Time-integrated propulsive and braking impulses do not depend on walking speed

Background: Enhancing propulsion during walking is often a focus in physical therapy for those with impaired gait. However, there is no consensus in the literature for assessing braking and propulsion. Both are typically measured from the anterior-posterior ground reaction force (AP-GRF). While normalization of AP-GRF force by bodyweight is commonly done in the analysis, different methods for AP-GRF time axis normalization are used. Research question: Does walking speed affect propulsion and/or braking, and how do different methods for calculating propulsion and braking impact the conclusion, in both healthy adults and those with lower limb impairment? Methods: We investigated three different analysis methods for assessing propulsion. 1. BW-TimeIntegration: Bodyweight (BW) normalized time integration of AP-GRF (units of BW center dot s). 2. BW-%StanceIntegration: BW normalized AP-GRF is resampled to percent stance phase prior to integration (units of BW center dot%Stance). 3. BW-Peak: BW normalized peak force (units of BW). We applied these methods to two data sets. One data set included APGRFs from trials of slow, self-selected, and fast walking speeds for 203 healthy controls (HCs); a second data set included subjects with lower limb orthopedic injuries. Results: Using the BW-TimeIntegration method, we found no effect of walking speed on propulsion for HCs. Time integration over the longer stance phase of slower walking balanced the lower magnitude AP-GRFs of slower walking, resulting in a time-integrated impulse that was the same regardless of walking speed. In contrast, the other two methods that are not time integration methods found that propulsion increased with walking speed. Similarly, in the gait pathology data set, differences in results were found depending on the analysis method used. Significance: For many gait studies concerning propulsion and/or braking, the impulse measure used should be related to the body's change of momentum, necessitating an analysis method with a time integration of the APGRF.

Automated summary

The study found that walking speed did not affect propulsion in healthy adults, with slower walking balancing the lower AP-GRFs through longer time integration. Other methods found that propulsion increased with walking speed, and results varied depending on the analysis method used in the gait pathology dataset.