Until December 2014, everybody who gets an Xbox One will have free access to something called Xbox Fitness. Which is basically a collection of videos that use the Kinect's sci-fi powers to help you lose the weight you accumulate playing all your other games.
The vids appear to simply be pre-existing fitness productions, but tie into the Kinect which is able to read your heart rate (remember, it can see under your skin) and "track the quality of your performance by measuring your balance, tempo and form".
Sounds a bit naff, especially compared to something more tailored to a console experience like Wii Fit, but hey, it's free. Or at least, it is until December 2014, after which a "paid Xbox Fitness Pass subscription and an Xbox Live Gold membership" will be required. So a paid subscription on top of a paid subscription? Great.