Motor adaptation and immediate retention to overground gait-slip perturbation training in people with chronic stroke: an experimental trial with a comparison group.

Background: Perturbation-based training has shown to be effective in reducing fall-risk in people with chronic stroke (PwCS). However, most evidence comes from treadmill-based stance studies, with a lack of research focusing on training overground perturbed walking and exploring the relative contributions of the paretic and non-paretic limbs. This study thus examined whether PwCS could acquire motor adaptation and demonstrate immediate retention of fall-resisting skills following bilateral overground gait-slip perturbation training. Methods: 65 PwCS were randomly assigned to either (i) a training group, that received blocks of eight non-paretic (NP-S1 to NP-S8) and paretic (P-S1 to P-S8) overground slips during walking followed by a mixed block (seven non-paretic and paretic slips each interspersed with unperturbed walking trials) (NP-S9/P-S9 to NP-S15/P-S15) or (ii) a control group, that received a single non-paretic and paretic slip in random order. The assessor and training personnel were not blinded. Immediate retention was tested for the training group after a 30-minute rest break. Primary outcomes included laboratory-induced slip outcomes (falls and balance loss) and center of mass (CoM) state stability. Secondary outcomes to understand kinematic contributors to stability included recovery strategies, limb kinematics, slipping kinematics, and recovery stride length. Results: PwCS within the training group showed reduced falls (p < 0.01) and improved post-slip stability (p < 0.01) from the first trial to the last trial of both paretic and non-paretic slip blocks (S1 vs. S8). During the mixed block training, there was no further improvement in stability and slipping kinematics (S9 vs. S15) (p > 0.01). On comparing the first and last training trial (S1 vs. S15), post-slip stability improved on both non-paretic and paretic slips, however, pre-slip stability improved only on the non-paretic slip (p < 0.01). On the retention trials, the training group had fewer falls and greater post-slip stability than the control group on both non-paretic and paretic slips (p < 0.01). Post-slip stability on the paretic slip was lower than that on the non-paretic slip for both groups on retention trials (p < 0.01). Conclusion: PwCS can reduce laboratory-induced slip falls and backward balance loss outcomes by adapting their post-slip CoM state stability after bilateral overground gait-slip perturbation training. Such reactive adaptations were better acquired and retained post-training in PwCS especially on the non-paretic slips than paretic slips, suggesting a need for higher dosage for paretic slips. Clinical registry number: NCT03205527.

Control of center of mass motion during walking correlates with gait and balance in people with incomplete spinal cord injury.

Background: There is evidence that ambulatory people with incomplete spinal cord injury (iSCI) have an impaired ability to control lateral motion of their whole-body center of mass (COM) during walking. This impairment is believed to contribute to functional deficits in gait and balance, however that relationship is unclear. Thus, this cross-sectional study examines the relationship between the ability to control lateral COM motion during walking and functional measures of gait and balance in people with iSCI. Methods: We assessed the ability to control lateral COM motion during walking and conducted clinical gait and balance outcome measures on 20 ambulatory adults with chronic iSCI (C1-T10 injury, American Spinal Injury Association Impairment Scale C or D). To assess their ability to control lateral COM motion, participants performed three treadmill walking trials. During each trial, real-time lateral COM position and a target lane were projected on the treadmill. Participants were instructed to keep their lateral COM position within the lane. If successful, an automated control algorithm progressively reduced the lane width, making the task more challenging. If unsuccessful, the lane width increased. The adaptive lane width was designed to challenge each participant's maximum capacity to control lateral COM motion during walking. To quantify control of lateral COM motion, we calculated lateral COM excursion during each gait cycle and then identified the minimum lateral COM excursion occurring during five consecutive gait cycles. Our clinical outcome measures were Berg Balance Scale (BBS), Timed Up and Go test (TUG), 10-Meter Walk Test (10MWT) and Functional Gait Assessment (FGA). We used a Spearman correlation analysis (ρ) to examine the relationship between minimum lateral COM excursion and clinical measures. Results: Minimum lateral COM excursion had significant moderate correlations with BBS (ρ = -0.54, p = 0.014), TUG (ρ = 0.59, p = 0.007), FGA (ρ = -0.59, p = 0.007), 10MWT-preferred (ρ = -0.59, p = 0.006) and 10MWT-fast (ρ = -0.68, p = 0.001). Conclusion: Control of lateral COM motion during walking is associated with a wide range of clinical gait and balance measures in people with iSCI. This finding suggests the ability to control lateral COM motion during walking could be a contributing factor to gait and balance in people with iSCI.

