The assessment of center of mass and center of pressure during quiet stance: Current applications and future directions

Postural behaviour in people with multiple sclerosis: A complexity paradox

BACKGROUND

Balance deficits are a major concern for people with multiple sclerosis (pwMS). Measuring complexity of motor behaviour can offer an insight into MS-related changes in adaptability of the balance control system when dealing with increasingly complex tasks.

QUESTION

Does postural behaviour complexity differ between pwMS at early stages of the disease and healthy controls (HC)? Does postural behaviour complexity change across increasingly complex tasks?

METHODS

Forty-eight pwMS and 24 HC performed four increasingly complex postural tasks with eyes open (EO), eyes closed (EC), on firm (FS) and compliant surface (CS). Lumbar and sternum sensors recorded 3D acceleration, from which complexity index (CI) was calculated using multiscale sample entropy (MSE) in the frontal and sagittal planes.

RESULTS

We found that only the complexity index in both planes during the eyes closed on compliant surface (EC-CS) task was significantly lower in pwMS compared to HC. We also found that complexity in pwMS was significantly lower during EC-CS compared to the other three tasks when using both lumbar and sternum sensors.

SIGNIFICANCE

Increasing the complexity of postural tasks reduces the complexity of postural behaviour in pwMS. This paradox may reflect reduced adaptability of the sensorimotor integration processes at early stages of MS. CI can provide a different perspective on balance deficits and could potentially be a more sensitive biomarker of MS progression and an early indicator of balance deficit.

A static posturography guide to implementing time-to-boundary

The emergence of time-to-boundary provides an advanced representation of the spatiotemporal characteristics of postural control through the estimation of the time required for the center of pressure to reach the boundary of the base of support. Time-to-boundary has demonstrated its utility in several healthy and clinical adoptions; however, unknown inconsistencies among studies exist. Text and graphical representations understandably highlight idealistic standards, but new investigators to this measure are forced to wade through the same potential pitfalls that others have addressed, but the field has neglected to concatenate. The purpose of this communication is to share recent methodological advancements made to enhance time-to-boundary and describe the components of the time-to-boundary code that is being made publicly accessible for the first time. We anticipate future researchers who wish to apply this methodology to their data processing toolbox could utilize our script in full, with any deviations in potential future developments noted in clear fashion. Historically, researchers (including ourselves) have had to interpret text-based descriptions of the existing literature into quantitative steps in a computational mathematics script. In contrast to fixed process measures that do not require investigator input (e.g., path length), time-to-boundary poses two distinct but connected challenges to investigators. The coding process itself can be a hurdle for novices or practitioners. Second, transferring logical considerations such as robust, objective event detection routines must be defended in the review process. This comprehensive guide to time-to-boundary, as used in our applications, should enhance adoption and advance the comprehension of postural control.

One-leg standing time is a simple measure for loss of skeletal muscle mass and fat deposition in muscle: the J-SHIPP study

BACKGROUNDS

One-leg standing time (OLST) has been frequently used physical performance measure; however, what muscular characteristics OLST represents remains uncertain.

AIM

This cross-sectional study aimed to investigate the association between OLST and muscle characteristics to clarify the possibility of using OLST as a physical performance measure.

METHODS

Study participants comprised 1144 older adults aged 65 years or older. Computed tomography images provided mid-thigh skeletal muscle cross-sectional area and mean attenuation value. OLST was measured for a maximum of 60 s. Static postural instability was assessed using a posturography.

RESULTS

A frequency of OLST < 20 s was increased by quartiles of muscle cross-sectional area (Q1: 33.6, Q2: 12.8, Q3: 13.6, Q4: 11.9%, P < 0.001) and mean attenuation value (Q1: 32.3, Q2: 21.7, Q3: 14.3, Q4: 7.7%, P < 0.001). Results of the multinomial regression analysis indicated that muscle cross-sectional area and mean attenuation value were independently associated with an OLST of less than 20 s. The crude odds ratio of OLST less than 20 s for the lowest quartiles of both cross-sectional area and mean attenuation value was 4.19 (95% CI: 3.01 - 5.84). The cross-sectional area of muscles with greater fat deposition was inversely associated with OLST, while that with smaller fat deposition showed a positive association with OLST, indicating why mean attenuation value and cross-sectional area were independently associated with OLST. No clear relationship was observed with static postural instability.

CONCLUSION

OLST was a simply measurable quantifiable physical measure representing the loss of muscle mass and quality in older adults.

