Olympic gold medalist Eliud Kipchoge explains how he was able to run a sub-2-hour marathon

• Eliud Kipchoge is the only person who has ever run a marathon in under 2 hours.
• A documentary shows how Kipchoge relied on pacers, a flat course, and Nike shoes for that event.
• Kipchoge told Insider that he doesn't think he'll be the last person to run a marathon that fast.

Imagine running about the length of a football field in 17 seconds - then doing that 422 times in a row. That's what it takes to run a marathon in under two hours.

Eliud Kipchoge, a two-time gold medal marathoner from Kenya, is the only person ever to achieve the feat. Two years ago, he ran 26.2 miles in 1 hour, 59 minutes, and 40 seconds.

A new documentary, "Kipchoge: The Last Milestone," explores how he did it. The event, called the Ineos 1:59 Challenge marathon and held in Vienna, Austria, was optimized to help him succeed - so much so that the international governing body of track and field didn't count it as a new record.

Kipchoge said he could not have run that fast without the dozens of people who helped him before and during the event.

"Teamwork, which I saw in Vienna in 2019, is extremely rare and good and that's why I performed well," he told Insider.

Kipchoge credited an international group of 41 runners who trained with him ahead of the race and served as a phalanx of pacers during the marathon. He also ran on a very flat course, in a Nike shoe designed to be more energetically efficient. A team also paid impeccable attention to his nutrition.

"It's not about me alone," Kipchoge said.

After failing once, Kipchoge was nervous

For the world's best male marathoner, the Vienna marathon offered redemption.

He had tried to run a sub-2-hour marathon on a Formula One track in Monza, Italy in 2017, but fell 26 seconds short. According to the new documentary, humid weather, a lack of sufficient carbohydrates ahead of the race, and the absence of a supportive crowd scuttled Kipchoge's effort.

"Failure is part of the challenge you encounter as an athlete," he said.

So he was nervous to try agin.

"The night before, I woke after 2 o'clock but I didn't sleep again," he says in the documentary, adding, "The pressure is really huge."

Kipchoge didn't talk to anybody the morning of the Ineos marathon. Then he gathered his initial group of pacers and they ran together to the starting line.

The documentary shows Kipchoge pause briefly after the starting gun, then get to work.

Immediately, his coach Patrick Sang knew this time would be different.

"When it started, it was beautiful," Sang says in the film."As a coach, you look at the body language. I saw the eyes of Eliud in the camera, he was very focused and relaxed."

Kipchoge said that's because he was more confident in his training: "What makes my mind to be more relaxed is the culmination of training for four or five months."

Half a million people across 196 countries tuned into the live broadcast.

The perfect track and a flock of pacers

Ineos, the UK-based petrochemical company that sponsored Kipchoge's second attempt, selected Prater Park in Vienna because it offered a route that has a 2.7-mile straightaway with roundabouts on either end. Minimizing curves was crucial, since they require runners to exert more energy than sprinting straight. And the entire route had just 8 feet of incline.

Event organizers transformed the two roundabouts into banked turns by repouring the asphalt in those parts of the course. That made them titled at an angle, a change that saved Kipchoge 12 seconds, according to the documentary.

Additionally, a team of researchers including Spencer Barden, an consultant for British Athletics, ran computer simulations and tests inside a wind tunnel to determine the optimal formation for Kipchoge's pacesetters.

In 2017, the pacers ran ahead of him in a V pattern, like geese in flight. But in Vienna, Kipchoge's team formed a Y to minimize air resistance, with five runners in front of him and two at his heels. The runners in that mobile shield rotated about every 11 minutes. The pacers knew where to run thanks to laser beams projected behind a pacing car that drove 50 feet in front of the flock. The car showed Kipchoge his time for every kilometer.

"My job was just to follow the formation," Kipchoge says in the film.

The pacers reduced Kipchoge's drag by about 83%. Ross Tucker, a sports scientist who consults for World Rugby, suggested the pacers and car combo saved Kipchoge two minutes.

He wore specialized Nike shoes, and nutritionists tracked his water and carbs

The Ineos organizers even tried to get the best weather for Kipchoge: Meteorology experts looked at Vienna's temperature, humidity, wind, and precipitation forecasts before picking October 12, 2019.

Then three days ahead of the race, Kipchoge's nutritionists put on a carb-loading diet. During the marathon, cyclists passed Kipchoge drinks and energy gels. In real time, nutritionists measured how much fuel Kipchoge consumed as he ran and modulated his subsequent intake accordingly.

Kipchoge also wore a prototype of Nike's Vaporfly shoe called the Alphafly. Studies have shown the Vaporfly's combination of carbon fiber and foam confers about 4% more energetic efficiency, which could allow long-distance runners of Kipchoge's caliber to shave three minutes or more off their marathon times.

Alphaflys also incorporate two air pods under the shoe sole for an added energy return per footfall.

'My job is done'

While Kipchoge ran, a crowd of 120,000 people cheered him on.

"It was really helpful to hear everybody actually screaming," Kipchoge says in the documentary, adding that he got a morale boost from hearing people say he would make it.

He waved off his pacers for the last 500 meters, giving a thumbs up. Kipchoge motioned between his eyes and the crowd.

"I was telling to the world, 'Please just sit and watch with your own two eyes that 12 October 2019 is the day whereby history has been made,'" he says in the film.

Kipchoge said that he thinks someday, it will be possible for someone to run a sub-2-hour marathon in a regular race - without the special setup he got.

"I have shown everybody the way," he said. "My aim was to show everybody that running under two hours is possible. My job is done."