If you're wondering what miCoach is, don't worry, I didn't have a clue either. At it's simplest miCoach is an app which runs on your phone or on Adidas 'bands' you affix to your person in order to track your workout progress.
But how does this relate to the Xbox 360 and how will it all work? Rather than tie myself in knots, this Press Release does a far better job. I'll sit down and eat a cherry bakewell whilst you read through it:
... the completely connected interactive experience will feature many of the world's most well-known adidas athletes, including Dwight Howard, Kaká, Tyson Gay, Jessica Ennis, Ana Ivanovic and Eric Berry, who will guide users through a wide selection of sport-specific personalized training programs. Users will also receive real-time feedback on their actual in-game performance during their workouts when wearing a miCoach heart rate monitor (or any ANT+ compatible monitor). For an even more connected gaming experience, the miCoach hardware interacts with THQ's new video game title, allowing users to wirelessly synchronize a miCoach Pacer and miCoach mobile app to KinectTM for Xbox 360® or PlayStation®Move, incorporating workout data gathered while away from the game.
In essence, the existing miCoach technology will be banded together with an Xbox title which you can use to help track your workouts, set goals and targets for yourself, and analyse your performance over time. The Press Release also notes how 'users will be able to create profiles[and] choose from several sports, such as running, tennis, football (soccer), American football and basketball'. More than this, the hardware will allow you to track your exercise and calorie busting activities away from the console.
Early 2012 is the release date, so you've plenty of time to pick up some extra sweatbands and do some warm ups. Me? I'm off for a second cherry bakewell.
We've got the full list of miCoach achievements - check the list for guides to unlocking them.