Couple's fitness options...

My girlfriend and I are in a very nice relationship, but she's always complaining that she could always lose a few extra pounds for me. The thing is that she has Osgood Slaughter (no idea how to spell it) which causes a lot of pain in her knee while running. This made her choose swimming as a sport when she was younger, but now she has terrible shoulder problems too. So does anyone know any good workouts we could do as a couple (i'm injury free, but I would like to be there to motivate her a bit and do the exercises)? I know sex is a good workout, but that's not the answer I'm looking for.
Couple's fitness options...
Post Opinion