A Health Action Process Approach Online Intervention for People With Multiple Sclerosis

Inclusion Criteria: * are 18 years old and above; * any type of multiple sclerosis * have not maintained 30 minutes of MVPA accumulated per day for 2 days of the week during the previous 6 months; * be relapse-free for the past 30 days; * show low risk for contraindications of physical activity indicated by no more than a single 'yes' response on the Physical Activity Readiness Questionnaire; * be able to walk with or without an assistive device; * are willing to be randomized to an intervention or control group, complete the surveys and questionnaires, and wear an accelerometer during the intervention period; * have a reliable Internet access. Exclusion Criteria: * have a score \>14 for the leisure score index of the Godin Leisure-Time Exercise Questionnaire; * No computer or mobile device access with the internet. * Patient determined disease steps (PDDS) Score = 7 i.e., using a wheelchair or scooter most of the time, or PDDS Score = 8 being bedridden. * Anyone living outside of the United States of America. * Anyone who is unable to speak, read and write in English. * not willing to be randomized to an intervention or control group, complete the surveys and questionnaires, and wear an accelerometer during the intervention period.