Effect of test duration and sensor location on the reliability of standing balance parameters derived using body-mounted accelerometers

BACKGROUND

Balance parameters derived from wearable sensor measurements during postural sway have been shown to be sensitive to experimental variables such as test duration, sensor number, and sensor location that influence the magnitude and frequency-related properties of measured center-of-mass (COM) and center-of-pressure (COP) excursions. In this study, we investigated the effects of test duration, the number of sensors, and sensor location on the reliability of standing balance parameters derived using body-mounted accelerometers.

METHODS

Twelve volunteers without any prior history of balance disorders were enrolled in the study. They were asked to perform two 2-min quiet standing tests with two different testing conditions (eyes open and eyes closed). Five inertial measurement units (IMUs) were employed to capture postural sway data from each participant. IMUs were attached to the participants' right legs, the second sacral vertebra, sternum, and the left mastoid processes. Balance parameters of interest were calculated for the single head, sternum, and sacrum accelerometers, as well as, a three-sensor combination (leg, sacrum, and sternum). Accelerometer data were used to estimate COP-based and COM-based balance parameters during quiet standing. To examine the effect of test duration and sensor location, each 120-s recording from different sensor locations was segmented into 20-, 30-, 40-, 50-, 60-, 70-, 80-, 90-, 100-, and 110-s intervals. For each of these time intervals, time- and frequency-domain balance parameters were calculated for all sensor locations.

RESULTS

Most COM-based and COP-based balance parameters could be derived reliably for clinical applications (Intraclass-Correlation Coefficient, ICC ≥ 0.90) with a minimum test duration of 70 and 110 s, respectively. The exceptions were COP-based parameters obtained using a sacrum-mounted sensor, especially in the eyes-closed condition, which could not be reliably used for clinical applications even with a 120-s test duration.

CONCLUSIONS

Most standing balance parameters can be reliably measured using a single head- or sternum-mounted sensor within a 120-s test duration. For other sensor locations, the minimum test duration may be longer and may depend on the specific test conditions.

Posturography Approaches: An Insightful Window to Explore the Role of the Brain in Socio-Affective Processes

A significant amount of research has highlighted the importance of a motor component in the brain's processing of emotional, motivational and social information. Posturography has emerged as an interesting way to assess motor correlates associated with this process. In this review, we highlight recent results within the functional context of painful stimulus perception and discuss the interest in broadening the use of posturography to other motivational and societal functional contexts. Although characterized by significant feasibility, the single measurement of the COP's anteroposterior displacement presents limitations for attesting approach-avoidance behavior towards a visual target. Here, we discuss a number of methodological avenues that could go some way towards overcoming these limitations.

Clinical Static Balance Assessment: A Narrative Review of Traditional and IMU-Based Posturography in Older Adults and Individuals with Incomplete Spinal Cord Injury

Maintaining a stable upright posture is essential for performing activities of daily living, and impaired standing balance may impact an individual's quality of life. Therefore, accurate and sensitive methods for assessing static balance are crucial for identifying balance impairments, understanding the underlying mechanisms of the balance deficiencies, and developing targeted interventions to improve standing balance and prevent falls. This review paper first explores the methods to quantify standing balance. Then, it reviews traditional posturography and recent advancements in using wearable inertial measurement units (IMUs) to assess static balance in two populations: older adults and those with incomplete spinal cord injury (iSCI). The inclusion of these two groups is supported by their large representation among individuals with balance impairments. Also, each group exhibits distinct aspects in balance assessment due to diverse underlying causes associated with aging and neurological impairment. Given the high vulnerability of both demographics to balance impairments and falls, the significance of targeted interventions to improve standing balance and mitigate fall risk becomes apparent. Overall, this review highlights the importance of static balance assessment and the potential of emerging methods and technologies to improve our understanding of postural control in different populations.

The Three-Dimensional Body Center of Mass at the Workplace under Hypogravity

The center of mass dynamics of the seated posture of humans in a work environment under hypogravity (0 < g < 1) have rarely been investigated, and such research is yet to be carried out. The present study determined the difference in the body system of 32 participants working under simulated 1/6 g (Moon) and 1 g (Earth) for comparison using static and dynamic task measurements. This was based on a markerless motion capture method that analyzed participants' center of mass at the start, middle and end of the task when they began to get fatigued. According to this analysis, there is a positive relationship (p < 0.01) with a positive coefficient of correlation between the downward center of mass body shift along the proximodistal axis and gravity level for males and females. At the same time, the same positive relationship (p < 0.01) between the tilt of the body backward along the anterior-posterior axis and the level of gravity was found only in females. This offers fresh perspectives for comprehending hypogravity in a broader framework regarding its impact on musculoskeletal disorders. It can also improve workplace ergonomics, body stability, equipment design, and biomechanics.

