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Bikram Yoga Sweat: Stumping the Rocket Scientists.

It started innocently: one day the Bikram Yoga room felt a little cool and I had come to get my sweat on! C’mon. What was going on here? This is Bikram Yoga. You know, the “torture chamber.” Here I was, being tortured by a cool breeze and goose bumps.

What to do? Add clothing. Problem solved.

If you haven’t practiced any sort of hot yoga, here’s the quickie summary: by adding heat and humidity, the body becomes more flexible, and the workload increases. The heart rate goes up and the sweat trickles down. In a nutshell, the higher the heat and humidity, the harder the class is. All 26 poses in the 90-minute Bikram Yoga sequence are beginner poses with very little movement. Without excruciating heat and humidity, it’s a cakewalk (or in Bikram parlance, a blueberry cheesecake walk). 

bikram sequenceGET HOTTER

I now come prepared to any hot yoga class. I have layers to add if the room isn’t up to snuff.  But, over the years teachers have bristled at this behavior. “Get your head out of the heater Erin.” Not so easy. I am there to work hard. The heat, humidity, AND poses deliver. ALL three. This yogi can’t balance on a 2-legged stool.

THE SCIENTIFIC CHALLENGE PRESENTED

Recently a teacher sent me a link to a WebMD article suggesting that layers, once wet, will make me feel cooler NOT hotter. The article specifically says “wet clothing greatly increases heat loss through conduction and evaporation.” What?? How could this possibly be? Shouldn’t my sweat warm up in that heat box? Adding layers, trapping heat, covering the skin…all of these strategies should keep me warm, right? Even when I sweat?

The Bikram/Hot Yoga environment is unique and articles like the one just mentioned don’t apply. The WebMD article is talking about temperatures under 68F (not Bikram). We all know wet clothing makes us cooler when the surrounding temperature is lower than our body temperature (think wet swim suit). But this is not the case in a hot yoga room. So we begin to dig.

Our athletic-minded traveler research team could not find ONE article, study, or research piece that dealt with OUR SPECIFIC situation: 105+ degree heat and relative humidity of 40-50% AND the desire to be hot…even hotter. We even went beyond the “research.” We contacted no fewer than 10 experts – in thermophysics, human performance, exercise science, neuromuscular function, and even a few authors of exercise physiology textbooks. Two dropped the ball, a few missed the point of contention (with ONE exception), and those that did reply gave us migraines with a bunch of scientific gibberish that said nada. Had we stumped the rocket scientists?

Let’s first get you up to speed about the body’s cooling mechanisms (thermoregulation). Understanding these basics is important.

BODY COOLING

  1. Radiation: transferring heat from one mass to the other without physical contact. Ever stood next to someone who just got done with a tough workout? They’re radiating heat! No need to touch…it’s coming off them like an oven with the door open.
  2. Conduction: losing heat through physical contact with another object or body. If you’ve ever sat on a freezing cold metal chair, then had the area under your butt become warmer, you’ve transferred the heat from your body to the cold metal chair.
  3. Evaporation: losing heat through the conversion of water to gas—SWEATING.
  4. Convection: losing heat through the movement of air or water molecules across the skin. This helps conduction and evaporation. Heat loss from convection depends on airflow across the skin. If you’re in a gym with industrial fans blowing, or in a Bikram studio with air movement, convection kicks in and you should cool down.

thermometerNow, let’s apply the above to working out. 80-85% of cooling during prolonged exercise comes from evaporationSWEAT! In humid environments like a hot yoga room, evaporation is slowed because the air already has a high level of moisture in it. There’s less “room” for the sweat to evaporate into the atmosphere. So if the body can’t sweat as efficiently, guess what? You feel hotter!

So when you’re in a Bikram class, with temperatures in excess of 105° F and relative humidity between 40-50%, it’s going to affect thermoregulation. With constant heat radiation from yogi to yogi, high humidity preventing sweat evaporation, and little to no airflow across the skin, it should be as easy as child’s pose to stay warm in class. But most Bikram Yogis don’t want warm. They want HOT.

