On postural stability and variability

doi:10.1016/0966-6362(93)90050-B

Gait & Posture

Volume 1, Issue 4, December 1993, Pages 225-230

https://doi.org/10.1016/0966-6362(93)90050-B Get rights and content

Abstract

The stability of posture is often assessed directly by the variability of certain centre of pressure parameters, such as length or area of the centre of pressure profiles. Increased variability of these parameters is usually taken as an index of decreased postural stability. In this paper we present data from normal and tardive dyskinetic adult subjects that support the notion that centre of pressure variability is not a sufficient measure of postural stability. It is shown that variability in a given centre of pressure parameter does not necessarily distinguish the different attractor dynamics that support postural control. Dimension estimates of the centre of pressure time series showed that: (1) there is more structure in the centre of pressure pattern of normal subjects than is traditionally interpreted; (2) the dimension of the centre of pressure in tardive dyskinetic individuals is systematically lower than in normals. The implication of these findings for assessing the relation between the variability and stability of posture is discussed. It is proposed that postural stability can only be assessed by considering the attractor dynamics of the postural control system.

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Cited by (115)

Clinic- and laboratory-based measures of postural control in patellofemoral pain: A systematic review with meta-analysis and evidence gap map
2024, Gait and Posture
Patellofemoral pain (PFP) is a prevalent musculoskeletal disorder associated with functional impairments. Although postural control is commonly assessed in people with PFP, there are inconsistent results regarding potential postural control deficits in this population.
This review aims to evaluate whether postural control is impaired in people with patellofemoral pain (PFP) and the effectiveness of interventions on postural control measures.
We searched six databases from their inception to May 5, 2023. We included studies assessing clinic- or laboratory-based postural control measures in people with PFP compared to pain-free controls, and intervention studies with PFP populations. We assessed risk of bias using the Joanna Briggs Institute critical appraisal checklists and the Cochrane Risk of Bias 2 tool. We assessed the certainty of evidence using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach. We used random-effects meta-analyses considering subgroups based on type of task, measure, and intervention.
Fifty-three studies were included. Very low certainty evidence indicated that people with PFP have shorter anterior (SMD = 0.53, 95 %CI:0.16,0.90), posteromedial (SMD = 0.54, 95 %CI:0.04,1.03) and posterolateral (SMD = 0.59, 95 %CI:0.11,1.07) reach distance, and worse composite score (SMD = 0.46, 95 %CI:0.22,0.70). Very low to moderate certainty evidence indicated that people with PFP have worse anterior-posterior and overall stability indexes during single-leg stance (SMD = −0.71, 95 %CI:−1.29,−0.14; SMD = −0.63, 95 %CI:−0.94,−0.32) and overall stability index during double-leg stance (SMD = −0.39, 95 %CI:−0.78,−0.00), but no differences in center of pressure area during stair ascent (SMD = 0.32, 95 %CI:−2.72, 3.36). Low certainty evidence indicated that kinesio taping improved anterior reach distance (SMD = −0.49, 95 %CI:−0.89,−0.09), while no significant differences were observed between pre- and post-intervention outcomes for conventional rehabilitation and rigid taping.
Clinicians should use clinic- (star excursion or Y-balance tests) and laboratory-based (stability indexes) measures to identify impairments of postural control in people with PFP. Low certainty of evidence suggests short-term improvement in postural control with kinesio taping.
Joint entropy analysis of anterior-posterior and medial-lateral body sway
2022, Medical Engineering and Physics
We studied the Shannon entropy of center of pressure (COP) trajectories under different sensory feedback conditions and analyzed the interrelations between medial-lateral (ML), anterior-posterior (AP) and joint (ML and AP) sway entropy.
Static balance was assessed on a force platform under different visual and proprioceptive feedback conditions: Standing on firm support with eyes open (condition 1) or closed (condition 2) and standing on foam with eyes closed (condition 3). Postural sway was analyzed by means of linear and nonlinear, information theoretic metrics (entropy of ML and AP sway, joint ML and AP entropy).
ML entropy, AP entropy and joint ML and AP entropy remained stable from condition 1 through condition 3. The values of ML and AP entropies were practically at their theoretical maximum in all conditions. On the other hand, joint ML and AP entropies were clearly submaximal.
Decreasing the reliability of visual and proprioceptive input does not alter the Shannon entropy of body sway, although it does increase the magnitude of conventional linear sway metrics. Importantly, individual ML and AP sway entropies tend towards absolute randomness, whereas the joint, ML and AP, sway entropy exhibits a higher degree of regularity, suggesting its role as the actual controlled variable.
The precision demands of viewing distance modulate postural coordination and control
2019, Human Movement Science
There are contrasting views on the role of vision in modifying postural organization (information-driven and postural facilitation) and limited direct tests of the underlying postural mechanisms. Here, we examined whether the distinction between the two views is appropriate given that both are interrelated parts of task constraints modulating postural coordination and control. The study investigated whether changes in the organization of the postural system are a function of the visual precision demands of a task and, in addition, whether such organization could be described as reflecting an intermittent controller. Sixteen participants were instructed to maintain quiet postural stance while fixating a point at different viewing distances (25, 50, 135, 220, 305 cm) or standing with eyes closed. The 25-cm condition showed the lowest standard deviation of the center of pressure (COP) and the highest correlation dimension (CD) in the anterior posterior direction. Analyses revealed that, contrary to the intermittent controller hypothesis, adaptations in the continuous COP and center of mass (COM) coupling characterized the observed changes in CD. The findings show that the natural act of looking to the same feature in the environment as a function of visual viewing distance can lead to quantitative and qualitative changes in the dynamics of posture. This is consistent with the view that postural facilitation and information availability are integrated in the perceptual-motor dynamics.
