The goal of this interventional study is to test the feasibility of 12 weeks of aerobic exercise for people with advanced multiple sclerosis (i.e., wheelchair users). The main questions it aims to answer are:
* Is the exercise intervention feasible in terms of study processes, resources, management, safety, and acceptability?
* Can the intervention improve aerobic fitness, function in daily life, cognition, symptoms of fatigue and pain, and sensation?
* What are participants' experiences of taking part in the exercise intervention?
Participants will take part in moderate-intensity aerobic exercise twice a week for 12 weeks in a supervised research setting. Outcomes will be measured at baseline (0 weeks), mid-intervention (6 weeks), post-intervention (12 weeks), and 12-weeks after the intervention (24 weeks). The outcomes include feasibility measures, aerobic fitness, function in daily life, cognition, symptoms of fatigue and pain, sensation, and participant experiences of taking part in the exercise intervention.