At the weekend, I encountered a new species, which must have emerged from the union of men and mountain goats - fell runners.

Fleet of foot, with incredible endurance, less fat than an anatomical skeleton and legs like trimmed pipe cleaners, they run up hill and down dale with apparent pleasure.

Meanwhile, us mere mortals plod along the same paths, equally cursing and admiring these superhumans who splash us with mud and make us feel like the organisms that emerged from primordial soup to begin the long evolutionary journey to homo sapien.

To add some background to this demoralised dispatch, on Saturday I was among 18 people from north Norfolk who tackled the Yorkshire Three Peaks to raise money for Cromer Youth FC.

Hundreds of fell runners were doing the slightly shorter (22-mile) route, including the direct approach to the top of the second peak, on all fours up a near-vertical grass slope.

On a map, the triple towers of Pen-y-ghent, Whernside and Ingleborough look like a doddle. In a pub planning meeting, beery bravado reduces them to mere pimples on Yorkshire's face.

But the reality is rather different.

I have never before done anything as challenging as this malevolent mixture of strength-sapping peat bogs, steep limestone cliffs and relentless paths that climb into the clouds.

With a snowstorm and disorientating fog at the top of the first peak, three falls in the bogs on the way down and gale-force winds to give us a hearty handshake on the summit of Whernside, I was close to breaking point at times.

On the way down Whernside, I thought my knees were going to give up. And on the way up Ingleborough, crawling on my hands and knees up a limestone cliff-face, not daring to look down, my nerve nearly failed me.

With something like 27 miles of distance to cover, including 5,200ft of ascent and descent, and some 7,000 calories burnt en route, my mood swung from despondency to delirium. I was so out of touch with reality that I sipped a can of ale made in Suffolk when we conquered the third peak.

But I succeeded. In fact, we all succeeded - some against awful odds. And the sense of achievement was enormous.

The fact that the fell runners completed a slightly shorter but more death-defying route in about one-third the time that I managed will soon be forgotten.

Completing the Yorkshire Three Peaks Challenge has made me certain that I will never do anything like it again. Next year, I will go for a cycling challenge, to save my crumbling knees from final disintegration. Either that, or the Norfolk Three Peaks - Roman Camp, Beeston Bump and Incleborough Hill.

But it has given me a deep admiration for those who take on long-distance challenges.

From the comfort of my sofa, I have often watched events like the London Marathon, cycling challenges and long-distance walks and wondered 'how hard can it be?'

I thought three peaks challenges sounded like a great way to earn sponsorship for a brisk walk while seeing some beautiful scenery.

In future, I will observe with a sense of solidarity, and dig deep whenever a sponsor form is thrust under my nose.

As for the superhumans - I admire them, but I do not understand or want to emulate them. Fell running seems like a good way to spoil a good walk.