Human Postural Control

The acute effects of brace use on lower extremity performance in individuals with adolescent idiopathic scoliosis

BACKGROUND

Braces have been a popular treatment option for scoliosis among healthcare professionals for many years. However, the effect of braces on scoliosis treatment remains a subject of ongoing debate and research.

AIMS

Our study aimed to evaluate the effects of wearing a spinal brace on vertical jump, postural control, reach distance, and fall risk in patients with Adolescent Idiopathic Scoliosis (AIS).

METHODS

We included 33 patients with AIS aged between 10 to 18 years old in our cross-sectional study. Patients were randomly subjected to vertical jump test, standing long jump test, timed up and go test, postural control, and forward reach test, while wearing and not wearing the scoliosis brace, respectively.

RESULTS

Our findings revealed that patients wearing scoliosis braces had significantly lower vertical jumps (p = .001), standing long jumps (p < .001), and forward reach distances with their dominant (p = .002) and non-dominant limbs (p = .007) compared to those who did not wear the brace. However, there was no significant difference in postural control and timed up and go test between the two groups (p > .05).

CONCLUSIONS

Our study suggests that wearing a scoliosis brace may negatively affect an individual's vertical and standing long jumps, and forward reach distances. However, wearing or not wearing the brace had no significant effect on postural control and timed stand-up test. Long-term follow-up studies are needed to evaluate the overall effectiveness of scoliosis braces in treating AIS.

Effect of Verbal Encouragement on Postural Balance in Individuals with Intellectual Disabilities

This study investigated the effect of verbal encouragement (VE) on static and dynamic balance in individuals with intellectual disabilities (IDs). A total of 13 mild IDs and 12 moderate IDs participants underwent static balance tests (bipedal stance on firm surface, under open eyes (OEs) and closed eyes (CEs), and foam surface, unipedal stance on firm surface) and dynamic balance assessments (Y Balance Test (YBT) and Expanded Timed Up-and-Go Test (ETUGT)) under VE and no VE (NO/VE) conditions. VE significantly reduced center of pressure mean velocity (CoPVm) values for mild IDs in firm bipedal CEs conditions. The mild IDs group exhibited improved YBT scores and enhanced ETUGT performances for both groups under VE. Incorporating VE as a motivational strategy in balance training interventions can positively impact static and dynamic balance in individuals with mild IDs, especially in challenging conditions like unipedal stances on firm surfaces.

Virtual reality skateboarding training for balance and functional performance in degenerative lumbar spine disease

BACKGROUND

Degenerative lumbar spine disease (DLD) is a prevalent condition in middle-aged and elderly individuals. DLD frequently results in pain, muscle weakness, and motor impairment, which affect postural stability and functional performance in daily activities. Simulated skateboarding training could enable patients with DLD to engage in exercise with less pain and focus on single-leg weight-bearing. The purpose of this study was to investigate the effects of virtual reality (VR) skateboarding training on balance and functional performance in patients with DLD.

METHODS

Fourteen patients with DLD and 21 age-matched healthy individuals completed a 6-week program of VR skateboarding training. The motion capture and force platform systems were synchronized to collect data during a single-leg stance test (SLST). Musculoskeletal simulation was utilized to calculate muscle force based on the data. Four functional performance tests were conducted to evaluate the improvement after the training. A Visual Analogue Scale (VAS) was also employed for pain assessment.

RESULTS

After the training, pain intensity significantly decreased in patients with DLD (p = 0.024). Before the training, patients with DLD took longer than healthy individuals on the five times sit-to-stand test (p = 0.024). After the training, no significant between-group differences were observed in any of the functional performance tests (p > 0.05). In balance, patients with DLD were similar to healthy individuals after the training, except that the mean frequency (p = 0.014) was higher. Patients with DLD initially had higher biceps femoris force demands (p = 0.028) but shifted to increased gluteus maximus demand after the training (p = 0.037). Gluteus medius strength significantly improved in patients with DLD (p = 0.039), while healthy individuals showed consistent muscle force (p > 0.05).

CONCLUSION

This is the first study to apply the novel VR skateboarding training to patients with DLD. VR skateboarding training enabled patients with DLD to achieve the training effects in a posture that relieves lumbar spine pressure. The results also emphasized the significant benefits to patients with DLD, such as reduced pain, enhanced balance, and improved muscle performance.

Single-Session Cerebellar Transcranial Direct Current Stimulation Improves Postural Stability and Reduces Ataxia Symptoms in Spinocerebellar Ataxia

Spinocerebellar ataxia (SCA) results in balance and coordination impairment, and current treatments have limited efficacy. Recent evidence suggests that combining postural training with cerebellar transcranial direct current stimulation (ctDCS) can improve these symptoms. However, the combined effects of ctDCS and postural training on individuals with spinocerebellar ataxia remain underexplored. Ten volunteers with (SCA type 3) participated in a triple-blind, randomized, crossover study to receive a single session of ctDCS (2 mA for 20 min) and a sham ctDCS session separated by at least one week. The Biodex Balance System was used to assess balance at each session, measuring overall stability index, anteroposterior stability index, and medial-lateral stability index. As secondary outcomes, cerebellar ataxia symptoms were evaluated using the 8-item Scale for Assessment and Rating of Ataxia. The assessments were conducted before and after each session. The results indicated that ctDCS enhanced the overall stability index when compared to sham ctDCS (Z = -2.10, p = 0.03), although it did not significantly affect the anteroposterior or medial-lateral stability indices. Compared to the baseline, a single session of ctDCS reduced appendicular symptoms related to cerebellar ataxia, as evidenced by improvements in the nose-finger test (Z = -2.07, p = 0.04), fast alternating hand movements (Z = -2.15, p = 0.03), and heel-to-shin slide (Z = -1.91, p = 0.05). In conclusion, our study suggests that a single session of ctDCS, in combination with postural training, can enhance balance and alleviate ataxia symptoms in individuals with cerebellar ataxia. This study was approved by the local research ethics committee (No. 2.877.813) and registered on clinicaltrials.org (NCT04039048 - https://www.clinicaltrials.gov/study/NCT04039048 ) on 2019-07-28.

Changes in postural stability after cerebrospinal fluid tap test in patients with idiopathic normal pressure hydrocephalus

Introduction

In patients with idiopathic normal pressure hydrocephalus (iNPH), the characteristics of balance disturbance are not as well understood as those related to gait. This study examined changes in postural stability in quiet standing after the cerebrospinal fluid tap test (CSFTT) in these patients. Furthermore, the study explored the relationship between the amount of spontaneous body sway and both gait and executive function.

Materials and methods

All patients diagnosed with iNPH underwent CSFTT. We evaluated their center of pressure (COP) measurements on a force plate during quiet standing, both pre- and post-CSFTT. Following the COP measurements, we calculated COP parameters using time and frequency domain analysis and assessed changes in these parameters after CSFTT. At pre-CSFTT, we assessed the Timed Up and Go (TUG) and the Frontal Assessment Battery (FAB). We investigated the relationship between COP parameters and the TUG and FAB scores at pre-CSFTT.

Results

A total of 72 patients with iNPH were initially enrolled, and 56 patients who responded positively to CSFTT were finally included. Post-CSFTT, significant improvements were observed in COP parameters through time domain analysis. These included the velocity of COP (vCOP), root-mean-square of COP (rmsCOP), turn index, torque, and base of support (BOS), compared to the pre-CSFTT values (p < 0.05). In the frequency domain analysis of COP parameters post-CSFTT, there was a decrease in both the peak and average of power spectral density (PSD) values in both the anteroposterior (AP) and mediolateral (ML) directions below 0.5 Hz (p < 0.05). In addition, the TUG scores showed a positive correlation with vCOP, rmsCOP, turn index, torque, BOS, and both the peak and average PSD values in the AP and ML directions below 0.5 Hz (p < 0.05). The FAB scores demonstrated a negative correlation with vCOP, rmsCOP, turns index, BOS, and both peak and average PSD values in the AP direction below 0.5 Hz (p < 0.05).

Conclusion

In patients with iNPH who responded to CSFTT, there was an improvement in spontaneous body sway during quiet standing after CSFTT. Increased spontaneous sway is associated with impaired gait and frontal lobe function. This may be linked to impaired cortico-cortical and cortico-subcortical circuits in patients with iNPH.

The effects of postural control and upper extremity functional capacity on functional Independence in preschool-age children with spastic cerebral palsy: a path model

PURPOSE

To investigate the effects of postural control and upper extremity functional capacity on functional independence and identify whether quality of upper extremity skills mediates the effects of postural control on functional independence in preschool-age children with spastic cerebral palsy (CP).

METHODS

106 children with CP -mean age 43.4 ± 11.3 (24-71 months)- were included in this cross-sectional study. Postural control, upper extremity functional capacity, and functional independence in activities of daily living were evaluated using the Early Clinical Assessment of Balance (ECAB), Quality of Upper Extremity Skills Test (QUEST), and the Functional Independence Measure of Children (WeeFIM), respectively. A path model was used to evaluate the total, direct, and indirect effects.

