Inclusion Criteria:

For persons with MS:

• - Physician-confirmed MS diagnosis and stable course of disease modifying therapies over the past 6 months.

• - Expanded Disability Status Scale (EDSS) score between 6.0 (intermittent or unilateral constant assistance (cane, crutch, brace) required to walk about 100 meters with or without resting) and 6.5 (constant bilateral assistance (canes, crutches, braces) required to walk about 20 meters without resting), based on a Neurostatus-certified assessor examination.

• - Relapse-free in the past 30 days.

• - Support Partner (i.e., relative or close friend) who provides greater than or equal to 1.0 hours per day of unpaid care.

Additional inclusion criteria for both persons with MS and caregivers:

• - Greater than or equal to 18 years of age.

• - Currently inactive (i.e., purposeful exercise less than or equal to 2 days/week for 30 minutes) - Asymptomatic (i.e. no major signs or symptoms of acute or uncontrolled cardiovascular, metabolic, or renal disease) based on the Get Active Questionnaire.

• - Ability to communicate in English.

Exclusion Criteria for both persons with MS and caregivers: - diagnosis of other neurological condition(s)

The study is an assessor-blinded pilot randomized controlled trial (RCT) for examining the feasibility and preliminary efficacy of a dyadic PA intervention approach for persons with MS (PwMS) affected by moderate-to-severe disability and their family caregivers (CGs). Dyads who meet the eligibility requirements will undergo the informed consent process and baseline assessment. Dyads will then be randomized to either an immediate intervention condition or a delayed control condition. Participants in the immediate intervention group will receive six group teleconference sessions, approximately 60 minutes each, every other week for 12 weeks. These sessions will be interspersed with one-on-one support calls in the weeks that group sessions do not occur. Participants will be provided with a manual for their individual use during the intervention. The intervention content will introduce participants to the concepts of shared appraisal and dyadic coping. The benefits of shared participation in PA as a coping strategy to optimize well-being at both the individual and dyadic level will be reinforced and illustrated. All participants will be taught techniques for monitoring PA behaviour, setting personalized goals to increase PA and reduce sedentary time, and strategies for overcoming challenges to PA participation. The one-to-one support calls will serve to reinforce the information provided during the group sessions, monitor safety, and troubleshoot any issues with the intervention content. All participants will undergo the assessment protocol again at 12 weeks.

Arms

Experimental: Immediate Intervention

PwMS-CG dyads will receive six group telerehabilitation sessions (~60 min each) every other week for a period of 12 weeks. This will be interspersed with brief one-on-one support telephone calls in the weeks that group sessions do not occur. All participants will be taught techniques for monitoring PA behaviour, setting personalized goals to increase PA and reduce sedentary time, and strategies for overcoming challenges to PA participation. Make-up sessions will be offered to those who miss group sessions. The one-on-one support telephone calls will serve to reinforce the information provided during the group sessions, monitor safety and troubleshoot any issues with intervention content.

No Intervention: Delayed Control

The delayed control group will not receive the intervention during the study period. Participants assigned to the control group will be offered the intervention once the study is completed.

Interventions

Behavioral: - Physical Activity Together for PwMS and their CGs (PAT-MS)

A dyadic physical activity intervention approach for PwMS and their family CGs affected by moderate-to-severe MS disability.