Feature selection of stabilometric parameters based on principal component analysis

Sensor-Based Balance Measures Outperform Modified Balance Error Scoring System in Identifying Acute Concussion

Balance assessment is an integral component of concussion evaluation and management. Although the modified balance error scoring system (mBESS) is the conventional clinical tool, objective metrics derived from wearable inertial sensors during the mBESS may increase sensitivity in detecting subtle balance deficits post-concussion. The aim of this study was to identify which stance condition and postural sway metrics obtained from an inertial sensor placed on the lumbar spine during the mBESS best discriminate athletes with acute concussion. Fifty-two college athletes in the acute phase of concussion and seventy-six controls participated in this study. Inertial sensor-based measures objectively detected group differences in the acutely concussed group of athletes while the clinical mBESS did not (p < 0.001 and p = 0.06, respectively). Mediolateral postural sway during the simplest condition of the mBESS (double stance) best classified those with acute concussion. Inertial sensors provided a sensitive and objective measure of balance in acute concussion. These results may be developed into practical guidelines to improve and simplify postural sway analysis post-concussion.

Training of support afferentation in postmenopausal women

We have recently shown a diminishing of the Menopause Index in old-aged women who underwent special training directed at the enhancement of support afferentation by increasing the plantar forefoot sensitivity (Bazanova et al., 2015). Based on these results we hypothesized, that purposeful training of support afferentation through stimulation of plantar graviceptors by Aikido practice will decrease excessive postural and psychoemotional tension not only in rest condition, but during cognitive and manual task performance too. Fluency of cognitive and motor task performance, EEG alpha power as an index of neuronal efficiency of cognitive control, amount of alpha power suppression as a visual activation measure and EMG power of forehead muscles as a sign of psychoemotional tension were compared in three groups of post-menopausal women: i) 8years training with forefeet support afferentation with Aikido practice (A), ii) 8years fitness training (F) and iii) no dedicated fitness training for past 8years (N). Simultaneous stabilometry, EEG, and frontal EMG recording were performed in sitting and standing up position in eyes closed and eyes open condition. Recording done at rest and while performing cognitive and finger motor tasks. We compared studied parameters between groups with one- and two-way analyses of variance (ANOVAs) with Bonferroni correction for multiple comparisons, followed by post hoc two-tailed unpaired t-tests. The fluency of tasks performance, EMG and alpha-EEG-activity displayed similar values in all groups in a sitting position. Center of pressure (CoP) sway length, velocity and energy demands for saving balance increased when standing up, more in group N than in groups F and A (all contrasts p values<0.002, η²>0.89). Post hoc t-tests showed increased fluency in standing in both Aikido (p<0.01) and Fitness (p<0.05) subjects in relation to untrained subjects. Increasing fluency in motor task performance was in parallel with enhancing the EEG alpha-2-power and decreasing EMG power only in A group (η²>0.77). Fluency in motor task and alpha EEG power decreased, but frontal EMG power increased in response to standing in untrained women (group N) and did not change in F group. Post hoc t-tests showed that EEG amount of alpha-2 power suppression in response to visual activation and frontal EMG power was lower in A than F and N groups (p<0.004) during motor task performance in the standing position. These results were interpreted as showing that training of forefoot plantar surface sensitivity in postmenopausal women decreases levels of psychoemotional tension and increases cognitive control caused by the psychomotor and postural challenges. Thus, Aikido training aimed at learning coordination between manual task performance and balance control by increasing the plantar support zones sensation decreases the cost of maintained vertical position and dependence of motor coordination on visual contribution.

Testing the assumption of normality in body sway area calculations during unipedal stance tests with an inertial sensor

The quantification of postural sway during the unipedal stance test is one of the essentials of posturography. A shift of center of pressure (CoP) is an indirect measure of postural sway and also a measure of a person's ability to maintain balance. A widely used method in laboratory settings to calculate the sway of body center of mass (CoM) is through an ellipse that encloses 95% of CoP trajectory. The 95% ellipse can be computed under the assumption that the spatial distribution of the CoP points recorded from force platforms is normal. However, to date, this assumption of normality has not been demonstrated for sway measurements recorded from a sacral inertial measurement unit (IMU). This work provides evidence for non-normality of sway trajectories calculated at a sacral IMU with injured subjects as well as healthy subjects.

Quantifying effects of age on balance and gait with inertial sensors in community-dwelling healthy adults

Although balance and gait deteriorate as a person ages, it is unknown if all balance and gait measures change similarly across the adult age span. We developed the Instrumented Stand and Walk test (ISAW) to provide a quick quantification of key components of balance and walking: postural sway, anticipatory postural adjustments during step initiation, gait, and turning using body-worn, inertial sensors. Our aims were to characterize how different balance and gait measures change with age and to identify key age-related measures of mobility, in a wide age range of healthy, community-dwelling adults. A total of 135 healthy, community-dwelling subjects of age range 21-89years with no history of falls were enrolled. Subjects wore inertial sensors on the wrists, ankles, sternum and lumbar area; 37 reliable and valid measures of postural sway, step initiation, gait and turning were computed. Univariate and multivariate regression analyses were performed to examine how the measures changed with age. Several distinct correlation patterns between age and ISAW measures were observed: linear deterioration, deterioration after plateau, and subtle, or no, worsening. Spatial, but not temporal, measures of gait were age-related. The strongest age correlation was found for centroidal frequency of mediolateral postural sway (r=-0.50, p≤0.001). A hierarchical regression model revealed that age was the most important predictor of mediolateral centroidal frequency, with lower sway frequencies associated with older age, independent of gender, weight, and height. Our results showed that balance and gait represent independent control systems for mobility and not all balance and gait measures deteriorate the same way with age. Postural sway during stance was more strongly related to age than any gait, gait initiation or turning measure.

