An HRV reference starts with the method
Age and sex influence study comparisons, but so do recording duration and conditions. A short watch reading, a five-minute test and a 24-hour recording should not share one universal grading table.
| Check | What it describes | Why it matters |
|---|---|---|
| SDNN | Standard deviation of normal beat intervals | The HRV metric used by Apple Health. |
| RMSSD | Successive differences between beat intervals | A different statistic; not interchangeable with SDNN. |
| Recording duration | Short sample, five minutes or 24 hours | Reference values depend on the measurement protocol. |
| Personal history | Repeated readings under comparable conditions | Useful context for interpreting a change. |
This page does not assign a good/bad threshold or exact percentile to every age. A reference needs the same statistic, duration and relevant population. A high HRV value alone does not establish health or readiness to train.
Apple HealthKit · heartRateVariabilitySDNN ↗Check what Apple Health actually recorded
Open Heart Rate Variability in Apple Health and inspect the dates and sources. Do not assume that a score called recovery in another app uses the same underlying statistic.
For a comparison in telo, request the available daily metric and its coverage. A daily summary is not a continuous beat-by-beat recording. Keep periods and sources consistent, and state when the original recording conditions are unavailable.
Compare the baseline before giving it a label
Start with two complete periods and show the days that contributed to each mean. If one period has many more gaps, the difference may not represent the same recording pattern. Do not fill missing days with zero.
If you also examine sleep or workouts, describe the timing without declaring a cause. A change in a short HRV series is a question to investigate, not a diagnosis or an automatic instruction to train harder or rest.
A comparison you can check
Two complete weeks. The same metric. Count the recorded days before interpreting the average.
| Period | Mean | Days recorded | Missing days |
|---|---|---|---|
| Week 1 | 40 | 6/7 | 1 |
| Week 2 | 46 | 6/7 | 1 |
The fictional daily SDNN averages move from 40 to 46 ms, with six recorded days in each week. That is a 6 ms difference. It is not a switch from a bad score to a good one, and the example does not predict recovery.
Now ask about your own history
Connect telo to your assistant, then copy this question. Ask it to show the records behind the answer so you can check the dates, units and gaps.
Use telo to compare my Apple Health HRV (SDNN, ms) across the last two complete 14-day periods. Show dates, daily values, means, days with data and gaps. Do not compare it directly with RMSSD, fill missing days or infer a diagnosis or training readiness. State which recording context is unavailable.Free covers the last 7 days. Comparisons with older history need Pro and the available records synced from your iPhone.
With your permission, telo syncs Apple Health records to its service. Records requested in a conversation are also processed by your chosen AI service.
Common questions
Is 40 ms a good HRV?
The number alone is insufficient. Check whether it is SDNN or another statistic, how long it was recorded and how it compares with repeated measurements under similar conditions.
Can I compare Apple Health HRV with another watch?
First check the statistic, measurement window and aggregation method. The same unit in milliseconds does not mean the two numbers measure exactly the same thing.
Can telo tell me why my HRV fell?
It can make the available history accessible to your assistant. A comparison can show changes and gaps; it cannot establish a medical cause from those records alone.
Sources and method
Prepared by the telo team with AI assistance using the sources linked here. The reference tables describe their cited populations and methods. Examples are synthetic and their averages are computed from the downloadable records. This is educational material, not an individual assessment or a clinical review.