If Christmas is the season of good will, then the New Year is the season of good intentions. January is a month for sorting our lives out, making changes, promising ourselves that this year will be different. In that spirit, it's the month that sees the highest number of new gym memberships.

That's all very well, except that our best intentions often don't live up to much. Research shows that most gyms in the UK lose 50-60% of their members every year, and only keep going because of the January rush. I sympathise entirely. I find gyms overly-serious, sterile and souless, with too many mirrors and not enough windows. Even if I can get past the lab-like atmosphere, the activity itself is all so pointless. I just can't bring myself to join the rows of sweaty people, all running on the spot, staring straight ahead with their ipods on.

But what if there was a completely different way of doing it, a gym that was fun, human, social, outside, maybe even useful? Leo Hickman mentioned just such a thing recently in his Guardian column, and I had to look it up. It's called the Green Gym, and it's run by the British Trust of Conservation Volunteers. Members of this particular gym meet up once a week for a three hour session. They start with some warm-up excercises, and then they get stuck in to some good old-fashioned manual labour - planting trees, digging, clearing waste ground, building gardens.

Participants get to hang out together and work together, learn new skills, and make new friends while they get their weekly workout, and important conservation work gets done at the same time. And if that doesn't sound like proper exercise, research done on the Green Gyms found a one hour conservation session burned a third more calories than a step aerobics class.

The Green Gyms have been running for over a decade in various parts of the UK, and there are now 65 of them working in partnership with local volunteer networks and healthcare trusts. Best of all, they're all free.

If you live in the UK, you can find your nearest Green Gym here. If you don't, why not read their guide to starting one, and re-invent it in your own community - it would make a great Celsias project. And who knows, maybe you'll still be doing it next January.