As we turned into the car park at Honister Pass, the clouds were grumbling. Geoff Cox appeared and shook my hand in greeting, with the same kindliness he might offer to his closest friend. Having roamed the fells since childhood, the bracing chill and spattering rain are all too familiar to him. A gust of wind blew me sideways as I struggled to catch the flyaway sleeve of my coat and hastily zip it up. Pulling a hat firmly down on my head, I gazed up at the fells. The day was bleak, and an ominous mist obscured the tops of the hills, which would provide a dramatic background for filming.

Today marked the penultimate day of shooting for the second documentary about Geoff’s experiences as a fell runner. During his sixtieth year he attempted to run three notorious Lake District endurance-running rounds: in the Joss Naylor Lakeland Challenge and Gerry Charnley he was successful, but the Bob Graham round defeated him. The film we’d be shooting today was a reflection of this unsuccessful round, and how Geoff found redemption to complete the Charnley. Geoff wrote poems about each round to process these challenging ordeals, and approached filmmaker Richard Berry to transform his words into films. Today, I was joining them to see what happened behind the scenes.

We set off, following Geoff and the other endurance runners up the first incline. Before long it became evident just how comfortable they were on this terrain; while I took my time negotiating uneven and slippy rocks, the rest of the group hiked with confidence and admirable swiftness. As we climbed higher, I was told that the views up here were usually breathtaking, but the fog hung over the entire horizon like an impenetrable curtain. We were completely enclosed, walking along a single clear track with white walls on all sides. “Drifting in the Skiddaw mist”, Geoff wrote in his poem; how apt this line was today.

Now 62, Geoff has been fell running for decades, and can’t remember a specific time when this habit became a continuous routine in his life. “Work and family pressures meant I needed a sport I could focus on which didn’t need other people,” Geoff explained, “With running I could drop everything and go anytime, day or night.”

Fell running in the wilderness of the Lake District is a lonely and secluded past time, something Geoff often welcomes. “I needed a place where I could have a bit of ‘me time’. Society seems to look upon somebody who needs these extended periods of time in isolation as strange and even a bit weird. Long days running in the hills gave me what I needed; something about the independence and self-sufficiency was very appealing.”

In a few hours we reached the right place to begin the day’s filming. Director Richard and camera operator Kerr McNicoll set up and before long shooting was in full swing. Agile as mountain goats, the runners cascaded down the rocky slopes with impressive assertiveness. Surrounded by the silent fells, the only sounds were the cracking of the colliding rocks and soft squelch of mud as feet drove through. Puffs of breath spilled into the sky, and as the runners headed further off, the mist soon swallowed them.

“And again!” Richard shouted, the echo of his words bouncing for miles. After a few moments, the group appeared again. From this distance they looked like small dashes of coloured paint on a white page – the only distinguishable features of the landscape. They looped around a small lake, reflections bouncing on the water. After several takes of this shot it was time for cake – a delicious fruitcake made by Jim, one of the runners. This burst of energy was welcomed with open arms, and once Richard had filmed Geoff scaling a large rocky outcrop on his gimbal, we began to snake back through the fells, gathering footage on the way and constantly referring to Geoff’s poems to capture the essence of his experiences and narrative.

Writing poetry has helped Geoff to process the challenges and obstacles associated with endurance running. “I started writing poetry as a way of processing the mental and emotional garbage floating around in my head, or ‘mental detritus’ as I call it. Prose didn’t work because it has the wrong rhythm. Poetry allowed me to talk about what I’m thinking and meant that I could introduce the pace and metre that matched my memories.”

One of these memories took the form of white theatrical masks, worn by three of the runners looking over their shoulders at Geoff while he hung back, exhausted and near defeat. It was an intriguing idea and as we walked back through the fells I asked Geoff why he decided to include masks in the film. “They’re a symbol of how small doubts kick in and grow more insistent as the run goes on” he explained, “So we made them progressively more obvious throughout. ” This feeling of doubt was linked to people coming out to support Geoff while he competes and the pressure of not letting them down, a burden that can hang heavy on a runner under such physical and emotional strain.

I was astonished to hear that the masks were also a representation of hallucinations that Geoff said will be very familiar to long distance fell runners out on the hills for 24 hours or more. This “sleep monster” phenomenon is a result of exhaustion and sleep deprivation. “My particular version seems to be that I find myself running across strips of beautifully patterned Axminster carpet” Geoff told me, “All the time I’m thinking ‘It’s amazing that somebody has been up here and laid this carpet across these mountains!’”

Fell running in the Lake District is not for the faint-hearted. Unpredictable weather, unforgiving terrain, and a vast secluded landscape, and all with a burning in your legs. Even today, after walking seven miles, I returned to the warm café with aching knees. Geoff has proven that age is no match for will and determination, and is continuously training for new rounds to run. For him, fell running is more than exercise but a way of managing stress and even inspiring poetry. Spending time with him and the other runners opened my eyes to a life spent high above the ground, where so few people think to look.