Is my FIT file uploaded to a server?

No. The file is read and parsed by JavaScript running in your own browser tab. It is never transmitted, there is no account, and closing the tab discards it.

Why did Garmin Connect give me a .zip instead of a .fit?

Garmin Connect wraps the Export Original download in a ZIP archive. Unzip it and drop the .fit file inside onto the page.

Why is there no power chart for my ride?

A panel is only drawn for a channel that is actually present in the file. If the ride was recorded without a power meter paired, the FIT file contains no power records and no power panel is shown.

Should I export FIT, TCX or GPX?

FIT, whenever the choice is offered. It is the file your device recorded and keeps every channel, including power and any third-party developer fields. TCX drops what its XML schema has no element for, and GPX keeps little more than position, elevation and time.

FIT file viewer

Drop a .fit file onto ActivityMaxxer and every channel it contains becomes its own chart, stacked on one shared timeline. The file is parsed in your browser and never uploaded.

What is in a FIT file

FIT — Flexible and Interoperable Data Transfer — is the binary format the ANT+ ecosystem settled on and the one your watch or bike computer actually records to. Unlike TCX and GPX it is not text: opening one in a text editor shows nothing useful, which is why a viewer is the only practical way to look inside a file you have exported.

Internally a FIT file is a stream of typed messages rather than a list of points. Most of it is record messages — one per sample, typically one per second — each carrying whichever channels were connected at that instant: timestamp, position, distance, altitude, heart rate, cadence, speed, power, temperature. Around those sit lap and session messages holding the summary figures your watch showed you, and optional developer fields, which is how third-party sensors such as running power pods record their own metrics into the same file.

This is why FIT is the format to keep when you have a choice. It is the richest of the three: a TCX export of the same activity drops anything Garmin's XML schema has no element for, and a GPX export keeps essentially only position, elevation and time.

Which fields get charted

ActivityMaxxer reads the record messages and builds one panel per channel it finds — pace or speed, heart rate, cadence, power, and elevation. Panels appear only for data that is genuinely present, so a ride recorded without a power meter shows no power chart rather than a flat line at zero. Running activities are charted as pace in minutes per kilometre; rides and generic tracks are charted as speed. Each panel can carry its own average, minimum and maximum reference lines, and the whole stack shares one x-axis that switches between elapsed time and distance.

Pauses are detected rather than averaged over, so a stop at a traffic light does not drag your average pace down, and the reported average matches what your watch told you.

Exporting a .fit file from your device

These are the current export paths for the three most common ecosystems.

Garmin

Use Garmin Connect on the web — the mobile app has no export option. Open the activity, click the gear icon at the top right of the activity page, and choose Export Original. That downloads a ZIP archive containing the .fit file, not the .fit file itself, so unzip it before dropping it here. The same menu offers Export to TCX and Export to GPX if you want one of the text formats instead.

COROS

In the COROS app, open the activity from the Activities list, tap the three dots at the top right, choose Export Data, and pick .FIT. The app then hands the file to the usual share sheet, so AirDrop or email it to wherever you want to open it.

Wahoo

Two options. In the Wahoo app, the three-dot menu on an activity card leads to Sharing, which sends the .fit to a connected third-party service. To get the raw file directly, connect an ELEMNT, BOLT or ROAM to a computer over USB — it mounts as an external drive — and copy the file you want out of its Activities folder.

On a phone

A .fit file is awkward to reach from a phone's file picker even when it is technically on the device. If you use intervals.icu, connecting it here is usually faster: your browser fetches the original uploaded file from intervals.icu directly, and the chart comes up without a download step.

Questions

Is my FIT file uploaded to a server?: No. The file is read and parsed by JavaScript running in your own browser tab. It is never transmitted, there is no account, and closing the tab discards it.
Why did Garmin Connect give me a .zip instead of a .fit?: Garmin Connect wraps the Export Original download in a ZIP archive. Unzip it and drop the .fit file inside onto the page.
Why is there no power chart for my ride?: A panel is only drawn for a channel that is actually present in the file. If the ride was recorded without a power meter paired, the FIT file contains no power records and no power panel is shown.
Should I export FIT, TCX or GPX?: FIT, whenever the choice is offered. It is the file your device recorded and keeps every channel, including power and any third-party developer fields. TCX drops what its XML schema has no element for, and GPX keeps little more than position, elevation and time.