The only man on the planet to run seven marathons in less than seven days on the seven continents is aiming to go one better by smashing the five-day barrier.
Richard Donovan, from Galway, starts his epic quest in the extremes of Antarctica, running the first 26 mile leg in -20C temperatures at the Russian Novo science base next Wednesday.
The 45-year-old father of one is doing the endurance challenge on a shoestring budget out of his own pocket to raise awareness of the humanitarian crisis in the Horn of Africa.
His record stands at five days, 10 hours and eight minutes -- 130h:08m. "It's been very hard to figure a way of knocking off the half day," he said.
"I'm keeping it real -- I'm not going in some privileged manner. I'm going against all the rules, no special diet, flying economy by myself, bringing whatever I can fit in one bag. I'll sleep where I can."
Donovan, who was inspired to first attempt the challenge in 2009 after the failed bid by British explorer Ranulph Fiennes, will set the countdown clock ticking from 120 hours.
The first run begins when pilots of the Russian cargo plane are given a take-off slot on Wednesday.
Donovan, an experienced marathon runner at both poles, said sleep deprivation and massive temperature fluctuations will be the biggest challenge. Despite this he has received no specific medical advice and has not seen a doctor in years.
"I found doing this challenge remarkably hard on the body in a way I did not expect -- the temperatures really hit me. I go from -20C to 30C in the space of a few hours," he said.
"The flying itself is hard. I was falling asleep in airports afraid I would miss flights. On the plane I could not sleep but coming into land I was falling asleep and was tired starting the run."
Money raised through online donations at www.worldmarathonchallenge.com will go to aid agency Goal, one of few charities working in the Horn of Africa. Running times will be independently verified at each location. Donovan has ruled out using energy gels or drinks for fear of sickness and the only supplement he will pack are salt tablets.
"The chances are that my stomach will fall ill so I'm going to eat as simply as I can. Even by the third marathon there will be a lot of fatigue," he said.
"I threw up on four continents the last time -- the huge effort and airline food as a staple diet will do that."
Donovan will have about nine hours in each location to disembark, run the course and fly out to the next destination.
"I'm used to moving on dead legs and not having to think about it but that does not deny that they are dead," he said.
"It's a unique thing to fly around the world in that time as it is, not to mention seven marathons."