How Safe is Hot Yoga?

Hot yoga is trending upward in the American yoga scene. Typical classes are held at a room temperature of 90 degrees or more with the humidity maintained at about 40%.  While this practice has had its share of controversy, the effects of hot yoga on heart rate and core temperature have not been studied. Recently the American Council on Exercise, affectionately called the country’s Workout Watchdog, commissioned Dr. John P. Porcari, head of the Department of Exercise and Sport Science at the University of Wisconsin-LaCrosse and his colleagues to research the effects of hot yoga for healthy adults

Twenty healthy, relatively fit men and women between the ages of 19 to 44 participated in this small, uncontrolled pilot study. Baseline data regarding their level of fitness was obtained at the beginning of the study. Individuals were required to swallow an ingestible core temperature body sensor and to wear a heart-rate monitor during two, 60-minute yoga classes. The first class occurred in a room where the temperature was maintained at 70 degrees. Twenty-four hours later, the same group of participants performed the identical sequence of postures with same instructor in a 92 degree room with an undisclosed degree of humidity.  Core temperature was recorded every five minutes beginning five minutes before the class, and ending five minutes after the session. Heart rate data were collected every minute for the duration of the class.

Researchers found that the average exercise intensity averaged 56% of maximal heart rate in the typical class and 57% of maximal heart rate in the yoga class. These heart rates are associated with ‘light’ exercise based on the guidelines provided by the fitness industry. Core body temperature increased by 3.1 degrees F in the typical class and 2.9 degrees F for the hot class respectively. The highest core temperature recorded in the hot class was 102.4 degrees F, which is below a critical temperature of 104 degrees. Participants’ subjective ratings of the two classes consistently suggested that they experienced the hot yoga classe as being more difficult than the typical class even though the physiological evidence did not indicate that their bodies were working harder.  Everyone sweated profusely in the hot classes.

This study demonstrated that neither heart rate nor core temperatures rise to unhealthy levels during a 60 minute hot yoga class in this sample of healthy, relatively fit adults, These findings do not apply to Bikram yoga classes during which classes are held at 105 degrees or higher for 90 minutes.  Further studies are needed to ascertain the safety of yoga classes of longer duration and those held at above 92 degrees farenheit.  Researchers emphasized that drinking lots of water, before, during, and after hot yoga classes is critical to help the body safely regulate its core temperature.

Critics of hot yoga argue that practitioners are at risk for muscle, ligament or tendon strain, sprain or tear during heated yoga practices as individuals may push their bodies beyond their natural limits. There are also legitimate concerns that practicing yoga in hot conditions may be dangerous for children or adults with cardiac, respiratory, neurologic and other diseases and is ill advised for pregnant women. This small pilot study was conducted with relatively young, healthy, fit participants and only addressed the issue of core temperature and heart rate. As such, there is no evidence to suggest that hot yoga may be safe for the general population. Individuals interested in participating in yoga classes should consult with their physical to determine which types of yoga practice are best for them.

ACE-sponsored Study: Hot Yoga—Go Ahead and Turn Up the Heat By Ashley Nereng, B.S., John P. Porcari, Ph.D., Clayton Camic, Ph.D., Cordial Gillette, Ph.D., and Carl Foster, Ph.D.


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