fresh public FIT files for decoder testing/benchmark from DC Rainmaker Enduro review

Sorry for delay in reply as I've been too busy for the forums past week

We should probably use that thread for further discussion of that but yes I am (attempting) calculating respiration rate from HRV data, which is only present when using HRM strap and HRV logging is turned on in the watch

That is how Garmin calculates it and unless I am mistaken, they don't bother to save the respiration rate itself in the FIT files even on supported watches but rather calculate it in realtime on garmin-connect

So they could activate that feature for any watch like Fenix5 but refuse to, probably to make people buy new watches every year but it's silly that lowest cost newer models have features the Fenix5 does not when it was the flagship until a couple years ago

Yes I am using the method OURA shared which basically made it far easier to figure out

The HRV data is found as developer fields appended to the type 20 records as message id 78, looks like this

hrv (78, type: 0, length: 11 bytes):
  time (0-5-UINT16): {0.434 s (434), 0.438 s (438), 0.432 s (432), 65535, 65535}

You have to gather all of them and them you have the sequence of timing between heartbeats for the entire activity, I believe that's called RR intervals or interbeat intervals  https://en.wikipedia.org/wiki/Interbeat_interval

Then you can do a lot of interesting calculations based on what we know about how the heart works during certain body behaviors. Respiration rate is just the start, there is a new exciting paper with open source code on how to identify the Lactate Threshold and aerobic threshold (LT1 LT2) from HRV data which I am investigating how to code myself but might take awhile:

https://colab.research.google.com/drive/1GUZVjZGhc2_JqV-J5m1mgbvbiTBV9WzZ

Oh there is another place you can get the HRV data if you have a HRM-TRI or HRM-PRO, if you use the "download heart rate data" after the activity on the watch, it then will directly append (chain) to the FIT file the HRV data directly from the strap so any lost ANT+ communications (dropouts) are bypassed which is nice. Then there is a special FIT file called HRDATA.FIT found in 

\GARMIN\TEMPFIT\SAF_HR\HRDATA.FIT

however that HRV is different than the main activity file (and that file is overwritten every time you download it, so make a different copy if it's important)

that data looks like

hr (132, type: 11, length: 21 bytes):
  filtered_bpm (6-8-UINT8): {57 bpm (57), 56 bpm (56), 57 bpm (57), 57 bpm (57), 57 bpm (57), 57 bpm (57), 57 bpm (57), 56 bpm (56)}
  event_timestamp_12 (10-12-BYTE): {0.219 s (224), 0.146 s (150), 0.174 s (178), 0.083 s (85), 0.140 s (143), 0.053 s (54), 0.164 s (168), 0.226 s (231), 0.186 s (190), 0.061 s (62), 0.016 s (16), 0.072 s (74)}

what's weird is it's not a direct integer if you look carefully, there's some kind of scaler I haven't calculated yet, ie "74" = "0.72" or "224" = "0.219" which is odd