Mechanisms used to increase peak propulsive force following 12-weeks of gait training in individuals poststroke

Articulated ankle-foot-orthosis improves inter-limb propulsion symmetry during walking adaptability task post-stroke

BACKGROUND

Community ambulation involves complex walking adaptability tasks such as stepping over obstacles or taking long steps, which require adequate propulsion generation by the trailing leg. Individuals post-stroke often have an increased reliance on their trailing nonparetic leg and favor leading with their paretic leg, which can limit mobility. Ankle-foot-orthoses are prescribed to address common deficits post-stroke such as foot drop and ankle instability. However, it is not clear if walking with an ankle-foot-orthosis improves inter-limb propulsion symmetry during adaptability tasks. This study sought to examine this hypothesis.

METHODS

Individuals post-stroke (n = 9) that were previously prescribed a custom fabricated plantarflexion-stop articulated ankle-foot-orthosis participated. Participants performed steady-state walking and adaptability tasks overground with and without their orthosis. The adaptability tasks included obstacle crossing and long-step tasks, leading with both their paretic and nonparetic leg. Inter-limb propulsion symmetry was calculated using trailing limb ground-reaction-forces.

FINDINGS

During the obstacle crossing task, ankle-foot-orthosis use resulted in a significant improvement in inter-limb propulsion symmetry. The orthosis also improved ankle dorsiflexion during stance, reduced knee hyperextension, increased gastrocnemius muscle activity, and increased peak paretic leg ankle plantarflexor moment. In contrast, there were no differences in propulsion symmetry during steady-state walking and taking a long-step when using the orthosis.

INTERPRETATION

Plantarflexion-stop articulated ankle-foot-orthoses can improve propulsion symmetry during obstacle crossing tasks in individuals post-stroke, promoting paretic leg use and reduced reliance on the nonparetic leg.

Société de Biomécanique young investigator award 2022: Effects of applying functional electrical stimulation to ankle plantarflexor muscles on forward propulsion during walking in young healthy adults

The triceps surae muscle, composed of the gastrocnemius and soleus muscles, plays a major role in forward propulsion during walking. By generating positive ankle power during the push-off phase, these muscles produce the propulsive force required for forward progression. This study aimed to test the hypothesis that applying functional electrical stimulation (FES) to these muscles (soleus, gastrocnemius or the combination of the two) during the push-off phase would increase the ankle power generation and, consequently, enhance forward propulsion during walking in able-bodied adults. Fifteen young adults walked at their self-selected speed under four conditions: no stimulation, with bilateral stimulation of the soleus, gastrocnemius, and both muscles simultaneously. Muscles were stimulated just below the discomfort threshold during push-off, i.e., from heel-off to toe-off. FES significantly increased ankle power (+22 to 28 % depending on conditions), propulsive force (+15 to 18 %) and forward progression parameters such as walking speed (+14 to 20 %). Furthermore, walking speed was significantly higher (+5%) for combined soleus and gastrocnemius stimulation compared with gastrocnemius stimulation alone, with no further effect on other gait parameters. In conclusion, our results demonstrate that applying FES to the gastrocnemius and soleus, separately or simultaneously during the push-off phase, enhanced ankle power generation and, consequently, forward propulsion during walking in able-bodied adults. Combined stimulation of the soleus and gastrocnemius provided the greatest walking speed enhancement, without affecting other propulsion parameters. These findings could be useful for designing FES-based solutions for improving gait in healthy people with propulsion impairment, such as the elderly.

Medial Temporal Lobe Atrophy in Older Adults With Subjective Cognitive Impairments Affects Gait Parameters in the Spatial Navigation Task

Both navigation abilities and gait can be affected by the atrophy in the medial temporal cortex. This study aimed to determine whether navigation abilities could differentiate seniors with and without medial temporal lobe atrophy who complained about their cognitive status. The participants, classified to either the medial temporal atrophy group (n = 23) or the control group (n = 22) underwent neuropsychological assessment and performed a spatial navigation task while their gait parameters were recorded. The study showed no significant differences between the two groups in memory, fluency, and semantic knowledge or typical measures of navigating abilities. However, gait parameters, particularly the propulsion index during certain phases of the navigation task, distinguished between seniors with and without medial temporal lobe lesions. These findings suggest that the gait parameters in the navigation task may be a valuable tool for identifying seniors with cognitive complaints and subtle medial temporal atrophy.

Differences in kinetic factors affecting gait speed between lesion sides in patients with stroke

The differences in kinetic mechanisms of decreased gait speed across brain lesion sides have not been elucidated, including the arrangement of motor modules reflected by kinetic interjoint coordination. The purpose of this study was to elucidate the differences in the kinetic factors of slow gait speed in patients with stroke on the lesion sides. A three-dimensional motion analysis system was employed to assess joint moment in the lower limb and representative gait parameters in 32 patients with right hemisphere brain damage (RHD) and 38 patients with left hemisphere brain damage (LHD) following stroke as well as 20 healthy controls. Motor module composition and timing were determined using principal component analysis based on the three joint moments in the lower limb in the stance phase, which were the variances accounted for principal components (PCs) and the peak timing in the time series of PCs. A stepwise multiple linear regression analysis was performed to identify the most significant joint moment and PC-associated parameter in explaining gait speed. A negligible difference was observed in age, weight, height, and gait speed among patients with RHD and LHD and controls. The following factors contributed to gait speed: in patients with RHD, larger ankle plantarflexion moment on the paretic (p = 0.001) and nonparetic (p = 0.002) sides and ankle dorsiflexion moment on the nonparetic side (p = 0.004); in patients with LHD, larger ankle plantarflexion moment (p < 0.001) and delayed peak timing of the first PC (p = 0.012) on the paretic side as well as ankle dorsiflexion moment on the nonparetic side (p < 0.001); in the controls, delayed peak timing of the first PC (p = 0.002) on the right side and larger ankle dorsiflexion moment (p = 0.001) as well as larger hip flexion moment on the left side (p = 0.023). The findings suggest that the kinetic mechanisms of gait speed may differ among patients with RHD following patients with stroke with LHD, and controls.

Longitudinal changes in trunk acceleration and their relationship with gait parameters in post-stroke hemiplegic patients

OBJECTIVE

The purpose of this study was to examine the longitudinal changes in trunk acceleration, gait speed, and paretic leg motion in patients with post-stroke hemiparesis, the relationships between variables at each time point, and whether initial trunk acceleration and gait parameters were related to gait speed 2 months later.

METHODS

Gait was assessed monthly in patients who could walk under supervision after stroke onset. Gait parameters, including gait speed and trailing limb angle (TLA), were measured. Trunk acceleration was quantified using acceleration root mean square (RMS) and stride regularity (SR) indices.

RESULTS

This study found statistically significant longitudinal changes in gait speed (p < .001), acceleration RMS of the total axes (p < .001), and SR of the vertical axes (p < .001). Gait speed correlated significantly with the acceleration RMS of the mediolateral (r = -0.815 to -0.901), vertical (r = -0.541 to -0.747), and anteroposterior (r = -0.718 to -0.829) axes, as well as the SR of the vertical axes (r = 0.558 to 0.724) at all time points from T0 to T2. For the TLA, only the acceleration RMS of the mediolateral axis correlated significantly over the entire study period (r = -0.530 to -0.724). In addition, initial TLA correlated significantly with gait speed after 2 months (r = -0.572).

CONCLUSION

This study showed that assessing trunk acceleration helps estimate the improvement in gait status in patients with post-stroke hemiparesis. The magnitude and regularity of trunk acceleration varied longitudinally and were related to gait speed and paretic leg motion at each time point; however, they could not predict future changes in gait speed.

