Originally Posted by
Yabby
Things that come to mind:
1. Swimming as you listed is amazing. You can still use your legs and it will not have much impact on your knees. If you can enjoy swimming, you have it made. Amazing cardio and gives nice wide shoulders.
2. Body combat classes and/or boxing in some form. Lots of upper body and anytime I do these for more than 30 mins, my back feels it the next day. Feels amazing.
3. Rowing: Most gyms have a rower somewhere and you can take your legs 100% out of it if you wanted.
If you are looking for something at home, Beachbody "The Work" has a lot of good workouts where they focus on push/pull. You still use your legs, but you can take a lot of that out and just do the upper body stuff.