Inclusion Criteria:

• - Diagnosis of MS (primary or secondary progressive) without relapses in the preceding 3 months.

• - Disability rate defined by Expanded Disability Status Scale (EDSS) score from 6 to 7.

• - Ability to perform the Timed 25-Foot Walk (T25-FW) test.

• - Mini-Mental Status Examination score ≥ 24/30.

Exclusion Criteria:

• - Other (neurological) conditions that may affect motor function.

• - Medical conditions might interfere with the ability to complete the study protocol safely.

• - Presence of spasticity with a Modified Ashworth Scale (MAS) score > 3 or retractions limiting the range of motion of the hip, knee or ankle.

• - MS relapses or medication changes or any other confounding factors during the study period.

- Rehabilitation treatment or botulinum toxin injection in the 3 months preceding the start of the study

Gait disorders are the most frequent symptoms associated to multiple sclerosis (MS).Robot-assisted gait training (RAGT) in people with MS (PwMS) has been proposed as a possible effective treatment option for severe motor disability. Although RAGT continues to prove effective in increasing patient mobility, no significant superiority was found when compared to intensive overground gait rehabilitation (OGT). In PwMS, RAGT at high-intensity may enhance fatigue and spasticity, compromising the effectiveness and applicability of the intervention. This study aims to evaluate the effects of a low-intensity RAGT at progressively increasing intensity compared to conventional RAGT and OGT in PwMS and moderate to severe walking impairment. We will recruit 24 PwMS from the patients afferent to Outpatient Rehabilitation Clinic at University Hospital of Ferrara and we will assign them to one of the three treatment groups: low-intensity RAGT at progressively increasing intensity, conventional RAGT and OGT. All participants will receive 3 weekly treatment sessions of 3 hours each for 4 weeks. In the first 2 hours of treatment, an experienced physiotherapist will propose a programme based on stretching exercises, muscle strengthening and educational interventions. During the last hour, subjects will undergo specific gait training according to the assignment group. Subjects allocated to low-intensity RAGT at progressively increasing intensity group will receive gait rehabilitation on the Lokomat device and a speed initially set at 1.0 km/h, with progressive increments of 0.1 km/h at each training session. The working time consists of bouts of 3 minutes of work alternated by 1 minute of recovery, to be repeated 8 times. Subjects allocated to conventional RAGT will receive gait rehabilitation on the Lokomat device and the machine parameters will be determined based on the patient's characteristics. Subjects allocated to OGT will perform a 40-minute walk on a flat surface supervised by a physiotherapist. Outcomes will be assessed before and after treatment and at 3-month follow-up. The primary outcome is walking speed. Secondary outcomes include mobility and balance, psychological measures, muscle oxygen consumption, electrical and hemodynamic brain activity, urinary biomarkers, usability, and acceptability of robotic devices for motor rehabilitation.

Arms

Experimental: Low-intensity RAGT at progressively increasing intensity

Participants will receive 3 weekly treatment sessions of 3 hours each, for a period of 4 weeks and a total of 12 sessions. In the first two hours of treatment, an experienced physiotherapist will propose a programme based on stretching exercises, muscle strengthening and educational interventions. During the last hour of treatment, subjects allocated to this group will receive gait rehabilitation on the Lokomat device (Hocoma). The device in use will be set at 60% robotic assistance, 50% of load suspension, and a speed initially set at 1.0 km/h, with progressive increments of 0.1 km/h at each training session. The working time consists of bouts of 3 minutes of work alternated by 1 minute of recovery, to be repeated 8 times.

Active Comparator: Conventional RAGT

Participants will receive 3 weekly treatment sessions of 3 hours each, for a period of 4 weeks and a total of 12 sessions. In the first two hours of treatment, an experienced physiotherapist will propose a programme based on stretching exercises, muscle strengthening and educational interventions. During the last hour of treatment, subjects allocated to this group will receive gait rehabilitation on the Lokomat device (Hocoma). . In this case the parameters for setting the machine will be determined by the physiotherapist in charge for treatment administration in relation to the specific characteristics of the patient.

Active Comparator: Over ground training (OGT)

Participants will receive 3 weekly treatment sessions of 3 hours each, for a period of 4 weeks and a total of 12 sessions. In the first two hours of treatment, an experienced physiotherapist will propose a programme based on stretching exercises, muscle strengthening and educational interventions. During the last hour of treatment, the subject will perform a 40-minute walk on a flat surface, preceded by a warm-up phase and followed by a 10 minute warm-down phase each. Subjects will walk back and forth over a distance of approximately 30 metres using their walking aid.

Interventions

Device: - Lokomat device (Hocoma AG, Volketswil, Switzerland).

Robot Assisted Gait Training device

Other: - Conventional walking training

Self-paced supervised walking training