The Study
David Wisner, a doctoral student in the Department of Kinesiology affiliated with the Institute for the Study of Youth Sports at Michigan State University, explains in an article he wrote for Spotlight on Youth Sports how to determine when sports training should be modified or canceled due to heat. Wisner describes what factors can lead to life threatening conditions for athletes exercising in hot, humid weather.

The Findings
The heat index, which combines temperature with relative humidity, gives us an "apparent temperature" that indicates what it really feels like outside. For example, if the temperature is 90°F and the humidity is 80 percent, then the apparent temperature is 113°F. For athletes, cramping and heat exhaustion are possible when the apparent temperature is between 90°F and 105°F. Heatstroke is possible, and cramps and heat exhaustion are likely, when the apparent temperature is between 105°F and 130°F. If the heat index rises above 130°F, athletes are highly likely to experience heatstroke. Sunshine can add to this likelihood by radiating additional heat to the body. Humidity plays a key factor in how our bodies loose excessive heat because perspiration is only effective if it can evaporate. Therefore, in highly humid conditions, an athlete may be dripping with perspiration, but unable to cool off because the moisture on the skin isn't evaporating. The body also can loose excessive heat when air flows over the skin. That is why windy days are more comfortable when exercising in high temperatures. Wearing clothing that lets the skin "breathe," such as those made from nylon, is better than materials like cotton, which can hold large amounts of perspiration. Also insisting that athletes drink water before, during and after exercising will help prevent heatstroke and heat exhaustion.

What It Means to You
Coaches and teachers planning training sessions in hot weather should be advised to consult the heat index before exercising begins. If the apparent temperature is between 90°F and 105°F, practice should be modified by reducing the intensity and duration of the training. If that temperature is between 105°F and130°F, then practice should be held in an air-conditioned facility or by doing some sort of pool workout. If that is not possible or if the apparent temperature is above 130°F, the practice should be canceled. If possible, practice sessions during hot weather should not be scheduled between 11 a.m. and 4 p.m. Coaches should instruct athletes about appropriate clothing to wear and the importance of drinking fluids to avoid becoming overheated.

More Information
For further guidelines about training in the heat, see Wisner, D., "Exercise and the Heat," Spotlight on Youth Sports, Spring 1996, Vol. 19, No. 1, pp. 4-6.

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