Physiological evaluation of gait disturbances post stroke

Delayed cortical engagement associated with balance dysfunction after stroke

Cortical resources are typically engaged for balance and mobility in older adults, but these resources are impaired post-stroke. Although slowed balance and mobility after stroke have been well-characterized, the effects of unilateral cortical lesions due to stroke on neuromechanical control of balance is poorly understood. Our central hypothesis is that stroke impairs the ability to rapidly and effectively engage the cerebral cortex during balance and mobility behaviors, resulting in asymmetrical contributions of each limb to balance control. Using electroencephalography (EEG), we assessed cortical N1 responses evoked over fronto-midline regions (Cz) during balance recovery in response to backward support-surface perturbations loading both legs, as well as posterior-lateral directions that preferentially load the paretic or nonparetic leg. Cortical N1 responses were smaller and delayed in the stroke group. While older adults exhibited weak or absent relationships between cortical responses and clinical function, stroke survivors exhibited strong associations between slower N1 latencies and slower walking, lower clinical mobility, and lower balance function. We further assessed kinetics of balance recovery during perturbations using center of pressure rate of rise. During backward support-surface perturbations that loaded the legs bilaterally, balance recovery kinetics were not different between stroke and control groups and were not associated with cortical response latency. However, lateralized perturbations revealed slower kinetic reactions during paretic loading compared to controls, and to non-paretic loading within stroke participants. Individuals post stroke had similar nonparetic-loaded kinetic reactions to controls implicating that they effectively compensate for impaired paretic leg kinetics when relying on the non-paretic leg. In contrast, paretic-loaded balance recovery revealed time-synchronized associations between slower cortical responses and slower kinetic reactions only in the stroke group, potentially reflecting the limits of cortical engagement for balance recovery revealed within the behavioral context of paretic motor capacity. Overall, our results implicate individuals after stroke may be uniquely limited in their balance ability by the slowed speed of their cortical engagement, particularly under challenging balance conditions that rely on the paretic leg. We expect this neuromechanical insight will enable progress toward an individualized framework for the assessment and treatment of balance impairments based on the interaction between neuropathology and behavioral context.

Treadmill Handrail-Use Increases the Anteroposterior Margin of Stability in Individuals' Post-Stroke

Treadmills are important rehabilitation tools used with or without handrails. The handrails could be used to attain balance, prevent falls, and improve the walking biomechanics of stroke survivors, but it is yet unclear how the treadmill handrails impact their stability margins. Here, we investigated how 3 treadmill handrail-use conditions (no-hold, self-selected support, and light touch) impact stroke survivors' margins of stability (MoS). The anteroposterior MoS significantly increased for both legs with self-selected support while the mediolateral MoS of the unaffected leg decreased significantly when the participants walked with self-selected support in comparison to no-hold in both cases. We concluded that the contextual use of the handrail should guide its prescription for fall prevention or balance training in rehabilitation programs.

Lower Limb Kinematic Coordination during the Running Motion of Stroke Patient: A Single Case Study

The purpose of this study was to clarify the lower limb joint motor coordination of para-athletes during running motion from frequency characteristics and to propose this as a method for evaluating their performance. The subject used was a 43-year-old male para-athlete who had suffered a left cerebral infarction. Using a three-dimensional motion analysis system, the angles of the hip, knee, and ankle joints were measured during 1 min of running at a speed of 8 km/h on a treadmill. Nine inter- and intra-limb joint angle pairs were analyzed by coherence and phase analyses. The main characteristic of the stroke patient was that there were joint pairs with absent or increased coherence peaks in the high-frequency band above 4 Hz that were not found in healthy subjects. Interestingly, these features were also observed on the non-paralyzed side. Furthermore, a phase analysis showed different phase differences between the joint motions of the stroke patient and healthy subjects in some joint pairs. Thus, we concluded there was a widespread functional impairment of joint motion in the stroke patient that has not been revealed by conventional methods. The coherence analysis of joint motion may be useful for identifying joint motion problems in para-athletes.

Assessment Methods of Post-stroke Gait: A Scoping Review of Technology-Driven Approaches to Gait Characterization and Analysis

Background: Gait dysfunction or impairment is considered one of the most common and devastating physiological consequences of stroke, and achieving optimal gait is a key goal for stroke victims with gait disability along with their clinical teams. Many researchers have explored post stroke gait, including assessment tools and techniques, key gait parameters and significance on functional recovery, as well as data mining, modeling and analyses methods.

Research Question: This study aimed to review and summarize research efforts applicable to quantification and analyses of post-stroke gait with focus on recent technology-driven gait characterization and analysis approaches, including the integration of smart low cost wearables and Artificial Intelligence (AI), as well as feasibility and potential value in clinical settings.

Methods: A comprehensive literature search was conducted within Google Scholar, PubMed, and ScienceDirect using a set of keywords, including lower extremity, walking, post-stroke, and kinematics. Original articles that met the selection criteria were included.

Results and Significance: This scoping review aimed to shed light on tools and technologies employed in post stroke gait assessment toward bridging the existing gap between the research and clinical communities. Conventional qualitative gait analysis, typically used in clinics is mainly based on observational gait and is hence subjective and largely impacted by the observer's experience. Quantitative gait analysis, however, provides measured parameters, with good accuracy and repeatability for the diagnosis and comparative assessment throughout rehabilitation. Rapidly emerging smart wearable technology and AI, including Machine Learning, Support Vector Machine, and Neural Network approaches, are increasingly commanding greater attention in gait research. Although their use in clinical settings are not yet well leveraged, these tools promise a paradigm shift in stroke gait quantification, as they provide means for acquiring, storing and analyzing multifactorial complex gait data, while capturing its non-linear dynamic variability and offering the invaluable benefits of predictive analytics.

Asymmetry and Variability Should Be Included in the Assessment of Gait Function in Poststroke Hemiplegia With Independent Ambulation During Early Rehabilitation

OBJECTIVE

To extract independent features from spatiotemporal data of poststroke gait.

DESIGN

Retrospective observational study.

SETTING

Motion analysis laboratory in the rehabilitation department of a university hospital.

PARTICIPANTS

Convenience sample from inpatients in subacute recovery stage post stroke. Of 98 patients post stroke who underwent gait assessment, 69 patients post stroke were included in the data analysis (N=69). They could walk more than 10 m without personal assist or assistive devices.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Spatiotemporal parameters during level walking and their asymmetry and variability were obtained by insole foot pressure measurement system.

RESULTS

Of independent components extracted by principal component analysis, 3 independent components explained 81.9% of total variance of spatiotemporal poststroke gait data. The first component has associations with walking speed and proportion of double support phase, and it explains 46.6% of total variance. The second component has association with temporal asymmetry, and it explains 21.1% of total variance. The third component has association with temporal variability, and it explains 14.2% of total variance. Principal component scores did not show significant differences between stroke types and among stroke lesions.

CONCLUSIONS

Temporal asymmetry and variability should be included in the assessment of poststroke gait during early rehabilitation. They are independent of each other and provide characteristics of poststroke gait that are independent to the walking speed. They are helpful for rehabilitation planning and developing treatment strategy in poststroke gait rehabilitation.

A Novel Multiple-Cue Observational Clinical Scale for Functional Evaluation of Gait After Stroke - The Stroke Mobility Score (SMS)

Background

For future development of machine learning tools for gait impairment assessment after stroke, simple observational whole-body clinical scales are required. Current observational scales regard either only leg movement or discrete overall parameters, neglecting dysfunctions in the trunk and arms. The purpose of this study was to introduce a new multiple-cue observational scale, called the stroke mobility score (SMS).

