When I was quite young I developed an affinity for climbing up things and jumping off them, and I kept doing it throughout my youth, working up to bigger and bigger things.<p>Parkour first showed up on YouTube when I was in my early 30s, but I was made for it, so I got involved. I trained it for 3 years, and at my peak I could jump down 12 feet to pavement, 16 feet to grass, and 22 feet to sand at this one beach cliff.<p>I'm 45 now, I rock climb and boulder. Still taking plenty of big hits with my legs. My tendons and ligaments are more brittle than they once we're, and falling more than 12 feet to a crash pad puts me at risk of a strain, but my knees are fine. They're fine because use them. I run up hills, and I run down them too.<p>I've gotten into enough arguments with sports science people, and lost because the science didn't support up my lived experience, or the experience of long list of athletes across many disciplines who have (supposedly) abused their knees persistently over multi-decade careers.<p>So this is all vindicating.