In 1990, the average top-100 runner had clocked in at just over 5ʹ8ʺ and 131 pounds; by 2011, those numbers had dropped to under 5ʹ7ʺ and 124 pounds. The reason, the researchers suspected, was simple: the heavier you are, the more heat you generate while running around. Tall people also have more skin surface area, which allows them to shed more heat by sweating—but the extra weight swamps the effects of the extra skin, putting bigger and taller runners at a subtle disadvantage.