Material/Methods

In a group of 131 patients, we developed a 1-page manual involving 6 subscores by Delphi method using the video-based SMS: trunk posture, leg movement of the most affected side, arm movement of the most affected side, walking speed, gait fluency and stability/risk of falling. Six medical raters then validated the SMS on a sample of 60 additional stroke patients. Conventional scales (NIHSS, Timed-Up-And-Go-Test, 10-Meter-Walk-Test, Berg Balance Scale, FIM-Item L, Barthel Index) were also applied.

Results

(1) High consistency and excellent inter-rater reliability of the SMS were verified (Cronbach’s alpha >0.9). (2) The SMS subscores are non-redundant and reveal much more nuanced whole-body dysfunction details than conventional scores, although evident correlations as e.g. between 10-Meter-Walk-Test and subscore “gait speed” are verified. (3) The analysis of cross-correlations between SMS subscores unveils new functional interrelationships for stroke profiling.

Conclusions

The SMS proves to be an easy-to-use, tele-applicable, robust, consistent, reliable, and nuanced functional scale of gait impairments after stroke. Due to its sensitivity to whole-body motion criteria, it is ideally suited for machine learning algorithms and for development of new therapy strategies based on instrumented gait analysis.

Investigating the relationship between spatiotemporal gait variability and falls self-efficacy in individuals with chronic stroke

AIM

To investigate the relationship between spatiotemporal gait variability and falls self-efficacy after chronic stroke while taking into account the effect of some known potential confounders including fall numbers and gait velocity.

METHODS

Participants (n = 62) walked at their preferred speed to calculate gait variability for stride time, stride length, swing time, and double-support percent. The Falls Efficacy Scale-International (FES-I) assessed falls self-efficacy. The linear regression tests were used for statistical analysis. Age, sex, time since stroke, paretic side, motor impairments, fall numbers, and gait velocity were considered as independent variables.

RESULTS

Increased FES-I score was related to higher stride time variability (R² = 0.65, F(8,53) = 15.44, P < .05). Increased FES-I was associated with higher stride length variability (R² = 0.42, F(6,55) = 8.44, P < .05). However, further adjustment on gait velocity and fall numbers made the association non-significant (R² = 0.41, F(8,53) = 6.4, P > .05). No significant relationship was identified between FES-I and swing time (R² = 0.08, F(8,53) = 0.39, P > .05) and FES-I and double-support percent variability (R² = 0.04, F(8,53) = 0.67, P > .05).

CONCLUSION

The results indicate that increased FES-I score may be related to increased stride variability post stroke.

A Review of Robot-Assisted Lower-Limb Stroke Therapy: Unexplored Paths and Future Directions in Gait Rehabilitation

Stroke affects one out of every six people on Earth. Approximately 90% of stroke survivors have some functional disability with mobility being a major impairment, which not only affects important daily activities but also increases the likelihood of falling. Originally intended to supplement traditional post-stroke gait rehabilitation, robotic systems have gained remarkable attention in recent years as a tool to decrease the strain on physical therapists while increasing the precision and repeatability of the therapy. While some of the current methods for robot-assisted rehabilitation have had many positive and promising outcomes, there is moderate evidence of improvement in walking and motor recovery using robotic devices compared to traditional practice. In order to better understand how and where robot-assisted rehabilitation has been effective, it is imperative to identify the main schools of thought that have prevailed. This review intends to observe those perspectives through three different lenses: the goal and type of interaction, the physical implementation, and the sensorimotor pathways targeted by robotic devices. The ways that researchers approach the problem of restoring gait function are grouped together in an intuitive way. Seeing robot-assisted rehabilitation in this unique light can naturally provoke the development of new directions to potentially fill the current research gaps and eventually discover more effective ways to provide therapy. In particular, the idea of utilizing the human inter-limb coordination mechanisms is brought up as an especially promising area for rehabilitation and is extensively discussed.

Use of Pelvic Corrective Force With Visual Feedback Improves Paretic Leg Muscle Activities and Gait Performance After Stroke

The purpose of this study was to examine the effects of combined pelvic corrective force and visual feedback during treadmill walking on paretic leg muscle activity and gait characteristics in individuals with post-stroke hemiparesis. Fifteen chronic stroke participants completed visual feedback only and combined pelvic corrective force and visual feedback conditions during treadmill walking. Each condition included: 1-minute baseline, 7-minute training with visual feedback only or additional pelvic corrective force, 1-minute post training, 1-minute standing break, and another 5-minute training. EMGs from the paretic leg muscles and step length were measured. Overground walking was evaluated before treadmill walking, immediately and 10 minutes after treadmill walking. Greater increases in integrated EMG of all muscles, except vastus medialis and tibialis anterior, were observed with the application of additional pelvic corrective force compared to visual feedback only during treadmill walking. Overground walking speed significantly increased after treadmill training with combined pelvic correction force and visual feedback, but was not significant for the visual feedback only condition. Voluntary weight shifting with additional pelvic corrective force enhanced paretic leg muscle activities and improved gait characteristics during walking. Individuals with post-stroke hemiparesis could adapt feedforward control and generalize the adaptation to overground walking.

Computational Design of FastFES Treatment to Improve Propulsive Force Symmetry During Post-stroke Gait: A Feasibility Study

Stroke is a leading cause of long-term disability worldwide and often impairs walking ability. To improve recovery of walking function post-stroke, researchers have investigated the use of treatments such as fast functional electrical stimulation (FastFES). During FastFES treatments, individuals post-stroke walk on a treadmill at their fastest comfortable speed while electrical stimulation is delivered to two muscles of the paretic ankle, ideally to improve paretic leg propulsion and toe clearance. However, muscle selection and stimulation timing are currently standardized based on clinical intuition and a one-size-fits-all approach, which may explain in part why some patients respond to FastFES training while others do not. This study explores how personalized neuromusculoskeletal models could potentially be used to enable individual-specific selection of target muscles and stimulation timing to address unique functional limitations of individual patients post-stroke. Treadmill gait data, including EMG, surface marker positions, and ground reactions, were collected from an individual post-stroke who was a non-responder to FastFES treatment. The patient's gait data were used to personalize key aspects of a full-body neuromusculoskeletal walking model, including lower-body joint functional axes, lower-body muscle force generating properties, deformable foot-ground contact properties, and paretic and non-paretic leg neural control properties. The personalized model was utilized within a direct collocation optimal control framework to reproduce the patient's unstimulated treadmill gait data (verification problem) and to generate three stimulated walking predictions that sought to minimize inter-limb propulsive force asymmetry (prediction problems). The three predictions used: (1) Standard muscle selection (gastrocnemius and tibialis anterior) with standard stimulation timing, (2) Standard muscle selection with optimized stimulation timing, and (3) Optimized muscle selection (soleus and semimembranosus) with optimized stimulation timing. Relative to unstimulated walking, the optimal control problems predicted a 41% reduction in propulsive force asymmetry for scenario (1), a 45% reduction for scenario (2), and a 64% reduction for scenario (3), suggesting that non-standard muscle selection may be superior for this patient. Despite these predicted improvements, kinematic symmetry was not noticeably improved for any of the walking predictions. These results suggest that personalized neuromusculoskeletal models may be able to predict personalized FastFES training prescriptions that could improve propulsive force symmetry, though inclusion of kinematic requirements would be necessary to improve kinematic symmetry as well.

