I was going to take my son with me to do this story but then I thought: “Nah, he’s 10, he has enough fun as it is.” Besides, we’d have just ended up fighting over the controls like at home. And then there was his sister to consider. To ask Sam to help me to test-drive the new Wii Fit, being launched this spring, and leave Rachel out of it would have been to invite total family meltdown.

The Wii Fit, which comes complete with its own special balance board, is one of the new fitness computer games from the Nintendo stable, which already includes virtual games such as tennis, boxing and bowling.

Parents have good reason to be grateful to the Nintendo Wii. Pack them off to their PlayStations or take the old telly-as-babysitter option, and you feel guilty. Not very guilty, admittedly, but a bit. But tell them to play with the Wii for half an hour and you can tell yourself that they’re getting a little exercise (a study in the British Medical Journalsaid as much). It may not be Swallows and Amazons, but it’s better than nothing. The new Wii Fit though, according to Nintendo, is the first it has marketed as a “fitness” game: it has four training categories aimed at improving players’ muscle condition, balance, flexibility and aerobic capacity.

For those not in the loop, the Nintendo Wii has sold more than 2 million consoles since its launch in Britain in December 2006. It is a hardware/software package that enables you to play games and solve puzzles on a TV screen. If that sounds old hat, you don’t play hunching over a console pressing buttons; you play by actively doing (more or less) what you would if you were you playing the game for real. It’s virtual reality, in other words. Hence, people becoming so engrossed in a game of tennis or a sword fight that they punch through patio doors and such like and end up in hospital.

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So if you’re playing golf, for instance, you swing the wireless control as if it were a golf club, and then watch your ball disappear off down the fairway on screen. Or you hurl your bowling ball into a phalanx of skittles. Or you shadow box as your computer-animated self smacks an opponent around a boxing ring.

Does that make any sense? Basically, if it weren’t in front of you, you’d think the Wii was science fiction. It’s the first piece of contemporary kit that’s made me shake my head and say: “Eeeh, what will they think of next?” It makes me feel as my own parents felt when confronted with a video, as an Edwardian felt holding a telephone, as an Elizabethan felt looking through a pane of glass. If it wasn’t such a laugh, the Wii could easily make you feel about 500 years old.

Sophie, a publicist, shows me the new hardware for Wii Fit at her office in Soho. On the floor in front of a giant TV is a pressure-sensitive balance board about the size of weighing scales. In fact, what the new Wii does is to weigh you straight away. Along with your height and age, the computer then works out your body mass index. Mine is 29.36, somewhere between Medically Obese and About To Drop Dead. “It’s not 100 per cent accurate,” Sophie says, tactfully. “Muscle weighs more than fat.” “Thanks,” I say. “I can see why you’re in PR.”

Next, after some rudimentary balance exercises in which I am revealed to be fundamentally lopsided, the machine computes my “Wii age”. It is 65 (my actual age is 43). “Oh dear,” says Sophie. I have to choose a “Mii”, an icon to represent myself on screen. I go for a perky little chap with a side part and pot belly. He introduces himself. In Japanese. The English language version is not available yet, but if its success over there is anything to go by – more than a million copies of the game sold in just over a month – this game won’t be sitting on shop shelves for long.

I select an on-screen tutor, wondering if it’s morally or legally OK to lust after a computer-generated fitness instructor. She greets me with what I take to be a provocative pose. “She’s saying, ‘Hello, you fat bastard’,” the photographer says. “Nah,” I say, “she’s saying she fancies me. You can always tell.” “It’s a good alternative for those people who aren’t, er, that confident about going to the gym,” Sophie offers.

For the next hour I submit myself to a series of sometimes gruelling, sometimes exciting, often humiliating exertions. I try some skiing, first slalom, then a jump. Neither is successful. I turn into a ball and try to roll myself down a hole. I endeavour to keep one hula hoop in motion while attempting to catch others. It’s all about minute transfers of weight, rhythm, fluidity of the pelvis, such as dancing, essentially.

I could feel my abdominal muscles taking the strain, so presumably it was doing some good. Improving core strength and stability is the order of the day. Nintendo is to ask Liverpool John Moores University to research the effects of Wii Fit, but anecdotally, I can confirm that you have to make an effort. Not as you would lifting weights or running, but similar to a beginners’ Pilates class, or some semi-serious stretching.

I try walking a tightrope between skyscrapers
“How did I do?” I ask Sophie. “Well, your Mii just fell to his knees crying, so not good,” she replies. We move on to heading a football, where you have to bend and lean on the balance board to connect with incoming footballs. Occasionally, in a nod to Sir Alex Ferguson’s motivational techniques, a boot rather than a ball will smack you in the face unless you dodge it. My heading wasn’t bad. Then I try walking a tightrope slung between two skyscrapers and came back to earth with a bump. Yoga is next and I’m not bad at standing on one leg.

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