Individual limb mechanical analysis of gait following stroke.

The step-to-step transition of walking requires significant mechanical and metabolic energy to redirect the center of mass. Inter-limb mechanical asymmetries during the step-to-step transition may increase overall energy demands and require compensation during single-support. The purpose of this study was to compare individual limb mechanical gait asymmetries during the step-to-step transitions, single-support and over a complete stride between two groups of individuals following stroke stratified by gait speed (≥0.8 m/s or <0.8 m/s). Twenty-six individuals with chronic stroke walked on an instrumented treadmill to collect ground reaction force data. Using the individual limbs method, mechanical power produced on the center of mass was calculated during the trailing double-support, leading double-support, and single-support phases of a stride, as well as over a complete stride. Robust inter-limb asymmetries in mechanical power existed during walking after stroke; for both groups, the non-paretic limb produced significantly more positive net mechanical power than the paretic limb during all phases of a stride and over a complete stride. Interestingly, no differences in inter-limb mechanical power asymmetry were noted between groups based on walking speed, during any phase or over a complete stride. Paretic propulsion, however, was different between speed-based groups. The fact that paretic propulsion (calculated from anterior-posterior forces) is different between groups, but our measure of mechanical work (calculated from all three directions) is not, suggests that limb power output may be dominated by vertical components, which are required for upright support.