The use of combination therapy in the treatment of lower limb spasticity among patients after stroke - a review of literature

Stroke is not only a medical problem, but also, due to the permanent disability of patients, a significant social issue. Therefore, gait disturbances resulting from lower limb muscle spastici-ty are a common subject of research. The ambiguities in the scientific literature have become justification for the creation of this systematic review, the aim of which is to collect and ana-lyse works describing the efficacy of combination therapy - including Botulinum toxin type A injections and physiotherapy following stroke. The following databases were searched: Pub-Med, EBSCO, Springer Link (date of access: 24 Jan. 2019). It was assumed that analysis will include scientific works published in English from 2000 to date (in accordance with search date). For the entry "combination therapy" (Botulinum toxin injections and physiotherapy), the search was conducted using the following keywords: physical therapy, Botulinum toxin type A, Botox A, lower limb, gait, brain, stroke, hemiparesis. Out of all the elaborate articles, 7 concerning combination therapy were ultimately evaluated. Analysis of the collected works indicates the effectiveness of combination therapy in the area of improving structural parame-ters. Some of the works prove that this type of therapy also improves functional indices and leads to increased activity of patients. We could not collect satisfactory evidence confirming its effectiveness in terms of increasing social participation and improving the quality of life of patients. This review indicates the need to develop specific therapeutic protocols accurately describing both Botulinum toxin injections and physiotherapy - taking the intensity, duration and type of therapy into account. Opoka K., Filip M., Mirek E., Pasiut S. The use of combination therapy in the treatment of lower limb spasticity among patients after stroke − a review of literature. Med Rehabil 2019; 23(2): 36-41. DOI: 10.5604/01.3001.0013.0875 This article is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License CC BY-SA (http://creativecommons.org/licenses/by-sa/4.0/) null

Gait Rehabilitation Using Functional Electrical Stimulation Induces Changes in Ankle Muscle Coordination in Stroke Survivors: A Preliminary Study

Background: Previous studies have demonstrated that post-stroke gait rehabilitation combining functional electrical stimulation (FES) applied to the ankle muscles during fast treadmill walking (FastFES) improves gait biomechanics and clinical walking function. However, there is considerable inter-individual variability in response to FastFES. Although FastFES aims to sculpt ankle muscle coordination, whether changes in ankle muscle activity underlie observed gait improvements is unknown. The aim of this study was to investigate three cases illustrating how FastFES modulates ankle muscle recruitment during walking.

Methods: We conducted a preliminary case series study on three individuals (53–70 y; 2 M; 35–60 months post-stroke; 19–22 lower extremity Fugl-Meyer) who participated in 18 sessions of FastFES (3 sessions/week; ClinicalTrials.gov: NCT01668602). Clinical walking function (speed, 6-min walk test, and Timed-Up-and-Go test), gait biomechanics (paretic propulsion and ankle angle at initial-contact), and plantarflexor (soleus)/dorsiflexor (tibialis anterior) muscle recruitment were assessed pre- and post-FastFES while walking without stimulation.

Results:Two participants (R1, R2) were categorized as responders based on improvements in clinical walking function. Consistent with heterogeneity of clinical and biomechanical changes commonly observed following gait rehabilitation, how muscle activity was altered with FastFES differed between responders. R1 exhibited improved plantarflexor recruitment during stance accompanied by increased paretic propulsion. R2 exhibited improved dorsiflexor recruitment during swing accompanied by improved paretic ankle angle at initial-contact. In contrast, the third participant (NR1), classified as a non-responder, demonstrated increased ankle muscle activity during inappropriate phases of the gait cycle. Across all participants, there was a positive relationship between increased walking speeds after FastFES and reduced SOL/TA muscle coactivation.

Conclusion:Our preliminary case series study is the first to demonstrate that improvements in ankle plantarflexor and dorsiflexor muscle recruitment (muscles targeted by FastFES) accompanied improvements in gait biomechanics and walking function following FastFES in individuals post-stroke. Our results also suggest that inducing more appropriate (i.e., reduced) ankle plantar/dorsi-flexor muscle coactivation may be an important neuromuscular mechanism underlying improvements in gait function after FastFES training, suggesting that pre-treatment ankle muscle status could be used for inclusion into FastFES. The findings of this case-series study, albeit preliminary, provide the rationale and foundations for larger-sample studies using similar methodology.

Mediolateral footpath stabilization during walking in people following stroke

Community dwelling stroke survivors most often fall while walking. Understanding how post-stroke individuals control mediolateral footpath during walking may help elucidate the mechanisms that contribute to walking instability. By applying the Uncontrolled Manifold (UCM) approach, we investigated (1) how post-stroke individuals coordinate lower-extremity joint motions to stabilize mediolateral footpath of the swing leg, and (2) how the inter-joint coordination in footpath stabilization correlates to their walking stability. Nine stroke subjects and nine healthy controls walked on a treadmill at four different speeds. UCM analysis partitions the variance of kinematic configurations across gait cycles into "good variance" (i.e., the variance component leading to a consistent footpath) or "bad variance" (i.e., the variance component leading to an inconsistent footpath). We found that both groups had a significantly greater "good" than "bad" variance (p<0.05) for most of the swing phase, suggesting that mediolateral footpath is an important variable stabilized by the central nervous system during walking. Stroke subjects had significantly greater relative variance difference (ΔV) (i.e. normalized difference between "good" and "bad" variance) (p<0.05), indicating a stronger kinematic synergy in footpath stabilization, than the controls. In addition, the kinematic synergy in mediolateral footpath stabilization is strongest during mid-swing but weakest during late swing in healthy gait. However, this phase-dependent strategy is preserved for mid-swing but not for late swing in stroke gait. Moreover, stroke and healthy subjects demonstrated different relationships between UCM and walking stability measures. A stronger kinematic synergy in healthy gait is associated with better walking stability whereas having more "good variance" or stronger kinematic synergy in stroke gait is associated with less walking stability. The current findings suggest that walking with too much "good variance" in people following stroke, despite no effect on the footpath, may adversely affect their walking stability to some extent.

Uncovering the structure of the mouse gait controller: Mice respond to substrate perturbations with adaptations in gait on a continuum between trot and bound

Animals, including humans, have been shown to maintain a gait during locomotion that minimizes the risk of injury and energetic cost. Despite the importance of understanding the mechanisms of gait regulation, ethical and experimental challenges have prevented full exploration of these. Here we present data on the gait response of mice to rapid, precisely timed, spatially confined mechanical perturbations. Our data elucidate that after the mechanical perturbation, the mouse gait response is anisotropic, preferring deviations away from the trot towards bounding, over those towards other gaits, such as walk or pace. We quantified this shift by projecting the observed gait onto the line between trot and bound, in the space of quadrupedal gaits. We call this projection λ. For λ=0, the gait is the ideal trot; for λ=±π, it is the ideal bound. We found that the substrate perturbation caused a significant shift in λ towards bound during the stride in which the perturbation occurred and the following stride (linear mixed effects model: Δλ=0.26±0.07 and Δλ=0.21±0.07, respectively; random effect for animal, p < 0.05 for both strides, n = 8 mice). We hypothesize that this is because the bounding gait is better suited to rapid acceleration or deceleration, and an exploratory analysis of jerk showed that it was significantly correlated with λ (p < 0.05). Understanding how gait is controlled under perturbations can aid in diagnosing gait pathologies and in the design of more agile robots.

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.

