Who hits the wall?

Late in the race, Kenya’s Catherine Ndereba went past. At 36 km she stopped. She looked back down the road, tried to run again, managed a few strides, and stopped for good. Millions watched her cry at the roadside.

What the cameras couldn’t show were the weeks before. A knee injury had been treated with cortisone and anti-inflammatories, and she had slept badly that night. In the race she felt “very, very cold” in the heat. The hardest part, she said later, was realising she couldn’t hold a straight line.

She has described stopping as self-preservation: the only way to finish was to push her body to complete collapse. Eleven weeks later she won the New York Marathon.

It was the first Boston Marathon after the 2013 bombing, and the city turned out in huge numbers. Meb Keflezighi became the first American man to win since 1983. But this story is about the other 31,983 finishers: the ones still on the course hours later, and what happened to them at around the 20-mile mark.

Every runner carried a timing chip, so every runner left a trail of 5 km splits. The replay below turns those splits back into a race. Each dot is one runner, placed by how much slower they are running than their own pace from 5 to 20 km. Press play and watch what happens after 30 km.

Now pick the runners who finished in 3:30 to 4:00, so that speed can’t explain the difference. By 40 km, 37% of the men in that group are in the wall, against 10% of the women.

In every one of the 42 races, more men hit the wall than women. The closest call was Berlin in 2010, with 9% of men and 6% of women.

Heat makes it worse for everyone. In 2007 Chicago was stopped early in a heatwave, and 77% of the men who finished hit the wall, against 58% of the women. London 2018 was the hottest London Marathon on record: 51% of men hit the wall, and 28% of women. Athens in 2004 was hotter than either.

Men are faster on average, and slower runners fade more, so a fair test compares runners who finish in the same time.

At every finishing time from 3:00 to 5:30, in all three cities, the men’s line sits above the women’s. Among runners who finished in 4:00 to 4:10, 22% of men hit the wall in Chicago and London, against 6% of women. In Berlin it was 11% against 2%.

Take the 648,000 runners who finished between 3:30 and 4:30. Most of them, men and women alike, slowed a little in the second half. That is normal. The difference is in the tail.

16% of the men ran the second half at least 20% slower, against 5% of the women. In the middle of the pack, men were three times as likely to blow up.

Pacing is a decision made under uncertainty. In a study of 92,000 runners in 14 American marathons, men were about three times as likely as women to slow by 30% or more, and the researchers’ best explanation was riskier decisions about early pace. At the 2013 Houston Marathon, men overestimated their abilities more than women did, and slowed down more in the later stages of the race.

The wall is often the bill for the first half.

Psychologists argue about where that confidence comes from. A biological account points to testosterone and risk-taking. A social learning account points to what boys see rewarded: going for it, never backing off. That is the same Bandura who appeared in Story 01.

Even in the middle of the pack, 84% of men did not hit the wall. Psychologists call it alpha bias when a real but small difference gets turned into a rule about everyone. The charts show a tendency, not a destiny.

And the most famous wall of all belongs to a woman. Radcliffe’s was not about pacing. It came from heat and injury, and from a body that she has said was close to collapse. It didn’t define her career either. She won New York that November, then London again and the world title in 2005.

The advice that follows from the data is not new, but the numbers make it hard to ignore. Run the first half as if the wall is waiting, because for about one man in six, it is.