Well here’s something potentially unsettling. Kind of a no-brainer headline (maybe?). Not to make your blood boil, ahem, but research is showing that your internal body temperature and heart-rate could reach super dangerous levels in this type of class causing the risk of heat-related illness if you’re not careful. A new study, sponsored by the American Council on Exercise (ACE) and published in the Gundersen Medical Journal, examined the physiological responses to Bikram Yoga, specifically heart-rate and core-temperature.
The team of researchers at the University of Wisconsin—La Crosse’s Department of Exercise and Sport Science monitored 20 healthy and willing men and women between the ages of 28 and 67, all regular Bikram practitioners, as they did their 90 minute practice in the standard 105 degree room. The participants all voluntarily swallowed a core body temperature sensor and wore a heart-rate monitor during their class to help determine whether or not the practice is really healthy for you. (By the way, we’re not so sure swallowing a thermometer is healthy, but hey, science says it’s ok!)
The participants’ core body temperature was checked every 10 minutes during the class and their heart rate every minute. By the end, the study revealed some potentially startling results:
The researchers found that many of the volunteers’ core temperatures reached higher than 103° F. One man in the study had a core temperature that was over 104° F. None of the men or women had symptoms of heat intolerance, but the researchers note that heat illness and heat stroke can happen when core temperatures reach 104° F. “Although there are potential benefits associated with practicing Bikram yoga, the potential for heat intolerance among some students, including those who may not yet be acclimatized to the heat, should not be entirely overlooked,” the study authors wrote.
In addition, the researchers found that average heart rate was 80% of the predicted maximum heart rate for men and 72% of the predicted maximum for women. The highest heart rate for women in the class was 85% of the predicted maximum heart rate for women and 92% for men.
Note: Increased heart rate is not necessarily a bad thing. In fact, it can help strengthen your heart muscle and is usually what happens when you do any kind of cardio (though we know yoga is just as good as for your heart aerobics). But in this case, the drastic increase in body temperature coupled with the lack of cardio due to mostly standing still, causes reason for concern. Also, the sweating that everyone does in buckets, our natural cooling mechanism, is not enough to do the job of cooling the body in these conditions which can be a problem. Emily Quandt, M.S., who led the study, explains:
“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,” says Quandt. She goes on to explain that, while the excessive perspiration that participants experienced during class is often cited by those who practice this style of yoga as a benefit in terms of the release of toxins, the results of this study show that this sweating was insufficient to cool down the body.
While the study was done on Bikram classes which have a strict 105 degree, 40 percent humidity rule, these findings would likely apply to any hot yoga class with extremely high temps. Now don’t go throwing in your sweat-soaked yoga towel just yet. There may be hope. Quandt’s suggestions? Shorten the class (60 mins or less), lower the temperature (like, maybe less than the Sahara Desert?) and hydrate, hydrate, hydrate.
Bikram teachers are notorious for allowing only a few (scripted) water breaks. But scientists say that’s not cool.
“Nothing is gained from withholding water in any setting,” says Dr. Porcari, head of the University of Wisconsin’s Clinical Exercise Physiology program. “Exercise leaders must actively encourage hydration, particularly when classes take place in extreme environments like those seen in Bikram yoga classes.”
“Knowing the risks associated with things like blood pooling and vasodilation, as well as the signs and symptoms of heat-related illness, is absolutely essential,” Porcari added.
In addition, Cedric X. Bryant, Ph.D., Chief Science Officer at ACE, agrees, “Bikram teachers should recognize that participants’ thermoregulatory systems will be challenged in this environment,” he said. “It is essential that they are aware of the early warning signs of heat intolerance.” Of course, anyone who has ever practiced Bikram or hot yoga, has likely experienced one, a few, or all of these symptoms which include: cramps, headache, dizziness and general weakness.
For good measure, it shall be noted that a 2013 study also sponsored by ACE and also overseen by Bryant, found results to be the total opposite – that core temperatures and heart rates were not adversely affected in hot yoga. However, the key factor to note is that the previous study tested yogis in a 60-min hot yoga class with an average of 92 degrees, nowhere near the Bikram 105. The biggest takeaway from that one, too? DRINK LOTS OF WATER. And, if you asked us, if you feel like crap in the class like you’re going to simultaneously barf, combust and pass out, maybe it’s not the right kind of yoga for you.