Updated May 07, 2017 12:02:56

Photo: Kipchoge ran the 42.2 kilometres around an oval track in 2 hours and 25 seconds. (AP: Luca Bruno)

Olympic champion Eliud Kipchoge has come within 26 seconds of running the first marathon in under two hours.

Kipchoge ran the 42.2 kilometres around an oval track in an impressive 2 hours and 25 seconds, unofficially smashing Dennis Kimetto's world mark of 2:02:57 by 2.5 minutes and raising hopes that one of world sport's most famous barriers can be broken.

"We are human. We are going up the tree ... I have lifted a branch and I am going onto the next one," Kipchoge said.

"This is not the end of the attempt of runners on 2 hours."

The time will not be an official world record, sanctioned by the IAAF, due to variables like pacers entering mid-race and drinks being given to runners via mopeds.

Dick Telford from the University of Canberra's Research Institute for Sport and Exercise said Kipchoge's effort was a thrilling achievement.

"What a shame he didn't quite go under but it really just shows what the human body is capable of, and that is definitely a sub two-hour marathon," he said.

"If we weren't convinced before that it was going to happen sooner or later, we have to be convinced now."

'A less than two-hour marathon is possible'

The attempt was orchestrated by Nike as part of its Breaking2 project, "a diverse team of leaders across several fields of science and sport" working towards enabling a sub-2-hour marathon.

"I rank this as the highest-ever performance in my life," Kipchoge said.

"The aim of Breaking2 was to pass the message that running a less than two-hour marathon is possible.

"That message is really special to me."

Considered the best marathon runner in the world, Kipchoge broke his personal best of 2:03:05, set at the London Marathon last year.

Kimetto set the world mark in Berlin in 2014.

Photo: Eliud Kipchoge said he ranked the race as his "highest ever performance". (AP: Luca Bruno)

Organisers first listed Kipchoge's time as a second faster, then changed it to 25 seconds off the 2-hour mark.

It was not a road race, with runners completing 17.5 laps around the 2.4-kilometre Monza Formula One track, which was selected after extensive research that included average temperature, air pressure, and wind levels.

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Nike planned the record attempt for three years, including making shoes that include a stiff carbon fibre plate designed to "propel" runners forward, which it said would make runners 4 per cent more efficient.

The shoes have been a point of controversy, with some contention around what crosses the line towards unnatural performance enhancement.

"How far do we go in improving the mechanical engineering of a runner before it becomes illegal?" Dr Telford said.

"If we're changing the design of shoes to alter the elasticity, then that's something that we've all got to question."

But he said Kipchoge's marathon was evidence a sub two-hour marathon would come in a "race-legitimate situation" within "the next few years".

"I want to see it done under the circumstances marathoners usually run in without any ergogenic aids," he said.

"It'll happen ... we're all expecting it, it's just a matter of when."

'It puts running on the map'

The attempt was held on the 63rd anniversary of Roger Bannister breaking the 4-minute mile in 1954.

Dr Telford said the event — which was streamed live on Twitter and Facebook — was a "win" for the sport of running.

"I think pushing the boundaries of human performance is just fascinating for all of us, there's no question about that," he said.

"It puts running on the map."

Two-time Boston Marathon winner Lelisa Desisa, from Ethiopia, and half-marathon world-record holder Zersenay Tadese of Eritrea, were also part of the attempt, which started at 5:45am (local time).

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They tried to help pace Kipchoge.

Desisa was dropped after 50 minutes with Tadese falling back shortly afterwards, but the duo still completed the marathon, with Tadese shaving nearly 4 minutes off his personal best to finish in 2:06:51.

Desisa finished in 2:14:10, leaving just Kipchoge chasing the landmark time.

He passed the halfway mark in 59:54, but his average pace of 2:52 per kilometre was not quite enough, despite a final sprint to the tape.

Kipchoge needed an average of 2:50 per kilometre — an improvement of around 2.5 per cent on Kimetto's record.

"I tried to maintain the pace," Kipchoge said.

"As a human you are not a machine, so you cannot go 2.50 exactly, and those micro-seconds really have an effect."

Photo: The time will not be an official world record due to variables like pacers entering mid-race. (Reuters: Alessandro Garofalo)

Dr Telford said that had other measures been put in place, the barrier could have fallen.

"They ran 17.5 times around a 2.4km loop — there's a real area for improvement without doing anything else," he said.

"If they had, for example, not a 17.5-times loop but four loops of a longer distance, that time might have come down under the two hours.

"Every time a runner changes direction ... that uses extra energy — steady running is going to be more efficient than change of pace."

ABC/AP

Topics: athletics, sport, science-and-technology, human-interest, italy

First posted May 07, 2017 09:55:10