There's a really cool (even, dare I say it, inspirational?) video making the rounds by Dr. Mike Evans:
(If embedding isn't working for you, here's the link 23 1/2 Hours.)
I like it because it's really well done, and (as Rvan would say) they "did some science on it".
And here's the anecdotal evidence to support the fact that being inactive will kill you:
On Monday I managed to tweak my upper back while sitting in my chair at work doing nothing, and that was while I was still recovering from the weekend when I hurt my shoulder while rolling over in bed.
As Jon says, you have to expect some health problems as you get older, but really? At 43?