Just confirming that you know the shortcuts for navigation tools that are provided out of the box: If those are suitable for your scenario you could save some time to use those instead.
Change the extent at runtime
A set of pre-defined keyboard and mouse shortcuts are enabled on a Map control by default. The following table lists the combination of key and mouse actions and the map actions that they trigger:
[TABLE="class: table, width: 1087"]Press left, right, up, down arrowNonePan in the direction of the arrow key pressed.+/-NoneZoom in (+) or zoom out (-) one zoom factor. The zoom factor is defined by the Map.ZoomFactor property.NoneLeft mouse button double clickZoom in one zoom factor.NoneLeft mouse button click, then hold and dragPan the map (default map action).Shift, press and holdLeft mouse button click, then hold and dragDefine an extent to zoom in.Shift+Ctrl, press and holdLeft mouse button click, then hold and dragDefine an extent to zoom out.NoneScroll wheel forward/backwardZoom in (forward), zoom out (backward).
[/TABLE]
[ATTACH=CONFIG]32997[/ATTACH]
http://resources.arcgis.com/en/help/runtime-wpf/concepts/index.html#/Navigating_the_map/01700000008m...