I can attest to the benefits of swimming, isometrics and any weight machines that don't involve your injury. After three surgeries on my foot and ankle and nine months on crutches that is what kept me from turning to mush. I used a pull buoy when I couldn't tolerate kicking yet. My orthopod was shocked I was going to the gym 4 days a week.

It's amazing the creative ways you can use your own body weight without actually even needing to stand. Do whatever you can and don't give up no matter how tiny a workout you can manage. I started with two minutes, really!, when I was post-op.