A dangerous place, the gym, where people go innocently expecting to work off a few calories but instead find themselves staring at endless reflections of themselves in wall-to-wall mirrors and getting lost in dangerous exercises in self-deception as they suck in sticky-out tummies, puff out flat chests or carefully position chins and arms to hide inconvenient sags. Those who have personal trainers costing as much as a shrink can at least use them as shrinks, sending eddies of mild depression out across the room as they expound on the big themes: (a) my boss is hell and (b) my love life is hell - but staying approximately in touch with reality. Apart from the furtive pleasure of eavesdropping on these conversations, the rest of us are left alone with our thoughts.
If you are alone at the gym in your power clothes, even if you're just loafing in the sauna or draping spotless towels around your neck in the changing room to create the impression you've been pumping iron for hours but are so superfit that you've hardly broken sweat, there's a risk that you'll eventually come to believe your own propaganda and start thinking you are the next Paula Radcliffe .
This is exactly what I did, down there in the basement with a thousand other puffing, panting office workers. I was warming up before doing some not very energetic exercise on one of those minimal-pain, maximum-feel good Heath Robinson resistance machines that gyms buy in clumps to take up space between the rowing machines and the weights. Next to me, a fit-looking young woman was stumbling along on a running machine in ever-greater discomfort, as her personal trainer sadistically turned up the speed. "I'm not half as out of breath as she is," I thought smugly, ignoring the fact that she was going twice as fast as I was, then: "That's it! I'll run the London Marathon!"
Suddenly it was blindingly clear. The training I'd need to do over the five months before the 26-mile race, to be run this year on April 23, would ensure that (a) I got disciplined (b) I got fit (c) I gave up smoking and drinking and (d) I lost what I still like to call baby weight as my first child approaches his sixth birthday. It would be like making, and keeping, the mother of all New Year's resolutions. I wasn't thinking about raising money for charity; just that doing this would make me instantly fabulous.
It's not easy to get a place. By the time I thought of doing it, the lottery through which people are selected - at the end of November - had been drawn. But charities get a few guaranteed places each. If you promise to raise between one and three thousand pounds, they'll put you on their team and let you bypass the lottery. So, after a day or two of furious emailing, and writing an initial £100 cheque, I was in.
And then I was swept away by a vast collective burst of enthusiasm coming at me from every corner of the city. The marathon, set up in 1981 by Olympic sportsman Chris Brasher as a way of making the city's many constituencies interact, has also become a giant marketing exercise. Suddenly, unexpectedly, glossy magazines were mailed to me. Friendly strangers emailed me. Charities that didn't know I was already spoken for petitioned me to run for them. Everyone showered me with advertising.
I was invited to run in half-marathons, to train not just at runs on weekday evenings but at Adi-runs sponsored by Adidas and starting from the Adidas shop, not to mention lunches and meetings and training sessions with my team. People wanted to take my picture on the day. I was offered merchandising, diet plans, exercise plans, inspiration, advice on raising money, web pages through which friends could make pledges to pay you for running, and the opportunity to start a marathon blog.
It was the marketing that seduced me. Obviously I was going to need new training clothes. At the specialist shop Runners Need, I discovered that my old gym shoes just wouldn't cut it. If I were going to destroy my body by running further than nature intended without getting sprained ankles and shin splints, I needed shoes specially selected for me after watching video footage of my feet pounding up and down on a treadmill conveniently located inside the shop.
In between the little bursts of running that would prove whether my feet leaned in or out, I found time to buy the T-shirt too. (And, while I was at it, a light running jacket, special running gloves, a black headsock to wear under a black baseball cap, special long-distance-running socks and an expensive wrist satellite gizmo that would tell me how far I'd run and how fast my heart was beating as a result.) It was even more expensive than signing up for the race had been in the first place. But it was worth it because of the inner fabulousness to follow. Wasn't it?
The actual running was less of a joy. Two or three miles a day to begin with, followed by a six-mile run at the weekend. You're supposed to work up to knocking off five miles a day without too much trouble; your weekly long runs are supposed to work up to a peak of about 20 miles about three weeks before the race. The first few weeks were harder work than the shopping had been. A bit cold if you were outside. A bit lonely if you were inside. Ennui was just waiting to set in.
My excuses got feebler. I couldn't run because of my cold. I couldn't run because I'd have to go abroad for a fortnight before April. I couldn't run because of a death in the family. Finally, I realised that I wasn't going to do it. Like all New Year's resolutions, this one, lightly made, was always going to be lightly broken.
So I've relapsed happily into sinful sloth - at least for now. But I haven't been left completely untouched by that brief enthusiasm. It's made me aware of the thousands of more dedicated people running in every London park in January, plugged determinedly into iPods, in warm (if often scruffy) hats and coats to keep out the cold, ready to go through the pain barrier to get to the moment when they stream through London in a great multi-coloured mass and puff up to the finish a lot more tired but with money in the bank for a good cause. I've started to feel ashamed that I took it so superficially.
Next year I'll do better. I'll accept my athletic limitations and - now that I've noticed that the most important things about the marathon are the charity fundraising bit and the city street-party atmosphere - get into them from my armchair. Sponsor some fitter people to do the legwork, and limit my own physical effort to going along on the big day to join the merry throng cheering them home. Now there's an idea that really does have the simplicity of genius.
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