RESULTS

According to the path model, ECAB (direct effect; r = 0.391, p < 0.01, indirect effect; r = 0.398) and QUEST (direct effect; r = 0.493, p < 0.01) had an impact on WeeFIM. In addition, QUEST had mediating effects on the relationship between ECAB and WeeFIM. The path model explained 71% of the variation in functional independence of the participants.

CONCLUSION

In the management of CP in preschool-age children, the focus should be on improving not only upper extremity capacity but also postural control to help improve functional independence in activities of daily living.

Nonlinear dynamics of postural control system under visual-vestibular habituation balance practice: evidence from EEG, EMG and center of pressure signals

Human postural control system is inherently complex with nonlinear interaction among multiple subsystems. Accordingly, such postural control system has the flexibility in adaptation to complex environments. Previous studies applied complexity-based methods to analyze center of pressure (COP) to explore nonlinear dynamics of postural sway under changing environments, but direct evidence from central nervous system or muscular system is limited in the existing literature. Therefore, we assessed the fractal dimension of COP, surface electromyographic (sEMG) and electroencephalogram (EEG) signals under visual-vestibular habituation balance practice. We combined a rotating platform and a virtual reality headset to present visual-vestibular congruent or incongruent conditions. We asked participants to undergo repeated exposure to either congruent (n = 14) or incongruent condition (n = 13) five times while maintaining balance. We found repeated practice under both congruent and incongruent conditions increased the complexity of high-frequency (0.5-20 Hz) component of COP data and the complexity of sEMG data from tibialis anterior muscle. In contrast, repeated practice under conflicts decreased the complexity of low-frequency (<0.5 Hz) component of COP data and the complexity of EEG data of parietal and occipital lobes, while repeated practice under congruent environment decreased the complexity of EEG data of parietal and temporal lobes. These results suggested nonlinear dynamics of cortical activity differed after balance practice under congruent and incongruent environments. Also, we found a positive correlation (1) between the complexity of high-frequency component of COP and the complexity of sEMG signals from calf muscles, and (2) between the complexity of low-frequency component of COP and the complexity of EEG signals. These results suggested the low- or high-component of COP might be related to central or muscular adjustment of postural control, respectively.

How virtual reality is impacting balance: An examination of postural stability

BACKGROUND

The interest in virtual reality (VR) applications has been on the rise in recent years. However, the impact of VR on postural stability remains unclear.

RESEARCH QUESTION

The study has two primary objectives: first, to compare postural stability in a 3D-immersed virtual reality environment (VE) and a real environment (RE), and second, to investigate the effect of positive and negative visual feedback, which are subconditions of VE on postural stability.

METHODS

The observational study recruited 20 healthy adults (10 male, 10 female, 22.8 ± 1.8 years) who underwent postural stability assessments in both RE and VE. In VE, participants received visual stimuli in three different ways: without visual feedback, with positive and negative visual feedback that they would consider themselves to be directed towards postural stability outcomes. The RE included two conditions: eyes open (EO) and eyes closed (EC). Postural stability was evaluated with sway velocity, sway area, and perimeter variables obtained from a force platform.

RESULTS

All postural stability variables were significantly lower in the RE than in the VE (p < 0.05). There was no significant difference between the VE and EC in terms of sway velocity and sway area (p > 0.05). The visual feedback in the VE did not affect participants' postural stability (p > 0.05). VE may cause an increase in postural sway variables compared to RE and postural requirements may be higher in VE compared to RE.

SIGNIFICANCE

This is the first and only study examining the effect of different visual feedback on postural stability in VE.

Unraveling the threads of stability: A review of the neurophysiology of postural control in Parkinson's disease

Postural instability is a detrimental and often treatment-refractory symptom of Parkinson's disease. While many existing studies quantify the biomechanical deficits among various postural domains (static, anticipatory, and reactive) in this population, less is known regarding the neural network dysfunctions underlying these phenomena. This review will summarize current studies on the cortical and subcortical neural activities during postural responses in healthy subjects and those with Parkinson's disease. We will also review the effects of current therapies, including neuromodulation and feedback-based wearable devices, on postural instability symptoms. With recent advances in implantable devices that allow chronic, ambulatory neural data collection from patients with Parkinson's disease, combined with sensors that can quantify biomechanical measurements of postural responses, future work using these devices will enable better understanding of the neural mechanisms of postural control. Bridging this knowledge gap will be the critical first step towards developing novel neuromodulatory interventions to enhance the treatment of postural instability in Parkinson's disease.

Repetitive temporal interference stimulation improves jump performance but not the postural stability in young healthy males: a randomized controlled trial

BACKGROUND

Temporal interference (TI) stimulation, an innovative non-invasive brain stimulation technique, has the potential to activate neurons in deep brain regions. The objective of this study was to evaluate the effects of repetitive TI stimulation targeting the lower limb motor control area (i.e., the M1 leg area) on lower limb motor function in healthy individuals, which could provide evidence for further translational application of non-invasive deep brain stimulation.

METHODS

In this randomized, double-blinded, parallel-controlled trial, 46 healthy male adults were randomly divided into the TI or sham group. The TI group received 2 mA (peak-to-peak) TI stimulation targeting the M1 leg area with a 20 Hz frequency difference (2 kHz and 2.02 kHz). Stimulation parameters of the sham group were consistent with those of the TI group but the current input lasted only 1 min (30 s ramp-up and ramp-down). Both groups received stimulation twice daily for five consecutive days. The vertical jump test (countermovement jump [CMJ], squat jump [SJ], and continuous jump [CJ]) and Y-balance test were performed before and after the total intervention session. Two-way repeated measures ANOVA (group × time) was performed to evaluate the effects of TI stimulation on lower limb motor function.

RESULTS

Forty participants completed all scheduled study visits. Two-way repeated measures ANOVA showed significant group × time interaction effects for CMJ height (F = 8.858, p = 0.005) and SJ height (F = 6.523, p = 0.015). The interaction effect of the average CJ height of the first 15 s was marginally significant (F = 3.550, p = 0.067). However, there was no significant interaction effect on the Y balance (p > 0.05). Further within-group comparisons showed a significant post-intervention increase in the height of the CMJ (p = 0.004), SJ (p = 0.010) and the average CJ height of the first 15 s (p = 0.004) in the TI group.

CONCLUSION

Repetitive TI stimulation targeting the lower limb motor control area effectively increased vertical jump height in healthy adult males but had no significant effect on dynamic postural stability.

A validation study to analyze the reliability of center of pressure data in static posturography in dogs

Introduction

Center of pressure (COP) parameters are frequently assessed to analyze movement disorders in humans and animals. Methodological discrepancies are a major concern when evaluating conflicting study results. This study aimed to assess the inter-observer reliability and test-retest reliability of body COP parameters including mediolateral and craniocaudal sway, total length, average speed and support surface in healthy dogs during quiet standing on a pressure plate. Additionally, it sought to determine the minimum number of trials and the shortest duration necessary for accurate COP assessment.

Materials and methods

Twelve clinically healthy dogs underwent three repeated trials, which were analyzed by three independent observers to evaluate inter-observer reliability. Test-retest reliability was assessed across the three trials per dog, each lasting 20 seconds (s). Selected 20 s measurements were analyzed in six different ways: 1 × 20 s, 1 × 15 s, 2 × 10 s, 4 × 5 s, 10 × 2 s, and 20 × 1 s.

Results

Results demonstrated excellent inter-observer reliability (ICC ≥ 0.93) for all COP parameters. However, only 5 s, 10 s, and 15 s measurements achieved the reliability threshold (ICC ≥ 0.60) for all evaluated parameters.

Discussion

The shortest repeatable durations were obtained from either two 5 s measurements or a single 10 s measurement. Most importantly, statistically significant differences were observed between the different measurement durations, which underlines the need to standardize measurement times in COP analysis. The results of this study aid scientists in implementing standardized methods, thereby easing comparisons across studies and enhancing the reliability and validity of research findings in veterinary medicine.

Comparing the effects of different circular vection stimuli on upright stance

BACKGROUND

Upright quiet stance is maintained through the complex integration of sensory information from the visual, vestibular, and somatosensory systems [1]. Virtual reality (VR) is a well-established tool that has been used to study sensory contributions to balance and induce visual perturbations. Previous assessments of virtual environments have suggested that VR can be used to create various visual stimuli that affect balance [2]; however, there is limited work examining which dynamic visual stimulus, in the form of circular vection (CV), is the most effective at inducing whole body lean.

RESEARCH QUESTION

Therefore, this study assessed the effects of two visual stimuli using VR to better understand their effects on postural control.

