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Is It Safe to Run Outside in the Summer?

One Sticky Runner asks:

I live in the south where, at times, the summer is so humid my runs feel more like swimming … in a swamp. I often feel like I can hardly move, much less breathe. How do I know if it’s safe to run outside and how do I alter my workouts to account for the added challenge of heat and humidity?

Nora Ayers, Training Program Director for Fleet Feet Sports Carrboro and Durham and Tim Scott, FITness Program Coordinator for Fleet Feet Sports Roanoke, offer this advice:

First of all, you’re not alone. We get this question a lot because summers in the south are an absolute SLOG. Just know that you're surrounded by people who are out there with you, in the same conditions, and that you’re all doing a great job by simply showing up!

PACE. Slow down, slow down, slow down.

Your pace and overall fitness will suffer a little bit in the heat. It’s not a bad thing; it’s merely your body protecting itself. Your muscles don’t perform quite as well in higher temperatures. So, do your workout based on perceived effort rather than the numbers on your watch.

Still, some days in the south the dew point--the actual measurement of the amount of moisture in the air—is so high that it’s not even safe to run outdoors. Here’s a useful chart to help you decide:

Dew Point (° F) Runner’s Perception How to Handle
50 - 54 Very comfortable Personal Best conditions
55 - 59 Comfortable Hard effort not likely affected
60 - 64 Uncomfortable for some people Expect race times to be slower than in optimal conditions
65 - 69 Uncomfortable for most people Easy training runs might feel okay, but hard efforts will be affected
70 - 74 Very humid and uncomfortable Expect pace to suffer greatly
75 + Extremely oppressive Skip it or dramatically alter goal

Invest in a watch with a heart-rate monitor.

If you’re a tech-savvy runner, invest in a watch with a heart rate monitor. You’ll see real-time, solid data about how hard your body is working, and you’ll know when it’s safe to ramp it up and when you need to back off. If you’re running at an easy an easy pace, for example, and your heart rate is near maximum threshold, it might indicate the onset of heat stroke/heat exhaustion.

Choose your run time wisely.

Run late (closer to sunset) or early (at sunrise) and try to avoid mid-day runs. If you have to run at lunch, you may need to log a few “dreadmill” miles. However, if outside is your only option, make sure you hydrate! (To learn more about proper hydration, read 5 Tips For Summer Hydration.)