February 15, 2008 - Nintendo has updated its Ask Iwata series with the latest roundtable on Wii Fit. In this edition President Satoru Iwata talks with Takao Sawano of the Entertainment Analysis & Development Division and Takeshi Nagareda from Development Group No. 2 about the origins of the Wii Balance Board. Among the many tidbits of information revealed is the fact that the idea to measure the user's balance came from sumo wrestling.
Since weight scales are a common household item, the team wasn't sure a plain old scale would be a marketable gaming accessory. Sawano remembered that sumo wrestlers are so heavy they have to weigh themselves with two scales. They hooked two scales up to a computer and developed a program that would measure a user's balance that way.
Nintendo shares a few photos of prototype Balance Boards:



source: http://wii.ign.com/articles/852/852685p1.html