Full Breakdown
Apple Watch Series 12 Heart-Rate Sensor Tested Against Clinical Chest Strap
By Drooid · · How we work
Core Findings from Independent Review
Rob ter Horst of The Quantified Scientist evaluated the Apple Watch Series 12’s newly redesigned heart-rate sensor by comparing its readings to a Polar H10 ECG chest strap during indoor cycling, running, and weightlifting. The sensor recorded heart rate every five seconds, even when the wearer was inactive. In indoor cycling the two devices produced a near-perfect correlation of 1.0. During a running session the correlation was 0.98, with minor deviations observed at higher heart-rate ranges. Weightlifting, traditionally challenging for wrist-based sensors, yielded a correlation of 0.97, which ter Horst described as “quite good” and placed the Series 12 above 85 % of devices he has tested for that activity. A separate step-count test involved manually counting roughly 5,000 steps; the watch’s count was essentially accurate, with only a slight tendency to over-count.
Testing Methodology
The review employed side-by-side measurements on the Apple Watch Series 12 and the Polar H10 chest strap. Each activity—indoor cycling on a stationary bike, a typical outdoor run, and a weight-lifting circuit—was performed while both devices recorded continuously. After each session ter Horst calculated Pearson correlation coefficients to quantify agreement. For the step-count assessment, he walked a predetermined route, manually tallying steps and then comparing the total to the watch’s recorded count.
Comparison to Prior Generation
When contrasted with the Apple Watch Series 11, the Series 12 showed broadly similar overall accuracy. The earlier model performed marginally better during running in ter Horst’s tests, suggesting that Apple may still be refining the new sensor’s algorithms.
Implications for Users
The high correlations indicate that the Series 12 can deliver reliable heart-rate data across a range of common workouts, including the more demanding weight-lifting scenario. Continuous five-second sampling may also provide users with finer-grained insight into heart-rate fluctuations during everyday activities such as grocery trips or brief stress episodes.
Limitations and Outlook
Minor discrepancies at elevated heart rates and the slightly lower performance relative to the Series 11 during running point to ongoing algorithmic adjustments. Apple has not issued an official comment on these findings, and further independent testing will be needed to confirm long-term accuracy across diverse user populations.