Somehow after enough yoga, sitting perfectly erect and also appearing at ease become no longer mutually exclusive. That’s how instructors Elizabeth Glover and Lara Atella sat in the foyer of their studio on H Street in Washington, D.C. this week, where they explained to me the draw of very hot yoga, as a group of soaking wet, barely clad people poured out of their 105-degree Fahrenheit noon Bikram class. Posture is contagious, like yawning or hepatitis, but with your spine. I tried to nonchalantly pull my shoulders back and stick out my chest as we talked.

If these two yoga instructors seemed especially erect and at ease, it may be because the yoga they practice is an especially intense and especially hot form of yoga. Actually, the neon sign on the brick facade still says “Bikram Yoga Capitol Hill,” but the studio is now called Hot Yoga Capitol Hill. Glover, the founder and director, declines to comment on whether the name change is a position statement—but it’s at least coincidental that, in the wake of multiple recent rape allegations against the guru who created the Bikram yoga method, Bikram Choudhury, some studios are distancing themselves from his name.

That distancing should only increase after Choudhury gave a deeply bizarre defense this month in a CNN interview, saying that he doesn’t need to rape his students because he has “millions” of women lining up to have sex with him. And, due respect for his non-native English, that did not appear to factor into his explanation that he has sex with his students only as a public service when they threaten to commit suicide if he does not.

"We love the yoga," Glover said, drawing me away from the guru and back to the reason I came. "We've seen that it works for people with all kinds of mental and physical conditions. It has helped people with high blood pressure, diabetes, chronic pain, autoimmune disorders—"

"I used to have cysts in my wrist," said Atella, who has a neurobehavioral research background and an eye for methodological analysis, "and my doctors told me I had to get surgery to have them removed because they'd been there so long they were calcified. But then I started yoga, and they went away."

These health anecdotes are far from isolated. Choudhury has positioned himself as more of a spiritual leader than as a fitness expert ("I implant my mind into your brain"), but many people turn to hot yoga with an eye to improving health by some unknown mechanism. The practice undeniably tends to make people feel good—even researchers at Massachusetts General Hospital are evaluating hot yoga as an adjunct therapy for depression—but almost no research has been done into whether hot yoga actually is good, or even prudent, as a bodily undertaking. So I was interested in concerns raised this week by the American Council on Exercise (ACE), which released a strongly worded warning about elevations in body temperatures during Bikram classes.

Leading up to the statement, the council studied people’s heart rates and core temperatures during the course of a class and found that several people experienced significant elevations in core temperature, up to 104 degrees Fahrenheit. “The dramatic increases in heart rate and core temperature are alarming when you consider that there is very little movement, and therefore little cardiovascular training, going on during class,” the researcher Emily Quandt said in the ACE statement.

Bikram yoga, by definition and decree of the guru, consists of 90 minutes at 105 degrees Fahrenheit and 40 percent humidity. The series follows a specific set of poses in a rigid order every time. "Hot yoga," on the other hand, is usually shorter and not so hot, and can be any amalgamation of poses. Even though the practice has been around since the 1970s—breaking into mainstream American consciousness when his friend Shirley MacLaine got Choudhury a spot on Johnny Carson—it has largely gone uninvestigated. But as its popularity continues to grow, along with growing popularity of hot workouts of other types—there are now hot spinning classes, hot kettle-bell classes, hot boot camps—the cumulative hotness drew the attention of ACE.


Body Temperatures During 90-Minute Bikram Yoga Class

American Council on Exercise

“I don't want to raise unnecessary fear and alarm, but I want instructors to be really aware of this, to look for signs and symptoms of heat intolerance,” Cedric Bryant, chief science officer at ACE, told me. We had met a couple months earlier when he was in D.C. for a conference on national fitness guidelines. Bryant is a serious and methodical person whose mission at ACE is to ensure that fitness trainers, in yoga and elsewhere, are certified by a centralized body of some kind (ACE or another, but, you know, ideally ACE) before advertising expertise and plying their trade. His takeaway in this case is that Bikram teachers and practitioners need to be attentive to heat intolerance and encourage hydration, not deprivation. “For the majority of people who are presumably healthy, [Bikram yoga] should present no problem,” Bryant said, but then added that diabetes, hypertension, and obesity can compromise body-temperature regulation, and most Americans have one of those conditions, so people should be careful.

