The Effects of Heat and Dehydration on Driver Performance

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While attending the 2012 Performance Racing Industry Show in Orlando, I was especially intrigued by one company in particular, CoolShirt Systems, manufacturers of personal cooling systems. Being a racer from the hottest place on the planet (central New Jersey in August), I've always known that heat affects racers. Some deal with it better than others, but most fade as the day goes on. During a 95-degree summer day at Englishtown one racer made the statement that "whoever stays hydrated today is winning." Although he made the comment in passing, it resonated with me; I knew there was truth to it. That's why I was so drawn to CoolShirt Systems at PRI; they've built a business out of keeping racers cool. Their website states, "After more than 20 years experience in the medical field and extensive research on cooling the human body, we have developed systems specifically for surgeons, racecar drivers, football players, fire/emergency services/hazmat, industrial applications and personal use."

Now that the warm weather racing season is approaching, I asked CoolShirt Systems if they would submit a technical piece on how the human body is affected by heat and dehydration. It's presented here for you. Stay cool, racers!

How the human body works. Heat energy always moves to cold, which is why a radiator works. The heat energy from the engine is trying to warm up the air as it travels past the radiator. The body works the same way to a point. The body has four different ways that it uses to cool itself: radiation, convection, evaporation (due to perspiration) and conduction. All of these different systems work very well to keep the body cool and running well as long as the environment stays below body temperature, roughly 95° F. However, when the temperature gets above 95° the heat energy from the environment starts flowing to the body because the body is cooler than the environment. That is except for perspiration which allows the body to cool despite the hot temperature because when evaporation occurs, it cools the surface from which it is evaporating. The body has four different ways to control its temperature and when the temperature of the environment gets above 90° to 95° three of those four ways no longer work. Now add a driver suit and helmet to the mix, sit behind an engine giving off even more heat and it can affect even the fittest driver.

What about just cooling the head? When the ambient temperature is below 90° the body sends 96% of the blood to the heart, brain and the other internal organs and muscles. However, when it is hot the body responds differently. The body sends almost 50% of the blood to the skin surface to try to cool the blood through radiation and to provide water for perspiration. Since the entire body becomes a radiator you don’t want to cool just the head, you want to cool as much skin surface as possible. Severe heat stress is treated in the hospital by putting the patient in a tub of ice and cover as much of the body’s surface as possible. The problem with only cooling the head is that the body’s thermostat is the Hypothalamus Gland. This gland is found in the middle of the head. If you only cool the head, the thermostat thinks the entire body has cooled and shuts down the cooling system and may try to start warming things up again. This is the opposite of what you want.

Why is hydration is so important? As you sweat, the water is coming from the blood which then causes the cells in the blood to become more dense and the blood becomes thicker. As the blood becomes thicker, it is harder to pump. Further, the heart is only working with 50% of the blood it normally gets, which means fewer nutrients and less oxygen. With reduced blood volume, the heart works harder and beats faster to make up for that loss. This is why heat stress can be so dangerous. The heart keeps trying to catch up and the blood keeps getting thicker. The end result could be a heart attack. So you must go to the track well hydrated. Studies have shown that it takes up to 24 hours to rehydrate the body, so drinking some water while you are at the track starts the process, but it will be the next day before you have fully rehydrated. Remember, drinking fluids does not affect core body temperature, but it does begin the process of replacing fluids that are lost.

At the same time that the heart is working with only half the blood that it normally uses, the brain is struggling with the same problem. What happens in the brain is that more mistakes are made, productivity goes down, attention and short term memory are impaired and most importantly reaction times are decreased significantly.

How can I tell when I am starting to get heat stressed? It has been shown that when you lose two percent of your body weight due to perspiration you are in heat stress. If you weigh 200 lbs then two percent would only be four lbs. It has further been shown that with a four percent weight loss (eight lbs.) reaction time goes down by 23 percent. Have you ever noticed on a hot summer day after everyone has been there all day long that you see more red lights as you get into the late afternoon? Now you know the reason why: drivers have sweated out a bunch of water, their core temperature is up and they are now in heat stress. Their reaction time and ability to concentrate are gone. If you can keep your core temperature down during the day, you will not have perspired as much and you may maintain better focus over other racers.

More information can be found in this abstract HERE.

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