How to Open and Analyze a FIT File on iPhone

What's actually inside a FIT file?

FIT (Flexible and Interoperable Data Transfer) is Garmin/ANT+'s compact binary format, produced by most sport watches and bike computers when they record – Garmin, Wahoo, Coros, Suunto, Hammerhead and others. Unlike GPX, it stores power, heart rate, cadence and elevation as a time series alongside GPS, usually once per second. That makes it the most accurate source for metrics like Normalized Power or time-in-zone – but also a pure raw-data format that no ordinary text editor or photo viewer can open.

Step 1: get the file onto your iPhone

The file usually starts out in your device maker's cloud. Export normally happens through the web portal, not the phone app: on Strava via "···" → "Export Original", on Garmin Connect via the gear icon → "Export Original". From a Mac you can also AirDrop it, or it arrives as an email attachment – either way it ends up in the iPhone Files app or directly in the share sheet.

Option 1: an online viewer in the browser

The fastest route without installing anything: upload the file in Safari to one of the common online FIT viewer sites, which render it as a table, chart or map. Handy for a quick one-off look – but technically "upload" means exactly that: your heart-rate trace and the GPS route of your regular loop leave the device and briefly sit on someone else's server. Fine for a one-time curiosity check, not something everyone wants for routine training data.

Option 2: an app that reads it on-device

The alternative is an app that accepts FIT files via "Share" or "Open in…" and processes them entirely locally – the file never leaves the iPhone. That's exactly what Endurance Debrief does: instead of a raw data table, you get a finished analysis right away – zone distribution, Normalized Power, IF, TSS, aerobic decoupling and a short coach note, all calculated within seconds of import.

Three steps

1. Get the file: export it from your device maker's web portal, or AirDrop/email it to your iPhone.
2. Tap or "Share": tap the .fit file in the Files app, or choose "Share" from another app.
3. Pick the app: choose "Endurance Debrief" from the list – the analysis opens automatically, no upload involved.

Catching up on a backlog of sessions? Select several files at once (batch import) or, even simpler, turn on Apple Health import so new workouts come in automatically as soon as they land in Health.