Why? Have you hit your fat head? Are you on the glue again? This was the response that most gave me when I told them I’d ridden from John O’Groats to Land’s End, unassisted, on a bicycle.

The journey was 950 miles from end to end and not even for charity – “just cuz, I guess”. I hadn’t even taken the time to do any training. And when I mean no training, I mean I can count the amount of times my body’s been moved to perspire this summer because the figure matches the amount of times I’ve shared a bed with someone.

And so back to that original question: why? A question that, despite its weighty pertinence, only came to me when I was sitting over the wing of a propeller-powered Saab 340 headed for Wick, Scotland’s most northerly airport. Dinner parties, perhaps? “It’ll be the perfect thing to cover my ignorance when the conversation inevitably turns to the rise of quinoa and its impact on the fertility of Andean soil. I’ve only just learnt how to say it properly, for Christ’s sake.”

But I knew this didn’t satisfy the answer to my bizarre motivation. No man alive goes through seven and half days of unremitting agony – tantamount, I’d posit, to a week’s worth of final-stage rheumatoid arthritis – merely to bamboozle overly informed friends of friends.

As we landed, I saw that a good pal had posted a picture of himself at the finishing line of a Tough Mudder race. For context’s sake, he’s a banker. It was then I realised something: you don’t see gardeners swimming the Solent; electricians don’t go to Dartmoor to be mentally sodomised by a platoon of hateful ex-Commandos. No, this sort of privilege is paid for by soft-handed people called Alexander or Edward. You know who they are: that man who wears trainers with his suit in the morning and fights his way through protein-laced muesli for breakfast. He’s the target of L’Oréal Men Expert adverts and pays too much attention to the topography of his stomach.

Yes – it’s because men like Alexander and myself work in an office. Tough Mudder’s co-founder, Guy Livingstone, said it succinctly in The Telegraph: “We live in an increasingly sanitised world where we sit behind computers, we don’t get our hands dirty, and health and safety seems to rule everything. Playing in the mud brings out the inner child in all of us.”

You’re right, Guy – apart from the child bit. It’s actually Mr Hyde that it brings out. Sedentary all day, I sometimes have to bite my colleague on the arm to relieve some of the boiling testosterone I’m not allowing myself to burn off. My adrenal gland sits angrily dormant like a neglected Aston in a collector’s garage. And I’m not the only one – we men, with our appetites for urban comfort, haven’t the faintest idea who we are or how we should behave. Our girlfriends earn more than us, Esquire magazine makes us think about umbrellas too much and we all suck on Brita filter water bottles because we think there’s a chance it’ll improve our complexions. But all we really want to do – if we allow ourselves to trust our biology – is go out and smash something to bits.

We are among the few generations of men in this country who have not been conscribed to military action; not experienced what must be the sheer bliss of still being alive in the face of near-certain death. Tough Mudder’s profits would freefall if we’d all done a stint at the Somme. But ersatz danger zones like this are all we have to sate our craving for fear and pain and the serotonin flood it induces.

It wasn’t until the police finally caught up with football hooliganism in the 1990s that it stopped being a national pastime. As Danny Dyer so eloquently puts it in Football Factory: “We’re an island people. It’s what we do best. It’s not about colour or race, it’s just about the buzz of being on the front line. Truth is, we just love to fight.”

Of course, for most desk drones (me, then) fighting is far too scary, so we cycle until we’re dead. Or we get chased by actors dressed as zombies in simulation post-apocalyptic theme parks. Most perverse of all, we allow ourselves to be electrocuted while climbing over brick walls in muddy fields in Gloucestershire.

So how does all this end? How do you ever feel a sense of achievement; of being alive, and spent of piss and vinegar? Assuming you’re not going to give up your latte lifestyle to chop English oak in a forest or risk it all in a war zone, there is no end. You just have to carry on doing these silly challenges. Then, for a short and evolution-defying moment, you’ll feel like a man.

The second we’d finished our big cycle, I asked my friend what he wanted to do next. “Oh fuck knows, right now I just want a Radox bath and some quiche.”

Donald Twain writes frankly on restaurants, liquor, and places that are not England. His real name may not be Donald Twain, but he does like chips and period dramas.