How to read your Apple Watch HRV

Apple Watch records HRV automatically and stores it in Apple Health. Here is which HRV that is, why it differs from ring numbers, and how ONDA uses it.

What Apple Watch shows

Apple Health stores HRV as SDNN — the standard deviation of the intervals between normal heartbeats — recorded automatically by Apple Watch.

Recent Apple Watch models on watchOS also show two variants, Recovery HRV and Overall HRV. Apple has not stated how Recovery HRV is computed.

SDNN and RMSSD are different measures, so an Apple Watch number cannot be compared directly with RMSSD from WHOOP or a ring.

HRV type: SDNN (Apple Health).

Sources

How to read it

Compare a night with your own usual range over the last weeks, not with another person or another device. A single low night is most often a reaction to something specific — a short night, alcohol, an infection, stress or hard training. Several days below your range together with a higher resting heart rate and feeling unwell are a reason to rest.

Scores such as Readiness, Recovery, Nightly Recharge or HRV Status are each maker’s own algorithm. Two devices on the same night can show different HRV numbers because they measure at different times and with different formulas; neither is “wrong”.

Can Apple Watch connect to ONDA?

Works with the ONDA app now

Apple Watch has no web API: its data stays in Apple Health on your iPhone. The ONDA iOS app reads it there, with your permission.

Through Apple Health

Yes. The ONDA app reads Apple Watch HRV from Apple Health to build your own nightly baseline (mean ± SD over your recent nights, never a population norm), and Apple Watch supplies live pulse during practice. Live breathing biofeedback needs Apple Watch; without it, ONDA measures your pulse with the iPhone camera.

Questions

Why is my Apple Watch HRV lower than my ring’s?

Apple Health stores SDNN; most rings report RMSSD, and devices measure over different windows. The numbers are not on the same scale.

Does ONDA read my Apple Watch HRV?

Yes, from Apple Health with your permission, to compare each night with your own baseline. It describes your numbers and does not diagnose anything.

When a number is not the point

No HRV reading can tell you whether symptoms are serious. Whatever your device shows, call emergency services or get emergency care for: chest pain or pressure; fainting or near-fainting; severe shortness of breath; fast, strong or irregular heartbeat that does not settle at rest (including with dizziness); sudden confusion, weakness on one side, trouble speaking. This page is not medical advice and does not diagnose anything.

Apple Watch is a trademark of its owner. ONDA is not affiliated with or endorsed by Apple Watch. Other devices