Want a ballerina body? "Back away from the barre," says Brynn Jinnett, 27, a Harvard University-educated former professional ballerina who danced in the film Black Swan.
 
Jinnett, who'd been dancing since the age of three, was frustrated by the fitness trend of barre method classes. She'd taught at various New York City studios, but knew that the way to be a lean fat-burning machine isn't to do the sort of quasi-plies and other exercises Jinnett calls "baby ballet."
 
"You have to work out like an athlete," says Jinnett, whose clients have included Kelly Ripa and Ivanka Trump. So she traveled around the country, studying kinesiology, how professional athletes train, and how that could be applied to mere mortals.
 
"I wanted to know how the body works, and how you change it well and safely and efficiently," says Jinnett, who deferred and then turned down management consulting offers after graduation. "I didn't want to make a better barre class; I wanted to make something different."
 
The result: The Refine Method, circuits of resistance training (Jinnett's in the process of patenting the pulley system she uses) mixed with high-intensity cardio. There is a barre at Refine, but it's "only because people need a balance aid," she says. "I wanted to get rid of it, but it's convenient."
 
She started teaching in a tiny 650-square-foot studio on New York's Upper East Side, the first week of October 2010. In March, at less than six months old, New York magazine named Refine Method the Hottest New Workout of 2011. That's no mean feat in a fitness-obsessed city crowded with exercise options. Her clients—there are approximately 1,000 of them—are a loyal, evangelical group. Nearly every morning, one runs some three miles from her neighborhood to attend the class (subway options between her apartment and the studio are poor). Others talk proudly and openly of results to first-timers.

The 70 or so weekly classes in the studio are fully booked, and Jinnett will open a second location in July. In May, she launched a shoe specially designed to be worn during her workout, and she's starting production on a workout clothing line. Is a DVD next? She's weighing it versus more studios. "I have to figure out how to stay true to the brand," she says.