Over the long years of my broadcasting career I have developed something of a reputation for being a good sport - dressing up in outlandish outfits, scaling tall buildings, playing cricket in a blinding snow storm, running the London marathon - but few seem to have generated quite as much interest from my friends and colleagues as the MoonWalk. I would like to think it has all sprung from a benevolent concern for my health and wellbeing, but let's face it, the only thing most people remember about the MoonWalk, a walking marathon in aid of a breast cancer charity, is that thousands of women pound the streets of London dressed in their bras.

I have been aware of the event for a long time now. Various girlfriends have badgered me for sponsorship, displaying their sequinned and feathered creations to prove their determination to sacrifice modesty in the name of fundraising. But this year I felt compelled to give it a go myself. My father recently died from cancer, and five women in my immediate circle are breast cancer survivors. What you realise when you start investigating cancer care is that we really are making amazing progress in diagnosing, treating and supporting people through the disease, and therefore cash generated by these sort of events can really make a difference.

Until I got started, I didn't know how amazing walking is as a form of exercise. I sent off my forms and vaguely considered some sort of training programme, but I run and play tennis and golf and swim. How hard could it be? It's not as tough as running, after all! How wrong I was ...

For a start, power-walking requires its very own technique - there's a completely different rhythm to conventional walking, which means a completely different footstrike, posture and set of muscles doing the work. I had read a few manuals about the importance of pumping your arms and driving off from your back foot, and even had a top tip from a trainer. She told me to imagine I was clutching a ten pound note between the cheeks of my bottom.

Imagine my surprise when after my first - fairly modest - effort, I awoke the next morning to aches and pains in places I never knew existed. The great news, though, is that power-walking produces astonishingly quick results in shaping up the old saddle-bag area. It burns amazing amounts of calories and is much kinder on the joints than running.

The even better news is that walking has to be one of the most social types of fitness training you can undertake. Whereas runners tend to jam their headphones into their ears, stare fixedly in front of them and power through the miles, the walkers I have been mixing with around Wimbledon common seem to have developed a delightful blend of socialising and shaping up. Moonwalkers all have a fantastic story to tell about what has inspired them to stick on the trainers and clock up the miles.

It's too late to get involved in the London event this year, but there are masses of opportunities to get involved in future MoonWalks around the country. The benefits include a shapelier bottom, a great sense of achievement, new friends and interesting blisters (such as the one on my thumb from sewing on sequins). If you don't fancy joining in yourself, you can still enjoy a rather unusual night out watching us all pound the streets around Hyde Park on the night of May 17.

· For more information, visit walkthewalk.org. If you would like to support Sandy Warr's efforts, you can donate online at justgiving.com/sandywarr