Heat injuries in Canadian mass participation runs.

In two Canadian runs with a total of approximately 2900 participants 26 people collapsed with heat injury and were taken to hospital. All were relatively young (13 to 38 years old). A retrospective survey showed that all were novices to 10-km races and that many had collapsed even though they had consumed fluids before and during the run. A review of etiologic factors suggested that the extremes in the Canadian climate, which preclude heat acclimatization in the spring and early summer, may be an important influence on the incidence of heat injury.