Eliud Kipchoge just broke the marathon’s two-hour barrier, and KU Leuven research helped him do it

Eliud Kipchoge (Flickr, M. Jelijs)

Eliud Kipchoge (Flickr, M. Jelijs)

Kipchoge broke the record thanks to a special arrangement of runners, among other things. Professor Bert Blocken (KU Leuven/TU Eindhoven) confirmed the superior performance of this formation with wind tunnel tests and computer simulations.

Kenyan athlete Eliud Kipchoge has become the first person to ever complete a marathon within two hours. Taking part in the INEOS 1:59 Challenge, the Olympic champion and world record holder for the marathon stopped the clock after 1 hour, 59 minutes, and 40 seconds. 

The record attempt was completed under optimised conditions. Part of this was a special arrangement of runners, who surrounded Kipchoge in order to lower the air resistance as much as possible. The superior performance of this formation was confirmed by wind tunnel tests and computer simulations by Professor Bert Blocken (KU Leuven and TU Eindhoven). 

Never before has a human being been able to run a marathon in under two hours. Kipchoge had already tried it in May 2017 at the Formula 1 circuit in Monza, Italy. His time of two hours and 25 seconds was impressive, but just above the magical limit. On Saturday 12 October 2019, at the Prater Hauptallee in Vienna, he was successful. This was partly thanks to extensive aerodynamic research in the INEOS 1:59 Challenge, including wind tunnel tests and computer simulations by Bert Blocken. 

In long-distance running, aerodynamics plays an important role. The so-called ’rabbits’ not only serve to indicate the pace of running but also keep the favourites shielded from the wind. A single rabbit can reduce the air resistance on the second runner by 50%. The formation in which these rabbits run determines the total reduction in air resistance that can be achieved. 

Analysing a hundred formations

At the previous record attempt in Monza, the rabbits ran in a triangle in front of the athlete, reducing air resistance by an estimated 70%. To further reduce this, more than a hundred formations were analysed using computer simulations by aerodynamics specialist Robby Ketchell of AvantCourse (USA) and later by KU Leuven and TU Eindhoven professor Bert Blocken. The most optimal formations from this analysis were then tested in the wind tunnel. 

Against everyone’s expectations, the formation of a reversed V with five to seven rabbits in front of the athlete and two to three behind him, proposed by Robby Ketchell, turned out to be the most optimal variant. This reduced Kipoche’s air resistance on paper by 85% compared to a runner without rabbits."

Bert Blocken: "Two sets of independently-performed computer simulations and the wind tunnel tests all clearly showed this formation to be the best. That was necessary in order to convince the runners of this arrangement."

Aerodynamically superior reversed V formation by @RobbyKetchell and tested in @tueindhoven #windtunnel applied in @INEOS159 Challenge marathon project. #marathon #INEOS159 #IneosChallenge #running #record pic.twitter.com/hy2AwEzkbS

- Bert Blocken (@BertBlocken) October 12, 2019

Counter-intuitive

The formation may seem counter-intuitive, but according to Blocken, the explanation is logical. "The rabbits have to endure a higher air resistance due to the flow resistance of the funnel, which keeps the athlete Kipchoge out of the wind. In cycling, typically a triangle formation is used at the head of the peloton. This is a good formation if you want to minimise the air resistance for everyone in the group. However, for this marathon record, it is only about minimising the air resistance for Eliud Kipchoge, not for the rabbits. In that case, the reserved V is superior." 

In addition to the formation of the rabbits, the researchers also looked at the distance between the rabbits themselves and between the rabbits and the athlete. The effect of a cyclist next to the athlete (who provided him with food and drink) was also tested in the wind tunnel, as was the effect of a car driving in front of the rabbits with a large clock showing the running times.

This project, called the INEOS 1:59 Challenge, was carried out on behalf of INEOS and in collaboration with Robby Ketchell (AvantCourse), Team INEOS, and Global Sports Communication. The wind tunnel tests were carried out in the wind tunnel of TU Eindhoven. KU Leuven and TU Eindhoven’s computer simulations were performed using ANSYS Fluent CFD software.

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