Dr. Cedric X. Bryant, chief science officer of the American Council, said people as a rule should consider curtailing exercise when the temperature is 90 degrees Fahrenheit and, concurrently, the relative humidity is 60 percent or higher.
One way to avoid heat injury while exercising in hot weather is to stay adequately hydrated, Bryant said.
"This can be accomplished by consuming copious amounts of fluid -- just short of feeling fully bloated -- 30 minutes before exercise, drinking at least 6 ounces of fluid after approximately every 20 minutes of exercise and drinking beyond thirst cessation during the recovery period," Bryant said in a statement. "Water is generally considered the best hydration fluid unless the duration of the exercise bout exceeds 60 minutes. If an individual exercises for longer than an hour, a sports drink such as Gatorade or PowerAde might be the more beneficial."
Bryant advised exercisers to become acclimatized to the environment. Acclimatization, the body's gradual adaptation to changes in environment usually takes 10-14 days of heat exposure combined with exercise. Following acclimatization, people sweat sooner, produce more sweat and lose fewer electrolytes in their sweat.
People should also lower the intensity level of exercise, especially during the acclimatization period, and avoid wearing clothing that is impermeable to water, such as rubberized sweat suits.