The punishing Marmotte 'sportive' event in France is for amateurs but it gives all cyclists – including our exhausted writer – a taste of riding like a pro

"You think 10 weeks' preparation will do it?" asked Huw. My friend Tom and I looked at our feet. "Most people train for a year. Even then, plenty fail."

We had contacted Huw Williams, trainer of cycling's elite, in desperation to help prepare us for the Marmotte, a legendary one-day "sportive" in the Alps. Sportives are timed cycling events for amateurs, with feed stations, marshals and medals.

Taking place on the first weekend in July, the Marmotte covers 109 miles and 5,180m of ascent over four of the Tour de France's infamous cols, and is regarded as the toughest sportive in Europe, if not the world.

Tom and I had been riding together for a couple of years: gentle jaunts through Surrey lanes, Tom in baggy board shorts, me with my middle-aged girth. The rides invariably involved a pub stop, and I believe it was at one of these that Tom, perhaps emboldened by our refuelling, had suggested we do the Marmotte, in just a couple of months' time. Similarly emboldened, I'd said: why not, sounds like a hoot.

Tour operator La Fuga specialises in packages for sportives. Tickets sell out fast, but La Fuga had had a couple of late dropouts – people who didn't think they'd done enough training, apparently. Tsk. We were in.

"You two are in for a world of problems," said Huw, holding up the course profile, which looked like a set of shark's teeth. "It's 18 miles uphill from the start, then 20 minutes downhill very fast. Then the Telegraph and Galibier for the next 20 miles, the worst thing in your life, like an instrument of torture. If you get up the Galibier alive …"

("If." Nice.)

"… you've got 30 miles of downhill. People have died, ridden straight off the mountain through exhaustion. Then come the tunnels – pitch black, potholed … Just pray."

Could it get any worse?

"The worst is yet to come," said Huw. "After 100 miles, when it's baking hot, you've got to get up the Alpe d'Huez to the finish."

Huw brought out the form I'd filled in: he'd scrawled the word "WEIGHT!!!!!!" on the top. To the question about my weaknesses and strengths, I'd replied going uphill and downhill respectively. He rolled his eyes and gave us a training plan for the first week: it used words such as periodisation and cadence pyramid workouts. On Sunday evenings, we'd have to email Huw our results, including weight, resting pulse and sleep pattern, get feedback, and then receive a new week's programme.

Huw's shock doctrine worked. We embraced our new training regime with gusto. We stopped talking about work or politics on our rides. In fact, unable to breathe most of the time, we stopped talking. On downhill stretches, we compared heart rates, and debated power bars and gear ratios. We may have been becoming better cyclists, but lordy we were dull.

And we'd end most rides with a trip not to the pub, but to a bike shop – in our case, that shrine to all things bike racing, Sigma Sport in Hampton Wick, Surrey – because, as all men know, the more money you chuck at unnecessary gadgets, the better you get.

Like La Fuga, Sigma is riding cycling's explosion in popularity. Britian's high-end bike market grew by 30% in 2010, catering largely to the wealthy Mamil (middle-aged man in Lycra) who will spend up to £10,000 on a bike. In Sigma, Mamils (and a few Mawils) stared lovingly at sinuous machines as if they were at the Uffizi.

In a Sigma back room, we met Nick Frendo, who measured us with the precision of a Savile Row tailor. He put us and our bikes on rollers, making minute adjustments to saddles, handlebars and pedals that can make the world of difference in an activity that involves repetition of the same movement tens of thousands of times. Nick said I'd been pedalling with my knees sticking out, like a circus bear, and losing a lot of efficiency.

Over the next two months, our rides got faster and longer. Centuries, as cyclist call 100-mile-plus rides, became the norm, the riding much more comfortable after Nick's efforts. The weight came off but my thighs were so sore I had to sleep on my back.

I may have become mildly obsessive, but Tom, erstwhile laid-back wearer of baggy shorts, would slap caffeine patches on his arms on rides and had removed the tiny, plastic dust caps from his tyre valves to save weight.

"What have you done to my boyfriend?" his partner emailed. "He's wearing his heart-rate monitor in bed!" Mercifully, she neglected to say what activity he was measuring.

