The temperature penalty in marathon running

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Marathon performance is more sensitive to air temperature than to any other measured environmental variable. A study of 1,791,972 finishers across six large marathons — Paris, London, Berlin, Boston, Chicago and New York — for the years 2001 to 2010 found an optimum air temperature that varied by ability, from about 3.8 C for the fastest runners to about 9.9 C for the slowest, with finishing times lengthening and withdrawal rates rising as temperature climbed above that optimum. Humidity mattered, but only for the faster men and women. This is why the marathon calendar clusters in early spring and autumn, why the six largest city races are held between February and November rather than in midsummer, and why weather is a confounder in any argument about which course is fastest.

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