Working Out in Intense Temperatures

Jennifer S. Altman for The New York Times

A yoga class at Pure Yoga on the Upper East Side. More Photos »

IT was 105 degrees — as hot as a typical steam room — at Pure Yoga on the Upper East Side on a recent Saturday, but for the 16 women already perspiring through a series of plié squats in a ballet-based barre method workout, it wasn’t blistering enough.

“We’re turning it up to 110 degrees by popular demand,” the instructor, Kate Albarelli, 31, announced in the sort of cheerful tone that would usually signal a time to rest. The women looked as delighted as if she’d given them one.

That’s because the heat is on for a workout promising not just the best body, but also the best sweat. A small but growing upscale clientele, most conditioned to years of regular workouts, won’t leave the locker room for much below 90 degrees. (Typical gyms are 68 to 72 degrees, in line with American College of Sports Medicine guidelines; Manhattan’s hottest recorded outdoor temperature is 106.)

For these religious exercisers, based mostly in New York and Los Angeles, only sweltering temperatures produce adequate workouts: a jackhammering heart rate, pliable muscles and a psychologically satisfying sweat that devotees describe as “detoxing.” So gyms and studios are trying to lure them with ever hotter, harder yoga classes, in addition to roasted versions of Pilates, kettlebells, group cycling and more. (Cue Nelly’s “Hot in Herre,” which seems to appear on every playlist.)

“You don’t waste three songs sitting around warming up — you can hit it hard from the start,” said Mimi Benz, 31, an owner of the Sweat Shoppe, a seven-month-old hot group cycling studio in North Hollywood, Calif. “I’m not going to lie, it’s intense.”

Alexandra Cohen, 42, the supervising producer of “The View,” said, “I don’t have time for hours in the gym doing cardio and weights and then sitting in the steam room to detox.”

She found Bikram yoga (a static 26-pose sequence practiced in 105-degree temperatures) too slow, and hot power yoga (a generic term for fast-flowing classes) too easy. So, twice a week she goes to the yoga teacher Carlos Rodriguez in New York for a grueling mash-up of the Brazilian martial art capoeira, explosive vinyasas, calisthenics and weights. For that hourlong workout, performed barefoot in a room hotter than the human body, Ms. Cohen lines up four exercise mats so she doesn’t waste time (or sneak a cheeky breather) when one becomes too sweat-slicked to use.

“A good day is when I have to literally wring my clothes out,” she said. “Some people do crazy cleanses. I do hot-room workouts.” She mused: “I tell you, your body adjusts. I probably need to make it harder at this point.”

The workouts don’t promise fat-melting or even weight loss; instead, the emphasis is on the “extreme” brag factor. In September, Crunch in New York introduced mat-based Pilates at 99 degrees, inviting clients to “turn it up a notch” and “sweat it out” in a workout “that will have you looking hotter than ever.”

Loren Bassett, 41, a demanding yoga teacher in Manhattan, lovingly calls some of her followers “insane.” It’s partly for them that she and her trainer, Cole McDonough, of David Barton Gym, cooked up Bassett’s Boot Camp for Pure last year. The class is 75 minutes of alternating high-intensity cardio, crow poses and core work. Marie Claire magazine pronounced it “America’s toughest workout”; spaces sell out weeks in advance. One Sunday in March, as the class tried to hold a plank after a round of jumps, squats and push-ups, the gentle thrum of what sounded like rain was audible when the music stopped. It was actually sweat landing on mats.

“You’re crawling through the desert in search of the oasis of a better body,” Ms. Bassett said softly, as students struggled to circle the room on all fours, bodies parallel to floor and feet on purple gliding discs the size of dinner plates. Later, she added: “I called an hour before class and told them to crank up the heat. Hot enough for you?”

Consensus: Yes.

Still, there’s the occasional discount request for “cold” classes. Devotees discuss studio-heating methods in the sort of detail befitting an electrician and know which corner of which studio is hottest. “I’m the crazy girl who gets there early just to get the spot under the heating vent,” said Karin Wilk, 45, an M.B.A. student in New York who takes hot classes exclusively. “I feel like it totally pushes me to the edge, and nothing else can bother me the rest of the day after surviving hell.”