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

Post-mechanotherapy differences in postural control in patients with Achilles tendinopathy - A randomized controlled trial

BACKGROUND

Neuromuscular deficits affecting functional ability can occur in patients with Achilles tendinopathy during difficult balance activities. This study aimed to assess postural control in patients with Achilles tendinopathy after shockwave and sonotherapy, using advanced analytical methods, including rambling-trembling signal decomposition and sample entropy.

RESEARCH QUESTION

What are the differences in postural control between patients with Achilles tendinopathy after shockwave therapy, ultrasound therapy, and placebo ultrasound?

METHODS

Thirty-nine patients were included in the study, and randomly assigned to 3 groups, i.e., shockwave therapy, ultrasound therapy and placebo ultrasound. Postural sway was assessed during quiet standing with eyes open and closed, with two force platforms, one for the affected and the other for the non-affected limb, at baseline and at weeks 1 and 6 after treatment. Rambling-trembling trajectories and sample entropy were calculated for the antero-posterior and medio-lateral directions.

RESULTS

The parameters of trembling trajectory in both directions were significantly smaller for the affected compared to non-affected limb. The ultrasound group had significantly larger rambling-trembling trajectories in the antero-posterior and medio-lateral sway directions than the shockwave therapy group. Also, all patients had more difficulty controlling their postural sway while standing with eyes closed compared to eyes open. Sample entropy was not significantly affected by the therapy type, timepoint and limb condition.

SIGNIFICANCE

As opposed to sample entropy, rambling-trembling decomposition can complement or replace traditional linear measures of COP time series in functional assessment of the Achilles tendon.

Fall assessment in healthy older adults: Approach using rambling-trembling decomposition method

BACKGROUND

This study explored useful indices of potential fall risk in healthy older adults based on comprehensive clinical and simple quantitative posturographic measurements.

METHODS

A total of 64 community-dwelling older adults aged ≥65 years were classified into fallers and non-fallers based on previous fall history. After excluding two participants due to missing data, 16 and 46 participants were included in the faller and non-faller groups, respectively. We conducted major clinical measurements, including timed up and go test, 10-m walk test, functional reach test, one-leg stand test, isometric muscle strength tests, open-close stepping test, and sit-to-stand test. For quantitative posturographic measurements, participants performed standing tasks with their eyes open and closed. In the standing tasks, the time series of the center of pressure in the anteroposterior and mediolateral directions were measured and decomposed into rambling and trembling components to evaluate postural control in detail, separately. The mean velocity and root mean square of the center of pressure, rambling, and trembling were calculated and compared between fallers and non-fallers.

FINDINGS

A significant fall-related difference was found only in the mean velocity of the rambling in the anteroposterior direction; fallers displayed greater values than non-fallers, especially while standing with their eyes closed.

INTERPRETATION

The clinical measures failed to distinguish differences in fall risk, whereas the rambling component in the anteroposterior direction could detect substantial differences. The mean velocity of the rambling component could be useful as a sensitive screening biomarker for potential fall risks in healthy older adults.

Sensory reweighting of postural control requires distinct rambling and trembling sway adaptations

BACKGROUND

Implementation of the Sensory Organization Test (SOT) under the rambling-trembling (RM-TR) framework allows for an examination of both individual sensory contributions and compensatory mechanisms, a valuable insight in research and clinical settings. Such investigation could substantially improve our ability to assess and treat fall risk in older adults and people living with neurological disorders.

RESEARCH QUESTION

How are RM and TR components of sway influenced by SOT-induced challenges in healthy adults?

METHODS

Twenty-three healthy adults (27.4±8 years; 10 male) volunteered to participate in this cross-sectional study. Each participant completed a VR-based SOT program, which included six conditions with varied visual environments (normal, blacked-out, conflict) and support surfaces (stable, unstable foam), while a force plate captured forces at the plantar surface. Center of pressure (COP) was calculated and decomposed into RM-TR components. For each time series, range, root-mean-square (RMS) and sample entropy (SampEn) were extracted. Individual contributions of somatosensation, vision, and vestibular sense, as well as the preference ratio, were calculated. Repeated measures ANOVA were used to compare the effects of time series type (COP, RM, TR) and SOT condition. Paired t-tests were used to assess the difference in preference ratio between RM and TR components.