Rollator usage lets young individuals switch movement strategies in sit-to-stand and stand-to-sit tasks

The transitions between sitting and standing have a high physical and coordination demand, frequently causing falls in older individuals. Rollators, or four-wheeled walkers, are often prescribed to reduce lower-limb load and to improve balance but have been found a fall risk. This study investigated how rollator support affects sit-to-stand and stand-to-sit movements. Twenty young participants stood up and sat down under three handle support conditions (unassisted, light touch, and full support). As increasing task demands may affect coordination, a challenging floor condition (balance pads) was included. Full-body kinematics and ground reaction forces were recorded, reduced in dimensionality by principal component analyses, and clustered by k-means into movement strategies. Rollator support caused the participants to switch strategies, especially when their balance was challenged, but did not lead to support-specific strategies, i.e., clusters that only comprise light touch or full support trials. Three strategies for sit-to-stand were found: forward leaning, hybrid, and vertical rise; two in the challenging condition (exaggerated forward and forward leaning). For stand-to-sit, three strategies were found: backward lowering, hybrid, and vertical lowering; two in the challenging condition (exaggerated forward and forward leaning). Hence, young individuals adjust their strategy selection to different conditions. Future studies may apply this methodology to older individuals to recommend safe strategies and ultimately reduce falls.

Characterizing postural balance on 2-dimensional compliant surfaces with directional virtual time-to-contact

BACKGROUND

This study aimed to (1) investigate postural balance control on 2-Dimensional (2D) compliant surfaces using directional virtual time-to-contact (d-VTC), a novel method for VTC calculation; and (2) compare d-VTC with conventional balance measures in this context.

METHODS

A dual-axis robotic platform was used to simulate 2D surfaces/grounds with varying compliance levels. Twenty healthy young adults stood on the platform with either open or closed eyes. Balance was evaluated using d-VTC in multiple aspects, including temporal (VTC mean), spatial (boundary contact - BC), and control aspects (switching rate - SR). Additionally, conventional balance measures, namely center-of-pressure (COP) area and COP root-mean-square (RMS), were employed for further comparisons with d-VTC measures. Normality checks were performed using Shapiro-Wilk tests. Two-way repeated measures ANOVA tests were used to examine the effects of surface compliance and vision on postural balance, followed by post-hoc pairwise comparisons across conditions with Bonferroni correction.

RESULTS

The results showed that increasing surface compliance and/or absence of vision caused a significant decrease in VTC mean (all p-values <0.001; all ηp2 > 0.816). Interaction effects between surface compliance and vision on 2D and ML VTC mean were also significant (all p-values <0.019; all ηp2 > 0.355). The AP and ML BC values indicated a converging trend to 50%. No vision effect was observed (p = 0.458), but both surface compliance (p = 0.001; ηp2 = 0.522) and interaction (p = 0.002; ηp2 = 0.492) effects were significant. Decreases in SR were significant due to the compliance of the standing surface (p = 0.01; ηp2 = 0.401) but not vision (p = 0.109). COP area increased due to both surface and vision conditions (all p-values <0.001; all ηp2 > 0.872). AP and ML RMS were altered by vision (all p-values <0.001; all ηp2 > 0.741), but not by surface condition (all p-values >0.06). No interaction effect was observed in the conventional measures (all p-values >0.07).

CONCLUSION

Balance control is compromised by 2D compliant surfaces, which is exacerbated when vision is absent. Among all balance measures, VTC mean measures demonstrated particularly high sensitivity in identifying decreased balance capabilities, while BC and SR provided new insights into fall risks and balance control mechanisms. These insights may facilitate the development of rehabilitation training or assistive devices for fall prevention.

Postural stability measures in healthy miniature Dachshunds obtained using a pressure mat and a force platform: a validity and reliability study

BACKGROUND

Miniature Dachshunds have a high prevalence of neurological and musculoskeletal diseases potentially affecting their balance. The postural stability of dogs in quiet standing is an indicator of postural control and can aid in diagnosing and monitoring lameness and other pathologies affecting balance. Measures of centre of pressure (CoP) can be obtained from force and pressure platform systems to evaluate postural stability, however the two systems have not been compared and the latter has not been validated in dogs. The aims of this study were to assess the validity and reliability of using a pressure mat compared to a force platform and report normative values of CoP measures in healthy miniature Dachshunds. Forty two healthy miniature Dachshunds of smooth, long and wire-haired breed types stood still on a pressure mat (Tekscan MatScan®) placed on a force platform and the two systems were synchronised. Maximum anterior-posterior (AP) and medial-lateral (ML) ranges, sway path and 95% area of a best-fit ellipse were computed. Bland-Altman plots and coefficients of correlation assessed validity; intra-class correlation coefficients (ICC) assessed inter-test reliability for both systems. Non-linear regression analyses were used to describe the relationship between CoP and demographic measures.