“We had seven people get core temperatures over 103 degrees, and one was 104.1, which is pretty warm,” Bryant’s research collaborator John Porcari explained. “In that range you can see heat-related illnesses, dizziness, drops in blood pressure, headaches, vomiting, even seizures." Porcari has lived in the small city of La Crosse, Wisconsin, for 26 years, where he’s a professor in the Department of Exercise and Sport Science at the University of Wisconsin-La Crosse—and where the energy cost of heating a studio to 105 degrees in winter raises additional questions of prudence. Porcari himself is not a regular practitioner of yoga, but he wouldn’t tell people not to do it.

“People seem to love it,” he said with a verbal shrug, the common refrain. He brought up the not-well-understood attraction of warm-blooded humans to saunas: “What's magical about a sauna? What makes you feel good? There's something anxiolytic about saunas, and about exercising in a hot environment.” Some people like it for the relief they get after they finish, and some like it more in the moment. There is also something at least slightly misleading about the amount of sweat a person produces, which is not indicative of an intense workout, but can be similarly gratifying. But that’s not necessarily bad. “I think when you look at the mental benefits, at the mind-body connection, people feel like they've accomplished something,” said Porcari. “They feel better about themselves."

His speculation ended when I asked about the spiritual element of the practice—if a feeling of transcendence or well-being that sometimes comes from hot yoga could be related to the low blood pressure and dizziness. (Porcari: "Transcendence meaning?" Me: "You know, if you're light-headed enough you might be having some spiritual experience?" Porcari: "That's beyond my realm. If you start feeling lightheaded and dizzy, I don't see that as a good thing.")

But Brian Tracy, a neuromuscular-function researcher at Colorado State University, didn’t leave me hanging. “There is a pretty distinct sense of well-being that you have after a class,” Tracy, who is himself a weekend Bikram warrior, said, “Physically, yes, but mentally also. And it's a real thing. People talk about the exercise high, and this seems different to me. There may be a whole different mechanism where exposure to heat, like going into a sauna, may feed back and have actual positive effects in the brain."

Tracy was not involved with the current study but has done other Bikram research, including the first peer-reviewed study of physiological effects—which was not published until 2008. At that point he found improved balance and strength, and control of the leg muscles, after regular Bikram practice. In 2013, he published another study showing improvement in flexibility and a small decrease in body fat. He was surprised by the new body-temperature findings, and a little suspicious. "My thing about all this concern is, there are thousands of people around the world that practice this on a regular basis and are practically ‘addicted’ to it, and they love it. So, it can't be that bad. Listen to your body."

If everything that my body told me to do were really good for me, the world would be a different, wonderful place.

Tracy’s more tangible counterpoint to the new evidence is his own research, which is forthcoming, which found that the highest body temperatures any Bikram practitioners experienced was 101.5. “That's nowhere near ringing alarm bells about core temperature,” he said. It must be noted that Tracy’s work at Colorado State has been underwritten by Bikram Yoga College. But he is adamant that the conflict of interest does not compromise his integrity. It’s an objection he’s heard before over his years of Bikram research, and he was upfront about the funding source. I warned him that readers would be skeptical, even though not all of his findings have been favorable to Bikram. “Well,” he said, “they can have my raw data if they want.”

