The same running workout feels harder on a hot day than on a cool one, and it's not just your imagination. We really do slow down in the heat — at least until we've adapted to it — and it's possible to calculate exactly how much.
Photo by bark.
The temperature calculator at Runners Connect is built with race times in mind, but it works just as well for figuring what's up with your everyday run. Today, for example, I missed my early morning run and made it up later in the day in the 26 degree heat. The calculator tells me that at my speed, about 10 minute miles, I should expect each mile to take about 15 seconds longer today than it did on a 65-degree morning last week.
The heat of an 26-degree day adds 20 per cent to your time compared to your pace on an 8-degree day, while a 21 degree day only adds 7 per cent. That means your exact slowdown will depend on your original time. Because it's a hassle to do percentage maths with minutes and seconds, this calculator is a handy tool.
Humidity above 60 per cent will slow you down even further, but that's not reflected in the temperature calculator. Take it easy out there on hot days, and don't be disappointed if your runs aren't as fast as usual.
Temperature Calculator [Runners Connect]