I came across this article on osteoarthritis the other day. It lists some key factors that increase the risk of arthritis over the years:
Loss of muscle mass
All three of these factors can be largely controlled by diet and exercise. A proper diet and exercise plan can minimize excess weight. Inflammation is heavily influenced by diet, and a Paleo diet can reduce levels of inflammation. Strength training can prevent/slow the loss of muscle mass.
Something else I found interesting in this article was the statement that muscle acts as a shock absorber, and that less muscle mass means more pounding on the joints. Yet I wonder why I never see this discussed as it relates to running.
For those people who run a lot (especially on pavement), they are placing a good deal of shock on the body. It would then make sense that a runner would want to build up their lower-body muscles to help absorb some of this shock. But I don't think I've ever seen this particular recommendation. Many people recommend strength training for runners, but it's often for the reason of better performance, not better protection for the joints. I also wonder whether the larger lower-body muscles of sprinters help protect their joints from damage.