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Too hot to trot: recognizing and preventing heat-related illness
American Fitness, May-June, 2003 by Scott O. Roberts
As summer approaches, even the most dedicated fitness enthusiasts start considering alternatives to outdoor exercise. For most individuals, even those in good physical condition, performing physical activities in the heat requires more effort and planning while performance is generally less than ideal. Although exercising in the heat may be uncomfortable, most people can generally tolerate it. However, poorly conditioned, obese or pregnant individuals and those with significant medical problems may need to avoid exercising in hot weather altogether.
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Body temperature is regulated through a process known as thermal balance (i.e., the regulation of heat production and loss). Heat gain or loss results from four heat exchange processes--convection, conduction, radiation and evaporation. The greatest amount of heat loss occurs through evaporation, which takes place via sweating. Profuse sweating is the most effective means of cooling the body. However, this cooling only takes place when sweat evaporates from the skin. Under high relative humidity conditions, evaporation decreases.
Anyone who exercises or works with clients who exercise in hot weather should be familiar with the following four heat overexposure symptoms.
Dehydration: In an attempt to counterbalance overheating, the body increases sweat rates. Since sweat is over 99 percent water, prolonged sweating may lead to dehydration. Dehydration in excess of 5 percent of total body weight limits sweating and circulatory capacity, thus exposing individuals to severe health hazards.
Heat Cramps, usually caused by inadequate fluid replacement, are characterized by painful muscle spasms following high exertion in hot weather. The most common heat cramp treatment involves moving to a cool environment and drinking plenty of fluids.
Heat Exhaustion is characterized by weakness, dizziness, nausea, profuse sweating, headaches and eventually collapse. If you suspect a person is suffering from heat exhaustion, administer fluids and have hint or her lie down in a shaded area.
Heat Stroke is a life-threatening reaction to heat exposure. It is characterized by high body temperature (usually above 40.6 degrees Celsius), cessation of sweating, rapid pulse and respiration and, usually, elevated blood pressure. Anyone suspected of suffering from heat stroke should be taken to an emergency medical facility immediately. Prior to and during transportation, patients should be kept cool--remove any extra clothing that might retain heat and, if conscious, administer fluids.
Factors that determine the ability to regulate heat and prevent heat illness during exercise include: (1) exercise intensity, (2) current health and fitness level, (3) temperature and relative humidity, (4) degree of wind and amount of shade, (5) hydration status and (6) whether acclimatization to exercising in the heat has taken place. Fitness professionals should make sure individuals who choose to exercise in hot weather acclimatize slowly to heat exposure, consume an adequate amount of fluids before and during exercise, are in relatively good physical condition and free from medical problems that would be aggravated by the heat (e.g., heart conditions), exercise during the coolest period of the day and, if needed, reduce the intensity and quantity of exercise.
Other Suggestions to Prevent Heat Distress
* Avoid exercising during the hottest part of the day (i.e., 11 a.m. to 3 p.m.).
* Acclimatize slowly to exercising in hot weather. Depending on your fitness level, this may take several days to weeks to accomplish. The best approach is a progressive exercise program for one to two weeks. Allowing the body to gradually acclimatize to the heat will improve sweating responses, which will better facilitate heat dissipation. Some of the physiological changes that occur during heat acclimatization include decreased heart rate, body temperature, salt loss in sweat and earlier onset of sweating.
* Avoid direct sunlight, if possible.
* Wear loose-fitting, cooling fabrics and a hat.
* You are most susceptible to heat illness when exercising in hot and humid conditions. For example, if the outside temperature is 80 degrees Fahrenheit and overall humidity is greater than 80 percent, the actual temperature could be well over 90 degrees. Under such conditions, the body struggles to maintain internal body core temperature and risk of heat illness increases. For more information, refer to the Temperature Humidity Index on AFAA's Fitness Gets Personal[R] card H7.
* Splash water on your skin when possible.
* Monitor your hydration status. Loss of more than 5 percent of your total body weight after one exercise bout in the heat requires significant rehydration. Another sign of adequate hydration is urination frequency and urine color. If you imbibe enough fluid, you should urinate regularly (i.e., about four to five times during the day) and your urine should be clear.
* Overall, slow down and pay attention to your body.
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