METHODS

33 healthy young adults between the ages of 18-40, free of neurological impairments, stood quietly on a force plate for 30 s while wearing a head-mounted display. Participants were exposed to a field of random white dots (DOTS) or a black and white striped tunnel (TUNNEL) that rotated in the roll plane at 60°/s clockwise or counterclockwise. Amplitude was calculated from head orientation data recorded from a head-mounted display, and centre of pressure (COP).

RESULTS

Independent of visual stimuli, postural lean was in the same direction as the stimulus. The DOTS stimulus increased Head orientation and COP position compared to the TUNNEL stimulus. There was no significant main effect or interaction with direction for Head or COP data.

SIGNIFICANCE

When comparing the effect of stimulus design on postural sway, a DOTS stimulus was most effective at inducing direction-modulated postural sway This study builds on our understanding of the VR-related destabilizing effects on postural control and shows evidence that a DOTS stimulus has a stronger effect than a TUNNEL stimulus. Overall, it is important to consider the design of visual stimuli when examining VR effects on upright stance.

On-Screen Visual Feedback Effect on Static Balance Assessment with Perturbations

In this study, the novel mobile dynamometric platform, OREKA, was utilized to perform an extensive analysis of the centre of pressure behaviour during different tilt motion exercises. This platform is based on a parallel manipulator mechanism and can perform rotations around both horizontal axes and a vertical translation. A group of participants took part in an experimental campaign involving the completion of a set of exercises. The aim was to evaluate the platform's potential practical application and investigate the impact of visual on-screen feedback on centre of pressure motion through multiple balance indicators. The use of the OREKA platform enables the study of the impact on a user's balance control behaviour under different rotational perturbations, depending on the availability of real-time visual feedback on a screen. Furthermore, it presented data identifying postural control variations among clinically healthy individuals. These findings are fundamental to comprehending the dynamics of body balance. Further investigation is needed to explore these initial findings and fully unlock the potential of the OREKA platform for balance assessment methodologies.

People with Long Covid and ME/CFS Exhibit Similarly Impaired Dexterity and Bimanual Coordination: A Case-Case-Control Study

PURPOSE

Dexterity and bimanual coordination had not previously been compared between people with long COVID and people with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). Therefore, this study determined dexterity and bimanual coordination in people with long COVID (∼16 month illness duration; n=21) and ME/CFS (∼16 year illness duration; n=20), versus age-matched healthy controls (n=20).

METHODS

Dexterity, and bimanual coordination was determined using the Purdue pegboard test.

RESULTS

The main findings of the present investigation were that people with ME/CFS and people with long COVID were generally comparable for Purdue pegboard tests (p>0.556 and d<0.36 for pairwise comparisons). It is worth noting however, that both these patient groups performed poorer in the Perdue pegboard test than healthy controls (p<0.169 and d>0.40 for pairwise comparisons).

CONCLUSIONS

These data suggest that both people with long COVID and people with ME/CFS have similarly impaired dexterity, and bimanual coordination. Therefore, there is an urgent need for interventions to target dexterity and bimanual coordination in people with ME/CFS, and given the current pandemic, people with long COVID.

Effects of Proprioceptive Insoles and Specific Core Training on Postural Stability for Preventing Injuries in Tennis

Tennis is a complex sport based on unpredictability that requires adequate physical and psychological preparation to prevent injuries. The aim of this study was to investigate the effects of 8-week specific core stability training on postural stability in competitive adolescent tennis players, aged between 14 and 19 years old. Sixty-one participants were randomly allocated into two groups: experimental (n = 32) and control (n = 29) groups. The first group wore proprioceptive insoles 8 h a day and performed a detailed training 3 times a week for 8 weeks; the second group only received proprioceptive insoles to wear 8 h a day for 8 weeks. The postural stability parameters (center-of-pressure length, center-of-pressure velocity, and 95% confidence ellipse sway area) included three assessment times: baseline (T0), intermediate test (T1), post-test (T2), and retention test (T3). Data analysis showed a significant improvement in the experimental group compared with the control group, indicating a large effect size in center-of-pressure length, ellipse sway area, and center-of-pressure velocity at T2 and T3 (p < 0.05). In conclusion, our results suggest that a specific and detailed core stability training plays a significant role in improving balance and postural stability in young tennis players, especially in terms of preventing the risk of injury.

Effect of Vision and Surface Slope on Postural Sway in Healthy Adults: A Prospective Cohort Study

Postural stability requires an interaction between cognitive, perceptual, sensory, and motor functions. Thus, impairment in any of these systems may affect postural balance. This study assessed the effect of visual input and surface slope on postural stability. The study was conducted on healthy participants, 11 females and 11 males who were 24-34 years of age. They were asked to perform still upright bipedal standing on flat and +/-20° sloped surfaces with eyes open (EO) and closed (EC). Six center of pressure (COP) parameters were measured by posturography. A significant relationship was observed between COP parameters, standing conditions, and body mass index. Gender had no significant effect on the COP. The loss of visual input within each standing condition did not affect the COP parameters. In contrast, differences were observed between standing on a flat surface and uphill with EC and between standing on a flat surface and downhill with EC and EO. When the participants were standing on inclined surfaces, the loss of vision significantly increased the postural instability. Young healthy adults demonstrated the greatest difficulty in standing uphill with EC. This was followed by standing downhill with EC and standing downhill with EO.

Effects of the Anchor System on Postural Balance of Women Undergoing Breast Cancer Treatment: A Clinical, Randomized, Controlled, and Crossover Trial

OBJECTIVE

Investigate the effects of multisensory training with and without the anchor system on breast cancer survivors' postural balance and self-efficacy of falls.

DESIGN

Clinical randomized, controlled, and crossover trial.

SETTING

Teaching, Research, and Assistance Center in Mastectomized Rehabilitation.

PARTICIPANTS

Eighty breast cancer survivors homogeneously distributed in the groups of adults and elderly affected, or not, by lymphedema.

INTERVENTIONS

Participants were randomized to multisensory training with and without the anchor system involving 3 sessions per week for 12 weeks. After the 4-week washout period, the remaining therapeutic intervention was applied.

MAIN OUTCOME MEASURES

The primary outcome was semi-static and dynamic balance as evaluated by baropodometry and Mini Balance Evaluation Systems Test, and the secondary outcome was self-efficacy of the fall episode as assessed by Falls Efficacy Scale - International in the pre-, post-immediate, and 4-week follow-up period.

RESULTS

Both therapeutic interventions caused positive and significant effects on postural balance and self-efficacy of falls in the immediate period. The multisensory training with the anchor system induced significant functional retention in the short term, related to the clinical effect of small to moderate variation.

CONCLUSIONS

Multisensory training with the anchor system is convenient for postural balance and self-efficacy for falls, regardless of age and upper limb volume, for breast cancer survivors.

Do increasingly unstable balance devices provide a graded challenge to bipedal stance in total hip arthroplasty patients?

BACKGROUND

Progressive balance exercises are critical to early functional rehabilitation after total hip arthroplasty (THA) but little is known regarding the challenge imposed by common balance devices.

RESEARCH QUESTION

Do progressively unstable balance devices provide a graded challenge to bipedal stance during early functional rehabilitation in THA patients?

METHODS

Postural control was evaluated in 42 patients (age, 63.7 ± 9.6 years; height, 1.72 ± 0.08 m and body mass, 78.9 ± 14.6 kg) approximately 3 weeks (23 ± 6 days) following unilateral primary THA. Patients were divided into two groups, based on their ability to complete a 20-second unipedal stance test (UPST) on the operated limb. A lumbar mounted inertial sensor monitored center of mass (COM) displacement during bipedal balance conditions involving three balance pads of progressive stiffness and an oscillatory platform, used in isolation and in combination with the most stable balance pad. COM displacement was normalised to bipedal stance on a hard surface. Differences between conditions and patient groups were assessed using a mixed-model analysis of variance.

RESULTS

Twenty patients (48%) were able to complete the UPST on their operated limb. There was a significant effect of balance condition on COM displacement during bipedal stance (F4,160 = 82.6, p < .01). COM displacement was lowest for the oscillatory platform but increased non-linearly across the three balance pads (p < .05). There was no significant difference in COM displacement between THA patients able and unable to complete the UPST.

SIGNIFICANCE

Increasingly compliant balance pads provided a progressive, though nonlinear, challenge to bipedal balance control in THA patients that was greater than that of an oscillating platform and independent of the ability to stand independently on the operated limb. These findings serve as a guide for the design of progressive training programs that enhance balance in THA patients.

