He said: “I’d had a blood clot, the size of which would normally pass through anybody without issue.
“But because my arteries were so narrow, the blood couldn’t get through, so my heart packed up.”
After a triple bypass operation, Mr Downes was told by his surgeon he could safely return to intense physical exercise.
Though he acknowledges he has unusually high levels of stamina and a resting heart rate in the mid-30s, he claims he is living proof that most people can become ultra marathon runners.
He said: “I’m not the fittest guy in the world. It just requires a lot of determination and mental strength, but you need to get the nutrition right as well.
“Unless you have a medical condition which stops you, anyone can do it.
“Part of the reason I do these things is because I think I’m so lucky to be here. I’ve got to make the most of it.”
Mr Downes said sponsorship money from the challenge would go to the Yorkshire Air Ambulance and Upper Wharfedale Fell Rescue Association, as well as contributing to the costs of installing defibrillators in public places.
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