Maria T. Tagliaferri and Inseung Kang
Embedded Files
Abtract
Objective: Falls are the leading cause of injury-related hospitalization and mortality among older adults. Consequently, mitigating age-related declines in gait stability and reducing fall risk during walking is a critical goal for assistive devices. Lower-limb exoskeletons have the potential to support users in maintaining stability during walking. However, most exoskeleton controllers are optimized to reduce the energetic cost of walking rather than to improve stability. While some studies report stability benefits with assistance, the effects of specific parameters, such as assistance magnitude and duration, remain unexplored.
Methods: To address this gap, we systematically modulated the magnitude and duration of torque provided by a bilateral hip exoskeleton during slip perturbations in eight healthy adults, quantifying stability using whole-body angular momentum (WBAM).
Results: WBAM responses were governed by a significant interaction between assistance magnitude and duration, with duration determining whether exoskeleton assistance was stabilizing or destabilizing relative to not wearing the exoskeleton device. Compared to an existing energy-optimized controller, experimentally identified stability-optimal parameters reduced WBAM range by 25.7% on average. Notably, substantial inter-subject variability was observed in the parameter combinations that minimized WBAM during perturbations.
Conclusion: We found that optimizing exoskeleton assistance for energetic outcomes alone is insufficient for improving reactive stability during gait perturbations. Stability-focused exoskeleton control should prioritize temporal assistance parameters and include user-specific personalization.
Significance: This study represents an important step toward personalized, stability-focused exoskeleton control, with direct implications for improving stability and reducing fall risk in older adults.
Experimental setup, protocol, and representative data. (A) Subjects experienced anteroposterior slip perturbations during treadmill walking while wearing the robotic exoskeleton. Anticipatory cues were minimized using noise-canceling headphones and visual-obscuring glasses. (B) The experimental design comprised 28 different assistance conditions, repeated across four sessions. (C) Treadmill belt velocity profile used to elicit the slip response. (D) Time-series data from a representative trial illustrating biological hip torque (blue), exoskeleton assistance (red), and the resulting WBAM (green), relative to the perturbation duration (gray area). Informed consent for publication of this image was obtained from the participants.
Influence of assistance duration and magnitude on gait stability. Decreases in WBAM range indicate improved stability. The duration of assistance directly modulated the effect of assistance magnitude. All data are normalized to no exoskeleton condition. β1 represents the slope of the line. Significance levels are indicated as: *p≤0.01.
Interpolated response surfaces for objective and subjective stability. (A) Surface map of WBAM range across the assistance parameter space. (B) Surface map of perceived stability (OPUS score). Higher scores indicate greater user-perceived stability. Alignment was observed between areas of high quantitative and high perceived stability.
Average percent change in WBAM compared across conditions using a within-subject design. The best-performing parameter set represents the parameter set that produced the lowest percent change in WBAM range for each subject, averaged across subjects. Significance levels are denoted as: * p≤0.05, ** p≤0.01. Best-performing parameters improved stability by 26% relative to the baseline controller.
Google Sites
Report abuse