We can't run a dipstick down our gullet and get a reading that says, "add a quart." We do have some physiological signs, but they function at the 'Warning-Danger!' level, too late to maintain optimal performance. Unfortunately, we don't come with built-in gauges or indicators that tell us just how much coolant we have left in our system. You use it once and then it's gone and needs to be replaced. Unlike a car, your body's coolant isn't in a sealed internal system. Just like a car, your body must dissipate the excess heat generated from burning fuel. Yes, this will cause problems before long, and we will discuss that issue below. You do need to know that under the worst of conditions you can produce up to three liters of sweat in an hour of strenuous exercise, but your body can only absorb about one liter from fluid consumption. On days when it's both hot and humid, well, you don't need to read about what's going to happen when you exercise in those conditions. Soaking, dripping sweat may give you a psychological boost, but it has no physical efficacy to cool. The sweat accumulates on your skin and soaks your clothes, but you don't get any cooling from it because it's not going into the vapor phase. On humid days, sweat evaporates more slowly because the atmosphere is already saturated with water vapor, retarding the evaporation rate. Humidity is the other major factor that affects sweat. Evaporative cooling must do all of the work. At 95° F (35° C) or above, you lose no heat at all from your skin and in fact, you actually start to absorb heat. On hot days, with little difference between skin surface and ambient temperatures, your skin surface provides only negligible convective cooling and you'll need to sweat more to maintain a safe internal core temperature. As the temperature increases, you gradually rely more on evaporation. In cool weather, you get substantial cooling from the heat that escapes directly from your skin. Weather conditions greatly affect sweat production and cooling effectiveness. The remaining water molecules have less energy and you feel cooler. As water molecules evaporate from your skin, they remove heat energy. Thus, water molecules in the gas phase have more energy than water molecules in the liquid phase. Sweat works on a basic physical premise: water evaporation is an endothermic process, requiring energy (heat) to change from liquid to gas. Sweat, however, glistening on your forearm or soaking your singlet won't cool you. But by far the most important part of the cooling system, accounting on average for about 75% of all cooling, is your ability to produce and excrete sweat. You breathe harder to get more oxygen, expelling heat when you exhale. Blood carries heat to the capillaries near the skin's surface, removing heat from the body core. An active person needs a reliable cooling mechanism.Īctually, you have several. The body must rid itself of this heat and maintain a core temperature within a few degrees of the well-known 98.6° F (37° C). That builds up and raises our core temperature. The breakdown of these energy providers releases heat. But we also burn some protein, fat, and blood glucose from ingested nutrients. When we exercise, we burn molecular fuel (mostly glycogen). By Steve Born How your cooling system works
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