Dom Joly: Fit? Me? I'm like a pot-bellied pig with a punchbag

Trying to get fit is not as simple an affair as I would have thought. I've been here before, of course – keen visits to the local gym, multiple purchasing of revolting sportswear and then, three weeks in, I get bored, the visits tail off and the sportswear joins the collection abandoned in the bottom drawer.

Last time, we even turned one of our outbuildings into a gym, to try to stop us making the excuse that it was "too far" to drive three miles into Cirencester.

All that happened was that we decked our gym out with a water-cooler, machines, mats – even a telly on a bracket. Then, nothing. The distance across the courtyard between our front door and the gym might as well have been as formidable as the Grand Canyon. Our gym would just sit there taunting us when we slunk past it on our way out somewhere unhealthy. At night, I swear that I would sometimes hear it chanting: "Loser, loser, who's the big, fat loser?"

On the other hand, that might have been any of my neighbours, so I mustn't be quick to accuse. I was moaning away to a friend about my worries, over some fish and chips and three bottles of wine. He looked at me in that slightly smug way in which friends often look at me and said, "I've got just the guy for you."

So this was how I came to meet my new personal trainer, a person to whom we pay a vast amount of money simply to force us into our own gym. It does work, but it's probably not the most financially sound option.

The problem with personal trainers is that they all have their own theories about how you get fit and, whatever you have done before is always "rubbish" or "outdated scientific thinking". It's a bit like going to see several doctors for the same complaint: they will all have their preferred methods for curing the grape nuts on your bottom. Just as when you take the car to the garage, you have no way of working out who is right and who is wrong.

Our new trainer is a mixed martial arts fighter and believes in "kicking arse" (best said in a Zimbabwean accent). For the past week, I have kicked and punched more things than Ross Kemp on an angry bender. I hurt everywhere, which is weird, considering that I'm the one attacking inanimate objects.

My trainer whispers things about what my body is doing as he tortures me: "The core is fighting back. Your abs are arguing with your triceps. Your body is producing growth hormones." Supposedly, the growth hormone is a good thing, and he assures me that I won't bulk up into Hulk Hogan proportions.

It turns out that this particular hormone is available to inject, if you know the right person. This is supposed to be the drug of choice for many professional sportsmen as well as several well-known Hollywood action heroes who have been arrested with bags of the stuff in their luggage.

I'm going to do things the natural way, although there is nothing "natural" about the sight of me in tight shorts kicking the crap out of a punchbag while sweating like a pot-bellied pig. I'm starting to smell a punch-yourself-fit Christmas fitness DVD coming on. I'm sure it'll be available in all good joke shops soon.