A recent side‑by‑side test compared the Apple Watch Ultra 4 and Garmin Fenix 9 Pro during a run monitored by an electrical heart‑rate sensor. Both devices delivered heart‑rate readings that matched the reference system within a fraction of a beat, proving their accuracy.
The test was conducted on a 10‑kilometre outdoor run in early October 2026. The runner wore both smartwatches simultaneously, each synced to the same training app. An external electrical heart‑rate monitor served as the gold standard. The data were recorded and analyzed after the run to assess each watch’s precision.
Both watches showed minimal deviation from the reference, with average errors under 2 beats per minute. The Apple Watch Ultra 4 recorded a mean error of 1.1 bpm, while the Garmin Fenix 9 Pro registered 1.3 bpm. The results indicate that both devices are reliable for athletes who depend on accurate heart‑rate monitoring during training sessions.
During the test, environmental factors such as temperature, sweat, and motion artifacts were present. Despite these challenges, the Ultra 4’s optical sensor maintained consistent performance, thanks to its improved sensor array and adaptive algorithms. Garmin’s Fenix 9 Pro, equipped with a multi‑frequency optical sensor, also handled motion well, but its slightly higher error margin suggests a minor lag in rapid heart‑rate changes.
The runner noted that both watches displayed smooth heart‑rate curves with no noticeable spikes or drops. Battery life was not a concern, as each device comfortably powered the run. The Ultra 4’s larger display and faster processor made navigation easier, while the Fenix 9 Pro’s rugged design appealed to outdoor enthusiasts.
The question many athletes ask is whether one device offers a distinct advantage for race pacing. Based on this test, both watches provide comparable accuracy, so the decision may hinge on other features. The Ultra 4 offers a more intuitive interface and integration with Apple’s fitness ecosystem. The Fenix 9 Pro delivers a longer battery life and a broader range of sport‑specific metrics.
For runners who prioritize seamless connectivity and a sleek design, the Apple Watch Ultra 4 is a strong choice. Those who value durability and extended battery performance may lean toward Garmin’s Fenix 9 Pro. Ultimately, the choice depends on personal preference and the specific training environment.
Q: Were there any noticeable differences in battery life during the test? A: Both watches completed the run without battery depletion. The Fenix 9 Pro typically offers longer usage between charges, but battery performance was not a limiting factor in this test.