Task constraints on foot movement and the incidence of compensatory stepping following perturbation of upright stance

doi:10.1016/0006-8993(93)90188-S

Brain Research

Volume 616, Issues 1–2, 9 July 1993, Pages 30-38

https://doi.org/10.1016/0006-8993(93)90188-S Get rights and content

Abstract

Our understanding of the postural control responses in the event of external perturbation has focused almost exclusively on the early automatic adjustments. The present study addresses another postural reaction that is functionally important: compensatory stepping. The purpose was to identify the relative importance by comparing the prevalence of compensatory stepping with and without instructions constraining the subjects' responses. Subjects stood on two force plates which were mounted on a “moveable” platform. Their posture was perturbed by the translation of the platform either forward or backward at various accelerations. Following a practice period, seven subjects each performed under two different tasks: “constrained” (keep feet in place) and “unconstrained” (no specific instructions given). The primary focus of the analysis was on responses to forward platform translations. Analysis revealed that the frequency of stepping tended to be higher in “unconstrained”, as opposed to “constrained”, tasks. The frequency of stepping was also related to the interaction between the tasks and the order in which they were given. Specifically, subjects stepped most frequently when they received the “unconstrained” task first. The frequency of stepping also increased as the magnitude of the platform acceleration increased. Time of onset of stepping, as defined from the force plate measures, began as early as 160 ms in one subject and averaged 250 ms across all subjects. These relatively fast response times suggest that step initiation often occurs well before the limits of stability are reached. A novel and unexpected finding was the identification of a third response type, intermediate to stepping and (bilaterally symmetrical) non-stepping responses. This intermediate response was characterized by a lateral weight shift and appeared to be the initiation of a stepping response which was aborted before the foot was lifted. In summary, it is concluded that stepping may be more prevalent in unconstrained behaviour. Paradigms that implicity or explicity constrain foot movement may well lead to misleading conclusions regarding ecologic validity of specific postural strategies. The occurrence of stepping is also strongly influenced by the magnitude of the perturbation, implying that some “decision” process occurs before initiation of stepping. Moreover, initiation of compensatory stepping (lateral weight shift) and continuation (foot lift and swing) may involve separate and sequential “decisions”, suggesting a more complex contribution from sensory cues than might be predicted for a completely preplanned reaction.

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Cited by (113)

