The troubled empire of Bikram yoga, aka “hot yoga”, suffered another blow last week when a new study found that practicing yoga in extreme heat can raise a person’s body temperature and heart rate to dangerous levels.

The Daily Mail is reporting on the study conducted by researchers at the University of Wisconsin-La Crosse which found that hot yoga can cause a person’s heart rate to fluctuate and their core body temperature to reach potentially dangerous levels.

Hot yoga is a series of 26 poses which are performed over a 90 minute period in a room heated to 105 degrees with only 40 percent humidity. It’s inventor, Bikram Choudhury, has been accused of several counts of sexual harassment and discrimination.

According to Emily Quandt, who led the study, “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 study involved 20 volunteers, seven men and 13 women, ranging in age from 28 to 67, who were all experienced in the practice of hot yoga. The volunteers swallowed a core body temperature sensor and were given heart-rate monitors to wear during class. Body temperatures were recorded before the class began, and at 10-minute intervals throughout the session. Heartrate was monitored every minute.

Researchers found that while heart rate fluctuated according to the difficulty of the pose being performed, body temperature steadily increased throughout the class in both men and women. The average body temperature for men reached 103 degrees and 102 degrees for women. The risk of heat stroke increases at 104 degrees.

Excessive sweating by the participants, which devotees claim release toxins from the body, were found to be insufficient to cool down the body.

The study is recommending safety improvemenst for Bikram yoga classes. For instance, because core temperature rose to dangerous levels around 60 minutes into the session, the length of classes should be reduced. Lower room temperatures should also be encouraged.

Even more important is supplying practitioners with more water breaks in order to keep themselves hydrated. Some Bikram proponents believe minimizing water breaks helps them to maintain the “mindful aspects” of the practice by decreasing the potential for mental distraction.

But Dr. John Porcari, who oversaw the research team, said that nothing is gained from withholding water in any setting.

“Exercise leaders must actively encourage hydration, particularly when classes take place in extreme environments like those seen in Bikram yoga classes,” he said, and called for Bikram yoga teachers to be familiar with essential science principles surrounding exercise, including a clear understanding of the physiology of the thermos-regulation.

“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,” he said.

This could be a problem because yoga instructors are only required to complete 200 hours of “contact” training meaning the training is “hands on” and takes place in classes. Some instructors complete their training in a month-long retreat, others acquire it over a few years of attending weekend workshops or retreats.

“All 200-hour training programs are required to offer instruction in more than just the exercise and relaxation components of yoga. You will also be introduced to yoga philosophy; anatomy and physiology; and teaching methods, including hands-on touch,” writes Kelly McGonigal Ph.D. for the Idea Health and Fitness Association.

However, because there are no agencies that provide examinations and certifications for teachers such as those that oversee training of fitness instructors and personal trainers, it’s anyone’s guess what kind of training these instructors are actually getting.

According to the U.S. Consumer Product Safety Commission, yoga injuries are indeed occurring. In 2010, the most recent year studied, there were more than 7,300 injuries reported.

Anisha Durve, a yoga instructor in the Cleveland area told Cleveland.com, "One reason for injuries is people pushing themselves past their limits and not knowing when to stop" and because too many teachers are not properly trained.

Even worse, students who start to feel the first effects of heat exhaustion in a hot yoga class, such as weakness, dizziness and nausea, may be met with disdain by teachers.

“When feeling like this you must move into a cooler environment,” warns Amber Larson in Breaking Muscle. “But having been in many hot yoga studios, many yoga instructors either look down upon seeking relief or encourage students to stay in the room.”