I didnt get around to answering until today, but I wanted to remark that this is the hardest thing to know: what is too hard, and what is the necessary amount of challenge and exertion?
When I went to Kaiser doc about knee, he kept saying "listen to the knee" when I asked whether or when I should start walking or doing leg machines at the gym. It was kind of frustrating though I understand the point.
I only use machines because the motions are proscribed and smooth, not jerky. When I look at the free weight guys, or the people over on the personal training floor, I see a million ways to torque wrists, ankles, knees, backs etc.
Hopefully I am doin it right but like I said, knowing what is too much is hard and as a geezer, it's very easy to be conservative about overdoing it.
I also wanted to say this about muscle mass loss: one of the simplest ways I can tell what is happening to my body is that, for the last ten years, I have generally only fueled my bike via a 5 gal gas can, because with the Bonnie, it gets messy at the station with overflows and such. In these ten years, that fucker has gotten heavier. It's really frustrating. The KIND of strength you have when you are young are handling tasks, like carrying a sack of concrete, carrying a 5 gal paint bucket, etc etc. It's noticeable, and even though I work out, it has gotten a bit harder. I mean, I ain't dead yet and I can manage, but I don't seem to have the "grunt" strength I once did for such things no matter what I do. And, no lie, it's hard on the ol male ego.