Step aside, hot yoga. Last year, New York City got its first cool-temperature fitness concept in Brrrn (thebrrrn.com), courtesy of personal trainers Jimmy Martin and Johnny Adamic. The Chelsea spot offers three workouts: Flow, a yoga class set at 60 degrees; Slide, a core-and-cardio circuit in a brisk 55-degree room; and Hit, a high-intensity rope-and-dumbbell routine at a nippy 45 degrees. “Heat limits your body’s ability to perform at its best,” claims Adamic. “When you’re exposed to temperatures between 40 and 64 degrees, you burn fat.” There’s science to support that exposure to the cold can burn calories: A 2014 study in the Journal of Clinical Endocrinology & Metabolism found that, in winter, the body can convert more white fat to beige fat, which burns calories. Other research shows cold temps moderately increase energy expenditure to compensate for heat loss. But studies tend to focus on freezing temps, so study up before warming up to the concept.