Age-related differences in reactive balance control and fall-risk in people with chronic stroke.

BACKGROUND: Impaired reactive responses to sudden environmental perturbations contribute to heightened fall-risk in healthy aging and neurologically impaired populations. Previous studies have demonstrated individual contributions of paretic and non-paretic sides to fall-risk in people with stroke with variable levels of motor impairment. However, the combined effect of aging and unilateral cortical lesion on reactive balance control is not clearly understood. We therefore aimed to examine age-related differences in reactive balance control and fall-risk during laboratory-induced gait-slips in people with comparable stroke-related motor impairments. METHODS: Thirteen younger (45.61 ± 4.61 years) and thirteen older (71.92 ± 6.50 years) adults with similar stroke-related impairment (on Fugl-Meyer Lower Extremity Assessment) were exposed to one overground gait-slip under each limb (paretic and non-paretic). Center of mass state stability and slipping kinematics (slip displacement and velocity) were computed. Clinical balance and mobility were also assessed. RESULTS: On non-paretic slips, older adults with chronic stroke demonstrated greater falls and lower center of mass stability (its position and velocity) at post-slip touchdown compared to younger adults with chronic stroke (p < 0.01). This was accompanied with a greater peak slip displacement and faster peak slip velocity (p < 0.01). However, there were no such group differences noted on the paretic slips (p > 0.01). CONCLUSION: Aging may have an independent, detrimental effect on reactive balance control in people with chronic stroke. Non-paretic deficits in controlling slip intensities (slip displacement and velocity) can accentuate fall-risk in older adults with chronic stroke. Further investigation is necessary to identify additional factors attributing to heightened fall-risk in older adults with chronic stroke.

Can prior exposure to repeated non-paretic slips improve reactive responses on novel paretic slips among people with chronic stroke?

This study examined if people with chronic stroke (PwCS) could adapt following non-paretic overground gait-slips and whether such prior exposure to non-paretic slips could improve reactive responses on novel paretic slip. Forty-nine PwCS were randomly assigned to either adaptation group, which received eight unexpected, overground, nonparetic-side gait-slips followed by two paretic-side slips or a control group, which received two paretic-side slips. Slip outcome, recovery strategies, center of mass (CoM) state stability, post-slip stride length and slipping kinematics were analyzed. The adaptation group demonstrated fall-reduction from first to eighth non-paretic slips, along with improved stability, stride length and slipping kinematics (p < 0.05). Within the adaptation group, on comparing novel slips, paretic-side demonstrated comparable pre-slip stability (p > 0.05); however, lower post-slip stability, increased slip velocity and falls was noted (p < 0.05). There was no difference in any variables between the novel paretic slips of adaptation and control group (p > 0.01). However, there was a rapid improvement on the 2nd slip such that adaptation group demonstrated improved performance from the first to second paretic slip compared to that in the control group (p < 0.01). PwCS demonstrated immediate proactive and reactive adaptation with overground, nonparetic-side gait-slips. However, PwCS did not demonstrate any inter-limb performance gain on the paretic-side after prior nonparetic-side adaptation when exposed to a novel paretic-side slip; but they did show significant positive gains with single slip priming on the paretic-side compared to controls without prior adaptation.Clinical registry number: NCT03205527.

Effect of robotic-assisted ankle training on gait in stroke participants: A case series study.

