Changing control strategies during standard assessment using computerized dynamic posturography with older women

Three Hertz postural leg tremor impairs posture maintenance in multiple system atrophy-cerebellar type

BACKGROUND

Three-Hz postural leg tremor has recently been identified as highly prevalent in patients with the cerebellar type of multiple system atrophy, but its impact on posture maintenance remains poorly understood.

PATIENTS AND METHODS

Thirty-seven patients with spinocerebellar ataxia and 58 others with cerebellar type of multiple system atrophy were given Synapsys posturography examinations. Fifty-three healthy controls were also tested. Low, medium, and high-frequency sway were recorded to compute energy values. Frequency shift and postural strategy predominance were evaluated from the postural sway distributions, mainly from the proportions of higher frequency values among the total values. The trajectories of postural sway components were evaluated with the generalized additive mixed model. Distributions of the components and their relationships with falls and tremors were assessed through repeated measures correlation analysis.

RESULTS

As the test difficulty increased, the standard controls showed slight increases in the energy values at every frequency. Distributions of the higher frequency (>0.5 Hz) values increased escalatingly with test difficulty, illustrating frequency shifts and hip strategy predominance. Medium and high-frequency values were strongly and positively inter-correlated in normal stances, but this was not observed among the spinocerebellar ataxia or multiple system atrophy patients. Unlike normal stances, the proportion of medium frequency values was negatively related to the total value among the spinocerebellar ataxia and multiple system atrophy patients, implying a failure of frequency shift in response to perturbation. Medium frequency proportions were also inversely correlated with tremors among the multiple system atrophy patients.

CONCLUSIONS

The observed synchronized changes in medium and high-frequency postural sway indicate that they constitute a complete hip strategy for posture control. The strategy was rigid in those with spinocerebellar ataxia but completely disrupted in those with multiple system atrophy. Three Hertz postural leg tremors destabilize the ankle joints and interfere with postural adjustment among those with multiple system atrophy.

Wearable sensors-based postural analysis and fall risk assessment among patients with diabetic foot neuropathy

AIMS

To investigate the cross-sectional association between deep and superficial diabetic neuropathy, postural impairment assessed by wearable inertial sensors, and the risk of fall among patients with diabetic foot.

METHODS

Diabetic patients attending a University Podiatric Clinic were evaluated for the presence of deep and superficial peripheral neuropathy in sensory tests. Postural impairment was assessed using a wearable inertial sensor, and the evaluation of balance/gait and risk of fall was determined by the Tinetti Scale and Downton Index, respectively. Glycemic control was measured by glycated haemoglobin concentration and fasting glycaemia. The postural parameters measured were the anteroposterior and medio-lateral sway of the center of mass (CoM) and the sway area (area traveled by the CoM per second). The results were analyzed through a logistic regression model to assess those posture variables mostly significantly associated with neuropathy and risk of fall scales.

RESULTS

A total of 85 patients were evaluated. Spearman's rank correlation coefficients showed a strong and significant relationship (p < 0.05) between deep diabetic neuropathy assessed by Semmes-Weinstein monofilament, diapason and biothensiometer and postural alterations, whereas no significant correlations between superficial (painful sensitivity) neuropathy and the postural parameters. The sway path of the displacement along the anterior-posterior axis recorded during tests performed with eyes open and feet close together were significantly (p < 0.05) correlated with a poor glycemic (glycated haemoglobin concentration) control and each other with all diabetic neuropathy tests, fall risk scales, muscular weakness, ankle joint limitation and history of ulcers.

CONCLUSIONS

The results support the existence of a strong association between alterations of the deep somato-sensitive pathway (although depending on the tool used to measure peripheral neuropathy), glycemic control and balance impairments assessed using a wearable sensors. Wearable-based postural analysis might be part of the clinical assessment that enables the detection of balance impairments and the risk of fall in diabetic patients with diabetic peripheral neuropathy.

