"Your Shape" will initially scan your body shape, help you select a workout suited to you, and ultimatley hopes to offer "the most efficient and personalized program ever made".
The cam will then track your body's movements and encourage you to match them to the correct stances on-screen. Apparently, it'll also be able to respond to head nods and shakes for yes and no.
So does this pose a threat to Project Natal? Well, in essence, no. It's not nearly as sophisticated as Microsoft's killer dev – there's no speech recognition, it only works for this particular title and there's not nearly so much interaction.
But what Nintendo does have in its favour is that Your Shape is an imminent release (it'll be coming out later in the year) whereas Microsoft has remained tight-lipped over just how long it'll take for Natal to be unleashed on the public.
In the meantime, limber up with our first play of Project Natal