BACKGROUND: Robotic rehabilitation therapy has grown rapidly during the last two decades allowing researchers and clinicians to deliver high-intensity training to persons with sensorimotor disorders caused by neurological injuries and diseases. METHODS: This case series reports the effect of robot-assisted, impairment-oriented training for persons recovering from stroke on impairment of the paretic ankle as well as on the kinematic and spatiotemporal parameters of gait. Five persons with chronic stroke (>6 months post-stroke) participated in a 10-week training protocol, receiving three, 30-min sessions per week of a robot-assisted therapy. The robot-assisted intervention cyclically induced dorsiflexion and plantarflexion to the ankle at 5 degrees/s through ±15 degrees while the participants assisted with the imposed movement. Concurrently, participants received visual feedback of their active, assistive torque as well as targeted mechanical vibration of the ankle tendons when lengthened by the applied motion. Walking speed, cadence, step length of the non-paretic leg, percentage of paretic single limb support during the gait cycle, and ankle strength were assessed just before training began (baseline), after the last training session (post-training), and 3 months post-training (follow-up). DISCUSSION: Robot-assisted training that provided assisted movement, biofeedback, and proprioceptive stimulation reduced ankle impairment and improved kinematic and spatiotemporal gait parameters, suggesting that impairment-oriented therapy applied to the paretic ankle may provide a valuable adjunct to locomotor therapies in persons with chronic gait disorders due to stroke.

Effect of Multisession Progressive Gait-Slip Training on Fall-Resisting Skills of People with Chronic Stroke: Examining Motor Adaptation in Reactive Stability.

BACKGROUND: This study examined whether a multisession gait-slip training could enhance reactive balance control and fall-resisting skills of people with chronic stroke (PwCS). METHODS: A total of 11 PwCS underwent a four-week treadmill-based gait-slip training (four sessions). Pre- and post-training assessment was performed on six intensities of gait-slips (levels 1-6). Training consisted of 10 blocks of each progressively increasing intensity (four trials per block) until participants fell at >2 trials per block (fall threshold). In the next session, training began at a sub-fall threshold and progressed further. Fall outcome and threshold, number of compensatory steps, multiple stepping threshold, progression to higher intensities, pre- and post-slip center of mass (CoM), state stability, clinical measures, and treadmill walking speed were analyzed. RESULTS: Post-training, PwCS demonstrated a reduction in falls and compensatory steps on levels 5 and 6 (p < 0.05) compared to pre-training. While an increase in pre-slip stability was limited to level 6 (p < 0.05), improvement in post-slip stability at lift-off was noted on levels 2, 3, and 5 (p < 0.05) along with improved post-slip minimum stability on levels 5 and 6 (p < 0.05). Post-training demonstrated improved fall (p < 0.05) and multiple stepping thresholds (p = 0.05). While most participants could progress to level 4 between the first and last training sessions, more participants progressed to level 6 (p < 0.05). Participants' treadmill walking speed increased (p < 0.05); however, clinical measures remained unchanged (p > 0.05). CONCLUSIONS: Multisession, progressively increasing intensity of treadmill-based gait-slip training appears to induce significant adaptive improvement in falls, compensatory stepping, and postural stability among PwCS.

Does stroke-induced sensorimotor impairment and perturbation intensity affect gait-slip outcomes?

People with chronic stroke (PwCS) demonstrate similar gait-slip fall-risk on both paretic and non-paretic side. Compensatory stepping and slipping limb control are crucial to reduce gait-slip fall-risk. Given the unpredictable intensities of real-life perturbations, this study aimed to determine whether recovery from paretic or non-paretic slips vary as a function of perturbation intensity among PwCS. Forty-four PwCS were assigned to non-paretic low intensity slip, non-paretic high intensity slip, paretic low intensity slip, or paretic high intensity slip group. Participants were subjected to a novel overground gait-slip with a distance of 24 cm (low) or 45 cm (high), under either limb. Recovery strategies, center of mass (CoM) state stability and slipping kinematics were analyzed. Both non-paretic high and low intensity groups demonstrated similar percentage of aborted and recovery stepping, however, paretic high intensity group demonstrated greater aborted stepping (p > 0.05). Both high and low intensity paretic slip groups demonstrated reduced post-slip CoM stability relative to the non-paretic slip groups (p < 0.05). Slip displacement was greater in paretic high group compared with non-paretic high group (p < 0.05). Greater slip displacement at higher intensity was noted only in paretic slip group (p < 0.05). The slip velocity was faster in paretic groups compared to non-paretic slip groups (p < 0.05). Paretic slips showed lower stability at both intensities associated with difficulty in modulating slipping kinematics and resorting to an increased aborted stepping strategy compared to non-paretic slip. These findings are suggestive of developing balance interventions for improving both compensatory non-paretic limb stepping and reactive control of slipping paretic limb for fall-risk reduction.

