This Sunday I will attempt to run a marathon, despite possessing no apparent sporting prowess. In fact, it would be fair to say I am to athletic ability what Edith Piaf was to regrets. I signed up for the event a sadly typical casualty of modern living - high blood pressure, a bit overweight, dodgy knees – and my (highly unscientific) training programme has emphatically failed to reverse this sorry state of affairs. Perhaps the problem has been my habit of celebrating the completion of every training run with an alcoholic drink. But then I've always been rather too fond of a glass of wine or two (often followed by a few beers, cocktail hour, a couple of nightcaps then one for the road). So, with the big day almost upon me, just how worried should I be? I decided to attempt to ascertain whether running a marathon is easy, or in fact hard, and my painstaking research took me in some unexpected and intriguing directions.

Running a marathon was once seen as the ultimate athletic achievement. In ancient Greece, the seemingly arbitrary distance of 26.2 miles was actually carefully calculated (by Copernicus) as the furthest a man could safely run without being in danger of falling off the edge of the world. Even by the time the London Marathon was launched in the early 80s the event was still seen as something special, only to be attempted by the foolhardy or the athletically gifted. But now the damn things are everywhere; if you look out of the window you'll probably see one going on right now. These days, those looking to really stand out run 'ultramarathons' or 'iron man' events in which contestants run through fields of landmines before being mauled by lions and finally nailed to a burning cross. For charity. In comparison, ordinary marathons can look a bit, well, weedy. You can't really blame people for thinking that 26 miles just isn't as far as it was back in the day.

But perhaps it would be a mistake to dismiss the event so lightly - because in reality marathons can be, quite literally, lethal. Around 10 people a year die running marathons (admittedly fewer than the number accidentally killed changing the bag on their hoover, but still). It is of course notoriously difficult to know whether to attribute such deaths to the act of running itself and the toll it can take on the human body; perhaps they were all run over. So marathons. Easy or hard - how can we know? It turned out that to shed some light on the matter I needed to delve deep into popular culture.

I first looked at the curious case of the man responsible more than any other for destroying the mystique of the marathon, Eddie Izzard. To recap: in the summer of 2009, Izzard ran 43 marathons in 51 days. With five weeks training. And no significant experience of running. The question was understandably asked: if a middle aged comedian best known for his passion for the AV voting system can run 43 marathons in a row, can it really be that difficult? And back came the answer loud and clear: no. Already notorious in countless ways, Izzard – who ironically competed under the first past the post system - became something of a bête noir to marathon runners who found they no longer commanded the same respect.

So far so good - all the evidence was pointing to marathons being easy. But what if Eddie Izzard is no ordinary mortal but in fact a rare and remarkable physical specimen, an outlier? Because when I looked at two other notable cases, the picture began to change drastically, taking on a significantly darker hue.

The HBO drama series In Treatment follows handsome, brooding pensioner psychiatrist Paul Weston and his roster of patients. One is Alex, a physically imposing fighter pilot recently returned from a mission in which he personally bombed and killed a whole bunch of Afghani schoolchildren. You must have been very badly affected, broods Paul. Nah, says Alex, it ain't keeping me awake at night any. Alex, we infer, is one tough dude.

It then emerges that Alex had recently gone through a near death experience. He'd been out running and, perhaps propelled by the demons lurking within, carried on way past the point of exhaustion. And, despite every bone, every sinew, every cell in his body screaming at him to stop, he just kept on running and running. Eventually, his shattered body simply gave in, and he suffered a near fatal heart attack. And how far had he travelled by this point? 22 miles. And this a fighter pilot in the US armed forces trained to the very peak of physical fitness. You may have guessed where I am going with this. If this highly trained, physically imposing child-killing machine couldn't make it past 22 miles, what chance do I - a poorly trained, confrontation-avoiding wimp who has never so much as (seriously) maimed a defenceless child in his life – what possible chance do I have to make it 26? 26 and a freakin' bit, mind you!

The picture darkened further still when I learned of the plight of Ricky Wilson, the singer from the Kaiser Chiefs. Earlier this year, Ricky ran the London Marathon, laudably raising many thousands of pounds for charity. But towards the end of the race he too began to feel the effects of exhaustion setting in. Yet Ricky also ploughed on and on, driven, perhaps, by the haunting failure of the Kaiser Chiefs' third album. And every man, every woman and every child was screaming at Ricky to please stop; to cut his losses, prevent any more damage, just please stop releasing records. Finally, with just over two miles to go, Ricky's poor battered body simply gave up the ghost. Like Alex before him he collapsed and had to be raced to hospital, where, with the nation holding its collective breath, he thankfully made a full recovery. But my point is this: If this highly trained, quick witted hit-making machine couldn't make it past 24 miles, what chance I?

Alex from In Treatment and Ricky Wilson off the Kaiser Chiefs: almost faster than I could take it all in, terrifying evidence of the (near) fatal effects of marathon running seemed to be mounting up. I began to panic. But I thought to myself, well, Ricky was probably too busy to train properly anyway. And then I realised that Alex is actually a fictional character and, strictly speaking, has no place in any serious forensic analysis. Finally I thought of Izzard and decided to pour myself a nerve-calming drink and toast the man and his exploits. My first choice was beer, but in the spirit of things I thought it only right to take my second, third and fourth preferences into account.