Symmetry of corticomotor input to plantarflexors influences the propulsive strategy used to increase walking speed 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.

Functional connectivity of proximal and distal lower limb muscles and impact on gait variability in stroke

BACKGROUND

Higher gait variability after stroke increases risk of falls and compromises safe community ambulation. Corticomotor connectivity plays an important role in walking after stroke, however, its relation to gait variability remains unknown.

RESEARCH QUESTION

Do corticomotor characteristics of the proximal and distal lower limb muscles predict gait variability in individuals with chronic stroke?

METHODS

Retrospective analysis of data from 30 individuals with chronic stroke was conducted. Corticomotor characteristics were measured in the paretic and non-paretic tibialis anterior (TA, distal muscle) and rectus femoris (RF, proximal muscle) using transcranial magnetic stimulation. We calculated corticomotor excitability ratio of paretic TA and RF (CME_TA/RF), corticomotor excitability symmetry (CME_sym) between hemispheres for the TA and RF, and ipsilateral corticomotor excitability (ICE) of the paretic TA. Gait variability was quantified as the coefficient of variation of the paretic step length (spatial) and step time (temporal) during comfortable walking. Relations between corticomotor characteristics and gait variability were tested with multiple linear regression.

RESULTS

CME_TA/RF and CME_sym of RF were significant predictors of spatial gait variability. Greater corticomotor input to the paretic RF compared to the paretic TA and greater symmetry of RF were related to higher spatial gait variability. There were no significant predictors of temporal gait variability.

SIGNIFICANCE

Corticomotor inputs to the proximal RF may be important for spatial gait variability, reflecting a compensatory role of RF in walking after stroke. Stroke survivors with relatively greater corticomotor input to the paretic RF may adopt compensatory strategy to enhance propulsion and achieve foot clearance, but it may also increase spatial gait variability, particularly when combined with impaired motor control of the paretic TA. These findings may provide novel rehabilitative targets to decrease gait variability and promote safe ambulation in individuals with stroke.

Motor Cortical Network Flexibility is Associated With Biomechanical Walking Impairment in Chronic Stroke

Background: The inability to flexibly modulate motor behavior with changes in task demand or environmental context is a pervasive feature of motor impairment and dysfunctional mobility after stroke. Objective: The purpose of this study was to test the reactive and modulatory capacity of lower-limb primary motor cortical (M1) networks using electroencephalography (EEG) measures of cortical activity evoked by transcranial magnetic stimulation (TMS) and to evaluate their associations with clinical and biomechanical measures of walking function in chronic stroke. Methods: TMS assessments of motor cortex excitability were performed during rest and active ipsilateral plantarflexion in chronic stroke and age-matched controls. TMS-evoked motor cortical network interactions were quantified with simultaneous EEG as the post-TMS (0-300 ms) beta (15-30 Hz) coherence between electrodes overlying M1 bilaterally. We compared TMS-evoked coherence between groups during rest and active conditions and tested associations with poststroke motor impairment, paretic propulsive gait deficits, and the presence of paretic leg motor evoked potentials (MEPs). Results: Stroke (n = 14, 66 ± 9 years, F = 4) showed lower TMS-evoked cortical coherence and activity-dependent modulation compared to controls (n = 9, 68 ± 6 years, F = 3). Blunted reactivity and atypical modulation of TMS-evoked coherence were associated with lower paretic ankle moments for propulsive force generation during walking and absent paretic MEPs. Conclusions: Impaired flexibility of motor cortical networks to react to TMS and modulate during motor activity is distinctly associated with paretic limb biomechanical walking impairment, and may provide useful insight into the neuromechanistic underpinnings of chronic post-stroke mobility deficits.

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.

The Dynamic Motor Control Index as a Marker of Age-Related Neuromuscular Impairment

Biomarkers that can identify age-related decline in walking function have potential to promote healthier aging by triggering timely interventions that can mitigate or reverse impairments. Recent evidence suggests that changes in neuromuscular control precede changes in walking function; however, it is unclear which measures are best suited for identifying age-related changes. In this study, non-negative matrix factorization of electromyography data collected during treadmill walking was used to calculate two measures of the complexity of muscle co-activations during walking for 36 adults: (1) the number of muscle synergies and (2) the dynamic motor control index. Study participants were grouped into young (18–35 years old), young-old (65–74 years old), and old–old (75+ years old) subsets. We found that the dynamic motor control index [χ²(2) = 9.41, p = 0.009], and not the number of muscle synergies [χ²(2) = 5.42, p = 0.067], differentiates between age groups [χ²(4) = 10.62, p = 0.031, Nagelkerke R² = 0.297]. Moreover, an impairment threshold set at a dynamic motor control index of 90 (i.e., one standard deviation below the young adults) was able to differentiate between age groups [χ²(2) = 9.351, p = 0.009]. The dynamic motor control index identifies age-related differences in neuromuscular complexity not measured by the number of muscle synergies and may have clinical utility as a marker of neuromotor impairment.

