Hi Frantik,
Yes, I was doing the test going uphill. I thought the gradient was fairly consistent but it seems it’s steeper in the first half than the second which – at least in part – explains why my HR in the second half was lower (same experience on three similar hikes last week). I will re-do the test on flat ground.
It’s possible to view HR data sampled at 1-second intervals in TP but unfortunately *not* to export that data. I was hoping to do so as the data from the .fit file was sampled irregularly and is missing distance and elevation.