On a cellular level, what stimulates your chondrocytes, the stem cells that grow new cartilage, is cyclical loading. It’s a pattern of force that’s associated with things like running, jumping or weight lifting. These cells aren’t stimulated in the same way by lower-impact activities like using an elliptical machine or cycling.
For cartilage to remain healthy and regenerate in the way that it does for someone who is in their teens or 20s, the preponderance of evidence suggests that cyclical loading in the form of running or weight lifting is a really effective way to do that.
To a physician of my age this is like treating asthma with smoking.
It does match my experience though. When my familial arthritis kicked in I thought my CrossFit days were done. Instead my knees feel better when I’m doing my wall balls and back squats…