That data, like the data used in La Crosse, consists of temperature measurements from an edible thermometer. Tracy describes it as “the biggest vitamin you've ever seen in your life, coated with a rubbery substance." Inside is a transmitter that sends temperature readings to a receiver while the thermometer works its way through a yogi’s small intestine. The subjects are not asked to retrieve the thermometer once its intestinal journey is complete. That is what graduate students are for. No, just kidding. The thermometer pill, like the Bikramites whose temperatures it once monitored, gets flushed.

Both core-temperature studies involved a very small number of subjects, so the reason for the discrepancy between the two studies is tough to parse. If more people would like to fund research of hot yoga—not you, Bikram Yoga College—that would be great. It might be especially worthwhile as more cardio-intensive forms of exercising in heat comes into fashion. “I have more concerns about those [types of exercises] with more upright work, with more pooling of blood and lightheadedness,” said Bryant.

The most important part of both studies is that no one actually experienced heat stroke, or any symptoms at all. Glover’s D.C. studio has been open since July 2006, and she remembers “maybe three times” that there was cause for acute medical concern. “In one case someone was on a diuretic and didn't tell us in advance, so of course, they were dehydrated," she recalled. In Atella’s experience, people have developed symptomatic dehydration in class after a night of drinking.

Tracy drinks a liter of water before class, and nearly another liter during. (Actually it’s lightly-salted water, because electrolytes prevent hyponatremia and swelling of the brain that can come with drinking too much pure water.) Porcari says water should be fine for most Bikram practitioners, because this isn’t a desert ultramarathon. Glover tells people to drink 16 to 20 ounces before class. As long as all practitioners are encouraging hydrating—rather than telling people to push through the thirst and master their bodily desires, which few do—the consensus seems to be that should be sufficient for safe practice.

Jessica Matthews, a senior advisor at ACE, offers a couple other points of advice. “Embrace the process of sweating and encourage students to do the same,” she writes, by which she means that because sweating cools the body through the evaporation process, students should be encouraged “to avoid becoming distracted in their practice by constantly wiping sweat from their skin, which, from a safety perspective, can lessen the amount of evaporative cooling that occurs, resulting in retained body heat and an increased risk of dehydration and overheating.”

I know in a piece like this, the writer would usually try Bikram yoga and report back on how sweaty they got. But I’m not that writer today. I stepped into the 105-degree room and out of it, and it was very hot and the air was thick and sweaty, and that’s all. After talking with so many people about it, though, I’m inclined to try it sometime. Ideally at a place that no longer uses the name of the guy who justifies sex with his students as a public service. It ultimately sounds a little bit like a drug, but one that might even be good for you.

“With every therapy there are risks and side effects,” said Atella. “Yes, when you do Bikram, there are risks, especially if you push it too hard.”

Usually in exercise, pushing hard is the goal.  So maybe “therapy” really is the best way to think about hot yoga, and that heat exposure is best considered apart from exercise. Like a sauna. More is not necessarily better, and nor is hotter. But regular practice provides elements that have very real physical manifestations: ritual, relaxation, and community. The Bikram community is tightly knit and a significant part of many practitioners lives. It provides social support and acceptance. This is a group of people that, no matter where you go in the world, does this exact set of poses in the exact same order, in the exact same environmental conditions. It seems that some of the hesitation of the community to distance itself from Bikram Choudhury comes from a reluctance to drift apart into the nebulous world of “hot yoga,” to dissolve the community, and thereby jeopardize the most evidence-based elements of the practice.

Meanwhile people’s physiologic explanations for why they benefit from practicing Bikram yoga will remain largely speculative. Atella was a runner before she started Bikram, but she was never much of a sweater. After she took up the practice, she began sweating more, even outside of class, which she believes helps her body thermoregulate. "This makes it possible for people to sweat like they never thought they could," she claims, after 16 years of experience doing Bikram. "We see people leaving here every day looking like they're walking on air."

And, yes, that was exactly what the people leaving the H Street studio looked like. Going off into the normal-temperature world, to sit perfectly upright someplace. They were just smiling for no clear reason, like crazy people.