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No. Open the app, allow location access, pick an activity type and tap Start recording. Recording, the trail network, energy estimates and Apple Health all work without signing up. An optional account will come with private sharing with friends and family, which is on its way.

Allow location access While Using the App and keep Precise Location on. A recording started in the app carries on when you lock the screen or switch apps, so Cardio Trails never needs “Always” access. Outside a recording, it reads your location only while it is on screen.

Yes. The recording in progress is saved every few seconds. If iOS, a force-quit or a flat battery interrupts it, Cardio Trails offers it back for saving the next time you open the app.

On the finish screen, tap Resume to continue the same activity instead of saving it. The time you were stopped is never bridged by an invented line on the map.

Cardio Trails runs on iPhone and iPad with iOS 18 or later. Reading heart rate from AirPods Pro during a recording needs iOS 26 or later.

As a grade — 100 × rise ÷ run, the number on road signs, not degrees. Each colored stretch is judged over a centered 60-meter window with a robust fit that sets altitude outliers aside, so the same hill reads the same whether you walked or ran it, up or down. Teal is flat, yellow about 5%, orange about 10% and purple 20% or more.

Gray means the slope couldn’t be trusted there: the GPS elevation was poor, there was too little route around that point, or the recording had a gap. While you record, the newest few meters also stay gray until there is enough route ahead to judge them.

Recordings that stay within the corridor width are treated as the same trail. Narrow it in Settings → Trail network → Corridor width, or split the segment by hand in edit mode.

Yes. On Explore, open the trail-network menu and choose Edit. You can move, add, merge, split, join and delete points and segments, with undo and redo. A double tap on a segment opens its sheet, where you set its soil type, vegetation, difficulty and notes.

Note that Rebuild trail network in Settings starts over from your recordings and drops hand edits.

Three ways, side by side: from the route (speed, slope, the ground of each segment, your weight that day and your gear), from each heart-rate sensor that read during the outing, and a mix that takes heart rate wherever a sensor read densely and the route elsewhere. Noting a segment’s soil or a watch syncing late updates past estimates.

Go to Settings → Apple Health integration and choose how many workouts to import. Outdoor workouts of the activity types Cardio Trails records come in with their routes and join your trail network. Importing again refreshes routes and drops workouts that turn out to be indoor.

Turn on Save to Apple Health in Settings → Apple Health integration. Activities are saved as workouts with their GPS routes and active energy, and saved again when the estimate changes. If routes don’t appear, tap Update Health permissions.

AirPods Pro: on iOS 26 and later, turn on Read AirPods Pro while recording in Settings → Body and gear. They give live estimates while you record. Apple Watch and any other wearable that saves heart rate to Apple Health also work: their readings reach Cardio Trails through Apple Health, so the heart-rate estimate comes at the end of the activity — and is updated if the device syncs later.

On your iPhone. If you use iCloud, they are also saved to your iCloud account and available on your other devices; and they are saved to Apple Health if you turn on the Apple Health integration. Your GPS location, heart rate and recordings are not shared with us or anyone else, unless you explicitly share them with friends or family (coming soon). Read the privacy policy for the details.

Only anonymous usage statistics that help us improve the app — which screens and features are used, and where errors happen. Never your GPS location, routes, place names or health data. The privacy policy lists exactly what is sent.