Modulation of reactive response to slip-like perturbations: effect of explicit cues on paretic versus non-paretic side stepping and fall-risk

Application of neuromuscular electrical stimulation on the support limb during reactive balance control in persons with stroke: a pilot study

The aim of the present study was to investigate the effect of the application of neuromuscular electrical stimulation to the quadriceps muscle of the paretic limb during externally induced stance perturbations on reactive balance control and on fall outcomes in people with chronic stroke. Ten participants experienced 12 stance treadmill perturbation trails, 6 forward balance perturbation trials and 6 backward balance perturbation trials. For each perturbation condition, three perturbation trials were delivered synchronized with neuromuscular electrical stimulation applied to the quadriceps of the paretic limb and three perturbation trials were delivered without stimulation. Behavioral outcome measures, such as incidence of laboratory falls and number of compensatory steps, kinematic outcome measures, such as margin of stability and minimum hip high values after the perturbation, step initiation time, step execution time and step length of the stepping leg were analyzed. The application of neuromuscular electrical stimulation on the paretic quadriceps between the range of 50 and 500 ms after stance forward and backward perturbations reduced the laboratory falls incidence (p < 0.05), improved stability values (p < 0.05) and reduced the hip height descent (p < 0.05) compared to the experimental condition in which participants were exposed to stance perturbations without neuromuscular electrical stimulation. Additionally, step initiation time of the recovery step was lower in neuromuscular electrical stimulation condition during the forward balance perturbation protocol. Our results showed that the application of neuromuscular electrical stimulation on the knee extensor muscles of the paretic limb reduces the incidence of laboratory falls, enhances reactive stability control and reduces vertical limb collapse after stance forward and backward perturbations in people with chronic stroke.

Posterior fall-recovery training applied to individuals with chronic stroke: A single-group intervention study

BACKGROUND

To assess the effects of the initial stepping limb on posterior fall recovery in individuals with chronic stroke, as well as to determine the benefits of fall-recovery training on these outcomes.

METHODS

This was a single-group intervention study of 13 individuals with chronic stroke. Participants performed up to six training sessions, each including progressively challenging, treadmill-induced perturbations from a standing position. Progressions focused on initial steps with the paretic or non-paretic limb. The highest perturbation level achieved, the proportion of successful recoveries, step and trunk kinematics, as well as stance-limb muscle activation about the ankle were compared between the initial stepping limbs in the first session. Limb-specific outcomes were also compared between the first and last training sessions.

FINDINGS

In the first session, initial steps with the non-paretic limb were associated with a higher proportion of success and larger perturbations than steps with the paretic limb (p = 0.02, Cohen's d = 0.8). Paretic-limb steps were wider relative to the center of mass (CoM; p = 0.01, d = 1.3), likely due to an initial standing position with the CoM closer to the non-paretic limb (p = 0.01, d = 1.4). In the last training session, participants recovered from a higher proportion of perturbations and advanced to larger perturbations (p < 0.05, d > 0.6). There were no notable changes in kinematic or electromyography variables with training (p > 0.07, d < 0.5).

INTERPRETATION

The skill of posterior stepping in response to a perturbation can be improved with practice in those with chronic stroke, we were not able to identify consistent underlying kinematic mechanisms behind this adaptation.

Maintaining sagittal plane balance compromises frontal plane balance during reactive stepping in people post-stroke

BACKGROUND

Maintaining balance in response to perturbations during walking often requires the use of corrective responses to keep the center of mass within the base of support. The relationship between the center of mass and base of support is often quantified using the margin of stability. Although people post-stroke increase the margin of stability following perturbations, control deficits may lead to asymmetries in regulation of margins of stability, which may also cause maladaptive coupling between the sagittal and frontal planes during balance-correcting responses.

