Yes, there's the Garmin Communicator Plugin API, and I'm pretty sure Strava uses...

		davidjohnstone on Aug 30, 2012 \| parent \| context \| favorite \| on: Show HN: I'm building a webapp for serious cyclist... Yes, there's the Garmin Communicator Plugin API, and I'm pretty sure Strava uses this. Having a small app running in the background that automatically uploads rides is exactly what I want to do someday.