Electromyography Exposes Heterogeneity in Muscle Co-Contraction following Stroke

Walking after stroke is often described as requiring excessive muscle co-contraction, yet, evidence that co-contraction is a ubiquitous motor control strategy for this population remains inconclusive. Co-contraction, the simultaneous activation of agonist and antagonist muscles, can be assessed with electromyography (EMG) but is often described qualitatively. Here, our goal is to determine if co-contraction is associated with gait impairments following stroke. Fifteen individuals with chronic stroke and nine healthy controls walked on an instrumented treadmill at self-selected speed. Surface EMGs were collected from the medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA) of each leg. EMG envelope amplitudes were assessed in three ways: (1) no normalization, (2) normalization to the maximum value across the gait cycle, or (3) normalization to maximal M-wave. Three co-contraction indices were calculated across each agonist/antagonist muscle pair (MG/TA and SOL/TA) to assess the effect of using various metrics to quantify co-contraction. Two factor ANOVAs were used to compare effects of group and normalization for each metric. Co-contraction during the terminal stance (TSt) phase of gait is not different between healthy controls and the paretic leg of individuals post-stroke, regardless of the metric used to quantify co-contraction. Interestingly, co-contraction was similar between M-max and non-normalized EMG; however, normalization does not impact the ability to resolve group differences. While a modest correlation is revealed between the amount of TSt co-contraction and walking speed, the relationship is not sufficiently strong to motivate further exploration of a causal link between co-contraction and walking function after stroke. Co-contraction does not appear to be a common strategy employed by individuals after stroke. We recommend exploration of alternative EMG analysis approaches in an effort to learn more about the causal mechanisms of gait impairment following stroke.

One year after ischemic stroke: Changes in leg movement path stability in a speed-accuracy task but no major effects on the hands

First year after the stroke is essential for motor recovery. The main motor control strategy (i.e., faster movement production at the expense of lower movement accuracy and stability, or greater movement accuracy and stability at the expense of slower movement) selected by poststroke patients during a unilateral speed-accuracy task (SAT) remains unclear. We aimed to investigate the poststroke (12 months after stroke) effects on the trade-off between movement speed and accuracy, and intraindividual variability during a motor performance task. Healthy right-handed men (n = 20; age ∼ 66 years) and right-handed men after ischemic stroke during their post rehabilitation period (n = 20; age ∼ 69 years) were asked to perform a simple reaction task, a maximal velocity performance task and a SAT with the right and left hand, and with the right and left leg. In the hand movement trial, reaction time and movement velocity (V_max) in the SAT were slower and time to V_max in the SAT was longer in the poststroke group (P < .01). In the leg movement trial, poststroke participants reached a greater V_max in the SAT than the healthy participants (P < .01). The greatest poststroke effect on intraindividual variability in movements was found for movement path in the SAT, which was significantly greater in the legs than in the hands. Poststroke patients in the first year after stroke mainly selected an impulsive strategy for speed over hand and leg motor control, but at the expense of lower movement accuracy and greater variability in movement.

Forced Use of the Paretic Leg Induced by a Constraint Force Applied to the Nonparetic Leg in Individuals Poststroke During Walking

BACKGROUND

Individuals with stroke usually show reduced muscle activities of the paretic leg and asymmetrical gait pattern during walking.

OBJECTIVE

To determine whether applying a resistance force to the nonparetic leg would enhance the muscle activities of the paretic leg and improve the symmetry of spatiotemporal gait parameters in individuals with poststroke hemiparesis.

METHODS

Fifteen individuals with chronic poststroke hemiparesis participated in this study. A controlled resistance force was applied to the nonparetic leg using a customized cable-driven robotic system while subjects walked on a treadmill. Subjects completed 2 test sections with the resistance force applied at different phases of gait (ie, early and late swing phases) and different magnitudes (10%, 20%, and 30% of maximum voluntary contraction [MVC] of nonparetic leg hip flexors). Electromyographic (EMG) activity of the muscles of the paretic leg and spatiotemporal gait parameters were collected.

RESULTS

Significant increases in integrated EMG of medial gastrocnemius, medial hamstrings, vastus medialis, and tibialis anterior of the paretic leg were observed when the resistance was applied during the early swing phase of the nonparetic leg, compared with baseline. Additionally, resistance with 30% of MVC induced the greatest level of muscle activity than that with 10% or 20% of MVC. The symmetry index of gait parameters also improved with resistance applied during the early swing phase.

CONCLUSION

Applying a controlled resistance force to the nonparetic leg during early swing phase may induce forced use on the paretic leg and improve the spatiotemporal symmetry of gait in individuals with poststroke hemiparesis.

Applying a pelvic corrective force induces forced use of the paretic leg and improves paretic leg EMG activities of individuals post-stroke during treadmill walking

OBJECTIVE

To determine whether applying a mediolateral corrective force to the pelvis during treadmill walking would enhance muscle activity of the paretic leg and improve gait symmetry in individuals with post-stroke hemiparesis.

METHODS

Fifteen subjects with post-stroke hemiparesis participated in this study. A customized cable-driven robotic system based over a treadmill generated a mediolateral corrective force to the pelvis toward the paretic side during early stance phase. Three different amounts of corrective force were applied. Electromyographic (EMG) activity of the paretic leg, spatiotemporal gait parameters and pelvis lateral displacement were collected.

RESULTS

Significant increases in integrated EMG of hip abductor, medial hamstrings, soleus, rectus femoris, vastus medialis and tibialis anterior were observed when pelvic corrective force was applied, with pelvic corrective force at 9% of body weight inducing greater muscle activity than 3% or 6% of body weight. Pelvis lateral displacement was more symmetric with pelvic corrective force at 9% of body weight.

CONCLUSIONS

Applying a mediolateral pelvic corrective force toward the paretic side may enhance muscle activity of the paretic leg and improve pelvis displacement symmetry in individuals post-stroke.

SIGNIFICANCE

Forceful weight shift to the paretic side could potentially force additional use of the paretic leg and improve the walking pattern.

Locomotor circumvention strategies are altered by stroke: I. Obstacle clearance

Background

Functional locomotion requires the ability to adapt to environmental challenges such as the presence of stationary or moving obstacles. Difficulties in obstacle circumvention often lead to restricted community ambulation in individuals with stroke. The objective of this study was to contrast obstacle circumvention strategies between post-stroke (n = 12) and healthy individuals (n = 12) performing locomotor and perceptuomotor (joystick navigation) tasks with different obstacle approaches.

Methods

Participants walked and navigated with a joystick towards a central target, in a virtual environment simulating a large room, while avoiding an obstacle that either remained stationary at the pre-determined point of intersection or moved from head-on or diagonally 30° left/right. The outcome measures included dynamic clearance (DC), instantaneous distance from obstacle at crossing (IDC), number of collisions and preferred side of circumvention. These measures were compared between groups (stroke vs. healthy), obstacle parameter (stationary vs. moving head-on) and direction of approach (left/paretic vs. right/non-paretic).

Results

DC was significantly larger when circumventing a moving obstacle that approached head-on as compared to a stationary obstacle for both groups during both tasks, while not significantly different in either diagonal approach in either group. IDC was smaller in the stroke group while walking and larger in both groups during joystick navigation when avoiding moving as compared to stationary obstacle. IDC was significantly larger in the stroke group compared to controls for diagonal approaches during walking, wherein two different strategies emerged amongst individuals with stroke: circumventing to the same (V_same n = 6) or opposite (V_opp n = 4) side of obstacle approach. This behavior was not seen in the perceptuomotor task, wherein post-stroke participants circumvented to opposite side of the obstacle approach as seen in healthy participants. In the locomotor task, the V_same subgroup that had greater functional limitations used larger DC as compared to the V_opp subgroup and healthy individuals. The remaining two individuals with stroke collided with obstacles in >50% trials of either obstacle approach. The underlying mechanisms for collision were however different for both individuals.

