Cool Suits: Safety, Performance Enhancement or Comfort?
Jim Malone, MD, FACS
This article is being written due to multiple questions asked of me by fellow drivers after the recent Cal Club races at California Speedway June 3 and 4, 2006. However, this article is not meant to be the definitive reference or provide the absolute science behind the issue of body cooling and performance. We will cover the physiology of body heat and cooling, data on performance as a function of cooling, in general the cooling systems available and a short discussion of the benefits and negatives of some of the various types cooling systems.
NASA (The National Aeronautics and Space Administration) has published numerous articles on performance and body heat. When air temperature is over 95 degrees, an individual can make 60 mistakes an hour. Body temperature is a complex result of air temperature, humidity, clothing, and exercise. As described another way, when the heat index is above 95 (any air temperature over 95 or an air temperature as low as 85 with humidity greater than 80%) our bodies can no longer lose heat effectively. In addition, if the individual is also dehydrated (2% loss in body weight - water weighs 7 pounds/4 liters, so 1-2 liters loss depending on body weight) our bodies cannot cool effectively by evaporation. By the time thirst hits, you ARE dehydrated. Analyzed another way, a ½ to 1 degree rise in body temperature results in 80 mistakes an hour. Heavy exercise can result in a 1.8 degree rise in body temperature every 15 minutes. Obesity (fat) insulates and decreases surface are/weight further decreasing our body’s ability to regulate heat loss/body cooling. There also is data to suggest that “the old guys” are more susceptible to heat problems.
Our bodies lose heat/regulate body temperature as follows (the percentages indicate how much of 100% cooling; baseline is a body core temperature 98.6 degrees and skin temperature 91.4 degrees):
-radiation 60-65% -- this process only occurs when air temperature is lower than skin temperature;
-evaporation 25% -- the process of sweat and cooling through evaporative loss is very effective, but this process looses efficiency with rising air temperature and dehydration;
-convection 10-15%-- heat loss due to air and water vapor around your body, but the air or water vapor must be lower than skin temperature;
-conduction (2%)—direct transfer of heat from warmer to cooler objects.
When the heat index is above 95, the body can no longer lose heat by radiation, convection, or conduction. As an example, at the time of my race (group 2), air temperature was 104 degrees, humidity was approximately 25%, add 15 degrees for the driver suit and the heat index is over 130. With a heat index of 105-130, sunstroke, heat cramps, and heat exhaustion are likely. With a heat index over 130, heat stroke will occur with continued exposure. By the way, in car temperature on the grid was 138 (which makes the heat index at greater than 150). Simply put, when we race in air temperatures over 95 degrees, especially with humidity over 40 per cent, our bodies cannot cool effectively. Equally important, body cooling issues are compounded by dehydration. It is not surprising then that driver performance deteriorates during a race. Also not surprising, driver errors appear to occur most often in corners.
There is not much research publicly available on race car drivers, but there is good data written about endurance runners and cyclists and weight lifters. In general, proper hydration before during and after exercise with body cooling increases measured performance 4 – 6 %. As a driver, think about your last 5 laps of a race. Proper hydration during exercise is 8 oz every 15 minutes. Since we do not “drink and drive” we finish a race ½ quart low (essentially ½ liter) on fluid replacement plus any fluid loss from evaporative heat loss (sweat) which I would estimate can range from ½ to several liters of loss—very significant dehydration. Remember radiation, convection, and conduction are not effective with air temperature over 95 and evaporation efficiency decreases and/or stops with significant dehydration. NASCAR/NASA data reports that cool suits can eliminate 40-60 percent of a racer’s stored heat and lower heart rates by 50-80 beats/min. (In general, professional drivers have the best cardiovascular fitness of all professional athletes. There is data showing sustained heart rates of 120-180 during a 2-3 hour race. Interestingly, heart rates are higher in the pits than on the track—the driver has no control in the pits.)
What to do? Training and exercise in hot humid environments (minimum 90 minutes for 7-10 days) will increase your endurance, but this effect is lost within several days of not exercising. Some pro racers actually train in a sauna but good luck for the weekend racer! Ice packs and cool towels trick the brain (hypothalamus) into thinking cool but these measures are not effective. There are some systems with ice cooling pouches that cover significant chest surface areas and those cooling systems are more effective than ice packs or cold towels. Excluding ice pack vests, we are left with cold air, water, or both as measures to cool.
Let us start with air cooling. Timothy Ackland at the University of Western Australia’s Department of Human Movement and Exercise Science (studying US National Association of Stock Car Drivers) reports that circular or oval tracks may prevent carbon monoxide from escaping the air surrounding race cars. In addition, that study notes that drafting might also increase track air carbon monoxide for the following car(s). That study also reports that high levels of carbon monoxide or heat by themselves can impair the ability to control motor function. But, most importantly, when heat and carbon monoxide are in combination, the effects are multiplied. So, a simple hose or NACA duct directing track air to the helmet or driver without air filtering or cooling merely routes hot air with track debris and possibly carbon monoxide to the driver’s face, so that he can breathe that air. In addition, inhaled warm air actually raises core body temperature. Body and helmet cooling with cool filtered air are much more effective and safer than simple “cooling ducts”.
With respect to ice water cooling, there are two key point in this whole discussion: cool water transfers heat 28-32 times faster than air and cooling shirts cover 30% or more of body surface area, making them very effective cooling devices. There are several manufactures of water and /or ice shirts (see reference list). I am not trying to endorse any manufacturer, but to answer the obvious question, I use a Cool Shirt with a pump speed control. My system is set up with a direct battery source so that I can keep cool on grid before the race even starts.
Many NASCAR teams use the Koolbox III by Comptech or Pump Systems Driver A/C units. Most of these and similar other high performance units are beyond the budget of club racers. However, good systems are available for several hundred dollars. The positives are discussed above. The obvious negatives are weight and cost. Most of us buy a set of new tires to gain lap times. However when those tires are gone we have to buy a new set. A good cooling system, which will last many seasons, costs about ½ the cost of new tires. My cooling system with water and ice weighs about 12-13 pounds and is mounted on the passenger floor area (where ballast would be placed). I simply found that much weight to remove from my car when I installed my cooling system (a small high performance gel battery saved 20 pounds so my net weight was a loss of 7 pounds). After reviewing this data in detail, I personally would argue that even if you gain 12 pounds, driver comfort, safety, and performance are worth the weight.
This article started as a response to questions. After researching and writing the article, I am now increasingly interested in this topic and I am trying to find a local university exercise/physiology lab to study these issues in club racers. If I do not find a lab I will try to do the study myself (I will need other drivers to participate/study) with temperature monitors and blood carbon monoxide levels.
If there is enough interest, I will be happy to write similar articles on the new SN2005 helmet standards (new helmets are lighter/safer and more frequently incorporate cooling ducts and have more efficient helmet air flow), new FIA approved driver suits (which breathe better improving evaporative and radiated heat loss) and CarbonX@ (in general more efficient at burn protection than Nomex@)(@patented/copyright names).
Good resources include: Computech Mfg. Co. (816-842-2011 or
Pump Systems Corp. (717-556-3111),
Fresh Air Technologies, Inc. (888-466-RACE or
and Shafer Enterprises (800-345-3176 or
Good references include:
NASA,
Training for Sports and Fitness by Rushall and Pyke and
Neither the references nor resources are meant to be inclusive.
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