FITFILES: Record HRV/ RR Intervals
Record HRV/ RR Intervals from a Heart Rate Monitor in the fit files for use by training apps. AI Endurance, Humango, Athletica.ai, spoked.ai, runalyze, golden cheetah all use HRV data. AI Endurance, Runalyze, HRV Logger, Golden Cheeetah, and FatMaxxer do analyze the RR intervals stored in the fit file.

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Ben Marshall commented
+1 for this. I would like to use TPV as a big part of my winter training. I'm testing out AIEndurance at the moment to see if live HRV can be of use. I cant get this data into that platform at the moment without dual recording all my TPV rides with a garmin.
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James Eastwood commented
+1 for this, but for me specifically or would be to make use of Suunto's ZoneSense algorithm which does a far better job than power or HR at showing your real physiological zone considering things like fatigue.