Finally, we took the train to Grenoble. To the smell of burning clutch, the La Fuga people drove us up 21 hairpins towards our hotel at the top of the Alpe d'Huez. Could a road go on climbing for so long without hitting the sky? Tom and I sat in silence.

The next morning we were up at 4.30, eating mountains of food from the breakfast buffet, surrounded by cyclists so stick thin it was like being in a Lowry painting. Outside, La Fuga's mechanics were working on our bikes and filling our bottles with energy drinks. It felt like being a pro.

Then we were flying down the Alpe in the freezing dawn, fingers so numb they could hardly work the brakes, to the start line in Bourg d'Oisans, where we joined the other 7,000 competitors, chatting in myriad languages, wearing club jerseys from all over Europe.

The hooter sounded and we were off. Huw had warned us not to get dragged into an insane speed at the start, but that was impossible: I found myself flying along in a big bunch at 30mph. I'd lost Tom already. Soon we hit the first climb. Chatting ceased and a sepulchral silence fell, riders locked into individual battles with gravity.

After two hours, I reached the Col du Glandon and dropped straight on to the descent, snaking down via a slew of hairpins. The road was slippery from discarded gel and energy bar wrappers. An ambulance attended a tangle of bodies and bikes, blood staining the tarmac. That was sobering: a rider had been killed on the Glandon in 2005.

Near the resort of Valloire Photograph: Jean-Pierre Clatot/AFP/Getty Images

Soon I was climbing the Telegraph, the coolness of early morning a distant memory as sweat ran in rivulets down my face. At a feed stop in the village of Valloire, riders plundered fruit and sandwiches like vultures with fresh kill. Soon after, the Galibier came into view. I wondered what the fuss was about, then looked up and saw Huw's "instrument of torture" reaching to the heavens, a series of steep switchbacks in bare rock. I didn't know whether to laugh or cry, so I did a bit of both.

For the next two hours, as meadows gave way to barren rock, then vertical banks of snow, I suffered as I have never suffered before, my feet on fire, my calves cramping, my head pounding from the altitude. Once more, riders were in cocoons of pain, monastic silence punctuated only by breathing and the odd creaky crank, which was strangely irritating, like rustling sweet wrappers at the cinema during a scene of great poignancy.

Over the summit at 2,646m, a 30-mile blaze downhill, and then those pitch-black tunnels, where the red tail lights of other bikes hit me in the face like a hammer. After 100 miles and 4,000m of ascent, there was the small matter of the Alpe d'Huez – 10 miles and 1,150m of ascent in a white-hot July afternoon.

As I hit the first of the 21 hairpins, it struck me that the race's name, after an Alpine groundhog, could not be more apposite. Like the Bill Murray film, this day involves repeating the same things – going up only to go down again – to end up where you started. But as I dragged myself on, passing riders pushing their bikes and Lycra-clad forms slumped by the roadside, some vomiting, it came to me that, like in the film, perhaps the repetition contains a lesson: that hills are a metaphor for life – it's shitty when you're struggling, but the pain ends when you reach the top, and you're stronger for it.

Or maybe I was delirious, and they will rename that hairpin Pseud's Corner in my honour.

My heart-rate monitor started making the kind of rapid beeping that precedes any flatlining scene in Casualty. So, not wanting to actually witness myself dying, I turned it off.

Around Dutch Corner, through a tunnel of people dressed in orange – which greatly added to my now hallucinative state – counting down the hairpins, daring to look up occasionally at the cluster of buildings at the summit, so close, so very close …

One last bend, and there was the finish line, across which I rode with tears in my eyes, as exhausted and exhilarated as I've ever been. Tom was waiting for me, beer in hand. He'd blitzed the course.

"It was the dust caps," I said.

"Obviously," he replied.

"Next time," I said. "Next time."

• The three-night Marmotte package was provided by La Fuga (020-8144 1441, lafuga.cc): it costs from £850pp, including half-board accommodation, and team jersey. Huw Williams provided coaching: his La Fuga Performance service costs £200 for three months. The bike fitting session provided by Nick Frendo (sigmasport.co.uk) costs £120. Rail Europe (raileurope.co.uk) provided travel to Grenoble: returns cost from £108. For forthcoming cycle sportives, see cyclosport.org





Mike Carter's One Man and His Bike, a life-changing journey all the way around the coast of Britain, is published by Ebury Press priced £7.99