Conclusion

Avoidance strategies in individuals with stroke can vary depending on the individual locomotor capabilities and obstacle characteristics.

Ultrasonic Measurement of Dynamic Muscle Behavior for Poststroke Hemiparetic Gait

Quantitative evaluation of the hemiparesis status for a poststroke patient is still challenging. This study aims to measure and investigate the dynamic muscle behavior in poststroke hemiparetic gait using ultrasonography. Twelve hemiparetic patients walked on a treadmill, and EMG, joint angle, and ultrasonography were simultaneously recorded for the gastrocnemius medialis muscle. Pennation angle was automatically extracted from ultrasonography using a tracking algorithm reported previously. The characteristics of EMG, joint angle, and pennation angle in gait cycle were calculated for both (affected and unaffected) sides of lower limbs. The results suggest that pennation angle could work as an important morphological index to continuous muscle contraction. The change pattern of pennation angle between the affected and unaffected sides is different from that of EMG. These findings indicate that morphological parameter extracted from ultrasonography can provide different information from that provided by EMG for hemiparetic gait.

Randomized comparison trial of gait training with and without compelled weight-shift therapy in individuals with chronic stroke

Objective:

To compare the effects of gait training combined with compelled weight-shift therapy and gait training alone on velocity and gait symmetry in patients with chronic stroke.

Design:

Single-blind randomized controlled trial.

Participants:

Patients ( N=28) with chronic stroke and stance asymmetry toward the non-paretic side.

Interventions:

Six weeks of gait training combined with compelled weight-shift therapy via a shoe lift applied under the non-paretic leg (experimental group, n=14) or gait training alone (control group, n=14).

Main measures:

Percentage of total body weight carried by the paretic limb, gait velocity and gait spatiotemporal symmetry ratios including step symmetry, stance symmetry, swing symmetry and overall temporal symmetry.

Results:

When comparing the two groups, weight bearing on the affected side increased more significantly in experimental group than in control group (40.14±3.77, 38.28±4.06) after the end of treatment and also after a three-month follow-up (44.42±3.5, 38.5±3.77) (P<0.05). Among the experimental and control groups, there were no significant differences of gait velocity (cm/s) after six weeks of treatment (49.82±16.82, 42.66±18.75) and also after a three-month follow-up (50.94±16.27, 41.66±17.58) ( P>0.05). There were no significant differences of gait spatiotemporal symmetry ratios including step symmetry, stance symmetry, swing symmetry and overall temporal symmetry between the two groups after six weeks of treatment and also at three-month follow-up ( P>0.05).

Conclusions:

This study did not confirm that the effect of gait training combined with compelled body weight shift therapy was better than gait training alone on improving velocity and gait symmetry in patients with chronic stroke.

Neuromechanical principles underlying movement modularity and their implications for rehabilitation

Neuromechanical principles define the properties and problems that shape neural solutions for movement. Although the theoretical and experimental evidence is debated, we present arguments for consistent structures in motor patterns, i.e., motor modules, that are neuromechanical solutions for movement particular to an individual and shaped by evolutionary, developmental, and learning processes. As a consequence, motor modules may be useful in assessing sensorimotor deficits specific to an individual and define targets for the rational development of novel rehabilitation therapies that enhance neural plasticity and sculpt motor recovery. We propose that motor module organization is disrupted and may be improved by therapy in spinal cord injury, stroke, and Parkinson's disease. Recent studies provide insights into the yet-unknown underlying neural mechanisms of motor modules, motor impairment, and motor learning and may lead to better understanding of the causal nature of modularity and its underlying neural substrates.

Interlimb Coordination During Step-to-Step Transition and Gait Performance

Most energy spent in walking is due to step-to-step transitions. During this phase, the interlimb coordination assumes a crucial role to meet the demands of postural and movement control. The authors review studies that have been carried out regarding the interlimb coordination during gait, as well as the basic biomechanical and neurophysiological principles of interlimb coordination. The knowledge gathered from these studies is useful for understanding step-to-step transition during gait from a motor control perspective and for interpreting walking impairments and inefficiency related to pathologies, such as stroke. This review shows that unimpaired walking is characterized by a consistent and reciprocal interlimb influence that is supported by biomechanical models, and spinal and supraspinal mechanisms. This interlimb coordination is perturbed in subjects with stroke.

Individual limb mechanical analysis of gait following stroke

The step-to-step transition of walking requires significant mechanical and metabolic energy to redirect the center of mass. Inter-limb mechanical asymmetries during the step-to-step transition may increase overall energy demands and require compensation during single-support. The purpose of this study was to compare individual limb mechanical gait asymmetries during the step-to-step transitions, single-support and over a complete stride between two groups of individuals following stroke stratified by gait speed (≥0.8 m/s or <0.8 m/s). Twenty-six individuals with chronic stroke walked on an instrumented treadmill to collect ground reaction force data. Using the individual limbs method, mechanical power produced on the center of mass was calculated during the trailing double-support, leading double-support, and single-support phases of a stride, as well as over a complete stride. Robust inter-limb asymmetries in mechanical power existed during walking after stroke; for both groups, the non-paretic limb produced significantly more positive net mechanical power than the paretic limb during all phases of a stride and over a complete stride. Interestingly, no differences in inter-limb mechanical power asymmetry were noted between groups based on walking speed, during any phase or over a complete stride. Paretic propulsion, however, was different between speed-based groups. The fact that paretic propulsion (calculated from anterior-posterior forces) is different between groups, but our measure of mechanical work (calculated from all three directions) is not, suggests that limb power output may be dominated by vertical components, which are required for upright support.

Virtual reality-based navigation task to reveal obstacle avoidance performance in individuals with visuospatial neglect

Persons with post-stroke visuospatial neglect (VSN) often collide with moving obstacles while walking. It is not well understood whether the collisions occur as a result of attentional-perceptual deficits caused by VSN or due to post-stroke locomotor deficits. We assessed individuals with VSN on a seated, joystick-driven obstacle avoidance task, thus eliminating the influence of locomotion. Twelve participants with VSN were tested on obstacle detection and obstacle avoidance tasks in a virtual environment that included three obstacles approaching head-on or 30 (°) contralesionally/ipsilesionally. Our results indicate that in the detection task, the contralesional and head-on obstacles were detected at closer proximities compared to the ipsilesional obstacle. For the avoidance task collisions were observed only for the contralesional and head-on obstacle approaches. For the contralesional obstacle approach, participants initiated their avoidance strategies at smaller distances from the obstacle and maintained smaller minimum distances from the obstacles. The distance at detection showed a negative association with the distance at the onset of avoidance strategy for all three obstacle approaches. We conclusion the observation of collisions with contralesional and head-on obstacles, in the absence of locomotor burden, provides evidence that attentional-perceptual deficits due to VSN, independent of post-stroke locomotor deficits, alter obstacle avoidance abilities.