Eye Movements Affect Postural Control in Young and Older Females

Visual information is used for postural stabilization in humans. However, little is known about how eye movements prevalent in everyday life interact with the postural control system in older individuals. Therefore, the present study assessed the effects of stationary gaze fixations, smooth pursuits, and saccadic eye movements, with combinations of absent, fixed and oscillating large-field visual backgrounds to generate different forms of retinal flow, on postural control in healthy young and older females. Participants were presented with computer generated visual stimuli, whilst postural sway and gaze fixations were simultaneously assessed with a force platform and eye tracking equipment, respectively. The results showed that fixed backgrounds and stationary gaze fixations attenuated postural sway. In contrast, oscillating backgrounds and smooth pursuits increased postural sway. There were no differences regarding saccades. There were also no differences in postural sway or gaze errors between age groups in any visual condition. The stabilizing effect of the fixed visual stimuli show how retinal flow and extraocular factors guide postural adjustments. The destabilizing effect of oscillating visual backgrounds and smooth pursuits may be related to more challenging conditions for determining body shifts from retinal flow, and more complex extraocular signals, respectively. Because the older participants matched the young group's performance in all conditions, decreases of posture and gaze control during stance may not be a direct consequence of healthy aging. Further research examining extraocular and retinal mechanisms of balance control and the effects of eye movements, during locomotion, is needed to better inform fall prevention interventions.

Directional measures of postural sway as predictors of balance instability and accidental falls

Despite the obvious advantages and popularity of static posturography, universal standards for posturographic tests have not been developed thus far. Most of the center-of-foot pressure (COP) indices are strongly dependent on an individual experimental design, and are susceptible to distortions, which makes results of their analysis incomparable. In this research, we present a novel approach to the analysis of the COP trajectory based on the directional features of postural sway. Our novel output measures: the sway directional indices (DI) and sway vector (SV) were applied to assess the postural stability in the group of young able-bodied subjects. Towards this aim, the COP trajectories were recorded in 100 students standing still for 60 s, with eyes open (EO) and then, with eyes closed (EC). Each record was subdivided then into 20, 30 and 60 s samples. Interclass correlation coefficients were calculated from the samples. The controlled variables (visual conditions) uniquely affected the output measures, but only in case of proper signal pretreatment (low-pass filtering). In filtering below 6 Hz, the DI and SV provided a unique set of descriptors for postural control. Both sway measures were highly independent of the trial length and the sampling frequency, and were unaffected by the sampling noise. Directional indices of COP filtered at 6 Hz showed high to very high reliability, with ICC range of 0.7-0.9. Results of a single 60 s trial are sufficient to reach acceptable reliability for both DI and SV. In conclusion, the directional sway measures may be recommended as the primary standard in static posturography.

Wearable inertial sensors for human movement analysis

INTRODUCTION

The present review aims to provide an overview of the most common uses of wearable inertial sensors in the field of clinical human movement analysis.

AREAS COVERED

Six main areas of application are analysed: gait analysis, stabilometry, instrumented clinical tests, upper body mobility assessment, daily-life activity monitoring and tremor assessment. Each area is analyzed both from a methodological and applicative point of view. The focus on the methodological approaches is meant to provide an idea of the computational complexity behind a variable/parameter/index of interest so that the reader is aware of the reliability of the approach. The focus on the application is meant to provide a practical guide for advising clinicians on how inertial sensors can help them in their clinical practice. Expert commentary: Less expensive and more easy to use than other systems used in human movement analysis, wearable sensors have evolved to the point that they can be considered ready for being part of routine clinical routine.

The use of force-plate posturography in the assessment of postural instability

Force-plate posturography is a simple method that is commonly used in the contemporary laboratory and clinic to assess postural control. Despite the obvious advantages and popularity of the method, universal standards for posturographic tests have not been developed thus far: most postural assessments are based on the standard spatiotemporal metrics of the center-of-foot pressure (COP) recorded during quiet stance. Unfortunately, the standard COP characteristics are strongly dependent on individual experimental design and are susceptible to distortions such as the noise of signal digitalization, which often makes the results from different laboratories incomparable and unreliable. The COP trajectories were recorded in subjects standing still, with eyes open (EO) and then, with eyes closed (EC). The 168 subjects were divided into 3 experimental groups: young adults, older adults, and patients with Parkinson's disease. Three novel output measures: the sway directional index (DI), the sway ratio (SR), and the sway vector (SV) were applied to assess the postural stability in the experimental groups. The controlled variables: age, pathology, and visual conditions, uniquely affected the output measures. The basic attributes of the SV: its reference position, magnitude, and azimuth, provided a unique set of descriptors for postural control that allowed me unambiguously to differentiate the decline in postural stability caused by natural ageing and Parkinson's disease. As shown in previous investigations, the SV attributes, when optimally filtered with a low-pass filter, were highly independent of the trial length and the sampling frequency, and were unaffected by the sampling noise. In conclusion, the SV may be recommended as the useful standard in static posturography.

Evaluation of an Expanded Disability Status Scale (EDSS) modeling strategy in multiple sclerosis

The Expanded Disability Status Scale (EDSS) is the most widely used scale to evaluate the degree of neurological impairment in multiple sclerosis (MS). In this paper, we report on the evaluation of an EDSS modeling strategy based on recurrence quantification analysis (RQA) of posturographic data (i.e., center of pressure, COP). A total of 133 volunteers with EDSS ranging from 0 to 4.5 participated in this study, with eyes closed. After selection of time delay (τ), embedding dimension (m) as well as threshold (radius, r) to identify recurrent points, several RQA measures were calculated for each COP's position and velocity data in the mono- and multi-dimensional RQAs. Estimation results lead to the selection of the recurrence rate (RR) of the COP's position as the most pertinent RQA measure. The performance of the models versus raw and noisy data was higher in the mono-dimensional analysis than in the multi-dimensional. This study suggests that the posturographic signal's mono-dimensional RQA is a more pertinent method to quantify disability in MS than the multi-dimensional RQA.

Fear and the Defense Cascade: Clinical Implications and Management

Evolution has endowed all humans with a continuum of innate, hard-wired, automatically activated defense behaviors, termed the defense cascade. Arousal is the first step in activating the defense cascade; flight or fight is an active defense response for dealing with threat; freezing is a flight-or-fight response put on hold; tonic immobility and collapsed immobility are responses of last resort to inescapable threat, when active defense responses have failed; and quiescent immobility is a state of quiescence that promotes rest and healing. Each of these defense reactions has a distinctive neural pattern mediated by a common neural pathway: activation and inhibition of particular functional components in the amygdala, hypothalamus, periaqueductal gray, and sympathetic and vagal nuclei. Unlike animals, which generally are able to restore their standard mode of functioning once the danger is past, humans often are not, and they may find themselves locked into the same, recurring pattern of response tied in with the original danger or trauma. Understanding the signature patterns of these innate responses--the particular components that combine to yield the given pattern of defense-is important for developing treatment interventions. Effective interventions aim to activate or deactivate one or more components of the signature neural pattern, thereby producing a shift in the neural pattern and, with it, in mind-body state. The process of shifting the neural pattern is the necessary first step in unlocking the patient's trauma response, in breaking the cycle of suffering, and in helping the patient to adapt to, and overcome, past trauma.

