There are just eight weeks to go and not everything is going to plan. My ankle has become stubbornly painful and although my sessions of physiotherapy are helping, I'm worried I'll collapse in a heap yards from the start of the marathon. I check my schedule. I should have been doing three runs a week, ranging from 50 minutes to more than an hour, with a long two-hour jog on the Saturday. My ankle has confined me to two weekly sessions in the gym, cross-training on cushioned equipment to prevent any more damage. I'm falling behind and I'm now on holiday which will mean the dual temptations of beer and cheese sandwiches without the normal limitations imposed on me back home - holidays do that.

Despite my marathon guilt, I'm in Val d'Isere, 1,850 metres above sea level, sunny, spectacular - pretty much everything that a dull March in Tufnell Park, north London, is not. I've convinced myself that the holiday is good training. Skiing, after all, is exhausting. There is also the benefit of the altitude which should - according to my sensible running mate Fran - make me better equipped for the coming endurance test.

Training at altitude does a number of things to your body. Because of the relatively lower levels of oxygen, the body needs to work harder to do the same things you would normally achieve at sea level. Long periods at altitude will make you more efficient in moving oxygen through the bloodstream and have the added benefit of increasing total blood volume as well as capillaries - this means more pathways for the blood to get to those muscle cells. With more blood getting there, there is more oxygen to convert to energy.

Altitude also does a whole load more things but the basic result is improved endurance for the runner and faster speeds at any given level of exertion.

OK, that's all straight out of a book. As I copy it out, I am starting to sweat. My beer is winking at me from its mat and a plate of chips has just arrived. I sit in a fug of smoke, a cigarette perched between my lips. If my physio could see me now, she would squeeze my sore ankle until I howled.

Eight weeks left. It's creeping nearer and I'm not prepared. I promise to be good when I get home.