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Your heart-rate variability through the night

Checked against an ECG chest strap, night by night
OPTICAL

Accuracy

93%

Overnight HRV Agreement

on a typical night, against an ECG chest strap

Reference standard

ECG chest strap

Sample size

9 participants

Night to night, the Ultrahuman Ring’s HRV lands within about four milliseconds of an ECG chest strap reading your heart’s electrical signal on a typical night.

-12-8-40+4+8+12Usual accuracy — a typical night±4.3Reliable range — 18 of 19 nights±10difference from the chest strap (milliseconds)0 = no difference
93%agreement with the chest strap
4.3 mson a typical night
18 of 19nights within 10 ms
0.96how closely the two move together
Figure 1
-30-20-100+10+20+3030507090110130upper limit of agreement (+16.5)lower limit of agreement (-12.2)average offset +2.2 ms (the ring reads high)the two devices averaged (milliseconds)ring minus chest strap (milliseconds)
Figure 2 — Every night, against the chest strap

Heart-rate variability is one of the most delicate things a ring measures. It is not a heart rate but the gap between one beat and the next, counted in thousandths of a second, so reading it from a finger means placing every individual beat rather than averaging a few seconds of them. It also varies enormously between people, and from one night to the next in the same person, so there is no typical value to fall back on.

Against an ECG chest strap, a typical night landed within 4.3 ms, and 18 of the 19 nights within 10 ms. On a scale where 1 is perfect, the two moved together at 0.96.

The second chart puts every night in the study on one plot, each dot a whole night, and the dots hold the same tight line from the lowest night to the highest rather than only agreeing in the middle of the range.

HRV is what Recovery is built on, so this sits underneath a large part of what your app tells you each morning.