You might think that Wii Fit was a reaction to the popularity of games like Wii Sports and Wii Play, but according to Wii Fit lead Takao Sawano, the health-centric game "existed in the center of Miyamoto's brain before the console was released". Sawano gave GDC attendees a rare look into the Nintendo design philosophy today, showcasing the initial design documents for the Wii's best-selling titles, as well as giving us a visual walkthrough of the development of the Wii Balance Board.
Shigeru Miyamoto's notes on what was then known as "the Health Pack" didn't provide much in the way of direction to those on the hardware and software development side at Nintendo. He simply passed on to the team how much he enjoyed weighing himself everyday and monitoring his weight. "This is bound to lead to something interesting", Miyamoto said to what would become the Wii Fit team.
It wasn't until those on the game development side created the first test software, an early version of Wii Fit's balance test, that worked with a dual-scale prototype board using Nintendo 64 controller parts to gauge weight that things started to take shape.
"I think you might be onto something fun with this movement based play control," Miyamoto told the team.
Incidentally, that dual scale prototype was born of a spark of inspiration that Sawano had while watching sumo wrestlers grapple. The deputy general manager at Nintendo EAD wasn't concerned about their unhealthy porkiness, though. He was merely inspired by some sumos being so portly that they required two traditional scales to measure their weight accurately.
Speaking of chubby folks, there's some good news for husky types. The Wii Fit Balance Board can actually withstand a 660 pound human being before buckling. It just doesn't measure beyond 330 pounds. So put down that pork chop or you'll be watching Wii Fit from the couch.