“Warning: Working out in the heat causes illness unless you drink lots -o- water,” reads a sign at Lied Recreation and Athletic Center.

Kathy Berrett, administrator specialist for Lied Recreation/Athletic Center, said the sign was put up in June after two people got sick at the rec center.

“It was a combination of the heat, no food and not enough liquids that probably made them sick,” Berrett said.

Jim Nespor, a physical therapist and athletic trainer at the rec center, said he was concerned about the heat and humidity while running in Midnight Madness last weekend.

“It’s not the heat, it’s the humidity — that’s certainly true for exercisers,” Nespor said.

Normally, a person will lose one quart of water per hour while exercising, but when the humidity reaches 65 percent, evaporation of sweat becomes significantly impaired and at 75 percent humidity evaporation stops, Nespor said.

Nespor said heat exhaustion and heatstroke are the two main forms of heat illness.

“Heat exhaustion is the milder form of heat illness,” Nespor said.

A person suffering from heat exhaustion may have red or flushed skin, an elevated body temperature, experience dizziness or have a rapid pulse, Nespor said.

If these symptoms progress and become worse the result may be a heat stroke, he said.

A tell-tale sign of heat stroke is a decrease in sweating, Nespor said, and if a person’s body temperature reaches 106 degrees the person’s life is in danger. At this point, they should be rushed to the emergency room right away.

Melissa Senti, a sophomore at Iowa State, recalled a day three years ago when she suffered from heat exhaustion.

Senti said she was outside life- guarding on a hot 90-degree day from about 8 a.m. to 4:30 p.m. and then went to play a softball game at 5:30 p.m.

Senti also said she had not been drinking a lot of water during the day and instead of resting during her lunch break at the pool, she swam laps.

In the 5th or 6th inning of the softball game, Senti said she became “headachy” and dizzy. After the inning was over, Senti said she ran off the field and collapsed onto a bench.

“The next thing I knew, I was sitting under a tree with an ice pack on my forehead,” Senti said.

In order to prevent heat exhaustion and stroke, Nespor said to drink water before and during a workout. He also suggested wearing loose and light-colored clothing.

Nespor said when temperatures are in the ’80s and ’90s and the humidity is at least 70 percent or greater, one should take “more frequent rest breaks” while exercising.

When temperatures reach between 90 and 100 and the humidity is over 70 percent, Nespor said it is best not to exercise at all.