This is an excerpt from TWO HOURS by Ed Caesar. Copyright © 2015 by Ed Caesar. Reprinted by permission of Simon & Schuster, Inc, NY.

Geoffrey Mutai had no doubt that running 26 miles and 385 yards in less than two hours was physically possible. The performance, he believed, was within his own body. What stopped marathoners from running faster, he believed, was not so much the structure of their bodies as the structure of races. There was no point thinking about the two-hour marathon when you saw how the sport existed in 2012—namely, a few exceptional athletes lined up twice a year in a great world city, barreling 26.2 miles through the streets.

Occasionally, at night in his mountain hideaway, Mutai would fantasize about how the sport might evolve so that it became more about the limits of physiology than about winners and losers. He knew that in the right set of circumstances, people could run so much faster.

For a niche sport like professional marathon running, record times at a Sunday marathon are sometimes the only way to generate a Monday headline. So, between the organizers, the athletes, and Mutai’s manager, a plan was drawn up for the 2012 Berlin Marathon. The pacemakers were to take the lead pack through the halfway mark in 61 minutes and 30 seconds. If all went according to schedule, Mutai would finish the race in an “even” split (for exactly two hours and three minutes), or he would run the second half faster than the first for a “negative” split of 2:02 and change.

To a marathon runner of almost any standard, these numbers are enough to provoke nightmares. For an elite competitor, one’s predicted halfway split time is significant because it is a marker of what one hopes to achieve in the race. The marathon is, at its highest level, a delicate exercise in expending energy evenly over the entire course, and the fastest times are generally achieved when the second half of the race is run at the same speed (an “even” split) as, or slightly faster (a “negative” split) than, the first. Sudden rises or dips in pace can kill a record attempt stone dead. At many marathons, race organizers employ pacemakers, or “rabbits”—other athletes who for reasons of schedule, finance, or talent are paid a few thousand dollars each to run only a limited section of the race—to ensure that the lead athlete’s desired pace is adhered to, and to offer some protection against the wind. The rabbits are generally paid by distance: some will travel to halfway, some to 25km, and the strongest to 30km or 32km. From there, the racers are on their own.

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At the prerace technical meeting in a drab conference room at Berlin’s Maritim Hotel, at noon on the day before the marathon, it was confirmed that Mutai had asked the rabbits to take him through halfway in 61:30. No athlete in the history of the sport had ever asked for such a fast split, but the other Kenyans in the room didn’t flinch. At least four of them felt confident that they could run 61:30 for the first half and still finish strong. However, when Jan Fitschen—an affable German marathon runner in the twilight of a career in which he had won, among other honors, the European 10,000m gold medal—was asked about the split Mutai had requested, he made an unfamiliar sound, somewhere between a giggle and a cough. A few minutes later, when the meeting was finished, he walked away shaking his head and laughing. Fitschen hoped to run the first half of the race in 67 minutes.

Ten years earlier, running the first half in 62 minutes and 30 seconds was considered suicidal. When Haile Gebrselassie ran his first marathon in London, in 2002, he asked the pacemakers for this very split—62:30—to widespread amazement. There was a belief that if a runner, even one as talented as Gebrselassie, were to start so fast, he would inevitably “blow up” in the second half of the race as his energy reserves dwindled and lactic acid flooded his muscles. A 62:30 split, it was thought, was a sure and painful way to lose money.

One of Haile’s competitors for the 2002 London Marathon was the world record holder Khalid Khannouchi, who was raised in Morocco and became an American citizen in 2000. When Khannouchi’s wife, Sandra, heard about the split Haile had proposed, she was apparently so incensed that she made a noisy demonstration of her feelings at the prerace technical meeting. There was no way, she said, that her husband would be joining this idiotic early pace. But come halfway, Khannouchi was with Haile and the other challenger, Paul Tergat—and evidently the pace did not finish him off. He went on to win the race and break the world record in 2:05:38.

Strange things had happened to professional marathon running since 2002. Not only had two minutes fallen from the world record, but the distance appeared to have changed genre. By 2012, the elite no longer considered the marathon a pure endurance event. It was a speed-endurance event. The world’s best had, in the words of the American commentator Toni Reavis, “out-trained the distance.” To explain the difference, many of the most experienced coaches used an automotive analogy. It used to be the case that marathon runners needed a diesel engine. Now the best had turbo-diesels. They were capable of both doughty endurance and devastating pace.

This is an excerpt from TWO HOURS by Ed Caesar. Copyright © 2015 by Ed Caesar. Reprinted by permission of Simon & Schuster, Inc, NY.