Garmin CIRQA Ultimate Scientific Review!
In a Nutshell
Garmin Circa delivers excellent biceps heart rate tracking (0.98-1.00 correlation across cardio) versus poor wrist performance during running (0.89) and strength training (0.73). Sleep staging shows similar location dependency—biceps placement achieves 91% deep sleep and 58% REM accuracy versus wrist's 81% and 45%, respectively. The device is recommended for biceps wear during exercise with wrist-only use at night when sleep stages aren't critical, though official biceps bands cost ~$60 and have limited availability.
These notes were generated by AI and may contain inaccuracies.
Systematic and scientific testing was performed on the Garmin Circa to evaluate heart rate tracking during exercise, nighttime measurements, and sleep stage tracking. Testing occurred both on the wrist and on the biceps, with the distinction between wear locations being important for performance and recommendations. The tester is a post-doctoral scientist specializing in biological data analysis.
The Garmin Circa was tested using official bands with settings according to specifications. All data presentations show wrist results first, followed by biceps results. Two colors were purchased, with one received from Garmin. The blue and black colors match the box appearance, but the reddish color appears significantly different - more of a faded pink than the dark red shown on the box.
Testing methodology involves comparing devices against the Polar H10 ECG chest strap as the reference device. The reference appears along the horizontal axis in plots, with Circa results along the vertical axis. Wrist-based testing appears on the left, biceps-based testing on the right.
Indoor cycling (spinning) showed excellent performance for both wear locations. Wrist testing achieved a correlation of 0.99, while biceps testing achieved a rounded correlation of 1.00. Example sessions showed good agreement on the wrist with minor deviations at the beginning, while biceps examples showed essentially no deviation and almost perfect tracking.
Running proved more challenging than cycling. Wrist testing showed a correlation of 0.89 with significant deviation, while biceps testing maintained a high correlation of 0.98. Individual wrist runs showed multiple deviations and incorrect heart rate spikes, while biceps runs tracked intervals correctly with only minor calibration delays at the beginning.
Biking showed a correlation of 0.92 on the wrist with some moments of both low and high heart rate detection. Biceps testing improved this to a correlation of 0.96. Wrist examples showed good tracking with minor delays in detecting heart rate changes, while biceps results were much closer to the reference with minimal deviations.
Strength training showed the largest difference between wear locations. Wrist testing achieved only a 0.73 correlation, making it unreliable for weightlifting. Biceps testing improved this to 0.91 correlation. Wrist examples missed many heart rate peaks and recorded incorrect values. Biceps examples were far from perfect but showed better performance, particularly during bench pressing and dips.
When compared to other devices tested, the Circa on the wrist performed well for spinning (better than 63% of devices), adequately for biking (better than just over 50% of devices), poorly for running (better than only 27% of devices), and poorly for weightlifting. On the biceps, performance was significantly better: spinning (better than 77% of devices), biking (better than 75% of devices), running (better than 63% of devices), and weightlifting (better than nearly 70% of devices).
Heart rate scores are calculated as the average correlation over three cardio exercises. The Circa on the biceps scored 98 (great rating), while on the wrist it scored 93 (good rating). The wrist rating is influenced by running and biking results.
Sleep stage testing compares against the ZMax EEG device, described as a silver standard for sleep studies. The reference device provides deep sleep, light sleep, and REM sleep classifications.
Wrist-based testing showed 81% agreement for deep sleep, 67% agreement for light sleep, and only 45% agreement for REM sleep. REM sleep was frequently misclassified as light sleep.
Biceps testing showed improved performance with 91% agreement for deep sleep, 69% agreement for light sleep, and 58% agreement for REM sleep. The improvement in REM sleep detection was particularly notable.
Example nights showed that deep sleep detection was generally accurate with some over-detection. REM sleep proved more challenging, with the device detecting fewer REM sleep periods than the reference. Five sleep cycles ending in REM sleep were detected as only three cycles by the wrist-worn device. Biceps testing showed better REM sleep detection with more accurate segment identification.
When plotted against other devices, the Circa on the biceps placed in the second tier of devices, while the wrist placement was in the third tier. This represents a significant difference in performance between wear locations.
Two explanations are proposed for better biceps performance: reduced artifacts due to fewer degrees of freedom and less noise in the signal, or chance results from limited testing. The tester plans to continue wearing the device on the biceps to determine if the pattern holds over time.
Devices are classified into four tiers based on sleep stage tracking performance. First tier includes Apple Watch, Pixel Watch, Fitbit devices, Whoop strap, and Oura Ring 4. The Eight Sleep Pod is noted as the favorite sleep improvement device but is expensive. Fitbit Air is mentioned as an affordable option at 99 dollars with good sleep stage tracking.
Sleep stage scores are 73 for biceps (good rating) and 64 for wrist (okay rating), placing the wrist version in third tier.
Nighttime heart rate tracking showed excellent performance for both wrist and biceps placements within the 39-55 bpm range. HRV tracking was also reliable, with most points close to the reference line, though Garmin tends to measure slightly lower HRV in higher ranges, possibly due to algorithmic differences.
The Garmin Circa is recommended with the button feature providing significant quality of life improvement for exercise tracking. Automatic activity detection could be improved. Heart rate and HRV tracking at night is great for both wear locations. Sleep stage tracking is good on biceps but only okay on wrist. Heart rate tracking during exercise is only good on wrist but great on biceps. The recommendation is to wear on wrist at night if sleep stages are not important, and switch to biceps for exercise. Biceps bands are currently expensive and difficult to obtain, with sizing compatibility concerns for third-party options.
At least in Austria at the moment, an official biceps band sets you back close to 60 bucks, whereas a whole Fitbit Air on your wrist is only 99 bucks. The biceps band is quite expensive and it usually takes quite a while to get it. The larger version only delivers in a couple of weeks. It is worth getting one and fine to wait for a bit until Alex I starts selling some. If you're really keen on getting the best results, bite the bullet and get the expensive armbands.
The performance of the Circa is not disappointing and it is a proper competitor to the Fitbit Air, the Whoop strap, and the Amazfit Helios strap. It is still on the more expensive side, not Whoop expensive, but the Amazfit Helios strap and the Fitbit Air will only set you back 99 bucks and also have really good performance.
A dedicated review is being worked on that puts the Garmin Circa and the Fitbit Air side by side where you can really judge which is the right device for you.
The Garmin Circa works a lot better offline than the Fitbit Air did at least up till a while ago where the Fitbit Air just wouldn't sync exercises when you're not connected to the internet. The Fitbit Air is also a great option otherwise.
If you do decide to get yourself a Garmin Circa, a Garmin Circa bicep band, a Whoop strap, a nice little Helios strap, an Ultrahuman Pro ring, an Oura ring, another device or anything at all on Amazon for that matter, even something as small as toilet paper or coffee beans, you want the best discount possible and to support the channel. There are different affiliate links down in the description below, many of which give you the best discount possible.
Don't forget to like and subscribe and also watch this video on the Fitbit Air and this video on the Eight Sleep Pod.
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