I was a runner for more than 50 years until increasingly frequent knee injuries and constant knee pain made me quit. It bothered me to have to quit running because (1) a part of my personal identity was that I was a runner, and I was losing that, and (2) It was a definite sign of ageing, because I had to give up something I'd done most of my life due to physical limitations. I substituted riding, which I've been doing a bit more than 2 1/2 years now. My knee pain is gone, I enjoy the riding, and I feel good because of the exercise. But I still miss the running.