On 18 April, I will be joining more than 30,000 others who possess more determination than good sense to run 26 miles, mainly in a point- less loop through London's Docklands. We have already amply demonstrated our foolhardiness by spending months pounding over hard surfaces in an effort to become capable of a feat we were never evolved to perform: to keep up high-energy exercise for hours on end without pause. Within half an hour of the starting gun, once the streets around us stop resembling Oxford Circus on a pre-Christmas Saturday, about 29,000 of us will commit a final act of folly. As soon as we're in the clear, we will start running too fast.
One of the benefits of running the London Marathon for Shelter (the other being the chance to support a good cause) is that the organisers lay on a superb training day where you are briefed on marathon technique. Most of it is common sense, but the most important pearl of wisdom, about how fast to run, is not self-evident.
Instinctively, your thinking goes something like this. I want to finish in three and a half hours, which is an average of eight minutes per mile, so I'll need to do the first 15 miles or so in seven and a half minutes each. Then once I hit the "wall" at 20 miles or so, I can afford to slow down. On the contrary, say the professors of marathonology, you should start the race at the speed you want to average for the whole thing. You'll feel you're going ridiculously slowly at the start, but by the end you'll be racing past many others.
My longer training runs have confirmed this is true: starting more slowly can mean finishing more quickly. But I will still probably not be able to resist shaving a couple of pointless minutes off the opening miles through Greenwich. I may feel dreadful anyway, once I reach the Embankment. So if I bank those minutes now, at least nobody can take them back.
Is there a lesson here, I wonder, for how we approach working life? People in high-pressure jobs often expect to hit some kind of wall in their fifties and, in an effort to make hay while the sun shines, put in those 50-hour weeks in mid-life to help provide a financial cushion for later on. Today, however, such a strategy is looking more foolish than it did ten years ago, as few people are able to create arrangements, whether through employer or personal pensions, that will allow them to retire comfortably at 55. Taking care of yourself for the long haul is starting to look far more prudent.
Clearly, gerontology will be worse than marathonologists at telling us what factors of ageing we can control and which are inevitable - if only because they can't perform the controlled experiment of asking the same person to run the race twice at different speeds. However, some clues emerge from research in Finland, where the population is ageing even faster than everywhere else. It has found that people with positive factors in their working lives - a healthy working environment, the freedom to use their own knowledge and take decisions, job satisfaction generally, and control over their working time - retain high "work ability" for longer. Such workers are less likely to want to retire and can be as effective as in their prime.
This does not prove directly that pacing yourself by working 40 rather than 50 hours a week will extend your total working life. But it does show that it may be counter-productive to take off at a breakneck speed. Employers should think about it. After all, by 2021, the fiftysomethings will have become more numerous than any other population group.
To sponsor Donald Hirsch in the London Marathon, go to www.justgiving.com/donaldhirsch