Any accurate watch that measures HRV (Heart rate variability) with public API?

@azure What’s your view on the value of RMSSD as a good enough measure for projects that want to explore autonomic effects and influences on a day-to-day basis?

I think it depends on the quality and frequency of the RMSSD measurement. I don’t think you’d easily pick up on day to day or week to week changes easily with once per day point measurements, but I do think that any quality nightly timeseries (every few minutes) or continuous 24 hour measure would work.

Check out this paper for occupational stress effects on different kinds of HRV, including rmssd. https://pubmed.ncbi.nlm.nih.gov/29910218/

Basically they note that parasympathetic withdrawal (having less rest and digest) is associated with lower rmssd, as you might expect

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