Real-Time Visual Kinematic Feedback During Overground Walking Improves Gait Biomechanics in Individuals Post-Stroke

Treadmill-based gait rehabilitation protocols have shown that real-time visual biofeedback can promote learning of improved gait biomechanics, but previous feedback work has largely involved treadmill walking and not overground gait. The objective of this study was to determine the short-term response to hip extension visual biofeedback, with individuals post-stroke, during unconstrained overground walking. Individuals post-stroke typically have a decreased paretic propulsion and walking speed, but increasing hip extension angle may enable the paretic leg to better translate force anteriorly during push-off. Fourteen individuals post-stroke completed overground walking, one 6-min control bout without feedback, and three 6-min training bouts with real-time feedback. Data were recorded before and after the control bout, before and after the first training bout, and after the third training bout to assess the effects of training. Visual biofeedback consisted of a display attached to eyeglasses that showed one horizontal bar indicating the user's current hip angle and another symbolizing the target hip extension to be reached during training. On average, paretic hip extension angle (p = 0.014), trailing limb angle (p = 0.025), and propulsion (p = 0.011) were significantly higher after training. Walking speed increased but was not significantly higher after training (p = 0.089). Individuals demonstrated a greater increase in their hip extension angle (p = 0.035) and propulsion (p = 0.030) after the walking bout with feedback compared to the control bout, but changes in walking speed did not significantly differ (p = 0.583) between a control walking bout and a feedback bout. Our results show the feasibility of overground visual gait feedback and suggest that feedback regarding paretic hip extension angle enabled many individuals post-stroke to improve parameters important for their walking function.

Increased trailing limb angle in hemiplegic patients after training with a knee orthosis: A randomized controlled trial

BACKGROUND

Stroke often induces gait abnormality, such as buckling knee pattern, compromising walking ability. Previous studies indicated that an adequate trailing limb angle (TLA) is critical for recovering walking ability.

OBJECTIVE

We hypothesized that correcting gait abnormality by immobilizing the knee joint using a knee orthosis (KO) would improve walking patterns and increase the TLA, and investigated whether walking training using a KO would increase the TLA in post-stroke patients.

METHODS

In a randomized controlled trial, thirty-four participants were assigned to KO (walking training using a KO) and non-KO (without using a KO) groups. Twenty-nine completed the three-week gait training protocol. TLA was measured at baseline and after training. A two-way repeated ANOVA was performed to evaluate TLA increases with training type and time as test factors. A t-test compared TLA changes (ΔTLA) between the two groups.

RESULTS

ANOVA showed a main effect for time (F = 64.5, p < 0.01) and interaction (F = 15.4, p < 0.01). ΔTLA was significantly higher in the KO group (14.6±5.8) than in the non-KO group (5.0±7.0, p < 0.001).

CONCLUSION

Walking training using a KO may be practical and effective for increasing TLA in post-stroke patients.

How Important is Position in Adaptive Treadmill Control?

To more closely mimic overground walking, researchers are developing adaptive treadmills (ATMs) that update belt speed in real-time based on user gait mechanics. Many existing ATM control schemes are solely based on position on the belt and do not respond to changes in gait mechanics, like propulsive forces, that result in increased overground walking speed. To target natural causal mechanisms to alter speed, we developed an ATM controller that adjusts speed via changes in position, step length, and propulsion. Gains on each input dictate the impact of the corresponding parameter on belt speed. The study objective was to determine the effect of modifying the position gain on self-selected walking speed, measures of propulsion, and step length. Twenty-two participants walked at their self-selected speed with four ATM controllers, each with a unique position gain. Walking speed, anterior and posterior ground reaction force peaks and impulses, net impulse, and step length were compared between conditions. Smaller position gains promoted more equivalent anterior and posterior impulses, resulting in a net impulse closer to zero (p = 0.0043), a characteristic of healthy gait. Walking speed, anterior and posterior ground reaction force peaks and impulses, and step length did not change between conditions (all p > 0.05). These results suggest that reducing the importance of position in the ATM controller may promote more balanced anterior and posterior impulses, possibly improving the efficacy of the ATM for gait rehabilitation by emphasizing changes in gait mechanics instead of position to naturally adjust speed.

Effects of backward-directed resistance on propulsive force generation during split-belt treadmill walking in non-impaired individuals

Introduction

Backward-directed resistance is the resistance applied in the opposite direction of the individual's walking motion. Progressive application of backward-directed resistance during walking at a target speed engages adaptive motor control to maintain that speed. During split-belt walking, a motor control strategy must be applied that allows the person to keep up with the two belts to maintain their position on the treadmill. This situation becomes more challenging when progressive resistance is applied since each limb needs to adapt to the greater resistance to maintain the position. We propose that strategies aimed at changing relative propulsion forces with each limb may explain the motor control strategy used. This study aimed to identify the changes in propulsive force dynamics that allow individuals to maintain their position while walking on an instrumented split-belt treadmill with progressively increasing backward-directed resistance.

Methods

We utilized an instrumented split-belt treadmill while users had to overcome a set of increasing backward-directed resistance through the center of mass. Eighteen non-impaired participants (mean age = 25.2 ± 2.51) walked against five levels of backward resistance (0, 5, 10, 15, and 20% of participant's body weight) in two different modalities: single-belt vs. split-belt treadmill. On the single-belt mode, the treadmill's pace was the participant's comfortable walking speed (CWS). In split-belt mode, the dominant limb's belt pace was half of the CWS, and the non-dominant limb's belt speed was at the CWS.

Results

We assessed differences between single-belt vs. split-belt conditions in the slope of the linear relationship between change in propulsive impulse relative to change of backward resistance amount. In split-belt conditions, the slower limb showed a significantly steeper increase in propulsion generation compared to the fast limb across resistance levels.

Discussion

As a possible explanation, the slow limb also exhibited a significantly increased slope of the change in trailing limb angle (TLA), which was strongly correlated to the propulsive impulse slope values. We conclude that the motor control strategy used to maintain position on a split-belt treadmill when challenged with backward-directed resistance is to increase the propulsive forces of the slow limb relative to the fast limb by progressively increasing the TLA.

Clinical trial registration

ClinicalTrials.gov, identifier NCT04877249.

Multi-Site Identification and Generalization of Clusters of Walking Behaviors in Individuals With Chronic Stroke and Neurotypical Controls

BACKGROUND

Walking patterns in stroke survivors are highly heterogeneous, which poses a challenge in systematizing treatment prescriptions for walking rehabilitation interventions.

OBJECTIVES

We used bilateral spatiotemporal and force data during walking to create a multi-site research sample to: (1) identify clusters of walking behaviors in people post-stroke and neurotypical controls and (2) determine the generalizability of these walking clusters across different research sites. We hypothesized that participants post-stroke will have different walking impairments resulting in different clusters of walking behaviors, which are also different from control participants.

METHODS

We gathered data from 81 post-stroke participants across 4 research sites and collected data from 31 control participants. Using sparse K-means clustering, we identified walking clusters based on 17 spatiotemporal and force variables. We analyzed the biomechanical features within each cluster to characterize cluster-specific walking behaviors. We also assessed the generalizability of the clusters using a leave-one-out approach.

RESULTS

We identified 4 stroke clusters: a fast and asymmetric cluster, a moderate speed and asymmetric cluster, a slow cluster with frontal plane force asymmetries, and a slow and symmetric cluster. We also identified a moderate speed and symmetric gait cluster composed of controls and participants post-stroke. The moderate speed and asymmetric stroke cluster did not generalize across sites.

CONCLUSIONS

Although post-stroke walking patterns are heterogenous, these patterns can be systematically classified into distinct clusters based on spatiotemporal and force data. Future interventions could target the key features that characterize each cluster to increase the efficacy of interventions to improve mobility in people post-stroke.

