OK after some sleep and thought I think the exercise bikes plus anything else you do is going to improve your overall fitness. Even though a recumbent bike uses some different muscles, this can be complemented with a regular bike for a total workout. There are others here on the forums that ride both type of bikes regularly. Talk to your doctor perhaps and get his feel on this. Maybe he has some other suggestions to round out your fitness regimen as well. Good Luck!
'bent Brian