Well, yeah. Our joints are mechanical.

(Note that I am agreeing with the notion that our bodies wear out, as do all machines. I am not endorsing the parent post's claims about shoes being better for running.)

Yet our bodies have excellent self-repairing facilities (as always, supported by appropriate diet, sleep, yada yada).

Parts of our bodies have excellent self-repairing facilities. Parts. Your liver won't repair itself if you damage it enough. You have one set of lungs, so if you smoke enough they most likely aren't growing back. And most critically for this discussion, ligaments and cartilage will not heal once damaged. They are optimized to be as tough as possible, at the expense of not healing at all once damaged.

As the recipient of 2 knee surgeries, and possibly an upcoming 3rd, believe me when I say that I would like nothing more than to have my knees "self-repair". But it just isn't going to happen naturally. You get one set of cartilage and ligaments, and once they are gone, they're gone.

Thank you... This seems like one of those basic things we should learn in elementary school -- the healing rates of various parts of our body. We should know what needs the most protection/care. I still do not know that information, and it seems that somebody has to be damaged in order for others to learn about it. Mentally putting "ligaments and knee cartilage" on my list of things to be careful about. I didn't know there was no regeneration there. :(

Sure, but not enough to keep our joints healthy indefinitely.