Long distance runners don't get arthritis of the knees.
maybe because if you have arthritis, you don't run?
and heavy women are probably that way because they have painful knees.
and since most long distance runners are athletically endowed by their gene pool, the rest of us who are klutzes are not runners.
in my case, it is my high arched feet and varicose veins, not my knees, which are fine.