HRV: why you should compare yourself with yourself
Your watch measures something different from a hospital Holter monitor. How to read your number properly.
What it is
Your heart does not beat like a metronome. The time between beats changes slightly all the time, speeding up as you breathe in and slowing down as you breathe out. Heart rate variability (HRV) measures how much that interval varies, in milliseconds.
Higher variability usually means your nervous system is in "rest and recover" mode. Lower variability, compared with your usual level, often shows up with stress, poor sleep, alcohol, illness or hard training.
Why your watch and the hospital disagree
Most watches and rings estimate HRV from an optical sensor on the skin, usually at night, and report a measure called RMSSD. Hospital tests use an ECG, often over 24 hours with a Holter monitor, and commonly report a different measure, SDNN.
They are different measurements taken in different ways, so the numbers are not interchangeable. A wearable figure should never be compared with a clinical result, or with another brand's figure.
Why there is no single normal range
HRV varies a lot between people. Age, genetics, fitness, and even the device and the time of measurement all shift it. Two healthy people of the same age can have values 30 ms apart.
That is why the useful comparison is with yourself:
| Compared with your own 30-day average | What it usually means |
|---|---|
| Around your usual level | Normal day-to-day variation |
| Clearly lower for one or two days | A hard workout, a late night, alcohol or stress |
| Lower for a week or more | Worth looking at sleep, stress, training load or illness |
In HumanGens: Vitals shows today's HRV in large type with your 30-day average beneath it, and colours the reading against your personal baseline, not a population range.
What improves it
- Sleep: regular, sufficient sleep is the most consistent lever.
- Alcohol: even moderate drinking lowers overnight HRV for most people.
- Fitness: regular aerobic exercise raises HRV over weeks and months.
- Recovery: hard training lowers HRV for a day or two, which is expected; persistently low values suggest you need more rest.
- Slow breathing: a few minutes of slow, steady breathing raises HRV in the moment.
A falling trend is a prompt to look at your habits, not a diagnosis. If it comes with symptoms such as palpitations, chest pain or breathlessness, see your GP.
Sources
- Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Frontiers in Public Health. 2017;5:258.
- Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation. 1996;93(5):1043–1065.
This article is general information, not personal medical advice. Ranges and targets vary by lab and by person; talk to your GP or a qualified clinician about your own results.