I had a female friend in college who worked out, despite debilitating MS. On days when she could not walk, she would train on machines and let them guide the motion, but she had no give-up in her.
Problem she then had was she looked healthy, so people thought she was pulling a scam when she parked in handicapped spaces, or that she was drunk when she swayed while walking.
The thing with MS is that there is generally remission, and during such it is as though there is no disease. These are definitely the times MS sufferers need to catch up on their exercise. I wish that were true of RA, which my wife suffers from. She has had NO remission in the entire 31 years she has had it. Steady destruction of her joints has cost her 9 replacement surgeries, and there is virtually no such thing as exercise in her vocabulary. Yet she is not a quadraplegic. Yet.