When it comes to smartwatch health sensors, accuracy is often what sets the best apart from the rest. A recent test by bioinformatics scientist Rob ter Horst—better known as The Quantified Scientist on YouTube—has given the Apple Watch Ultra 2 a noticeable edge over its competitors, especially in heart rate and sleep tracking performance.
Heart Rate Tracking: Close to Professional Gear
To measure accuracy, Horst compared the watches to the Polar H10 chest strap, which is widely considered one of the most reliable trackers. The Apple Watch Ultra 2, running on watchOS 26 beta, came impressively close to the strap’s readings during indoor runs.
Other wearables like the Huawei Watch 5 performed nearly as well, while the Galaxy Watch 7 showed a small 3% deviation. On the other hand, the Garmin Forerunner 570 (7%), Garmin Fenix 7 (9%), and Whoop MG (6%) lagged behind.
During outdoor running and cycling, the Apple Watch Ultra 2 continued to perform consistently, while devices like the Forerunner and Whoop showed even wider gaps—sometimes up to 15%.
Sleep Tracking: Better Than Rivals
For sleep analysis, the data was compared against the Hypnodyne ZMax EEG device, which itself is about 83% accurate. The Apple Watch Ultra 2 scored well, reaching 73% accuracy in tracking REM and deep sleep, and 86.5% for light sleep.
This placed it ahead of rivals such as the Oura Gen 4 ring, Whoop 4.0, and Garmin Fenix 7, showing that Apple’s device isn’t just about fitness—it’s also strong in monitoring rest and recovery.
What This Means for Users
While this was a single-user study and larger-scale testing would give a clearer picture, the results point to the Apple Watch Ultra 2 being one of the most dependable wrist-based trackers available today.
Chest straps like the Polar H10 are still the gold standard for weight training sessions where wrist tension interferes with readings. But for everyday workouts, running, cycling, and sleep monitoring, Apple’s flagship watch delivers some of the most consistent results you can get on your wrist.