METHODS

We assessed how paretic and non-paretic margins of stability are controlled during recovery from forward perturbations and determined how stroke-related impairments influence the coupling between the anteroposterior and mediolateral margins of stability. Twenty-one participants with post-stroke hemiparesis walked on a treadmill while receiving slip-like perturbations on both limbs at foot-strike. We assessed anteroposterior and mediolateral margins of stability before perturbations and during perturbation recovery.

FINDINGS

Participants walked with smaller anteroposterior and larger mediolateral margins of stability on the paretic versus non-paretic sides. When responding to perturbations, participants increased the anteroposterior margin of stability bilaterally by extending the base of support and reducing the excursion of the extrapolated center of mass. The anteroposterior and mediolateral margins of stability in the paretic limb negatively covaried during reactive steps such that increases in anteroposterior were associated with reductions in mediolateral margins of stability.

INTERPRETATION

Balance training interventions to reduce fall risk post-stroke may benefit from incorporating strategies to reduce maladaptive coupling of frontal and sagittal plane stability.

Immediate effect of voluntary-induced stepping response training on protective stepping in persons with chronic stroke: a randomized controlled trial

Purpose: To compare the immediate effects of voluntary-induced stepping response training (VSR) and DynSTABLE perturbation training (DST) on protective stepping in patients with stroke.Methods: A randomized controlled trial (registration number: TCTR20170827001) was conducted in 34 patients with chronic stroke who were randomly allocated to the VSR (n = 17) or DST (n = 17) group. The VSR group was instructed to lean forward to induce protective stepping, while the DST group experienced support surface translation. All participants received one session of training (3 set, 10 min for each set with 10-minute rest in between). Step length, step width, number of steps and center of mass (CoM) position during protective stepping were assessed using a computer-assisted rehabilitation environment (CAREN) system prior to and immediately after training. Two-way ANOVA was used to compare between groups and times.Results: Both types of training resulted in an increase in step width, but step length increased and there was a more positive COM position exhibited following DST (p < .05) than following VSR. Single-step incidence increased, whereas multiple-step incidence decreased significantly in both groups. Only participants in the VSR group generated protective stepping with the affected leg in a larger percentage of trials (27%) after training than before training.Conclusion: Both DST and VSR led to changes in protective stepping parameters after a single session of training. VSR may be a feasible alternative to equipment-based training but requires further study.Implication for RehabilitationVSR and DST trainings improved protective stepping in stroke.Step length and CoM control at foot touchdown increased after DST training.VSR training for 50 minutes led to increase affected stepping and reduce grasping.Step width, affected step length, and single step increased after both trainings.Without instrument, VSR increased steps execution and performance similar to DST.

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.

Perturbation-Induced Stepping Post-stroke: A Pilot Study Demonstrating Altered Strategies of Both Legs

Introduction: Asymmetrical sensorimotor function after stroke creates unique challenges for bipedal tasks such as walking or perturbation-induced reactive stepping. Preference for initiating steps with the less-involved (preferred) leg after a perturbation has been reported with limited information on the stepping response of the more-involved (non-preferred) leg. Understanding the capacity of both legs to respond to a perturbation would enhance the design of future treatment approaches. This pilot study investigated the difference in perturbation-induced stepping between legs in stroke participant and non-impaired controls. We hypothesized that stepping performance will be different between groups as well as between legs for post-stroke participants.

Methods: Thirty-six participants (20 persons post-stroke, 16 age matched controls) were given an anterior perturbation from three stance positions: symmetrical (SS), preferred asymmetrical (PAS−70% body weight on the preferred leg), and non-preferred asymmetrical (N-PAS−70% body weight on the non-preferred leg). Kinematic and kinetic data were collected to measure anticipatory postural adjustment (APA), characteristics of the first step (onset, length, height, duration), number of steps, and velocity of the body at heel strike. Group differences were tested using the Mann-Whitney U-test and differences between legs tested using the Wilcoxon signed-rank test with an alpha level of 0.05.