Abnormal postural behavior in patients with functional movement disorders during exposure to stress
2019, Psychoneuroendocrinology
Citation Excerpt :
If classic static measures of body movement mainly investigate how much movement is recorded, fractality focuses on how the movement is dynamically performed. Fractality has already been found to be altered in neurological (Manabe et al., 2001; Newman et al., 2017) and psychiatric disorders (Bolbecker et al., 2011), with patients showing higher regularity of the movement pattern, compared to controls in Huntington’s disease (Hausdorff et al., 1997), dyskinesia (Newell et al., 1993), Parkinson disease (Sekine et al., 2004), bipolar disorders (Bolbecker et al., 2011) or stereotypical movement disorders (Bodfish et al., 2001). This underlies the importance of studying postural behavior under pathological conditions not only as movement variability (e.g., body sway), but also as regularity of movement.
Patients affected by functional (psychogenic) movement disorders (FMD) have abnormal processing of stress responses. However, little is known about the influence of this abnormal stress processing on automatic motor defense behavior, such as freeze response. Our aim was thus to investigate stress-induced postural motor responses in FMD.
Nine FMD patients and thirteen healthy controls were engaged in the Trier Social Stress Test, while we measured the movement of their body by means of accelerometers and gyroscopes attached to the thorax. Standard deviation of thorax acceleration, reflecting the variability of movement amplitude (body sway), was compared across groups over time in a 2 × 2 ANOVA design. Higuchi’s fractal dimension (HFD), reflecting the complexity of movement pattern over time, was also analyzed. Salivary cortisol and α-amylase samples were collected before and after the experiment, as stress biomarkers. Pearson’s correlation coefficients were calculated between these biomarkers and movement parameters.
A significant interaction effect was found, showing that healthy controls reduced their thorax sway over time during exposure to stress (from 0.027 ± 0.010 m/s² to 0.023 ± 0.008 m/s², effect size of Cohen’s d = 0.95), whereas patients with FMD did not. This change in body sway in controls over time negatively correlated with salivary cortisol values (ρ = –0.67, p = 0.012). A significant group effect revealed that FMD patients had an overall larger body sway (0.038 ± 0.013 m/s²) compared to controls (0.025 ± 0.009 m/s² – effect size of Cohen’s d = 1.29) and a lower HFD (1.602 ± 0.071) than controls (1.710 ± 0.078 – Cohen’s d = 1.43).
Patients with FMD failed to show a reduction of body sway over time, i.e., freeze response observed in the controls, thus suggesting an impairment in the automatic defense behavior. Moreover, our analysis found a lower complexity of movement (HFD) in FMD, which deserves future research in order to verify whether this could represent a characteristic trait of the disorder.
Constraints specific influences of vision, touch and surface compliance in postural dynamics
2018, Gait and Posture
Studies that have manipulated vision and touch in posture usually emphasize the prescriptive closed-loop function of the information to reduce the amount of postural motion. In contrast, we examine here the hypothesis that the standard sensory manipulations to maintain quiet stance also change in specific ways the constraints on the task goal and the emergent movement organization. Twelve participants were instructed to maintain quiet postural stance under three sensory factors: surface compliance (foam/no foam), visual information (open/closed eyes) and tactile information (finger touch/no finger touch). The standard deviation of center of pressure (COP) motion decreased with the presence of vision, touch and rigid surface. The correlation dimension showed that the manipulation of touch and vision produced different attractor dynamics that also interacted with surface compliance. Vision decreased the correlation dimension in the foam surface while the touch manipulation increased dimension in the rigid surface. The sensory information manipulations changed the qualitative properties of the attractor dynamics as well as the quantitative properties of the amount of postural motion providing evidence for the specific nature of the postural organization across information conditions.
Dynamical analysis of balance in vestibular schwannoma patients
2017, Gait and Posture
The analysis of the complexity of postural fluctuations is a recent method for assessing postural control. Complexity relates to the irregularity of the center of pressure time series and characterizes the ability of postural control to meet a changing environment. In our study, we used the sample entropy (SampEn) parameter to evaluate the complexity of postural sway velocity time series in patients with vestibular schwannoma (n = 19) compared to healthy controls (n = 20), using the sensory organization test. Patients performed postural assessments three days before surgical ablation of the tumor, then three times after surgery, at eight, thirty, and ninety days. The control group underwent posturographic tests only once. Our results demonstrated that SampEn values distinguished both groups before surgery only in postural tasks where vestibular afferences significantly contribute to maintaining balance. We also found an immediate decrease of complexity after the surgical resection of the tumor. Our results are in line with the theory of complexity loss of physiological systems stating that reducing the number of their structural components or altering their coupling leads to a decrease in complexity. Finally, our findings showed that progressive restoration of complexity over time was such that no difference was found between the two groups ninety days after surgery, due to the implementation of central adaptive mechanisms and the substitution by other sensory afferences. Thus, the SampEn parameter can highlight the postural effects of vestibular pathology, and complexity analysis appears to be a valuable tool for investigating the temporal structure of CoP time series.

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PaperOn postural stability and variability

Abstract

Electroencephalog Clin Neurophysiol

Human Mov

Physica

Bull Math Biol

Force measures for evaluating postural control: reliability and validity

Arch Phys Med Rehab

Normal postural stability and steadiness: quantitative assessment

J Bone Joint Surg

Postural sway profiles: normal subjects and subjects with cerebellar ataxia

Physio Canada

Quantitative analysis of stance in late cortical cerebellar atrophy of the anterior lobe and other forms of cerebellar ataxia

Brain

A mathematics for physiology

Amer J Phys

Skilled action: a task dynamic approach

Psychol Rev

Tardive dyskinesia and the mentally retarded: a review

Toward a movement control perspective of tardive dyskinesia

Paper
On postural stability and variability