What is FLUX?
FLUX is an iOS running app that syncs your music's BPM to your live heart rate in real time, based on your personal physiological profile. Instead of a static playlist, the right track from your own library plays automatically, matched to your effort.
Do I need a watch or heart-rate sensor?
Not necessarily — FLUX works both ways, and you choose. With a Bluetooth heart-rate sensor, FLUX syncs to your live heart rate and your personal training zones. Without one, it syncs to your cadence — your phone counts your steps per minute and matches the music's BPM to your stride. Same real-time sync, no extra gear. Have a sensor but still want to run by cadence? That works too.
Which watches and sensors work with FLUX?
Bluetooth heart-rate devices: chest straps (Polar, Wahoo, COROS, Garmin HRM), plus Garmin, Polar, COROS and WHOOP watches in "broadcast heart rate" mode. Chest straps are the most reliable. Apple Watch is a special case — iOS only syncs its heart rate to your iPhone every so often, so it lags behind your effort. Run on cadence instead, or put a heart-rate broadcast app on the watch and pair it like any Bluetooth sensor. Fitbit and Samsung Galaxy Watch don't broadcast to third-party apps at all.
Do I need Apple Music?
Yes — FLUX plays from your own Apple Music library, so an active Apple Music subscription is required.
Is my data private — especially my heart rate?
Yes. Health data from Apple Health is used only to power app features. We never use it for advertising and never sell it. See our
Privacy Policy for details.
What is a Sync Score?
A score for how closely your body stayed in sync with the music during your run. It turns an abstract metric into something you can chase — and share.
How much does it cost?
FLUX is free to download and free to use. You will need an active Apple Music subscription, since FLUX plays from your own library.
When will FLUX be on the App Store?