There are many silly new year's resolutions knocking about: "eat a small orange every day", "shave my legs when they need shaving" and "stop posting pointless and rambling messages on political blogs" were some choice suggestions submitted to the Guardian's newsblog last week.

But deciding to join the 7 million Britons with gym memberships - in the misguided belief that paying an average of £41 a month will somehow be the shove up the bum you need to turn from lumpy sloth into body beautiful - must be the most stupid.

Especially as, according to the Fitness Industry Association, 30% of people who join gyms in January will be attending less than once a week by the time February rolls around. Worse, this time next year, 40% of these well-intentioned recruits will have thrown in the towel altogether - and the direct-debit illiterate among them will probably still be paying for it, too.

It's thanks to this widespread flakiness that the fitness industry can survive, of course, but why contribute to the estimated £200m wasted every year on lapsed or unused gym memberships when it's actually less effort to exercise for free?

When I moved to London two years ago, I made a conscious decision never to pay for exercise. My motivation was mostly borne out of tightwaddery, rather than any moral objection to paying money for the privilege of breathing the sweat of a thousand other common sense-challenged individuals. Indeed, I did use to go to the gym at university - as a displacement activity during my finals - and quite enjoyed it. But then, with the golden ticket that was my student card, it cost £30 for the whole year. Now, if I wanted to go to, say, Holmes Place at the Barbican - the nearest gym to work with a pool - I was being asked to part with around £75 every month. Even if you nicked the free fluffy towels every visit, and sold on the complimentary bottles of shampoo, that can never make financial sense.

At the risk of coming on all Raj Persaud and stating the bleeding obvious: exercise can, and should, be free - at least once you've invested in the most basic of equipment. A brisk walk half an hour a day is within the grasp of everyone with legs, and if you fancy having two feet off the floor at the same time and getting your heart working harder, buy a half-decent pair of trainers and you can start running. Snap up even the tattiest of secondhand bikes, and you'll actually save money not shelling out for petrol or public transport. And, unlike at the gym at this time of year, you will never have to queue for the privilege. Or smell anyone else while you're at it.

I got a bit carried away and began swimming for free in Hampstead Ladies pond, instead of a proper swimming pool, but paying per-go at your local leisure centre - even three times a week - is unlikely to add up to the full whack of gym membership; and if you get bored, you're not locked in. It's quite emancipating, really.

So why do people join up, despite all this? I think it's because buying into a dream makes people feel that they are on the track to wellbeing. That by paying money towards a goal, they are in some way closer to it - even if they have not moved an inch off the sofa. Like buying too-small jeans for thinner days ahead, this is clearly idiotic.

So, eat more small oranges, even shave your legs every day if that makes you feel better ... but don't waste your money on a gym membership this year.