Reliability of modified sensory interaction test as measured with force platform

The test-retest reliability of the modified sensory interaction test on a force platform was performed in a group of 26 young and 15 elderly females for four sensory conditions: standing on firm and compliant surface with eyes open and closed. The test-retest reliability was good to excellent in both groups, with higher level of test-retest reliability in more demanding conditions. The most reliable time-domain variables for standing on firm surface with eyes open were: sway area from principal components (ICC = 0.77) for young and mean velocity, medio-lateral and total path lengths (ICC = 0.91) for elderly. For eyes closed, the most reliable variables were antero-posterior path length and sway area calculated by Fourier coefficients (ICC = 0.85) for young and medio-lateral path length (ICC = 0.93) for elderly. For compliant surface with open eyes, the most reliable variable was medio-lateral variability (ICC = 0.83) for young and total path length and mean velocity (ICC = 0.92) for elderly participants, whereas for eyes closed the most reliable variables were mean velocity, total and medio-lateral path lengths for young, and mean velocity for elderly group, all with ICC = 0.90. Modified sensory interaction test is therefore a reliable measure for balance and could be recommended as an outcome measure for balance retraining programmes.

Fuzzy logic selection as a new reliable tool to identify molecular grade signatures in breast cancer--the INNODIAG study

BACKGROUND

Personalized medicine has become a priority in breast cancer patient management. In addition to the routinely used clinicopathological characteristics, clinicians will have to face an increasing amount of data derived from tumor molecular profiling. The aims of this study were to develop a new gene selection method based on a fuzzy logic selection and classification algorithm, and to validate the gene signatures obtained on breast cancer patient cohorts.

METHODS

We analyzed data from four published gene expression datasets for breast carcinomas. We identified the best discriminating genes by comparing molecular expression profiles between histologic grade 1 and 3 tumors for each of the training datasets. The most pertinent probes were selected and used to define fuzzy molecular grade 1-like (good prognosis) and fuzzy molecular grade 3-like (poor prognosis) profiles. To evaluate the prognostic performance of the fuzzy grade signatures in breast cancer tumors, a Kaplan-Meier analysis was conducted to compare the relapse-free survival deduced from histologic grade and fuzzy molecular grade classification.

RESULTS

We applied the fuzzy logic selection on breast cancer databases and obtained four new gene signatures. Analysis in the training public sets showed good performance of these gene signatures for grade (sensitivity from 90% to 95%, specificity 67% to 93%). To validate these gene signatures, we designed probes on custom microarrays and tested them on 150 invasive breast carcinomas. Good performance was obtained with an error rate of less than 10%. For one gene signature, among 74 histologic grade 3 and 18 grade 1 tumors, 88 cases (96%) were correctly assigned. Interestingly histologic grade 2 tumors (n = 58) were split in these two molecular grade categories.

CONCLUSION

We confirmed the use of fuzzy logic selection as a new tool to identify gene signatures with good reliability and increased classification power. This method based on artificial intelligence algorithms was successfully applied to breast cancers molecular grade classification allowing histologic grade 2 classification into grade 1 and grade 2 like to improve patients prognosis. It opens the way to further development for identification of new biomarker combinations in other applications such as prediction of treatment response.

The filtering of the posturographic signals shows the age related features

Objective. Lower frequencies of slow oscillations of the posturographic signals can be removed using high-pass filtering. This procedure releases postural reflexes possessing higher frequencies and lower amplitude range. Mutual dependence between the x and y components of posturographic signals was analyzed using principal component analysis (PCA). The posturographic signals of old patients with idiopathic gait disturbance were compared with the control group of similar age and with younger patients. There was also the analysis of the influence of the eyes state (open versus closed) and the head position (normal or bent back). The statistically significant differences in the mutual dependence between x and y components between the groups of patients were analyzed using MANOVA. The significant differences were observed mainly in the range of filter frequencies f = 0.1–1.5 Hz and f = 2.2–5.5 Hz with a maximum effect at approximately 4-5 Hz. A detailed post-hoc analysis is also presented. The differences in the higher frequency range suggest the main disturbance to be connected with the spinal reflexes. Visual and vestibular support appear insufficient for postural stability control in the idiopathic gait disturbance group. The results suggest that idiopathic gait disturbance is the final stage of the aging process of postural system.

Objective and subjective measures reflect different aspects of balance in multiple sclerosis

The objective of this study was to evaluate relationships between subjective and objective measures of balance in multiple sclerosis (MS). In 54 subjects with MS, balance was measured objectively with the Sensory Organization Test (SOT) using dynamic posturography and subjectively with the Activities-specific Balance Confidence (ABC) Scale and the Falls Efficacy Scale-International (FES-I). MS-related disability was assessed with the Expanded Disability Status Scale (EDSS). Relationships between the magnitude (root mean square, range, and area) as well as velocity of center of pressure sway (calculated from the center of pressure signal from the SOT), composite SOT, ABC Scale, FES-I, and EDSS scores were assessed. The magnitude and velocity of center of pressure sway was statistically significantly correlated with the ABC Scale (rho = -0.2 to -0.5), FES-I (rho = 0.3 to 0.5), and EDSS (rho = 0.3 to 0.4). The composite SOT was also statistically significantly correlated with the ABC Scale, FES-I, and EDSS. Objective balance measures, as reflected by posturography, were significantly related to subjective reports of imbalance and clinical measures of disability in MS. The relationships are moderate to weak, indicating that a comprehensive description of balance problems in people with MS likely requires both objective and subjective balance measures.

Postural control in Parkinson's disease

Introduction

Postural instability is one of the most disabling features of Parkinson's disease.

Objective

To evaluate postural balance in Parkinson's disease.

Methods

Thirty patients with Parkinson's disease were compared with controls using Tetrax™ interactive balance system posturography.

Results

For different positions, patients with Parkinson's disease showed a significantly higher weight distribution index, fall index, Fourier transformation at low-medium frequencies (F2–F4), and significantly lower right/left and toe/heel synchronization versus controls.

Conclusion

Postural imbalance in Parkinson's disease patients is characterized by the abnormalities of weight distribution index, synchronization index, Fourier transformation index, and fall index as measured by Tetrax™ posturography.

