Why do men crash?

It’s a robust and repeatable finding: men consistently slow down more than women in the second half of marathons. There are several theories to explain this pattern, ranging from sociological to physiological. One of the most familiar is that women burn fat more efficiently than men, giving them a more stable source of fuel late in a marathon, once limited carbohydrate stores have been exhausted.

A team of researchers at the University of Minnesota tested this theory by measuring fat-burning in a group of 91 novice marathoners prior to their race. As expected, the women did burn more fat, and they also paced themselves more evenly in the race. But further analysis found no link between individual rates of fat-burning and pacing patterns, suggesting that fuel supply wasn’t the key factor. For now, the leading explanation for late-race fades remains the simplest: whether you’re male or female, if you blow up the final miles, your initial pace was probably too optimistic.