Quote Originally Posted by Mike T View Post
Normally, if we use more power, we use the anaerobic pathway more, but in addition to the aerobic pathway, so it feels harder and if anything our heart rate goes up. Presumably you are referring to the fact that when we stop running and start walking because of the increasing gradient we are using our muscles differently, so that, to an extent, it is as if we are starting again. Once we have reached a new equilibrium, walking uphill can be as hard or harder than running on the flat - the easiest way to monitor this is to observe your breathing.
Maybe I'm not normal, but when I start to climb steeply I find my heart rate can drop when I reduce my cadence. I need to drop my stride length and try to increase my cadence again to keep my aerobic system working as hard as when I run. The other thing that I'm mindful of is keeping as upright as possible so as not to inhibit my breathing. I can understand that it might be using slightly different muscles too, which may make things feel easier. It is all interesting stuff.