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Forerunner 955 HRV values differs from ones of several Android Apps

Andris
2 months ago

I have noticed that HRV values estimated by Forerunner 955 are noticeably higher than ones from 2 Android Apps.

I used chest strap (Polar H10), so possible optical sensor problems should not have influence here

Polar H10 was configured to provide:

Note: EliteHRV is noticeably weaker in handling pulse artifacts (like ectopic beats) and measurement noise, but one can see it from raw data and discard data in case of bad data quality

I'm took health snapshot and measurement using Android apps at the same time. Kubios HRV tapauksessa overlap of time intervals is perhaps 70% or higher. Elita HRV measurement intervals is slightly longer but begin part of it was mostly common.

Results (tested today - 2024/09/08):

Forerunner 955 Kubios HRV Elite HRV
Avg. pulse 55 55 55
RMSSD 39 24 25.37
SDRR 41 N/A N/A
SDNN N/A 21.04 31,59

The results are similar also for other days (not given here). Of course cases with bad nḿeasurement quality, artifacts present, measurements not done at the same time were not considered

RMSSD value is noticeably higher for Forerunner 955 health snapshot, than got from 2 specified Android apps.

What could be reason for such discrepancy. RMSSD should be calculated in the same way from raw R-R intervals.

  • 0 2 months ago

    I’d be interested to understand the same. This is what ChatGPT came up with.


    The discrepancies you’re noticing between the Garmin Forerunner 955, Kubios HRV, and Elite HRV in RMSSD values are quite common, and Garmin’s higher RMSSD value compared to the other two is likely due to the following factors:

    1. Preprocessing and Filtering (Garmin vs. Kubios/Elite HRV)

    • Garmin: Garmin devices (like the Forerunner 955) may use proprietary algorithms to filter and clean the raw data from the chest strap, possibly applying less aggressive artifact correction than apps like Kubios and Elite HRV, resulting in higher RMSSD values. Garmin might prioritize “real-time” analysis, which can be less refined compared to specialized HRV tools like Kubios, which focus on more detailed statistical analysis.
    • Kubios/Elite HRV: These are more specialized HRV apps, which might apply stricter artifact detection and correction, leading to lower RMSSD values by discarding more noisy or irregular RR intervals.

    2. Averaging or Smoothing Differences

    • Garmin could be using averaging techniques or smoothing the data over a slightly longer time frame, which can result in higher values for metrics like RMSSD. Garmin’s systems are optimized for ease of use and practicality during workouts, and they might apply less rigorous short-term smoothing than dedicated HRV apps like Kubios or Elite HRV.

    3. Data Sampling & Resolution Differences

    • Kubios HRV and Elite HRV typically allow users to import high-resolution data and analyze it in depth, which might not be the case with Garmin. If Garmin is sampling at a lower rate or using a different internal processing rate, this could impact the derived metrics like RMSSD.

    4. RR Interval Differences (Measurement Inclusion)

    • Garmin may include a larger range of RR intervals in the calculation compared to the stricter thresholds applied by Kubios or Elite HRV. The inclusion of more RR intervals might artificially inflate the RMSSD value.

    5. SDRR and SDNN Variations

    • The SDRR (standard deviation of RR intervals) and SDNN (standard deviation of normal-to-normal intervals) also show some discrepancies. Since SDNN reflects overall HRV and is often higher when more variability is included, Garmin might be calculating this differently from Elite HRV, which gives a much lower SDNN. It seems that Garmin’s RMSSD and SDRR values are in line with this greater variability.

    Summary

    • Garmin’s higher RMSSD is likely due to its algorithm’s handling of artifacts, smoothing, and perhaps more lenient inclusion of RR intervals, making it less focused on fine-grained HRV analysis compared to Kubios HRV and Elite HRV, which are more specialized.
    • Kubios and Elite HRV are closer to each other because they likely use more refined and consistent artifact correction and RR interval filtering.

    For more accurate HRV tracking, using tools like Kubios might provide a more reliable and detailed HRV analysis, while Garmin’s values are more practical for everyday monitoring but less precise for in-depth analysis.