And it was all going so well. All right, not so well, but better than it had been. I had finally found a friend willing to attend the gym with me, which meant I was going almost every evening. We were watching the numbers on the machines slowly rise. Very slowly - each of us is there doing penance for three decades of inertia, providing mutual support and succour rather than competition. There will be no spurring each other on to scaling ever greater peaks of effort while we are in semi-athletic tandem, but weights and speeds increased, timings lengthened, more calories were burned. (Jenni measures the last in Smarties; I translate it into supplementary chunks of Dairy Milk, which probably tells you all you need to know about our motivation.)

Still, whatever the reasons behind it, an hour a day of concentrated exercise is making a difference. I feel livelier, more willing to bound up stairs, skip to the shops or to go for a walk instead of watching another Friends re-run (I don't actually do any of these things, you understand, I'm just more willing to - in the unlikely event, say, that someone makes it a condition of the mortgage or something).

Or rather, I felt livelier, more willing, etc. Since then, I have succumbed to every pre-Christmas cliche in the book - meeting friends for meals out instead of at the gym for aerobic stimulation, boozing at parties instead of swilling down mineral water and pomegranate juice at home, and then not moving off the sofa until the hangover dissipates - which these days takes about 72 hours.

But do you know what? I don't really care. I love Christmas so much. It's just the same as when I was a kid - my sister and I still get stockings at the foot of the bed, we're still not allowed in the sitting room where all the presents are until we've had breakfast and got dressed, and we still sit opening presents under the tree while mum gets overexcited and dad runs back and forth to baste the turkey. I've gone 30 years without worrying about my health and fitness over this holiday of holidays, and I'm not going to start now. Merry Christmas!

· Next month: Tim Dowling is bio-stimulated