Energetic Cost of Walking and Its Physiological Correlates in Multiple Sclerosis

Background: There is evidence that the energetic cost of walking (C_w) is higher in persons with multiple sclerosis (MS) than healthy controls and may influence fatigue and everyday life functioning in this population. Such observations support the importance of identifying variables that can be targets of interventions for reducing C_w and its consequences in MS.

Objectives: The current study examined aerobic capacity, lower extremity muscle strength, and standing postural control as correlates of C_w in adults with moderate MS.

Methods: Persons with MS (N=44) who had moderate disability performed the 6-Minute Walk (6MW). C_w was based on (a) net oxygen consumption collected using a portable metabolic unit and (b) walking speed during the last three minutes of the 6MW. Participants underwent standard assessments of peak aerobic capacity, muscle strength of the knee flexors and extensors, and postural control. The data were analyzed using bivariate correlation and linear regression analyses.

Results: C_w was inversely correlated with VO_2peak (r = ‒.308, p<0.05), peak power output (r = ‒.548, p<0.00), and peak torque at 75° flexion (r = ‒.340, p<0.05), whereas C_w was positively correlated COP total area sway (r = 0.319, p<0.05), and mediolateral sway velocity (r = .411, p<0.05). Linear regression analysis indicated that 40.3% of variance in C_w was explained by peak power output (β = ‒.526, p<0.01) and mediolateral sway velocity (β = .339, p<0.05). 

Conclusions: Our findings demonstrate that aerobic power and postural sway may be important correlates of C_w in MS. Peak power output reflects a person’s physiological functional reserve that is directly relevant for understanding the penalty of gait impairment on the energetic demands of walking. The association between mediolateral postural sway and C_w suggests that mechanical inefficiency controlling the trajectory of the body’s COP during ambulation may contribute to the elevated C_w. Studies might consider interventions that focus on high-intensity interval and postural control training and its effect on the C_w.