Still, whatever the benefits of the exercise studio, some men think it's not a workout if it doesn't happen in the weight room. Burr Leonard, who founded the Bar Method, has even tried to lure guys with beer after class. "Some of them are put off by walking into a room full of women in their socks," she explains. "They don't like the idea of standing at the barre. They just want to pick up some weights and pump them."

And while many men might relish the idea of mingling for an hour with a room full of scantily clad ladies, it can be intimidating—much like boot camp. "We're shouting, 'Get down! Get lower!' " says Shelly Knight, the director of training for Physique 57 in Los Angeles. When women bring a guy in for the first time, she adds, they always ask her to make sure he's fried by the end. "I don't even have to try."

At his first Nalini Method class, David Barrett, 32, who works in finance in Manhattan and regularly runs and lifts weights, started with 12-pound hand weights but soon realized they were too heavy. "Next thing you know, the instructor was bringing me six-pound weights," he says. His trunk is now the strongest part of his body. "There are usually only about two guys a class," Barrett says. "I don't care, though. I'm not there to make friends. I'm there to kick ass."

Even the fearless Peter Shin admits to getting picked on. He goes back for more abuse every week because he likes the way the workout makes him look. "It gets you long and lean," he says. "That's the type of body I want to keep, the one I like. Plus, lifting weights is really boring."

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