RESULTS

Strong correlations for AP range, ML range and 95% ellipse area and moderate correlation for sway path were found between the two devices. ICC showed good reliability (0.75-0.90) for AP range and moderate (0.5-0.75) for ML range and the 95% ellipse area for both devices. Sway path reliability was excellent (> 0.90) with the force platform but moderate with the pressure mat. Age was positively correlated with balance (inversely correlated with all measures except sway path), while weight explained 94% (force platform) and 27% (pressure mat) of the variance in sway path.

CONCLUSIONS

Pressure mats can be used to obtain valid and reliable measures of CoP and replace use of force platforms. Older (non-senior) and heavier (non-obese) dogs show better postural stability. Clinical examinations should include the use of a range of CoP measures when assessing postural balance, while accounting for the effects of age and body weight.

Effects of jaw clenching on dynamic reactive balance task performance after 1-week of jaw clenching training

Introduction

Good balance is essential for human daily life as it may help to improve the quality of life and reduce the risk of falls and associated injuries. The influence of jaw clenching on balance control has been shown under static and dynamic conditions. Nevertheless, it has not yet been investigated whether the effects are mainly associated with the dual-task situation or are caused by jaw clenching itself. Therefore, this study investigated the effects of jaw clenching on dynamic reactive balance task performance prior to and after 1 week of jaw clenching training. It was hypothesized that jaw clenching has stabilizing effects resulting in a better dynamic reactive balance performance, and these effects are not related to dual-task benefits.

Methods

A total of 48 physically active and healthy adults (20 women and 28 men) were distributed into three groups, one habitual control group (HAB) and two jaw clenching groups (JAW and INT) that had to clench their jaws during the balance tasks at T1 and T2. One of those two groups, the INT group, additionally practiced the jaw clenching task for 1 week, making it familiar and implicit at T2. The HAB group did not receive any instruction regarding jaw clenching condition. Dynamic reactive balance was assessed using an oscillating platform perturbed in one of four directions in a randomized order. Kinematic and electromyographic (EMG) data were collected using a 3D motion capture system and a wireless EMG system, respectively. Dynamic reactive balance was operationalized by the damping ratio. Furthermore, the range of motion of the center of mass (CoM) in perturbation direction (RoM_{CoM_AP} or RoM_{CoM_ML}), as well as the velocity of CoM (V_CoM) in 3D, were analyzed. The mean activity of the muscles relevant to the perturbation direction was calculated to investigate reflex activities.

Results

The results revealed that jaw clenching had no significant effects on dynamic reactive balance performance or CoM kinematics in any of these three groups, and the automation of jaw clenching in the INT group did not result in a significant change either. However, high learning effects, as revealed by the higher damping ratio values and lower V_CoM at T2, were detected for the dynamic reactive balance task even without any deliberate balance training in the intervention phase. In the case of backward perturbation of the platform, the soleus activity in a short latency response phase increased for the JAW group, whereas it decreased for HAB and INT after the intervention. In the case of forward acceleration of the platform, JAW and INT showed a higher tibialis anterior muscle activity level in the medium latency response phase compared to HAB at T1.

Discussion

Based on these findings, it can be suggested that jaw clenching may lead to some changes in reflex activities. However, the effects are limited to anterior-posterior perturbations of the platform. Nevertheless, high learning effects may have overall overweighed the effects related to jaw clenching. Further studies with balance tasks leading to less learning effects are needed to understand the altered adaptations to a dynamic reactive balance task related to simultaneous jaw clenching. Analysis of muscle coordination (e.g., muscle synergies), instead of individual muscles, as well as other experimental designs in which the information from other sources are reduced (e.g., closed eyes), may also help to reveal jaw clenching effects.

Center of Mass Estimation Using a Force Platform and Inertial Sensors for Balance Evaluation in Quiet Standing

Accurate estimation of the center of mass is necessary for evaluating balance control during quiet standing. However, no practical center of mass estimation method exists because of problems with estimation accuracy and theoretical validity in previous studies that used force platforms or inertial sensors. This study aimed to develop a method for estimating the center of mass displacement and velocity based on equations of motion describing the standing human body. This method uses a force platform under the feet and an inertial sensor on the head and is applicable when the support surface moves horizontally. We compared the center of mass estimation accuracy of the proposed method with those of other methods in previous studies using estimates from the optical motion capture system as the true value. The results indicate that the present method has high accuracy in quiet standing, ankle motion, hip motion, and support surface swaying in anteroposterior and mediolateral directions. The present method could help researchers and clinicians to develop more accurate and effective balance evaluation methods.

