UF Professor: Extreme Heat Poses Threat To Midday Exercisers

July 8, 1997

GAINESVILLE — A temperature of 90 degrees. Humidity at 85 percent. Heat index of 117 degrees and a UV index of 9.

Forget the numbers — it doesn’t take an genius to figure out it’s hot.

As the sweltering days of a Florida summer finally arrive, an expert in exercise physiology from the University of Florida warns midday joggers and outdoor laborers to make sure their bodies have adapted to the intense heat and humidity.

“For someone not accustomed to the climate, a prolonged workout could mean serious trouble,” said Stephen Dodd, an associate professor of exercise and sports science at UF. “It takes about 10 days to two weeks for the body to adapt physiologically to extreme heat.”

Newcomers to the state are at risk for heat injuries, as are those who overdo it during the first days of stifling humidity and blistering sun, Dodd said. He advises people who exercise during the day to limit their exposure to the heat in order to gradually acclimatize to the conditions.

“Our body needs time to increase the amount of sweat it can produce and increase the blood volume,” he said. “If it can’t do this, then the heart is overloaded. This is why we always read about senior citizens collapsing during the first days of summer when they go outside to garden or take a brisk walk.”

Dodd said Florida’s brutal humidity makes coping with heat even worse. He explained that the moisture in the air hampers the evaporation of the sweat, which pulls heat from the skin and cools us.

“If the sweat is just dripping off you, then it means it’s not evaporating,” Dodd said. “This is a signal that you’re getting too hot and if it continues for more than an hour, you could be in trouble.”

Trouble could be anything from heat cramps to heat stroke. Although heat illnesses usually occur in stages, Dodd said it is possible for someone to suffer heat stroke without experiencing the two lesser degrees of heat illness.

With heat cramps, the exhausted muscles cramp up because of water imbalance. This is a signal to slow down or stop activity and increase fluids, Dodd said.

When the body gets to a point of exhaustion, it no longer is able to cool itself. A person suffering from heat exhaustion becomes tired, lethargic and even dizzy while the skin feels cold and clammy.

During heat stroke, the most dangerous illness, the body cannot produce sweat and becomes red hot and feverish. Dodd said brain damage and even death could result from severe heat stroke.

“If a person has heat stroke, you should do whatever it takes to cool them off,” Dodd said. “Pour water or any liquid available on them and then fan them to get the evaporation.”

If you have a job working outdoors or you must exercise during the day, Dodd said the best thing to do is to drink plenty of nonalcoholic fluids beforehand. However, this does not completely guard against overheating because we sweat more than we can ingest. While the body is able to absorb approximately one liter of fluid per hour, it can sweat up to three liters.

“Get plenty of fluids in you before you start outside activity,” he said. “Take a break every 15 minutes to drink a couple cups of water. The fluids you sweat can’t be replaced at the same rate, but this will help you to prolong your stay in the heat.”

And the fluid Dodd suggests? Water is the best bet.

The sugar in soft drinks, fruit juices or even sport drinks can retard the absorption of fluid in the stomach.

“If a Coke is all you have, then it’s better than nothing,” Dodd said. “But you’re always better off with water.”