Compensatory postural responses to backward loss of balance in patients with cerebellar disease
2021, Gait and Posture
Impaired control of balance and coordinated reactions are a primary deficit of cerebellar dysfunction. As compared to other neurological patients with balance impairments, there has been little research assessing the characteristics of compensatory responses associated with falls in patients with cerebellar disease (CD).
The aim of this study was to examine the effects of cerebellar disease on compensatory balance control in response to postural perturbation. Do CD patients increase the number of steps when responding to instability because of inappropriate initial step reactions or poor control of trunk motion or both?
In this explorative study, 10 patients suffering from degenerative cerebellar ataxia and 10 age-matched healthy controls were examined. The balance recovery reactions were assessed using a lean-and-release postural perturbation method. Spatiotemporal characteristics of stepping movement and COM variables associated with torso motion were analyzed using 3D motion capture system.
CD patients took multiple steps whereas matched controls generally took single steps to recover balance following perturbation. The characteristics of the initial step at the time of the fall revealed that foot reaction time, foot response time, and step distance of the initial step were similar between CD patients and matched controls. However, CD patients exhibited a shorter foot-to−COM distance, higher COM velocity, and less trunk flexion with which to attenuate their body momentum after the landing of the first step than did matched controls.
Although initial step responses were probably adequate, poor control of torso motion appears to be a particular problem that causes multiple-step reactions in CD patients. This observation would help to guide the development of tailored fall intervention strategies in CD patients aimed at promoting their recovery capacity in response to a pronounced balance challenge.
Stepping impairment and falls in older adults: A systematic review and meta-analysis of volitional and reactive step tests
2021, Ageing Research Reviews
Citation Excerpt :
The majority of falls among community-dwelling older adults occur while walking and are often due to trips and slips (Berg et al., 1997; Talbot et al., 2005). The postural perturbations in such instances usually require a change-in-support through stepping and/or grasping to avoid a fall(Jensen et al., 2001; McIlroy and Maki, 1993b; Mille et al., 2003; Rogers et al., 1996). In daily life, protective stepping may be a) initiated voluntarily when a balance disturbance is anticipated, or b) reactive in response to an unanticipated perturbation (Patla, 2003).
To systematically examine stepping performance as a risk factor for falls. More specifically, we examined (i) if step tests can distinguish fallers from non-fallers and (ii) the type of step test (e.g. volitional vs reactive stepping) that is required to distinguish fallers from non-fallers.
PubMed, EMBASE, CINAHL, Cochrane Database of Systematic Reviews and reference lists of included articles.
Study selection: Cross-sectional and cohort studies that assessed the association between at least one step test and falls in older people (age ≥ 60 and/or mean age of 65).
A meta-analysis of 61 studies (n = 9536) showed stepping performance was significantly worse in fallers compared to non-fallers (Cohen’sd 0.56, 95 % CI 0.48 to 0.64, p < 0.001, I² 66 %). This was the case for both volitional and reactive step tests. Twenty-three studies (n = 3615) were included in a diagnostic meta-analysis that showed that step tests have moderate sensitivity (0.70, 95 % CI 0.62 to 0.77), specificity (0.68, 95 % CI 0.58 to 0.77) and area under the receiver operating characteristics curve (AUC) (0.75, 95 % CI 0.59 to 0.86) in discriminating fallers from non-fallers.
Conclusions: This large systematic review demonstrated that both volitional and reactive stepping impairments are significant fall risk factors among older adults. Step tests can identify fallers from non-fallers with moderate accuracy.
Investigation of the effect of tonus on the change in postural control strategy using musculoskeletal simulation
2020, Gait and Posture
Humans use different postural control strategies depending on perturbations. The shift from an ankle strategy to a hip strategy occurs at different perturbation magnitudes for different individuals. Although such differences relate to the differences in body parameters such as muscle strength, the parameter changes that affect the strategy shift are unclear. The relationship between tonus and strategy is especially unclear, but humans control tonus, which contributes to body stability. The objective of this study was to investigate the influence of tonus on postural control strategy.
Is there a trend toward the use of a hip strategy with a decrease in the magnitude of tonus?
Predictive simulations were performed for changing parameters of muscle weakness and increased sensory noise, which are considered the causes of different strategies and decreased tonus. A musculoskeletal model with 70 muscles and 15 degrees of freedom of joints was controlled using a neural controller model, and the support surface was translated backward to introduce perturbations. The parameters of the musculoskeletal and neural controller models were changed for 48 conditions of different muscle strengths, sensory noise, and tonus. The control parameters were optimized for each condition. Simulations were performed with the optimized control parameters to calculate an evaluation index to show the difference in postural control strategies (peak hip angle), and the relationship between the index and parameters was analyzed using analysis of variance and multiple regression.
The main effects of muscle weakness and decreased tonus and their interaction were confirmed. The results recognized a positive response to the research question.
The study emphasizes the importance of considering tonus while investigating the postural control strategy. Furthermore, it was suggested that when the magnitude of tonus was larger than a threshold, only the ankle strategy was used, regardless of muscle strength.
Does Perturbation-Based Balance Training Improve Control of Reactive Stepping in Individuals with Chronic Stroke?
2019, Journal of Stroke and Cerebrovascular Diseases
Citation Excerpt :
The ability to execute balance reactions is critical to maintaining stability following a loss of balance.2 Change-in-support reactions (reactions that increase base-of-support size), including reactive stepping, are crucial for preventing falls.3 However, these responses are often impaired with 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.
Cortical dynamics during preparation and execution of reactive balance responses with distinct postural demands
2019, NeuroImage
The contributions of the cerebral cortex to human balance control are clearly demonstrated by the profound impact of cortical lesions on the ability to maintain standing balance. The cerebral cortex is thought to regulate subcortical postural centers to maintain upright balance and posture under varying environmental conditions and task demands. However, the cortical mechanisms that support standing balance remain elusive. Here, we present an EEG-based analysis of cortical oscillatory dynamics during the preparation and execution of balance responses with distinct postural demands. In our experiment, participants responded to backward movements of the support surface either with one forward step or by keeping their feet in place. To challenge the postural control system, we applied participant-specific high accelerations of the support surface such that the postural demand was low for stepping responses and high for feet-in-place responses. We expected that postural demand modulated the power of intrinsic cortical oscillations.
Independent component analysis and time-frequency domain statistics revealed stronger suppression of alpha (9–13 Hz) and low-gamma (31–34 Hz) rhythms in the supplementary motor area (SMA) when preparing for feet-in-place responses (i.e., high postural demand). Irrespective of the response condition, support-surface movements elicited broadband (3–17 Hz) power increase in the SMA and enhancement of the theta (3–7 Hz) rhythm in the anterior prefrontal cortex (PFC), anterior cingulate cortex (ACC), and bilateral sensorimotor cortices (M1/S1). Although the execution of reactive responses resulted in largely similar cortical dynamics, comparison between the bilateral M1/S1 showed that stepping responses corresponded with stronger suppression of the beta (13–17 Hz) rhythm in the M1/S1 contralateral to the support leg. Comparison between response conditions showed that feet-in-place responses corresponded with stronger enhancement of the theta (3–7 Hz) rhythm in the PFC. Our results provide novel insights into the cortical dynamics of SMA, PFC, and M1/S1 during the control of human balance.
Exploring the relationship between stability and variability of the centre of mass and centre of pressure
2018, Gait and Posture
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.
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.
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.
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).
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.

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Task constraints on foot movement and the incidence of compensatory stepping following perturbation of upright stance

Abstract

Electroencephalogr. Clin. Neurophysiol.

J. Biomech.

Biomed. Eng.

Invariant characteristics of gait initiation

Am. J. Phys. Med. Rehabil.

The initiation of walking

Acta Anat.

Sensory triggering of a sequence of postural responses

Neurosci. Abstr.

Mechanisms controlling accurate changes in elbow torque in humans

J. Neurosci.

A motor programme for the initiation of forward-oriented movements in humans

J. Physiol.

The influence of a reduced plantar support surface area on the compensatory reactions to a forward fall

Exp. Brain Res.

Influence of plantar cutaneous afferents on early compensatory reactions to forward fall

Exp. Brain Res.

Postural responses to changing task conditions

Exp. Brain Res.