and the heat goes on…

Monday, September 1, 2014

She was hunched over, sitting in the courtside chair, an iced towel draped across her neck. The trainer was taking her blood pressure as she sipped a sports drink. While it was her opponent across the net who was ahead on the scoreboard, it was the weather that was the true foe. The combination of heat and humidity had caused Eugenie Bouchard’s body to fail her. While the air temperature was only in the mid-80s, the sun beating down on the Louis Armstrong Court in Flushing Meadows likely drove the temperature higher by 10 degrees or more. However, it was the 70% humidity that was the true villain and that dramatically increased her risk of heat exhaustion.

The body is always producing heat as it goes about its routine daily activities, like breathing and digesting food. Exercise increases that heat production by more than a hundred fold and the body needs to cool itself to be able to function. While we think of exercise as working out or playing a sport, many people exercise on the job. The person doing manual labor is as much an athlete as the person on the field and their body reacts to the environment in just the same way.

The body cools itself by sweating, depositing water on the skin to evaporate and cools. There are certain basic requirements for this to happen. The body needs to have enough water to produce sweat and the air needs to have enough room to accept it. If the air is full, meaning that the relative humidity is very high, the air cannot accept any more water molecules and evaporation from the skin cannot occur. All the sweat in the world will not help cool the body if there is no place for the sweat to go. This is where the heat index comes in to provide a guide to dangerous circumstances.


If sweating and evaporation break down, the body’s temperature begins to rise and all sorts of bad things can happen. The spectrum of heat related illness begins with heat cramps, moves to heat exhaustion and finally to heat stroke, which is a life threatening condition.

But back to the numbers. With exercise, the body can generated up to 10 kilocalories per kilogram per hour of heat. For Ms. Bouchard, who weighs about 60 kilos (130 pounds), that adds up to about 600 kcal per hour. The heat of the sun adds another 150 kcal per hour, so that her body needs to get rid of 750 kcal every hour she is on the court. For a person not used to the heat, the body can produce about 1 liter or a little more than 2 pounds of sweat an hour, just enough to get rid of 580 kcal every hour. Doing the math, if Ms. Bouchard’s body was not acclimated to the heat and humidity, she was falling behind the heat equation every minute she was on the court.

An acclimated athlete can sweat up to 3 liters per hour, more than 6 ½ pounds, and get rid of more than 1700 kcal of heat every hour, but it takes 7-10 days for the body to acclimate to the heat. Even with the awareness that fluid intake is crucial, athletes often fall behind on that equation, and it is not uncommon to see elite athletes requiring IV fluids at halftime and after the game is over.

The loss of water and electrolytes can cause dehydration that also affects the way nerves and muscles interact, leading to muscle cramps. Continued water loss and rising body temperature can cause heat exhaustion with fatigue, lightheadedness, nausea and vomiting. If not removed from the hot environment, the body’s temperature can spiral out of control leading heat stroke with seizures, coma and death.

How to cool the body? The first step is to remove the patient from the hot environment; it may be an air conditioned car that might be the closest best option. Undressing and fanning the patient helps with evaporation, by allowing more air to come into contact with the skin and increasing evaporation. Rehydration is important so that there is enough fluid in the body to continue the sweating process.

The body operates in a narrow range of normal and when it falls outside that range, it works every inefficiently, slowly breaking down. Once Ms. Bouchard started on the downward spiral of getting too hot and too dry, it was inevitable that her performance on the court would deteriorate. Ekatarena Makarova won the match, but aggressive exercise in the heat can cause delayed problems and she may yet develop muscle cramps and fatigue later in the evening or night.

Her responsibility to get hydrated remains, as it does for the construction or foundry worker athlete. Urine production is one signal that the body is finally getting enough fluid. When the body is dry, the kidneys try to hold onto as much water as possible and the amount of urine produced decreases and it becomes very concentrated and yellow. As the fluid status of the body improves, the kidneys begin producing more urine and it becomes clearer.

The ability to compete under any and all conditions perhaps is the mark of a champion, but the conditions at this year’s Open are once again a reminder that Mother Nature a tough opponent and a lady not to be messed with.

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