[1] When comparing one mode of excercise to another (e.g. stationary bike vs treadmill-running ) - is H.R. during a session likely to correlate with work rate (i.e. cals burned per hour) any more or less accurately than say 2 different type of gym machine's own cal estimates.
In the situations i've got in mind H.R. vs perceived effort (and perceived effort vs gym-machine's cal estimate) can be very different.. I think more muscle-mass used makes it easier to burn more cals, but is HR a reliable way of comparing how much more ?
I know temperature is a factor so indoor vs outdoor isn't going to work.. (?)
[2] Is average H.R. over time likely to correlate with total work done between 2 different types of session on the same machine.. i.e. intervals on a bike vs steady state on a bike, grinding up hills vs spinning on flat terrain. I'd wonder about this because what's the graph of HR vs power going to look like in terms of lag (recovery..) Of course in this situation a gym machines' own cal estimate is probably going to be a reliable comparison.
Actually I guess this would be pretty easy to answer experimentally.
[3] Indoor vs Outdoor (i.e. static & warmer vs colder & moving)- which way is H.R vs work-rate going to change...
( for the same perceived effort, HR is easier to get higher outdoors than on an indoor bike .. i think i recall another thread covering this one )