I knocked out Oscar with one hand behind my back, walloping his little glassy-eyed head with a series of right jabs.

Hiroshi and Daisuke came out swinging, but both went down in the second round for my sixth and seventh knockouts of the day.

Andy posed a challenge, and had me on the mat in Round 3. But I prevailed on points and so far am undefeated in my boxing career.

After half an hour with Nintendo's new Wii game system, the television was drenched with the sweat that came flying off my arms and hands with each punch, and I think I proved a point: The Wii is marketed as a game and advertised with laughing families playing together politely; but it can give you an aggressive workout.

If you are unfamiliar with it, the Wii is a video-game system that is taking on new life as a fitness tool, thanks to its use of hand-held motion controllers and its release of tennis, golf, bowling and baseball programs as well as boxing. The hand units substitute full arm and body motions for the notorious thumb-driven controllers that helped plant a generation of kids on the couch while the Mario Brothers and Donkey Kong did all the work.

No more. Retirement homes are starting Wii bowling leagues; schools must be discussing phys ed applications — The New York Times recently reported, after all, that gym programs in at least 10 state school systems are using Dance Dance Revolution, a video game that is kind of like Twister set to music — and it can't be long before one of the gym chains builds the Wii into its equipment.

Now I am old-school (not to mention old) enough to wonder about this. Shouldn't we actually BOWL instead of staring at the television and swinging a hand that holds nothing heavier than a piece of circuit-filled plastic? Is Nintendo going to add WiiFieldhand or WiiWoodchopper to its titles to mimic actual manual labor?

But the technology is here, and it could offer a real contribution to fitness among sedentary adults, the elderly and kids who might be drawn not only to the sports games, but also to the opportunity to swing a virtual sword in other Nintendo releases.

When the company sent a demo unit, I decided to approach it with a game face: Look for the most rambunctious contest (boxing) and try to get the best possible workout from it. So I booted it up, put up my guard and started throwing combination punches and weaving with my body as if the guy on screen were real. (The controllers let you duck and dodge like Keanu Reeves.)

Sound crazy? OK, so I've never actually thrown a punch at another human being. (Can my wife say the same? Hmmm ... ) But five minutes into this, my heart rate was well into the aerobic zone and stayed there for half an hour — enough time to cream eight little Nintendo creeps and get halfway to pro status.

You can practice successive jabs to work the shoulder; throw crosses to work with the hips; focus on your footwork and upper body to avoid punches.

And according to the heart rate monitor, I was 500 calories lighter for the effort.

There's more to come: A more deliberately fitness-themed software, called WiiFit, is due for release in Japan this year and should be out in the United States in 2008.

For these programs, users will stand on an electronic platform that turns their body into a game controller, with pressure on the platform translating into televised motion. The user shifts slightly in response to cues on the screen; yoga poses ask you to keep a red dot centered in a yellow circle as you move into a "half moon" or "tree" position.

One surprising element, which no doubt plays into Nintendo's hope that this system will find broad appeal among women and older users, was the almost therapeutic nature of some of the games.

Could building balance exercises into a video game succeed where the hectoring of a doctor or therapist does not?

And a ski-jump program that requires the user to squat and spring up as the virtual racer approaches the end of a ramp is akin to a move you'll see many people struggle with in nursing homes.