Polar Loop: Long-term Scientific Review (Watch Out WHOOP!)
These notes were generated by AI and may contain inaccuracies.
Spent the last few months retesting the Polar Loop. Comparing it to the Amazfit Helio Strap and especially the Whoop Strap, as the Polar Loop could be a cheaper equivalent if Polar improves some aspects. Focus on: heart rate tracking performance, sleep stage tracking, how and where to wear it (automatic workout detection or not, wrist vs. biceps). Results are super interesting and somewhat surprising.
Polar Loop: $199 or euros, now slightly over $200 in the US. No subscription required. Amazfit Helio Strap: $99, no subscription. Whoop Strap: Monthly fee adds up over years; free hardware upgrade if at least a year left on membership, but still more expensive long-term than Helio Strap or Polar Loop. Whoop excels in app experience, not fully replicated by others.
Tested Polar Loop three ways: (1) wrist without starting activity, (2) wrist with activity started and recorded on device (better processing than live app recording), (3) biceps (mostly started on device, sometimes auto-detected).
Correlation with ECG chest strap reference. Wrist (auto-detect or on-device): not great. Biceps: 0.99 correlation, really high. No difference between auto-detect and on-device on wrist. Recommend Polar Loop on biceps for indoor cycling (easier exercise). Combine bands for biceps band; some reports Polar might ship new ones with biceps band included.
Wrist (auto or on-device): really not doing well. Pixel Watch 4 fluke poor result (one weird workout; retesting soon). Biceps: really well, close to top devices like Amazfit Helio Strap (biceps/wrist), Pixel Watch 4, Huawei Watch GT 6, Apple Watch Ultra, Apple Watch Series 11.
Wrist: some of the worst for 2025 devices. Biceps: also not good (bumpiness/vibration issue). Worse than Apple Watch Ultra, Amazfit Helio Strap (biceps), Pixel Watch, Huawei devices. Tested ~2 months full-time.
Wrist: not great. No biceps data with active start (auto-detect didn't pick up). Automatic workout detection improved but still not great: detects most workouts on HR increase, but splits if breaks (e.g., 1-3 min intervals in indoor cycling, 10 min bike ride breaks). Recommend biceps for indoor cycling/running; avoid for outdoor cycling.
Wrist runs: detects after HR rise from ~60 BPM to 120+ BPM, but poor performance. Biceps nearly perfect. Biking (indoor/outdoor): often misses half/third/beginning, inaccurate. Indoor cycling: detects half/third, takes time to start. Set to second-most sensitive level. Wouldn't rely on auto-detect unless continuous workout with sharp initial HR increase (HR-based detection). Avoid wrist/auto-detect.
Worn on biceps (notch toward thumb, as on wrist). Reference: Zmax EEG headband (brain waves).
Deep sleep agreement: 71%. Light sleep: 64-65%. REM: 41-42% (low; often misdetected as light sleep). Similar to Garmin/Amazfit struggles on REM.
Deep: 65%. Light: worse than biceps. REM: worst (misdetected as light).
Average agreement (x-axis), worst stage (y-axis). Polar Loop (biceps/wrist/auto/on-device) near Polar Grit X2, Garmin (Forerunner 570/970), Whoop, Pixel Watches, Galaxy. Top: Eight Sleep Pod 5, Apple Watch Ultra/Series 11 (recent update), Whoop Strap, Pixel Watch, Oura Ring, Sleep2/NUA (retest planned). Worse: some Chinese (e.g., Huawei).
HR correlation (x), sleep sensitivity (y). Top: Whoop, Apple Watch Ultra 3/Series 11, Pixel Watch, Galaxy. Amazfit Helio Strap: great HR, poor sleep. Polar Loop biceps: decent HR (pulled down by outdoor cycling), sleep like Garmin—not worst.
App outdated; Polar working on 2026 release for better health/recovery overview. Polar improves continuously, listens to feedback (including reviewer's), EU-based (data stored in Europe). Biceps wear yields decent performance. Affiliate links for Oura Ring, Whoop, Polar Loop, Amazfit Helio Strap, Eight Sleep Pod (heats/cools bed sides independently, expensive).
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