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.

Differential corticomotor mechanisms of ankle motor control in post stroke individuals with and without motor evoked potentials

OBJECTIVE

Deficits in ankle motor control has been identified as a significant contributor to impaired walking after stroke. Corticomotor excitability has been related to impaired upper limb motor control and poor recovery in stroke, however contributions to lower limb function are still unclear. This study used transcranial magnetic stimulation (TMS) to determine the influence of corticomotor characteristics on lower limb motor control in chronic stroke survivors.

METHODS

This retrospective study assessed 28 individuals with post stroke hemiparesis. Motor evoked potentials (MEP) measured from the paretic and non-paretic tibialis anterior (TA) muscles were used to calculate corticomotor excitability symmetry (CME_sym) and relative ipsilateral corticomotor excitability (ICE). Participants were assigned to MEP+ and MEP- groups depending on the presence (+) or absence (-) of MEPs. Ankle motor control was quantified by the ability of participants to track a sinusoidal target using dorsiflexion-plantarflexion movements of the paretic ankle and tracking error was calculated using root mean square error (RMSE).

RESULTS

Multiple linear regression model for all participants revealed only CME_sym and FMLE (p < 0.01) to significantly predict RMSE. In the MEP+ group, CME_sym significantly predicted RMSE (p = 0.03) while FMLE (p = 0.02) was a significant predictor for the MEP-.

CONCLUSION

Our results indicate that CME_sym between the ipsilesional and contralesional hemispheres does not necessarily translate to better paretic ankle motor control in chronic stroke. Presence or absence of a MEP in the TA muscle did not affect the ankle tracking performance, however, it was noted that different strategies maybe used by those with and without a MEP.

The usefulness of isometric protocol for foot flexors and extensors in assessing the effects of 16-week rehabilitation regiment in poststroke patients

BACKGROUND

Ankle joint function in a paretic limb has a fundamental impact on mobility. Return of joint function is a measure of early poststroke physical rehabilitation. This study aims to assess the suitability of using the isometric protocol for objective evaluation of flexor and extensor muscle strength in the paretic limb of poststroke patients.

METHODS

34 patients (F: 9, M: 25) aged 51-79 years with hemiparesis following an acute ischemic stroke and 34 healthy controls were examined using the isometric protocol measured on the Biodex System^®. The following parameters were analyzed: peak torque [PT], average torque [AVGT], average torque/body weight [AVGT/BW] for flexors and extensors, and AVGT flexor/AVGT extensor [agonist/antagonist ratio] of the paretic foot, the nonparetic foot and foot of healthy controls using three foot-shank positions (15°, 0°, and - 15°) prior to rehabilitation commencement and at its completion 16 weeks later.

RESULTS

Prior to rehabilitation commencement, nonparetic foot differed significantly (p < 0.05) from healthy foot controls in all parameters and all positions for flexors and in all positions for foot-shank positions of 0° and - 15° for extensors. At rehabilitation program completion the following parameters increased significantly for the paretic foot: PT, AVGT, and AVGT/BW for foot extensors in all tested positions, and PT for foot flexors in foot-shank position of - 15°. The nonparetic foot however, showed no significant difference following rehabilitation regardless parameter or foot position tested for flexors and extensors alike. Prior to rehabilitation agonist/antagonist ratio in the paretic foot differed significantly from corresponding parameter in the control group for the foot-shank positions of 15° and 0°, whereas at rehabilitation completion, the two groups showed significant difference only in foot-shank position of 0°.

CONCLUSIONS

In the early period following stroke, there is a significant strengthening of the paretic limb, but no improvement in the strength of nonparetic limb.

Contribution of corticospinal drive to ankle plantar flexor muscle activation during gait in adults with cerebral palsy

Impaired plantar flexor muscle activation during push-off in late stance contributes importantly to reduced gait ability in adults with cerebral palsy (CP). Here we used low-intensity transcranial magnetic stimulation (TMS) to suppress soleus EMG activity during push-off as an estimate of corticospinal drive in CP adults and neurologically intact (NI) adults. Ten CP adults (age 34 years, SD 14.6, GMFCS I-II) and ten NI adults (age 33 years, SD 9.8) walked on a treadmill at their preferred walking speed. TMS of the leg motor cortex was elicited just prior to push-off during gait at intensities below threshold for motor-evoked potentials. Soleus EMG from steps with and without TMS were averaged and compared. Control experiments were performed while standing and in NI adults during gait at slow speed. TMS induced a suppression at a latency of about 40 ms. This suppression was similar in the two populations when differences in control EMG and gait speed were taken into account (CP 18%, NI 16%). The threshold of the suppression was higher in CP adults. The findings suggest that corticospinal drive to ankle plantar flexors at push-off is comparable in CP and NI adults. The higher threshold of the suppression in CP adults may reflect downregulation of cortical inhibition to facilitate corticospinal drive. Interventions aiming to facilitate excitability in cortical networks may contribute to maintain or even improve efficient gait in CP adults.

