What I needed was a kind of functional exercise, where a quick blast of activity came wrapped in an activity with a purpose beyond getting fit - stealth exercise, if you will.

What better than a bike? Here the exercise benefits are a by-product of the actual aim: transport. I was sold. So was a beautiful new cruiser, delivered in its full retro-glory to my door, complete with basket, bell, helmet and unbreakable lock.

The gleam of freshly-polished fenders was slightly dulled by the non-stop rain that heralded the bike's arrival - but I was hardy. One kagoule later, and I was off on the road, wobbling violently, grocery list in pocket. And for someone who hadn't been near a bike for six years, I was doing pretty well. Or at least I didn't actually fall off.

There was (and is still) only one hitch. I live in south-east London, in Forest Hill, near One Tree Hill, down the road from Gypsy Hill. You get the picture. I cannot leave the house without facing a steep climb or treacherous descent - so I spend much of my cycling life either perilously out of control, or about to expire from exhaustion.

But the health returns have been gratifyingly swift. When I first took the bike out for a spin, a (hilly) 5km ride left me red-faced and sore-thighed. Last week, I managed a 10km jolly without having to get off and weep at any point.

And then there are the other benefits. Instead of the supermarket, I'll cycle off to the fishmonger, baker, and greengrocer. Everything gets done more quickly when you're not waiting for a bus to ferry you to it; and for a non-driver, there's a certain freedom in just getting on your bike and heading off.

There might even be slightly more to it than that. Never mind stealth exercise - sometimes I even spurn the sofa for the joys of a quick ride around the neighbourhood. Even in my wildest dreams, I didn't expect that.