Enlarge  THE WII BOARD How it works: The board contains four strain-gauge force sensors, similar to those used in airplanes to detect stress on the fuselage and wings. In the Wii Balance Board, the sensors expand and contract as players shift their balance when standing on the board. The board can accurately determine a person's weight, as well as where and how that weight is shifting. Wireless function: A Bluetooth connection communicates with the Wii. Specs: 3.2 inches thick 20.5 inches long 13.5 inches wide Made of plastic, weighs 10 pounds Handles weights up to 330 pounds  WII FIT IN ACTION

That's why his latest project, Wii Fit, which arrives in stores Wednesday, is not really a game at all.

It's a $90 software-and-gadget fitness package for Nintendo's revolutionary Wii, reflecting Miyamoto's interest in his own physical health. Wii Fit, which comes with a balance board, has a built-in virtual trainer that helps players with yoga, aerobics and muscle toning.

And Wii Fit is expected to not only tone up its audience but also to bulk up Wii's already phenomenal success.

Miyamoto, 55, "has a Zelig-like ability to adapt his design to different audiences," says Geoff Keighley, host of Spike TV's Gametrailers TV. "Other companies would have made nothing more than a digital scale. Nintendo has made Wii Fit into something that's as fun as an amusement park ride and as effective as an elliptical trainer."

After a year and half, Wii units still disappear from shelves as fast as they arrive. The $250 system, with its wireless motion-sensing remote rather than a button-covered controller, appeals to a wider range of consumers than any system before it. Wii Fit could bring even more women and other non-traditional players to the Wii, which has sold more than 9 million systems in the USA.

In Japan, where Wii Fit was released five months ago, 2 million copies have been sold. Analyst Michael Pachter with Wedbush Morgan Securities expects about 30% of Wii owners in the USA to buy Wii Fit, similar to the sales rate in Japan, which would mean about 2.5 million initially and perhaps another 5 million over Wii's lifetime.

Wii Fit "looks like it is going to be huge," Pachter says. "It's not Guitar Hero (which sold more than $1 billion over the past two years), but it's more than half of Guitar Hero. It's going to be in the top franchises of all time if I'm right."

Over the years, Miyamoto's muses have had a commanding impact on games. His early Nintendo creations, such as Donkey Kong, Zelda and Super Mario Bros., helped resurrect the market from the post-Atari doldrums of the '80s. Time listed him among the 100 most influential people in the world last year. The Wii, which Miyamoto helped conceive, even has competitors Microsoft and Sony looking to grow beyond hard-core players.

"Wii Fit is exactly why Nintendo is walking all over the competition this generation," Keighley says. "It's expanding the market. Wives and girlfriends see the purchase of Wii Fit as part of an exercise routine. It's bigger than Grand Theft Auto in its appeal.

"The only limit will be the number of balance boards Nintendo can make."

Says the boyish Miyamoto as he demonstrates his creation: "When I design games, what I am trying to do is find a way to take something that is fun or entertaining from something I have experienced and to bring that to other people so they can experience that same degree of joy."

Miyamoto, who is married to a former Nintendo executive and has two children, often spins projects from his personal interests. Fitness and health are his latest passions.

"I had been interested in my own health for several years," he says. "I had actually been weighing myself on a daily basis and recording that and tracking it. So that became the inspiration."

Wii Fit can provide a serious workout. On a spring afternoon in a New York hotel room, Miyamoto has been holding the yoga pose tree for minutes at a time. He towels off his forehead and does extended warrior poses, then talks about how Wii Fit came to be.

Miyamoto, whose title now is Nintendo's senior marketing director and general manager of entertainment analysis and development, made the final decisions about what to include.

"Technically, my title is manager, but I would say I am not really managing so much as I am playing an oversight role with the creative process for all of our big titles."

Because Miyamoto's initial interest involved weight, early development focused on scales. A member of the creative team noted that sumo wrestlers use two scales to handle the excess weight. "In the process, they try to balance their weight to keep it even on both scales," Miyamoto says.

When designers experimented with two scales, they found that "trying to keep your weight perfectly balanced in the middle was very difficult but at the same time, very fun," Miyamoto says. That led to the creation of a board with sensors that measured how much weight a person had on each foot.

Pushing the limits

"From there, we created a game where you tried to hold your balance perfectly even, and we decided, 'Let's see if we can use this to create a skiing game,'" he says.