Short- and Long-Term Changes in Balance After Active Video Game Training in Children With and Without Developmental Coordination Disorder: A Randomized Controlled Trial

Active video games (AVG) have been used as training tools and are known to ameliorate balance performance in children with Developmental Coordination Disorder (DCD). Our aim was to evaluate balance using clinical tests and by measuring body sway using a force plate with a mixed design of vision (eyes open/eyes closed), surface (rigid/soft), and support (stance/semitandem) before, and after, training and 4 months later (follow-up). Thirty-six DCD children and 40 typically developing children participated in the study, of which 50 children (26 DCD; 24 typically developing) were retested after 4 months. Balance improved on the clinical measures after the training, which was independent of type of AVG (Wii-Fit and Xbox Kinect) used, and this effect was still present after 4 months. The AVG training did not influence general sway behavior, but only sway in the eyes-open condition, corresponding with task demands of the training and indicating a training-specific effect. Overall, DCD children and typically developing children responded comparably to the AVG training, thereby maintaining the gap in performance between the two groups. The changes in postural sway are interpreted as a sign of more confidence and less freezing of the joints, enabling greater flexibility of movements and balance strategies as supported by the improved performance on balance tests in the DCD children. This is the first study that showed long-term effects of AVG training on balance performance. However, these follow-up results should be interpreted with caution given that 35% of the children were lost in follow-up.

Trunk postural control during unstable sitting among individuals with and without low back pain: A systematic review with an individual participant data meta-analysis

INTRODUCTION

Sitting on an unstable surface is a common paradigm to investigate trunk postural control among individuals with low back pain (LBP), by minimizing the influence lower extremities on balance control. Outcomes of many small studies are inconsistent (e.g., some find differences between groups while others do not), potentially due to confounding factors such as age, sex, body mass index [BMI], or clinical presentations. We conducted a systematic review with an individual participant data (IPD) meta-analysis to investigate whether trunk postural control differs between those with and without LBP, and whether the difference between groups is impacted by vision and potential confounding factors.

METHODS

We completed this review according to PRISMA-IPD guidelines. The literature was screened (up to 7th September 2023) from five electronic databases: MEDLINE, CINAHL, Embase, Scopus, and Web of Science Core Collection. Outcome measures were extracted that describe unstable seat movements, specifically centre of pressure or seat angle. Our main analyses included: 1) a two-stage IPD meta-analysis to assess the difference between groups and their interaction with age, sex, BMI, and vision on trunk postural control; 2) and a two-stage IPD meta-regression to determine the effects of LBP clinical features (pain intensity, disability, pain catastrophizing, and fear-avoidance beliefs) on trunk postural control.

RESULTS

Forty studies (1,821 participants) were included for the descriptive analysis and 24 studies (1,050 participants) were included for the IPD analysis. IPD meta-analyses revealed three main findings: (a) trunk postural control was worse (higher root mean square displacement [RMSdispl], range, and long-term diffusion; lower mean power frequency) among individuals with than without LBP; (b) trunk postural control deteriorated more (higher RMSdispl, short- and long-term diffusion) among individuals with than without LBP when vision was removed; and (c) older age and higher BMI had greater adverse impacts on trunk postural control (higher short-term diffusion; longer time and distance coordinates of the critical point) among individuals with than without LBP. IPD meta-regressions indicated no associations between the limited LBP clinical features that could be considered and trunk postural control.

CONCLUSION

Trunk postural control appears to be inferior among individuals with LBP, which was indicated by increased seat movements and some evidence of trunk stiffening. These findings are likely explained by delayed or less accurate corrective responses.

SYSTEMATIC REVIEW REGISTRATION

This review has been registered in PROSPERO (registration number: CRD42021124658).

Postural Balance in Boys With Intellectual Disabilities Who Participate in Soccer Training

PURPOSE

The aim of this study is to investigate the postural balance in children with intellectual disabilities who participate in soccer training compared with their sedentary peers.

METHOD

Two groups of boys with intellectual disabilities aged 8-10 years participated in this study: a soccer group (n = 12) and a sedentary group (n = 12). Postural balance was assessed using a force platform under 4 different conditions: open eyes, and closed eyes, on firm and foam surfaces. The Timed Up and Go Test, 10-m Walking Test, and Four-Square Step Test were also conducted.

RESULTS

The soccer group had significantly lower (P < .05) center of pressure values compared with the sedentary group, on both firm and foam surfaces, but only under the open eyes condition. They were significantly faster (P < .05) in the Timed Up and Go Test, 10-m Walking Test, and Four-Square Step Test compared with their sedentary peers. However, there were no significant differences between the 2 groups on the sit-to-stand and turn-to-sit phases of the Timed Up and Go Test.

CONCLUSION

Soccer participation may have a positive effect on postural balance in boys with intellectual disabilities. These findings may have implications for the development of exercise programs to improve postural balance and reduce the risk of falls in this population.

Feasibility of a new intervention addressing group-based balance and high-intensity training, physical activity, and employment in individuals with multiple sclerosis: a pilot randomized controlled trial

Background and purpose

Impaired sensorimotor function, reduced physical activity and unemployment are common challenges in persons with multiple sclerosis (pwMS), even when disability is low. CoreDISTparticipation is a new, multidisciplinary intervention delivered across healthcare levels systematically addressing these elements. This study primarily aimed to evaluate the feasibility of CoreDISTparticipation in terms of process, resources, management, and scientific outcomes. The secondary aim was to evaluate initial efficacy in terms of possible short-term effects compared with the usual care on barriers to employment, balance, walking, health-related quality of life (HRQoL), and physical activity.

Methods

This assessor-blinded prospective pilot randomized controlled trial included 29 pwMS [Expanded Disability Status Scale (EDSS): 0-3.5] randomly allocated to the intervention group (CoreDISTparticipation) (n = 15) or usual care (n = 14). CoreDISTparticipation consists of three phases: (1) hospital outpatient clinic: MS nurse work-focused session and physiotherapist exploring balance; (2) municipality: a digital meeting with pwMS, employer, MS nurse, and physiotherapist addressing employment and physical activity, 4 weeks indoor CoreDIST balance training (60 min × 2/week); and (3) 4 weeks outdoor CoreDIST balance training and high-intensity running/walking (60 min × 2/week). Assessments were undertaken at baseline and at weeks 6 and 11. Primary feasibility metric outcomes were the reporting of process, resources, management, and scientific outcomes. Efficacy measures included evaluation of the Multiple Sclerosis Work Difficulties Questionnaire-23 Norwegian Version (MSWDQ-23NV) and 6 Minute Walk-test as well as the Trunk Impairment Scale-modified Norwegian Version, Mini-Balance Evaluation Systems Test (Mini-BESTest), Multiple Sclerosis Walking Scale-12, Multiple Sclerosis Impact Scale-29 Norwegian Version (MSIS-29NV), ActiGraph wGT3x-BT monitors, and AccuGait Optimized force platform. The statistical analyses included repeated-measures mixed models performed in IBM SPSS Version 29.

Results

The primary feasibility metric outcomes demonstrated the need for minor adjustments in regard to the content of the intervention and increasing the number of staff. In regard to the efficacy measures, one person attended no postintervention assessments and was excluded, leaving 28 participants (mean EDSS: 1.8, SD: 1). The mean percentage employment was 46.3 (SD: 35.6) and 65.4 (SD: 39.3) in the CoreDISTparticipation and usual care group, respectively. No between-group differences were found. MSWDQ-23NV demonstrated a within-group difference of 5.7 points from baseline to Week 11 (P = 0.004; confidence interval: 2.2-9.3). Mini-BESTest and MSIS-29NV demonstrated within-group differences. The study is registered in ClinicalTrials.gov (Identifier: NCT05057338).

Discussion

The CoreDISTparticipation intervention is feasible to support pwMS when the identified feasibility metric outcomes in regard to process, resource, management, and scientific outcome metrics are adjusted to improve feasibility. Regarding efficacy measures, no between-group differences were detected; however, within-group differences in barriers to employment, balance, and HRQoL were detected for the CoreDISTparticipation group. A larger comparative trial is needed to explore between-group differences and should accurately and precisely define usual care and address the identified limitations of this study.

Analysis of postural stability using foam posturography in patients with persistent postural-perceptual dizziness

BACKGROUND/OBJECTIVE

Persistent postural-perceptual dizziness (PPPD) is worsened in a standing posture, or by body movement, or visual stimulation. We aimed to evaluate postural stability in PPPD patients using foam posturography and to investigate the dependence on visual and somatosensory input in the standing posture.

METHODS

Foam posturography was performed on 53 PPPD patients, and data from the PPPD patients were compared with the data from an age- and sex-matched healthy controls. The PPPD patients were divided into four groups based on the findings of vestibular function tests and the effect of vestibular function on posturographic data was examined.

RESULTS

Romberg's ratios were significantly higher in PPPD patients than in controls. The median Romberg's ratios in PPPD patients with normal vestibular function were also higher than those in controls. However, foam ratio was significantly lower in PPPD patients than in controls. The median foam ratios in PPPD patients with vestibular dysfunction were also lower than those in controls.

CONCLUSIONS

In a standing posture, PPPD patients may be more dependent on visual input and less dependent on somatosensory input than healthy subjects. Higher dependence on visual and lower dependence on somatosensory input in PPPD may be a feature unaffected by vestibular function.

