thanks for posting this, it’s pretty interesting. i was trying to imagine how this could possibly be true, given the immense magnitude of gravity on a hill compared to wind resistance or other “upper body movements” as they say. i suppose an analog is downhill skiing, which is quite tiring for both the heart and the muscles, but of course has no uphill component typically. all the work done is battling friction or the localized gravity required to lift a part of the body or piece of equipment up or down.
very different from road cycling, where the goal of course is the absolutely minimize those parasitic losses and to get as much of the energy into the cranks and forward progress as possible.
definitely not my cup of tea, but interesting for sure!