A novel optimization-based convolution neural network to estimate the contribution of sensory inputs to postural stability during quiet standing

Adequate postural control is maintained by integrating signals from the visual, somatosensory, and vestibular systems. The purpose of this study is to propose a novel convolutional neural network (CNN)-based protocol that can evaluate the contributions of each sensory input for postural stability (calculated a sensory analysis index) using center of pressure (COP) signals in a quiet standing posture. Raw COP signals in the anterior/posterior and medial/lateral directions were extracted from 330 patients in a quiet standing with their eyes open for 20 seconds. The COP signals augmented using jittering and pooling techniques were transformed into the frequency domain. The sensory analysis indices were used as the output information from the deep learning models. A ResNet-50 CNN was combined with the k-nearest neighbor, random forest, and support vector machine classifiers for the training model. Additionally, a novel optimization process was proposed to include an encoding design variable that can group outputs into sub-classes along with hyperparameters. The results of optimization considering only hyperparameters showed low performance, with an accuracy of 55% or less and F-1 scores of 54% or less in all models. However, when optimization was performed using the encoding design variable, the performance was markedly increased in the CNN-classifier combined models (r = 0.975). These results suggest it is possible to evaluate the contribution of sensory inputs for postural stability using COP signals during a quiet standing. This study will facilitate the expanded dissemination of a system that can quantitatively evaluate the balance ability and rehabilitation progress of patients with dizziness.

Reduced Gain and Shortened Time Constant of Vestibular Velocity Storage as a Source of Balance and Movement Sensitivities in Gravitational Insecurity

Gravitational insecurity (GrI) involves lifetime movement and balance concerns whose pathophysiological origins are unclear. We tested whether balance symptoms in mild GrI might involve anomalies in vestibular velocity storage (VVS), a brainstem/cerebellar circuit that amplifies gain and prolongs the persistence of weak vestibular signals from small/slow head movements. A Provisional Gravitational Insecurity Index (PGrI) was developed, evaluated for psychometrics/demographics, and used to identify otherwise healthy adults with life-long balance challenges as well as sex, age, and ethnicity-matched comparison adults without such challenges. Balance confidence, sensory hypersensitivities, spatial orientation, anxiety, and hearing loss were self-reported. Standing balance under visual/proprioceptive restrictions and perrotary vestibulo-ocular nystagmus were evaluated. The PGrI showed approximated test-retest reliability and convergent and discriminant validity. When only vestibular input was available, mild GrI participants on a tilting platform used effortful hip strategies for balance significantly more than did comparison participants. Rotation testing revealed that mild GrI participants had significantly less low frequency gain and shortened VVS persistence. Combined, these two parameters correlated significantly with PGrI. The PGrI also correlated with problematic spatial orientation, but surprisingly, not to anxiety. Balance/movement issues in GrI are likely due to VVS deficiencies. Additional mechanisms may account for other GrI symptoms. Better understanding of GrI’s pathophysiological basis will be useful in informing the larger health-provider community about this condition.

Sensory reweighting in frail aged adults: Are the balance deficiencies mainly compensated by visual or podal dependences?

BACKGROUND

Postural control is based on the integration of different sensory inputs. The process of scaling the relative importance of these sensory cues (visual, vestibular and proprioceptive) depends on individuals and creates sensory preferences, leading to sensory dependences when one particular source is preponderant. In this context, the literature showed a frequent visual dependence (visual inputs weighting) in aged adults. However, the somaesthetic inputs can also be prioritised in a podal-dependent profile. In the frail aged adults, none study has shown the distribution of these two dependences.

RESEARCH QUESTION

Which sensory orientation profile is preferentially adopted by frail aged males and females?

METHODS

In this cross-sectional study, we compared 33 frail aged adults to 16 non frail aged adults during a static postural control task in three conditions on a force platform: i) a standard condition, ii) a no-vision condition and iii) a foam condition. An analysis with the factor sex was also performed in each group of participants.

RESULTS

The analysis of stabilometric parameters (mean velocity and mean velocity variance) highlighted a significant difference in no-vision or foam conditions when compared to the standard condition in frail aged males and only in the foam condition when compared to the standard condition for females in the frail group. No significant difference was observed between conditions in the control group.

