I think I'm making progress with my exercise. It has been at least 13 years since both of my legs felt well enough to do any real challenging exercise. Now I'm able to participate fully in water aerobics (quite vigorous) and ride the stationery bike. Today I rode the bike for 45 minutes (16.2 miles) , mainly on levels 3 and 4 and then (this is the big part for me) I walked on the treadmill and got up to 4.0 mph!!!! I briefly tried to walk that fast in 2002 when I was rehabbing after my first knee replacement but my other knee really couldn't handle it. I know that they told me not to go above 4.2-4.6 on the treadmill because of the replacements but I never dreamed 6 months ago that I'd be able to achieve this! (I had the other knee replacement done in April 2008). I could only manage about 4 minutes at this speed but I was really psyched about it. I'll keep working at it on days when I don't have water aerobics and now I know that I will be able to increase my endurance and time over the next few months.
Yippee!