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Your heart rate through a treadmill run

6 km/h building to 9 km/h
OPTICAL

Accuracy

91.5%

Indoor Running Heart Rate Agreement

with an ECG chest strap reading the same treadmill run

Reference standard

ECG chest strap

Sample size

43 participants

Through a treadmill run building to a faster pace, the Ultrahuman Ring stays within eleven beats a minute of an ECG chest strap, on average.

Ultrahuman RingECG chest strapbeats per minute
91.5%agreement with the chest strap
10.8 bpmaverage difference
60%of readings inside the ±5 bpm / 10% tolerance
91–177beats 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.
-40-200+20+4090100110120130140150160170180190upper limit of agreement (+29)lower limit of agreement (-12.7)average offset +8.2 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.

Your arm swings at close to your stride rate, which falls in the same frequency band as the pulse itself, so the sensor has to tell a heartbeat apart from a footfall. The hand also travels through a wider arc than the wrist at the same cadence, so a ring meets more of that movement than a device worn further up the arm. At the same time blood is being pushed out to the working muscles and away from the skin, which quietens the very signal it is reading.

The two traces follow the same broad changes in heart rate, rising together as the effort increases. The Ring generally reads marginally higher than the ECG chest strap, with the difference becoming more noticeable during the larger rise in heart rate.

As effort increases, the body prioritises blood flow to the working muscles, which can reduce blood flow through the small vessels near the skin and make the pulse at the fingertip harder to detect. Above roughly 150 beats a minute, that weaker signal is combined with more movement from each arm swing. The ECG chest strap measures the heart's electrical activity instead, so it is not affected by reduced fingertip blood flow in the same way.