Center Of Pressure Time Series Research Articles

A comprehensive multivariate analysis of the center of pressure during quiet standing in patients with Parkinson's disease

BackgroundWe hypothesized that postural instability observed in individuals with Parkinson's disease (PD) can be classified as distinct subtypes based on comprehensive analyses of various evaluated parameters obtained from time-series of center of pressure (CoP) data during quiet standing. The aim of this study was to characterize the postural control patterns in PD patients by performing an exploratory factor analysis and subsequent cluster analysis using CoP time-series data during quiet standing.Methods127 PD patients, 47 aged 65 years or older healthy older adults, and 71 healthy young adults participated in this study. Subjects maintain quiet standing for 30 s on a force platform and 23 variables were calculated from the measured CoP time-series data. Exploratory factor analysis and cluster analysis with a Gaussian mixture model using factors were performed on each variable to classify subgroups based on differences in characteristics of postural instability in PD.ResultsThe factor analysis identified five factors (magnitude of sway, medio-lateral frequency, anterio-posterior frequency, component of high frequency, and closed-loop control). Based on the five extracted factors, six distinct subtypes were identified, which can be considered as subtypes of distinct manifestations of postural disorders in PD patients. Factor loading scores for the clinical classifications (younger, older, and PD severity) overlapped, but the cluster classification scores were clearly separated.ConclusionsThe cluster categorization clearly identifies symptom-dependent differences in the characteristics of the CoP, suggesting that the detected clusters can be regarded as subtypes of distinct manifestations of postural disorders in patients with PD.

Enhancing age-related postural sway classification using partial least squares-discriminant analysis and hybrid feature set

Feature sets in a machine learning algorithm can have an impact on the robustness, interpretability, and characterization of the data. To detect age-related changes, traditional linear methods for analyzing center of pressure (COP) signals offer limited insight into the complex nonlinear dynamics of postural control. To overcome this limitation, a novel approach that combines a partial least squares-discriminant analysis (PLS-DA) classifier with the nonlinear dynamics of COP time series was proposed. Three small feature sets were compared: time-domain features alone, entropy-based features alone, and a hybrid approach incorporating both types of features. The performance of the PLS-DA model was assessed in four different eyes and surface conditions by using the accuracy, sensitivity, selectivity, precision metrics, and ROC curves. The results indicated that the PLS-DA model utilizing the hybrid feature set achieved significantly higher accuracy than the time-domain and entropy-based feature sets. The best classification performance was observed when the eyes were open on a compliant surface, with an overall accuracy of 89% for training and 88% for cross-validation. For the old group, while the results indicated 93% sensitivity, 94% specificity, and 93% precision in the training, the results revealed 88% sensitivity, 93% specificity, and 91% precision in cross-validation. Notably, the hybrid feature set yielded an AUC value of 0.96, indicating a superior performance. This study emphasizes the robust classification capabilities of PLS-DA for age-related postural changes and highlights the effectiveness of utilizing a small hybrid feature set to improve classification accuracy and reliability.

Spatial variability and directional shifts in postural control in Parkinson’s disease

Individuals with Parkinson’s disease exhibit tremors, rigidity, and bradykinesia, disrupting normal movement variability and resulting in postural instability. This comprehensive study aimed to investigate the link between the temporal structure of postural sway variability and Parkinsonism by analyzing multiple datasets from young and older adults, including individuals with Parkinson’s disease, across various task conditions. We used the Oriented Fractal Scaling Component Analysis (OFSCA), which identifies minimal and maximal long-range correlations within the center of pressure time series, allowing for detecting directional changes in postural sway variability. The objective was to uncover the primary directions along which individuals exerted control during the posture. The results, as anticipated, revealed that healthy adults predominantly exerted control along two orthogonal directions, closely aligned with the anteroposterior (AP) and mediolateral (ML) axes. In stark contrast, older adults and individuals with Parkinson’s disease exhibited control along suborthogonal directions that notably diverged from the AP and ML axes. While older adults and those with Parkinson’s disease demonstrated a similar reduction in the angle between these two control directions compared to healthy older adults, their reliance on this suborthogonal angle concerning endogenous fractal correlations exhibited significant differences from the healthy aging cohort. Importantly, individuals with Parkinson’s disease did not manifest the sensitivity to destabilizing task settings observed in their healthy counterparts, affirming the distinction between Parkinson’s disease and healthy aging.

