Blue skies and brilliant sunshine lure exercisers outdoors like a Porsche attracts speeding tickets. Just throw on shorts and a T-shirt and go. But if you don't pay attention to your body's reaction to the heat and humidity, a heat-related injury can quickly put an end to your fun, and lead to more serious problems. Fortunately, heat-related illnesses are easy to prevent, and if caught early, simple to treat.
Robert Karch, Ed.D., director of the National Center for Health and Fitness at American University in Washington D.C., likens the body's cooling system to that of a car. As your car engine produces heat, coolant carries the heat to the radiator, where it dissipates into the surrounding environment. Without the coolant, the radiator can't do its job, the engine overheats and breaks down.
Your body works the same way as a car engine. When you exercise, your muscles (the engine) produce heat. Skin is your radiator, and water—in the form of sweat—is your coolant. Sweat carries the heat from your body's core to your skin, where it dissipates. If the system breaks down, you will overheat and eventually, break down.
Prevention
Long exposure to extreme heat or too much activity in the hot sun causes excessive sweating. Sweat removes large quantities of salt and fluids from the body. When the amount of salt and fluids falls too far below normal, overheating can result.
The key to keeping yourself from becoming overheated is to keep your body well supplied with its coolant—water. That means drinking before and during exercise. "For about every thirty minutes of exercise, a person should drink about a cup of water or sports drink," advises Jane Corboy, MD, a family practitioner and marathoner in Houston, Texas. If you're exercising for less than 45 minutes, water is best, says Dr. Corboy. For longer sessions, your body will benefit from the sodium, chloride, sugars, and other ingredients found in sports drinks. Take water stops even if you don't feel thirsty—by the time thirst kicks in, you've already begun to dehydrate. Before you even feel thirsty, sweating can result in a loss of 2-3% of your body weight.
Certain medications—including many psychiatric drugs and blood pressure medications—affect your body's water balance. People who take them need to drink more than those who don't. Beverages that contain alcohol and, to a lesser extent, caffeine have a paradoxic diuretic effect—even though you are consuming liquid, they actually cause your body to excrete extra fluids. So drinking beer, coffee, or caffeinated sodas can actually decrease your hydration level. (With coffee and other sources of caffeine, however, this diuretic effect disappears after a few days of consumption at the same level.)
Athletes who exercise regularly should watch out for cumulative dehydration during hot weather. "Lose a little today, a little tomorrow, and a little the next day, and then you wonder why you're feeling lightheaded a week down the road," says Dr. Karch.
On hot days, choose clothing with heat control in mind. A well-ventilated cap will help you keep cool, but one made of dense fabric will actually cut down on your ability to dissipate heat. Light-weight, light-colored clothing will keep you coolest. Going shirtless is an option, but if you do, remember to put on sunscreen to avoid sun damage. According to Dr. Corboy, water, and alcohol-based sunscreens work best for athletes because they don't inhibit sweating.
On extremely hot and humid days, reduce the intensity of your workout and move it into an air-conditioned room.
Symptoms and Treatment
In addition to knowing how to prevent heat-related illnesses, you should also learn how to recognize and treat them. The three forms of heat illness are heat cramps, heat exhaustion, and heat stroke. These aren't really three separate conditions, just increasingly severe stages of overheating.
Heat cramps are basically muscle cramps. According to Dr. Corboy, they happen when dehydrated muscles clamp up in an attempt to hold onto the water they have left. They usually occur in the whichever muscles are being used most. A soccer player or sprinter, for example, would get them in his calf muscles.
Treatment of heat cramps is straightforward and self-administered. Stop the activity, go to a cool place if possible, and drink cool liquids. Gentle massage or firm pressure to the affected muscles will relieve the cramping. It's okay to resume the exercise when the cramps are gone.
If you're a victim of heat exhaustion, you will feel a little bit light-headed or dizzy and will probably develop heat cramps. You may also feel nauseous, a bit disoriented, and you will usually be sweating profusely. As heat exhaustion progresses, you will first look very flushed, and then become pale. "At the end of this stage the skin is cold to touch with goose bumps and shivering. Those are pretty serious signs," says Dr. Corboy.
Treatment of heat exhaustion is similar to treatment for heat cramps, but more aggressive. You should stop exercising immediately, move to a cool area, and drink cool (not iced) fluids. "At this point it's useful to have some cooling blankets or wet towels that have been soaked in ice to put on your skin to help cool off," says Dr. Corboy.
Heat stroke is the most serious of the heat conditions and is considered a medical emergency. People with heat stroke may have the symptoms of heat exhaustion. However, their skin is hot and dry—not cold— because the body loses its ability to sweat and cool itself. People with heat stroke also have an extremely rapid pulse and may be delirious or combative and even pass out. Their body temperature is usually over 104°F, as they have lost the ability to cool down.
If you suspect someone is suffering from heat stroke, call an ambulance immediately. Move the victim to a cool area and use ice, fans, and other methods to lower their body temperature while you wait for help to arrive.
It's important to remember that heat illnesses can strike suddenly and severely. "There are people who don't experience some of the earlier signs and they can very quickly become seriously ill with heat stroke," explains Dr. Corboy.
"The reality is that most people won't be affected by it [heat injuries], but the risk is present for everybody," adds Dr. Karch. So when you're enjoying the outdoors this summer, remember to pay attention to the temperature and keep your body's radiator topped off with water, because even a Porsche will overheat if its fluid level drops too low.
RESOURCES:
Heat Exhaustion - The Heat Equation
U.S. Department of Labor, Occupational Safety and Health Administration
http://www.osha.gov/Publications/osha3154.pdf
National Weather Service - Heat Index table
http://www.erh.noaa.gov
CANADIAN RESOURCES:
BC Health Guide
http://www.bchealthguide.org/
Health Canada
http://www.hc-sc.gc.ca/index_e.html
References:
Bross, MH, Nash, BT, Carlton, FB. Heat emergencies. Am Fam Physician 1994; 50:389.
Heat and Athletic Activities. American Orthopedic Society for Sports Medicine website. Available at: http://www.sportsmed.org/sml/document.asp?did=70. Accessed July 11, 2005.
Heat Injury. American Academy of Orthopedic Surgeons website. Available at: http://orthoinfo.aaos.org/fact/thr_report.cfm?Thread_ID=42&topcategory=Sports&searentry=heat%20injury. Accessed July 11, 2005.
Hinton, M. Alan. Environmental Stress: Heat Intolerance. DeLee and Drez’s Orthopaedic Sports Medicine. 2nd edition. London: Elsevier, 2003.
Khosla, R, Guntapalli, KK. Heat-related illness. Crit Care Clin. 1999; 15:251.
Simon, HB. Hyperthermia. N Engl J Med. 1993; 329:483.
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