body as a source of wisdom and intelligence instead of something that you should occupy while you were on earth,” she said.

To become a Forrest Guardian, after a 200-hour foundational teacher training in 2006, Ms. Mather completed 400 hours of field work, a nine-day advanced teacher training and, upon invitation, a one-week Forrest Yoga mentorship training last year with Ms. Forrest. The Guardians meet with Ms. Forrest annually and mentor instructors who are in the equivalent of a post-graduate program.

Ms. Mather will help Ms. Forrest when she comes to New York to teach at Pure Yoga in early November as part of a tour for her new book, “Fierce Medicine: Breakthrough Practices to Heal the Body and Ignite the Spirit.” Like her mentor, Ms. Mather can do controlled handstands worthy of Cirque du Soleil, explain poses vividly and provide a comforting hands-on assist.

In New York, Forrest Yoga remains a boutique cult brand. “This is a very unique niche thing going on in New York City,” said Denise Hopkins, who teaches it mostly privately and at Bend and Bloom in Brooklyn. “It’s an underground scene.”

Erica Mather, a Forrest Yoga Guardian. Credit: Michelle V. Agins/The New York Times

Forrest Yoga also resonates in classes that do not bear the moniker. Ms. Hopkins first heard of the style from teachers who led classes in a Forrest abdominal series, crediting the creator. Aarona Pichinson, who leads classes at the Kula Yoga Project in TriBeCa and at a YogaWorks in SoHo, once taught Forrest Yoga but dropped the name when her practice morphed into a more flowing vinyasa style.

“I’m so glad Erica is out there doing this because she does it really well and embodies what Ana does in so many ways,” said Ms. Pichinson, who added that her practice remained Forrest-inspired.

In addition to Ms. Mather and Ms. Hopkins, the Forrest cadre in New York includes Anna Mumford, who teaches at the Red Hook Recreation Center in Brooklyn, and Ramona Bradley and Emilia Conradson, who teach at the Om Factory in Manhattan. In Southampton, Leslie Pearlman teaches at the Ananda Yoga and Wellness Center.

“It’s great to have a network of really, really supportive Forrest teachers,” Ms. Mumford said. When she was laid off in February 2010 as a videographer from the American Civil Liberties Union, she said, the group encouraged her to commit to teaching along with starting a freelance video production company.

Ms. Mather theorized that the growth of Forrest Yoga in New York has been stalled by Ms. Forrest’s West Coast roots and the fact that a majority of urban dwellers go to the nearest yoga studio. But she said, “There is a critical mass of dedicated teachers to start to tip the scales in New York.”

She herself is having a breakthrough year in yoga. Ms. Mather taught in June at Wanderlust in Vermont with marquee names like Seane Corn and Rodney Yee. She taught last week at the Kripalu Center for Yoga and Health in the Berkshires. In New York, she will be leading Forrest Yoga Intensive workshops at Pure Yoga next weekend.

A vigilant guardian of the name, Ms. Mather insists that what she teaches be designated Forrest Yoga. “I’ve battled with some people about this, and ultimately I teach Forrest Yoga,” she said. “So let’s call it what it is, like Bikram or Iyengar.”