The impact of external perturbations on postural control

Purpose External factors can disrupt postural control, but the intricate workings of the postural control system enable an appropriate response. This study seeks to assess how external perturbations affect postural control. Methods Twenty women participated in study, which consisted four trials involved quiet standing and experiencing induced perturbations by being struck with a boxing bag from the back, right, and left sides, respectively. The center of pressure (CoP) path length was recorded for each of the mentioned trials. Sample Entropy (SampEn), Lyapunov Exponent (LyE), and Fractal Dimension (FD) were computed for the CoP time series, separately for the anterior-posterior (AP) and mediolateral (ML) directions. The nonparametric Friedman ANOVA with Dunn-Bonferroni post-hoc analysis was employed to investigate the influence of external perturbations on both linear and nonlinear parameters on postural control. Results The post-hoc analysis showed for LyE_AP_quiet (1.02 ± 0.18) significantly higher values than for LyE_AP_right (0.92 ± 0.22) and significantly higher for LyE_AP_left. Lyapunov Exponent was the parameter that differentiated the most between samples. Conclusions The greatest number of significant differences between samples were demonstrated by the Lyapunov Exponent. This nonlinear parameter should be used to evaluate various perturbations during upright position in healthy subjects.

Using the center of pressure movement analysis in evaluating spontaneous movements in infants: a comparative study with general movements assessment

BackgroundResearchers have attempted to automate the spontaneous movement assessment and have sought quantitative and objective methods over the past decade. The purpose of the study was to present a quantitative assessment method of spontaneous movement using center-of-pressure (COP) movement analysis.MethodsA total of 101 infants were included in the study. The infants were placed in the supine position on the force plate with the cranial-caudal orientation. In this position, the recording of video and COP movement data were made simultaneously for 3 min. Video recordings were used to observe global and detailed general movement assessment (GMA), and COP time series data were used to obtain quantitative movement parameters.ResultsAccording to the global GMA, 13 infants displayed absent fidgety movements (FMs) and 88 infants displayed normal FMs. The binary logistic regression model indicated significant association between global GMA and COP movement parameters (chi-square = 20.817, p < 0.001). The sensitivity, specificity, and overall accuracy of this model were 85% (95% CI: 55–98), 83% (95% CI: 73–90), and 83% (95% CI: 74–90), respectively. The multiple linear regression model showed a significant association between detailed GMA (motor optimality score-revised/MOS-R) and COP movement parameters (F = 10.349, p < 0.001). The MOS-R total score was predicted with a standard error of approximately 1.8 points (6%).ConclusionsThe present study demonstrated the possible avenues for using COP movement analysis to objectively detect the absent FMs and MOS-R total score in clinical settings. Although the method presented in this study requires further validation, it may complement observational GMA and be clinically useful for infant screening purposes, particularly in clinical settings where access to expertise in observational GMA is not available.

DFA as a window into postural dynamics supporting task performance: does choice of step size matter?