What is the role body sway deviation and body sway velocity play in postural stability in older adults?

This cross sectional study focused on how Postural Stability (PS) indicators: body sway deviation (BSD) and body sway velocity (BSV), change with age and their association with levels of social and physical activity. Observational study: 80 older adults (aged: 60-96) were purposefully recruited from two sources: the University of the Third Age (TAU) (n = 35) and a residential care home (CH) (n = 45). Differences in the indicators of PS, approximated through Centre of Pressure (COP) measurements, were assessed by the Romberg Stance Test (Test A) subsequently repeated on 10 cm foam surface (Test B), using a Kistler Dynamometric Platform. The RCH Group was older, had higher BMI and was less socially and physically active, showed more body sway in all indicators compared to TAU group. For all participants body sway velocity (BSV) was significantly correlated with age. The strength of correlation of body sway deviation (BSD) with age was also significant but not as strong. The findings indicate in line with previous studies that deterioration in BSV is associated with poor PS more than deterioration in BSD.

Objective biomarkers of balance and gait for Parkinson's disease using body-worn sensors

Balance and gait impairments characterize the progression of Parkinson's disease (PD), predict the risk of falling, and are important contributors to reduced quality of life. Advances in technology of small, body-worn, inertial sensors have made it possible to develop quick, objective measures of balance and gait impairments in the clinic for research trials and clinical practice. Objective balance and gait metrics may eventually provide useful biomarkers for PD. In fact, objective balance and gait measures are already being used as surrogate endpoints for demonstrating clinical efficacy of new treatments, in place of counting falls from diaries, using stop-watch measures of gait speed, or clinical balance rating scales. This review summarizes the types of objective measures available from body-worn sensors. The metrics are organized based on the neural control system for mobility affected by PD: postural stability in stance, postural responses, gait initiation, gait (temporal-spatial lower and upper body coordination and dynamic equilibrium), postural transitions, and freezing of gait. However, the explosion of metrics derived by wearable sensors during prescribed balance and gait tasks, which are abnormal in individuals with PD, do not yet qualify as behavioral biomarkers, because many balance and gait impairments observed in PD are not specific to the disease, nor have they been related to specific pathophysiologic biomarkers. In the future, the most useful balance and gait biomarkers for PD will be those that are sensitive and specific for early PD and are related to the underlying disease process.

The effects of wobble board training on the eyes open and closed static balance ability of adolescents with down syndrome

[Purpose] The aim of the present study was to examine the influence of wobble board training on static balance, with and without vision, of adolescents with Down syndrome (DS). [Subjects] Ten adolescents with DS were recruited for this study. [Methods] Participants performed quiet standing with their eyes open and closed, pre- and post-wobble board training. During quiet standing, the center of pressure (COP) data was recorded using a force plate. To assess the static balance ability of the participants, the 95% confidence ellipse area of COP was calculated. The paired t-test was used to compare the 95% confidence ellipse area of COP between the eyes open and closed conditions, and between pre- and post-training. [Results] Although there was no significant difference in the 95% confidence ellipse area of COP between with and without vision, the 95% confidence ellipse area of COP decreased significantly after wobble board training. [Conclusion] These findings suggest that wobble board training is an effective at improving the static balance ability of adolescents with DS.

Between-day reliability of centre of pressure measures for balance assessment in hemiplegic stroke patients

Background

Stroke patients have impaired postural balance that increases the risk of falls and impairs their mobility. Assessment of postural balance is commonly carried out by recording centre of pressure (CoP) displacements, but the lack of data concerning reliability of these measures compromises their interpretation. The purpose of this study was to investigate the between-day reliability of six CoP-based variables, in order to provide i) reliability data for monitoring postural sway and weight-bearing asymmetry of stroke patients in clinical practice and ii) consistent assessment method of measurement error for applications in physical medicine and rehabilitation.

Methods

Postural balance of 20 stroke patients was assessed in quiet standing on a force platform, in two sessions, 7 days apart. Six CoP-based variables were collected in eyes open and eyes closed conditions: postural sway was assessed with mean and standart deviation of CoP-velocity, CoP-velocity along the mediolateral and anteroposterior axes, and confidence ellipse area (CE_AREA); weight-bearing asymmetry was assessed with mean CoP position along the mediolateral axis (CoP_ML). The intraclass correlation coefficient (ICC) was used to determine the level of agreement between test-retest. Small real difference (SRD), corresponding to the smallest change that indicates a real improvement for a single individual, was used to determine the extent of measurement error.

Results

ICCs were satisfactory (>0.9) for all CoP-based variables, except for CE_AREA in eyes open condition and CoP_ML (<0.8). The SRDs (eyes open/closed conditions) were: 6.1/9.5 mm.s^-1 for mean velocity; 12.3/12.2 mm.s^-1 for standard deviation of CoP-velocity; 3.6/5.5 mm.s^-1 and 4.9/7.3 mm.s^-1 for CoP-velocity in mediolateral and anteroposterior axes, respectively; 17.4/21.4 mm for CoP_ML. Because CE_AREA showed heteroscedasticity of measurement error distribution, SRD (eyes open/closed conditions) was expressed as a percentage (121/75%) and a ratio (3.68/2.16) obtained after log-antilog procedure.

Conclusions

In clinical practice, the CoP-based velocity variables should be prefer to CE_AREA to assess and monitor postural sway over time in hemiplegic stroke patients. The poor reliability of CoP_ML compromises its use to assess weight-bearing asymmetry. The procedure we used could be applied in reliability studies concerning other CoP-based variables or other biological variables in the field of physical medicine and rehabilitation.

Center-of-pressure total trajectory length is a complementary measure to maximum excursion to better differentiate multidirectional standing limits of stability between individuals with incomplete spinal cord injury and able-bodied individuals

Background

Sensorimotor impairments secondary to a spinal cord injury affect standing postural balance. While quasi-static postural balance impairments have been documented, little information is known about dynamic postural balance in this population. The aim of this study was to quantify and characterize dynamic postural balance while standing among individuals with a spinal cord injury using the comfortable multidirectional limits of stability test and to explore its association with the quasi-static standing postural balance test.

Methods

Sixteen individuals with an incomplete spinal cord injury and sixteen able-bodied individuals participated in this study. For the comfortable multidirectional limits of stability test, participants were instructed to lean as far as possible in 8 directions, separated by 45° while standing with each foot on a forceplate and real-time COP visual feedback provided. Measures computed using the center of pressure (COP), such as the absolute maximal distance reached (COP_max) and the total length travelled by the COP to reach the maximal distance (COP_length), were used to characterize performance in each direction. Quasi-static standing postural balance with eyes open was evaluated using time-domain measures of the COP. The difference between the groups and the association between the dynamic and quasi-static test were analyzed.

