During a Wendesday GDC session, Nintendo's Takao Sowano gave attendees the most in-depth look at Wii Fit to date. With the European version of Wii Fit set to release before the North American version, the demonstration Sowano gave used the European version of the game.

Sowano described Wii Fit as "a tool that helps family members manage their health just by playing casually every day." Understanding that people may not want to insert a Wii disc every time they go to check their Wii Fit progress each day, the game will come with a special feature: The Wii Fit Channel for the Wii Menu. After a disc-loaded firmware update, the game will install the channel, making it possible for people to track their progress without needing to change out games. The update will also enable other, future software to possibly install channels of their own from disc, instead of exclusively through the Wii Shop Channel.

Sowano began a detailed explanation of the game's features. The two main game modes are Body Test and Training. Body Test works like the brain tests in Brain Age, and also like Brain Age, you will be given a Wii Fit age based on how well you perform the tests. This mode can be accessed through the Wii Fit channel. If someone wants to play the training exercises, however, they must use the Wii Fit disc.

The training exercises in Wii Fit are very similar to those in Wii Sports, except there are more exercises in more categories. Over forty training exercises will be in Wii Fit, broken down into four categories. There are fifteen yoga poses, fifteen strength training exercises, nine aerobics exercises and nine balance games. All the games and exercises are built to help improve your general fitness, but users can choose which exercises to do if they want to work on a specific type of fitness plan.

During the strength and yoga training exercises, Wii Fit will have a virtual trainer of sorts on the television screen, instructing and advising users on how to properly perform exercises. The trainer can be male or female, and through the game and balance board, can detect how well a user is performing, or even if they've stopped completely. The example Sowano showed off was one person who started off well with a knee-lifting exercise, but stopped halfway through. The virtual trainer started to say what was wrong with the user's movements as they started to break down, and then told them to get back on the board once they'd left it.

Another aerobics game doesn't use the Wii Balance Board (which appears to now be its final name) at all, but only the Wii Remote. A running (in place) course, called Wii Fit Island, allows users to set a running time (of ten or more minutes) or a running distance around various paths on the island. The game detects controller oscillation to track your steps, and can instruct you to run faster or slower based on the movement of the Wii Remote.

The game will have Miis, animals, and other objects appear on the running course to help convey the feeling of running outside with other people. To drive that point home, two players can run together if the second player uses another Remote.

The running mode also has a feature that allows people to change the channel from the Wii to regular television, but still be given instructions and prompts through the speaker on the Wii Remote. In this way, people can still interact with the game and exercise while watching TV, similarly to how people on treadmills can watch TV while in a gym.

Wii Fit will reward regular workouts and progress with Fit Credits, which show how far someone has come along in the game. Sowano did not mention what use Fit Credits would have in the game, but did say players can manually enter exercise time performed outside of Wii Fit to earn more Fit Credits. Also, Sowano said that Fit Credit data was not exclusive to Wii Fit. Other developers would have an opportunity to access Wii Fit data in order to potentially incorporate it into their own games in the future.