Effects of selectively assisting impaired subtasks of walking in chronic stroke survivors

Abstract

Background Recently developed controllers for robot-assisted gait training allow for the adjustment of assistance for specific subtasks (i.e. specific joints and intervals of the gait cycle that are related to common impairments after stroke). However, not much is known about possible interactions between subtasks and a better understanding of this can help to optimize (manual or automatic) assistance tuning in the future. In this study, we assessed the effect of separately assisting three commonly impaired subtasks after stroke: foot clearance (FC, knee flexion/extension during swing), stability during stance (SS, knee flexion/extension during stance) and weight shift (WS, lateral pelvis movement). For each of the assisted subtasks, we determined the influence on the performance of the respective subtask, and possible effects on other subtasks of walking and spatiotemporal gait parameters. Methods The robotic assistance for the FC, SS and WS subtasks was assessed in nine mildly impaired chronic stroke survivors while walking in the LOPES II gait trainer. Seven trials were performed for each participant in a randomized order: six trials in which either 20% or 80% of assistance was provided for each of the selected subtasks, and one baseline trial where the participant did not receive subtask-specific assistance. The influence of the assistance on performances (errors compared to reference trajectories) for the assisted subtasks and other subtasks of walking as well as spatiotemporal parameters (step length, width and height, swing and stance time) was analyzed. Results Performances for the impaired subtasks (FC, SS and WS) improved significantly when assistance was applied for the respective subtask. Although WS performance improved when assisting this subtask, participants were not shifting their weight well towards the paretic leg. On a group level, not many effects on other subtasks and spatiotemporal parameters were found. Still, performance for the leading limb angle subtask improved significantly resulting in a larger step length when applying FC assistance. Conclusion FC and SS assistance leads to clear improvements in performance for the respective subtask, while our WS assistance needs further improvement. As effects of the assistance were mainly confined to the assisted subtasks, tuning of FC, SS and WS can be done simultaneously. Our findings suggest that there may be no need for specific, time-intensive tuning protocols (e.g. tuning subtasks after each other) in mildly impaired stroke survivors.

Inertial sensors for gait monitoring and design of adaptive controllers for exoskeletons after stroke: a feasibility study

“…At a group level, strong correlations were found for the peak knee flexion torque and the estimation of circumduction, minimum foot clearance, maximum vertical displacement, and stance and swing phases of the paretic side. Our findings agree with those of Sulzer et al (2010 ) and Fricke et al (2020b ), where the authors also found positive relationships between peak knee flexion torque and step length, circumduction, minimum foot clearance, foot maximum vertical displacement, and stance time.…”

“…An alternative to these control strategies based on predefined joint references might be to adapt the assistance based on spatiotemporal metrics, e.g., stance duration, stride length, or foot clearance. This approach has the main benefit of using metrics that are good biomechanical descriptors of the level of gait impairment post stroke and have a strong relationship with the exoskeleton control parameters ( Sulzer et al, 2009 ; Koopman et al, 2013 ; Mizukami et al, 2018 ; Fricke et al, 2020b ; Pan et al, 2022 ). Therefore, these adaptive controllers based on spatiotemporal metrics can also be useful to complement or guide the automatic tuning of the control parameters.…”

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

“…3.B) were considerably lower than the reported minimum adaptation time needed for unimpaired people to get used to powered ankle assistance [27]. This limitation is shared with the existing publications on the same topic for people with stroke (the total time spent walking with the exoskeleton was 20.00 ± 11.66 minutes [5], [11], [14], [15], the number of sessions was 1.17 ± 0.37 [5], [10]- [12], [14], [15], and the time per condition was 2.25 ± 0.83 [5], [11], [14], [15] without including our study; see Fig. 3.B-D) and cerebral palsy (the total time spent walking with the exoskeleton was 16.25 ± 0.00 minutes [17], the number of sessions was 5.66 ± 2.05 [16]- [18] and time per condition was 5.00 ± 0.00 [17]; see Fig.…”

Control strategies used in lower limb exoskeletons for gait rehabilitation after brain injury: a systematic review and analysis of clinical effectiveness

“…Thus, it is an open question whether adaptive controllers would potentially outperform current solutions. Comprehensive studies analyzing the effect of the exoskeleton control parameters on clinically meaningful biomechanical metrics might allow the development of adaptive control rules that directly tackle the main gait abnormalities of individuals with brain injuries [ 97 , 262 , 263 ].…”

“…Adaptive control strategies aim to modify the control parameters based on the patient's specific needs [ 97 ]. In general, the control parameters of the exoskeletons have to be tuned to properly adapt to each specific patient's walking capabilities, as they are not generalized enough to capture the heterogeneity of gait disorders [ 98 , 99 ].…”