I propose that SAA updates the default HRV data provided to users from SDNN/SDANN to rMSSD. Alternatively, users could be given the option to toggle between these metrics or select their preferred default for graphs and charts.
Most fitness trackers that measure HRV, such as Garmin, Fitbit, Oura, Samsung, Eight Sleep, Polar, and Suunto, provide HRV data in the form of rMSSD:
Terra API blog post: HRV metrics: SDNN and RMSSD
Additionally, most readiness apps that utilize these devices for HRV measurements (including Elite HRV, HRV4Training, and Welltory) also use rMSSD as their primary method to analyze the body’s recovery state.
rMSSD is widely regarded as the standard for HRV analysis, effectively indicating the body’s recovery process:
Research strongly supports RMSSD as the most relevant and accurate measure of Autonomic Nervous System activity over the short term:
Elite HRV article: What are HRV score, RMSSD, ln(RMSSD), SDNN and PNN50?
The primary outliers in the HRV data world are Apple Watch and SAA. As highlighted by the HRV4Training article, while SDNN and rMSSD are strongly correlated, rMSSD offers a superior picture of parasympathetic regulation.
Although SDNN and SDANN are valuable, and some readiness apps provide this data in addition to rMSSD, they are typically used during 24-hour measurements, with SDANN being the gold standard for such durations:
Pubmed Article: An Overview of Heart Rate Variability Metrics and Norms
SAA is a great app, and when paired with highly accurate sensors, it provides very meaningful data. Updating to include rMSSD would align SAA with current research, offering users even better insights. I hope you will consider integrating rMSSD into SAA. This change will enhance the experience for existing users and attract more users seeking the best in sleep tracking applications.
If not apparent, I could only add two links so the other sources are highlighted in bold. TY!