Three years ago I took a nasty, nasty fall on the ice. It caused a fluid build up in my left knee and a weak back. Not sure what happened there. The muscle that got pulled is now easily pulled if I'm not very careful. I can tell if I lift something heavy, it twitches and threatens to pull again.

I read that squats are the best way to strengthen a weak back. . . but squats kill my knee. So, what the heck do I do? Also have about 100lbs to lose, so I'm at rather a loss as to what strengthen exercises I can do and not hurt myself for the time being. Should I still to walking for now, or?