I ran competitively from college into my 50s, loved it and did OK at 10K to half marathon distance, better than I did on the bike. I alternated periods or seasons of cycling and running to give my legs a break and to deal with injuries. There is much to be said for just going out the door with no gear but your shoes and the clothes on your back. I had good mechanics and the nice pop in the legs most of the time and it felt great. However, I blame it for the cervical spine problem that almost made me a C6 quad and, although no one told me I had to, I stopped after I had my neck rebuilt. Now, because I’m worried about bone loss, I am building in some walking and taking the stairs at work. I also do plenty of squats and other resistance exercises in the gym, but I wonder if that’s as effective as the shock loading from gait.