How far away are we from a sub-two hour marathon?

The current world record is held by Kenya’s Dennis Kimetto, who ran 2:02:57 at the 2014 Berlin Marathon while wearing Adidas’ adizero Adios Boost 2.0 racing flats. The past four men’s marathon world records were set by runners wearing Adidas running shoes. Adidas also owns seven of the top 10 fastest all-time marathons, including Boston which is a net downhill course not valid for world records. Kipsang was also wearing the Adios Boost 2.0 when he ran 2:03:23 at the 2013 Berlin Marathon for a then-world record.                            

When asked about what other companies are doing with their respective "sub-two" shoes, Amm says that there are no springs or shox in the adizero Sub2, just the Boost light technology.

"Within Boost we're constantly innovating and with the Adios we had the first big milestone there. Boost Light is the next major milestone in distance running because it allows us to keep the energy return from Boost but in a much more lighter form," Amm says. "That was a key ingredient for the shoe as well as the Continental stretch on the outsole which allows for less slip and more grip. If you accumulate all those little things, it can make the difference between a world record and non-world record or running 1:59:59 or 2:00:01."
British author Ed Caesar is following the Nike project for Wired and recently wrote the book Two Hours: The Quest to Run the Impossible Marathon. He estimates that a sub-two could be possible by 2025 or even 2020. Back in 1991, Michael Joyner, a polymathic anesthesiologist at the Mayo Clinic in Minnesota, estimated that the physiological limit for a man in the marathon was 1:57:58. He later told SI that he was just hoping to see it in his lifetime.
Kipsang has been working with Yannis Pitsiladis, a professor of sports science at the University of Brighton in England, on their independent Sub2 project, which relies on science and medicine to try to get under the two-hour barrier. Kipsang joined the team shortly after finishing second to Ethiopian runner and Olympic champion Kenenisa Bekele at the 2016 Berlin Marathon. Bekele just missed the world record by crossing the tape in 2:03:03. Kipsang was second in a personal best of 2:03:13, which is tied for the sixth-fastest of all-time.

What was the testing process like?
"We took all the shoes from [marathon world record holders] Haile [Gebrselassie], Patrick Makau, Dennis Kimetto and Wilson to look at the wear of the rubber and how they used the shoes. We put those ingredients together. We had them come in for extensive research with the first prototype. We went back and created a finalized prototype before traveling to Kenya with a small team. We gave them the chance to run in the shoes in fast conditions and with high speed filming. A lot of testing happened with key athletes and local athletes. We're now confident to release the shoe with Wilson," Amm says.