Energetic Cost of Walking and Its Physiological Correlates in Persons With Multiple Sclerosis Who Have Moderate Mobility Disability

Abstract

ObjectiveThis study examined aerobic capacity, upper leg muscular strength, and static postural control as correlates of the energetic cost of walking (Cw) in moderate multiple sclerosis (MS) mobility disability. DesignCross-sectional study. SettingUniversity-based laboratory. ParticipantsPersons (N=44) with MS (aged 48.43±8.64 years) who have reached a benchmark of moderate mobility disability (ie, Expanded Disability Status Scale scores between 4.0 and 6.0) participated in the study. Main Outcome MeasuresCw was based on (1) net oxygen consumption collected using a portable metabolic unit and (2) walking speed during the 6-minute walk test. Participants underwent standard assessments of peak aerobic capacity, upper leg muscular strength, and static postural control. ResultsThe data were analyzed using bivariate correlation and linear regression analyses. Cw was inversely correlated with peak oxygen consumption (r=–.308, P<.05), peak power output (r=–.548, P<.00), and peak torque at 75° knee flexion (r=–.340, P<.05), whereas Cw was positively correlated center of pressure area sway (r=.319, P<.05), and mediolateral sway velocity (r=.411, P<.05). 40.3% of variance in Cw was explained by peak power output (β=–.526, P<.01) and mediolateral sway velocity (β=.339, P<.05). ConclusionOur findings demonstrate that aerobic power and postural sway may be important correlates of Cw in moderate MS mobility disability. Peak power output reflects a person’s physiological functional reserve that is directly relevant for understanding the penalty of walking impairment on the energetic demands of walking. The association between mediolateral postural sway and Cw suggests that mechanical inefficiency controlling the trajectory of the body’s center of pressure during ambulation may contribute to the elevated Cw.