Lewis taunts his rivals over fitness

Hamilton heads for the Northamptonshire circuit claiming to be in better physical condition than Button, an accomplished amateur triathlete, and having revealed rather delicate details about the bladder control of Scotsman Coulthard - 14 years his senior.

Hamilton's comments will add spice to the competition for support from a sell-out crowd of 90,000 on Sunday.

Button goes into the ninth round of the Formula One title chase believing his performance in last month's Royal Windsor Triathlon, in which the Honda driver finished a highly-respectable 117th out of 1,700 entrants, proves his physical competence.

Hamilton was impressed by 28-year-old Button's effort, admitting 'that's pretty good', but still thinks he would have the edge in a battle of the fittest - and would love the chance to find out.

He said: "I think I'm fitter than Jenson - but I've got to prove it. So if someone wants to get us going up against each other I'd look forward to it."

Hamilton, 23, at least has some scientific evidence to back up his bravado. He was speaking after experts with Reebok, with whom he has just signed a five-year sponsorship deal understood to be worth £10million, had assessed his physical fitness.

They found the McLaren ace has less body fat than a skinny supermodel; that he can maintain a heartbeat level throughout a Grand Prix of 170 beats per minute (the equivalent of a footballer playing two games back-to-back games), and that he can keep concentrating despite losing up to four kilogrammes in fluids during a race.

"That's like doing an hour and a half of gym work in a sauna," said Hamilton. "That's one of the biggest things we have to contend with. On the day of the race, from around 10am to the start at 2pm, I have to have three to four litres of fluid. It's ridiculous. I can barely drink that. To get all that into your body in such a short period of time is tough.

"Before I get into the car I have to go to the toilet. Then I do the formation lap, get back to the grid, and I have to go again."

That comfort regime is enough to keep Hamilton dry, but apparently it doesn't work for all drivers . . .

"Fortunately, I've never had to go to the toilet in the car. The only driver I've heard who's done it is David Coulthard. He said he's done it in his suit," added the McLaren driver.

"I'd find that very difficult, while trying to focus on your driving. You'd be a bit distracted by it."

Hamilton's apparent pursuit of an A-list celebrity lifestyle and lucrative deals has drawn criticism from those who believe recent mistakes in Canada, where he failed to spot a red light and rammed the stationary Ferrari of Kimi Raikkonen, and during last week's French Grand Prix in which he was penalised for cutting a chicane, prove he is not focusing totally on his driving.

But the Briton, 10 points adrift of title leader Felipe Massa in the second Ferrari, maintains a gruelling training regime that stands as testimony to his commitment to the sport.

He regularly runs for up to two hours around the lake of his tax exile home in Geneva and also hikes, goes on marathon bike rides and indulges in kayaking. Indeed, as he spoke Hamilton sported a small plaster on his lip where he got hit by an oar.

It's not just outdoor pursuits that Hamilton uses to keep himself in race trim. He said: "I have a crash helmet at home with 10 kilos of lead bolted on the top. To build up my neck muscles I sit on the edge of my bed and do repetitions usually lasting an hour. At the end I can barely hold my head up.

"I also have a steering wheel at home, exactly like the one in my McLaren, which I plug into my laptop and try to improve my reaction time for the start of the race."

And after what he has said about Button and Coulthard, Hamilton might need to make a quick getaway on Sunday.