"Then we thought, if we also track balance from front to back, not just for left to right, we could create a device that is not just simply a scale but could actually have additional functionality."

A trio of creative directors suggested physical activities that might be a good fit. In addition to skiing, ski jumping, snowboarding, yoga and strength challenges, some of the 40-plus activities include soccer, with the player as goalie; jogging in place as screen avatars, or "Miis," move through a virtual space; hula-hoop shaking; and tightrope walking.

Miyamoto urged the young developers to "really push the boundaries with new ways people can play," says Nintendo executive Cammie Dunaway.

The wireless motion-sensitive balance board is slightly larger than a set of bathroom scales. A virtual trainer demonstrates the exercises and monitors your performance. The program also computes and tracks your body mass index and "Wii Fit age," an assessment based on your ability to keep your balance and how active you are.

Wii Fit will maintain and track eight family members. "We wanted Wii Fit to play an important role in helping families communicate about overall health, (and) we're getting feedback that it is in fact playing that role," says Miyamoto, whose Wii Fit age is in the late 30s. "I'm very happy to see that happening in Japan."

As a boy, Miyamoto explored the woods surrounding his home near Kyoto. During those formative adventures, he found a cave and a lake, which later inspired 1986's The Legend of Zelda, a virtual world that paved the way for games such as Myst and even Grand Theft Auto.

Miyamoto's gardening hobby became Pikmin, a 2001 GameCube game starring colorful carrot-like seedlings. When his family got a puppy a few years later, doggone it if that didn't lead to Nintendogs, a virtual pet game released in 2005 for the portable Nintendo DS. "His ordinariness is what leads him to come up with games that resonate with everyone," Pachter says.

'The fun is in the details'

"The complexity of life breaks into single notes that Miyamoto extracts and uses to compose symphonies," says game designer American McGee, who worked on Doom and Quake before developing his own games, such as the upcoming Grimm. Miyamoto's games, he says, "remind the industry again and again, the fun is in the details."

The Wii's fun factor surprised industry observers by not only appealing to longtime Nintendo fans but also to hard-core gamers looking for fresh approaches, as well as people who had never played video games. Wii buyers are more than twice as likely (34% vs. 14% for all systems) to say the system will be used by multiple players, according to surveys conducted in March by industry tracking firm NPD Group.

That disparity, says NPD's Anita Frazier, "alludes to (its) broad appeal and family adoption."

A look at the best-selling games for the various systems also speaks to Wii's engaging nature. The top seller for the Wii is Wii Play, a game rated "E" for all ages that has sold 5.1 million copies — as many as Halo 3, the mature-rated top seller for the Microsoft Xbox 360.

The biggest seller for Sony's PlayStation 3 is Call of Duty 4, also an M-rated game (1.4 million).

"People are looking at the Wii as a different type of gaming experience," says Jeremy Dunham of IGN Games. "It's touched into a broader demographic, even senior citizens, people who don't play games."

Even without Wii Fit, the Wii is turning up in unlikely places. Retirement communities, where residents are typically 60 and older, are using the system to energize their social scene. Hospitals have begun making the Wii part of rehabilitation regimens. And the Army is trying out the Wii for therapy at its Landstuhl, Germany, medical center and Walter Reed Hospital.

Physical rehab clinics have used computer and video games for many years, says Laurel Cargill Radley of the American Occupational Therapy Association, but the Wii "uses much more complex and much broader use of movement. … It's like a simulation machine."

Could the Wii start a new fitness revolution? University of South Carolina exercise science professor Russell Pate won't go quite that far.

But the past president of the American College of Sports Medicine and National Coalition on Promoting Physical Activity says he is "reasonably optimistic approaches like (Wii Fit) can be part of the solution (to obesity). I think electronic media has, up to this point, been more a part of the problem than part of the solution. I hope this is starting to turn that around."

With Wii Fit finished, Miyamoto has turned his attention to a new passion, a project called Wii Music.

Two years ago at Nintendo's press event at the Electronic Entertainment Expo in Los Angeles, Miyamoto gave a hint at its development when he took the stage in a tuxedo and used a Wii remote to conduct a symphony of instrument-playing screen avatars.

Miyamoto, who plays piano and banjo, hopes with Wii Music to create "an experience where people who can't play music can enjoy the experience and the joy that people who can play music get out of it."

Enlarge By Garrett Hubbard, USA TODAY Shigeru Miyamoto designed the Wii Fit software and balance board package, on sale Wednesday, because he was interested in his own health.