Pedometers are rubbish, aren't they? When they're not completely inaccurate, they have an irritating tendency to reset themselves just as the sun is going down on your active day. And they measure walking, which is hardly the most taxing physical pursuit. Why then, after wearing one of these cheap plastic gizmos for a couple of days, are my legs so tired?

The reason, it seems, is that clipping one to your belt turns you into a compulsive mover. I've had one on for less than 48 hours but already I've clocked up over 30,000 steps. I've walked to work, walked a dog that didn't belong to me, and walked up and down rooms while pretending to think. I've even made 12 rounds of tea in the office just to give me an excuse to walk to the kitchen and keep those digital numbers ticking over.

My initial motivation was to avoid floundering in the sub-5,000 steps per day category, which, according to leading pedometer scientist Dr Catrine Tudor-Locke, would class me as sedentary. 5,000-7,499 is 'low active', 7,500-9,999 is 'somewhat active' and over 10,000 is 'active'. But my real goal was to clock up the 12,500 steps needed to reach the top bracket of 'highly active'. And once I got there, I kept going.

It's true that ambling around will never give you the fitness benefits of an intense interval session. But that's not really the point of a pedometer. No-one seriously suggests that you should replace a gym session with a saunter round the block. As John Brewer, director of the Lucozade Sports Science Academy says, 'The whole idea behind pedometers is to get people excited about taking exercise, and achieving targets and goals, and that is a good thing.'

Sports science studies agree. The gadgets can help you lose weight, exercise more and reduce blood pressure, according to recent US research. Maybe they're not so rubbish after all.