Exertional heatstroke in novice runners.

Heatstroke occurred in four apparently normal but inexperienced runners who were involved in road races of 10, 16, 32, and 42 km. Each of the runners attempted to increase his running pace by approximately 1 min/km during the last 5 km of the race. Symptoms of heatstroke occurred within five to ten minutes of the onset of increased effort. In three cases, environmental conditions (temperatures, 24 to 26 degrees C) were contributory. Specific guidelines and instructions are needed for inexperienced runners who enter distance road races.