Nintendo's Wii home video-game console is no longer content only to play. Now it wants to tone your body too.

The Wii Fit exercise game arrives in stores nationwide Wednesday with more than 40 fitness activities ranging from yoga and aerobics to balance and strength training.

Ever since the little white Wii hit the market 18 months ago, fans haven't been able to get enough of its physically interactive games, which get players up off the couch and make them simulate boxing, bowling and tennis.

Old-folks homes and hospitals followed suit, using the motion-sensitive controllers for what was quickly dubbed "Wiihabilitation."

Now Nintendo is betting that the marriage of gaming and movement will ensure the success of Wii Fit — which, for $89.99, includes the "Balance Board" and the Wii Fit game disc — and make a stronger, leaner and generally healthier gamer.

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The Balance Board is actually a dual scale that measures both the player's left and right sides for pressure and weight.

Developers got the idea from watching the weigh-ins for sumo wrestlers, who are so heavy they have to use two scales placed side by side.

Like a sumo wrestler, gamers will have to step up to the scale to discover their own weight. Depending on your own extra poundage, the experience can be just as depressing as middle-school gym class.

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Using each player's personal avatar, or Mii, users enter the world of the virtual — and hopefully actual — workout with a weigh-in that measures body mass index (BMI) based on height and weight.

Players are labeled "underweight," "normal," "overweight" or "obese"; the Wii then adds or subtracts the pounds to your hapless Mii, depending on what it finds.

The practice is already controversial, with one unnamed British father lamenting to London's Daily Mail that his 10-year-old daughter, who stands 4-foot-9 and weighs about 90 pounds, was labeled "fat" — Wii Fit doesn't actually use that word — despite her active lifestyle.

Nintendo's British division quickly put out a press statement that calculations on children may not be indicative of their actual health.

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If you're an adult, though, tough luck; this is a game, albeit one that tries to motivate. If you have a tubby Mii, Wii Fit offers an opportunity to decide weight-loss goals, and even creates a schedule to achieve them.

(Don't worry: Wii Fit knows that weight is personal, so it includes an option to password-protect the character so no one but you and your Wii have to know exactly how much you've let yourself go.)

Once the initial embarrassment is over, it's time for the fun and the sweating to begin.

Wii Fit divides its workout program into four categories — yoga, strength training, aerobics and balance.

A trainer — players get a choice of male or female — leads the first two groups, while the latter two are filled with games that feel more like, well, games.

Unfortunately, Wii Fit doesn't have a set exercise routine, so gamers will have to find the combination that works best for them.

For those who've never ventured into a real gym, demonstrations of each strength-training and yoga move give a good overview, with the trainer offering tips as the gamer tries to mirror him or her.

Novices, though, may find themselves more concerned with keeping their balance in the shaded yellow areas than with focusing on proper form.

The best activities are the aerobic and balance games. Hula Hoop lets one gyrate like Dita Von Teese on Pixy Stix, while the winter sports that hone balance — ski slalom, ski jump and snowboard slalom — are surprisingly addictive approximations of the real events.

Kids are likely to love soccer heading and the penguin slide, which turns the Mii into a penguin on the hunt for dinner while sliding around on an iceberg.

Other activities, such as basic step, fall short. That program moves at a snail's pace and the "Dance Dance Revolution"-style footprint system is likely to confuse users unfamiliar with the format.

Wii Fit does its best to motivate users, but it's pretty easy to cheat.

On aerobic activities such as the Basic Run — which doesn't require the balance board, only the Wii remote — just moving your arms back and forth will make the Mii jog through the course.

With strength-training jackknifes, Wii Fit records your progress by the time your feet touch the board. That makes it easy for a tired user to just lie on the floor and tap his or her feet to the proper time, outsmarting the system.

To counteract cheaters, Wii Fit works on a rewards system. The more Wii Fit is used, the more varied the activities.

For every minute of activity, a Fit Credit will be placed in the Mii's piggy bank. As the credits add up, Wii Fit unlocks more advanced activities for users to tackle.

Wii Fit is what you make it. Users who want to work up a sweat will. And they'll do so through all that Wii Guilt that starts at the initial weigh-in.

Will Wii Fit help a chubby gamer lose 50 pounds? Probably not. But it could be the gateway game that gets him up on the balance board to better health.