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Running in the Heat and Humidity - What to Dew?

Updated: May 30

Memorial Day has passed, marking the unofficial start of summer. Here in Atlanta, temperatures have been creeping up since the end of April, but in the past few weeks, I've noticed a stark increase in the humidity - and we all know that's what really gets you.

While slogging through my Saturday morning run, which felt a bit more like a swim based on the water concentration in the air, I noticed that I had to slow my pace down significantly to run at my usual "easy" effort. I've taken enough exercise physiology courses to understand why this happens (primarily, our sweat can't evaporate as efficiently into air that is already saturated with water, thus making it more difficult to cool our bodies while exercising), however I wanted to find a more objective approach to adjust my pace for the hotter and more humid weather.

What I found with a bit of Googling, is that dew point, rather than relative humidity, is a better metric to track along with temperature, to determine how your running pace should be adjusted. Dew point is the temperature that the air would need to be cooled to achieve 100% relative humidity. It, according to the National Weather Source, is a better predictor of how muggy it will feel, since higher dew points mean more water in the air.

According to a dew point at or below 55 feels "dry and comfortable", 55 to 65 feels muggy, and a dew point above 65 feels "oppressive". The average dew point in July in Atlanta according to 69 degrees 🥵

So, what does this mean for your running? I found these helpful tables that utilize temperature and dew point to calculate how much you need to slow your running down, as a function of percentage of pace.

First, locate the current temperature and dew point on the x and y axes, respectively, and see where they meet to obtain the number that correlates to the recommended pace change. You can also just add the Temperature and Dew Point to calculate this number. The recommended pace changes are as follows:

100 or less:   no pace adjustment

101 to 110:   0% to 0.5% pace adjustment

111 to 120:   0.5% to 1.0% pace adjustment

121 to 130:   1.0% to 2.0% pace adjustment

131 to 140:   2.0% to 3.0% pace adjustment

141 to 150:   3.0% to 4.5% pace adjustment

151 to 160:   4.5% to 6.0% pace adjustment

161 to 170:   6.0% to 8.0% pace adjustment

171 to 180:   8.0% to 10.0% pace adjustment

Above 180:   hard running not recommended

To quickly put this into practice, you can find your typical pace in the chart below, and see what each percentage change equals, in mile pace.

For example, if it is 75 degrees out, and the dew point is 65 degrees, the sum is 140. This suggests a 2-3% pace adjustment. If I were planning to run a 10 minute mile pace, I would want to back off to a 10:12 or 10:18 minute mile to account for the weather.

I hope that you find this information helpful as you tackle summer running! Stay hydrated, and remember that you can, and should, slow down!

Thanks for reading!

Dr. Elizabeth Karr PT, DPT



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