Heart Rate Variability (HRV)
Average RR-interval variability (RMSSD) during sleep, in milliseconds.
Detailed Description
HRV — heart rate variability — is the variation in the intervals between consecutive heartbeats. A pulse of 60 doesn't mean one beat exactly every second: the gaps drift slightly all the time, and that drift is HRV. It's measured in milliseconds, most often via RMSSD.
What it reflects. The variation is set by autonomic balance: the parasympathetic branch ("rest and digest") widens it, the sympathetic branch ("fight or flight") suppresses it. So high HRV usually means the body has recovered and is ready for load, while a drop means it's under load: stress, short sleep, illness, alcohol, or overtraining.
What counts as normal. The spread between people is huge: 20–100+ ms can all be healthy. HRV falls markedly with age and runs notably higher in endurance-trained people. Comparing your number to someone else's is close to meaningless — only your own baseline and deviations from it carry information. A 15%+ drop below your norm across several days signals that recovery isn't keeping up with load.
Why it's measured at night. During the day everything moves HRV: posture, speech, coffee, breathing, movement. Rings and watches (Oura, Whoop, Garmin) measure it during sleep when that interference is minimal, which makes night-to-night numbers comparable. Side effect: a nightly RMSSD can't be compared against a morning reading from a breathing app — different measurement conditions.
HRV (RMSSD) reference ranges by age
| Age | Typical RMSSD | Note |
|---|---|---|
| 20–29 | 40–70 ms | peak values; men typically higher than women |
| 30–39 | 35–60 ms | gradual decline |
| 40–49 | 30–50 ms | sex differences start to flatten |
| 50–59 | 25–40 ms | the sharpest age-related drop |
| 60+ | 20–35 ms | low values here are an age norm |
Approximate ranges from population data on short (5-min) recordings; individual variation overlaps these bands, and nightly ring values differ from a 5-minute resting measurement. Use the table as context, not as a diagnosis.
How to Improve
- Diaphragmatic breathing before bed (5 min)
- Regular aerobic exercise
- Limit alcohol intake
- Cold exposure (cold showers)
Frequently asked questions
What is HRV in simple terms?
It's how uneven the gaps between heartbeats are. At a pulse of 60 the heart doesn't beat exactly once per second — the gaps drift slightly, and the more they drift the higher your HRV. Counterintuitively, more variation is better: it means the nervous system is adapting flexibly.
What is a normal HRV?
Anything from 20 to 100+ ms can be a healthy norm — the spread between people is enormous. HRV declines sharply with age and runs higher in endurance athletes. The only meaningful reference point is your own two-week average.
Why is my HRV low or dropping?
Most often: alcohol the night before, short sleep, a hard workout, an oncoming illness, acute stress, or dehydration. Alcohol has the most predictable effect — HRV drops the same night. A single low morning means nothing; look at 3–7 days in a row.
How do I increase my HRV?
The same things that improve recovery overall: regular aerobic exercise (effect over 6–12 weeks), a consistent sleep schedule, less alcohol, and slow diaphragmatic breathing at around 6 breaths per minute for 5–10 minutes a day. There's no quick way to game the number.
Why does HRV in my ring differ from a breathing app?
Because the measurement conditions differ. A ring measures HRV during sleep, free from the influence of posture, coffee, and movement. A morning app reading is 1–5 minutes while awake. The numbers aren't directly comparable — compare each source only against itself.