The investigators propose to conduct a randomized 6-month intervention study comparing cognitive functioning in individuals with relapsing-remitting multiple sclerosis assigned to either a physical activity or an active water-intake control group. Individuals will complete pre-, mid- and post-assessments of cognitive, physical, and behavioral functioning.

Interventions to increase physical activity through aerobic exercise are some of the only known treatment options to improve domains of cognition such as executive function. While increased physical activity is associated with preserved cortical functioning during exogenous executive functioning tasks in older adults, little is known about the relationship between physical activity and executive functioning in multiple sclerosis. Thus, the investigators propose to conduct a randomized 6-month accelerometry-based intervention designed to increase overall physical activity in sedentary relapsing-remitting multiple sclerosis with known cognitive challenges. The overall objective is to determine how a 6-month activity tracking intervention impacts the behavioral, neural and mechanistic associations between physical activity and cognitive functioning. All individuals who contact the Clinical Neuroscience Laboratory (CNL) with interest in this study will undergo a phone/online screening assessing inclusion/exclusion criteria. Those participants meeting I/E criteria will be invited to the lab for 2 pre-assessment sessions, one session at midpoint, and 2 post-assessment sessions at the completion of the 6 month intervention. Participants will also be asked to complete a number of online questionnaires following the first assessment session. The two pre-assessments will involve a through measure of cognitive functioning, both through the use of neuropsychological batteries and neuroimaging, and inflammatory markers through collection of a blood sample. Following the pre-assessment sessions, conducted by blind personnel, participants will be randomized to one of the two groups. Participants will be asked to self-monitor their assigned health behavior with the aid of a behavioral tracker (accelerometer or smart water bottle). Via a mobile application designed by the laboratory, participants will receive daily and weekly summaries of their health behavior progress, and motivational materials to encourage goal attainment. The 6-month intervention will involve minimal contact from study coordinators. Participants who do not adhere to study goals will be contacted by a study coordinator via phone who will use motivational interviewing to promote behavior change. Following the 6-month intervention the 2 assessment sessions will be repeated to obtain post-intervention data for comparison.

Inclusion Criteria:

• Clinically definite diagnosis of Relapsing-Remitting Multiple Sclerosis
• Score higher than 23 on the Mini-Mental Status Examination (MMSE)
• Expanded Disability Status Scale (EDSS) under 5.5
• Right-handed

Exclusion Criteria:

• Clinically isolated syndrome or progressive MS subtype
• Presence of any other neurological disorders
• Presence of psychiatric disorder diagnosed by a licensed mental health provider in the last two years
• Clinically definite relapse or use of high dose corticosteroids within the last 30 days
• Recreational drug use in the last 6 months
• Without access to a smart phone or no access to the internet
• Current use of accelerometer, pedometer, and/or physical activity monitoring equipment
• Presence of ferromagnetic implanted devices or self-reported claustrophobia