Multi-site identification and generalization of clusters of walking behaviors in individuals with chronic stroke and neurotypical controls

Background

Walking patterns in stroke survivors are highly heterogeneous, which poses a challenge in systematizing treatment prescriptions for walking rehabilitation interventions.

Objective

We used bilateral spatiotemporal and force data during walking to create a multi-site research sample to: 1) identify clusters of walking behaviors in people post-stroke and neurotypical controls, and 2) determine the generalizability of these walking clusters across different research sites. We hypothesized that participants post-stroke will have different walking impairments resulting in different clusters of walking behaviors, which are also different from control participants.

Methods

We gathered data from 81 post-stroke participants across four research sites and collected data from 31 control participants. Using sparse K-means clustering, we identified walking clusters based on 17 spatiotemporal and force variables. We analyzed the biomechanical features within each cluster to characterize cluster-specific walking behaviors. We also assessed the generalizability of the clusters using a leave-one-out approach.

Results

We identified four stroke clusters: a fast and asymmetric cluster, a moderate speed and asymmetric cluster, a slow cluster with frontal plane force asymmetries, and a slow and symmetric cluster. We also identified a moderate speed and symmetric gait cluster composed of controls and participants post-stroke. The moderate speed and asymmetric stroke cluster did not generalize across sites.

Conclusions

Although post-stroke walking patterns are heterogenous, these patterns can be systematically classified into distinct clusters based on spatiotemporal and force data. Future interventions could target the key features that characterize each cluster to increase the efficacy of interventions to improve mobility in people post-stroke.

Effects of foot-ankle exercises on foot-ankle kinematics, plantar pressure, and gait kinetics in people with diabetic neuropathy: Secondary outcomes from a randomized controlled trial

BACKGROUND

Follow-up report of secondary outcomes of a randomized, single-blinded, parallel controlled trial that investigated the benefits of a foot-ankle therapeutic exercise program on foot-ankle kinematics, plantar pressure, and lower limb kinetics during gait in individuals with diabetic neuropathy (DPN).

METHODS

Sixty-six participants with DPN were randomly allocated into a control group (CG; n = 31), which received usual care, and an intervention group (IG; n = 35), which received usual care plus a 12-week group-based foot-ankle exercise program. Outcomes were assessed at baseline and 12 weeks by an assessor blinded to group allocation.

RESULTS

The generalized linear mixed model and intention-to-treat analysis revealed a greater hip extensor moment at push-off and greater hallux contact area in the IG than CG after 12 weeks. A within-group analysis revealed a larger arch height during stance and higher peak pressure and pressure-time integral at the central forefoot region in the IG after 12 weeks compared to baseline. There were no other significant group difference or changes over time in foot-ankle kinematics or in any other joint moment related to overall lower limb biomechanics.

CONCLUSION

The increases in hip moment at push-off and hallux surface contact area suggest an improvement in the propulsion phase with greater participation of the toes in foot rollover after 12 weeks of a group-based foot-ankle exercises program for people with DPN. Individual face-to-face, longer-term, and more intensive interventions may be needed to positively influence foot-ankle biomechanics and pressure parameters in other plantar areas.

Kinetic and kinematic parameters associated with late braking force and effects on gait performance of stroke patients

Late braking force (LBF) is often observed in the late stance phase of the paretic lower limb of stroke patients. Nevertheless, the effects and association of LBF remain unclear. We examined the kinetic and kinematic parameters associated with LBF and its effect on walking. Herein, 157 stroke patients were enrolled. Participants walked at a comfortable speed selected by them, and their movements were measured using a 3D motion analysis system. The effect of LBF was analyzed as a linear relationship with spatiotemporal parameters. Multiple linear regression analyses were performed with LBF as the dependent variable and kinetic and kinematic parameters as independent variables. LBF was observed in 110 patients. LBF was associated with decreased knee joint flexion angles during the pre-swing and swing phases. In the multivariate analysis, trailing limb angle, cooperativity between the paretic shank and foot, and cooperativity between the paretic and non-paretic thighs were related to LBF (p < 0.01; adjusted R² = 0.64). LBF in the late stance phase of the paretic lower limb reduced gait performance in the pre-swing and swing phases. LBF was associated with trailing limb angle in the late stance, coordination between the paretic shank and foot in the pre-swing phase, and coordination between both thighs.

Acclimatization of force production during walking in persons with Parkinson's disease

Individuals with Parkinson's disease walk slowly, with short strides resulting in decreased mobility. Treadmill walking assessments are utilized to understand gait impairment in persons with Parkinson's disease and treadmill-based interventions to mobility have become increasingly popular. While walking on a treadmill, there is a reported initial acclimatization period where individuals adjust to the speed and dynamics of the moving belt before producing consistent walking patterns. It is unknown how much walking time is required for individuals with Parkinson's disease to acclimate to the treadmill. We investigated how spatiotemporal parameters and ground reaction forces changed during treadmill acclimatization. Twenty individuals with idiopathic Parkinson's (15 Males, 5 Females) walked for a five-minute treadmill session on an instrumented treadmill while motion capture data were collected. The measures of interest included ground reaction force measures (peak propulsive force, peak braking force, propulsive impulse, and braking impulse) and spatiotemporal measures (stride length, stride time, or double support time). Analyses demonstrated significantly increased propulsive impulse (p <.001) after the first minute, with no significant difference for the remaining minutes (p ≥ 0.395). There were no significant changes in the spatiotemporal measures (P =.065). These results quantify the stabilization of ground reaction force during the treadmill acclimatization period. Based on our findings, if steady-state gait is desired, we recommend participants walk for at least two minutes before data collection. Future clinical investigations should consider ground reaction force as sensitive parameters for evaluating gait in persons with Parkinson's disease in treadmill-based assessments or interventional therapies.

Speed-dependent biomechanical changes vary across individual gait metrics post-stroke relative to neurotypical adults

BACKGROUND

Gait training at fast speeds is recommended to reduce walking activity limitations post-stroke. Fast walking may also reduce gait kinematic impairments post-stroke. However, it is unknown if differences in gait kinematics between people post-stroke and neurotypical adults decrease when walking at faster speeds.

OBJECTIVE

To determine the effect of faster walking speeds on gait kinematics post-stroke relative to neurotypical adults walking at similar speeds.

METHODS

We performed a secondary analysis with data from 28 people post-stroke and 50 neurotypical adults treadmill walking at multiple speeds. We evaluated the effects of speed and group on individual spatiotemporal and kinematic metrics and performed k-means clustering with all metrics at self-selected and fast speeds.

RESULTS

People post-stroke decreased step length asymmetry and trailing limb angle impairment, reducing between-group differences at fast speeds. Speed-dependent changes in peak swing knee flexion, hip hiking, and temporal asymmetries exaggerated between-group differences. Our clustering analyses revealed two clusters. One represented neurotypical gait behavior, composed of neurotypical and post-stroke participants. The other characterized stroke gait behavior-comprised entirely of participants post-stroke with smaller lower extremity Fugl-Meyer scores than the post-stroke participants in the neurotypical gait behavior cluster. Cluster composition was largely consistent at both speeds, and the distance between clusters increased at fast speeds.

CONCLUSIONS

The biomechanical effect of fast walking post-stroke varied across individual gait metrics. For participants within the stroke gait behavior cluster, walking faster led to an overall gait pattern more different than neurotypical adults compared to the self-selected speed. This suggests that to potentiate the biomechanical benefits of walking at faster speeds and improve the overall gait pattern post-stroke, gait metrics with smaller speed-dependent changes may need to be specifically targeted within the context of fast walking.

