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Your heart rate on the bike

Stationary bike and cycle ergometer
OPTICAL

Accuracy

90.5%

Indoor Cycling Heart Rate Agreement

compared with an ECG chest strap through the same ride

Reference standard

ECG chest strap

Sample size

85 participants

On an indoor bike the Ultrahuman Ring stays within ten beats a minute of an ECG chest strap, on average.

Ultrahuman RingECG chest strapbeats per minute
90.5%agreement with the chest strap
9.9 bpmaverage difference
57%of readings inside the ±5 bpm / 10% tolerance
75–180beats per minute the reference covered in study
Figure 1 — One continuous stretch from a single recording. The figures beside it are for the study as a whole, not for the stretch drawn.
-20-100+10+20+308090100110120130140150160170180190upper limit of agreement (+27.2)lower limit of agreement (-9.5)average offset +8.9 bpmthe two devices averaged (beats per minute)ring minus chest strap (beats per minute)
Figure 2 — Every five seconds, against the chest strap
One dot is one paired five-second reading, as recorded, pooled across recordings.

Indoor cycling produces the combination that catches sensors out: your heart rate climbing towards maximum while your hands barely move at all. A great deal of what a heart rate algorithm knows about how hard you are working comes from movement, and on a stationary bike that clue is simply absent. A sustained grip on the bars adds to it: the forearm stays tense above a sensor that is reading downstream of it, so the pulse arriving at the fingertip grows quieter as the effort grows harder.

The trace below is a long, stepped climb in effort, from an easy spin up towards the point where the rider stops. The Ultrahuman Ring reproduces every stage of the ramp, turning each corner at the same moment as the reference and carrying the same offset from the bottom of it to the top.

The figure covers the whole ramp, from an easy spin up to 180 beats a minute. Where the two devices differ, where each of them sits accounts for much of it: on a bike the hand is still and warm against the bars, while the reference reads through a strap pressed to a chest that is moving and sweating under it.