Affect of heat humidity and dew points on running pace. As a competitive road racer, I am very aware of the impact that heat, humidity, and dew points have on my pace and overall time. The tables included in this post give you the hard numbers.
Now in my 60’s, I have aches and pains in my legs that I never had as a twenty something runner, or even in my 50’s. As such, I have learned to focus my efforts on quality runs vs. quantity, keeping my mileage somewhere in the 15 to 20 mile per week range. This translates into about 60 miles per month during the two hottest months of the year in the Myrtle Beach, SC area, July and August; to 80+ miles during the nicest months of the year from October through March.
During the summer, I typically try to get my runs in just before sundown so that the temperature and heat index are at a tolerable range. Even then, I have run many times when the temperature is 85, the heat index 95 and the dew point is 75. It is brutal.
In the fall and winter months, I run whenever I want as the temperature, heat index and dew point are all very favorable.
I have the same questions that you do with regard to how the heat affects my pace and runs and these tables do a great job of relaying that information. At my age I do not push my luck, which keeps my wife happy. On the hottest days I run slow and easy, knowing that I am still getting a great workout because of the extra load on my heart. The hottest days can put at least a one minute per mile penalty on my pace and I accept that.
Drink lots of fluids, listen to your body and stop running if you feel feint or lightheaded. I have personally seen people fall face first from the effects of heat and humidity during a race – don’t let that be you.