Intrafusal cross-bridge dynamics shape history-dependent muscle spindle responses to stretch

Computational models can be critical to linking complex properties of muscle spindle organs to the sensory information that they encode during behaviours such as postural sway and locomotion where few muscle spindle recordings exist. Here, we augment a biophysical muscle spindle model to predict the muscle spindle sensory signal. Muscle spindles comprise several intrafusal muscle fibres with varied myosin expression and are innervated by sensory neurons that fire during muscle stretch. We demonstrate how cross-bridge dynamics from thick and thin filament interactions affect the sensory receptor potential at the spike initiating region. Equivalent to the Ia afferent's instantaneous firing rate, the receptor potential is modelled as a linear sum of the force and rate change of force (yank) of a dynamic bag1 fibre and the force of a static bag2/chain fibre. We show the importance of inter-filament interactions in (i) generating large changes in force at stretch onset that drive initial bursts and (ii) faster recovery of bag fibre force and receptor potential following a shortening. We show how myosin attachment and detachment rates qualitatively alter the receptor potential. Finally, we show the effect of faster recovery of receptor potential on cyclic stretch-shorten cycles. Specifically, the model predicts history-dependence in muscle spindle receptor potentials as a function of inter-stretch interval (ISI), pre-stretch amplitude and the amplitude of sinusoidal stretches. This model provides a computational platform for predicting muscle spindle response in behaviourally relevant stretches and can link myosin expression seen in healthy and diseased intrafusal muscle fibres to muscle spindle function.

The impacts of exercise training programs on balance in children with hearing loss: A systematic review and meta-analysis

INTRODUCTION AND PURPOSE

According to the prevalence of balance disorders among children with hearing loss (HL), researchers used exercise programs to improve balance in children with HL. So, the present systematic review and meta-analysis briefly summarize findings regarding the impacts of exercise training programs on balance in children with HL.

METHODS

Science Direct, MEDLINE/PubMed, SCOPUS, LILACS, CINAHL, CENTRAL, Web of Science, PEDro, and Google Scholar were searched from inception until November 11th, 2023. Two independent researchers analyzed and extracted the data from potential papers whose eligibility was confirmed. Then, the PEDro scale was used to obtain quality assessment scores. The total PEDro score is 11 and incorporates the presentation of statistical analysis and evaluation criteria of internal validity. Studies that scored 7-11 were considered methodologically "high", 5 to 6 were "fair", and ≤4 were considered "poor".

RESULTS

10 studies involving a total of 304 participations were included in the systematic review. Our results demonstrate that exercise training programs positively impact static balance (p = 0.001) with level 1a evidence, the postural sway (p = 0.001) with level 1a evidence, and dynamic balance (p = 0.001) with level 1a evidence in children with HL.

CONCLUSION

The findings of this systematic review and meta-analysis related to studies with excellent methodological quality revealed that the intended training programs significantly impact postural sway along with static and dynamic balance in children with HL. It is recommended that future exercise training programs be paired with rehabilitation programs for children with HL.

Verbal Encouragement Provokes Significant Increases in Maximal Volitional Dynamic Postural Sway

Limits of Stability protocols are typically target-oriented, leaving volitional aspects of control unobservable. A novel unconstrained protocol, volitional Limits of Stability (vLOS), shows high test-retest-reliability. We tested if verbal encouragement impacts this protocol. Forty healthy young adults (age 20.1 ± .9 years) performed three trials of vLoS with instructions that were agnostic to strategy or vigor, except trial three included verbal encouragement. Total sway area was used to metric the maximum volitional dynamic sway during each 1-min trial. One-way, repeated-measures ANOVA revealed significant differences (F(2,117) = 41.56, p < 0.0001, η p 2 = 0.52) due to encouragement. Specifically, follow-up paired t-tests showed no difference in sway area between the first two trials (p = 0.61), while trial three was much larger than trials one and two (p < 0.0001). Significant, large increases in sway area with verbal encouragement indicate that top-down mechanisms should be considered in theories of postural control. As well, clinical utilization of novel vLOS should be careful with word selection and delivery of protocol instructions.HIGHLIGHTSLimits of Stability balance tests typically include a goal directed instruction and metrics.Dynamic postural sway should be tested in a task affording participant volitional control.A novel volitional Limits of Stability protocol has been developed.Maximal dynamic postural sway responds to motivating instructions.Psychological factors of postural sway control deserve further investigation.

Effect of cooling on static postural balance while wearing firefighter's protective clothing in a hot environment

Objectives. Postural imbalance can result from hyperthermia-mediated muscular fatigue and is a major factor contributing to injuries from falling. The objective of this study was to investigate the effect of exercise-induced hyperthermia and the impact of cooling on postural balance while wearing firefighters' protective clothing (FPC) in a hot environment. Methods. A portable force platform measured postural balance characterized by postural sway patterns using center of pressure metrics. Twelve healthy, physically fit males were recruited to stand on the force platform once with eyes open and once with eyes closed before and after treadmill exercise (40% V ˙ O 2 max ) inside an environmental chamber under hot and humid conditions (30 °C and 70% relative humidity) while wearing FPC. Subjects participated in two randomly assigned experimental phases: control and cooling intervention. Results. A significant increase in physiological responses and postural balance metrics was observed after exercising in the heat chamber while wearing FPC. Cooling resulted in a significant effect only on postural sway speed after exercise-induced hyperthermia. Conclusions. Hyperthermia can negatively alter postural balance metrics, which may lead to an increased likelihood of falling. The utilization of body cooling reduced the thermal strain but had limited impact on postural balance stability.

Sitting vs. standing: an urgent need to rebalance our world

During their activities of daily living, humans run, walk, stand, sit and lie down. Recent changes in our environment have favored sedentary behavior over more physically active behavior to such a degree that our health is in danger. Here, we sought to address the problem of excessive time spent seated from various theoretical viewpoints, including postural control, human factors engineering, human history and health psychology. If nothing is done now, the high prevalence of sitting will continue to increase. We make a case for the standing position by demonstrating that spending more time upright can mitigate the physiological and psychological problems associated with excessive sitting without lowering task performance and productivity. The psychological literature even highlights potential benefits of performing certain tasks in the standing position. We propose a number of recommendations on spending more time (but not too much) in the standing position and on more active, nonambulatory behaviors. There is a need to inform people about (i) harmful consequences of excessive sitting and (ii) benefits of spending more time performing active, nonambulatory behaviors. One clear benefit is to reduce detrimental health consequences of excessive sitting and to provide potential additional benefits in terms of productivity and performance.

Phasic and tonic muscle synergies are different in number, structure and sparseness

In the last two decades, muscle synergies analysis has been commonly used to assess the neurophysiological mechanisms underlying human motor control. Several synergy models and algorithms have been employed for processing the electromyographic (EMG) signal, and it has been shown that the coordination of motor control is characterized by the presence of phasic (movement-related) and tonic (anti-gravity and related to co-contraction) EMG components. Neural substrates indicate that phasic and tonic components have non-homogeneous origin; however, it is still unclear if these components are generated by the same set of synergies or by distinct synergies. This study aims at testing whether phasic and tonic components are generated by distinct phasic and tonic synergies or by the same set of synergies with phasic and tonic activation coefficients. The study also aims at characterizing the differences between the phasic and the tonic synergies. Using a comprehensive mapping of upper-limb point-to-point movements, synergies were extracted from phasic and tonic EMG signal separately, estimating the tonic components with a linear ramp model. The goodness of reconstruction (R2) as a function of the number of synergies was compared, and sets of synergies extracted from each dataset at three R2 threshold levels (0.80, 0.85, 0.90) were retained for further analysis. Then, shared, phasic-specific, and tonic-specific synergies were extracted from the two datasets concatenated. The dimensionality of the synergies shared between the phasic and the tonic datasets was estimated with a bootstrap procedure based on the evaluation of the distribution of principal angles between the subspaces spanned by phasic and tonic synergies due to noise. We found only few shared synergies, indicating that phasic and tonic synergies have in general different structures. To compare consistent differences in synergy composition, shared, phasic-specific, and tonic-specific synergies were clustered separately. Phasic-specific clusters were more numerous than tonic-specific ones, suggesting that they were more differentiated among subjects. The structure of phasic clusters and the higher sparseness indicated that phasic synergies capture specific muscle activation patterns related to the movement while tonic synergies show co-contraction of multiple muscles for joint stabilization and holding postures. These results suggest that in many scenarios phasic and tonic synergies should be extracted separately, especially when performing muscle synergy analysis in patients with abnormal tonic activity and for tuning devices with gravity support.

Acute short term effects of endurance and resistance training on balance control in patients with diabetic peripheral neuropathy

PURPOSE

Exercise training have numerous beneficial effects on the complications of diabetic peripheral neuropathy. Exercise training may cause immediate effects on balance control in DPN patients. This study aims to assess the Acute Short Term effects of endurance and resistance exercise training on balance control in DPN patients.

