A long time ago I worked in a sports rehab clinic. You should have seen how many joggers and runners came in complaining about knee pain, only to have the Dr. tell them: "Your knees aren't strong enough. If you want to jog and not have the knee pain you will have to exercise the knee more - but differently..."  Those runners were shocked: How could my knees be too weak when I run all the time? The body works in mysterious ways, that's why!