Forward propulsion asymmetry is indicative of changes in plantarflexor coordination during walking in individuals with post-stroke hemiparesis

BACKGROUND

A common measure of rehabilitation effectiveness post-stroke is self-selected walking speed, yet individuals may achieve the same speed using different coordination strategies. Asymmetry in the propulsion generated by each leg can provide insight into paretic leg coordination due to its relatively strong correlation with hemiparetic severity. Subjects walking at the same speed can exhibit different propulsion asymmetries, with some subjects relying more on the paretic leg and others on the nonparetic leg. The goal of this study was to assess whether analyzing propulsion asymmetry can help distinguish between improved paretic leg coordination versus nonparetic leg compensation.

METHODS

Three-dimensional forward dynamics simulations were developed for two post-stroke hemiparetic subjects walking at identical speeds before/after rehabilitation with opposite changes in propulsion asymmetry. Changes in the individual muscle contributions to forward propulsion were examined.

FINDINGS

The major source of increased forward propulsion in both subjects was from the ankle plantarflexors. How they were utilized differed and appears related to changes in propulsion asymmetry. Subject A increased propulsion generated from the paretic plantarflexors, while Subject B increased propulsion generated from the nonparetic plantarflexors. Each subject's strategy to increase speed also included differences in other muscle groups (e.g., hamstrings) that did not appear to be related to propulsion asymmetry.

INTERPRETATION

The results of this study highlight how speed cannot be used to elucidate underlying muscle coordination changes following rehabilitation. In contrast, propulsion asymmetry appears to provide insight into changes in plantarflexor output affecting propulsion generation and may be useful in monitoring rehabilitation outcomes.

Dynamic instability during post-stroke hemiparetic walking

Falls and fall-related injuries cause extremely costly and potentially fatal health problems in people post-stroke. However, there is no global indicator of walking instability for detecting which individuals will have increased risk of falls. The purposes of this study were to directly quantify walking stability in stroke survivors and neurologically intact controls and to determine which stability measures would reveal the changes in walking stability following stroke. This study thus provided an initial step to establish objective measures for identifying potential fallers. Nine post-stroke individuals and nine controls walked on a treadmill at four different speeds. We computed short-term local divergence exponent (LDE) and maximum Floquet multiplier (maxFM) of the trunk motion, average and variability of dynamic margins of stability (MOS) and step spatiotemporal measures. Post-stroke individuals demonstrated larger short-term LDE (p = 0.002) and maxFM (p = 0.041) in the mediolateral (ML) direction compared to the controls but remained orbitally stable (maxFM < 1). In addition, post-stroke individuals walked with greater average step width (p = 0.003) but similar average ML MOS (p = 0.154) compared to the controls. Post-stroke individuals also exhibited greater variability in all MOS and step measures (all p < 0.005). Our findings indicate that post-stroke individuals walked with greater local and orbital instability and gait variability than neurologically intact controls. The results suggest that short-term LDE of ML trunk motion and the variability of MOS and step spatiotemporal measures detect the changes in walking stability associated with stroke. These stability measures may have the potential for identifying those post-stroke individuals at increased risk of falls.

Intelligent data analysis of instrumented gait data in stroke patients-a systematic review

Instrumented gait analysis (GA) may be used to analyze the causes of gait deviation in stroke patients but generates a large amount of complex data. The task of transforming this data into a comprehensible report is cumbersome. Intelligent data analysis (IDA) refers to the use of computational methods in order to analyze quantitative data more effectively. The purpose of this review was to identify and appraise the available IDA methods for handling GA data collected from patients with stroke using the standard equipment of a gait lab (3D/2D motion capture, force plates, EMG). Eleven databases were systematically searched and fifteen studies that employed some type of IDA method for the analysis of kinematic and/or kinetic and/or EMG data in populations involving stroke patients were identified. Four categories of IDA methods were employed for the analysis of sensor-acquired data in these fifteen studies: classification methods, dimensionality reduction methods, clustering methods and expert systems. The methodological quality of these studies was critically appraised by examining sample characteristics, measurements and IDA properties. Three overall methodological shortcomings were identified: (1) small sample sizes and underreported patient characteristics, (2) testing of which method is best suited to the analysis was neglected and (3) lack of stringent validation procedures. No IDA method for GA data from stroke patients was identified that can be directly applied to clinical practice. Our findings suggest that the potential provided by IDA methods is not being fully exploited.

Effect of Gua Lou Gui Zhi decoction on focal cerebral ischemia-reperfusion injury through regulating the expression of excitatory amino acids and their receptors

Gua Lou Gui Zhi decotion (GLGZD) has been reported to be an effective treatment for post‑apoplectic limb spasm in the clinic. The present study aimed to investigate whether GLGZD had an affect on cerebral injuries induced by middle cerebral artery occlusion (MCAO) in rats and its possible mechanism. High‑performance liquid chromatography was performed to analyze GLGZD. Furthermore, a model was established to assess the efficacy of GLGZD. Neurological defect scores and screen tests were analyzed. Brain ischemic infarct volume was measured using 2,3,5‑triphenyl tetrazolium chloride staining and glutamic acid (Glu), aspartic acid (Asp) and glycine (Gly) levels in the cerebrospinal fluid were measured using the Hitachi automatic amino acid analyzer. Immunohistochemistry was performed to determine the expression of the α‑amino‑3‑hydroxy‑5‑methyl‑4‑isoxazole‑propionic acid (AMPA) and N‑methyl‑D‑aspartic acid (NMDA) glutamate receptors, and to analyze histopathological change. GLGZD was found to improve neurological performance and reduce infarct volumes in MCAO rats. In addition, GLGZD was observed to enhance motor performance, which was assessed using the screen test. Furthermore, GLGZD was found to reduce Glu, Asp and Gly levels in the cerebrospinal fluid and downregulate the protein expression of the AMPA and NMDA glutamate receptors. Thus, it was demonstrated that GLGZD may exert neuroprotective effects through the modulation of excitatory amino acids, and AMPA and NMDA receptor expression.

Perceptual and locomotor factors affect obstacle avoidance in persons with visuospatial neglect

Background

For safe ambulation in the community, detection and avoidance of static and moving obstacles is necessary. Such abilities may be compromised by the presence of visuospatial neglect (VSN), especially when the obstacles are present in the neglected, i.e. contralesional field.

Methods

Twelve participants with VSN were tested in a virtual environment (VE) for their ability to a) detect moving obstacles (perceptuo-motor task) using a joystick with their non-paretic hand, and b) avoid collision (locomotor task) with moving obstacles while walking in the VE. The responses of the participants to obstacles approaching on the contralesional side and from head-on were compared to those during ipsilesional approaches.

Results

Up to 67 percent of participants (8 out of 12) collided with either contralesional or head-on obstacles or both. Delay in detection (perceptuo-motor task) and execution of avoidance strategies, and smaller distances from obstacles (locomotor task) were observed for colliders compared to non-colliders. Participants’ performance on the locomotor task was not explained by clinical measures of VSN but slower walkers displayed fewer collisions.

Conclusion

Persons with VSN are at the risk of colliding with dynamic obstacles approaching from the contralesional side and from head-on. Locomotor-specific assessments of navigational abilities are needed to appreciate the recovery achieved or challenges faced by persons with VSN.

Gait disturbances in patients with stroke

Poststroke hemiplegic gait is a mixture of deviations and compensatory motion dictated by residual functions, and thus each patient must be examined and his/her unique gait pattern identified and documented. Quantitative 3-dimensional gait analysis is the best way to understand the complex multifactorial gait dysfunction in hemiparetic patients. The goals of the present work are to (1) review the temporospatial, kinematic, kinetic, and electromyographic deviations from normal gait that commonly occur after stroke and are of clinical significance, along with the most likely causes of these deviations, and (2) differentiate the departures from normal gait parameters that arise as a direct consequence of poststroke motor problems and those that arise as learned or adaptive compensations for poststroke motor problems.

