I guess it would be possible to reverse engineer a similar stress level calculation. Perhaps AI-powered?
Garmin has absolutely shitty sleep tracking but it doesn't matter; any wearable more or less nowadays can get static heart rate correct, leading to more or less accurate recovery metrics.
"Collect every paper you can find on RHR/HRV/etc. recovery metrics. Develop an algorithm for predicting recovery score per day based on the research" as a prompt to a Codex or Claude agent can probably get you 98-100% of the way there.
Edit: As a proof of concept, I had ChatGPT Pro 5.6 write the algorithm with my Fitbit data. Looks great.
I’ve had Claude work on a body battery type solution, which I’ll fully deploy over the coming days. It’s to manage and track brain fog/long COVID type symptoms and see if there’s correlation between foods eaten the day prior, resting heart rate etc and perceived brain fog. I’ll see if it’s possible to incorporate some of your work into my solution too.
Not that I put a whole lot of weight in those data personally.
My body battery and stress often starts declining for no apparent reason and then 12-24 hours later I feel the symptoms of an illness. Similarly, when in a tough training block, HRV is a great tool to gauge how hard I ought to be able to go: I've tried to push through and just do a tough workout anyways when it's out of range, but failed to complete the workout in good form, or felt superficially crappy but had good training readiness according to the watch and was able to do better than expected.
The same holds true in the other direction, I don't log into Connect or scroll through the multitudinous widgets of data often enough to really keep tabs on this stuff, and when I get sick or feel good or bomb a workout or succeed at a workout when I felt off, the metrics consistently back up the actual results.
Personally, I've been thinking about jumping ship to a Coros Apex 4 if my battered Fenix 6 ever gives up the ghost - Garmin's prices are insane these days. At $270, this is cheap enough in comparison to a $1200 Fenix 8 Pro to take the chance. I could buy this and a $480 Apex 4, and then decide I didn't like either of them and go back to a used Forerunner 955, before spending as much as a new top-end Garmin.
The newest watches seem insanely priced though and don't seem to add much. But the newest Enduro with decent solar is tempting
and post-2020 Garmin has totally lost their way with development/algorithms