Monitoring Road Racing in the Heat.

In brief: The guidelines that have been published to prevent runners from collapsing with heat injury have been based on laboratory studies with different conditions from those experienced in actual road races. A new portable heat stress monitor was used to test whether high levels of solar radiation raised rectal temperature more than no-sun conditions. The authors propose guidelines using color codes to alert runners to the degree of danger during races. They say that below 18 C (64 F) there is a low risk of heat injury, and races should not be started at temperatures above 28 C (82 F).