As a Dominant you are meant to protect and care for your submissive.  Therefore, it is crucial that your slave gets the exercise they need to stay healthy.  Even if this means that you must put a collar and leash on them and have them follow behind while you exercise. 

Of course, I don't think taking your submissive for a walk on their leash is the worst thing they could experience.  So they should be more then happy to follow their Dominant's lead and the best part is they won't even realize they are exercising.