Because they are so huge, sumo wrestlers need two scales to weigh themselves. Wii Fit's balance board works like two scales fused together, which, as its designers found, makes it instantly more fun than just one. The game has sold more than 2 million copies in Japan and has been a hit in Europe. Nintendo hopes to re-create that success when Wii Fit goes on sale in the U.S. on Monday.

In the United States, pre-launch buzz about the game -- with activities including yoga and snowboarding -- is reminiscent of the Wii's debut. The console, initially elusive in stores and online, is still often in short supply a year and a half after its release.

Wii Fit, which costs $89.99, is being sold out in pre-launch sales on Amazon.com and the Web sites of retailers GameStop and Wal-Mart; Best Buy's Web site lists it as "coming soon."

"Our main premise in creating Wii Fit was [to] create a game that allows you to check your weight," Shigeru Miyamoto, the legendary game designer behind Mario and Zelda, said through a translator during a recent visit to the United States.

With a scale as a launching pad, Miyamoto and Wii Fit's other developers added balance-based fitness activities and games. In one, you play a penguin trying to catch fish in the air while balancing on a block of ice. Like the Wii's motion-sensitive wireless controller, Wii Fit's balance board is intuitive and requires no video game skills.

During play, the balance board becomes a snowboard, skis or a tightrope. The game's fitness regimen includes yoga, aerobics and strength training as well as tracking of your weight and body mass index. You can even jog without the board, holding the Wii's wireless controller in your hand. The exercises start in one- or two-minute spurts, so you don't overextend yourself, and you progress to new levels as you get more proficient.

The goal of Wii Fit, Miyamoto said, is simply to get people to think more consciously about their health.

Instead of going after core gamers -- the "Grand Theft Auto" audience of boys and young men -- Nintendo has been roping in the whole family, including mothers and grandmothers.

Wii Fit seems to be expanding the audience even more. In Japan, between 30 percent and 40 percent of people who bought Wii Fit also bought a video game system for the first time, Miyamoto said.

Mike Hickey, an analyst with Janco Partners, said Wii Fit exemplifies how the appeal of video gaming has expanded.

"It's becoming less threatening, easier to digest," Hickey said.

Not just at Christmas

The game's launch outside the holiday season may also show the industry is maturing. While game companies still make most of their money around the holidays, Hickey and other analysts expects this to change.

"There is no reason you have to be tied to the holiday months any more," he said. "Like the movie business, ... [games are] a legitimate form of entertainment in the non-Christmas tree months."

While some in the industry have questioned how long Nintendo can keep its momentum -- after all, more causal gamers may not want to spend every spare dollar on a new video game -- analysts are upbeat.

"I don't think we even had the imagination a year ago that Wii Fit could be compared to 'Grand Theft Auto,' " Hickey said, referring to the popular crime game franchise.

If U.S. sales compare to Japan's, Hickey said Wii Fit will likely sell about 3 million copies in its first couple of months.