Meteorologists are calling this week’s 90 degree temperatures an “unrelenting heat wave.”

But some relentless Chicago runners are unfazed.

Marge Garcia was training for the Chicago triathlon this week along the Lakeshore Drive path. WBEZ talked to her in the middle of a run at 1 p.m.

“A lot of people here are training seriously,” Garcia said. “If you’ve been doing it a bit, you know to just listen to your body.”

Garcia says she learned that lesson the hard way.

“I did a twenty miler, and I ended up in the hospital,” Garcia said. “I ended up needing three bags of IV’s because I didn’t have proper hydration.”

Endurance athletes like Garcia say electrolytes, sodium tablets and plenty of water are critical to preventing dehydration.

But Meteorologist Gilbert Sebenste warns that exercise enthusiasts should head outside earlier in the morning to avoid heat-related illnesses.

“For those who are running in the late morning through the mid to late afternoon hours, you’re really putting a lot of stress on your body,” Sebenste said. “Even if you’re in great physical condition that doesn’t mean that you’re not hurting your body by running in such weather.”

The term “unrelenting heat wave” refers to the high temperature and humidiy that put stress on our bodies and continue through the night, Sebenste said.