Centre of pressure golf swing movement strategies are better defined using a continuous approach than by segregated styles

The relationships between movement style and golf performance have been well researched, but the premise of segregated movement styles has not been fully examined. The purpose of this investigation was to examine the postulation that centre of pressure data are not best described by segregated styles but instead by a continuum and to determine relationships between centre of pressure, handicap and clubhead speed using a continuous approach. Centre of pressure paths of driver and 5-iron shots from 104 amateur golfers were analysed using discrete and continuous methods. Discrete methods used different cluster evaluation criteria which result in two-cluster and twenty-cluster solutions being considered "optimum". The two-cluster solution showed the characteristics of "front-foot" and "reverse" centre of pressure styles. However, a continuous principal component analysis method revealed that the clusters were not well separated and provided support for a multidimensional continuum. The principal components had a high correlation with handicap and clubhead speed. Lower handicap and higher swing speed golfers tended to display a centre of pressure with a "front-foot" style and a fast transition towards the front foot at the start of the downswing. A continuous characterisation of centre of pressure styles has more utility than the segregated styles previously described.

Early Postural Stability Changes in Patients Undergoing Correction of Spinal Deformity: A Prospective, Controlled Pilot Study

BACKGROUND CONTEXT

Adult spinal deformity (ASD) is a prevalent condition often requiring surgical intervention. Improved outcomes among ASD patients have been shown to correlate with postoperative spinopelvic parameters, yet little is currently known about the role of postural stability and balance assessment for ASD patients.

PURPOSE

Explore early changes in postural stability following ASD correction.

STUDY DESIGN

Prospective cohort study.

PATIENT SAMPLE

Sixteen adult patients who underwent four-level or greater posterolateral fusion to address global spinal malalignment and 14 healthy controls with no known spinal deformity nor surgery.

OUTCOME MEASURES

Postural stability parameters, spinopelvic parameters preoperatively and postoperatively.

METHODS

Force plate balance assessment was completed where participants and healthy controls were instructed to stand with their hands at their sides, standing still, with eyes open. Center of pressure (COP), center of gravity (COG), and cone of economy (COE) parameters were analyzed with paired and unpaired t tests with an alpha of 0.05.

RESULTS

Preoperatively, ASD patients demonstrated more COG (P=0.0244) and sagittal and coronal head (P<0.05) sway than healthy controls. Postoperatively, ASD patients exhibited less COP (P=0.0308), COG (P=0.0276) and head (P=0.0345) sway. Compared to healthy controls, ASD patients postoperatively exhibited similar postural stability, aside from COP and COG sway amplitudes (P<0.05), and coronal head sway (P=0.0309). Pelvic incidence-lumbar lordosis and sagittal vertical axis improved from 16.2° to 4.8° (P<0.01) and 82.2 to 22.5 mm (P<0.01), respectively.

CONCLUSION

We report a novel early improvement in postural stability, comparable to healthy controls, following ASD correction that may be related to improved spinopelvic alignment. Force plate evaluation may be a useful tool for ASD patients postoperatively. Future clinical trials assessing the impact of postural stability on clinical and radiographic outcomes are warranted.

Directional virtual time-to-contact: A new measure for investigating temporal, spatial, and control aspects of postural balance control

Virtual time-to-contact (VTC) is a promising approach for investigating postural balance control. However, current VTC calculation approaches are limited as they (1) cannot be used to evaluate directional components of balance, and (2) only assess a single, temporal aspect of balance control. This study introduces a new approach for VTC calculation, namely directional VTC, expanding VTC to assess temporal, spatial, and control aspects of balance. Three case studies were conducted across varying populations and conditions as a proof-of-concept of the presented method. The first study examined quiet stance on a firm surface in people with Parkinson's disease (PD; n = 10) in comparison to their healthy peers (n = 10). The second and third studies assessed balance control of healthy individuals under challenging environments. Ten healthy individuals participated in standing tasks on compliant ground surfaces, while another ten on oscillatory ground surfaces, all simulated by a dual-axis robotic platform. Preliminary results not only provided a closer look at balance control with multiple aspects, including temporal, spatial, and control aspects, but also showed how different aspects of balance changed due to neurological diseases (Case Study I) or challenging standing grounds (Case Studies II and III). This study advances our understanding of posture biomechanics and its clinical applications.