METHODS

In this study, 11 patients with DPN and 11 healthy subjects participated. Patients and healthy subjects did endurance and resistance training in two separate exercise sessions. Dynamic balance and functional balance test were assessed before and after the interventions. Independent t-test was used to compare balance indices before and after training, the intervention effects were examined using ANOVA repeated measure test. The statistical significance level was set at p < 0.05.

RESULTS

The results showed that dynamic and functional balance in DPN patients were significantly lower than in healthy subjects. Anterior-posterior stability and total stability indices and functional balance test deteriorated significantly after training.

CONCLUSION

Endurance or resistance training may lead to acute disturbance of dynamic and functional balance in DPN patients. Hence, immediately after exercise, patients with diabetes are at an increased risk of falling, therefore, preventive considerations are necessary.

Effects of Smartphone Activities on Postural Balance in Adolescents with Intellectual Disabilities

Considering the rising prevalence of smartphone usage among adolescents with intellectual disabilities and their frequent motor challenges, understanding its impact on their physical well-being is important. This study aims to investigate the impact of smartphone activities on postural balance in adolescents with intellectual disabilities. Two groups of adolescents participated in the study: an intellectual disability group (IDG) (n = 16) and atypical development group (TDG) (n = 12). Static postural balance, using a stabilometric platform on firm and foam surfaces, and dynamic balance, using the Timed Up-and-Go Test (TUGT), were performed under various conditions, such as playing a game, watching videos, video calls, and listening to music. The center of pressure (CoP) values significantly increased (p < 0.05) during all smartphone activities (except listening to music) compared to the control condition in both groups, with the IDG demonstrated a more pronounced increase (p < 0.05) during playing video games and video calls on the firm surface. TUGT scores significantly increased (p < 0.05) during smartphone activities, with greater changes observed in the IDG (p < 0.05), and significantly decreased (p < 0.01) during listening to music in both groups. Our study suggests that adolescents with intellectual disabilities need special tools and guidance to ensure their safety and well-being when using smartphones.

Balance and Muscle Synergies During a Single-Limb Stance Task in Individuals With Chronic Ankle Instability

The aim of this study was to investigate balance performance and muscle synergies during a Single-Limb Stance (SLS) task in individuals with Chronic Ankle Instability (CAI) and a group of healthy controls. Twenty individuals with CAI and twenty healthy controls were asked to perform a 30-second SLS task in Open-Eyes (OE) and Closed-Eyes (CE) conditions while standing on a force platform with the injured or the dominant limb, respectively. The activation of 13 muscles of the lower limb, hip, and back was recorded by means of surface electromyography. Balance performance was assessed by identifying the number and the duration of SLS epochs, and the Root-Mean-Square (RMS) in Antero-Posterior (AP) and Medio-Lateral (ML) directions of the body-weight normalized ground reaction forces. The optimal number of synergies, weight vectors, and activation coefficients were also analyzed. CAI group showed a higher number and a shorter duration of SLS epochs and augmented ground reaction force RMS in both AP and ML directions compared to controls. Both groups showed an increase in the RMS in AP and ML forces in CE compared to OE. Both groups showed 4 optimal synergies in CE, while controls showed 5 synergies in OE. CAI showed a significantly higher weight of knee flexor muscles in both OE and CE. In conclusion, muscle synergies analysis provided an in-depth knowledge of motor control mechanisms in CAI individuals. They showed worse balance performance, a lower number of muscle synergies in a CE condition and abnormal knee flexor muscle activation compared to healthy controls.

Coupling Between Posture and Respiration Among the Postural Chain: Toward a Screening Tool for Respiratory-Related Balance Disorders

Alteration of posturo-respiratory coupling (PRC) may precede postural imbalance in patients with chronic respiratory disease. PRC assessment would be appropriate for early detection of respiratory-related postural dysfunction. PRC may be evaluated by respiratory emergence (REm), the proportion of postural oscillations attributed to breathing activity; assessed by motion analysis) as measured from the displacement of the center of pressure (CoP) (measured with a force platform). To propose a simplified method of PRC assessment (using motion capture only), we hypothesized that the REm can appropriately be measured derived from single body segment the postural oscillations of a single body segment rather than whole body postural oscillations. An optoelectronic system recorded the breathing pattern and the postural oscillations of six body segments in 50 healthy participants (22 women), 34 years [26; 48]. The CoP displacements were assessed using a force platform. One-minute recordings were made in standing position in four conditions by varying vision (eyes opened/closed) and jaw position (rest position/dental contact). The Sway Path and Mean Velocity of the CoP and of the representative point of each body segment were recorded. The REm was measured along the major and the minor axis of the 95% confidence ellipse of the CoP position (REm_MajorAxisCoP; REm_MinorAxisCoP) and of that of each body segment. SwayPathCoP and MVCoP varied widely across the four conditions (par< 0.000001). These changes were related to the visual condition ( [Formula: see text]) while the jaw position had no effect. The REm_MajorAxisCoP and the REm_MinorAxisCoP changed across conditions ( [Formula: see text]); this was related to vision while jaw induced changes only for the REm_MinorAxisCoP. The SwayPath, the Mean Velocity and the REm of all body segments were significantly correlated to the CoP, but the highest correlations were observed for the thorax, the pelvis and the shoulder. PRC may be assessed from the postural oscillations of thorax, pelvis and shoulder. This should simplify the evaluation of respiratory-related postural interactions in the clinical environment, by using a single device to simultaneously assess postural oscillations on body segments, and breathing pattern. In addition, this study provides reference data for PRC and its sensory-related modulations on body segments along the postural chain.

Analysis of abnormal posture in patients with Parkinson's disease using a computational model considering muscle tones

Patients with Parkinson's disease (PD) exhibit distinct abnormal postures, including neck-down, stooped postures, and Pisa syndrome, collectively termed "abnormal posture" henceforth. In the previous study, when assuming an upright stance, patients with PD exhibit heightened instability in contrast to healthy individuals with disturbance, implying that abnormal postures serve as compensatory mechanisms to mitigate sway during static standing. However, limited studies have explored the relationship between abnormal posture and sway in the context of static standing. Increased muscle tone (i.e., constant muscle activity against the gravity) has been proposed as an underlying reason for abnormal postures. Therefore, this study aimed to investigate the following hypothesis: abnormal posture with increased muscle tone leads to a smaller sway compared with that in other postures, including normal upright standing, under the sway minimization criterion. To investigate the hypothesis, we assessed the sway in multiple postures, which is determined by joint angles, including cases with bended hip joints. Our approach involved conducting forward dynamics simulations using a computational model comprising a musculoskeletal model and a neural controller model. The neural controller model proposed integrates two types of control mechanisms: feedforward control (representing muscle tone as a vector) and feedback control using proprioceptive and vestibular sensory information. An optimization was performed to determine the posture of the musculoskeletal model and the accompanied parameters of the neural controller model for each of the given muscle tone vector to minimize sway. The optimized postures to minimize sway for the optimal muscle tone vector of patients with PD were compared to the actual postures observed in these patients. The results revealed that on average, the joint-angle differences between these postures was <4°, which was less than one-tenth of the typical joint range of motion. These results suggest that patients with PD exhibit less sway in the abnormal posture than in other postures. Thus, adopting an abnormal posture with increased muscle tone can potentially serve as a valid strategy for minimizing sway in patients with PD.

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.

History-dependent muscle resistance to stretch remains high after small, posturally relevant pre-movements

The contributions of intrinsic muscle fiber resistance during mechanical perturbations to standing and other postural behaviors are unclear. Muscle short-range stiffness is known to vary depending on the current level and history of the muscle's activation, as well as the muscle's recent movement history; this property has been referred to as history dependence or muscle thixotropy. However, we currently lack sufficient data about the degree to which muscle stiffness is modulated across posturally relevant characteristics of muscle stretch and activation. We characterized the history dependence of muscle's resistance to stretch in single, permeabilized, activated, muscle fibers in posturally relevant stretch conditions and activation levels. We used a classic paired muscle stretch paradigm, varying the amplitude of a 'conditioning' triangular stretch-shorten cycle followed by a 'test' ramp-and-hold imposed after a variable inter-stretch interval. We tested low (<15%), intermediate (15-50%) and high (>50%) muscle fiber activation levels, evaluating short-range stiffness and total impulse in the test stretch. Muscle fiber resistance to stretch remained high at conditioning amplitudes of <1% optimal fiber length, L0, and inter-stretch intervals of >1 s, characteristic of healthy standing postural sway. An ∼70% attenuation of muscle resistance to stretch was reached at conditioning amplitudes of >3% L0 and inter-stretch intervals of <0.1 s, characteristic of larger, faster postural sway in balance-impaired individuals. The thixotropic changes cannot be predicted solely on muscle force at the time of stretch. Consistent with the disruption of muscle cross-bridges, muscle resistance to stretch during behavior can be substantially attenuated if the prior motion is large enough and/or frequent enough.

