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Beijing

Don't worry about the pollution, the Beijing authorities have been telling us.

Factories will shut down. Cars will be taken off the roads. Skies will be seeded with silver nitrate and clouds conjured away to leave the air perfect for the world's athletes.

That's the theory. Happy to lay my lungs on the line in the name of unscientific research, I decide to head out into the city on a long run to test conditions first-hand.

The initial signs are disconcerting.

As I jog down the stairs and out into Monday morning, the concrete tower-blocks of the are shrouded in what looks like a heavy autumnal fog.

Even with the sun completely hidden away in the grey blanket up above, the heat is intense.

Traffic is roaring by on the expressway, soldiers in pale khaki shirts and white gloves marching in rectangles around the security barriers. I wave at a group of staring schoolkids and head south towards the Olympic Green.

Five minutes down the road, my t-shirt is already drenched, hanging heavy off my shoulders.

It's 9am. At this time of day, the runners will still have seven or eight miles to go.

The triathletes won't even be starting the run leg of their races for another three hours.

I pass a woman whose mobile has an ring-tone and realise that my throat has started to feel sore, as if I had a cold coming on.

Maybe it's the road I'm running alongside, I think, and head down a side-street in search of a patch of greenery.

Another five minutes down the line, there's a strange lumpy feeling halfway down my throat. An old chap watering a freshly-planted verge and flobs it expertly into a plant-pot.

When in Rome, I think, and spit into the gutter with relish. The metallic taste in my mouth remains.

It's not easy working out where to go. The haze obscures anything more than 100m away. I've picked a bad day - today (the World Health Organisation target is 50).

I'd planned to aim for the Bird's Nest Stadium 5km away, but there's as much chance of me spotting it in these conditions as there is of me doing the pole vault there in 10 days' time.

The road stretches into the gloom, the two dedicated Olympic lanes completely empty of traffic while buses and bikes fight for position in the other lane.

"One world, one dream," read the banners flapping from the lamp-posts. My map shows a large park off to the left, but everywhere you look are tall fences and short officials with strict instructions to keep you out.

At the halfway stage, my eyes have started to feel gritty, as if I'd been out all night in a club full of smokers. Three weary-looking blokes slumped on a bench ni-hao in my direction as I rub my eyes and I ni-hao back.

The stinging in my throat gets worse as I head back north, the Bird's Nest lost somewhere in the smog.

Towers of apartment blocks loom slowly out of the mist. Young blokes on mountain-bikes pedal past while shouting into mobiles, which at least makes me feel more at home.

Every now and then a solitary soldier stands on a small plinth, staring into a seemingly random direction with a blank expression.

My lungs feel half their normal size. No wonder an asthma sufferer like , even though he's the world record holder.

The only other time my lungs have felt this bad was when I got stuck behind a brigade of belching buses while foolishly cycling down Oxford Street.

By the final few miles I'm dragging my legs along like sandbags. There could be several reasons for that - seven hours of jet-lag, the cannonball-like lump of egg-fried rice lodged halfway down my digestive tract, a delusional attitude towards my own fitness - but I've also taken it incredibly easy.

How much worse would I be feeling if I'd really opened the lungs up and got my heart-rate going?

At the end I'm coughing like a 20-a-day man. It's like I've borrowed the lungs of my colleague Ben Dirs - and if you've ever seen Dirsy trying to walk up a flight of stairs, you'd know that's a very bad thing indeed.

In the long list of cities that you'd never want to run in again, the competition is fierce.

Choosing between the traffic-choked hell of San Salvador or the dusty madness of Delhi, for example, is almost impossible, while a man can lose so much fluid in sweat in Kuala Lumpur that he'll grow a beard before he visits a urinal again.

Until today, however, I'd always considered Cairo to be out there alone at the top of the pile.

Not any more. And when would they ever stage an Olympics in Cairo?