August 29, 2003, Newsletter Issue #85: Playing Tennis in the Heat

Tip of the Week

Humans are homeothermic, meaning that we maintain a constant internal body temperature usually in the range of 36.1 to 37.8 C (97 100 F). Body heat is transferred by conduction, convection, radiation and evaporation. At rest, most heat is lost via radiation, but during exercise, evaporation becomes the most important avenue of heat loss. Higher humidity decreases the capacity to lose heat by evaporation. Air temperature alone is not an accurate index of the total physiological stress imposed on the body in a hot environment.

At least four variables must be taken into account when calculating heat stress:

air temperature,
humidity,
air velocity,
the amount of radiation.
The most obvious is air temperature. Somebody who is exercising in the heat, with no wind, puts their body at a higher stress level than someone who exercises in the same temperature, but under a cloud cover and a slight breeze. The other variables change according to the external conditions.

So, with all this background knowledge, how do we treat heat cramps, heat exhaustion, and heat stroke (most severe)? Heat cramps are caused by dehydration (from sweating) and mineral losses. Treat it by moving the individual to a cooler location, and administering fluids or a saline solution. Heat exhaustion is accompanied by extreme fatigue, breathlessness, dizziness, vomiting, fainting, cold and clammy skin, or hypotension (low blood pressure). These symptoms occur when the body cannot meet all the demands placed upon it, and occurs mostly in people not acclimated to exercising in high temperatures or in a poor physical condition. Place the person in a cool environment with their feet elevated to avoid shock. If they are conscious, give them salt water. If they are unconscious, they will need to get an intravenously administered saline solution (medically supervised). If heat exhaustion is not taken care of medically, it can lead to heat stroke which can be life threatening.

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