Multiple sclerosis (MS) is a chronic, inflammatory disease of the central nervous system. Lack of physical activity is common in people with MS (pwMS). This can lead to several comorbid conditions such as obesity, metabolic syndrome, osteoporosis, hypertension, diabetes and worse prognosis. An increasing number of studies suggest that physical exercise can play an important role in managing symptoms, preventing complications and comorbidities in pwMS, and may possibly be neuroprotective. However, doing exercise can be very challenging for pwMS who have moderate/severe mobility disability and who have problems with walking. In this project, the investigators will explore the use of a powered Exoskeleton as an exercise tool for people with moderate to severe difficulty walking due to MS. Powered Exoskeletons are wearable robots that offer opportunity to persons with lower limb weakness to stand and walk. The Exoskeleton-assisted training provides active training with potentially much less intervention needed from therapists. However, it is not clear whether pwMS can walk with a powered Exoskeleton at speeds and intensities sufficient to positively affect health and fitness outcomes. Thus, in this study, the investigators aim to explore whether using an Exoskeleton will enable people with MS to exercise at a moderate intensity and whether people with MS find this acceptable and safe to do on a regular basis. The investigators will also explore whether training with an Exoskeleton can improve walking. The investigators will train 12 patients with MS to walk with an Exoskeleton twice a week for 8 weeks. The investigators will compare the effects with another group of 12 patients who will do exercises with a fitness instructor twice a week for 8 weeks. The investigators will study whether walking with Exoskeleton is better than fitness training in terms of fitness outcomes, walking and cognitive, psychological factors.