After yet another Christmas of gluttony and sloth, I have resolved to get fit. But I can't stand the thought of joining a gym. What could I do to get some exercise and actually do something constructive at the same time?

P Thomas, Dyfed

There are about seven million gym members in the UK: how much power could be generated by all those treadmills and exercise bikes? Broadly speaking, the average person can generate about 100-200W of power when exercising. I discovered this for myself a couple of years ago when I rode a demonstration bike rigged up to power a 100W lightbulb in order to teach children about energy consumption. I had to huff and puff really hard to keep it illuminated, which gives you a good indication of my own woeful levels of fitness.

Every little helps, as they say, but I am not convinced we will ever be adding gyms to our nation's energy mix. For example, last year a fitness club opened in Hong Kong offering 13 exercise bikes that were adapted to generate power, but even when all of them are in use it is only enough to keep three 27in television sets running.

If, like most people, you need some kind of motivation to keep you from straying to the sofa when exercising, there are alternatives to the gym that don't just involve taking up a sport or taking to the pool. It's now more than a decade since the British Trust of Conservation Volunteers set up its popular Green Gyms initiative (www2.btcv.org.uk/display/greengym). Groups of volunteers meet up, say, once a week for three hours to undertake some strenuous exercise in the form of clearing an overgrown public footpath or planting a new native hedge. Everyone wins. And it is free, so there is no wasting £40 a month or more on a rarely used gym membership.

Some areas of the UK are much better served with green gyms than others. For example, the Bristol and Bath area boasts four green gyms, whereas there is only one in the rest of the south-west (in St Ives). There are also no such gyms in Northern Ireland. But Wales can boast 10 and the north-west has eight. Perhaps your new year's resolution could be to set up a green gym in your area? If this doesn't suit, why not sign up to a charity run later in the year?

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