oxygen cost of walking in persons with multiple sclerosis: disability matters, but why?

Background. The oxygen cost (O2 cost) of walking is elevated in persons with MS, particularly as a function of increasing disability status. Objective. The current study examined symptomatic (i.e., fatigue, pain, anxiety, and depression) and gait (i.e., velocity, cadence, and step length) variables that might explain why disability status is associated with O2 cost of walking in persons with MS. Materials and Methods. 82 participants completed the Patient-Determined Disease Steps, Fatigue Severity Scale, McGill Pain Questionnaire, and Hospital Anxiety and Depression Scale and undertook 2 trials of walking on a GAITRite electronic walkway. Participants then completed a six-minute walk test with concurrent assessment of expired gases for quantifying oxygen consumption and O2 cost of walking. Results. Disability (r=0.55) as well as fatigue (r=0.22), gait velocity (r=-0.62), cadence (r=-0.73), and step length (r=-0.53) were associated with the O2 cost of walking. Cadence (β=-0.67), but not step length (β=-0.14) or fatigue (β=-0.10), explained the association between disability and the O2 cost of walking. Conclusions. These results highlight cadence as a target of rehabilitation for increasing metabolic efficiency during walking among those with MS, particularly as a function of worsening disability.