Characterization of trial duration in traditional and emerging postural control measures

Researchers may select from varied technological and practical options when evaluating balance. Methodological choices inform the quantitative outcomes observed and allow practitioners to diagnose balance abnormalities. Past investigations have differed widely on sampling duration, and these discrepancies hinder comparisons among studies and confidence in outcomes where trials were excessively short. This study aimed to identify necessary trial lengths for common and emerging center of pressure-based measures. We hypothesized that dependent variables would fluctuate over time but eventually reach a stable magnitude. Ninety-seven apparently healthy adults performed quiet standing for 180-seconds (s) with eyes (A) open and (B) closed on a force platform. Anterior-posterior and medial-lateral elements of the center of pressure were used to calculate velocity, time-to-boundary, and Hurst exponents using 15, 30, 90, 120, 150, and 180 s of data. Two-way repeated measures ANOVAs were used to differentiate postural measures over time and between vision conditions. Outcomes were considered stable when significant changes in the measure were no longer observed in the time factor. Dependent measures stabilized for velocity between 60 and 120 s, time-to-boundary between 120 and 150 s, and the Hurst exponent between 30 and 120 s. Velocity measures stabilized quicker with eyes open, whereas vision had no effect or the eyes closed condition was faster to stabilize in time-to-boundary and detrended fluctuation analysis measures. We conclude that 150 s of standing data is sufficient to capture a broad range of postural stability outcomes regardless of vision condition.

Effects of Load Carriage on Postural Sway and Relative Ground Reaction Forces in Special Police Officers: A Cross-Sectional Study

Although excessive load carriage results in biomechanical gait changes, little evidence has been provided regarding its impact on postural sway. Therefore, the main purpose of this study was to determine whether heavier loads have effects on changing foot stability and postural sway in special police officers. Thirty male special police officers (age = 40 ± 6 years, height = 180 ± 5 cm, weight = 89 ± 8 kg) were assessed in four conditions: (1) carrying no load, (2) carrying a 5 kg load, (3) carrying a 25 kg load, and (4) carrying a 45 kg load. Foot characteristics during standing were assessed with Zebris pedobarographic pressure platform. Heavier loads increased the center of pressure (COP) path length and average velocity, length of minor and major axis, and 95% confidence ellipse area, while a decrease in angle between Y and major axis was observed. Relative forces beneath the left forefoot and right backfoot regions decreased and an increase in relative forces beneath the left backfoot and right forefoot was observed. When carrying heavy loads, static foot parameters rapidly changed, especially in COP path length and average velocity.

Whole-body movement analysis using principal component analysis: What is the internal consistency between outcomes originating from the same movement simultaneously recorded with different measurement devices?

A growing number of studies apply Principal Component Analysis (PCA) on whole-body kinematic data to facilitate an analysis of posture changes in human movement. An unanswered question is, how much the PCA outcomes depend on the chosen measurement device. This study aimed to assess the internal consistency of PCA outcomes from treadmill walking motion capture data simultaneously collected through laboratory-grade optical motion capture and field-suitable inertial-based motion tracking. Data was simultaneously collected using VICON (whole-body plug-in gait marker positions) and Xsens (body segment positions) from 20 participants during 2-min treadmill walking. Using PCA, Principal Movements (PMs) were determined using two commonly used practices: on an individual and a grouped basis. For both, correlation matrices were used to determine internal consistency between outcomes from either measurement system for each PM. Both individual and grouped approach showed excellent internal consistency between outcomes from the two systems among the lower order PMs. For the individual analysis, high correlations were only found along the diagonal of the correlation matrix while the grouped analysis also showed high off-diagonal correlations. These results have important implications for future application of PCA in terms of the independence of the resulting PM data, the way group-differences are expressed in higher-order PMs and the interpretation of movement complexity. Concluding, while PCA-outcomes from the two systems start to deviate in the higher order PMs, excellent internal consistency was found in the lower order PMs which already represent about 98% of the variance in the dataset.

Young Individuals Are More Stable and Stand More Upright When Using Rollator Assistance During Standing up and Sitting Down

