Is my TCX file uploaded anywhere?

No. It is parsed by JavaScript in your own browser tab and never leaves your device. There is no account and nothing is stored.

What is the difference between TCX and FIT?

FIT is the binary format your device records to; TCX is a lossy XML conversion of it produced by Garmin Connect. TCX is human-readable and stores distance per point, but drops developer fields and some per-lap detail that FIT keeps.

Why does my TCX show heart rate but no cadence?

Cadence, speed and power are stored in a Garmin extensions namespace rather than in the core TCX schema. If the recording device never wrote those extensions, the file genuinely has no cadence in it.

Can I export any activity as TCX?

Almost any, but not all. Some activity types, multisport in particular, can only be exported from Garmin Connect in the original FIT format.

TCX file viewer

Drop a .tcx file onto ActivityMaxxer to chart it. TCX is the XML format Garmin Connect exports on request, and it carries enough per-point detail to plot a full activity.

What a TCX file contains

TCX stands for Training Center XML — the format Garmin built for its old Training Center desktop software, and still what Garmin Connect produces when you ask for an XML export. Being XML, it is plain text: you can open one in any editor and read it, which makes it the easiest of the three formats to sanity-check by eye when something looks wrong.

The structure is an Activity containing Laps, each containing a Track of Trackpoints. A Trackpoint holds a Time, usually a Position with latitude and longitude, an AltitudeMeters, a DistanceMeters, and a HeartRateBpm. Cadence, instantaneous speed and power live in a separate extensions namespace that Garmin bolted on afterwards — which is why some tools that claim TCX support show you heart rate but silently ignore cadence.

One property makes TCX genuinely useful rather than merely adequate: it stores DistanceMeters explicitly, per point, as measured by the device. Distance does not have to be reconstructed from coordinates, so the distance x-axis matches what your watch reported instead of drifting from it.

TCX versus FIT

They are not competing formats so much as different stages. FIT is what the device records; TCX is a conversion of it. Every TCX file therefore started life as a FIT file, and the conversion is lossy — anything Garmin's schema has no element for is dropped, including developer fields from third-party sensors and most of the per-lap detail.

Being text also makes TCX several times larger than the FIT it came from: a half-hour run that is a couple of hundred kilobytes as FIT is comfortably over a megabyte as TCX. That matters for storage, not for charting — both parse quickly here.

Practical rule: export FIT for archiving and for anything you want to re-analyse later, and export TCX when a tool only accepts XML, or when you want to read the numbers yourself. Note also that Garmin cannot export every activity type to TCX — multisport activities in particular are FIT-only.

Exporting a .tcx from Garmin Connect

The export lives in Garmin Connect on the web only; the mobile app does not offer it.

Sign in at Garmin Connect in a browser.
Open Activities from the left-hand menu and click the activity you want.
Click the gear icon at the top right of the activity page.
Choose Export to TCX. Unlike Export Original, this downloads a plain .tcx file rather than a ZIP archive.
Drop that file anywhere on this page.

What gets charted

One panel per channel found in the file — pace or speed, heart rate, cadence, power where the extensions carry it, and elevation — all stacked on one x-axis that switches between elapsed time and distance, with a shared crosshair so hovering anywhere highlights the same instant in every panel. Each panel can show its own average, minimum and maximum reference lines. Average pace is computed as total moving time divided by total distance, with detected pauses excluded, rather than as a naive average of instantaneous pace values — which is the usual reason a third-party viewer disagrees with your watch.

Questions

Is my TCX file uploaded anywhere?: No. It is parsed by JavaScript in your own browser tab and never leaves your device. There is no account and nothing is stored.
What is the difference between TCX and FIT?: FIT is the binary format your device records to; TCX is a lossy XML conversion of it produced by Garmin Connect. TCX is human-readable and stores distance per point, but drops developer fields and some per-lap detail that FIT keeps.
Why does my TCX show heart rate but no cadence?: Cadence, speed and power are stored in a Garmin extensions namespace rather than in the core TCX schema. If the recording device never wrote those extensions, the file genuinely has no cadence in it.
Can I export any activity as TCX?: Almost any, but not all. Some activity types, multisport in particular, can only be exported from Garmin Connect in the original FIT format.