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.

Inclusion Criteria:

• Diagnosis of MS as per the McDonald criteria (Polman et al., 2011).
• Age 18 years or older.
• Cognitive ability to give consent and participate in the protocol.
• Walking limitations with Expanded Disability Status Scale (EDSS) scores ranging from 5.0 to 7.5.
• Enough strength in hands and shoulders to support themselves standing and walking using crutches or a walker.
• Meet the general requirements to fit with the Phoenix Exoskeleton (160-190.5 cm in height, weight below 80 Kg, hip width no greater than 42.7 cm measured when sitting, healthy skin where it touches Phoenix Exoskeleton).
• Able to tolerate exercise twice per week as judged by the PI during screening.

Exclusion Criteria:

• Any illness, other than MS, affecting walking and exercise performance.
• Severe cognitive or behavioral impairment.
• Relapses 3 months prior to enrolment.
• Change in disease modifying drugs for MS 6 months before enrolment.
• Botulin toxin injections for the lower limbs the previous 3 months.
• Any medical contraindications to assisted walking (e.g., cardiovascular condition, weight-bearing restrictions, osteoporosis or other fracture risk, pregnancy, uncontrolled seizure).
• Significant flexion contractures limited to 35 degrees at the hip and 20 degrees at the knee that precluded Phoenix Exoskeleton fit.
• Psychopathology or other health conditions that the physiotherapist, in his or her clinical judgement, considers to be exclusionary to safely use an Exoskeleton.
• Living more than 20 miles away from the experiment location to reduce burden on patients due to the number of planned study visits.

It is not practical to blind the participants to the intervention as the study team are studying two different types of physical activities. The study team will explore whether it is feasible for the outcome assessor to be blind to the treatment allocation.