HealthKit provides a nice set of API to interact with the heath data store on your iPhone – reading various types of data, writing health data you collect from your user, and even running statistics on that data to present summary information on screen.
RW Team Member
In my day job, I write apps (Java, iOS) for space and health at APL. I also teach at the JHU Whiting School Engineer for Professionals Program ("Mobile Applications for the iOS Platform"). Now I'm also a iOS screencaster at raywenderlich.com!