HRV01
What is Apple Watch HRV? How it differs from heart rate
What the HRV figure on your Apple Watch actually represents, how it differs from heart rate, what SDNN means, and what to watch for when reading the number.
4 min readFeelmo Journal
What the numbers
actually mean.
Apple Watch HRV, heart rate and sleep, explained for anyone starting out — written to help you follow your own trend rather than judge a single value.
Start here
Begin wherever you like.
HRV02
Your HRV is low — four things to check first
How to read a low HRV reading on Apple Watch. Rather than judging by a single value, work through measurement conditions, your own baseline, sleep and exercise, and your symptoms.
5 min readApple Watch03
Sleep and heart rate on Apple Watch — from setup to the morning check
How to record sleep with Apple Watch and read sleep duration, sleep stages, heart rate and HRV on iPhone — from the initial setup to what to look at in the morning.
5 min readSleep04
Sleeping long but still tired — five things to look at besides duration
Why a long night can still leave you tired: how rested you feel, waking in the night, your body clock, daily habits, and the possibility of a sleep disorder.
6 min readHRV05
HRV and how you feel — reading the number without calling it your condition
How HRV relates to fatigue, stress and recovery, and how to read it alongside your own baseline, your sleep, your heart rate and your symptoms.
5 min readSleep06
How accurate is Apple Watch sleep tracking? What we found testing it against PSG
How far heart rate alone can go in estimating sleep stages, tested against clinical polysomnography. Stage estimation holds up; the nightly summary figures such as REM% do not.
6 min readHRV07
Can HRV identify you? What 202 public records showed, and what they did not
Using thirty HRV measures, we linked two windows from the same session among 202 people. The signal exceeded a random baseline, but it does not establish identity verification or performance across days. Aggregate results and an audit script are public.
7 min readHRV08
Are there sex differences in HRV? Why age, metric and measurement method change the answer
Sex differences in HRV depend on the metric — including SDNN and RMSSD — as well as age, recording length and device. Large studies and a public-data re-analysis show why group averages must not be used to judge an individual.
10 min read