I wondered why I'd see people at the gym going backwards on the ellipticals.
SN, I'm curious what heart rates you aim for. I'd assume a longer workout would have a lower rate??
I use a heart rate monitor all the time for hikes, running and everything. For hiking at altitude on a steady climb like Whitney, my heart during the first few hours is in the 120s or 130s (my max is around 190). Of course accumulative fatigue (and the effects of altitude) sets in as you go along and on the switchbacks and after it's in the 140s and sometimes in the low 150s.
For the practice on the treadmill I set the speed so that my HR was in the low 120s to start. My average speed was roughly the same through my four sets of 50 minutes each. But my average HR rose during each set: from 120 to 124 to 128 and finally 132.
But true, the longer the workout, the lower the average HR.