I'm sort of fascinated by the estimate that walking would be at a pace of 20 km a day, because a modern human can maintain about 25 km a day indefinitely withou

I'm sort of fascinated by the estimate that walking would be at a pace of 20 km a day, because a modern human can maintain about 25 km a day indefinitely without an inordinate amount of training (worst part will be conditioning your feet) so this is either an incredibly sophisticated and well reasoned or incredibly arbitrary estimate and I wish I knew which. (It is possible too that it comes down to shoes, legends of Kenyan marathon training notwithstanding.)