Four-wheeled walkers or rollators are often used to assist older individuals in maintaining an independent life by compensating for muscle weakness and reduced movement stability. However, limited biomechanical studies have been performed to understand how rollator support affects posture and stability, especially when standing up and sitting down. Therefore, this study examined how stability and posture change with varying levels of rollator support and on an unstable floor. The aim was to collect comprehensive baseline data during standing up and sitting down in young participants. In this study, 20 able-bodied, young participants stood up and sat down both 1) unassisted and assisted using a custom-made robot rollator simulator under 2) full support and 3) touch support. Unassisted and assisted performances were analyzed on normal and unstable floors using balance pads with a compliant surface under each foot. Using 3D motion capturing and two ground-embedded force plates, we compared assistive support and floor conditions for movement duration, the relative timing of seat-off, movement stability (center of pressure (COP) path length and sway area), and posture after standing up (lower body sagittal joint angles) using ANOVA analysis. The relative event of seat-off was earliest under full support compared to touch and unassisted conditions under normal but not under unstable floor conditions. The duration of standing up and sitting down did not differ between support conditions on normal or unstable floors. COP path length and sway area during both standing up and sitting down were lowest under full support regardless of both floor conditions. Hip and knee joints were least flexed under full support, with no differences between touch and unassisted in both floor conditions. Hence, full rollator support led to increased movement stability, while not slowing down the movement, during both standing up and sitting down. During standing up, the full support led to an earlier seat-off and a more upright standing posture when reaching a stable stance. These results indicate that rollator support when handles are correctly aligned does not lead to the detrimental movement alterations of increased forward-leaning. Future research aims to verify these findings in older persons with stability and muscle weakness deficiencies.

Changes in static balance during pregnancy and postpartum: A systematic review

BACKGROUND

Because pregnant women show a high risk of falling, some researchers examined their balance during static standing. This systematic review summarized the findings from all studies evaluating static balance in women during pregnancy and postpartum.

RESEARCH QUESTION

Do pregnant and postpartum women show differences in static balance compared to non-pregnant women, and does static balance change during pregnancy and postpartum?

METHODS

Pubmed, Embase, CINAHL, and Web of Science databases were searched systematically from inception until Feb 23, 2022. Studies were eligible for inclusion if they measured COP sway with a force plate during bipedal static standing, and compared COP outcomes between healthy pregnant or postpartum women and non-pregnant women, and/or during different stages of pregnancy and the postpartum period. Methodological quality was assessed overall with a modified version of the Downs and Black checklist, and specifically related to COP measurement by using recommendations of Ruhe et al. (2010). The protocol was registered in PROSPERO (CRD42020166302).

RESULTS

Thirteen studies were included. Because methodological approaches varied greatly between studies, results were summarized descriptively. Studies reported either greater overall and anteroposterior COP sway magnitude, velocity and variability in women from the second half of pregnancy until six months postpartum compared to non-pregnant controls, or no differences in static balance. Changes in static balance throughout pregnancy were generally not found. Finally, there was no clear consensus on the influence of pregnancy on the reliance on visual inputs for balance control, and on whether differences in balance in pregnant and postpartum women reflect poorer balance or positive adaptations to the physical changes experienced during pregnancy.

SIGNIFICANCE

Methodological heterogeneity between studies prevented us from drawing strong conclusions regarding the effect of pregnancy on static balance. Assessing the methodological quality of the studies revealed weaknesses that should be taken into account in future studies.

Novel applications of Bayesian inference clarify sensorimotor uncertainty during stepping movements

The human nervous system relies on sensory information from the feet and legs to control the way we balance and walk. However, even in healthy individuals this sensory information is inherently variable and clouded with uncertainty. Researchers have found that the central nervous system (CNS) estimates body position amid the uncertainty of sensory signals in a way consistent with Bayesian inference. Bayesian inference posits that the brain accounts for variability in sensory data by combining it with learned expectations built from previous movement attempts. While initial findings on this topic are promising, they have neglected to study full-body movements such as gait and balance. The purpose of this research was to determine if the CNS controls balance-related stepping tasks in a way that fits a Bayesian framework. To address this purpose, we created a virtual reality protocol where participants moved their center of mass (CoM) to various targets while relying on uncertain visual cues and compensating for an alternating shift to the cursor position. We showed that as incoming sensory information became less certain, participants relied more on their learned expectation of body position and demonstrated more uncertainty in their responses. Accordingly, as participants learned to control and estimate their CoM position during our mobility task, they relied both on the sensory information they were receiving as well as learned expectations for its location. These results provide further evidence that the CNS is aware of the variability in sensory information and is proficient at compensating for the resultant uncertainty. We aim to apply these findings as a method for measuring the efficacy of interventions targeting sensory function.

Running-Induced Fatigue Changes the Structure of Motor Variability in Novice Runners

Understanding the effects of fatigue is a central issue in the context of endurance sports. Given the popularity of running, there are numerous novices among runners. Therefore, understanding the effects of fatigue in novice runners is an important issue. Various studies have drawn conclusions about the control of certain variables by analyzing motor variability. One variable that plays a crucial role during running is the center of mass (CoM), as it reflects the movement of the whole body in a simplified way. Therefore, the aim of this study was to analyze the effects of fatigue on the motor variability structure that stabilizes the CoM trajectory in novice runners. To do so, the uncontrolled manifold approach was applied to a 3D whole-body model using the CoM as the result variable. It was found that motor variability increased with fatigue (UCMꓕ). However, the UCMRatio did not change. This indicates that the control of the CoM decreased, whereas the stability was not affected. The decreases in control were correlated with the degree of exhaustion, as indicated by the Borg scale (during breaking and flight phase). It can be summarized that running-induced fatigue increases the step-to-step variability in novice runners and affects the control of their CoM.

