Microsoft is prepping for Kinect Play Fit and releasing hardware codenamed "Joule" to accompany it, according to sources speaking to The Verge. Kinect Play Fit will track exercise across "most Kinect games," providing metrics that'll be stored in the cloud. Joule is expected to be a heart-rate monitor, allowing wireless monitoring to keep exercise "within a target goal for weight loss, strength, or cross-fitness workouts."
Joule and Kinect Play Fit are compatible, but are two separate products. There is no expected launch window, but Verge sources also claim a future dashboard update will introduce the system. We're checking with Microsoft if it has any comment, but most of this (if true) will likely be revealed at E3 in a month.
Update: "Microsoft does not comment on rumors or speculation."