By Dorene Internicola
NEW YORK, July 8 (Reuters) - Can't take the heat?
Fitness experts say one way for outdoor exercisers who dread the long, hot summer days of steamy runs and breathless aerobics during a heat wave is to embrace it.
"It takes most healthy people 10 to 14 days to fully acclimate to exercising in the heat," said Dr. Cedric X. Bryant, chief science officer of the American Council on Exercise. "In order to achieve that you need to be exercising in heat."
The heat-acclimated individual will sweat sooner and that sweat will be more dilute, Bryant said. There will be a lower risk for dehydration and a reduction in the heat gained through exercise that will help maintain a lower core temperature and heart rate response.
He said as much as 25 percent of the healthy population is estimated to be heat intolerant in an unacclimated state. Once they get acclimated that drops to 2 percent.
A 2011 report from the U.S. Centers for Disease Control showed that about 6,000 people a year seek emergency treatment for heat illnesses suffered while playing sports or participating in other recreational activities outdoors.
While acclimating to the physiological demands of the heat, Bryant said, be sure to tone down your workout.
"Strictly adhere to the talk test (the ability to talk as a gauge of correct exercise intensity)," he said. "It's not a time to do intervals or high-intensity exercises. Afterwards, when you're fully acclimated, you can ramp up intensity."
Connecticut-based fitness instructor Ellen Barrett said a daily dose of hot yoga primed her for the heat wave that slammed the U.s. East Coast in June.
"I did the Bikram yoga challenge every day for a month, so when that heat wave hit I didn't even notice it," said Barrett, author of the upcoming book, "The 28 Days Lighter Diet."
She said Swiss tennis ace Roger Federer trains in Dubai.
"He plays all day in the hot sun so when he's at the U.S. Open at the end of summer in New York City, he looks fresh as a daisy," she said.
Exercise physiologist and running coach Tom Holland is a veteran of more than 60 marathons and 21 Ironman triathlons, many held in sweltering conditions including an Ironman in Malaysia, where the temperature soared to 104 degrees (40 Celsius) and humidity to 99 percent.
"I actually love running in the brutal heat and humidity and have trained myself accordingly," said Holland, author of "The Marathon Man."
When running in the heat, he recommends adjusting speed and goals and said runners should expect to run more slowly and should focus on covering the distance.
"I paced a 60-year-old client in the 2012 Boston Marathon where the race hit 90 degrees," he said. "When I saw how hot it would be, we adjusted his race goal from 3:40 (three hours, 40 minutes) to just finishing."
Running in heat is difficult, Holland explained, because blood has two conflicting interests - supplying working muscles and going to the skin to cool the body down.
"So there is less blood for the muscles, our hearts have to work harder, our heart rate increases, and the relative intensity of the run increases," he said. "You simply cannot run as fast in hot conditions."
Bryant said that even the fully heat-acclimated exerciser reverts rapidly when the training stops.
"Unfortunately the benefits of heat acclimation are lost quite quickly," he said. "For every two days an individual abstains from heat exposure, one day of acclimation is lost. So after two to three weeks you're back to starting over." (Editing by Patricia Reaney and Bill Trott)