I don't know what the underlying factors would be that makes one group different from another; but I agree that some people should probably curb physical labor at some point to avoid future problems. Whereas others seem to remarkably benefit from continuing to chug along. Mental attitude might be involved with the latter, but it's difficult to see how mere psychological stimulus / determination in itself would get converted into actual bodily results, maintenance or repair. I certainly wouldn't count high pain tolerance in regard to degenerative and autoimmune disease consequences as being a physically manifested solution to the problem or countering of the structural / mechanistic / biochemical causes.
Indeed if it were pain tolerance that accounted for it then like with lepers, damage would become destructive, with joints eventually breaking. With leprosy, the affected areas even fall off eventually.
Recently I've been looking at
PAD (Peripheral Arterial Disease) (wikipedia.org) since I've been having some problems walking. I'd wondered if it had been down to repetitively long sessions of sitting in front of a computer (
Repetitive Strain Injury (wikipedia.org)) or whether it might even be a concern for
DVT (Deep Vein Thrombosis) (wikipedia.org). I consider it's not the later as the only symptoms is the cramping of calve muscles due to poor oxygenation when walking at speed and up an incline. (In short it's suggests that plaque build up in the blood vessels causes them to restrict flow and can lead to far worse side effects than just pain when walking, such as the worst case scenarios of clots and bleeds)
There isn't much that can be done other than dietary changes (Reducing Cholesterol etc.) and maintaining some exercise so as to increase how far I can walk before it becomes a problem.
Where as it's usually suggested that people suffering it should walk until they feel they can't bare it anymore, I've actually been walking through the pain barrier. I'm currently attempting to do a walk (once every two days, so allow muscle recovery time.) that works out to be 8km (5 miles) in total, the pain usually kicks in at a bridge that I walk over (about 250m's into the walk) although the last time I walked it I was able to sustain my speed better, I didn't start getting pains until about 500m's in and even then it didn't cripple me as much as previously.
I realised that if I walk through the pain onto the beach for the first mile or so that the pain subsides and I can walk without issue, however I'm reluctant to stop when walking just in case all my muscles stiffen up.
I therefore over-exert to overcome the problem that would otherwise limit how far I can walk.