Giovanny Gutierrez, a marketing executive from Florida, posted the footage of his girlfriend Lauren Bernat playing the game wearing just a T-shirt, stripy knickers and glasses two weeks ago, and it has proved a big hit with over 2m views on YouTube. Gutierrez is director of interactive media at US ad agency Tinsley Advertising.
However the one-minute clip, called 'Why every guy should buy their girlfriend a Wii Fit', has aroused suspicions from some viewers who pointed out that Gutierrez works in advertising.
His clip was posted as a response to another clip called "Wii Fit Hula Hoop makes you look stupid".
Nintendo has been forced to deny giving Gutierrez a secret brief to market the game, claiming that it is "absolutely, 100% nothing to do with Nintendo", adding that Nintendo did not create it and was not aware of it until it was brought to their attention.
The Wii Fit game allows users to do a range of exercises and stretches, such as hula hooping, step aerobics and yoga poses, with the guidance of an on-screen instructor. It went on sale in the UK in April and sold more than 300,000 copies in the first two weeks.
Gutierrez filmed his 25-year-old girlfriend, who also works in advertising, without her knowledge and he said that she was furious when she first found out, but has since calmed down.
The YouTube clip has already spawned a spoof in which a woman films her boyfriend playing Wii Fit with his T-shirt tucked into his pants.