Slip-Fall Predictors in Community-Dwelling, Ambulatory Stroke Survivors: A Cross-sectional Study.

BACKGROUND AND PURPOSE: Considering the multifactorial nature and the often-grave consequences of falls in people with chronic stroke (PwCS), determining measurements that best predict fall risk is essential for identifying those who are at high risk. We aimed to determine measures from the domains of the International Classification of Functioning, Disability and Health (ICF) that can predict laboratory-induced slip-related fall risk among PwCS. METHODS: Fifty-six PwCS participated in the experiment in which they were subjected to an unannounced slip of the paretic leg while walking on an overground walkway. Prior to the slip, they were given a battery of tests to assess fall risk factors. Balance was assessed using performance-based tests and instrumented measures. Other fall risk factors assessed were severity of sensorimotor impairment, muscle strength, physical activity level, and psychosocial factors. Logistic regression analysis was performed for all variables. The accuracy of each measure was examined based on its sensitivity and specificity for fall risk prediction. RESULTS: Of the 56 participants, 24 (43%) fell upon slipping while 32 (57%) recovered their balance. The multivariate logistic regression analysis model identified dynamic gait stability, hip extensor strength, and the Timed Up and Go (TUG) score as significant laboratory-induced slip-fall predictors with a combined sensitivity of 75%, a specificity of 79.2%, and an overall accuracy of 77.3%. DISCUSSION AND CONCLUSIONS: The results indicate that fall risk measures within the ICF domains-body, structure, and function (dynamic gait stability and hip extensor strength) and activity limitation (TUG)-could provide a sensitive laboratory-induced slip-fall prediction model in PwCS.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A323).

Mixed slip-trip perturbation training for improving reactive responses in people with chronic stroke.

This study determined the effect of mixed (slip- and trip-like stance perturbation) training on reactive responses in people with chronic stroke (PwCS) and examined modulation of their reactive responses on higher intensity perturbations posttraining (scaling). Twelve PwCS were exposed to consecutive blocks of treadmill-based slip-like and trip-like perturbations and mixed-stance perturbations. A higher intensity trial was provided postblock and postmixed training. Postural stability [center-of-mass position (CoMP) and velocity (CoMV)], compensatory step length, step count, and trunk angle were examined. PwCS demonstrated an anterior positioning of the CoM, increased step length, and reduced compensatory step count with slip-like block training (P < 0.05). Trip-like block training resulted in reductions in step count, step length, and trunk angle (P < 0.05); however, CoMP remained unchanged (P > 0.05). With mixed training, there was a decrease rather than an increase in step length for slip-like perturbations but a continued decrease in step length and trunk angle was seen on trip-like perturbations (P < 0.05); however, CoMP and step count remained unchanged for both. For both perturbations, the higher intensity trials demonstrated no change from the last block trial. Postmixed block, the higher intensity trial demonstrated an increase only in step count on trip-like perturbation. Between postblock and postmixed higher intensity trials, an increase in step count and decrease in step length was noted only for slip-like perturbations. Block training with slip- and trip-like stance perturbations can enhance reactive responses among PwCS. Although mixed perturbation training continued to improve trip-induced adaptation, prior slip-induced adaptive changes were not maintained and further slip-adaptation was not seen. PwCS demonstrated partial scaling of reactive responses postblock and postmixed training.NEW & NOTEWORTHY Block perturbation training led to development of favorable reactive responses to counteract treadmill-based, slip-like and trip-like stance perturbations among people with chronic stroke. During mixed block, previously acquired adaptive changes in reactive responses from slip-block training were not maintained, probably due to interference offered by trip block. Instead, on trip-like perturbations, trip block-induced adaptation was maintained and continued to show further improvement. Our findings might provide future direction for designing effective mixed perturbation training paradigms to counteract both opposing perturbation types.

Slip-induced fall-risk assessment based on regular gait pattern in older adults.

