Last updated: May 1, 2026
Four by Four (“the app”) is a workout coaching app for the Norwegian 4x4 interval protocol. Your privacy matters. This policy explains what data the app accesses, how it is stored, and what is shared (spoiler: nothing).
Heart Rate — Read from your Apple Watch during workouts via HealthKit. Used in real time to provide coaching cues and display your current heart rate zone.
Workout Duration & Phases — Timestamps for each interval and recovery period within a workout session. Used to display your workout summary and history.
Age — Entered during onboarding. Used solely to calculate your personalized heart rate training zones using the Karvonen formula. Stored locally on your device.
All workout data is stored locally on your device using AsyncStorage. Nothing is uploaded to a server.
Heart rate samples and completed workouts are written to Apple Health (HealthKit) on your device, with your permission. This data is governed by Apple's own privacy policies and is not accessible to us.
The app does not use any analytics, crash reporting, advertising, or tracking SDKs.
If you choose to connect Spotify for music during workouts, the Spotify app will handle playback on your device. Four by Four does not access your Spotify account data, listening history, or any other Spotify information.
We do not share, sell, or transmit any of your data to third parties. Period.
Deleting the app removes all locally stored data (workout history, age, preferences). Workout data written to Apple Health can be managed through the Health app on your iPhone.
The app is not directed at children under 13. We do not knowingly collect personal information from children.
If we update this policy, the revised version will be posted at this URL with an updated date. Continued use of the app after changes constitutes acceptance.
Questions about this privacy policy? Reach out at hello@fourbyfour.run.