Garmin CIRQA Update!
In a Nutshell
The Garmin Circa shows strong nighttime heart rate tracking against ECG reference but struggles with REM sleep detection, often misclassifying it as light sleep in the first half of nights. Exercise heart rate performs well during steady-state activities (cycling 0.99 correlation, running 0.93, outdoor biking 0.94) but shows artifacts during interval training. Overall, it's a third-tier sleep tracker despite using the same sensor as higher-performing Forerunners, making the Forerunner 70 a better alternative at similar pricing.
These notes were generated by AI and may contain inaccuracies.
Early insights from the first four days and three nights of Garmin Circa testing focus on heart rate tracking during exercise and sleep, heart rate variability measurements, and sleep stage tracking. The full review will require an additional week or two for comprehensive data collection. Results may change slightly with more data, but this provides initial impressions for those considering purchase.
Nighttime measurements were prioritized as they were not included in the initial review. Data is based on two nights for heart rate and heart rate variability, with three nights available for sleep stages. The Polar H10 ECG chest strap serves as the reference device for heart rate measurements.
Heart rate measurements during sleep showed strong agreement with the Polar H10 reference. The Garmin Circa effectively distinguished heart rates within the narrow 42-52 bpm window. Example nights demonstrated that patterns aligned closely between the reference (red) and Circa (blue-green), with occasional momentary higher readings from the Circa possibly due to differences in calculation methods when getting out of bed. The Circa tends to emphasize higher heart rates more than the reference calculations.
Heart rate variability measurements showed slightly reduced performance compared to heart rate. In higher HRV ranges, the Circa tends to detect slightly lower values than the reference. Individual night analysis revealed that while the reference showed higher values in elevated HRV ranges, overall agreement remained quite good. Patterns aligned well across both tested nights, with minor deviations at the beginning and end of recordings.
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