Aging-associated fall-risk assessment is crucial for fall prevention. Thus, this study aimed to develop a prognostic model to predict fall-risk following an unexpected over-ground slip perturbation based on normal gait pattern in healthy older adults. 112 healthy older adults who experienced a novel slip in a safe laboratory environment were included. Their slip trial and natural walking trial immediately prior to it were analyzed. To identify the best fall-risk predictive model, gait related variables including step length, segment angles, center of mass state, and ground reaction force (GRF) were determined and inputted into a stepwise logistic regression. The optimal slip-induced fall prediction model was based on the right thigh angle at slipping foot touchdown (TD), the maximum GRF of the slipping limb after TD, and the momentum change from TD to recovery foot liftoff (LO), with an overall prediction accuracy of 75.9%, predicting 74.5% of falls (sensitivity) and 77.2% of recoveries (specificity). Conversely, a model based on clinical and demographic measures predicted 78.2% of falls and 47.4% of recoveries, resulting in a much lower overall accuracy of 62.5%. The fall-risk model based on normal gait pattern which was developed for slip-induced perturbations in healthy older adults was able to provide a high predictive accuracy. This information could provide insight about the ideal normal gait measures which could be used to contribute towards development of therapeutic strategies related to dynamic balance and fall prevention to enhance preventive interventions in populations with high-risk for slip-induced falls.

Transfer of reactive balance adaptation from stance-slip perturbation to stance-trip perturbation in chronic stroke survivors.

BACKGROUND: Chronic stroke survivors demonstrate the potential to acquire reactive adaptations to external perturbations. However, such adaptations in postural stability and compensatory stepping responses are perturbation-type specific and the ability to generalize such adaptation to an opposing perturbation has not been studied. OBJECTIVE: The study aimed to examine whether improved reactive balance control acquired through prior slip-perturbation training would positively transfer to, or interfere with, the reactive response to an unexpected novel trip. METHODS: Twenty-six chronic stroke survivors were assigned to either the training group (TR) who received treadmill-induced slips (12 m/s2) while standing followed by a novel trip (16.8 m/s2) or the control group (TC) who experienced a single unannounced trip. The primary outcome measure was postural stability (examined by relative center of mass position (RCoMP) and velocity (RCoMV)) with step length and trunk angle being secondary measures. Perturbation outcome (fall vs recovery) and number of compensatory steps were also recorded. RESULTS: The TR group showed an anterior shift in RCoMP via longer compensatory backward step and reduced number of steps from first to last slip-perturbation (p < 0.05). Post-slip adaptation, the TR group exhibited a more posterior RCoMP on the novel trip along with a longer forward step and decreased trunk flexion compared to the TC group (p < 0.05). CONCLUSIONS: Chronic stroke survivors demonstrated improved direction-specific compensatory stepping response on a novel trip-perturbation following reactive adaptation to large-magnitude, stance-slip perturbation training.The present study investigates the ability of chronic stroke survivors to generalize motor adaptation from stance-slip perturbation training to a novel, diametrically opposing trip-perturbation. We report that people with chronic hemi-paretic stroke could execute the acquired adaptation in reactive postural stability to improve reactive stepping responses to a novel stance-trip perturbation via generation of a direction-specific effective compensatory stepping response, such that the training group demonstrated a longer forward compensatory step and better control of postural stability than the control group.

Does severity of motor impairment affect reactive adaptation and fall-risk in chronic stroke survivors?

BACKGROUND: A single-session of slip-perturbation training has shown to induce long-term fall risk reduction in older adults. Considering the spectrum of motor impairments and deficits in reactive balance after a cortical stroke, we aimed to determine if chronic stroke survivors could acquire and retain reactive adaptations to large slip-like perturbations and if these adaptations were dependent on severity of motor impairment. METHODS: Twenty-six chronic stroke participants were categorized into high and low-functioning groups based on their Chedoke-McMaster-Assessment scores. All participants received a pre-training, slip-like stance perturbation at level-III (highest intensity/acceleration) followed by 11 perturbations at a lower intensity (level-II). If in early phase, participants experienced > 3/5 falls, they were trained at a still lower intensity (level-I). Post-training, immediate scaling and short-term retention at 3 weeks post-training was examined. Perturbation outcome and post-slip center-of-mass (COM) stability was analyzed. RESULTS: On the pre-training trial, 60% of high and 100% of low-functioning participants fell. High-functioning group tolerated and adapted at training-intensity level-II but low-functioning group were trained at level-I (all had > 3 falls on level-II). At respective training intensities, both groups significantly lowered fall incidence from 1st through 11th trials, with improved post-slip stability and anterior shift in COM position, resulting from increased compensatory step length. Both groups demonstrated immediate scaling and short-term retention of the acquired stability control. CONCLUSION: Chronic stroke survivors are able to acquire and retain adaptive reactive balance skills to reduce fall risk. Although similar adaptation was demonstrated by both groups, the low-functioning group might require greater dosage with gradual increment in training intensity.

