How does the heat affect your running?

Heat is tough, VERY tough

Last week, I did a workout in some extreme heat and humidity on Tuesday, then bounced back with an up tempo run on Thursday in relatively cool weather.

I thought a comparison of paces between these runs was an interesting study in what the heat can do to a runner so I figured I’d share the comparison between these runs with you. It’s not meant to be a study of exactly how one can compare splits in the heat but more an illustration that, yes, it can significantly affect your running and the best thing you can do in the heat is accept slower paces.

First, the weather details. On Tuesday, Strava reports I was running in 84 degree weather with a 91 degree “feels like” temp. Garmin says 86 degrees with a 93 degree “feels like”. It was also very sunny. Either way, for a Wisconsinite, it was blistering. On Thursday, Strava and Garmin agree that it was 61 degrees with a matching 61 degree “feels like”. It was also cloudy, not a hint of sun getting through. I can confirm that it felt at least 30 degrees warmer on Tuesday than it did on Thursday.

On Tuesday, I wore my workout shoes and did a workout that included a couple short, fast repeats, followed by 3×1 mile with 1:00 recoveries. On Thursday, I wore normal trainers and just did a straight progression through the first couple of miles before settling into an up tempo but not “hard” pace for the remaining 5 miles.

All other things equal, the Tuesday miles should have been significantly faster than the Thursday run. However, in this case, my average pace on the last 5 miles of Thursday’s run was actually just over 7 seconds per mile faster than the average of Tuesday’s mile repeats. I also look at GAP (Strava’s grade adjusted pace) due to the plentiful rolling hills around my home. The average GAP was just short of 4 seconds per mile slower for a straight 5 miles with no recovery than for 3 mile repeats with recoveries.

My last mile on Thursday was actually the fastest mile of either day and the GAP of each of the last 5 miles of Thursday’s run was faster than the GAP of my slowest mile repeat on Tuesday.

As I already mentioned, this isn’t intended to be extrapolated to say that an X degree change in temperature will change your pace by Y minutes per mile. The exact effect will vary from person to person and can even vary for a person from day to day. Instead, I just want to illustrate the fact that the heat can play a significant role in our paces and we should be willing to accept that. Don’t be afraid to slow down as it gets hot. Instead, focus on getting in the right effort and know that your paces will return as the summer heat subsides.

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