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

PurposePost-stroke hemiparetic gait is commonly characterized by reduced paretic propulsion and interlimb asymmetry, yet the mechanical consequences of sever insufficient push-off for gait regulation remain unclear. We examine how unilateral push-off limitation reorganizes mechanical work across the gait cycle and regulates step length. MethodsWe use a simple powered walking model along with center-of-mass (COM) power derived from ground reaction forces. Experimental analysis was performed across walking speeds (0.2-0.7 m{middle dot}s-1). ResultsThe model predicts a mechanical regime switch: when paretic push-off falls below ~25% of nominal, step-to-step transition mechanics can no longer be satisfied within the transition window, forcing compensation to shift to pre-transition phases and mechanically favoring shorter paretic steps, 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 step length remains disproportionately short relative to speed. As limited paretic push-off emerges, COM performs double pendular motion per stride and the healthy four-phase COM power structure reappears; however, paretic positive work and propulsive impulse does not scale with speed, indicating persistent transition incapacity. Elevated paretic negative work and reduced vertical impulse constrain step length and increase stance-phase energy dissipation. Paretic net COM work remains negative across speeds, whereas the nonparetic limb exhibits persistent positive net work. ConclusionHemiparetic walking can be considered a constrained optimization problem in which step length shortening and phase-redistributed work compensate for impaired transition mechanics, extending classical step-to-step transition and total-step work theories to pathological gait.