Apple's new iPhone 5S comes packed with the new M7 motion coprocessor, which among other things, can make for some very powerful fitness and motion tracking applications. Popular fitness app RunKeeper has just released an update designed to take full advantage of Apple's latest iPhone, that features some interesting capabilities made possible by the M7 chip.

Developer FitnessKeeper has introduced a new feature with the update called "Pocket Track" that will track your walking activity without you having to start or stop the app. The feature will run as an optional background process and will auto-track any walking activity that lasts for 15 minutes or longer. The data is then saved where users can review it and decide whether or not to include it in their official daily log. Additional information can be derived due to the motion coprocessor in the iPhone 5S, including the app's ability to track your number of steps per minute within a given auto-tracked time frame.

Even though the "Pocket Track" feature is only available to those with the 5S, FitnessKeeper has added AirDrop support for all of the iPhone 5 devices. With AirDrop, you will have another option for sharing workout routines and viewing/sending friend requests to nearby RunKeeper users.

Update 4.1 for RunKeeper is now live on the App Store. The free app requires iOS 5 or later and is compatible with iPhone, iPad, and iPod touch.