Results

The COP_length of individuals with SCI was significantly greater (p ≤ 0.001) than that of able-bodied individuals in all tested directions except in the anterior and posterior directions (p ≤ 0.039), indicating an increased COP trajectory while progressing towards their maximal distance. The COP_max in the anterior direction was significantly smaller for individuals with SCI. Little association was found between the comfortable multidirectional limits of stability test and the quasi-static postural balance test (r ≥ −0.658).

Conclusion

Standing dynamic postural balance performance in individuals with an incomplete spinal cord injury can be differentiated from that of able-bodied individuals with the comfortable limits of stability test. Performance among individuals with an incomplete spinal cord injury is characterized by lack of precision when reaching. The comfortable limits of stability test provides supplementary information and could serve as an adjunct to the quasi-static test when evaluating postural balance in an incomplete spinal cord injury population.

Influence of visual inputs on quasi-static standing postural steadiness in individuals with spinal cord injury

Postural steadiness while standing is impaired in individuals with spinal cord injury (SCI) and could be potentially associated with increased reliance on visual inputs. The purpose of this study was to compare individuals with SCI and able-bodied participants on their use of visual inputs to maintain standing postural steadiness. Another aim was to quantify the association between visual contribution to achieve postural steadiness and a clinical balance scale. Individuals with SCI (n = 15) and able-bodied controls (n = 14) performed quasi-static stance, with eyes open or closed, on force plates for two 45 s trials. Measurements of the centre of pressure (COP) included the mean value of the root mean square (RMS), mean COP velocity (MV) and COP sway area (SA). Individuals with SCI were also evaluated with the Mini-Balance Evaluation Systems Test (Mini BESTest), a clinical outcome measure of postural steadiness. Individuals with SCI were significantly less stable than able-bodied controls in both conditions. The Romberg ratios (eyes open/eyes closed) for COP MV and SA were significantly higher for individuals with SCI, indicating a higher contribution of visual inputs for postural steadiness in that population. Romberg ratios for RMS and SA were significantly associated with the Mini-BESTest. This study highlights the contribution of visual inputs in individuals with SCI when maintaining quasi-static standing posture.

Relationship between postural control and restricted, repetitive behaviors in autism spectrum disorders

Restricted, repetitive behaviors (RRBs) are one of the core diagnostic criteria of autism spectrum disorders (ASD), and include simple repetitive motor behaviors and more complex cognitive behaviors, such as compulsions and restricted interests. In addition to the core symptoms, impaired movement is often observed in ASD. Research suggests that the postural system in individuals with ASD is immature and may never reach adult levels. RRBs have been related to postural sway in individuals with mental retardation. Our goals were to determine whether subjects with ASD had greater postural sway and whether RBS-R scores were related to the magnitude of postural sway. We compared the center of pressure (COP) sway area during quiet stance with scores on the Repetitive Behavior Scale-Revised (RBS-R) in children with ASD and typically developing (TD) controls ages 3-16. All subjects had Non-verbal IQ > 70. Subjects performed four quiet stance trials at a self-selected stance width for 20 s. Subjects with ASD had greater postural sway area compared to controls. Not surprisingly, subjects with ASD exhibited greater frequencies and intensities of RRBs overall and on all six subscales. Further, there was a positive correlation between postural sway area and presence of RRBs. Interestingly, results of the postural sway area for the ASD group suggests that roughly half of the ASD subjects scored comparable to TD controls, whereas the other half scored >2 SD worse. Motor impaired children did not have significantly worse IQ scores, but were younger and had more RRBs. Results support previous findings of relationships between RRBs and postural control. It appears that motor control impairments may characterize a subset of individuals with ASD. Better delineation of motor control abilities in individuals with ASD will be important to help explain variations of abilities in ASD, inform treatment, and guide examination of underlying neural involvement in this very diverse disorder.

Dynamical and stabilometric measures are complementary for the characterization of postural fluctuations in older women

We investigate the complementarities of several measures extracted from center of pressure (COP) recordings during quiet standing, in older women. The selected variables include classical stabilometric measures (SMs) and several dynamical measures (DMs). The computed DMs quantify various features of the temporal structure of COP signals, including predictability, regularity and smoothness of the trajectories. The postural fluctuations of a group of 101 healthy older women were recorded by means of a force platform. After estimating the SMs and DMs from the COP data, we used principal components analysis (PCA) to quantify the contribution of each measure. The results suggest that SMs and DMs are complementary. In addition, the different DMs are globally not redundant. This finding is a reinforcement argument in favor of the use of DMs as postural signatures.

Measuring regularity of human postural sway using approximate entropy and sample entropy in patients with Ehlers-Danlos syndrome hypermobility type

Ligament laxity in Ehlers-Danlos syndrome hypermobility type (EDS-HT) patients can influence the intrinsic information about posture and movement and can have a negative effect on the appropriateness of postural reactions. Several measures have been proposed in literature to describe the planar migration of CoP over the base of support, and the most used in clinical field are the CoP excursions in antero-posterior and medio-lateral direction. In recent years a growing number of studies have been designed to explore the complexity of the COP trajectories during quiet standing. We assessed 13 adults with EDS-HT (EDSG) and 20 healthy adults (CG) during static posture, evaluating the CoP using time and frequency domain analysis and entropy analysis (SampEn and ApEn parameters). Higher values of CoP displacements in medio-lateral and anterior-posterior directions for EDSG than CG were found; no differences were observed in CoP frequency. The entropy analysis showed lower value for EDSG than CG, pointing out the needing of EDSG to concentrate more attention on postural control, loosing complexity and reflecting a less automatized postural control.

Biomechanical assessment of balance and posture in subjects with ankylosing spondylitis

Background

Ankylosing spondylitis is a major chronic rheumatic disease that predominantly affects axial joints, determining a rigid spine from the occiput to the sacrum. The dorsal hyperkyphosis may induce the patients to stand in a stooped position with consequent restriction in patients’ daily living activities. The aim of this study was to develop a method for quantitatively and objectively assessing both balance and posture and their mutual relationship in ankylosing spondylitis subjects.

