Why So Hot?

What’s the deal with the heat in Bikram yoga? As teachers we get asked this question a lot. We always try to give an answer that’s straightforward and easy to understand, but the real reasons are perhaps a little more complex.


The heat is one of the first things you notice when you step into the yoga room in a Bikram yoga studio. If set correctly, the thermometer sits at 40 degrees celsius, and the hygrometer at 40% It’s a noticeable heat, and it can feel a little overwhelming at first, like walking into a sauna. But as you start to practice your yoga postures, and you start to sweat, it becomes less noticeable. The Bikram series of 26 postures and 2 breathing exercises was the first yoga sequence that was practiced in an artificially heated room. Recent research by Jerome Armstrong points to a similar series having been practiced in Japan by some of Bishnu Ghosh’s other students in the mid 1960’s, without heat. When Bikram Choudhury came along he changed the sequence a little, and added heaters in the yoga room, to mimic the temperature in his native Calcutta.

When Bikram started teaching his yoga in the US in the early 1970s he kept the heated yoga room environment. Most people who have tried practicing in this kind of environment agree that the heat does make the yoga feel different. It can make things more challenging, but also more rewarding, as the heat allows the muscles to stretch further, and the ligaments to relax, allowing a deeper and more effective full body workout. A lot of people with old injuries testify to the fact that hot yoga seems to somehow bring the old injury to the surface, allowing them to work through the injuries and to attain new levels of mobility that they had struggled to achieve for years. The heat also seems to add  a mental dimension to the practice, as the heat makes it harder to focus on that which is beyond the here and now in the yoga room. In other words, it is simply too hot to think!

But what is the science behind doing exercise in a hot environment? Our practical experience of this yoga is that the heat raises the heart rate, and allows these relatively simple movements - which almost everyone can engage in – to have much more potent cardiac benefits. The heart rate generally rises in the standing series, even though the postures are relatively low impact and static. This means that for people with injuries or other factors that restrict their ability to engage in high-impact cardio exercise,  the heat can provide a shortcut to some very potent cardiac benefits.The heat also induces a temporary analgesic (pain-numbing) effect, which can allow people with chronic pain to exercise areas of their body that cause them pain. This is turn will allow them to strengthen atrophied muscles whose atrophy is often directly related to their chronic pain in the first place.

It takes time to get used to exercising in a hot environment, but after seven to fourteen days the human body will undergo a series of changes known as acclimatisation. These changes include increased oxygen consumption and increased exercise efficiency, as the muscles show reduced glycogen utilization and diminished post-exercise lactate concentration, meaning they use less food to accomplish the same effort and give off less waste during the process. Studies show that all over blood cortisol levels drop as the body acclimatises to the heat. As blood cortisol is a measure of stress this seems to imply that training in a hot environment can reduce stress levels.  The heat also allows the blood vessels to dilute, lowering blood pressure and allowing blood to flow more freely though parts of the cardiovascular system that may otherwise have been blocked.

The Human Physiology Department at the University of Oregon has published research showing that training in a hot environment, and acclimatizing to that environment, could produce athletic performance benefits that carry over to a cool environment. The study examined the performance of twelve trained cyclists after ten days of heat acclimation. Dr Santiago Lorenzo who led the study says: “We found a seven percent increase in performance. Seven percent is a gigantic gain in competitive cycling.” The research subjects who had trained in a hot environment improved almost every area of their performance in both hot and cold environments, and also showed corresponding physiological changes. These changes included increased blood plasma, increased maximal cardiac output and increased power output at lactate threshold. Dr Lorenzo says: “I wouldn’t be surprised if some day lots of athletes use heat as a training tool. Just as athletes use altitude training or hypoxic tents now, heat acclimatization could provide a very real edge in the future.”

But what are the counter indications to exercise in heat? Could it actually be dangerous? Two studies have been made that measured core temperature during a Bikram yoga class, to see whether the high room temperature could affect core temperature in the human body in a way that could be dangerous. In both studies the research subjects had to swallow a very small thermometer, which was then used to monitor their core temperature during class. One of the studies was done in an actual Bikram yoga studio, in the Chicago area. The other one was done in a research lab at Colorado State University. The outcome of the two studies was somewhat contradictory, as the one in the yoga studio showed a slight elevation in core temperature, but the one in the lab didn’t. The study from the lab seemed to be the more accurate one, as in this one the researchers had 100% control of the heat and humidity of the room, but in the yoga studio they didn’t. The study from Colorado State University also considered things like fluid intake, age of subjects, clothing and levels of exertion.

These studies were only pilot studies, and the samples and length of study were far too short to draw any definite scientific conclusions. But the indications that came out of this research seem to be a perfect echo of the advice that we always give our students. Advice that is based on common sense, and on more than 30 years of experience from our Bikram yoga teaching community:

·      Try to come to class fully hydrated, but don’t overdo it. Your body can only take up 2 dl per hour so try to sip water throughout the day.

·      Wear light clothing and don’t cover more skin surface with clothing than you have to. The evaporating sweat on bare skin in the best thing to cool you down in class.

·      Drink water when you need to drink, add electrolytes if you practice a lot.

·      Don’t push yourself over the edge, sit down and take a break if you need to.

·      Give your body time to acclimatise to the heat. Even if you are otherwise fit and healthy, if you are a beginner at hot yoga you may not be able to do as much as a more experienced practicioner.

Practicing yoga in a hot room can be a challenging but also very rewarding experience. If you approach it carefully and with common sense it is a safe and effective way to reach new levels of physical and mental well being.