Activity app appears on iPhones running iOS 8.2 when paired with an Apple Watch
The Activity app works with the Apple Watch to help track your workouts and activities that keep you fit. It also releases this information to the Health app on the iPhone. The Apple Watch itself has an Activity application that shares a common UI with the iPhone version. With the permission of the user, the data on the Activity app can be passed along to a third party fitness application for further analysis.
Here's a Public Service Announcement for prospective Apple Watch buyers who can't wait to track their exercise regimen on the timepiece. Pre-orders of the wearable begin on April 10th. The Apple Watch will launch on April 24th
source: @hamzasood via 9to5Mac, SlashGear