Effective assistance timing using characteristics of paretic ground reaction force in ankle robotic gait training for individuals with hemiparesis after stroke: a cross-sectional study.

Background: Effective ankle plantarflexion assistance (PF assistance) requires precise timing and personalized adjustment using an ankle joint robot that assists both dorsiflexion and plantarflexion during walking. Previous studies suggest that peak paretic propulsion timing (Peak PP timing) is earlier in some individuals, indicating differences in ground reaction force (GRF) characteristics among individuals with stroke. Therefore, this study aimed to identify the effective timing of PF assistance according to anteroposterior GRF characteristics.

Methods: The study included twenty-three post-stroke individuals with hemiparesis. The participants walked on a treadmill under an unassisted condition, and at 30-50% and 40-60% gait cycle (GC) PF assisted conditions. The participants were clustered into two groups based on the waveform data of the paretic anteroposterior GRF in the unassisted condition using k-means clustering, and differences in the characteristics between the two groups, and changes in paretic propulsion in each assistance condition within the cluster were analyzed. Additionally, the relationship between changes in paretic propulsion and the timing of paretic propulsion (PP timing) and Peak PP timing, were analyzed within each cluster, relative to the unassisted condition, under each assistance condition.

Results: Participants were clustered into Clusters A (N = 13) and B (N = 10). Cluster A showed earlier Peak PP timing and increased paretic propulsion in both PF assistance conditions, while Cluster B only improved in the 40-60% GC condition. A significant negative correlation was observed between changes in paretic propulsion and PP timing in Cluster A under the 30-50% GC PF assistance condition (ρ = - 0.665, P = 0.012).

Conclusions: Our results suggest that applying PF assistance, particularly during the late paretic stance phase, might be effective for individuals with hemiparesis, as it led to improvements in paretic propulsion in both clusters. Additionally, the results suggest that for participants in Cluster A, it may be important to apply PF assistance at the 30-50% GC while monitoring changes in the GRF waveform data, as this approach may be more effective for some participants in improving paretic propulsion.