Bilateral Assessment of the Corticospinal Pathways of the Ankle Muscles Using Navigated Transcranial Magnetic Stimulation

Distal leg muscles receive neural input from motor cortical areas via the corticospinal tract, which is one of the main motor descending pathway in humans and can be assessed using transcranial magnetic stimulation (TMS). Given the role of distal leg muscles in upright postural and dynamic tasks, such as walking, a growing research interest in the assessment and modulation of the corticospinal tracts relative to the function of these muscles has emerged in the last decade. However, methodological parameters used in previous work have varied across studies making the interpretation of results from cross-sectional and longitudinal studies less robust. Therefore, use of a standardized TMS protocol specific to the assessment of leg muscles' corticomotor response (CMR) will allow for direct comparison of results across studies and cohorts. The objective of this paper is to present a protocol that provides the flexibility to simultaneously assess the bilateral CMR of two main ankle antagonistic muscles, the tibialis anterior and soleus, using single pulse TMS with a neuronavigation system. The present protocol is applicable while the examined muscle is either fully relaxed or isometrically contracted at a defined percentage of maximum isometric voluntary contraction. Using each subject's structural MRI with the neuronavigation system ensures accurate and precise positioning of the coil over the leg cortical representations during assessment. Given the inconsistency in CMR derived measures, this protocol also describes a standardized calculation of these measures using automated algorithms. Though this protocol is not conducted during upright postural or dynamic tasks, it can be used to assess bilaterally any pair of leg muscles, either antagonistic or synergistic, in both neurologically intact and impaired subjects.

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.

The use of transcranial magnetic stimulation to evaluate cortical excitability of lower limb musculature: Challenges and opportunities

Neuroplasticity is a fundamental yet relatively unexplored process that can impact rehabilitation of lower extremity (LE) movements. Transcranial magnetic stimulation (TMS) has gained widespread application as a non-invasive brain stimulation technique for evaluating neuroplasticity of the corticospinal pathway. However, a majority of TMS studies have been performed on hand muscles, with a paucity of TMS investigations focused on LE muscles. This perspective review paper proposes that there are unique methodological challenges associated with using TMS to evaluate corticospinal excitability of lower limb muscles. The challenges include: (1) the deeper location of the LE motor homunculus; (2) difficulty with targeting individual LE muscles during TMS; and (3) differences in corticospinal circuity controlling upper and lower limb muscles. We encourage future investigations that modify traditional methodological approaches to help address these challenges. Systematic TMS investigations are needed to determine the extent of overlap in corticomotor maps for different LE muscles. A simple, yet informative methodological solution involves simultaneous recordings from multiple LE muscles, which will provide the added benefit of observing how other relevant muscles co-vary in their responses during targeted TMS assessment directed toward a specific muscle. Furthermore, conventionally used TMS methods (e.g., determination of hot spot location and motor threshold) may need to be modified for TMS studies involving LE muscles. Additional investigations are necessary to determine the influence of testing posture as well as activation state of adjacent and distant LE muscles on TMS-elicited responses. An understanding of these challenges and solutions specific to LE TMS will improve the ability of neurorehabilitation clinicians to interpret TMS literature, and forge novel future directions for neuroscience research focused on elucidating neuroplasticity processes underlying locomotion and gait training.

Control of lateral weight transfer is associated with walking speed in individuals post-stroke

Restoring functional gait speed is an important goal for rehabilitation post-stroke. During walking, transferring of one's body weight between the limbs and maintaining balance stability are necessary for independent functional gait. Although it is documented that individuals post-stroke commonly have difficulties with performing weight transfer onto their paretic limbs, it remains to be determined if these deficits contributed to slower walking speeds. The primary purpose of this study was to compare the weight transfer characteristics between slow and fast post-stroke ambulators. Participants (N=36) with chronic post-stroke hemiparesis walked at their comfortable and maximal walking speeds on a treadmill. Participants were stratified into 2 groups based on their comfortable walking speeds (≥0.8m/s or <0.8m/s). Minimum body center of mass (COM) to center of pressure (COP) distance, weight transfer timing, step width, lateral foot placement relative to the COM, hip moment, peak vertical and anterior ground reaction forces, and changes in walking speed were analyzed. Results showed that slow walkers walked with a delayed and deficient weight transfer to the paretic limb, lower hip abductor moment, and more lateral paretic limb foot placement relative to the COM compared to fast walkers. In addition, propulsive force and walking speed capacity was related to lateral weight transfer ability. These findings demonstrated that deficits in lateral weight transfer and stability could potentially be one of the limiting factors underlying comfortable walking speeds and a determinant of chronic stroke survivors' ability to increase walking speed.

