SlowpulseHeart rate variability is the variation in time between consecutive heartbeats. People usually arrive at the question wanting a threshold: a figure to sit above, and to worry beneath. That figure does not exist, and the reason it doesn't is more useful than the number would have been.
The published range is enormous
The most-cited attempt to establish normal values pooled 44 studies covering 21,438 healthy adults. Among those healthy people, SDNN — one of the standard measures — ranged from 32 ms to 93 ms, and RMSSD from 19 ms to 75 ms.
That is a three- to four-fold spread across people with nothing wrong with them. Two readers of this page could differ by a factor of three and both be entirely ordinary. An average drawn across a range that wide describes nobody in particular.
Why the spread is so wide
Some of it is real variation between people. A lot of it is that HRV is unusually sensitive to how it was measured:
- Which metric. SDNN and RMSSD are different calculations and are not interchangeable.
- How long the recording ran. A sixty-second reading and a full night produce different numbers from the same heart.
- Posture. Lying down, sitting and standing all read differently.
- Time of day. Overnight values are quieter and more comparable than afternoon ones.
- Breathing rate during the reading, which shifts the beat-to-beat interval directly.
- Age, fitness and genetics, none of which you can normalise away with a chart.
Change any one of those and the number moves. Compare across two studies that made different choices, and you are not comparing like with like — which is exactly how a “normal range” ends up three times wider than any individual's own variation.
What the number is actually for
HRV is not a score to rank yourself on. It is a signal that means something when it moves relative to your recent normal.
A reading of 45 ms is not good or bad. It is interesting if your own recent nights have run around 70 ms, and unremarkable if they have run around 45. The same figure carries opposite meanings for two different people, and there is no table that can resolve that for you.
This is why the question “what is a good HRV” quietly has no answer, while “is this normal for me” has a very good one — as long as something has been recording your normal.
What to do instead of looking up a threshold
- Wear your watch consistently, especially overnight, so the readings are comparable night to night.
- Look at the trend across weeks rather than any single reading.
- Read HRV alongside heart rate. The two moving together says more than either alone.
- Ignore comparisons with other people entirely. They are the least informative thing you can do with the number.
Sources
- Nunan, Sandercock & Brodie (2010) — systematic review of 44 studies, 21,438 adults
- American Heart Association, Target Heart Rates Chart
Related
Not a medical device. Does not diagnose, treat or monitor any condition.