Recently I wrote about how gender differences and fitness levels affect sweat rates . Now that the weather is finally turning warmer, it’s a good time to discuss the science of sweat itself. Though it runs down your face, gets in your eyes, dampens your clothes and leaves that unpleasant odor, perspiration is one of the most important physiological survival tools you have. Like the coolant fluid you put in your car to keep your engine from overheating, sweat keeps your body from burning up.
Your body consists of at least 70 percent water. Very fit athletes, because of their higher blood volume and greater lean muscle mass (which contains more water than fat or bone), are typically as much as 75-80 percent water. One of the many benefits of increasing your fitness is the enlargement and increase in the number of your sweat glands, which lets you cool your body more efficiently. Furthermore, fit athletes not only sweat more, they also have a greater sweat response so they sweat sooner when exercising. The fit person’s sweat is also more dilute as their body excretes fewer electrolytes per volume of water lost.
The combination of heat, humidity and exercise can be lethal. When exercising in the heat, your cardiovascular system not only supplies your working muscles with oxygen, it also cools your body by increasing blood flow to your skin. This second demand can cause a system overload if the outside temperature is higher than your body temperature and your body is unable to dissipate heat adequately through convection (the process of giving off heat to air or water). Your body’s primary cooling mechanism in hot weather is evaporation, the process of evaporating water (sweat) on your skin. Thus when the temperature and humidity are high, your sweat cannot evaporate as easily because the air is already saturated with water.
Exercise combined with high temperatures, humidity, lack of wind and the blazing sun can lead to heat related illnesses, including heat cramps, heat exhaustion and heat stroke. Heat cramps typically occur in the leg muscles (calves, quads and hamstrings) and are a common sign of dehydration. They are usually alleviated with adequate hydration, electrolyte replenishment and rest. Next in severity is heat exhaustion, caused by prolonged perspiration and inadequate hydration and characterized by flushed skin, profuse sweating, chills, fatigue, thirst and diminished coordination. If you experience heat exhaustion, stop exercising immediately, hydrate and cool yourself off with wet towels. Be sure to take a few days off from exercising to give your body a chance to recover. Heat stroke, the most severe heat illness, requires immediate medical attention. Symptoms include little or no sweating, clammy skin, fatigue, nausea, incoherent speech, elevated heart rate and body temperature, acute mental confusion and rapid breathing. If not tended to, heat stroke can lead to cardiac arrest and even death.
In my next post I’ll discuss ways to prevent dehydration when you exercise in warm weather. Until then…..