Fit or fitness-file is a file format used by Garmin to store logging and fitness data about your trip on Garmin fitness devices like the edge series or forerunner serie. RouteYou does support upload of these files. Only FIT types with an 'activity' are supported for the moment.
Read here more about the upload on RouteYou.
A good website with some tools for Fit files is www.fitfiletools.com