Psychophysiological Indicators of Postural Control. Contribution of the Russian Scientific School. Part I

This article aimed to systematically review the published results of studies of psychophysiological mechanisms of posture maintenance and identify the key factors that influence the effectiveness of postural control. The recommendations of "Preferred Reporting Elements for Systematic Reviews and Meta-Analyzes" (PRISMA) were followed for the review. The results were classified, taking into account the target psychophysiological mechanisms and factors affecting postural control. The article presents the theoretical and empirical results of the Russian scientific school of research on the role of support afferentation in the sensorimotor mechanisms of cognitive and postural functions. Due to the limited number of randomized studies found, it was impossible to make meta-analytic comparisons, so the literature analysis was carried out only qualitatively. Meanwhile, our systematic review provides promising information about possible relationships between stabilometric and psychological indicators of postural control, which have theoretical significance and application in the correction and training of posture control. However, more thorough research is needed to overcome the methodological shortcomings that we have encountered in our qualitative analysis.

Influence of Controlled Stomatognathic Motor Activity on Sway, Control and Stability of the Center of Mass During Dynamic Steady-State Balance—An Uncontrolled Manifold Analysis

Multiple sensory signals from visual, somatosensory and vestibular systems are used for human postural control. To maintain postural stability, the central nervous system keeps the center of mass (CoM) within the base of support. The influence of the stomatognathic motor system on postural control has been established under static conditions, but it has not yet been investigated during dynamic steady-state balance. The purpose of the study was to investigate the effects of controlled stomatognathic motor activity on the control and stability of the CoM during dynamic steady-state balance. A total of 48 physically active and healthy adults were assigned to three groups with different stomatognathic motor conditions: jaw clenching, tongue pressing and habitual stomatognathic behavior. Dynamic steady-state balance was assessed using an oscillating platform and the kinematic data were collected with a 3D motion capturing system. The path length (PL) of the 3D CoM trajectory was used for quantifying CoM sway. Temporal dynamics of the CoM movement was assessed with a detrended fluctuation analysis (DFA). An uncontrolled manifold (UCM) analysis was applied to assess the stability and control of the CoM with a subject-specific anthropometric 3D model. The statistical analysis revealed that the groups did not differ significantly in PL, DFA scaling exponents or UCM parameters. The results indicated that deliberate jaw clenching or tongue pressing did not seem to affect the sway, control or stability of the CoM on an oscillating platform significantly. Because of the task-specificity of balance, further research investigating the effects of stomatognathic motor activities on dynamic steady-state balance with different movement tasks are needed. Additionally, further analysis by use of muscle synergies or co-contractions may reveal effects on the level of muscles, which were not visible on the level of kinematics. This study can contribute to the understanding of postural control mechanisms, particularly in relation to stomatognathic motor activities and under dynamic conditions.

Test-Retest Reliability of the Balance Tracking System Modified Clinical Test of Sensory Integration and Balance Protocol Across Multiple Time Durations

Background

Postural control is critical for body sway control and is subserved by three sources of sensory feedback (ie, vision, proprioception and vestibulation). A method for determining the relative contribution of each sensory feedback source to postural control is the modified clinical test of sensory integration and balance for the balance tracking system (BTrackS). However, this method has not yet been evaluated for test–retest reliability.

Purpose

To determine the test–retest reliability of the modified clinical test of sensory integration and balance protocol for the BTrackS across multiple time intervals.

Methods

Three groups of healthy young adults performed the BTrackS modified clinical test of sensory integration and balance protocol four times separated by either one day, one week or one month. Within each time duration group, and condition, differences in total center of pressure path length were determined from one test session to the next and intra class correlation coefficient categorizations were made.

Results

In all but one case, no significant difference in performance was seen from one testing session to the next. The one significant difference found was a decrease in total center of pressure path length from day 1 to day 2 in the vestibular condition of the group tested daily. Intra class correlation coefficient results largely indicated fair-good reliability across time durations and test conditions.

Conclusion

The present study largely supports use of the BTrackS modified clinical test of sensory integration and balance protocol as a means of probing the sensory contributions to balance performance across multiple time durations.