Aims: This study aims to explore the potential of an aerobic exercise program on brain structure and function in MS in a single-blind, randomized controlled phase IIa trial. We hypothesize that exercise will improve verbal learning and memory (primary endpoint) as well as induce changes in neuroimaging markers of structural and functional central nervous system (CNS) connectivity (secondary endpoints). Tertiary outcomes will include walking ability, motor function and coordination, as well as patient-based outcomes (depression, fatigue, and health-related quality of life).