Amazfit Cheetah 2 Ultra HR Accuracy: Bike, HYROX, and Heat Tested

The Amazfit Cheetah 2 Ultra has now been put through three separate HR accuracy tests, and the results are consistent enough to say something real. Across a road bike sprint, a HYROX simulation at 33°C, and multiple reference comparisons, the wrist optical PPG sensor keeps returning clean numbers. That is not a given at this price point, and it is worth unpacking exactly what the data shows.

Bike Sprint HR: The Hardest Test for Wrist Optical

Sprint efforts on a bike are brutal for wrist PPG. Your arms are locked out, vibration from the road feeds straight into the sensor, and HR can spike 40 bpm in under 20 seconds. The Cheetah 2 Ultra returned limits of agreement of ±3 bpm in a road bike sprint test, compared directly against the Fitbit Air's ±6 bpm in the same protocol. For context, ±5 bpm is roughly where most decent optical sensors land in controlled steady-state conditions. Getting to ±3 bpm during a sprint, on a bike, is a solid result. The Whoop MG and Polar Verity Sense were also included as references in that test, which keeps the methodology honest.

The Fitbit Air's ±6 bpm is not a disaster for casual use, but it matters if you are training with HR zones. A 6 bpm error at threshold can push you from zone 4 into zone 5 on paper while your body is still in zone 3. For more on how the Fitbit Air compares as a daily training tool, see our [Fitbit Air review](/en/articles/fitbit-air-review-comfort-and-ai-coach-tested-by-athletes-2026-05-24).

HYROX Simulation: Heat, Sweat, and Mixed Modalities

The second major test was a HYROX simulation indoors at 33°C. Heat is the other enemy of wrist optical sensors. Vasodilation changes blood volume distribution near the skin, and heavy sweating can lift the sensor slightly off the wrist, both of which introduce noise into the PPG signal. Despite those conditions, the Cheetah 2 Ultra showed near-zero bias against the Garmin HRM600, the Whoop MG, and the Polar Verity Sense. The HRM600 uses an electrical ECG-based signal from a chest strap, which is the gold standard for real-time HR accuracy. The Polar Verity Sense is an optical armband, so it sits closer to the brachial artery and typically outperforms wrist sensors in mixed-modality efforts. Matching both across a HYROX sim is a strong performance.

Three tests, three clean results. That pattern matters more than any single data point. One good test can be luck or favorable conditions. Three in a row, across different activity types and environments, suggests the sensor and its signal processing are genuinely well-tuned. The Cheetah 2 Ultra is positioned as a serious multisport watch, and this HR data supports that positioning more than most marketing claims would.

How This Compares to the Broader Market

For reference, Garmin's own Elevate v5 sensor (found in the Forerunner 965 and Fenix 8) typically returns limits of agreement around ±4 to ±5 bpm in hard cycling efforts, depending on the study. Coros's optical sensor on the Vertix 2S sits in similar territory. The Cheetah 2 Ultra's ±3 bpm in the sprint test is competitive with the best wrist optical results published across the category. Whoop MG relies on a different use case entirely, prioritizing HRV recovery metrics over real-time HR accuracy during exercise, so direct comparisons during workouts should be read carefully. The Polar Verity Sense armband remains the benchmark for optical HR during bike and gym work, and the fact that the Cheetah 2 Ultra tracks it closely is a genuine credibility signal.

The SmO2 sensor mentioned in the HYROX test report is worth flagging separately. Muscle oxygen saturation (SmO2) is measured optically, similar in principle to SpO2 but targeting a different wavelength and tissue depth. It is a different metric from blood oxygen saturation. SmO2 data is still in early stages for wrist-based consumer devices, and validation against reference devices like Moxy monitors is thin across the industry. Treat it as directional data for now, not clinical-grade.

What Is Missing

The tests published so far do not include a dedicated running HR accuracy test with rapid pace changes, which is a real gap. Running introduces wrist movement artifacts that differ from cycling vibration, and sprint intervals on a track are a different stress than HYROX stations. There is also no published data on how the sensor performs in cold conditions, which matters for cyclists and trail runners in autumn and winter. Battery life and GPS accuracy have been covered separately (see our [GPS and battery test](/en/articles/amazfit-cheetah-2-ultra-gps-battery-and-trail-climb-feature-tested-2026-05-25) and [55-hour ride test](/en/articles/amazfit-cheetah-2-ultra-battery-test-55-hours-on-a-real-ride-2026-05-24)), but a complete swimming HR test is also absent from the current dataset.

The Amazfit Cheetah 2 Ultra is shaping up as a credible multisport option for athletes who want accurate wrist HR without paying Garmin Fenix 8 or Coros Vertix 2S prices. Three HR tests returning tight limits of agreement across bike, heat, and mixed modalities is enough to take seriously. If you are cross-shopping against the Cheetah 2 Pro, which adds titanium and sapphire at a 50% price premium, the HR sensor performance appears comparable based on current data (our [full Cheetah 2 Pro review](/en/articles/amazfit-cheetah-2-pro-review-running-cycling-and-swimming-tested-2026-05-29) covers that in detail). For triathletes and Hyrox athletes who prioritize training zone accuracy and do not want a chest strap for every session, this watch belongs on the shortlist.