Gotta’ Run: How hot is too hot to run?

Published 12:00 am Saturday, June 25, 2022

Every year, I get asked about running in the heat. I don’t miss days due to the heat, but I’ve learned that running is the toughest when the early morning temperatures and humidity are higher than usual. And it only gets worse later in the day. We’ve had a few mornings recently when the 5 a.m. temperatures were in the mid-70s and the humidity also in that range. I have been hitting the road with some dark still in the sky. So do many others, while sweating, suffering a little and complaining about the conditions.

First, the good news. “If you’re well prepared and make adequate adjustments, you can safely exercise most days of the year,” says Brett Ely, a 2:38 female marathoner and thermal physiologist at Salem State University in Salem, Massachusetts. Her research focused on the impact of heat stress on exercise performance and health.

Normally, our core temperature is around 98.6, but when we exercise, it starts to rise. Ely said, “People can get up to about 104 degrees in exercise without consequence.” We want to shed heat to the environment which can happen in three ways. Radiation away from hot skin, cool air flowing across the skin and evaporative cooling of the sweat are three ways to dissipate the heat runners create.

Humidity adds to the issue since we have a hard time evaporating the sweat. And on warm days, running in intense sunlight can cause added heat, both from above and by bouncing back from sun-warmed surfaces.

There are a lot of studies out that concern long-distance races and how heat affects them. The military branches pay attention to levels of the wet bulb globe temperature which includes not only the temperature but the effect of evaporative cooling and intensity and reflection of the sun. But most of us aren’t running marathon distances in the heat or doing overdressed runs in boots with the military. We just want to maintain our conditioning during the hottest months of the summer.

So bottom line, how hot is too hot? Most regular runners know what works for them by listening to their body. With core temperatures rising quicker than any of time other the year, most of us will slow the pace and shorten the distance ran on at least some of the days.

“If someone is well-adapted to heat, they’re probably OK listening to their bodies. Monitor how you feel. If you get dizzy, lightheaded or uncomfortably hot, that’s the time to stop,” said Ely.

She added, “If you run in heat, adjust your pace as needed to maintain similar effort to what you’d feel on a cool day. You might be 30 seconds to a minute a mile slower. If so, don’t worry. What you’re doing by running slower is reducing the amount of heat your body is producing as you run, allowing you to go longer before you have to quit.”

The last week had uncomfortable temperatures well above normal but many of the mornings were cool especially for those out early. We just experienced the summer solstice on Tuesday and daylight hours are already getting shorter. If you’re a morning runner or walker, these are good points. I love running in the dark or as the sky brightens in the east.

And finally, if you run in the heat daily, your body will get more used to it in 7-14 days. Hydration will be your biggest friend in making warm weather running work. Remember that a body on the move needs to drink a minimum of half the body weight in ounces daily, not counting extra for exercise. That is 75 ounces of water minimum for a 150-pound person. Don’t skimp on the water.

Rowan’s two warm weather races are just ahead. The Shiloh Missions 5K is Saturday, July 2, in Faith. Then two weeks later, running and walking shifts to Knox Middle School and the Greenway 5K. Check these and other upcoming events at