In Multiple Sclerosis, weakness usually appears because of the decreased central conduction which succeeds demyelination. Deconditioning itself occasionally causes weakness. Depending on the case, a strengthening program will help bring the muscle back to normality. Even if the muscle is neurologically weakened, it should be stimulated regularly to prevent atrophy.

Your therapist can aid you with strengthening your muscles by providing you with a routine which you can do on your own. 

Not only exercise, but also medication can boost nerve conduction. Aminopyridines, potassium channel blockers, allow faster and more efficient transmission in the demyelinated nerves. These chemicals can be found in pharmacies.  However, since the FDA did not yet approve the compound, its use is not recommended.