Depends! People that train for Ironman average something like 20h a week over a year (some peak at closer to 40 during their race buildup)

But most of us are way less than that, more like 10 hours a week. And if you are careful your body rebuilds stronger each time.

My knees are not shot from running. In fact I’d wager they are in better health than a desk potatoe that never exercises.