The least severe is heat cramps, and the most severe is heat stroke. If not properly treated, heat cramps can progress to heat exhaustion or even to heat stroke, which is a medical emergency. Heat cramps typically occur in the calf muscle. In this situation, allow the athlete to rest in a cool place and encourage rehydration. Monitor the athlete to be sure they do not progress to heat exhaustion.
Heat exhaustion is characterized by an increase in core temperature and heart rate.
Athletes suspected to have heat exhaustion should be removed from exercise immediately, and ice should be applied over the athlete's groin, neck and armpits. Rehydration is essential and these individuals should be closely monitored for signs and symptoms of heat stroke. When dehydration is extreme and too much blood volume is lost, the body stops sweating to preserve the remaining blood volume. This is a serious medical emergency and these athletes need to be transported to a medical facility as quickly as possible. Heat stroke is characterized by a high core temperature, reddened skin and initially normal to profuse sweating.