Re: preserving knees and shoulders....
All this business about staying away from "heavy" weights is also nonsense. You have to lift at a certain level of resistance in relation to your maximum in order to provide enough stimulus to actually strengthen any tissue or gain strength. It's nothing to be afraid of.
There is some risk of injury doing extremely heavy or intense lifting. Unless you are some kind of strength athlete, you would rarely need to use weight that you can't do at least 4 or 5 proper reps with, except with the Olympic lifts. There is also virtually no reason to ever train to concentric muscle failure, do negatives, or any other such intensity tricks.
People are not made of porcelain. We can pick up heavy stuff and put it back down. If we do it a few times in a row, a couple times a week, we get strong. It's not rocket science. What destroys the human body more than anything is precisely the opposite: inactivity.