RESULTS AND SIGNIFICANCE

TR sway behavior was impacted significantly by the sensory challenges induced by the SOT procedure, while RM was largely unaffected. Such findings are characteristic of healthy individuals, capable of competently re-weighting sensory input, but still facing challenge-based adaptations. Additionally, the mediolateral SampEn preference ratio was higher in TR compared to RM, indicating potential differences in compensation strategies between supraspinal and spinal/peripheral control mechanisms. These findings serve as a foundation for future RM-TR analyses using SOT procedures, aiding in our ability to implement targeted diagnostic and treatment methods, ultimately reducing the incidence of falls in aging and individuals with neurological conditions.

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.

How partnering changes the process of postural control?

The aim of the study was to identify changes in the mechanism of postural control among ballroom dancers between standing solo and standing with a partner during specific standard dance positions. Specifically, the study attempted to determine whether the male partner plays a stabilising role in the dance couple. A total of seven competitive dance couples participated in the study. The experimental procedure comprised four dance positions characteristic of international standard dances: standard, starting, chasse and contra check. The dance positions were staged twice - while standing solo and while standing with a partner. The assumption of the assessed position was preceded by a dance phase after which the participants were instructed to freeze on a force plate and hold the position for 30 s. To examine whether subjects standing solo or with partners had greater rambling (RM) or trembling (TR) components in their dance postural profile, the ratios of RM to the center of foot pressure (COP) and TR to COP were computed for velocity. No significant differences were observed in the velocity of COP between standing solo and standing with a partner (p > 0.05). However, during the standard and starting positions, female and male dancers standing solo were characterised by higher values of the velocity of RM/COP ratio and lower values of the velocity of TR/COP ratio than those standing with a partner (p < 0.05). According to the theory behind the RM and TR decomposition, an increase in TR components could indicate a higher reliance on spinal reflexes, which would suggest greater automaticity.

Modulation of center-of-pressure signal in children on the autism spectrum: A case-control study

BACKGROUND

Proper postural and motor control plays a fundamental role in the child's ontogenetic development. So far, the postural control in children on the autism spectrum has mainly been assessed with standard posturographic measurements of center of pressure (COP) displacements.

RESEARCH QUESTION

What are the differences in postural control between autistic and typically developing children?

METHODS

The study group comprised 16 autistic children aged 6-10 years, identified by a psychiatrist. The control group consisted of 16 typically developing children aged 6-10 years with no posture deformities, no pervasive developmental disorder and no history of postural control or movement deficits. The data were collected during quiet standing with eyes open using a force plate. To gain a better insight into the postural control processes, the rambling-trembling and sample entropy analyses were used in COP data processing.

RESULTS

Compared to typically developing children, those with autism spectrum had significantly higher values of COP and rambling trajectory parameters in the antero-posterior direction during quiet standing. The variables of the trembling trajectory did not differ significantly between the groups. The autistic children had significantly lower values of sample entropy in the antero-posterior direction compared to typically developing children.

SIGNIFICANCE

More advanced measures of COP displacements including the rambling-trembling method and sample entropy revealed differences in postural control between autistic and typically developing children. These methods may therefore contribute to functional assessment of postural control deficits in children on the autism spectrum.

Multi-muscle Synergies of Postural Control in Self- and External-Triggered Force Release During Simulated Archery Shooting

We investigated postural stability during simulated archery shooting. The experiment consisted of two force release conditions: self-triggered (time-set in a feedforward fashion) and external cue-triggered (time-set by reacting to external cue) conditions while standing on the force platform. The electromyography of leg muscles and the center of pressure (COP) were recorded. The notions of muscle-modes (M-modes) and multi-muscle synergies were employed to quantify the postural stability, which described covariation patterns of the M-modes to stabilize the COP. The result showed relatively strong postural stability in a self-triggered condition associated with consistent shooting performance. The current findings suggested that initiating force release in a feedforward fashion would be a beneficial strategy to ensure the consistency in shooting performance.

