When you run, which I do on a treadmill in a gym (unromantic, I know, but I am less able to fool myself that I have run twenty ks and am close to breaking world records etc) what goes through your head?

I know some people run in order to not think at all. That doesn't seem to happen to me. I have to think. I have to think or I stop running. Lately, I have realised that not only do I have to think but I have to have a soundtrack.

I don't really care what my soundtrack is, although it's probably best that it's fast-paced, somewhat melodic and, most importantly, heroic. This is because, when I run, I am in fact winning something. I am winning a race of some kind, or perhaps I am just impressing a local selector with my innate natural athletic ability (a selector in what, you may ask. A selector in short-distance treadmill gym-running? A selector in international frisbee championships SUBSECTION: long distance? A selector in lifting 4kg weights and going all red in the face?). It matters not. I am in their sights. I am on their radar. The AIS wants me, in my scuff-bottomed tracksuit pants and free Jetstar earphones. They are desparate for a writer with a part-time job and a gym routine that peaks at twice a week (I've just bought new runners) petering out in the quieter months to what my friend Finn calls Donating To A Gym.

They say writers need to be obsessive. I am not obsessive all the time, though. That's the annoying thing about my obsessive behaviour. It has no consistency. I don't obsess about cleaning, or eating, or rising at a certain time of day (particularly that one). I obsess with no apparent pattern at all.

Not that anyone else would notice anyway. But I've figured it out: the one determining factor in charge of my obsessive bursts of activity is my imagination. If I need to clean the house, I make the decision to clean the house, decide that I am the sort of person who cleans houses (because that is important and I yield to no man in my desire for hygeine and presentation) and I then turn on the radio and clean for hours. Sometimes days. I get the toothbrush and clean the tiny unreachable bits in the laundry sink. I alphabetise the DVDs. I will not rest until I have become the kind of person who has a clean house from top to bottom and I will never again be a messy person because I have learned my lesson. I have also, most of the time, learned other things too (if you listen to News Radio while you clean, you often learn the same thing over and over again).

With my writing, I avoid, avoid, avoid, obsess. I will NOT stop writing once I've started unless I am ALREADY SUPPOSED TO BE WHERE I AM GOING THAT EVENING. I get resentful that someone has invited me out. I get resentful that I can't get on with my writing. How dare people not let me get on with my writing. The fact that I spent the greater part of the morning writing silly emails and buggering about online is a sore disappointment to me, because when I am obsessed with something, I cannot picture myself ever not being obsessed with that thing ever again. When I'm cleaning, I cannot imagine ever leaving a pair of shoes on the bedroom floor. When I'm obsessively writing, I can't imagine ever going outside. So much to do, so little time. Head down, focus, eat and sleep later. Like, maybe, Friday.

When I say these obsessive moments are driven by imagination, it's not as though I'm imagining an Olympic Writing Selector picking me out from a lineup of writers. I'm not even picturing (like with the cleaning) that this will make me a better person. In fact, writing is one of the purest forms of imaginative obsessing, because it's not the act of writing into which the imagination projects creativity, it's into the writing itself.

So you look at a blank page, or a blank screen, and you're off.

Or, in the case of me, today, you think maybe the focus of your obsession might have to be the gym routine after all. Just as soon as you've downloaded a few ridiculously upbeat songs onto your iPod and put on your bouncy new runners.