"Keep at it!" urges Alex, my training adviser, "you've only two-and-a-half minutes to go. You can do it!" Katie Jarvis is suffering at the gym

"Keep at it!" urges Alex, my training adviser, "you've only two-and-a-half minutes to go. You can do it!"

I'm on a road to nowhere - literally - cycling for all I'm worth. Five minutes eating popcorn, watching television, or (one of my personal favourites) asleep, goes in seconds. But on a static exercise bike, trying to keep some dial-thingy above 100 (whatever that means), five minutes lasts for at least half an hour.

I pride myself on a number of idiosyncratic achievements, though I use the word 'achievement' loosely. Wrongly, even. One of them is the boast that I've never set foot in a gym. My theory has always been that, if you want to exercise, then you live in the Cotswolds, for goodness sake! Walk the hills; go and dig an elderly neighbour's garden!

But the problem is that I don't. Not as often as I should, anyway. So here I am, in Fifth Dimension, Stroud's cutting-edge gym, having accepted an invitation to get fit in six months.

It's not the Large Hadron Collider, and we're not looking for the God particle, I accept that. But on my first afternoon, the machinery looks as complicated and the task as elusive. Alex sets me a personal work-out programme that looks suspiciously as if every setting is on minimum. But I'm not protesting. I might only be pulling 15kg weights - but have you tried lifting 15 bags of sugar? Nemesis in glucose form.

In some ways, I'm the perfect person to undertake this: bored by the concept of exercise; a reluctant participant who barely has time to read a book, never mind go to a gym twice (at least) a week: if I can do this, then anyone can... And, I grudgingly admit, it's not as bad as I thought; firstly, if I remember to bring headphones next time, I can plug into the TVs that are scattered conveniently around. Secondly, there's no doubt you feel better after exercise. Mens sana in corpore sano, and all that.

After completing my first routine, which included running a marathon (a short walk on a running machine), rowing across the Amazon (bit of weights), and cycling the Tour de France (for five minutes), I discover I've lost 170 calories. 170 calories??? Two Quality Street? Surely I lose more than that simply deaminating amino acids?

Am I defeated? Certainly not: if anything, I'm more determined. Next time, I vow to lose at least a Crunchie.

Katie Jarvis will be training each week at Fifth Dimension at Ebley Wharf Mill, Ebley, Stroud; 01453 769120; www.fifthdimension.org.uk