Methods

The data of 12 healthy and 12 ankylosing spondylitis subjects (treated with anti-TNF-α stabilized), with a mean age of 51.42 and 49.42 years; mean BMI of 23.08 and 25.44 kg/m² were collected. Subjects underwent a morphological examination of the spinal mobility by means of a pocket compass needle goniometer, together with an evaluation of both spinal and hip mobility (Bath Ankylosing Spondylitis Metrology Index), and disease activity (Bath Ankylosing Spondylitis Disease Activity Index). Quantitative evaluation of kinematics and balance were performed through a six cameras stereophotogrammetric system and a force plate. Kinematic models together with a test for evaluating balance in different eye level conditions were developed. Head protrusion, trunk flexion-extension, pelvic tilt, hip-knee-ankle flexion-extension were evaluated during Romberg Test, together with centre of pressure parameters.

Results

Each subject was able to accomplish the required task. Subjects’ were comparable for demographic parameters. A significant increment was observed in ankylosing spondylitis subjects for knee joint angle with the target placed at each eye level on both sides (p < 0.042). When considering the pelvic tilt angle a statistically significant reduction was found with the target placed respectively at 10° (p = 0.034) and at 30° (p = 0.019) less than eye level. Furthermore in ankylosing spondylitis subjects both hip (p = 0.048) and ankle (p = 0.029) joints angles differs significantly. When considering the posturographic parameters significant differences were observed for ellipse, center of pressure path and mean velocity (p < 0.04). Goniometric evaluation revealed significant increment of thoracic kyphosis reduction of cervical and lumbar range of motion compared to healthy subjects.

Conclusions

Our findings confirm the need to investigate both balance and posture in ankylosing spondylitis subjects. This methodology could help clinicians to plan rehabilitation treatments.

ISway: a sensitive, valid and reliable measure of postural control

BACKGROUND

Clinicians need a practical, objective test of postural control that is sensitive to mild neurological disease, shows experimental and clinical validity, and has good test-retest reliability. We developed an instrumented test of postural sway (ISway) using a body-worn accelerometer to offer an objective and practical measure of postural control.

METHODS

We conducted two separate studies with two groups of subjects. Study I: sensitivity and experimental concurrent validity. Thirteen subjects with early, untreated Parkinson's disease (PD) and 12 age-matched control subjects (CTR) were tested in the laboratory, to compare sway from force-plate COP and inertial sensors. Study II: test-retest reliability and clinical concurrent validity. A different set of 17 early-to-moderate, treated PD (tested ON medication), and 17 age-matched CTR subjects were tested in the clinic to compare clinical balance tests with sway from inertial sensors. For reliability, the sensor was removed, subjects rested for 30 min, and the protocol was repeated. Thirteen sway measures (7 time-domain, 5 frequency-domain measures, and JERK) were computed from the 2D time series acceleration (ACC) data to determine the best metrics for a clinical balance test.

RESULTS

Both center of pressure (COP) and ACC measures differentiated sway between CTR and untreated PD. JERK and time-domain measures showed the best test-retest reliability (JERK ICC was 0.86 in PD and 0.87 in CTR; time-domain measures ICC ranged from 0.55 to 0.84 in PD and from 0.60 to 0.89 in CTR). JERK, all but one time-domain measure, and one frequency measure were significantly correlated with the clinical postural stability score (r ranged from 0.50 to 0.63, 0.01 < p < 0.05).

CONCLUSIONS

Based on these results, we recommend a subset of the most sensitive, reliable, and valid ISway measures to characterize posture control in PD: 1) JERK, 2) RMS amplitude and mean velocity from the time-domain measures, and 3) centroidal frequency as the best frequency measure, as valid and reliable measures of balance control from ISway.

Invariant density analysis: modeling and analysis of the postural control system using Markov chains

In this paper, a novel analysis technique, invariant density analysis (IDA), is introduced. IDA quantifies steady-state behavior of the postural control system using center of pressure (COP) data collected during quiet standing. IDA relies on the analysis of a reduced-order finite Markov model to characterize stochastic behavior observed during postural sway. Five IDA parameters characterize the model and offer physiological insight into the long-term dynamical behavior of the postural control system. Two studies were performed to demonstrate the efficacy of IDA. Study 1 showed that multiple short trials can be concatenated to create a dataset suitable for IDA. Study 2 demonstrated that IDA was effective at distinguishing age-related differences in postural control behavior between young, middle-aged, and older adults. These results suggest that the postural control system of young adults converges more quickly to their steady-state behavior while maintaining COP nearer an overall centroid than either the middle-aged or older adults. Additionally, larger entropy values for older adults indicate that their COP follows a more stochastic path, while smaller entropy values for young adults indicate a more deterministic path. These results illustrate the potential of IDA as a quantitative tool for the assessment of the quiet-standing postural control system.

The effect of vision on postural strategies in Prader-Willi patients

The aim of this study was to quantify the role of visual contribution in patients with Prader-Willi syndrome (PWS) on balance maintenance using a force platform. We enrolled 14 individuals with PWS free from conditions associated with impaired balance, 44 obese (OG) and 20 healthy controls (CG). Postural sway was measured for 60s while standing on a force platform (Kistler, CH; acquisition frequency: 500 Hz) integrated with a video system. Patients maintained an upright standing position with Open Eyes (OE) and then with Closed Eyes (CE). The ratio between the value of the parameter under OE and CE conditions was measured. Under OE condition PWS and OG were characterized by higher postural instability than CG, with the PWS group showing poorer balance capacity than OG. The Romberg ratio showed that while OG and CG had lower balance without vision, PWS maintained the same performance changing from OE to CE. The integration of different sensory inputs appears similar in OG and CG with higher postural stability under OE than CE. Balance in PWS is not influenced by the elimination of visual input.

Fractal dimension approach in postural control of subjects with Prader-Willi Syndrome

BACKGROUND

Static posturography is user-friendly technique suitable for the study of the centre of pressure (CoP) trajectory. However, the utility of static posturography in clinical practice is somehow limited and there is a need for reliable approaches to extract physiologically meaningful information from stabilograms. The aim of this study was to quantify the postural strategy of Prader-Willi patients with the fractal dimension technique in addition to the CoP trajectory analysis in time and frequency domain.

METHODS

11 adult patients affected by Prader-Willi Syndrome (PWS) and 20 age-matched individuals (

CONTROL GROUP

CG) were included in this study. Postural acquisitions were conducted by means of a force platform and the participants were required to stand barefoot on the platform with eyes open and heels at standardized distance and position for 30 seconds. Platform data were analysed in time and frequency domain. Fractal Dimension (FD) was also computed.

