June 21, 2013
Over the past decade yoga studios across the country have been turning up the heat and offering more hot-style yoga class, where students break a serious sweat exploring poses for 60 minutes in temperatures ranging from 90° to 105°F, with humidity running upwards of 40 percent. These particular classes are a little bit different from the equally popular Bikram yoga, which features a set series of 26 postures and two breathing exercises performed for 90 minutes in a room ranging from 105 to 115°F with humidity at least 40 percent.
For those who like it hot and opt to practice yoga in the heat, exploring postures while dripping with sweat offers a serious physical challenge, while striving to maintain focus in the present moment and remain connected with the breath despite the sweltering heat can be viewed as a psychological test.
But while some yogis gravitate to hot yoga classes, others choose to steer clear of these heated spaces, citing concerns of dehydration, heat exhaustion and heat stroke related to the high temperatures. To date, there has been little research focusing on hot yoga, so the American Council on Exercise (ACE) recruited Dr. John Pocari, Ph.D., head of the Department of Exercise and Sport Science at the University of Wisconsin-LaCrosse, and his team to identify the true physiological responses to performing yoga in extreme temperatures.
Is Hot Yoga Safe?
To finally answer the question of whether or not these classes are safe, the ACE-sponsored hot yoga study focused on how heart rate and core body temperature are affected by a hot yoga practice—and how they compare to non-heated yoga practice. Researchers recruited 20 healthy, relative fit individuals—both males and females—ranging in age from 19 to 44. A baseline of fitness was established using a treadmill-based VO2max test, with ratings of perceived exertion (RPE) assessed at the end of each stage and at a maximal exertion using the 6-20 Borg scale. The subjects first participated in 60-minute basic yoga class conducted in room with a temperature of 70°F. Prior to class, each subject swallowed a Core Temp Ingestible Core Body Temperature Sensor to enable researchers to monitor core body temperature throughout class, and each subject also wore a heart-rate monitor throughout the experience. Core body temperature was recorded five minutes before class, every five minutes during class and five minutes after class. Heart rate was recorded every minute and participants’ ratings of perceived exertion were noted at the conclusion of the class experience.
Within 24 hours, the same subjects took part in another 60-minute class, this time in a room heated to 92°F with significantly more humidity. Participants were led through the same series of yoga postures performed in the non-heated class guided by the same instructor. Heart rate and RPE were measured in the same manner as the previous class. While it was clear that participants sweated much more during the heated class than the non-heated session—no surprise there—researchers were most curious to see how the hot yoga experience affected core body temperature.
After crunching the numbers, the researchers did not find any major differences in core temperature or heart rate. Interestingly, participants’ core body temperature increased by 3.1° for the non-heated yoga class and increased by only 2.9° in the hot class. The highest core body temperature recorded for an individual during the hot yoga class was 102.4°F, well below the zone in which fatigue and heat-related problems are imminent, which is at 104°F.
It is worth noting that participants perceived the hot yoga practice to be more challenging than the non-heated class, based on RPE, even though, physiologically, the subjects weren’t working harder based on their heart rates. During the hot yoga, participants averaged 57 percent of maximal heart rate compared to an average of 56 percent of maximal heart rate during the non-heated experience. The intensity of each class—according to fitness industry guidelines—would be categorized as “light” exercise.
The Take-home Message
Based on these findings, the concern that heated yoga classes—those with temperatures ranging from 90 to 95°F — are dangerous is unfounded. However, the importance of properly hydrating before, during and after class shouldn’t be overlooked, as doing so can help your body to better regulate its core temperature while on your mat. Also keep in mind that it can take anywhere from 10 to 14 days for most people to fully acclimate to exercising in the heat, so give yourself time to get adjusted. Dr. Pocari notes that, while this study looked at the way in which many hot-style yoga classes are being offered, it did not explore styles of yoga like Bikram, which are practiced in much higher temperatures for a longer duration, which is where he feels the research needs to go next.