TITLE: Immersive Virtual Reality and Exercise Programs in Multiple Sclerosis: ExeRVIEM III. INTRODUCTION: Multiple sclerosis (MS) is a chronic neuroimmunological and degenerative disease characterized by demyelination within the central nervous system. Its clinical course involves motor impairment, sensory disturbances, cognitive dysfunction, and a progressive decline in functional independence. MS is one of the leading causes of non-traumatic disability in young adults. This highlights the considerable impact of the disease, both in terms of healthcare burden and healthcare expenditure. Within this context, therapeutic exercise has evolved from being considered potentially harmful to being recognized as a safe and effective intervention capable of improving gait, balance, cardiorespiratory fitness, fatigue, and quality of life in people with MS. A model has been proposed for prescribing and progressing exercise at different stages of MS: passive range-of-motion exercises designed for patients with the most severe symptoms, a second stage incorporating active muscle-strengthening exercises, and finally, integrated exercise programs that incorporate strength, endurance, balance, and coordination training. Evidence from systematic reviews and meta-analyses shows that structured exercise (including high-intensity protocols when performed under supervision) is safe and can improve functional outcomes. Our ExeRVIEM III project (Physiotherapy program with High-Intensity Exercise Program and Immersive Virtual Reality in Multiple Sclerosis) represents a novel strategy to facilitate rehabilitation exercise programs using head-mounted virtual reality displays. HYPOTHESIS: The ExeRVIEM III project, based on training physical function in people with MS, is feasible and safe, and could have a potential clinical impact in the motor and cognitive domains, as well as applicability in community settings, such as patient associations. GENERAL OBJECTIVES: 1.1 To design and implement an ExeRVIEM III exercise program/protocol for people with MS. 1.2 To evaluate the safety of the high-intensity virtual reality exercise program. SPECIFIC OBJECTIVES: 2.1 To analyze the possible changes in disability, functional variables, cognitive domains and biomarkers in the short and medium term in people who attend a patient association and carry out the ExeRVIEM III exercise program for people with MS. METHODOLOGY: A randomized controlled trial, double-arm (experimental and control group) study will be conducted at a patient association (Santiago de Compostela, Spain). The intervention will consist of an 6-month supervised virtual rehabilitation program, with two weekly sessions on alternate days, in addition to the standard rehabilitation prescribed by the patient association clinical team (physiotherapy, occupational therapy, and cognitive training sessions). An inmersive virtual reality (IVR) body combat exercise videogame will be used, administered via a virtual reality headset. In accordance with clinical guidelines for IVR, sessions will be intentionally brief (10 minutes) to minimize cybersickness and excessive fatigue. Assessments will be conducted at baseline (week 0) and immediately after the intervention (week 24). Demographic and clinical data will also be collected, including sex, age, comorbidities, disease duration, MS subtype, and pharmacological treatment. Assessments will be conducted at the patient association and in the Neurology Department of the referral hospital. Feasibility, safety, strength parameters, dual-task performance and fatigue levels assessments will be performed at the patient association by physiotherapists, while the remaining assessments will be completed at the hospital by a neurologist specializing in MS. The content of the assessments will be: Patient characteristics that will include data on age, sex, years since diagnosis, MS subtype, and pharmacological treatment. Feasibility: Number of virtual sessions attended by each participant (adherence rate via registration sheet). Rate Perceived Effort using the modified Borg scale, which measures the level of perceived exertion on a scale of 0 to 10 from no effort to maximum effort. Safety: adverse events using the Simulator Sickness Questionnaire (SSQ).Strength parameters using Five times sit to stand test (FTSST) and handgrip test. Functional mobility will be assessed using Timed and Go test (TUG) and with dual task performance using TUG-cog. Level of fatigue using the Fatigue Severity Scale (FSS). Level of disability: using the Expanded Disability Status Scale (EDSS).Gait will be evaluated using the 25Foot Walk Test (25FWT). Manual dexterity will be assessed using 9-Hole Peg Test (9HPT). Cognitive domains evaluated by the Symbol Digit Modalities Test (SDMT)Axonal injury biomarker evaluated by Neurofilament light chain (sNfL) concentrations.