This spring, Forbes Magazine placed Philadelphia third in the nation on the list of most yoga-friendly cities - only a breath of fire behind the far more Zen metropoli of San Francisco and Seattle.
The ranking was based on data collected by GfK MRI, a New York-based consumer marketing firm that surveyed 205 markets to determine the popularity of yoga in each. The survey found Philadelphians 42 percent more likely to do yoga than the general population.
"The yoga trend is really growing," said Silverstein, a real estate agent in her 30s. She was talked into trying an early-morning class at Philly Power Yoga with her colleague Silva, who goes two or three times a week.
It is nearly impossible to quantify how many places offer yoga in the region, said Mary Fetterman, who runs Philadelphia Area Yoga, a website listing area studios.
Teachers give lessons in their homes. Classes take place in YMCAs, community centers, churches, the Art Museum steps, and practically every gym, where students practice the pigeon pose a few yards from grunters heaving 30-pound kettle bells.
What is clear, though, is that the expansion remains steady, says Fetterman, a yoga teacher for 10-plus years. Since launching her site in March 2011 to help students find studios, she has gained more than 100 members - yoga teachers and studios who pay $50 to $150 a year.
"Philadelphia gets rated one of the unhealthiest cities . . . yet we have a very aware community here about the things we need to do for our health," she said. "We have such an abundance of yoga that it makes it easier to do it."
The newest studio, Fishtown's Pacific Yoga, opened June 7.
"I thought it would be hard to get people to come to a studio in a residential area like this," said studio founder Nicole McLane. To her surprise, classes filled up immediately.
In 2000, when Corina Benner first thought about opening a studio, she says, there were few places to practice.
The highly respected Iyengar teacher Joan White had been teaching in the city since 1973, starting in a classroom at the University of Pennsylvania. Over the next decade, more teachers emerged, giving classes at the University City Arts League.
Yoga on Main opened in Manayunk. Vijayendra Pratap taught Hatha in the basement of Garland of Letters, and still does. Miko-Doi Smith was teaching in her house. That was about it.
At first, Benner commuted to New York to teach. Then, in 2002, she set up in Philadelphia. By coincidence, two other teachers, Diana D'Amato and Ellen Greenberg, had the same thought, and within a few months, the city had three new studios.
All of them - Benner's Wakeup Yoga, D'Amato's Dhyana Yoga, and Greenberg's Practice Yoga - have grown and thrived.
"When we started . . . a good week was 60 students," says Benner, now 44. These days, 200 to 300 a week take classes at each of her two studios.
As in any field, some teachers are better trained than others. Those who are more knowledgeable about anatomy tend to be more cautious, offering alternative movements to accommodate aging knees, bad backs, and ironbound hamstrings.
Others push limits, which can help the timid achieve positions they had never dreamed possible. But people get hurt, too. Over the last 10 years, yoga injuries have resulted in an estimated 20,000 emergency-room visits nationally.
"Not every pose is for everyone," says McLane, of Pacific Yoga. Part of the responsibility lies with the student, she says, to let the teacher know about injuries and limits.
Given the breadth of yoga styles and philosophies, students naturally gravitate to the classes that suit them best.
Restorative. Meditative. Power. Yin. Kundalini. Hatha. Vinyasa. Iyengar. Two studios in the city - Kaya and Amrita - offer aerial yoga, in which students are suspended from the ceiling by long loops of silky fabric.
Within each studio, personalities and philosophies can differ dramatically. Some teachers are acrobatic show-offs, balancing on a hand while cantilevering their bodies in effortless contortion - to inspiring or demoralizing effect.
Some spend 15 minutes leading chants in Sanskrit. Some ring bells, burn incense, or sing. Some play CDs - usually Indian music, but also classical, new age, soft rock, and rippling brooks.
In workshop classes, students may devote 30 minutes positioning their elbows or trying to redistribute the weight in their hands.
White, 70, an advanced teacher of the rigorous Iyengar method who gave classes at Penn for 27 years, has watched the recent boom with concern.
"It's a fad," she said. "It started when aerobics became less popular. . . . People were looking for another form of workout."
Most studios teach exercise routines rather than true yoga, she says - "yoga is a transformative discipline for the mind."
White, who continues to train students and teachers in her West Philadelphia school, says much of what passes for teacher training now is insufficient and misguided. As a result, students are encouraged to compete with themselves or others to achieve difficult poses, risking injury.
Nevertheless, White sees an upside to the yoga (or yoga-like) movement: that people may be drawn to serious study.
To do that, White says, students need to turn inward.
"Where are people taught to find peace in themselves? To go beyond all this materialism?" she asked. "You never get what you want if you are constantly in a state of desire."
Contact Melissa Dribben at 215-854-2590 or firstname.lastname@example.org or @dribbenonphilly on Twitter.