Thirsty (for knowledge) Thursday: Running in the Heat

>> Thursday, July 02, 2015

Last week, I came across someone tweeting this:

That can't really be right. I'm confused though... it's on the internet, so it must be true. But it's a little exaggerated.

The "summary" bullet points at the bottom make sense to me. I've always said that 50 degrees is my optimal race temp, and this sort of backs that up, but I don't think those adjusted times are right. I think you could cut those times in half and they'd STILL be high. I remember running the hot Victory 10K in 2012 where it was 80 degrees and over 60% humidity. Everyone's times were slow, but you can't take off 3:00/mile because of that. If that were true, my "adjusted" pace was 3:07/mile (I actually ran a 38:02, which was 6:07/mile). I remember hearing "legitimate" runners commenting that times were about 20-30 seconds per mile slower. Not 3 minutes. (I was realistically hoping to run about 15 seconds per mile faster if it weren't so hot.)

I had to share this because I know the heat slows me down, but this over-compensated times too much. Right?

UPDATE: I think I found the source on of the chart on, and he notes that the info is from a class at a running store in Texas. So yeah, totally sound science backs this up. *sarcasm*

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Joe 8:12 AM, July 02, 2015  

I think the chart is saying how much you *should* adjust your pace by on a training run, not how much the temperature / humidity will affect your pace.

And the fitter you are, the less you'd lose or would need to lose from your pace.

Anonymous,  8:45 AM, July 02, 2015  

I agree those adjustments seem way overblown, especially when racing (perhaps not a bad starting point for longer training runs though).

I think your memory of the 2012 Victory 10K conditions may be a bit overblown though - according to it was 73 degrees at 7:53am and 75.9 degrees at 8:53am (with humidity from 76%-69%) so that chart would recommend running around 1:05 per mile slower (not 3:00).

Steve Stenzel 9:00 AM, July 02, 2015  

Joe, that's a good point! And Anonymous, it was a mid-day race that had a few races (they had a least a 5K back then, and they maybe had a kids race too). So it was hotter at 11 am!

Steve Stenzel 9:06 AM, July 02, 2015  

I followed that link, Anon, and at 11 am, it was 85 degrees with a dew point over 60, which is around 75% humidity. Regardless of if that's 100% right or not, the chart still seems quite exaggerated for racing. But it might be a bit closer for training runs (but still a bit exaggerated).

Steve Stenzel 9:13 AM, July 02, 2015  

Wait Anon, maybe that one did start earlier and I'm thinking of something else… regardless, those numbers are also creeping up on the 1:45 "adjustment" time. I ran 6:07s and couldn't have ran 5:02s or 4:22s, so even in my multiple (potentially confused) comments, it's still very exaggerated.

Anonymous,  3:09 PM, July 02, 2015  

I believe the 10K at Victory is always run first at 8am. That said the conditions were definitely horrid for racing that day.

Since lots of the same people run Victory every year, and since the conditions in 2011 were near perfect, I compared those results to get a more accurate slowdown factor. Of the 32 people I found who ran it both years at 7:00 pace or faster the median slowdown was 2.74%. That would convert your 38:02 to 37:01 under more ideal conditions (5:57 pace), for a heat adjustment of around 10 seconds per mile on that day.

This may be too optimistic but however you look at it there's no doubt that the pace adjustments in that chart you found seems fairly bogus!

Steve Stenzel 5:14 PM, July 02, 2015  

Thanks for running those numbers Anon! That's an interesting comparison...

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