Neural Mechanisms Involved in Mental Imagery of Slip-Perturbation While Walking: A Preliminary fMRI Study.

Background: Behavioral evidence for cortical involvement in reactive balance control in response to environmental perturbation is established, however, the neural correlates are not known. This study aimed to examine the neural mechanisms involved in reactive balance control for recovery from slip-like perturbations using mental imagery and to evaluate the difference in activation patterns between imagined and observed slipping. Methods: Ten healthy young participants after an exposure to regular walking and slip-perturbation trial on a treadmill, performed mental imagery and observation tasks in the MR scanner. Participants received verbal instructions to imagine walking (IW), observe walking (OW), imagine slipping (IS) and observe slipping (OS) while walking. Results: Analysis using general linear model showed increased activation during IS versus IW condition in precentral gyrus, middle frontal gyrus, superior, middle and transverse temporal gyrus, parahippocampal gyrus, cingulate gyrus, insula, pulvinar nucleus of the thalamus, pons, anterior and posterior cerebellar lobes. During IS versus OS condition, there was additional activation in parahippocampus, cingulate gyrus, inferior parietal lobule, superior temporal, middle and inferior frontal gyrus. Conclusion: The findings of the current study support involvement of higher cortical and subcortical structures in reactive balance control. Greater activation during slipping could be attributed to the complexity of the sensorimotor task and increased demands to maintain postural stability during slipping as compared with regular walking. Furthermore, our findings suggest that mental imagery of slipping recruited greater neural substrates rather than observation of slipping, possibly due to increased sensory, cognitive and perceptual processing demands. New and Noteworthy: The behavioral factors contributing to falls from external perturbations while walking are better understood than neural mechanisms underlying the behavioral response. This study examines the neural activation pattern associated with reactive balance control during slip-like perturbations while walking through an fMRI paradigm. This study identified specific neural mechanisms involved in complex postural movements during sudden perturbations, to particularly determine the role of cortical structures in reactive balance control. It further highlights the specific differences in neural structures involved in regular unperturbed versus perturbed walking.

Examining Neural Plasticity for Slip-Perturbation Training: An fMRI Study.

Perturbation-based balance training has shown to induce adaptation of reactive balance responses that can significantly reduce longer-term fall risk in older adults. While specific cortical and subcortical areas in control of posture and locomotion have been identified, little is known about the training-induced plasticity occurring in neural substrates for challenging tasks involving reactive balance control. The purpose of this study was to use functional neuroimaging to examine and determine the neural substrates, if any, involved in inducing adaptation to slip-like perturbations experienced during walking over 3 consecutive training days. We used a mental imagery task to examine the neural changes accompanied by treadmill-slip perturbation training. Ten healthy young adults were exposed to increasing magnitude of displacements during slip-like perturbations while walking, with an acceleration of 6 m/s2 on a motorized treadmill for 3 consecutive days. Brain activity was recorded through MRI while performing imagined slipping and imagined walking tasks before and after the perturbation training. The number of compensatory steps and center of mass state stability at compensatory step touchdown were recorded. As compared with day 1 (first trial), on day 3 (last trial) there was a significant reduction in number of compensatory steps and increase in stability at compensatory step touchdown on the mid and highest perturbation intensities. Before perturbation training, imagined slipping showed increased activity in the SMA, parietal regions, parahippocampal gyrus, and cingulate gyrus compared with rest. After perturbation training, imagined slipping showed increased activation in DLPFC, superior parietal lobule, inferior occipital gyrus, and lingual gyrus. Perturbation training was not associated with decline in activity in any of the brain regions. This study provides evidence for learning-related changes in cortical structures while adapting to slip-like perturbations while walking. The findings reflect that higher-level processing is required for timing and sequencing of movements to execute an effective balance response to perturbations. Specifically, the CNS relies on DLPFC along with motor, parietal, and occipital cortices for adapting to postural tasks posing a significant threat to balance.