Introduction: Detrended Fluctuation Analysis (DFA) has been used to investigate self-similarity in center of pressure (CoP) time series. For fractional gaussian noise (fGn) signals, the analysis returns a scaling exponent, DFA-α, whose value characterizes the temporal correlations as persistent, random, or anti-persistent. In the study of postural control, DFA has revealed two time scaling regions, one at the short-term and one at the long-term scaling regions in the diffusion plots, suggesting different types of postural dynamics. Much attention has been given to the selection of minimum and maximum scales, but the choice of spacing (step size) between the window sizes at which the fluctuation function is evaluated may also affect the estimates of scaling exponents. The aim of this study is twofold. First, to determine whether DFA can reveal postural adjustments supporting performance of an upper limb task under variable demands. Second, to compare evenly-spaced DFA with two different step sizes, 0.5 and 1.0 in log2 units, applied to CoP time series. Methods: We analyzed time series of anterior-posterior (AP) and medial-lateral (ML) CoP displacement from healthy participants performing a sequential upper limb task under variable demand. Results: DFA diffusion plots revealed two scaling regions in the AP and ML CoP time series. The short-term scaling region generally showed hyper-diffusive dynamics and long-term scaling revealed mildly persistent dynamics in the ML direction and random-like dynamics in the AP direction. There was a systematic tendency for higher estimates of DFA-α and lower estimates for crossover points for the 0.5-unit step size vs. 1.0-unit size. Discussion: Results provide evidence that DFA-α captures task-related differences between postural adjustments in the AP and ML directions. Results also showed that DFA-α estimates and crossover points are sensitive to step size. A step size of 0.5 led to less variable DFA-α for the long-term scaling region, higher estimation for the short-term scaling region, lower estimate for crossover points, and revealed anomalous estimates at the very short range that had implications for choice of minimum window size. We, therefore, recommend the use of 0.5 step size in evenly spaced DFAs for CoP time series similar to ours.

The 'Postural Rhythm' of the Ground Reaction Force during Upright Stance and Its Conversion to Body Sway-The Effect of Vision, Support Surface and Adaptation to Repeated Trials.

The ground reaction force (GRF) recorded by a platform when a person stands upright lies at the interface between the neural networks controlling stance and the body sway deduced from centre of pressure (CoP) displacement. It can be decomposed into vertical (VGRF) and horizontal (HGRF) vectors. Few studies have addressed the modulation of the GRFs by the sensory conditions and their relationship with body sway. We reconsidered the features of the GRFs oscillations in healthy young subjects (n = 24) standing for 90 s, with the aim of characterising the possible effects of vision, support surface and adaptation to repeated trials, and the correspondence between HGRF and CoP time-series. We compared the frequency spectra of these variables with eyes open or closed on solid support surface (EOS, ECS) and on foam (EOF, ECF). All stance trials were repeated in a sequence of eight. Conditions were randomised across different days. The oscillations of the VGRF, HGRF and CoP differed between each other, as per the dominant frequency of their spectra (around 4 Hz, 0.8 Hz and <0.4 Hz, respectively) featuring a low-pass filter effect from VGRF to HGRF to CoP. GRF frequencies hardly changed as a function of the experimental conditions, including adaptation. CoP frequencies diminished to <0.2 Hz when vision was available on hard support surface. Amplitudes of both GRFs and CoP oscillations decreased in the order ECF > EOF > ECS ≈ EOS. Adaptation had no effect except in ECF condition. Specific rhythms of the GRFs do not transfer to the CoP frequency, whereas the magnitude of the forces acting on the ground ultimately determines body sway. The discrepancies in the time-series of the HGRF and CoP oscillations confirm that the body's oscillation mode cannot be dictated by the inverted pendulum model in any experimental conditions. The findings emphasise the robustness of the VGRF "postural rhythm" and its correspondence with the cortical theta rhythm, shed new insight on current principles of balance control and on understanding of upright stance in healthy and elderly people as well as on injury prevention and rehabilitation.

Cortical potentials time-locked to discrete postural events during quiet standing are facilitated during postural threat exposure.

