A report published October 10, 2026, described one 30-minute hilly run in which Apple Watch Ultra 4 averaged 160 bpm, Garmin Fenix 9 Pro 159 bpm and chest-worn Frontier X2 158 bpm. The runner wore the watches simultaneously, one on each wrist, with Frontier X2 on the chest.
Three reported averages from one run
| Device | Average heart rate | Role in the test |
| Frontier X2 | 158 bpm | Chest-worn, ECG-capable electrical reference |
| Garmin Fenix 9 Pro | 159 bpm | Wrist-worn watch |
| Apple Watch Ultra 4 | 160 bpm | Wrist-worn watch |
The route was very hilly, with a long incline near the midpoint. The two watch averages were 1 bpm apart; Garmin’s average was 1 bpm above Frontier X2’s, and Apple’s was 2 bpm above it. Those are differences between session averages, not point-by-point agreement throughout the run.
What the setup tells us
Apple Watch Ultra 4 and Garmin Fenix 9 Pro supplied wrist-based optical readings. Frontier X2 was a chest-worn, ECG-capable electrical reference. The devices therefore used different measurement approaches, and the reported figures summarize one runner’s 30-minute session rather than repeated runs or multiple activities.
For this outing, the averages were close. A single session does not provide an overall accuracy ranking between the two watches.
Apple’s separate study used different watches
Apple published its Apple Watch Heart Rate Accuracy Study in September 2026, following testing conducted in July and August. It compared Apple Watch Series 12 with Garmin Forerunner 970, Pixel Watch 4, Huawei Watch 5, Galaxy Watch 8, WHOOP 5 and Oura Ring 5, using Polar H10 as the reference. The study enrolled 1,460 people; 1,254 contributed at least one paired measurement to the final analysis.
Apple reported that Series 12 was favored in 139 of 159 activity-and-measure comparisons at the 99% confidence level. Eighteen comparisons were indeterminate and two favored a comparison device. In the study, Series 12’s user-facing heart-rate stream was a single value reported every five seconds; Apple describes that model’s system as using an optical photoplethysmography sensor and signal processing.
Our earlier coverage examined Apple Watch audio features and eavesdropping-law questions in four states.
