Midway through their yoga class, the teachers realized they need a megaphone.

Cars honked and a DJ was playing funky tunes as dozens of arms reached toward the sky.

More than 100 people had brought mats to a parking lot on Lyndale Avenue in Minneapolis for the fifth session of Gorilla Yogis -- urban, studio-free yoga that's springing up around the Twin Cities this summer in various forms.

Their name is an offshoot of a fringe movement known more widely as "guerrilla" or no-frills yoga. Regardless of the name, it's defined by a focus on the essence of yoga without the trappings of accessories ($90 yoga mat, anyone?), an effort at affordability (prices range from free to a sliding scale to a charitable donation) and sometimes a slightly underground nature.

Yogis have been seen practicing the downward-facing dog at the Mill City Farmers Market or the triangle pose by Lake Calhoun.

"At our Mill City event, people showed up in tennis shoes, with their dogs, without mats," said Nan Gane Arundel, one of the leaders in the local movement. "We're reinforcing that you are already whole; you don't need anything else. I find that really liberating."

Arundel and Jessica Rosenberg founded Gorilla Yogis in March, looking for a way to practice yoga in urban, offbeat places, and to build community, raise money for local causes and create awareness for yoga. After posting their first event on Facebook, about 150 people showed up at the Mpls. Photo Center on a fluke 80-degree day.

"A lot of times yogis tend to go to the same places and don't get out of ruts and patterns," Arundel said. "We wanted to find out, How do you do something different, how do you tear down the studio walls?"

Gorilla Yogis partners with a space, usually a nonprofit that gets a percentage of their donations, and has sponsors such as French Meadow Bakery, Peace Coffee and Lululemon Athletica, a yoga apparel company.

"It really is a movement. The emphasis is on having a really fun time, on laughing and smiling," Rosenberg said. "It's about unity and community and freedom, allowing yourself to tap into authenticity. It's fun and easy, and no attitude that you need to look like this."

Gorilla Yogis fan Paul Johnson agrees.

"It transcends the idea of self and is powered by the community of the yogis," he said. "We'll find ourselves in group forms to encourage community and trust. We simply do not do that in daily studio practice."

Given its nature, it's impossible to know how many people are practicing yoga outside of studios. In many ways, studio-free yoga harkens to the ancient essence of yoga. But technology has made it easier to connect.

On the shores of Minneapolis lakes, recent graduates from CorePower's teacher training programs lead free classes with the twin purposes of gaining teaching experience and making yoga accessible to those who can't afford studio yoga.

"It's a win-win," said Joe Pollock, who started Saturday classes at Lake of the Isles. "It's a fun way to practice in an outdoor setting. People running by always want to know what's going on ... one random person came because someone else tweeted about it. ... The reality is, yoga is a huge business. I think that's fine, as long as there's a way to make it accessible to other people too."

Some classes rely completely on technology. Sarah Baumert led a popular grassroots, donation-based class in the Twin Cities until she moved to Boston.

"When I decided to move, the group was a bit bummed and one of my students suggested that I start recording some of my classes to make into podcasts," she said. "I have some die-hard followers who do the podcasts every week."

One reason followers like the guerrilla aspect is that it's less formal, less expensive, is playful with "no fancy outfits required," she said.

"Yoga has really blown up in America in the past 10 years or so, and it has become exploited quite a bit," Baumert said. "There is no reason you have to be rich, look a certain way, or live in a certain neighborhood to live a yogic lifestyle. I think guerrilla yoga is really about that more than anything."

Some studios have gotten in on the no-frills vibe. One Yoga in Minneapolis became a nonprofit in 2007, and started an outreach mission with the goal of making yoga accessible to all.

"There are populations that typically lack access, due to income or physical limitations," executive director Kris Kiel said. "Yoga can be done in a chair, by people with disabilities, the visually impaired -- we even have a teacher who is trained in bedside yoga and can work with people in hospice or who are bed-ridden."

Teachers from One Yoga bring their classes to recent immigrants, teaching Spanish-speaking classes at local churches, or leading groups without any common language. They've also taught in public schools and to people who have recently been homeless.

"I still think studio classes are wonderful," Kiel said. "But the economic reality is that not everyone can get to a studio. More and more people of different income levels and backgrounds are becoming aware of the benefits of yoga. It's not an elite practice; it's a practice for everyone."