I like the Nike+ running app and whole thing with Fuel points but I am running with my Garmin Forerunner watch only. Garmin Connect syncs automatically with Strava, Endomondo, MapMyRun but not with Nike+. Fortunately it is possible to manually sync thanks to Angus Smithson’s Garmin Forerunner TCX to Nike+ Converter & Uploader tool.
You can upload a GPX/TCX file or enter Garmin Activity ID (the numbers in the URL). For example the ID for connect.garmin.com/modern/activity/708414574 activity is 708414574. The tool needs Nike+ email and password for authentication and that’s all. I managed to transfer around 35 activities without problem and I have 54000 NikeFuel points now and just 37 km left until green level.