Please install this TCX Export plugin to export Sporttracks activities into the TCX file format.
Afterwards you can import these TCX files into the Garmin Trainingcenter software or any other training software supporting the TCX file format.
The export of activities is quite simple:
Inside Sporttracks v3 switch to the activity overview, select all activities you want to export into the TCX file and chose Export/Export2Tcx at the menu on the left side, acknowledge the following dialog and you are done!
There are some enhancements available for Apple Mac users to import the Sporttracks activities via TCX into the Trailrunner software (min. v3.2.576 of Trailrunner required). If you want to use these enhancements (import equipment, map to diaries etc) with Trailrunner, just check the box "Include Trailrunner specifics" at the export dialog. Keep in mind, that enabling this feature will break the Garmin compatibility of the TCX files!