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.
Sleep stage tracking was evaluated using an EEG device measuring brain waves as the silver standard reference. The comparison matrix shows deep sleep agreement at 77%, light sleep at 64%, and REM sleep at 46%. The Circa most frequently misclassified REM sleep as light sleep. This performance appears worse than recent devices tested, including the Forerunner 70 and 170, which use the same sensor.
Deep sleep detection showed strong performance, with most reference-identified deep sleep also detected by the Circa. However, the device identified additional deep sleep periods beyond what the reference recorded. This pattern held consistent across multiple example nights.
REM sleep detection presented significant issues, particularly during the first half of nights. Multiple example nights showed the Circa detecting no REM sleep for the first three-quarters, two-thirds, or first half of the night. REM sleep detection improved in the latter portions of nights, where timing aligned more closely with reference measurements.
The sleep tracking algorithm appears identical to that used in the Forerunner 70 and 170. More extensive testing may yield improved results. Current performance places the Circa in the higher end of third-tier devices for sleep stage tracking, rather than second-tier performance seen in recent Forerunner models.
Heart rate tracking during exercise falls in the middle to higher-middle class category, approaching but not matching second-tier performance of devices like the Forerunner 470. Indoor cycling sessions demonstrated excellent performance with a 0.99 correlation coefficient. Two spinning sessions showed strong agreement with the reference, with only minor initial deviations in the second session.
Running performance showed mixed results. Interval training with quick pace changes revealed artifacts and incorrect heart rate peaks. However, steady-state running produced excellent agreement with the reference, even during breaks between faster and slower segments. Combined running data yields a 0.93 correlation coefficient. The older sensor may struggle more with rapid interval training.
Outdoor biking performance exceeded expectations with a 0.94 correlation coefficient. Most intervals were accurately captured with only minor deviations. The lighter weight of the Epix Pro may contribute to better performance compared to other Garmin devices with the same or newer sensors.
Weightlifting sessions were not additionally tested as wrist-based measurements proved unreliable due to wrist tension interfering with the signal. This limitation affects most wrist-worn devices during weightlifting activities.
Five different biceps bands from various companies have been ordered, with delivery expected in weeks. The Epix Pro uses unusually small connectors that may not accommodate generic bands typically sized at 22 or 26 mm. Biceps placement generally provides superior heart rate measurements, though sleep stage tracking algorithms may require settings adjustments for optimal performance.
Initial testing indicates solid performance for heart rate and heart rate variability measurements during sleep. Sleep stage tracking, particularly REM detection, represents the primary area needing improvement. Manual exercise logging occasionally fails to record activities. Device synchronization with phones takes longer than competing devices, creating occasional inconvenience.
The standard Garmin app interface is somewhat clunky due to accommodating numerous device types and historical development. While not ideal for data overview and interpretation, it excels as a data aggregation platform supporting multiple device connections for comprehensive training analysis.
The Garmin Forerunner 70 is recommended as an alternative at similar pricing with a screen and strong testing performance. Affiliate links are available for various fitness devices including the Fitbit Air, Apple Watch Ultra 3, Whoop Strap, Aura Ring, and Ultrahuman Ring Pro.
Keep The Quantified Scientist in your library
Save the videos and channels worth coming back to, and find them again in one place.
