My love for Runtastic grows by the day. Not only is the service very useful to track my runs and hikes, but its Android app is almost always on the forefront of the latest Google and Android features and guidelines. Case in point: it was one of the first fitness apps to add support for Android Wear and it just got updated with Google Fit integration.

The first time you launch the app you'll be asked to give it access to your Google account (or you can find the option under Settings, Partner Accounts) so it can view and store activity information, location data, and body sensor data (presumably heart rate stats).