The heat used in Bikram's class (105 degrees F) is the subject of a lot of passionate discourse both for and against. I practiced regularly in the heat for 3 years. For the past 6 months I have also been practicing at room temperature, usually between 60-80 degrees F. Based on my experience in both situations and what I have learned from listening and reading, here are my thoughts about the heat. It has pros and cons. But the strange part is that many of what people consider to be benefits of the heat are either untrue or actually detrimental.
PRO - Burn more calories and lose more weight
I have been in Bikram classes where the teacher claims that you can burn up to 800 calories in a 90 minute class. Luckily, the Bikram Yoga College of India recently sponsored a study where they hooked up a bunch of yogis to monitors while they practiced. They measured metabolic rate, heart rate and core temperature over the course of the class, so we have a pretty clear idea of what is happening to the body. According to the study, women burn about 330 calories during a Bikram class. Men burn about 460. The difference between men and women is mostly due to body size.
The other issue, weight loss, is a tricky one. As I just mentioned, a class in the heat doesn't burn nearly the calories that some claim it does. The main way to lose weight in the heat is through water loss. Water is very heavy, and we can sweat out 2-4 pounds of water throughout a class. Sadly this loss is very bad for you because it is dehydration. Also, the weight goes right back in when you drink enough water to hydrate your body, which I hope you do.
PRO - Reduced warm up time
In a super heated room, the warm up gets cut down to Breathing, Half Moon Series, Chair and Eagle. 15-20 minutes. Even the Triangle series (Triangle and Standing Separate Legs Forehead to Knee), which in Ghosh's original sequencing goes right after Half Moon, gets moved later in the class to act more as therapeutic and less as a warm up. Our muscles get good and warm in that short 15-20 minutes. Incredible. The heat practically eliminates the need to do postures to warm the body. In 90 minutes we can do a good amount of therapeutic postures, from Wind Removing all the way to the end. When I practice at room temperature it takes 60-90 minutes to get my body sufficiently warm. As far as I can tell, this is the greatest advantage of the hot room.
PRO/CON - Warm muscles are more flexible
Yes, it's true that we can stretch farther in the hot room. Our muscles loosen significantly, but this is as bad as it is good. The hyper loose muscles allow us to overstretch and strain our muscles. We can't feel the usual neurological feedback from the muscles when they are tight or at the edge of their comfort zone, so we push them farther than we would in normal circumstances. We can strain the muscles and, even worse, we can strain the connective tissue. Our tendons and ligaments. Tiny tears in our connective tissues don't heal nearly as fast as our muscles, so if we practice in the hot room on a regular basis we can generate real damage in the tissues. This can lead to torn ligaments and loose joints, both things that take a very long time to heal if ever.
PRO/CON - Lots of sweat
When we practice asana in a hot room we sweat like crazy. The supposed benefits are twofold. 1)Your body sweats out toxins, making the extreme sweat a purifying process for your entire body. 2)Your skin gets clean and exfoliated from all the sweat. All the gunk and grime and dead skin washes right off, like scrubbing every inch of your skin from the inside out.
The problem with perceived benefit #1, that we sweat out toxins, is that it has no foundation in biology. Our sweat is made up of water and electrolytes for the singular purpose of cooling the body. There is a fraction of a percent of anything that might be considered a toxin in our sweat. Medically speaking, our body eliminates toxins through excretion (urine and feces) and to a lesser extent exhalation. So we don't actually sweat out any toxins, just water. And that raises a significant Con with practicing in the heat - dehydration.
The hot and humid room actually short circuits our body's natural cooling mechanism, so we hemorrhage water. Sweating is designed to cool us by evaporating from our skin, taking large amounts of heat with it. When the air is humid, our sweat cannot evaporate effectively, so we cannot cool. Our body keeps sweating more and more in hopes that it will help. It flows out of us in vast quantities as our bodies try to regulate their temperature. So at the end of a practice in a hot room, we are likely to be severely dehydrated even if we started the practice at optimal hydration.
CON - Heat Stroke
Heat stroke and heat exhaustion are so common in the hot room that teachers act like it is normal behavior. "We are ridding ourselves of toxins," they say. "Stay in the room no matter what." Cramping, lightheadedness, headache, nausea and vomiting are all signs of heat exhaustion. And it gets worse when a person is dehydrated. I have seen all of these symptoms and experienced most of them myself while practicing in the hot room. The recommended treatment for heat exhaustion is immediate cooling through air, ice packs or cold water, which goes directly against the usual refrain of "stay in the room." If we are feeling lightheaded or nauseous we should leave immediately and cool our bodies.
In conclusion, I think the heat does more potential harm than good. The greatest advantage I see to the heat is that it saves time by warming the muscles externally. The possible dangers include strained connective tissue, loose joints, dehydration and heat stroke (which causes brain damage).
This journal honors my ongoing experience with the practice, study and teaching of yoga.
1) Sridaiva Yoga: Good Intention But Imbalanced
2) Understanding Chair Posture
2) Why I Don't Use Sanskrit or Say Namaste
3) The Meaningless Drudgery of Physical Yoga
5) Beyond Bikram: Why This Is a Great Time For Ghosh Yoga