Results: Stepping with the more-involved leg increased from 11.5% of trials in SS and N-PAS up to 46% in PAS stance position for participants post-stroke. Post-stroke participants had an earlier APA and always took more steps than controls to regain balance. However, differences between post-stroke and control participants were mainly found when stance position was modified. Compare to controls, steps with the preferred leg (N-PAS) were earlier and shorter (in time and length), whereas steps with the non-preferred leg (PAS) were also shorter but took longer. For post-stroke participants, step duration was longer and utilized more steps when stepping with the more-involved leg compared to the less-involved leg.

Conclusions: Stepping with the more-involved leg can be facilitated by unweighting the leg. The differences between groups, and legs in post-stroke participants illustrate the simultaneous bipedal role (support and stepping) both legs have in reactive stepping and should be considered for reactive balance training.

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.

Body configuration at first stepping-foot contact predicts backward balance recovery capacity in people with chronic stroke

Objective

To determine the predictive value of leg and trunk inclination angles at stepping-foot contact for the capacity to recover from a backward balance perturbation with a single step in people after stroke.

Methods

Twenty-four chronic stroke survivors and 21 healthy controls were included in a cross-sectional study. We studied reactive stepping responses by subjecting participants to multidirectional stance perturbations at different intensities on a translating platform. In this paper we focus on backward perturbations. Participants were instructed to recover from the perturbations with maximally one step. A trial was classified as ‘success’ if balance was restored according to this instruction. We recorded full-body kinematics and computed: 1) body configuration parameters at first stepping-foot contact (leg and trunk inclination angles) and 2) spatiotemporal step parameters (step onset, step length, step duration and step velocity). We identified predictors of balance recovery capacity using a stepwise logistic regression. Perturbation intensity was also included as a predictor.

Results

The model with spatiotemporal parameters (perturbation intensity, step length and step duration) could correctly classify 85% of the trials as success or fail (Nagelkerke R² = 0.61). In the body configuration model (Nagelkerke R² = 0.71), perturbation intensity and leg and trunk angles correctly classified the outcome of 86% of the recovery attempts. The goodness of fit was significantly higher for the body configuration model compared to the model with spatiotemporal variables (p<0.01). Participant group and stepping leg (paretic or non-paretic) did not significantly improve the explained variance of the final body configuration model.

Conclusions

Body configuration at stepping-foot contact is a valid and clinically feasible indicator of backward fall risk in stroke survivors, given its potential to be derived from a single sagittal screenshot.

The effect of weight-bearing asymmetry on dynamic postural stability in people with chronic stroke

After stroke, weight-bearing asymmetry (WBA) towards the non-paretic side is associated with postural instability. It remains unknown whether WBA is a cause or consequence of postural instability, as both phenomena depend on stroke severity. We investigated the effect of WBA on the ability to recover from balance perturbations in people with stroke. Fourteen people in the chronic phase of stroke underwent multidirectional translational perturbations at three levels of initial WBA (0, 10 and 20% of body weight unloading of the paretic leg). We iteratively determined the highest perturbation intensity that could be sustained with a feet-in-place response (i.e. stepping threshold) for each WBA condition and in four perturbation directions (forward, backward, towards paretic and towards non-paretic side). For perturbations above the stepping threshold we determined the choice of stepping leg. WBA increased the stepping threshold for perturbations towards the paretic side, whereas it decreased the stepping threshold for perturbations towards the non-paretic side (p<0.05). No effects of WBA were found on forward or backward stepping thresholds. Yet, the frequency of stepping with the paretic leg in the anteroposterior directions increased with greater WBA. Similarly, greater initial WBA resulted in a larger number of side steps towards the paretic side. In conclusion, the results suggest that people with stroke can benefit from some paretic leg unloading when perturbed towards the paretic side. It remains to be investigated, however, to what extent these benefits outweigh the potentially detrimental effects of WBA that were observed when recovering from perturbations in the other directions.