Verification of gait analysis method fusing camera-based pose estimation and an IMU sensor in various gait conditions

A markerless gait analysis system can measure useful gait metrics to determine effective clinical treatment. Although this gait analysis system does not require a large space, several markers, or time constraints, it inaccurately measure lower limb joint kinematics during gait. In particular, it has a substantial ankle joint angle error. In this study, we investigated the markerless gait analysis method capability using single RGB camera-based pose estimation by OpenPose (OP) and an inertial measurement unit (IMU) sensor on the foot segment to measure ankle joint kinematics under various gait conditions. Sixteen healthy young adult males participated in the study. We compared temporo-spatial parameters and lower limb joint angles during four gait conditions with varying gait speeds and foot progression angles. These were measured by optoelectronic motion capture, markerless gait analysis method using OP, and proposed method using OP and IMU. We found that the proposed method using OP and an IMU significantly decreased the mean absolute errors of peak ankle joint angles compared with OP in the four gait conditions. The proposed method has the potential to measure temporo-spatial gait parameters and lower limb joint angles, including ankle angles, in various gait conditions as a clinical settings gait assessment tool.

Ankle stiffness modulation during different gait speeds in individuals post-stroke

BACKGROUND

Neurotypical individuals alter their ankle joint quasi-stiffness in response to changing walking speed; however, for individuals post-stroke, the ability to alter their ankle quasi-stiffness is unknown. Individuals post-stroke commonly have weak plantarflexor muscles, which may limit their ability to alter ankle quasi-stiffness. The objective was to investigate the relationship between ankle quasi-stiffness and propulsion, at two walking speeds. We hypothesized that in individuals post-stroke, there would be no difference in their paretic ankle quasi-stiffness between walking at a self-selected versus a fast speed. However, we hypothesized that ankle quasi-stiffness would correlate with gait speed and propulsion across individuals.

METHODS

Twenty-eight participants with chronic stroke walked on an instrumented treadmill at their self-selected and fast-walking speeds. Multilevel models were used to determine the relationships between ankle quasi-stiffness, speed, and propulsion.

FINDINGS

Overall, ankle quasi-stiffness did not increase within individuals from a self-selected to a fast gait speed (p = 0.69). A 1 m/s increase in speed across participants predicted an increase in overall ankle quasi-stiffness of 0.02 Nm/deg./kg (p = 0.03) and a 1 N/BW change in overall propulsion across participants predicted a 0.265 Nm/deg./kg increase in overall ankle quasi-stiffness (p < 0.0001).

INTERPRETATION

Individuals post-stroke did not modulate their ankle quasi-stiffness with increased speed, but across individuals there was a positive relationship between ankle quasi-stiffness and both speed and peak propulsion. Walking speed and propulsion are limited in individuals post-stroke, therefore, improving either could lead to a higher functional status. Understanding post-stroke ankle stiffness may be important in the design of therapeutic interventions and exoskeletons, where these devices augment the biological ankle quasi-stiffness to improve walking performance.

Robotic ankle control can provide appropriate assistance throughout the gait cycle in healthy adults

Ankle foot orthoses are mainly applied to provide stability in the stance phase and adequate foot clearance in the swing phase; however, they do not sufficiently assist during the entire gait cycle. On the other hand, robotic-controlled orthoses can provide mechanical assistance throughout the phases of the gait cycle. This study investigated the effect of ankle control throughout the gait cycle using an ankle joint walking assistive device under five different robotic assistance conditions: uncontrolled, dorsiflexion, and plantar flexion controlled at high and low speeds in the initial loading phase. Compared with the no-control condition, the plantar flexion condition enhanced knee extension and delayed the timing of ankle dorsiflexion in the stance phase; however, the opposite effect occurred under the dorsiflexion condition. Significant differences in the trailing limb angle and minimum toe clearance were also observed, although the same assistance was applied from the mid-stance phase to the initial swing phase. Ankle assistance in the initial loading phase affected the knee extension and ankle dorsiflexion angle during the stance phase. The smooth weight shift obtained might have a positive effect on lifting the limb during the swing phase. Robotic ankle control may provide appropriate assistance throughout the gait cycle according to individual gait ability.

Walking and Balance Outcomes Are Improved Following Brief Intensive Locomotor Skill Training but Are Not Augmented by Transcranial Direct Current Stimulation in Persons With Chronic Spinal Cord Injury

Motor training to improve walking and balance function is a common aspect of rehabilitation following motor-incomplete spinal cord injury (MISCI). Evidence suggests that moderate- to high-intensity exercise facilitates neuroplastic mechanisms that support motor skill acquisition and learning. Furthermore, enhancing corticospinal drive via transcranial direct current stimulation (tDCS) may augment the effects of motor training. In this pilot study, we investigated whether a brief moderate-intensity locomotor-related motor skill training (MST) circuit, with and without tDCS, improved walking and balance outcomes in persons with MISCI. In addition, we examined potential differences between within-day (online) and between-day (offline) effects of MST. Twenty-six adults with chronic MISCI, who had some walking ability, were enrolled in a 5-day double-blind, randomized study with a 3-day intervention period. Participants were assigned to an intensive locomotor MST circuit and concurrent application of either sham tDCS (MST+tDCS_sham) or active tDCS (MST+tDCS). The primary outcome was overground walking speed measured during the 10-meter walk test. Secondary outcomes included spatiotemporal gait characteristics (cadence and stride length), peak trailing limb angle (TLA), intralimb coordination (ACC), the Berg Balance Scale (BBS), and the Falls Efficacy Scale-International (FES-I) questionnaire. Analyses revealed a significant effect of the MST circuit, with improvements in walking speed, cadence, bilateral stride length, stronger limb TLA, weaker limb ACC, BBS, and FES-I observed in both the MST+tDCS_sham and MST+tDCS groups. No differences in outcomes were observed between groups. Between-day change accounted for a greater percentage of the overall change in walking outcomes. In persons with MISCI, brief intensive MST involving a circuit of ballistic, cyclic locomotor-related skill activities improved walking outcomes, and selected strength and balance outcomes; however, concurrent application of tDCS did not further enhance the effects of MST.

Effect of Leg Extension Angle on Knee Flexion Angle during Swing Phase in Post-Stroke Gait

Background and Objectives: Leg extension angle is important for increasing the propulsion force during gait and is a meaningful indicator for evaluating gait quality in stroke patients. Although leg extension angle during late stance might potentially also affect lower limb kinematics during the swing phase, the relationship between these two remains unclear. This study aimed to investigate the relationship between leg extension angle and knee flexion angle during pre-swing and swing phase in post-stroke gait. Materials and Methods: Twenty-nine stroke patients walked along a 16 m walkway at a self-selected speed. Tilt angles and acceleration of pelvis and paretic lower limb segments were measured using inertial measurement units. Leg extension angle, consisting of a line connecting the hip joint with the ankle joint, hip and knee angles, and increments of velocity during pre-swing and swing phase were calculated. Correlation analysis was conducted to examine the relationships between these parameters. Partial correlation analysis adjusted by the Fugl-Meyer assessment-lower limb (FMA-LL) was also performed. Results: On the paretic side, leg extension angle was positively correlated with knee flexion angle during the swing phase (r = 0.721, p < 0.001) and knee flexion angle and increments of velocity during the pre-swing phase (r = 0.740–0.846, p < 0.001). Partial correlation analysis adjusted by the FMA-LL showed significant correlation between leg extension angle and knee flexion angle during the swing phase (r = 0.602, p = 0.001) and knee flexion angle and increments of velocity during the pre-swing phase (r = 0.655–0.886, p < 0.001). Conclusions: Leg extension angle affected kinematics during the swing phase in post-stroke gait regardless of the severity of paralysis, and was similar during the pre-swing phase. These results would guide the development of effective gait training programs that enable a safe and efficient gait for stroke patients.

