What is TCX?

Garmin's training format, and far more than a route: heart rate, cadence, laps, calories, all sampled through the workout. Converting it to anything else means deciding which of that to lose, because GPX and GeoJSON have nowhere to put most of it.

What is GPX?

The GPS exchange format: tracks, routes and waypoints, as XML. It's what watches, bike computers and handheld units produce, and what hiking and cycling apps import. Fixed fields, no room for extras, works everywhere.