What’s the best temperature for running a marathon?

It’s no secret that extreme temperatures impact performance in distance running, and anyone who’s gone for a run on a hot summer day can attest to that. We saw the effects of high temperatures very clearly this year, as dozens of athletes dropped out of the Olympic marathon in the extreme heat of Sapporo. You could also see the effects of temperature this fall at both the Chicago and Berlin marathons, which turned out to be much warmer than in previous years. But just how much does temperature affect marathon performance? Researchers in Europe recently analyzed thousands of race results to determine which temperature is best to run a fast marathon, and at what point the temperature starts to slow you down.

Seifu Tura and Ruth Chepngetich are your 2021 Chicago Marathon winners

The best marathon temperature is…

According to the researchers, if you want to run a fast marathon, you should do it on a day that’s between 10 and 17.5 C (50 F to 62 F). Any hotter than that, and things start to go south. They determined this number from analyzing 1,258 races held between 1936 and 2019 (including the marathon, 50K race-walk, 20K race-walk, 10,000m, 5,000m and 3,000m steeplechase) and comparing the results with the meteorological data from nearby weather stations.

For every degree (Celsius) outside the ideal temperature range, performance declined by about 0.3 to 0.4 per cent. The researchers pointed out that more than one-quarter of the races they analyzed were held in moderate, high or extreme heat, and this number increased to half when you removed marathons from the analysis.

When is it too hot to run outside?

Of course, you can’t control what the weather does on race day, and even a fall marathon has the potential to be hotter than expected, as we saw during this year’s racing season. A warmer day doesn’t mean you can’t perform well, but it’s important to understand how the heat affects performance and health, and adjust your race day expectations when the temperature spikes.