How to export and edit a Polar FIT file

Polar Flow can trim the start and end of a training session, and it can export the session as a .fit file. Trim covers the common case. For anything else, like a section in the middle, a heart rate spike, a session that ended up in two parts, or the wrong sport, edit the file itself and upload the clean version.

What Polar Flow already does

If you only forgot to stop your watch, try this first:

Find the session in your Diary on the Polar Flow website.
Open the Edit menu in the training summary and choose Trim.
Drag the red handles to the new start and end, then click Trim and confirm.

You can undo a trim later, and the Polar Flow app has the same tool. Two limits matter here. Polar describes moving the start and end points only, not removing a stretch from the middle. And if your account is connected to another service, a trimmed session doesn't transfer there by itself: Polar says to export it and import it manually.

Step 1: export the file

This is on the Polar Flow website:

Open your Diary and click the session.
Open the Export drop-down at the top right of the page.
Choose FIT. Polar also offers TCX, CSV, and GPX, but FIT holds the route along with heart rate, cadence, and the rest. GPX holds only the route.

The file goes to your computer's Downloads folder. Polar also offers a zip package for slow connections or large files, and the editor opens a zip as it is.

From Strava: open the activity on the Strava website, three-dot menu, Export Original.

Step 2: fix it

Open the file in FIT File Editor. The route is on the map, with pace, heart rate, cadence, power, and elevation on the timeline underneath.

A section in the middle. A train ride, a wrong turn, a long stop where the GPS drifted. Drag across it and press Cut. Distance, time, and averages are recalculated, and the gap becomes a pause. See crop a FIT file.
The battery died, or you started a second session by mistake. Open the first file, press the plus button, and add the second. They join into one activity. The merge guide explains how the gap is handled.
Heart rate spikes. Select the stretch and cap, smooth, or fill it with the fix tool. The heart rate spike guide covers which to pick.
GPS drift. Smooth a jumpy stretch or drag a stray point back. See the GPS drift guide.
Data from a second device. Open the Polar file and add the other device's file. Power, cadence, heart rate, or GPS that the Polar file has none of is filled in over the time they overlap. What the Polar file already recorded stays as it was.
The wrong sport. Set any sport and sub-type in the details panel. See change the sport.
Wrong time. Shift the start time in the details panel with the time tool.

Press Export to save the edited .fit. The file stays in your browser the whole time.

Step 3: upload it

Delete the old copy on each platform first, then upload the edited file. Platforms reject a file that overlaps an activity they already have. The duplicate activity guide has the order for Strava and Garmin Connect.

Strava, Garmin Connect, TrainingPeaks: if Polar Flow syncs to one of these, delete the copy it sent, then upload the edited file on the platform's website.

Polar Flow: Polar's help describes importing routes as GPX or TCX, not recorded sessions, so plan on the original staying in Flow.

Worth knowing

Other tools may read the numbers differently. Polar notes that some services use the data as it is while others recalculate or filter it, so a session can look slightly different after an upload, even with no edits.
Keep the original. Hold on to the exported file until the edited one is in place everywhere you want it.