 THE LAYERING QUESTION

  1. Does adding layers work? Yep. More layers should mean an increase in body temperature, especially in hot and humid Bikram studios.
  2. Do clothes curtail the evaporation process? Likely. All clothes get wet quickly due to the humidity. Could those wet clothes actually cool the body? Only if a strong gust of wind is blowing. It’s still likely the cooling is no more than bare skin and most likely less.
  3. Are we better off wearing as little clothing as possible? Not if you are trying to up the workload.
  4. How about adding as much clothing as possible? Go ahead! People will think you’re a bit “loco.” 

So listen up YOGIS:  Nah, nah, nah, na, nah, nah…We are RIGHT. Yes, a little childish…but hey we spent a LOAD of time on this! 

Our review of research (over 48 studies on MEDLINE) and email conversations with scientists suggests that layering WILL increase the workload because the body's evaporation is slowed. Along with studies that suggest this conclusion, a professor of neuromuscular function at Colorado State University corroborated our findings that layers of clothing reduce evaporative cooling (which accounts for 80-85% of the body's cooling during exercise). Hooray! He understood our question because he understands Bikram yoga!

The studies we found aren’t perfect. They don’t address heat, humidity, exercise, AND wanting to STAY WARM! Every study assumes you want to cool the body.

RESEARCH SUPPORT

  1. Sports Medicine (2003) says layers impose a barrier and in warm temps, increases body temp during exercise and slows evaporation. BINGO! BUT, what about wet clothing? Hmmmm…
  2. Another study (AIHAJ 2002) looked at clothing ventilation and thermal insulation. The results? More airflow through the clothing, the cooler the skin. Am I supposed to wear a garbage bag to class now vs. the “wicking” materials present in nearly ALL sport clothing?
  3. A study out of China looked at heat strain while wearing different ensembles for varying workloads. Simply put, you need to restrict sweat evaporation and exercise to increase heat strain and heat production.
  4. In a 1995 article from Ergonomics, protective clothing impeded heat exchange through sweat exchange for those working in hot environments. But…the specifics of “protective clothing” were not shared, so there’s no way to tell if it’s something we wear already!

Bottom line is this: those teachers who say layers can cool you down can zip it! Unless a constant breeze is blowing through the room, this just isn’t true. Those teachers that want you to get your “head out of the heater” should do the same. It’s all about personal preference, and if there’s a need to increase my heat, so be it. If I’m fine with the increase in workload, it’s my option to add layers. Bikram yoga is about the heat…it’s the honest truth. Those schools that coddle students with fans and open windows are missing the point, and we would guess they’re missing business too.

** This article was written by Daniel Gaz and Erin Kaese. Along with Dan's clinical research work at Mayo Clinic, he is also a contributing editor to Athletic-Minded Traveler. Erin Kaese is Managing Editor of Athletic-Minded Traveler and a Bikram Yoga "loca."

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Comments

Comments

My personal view in this

My personal view in this matter is that all clothing insulates and when exercising in a hot environment being nude is optimal for thermoregulation. In practice of course various personal, social, and cultural factors obtain [1]

I think you're correct in identifying that humidity, airflow, textile composition, size of the person etc etc would all impact on physical tolerance of a hot environment. Howerver, how hot one enjoys feeling, rather than how much heat one can tolerate before becoming unwell, is a question of personal preference, and the freedom to choose to add or remove layers as one wishes is helpful here. Maybe this could be subject to an N-of-1 randomised controlled trial? [2]

Hope this is of some use.

Best wishes, Carl

[1] http://books.google.co.uk/books?id=aPwPjVIxbGQC&lpg=PA148&ots=U1kmEZ-n5m...
[2] http://www.randomiseme.org/

Dr. Carl J. Reynolds
Academic Clinical Fellow in Occupational Lung Disease. General Internal Medicine and Respiratory Medicine
Imperial College Healthcare (London)

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