Targeting Paretic Propulsion and Walking Speed With a Soft Robotic Exosuit: A Consideration-of-Concept Trial

Background: Soft robotic exosuits can facilitate immediate increases in short- and long-distance walking speeds in people with post-stroke hemiparesis. We sought to assess the feasibility and rehabilitative potential of applying propulsion-augmenting exosuits as part of an individualized and progressive training program to retrain faster walking and the underlying propulsive strategy.

Methods: A 54-yr old male with chronic hemiparesis completed five daily sessions of Robotic Exosuit Augmented Locomotion (REAL) gait training. REAL training consists of high-intensity, task-specific, and progressively challenging walking practice augmented by a soft robotic exosuit and is designed to facilitate faster walking by way of increased paretic propulsion. Repeated baseline assessments of comfortable walking speed over a 2-year period provided a stable baseline from which the effects of REAL training could be elucidated. Additional outcomes included paretic propulsion, maximum walking speed, and 6-minute walk test distance.

Results: Comfortable walking speed was stable at 0.96 m/s prior to training and increased by 0.30 m/s after training. Clinically meaningful increases in maximum walking speed (Δ: 0.30 m/s) and 6-minute walk test distance (Δ: 59 m) were similarly observed. Improvements in paretic peak propulsion (Δ: 2.80 %BW), propulsive power (Δ: 0.41 W/kg), and trailing limb angle (Δ: 6.2 degrees) were observed at comfortable walking speed (p's < 0.05). Likewise, improvements in paretic peak propulsion (Δ: 4.63 %BW) and trailing limb angle (Δ: 4.30 degrees) were observed at maximum walking speed (p's < 0.05).

Conclusions: The REAL training program is feasible to implement after stroke and capable of facilitating rapid and meaningful improvements in paretic propulsion, walking speed, and walking distance.

Central Drive to the Paretic Ankle Plantarflexors Affects the Relationship Between Propulsion and Walking Speed After Stroke

BACKGROUND AND PURPOSE

The ankle plantarflexor muscles are the primary generators of propulsion during walking. Impaired paretic plantarflexion is a key contributor to interlimb propulsion asymmetry after stroke. Poststroke muscle weakness may be the result of a reduced force-generating capacity, reduced central drive, or a combination of these impairments. This study sought to elucidate the relationship between the neuromuscular function of the paretic plantarflexor muscles and propulsion deficits across individuals with different walking speeds.

METHODS

For 40 individuals poststroke, we used instrumented gait analysis and dynamometry coupled with supramaximal electrostimulation to study the interplay between limb kinematics, the neuromuscular function of the paretic plantarflexors (ie, strength capacity and central drive), propulsion, and walking speed.

RESULTS

The strength capacity of the paretic plantarflexors was not independently related to paretic propulsion. Reduced central drive to the paretic plantarflexors independently contributed to paretic propulsion deficits. An interaction between walking speed and plantarflexor central drive was observed. Individuals with slower speeds and lower paretic plantarflexor central drive presented with the largest propulsion impairments. Some study participants with low paretic plantarflexor central drive presented with similarly fast speeds as those with near-normal central drive by leveraging a compensatory reliance on nonparetic propulsion. The final model accounted for 86% of the variance in paretic propulsion (R = 0.86, F = 33.10, P < 0.001).

DISCUSSION AND CONCLUSIONS

Individuals poststroke have latent paretic plantarflexion strength that they are not able to voluntarily access. The magnitude of central drive deficit is a strong indicator of propulsion impairment in both slow and fast walkers.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A298).

These legs were made for propulsion: advancing the diagnosis and treatment of post-stroke propulsion deficits

Advances in medical diagnosis and treatment have facilitated the emergence of precision medicine. In contrast, locomotor rehabilitation for individuals with acquired neuromotor injuries remains limited by the dearth of (i) diagnostic approaches that can identify the specific neuromuscular, biomechanical, and clinical deficits underlying impaired locomotion and (ii) evidence-based, targeted treatments. In particular, impaired propulsion by the paretic limb is a major contributor to walking-related disability after stroke; however, few interventions have been able to target deficits in propulsion effectively and in a manner that reduces walking disability. Indeed, the weakness and impaired control that is characteristic of post-stroke hemiparesis leads to heterogeneous deficits that impair paretic propulsion and contribute to a slow, metabolically-expensive, and unstable gait. Current rehabilitation paradigms emphasize the rapid attainment of walking independence, not the restoration of normal propulsion function. Although walking independence is an important goal for stroke survivors, independence achieved via compensatory strategies may prevent the recovery of propulsion needed for the fast, economical, and stable gait that is characteristic of healthy bipedal locomotion. We posit that post-stroke rehabilitation should aim to promote independent walking, in part, through the acquisition of enhanced propulsion. In this expert review, we present the biomechanical and functional consequences of post-stroke propulsion deficits, review advances in our understanding of the nature of post-stroke propulsion impairment, and discuss emerging diagnostic and treatment approaches that have the potential to facilitate new rehabilitation paradigms targeting propulsion restoration.

A Music-Based Digital Therapeutic: Proof-of-Concept Automation of a Progressive and Individualized Rhythm-Based Walking Training Program After Stroke

BACKGROUND

The rhythm of music can entrain neurons in motor cortex by way of direct connections between auditory and motor brain regions.

OBJECTIVE

We sought to automate an individualized and progressive music-based, walking rehabilitation program using real-time sensor data in combination with decision algorithms.

METHODS

A music-based digital therapeutic was developed to maintain high sound quality while modulating, in real-time, the tempo (ie, beats per minute, or bpm) of music based on a user's ability to entrain to the tempo and progress to faster walking cadences in-sync with the progression of the tempo. Eleven individuals with chronic hemiparesis completed one automated 30-minute training visit. Seven returned for 2 additional visits. Safety, feasibility, and rehabilitative potential (ie, changes in walking speed relative to clinically meaningful change scores) were evaluated.

RESULTS

A single, fully automated training visit resulted in increased usual (∆ 0.085 ± 0.027 m/s, P = .011) and fast (∆ 0.093 ± 0.032 m/s, P = .016) walking speeds. The 7 participants who completed additional training visits increased their usual walking speed by 0.12 ± 0.03 m/s after only 3 days of training. Changes in walking speed were highly related to changes in walking cadence (R² > 0.70). No trips or falls were noted during training, all users reported that the device helped them walk faster, and 70% indicated that they would use it most or all of the time at home.

CONCLUSIONS

In this proof-of-concept study, we show that a sensor-automated, progressive, and individualized rhythmic locomotor training program can be implemented safely and effectively to train walking speed after stroke. Music-based digital therapeutics have the potential to facilitate salient, community-based rehabilitation.

Persons post-stroke improve step length symmetry by walking asymmetrically

BACKGROUND AND PURPOSE

Restoration of step length symmetry is a common rehabilitation goal after stroke. Persons post-stroke often retain the ability to walk with symmetric step lengths ("symmetric steps"); however, the resulting walking pattern remains effortful. Two key questions with direct implications for rehabilitation have emerged: 1) how do persons post-stroke generate symmetric steps, and 2) why do symmetric steps remain so effortful? Here, we aimed to understand how persons post-stroke generate symmetric steps and explored how the resulting gait pattern may relate to the metabolic cost of transport.

METHODS

We recorded kinematic, kinetic, and metabolic data as nine persons post-stroke walked on an instrumented treadmill under two conditions: preferred walking and symmetric stepping (using visual feedback).

