Military rucking studies have shown muscle strength and endurance matters more than cardiovascular training when rucking with heavy weight, which is why I have no issue carrying a bit more muscle mass.
Do you have any kind of a link to one of those studies? I’d be interested in reading one as I have noticed a somewhat different conclusion. The lighter a person is, the better off they generally have been hiking around, IME. The exception is having some muscle on your core, as it does help with carrying pack weight.
More muscle requires more oxygen and more muscle also is more weight that a person has to carry around with them. It it better positioned for center of gravity than a heavy pack, however.
I have seen some incredibly in shape college football players with serious muscle straight up get whooped by what I consider easy morning hikes.
