Someone told me once that serious runners can expect only about 10 or so years of running before their knees give out. I've been running more than that, but I only do 6-7 miles at a time. So maybe they were talking about marathoners. I'm 40 and wondering how soon I'll have to switch to swimming or something else.
im guessing its a progressive degeneration of the tendons/ligaments/bones at major impact points (like knees, ankles, etc.)... i dont think its going to be like they are good one day and bad the next. So if you've been running for a while and have no pain or that kind of think, you'll probably be alright for some time.
This is a question for a doctor experienced in sports medicine. IF you've been using good shoes, IF you're a gifted runner with a smooth gait, IF you are genetically well set up for running, IF you've had no bad falls or injuries, and IF your joints stay well-lubricated - you might run for years. But you could also start having problems tomorrow.
Running is obviously important to you - but could you divide your time between running and perhaps swimming NOW and slowly transition a bias towards running to a bias towards swimming over time?
Remember that you are entering "middle age" when testosterone values decline, as does GH production. Your joints and tendons will not be as healthy in the future as they are now.
My knees always used to hurt and pop when I tried to run, when I was more out of shape. Now that I've lost some pounds and I have some calves, I can run a bit and my knees are fine. No marathons, but what I thought was a knee problem isn't. My feet are flat, but my shoes are good. I do go through them fast, though...