RESULTS

Gait kinematics and kinetics remained markedly asymmetric even when persons post-stroke improved step length symmetry. Impaired paretic propulsion and aberrant movement of the center of mass were evident during both preferred walking and symmetric stepping. These deficits contributed to diminished positive work performed by the paretic limb on the center of mass in both conditions. Within each condition, decreased positive paretic work correlated with increased metabolic cost of transport and decreased walking speed across participants.

CONCLUSIONS

It is critical to consider the mechanics used to restore symmetric steps when designing interventions to improve walking after stroke. Future research should consider the many dimensions of asymmetry in post-stroke gait, and additional within-participant manipulations of gait parameters are needed to improve our understanding of the elevated metabolic cost of walking after stroke.

Heel lift improves walking ability of persons with traumatic cauda equina syndrome-a pilot experimental study

STUDY DESIGN

Non-randomized within-subject experimental study.

OBJECTIVE

To determine whether the addition of the 1 cm heel lift to the footwear improves the walking ability of the persons with Cauda Equina Syndrome (CES).

SETTING

Department of Physical Medicine and Rehabilitation, Christian Medical College, India.

METHODS

Fourteen people with bilateral plantar flexor weakness following traumatic CES (mean age 43.7 years) were recruited for the study. Their walking speed, stride length, cadence, and time taken to complete Timed Up and Go (TUG) were measured using footwear with back straps. Then, the 1 cm heel lift was attached to the sole of the footwear. After sufficient practice, all the parameters were reassessed to find out the effectiveness of the heel lift.

RESULTS

With the 1 cm heel lift, the participants walked 0.13 m/s (95% CI, 0.08-0.17) faster than their regular footwear. They were able to complete the TUG test 2.6 s (95% CI, 1.4-3.7) earlier than before. There was an increase of 5.2 in. in stride length (95% CI, 2.9-9) and an eight steps increase in cadence (95% CI, 4.9-11.3) observed after the heel lift.

CONCLUSIONS

This pilot study has demonstrated that addition of 1 cm heel may be effective in improving the walking performance of persons with Cauda Equina Syndrome. Future studies should investigate the kinetic and kinematic changes of this modification using a randomized controlled trial study design.

Validity of Measurement for Trailing Limb Angle and Propulsion Force during Gait Using a Magnetic Inertial Measurement Unit

Propulsion force and trailing limb angle (TLA) are meaningful indicators for evaluating quality of gait. This study examined the validity of measurement for TLA and propulsion force during various gait conditions using magnetic inertial measurement units (IMU), based on measurements using a three-dimensional motion analysis system and a force platform. Eighteen healthy males (mean age 25.2  ±  3.2 years, body height 1.70   ±  0.06 m) walked with and without trunk fluctuation at preferred, slow, and fast velocities. IMU were fixed on the thorax, lumbar spine, and right thigh and shank. IMU calculated the acceleration and tilt angles in a global coordinate system. TLA, consisting of a line connecting the hip joint with the ankle joint, and the laboratory's vertical axis at late stance in the sagittal plane, was calculated from thigh and shank segment angles obtained by IMU, and coordinate data from the motion analysis system. Propulsion force was estimated by the increment of velocity calculated from anterior acceleration measured by IMU fixed on the thorax and lumbar spine, and normalized impulse of the anterior component of ground reaction force (AGRF) during late stance. Similarity of TLA measured by IMU and the motion analysis system was tested by the coefficient of multiple correlation (CMC), intraclass correlation coefficient (ICC), and root mean square (RMS) of measurement error. Relationships between normalized impulse of AGRF and increments of velocity, as measured by IMU, were tested using correlation analysis. CMC of TLA was 0.956–0.959. ICC between peak TLAs was 0.831–0.876 (p < 0.001), and RMS of error was 1.42°–1.92°. Velocity increment calculated from acceleration on the lumbar region showed strong correlations with normalized impulse of AGRF (r = 0.755–0.892, p < 0.001). These results indicated a high validity of estimation of TLA and propulsion force by IMU during various gait conditions; these methods would be useful for best clinical practice.

Effects of walking speed on gait biomechanics in healthy participants: a systematic review and meta-analysis

BACKGROUND

Understanding the effects of gait speed on biomechanical variables is fundamental for a proper evaluation of alterations in gait, since pathological individuals tend to walk slower than healthy controls. Therefore, the aim of the study was to perform a systematic review of the effects of gait speed on spatiotemporal parameters, joint kinematics, joint kinetics, and ground reaction forces in healthy children, young adults, and older adults.

METHODS

A systematic electronic search was performed on PubMed, Embase, and Web of Science databases to identify studies published between 1980 and 2019. A modified Quality Index was applied to assess methodological quality, and effect sizes with 95% confidence intervals were calculated as the standardized mean differences. For the meta-analyses, a fixed or random effect model and the statistical heterogeneity were calculated using the I² index.

RESULTS

Twenty original full-length studies were included in the final analyses with a total of 587 healthy individuals evaluated, of which four studies analyzed the gait pattern of 227 children, 16 studies of 310 young adults, and three studies of 59 older adults. In general, gait speed affected the amplitude of spatiotemporal gait parameters, joint kinematics, joint kinetics, and ground reaction forces with a decrease at slow speeds and increase at fast speeds in relation to the comfortable speed. Specifically, moderate-to-large effect sizes were found for each age group and speed: children (slow, - 3.61 to 0.59; fast, - 1.05 to 2.97), young adults (slow, - 3.56 to 4.06; fast, - 4.28 to 4.38), and older adults (slow, - 1.76 to 0.52; fast, - 0.29 to 1.43).

CONCLUSIONS

This review identified that speed affected the gait patterns of different populations with respect to the amplitude of spatiotemporal parameters, joint kinematics, joint kinetics, and ground reaction forces. Specifically, most of the values analyzed decreased at slower speeds and increased at faster speeds. Therefore, the effects of speed on gait patterns should also be considered when comparing the gait analysis of pathological individuals with normal or control ones.

The Presence of a Paretic Propulsion Reserve During Gait in Individuals Following Stroke

BACKGROUND

The residual hemiparesis after stroke results in a unilateral reduction in propulsive force during gait. Prior work has suggested the presence of a propulsive reserve in the paretic limb.

OBJECTIVE

The purpose of this study was to quantify the paretic propulsive reserve in individuals poststroke and to determine the biomechanical mechanism underlying the generation of additional paretic propulsive limb force.

METHODS

Ten individuals with chronic hemiparesis poststroke walked on a treadmill against an impeding force (ascending 0% to 10% body weight [BW], in 2.5% BW increments, followed by descending 10% to 0% BW, also in 2.5% BW increments) applied to the body's center of mass. The resulting propulsive forces were measured bilaterally and compared between impeding force levels. We then assessed potential mechanisms (trailing limb angle and plantarflexion moment) underlying the changes in propulsion.

RESULTS

Overall, peak paretic propulsive force increased by 92% and the paretic propulsive impulse increased by 225%, resulting in a significant increase in the paretic limb's contribution to propulsion. Participants continued to produce increased paretic propulsion on removal of the impeding force. The trailing limb angle contributed significantly to the increase in paretic propulsion, whereas the plantarflexion moment did not.

CONCLUSIONS

Participants exhibited a robust propulsive reserve on the paretic limb, suggesting that there is untapped potential that can be exploited through rehabilitation to improve gait recovery. The increase in propulsive symmetry indicates that a greater response was observed by the paretic limb rather than increased compensation by the nonparetic limb.

