On a mission to try the most extreme of extreme sports, I ran up against the brick wall that is the Tough Guy Competition, heralded as the world's most demanding one day survival course. These words come at me from the guy beside me on the starting line.

Yeah, I've got a lot of scars, thick pads on my knees from mountain biking as a kid, a big crescent on my side from a BMX handle puncture, a missing chunk out of one ankle from landing funny from a sky dive and my bone breaking through the skin and a sandpaper graze currently covers most of one of my chicken wings from an incident skeleton luging a month earlier, but this guy has a head dink which beats me hands, complete with all ten digits, down. "My dick's bigger than yours," is his next smirking comment, "Wow, I should bow out now then", I answer him in my head, "'Cause penis size is the most important thing when it comes to an assault course." But all he sees is the steely grimace I direct at him which I'm trying to make say "We'll see who has the last laugh, big-dick."

The Tough Guy isn't an event that's easy to train for. It's an assault course in the military style but with the added health risks of barbed wire, flames, hypothermia - care of the freezing mud, claustrophobia - care of the rubber tubes, electrocution, drowning and bone shattering drops. Basically there are lots of ways it can hurt you, and hurt you it will – before you start you have to sign a 'death warrant' just to put it into writing that you're taking your life into your own hands and you and your estate aren't going to sue - in case too many head dinks mean it's not clear to you. But to be fair the 5000 strong field is made up of people who're mentally strong as well as physically – if you're not mentally strong you're not supposed to be able to make it. And that's why I'm keeping my attitude in reserve. From what I've heard about Tough Guy I'm anticipating needing it.

The starting line is ragged. They wear you out before caning you into the ground and it's a six mile cross country run first which most people breeze though – these guys are marines and firemen, people who like to challenge their bodies. They don't start you all at once, but staggered, with the elite athletes and hard core repeat Tough Guys at the front. I'm in with the first timers. The general consensus is that filling in forms drunk may not be the best plan. Aside from big-dick everyone else starting around me signed up drunk. I'm not the only nervous one feeling all too cold and sober for this kind of thing. Guys dressed in gladiator skirts, who'll come to regret that later, take the mick with each other but a lot of competitors have a nervous vibe. There's a lot of adjusting of laces and going behind trees.

At the line I do what you're supposed to – imagine my successful passage through the Killing Fields, what they've named the course. The obstacles have names. The Tiger is a 40ft frame hung with electrified cables called tentacles charged with enough juice to stop a bull, the Colditz Walls are four metre high walls, the Fiery Holes are mud holes filled with kerosene soaked burning straw, the Vietcong Tunnels, old sewerage pipes too narrow in places to get thought and the Stalag Escape, a 20ft crawl under barbed wire.

What I haven't factored into my positive visualisation is the mud - it's everywhere and it's freezing - and the waiting. I have to wait before I get onto the Killing Fields and once I do I'm stuck behind the three men in the gladiator skirts. Seeing their naked torsos turning from bright pink to purple to blue is an extra torture the course designers didn't consider, but I'm sure it makes me colder and seeing one of them go down screaming with cramps frankly scares the be-Jesus out of me. We lay him to the side and I join forces with the other gladiators. It's like if I'm looking after them my mind is off my own pain, which is beginning to get grim. It's the mud, it reeks of manure and is getting everywhere. The Tyre Torture tears up any exposed skin so the mud gets in and when added to the cold it makes my skin start to sting all over. I think our three minds narrow. We're moving slowly, through mud and water and fire and mud and icy water and across beams and though nets and the cold is making us slower and when the mud comes off briefly and I see the blue flesh around me I almost want to vomit. The three of us make it to the Underwater Tunnels, one of the hardest parts of the course. Up to your neck in frigid water you think you're as cold as you can be but you have to duck under a few logs before going though a tunnel – fighting the guy in front to get to the two air holes. Jumping out of a plane is easy. Being blind, submerged in thick grimy, stenchy water and pushing though a tunnel against a man in front who's starting to panic from the cold is really terrifying. In those moments I felt the panic rise in me too... The guy in front was hauled out by a marshal just before I started to thrash out violently, I'm sure. It was big-dick and he was taken to the side of the course. Ha ha!

That was enough to steel me and I grabbed for my skirt clad responsibilities soundlessly and kept going. If I had have been able to think in more than one syllable I would have likened us to the men riled up in that scene from Braveheart, blue men in skirts screaming in fear and pain and triumph - but with less screaming. We fell though wire and tires and off beams and though nets but always into mud and freezing water. We past people with vacant expressions and were helped up when we tripped or fell by fellow athletes. The course designers are right. It's the mental strength that will keep you moving. Or else just the ability to switch off and keep going. Sheer bloody mindedness that ignored actual blood. We were over taken by women and older guys but when it come to the crunch the three of us finished. So much of it was a blur of mud and cold and blue flesh, but by god we were sharing an achievement. For a lot of the last section all I could think of were the hot showers waiting. The power of comfort.

We were men in the trenches, fighting the fear and exhaustion and the extremities of human experience and endurance and it was bloody marvellous.

Big-dick was right. What's the point of living if you don't know you're alive and on the terrible field I was damn sure I was alive and that my gladiators and I were going to make it. We lost a man and it steeled us and at the end of the day, this was one of the best experiences of my life. What most surprised me is that I actually want to go back and do it again. I must be mad, but there's no greater kick than when the adrenalin turns into achievement.