Mechanistic Reorganization of Step Work in Hemiparetic Walking: Modeling and Center-of-Mass Power/Work Analysis

Post-stroke hemiparetic gait is commonly characterized by reduced paretic propulsion and interlimb asymmetry, yet the mechanical consequences of severely insufficient push-off for gait regulation remain unclear.

We examine how unilateral push-off deficiency reorganizes mechanical work across the gait cycle and regulates step length. We explored the mechanisms underlying how and why hemiparetic gait is expressed using a simple powered model and compared the model predictions against empirical data.

The model predicts a threshold behavior: when paretic push-off falls below ~ 25% of optimal, compensation shifts from post-transition restoration to pre-transition energy induction, and reduced paretic step length becomes mechanically favorable, which is also seen empirically. When paretic late-stance push-off is absent, early-stance positive work emerges, vertical COM motion collapses to a single pendular motion per stride, and paretic limb step length remains disproportionately short relative to speed. As limited paretic push-off emerges, COM undergoes double pendular motion per stride, and the four-phase COM power structure previously reported in able-bodied walking reappears. Reduced single-support duration and paretic positive work capacity constrains step length, which increases step length asymmetry and stance-phase energy dissipation. Paretic net COM work remains negative across speeds, whereas the nonparetic limb exhibits persistent positive net work.

Hemiparetic walking can be considered a constrained optimization problem in which decreased step length and phase-redistributed work may reflect mechanical adaptations to impaired transition mechanics, extending classical step-to-step transition and total step work theories to pathological gait.