Posture of Healthy Subjects Modulated by Transcutaneous Spinal Cord Stimulation

Transcutaneous electrical stimulation of the spinal cord is used to restore locomotion and body weight support in patients with severe motor disorders. We studied the effects of this non-invasive stimulation on postural control in healthy subjects. Stimulation at the L1-L2 vertebrae was performed to activate the extensor muscles of the lower limbs. Because postural regulation depends on the cognitive style, the effects of the stimulation were analyzed separately in field-dependent (FD) and field-independent (FI) participants. During the study, FD and FI participants (N = 16, 25 ± 5 years, all right dominant leg) stood on a force platform in a soundproof chamber with their eyes closed. Stimulation was applied in the midline between the L1 and L2 vertebrae or over the left or right dorsal roots of the spinal cord; under the control condition, there was no stimulation. Stimulation destabilized posture in healthy subjects, whereas patients with movement disorders usually showed an improvement in postural control. In the FD participants, left dorsal root and midline stimulation increased several postural parameters by up to 30%. Dorsal root stimulation on the side of the supporting leg reduced postural control, while stimulation on the side of the dominant leg did not. No significant changes were observed in the FI participants.

Short-Term Cast Immobilization of a Unilateral Lower Extremity and Physical Inactivity Induce Postural Instability during Standing in Healthy Young Men

Previous studies have reported an increased postural sway after short-term unilateral lower limb movement restriction, even in healthy subjects. However, the associations of motion limitation have not been fully established. The question of whether short-term lower limb physical inactivity and movement restriction affect postural control in the upright position remains. One lower limb of each participant was fixed with a soft bandage and medical splint for 10 h while the participant sat on a manual wheelchair. The participants were instructed to stand still for 60 s under eyes-open (EO) and eyes-closed (EC) conditions. Using a single force plate signal, we measured the center of pressure (COP) signal in the horizontal plane and calculated the total, anterior-posterior (A-P), and medial-lateral (M-L) path lengths, sway area, and mean COP displacements in A-P and M-L directions. The COP sway increased and the COP position during the upright stance shifted from the fixed to the non-fixed side after cast removal, compared to before the cast application, under both EO and EC conditions. These findings indicated that 10 h of unilateral lower limb movement restriction induced postural instability and postural control asymmetry, suggesting the acute adverse effects of cast immobilization.

Treadmill Training Plus Semi-Immersive Virtual Reality in Parkinson's Disease: Results from a Pilot Study

Parkinson's disease (PD) is one of the most common neurodegenerative disorders that causes postural instability and gait alterations, such as reduced walking speed, shorter step length, and gait asymmetry, exposing patients to a higher risk of falling. Recently, virtual reality (VR) was added to a treadmill, in order to promote motor functional recovery and neuroplastic processes. Twenty PD patients were enrolled and randomly assigned to two groups: the experimental group (EG) and the control group (CG). In particular, patients in the EG were trained with the C-Mill, an innovative type of treadmill, which is equipped with semi-immersive VR, whereas the CG performed conventional physiotherapy. Patients in both groups were evaluated through a specific motor assessment battery at baseline (T0) and after the training (T1). Comparing pre-(T0) and post-(T1) treatment scores, in the EG, we found statistical significances in the following outcome measures: 6 Minutes Walking Test (6MWT) (p < 0.0005), Timed up and go (TUG right) (p < 0.03), Berg Balance Scale (BBS) (p < 0.006), Tinetti Scale (TS) (p < 0.002), Falls Efficacy Scale- International (FES-I), (p < 0.03) Unified PD Rating Scale-III (UPDRS) (p < 0.002), and Functional Independence Measure (FIM) (p < 0.004). Also, the CG showed statistical significances after the training. Between-group (EG and CG) analysis showed significative statistical differences in 6MWT (p < 0.006), BBS (p < 0.006), TS (p < 0.008), FES-I (p < 0.01), and FIM (p < 0.009). From our results it emerges that both groups (EG and CG) achieved better outcome scores after the treatment, suggesting that both physiotherapy interventions were effective. However, the EG training using VR seemed to have induced more improvements, especially in gait and balance skills. Then, C-Mill could be a valid adjunctive treatment in the context of gait and balance disturbances, which are very common in the PD population.

The role of torque feedback in standing balance

It has been proposed that sensory force/pressure cues are integrated within a positive feedback mechanism, which accounts for the slow dynamics of human standing behavior and helps align the body with gravity. However, experimental evidence of this mechanism remains scarce. This study tested predictions of a positive torque feedback mechanism for standing balance, specifically that differences between a "reference" torque and actual torque are self-amplified, causing the system to generate additional torque. Seventeen healthy young adults were positioned in an apparatus that permitted normal sway at the ankle until a brake on the apparatus was applied, discreetly "locking" body movement during stance. Once locked, a platform positioned under the apparatus remained in place (0 mm) or slowly translated backward (3 mm or 6 mm), tilting subjects forward. Postural behavior was characterized by two distinct responses: the center of pressure (COP) offset (i.e., change in COP elicited by the surface translation) and the COP drift (i.e., change in COP during the sustained tilt). Model simulations were performed using a linear balance control model containing torque feedback to provide a conceptual basis for the interpretation of experimental results. Holding the body in sustained tilt positions resulted in COP drifting behavior, reflecting attempts of the balance control system to restore an upright position through increases in plantar flexor torque. In line with predictions of positive torque feedback, larger COP offsets led to faster increases in COP over time. These findings provide experimental support for a positive torque feedback mechanism involved in the control of standing balance.NEW & NOTEWORTHY Using model simulations and a novel experimental approach, we tested behavioral predictions of a sensory torque feedback mechanism involved in the control of upright standing. Torque feedback is thought to reduce the effort required to stand and play a functional role in slowly aligning the body with gravity. Our results provide experimental evidence of a torque feedback mechanism and offer new and valuable insights into the sensorimotor control of human balance.

Does vibration frequency and location influence the effect of neck muscle vibration on postural sway? A cross-sectional study in asymptomatic participants

INTRODUCTION

Postural control is of utmost importance for human functioning. Cervical proprioception is crucial for balance control. Therefore, any change to it can lead to balance problems. Previous studies used neck vibration to change cervical proprioception and showed changes in postural control, but it remains unknown which vibration frequency or location causes the most significant effect. Therefore, this study aimed to investigate the effect of different vibration frequencies and locations on postural sway and to serve as future research protocol guidance.

METHODS

Seventeen healthy young participants were included in the study. We compared postural sway without vibration to postural sway with six different combinations of vibration frequency (80, 100, and 150 Hz) and location (dorsal neck muscles and sternocleidomastoid). Postural sway was evaluated using a force platform. The mean center of pressure (CoP) displacement, the root mean square (RMS), and the mean velocity in the anteroposterior and mediolateral direction were calculated, as well as the sway area. The aligned rank transform tool and a three-way repeated measures ANOVA were used to identify significant differences in postural sway variables.

RESULTS

Neck vibration caused a significant increase in all postural sway variables (p < 0.001). Neither the vibration frequency (p > 0.34) nor location (p > 0.29) nor the interaction of both (p > 0.30) influenced the magnitude of the change in postural sway measured during vibration.

CONCLUSION

Neck muscle vibration significantly changes CoP displacement, mean velocity, RMS, and area. However, we investigated and found that there were no significant differences between the different combinations of vibration frequency and location.

Postural Instability and Risk of Falls in Patients with Parkinson's Disease Treated with Deep Brain Stimulation: A Stabilometric Platform Study

Postural instability (PI) in Parkinson's disease (PD) exposes patients to an increased risk of falls (RF). While dopaminergic therapy and deep brain stimulation (DBS) improve motor performance in advanced PD patients, their effects on PI and RF remain elusive. PI and RF were assessed using a stabilometric platform in six advanced PD patients. Patients were evaluated in OFF and ON dopaminergic medication and under four DBS settings: with DBS off, DBS bilateral, and unilateral DBS of the more- or less-affected side. Our findings indicate that dopaminergic medication by itself exacerbated PI and RF, and DBS alone led to a decline in RF. No combination of medication and DBS yielded a superior improvement in postural control compared to the baseline combination of OFF medication and the DBS-off condition. Yet, for ON medication, DBS significantly improved both PI and RF. Among DBS conditions, DBS bilateral provided the most favorable outcomes, improving PI and RF in the ON medication state and presenting the smallest setbacks in the OFF state. Conversely, the more-affected side DBS was less beneficial. These preliminary results could inform therapeutic strategies for advanced PD patients experiencing postural disorders.

