Characterization of Reactions to Laterally Directed Perturbations in People With Chronic Stroke

Characteristics of proactive balance and gait performance in subacute stroke patients demonstrating varying reactive balance capacity: A research study

BACKGROUND

Persons with stroke (PwS) demonstrate impaired reactive balance control placing them at increased risk of falls. Yet, tests used in clinical practice to assess this risk usually rely on proactive balance control.

OBJECTIVE

To investigate differences in proactive balance in PwS with varying reactive balance capacity.

METHODS

Reactive balance control was assessed in 48 first-event subacute PwS by measuring multiple-step threshold and fall threshold in response to unannounced surface perturbations. They were classified as low-, medium- high- threshold fallers and non-fallers in accordance with the perturbation magnitude at which they were unable to maintain balance (fall threshold). Proactive balance control and gait performance were tested using the Berg Balance test, 10-meter walk test, 6-minute walk test and the Activities-specific Balance Confidence Scale (ABC).

RESULTS

PwS who demonstrated poor reactive balance capacity were also more impaired in their proactive balance and gait. Proactive balance and gait performance were significantly different between the 4 groups while ABC was not. The associations between reactive and proactive measures of balance were moderate (r = 0.53-0.67).

CONCLUSIONS

The moderate correlations between reactive and proactive balance control suggest the recruitment of different neural mechanisms for these two operations, highlighting the importance of assessing and treating reactive balance in clinics.

Characterizing slip-like responses during gait using an entire support surface perturbation: Comparisons to previously established slip methods

BACKGROUND

The characteristics of experimentally induced slips (low-friction surfaces and non-motorized platforms) in laboratory settings are influenced by participant gait velocity, contact surface area, and level of friction between the foot and surface. However, motorized platforms that could account for these factors during slip-like paradigms have not been extensively used.

RESEARCH QUESTION

How does slip-like perturbations evoked via a motorized platform change gait characteristics and postural stability during overground walking?

METHODS

Ten healthy young adults performed 4 overground, self-paced walking trials, with the 4^th trial including an unexpected forward support surface translation at heel-strike during steady state walking. Kinematic and kinetic data were collected, with step characteristics (time, distance, velocity) and postural stability calculated to compare between normal gait and slip-like trials. Slip foot characteristics were also determined.

RESULTS

Peak slipping foot velocity variability was considerably smaller compared to previously reported low-friction and non-motorized perturbations. The centre of mass was shifted more posteriorly (thus in a less stable location) by the end of the platform acceleration phase compared to the same time point post-heel strike during normal gait trials. Participants successfully responded to every slip-like perturbation by significantly increasing step time, decreasing step distance, and decreasing step velocity.

SIGNIFICANCE

Our results demonstrate the repeatability and consistency of a motorized support surface paradigm to induce slip-like perturbations. Furthermore, stability and step characteristic results confirm posterior shifts in stability and appropriate stepping responses, mimicking how participants would react if responding to a real world slip.

Does Perturbation-Based Balance Training Improve Control of Reactive Stepping in Individuals with Chronic Stroke?

BACKGROUND

Although perturbation-based balance training (PBT) may be effective in improving reactive balance control and/or reducing fall risk in individuals with stroke, the characteristics of reactive balance responses that improve following PBT have not yet been identified. This study aimed to determine if reactive stepping characteristics and timing in response to support-surface perturbations improved to a greater extent following PBT, compared to traditional balance training.

MATERIALS AND METHODS

This study represents a substudy of a multisite randomized controlled trial. Sixteen individuals with chronic stroke were randomly assigned to either perturbation-based or traditional balance training, and underwent 6-weeks of training as a part of the randomized controlled trial. Responses to support-surface perturbation were evaluated pre- and post-training, and 6-months post-training. Reactive stepping characteristics and timing were compared between sessions within each group, and between groups at post-training and 6-months post-training while controlling for each measure at the pre-training session.

RESULTS

The frequency of extra steps in response to perturbations decreased from pre-training to post-training for the PBT group, but not for the control group.

CONCLUSIONS

Improvements in reactive balance control were identified after PBT in individuals with chronic stroke. Findings provide insight into the mechanism by which PBT improves reactive balance control poststroke, and support the use of PBT in balance rehabilitation programs poststroke.

Exploring the relationship between stability and variability of the centre of mass and centre of pressure

BACKGROUND

There are competing perspectives in the literature regarding the role of movement variability in quiet standing and balance control. Some view high variability as indicative of poor balance control and a contributor to increased fall risk, whereas others view variability as beneficial in providing sensory information that aids balance control.

RESEARCH QUESTION

This study aimed to help to clarify the role of variability in balance control by testing two competing hypotheses: that increased variability would lead to instability, or that increased variability would improve stability, where stability is defined as the ability to respond to a perturbation.

METHODS

Fourteen healthy young adults (20-35 years old) were recruited. Participants experienced postural perturbations of varying magnitudes, delivered via sudden backward movement of the support surface. Magnitudes of postural perturbation were chosen such that both step and no-step responses could be observed at each magnitude. Variability in the centre of mass and centre of pressure movement was measured for 10 s prior to the postural perturbation. Multiple regression was used to determine if movement variability predicted step responses when controlling for perturbation magnitude, trial order, and margin of stability at perturbation onset.

RESULTS

Lower variability in medio-lateral centre of mass and centre of pressure position, and lower variability in medio-lateral centre of pressure velocity were related to increased odds of stepping in response to the perturbation (p-values ≤0.001).

SIGNIFICANCE

This study provides support for the hypothesis that, at least for relatively low variability values, increased centre of pressure and mass movement variability improves stability. Specifically, increasing movement of the centre of pressure and mass in the medio-lateral direction may help to preserve stability in the antero-posterior direction by providing the central nervous system with information about the antero-posterior centre of mass across a wide range of medio-lateral positions.

Stroke

Stroke, or cerebrovascular accident, involves injury to the central nervous system as a result of a vascular cause, and is a leading cause of disability worldwide. People with stroke often experience sensory, cognitive, and motor sequelae that can lead to difficulty walking, controlling balance in standing and voluntary tasks, and reacting to prevent a fall following an unexpected postural perturbation. This chapter discusses the interrelationships between stroke-related impairments, problems with control of balance and gait, fall risk, fear of falling, and participation in daily physical activity. Rehabilitation can improve balance and walking function, and consequently independence and quality of life, for those with stroke. This chapter also describes effective interventions for improving balance and walking function poststroke, and identifies some areas for further research in poststroke rehabilitation.