Under normal conditions, exercise heats up the body. During the summer, the temperature, humidity and direct sunlight together with exertion all contribute to the potential for heat stress. Here are some tips to prevent overheating and succumbing to the effects of heat stress.
The body loses a lot of water during exercise--as much as one quart over the course of an hour-long workout. During exercise the body sweats, cooling the body as the sweat evaporates. Too often we wait until we are thirsty to drink, and that is too late. If you do not replace water lost during exercise, it may result in dehydration and other forms of heat stress such as heat exhaustion and heat stroke. Timothy P. White of the University of California at Berkeley recommends the following guidelines for fluid intake related to exercise in warm weather:
*Two hours before exercise: 16-20 ounces of fluid
*15-30 minutes before exercise: eight ounces
*During exercise: four to six ounces every 15-20 minutes
*After exercise: enough fluid to replace lost fluids (one pint for each pound of fluid lost during exercise).
There has been some question regarding the efficacy of sports drinks versus water for fluid replacement. Those drinks, with minimal amounts of sugar, are absorbed as well as water and, according to recent research, may aid in the body's maintenance of carbohydrate stores and normal blood volume sugar levels, as well as delaying fatigue for those individuals exercising more than an hour at a time. What is important is not so much what you drink, but that you drink something (no alcoholic beverages), and do so even if you do not feel thirsty.
Be sure to acclimatize yourself to hot-weather exercise. Increase your exercise time gradually over a 10- to 14-day period. Doing so will help your body become more efficient in its sweat production and maintain a lower temperature and heart rate during exercise. This acclimation is lost easily, with one day of acclimation lost for every two to three days without heat exposure. Exercise at moderate levels, monitoring you heart rate frequently. Elevated heart rate (relative to the degree of activity) is a valid and useful indicator of the additional stress imposed by an environmental heat load. Choosing the proper clothing is also important for safe warm-weather exercise. Select lightweight, loose-fitting, light-colored clothing, preferably made of absorbent cotton. This allows sweat to evaporate, cooling the body.
Whenever possible, exercise during the coolest times of the day--early morning or later in the evening. On particularly hot days, consider moving your exercise indoors where it is air conditioned. These may be good days to swim, take an aerobics class, use the stair machine or rower, and work on strength training exercises.
Be aware of symptoms of heat exhaustion (which is caused by dehydration) and heat stroke (which occurs when the body's heating mechanism fails). These may include headache, nausea, loss of coordination, dizziness, muscle cramps, decreased sweating and/or general weakness. At the first sign of any of these symptoms, stop exercising, get into the shade and drink plenty of fluids.
Air pollution, especially in a city such as Atlanta, can adversely affect one's health and exercise performance, and should be considered when planning any exercise regimen. A good rule of thumb is to avoid physical activity in areas or times of day when pollution levels are highest. For instance, carbon monoxide levels increase during rush hours in the summer with daily peaks around 3 p.m. Listen to daily weather reports during the summer months to find out the latest temperature, humidity, ultraviolet index and air pollution conditions before you exercise.
Finally, be sure to apply a waterproof sunscreen of SPF 15 or higher to avoid sunburn.
There are many benefits to regular exercise, which we have outlined in previous columns. Following the guidelines described above will allow you to maintain physical activity levels throughout the warm months.
John D. Lisco is program manager for the Seretean Center for Health Promotion, and Jill E. Welkley is an assistant professor in the Department of Health and Physical Education. The publication of Wellness is coordinated through the Seretean Center for Health Promotion.