'You'll need to wear them quite a lot to see a difference,' said a highly toned woman at work, to which the only answer, surely, is: 'Are you saying I'm fat?' I bit my tongue. After all, when you're about to embark on a footwear experience that promises you significantly increased muscle tone and an overhaul of your under-performing hamstrings and calf muscles, what profiteth the scepticism of others?

Nonetheless, that is a lot of body-enhancing activity to take on board; no wonder the makers of the Fitflop, currently sweeping the nation to such an extent that when a new shipment arrives the sirens go off in Sloane Street, counsel caution. 'We recommend,' they intone seriously, 'that the Fitflop be used progressively to avoid excessive muscle soreness.' Indeed: you wouldn't want to be put in traction by your shoes.

OK. I decided to try them out at home first, not least because it was clearly going to take me a while to adjust to what they looked like, never mind how much they might make my bum ache. I've never quite got used to the idea of the flip-flop as high fashion, though I can see there's much to be said for some-thing that costs a fiver and can be hosed down as necessary. Fitflops, however, have none of that cheap and cheerful quality: they'll set you back a few quid, for a start, and you'll put them in the washing machine at your peril.

I really wasn't sure about the thick white plastic base (that would be the 'safely tapered midsole that creates a micro-wobbleboard workout in every step'), not to mention the great big toes (to promote 'a propulsive gate', apparently, though I imagine they might mean 'gait'). Were they not, perhaps, just a little medical looking?

The lucky few who had managed to secure a pair, presumably by ambushing a van en route for Harvey Nicks, assured me that, on the contrary, they are the height of chic and that I could wear them to wedding and work alike. I started by wearing them to watch the television, for which they were perfectly comfortable. Later I did a bit of gardening and found them most bouncily useful for sweeping up leaves on the path. So far so good. Emboldened, I decided to risk them on that evening's trip to the pub.

Naturally, they obeyed the Law of All New Shoes: virtually a second skin when you're in the shop or at home, then harbingers of agony the minute you step out of the door, the pain bearable in inverse proportion to the difficulty of accessing another pair of shoes. On the grounds that the pub was nearby, I had failed to pack my emergency pumps. The following morning, I had no idea whether I ached from my invisible workout or from the strain of walking oddly. But two things have emerged, now that a few weeks have elapsed. The first is that people really do look at you when you're wearing a pair. The second is that my legs are still chunky. But I must say that I think they ache a bit more after a brisk trot and that - if it means trimmer pins in the long run without having to go to the gym - is not to be sneezed at. In future, I shall reject all shoes that fail to provide me with a built-in wobbleboard as inferior.

· Fitflops £36, Harvey Nichols, 020 7235 5000; www.runningbare.co.uk