the consequences of hot

Monday, May 28, 2012

May was a tough month to be a runner in Wisconsin. Imagine training all winter for a spring marathon, braving winter cold and spring rain, only to have the race cancelled because Mother Nature didn’t cooperate. First came the La Crosse Marathon called off because of torrential rains and lightning. The Green Bay Marathon began in high heat and humidity but the race was aborted and the course closed when runners succumbed to conditions and the trifecta was the Madison Marathon that never was because the temperatures and humidity were too high even at 7am. Race organizers are beginning to realize that runners may be a bit crazed and must be protected from themselves because they will take on challenges that are not safe.

The body cools itself by evaporating sweat and it needs three things: enough water to produce the sweat, air that can accept the sweat when it evaporates and wind that sweeps the sweat off the body. As temperatures rise, the body needs to take in extra water to compensate and it doesn’t matter what the exertion level is. The athlete sweats more, the roofer sweats more and the elderly lady in her non-air conditioned apartment also sweats more. When acclimated, the body can make 2 to 3 liters of sweat an hour, about 5 or 6 pounds give or take, and that water needs to be replenished or the body can shut down very quickly. It takes a week or two to get used to the heat. Off to Hawaii for winter vacation? Your body will only generate half as much sweat, meaning that cooling is much less efficient.

Humidity may be almost as important as the temperature. As the relative humidity increases, air is less able to accept sweat from the body and evaporation and its cooling effect decreases. The wet bulb globe temperature formula adds temperature (dry bulb), humidity (wet bulb) and wind and type of surface (black bulb) to measure when too hot and too humid is too dangerous. The surface is just common sense icing on the cake. Working on a black roof or asphalt driveway increases the actual temperature because of the absorbed and reflected heat. Air movement is the final need for evaporation since air that doesn’t move gets filled up and can’t accept more sweat. It’s why fans work so well to cool.

But back to the athletes. It would seem that people who have trained for a marathon would know their body and pay attention to the warning signs of impending heat exhaustion. Unfortunately, that isn’t always the case and there have been a couple recent examples when reasonable people have done unreasonable things and have suffered the consequences. T the 2007 Chicago Marathon, more than 10,000 of the 35,000 runners who began the race had to drop out. It was 72F with 75% relative humidity at the start. 685 runners had heat exhaustion, 320 ambulance transports to the hospital and 66 people were admitted. Even for a city the size of Chicago this number of patients is such a short period of time, is a major strain on their ambulance and paramedic system.

Cancelling a race is not a popular move but it is happening more frequently. The American College of Sports Medicine sets safety guidelines but runners usually are not happy. They have invested months in training, taken time off from work and spent hundred on airfare, hotels and entry fees, only to be denied the chance to run because of a little heat and humidity…and the opportunity to collapse by the side of the road.

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