Paretic propulsion as a measure of walking performance and functional motor recovery post-stroke: A review

BACKGROUND

Although walking speed is the most common measure of gait performance post-stroke, improved walking speed following rehabilitation does not always indicate the recovery of paretic limb function. Over the last decade, the measure paretic propulsion (Pp, defined as the propulsive impulse generated by the paretic leg divided by the sum of the propulsive impulses of both legs) has been established as a measure of paretic limb output and recently targeted in post-stroke rehabilitation paradigms. However, the literature lacks a detailed synthesis of how paretic propulsion, walking speed, and other biomechanical and neuromuscular measures collectively relate to post-stroke walking performance and motor recovery.

OBJECTIVE

The aim of this review was to assess factors associated with the ability to generate Pp and identify rehabilitation targets aimed at improving Pp and paretic limb function.

METHODS

Relevant literature was collected in which paretic propulsion was used to quantify and assess propulsion symmetry and function in hemiparetic gait.

RESULTS

Paretic leg extension during terminal stance is strongly associated with Pp. Both paretic leg extension and propulsion are related to step length asymmetry, revealing an interaction between spatiotemporal, kinematic and kinetic metrics that underlies hemiparetic walking performance. The importance of plantarflexor function in producing propulsion is highlighted by the association of an independent plantarflexor excitation module with increased Pp. Furthermore, the literature suggests that although current rehabilitation techniques can improve Pp, these improvements depend on the patient's baseline plantarflexor function.

SIGNIFICANCE

Pp provides a quantitative measure of propulsion symmetry and should be a primary target of post-stroke gait rehabilitation. The current literature suggests rehabilitation techniques that target both plantarflexor function and leg extension may restore paretic limb function and improve gait asymmetries in individuals post stroke.

Effect of forward-directed aiding force on gait mechanics in healthy young adults while walking faster

BACKGROUND

Forces can be applied to people while they are walking on a treadmill in different ways that aid individuals to walk at faster walking speeds with potentially less effort. Forward-directed aiding forces (FAF) are a special class of aiding forces where "push" or "pull" forces are mechanically applied to the person's pelvis in the forward direction.

OBJECTIVE

To determine if FAF, applied by a robotic interface, can be effective in providing assistance to walk at a faster walking speed with reduced kinetic requirements.

METHODS

Twenty non-neurologically impaired physical active young adults were recruited and biomechanical gait mechanics were measured during walking at two constant treadmill belt speeds (1.0 m/s and 1.6 m/s), with the robotic device in aiding mode to provide FAF (FAF), and also outside of the robotic device (no-FAF). The spatiotemporal gait parameters, anterior-posterior force, sagittal impulse, and hip, knee and ankle power and net work were calculated from kinematic and kinetic data, comparing changes in parameters from slower to faster speeds within each mode, and then, comparing values between each mode.

RESULTS

The spatiotemporal gait parameters were not different between conditions, but in FAF condition, the propulsive force impulse change was not increased, there was smaller propulsion increase, and smaller maximal power generation and ankle work done at the faster speed, whereas all of these parameters were appropriately increased in the no-FAF condition.

CONCLUSIONS

These results indicate that providing FAF at the pelvis is an effective means for reducing the amount of mechanical effort required to walk faster and thus could be used as a training tool to improve walking ability.

[The application of kinesiotaping for the rehabilitation of the post-stroke patients]

This review of the scientific literature was designed to consider the prospects for the application of kinesiotaping for the rehabilitation of the post-stroke patients. The relevance of the work arises from the absence of a systemic analysis of the large number of investigations that have been carried out during the past two years. The objective of the present review article was to evaluate the influence of kinesiotaping on the health status of the post-stroke patients and the course of their rehabilitative treatment based on the results of analysis of the scientific reports published during the period from 2015 to 2017. The analysis has demonstrated that the method under consideration makes it possible to effectively reduce spasticity, increase the paretic limb power, improve the static and dynamic balance, and alleviate the pain syndrome by virtue of the ability to improve the articulation proprioception and to regulate the muscle tone. Such effects are known to promote the reduction of muscle tone asymmetry in the patients suffering from hemiparesis and articulation instability which in its turn improves the patients' gait and walking ability, hightens their living standards, and allows to tolerate enhanced physical exertion. Kinesiotaping actually improves the locomotor function in the post-stroke patients Taken together, the advantages of the approach in question give reason to recommend kinesiotaping for the wide application for the combined rehabilitative treatment of the post-stroke patients.

A soft robotic exosuit improves walking in patients after stroke

Stroke-induced hemiparetic gait is characteristically slow and metabolically expensive. Passive assistive devices such as ankle-foot orthoses are often prescribed to increase function and independence after stroke; however, walking remains highly impaired despite-and perhaps because of-their use. We sought to determine whether a soft wearable robot (exosuit) designed to supplement the paretic limb's residual ability to generate both forward propulsion and ground clearance could facilitate more normal walking after stroke. Exosuits transmit mechanical power generated by actuators to a wearer through the interaction of garment-like, functional textile anchors and cable-based transmissions. We evaluated the immediate effects of an exosuit actively assisting the paretic limb of individuals in the chronic phase of stroke recovery during treadmill and overground walking. Using controlled, treadmill-based biomechanical investigation, we demonstrate that exosuits can function in synchrony with a wearer's paretic limb to facilitate an immediate 5.33 ± 0.91° increase in the paretic ankle's swing phase dorsiflexion and 11 ± 3% increase in the paretic limb's generation of forward propulsion (P < 0.05). These improvements in paretic limb function contributed to a 20 ± 4% reduction in forward propulsion interlimb asymmetry and a 10 ± 3% reduction in the energy cost of walking, which is equivalent to a 32 ± 9% reduction in the metabolic burden associated with poststroke walking. Relatively low assistance (~12% of biological torques) delivered with a lightweight and nonrestrictive exosuit was sufficient to facilitate more normal walking in ambulatory individuals after stroke. Future work will focus on understanding how exosuit-induced improvements in walking performance may be leveraged to improve mobility after stroke.

Biomechanical mechanisms underlying exosuit-induced improvements in walking economy after stroke

Stroke-induced hemiparetic gait is characteristically asymmetric and metabolically expensive. Weakness and impaired control of the paretic ankle contribute to reduced forward propulsion and ground clearance - walking subtasks critical for safe and efficient locomotion. Targeted gait interventions that improve paretic ankle function after stroke are therefore warranted. We have developed textile-based, soft wearable robots that transmit mechanical power generated by off-board or body-worn actuators to the paretic ankle using Bowden cables (soft exosuits) and have demonstrated the exosuits can overcome deficits in paretic limb forward propulsion and ground clearance, ultimately reducing the metabolic cost of hemiparetic walking. This study elucidates the biomechanical mechanisms underlying exosuit-induced reductions in metabolic power. We evaluated the relationships between exosuit-induced changes in the body center of mass (COM) power generated by each limb, individual joint power and metabolic power. Compared with walking with an exosuit unpowered, exosuit assistance produced more symmetrical COM power generation during the critical period of the step-to-step transition (22.4±6.4% more symmetric). Changes in individual limb COM power were related to changes in paretic (R2=0.83, P=0.004) and non-paretic (R2=0.73, P=0.014) ankle power. Interestingly, despite the exosuit providing direct assistance to only the paretic limb, changes in metabolic power were related to changes in non-paretic limb COM power (R2=0.80, P=0.007), not paretic limb COM power (P>0.05). These findings contribute to a fundamental understanding of how individuals post-stroke interact with an exosuit to reduce the metabolic cost of hemiparetic walking.

