When you reach my age (and without giving too much away there is a four in there somewhere) strange things can begin to happen to your body. Your muscles, particularly your legs, become stronger, your fat ratio begins to drop and you can run farther and faster then you could a year previously.

Of course this does not happen to everyone. If your idea of exercise is a trip to the kitchen to butter a little more challah, you will not see these improvements.

This was me until the beginning of the year, at which point I decided, to quote Woody Allen, that I didn't want immortality through my work, I wanted it through not dying. And fitness was my chosen method of cheating death.

I am well aware that, as of this point in history, an alarming percentage of people do seem to be expiring - estimates put it as high as 100 per cent. But there is hope. My Ashkenazi genes are good - all my grandparents lived to ripe ages despite diets rich in lockshen. And then of course there are the mice.

In a fascinating experiment undertaken in Canada, mice which had been genetically programmed to age quickly were given an exercise routine which involved running on the treadmill for the mousey equivalent of 10k, three times a week.

While an inactive control group were frail and grey after eight months (around 60 in mouse years) and barely moved away from their tartan blankets and slippers, the active mice had dark fur, plenty of muscle mass and had lost none of their brain volume. The only downside was a growing interest in Lycra.

At one year, the treadmill mice were still going strong with not a single death due to natural causes, although the scientists had, rather paradoxically, killed some of them so as to discover why they were living so long.

Whether this research can be extrapolated to humans is not yet proven and, to be fair, my grandmother, who lived to be 100, did not break into a jog during any part of the 20th century. However, I am not leaving it to chance. I take as my inspiration British marathon runner Ron Hill who went more than 16,000 days without missing a run. He is now 72 and still goes for a run every day. There is no way to examine his brain volume (without annoying him), but apparently his weight is the same as it was 50 years ago, his hair is not completely grey and, most crucially, he is not in any way dead.

I hope that, like Hill, I might be able to keep running into my dotage. Of course there are disadvantages. Recovery takes longer when you are in your 40s. It takes about 24 hours to overcome the tiredness after a run, by which time I have my running shoes on again.

But, at the risk of alienating all my friends and family, I'm going to stick at it. After all there is strange comfort in the fact that the longer I run, the further I might be from the finish line.