During unperturbed bipedal standing, postural control is governed primarily by subcortical and spinal networks. However, it is unclear if cortical networks begin to play a greater role when stability is threatened. This study investigated how initial and repeated exposure to a height-related postural threat modulates cortical potentials time-locked to discrete centre of pressure (COP) events during standing. Twenty-seven young adults completed a series of 90-s standing trials at LOW (0.8m above the ground, away from edge) and HIGH (3.2m above the ground, at edge) threat conditions. Three LOW trials were completed before and after 15 consecutive HIGH trials. Participants stood on a force plate while electroencephalographic (EEG) activity was recorded. To examine changes in cortical activity in response to discrete postural events, prominent forward and backward peaks in the anterior-posterior COP time series were identified. EEG data were waveform-averaged to these events and the amplitude of event-related cortical activity was calculated. At the LOW condition, event-related potentials (ERPs) were scarcely detectable. However, once individuals stood at the HIGH condition, clear ERPs were observed, with more prominent potentials being observed for forward (edge-directed), compared to backward, COP events. Since forward COP peaks accelerate the centre of mass away from the platform edge, these results suggest there is intermittent recruitment of cortical networks that may be involved in the detection and minimization of postural sway toward a perceived threat. This altered cortical engagement appears resistant to habituation and may contribute to threat-related balance changes that persist following repeated threat exposure. KEY POINTS: While standing balance control is regulated primarily by subcortical and spinal processes, it is unclear if cortical networks play a greater role when stability is threatened. This study examined how cortical potentials time-locked to prominent peaks in the anterior-posterior centre of pressure (COP) time series were modulated by exposure to a height-related postural threat. While cortical potentials recorded over the primary sensorimotor cortices were scarcely detectable under non-threatening conditions, clear cortical potentials were observed when individuals stood under conditions of height-related threat. Cortical potentials were larger in response to COP peaks directed toward, compared to away from, the platform edge, and showed limited habituation with repeated threat exposure. Since forward COP peaks accelerate the centre of mass away from the platform edge, these findings suggest that when balance is threatened, there is intermittent recruitment of cortical networks, which may minimize the likelihood of falling in the direction of a perceived threat.

Multiscale Fuzzy Entropy Analysis of Balance: Evidences of Scale-Dependent Dynamics on Diabetic Patients With and Without Neuropathy.

Postural control is usually assessed by examining the fluctuations of the center of pressure (COP). Balance maintenance is based on sensory feedback and neural interactions, deployed over multiple temporal scales and producing less complex outputs with aging and disease. This paper aims to investigate postural dynamics and complexity on diabetic patients, since diabetic neuropathy (DN) affects the somatosensory system and impairs postural steadiness. A multiscale fuzzy entropy (MSFEn) analysis, over a wide range of temporal scales, was performed on COP timeseries during unperturbed stance in a group of diabetic individuals without neuropathy and two groups of DN patients, with and without symptoms. A parameterization of the MSFEn curve is also proposed. A significant loss of complexity was recognized for the medial-lateral direction in DN groups with respect to non-neuropathic population. For the anterior-posterior direction, symptomatic DN group showed a lowered sway complexity for longer time scales with respect to non neuropathic and asymptomatic patients. The MSFEn approach and the related parameters highlighted that the loss of complexity might be attributed to different factors depending on sway direction, i.e. related to the presence of neuropathy along the medial-lateral axis and to a symptomatic state on the anterior-posterior direction. Results of this study support the use of the MSFEn for gaining insights into balance control mechanisms for diabetic patients, in particular when comparing non neuropathic with neuropathic asymptomatic patients, whose identification by posturographic analysis would be of great value.

The Impact of Hoffmann Reflex on Standing Postural Control Complexity in the Elderly with Impaired Plantar Sensation

In people with peripheral neuropathy (PN), impaired plantar sensation can cause adaptive changes in the central nervous system (CNS), resulting in changes in the standing postural control, which is reflected in the variability of standing output signals. Standard deviation (SD) and entropy are reliable indicators of system variability, especially since entropy is highly sensitive to diseased populations. The relation between SD and entropy, CNS and center of pressure (COP) variability is unclear for people with severe PN. The purpose of this study was to explore the adaptability of the CNS to the severe of PN and its effect on the degree and complexity of COP variability. Here, people with PN were divided into less affected (LA) and more affected (MA) groups based on plantar pressure sensitivity. We studied Hoffmann reflex (H-reflex) and standing balance performance with the control group (n = 8), LA group (n = 10), and MA group (n = 9), recording a 30 s COP time series (30,000 samples) of double-leg standing with eyes open. We observed that the more affected group had less COP complexity than people without PN. There is a significant negative correlation between the SD and sample entropy in people without PN, less affected and more affected. The COP complexity in people without PN was inversely correlated with H-reflex. We concluded that: (1) The complexity of COP variability in patients with severe plantar sensory impairment is changed, which will not affect the degree of COP variability; (2) The independence of the COP entropy in the AP and ML directions decreased, and the interdependence increased in people with PN; (3) Although the CNS of people with PN has a greater contribution to standing balance, its modulation of standing postural control is decreased.

