Re: Chronic Joint/Tendon Damage
What I wonder about is not so much breakfalls, but movements like tenkan. Depending how precisely you move, it's very easy to do them in such a way that there's a kind of sideways twisting on your knee, e.g., feet facing the wrong way while there's weight on your knee as you rotate your body. From the little I know of knees, that sounds like the kind of thing where your joint is being used in a way it really isn't designed to work, and we do a LOT of tenkans in Aikido. Seems like the kind of thing where if it's done in a way that uses poor biomechanics, it could add up pretty badly over the years.
I have also read and been shown by various dojomates some interesting things with plyometrics, toe raises, balance exercises, and other such exercises in injury prevention, and have tried in the past couple of years to incorporate some of these into my own training. Anecdotally I do feel more stable on my feet.