Modern Garmin devices save data to the .FIT file format. The format description is open and widely known. If you add support for .FIT it will allow people with garmin running watches to view and analyse their Activities without an internet connection. This is possible by connecting the garmin to the phone in OTG mode, copying the .FIT file from the garmin then importing the file into locus. Locus already supports the .TCX format, .FIT is not too different.