The effect of ageing on between-limb centre of pressure coordination in standing balance: Is there evidence for reactive control challenges among older adults?

Interlimb temporal synchrony and spatial symmetry of centre of pressure (COP) displacements may be vital contributors to standing balance control. In previous work among stroke survivors, low-frequency COP displacements (< 0.4 Hz) were proposed to arise from centre of mass (COM) dynamics, or from proactive exploratory processes. COP displacements among higher frequencies (>0.4 Hz), in contrast, have been attributed to corrective balance responses to internal perturbations. The present study extends this work to explore age-related alterations in such stability control processes during standing balance. The combined COP displacements from both limbs (COPnet) in addition to individual-limb COP timeseries were calculated from synchronous force platform data obtained from 19 younger adults and 19 older adults during a 60 s trial of quiet standing. The discrete wavelet transform was used to decompose the anteroposterior and mediolateral COPnet, in addition to the individual-limb timeseries, into low-frequency and high-frequency bandwidths. Root-mean-squared (RMS) amplitudes of high- and low-frequency COPnet displacements were calculated. The cross-correlation coefficient was used to assess the extent of between-limb temporal synchronization, while the ratio of individual-limb RMS amplitudes was used to assess between-limb spatial symmetry within each high- and low-frequency bandwidth. We observed greater high-frequency anteroposterior COPnet displacements among older adults, without age related differences in the lower frequency bandwidth or in the mediolateral direction. Further, older adults exhibited greater high-frequency anteroposterior between-limb synchronization, without age-related differences in the low frequency bandwidth, or among any of the spatial symmetry variables. The present age-related alterations in COPnet could represent a conservative strategy to ensure stability, whereby age-related challenges in stability maintenance during standing are offset by greater demands on stability control. Further, increased high frequency between-limb temporal synchronization among older adults may suggest a loss of adaptability in balance corrective responses during standing.

Comparison of Postural Control of Females with and without Urinary Incontinence: A Case-Control Study.

Background: So far, there is much less information about the effects of urinary incontinence on postural control. Therefore the aim of this study is to investigate the differences in postural control using linear and non-linear analyses of the center of pressure (COP) time-series in anteroposterior (AP) and mediolateral (ML) directions between females with and without stress urinary incontinence (SUI). Methods: This case-control study included 22 continent females and 22 SUI females. In this study, static postural control during four different postural tasks was evaluated using a force plate. All participants performed separate 60-sec standing trials with eyes open in the empty bladder and full bladder conditions. Mean, range, velocity, area circle of COP displacements, and approximate entropy (ApEn) of COP time-series were calculated from the 60-sec standing trials for all participants. The independent sample t-test was also used to compare COP variables between the two groups and paired sample t-test was used to assess changes between the full bladder and empty bladder conditions within each group. The effect size of Cohen's d was used to assess the magnitude of the differences between the two groups. Results: The findings revealed a significant group × task interaction for the mean of ML displacement and ApEn of COP. SUI females showed more AP displacement range in the full bladder (pvalue= 0.020, effect size=0.74) and a higher velocity (empty bladder: p=0.040, effect size=0.63) (full bladder: p=0.020, effect size=0.75) than the continent group. Generally, the SUI females had lower ApEn than the continent females, although the differences were not significant. While the variables of COP were unaffected by bladder fullness in the continent group, the SUI group in full bladder condition experienced more AP range (p=0.030), and area circle (p=0.007) of COP sway in quiet standing. Conclusion: These results provide more support for the hypothesis that postural control can be impaired following SUI, although future investigations on this topic are recommended.

