[arnejenssen]

For me the value of Garmin (Forerunner) is their proprietary algorithm for calculating Stress Level from HRV. It is the basis for the Body Battery measure. I find it useful to see how food and activity affects my stress levels.

I guess it would be possible to reverse engineer a similar stress level calculation. Perhaps AI-powered?

[scheme271]

I'm not sure the body battery/stress measures are that great. Garmin is infamous for having an awful sleep algo and it still has a lot of trouble detecting naps. It doesn't bode well for being able to get stress data. I think it's good for generally determining high stress vs low stress and when you've overdone exercise recently but probably not much more.

[rolisz]

Body battery is amazing. I had long COVID/ME/CFS, and looking at the body battery when waking up was an outstanding predictor of how my day was going to be. When I hit 5% body battery, I was really feeling horrible.

[throwaway270925]

Interesting. What did you have to do to "charge" the body battery tough? And how does the garmin keep track of that?

[mikestew]

Naps and rest “charge”, and yes, Garmin keeps track of that.

Not that I put a whole lot of weight in those data personally.

[catigula]

It's just a collation of sleep-end RHR/HRV. It's completely trivial and many manufacturers do this correctly; both are extremely reliable predictors of recovery metrics.

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.

[TekMol]

If the algorithm is proprietary, how do you know it is calculating something meaningful?

[LeifCarrotson]

It matches my lived experience.

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.

[ck2]

HRV from optical is garbage-in garbage-out

and post-2020 Garmin has totally lost their way with development/algorithms

[kilroy123]

Yes, and the sleep tracking that adds or subtracts. While not super accurate, it's good enough for me.