Vertical ground reaction force oscillation during standing on hard and compliant surfaces: The “postural rhythm”

When a person stands upright quietly, the position of the Centre of Mass (CoM), the vertical force acting on the ground and the geometrical configuration of body segments is accurately controlled around to the direction of gravity by multiple feedback mechanisms and by integrative brain centres that coordinate multi-joint movements. This is not always easy and the postural muscles continuously produce appropriate torques, recorded as ground reaction force by a force platform. We studied 23 young adults during a 90 s period, standing at ease on a hard (Solid) and on a compliant support (Foam) with eyes open (EO) and with eyes closed (EC), focusing on the vertical component of the ground reaction force (VGRF). Analysis of VGRF time series gave the amplitude of their rhythmic oscillations (the root mean square, RMS) and of their frequency spectrum. Sway Area and Path Length of the Centre of Pressure (CoP) were also calculated. VGRF RMS (as well as CoP sway measures) increased in the order EO Solid ≈ EC Solid < EO Foam < EC Foam. The VGRF frequency spectra featured prevailing frequencies around 4–5 Hz under all tested conditions, slightly higher on Solid than Foam support. Around that value, the VGRF frequencies varied in a larger range on hard than on compliant support. Sway Area and Path Length were inversely related to the prevailing VGRF frequency. Vision compared to no-vision decreased Sway Area and Path Length and VGRF RMS on Foam support. However, no significant effect of vision was found on VGRF mean frequency for either base of support condition. A description of the VGRF, at the interface between balance control mechanisms and sway of the CoP, can contribute information on how upright balance is maintained. Analysis of the frequency pattern of VGRF oscillations and its role in the maintenance of upright stance should complement the traditional measures of CoP excursions in the horizontal plane.

Visual feedback in the lower visual field affects postural control during static standing

BACKGROUND

The dorsal parietal visual system plays an important role in self-motion perception and spatial cognition. It also strongly responds to visual inputs from the lower visual field. Postural control is modified in a process called sensory reweighting based on the reliability of available sensory sources. The question of whether visual stimuli presented to either the lower or upper visual field affect postural control and sensory reweighting has not been resolved.

RESEARCH QUESTION

Do visual stimuli presented to the lower and upper visual fields affect postural control and sensory reweighting?

METHODS

Twenty-nine healthy young adults participated in the study. Four conditions (full visual field, upper visual field, lower visual field, and no optic flow condition) were simulated in a VR environment using a head-mounted display. The optic flow stimuli used were swarms of small white spheres originating from the central point of the visual field, moving radially towards the periphery, and expanding across the scene. Participants were instructed to stand quietly for 50 s under each visual condition. Using force plate signals, we measured the center of pressure (COP) signal in the horizontal plane and calculated its 95 % ellipse area, root mean square (RMS) deviations, the mean velocity, and power spectral density (PSD).

RESULTS

Optic flow in the full and lower visual fields produced significantly smaller 95 % ellipse area and RMS of COP in the anterior-posterior direction compared to optic flow in the upper visual field. Furthermore, the PSD of the lower frequency band (0-0.3 Hz) was decreased and that of higher frequency bands (0.3-1 Hz and 1-3 Hz) was increased for the lower compared to the upper visual field.

SIGNIFICANCE

Visual feedback affects static postural control more when presented in the lower visual field compared to the upper visual field.

