Ruth Walker: 'It's at moments like these you can pat yourself on the back(side)

And you can finally button up that shirt you bought in the sale that was really a size too small but you HAD TO HAVE IT and, besides, it was half price. So what if it gapes in all the wrong places and closely resembles an Austrian blind when you sit down.

It's at moments like these you can pat yourself on the back(side) and congratulate yourself on all that hard work and self-sacrifice. Maybe have a wee spirulina and banana shake in celebration.

Most of us, admittedly, aren't too familiar with this feeling at the moment. Nigh on a fortnight of gluttony has taken its toll on our livers and our waistlines. But allow me a moment of smug gloating, if you will. For, while the rest of you were stuffing Lorne sausage, black pudding and hot buttered toast in your faces on Christmas morning - maybe a bucks fizz or two; heck, why not start the day as you mean to go on? - I was (pause for full effect) running. In the snow. For miles. A deserted coastline, just one or two dog walkers for company, not even a child on their shiny new bike to be seen.

I know, I know. I mocked those similarly afflicted not two weeks ago. Assumed those who felt the need to get out on the roads in white-out conditions rather than snuggle up in front of 100 Greatest Musicals (all very well but, excuse me, Buffy The Vampire Slayer at No 13? What's that all about?) were merely betraying the fact that they have sad, empty existences. Nae mates. Or at least nae satellite telly.

Yet there I was. Sweating out the toxins of the previous week's excesses. And you know what? It felt great. Invigorating. Brand new. At one point I actually had to stop, breathe in the frigid air and almost weep at the pure beauty of the moment.

It was so good, in fact, that I went out again on Boxing Day. And every day after that. Sheesh, I've been so active over the Christmas jollies I feel like a new woman. My body is a temple (well, if you don't count Hogmanay ... and that night out on Thursday ... and then again on Friday ...).

Indeed, my stretchy gym trousers seem to be agreement. On my last visit, I looked down and could barely conceal my glee. Tightly hugging my increasingly pert gluteus maximus, they were positively baggy around the front. Oh joy. Oh festive delight. I did some sit-ups - they only puckered!

This must be what those gym bunnies feel like; the types who gawp in the mirrors in admiration of their own physical perfection. I skipped off to the showers in a haze of indecent self-satisfaction. Allowed myself just the hint of a swagger. I kicked my trainers away and tugged off my trousers with a single flick. Which is when I realised the uncomfortable truth. I'd put my breeks on back to front.

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• This article was first published in the Scotland on Sunday on January 16, 2011