If you sense something burning at the Franconia Fire Station, don’t worry — it’s just calories. Six days a week, Roberson Magalhaes and Leonardo Lins take over the station’s bingo hall to teach Zumba, a Latin dance-based form of fitness that aims to get participants to “Ditch the Workout, Join the Party.”

Maybe that slogan should really be “Ditch the Gym.” That’s because popular instructors are building such enormous followings that the crowds can’t fit inside typical health club exercise studios. So several have started businesses to cater exclusively to the hordes of Zumba zealots, and they’re finding that no matter where they set up shop, they often don’t have enough space to meet demand.

Pop your head into one of Magalhaes and Lins’ classes, for instance, and you’ll probably see upward of 150 people. When they launched their business, Chakaboom Fitness, Jan. 1, they expected 30 students at their first class, but 70 showed up. It’s kept growing. “We knew it was going to happen, but not this fast,” Magalhaes says.

Although at least a half dozen other area instructors attract similar crowds, the Zumba Fitness company isn’t sure how common these regularly scheduled mega-classes are.

But because no accessories are required, Zumba is one of the few fitness formats that can feasibly be taught in such big numbers. That leads to an economy of scale that the studios can pass on to clients. A Chakaboom class is only $5.

On a recent Thursday night, Lins took to the stage and asked through his mic, “How’s everybody doing?” There’s no question that 43-year-old Kathy Bryant was doing great, from the smile plastered on her face. “I don’t know that I love the size. But I love the energy,” she gushed. That’s easy for her to say from the front row, where she can study every gyration. Further back, however, the vantage point is a problem.

Magalhaes and Lins are considering setting up TV monitors to provide better views. For now, folks who can’t see the instructors follow the people in front of them. Magalhaes and Lins also often hop off the stage and work the room to give more students a closer look.

But if 33-year-old Cynthia Hawkin doesn’t know exactly what to do all the time, she just makes it up. “The thing I like is there are all kinds of people here. I don’t have to be self-conscious,” she says. “You can do your thing and not worry about people looking at you.”

Going unnoticed in class doesn’t sound nearly as appealing to Kevin Burns, a spokesman for the American Council on Exercise, who worries that students lost in a crowd are more likely to get hurt. He urges newbies to stake out spots where they can see (and be seen) and to talk to the instructor before class about injuries or other concerns.

Keep yourself safe, and no one will need medical attention — except for maybe your friends. “People are sick of hearing me talk about it,” says 48-year-old Vicky McVey, who credits Chakaboom with helping her lose 15 pounds. Now those are some impressive numbers.

Photo by Astrid Riecken/ The Washington Post