Effects of light finger touch on the regularity of center-of-pressure fluctuations during quiet bipedal and single-leg postural tasks

BackgroundThe use of extra sources of sensory information associated with light fingertip touch to enhance postural steadiness has been associated with increased attentional demands, whereas the regularity of center of pressure (COP) fluctuations has been interpreted as a marker of the amount of attention invested in posture control. Research questionThis study addressed whether increased attentional demands associated with postural tasks involving light finger touch might be reflected by measures of COP regularity. MethodsThe experiments involved quiet bipedal stance (n = 8 participants) and single-legged stance (n = 14 participants). Each participant was instructed to stand as quietly as possible on a force plate, either touching an external rigid surface (applied force < 1 N, light touch condition), or not (no touch condition). Postural steadiness was assessed by traditional COP measurements (COP Area, RMS, and velocity), whereas the regularity of postural sway was based on estimates of the sample entropy (SaEn) of the COP time series. ResultsTraditional parameters of postural sway and COP regularity (inversely related to SaEn COP measurements) were reduced during the touch conditions as compared to the no-touch conditions, for both bipedal quiet stance and single-legged stance. Decreased COP regularity with light touch was mainly reflected in the direction of the largest postural sway (i.e. in the sagittal plane for bipedal stance and in the frontal plane for single-legged stance). SignificanceThe present results suggest that actively touching an external surface with the fingertip, besides increasing postural steadiness, generated an externally oriented (presumably cognitive-dependent) focus of attention, so that participants invested less attention on the postural task per se (as suggested by increased SaEn), which might be associated with a more “automatic” control of posture.

The effect of a light finger touch on the signal complexity during quiet standing

Purpose The purpose of the study was to investigate the influence of additional tactile information (light fingertip touch) on the postural sway and regularity of center-of-pressure (COP) fluctuations. Methods Thirty-two young, healthy participants performed a quiet standing task (30s) on a force platform with and without light touch. COP time-series were analyzed using standard postural sway measures (range, root mean square error, velocity), COP regularity was measured with Sample entropy. Results Participants demonstrated significantly smaller postural sway with a light touch, but only in the anteroposterior direction. The amount of sway with additional tactile information in the sagittal plane reached the level of sway in the frontal plane without this information. Similarly, COP fluctuations were more irregular during light touch condition only in the anteroposterior direction, as evidenced by significantly higher Sample entropy. Furthermore, COP regularity decreased in the sagittal plane and reached level in the frontal plane without light touch. Conclusions These results suggest that postural sway is mostly controlled in the sagittal plane and that in the mediolateral direction the control is mostly automated. In conclusion, our results support the notion that the light touch provides additional information which enhances postural stabilization. Our results expand the relation between COP regularity and the attention invested in posture in the touch domain and prove that light touch, as an attentional demanding task, leads to increased COP irregularity. Nonlinear measures of signal regularity (i.e. SampEn) provide surplus insight into human postural control and can be used as an useful tool to traditional balance measures.

Long term correlation and inhomogeneity of the inverted pendulum sway time-series under the intermittent control paradigm

In this study the extended detrended fluctuation analysis (EDFA) was applied to the sway data generated from an inverted pendulum (IP) model, intermittently controlled at the ankle. The time series taken into account was the center of pressure (COP), since it represents the widest used time series in posturography, and it constitutes a natural link between model and data-based analysis approaches for studying the dynamics of the human balance maintenance. COP time-series were obtained by varying the intermittent control parameters (ICP) in a uniform distribution range that ensures IP stability to quantify changes in the long-term correlation and inhomogeneity of the time-series. Globally, EDFA coefficients (α and β) showed to be sensitive to the variations of derivative control gain (D), whereas for proportional gain (P) and ρ parameters no significant trends were observed. However, relations between EDFA coefficients and ρ arose whether derivative gain is examined within a low and high regions of value. For low D gains, both α and β showed a significant correlation with ρ, which disappears when higher D values were considered. Thus EDFA coefficients can provide useful insights about the long-term correlation and local characteristics of COP timeseries, which are strictly related to the control policy adopted for maintaining balance. This supports the validity of the intermittent motor control paradigm for the human upright stance and suggests the use of EDFA in real posturography applications, in order to extract meaningful information regarding the properties of COP timeseries for different groups of patients.

