Center-of-Mass Work Organization Supplements Walking Speed: a Biomechanical Characterization of Hemiparetic Gait

Abstract Background and Purpose Walking speed is the dominant clinical metric used to classify post-stroke hemiparetic gait severity. However, speed does not describe how mechanical energy is generated and redistributed. We tested whether whole-body center-of-mass (COM) work patterns provide a biomechanically grounded supplement to speed-based severity classification. Methods Limb-specific COM power and work were computed from ground reaction forces using the individual-limbs method across five walking speeds (0.2–0.7 m/s). We quantified net COM work index of asymmetry (IA_Wnet), positive COM work asymmetry (IA_Wpos), and the Propulsion–Support Ratio (PSR = impFy/impFz). Piecewise and quadratic regressions were used to assess speed-dependent trends. Results IA_Wnet remained elevated across speeds and showed no significant high-speed association. IA_Wpos demonstrated a significant quadratic relationship with speed (p=0.023, R²=0.23), decreasing near 0.5 m/s before rising again. Paretic limb PSR remained constrained and exhibited a quadratic association (p=0.012, R²=0.14), while unaffected limb PSR declined significantly at higher speeds (p=0.019, R²=0.38). Below 0.5 m/s, COM power profiles collapsed to a two-phase pattern without paretic limb push-off; at ≥0.5 m/s, a four-phase structure emerged. Conclusion Increasing walking speed did not normalize interlimb mechanical imbalance. COM work organization revealed a biomechanical transition near 0.5 m/s and distinguished compensation from recovery-based restoration. Supplementing speed with COM work and propulsion–support metrics may refine severity stratification and guide mechanism-targeted rehabilitation.