Stu Westfield, 48, finished the Peak District Boundary Trail in just over 105 hours - suffering hallucinations and ataxia on the final day.
He took on the challenge along with friend and doctor Nicki Lygo after hearing about Tom - who was diagnosed with Duchenne Muscular Dystrophy aged four.
Tom Burnett - the son of Nicki’s friend Becky and who is barely able to walk - is unlikely to survive beyond his mid-twenties.
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Duchenne principally affects boys and those affected are usually wheelchair-bound by 12-14 years old.
Eventually the heart is affected - leading to sufferers’ deaths.
Mountain guide and former aerospace engineer Stu told how he and challenge partner Nicki - who finished in 108 hours and 35 minutes - tackled the mammoth mission with a mix of show jogging and fast walking.
He said: “It was a challenge but there was never really any thought of not finishing - it was just a case of sucking it up and enjoying the process.”
Stu told how on the last day of the challenge between Peak Forest and Hayfield hallucinations kicked in after just one hour’s sleep the night before.
He said: “A stile just sort of turned in to a fox’s head - I thought ‘that’s a bit strange’ but it wasn’t frightening.
“It was just a bit surreal.”
Stu and Nicki are fundraising for Duchenne UK - a charity which aims to eradicate the condition with in a decade.
To make a donation visit www.duchenneuk.org.
To see the pair’s finishing times visit peakboundarychallenge.legendstracking.com/#