Rambling-trembling center-of-pressure decomposition reveals distinct sway responses to simulated somatosensory deficit

BackgroundFalls in older adults are often multifactorial, but can be linked to diminished sensation capabilities from age-related neural degeneration. Rambling-trembling (RM-TR) decomposition may provide insight into the relation between sensorineural function and postural sway, with both research and clinical applications. Research questionWhat are the effects of perturbed somatosensation on RM-TR-derived measures of center of pressure (COP) during quiet standing? MethodsFifty-two healthy young adults (22.10 ± 1.88 years) participated in the study. Participants stood on two force plates with a standardized stance width and foot angle, with eyes open (EO) or eyes closed (EC). Foam with different thicknesses ranging from 1/8″ to 1″ (F1-F4) was placed under the feet to interfere with intact sensory input and simulate varying degrees of somatosensory deficit. Force and moment data were used to calculate COP, RM, and TR time series. Mean velocity, acceleration, and jerk in the anteroposterior (AP) and mediolateral direction (ML) were extracted for comparison. ResultsThe EO condition remained relatively constant regardless of foam thickness. The EC condition showed increasing changes from baseline to each of the foam conditions. COP captures the smallest change in foam thickness, but RM provides a robustness across parameters that is not found in COP or TR. RM jerk in the AP direction showed significantly greater changes from baseline to F4 than the COP or TR counterparts. In the ML direction, TR jerk showed a sharper contrast between foam conditions than COP and RM. SignificanceFindings suggest that RM-TR-derived measures may act as a compliment to, or provide a greater degree of sensitivity than, traditional COP measures and aid in the initial detection and monitoring of fall risk in aging and pathological populations.

Low Back Pain Exacerbation Is Predictable Through Motif Identification in Center of Pressure Time Series Recorded During Dynamic Sitting.

Background: Low back pain (LBP) is a common health problem — sitting on a chair for a prolonged time is considered a significant risk factor. Furthermore, the level of LBP may vary at different times of the day. However, the role of the time-sequence property of sitting behavior in relation to LBP has not been considered. During the dynamic sitting, small changes, such as slight or big sways, have been identified. Therefore, it is possible to identify the motif consisting of such changes, which may be associated with the incidence, exacerbation, or improvement of LBP.Method: Office chairs installed with pressure sensors were provided to a total of 22 office workers (age = 43.4 ± 8.3 years) in Japan. Pressure sensors data were collected during working days and hours (from morning to evening). The participants were asked to answer subjective levels of pain including LBP. Center of pressure (COP) was calculated from the load level, the changes in COP were analyzed by applying the Toeplitz inverse covariance-based clustering (TICC) analysis, COP changes were categorized into several states. Based on the states, common motifs were identified as a recurring sitting behavior pattern combination of different states by motif-aware state assignment (MASA). Finally, the identified motif was tested as a feature to infer the changing levels of LBP within a day. Changes in the levels of LBP from morning to evening were categorized as exacerbated, did not change, or improved based on the survey questions. Here, we present a novel approach based on social spider algorithm (SSA) and probabilistic neural network (PNN) for the prediction of LBP. The specificity and sensitivity of the LBP inference were compared among ten different models, including SSA-PNN.Result: There exists a common motif, consisting of stable sitting and slight sway. When LBP level improved toward the evening, the frequency of motif appearance was higher than when LBP was exacerbated (p < 0.05) or the level did not change. The performance of the SSA-PNN optimization was better than that of the other algorithms. Accuracy, precision, recall, and F1-score were 59.20, 72.46, 40.94, and 63.24%, respectively.Conclusion: A lower frequency of a common motif of the COP dynamic changes characterized by stable sitting and slight sway was found to be associated with the exacerbation of LBP in the evening. LBP exacerbation is predictable by AI-based analysis of COP changes during the sitting behavior of the office workers.

Effects of additional load at different heights on gait initiation: A statistical parametric mapping of center of pressure and center of mass behavior.