Cortical control of posture in fine motor skills: evidence from inter-utterance rest position

The vocal tract continuously employs tonic muscle activity in the maintenance of postural configurations. Gamma-band activity in the sensorimotor cortex underlies transient movements during speech production, yet little is known about the neural control of postural states in the vocal tract. Simultaneously, there is evidence that sensorimotor beta-band activations contribute to a system of inhibition and state maintenance that is integral to postural control in the body. Here we use electrocorticography to assess the contribution of sensorimotor beta-band activity during speech articulation and postural maintenance, and demonstrate that beta-band activity corresponds to the inhibition of discrete speech movements and the maintenance of tonic postural states in the vocal tract. Our findings identify consistencies between the neural control of posture in speech and what is previously reported in gross motor contexts, providing support for a unified theory of postural control across gross and fine motor skills.

Corticospinal Adaptation to Short-Term Horizontal Balance Perturbation Training

Sensorimotor training and strength training can improve balance control. Currently, little is known about how repeated balance perturbation training affects balance performance and its neural mechanisms. This study investigated corticospinal adaptation assessed by transcranial magnetic stimulation (TMS) and Hoffman-reflex (H-reflex) measurements during balance perturbation induced by perturbation training. Fourteen subjects completed three perturbation sessions (PS1, PS2, and PS3). The perturbation system operated at 0.25 m/s, accelerating at 2.5 m/s2 over a 0.3 m displacement in anterior and posterior directions. Subjects were trained by over 200 perturbations in PS2. In PS1 and PS3, TMS and electrical stimulation elicited motor evoked potentials (MEP) and H-reflexes in the right leg soleus muscle, at standing rest and two time points (40 ms and 140 ms) after perturbation. Body sway was assessed using the displacement and velocity of the center of pressure (COP), which showed a decrease in PS3. No significant changes were observed in MEP or H-reflex between sessions. Nevertheless, Δ MEP at 40 ms demonstrated a positive correlation with Δ COP, while Δ H-reflex at 40 ms demonstrated a negative correlation with Δ COP. Balance perturbation training led to less body sway and a potential increase in spinal-level involvement, indicating that movement automaticity may be suggested after perturbation training.

Balance Control in Individuals with Hearing Impairment: A Systematic Review and Meta-Analysis

Comprehensive insights into balance control of individuals with hearing impairment are compared with individuals with hearing. Primary sources were obtained from 7 databases including PubMed, LILACS, SCOPUS, CINAHL, PEDro, CENTRAL, and Web of Science. The search period extended from inception until January 5, 2022. The systematic review included 24 studies and 27 trials, with a total of 2,148 participants. The meta-analysis showed a significant difference in the average balance control between individuals with hearing impairment and individuals with hearing, with individuals with hearing having a favorable advantage (p = 0.001). Additionally, average balance control was found to be in favor of individuals with hearing (p = 0.001) when comparing individuals with hearing impairment who participated in sports. Finally, individuals with hearing impairment who participated in sports demonstrated a significantly higher average difference in balance control (p = 0.001) when compared to sedentary people with hearing impairment. Our meta-analysis results indicate a balance defect in individuals with hearing impairment compared to individuals with hearing. In addition, with increasing age, the balance in individuals with hearing impairment improved. Additionally, the dependence of individuals with hearing impairment on the visual and proprioception systems to maintain balance increased. Finally, there was more dependence on the proprioception than the visual system, while individuals with hearing had stronger average balance control than individuals with hearing impairment who participated in sports, when compared to sedentary people with hearing impairment.

Sleep-push movement performance in elite field hockey champions with and without training specialization

Objective

To investigate kinematic and muscle activity differences during the sleep-push movement in elite field hockey players. We hypothesized that players with specialized sleep-push movement training (specialists) would possess a lower center of mass (CoM) and enhanced reproducibility of muscle activations during the movement, compared to players without explicit movement training (non-specialists).

Methods

Ten field hockey players of the Belgian national field hockey team performed the sleep-push movement (5 specialists and 5 non-specialists). Muscle activity and kinematic data were recorded using EMG to evaluate the reproducibility of muscle activations by cross-correlation analysis and power spectral features across the movement, while a motion capture system was used to assess kinematics.

Results

Compared to non-specialists, specialists had significantly (p < 0.05) increased stick velocity (9.17 ± 1.28 m/s versus 6.98 ± 0.97 m/s) and lower CoM height (141 ± 52 mm versus 296 ± 64 mm), during the second part of the shot. Specialists also showed a significant (p < 0.05) lower power spectrum in the activity of the upper limb muscles before the shot. Superimposition of the auto crosscorrelation results demonstrated a high degree of reproducibility in specialists' muscle activations.

Conclusion

Sleep-push movements realized by elite players who are specialists in the sleep-push movement presented significant kinematics and muscular activation differences when compared to the sleep-push movements realized by elite players who were not specialists in such movement. Characterization of the specific movement and the related high-level performer's muscular strategies offers the possibility of translating sport science findings into functional training with concrete applications for coaches, players, and other key stakeholders for the continued development of the field.

People with Long Covid and ME/CFS Exhibit Similarly Impaired Balance and Physical Capacity: A Case-Case-Control Study

PURPOSE

Postural sway and physical capacity had not previously been compared between people with long COVID and people with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Therefore, this study determined postural sway and physical capacity in people with long COVID (∼16-month illness duration; n = 21) and ME/CFS (∼16-year illness duration; n = 20), vs age-matched healthy controls (n = 20).

METHODS

Postural sway was during a 30-s static stand test. Physical capacity was determined using the Timed Up and Go test and 5 Times Sit to Stand test. Throughout, participants wore isoinertial measurement units.

RESULTS

Postural sway was worse (ie, greater) in people with long COVID and ME/CFS than controls, but not different between long COVID and ME/CFS. Performance of the Timed Up and Go test and 5 Times Sit to Stand test were worse in long COVID and ME/CFS than controls, but not different between long COVID and ME/CFS. Of long COVID and ME/CFS participants, 87% and 13% exceeded the threshold for muscle weakness in the 5 Times Sit to Stand test and Timed Up and Go test, respectively.

CONCLUSIONS

These data suggest that both people with long COVID and people with ME/CFS have similarly impaired balance and physical capacity. Therefore, there is an urgent need for interventions to target postural sway and physical capacity in people with ME/CFS, and given the current pandemic, people with long COVID.

Postural stability and plantar pressure parameters in healthy subjects: variability, correlation analysis and differences under open and closed eye conditions

Introduction: The "postural control system" acts through biomechanical strategies and functional neuromuscular adaptations to maintain body balance under static and dynamic conditions. Postural stability and body weight distribution can be affected by external sensory inputs, such as different visual stimuli. Little information is available about the influence of visual receptors on stabilometric and plantar pressure parameters. The aim of this study was to analyze variability, correlations, and changes in these parameters under open- (OE) and closed-eye (CE) conditions. Methods: A total of 31 stabilometric and plantar pressure parameters were acquired in 20 young and healthy adults during baropodometric examination performed in bipedal standing under both visual conditions. Variability of parameters was evaluated via the coefficient of variation, correlation analysis via Pearson's R2, and statistical differences via the Wilcoxon test. Results: High intra-subject repeatability was found for all plantar pressure parameters and CoP-speed (CV < 40%) under OE and CE conditions, while CoP-sway area (CoPsa) and length surface function (LSF) showed larger variability (CV > 50%). Mean and peak pressures at midfoot and total foot loads showed the least number of significant correlations with other parameters under both visual conditions, whereas the arch-index and rearfoot loads showed the largest number of significant correlations. The limb side significantly affected most plantar pressure parameters. A trend of larger LSF and lower CoPsa and mean and peak pressures at the right forefoot was found under the CE condition. Discussion: The present study provides a deeper insight into the associations between postural stability and foot load. Interesting postural adaptations, particularly with respect to different visual stimuli, the effect of the dominant side, and the specific role of the midfoot in balance control were highlighted.

Analysis of the Relationship Between Muscle Tones and Abnormal Postures in a Computational Model

Patients with Parkinson's disease (PD), a neurodegenerative disorder, exhibit a characteristic posture known as a forward flexed posture. Increased muscle tone is suggested as a possible cause of this abnormal posture. For further analysis, it is necessary to measure muscle tone, but the experimental measurement of muscle tone during standing is challenging. The aim of this study was to examine the hypothesis that "In patients with PD, abnormal postures are those with a small sway at increased muscle tones" using a computational model. The muscle tones of various magnitudes were estimated using the computational model and standing data of patients with PD. The postures with small sway at the estimated muscle tones were then calculated through an optimization method. The postures and sway calculated using the computational model were compared to those of patients with PD. The results showed that the differences in posture and sway between the simulation and experimental results were small at higher muscle tones compared to those considered plausible in healthy subjects by the simulations. This simulation result indicates that the reproduced sway at high muscle tones is similar to that of actual patients with PD and that the reproduced postures with small sway locally at high muscle tones in the simulations are similar to those of patients with PD. The result is consistent with the hypothesis, reinforcing the hypothesis.Clinical relevance- This study implies that improving the increased muscle tone in patients with PD may lead to an improved abnormal posture.

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.