Apple Watch Ultra 4 - First Scientific Test!
In a Nutshell
The Apple Watch Ultra 4 delivers near-perfect heart rate accuracy for indoor cycling (r=1.00) and weightlifting (r=0.99), but struggles during running with initial detection delays, dropouts, and a lower correlation (r=0.94) that ranks it below average compared to other devices. GPS tracking shows significant deviations during runs, unlike the Ultra 3, while step counting remains accurate with a median error of just 5 steps. The main upgrade is power efficiency enabling continuous 5-second heart rate monitoring rather than improved tracking accuracy over the Ultra 3.
These notes were generated by AI and may contain inaccuracies.
The test began with indoor cycling using the Polar H10 ECG chest strap as reference. The correlation value between the Apple Watch Ultra 4 and Polar H10 reached a rounded value of 1.00. The red line of the Apple Watch Ultra 4 tracked super close to the Polar H10 throughout the session with multiple intervals.
Running results showed a correlation of 0.94. During the first 5 minutes of the run, the Apple Watch Ultra 4 had issues detecting heart rate, resulting in points below the blue line indicating too low heart rate detection. There was also a deviation showing too high heart rate at one point. Dropouts occurred where no heart rate was recorded. Two different exports were tested - one with Straa and another app - both showing the same patterns. The Apple Fitness app displayed interval ranges that appeared between the Apple Watch measurement and the reference value.
The new heart rate sensor on the Apple Watch Ultra 4 has a different appearance from the previous version. The Ultra 4 is heavier than the Series 12, which may contribute to tracking issues. The new sensor may require optimization for signal processing across a larger population.
Weightlifting showed a correlation of 0.99. In the higher heart rate range, almost all points aligned with or were close to the blue line. The Apple Watch sometimes fully detected heart rate peaks but occasionally stopped detecting at the very peak. No severe dropouts occurred, though minor dropouts were possible. This performance ranked better than 94% of devices tested for weightlifting.
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