The purpose of this study was to investigate the effects of different vertical positions of an asymmetrical load on the anticipatory postural adjustments phase of gait initiation. Sixty-eight college students (32 males, 36 females; age: 23.65 ± 3.21 years old; weight: 69.98 ± 8.15 kg; height: 1.74 ± 0.08 m) were enrolled in the study. Ground reaction forces and moments were collected using two force platforms. The participants completed three trials under each of the following random conditions: no-load (NL), waist uniformly distributed load (WUD), shoulder uniformly distributed load (SUD), waist stance foot load (WST), shoulder stance foot load (SST), waist swing foot load (WSW), and shoulder swing foot load (SSW). The paired Hotelling's T-square test was used to compare the experimental conditions. The center of pressure (COP) time series were significantly different for the SUD vs. NL, SST vs. NL, WST vs. NL, and WSW vs. NL comparisons. Significant differences in COP time series were observed for all comparisons between waist vs. shoulder conditions. Overall, these differences were greater when the load was positioned at the shoulders. For the center of mass (COM) time series, significant differences were found for the WUD vs. NL and WSW vs. NL conditions. However, no differences were observed with the load positioned at the shoulders. In conclusion, only asymmetrical loading at the waist produced significant differences, and the higher the extra load, the greater the effects on COP behavior. By contrast, only minor changes were observed in COM behavior, suggesting that the changes in COP (the controller) behavior are adjustments to maintain the COM (controlled object) unaltered.

An interventional exploratory study to assess the effect of footwear on postural stability and strategy during quiet standing

ABSTRACT A stable quiet stance is achieved by controlling the relative position of the center of pressure and the vertical projection of the center of mass. The best postural performances include efficient strategies to mitigate external perturbations. Footwear impacts postural stability and strategy by affecting cutaneous proprioception and ankle proprioception in the case of heeled shoes. The purpose of this study was to quantify the effects of four common footwear conditions, i.e. barefoot, sports, flats, and heels, on postural stability and strategy during quiet standing of healthy young women. Postural stability and strategy were assessed overall and in the antero-posterior and medio-lateral directions using five parameters: total sway, average center of pressure (COP) velocity, α value computed using detrended fluctuation analysis, hip over ankle ranges of motion, and power of the COP time series. Significant differences with barefoot were consistently found when wearing heels, namely a decrease in postural sway and average COP velocity. Results seemed counter-intuitive as they indicate an apparent increase in postural stability when wearing heels. A deeper analysis revealed a more complex scheme. A potential tightening of the motion when wearing heels, combined with an increase of the neutral plantarflexion angle, shifts the postural strategy towards a predominant hip strategy. Finally, proprioception did not play a key role. This study highlighted the complexity of the multifactorial interactions between footwear characteristics and postural strategies. Additional work is needed to develop footwear that will enhance postural stability of populations at risk, such as pregnant women or the elderly.

Difference of static postural balance in patients with Parkinson's Disease and scans without evidencec of dopaminergic deficits

Differentiating scans without evidence of dopaminergic deficit (SWEDD) from Parkinson's disease (PD) is very important to avoid costly and inappropriate interventions. Little is known of postural balance strategy of SWEDD patients. The purpose of this study was investigate difference of static postural balance between SWEDD and PD patients. Eleven patients with SWEDD, 11 patients with PD and normal subjects were instructed to quietly stand on a force plate in a comfortable self selected stance width. Center of pressure (COP) was measured for quantitative evaluation during static standing. As outcome measure, mean distance, mean velocity, 95% confidence ellipse area, mean frequency, peak frequency and peak power were derived from the COP time series in overall, anterio-posterior (AP) and medio-lateral (ML) directions. ANOVA and post hoc test were evaluated for comparison between SWEDD patients and PD patients. SWEDD patients presented a smaller postural sway size and a more frequent postural sway manly in ML direction (p< 0.05). In contrast, there was no significant differences in mean velocity and peak power (p>0.05). There were no significant difference between SWEDD patients and normal subjects (p>0.05). These results indicate that some COP-based outcome variables might be useful to distinguish SWEDD patients with PD patients. This study suggests that static postural balance test could aid clinicians in the identification of potential SWEDD.