How Accurate Is Apple Watch Ultra 2 on watchOS 26?

TL;DR

Apple Watch Ultra 2 delivered highly accurate wrist-based heart-rate tracking with the watchOS 26 public beta, closely matching a Polar H10 ECG chest strap during indoor cycling, running, and outdoor cycling. Correlations ranged from 0.99 to a rounded 1.00, although one run had heart-rate data missing for roughly its first half and several sessions contained small deviations.

Transcript

Over the last few weeks, I've been testing out the Apple Watch Ultra 2 with the beta version of Watch OS 26 to see if the Apple Watch Ultra 2 is still one of the best smart watches out there to track your health and your sports. And of course, that also includes testing out a workout body. Basically, a coach that guides you through your different w... Read More

Key Insights

• The Apple Watch Ultra 2 achieved a rounded heart-rate correlation of 1.00 during indoor cycling when compared with the Polar H10 ECG chest strap. Across three interval spinning sessions, its measurements almost perfectly overlapped the reference, with only minor early or isolated deviations.
• The Polar H10 ECG chest strap served as the heart-rate reference because it measures the heart's electrical activity. The analysis plotted reference measurements on the horizontal axis and Apple Watch measurements on the vertical axis, with proximity to the blue agreement line indicating better correspondence.
• Running heart-rate tracking produced a correlation of 0.99 against the chest strap. When measurements were available, accuracy remained strong enough that the reviewer said decisions about running pace would not have changed between the Apple Watch data and the ECG reference.
• One running session contained missing Apple Watch heart-rate data for approximately its first half in the exported results. The reviewer could not determine whether the watch had not been activated, the data had been lost, or the device had failed to detect heart rate.
• Outdoor cycling heart-rate tracking achieved a 0.99 correlation despite conditions that generally make wrist measurement difficult, including bumpiness and arm tension. Across several individual rides, the Apple Watch line usually overlapped closely with the reference, although some details and isolated sections were missed.
• A long outdoor ride of about 126 kilometers and 1.5 thousand height meters still showed generally strong agreement between the Apple Watch Ultra 2 and the chest strap. Some details were absent, but the red Apple Watch trace largely followed the blue-green reference trace.
• The Apple Watch Ultra 2 remained among the top-performing devices in the reviewer's comparative heart-rate charts. Its watchOS 26 public beta results were similar to earlier tests of the Ultra 2, Ultra 1, Series 9, and another Ultra 2 unit.
• The watchOS 26 testing used a public beta rather than the final software release. The reviewer described it as likely close to the final version, but the reported conclusions specifically reflect beta testing and the individual sessions presented in the supplied transcript.

Questions & Answers

Q: How accurate is Apple Watch Ultra 2 heart-rate tracking on watchOS 26?

Apple Watch Ultra 2 heart-rate tracking was highly accurate in the presented watchOS 26 public beta tests. Compared with a Polar H10 ECG chest strap, it achieved a rounded correlation of 1.00 for indoor cycling and 0.99 for both running and outdoor cycling. Most measurements appeared on or very close to the agreement line, although isolated deviations and one incomplete running record occurred.

Q: How was Apple Watch Ultra 2 heart-rate accuracy tested?

The reviewer compared Apple Watch Ultra 2 measurements with data from a Polar H10 ECG chest strap, which measures the heart's electrical activity. Reference measurements were placed on the horizontal axis and Apple Watch measurements on the vertical axis. Points closer to the blue agreement line indicated stronger correspondence, while individual session traces were inspected separately to reveal deviations or missing data.

Q: Is Apple Watch Ultra 2 accurate for indoor cycling?

Apple Watch Ultra 2 performed exceptionally well during indoor cycling, reaching a rounded correlation of 1.00 against the Polar H10 reference. Across three interval spinning sessions, the Apple Watch trace overlapped the chest-strap trace almost perfectly for most of each workout. Only slight deviations appeared near the beginning of one session and at a few isolated points, which the reviewer considered insignificant.

Q: Is Apple Watch Ultra 2 accurate for running?

Apple Watch Ultra 2 produced a 0.99 correlation with the Polar H10 during running. One interval run showed a few modest deviations, including readings that were slightly too high or slightly too low. Overall, the reviewer considered the performance sufficiently accurate that choices about running pace would have remained the same whether based on the watch or the ECG chest strap.

Q: Why was heart-rate data missing from one Apple Watch run?

The precise reason was not established. In the exported data, Apple Watch heart-rate measurements were absent for approximately the first half of one run. The reviewer identified several possibilities: the workout might not have been activated, automatically recorded heart-rate data might have been shown instead, the measurements might have been lost during export, or the watch might have failed to detect heart rate.

Q: How accurate is Apple Watch Ultra 2 for outdoor cycling?

Apple Watch Ultra 2 achieved a 0.99 correlation with the Polar H10 during outdoor cycling, an activity described as difficult for wrist trackers because of bumpiness and tension on the arms. Individual ride traces generally showed close overlap with the reference. There were small deviations and missed details in some sections, but the overall agreement remained very strong across the presented sessions.

Q: Did Apple Watch Ultra 2 remain accurate on a long bike ride?

The watch remained generally accurate during a ride of about 126 kilometers with 1.5 thousand height meters. Its heart-rate trace usually overlapped well with the Polar H10 reference throughout the session. Although some details appeared to be missed, the overall agreement was described as almost perfect, supporting the broader 0.99 outdoor-cycling correlation reported across the tested rides.

Q: Does watchOS 26 improve Apple Watch Ultra 2 heart-rate tracking?

The presented results do not establish a meaningful improvement over earlier software or hardware tests. Apple Watch Ultra 2 on the watchOS 26 public beta performed among the best devices, but its results were approximately the same as the reviewer's previous Ultra 2 testing and similar to results for the Ultra 1 and another Ultra 2 unit. Performance remained excellent and consistent rather than clearly improved.

Summary & Key Takeaways

• The reviewer systematically compared Apple Watch Ultra 2 heart-rate measurements from the watchOS 26 public beta against a Polar H10 ECG chest strap. Across indoor cycling, running, and outdoor cycling, plotted measurements generally remained on or close to the agreement line, producing correlations between 0.99 and a rounded value of 1.00.

• Indoor cycling produced the strongest presented result, with a rounded correlation of 1.00 and near-perfect overlap during three interval spinning sessions. Running remained highly accurate at 0.99, but one exported session lacked data for roughly its first half, and another interval run showed several modest overestimations and underestimations.

• Outdoor cycling also achieved a 0.99 correlation despite bumpiness and tension on the arms. Individual sessions showed strong agreement, including a ride of about 126 kilometers with 1.5 thousand height meters. Comparisons with previous Apple Watch tests indicated consistently strong heart-rate performance across different Apple Watch models and testing periods.