The filing found by MacRumors addresses an issue with the device while carried and used by a user while the user is in motion. While the user and the device is in motion, the user's dexterity with respect to the touch-sensitive display can be disrupted by the motion, detracting form the user's experience with the graphical user interface.
Apple's solution is to adjust the interface when motion such as jogging is detected. The adjustments would do things to make navigating the interface easier. ie enlarge text, buttons, etc
Below you can see an example where the size of each contact is made larger in response to the detection of motion. Interestingly the diagram below also shows a front facing camera (labeled 180) which hints at video chat.