29 August, 2012

How hot is your yoga?

We do hot yoga.

Some of us do Bikram yoga. Some of us do Baptiste yoga. Some of us do other versions of hot yoga. Everyone has a good sense of what the temperature is for these different styles. Bikram is between 104-106 degrees Fahrenheit. Baptiste ranges between 90-95 degrees Fahrenheit. There's another factor that comes into play, and it's an important one. It's called "Heat Index." There's a website by NOAA that you can visit for explanations and calculations of this index, which is based on temperature and relative humidity. The heat index, in simplest terms, tells you how hot it feels for a given combination of temperature and humidity. The two charts below (one from the NOAA site, and one by me) show you how heat index increases quite dramatically as temperature increases. For your convenience, I have placed a dot where Bikram and Baptiste have set their studios.

As you can see above, there's quite a big gap in heat index between those two styles of yoga. Though the actual temperature difference is only about 15 degrees, the heat indices differ by closer to 25 degrees, and that's even taking into account that Bikram is nominally done at lower humidity. Basically, humidity exaggerates increases in temperature. At the highest temperatures and humidities, the above curves likely start to become inaccurate, as humidity probably hits a cap when temperature keeps going up.

It's interesting to note that, according to NOAA, conditions in a Bikram studio are considered to be on the border of the "Danger" zone.

And, it's even more important to note that, often in hot yoga classes, especially in the summer, or in heavily attended classes, the humidity of a studio can go far above the 40-50% ranges that are prescribed for these two styles of yoga. And from the two charts above, you can quickly see that the effect on heat index, which is a more accurate measure of what your body experiences, are dramatic, and take it far into the "Extreme Danger" zone. For example, a class that is at 105 degrees, with only a moderately elevated humidity level of 60% will have a heat index of about 149 degrees. That is a full 25 degrees higher heat index than Bikram's prescribed conditions.

It is important to regulate not only temperature, but humidity, in order to keep conditions safe and healthy. This requires a mechanism of circulating air to return humidity levels into the desired range as a room gets moist with 50-100 people sweating for an hour or more.

Something to think about.

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