As dawn breaks over the foothills of the Rift Valley, Eliud Kipchoge's feet beat a steady rhythm along ochre trails and his mind is still, undaunted by a goal many think impossible.
It is the next mythical barrier in running: smashing a sub-2 hour marathon.
Kenya's Kipchoge is one of three elite runners chosen by American sportswear giant Nike to attempt to run the 42.195 kilometres (26.219 miles) distance in under two hours, combining the latest science on training, nutrition, psychology and sportswear.
He, Ethiopia's former Boston marathon winner Lelisa Desisa and veteran Eritrean distance runner Zersenay Tadese are the cream of East Africa's storied running crop and each is believed to hold the potential to run 1:59.59 or faster.
This means shaving nearly three minutes off the current record of 2:02.57, run by Kenyan Denis Kimetto in 2014, a mind-boggling leap that Kipchoge is convinced he can achieve.
"I didn't think it was crazy. No human being has run under two hours. And I want to be the first human being to run under two hours," he told AFP in an interview in the village of Kaptagat, a popular training site in western Kenya at an altitude of over 2,000m.
Kipchoge, a former world 5,000m champion, ran the world's third fastest marathon time of 2:03.05 when he successfully defended his London marathon title last April.
Since switching from a stellar track career to marathon running in 2013 he has won seven of eight races in which he has competed.
Respected track and field magazine Runners World has predicted that, based on data analysis, the barrier would only be broken in 2075, and called Nike's bid "audacious".
"I accept the freedom of those who are pessimists," says a serene Kipchoge. "In this world there are three types of people. Those who wait for things to happen. Those who go with the people who have started. And those who think about how to make things happen.
"I think it's possible to run under two hours. That's why I'm going for it."
- Adidas also in race -
In 1908, Irishman Johnny Hayes won the first marathon set at the modern distance of 42.195 kilometres (26.219 miles) in a time of 2:55:18.
It took 109 years for the record to crumble to the current level run by Kimetto.
Kimetto is sponsored by Adidas, who quietly referred to their own sub-2 bid in February with the announcement of the Adidas Adizero Sub2 shoe.
Nike, meanwhile, is taking everything that is known about nutrition, training and biomechanics to optimise the runners' chances.
During a half-marathon test at a Formula 1 track in Monza in Italy in March, the runners ingested core-temperature pills and taped on sensors to measure muscle oxygen and skin temperature, according to Runners World.
Kipchoge ran a promising 59 min 17 sec and was followed by Tadese, who holds the world half-marathon record but has only ever managed to run a 2:10:41 marathon.
"Based on what is presently known, whoever breaks the 2hr barrier will have a favourable genetic profile (yet to be determined), an outstanding running economy and small body size along with chronic exposure to high altitude and significant physical activity early in life," Nike wrote on its website dedicated to the challenge.
- All in the mind -
The race will take place sometime in May, also at Monza, where wind, temperature and the possible presence of hares on the track all pose a threat to optimal conditions.
Kipchoge's coach Richard Metto is also confident.
"Eliud has set a goal, 'My limit will be the sky', and that is it. Nobody will stop him on the way."
To aid their runners, Nike has created a specialist racing shoe, the Zoom Vaporfly Elite, built to reduce weight, maximise aerodynamics and customised to each of the three competitors.
However Kipchoge believes it is not all the fancy training techniques and state of the art equipment that will make the difference, but the will and confidence to succeed.
"The difference only is thinking. You think it's impossible, I think it's possible," he said.
"If I do it, and I will do it, the benefit won't only be for me ... This thing is not about running, it is about every human being. After running under two hours, I think I will have ... kicked out that notion that a human being has limitations."