I have been using my Fitbit Alta for about a year and a half and I noticed my RHR seems to oscillate with a period of about 3-4 months when it aggregates the data by month. Not sure if this is a hormonal thing or an artefact of the way Fitbit averages the data.
How Fitbit calculates the resting heart rate remains one of the great mysteries of our times…
I think you’d be better off just noting your heart rate every morning after sitting still for ten minutes or so.
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