# How the Heat Affects Running Performance

It's a scorcher out there today. Before you lace up your running shoes, you might want to read this.

Local running coach John Goldthorp posted a link on his Facebook page yesterday that immediately sucked me in. It’s an article on runningstrong.com that talks about how heat impacts running performance—more specifically, how many minutes hot temperatures can add to your finish time. Given that it’s supposed to be over 90 degrees every day through the weekend, the topic seemed more than appropriate to discuss here.

The article focuses on a 2007 study which looked at marathon finish times under a variety of different temperature scenarios and found a pattern: the hotter it was, the worse a runner’s performance became.

I should note before going further that the study authors didn’t just look at temperature readings for the purposes of the study. They used something called Wet Bulb Globe Temperature (WBGT) to determine how hot it actually feels on race day—because as we in Philly know for a fact, there’s a lot more involved in perceived heat than just what the thermometer says. You also have to take into account humidity, wind speed and other factors, such as the sun’s radiation, which is exactly what WBGT does. It’s sort of like the “Real Feel” thing on the AccuWeather app, if you use it.

The other thing you should know: The researchers divided the WBGT ranges into categories, with 41 to 50 degrees Fahrenheit (that’s 5 to 10 degrees Celsius) being the baseline and each subsequent category increasing by 5 degrees Celsius.

Using the baseline as a sort of the “optimal running temperature,” the researchers learned that the performance of the fastest marathon runners diminished by 0.9 percent for every 5-degrees-Celsius increase in temperature. And the effect was more apparent the slower a runner got, diminishing by as much as 3.2 percent per 5 degrees Celsius increase among the slower set.

Meaning? The hotter it gets, the worse you’ll do.

You can use this calculator, which appears to operate on similar principles to those outlined above, to predict how you’ll fare in these sweltering temps, but know this: Your performance will suffer in this god-awful heat, and you should adjust your pace and expectations accordingly, especially if you want to be safe about it.

Another tip: Please, please, pleeeeease hydrate, people. You should at least aim to take in half your body weight in ounces of water each day, and significantly increase that intake when temps soar (like, you know, today). For more tips on working out safely in the heat, read what our resident health coach has to say.

Photo: Shutterstock