The Heat is On, Then Off
This morning it was a cool, sunny sixty degrees. Perfect running weather! The type of day that showcases Vermont in the summer. It’s why people come here—to escape the big city summer heat. But the past 10 days have not been like this. Rather, it’s been hot, very hot. Most days went well above 90, even approaching 100. A few thunderstorms temporarily cooled things off a bit, but they brought high humidity. And mornings were is the 70s, and a few days close to 80, something unheard of in Vermont. The “typical” July day here is a low of 60 and high of 80. But as we know, typical is becoming nostalgic. The extremes are becoming normal and planning ahead problematic. Climate change is having its way.
Yesterday, on July 4th, Green Mountain Athletic Association held the Clarence DeMar 5K road race in South Hero. It’s been going on for over 40 years. In the past it had both 5K and 10K races. Now just the 5K. The current course is a rather boring, out-and-back. Not a PR course but fair nevertheless. I think I’ve run it 12 times. CDM draws about 300 runners, starting at 8:30 a.m. to avoid a conflict with the annual town parade later that morning. It draws many of the locals taking a break from fireworks and cookouts as well as people visiting friends and families in the area for the holiday. There is a festive feel in the air.
This year it was 78 degrees at the start under partly sunny skies with very high humidity. I have not run many races under those conditions. In New England, except for these mid-summer heat waves, the issue is usually about how many layers to wear. When it’s this hot, the wish is to be able to shed some of our skin. Clearly not an option, especially when layering on sunscreen.
So, it was a day to be cautious. And I was. Ran pretty much even splits at a pace 10 seconds per mile slower than the prior year. Interestingly, my age-graded time was about the same: just under 82%. I am, after all, a year older and expected to materially slow down each year. Overall, I was pleased to finish in a decent time and age grading. But I’m definitely looking forward to running races in cooler weather down the road.
I do notice that the heat impacts me more than it used to. The science says our internal venting systems lose some resilience. And I believe it. Yet, the races happen when they do and our choice is either to skip racing on a hot day or adjusting our expectations. I am likely to opt for the latter.
I am adding to this post as a result of reading an article in the July 29 Marathon Handbook feed. They drew from studies showing how heat and humidity changes the performance of various levels of runners. At the upper end, they suggest 88o feels (the heat index) like 100 o when the humidity is 70% and 110 o when the humidity is 85%. These are conditions not unlike what seems to be happening more regularly in the Northeast. They note the ideal temperature for running is about 44o — race temps we often see here in March. It goes on to describe the body’s cooling mechanism, in particular how heart rate increases as a result of pushing blood to the skin for cooling. They note studies have shown HR increases 10-20 BPM when going from 75% to 90% humidity. They finish by saying there is evidence that for every degree above 59o, runners slow about two seconds per mile.
My own experience with this is I find 50o perfect for racing, close to what they found. However, I’m not sure that at 65o I slow down 12 seconds a mile compared to 59o. In a 5M race that would be a minute. Nevertheless, the 78o temps greeting us at Clarence DeMar were formidable and I think most in the race scaled back their expectations a bit. Yet, I certainly did not slow down 1:54 (2 seconds per mile per degree over 59o. It was more like 30 seconds. I’m not sure who was in those studies, but it wasn’t the people at our July4th race!