RESULTS

The analysis of CoP vs. time showed that in PWS participants all the parameters were statistically different from CG, with greater displacements along both the antero-posterior and medio-lateral direction and longer CoP tracks. As for frequency analysis, our data showed no significant differences between PWS and CG. FD evidenced that PWS individuals were characterized by greater value in comparison with CG.

CONCLUSIONS

Our data showed that while the analysis in the frequency domain did not seem to explain the postural deficit in PWS, the FD method appears to provide a more informative description of it and to complement and integrate the time domain analysis.

Trunk accelerometry reveals postural instability in untreated Parkinson's disease

While several studies have shown that subjects with advanced Parkinson's disease (PD) exhibit abnormalities in sway parameters during quiet standing, abnormalities of postural sway associated with untreated PD have not been reported. Although not clinically apparent, we hypothesized that spontaneous sway in quiet stance is abnormal in people with untreated PD. We examined 13 subjects, recently diagnosed with PD, who were not yet taking any anti-parkinsonian medications and 12 healthy, age-matched control subjects. Postural sway was measured with a linear accelerometer on the posterior trunk (L5 level) and compared with traditional force plate measures of sway. Subjects stood for 2 min under two conditions: eyes open (EO) and eyes closed (EC). One of the most discriminative measures of postural changes in subjects with untreated PD was the increased 'JERK' of lower trunk in the EO condition, measured with the accelerometer. Root mean square and the frequency dispersion of postural sway in the EO condition also discriminated sway in untreated PD subjects compared to control subjects. We conclude that accelerometer-based sway metrics could be used as objective measures of postural instability in untreated PD. Accelerometer-based analysis of spontaneous sway may provide a powerful tool for early clinical trials and for monitoring the effects of treatment of balance disorders in subjects with PD.

Postural control after traumatic brain injury in patients with neuro-ophthalmic deficits

Postural instability is a common and devastating consequence of traumatic brain injury (TBI). The majority of TBI patients also suffer from neuro-ophthalmic deficits that can be an important contributing element to their sensation of vertigo and dizziness. Static posturography aims at the objective evaluation of patient balance impairment, but is usually affected by large inter- and intra-subject variability. Here we propose a protocol based on 10 randomized trials stimulating in different ways the visual and vestibular systems. Due to its completeness, our protocol highlights the specific residual difficulties of each patient in the various conditions. In this way, it was possible to evidence significant balance abnormalities in TBI patients with respect to controls. Moreover, by means of a multivariate analysis we were able to discriminate different levels of residual neuro-ophthalmic impairment.

Postural adaptations to long-term training in Prader-Willi patients

Background

Improving balance and reducing risk of falls is a relevant issue in Prader-Willi Syndrome (PWS). The present study aims to quantify the effect of a mixed training program on balance in patients with PWS.

Methods

Eleven adult PWS patients (mean age: 33.8 ± 4.3 years; mean BMI: 43.3 ± 5.9 Kg/m2) attended a 2-week training program including balance exercises during their hospital stay. At discharge, Group 1 (6 patients) continued the same exercises at home for 6 months, while Group 2 (5 patients) quitted the program. In both groups, a low-calorie, well-balanced diet of 1.200 kcal/day was advised. They were assessed at admission (PRE), after 2 weeks (POST1) and at 6-month (POST2). The assessment consisted of a clinical examination, video recording and 60-second postural evaluation on a force platform. Range of center of pressure (CoP) displacement in the antero-posterior direction (RANGE_AP index) and the medio-lateral direction (RANGE_ML index) and its total trajectory length were computed.

Results

At POST1, no significant changes in all of the postural parameters were observed. At completion of the home program (POST2), the postural assessment did not reveal significant modifications. No changes in BMI were observed in PWS at POST2.

Conclusions

Our results showed that a long-term mixed, but predominantly home-based training on PWS individuals was not effective in improving balance capacity. Possible causes of the lack of effectiveness of our intervention include lack of training specificity, an inadequate dose of exercise, an underestimation of the neural and sensory component in planning rehabilitation exercise and failed body weight reduction during the training. Also, the physiology of balance instability in these patients may possibly compose a complex puzzle not affected by our exercise training, mainly targeting muscle weakness.

Relevance of orthostatic posturography for clinical evaluation of hip and knee joint arthroplasty patients

In order to verify whether orthostatic posturography (OP) can support clinical assessment of total hip (THA) and knee arthroplasty (TKA), 81 subjects with THA and 100 with TKA were recruited and compared with 59 healthy volunteers. All patients were tested one or two days prior to surgery; 42 subjects (20 THA and 22 TKA) were tested again after six months, and 34 (14 THA and 20 TKA) yet again after 12 months. OP was performed using a Kistler 9286A piezoelectric force plate and the following postural parameters (PPs) were adopted on account of their functional meaning: mean velocity and the root mean square of the distance of the centre of pressure (CoP), sway area, and 95% of the CoP power frequency. Eye condition and fatigue related to the test duration were also examined. The three most meaningful PPs were identified and a logarithmic transformation was then applied to these, as well as standardization. Almost all the PP values were higher preoperatively in the patients as compared with the healthy subjects and it was possible to detect many statistically significant differences between patients and healthy subjects. However, when examining the 181 subjects at the preoperative stage, the PPs did not show congruence with the clinical scores as well as they did during follow-up. Therefore, the use of the OP is not recommended to monitor patients undergoing THA or TKA.

Mechanisms underlying center of pressure displacements in obese subjects during quiet stance

Objective

the aim of this study was to assess whether reduced balance capacity in obese subjects is secondary to altered sensory information.

Design

cross sectional study.

Subjects

44 obese (BMI = 40.6 ± 4.6 kg/m² , age = 34.2 ± 10.8 years, body weight: 114,0 ± 16,0 Kg, body height 167,5 ± 9,8 cm) and 20 healthy controls (10 females, 10 males, BMI: 21.6 ± 2.2 kg/m², age: 30.5 ± 5.5 years, body weight: 62,9 ± 9,3 Kg, body height 170,1 ± 5,8 cm) were enrolled.

Measurements

center of pressure (CoP) displacements were evaluated during quiet stance on a force platform with eyes open (EO) and closed (EC). The Romberg quotient (EC/EO) was computed and compared between groups.

