Not even a sore bottom and pain from handlebar vibrations could stop the Inverness-based athlete from wiping hours off the fastest known time on the An Turas Mor route from Glasgow to Cape Wrath, which spans some 570 km (354 miles).
With the help of a break at Contin, where he met his wife Rachael, ate a bag of chips, snoozed for 30 minutes and drank a Red Bull, he smashed the previous known fastest time after completing the ride in 33 hours and 31 minutes.
The previous record sat at just over three days.
Campbell left Kelvingrove Art Gallery and Museum around 5.30am on Saturday morning and reached Cape Wrath just before 3pm on Sunday.
It follows on from his 2020 record when he scaled Scotland’s 282 Munros in just 31 days.
Campbell, 36, said An Turas Mor had been an enjoyable route but that he suffered a lot of pain from vibration caused by the rugged stretches of tracks.
Campbell said: “When I set off on Saturday, it was quite nice, the sun was shining, there were blue skies, everything was going well.
"I was on a gravel bike and it is built for more speed that comfort so you feel a lot of vibration. By the time I reached the The Corrieyairack Pass near Fort Augustus, my hands were very sore. There is still tingling in my little finger.
"My fitness levels felt good but there was this pain from a long time in the saddle. Going into Sunday evening, my backside was really tender.”
After his stop in Contin, Campbell cycled through the night, with the darkness demanding high concentration given he could see just a few metres ahead.
The early sunrise in the north mean that light came quickly – but the next challenge lay in wait at Ben Hope near Cape Wrath lighthouse.
Campbell, a former Royal Marine originally from Skye, said: “I knew it was going to be a rough section. You go up a summit of 450 metres and descend down to a loch. I came into these really big landrover tracks. It was much more mountain bike terrain.
"I didn’t see the fun in it. It’s meant to be a bike ride. I made it to the summit carrying it and pushing it, a bit of cycling. I was in cycling shoes too so it took ages. I thought ‘this is rubbish!’”
Campbell said he was “happy” to have completed the route with an average speed of 16 kph. He is now relaxing by training and running in the hills with friends. His next challenge will be the The Salomon Glen Coe Skyline mountain running challenge in September.
Obscura Mondo Cycle Club, the group behind An Turas Mor, congratulated Campbell on his time
Rich Dee, club secretary, said: “It’s an exceptional effort on An Turas Mor that we hope might spur on riders to participate in the official timed event, Sportiva21, in September. Maybe Donnie will join us for the sportive next year.”