Propulsive Forces Applied to the Body’s Center of Mass Affect Metabolic Energetics Poststroke

Abstract

ObjectiveTo investigate the effect of timing and magnitude of horizontally directed propulsive forces to the center of mass (COM) on the metabolic cost of walking (COW) for individuals poststroke. DesignRepeated-measures, within-subject design. SettingResearch laboratory. ParticipantsA total of 9 individuals with chronic hemiparesis poststroke and 7 unimpaired similarly aged controls (N=16). InterventionIndividuals walked on a treadmill in 2 separate studies. First, we compared the metabolic COW with an anterior force applied to the COM that (1) coincided with paretic propulsion or (2) was applied throughout the gait cycle. Next, we compared the metabolic COW with anterior (assistive) or posterior (resistive) forces applied during paretic propulsion. Main Outcome MeasureMetabolic COW. ResultsThe COW was significantly greater in the Stroke group. Anterior (propulsive) assistance reduced the COW differently based on group. The Stroke group exhibited a 12% reduction in COW when assistance was provided only during paretic propulsion, but not when assistance was provided throughout the gait cycle. In contrast, the Control group demonstrated reduced COW during both anterior assistance conditions. In addition, we observed that resistance during paretic propulsion (simulated hemiparesis for Control group) significantly increased the COW. ConclusionsSystematically manipulating propulsive forces at the body’s COM had a profound influence on metabolic cost. The timing of propulsive forces to the COM is important and needs to coincide with paretic terminal stance. Additional internally or externally generated propulsive forces applied to the body’s COM poststroke may produce a lower metabolic COW.