Single Session of Functional Electrical Stimulation-Assisted Walking Produces Corticomotor Symmetry Changes Related to Changes in Poststroke Walking Mechanics

BACKGROUND

Recent research demonstrated that the symmetry of corticomotor drive with the paretic and nonparetic plantarflexor muscles was related to the biomechanical ankle moment strategy that people with chronic stroke used to achieve their greatest walking speeds. Rehabilitation strategies that promote corticomotor balance might improve poststroke walking mechanics and enhance functional ambulation.

OBJECTIVE

The study objectives were to test the effectiveness of a single session of gait training using functional electrical stimulation (FES) to improve plantarflexor corticomotor symmetry and plantarflexion ankle moment symmetry and to determine whether changes in corticomotor symmetry were related to changes in ankle moment symmetry within the session.

DESIGN

This was a repeated-measures crossover study.

METHODS

On separate days, 20 people with chronic stroke completed a session of treadmill walking either with or without the use of FES of their ankle dorsi- and plantarflexor muscles. We calculated plantarflexor corticomotor symmetry using transcranial magnetic stimulation and plantarflexion ankle moment symmetry during walking between the paretic and the nonparetic limbs before and after each session. We compared changes and tested relationships between corticomotor symmetry and ankle moment symmetry following each session.

RESULTS

Following the session with FES, there was an increase in plantarflexor corticomotor symmetry that was related to the observed increase in ankle moment symmetry. In contrast, following the session without FES, there were no changes in corticomotor symmetry or ankle moment symmetry.

LIMITATIONS

No stratification was made on the basis of lesion size, location, or clinical severity.

CONCLUSIONS

These findings demonstrate, for the first time (to our knowledge), the ability of a single session of gait training with FES to induce positive corticomotor plasticity in people in the chronic stage of stroke recovery. They also provide insight into the neurophysiologic mechanisms underlying improvements in biomechanical walking function.

Characterizing differential poststroke corticomotor drive to the dorsi- and plantarflexor muscles during resting and volitional muscle activation

Imbalance of corticomotor excitability between the paretic and nonparetic limbs has been associated with the extent of upper extremity motor recovery poststroke, is greatly influenced by specific testing conditions such as the presence or absence of volitional muscle activation, and may vary across muscle groups. However, despite its clinical importance, poststroke corticomotor drive to lower extremity muscles has not been thoroughly investigated. Additionally, whereas conventional gait rehabilitation strategies for stroke survivors focus on paretic limb foot drop and dorsiflexion impairments, most contemporary literature has indicated that paretic limb propulsion and plantarflexion impairments are the most significant limiters to poststroke walking function. The purpose of this study was to compare corticomotor excitability of the dorsi- and plantarflexor muscles during resting and active conditions in individuals with good and poor poststroke walking recovery and in neurologically intact controls. We found that plantarflexor muscles showed reduced corticomotor symmetry between paretic and nonparetic limbs compared with dorsiflexor muscles in individuals with poor poststroke walking recovery during active muscle contraction but not during rest. Reduced plantarflexor corticomotor symmetry during active muscle contraction was a result of reduced corticomotor drive to the paretic muscles and enhanced corticomotor drive to the nonparetic muscles compared with the neurologically intact controls. These results demonstrate that atypical corticomotor drive exists in both the paretic and nonparetic lower limbs and implicate greater severity of corticomotor impairments to plantarflexor vs. dorsiflexor muscles during muscle activation in stroke survivors with poor walking recovery.NEW & NOTEWORTHY The present study observed that lower-limb corticomotor asymmetry resulted from both reduced paretic and enhanced nonparetic limb corticomotor excitability compared with neurologically intact controls. The most asymmetrical corticomotor drive was observed in the plantarflexor muscles of individuals with poor poststroke walking recovery. This suggests that neural function of dorsi- and plantarflexor muscles in both paretic and nonparetic limbs may play a role in poststroke walking function, which may have important implications when developing targeted poststroke rehabilitation programs to improve walking ability.

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.