Harmonic ratio is the most responsive trunk-acceleration derived gait index to rehabilitation in people with Parkinson's disease at moderate disease stages.

Background: Harmonic ratios (HRs), recurrence quantification analysis in the antero-posterior direction (RQA _detAP ), and stride length coefficient of variation (CV) have recently been shown to characterize gait abnormalities and fall risk in people with Parkinson's disease (pwPD) at moderate disease stages.
Research Question: This study aimed to i) assess the internal and external responsiveness to rehabilitation of HR, RQA _detAP , and CV, ii) identify the baseline predictors of normalization of the gait stability indexes, and iii) investigate the correlations between the gait indexes modifications (∆) and clinical and kinematic ∆s in pwPD at Hoehn and Yahr disease staging classification 3.
Methods: The trunk acceleration patterns of 21 pwPD and 21 age- and speed-matched healthy subjects (HSmatched) were acquired during gait using an inertial measurement unit at baseline (T0). pwPD were also assessed after a 4-week rehabilitation period (T1). Each participant's HR in the antero-posterior (HR _AP ), medio-lateral (HR _ML ), and vertical directions, RQA _detAP , CV, spatio-temporal, and kinematic variables were calculated.
Results: At T1, HR _AP and HR _ML improved to normative values and showed high internal and external responsiveness. Lower HRs and higher pelvic rotation values at baseline were predictors of ∆HRs. A minimal clinically important difference (MCID) ≥ 21.5 % is required to normalize HR _AP with 95 % probability. MCID ≥ 36.9 % is required to normalize HR _ML with 92 % probability. ∆HR _AP correlated with ∆HR _ML and both correlated with ∆stride length and ∆pelvic rotation, regardless of ∆gait speed. RQAdetAP and step length CV were not responsive to rehabilitation.
Significance: When using inertial measurement units, HR _AP and HR _ML can be considered as responsive outcome measures for assessing the effectiveness of rehabilitation on trunk smoothness during walking in pwPD at moderate disease stages.
Competing Interests: Conflict of interest statement The authors declare no conflicts of interest.
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