Need Exercise Ideas

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Hi, I'm newish here. I've been around before, but moved to a new place and didn't have internet for a while and started slipping up without this site to keep me motivated. I'm back now though and more determined than ever. But! I have a problem. I have a sprained knee and need some ideas for exercises I can do until it heals. I have bad lungs (hereditary disease) and that also restricts my options sometimes. So, anybody have any ideas?