Thursday, January 28, 2010

The Temperature-Humidity Equation

Nothing too deep here, but it’s an observation I’ve had for a few years now. With Houston’s generally warm, okay, hot, temperatures and high humidities, there seems to be a relationship between the two that impacts my running. Now we know that a formalized relationship in summer is the so-called “heat index”, but I’ve never really known what that means to my body, or exactly what went into the number anyway. And besides, nobody seems to talk about the heat index until it is around 95 or higher, and for me that is a no-run day, at least outside, no matter what.

So how can we use a number to help guide us in our running? I have been using a simple addition factor to help me out. Add the temperature in Fahrenheit to the relative humidity percentage and, voila, we have a number that is usable. My rule is that if the number is over 150 it will be difficult to run much more than five or six miles at a reasonable pace, and when the number approaches 160, especially if I’m running in daylight hours, caution should be made. Over 160 and it’s time to stay in the air conditioning or find an indoor treadmill. No exceptions.

This formula has worked well for me. The most significant problem I have found with it is that in summer the number rarely falls below 150 (but thankfully it seldom rises above 160). So summer running, as is widely known, is difficult in Houston. But not impossible.

Luckily today is not summer, and the number as I’m sitting here is 64 plus 71 equals 135, a bit high for winter but still comfortable. I’ll break a sweat, and if I go over five miles my cotton tee shirt will be soaked to my belly button, but I won’t overheat. And that’s a good thing.

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