Effects of real-time gait biofeedback on paretic propulsion and gait biomechanics in individuals post-stroke

Objectives Gait training interventions that target paretic propulsion induce improvements in walking speed and function in individuals post-stroke. Previously, we demonstrated that able-bodied individuals increase propulsion unilaterally when provided real-time biofeedback targeting anterior ground reaction forces (AGRF). The purpose of this study was to, for the first time, investigate short-term effects of real-time AGRF gait biofeedback training on post-stroke gait. Methods Nine individuals with post-stroke hemiparesis (6 females, age = 54 ± 12.4 years 39.2 ± 24.4 months post-stroke) completed three 6-minute training bouts on an instrumented treadmill. During training, visual and auditory biofeedback were provided to increase paretic AGRF during terminal stance. Gait biomechanics were evaluated before training, and during retention tests conducted 2, 15, and 30 minutes post-training. Primary dependent variables were paretic and non-paretic peak AGRF; secondary variables included paretic and non-paretic peak trailing limb angle, plantarflexor moment, and step length. In addition to evaluating the effects of biofeedback training on these dependent variables, we compared effects of a 6-minute biofeedback training bout to a non-biofeedback control condition. Results Compared to pre-training, significantly greater paretic peak AGRFs were generated during the 2, 15, and 30-minute retention tests conducted after the 18-minute biofeedback training session. Biofeedback training induced no significant effects on the non-paretic leg. Comparison of a 6-minute biofeedback training bout with a speed-matched control bout without biofeedback demonstrated a main effect for training type, with greater peak AGRF generation during biofeedback. Discussion Our results suggest that AGRF biofeedback may be a feasible and promising gait training strategy to target propulsive deficits in individuals post-stroke.

Effects of task-specific paretic ankle plantar flexor training on walking in a stroke patient: a single-case study

[Purpose] The purpose of this study was to examine the effects of task-specific plantar flexor training on walking ability indices in a patient with a paretic ankle. [Subject and Methods] The subject was a 65-year-old male patient with right hemiplegia due to a left medullary ventral infarction. An ABA’ single-subject design was adopted. The independent variable was a task-specific plantar flexor training exercise, similar to that during walking, targeting the paretic ankle. The dependent variables were the isometric ankle plantar flexor strength, maximum walking speed, step length, and trailing limb angle in the paretic terminal stance phase. The B study phase was divided into B1 and B2 phases. A two standard-deviation-band method was used to evaluate improvement. [Results] Improvements in the paretic plantar flexor strength, maximum walking speed, step length, and trailing limb angle in the B2 phase were observed. The improvements in the maximum walking speed, step length, and trailing limb angle were sustained in the A’ study phase. [Conclusion] These results suggest that task-specific plantar flexor training exercise is efficacious in improving the walking ability index of a paretic ankle.

Effects of unilateral real-time biofeedback on propulsive forces during gait

BACKGROUND

In individuals with post-stroke hemiparesis, reduced push-off force generation in the paretic leg negatively impacts walking function. Gait training interventions that increase paretic push-off can improve walking function in individuals with neurologic impairment. During normal locomotion, push-off forces are modulated with variations in gait speed and slope. However, it is unknown whether able-bodied individuals can selectively modulate push-off forces from one leg in response to biofeedback. Here, in a group of young, neurologically-unimpaired individuals, we determined the effects of a real-time visual and auditory biofeedback gait training paradigm aimed at unilaterally increasing anteriorly-directed ground reaction force (AGRF) in the targeted leg.

METHODS

Ground reaction force data during were collected from 7 able-bodied individuals as they walked at a self-selected pace on a dual-belt treadmill instrumented with force platforms. During 11-min of gait training, study participants were provided real-time AGRF biofeedback encouraging a 20-30% increase in peak AGRF generated by their right (targeted) leg compared to their baseline (pre-training) AGRF. AGRF data were collected before, during, and after the biofeedback training period, as well as during two retention tests performed without biofeedback and after standing breaks.

RESULTS

Compared to AGRFs generated during the pre-training gait trials, participants demonstrated a significantly greater AGRF in the targeted leg during and immediately after training, indicating that biofeedback training was successful at inducing increased AGRF production in the targeted leg. Additionally, participants continued to demonstrate greater AGRF production in the targeted leg after two standing breaks, showing short-term recall of the gait pattern learned during the biofeedback training. No significant effects of training were observed on the AGRF in the non-targeted limb, showing the specificity of the effects of biofeedback toward the targeted limb.

CONCLUSIONS

These results demonstrate the short-term effects of using unilateral AGRF biofeedback to target propulsion in a specific leg, which may have utility as a training tool for individuals with gait deficits such as post-stroke hemiparesis. Future studies are needed to investigate the effects of real-time AGRF biofeedback as a gait training tool in neurologically-impaired individuals.

Associations Between Foot Placement Asymmetries and Metabolic Cost of Transport in Hemiparetic Gait

Stroke survivors often have a slow, asymmetric walking pattern. They also walk with a higher metabolic cost than healthy, age-matched controls. It is often assumed that spatial-temporal asymmetries contribute to the increased metabolic cost of walking poststroke. However, elucidating this relationship is made challenging because of the interdependence between spatial-temporal asymmetries, walking speed, and metabolic cost. Here, we address these potential confounds by measuring speed-dependent changes in metabolic cost and implementing a recently developed approach to dissociate spatial versus temporal contributions to asymmetry in a sample of stroke survivors. We used expired gas analysis to compute the metabolic cost of transport (CoT) for each participant at 4 different walking speeds: self-selected speed, 80% and 120% of their self-selected speed, and their fastest comfortable speed. We also computed CoT for a sample of age- and gender-matched control participants who walked at the same speeds as their matched stroke survivor. Kinematic data were used to compute the magnitude of a number of variables characterizing spatial-temporal asymmetries. Across all speeds, stroke survivors had a higher CoT than controls. We also found that our sample of stroke survivors did not choose a self-selected speed that minimized CoT, contrary to typical observations in healthy controls. Multiple regression analyses revealed negative associations between speed and CoT and a positive association between asymmetries in foot placement relative to the trunk and CoT. These findings suggest that interventions designed to increase self-selected walking speed and reduce foot-placement asymmetries may be ideal for improving walking economy poststroke.

Identifying candidates for targeted gait rehabilitation after stroke: better prediction through biomechanics-informed characterization

BACKGROUND

Walking speed has been used to predict the efficacy of gait training; however, poststroke motor impairments are heterogeneous and different biomechanical strategies may underlie the same walking speed. Identifying which individuals will respond best to a particular gait rehabilitation program using walking speed alone may thus be limited. The objective of this study was to determine if, beyond walking speed, participants' baseline ability to generate propulsive force from their paretic limbs (paretic propulsion) influences the improvements in walking speed resulting from a paretic propulsion-targeting gait intervention.

METHODS

Twenty seven participants >6 months poststroke underwent a 12-week locomotor training program designed to target deficits in paretic propulsion through the combination of fast walking with functional electrical stimulation to the paretic ankle musculature (FastFES). The relationship between participants' baseline usual walking speed (UWS_baseline), maximum walking speed (MWS_baseline), and paretic propulsion (prop_baseline) versus improvements in usual walking speed (∆UWS) and maximum walking speed (∆MWS) were evaluated in moderated regression models.

RESULTS

UWS_baseline and MWS_baseline were, respectively, poor predictors of ΔUWS (R ²  = 0.24) and ΔMWS (R ²  = 0.01). Paretic propulsion × walking speed interactions (UWS_baseline × prop_baseline and MWS_baseline × prop_baseline) were observed in each regression model (R ² s = 0.61 and 0.49 for ∆UWS and ∆MWS, respectively), revealing that slower individuals with higher utilization of the paretic limb for forward propulsion responded best to FastFES training and were the most likely to achieve clinically important differences.

CONCLUSIONS

Characterizing participants based on both their walking speed and ability to generate paretic propulsion is a markedly better approach to predicting walking recovery following targeted gait rehabilitation than using walking speed alone.