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.
MS has a number of categories, including relapsing-remitting and progressive.
These are indications of the outwards symptoms of the disease, and are not an indicator of the actual progress of the disease in the CNS.
Even during a period of remitting the damage done is still there, and certain stressors can cause symptoms that have remitted to show up again.
One very common stressor is heat.
Anything that raises the body temperature can cause symptoms to reappear.
For many years if I could not even walk in temperatures above 90 F for more than about 20 feet.
As soon as my body temperature moved up even slightly the old symptoms of loss of control of leg muscles and no position sense for my extremities returned.
How MS affects any individual patient is a complete crap shoot.
It depends on the location of the damage in the CNS.
Optical effects are common since we rely on our vision heavily, and tend to be sensitive to any distortions.
Walking takes a lot of coordination between the brain, senses and muscles. The length of the nerves to reach the lower extremities increases the chance of a problem affecting them.
The fact that you need both afferent (motor and descending) and efferent (sensory and ascending) nerve conduction only makes the places that can cause observable symptoms larger. You cannot walk if you cannot both control and know the position of your body parts.
One of the tests (before MRI) for MS was to immerse the patient in a tank of hot water and see if their symptoms became worse.
Even with MRI to locate lesions in the CNS, many do not produce any overt symptoms, while others can be clearly ties to symptoms being exhibited.
The inability to exert resistance during ‘automated’ exercise decreases its possible benefit.