Incongruity of Geometric and Spectral Markers in the Assessment of Body Sway

Different measurements of body oscillations in the time or frequency domain are being employed as markers of gait and balance abnormalities. This study investigates basic relationships within and between geometric and spectral measures in a population of young adult subjects. Twenty healthy subjects stood with parallel feet on a force platform with and without a foam pad. Adaptation effects to prolonged stance were assessed by comparing the first and last of a series of eight successive trials. Centre of Foot Pressure (CoP) excursions were recorded with Eyes Closed (EC) and Open (EO) for 90s. Geometric measures (Sway Area, Path Length), standard deviation (SD) of the excursions, and spectral measure (mean power Spectrum Level and Median Frequency), along the medio-lateral (ML) and antero-posterior (AP) direction were computed. Sway Area was more strongly associated than Path Length with CoP SD and, consequently, with mean Spectrum Level for both ML and AP, and both visual and surface conditions. The squared-SD directly specified the mean power Spectrum Level of CoP excursions (ML and AP) in all conditions. Median Frequency was hardly related to Spectrum Level. Adaptation had a confounding effect, whereby equal values of Sway Area, Path Length, and Spectrum Level corresponded to different Median Frequency values. Mean Spectrum Level and SDs of the time series of CoP ML and AP excursions convey the same meaning and bear an acceptable correspondence with Sway Area values. Shifts in Median Frequency values represent important indications of neuromuscular control of stance and of the effects of vision, support conditions, and adaptation. The Romberg Quotient EC/EO for a given variable is contingent on the compliance of the base of support and adaptation, and different between Sway Area and Path Length, but similar between Sway Area and Spectrum Level (AP and ML). These measures must be taken with caution in clinical studies, and considered together in order to get a reliable indication of overall body sway, of modifications by sensory and standing condition, and of changes with ageing, medical conditions and rehabilitation treatment. However, distinct measures shed light on the discrete mechanisms and complex processes underpinning the maintenance of stance.

Increased 18F-FDG Uptake in the Axillary Lymph Nodes of the Vaccinated Side Associated with COVID-19 Vaccination

A 50-year-old female patient underwent (¹⁸fluorine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) following modified radical mastectomy for cancer of the left breast. Ten days before the PET/CT, the coronavirus disease-2019 (COVID-19) vaccine was injected intramuscularly into the right deltoid muscle. Increased (¹⁸F-FDG uptake of maximum standardized uptake value (11.0) was observed in the lymph nodes of the right axilla, which had not been observed in the previous PET/CT. The size of the oval-shaped lymph nodes was up to approximately 11×9 mm; however, it was larger than that observed on the previous PET/CT. We contemplate that the increased (¹⁸F-FDG uptake was a reactive change in the lymph nodes associated with the COVID-19 vaccine.

Balance Adaptation While Standing on a Compliant Base Depends on the Current Sensory Condition in Healthy Young Adults

Background

Several investigations have addressed the process of balance adaptation to external perturbations. The adaptation during unperturbed stance has received little attention. Further, whether the current sensory conditions affect the adaptation rate has not been established. We have addressed the role of vision and haptic feedback on adaptation while standing on foam.

Methods

In 22 young subjects, the analysis of geometric (path length and sway area) and spectral variables (median frequency and mean level of both total spectrum and selected frequency windows) of the oscillation of the centre of feet pressure (CoP) identified the effects of vision, light-touch (LT) or both in the anteroposterior (AP) and mediolateral (ML) direction over 8 consecutive 90 s standing trials.

Results

Adaptation was obvious without vision (eyes closed; EC) and tenuous with vision (eyes open; EO). With trial repetition, path length and median frequency diminished with EC (p < 0.001) while sway area and mean level of the spectrum increased (p < 0.001). The low- and high-frequency range of the spectrum increased and decreased in AP and ML directions, respectively. Touch compared to no-touch enhanced the rate of increase of the low-frequency power (p < 0.05). Spectral differences in distinct sensory conditions persisted after adaptation.

Conclusion

Balance adaptation occurs during standing on foam. Adaptation leads to a progressive increase in the amplitude of the lowest frequencies of the spectrum and a concurrent decrease in the high-frequency range. Within this common behaviour, touch adds to its stabilising action a modest effect on the adaptation rate. Stabilisation is improved by favouring slow oscillations at the expense of sway minimisation. These findings are preliminary to investigations of balance problems in persons with sensory deficits, ageing, and peripheral or central nervous lesion.