Since i bought FR 920 i was looking for the way to sync my activities with previous historical data in one single place. As i has discovered a lot of tracking programs i stopped on Runtastic (due to it's wide training functionality with additional apps like 6 pack trainings etc.). And it was no direct way to sync all activities to Runtastic.
Neither Garmin or Runtastic does not provide such option.
So i was looking for the way to track all activities and more important to share it with my current friends on Runtastic for a long time till i unxpextedly found an app for Android (unfortunately still no support for iOS)
So it was a little tricky to use it (i use android emulator on my mac) but for those who use Android devices it will be native.
So here is the app that i found: http://syncmytracks.com
If you struggle from the same issue please comment and even better send an request to developers to add standard integration to Garmin Connect.
you can do it here: http://www8.garmin.com/contactUs/ideas/