Beijing winters are dreaded by many for their chill that digs into the bones, causing many Beijingers to spend hours on the couch buried under blankets. But the impulse to stay active and fit need not be smothered by sub-zero temperatures, when hot yoga studios around the city are roasting away, just waiting to open up some pores.

Fine Yoga has two downtown studios, both offering daily hot yoga classes. Drop-in prices are standard at 150 yuan. The hot classes are held at temperatures up to 42 degrees, the heat serving to relax muscles, loosen joints and encourage detoxification through sweating. Electric heaters line the perimeter of the mirrored studio, and today's instructor Li Jing dutifully checks on the temperature several times.

Li teaches several yogic disciplines at Fine Yoga, but admits that she particularly enjoys teaching hot yoga. "Ashtanga yoga can help your body to sweat and detox as well," she explains, "but the feeling for hot yoga is much more intense."

The student body of today's afternoon class is half men and half women, a particularly surprising balance for Beijing, or pretty much any yoga studio in the world. Two of the students are new to hot yoga, and Li checks in with them before starting class.

Hot yoga has its critics, as it is more risky than conventional forms of yoga. Excessive sweating from the combination of heat and exercise can lead to dehydration or hyperthermia (overheating of the body). Pragmatically, Li insists on setting the thermostat at 38 degrees, "the lowest temperature for hot yoga," apparently.

Students do their best to mimic the postures that Li's svelte body so naturally assumes. After a quick warm up, the first beads of sweat appear on students' brows, soon followed by more as they quickly progress through a series of poses.

It's clear that the heat increases students' flexibility, but when it comes to balance, everyone's on their own. Li wraps fingers around her left ankle behind her, stretches her right arm out forward, and lithely leans forward into a ballerina-esque pose. Her left toes effortlessly point toward the sky.

Student approximations are somewhat less graceful, but impressive nonetheless. "Ok, take a minute to drink some water and wipe off," Li allows. Fine Yoga graciously provides complimentary bottles of water and towels. Li studies one of the new students, before informing her that she's not drinking enough.

The temperature is definitely hot, but is surprisingly comfortable. Everyone is sweating, but not profusely. Today, the idea of hot yoga being dangerous seems remote, if not bizarre. "A very professional teacher can teach a class safely," Li explains. "From the first class, the teacher interacts with students to be aware of student health and capabilities. Students shouldn't need to worry about pushing themselves too hard."

Yuan Wei wipes her face and neck with a damp towel, having just completed her first hot yoga class. "I think trying different styles of yoga is good," she says between breaths. "Different styles of yoga feel totally different so I want to keep exploring."

Fine Yoga's instructor Li Jing eases new students through some basic hot yoga poses. (Photo: CRIENGLISH.com/William Wang)