Children’s HRV runs well above adult values and starts falling in the teens. In a 5-minute resting ECG ECG A recording of the heart's electrical activity, taken with electrodes on the skin. ECG-based RR intervals are the reference standard for measuring HRV. More about ECG study of 377 Finnish children aged 6 to 9, RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD averaged 70 ms in boys and 66 ms in girls, with a wide spread. In a 24-hour study across nine decades, RMSSD averaged 53 ms at ages 10 to 19 and 43 ms at 20 to 29.
What the studies measured
Ages 6 to 9, resting ECG. The PANIC study in Kuopio, Finland, recorded a 5-minute 12-lead ECG in 377 children lying down after 10 minutes of rest, and analysed it with standard software after correcting bad beats. Table 1 of Veijalainen and colleagues (2019) gives the means:
| Measure | Boys (n = 185) | Girls (n = 192) |
|---|---|---|
| RMSSD | 70.2 ms (SD 43.2) | 65.5 ms (SD 39.3) |
| SDNN SDNN The standard deviation of all NN intervals in a recording, in milliseconds. It measures overall variability, and its value depends strongly on how long the recording lasts. More about SDNN | 62.0 ms (SD 28.8) | 58.5 ms (SD 27.9) |
The differences between boys and girls were not significant. An earlier paper from the same study, Seppälä and colleagues (2014), set reference percentiles for 465 children aged 6 to 8 and concluded that the same values can be used for both sexes.
Notice the spread. A standard deviation of 43 ms around a mean of 70 ms means children two years apart in the same class can differ by a factor of two or three, all of them well.
Ages 6 to 13, the role of heart rate. Gąsior and colleagues (2018) recorded 5-minute supine ECGs in 312 schoolchildren aged 6 to 13 and found that heart rate was the main predictor of every standard HRV measure. By quarter of resting heart rate Resting heart rate How many times your heart beats per minute while you are fully at rest. For adults it is usually 60 to 100 beats per minute, and lower in well-trained athletes. More about Resting heart rate , the median RMSSD was 86 ms in the slowest quarter (55 to 78 beats a minute) and 33 ms in the fastest (over 92), with SDNN 75 ms and 35 ms. After correcting for heart rate, the values no longer differed by sex and depended only weakly on age. So a child with a quick resting pulse will show a lower HRV for the same nervous system, which is worth remembering before reading any single number. HRV vs resting heart rate explains the link.
Ages 10 and up, 24 hours. Umetani and colleagues (1998) fitted 260 healthy people aged 10 to 99 with a 24-hour Holter monitor. Their Table 2 gives, for 24-hour RMSSD, 53 ms (SD 17) at ages 10 to 19, 43 ms (SD 19) at 20 to 29 and 35 ms (SD 11) at 30 to 39, with 24-hour SDNN at 176, 153 and 143 ms. The decline was fastest in the measures that track the parasympathetic Parasympathetic nervous system The "rest and digest" branch of the autonomic nervous system. It slows the heart, mainly through the vagus nerve, and drives most of the beat-to-beat variation in HRV. More about Parasympathetic nervous system branch, and it slowed after 60. Can HRV improve after 60 continues the story at the other end of life.
See a child’s number on the line
Where does my number sit?
Published reference data, not a diagnosis
60 ms is within the usual range for boys aged 6–9 (about two thirds sit between 27 and 113 ms).
If this number comes from a ring or watch, treat it as a rough guide: the reference values come from ECG recordings taken awake at rest.
Group: boys aged 6–9. 5-minute resting 12-lead ECG, lying down, after 10 minutes of rest; beats corrected in Kubios. Source: Associations of physical activity, sedentary time, and cardiorespiratory fitness with heart rate variability in 6- to 9-year-old children: the PANIC study (European Journal of Applied Physiology 2019).
Position is not health: many well people sit in the lower quarter of any group. What moves HRV explains the day-to-day causes.
The controls work when JavaScript is on.
A horizontal line from 0 to 140 ms with a shaded span for the middle half of the reference group and a marker for the reader's number. Controls set the number, the statistic (RMSSD or SDNN), where the number comes from, age and sex. 60 ms is within the usual range for boys aged 6–9 (about two thirds sit between 27 and 113 ms). Source: Associations of physical activity, sedentary time, and cardiorespiratory fitness with heart rate variability in 6- to 9-year-old children: the PANIC study, European Journal of Applied Physiology 2019.
The line uses the PANIC rows for ages 6 to 9 and the 24-hour rows for ages 10 to 19 (choose a 24-hour recording in the HRV checker for those). There is no short-recording reference for ages 10 to 17 in the site’s data yet, so the checker says so rather than comparing a teenager with adults. Every row and its source is on the reference data page.
What this means for a wearable on a child
The reference numbers come from ECGs in clinics with the child lying still. Rings and watches estimate beats from the pulse, overnight or in short samples, and the validation studies behind them were done in adults. A wearable on a child or teenager will give a number, and that number can be tracked against itself over weeks, but it cannot be set against the tables above. Comparing your HRV to norms lists the checks that apply at any age.
When to talk to a doctor
HRV from a wearable cannot diagnose anything in a child. Talk to a doctor if a child has fainting, chest pain, breathlessness, a racing or irregular heartbeat, or unusual tiredness, whatever any device shows.