The 35-year-old surged early in Saturday's marathon and led for more than 25km, ultimately finishing fourth - just seven seconds off a medal.

It is the best result of Adams' career, which has included two Olympics and three Commonwealth Games, without a shoe or clothing sponsor.

"Tough but I'll take that. I'm pretty proud of that run," Adams told reporters.

"Those guys are professionals. I'm amateur.

"So I'm working 40-hour weeks, they're not - they're probably running 40-hour weeks."

Adams surprised all comers when he kicked away after two kilometres and led for more than half the race.

He was overtaken by Ugandan winner Victor Kiplangat and Tanzania's Alphonce Simbu, then couldn't chase down bronze medallist Michael Githae.

"It was really slow at the start and it was just way too easy and I felt like I might as well just make a bit of a gap," Adams said.

"I thought that the Kenyans and the Africans would go 'oh this Muzungu's (African term for white man) no good, we'll just let him go' and see if I could get a bit of a distance, and then they never let me go."

Adams admitted his early burst, and a lack of pre-race research, took its toll.

"I was setting the map of the course and the format didn't work on my phone so I didn't have a clue, I was just guessing the whole way," he said.

"So I didn't know how many hills there were and that last half was absolutely brutal.

"Probably a bit too hard at the start and just was carnage in the end."

It's still a landmark achievement for Adams, who juggled his preparation with work installing solar panels.

"Sometimes I just have to go home, have a nap and then I'm going for a run after work and still out at 10 o'clock at night, eating dinner late," he said.

"Hopefully all the weekend warriors, anyone working a nine-to-five who's battling with the work-running type of lifestyle, can look at that and find some inspiration."

Australian Associated Press