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Running in the Summer Time.

© Lynn Seely

I have included race information at the end of this article. Be sure to check it out.

I have had a lot of requests lately to provide information on running in the hot weather of summer.

Thank you to Dr. Pribut for permission to reprint the following information.

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Ouote: from Dr. Pribut's web site;

Running and the heat. With the humidity at greater than 70%, 100 degrees would feel like 144 degrees. When the humidity is 90%, 90 degrees will feel like 113 degrees. Hmmmmm, maybe it is not such a good idea to run then!

(For the chart and further information, please check out Dr. Pribut's web page here.)

WBGT (Wet Bulb Globe Temperature) Index & Thermal Stress

Humidity plays a great role in the risks associated with heat and exercise. Clearly, humidity will decrease the evaporation of perspiration, and thereby inhibit one of the primary means by which the body can cool itself. This is what led the development of the WBGT Index method of determining heat illness risk. This is also known as the wet bulb globe temperature. This method depends upon temperature measured with 1) a dry thermometer to measure ambient temperature, 2) wet bulb temperature, and 3) black globe temperature to determine radiant heat.

The wet bulb temperature is measured by placing a wet wick over a thermometer bulb. This reading will be affected significantly by both humidity and wind velocity. The relative humidity is the ratio of the wet bulb to dry bulb temperatures. If the humidity is high, evaporation and consequent cooling will not take place and the reading will be close to that of the ambient temperature. Likewise, higher wind velocity will increase evaporation and lower the wet bulb reading. The wet bulb reading can never exceed the ambient temperature.

Neat Formula

But the table is easier to understand:

WBGT = 0.7 x Twb + 0.2 x Tg + 0.1 xTdb

Twb = Wet bulb temperature
Tg = Black globe temperature
Tdb = Dry globe temperature

From this formula, it is evident that the humidity is valued as the major determinant of heat stress, as it is weighted at 70% of the value. Below a WBGT value of 64 F (18 C), the risk of heat injury is small. Above a WBGT value of 82 F (28 C), races should not be undertaken.

Heat Regulation

Body core temperature is the result of the balance between those processes that create body heat and those that dissipate heat. Winslow, Herrington and Gagge in 1937 used the following formula to

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