Runners knees take a pounding. Look at knee geometry and you'll see that locking the knee takes it past center, lots of stress on a joint when you do that and runners do it all the time.

I started doing more leg exercises with weights (leg presses, squats, leg curls) and rather than damaging/tearing down my legs, weight training has made walking and even the occasional run much easier. More muscle is there to absorb the stress rather than putting it onto the knee joint.

Long time back one of the other lifters gave me a clue about how to not cause damage to your knees -- do not allow them to lock out. Don't fully straighten your knees when lifting so the weight stays on the muscle rather than being shifted onto bone. You can do that when walking downhill also; It's a great leg exercise, will strengthen muscle and reduce the damage to your knees.

FWIW