Spatio-temporal parameters and intralimb coordination patterns describing hemiparetic locomotion at controlled speed

Background

Comparison between healthy and hemiparetic gait is usually carried out while subjects walk overground at preferred speed. This generates bias due to the lack of uniformity across selected speeds because they reflect the great variability of the functional level of post-stroke patients. This study aimed at examining coordinative adaptations during walking in response to unilateral brain damage, while homologous participants walked at two fixed speeds.

Methods

Five patients with left and five with right chronic hemiparesis, characterized by similar level of motor functioning, were enrolled. Ten non-disabled volunteers were recruited as matched control group. Spatio-temporal parameters, and intralimb thigh-leg and leg-foot coordination patterns were used to compare groups while walking on a treadmill at 0.4 and 0.6 m/s. The likelihood of Continuous Relative Phase patterns between healthy and hemiparetic subjects was evaluated by means of the root mean square of the difference and the cross correlation coefficient. The effects of the group (i.e., healthy vs. hemiparetics), side (i.e., affected vs.unaffected), and speed (e.g., slow vs. fast) were analyzed on all metrics using the Analysis of Variance.

Results

Spatio-temporal parameters of all hemiparetic subjects did not significantly differ from those of healthy subjects nor showed any asymmetry between affected and unaffected limbs. Conversely, both thigh-leg and foot-leg coordination patterns appeared to account for pathology related modifications.

Conclusion

Comparisons between hemiparetic and healthy gait should be carried out when all participants are asked to seek the same suitable dynamic equilibrium led by the same external (i.e., the speed) and internal (i.e., severity of the pathology) conditions. In this respect, biomechanical adaptations reflecting the pathology can be better highlighted by coordinative patterns of coupled segments within each limb than by the spatio-temporal parameters. Accordingly, a deep analysis of the intralimb coordination may be helpful for clinicians while designing therapeutic treatments.

Measuring ambulation in adults with central neurologic disorders

This review discusses challenges faced by clinicians and researchers when measuring ambulation in individuals with central neurologic disorders within 3 distinct environments: clinical, laboratory, and community. Even the most robust measure of ambulation is affected by the environment in which it is implemented and by the clinical or research question and the specificity of the hypothesis being investigated. The ability to accurately measure ambulation (one of the most important metrics used to show transition into a community environment) is essential to measure treatment effectiveness and rehabilitation outcomes in populations with central neurologic disorders.

Biomechanics of human bipedal gallop: asymmetry dictates leg function

Unilateral skipping or bipedal galloping is one of the gait types that humans are able to perform. In contrast to many animals, where gallop is the preferred gait at higher speeds, human bipedal gallop only occurs spontaneously in very specific conditions (e.g. fast downhill locomotion). This study examines the lower limb mechanics and explores the possible reasons why humans do not spontaneously opt for gallop for steady-state locomotion on level ground. In 12 subjects, who were required to run and gallop overground at their preferred speed, kinematic and kinetic data were collected and mechanical work at the main lower limb joints (hip, knee, ankle) was calculated. In a separate treadmill experiment, metabolic costs were measured. Analysis revealed that the principal differences between running and galloping are located at the hip. The asymmetrical configuration of gallop involves distinct hip actions and foot placing, giving galloping legs different functions compared with running legs: the trailing leg decelerates the body in the vertical direction but propels it forward while the leading leg acts in the opposite way. Although both legs conserve mechanical energy by interchanging external mechanical energy with potential elastic energy, the specific orientation of the legs causes more energy dissipation and generation compared with running. This makes gallop metabolically more expensive and involves high muscular stress at the hips, which may be why humans do not use gallop for steady-state locomotion.

Gait disorders

This chapter deals with the neuronal mechanisms underlying impaired gait. The aim is, first, a better understanding of the underlying pathophysiology and, second, the selection of an adequate treatment. One of the first symptoms of a lesion within the central motor system perceived by patients is a movement disorder, which is most characteristic during locomotion, e.g. in patients suffering spasticity after stroke or a spinal cord injury or Parkinson disease. By the recording and analysis of electrophysiological and biomechanical signals during a movement, the significance of impaired reflex behavior or muscle tone and its contribution to the movement disorder can reliably be assessed. Adequate treatment should not be restricted to the correction of an isolated clinical sign but should be based on the mechanisms underlying the movement disorder that impairs the patient. Therapy should be directed toward functional training, which takes advantage of the plasticity of the nervous system. In the future a combination of repair and functional training will further improve the mobility of disabled patients.

Increased power generation in impaired lower extremities correlated with changes in walking speeds in sub-acute stroke patients

BACKGROUND

Establishing changes in net joint power in the lower extremity of patients during recovery of walking might direct gait training in early stroke rehabilitation. It is hypothesized that (1) net joint power in the lower extremity joints would increase in sub-acute stroke patients following gait rehabilitation, and (2) the improvements in net joint power would be significantly correlated with changes in walking speed.

METHODS

Thirteen sub-acute patients (<3 months from stroke onset) participated in the study. All patients completed 6 weeks of gait training (3 weeks of robotic gait training and 3 weeks of physiotherapy). The gait patterns were analyzed using 3D motion analysis before and after training. The assessed variables were; gait speed and the net peak joint power of the ankle plantar flexors, hip extensors, hip flexors, hip abductors, and knee extensors.

FINDINGS

Ankle plantar flexor power in the impaired limb and hip extensor power in the unimpaired limb increased significantly following training (133% and 77%, respectively; P<0.002). Improvements (from 20% to 133%) in net joint power of the ankle plantar flexors, hip extensors, hip flexors, and hip abductors of the impaired limb and ankle plantar flexors and hip abductors of the unimpaired limb significantly correlated with the recovery of walking speed following training (0.24 m/s to 0.51 m/s) (r=0.71-0.86).

INTERPRETATION

The findings suggested investigations for strengthening the plantar flexors, hip flexors, hip extensors, and hip abductors concentrically, and knee extensors eccentrically in the impaired limb to determine the effectiveness in improving gait performance.

Quadrupedal coordination of bipedal gait: implications for movement disorders

During recent years, evidence has come up that bipedal locomotion is based on a quadrupedal limb coordination. A task-dependent neuronal coupling of upper and lower limbs allows one to involve the arms during gait but to uncouple this connection during voluntarily guided arm/hand movements. Hence, despite the evolution of a strong cortico-spinal control of hand/arm movements in humans, a quadrupedal limb coordination persists during locomotion. This has consequences for the limb coordination in movement disorders such as in Parkinson's disease (PD) and after stroke. In patients suffering PD, the quadrupedal coordination of gait is basically preserved. The activation of upper limb muscles during locomotion is strong, similar as in age-matched healthy subjects although arm swing is reduced. This suggests a contribution of biomechanical constraints to immobility. In post-stroke subjects a close interactions between unaffected and affected sides with an impaired processing of afferent input takes place. An afferent volley applied to a leg nerve of the unaffected leg leads to a normal reflex activation of proximal arm muscles of both sides. In contrast, when the nerve of the affected leg was stimulated, neither on the affected nor in the unaffected arm muscles EMG responses appear. Muscle activation on the affected arm becomes normalized by influences of the unaffected side during locomotion. These observations have consequences for the rehabilitation of patients suffering movement disorders.

