It's not just about walking. It's about walking while carrying stuff (not in a backpack either), interspersed with other kinds of physical effort. "13 miles" is

It's not just about walking. It's about walking while carrying stuff (not in a backpack either), interspersed with other kinds of physical effort. "13 miles" is just a proxy for total effort, requiring multiplication by some factor to get an equivalent number for walking alone. What would that factor be? A clue might be in the "400 calories per hour" number also mentioned in the story. That's nearly 7km/h at average (male) weight, or 56km equivalent during a shift. Would you feel comfortable walking 40% faster for 60% longer? Every day? It doesn't get that much easier. Appalachian Trail through-hikers would consider 35km to be a good day. I can cover 20km in under two hours, not five, but if I did that every day I'd be seriously over-training and probably headed for an overuse injury. Requiring even half that level of daily effort for people who are not in their twenties any more, who are sleep deprived due to non-work (or other-work) demands, or who already have one or more other injuries or chronic conditions, really is a bit problematic.