Immediate Biomechanical Effects of Providing Adaptive Assistance With an Ankle Exoskeleton in Individuals After Stroke

Abstract

Recent studies on ankle exoskeletons have shown the feasibility of this technology for post-stroke gait rehabilitation. The main contribution of the present work is a comprehensive experimental analysis and protocol that focused on evaluating a wide range of biomechanical, usability and users' perception metrics under three different walking conditions: without exoskeleton, with an ankle exoskeleton unpowered, and with an ankle exoskeleton powered. To carry out this study, we developed the ABLE-S exoskeleton that can provide time-adapted ankle plantarflexion and dorsiflexion assistance. Tests with five participants with chronic stroke showed that walking with the ABLE-S exoskeleton significantly corrected foot drop by 25 % while reducing hip compensatory movements by 21 %. Furthermore, asymmetrical spatial gait patterns were significantly reduced by 51 % together with a significant increase in the average foot tilting angle at heel strike by 349 %. The total time to don, doff and set-up the device was of 7.86 ± 2.90 minutes. Finally, 80 % of the participants indicated that they were satisfied with their walking performance while wearing the exoskeleton, and 60 % would use the device for community ambulation. The results of this study add to the existing body of evidence supporting that ankle exoskeletons can improve gait biomechanics for post-stroke individuals.

Relationship Between Ankle Assistive Torque and Biomechanical Gait Metrics in Individuals After Stroke

“…1.A). Previous experiments in stroke survivors showed relevant benefits of the ABLE-S exoskeleton to improve spatial and temporal gait parameters [9]. Specifically, we found that walking with the ABLE-S reduced abrupt loading responses, foot drop, hip compensatory movements and asymmetrical gait patterns compared to walking with no exoskeleton.…”

“…The ABLE-S device [9] is a unilateral ankle exoskeleton that provides PF and DF assistance to increase forward propulsion and foot clearance in hemiplegic individuals (see Fig. 1.A).…”

“…For the majority of the control strategies, the parameter tuning is laborious, as therapists must manually adjust the parameters relying only on subjective feedback from the patients and visual assessments of the gait pattern [6], [7]. A few studies have shown that the process of tuning the control parameters requires the highest amount of time when setting up the device together with donning process [4], [8], [9]. Manual tuning might often lead to a sub-optimal set of parameters, and does not take advantage of the data gathered by the exoskeleton to facilitate the parameter tuning.…”

Recent advances in wearable actuated ankle-foot orthoses: Medical effects, design, and control

“…However, since they are commonly connected to gearboxes with large velocity transmission ratios, the rotary inertia of devices is large; it curbs free foot motion. Accordingly, motors with large output torque and low rotary velocity 24 can effectively limit their inertia levels.…”

“…Results indicated that the identified assistance timing improved the activity of the tibialis anterior. de Miguel-Fernandez et al 24 designed assistive torque profiles for PF and DF assistance, with adjustable timing and level following a pi-shaped function. Wu et al 92 conceived assistive torque for an ankle exoskeleton based on timing during a gait cycle.…”