Lots of good answers, but I would add that long-term hiking in particular is remarkably sustainable. As far as I know, hikes like the one described here (8 hou

Lots of good answers, but I would add that long-term hiking in particular is remarkably sustainable. As far as I know, hikes like the one described here (8 hour days at a mild/moderate pace) can be kept up almost indefinitely if you have a good diet and don't run into acute injuries. Lots of overtraining injuries like shin splints are much less likely than in other sports. That said, you can get badly burned by fairly tame risks just because you're doing something so repetitive. Even simple dietary stuff can blow up - if you're eating the same handful of meals every day you can run into uncommon issues like micronutrient deficiencies. The risks you mentioned are definitely real, but most of the stories are hear suggest that there are solid warning signs (even just "I feel shitty now"). Most of the people who burn out seem to be ignoring those signs or pushing through them for some goal.