Results

we found statistically significant differences between obese and controls in CoP displacements (p < 0.01) and no statistically significant differences in Romberg quotients (p > 0.08).

Conclusion

the increased CoP displacements in obese subjects do not need an hypothesis about altered sensory information. The integration of different sensory inputs appears similar in controls and obese. In the latter, the increased mass, ankle torque and muscle activity may probably account for the higher CoP displacements.

The effect of neck torsion on postural stability in subjects with persistent whiplash

Dysfunction of cervical receptors in neck disorders has been shown to lead to disturbances in postural stability. The neck torsion manoeuvre used in the smooth pursuit neck torsion (SPNT) test is thought to be a specific measure of neck afferent dysfunction on eye movement in those with neck pain. This study aimed to determine whether neck torsion could change balance responses in those with persistent whiplash-associated disorders (WADs). Twenty subjects with persistent WAD and 20 healthy controls aged between 18 and 50 years stood on a computerised force plate with eyes closed in comfortable stance under 5 conditions: neutral head, head turned to left and right and neck torsion to left and right. Root mean square (rms) amplitude of sway was measured in the anterior-posterior (AP) and medial-lateral (ML) directions. The whiplash group had significantly greater rms amplitude in the AP direction following neck torsion compared to the control group (p < 0.03). The results show that the neck torsion manoeuvre may lead to greater postural deficits in individuals with persistent WAD and provides further evidence of neck torsion to identify abnormal cervical afferent input, as an underlying cause of balance disturbances in WAD. Further research is warranted.

Time and frequency analysis of the static balance in young adults with Down syndrome

The main objective of this study is to understand the differences in equilibrium control between normal subjects and those with Down syndrome. A total of 54 subjects participated voluntarily, divided into control group and Down syndrome group. The equilibrium of the subjects was tested under two conditions: bipedal support with eyes open and closed. The signals were analyzed in a time and frequency domain. The statistical parameters selected (i.e., RMS distance, mean velocity, mean frequency and sway area) to analyze the behavior of the center of pressures (CoP) are calculated employing the result of the combination of the time series data in both directions (i.e. resultant distance). In order to calculate the frequency bands produced by the displacements of the CoP, a Fast Fourier Transform of the data was performed. The group with Down syndrome showed poorer static equilibrium control than the control group in the time domain. In the frequency domain, we found differences between the groups in the distribution of energy in the frequency bands analyzed. In addition, we observed the existence of an interaction effect of the group and the condition tested (p<0.001). These findings show that in the absence of visual information, the control group increases the energy at low frequencies, while the group with Down syndrome decreases it. Additionally, the lower amount of energy observed in this band under the 'eyes closed' condition may serve to identify abnormalities in the functioning of the vestibular apparatus of individuals with Down syndrome and/or difficulties experienced by these individuals in extracting relevant information from this route.

Characterisation of balance capacity in Prader-Willi patients

Being severely overweight is a distinctive clinical feature of Prader-Willi Syndrome (PWS). This explorative study aims to characterise balance capacity in PWS as compared to non-genetically obese patients (O) and to a group of normal-weight individuals (CG). We enrolled 14 PWS patients: 8 females and 6 males (BMI = 41.3 ± 7.3 kg/m(2), age = 32.86+4.42 years), 44 obese individuals, 22 males and 22 females (BMI = 40.6 ± 4.6 kg/m(2), age = 34.2 ± 10.7 years) and 20 controls (CG: 10 females and 10 males; BMI: 21.6 ± 1.6 kg/m(2); age: 30.5 ± 5.3 years). Postural acquisitions were conducted by means of a force platform from which the COP pattern vs time was analysed. The participants were required to stand barefoot on the platform with eyes open and heels at standardized distance and position for 60s. All of the analysed parameters were statistically different from O and CG groups. PWS individuals showed greater displacements in both the A/P and M/L direction (RMS, RANGE and MV indices). Analysis of the overall planar movement of the CoP showed that the PWS patients were characterised by higher RMS distance from the centre (RMS(CoP) index) and area of confidence ellipse (AREA(CoP) index) when compared both to obese and healthy individuals. PWS patients showed a poorer balance capacity than their non-genetically obese counterparts and healthy individuals, with greater differences in both the A/P and M/L direction than O. Rehabilitation programs for PWS should take this finding into account. In addition to weight loss, strengthening of ankle flexors/extensors, and balance training, tailored interventions aimed at improving A/P control should be given particular consideration.

Development of a protocol for improving the clinical utility of posturography as a fall-risk screening tool

BACKGROUND

The usefulness of posturography in the clinical screening of older adults for fall risk has been limited by a lack of standardization in testing methodology and data reporting. This study determines which testing condition and postural sway measures best differentiate recurrent fallers and nonrecurrent fallers.

METHODS

One hundred and fifty older adults were categorized based on their fall status in the past year. Participants performed four quiet-standing tasks, eyes open and eyes closed in both comfortable and narrow stance, for 60 seconds while standing on a force-measuring platform. Traditional and fractal measures were calculated from the center of pressure data. Logistic regression was performed to determine the model for each condition that best discriminated between recurrent fallers and nonrecurrent fallers.

RESULTS

The eyes closed comfortable stance condition, with its associated model, best differentiated recurrent fallers and nonrecurrent fallers. Medial-lateral sway velocity, anterior-posterior short-term α-scaling exponent, medial-lateral short-term α-scaling exponent, mean frequency, body mass index, and age were included in this model. Sensitivity of the model was 75%, and specificity was 94%.

CONCLUSIONS

This resulting model demonstrates potential to differentiate recurrent fallers and nonrecurrent fallers in an eyes closed comfortable stance condition. The inclusion of traditional sway parameters, fractal measures, and personal characteristics in this model demonstrates the importance of considering multiple descriptions of postural stability together rather than using only a single measure to establish fall risk.

Principal component analysis detects sleepiness-related changes in balance control

Computerized posturography exploits balance scores that quantify the size, dynamics, or structure of the recorded sway. Since people employ different balance strategies, one single balance score will not detect balance changes in all subjects. Principal component analysis (PCA) can combine balance scores that quantify different features into one new balance score. We tested the score with 20 subjects by measuring their balance every 2 h during 28 h of sustained waking. The new balance score was more sensitive than its components (p<0.001 vs. p≥0.051) to the small sleepiness-related balance decrements that occurred during the short 28-h period. PCA provided a more sensitive balance score that applied to all of the subjects.