I have conducted a similar test using real time HRV to determine AeT on XC skiers before. It was 10 years ago and the there was only one watch, a Polar that had the ability to display real time R-R intervals during the rest. We couldn’t record or export the data but we could see where R-R reached its minimum. We didn’t compare to a gas test but to a lactate test and it did correspond to 2mMol/L of blood lactate concentration.
I have not kept up on the newer watches but this is very interesting as long as the watch is able to record and download the R-R intervals.
I’ll read the paper you attached to and be interested in hearing your test results
Thanks for this info,