Step length asymmetry is representative of compensatory mechanisms used in post-stroke hemiparetic walking

Post-stroke hemiparetic subjects walk with asymmetrical step lengths that are highly variable between subjects and may be indicative of the underlying impairments and compensatory mechanisms used. The goal of this study was to determine if post-stroke hemiparetic subjects grouped by step length asymmetry have similar abnormal walking biomechanics compared to non-impaired walkers. Kinematic and ground reaction force data were recorded from 55 hemiparetic subjects walking at their self-selected speed and 21 age and speed-matched non-impaired control subjects. Hemiparetic subjects were grouped by paretic step ratio, which was calculated as the paretic step-length divided by the sum of paretic and nonparetic step-lengths, into high (>0.535), symmetric (0.535-0.465) and low (<0.465) groups. Non-parametric Wilcoxin signed-rank tests were used to test for differences in joint kinetic measures between hemiparetic groups and speed-matched control subjects during late single-leg stance and pre-swing. The paretic leg ankle moment impulse was reduced in all hemiparetic subjects regardless of their paretic step ratio. The high group had increased nonparetic leg ankle plantarflexor and knee extensor moment impulses, the symmetric group had increased hip flexor moment impulses on both the paretic and nonparetic leg and the low group had no additional significant differences in joint moment impulses. These results suggest that the direction of asymmetry can be used to identify both the degree of paretic plantarflexor impairment and the compensatory mechanisms used by post-stroke hemiparetic subjects.

Locomotion in stroke subjects: interactions between unaffected and affected sides

The aim of this study was to evaluate the sensorimotor interactions between unaffected and affected sides of post-stroke subjects during locomotion. In healthy subjects, stimulation of the tibial nerve during the mid-stance phase is followed by electromyography responses not only in the ipsilateral tibialis anterior, but also in the proximal arm muscles of both sides, with larger amplitudes prior to swing over an obstacle compared with normal swing. In post-stroke subjects, the electromyography responses were stronger on both sides when the tibial nerve of the unaffected leg was stimulated compared with stimulation of the affected leg. This difference was more pronounced when stimuli were applied prior to swing over an obstacle than prior to normal swing. This indicates an impaired processing of afferent input from the affected leg resulting in attenuated and little task-modulated reflex responses in the arm muscles on both sides. In contrast, an afferent volley from the unaffected leg resulted in larger electromyography responses, even in the muscles of the affected arm. Arm muscle activations were stronger during swing over an obstacle than during normal swing, with no difference in electromyography amplitudes between the unaffected and affected sides. It is concluded that the deficits of the affected arm are compensated for by influences from the unaffected side. These observations indicate strong mutual influences between unaffected and affected sides during locomotion of post-stroke subjects, which might be used to optimize rehabilitation approaches.

Joint kinetic response during unexpectedly reduced plantar flexor torque provided by a robotic ankle exoskeleton during walking

During human walking, plantar flexor activation in late stance helps to generate a stable and economical gait pattern. Because plantar flexor activation is highly mediated by proprioceptive feedback, the nervous system must modulate reflex pathways to meet the mechanical requirements of gait. The purpose of this study was to quantify ankle joint mechanical output of the plantar flexor stretch reflex response during a novel unexpected gait perturbation. We used a robotic ankle exoskeleton to mechanically amplify the ankle torque output resulting from soleus muscle activation. We recorded lower-body kinematics, ground reaction forces, and electromyography during steady-state walking and during randomly perturbed steps when the exoskeleton assistance was unexpectedly turned off. We also measured soleus Hoffmann- (H-) reflexes at late stance during the two conditions. Subjects reacted to the unexpectedly decreased exoskeleton assistance by greatly increasing soleus muscle activity about 60ms after ankle angle deviated from the control condition (p<0.001). There were large differences in ankle kinematic and electromyography patterns for the perturbed and control steps, but the total ankle moment was almost identical for the two conditions (p=0.13). The ratio of soleus H-reflex amplitude to background electromyography was not significantly different between the two conditions (p=0.4). This is the first study to show that the nervous system chooses reflex responses during human walking such that invariant ankle joint moment patterns are maintained during perturbations. Our findings are particularly useful for the development of neuromusculoskeletal computer simulations of human walking that need to adjust reflex gains appropriately for biomechanical analyses.

Enhanced spinal excitation from ankle flexors to knee extensors during walking in stroke patients

OBJECTIVES

It is still unclear to what an extent altered reflex activity contributes to gait deficit following stroke. Spinal group I and group II excitations from ankle dorsiflexors to knee extensors were investigated during post-stroke walking.

METHODS

Electrical stimulation was applied to the common peroneal nerve (CPN) in the early stance, and the short-latency biphasic excitation in Quadriceps motoneurones was evaluated from the Vastus Lateralis (VL) rectified and averaged (N=50) EMG activity in 14 stroke patients walking at 0.6-1.6 km/h, and 14 control subjects walking at 3.2-4.8 and at 1 km/h.

RESULTS

The second peak of the CPN-induced biphasic facilitation in VL EMG activity, which is likely mediated by group II excitatory pathways, was larger on the paretic side of the patients, as compared to their nonparetic side or control subjects, whatever their walking speed.

CONCLUSIONS

The spinal, presumed group II, excitation from ankle dorsiflexors to knee extensors is particularly enhanced during post-stroke walking probably due to plastic adaptations in the descending control.

SIGNIFICANCE

This adaptation may help to stabilize the knee in early stance when the patients have recover ankle dorsiflexor functions.

Effect of ankle-foot orthosis alignment and foot-plate length on the gait of adults with poststroke hemiplegia

OBJECTIVE

To investigate the effect of ankle-foot orthosis (AFO) alignment and foot-plate length on sagittal plane knee kinematics and kinetics during gait in adults with poststroke hemiplegia.

DESIGN

Repeated measures, quasi-experimental study.

SETTING

Motion analysis laboratory.

PARTICIPANTS

Volunteer sample of adults with poststroke hemiplegia (n=16) and able-bodied adults (n=12) of similar age.

INTERVENTIONS

Subjects with hemiplegia were measured walking with standardized footwear in 4 conditions: (1) no AFO (shoes only); (2) articulated AFO with 90 degrees plantar flexion stop and full-length foot-plate-conventionally aligned AFO (CAFO); (3) the same AFO realigned with the tibia vertical in the shoe-heel-height compensated AFO (HHCAFO); and (4) the same AFO (tibia vertical) with 3/4 length foot-plate-3/4 AFO. Gait of able-bodied control subjects was measured on a single occasion to provide a normal reference.

MAIN OUTCOME MEASURES

Sagittal plane ankle and knee kinematics and kinetics.

RESULTS

In adults with hemiplegia, walking speed was unaffected by the different conditions (P=.095). Compared with the no AFO condition, all AFOs decreased plantar flexion at initial contact and mid-swing (P<.001) and changed the peak knee moment in early stance from flexor to extensor (P<.000). Both AFOs with full-length foot-plates significantly increased the peak stance phase plantar flexor moment compared with no AFO and resulted in a peak knee extensor moment in early stance that was significantly greater than control subjects, whereas the AFO with three-quarter length foot-plate resulted in ankle dorsiflexion during stance and swing that was significantly less than control subjects.

CONCLUSIONS

These findings suggest that when an articulated AFO is to be used, a full-length foot-plate in conjunction with a plantar flexion stop may be considered to improve early stance knee moments for people with poststroke hemiplegia.