SIGNIFICANCE

Our study showed the predominance of both visual and podal information in frail aged adults when controlling their posture. Considering the sex factor, frail males were more dependents to their visual cues than frail females. This result should be used when designing the rehabilitation programs in this population.

Impaired Multisensory Integration Predisposes the Elderly People to Fall: A Systematic Review

Background: This systematic review pooled all the latest data and reviewed all the relevant studies to look into the effect of multisensory integration on the balance function in the elderly.

Methods: PubMed, Web of Science and Scopus were searched to find eligible studies published prior to May 2019. The studies were limited to those published in Chinese and English language. The quality of the included studies was assessed against the Newcastle-Ottawa Scale or an 11-item checklist, as recommended by Agency for Healthcare Research and Quality (AHRQ). Any disagreement among reviewers was resolved by comparing notes and reaching a consensus.

Results: Eight hundred thirty-nine records were identified and 17 of them were included for systematic review. The result supported our assumption that multisensory integration works on balance function in the elderly. All the 17 studies were believed to be of high or moderate quality.

Conclusions: The systematic review found that the impairment of multisensory integration could predispose elderly people to fall. Accurate assessment of multisensory integration can help the elderly identify the impaired balance function and minimize the risk of fall. And our results provide a new basis for further understanding of balance maintenance mechanism. Further research is warranted to explore the change in brain areas related to multisensory integration in the elderly.

Weighting and reweighting of visual input via head mounted display given unilateral peripheral vestibular dysfunction

We translated a well-established laboratory paradigm to study sensory integration into a Head-Mounted-Display (HMD). In the current study, a group of 23 individuals with unilateral vestibular dysfunction and 16 age-matched controls observed moving spheres projected from the Oculus Rift. We confirmed increased visual weighting with an unstable surface and decreased visual weighting (i.e., reweighting) with increased visual amplitude. We did not observe significant differences in gains and phases between individuals with vestibular dysfunction and age-matched controls. The vestibular group increased sway in mid and high frequencies significantly more than controls with the change in surface or visual amplitude. Mild visual perturbations within HMDs carry the potential to become a useful portable assessment of postural control in individuals with vestibular disorders.

Standing balance of professional ballet dancers and non-dancers under different conditions

Ballet training has been reported to positively influence balance ability. It is not entirely clear how improved balance ability manifests under standing conditions with different demands on postural control. The aim of the study was to compare balance of ballet dancers and non-dancers in a unipedal stance under different conditions. Twenty-five professional ballet dancers and twenty-five controls completed four unipedal standing balance tests: firm surface with eyes open and closed; foam mat surface with eyes open; and firm surface with eyes open immediately after performing ten 360° whole-body turns. The centre of pressure (COP) data were obtained with a force platform and the direction-specific standard deviations, velocities, and sample entropy of the COP displacement were computed. A three-way analysis of variance was used to compare groups, genders, and conditions. For standing immediately after performing ten turns, the postural sway parameters were significantly larger in the control group compared to the ballet dancers in both men and women. In this stance condition the values of postural sway and COP velocities in the control group were larger in the men compared to the women. For both genders in the control group all postural sway and COP velocity parameters were larger in standing with eyes closed and standing after performing 10 turns compared to standing with eyes open on both firm and foam surface. In the ballet dancers all COP velocity parameters were larger in standing with eyes closed compared to all other conditions. The results from the present study indicate that professional ballet dancers do not have a better general balance ability than untrained subjects.

Learning effect of dynamic postural stability evaluation system

BACKGROUND

Repeated exposure to a given perturbation of the postural control system has been shown to cause learning of more efficient postural strategies for maintaining balance both within a session and over time. It is important to show whether outcomes from treatment strategies are related to the effectiveness of training or are the result of the learning of the test process.

OBJECTIVE

To investigate the learning effect of the dynamic postural stability evaluation system.

METHODS

We studied 20 healthy young subjects (13 females and 7 males), with a mean age of 22.3 ± 1.9 years. Limits of stability and postural sway were assessed. All participants completed the standardized dynamic postural stability evaluation test (Bertec, Bertec Corporation, Columbus, OH, USA) seven times. The test was performed in both eyes open and eyes closed conditions.

RESULTS

There were differences in the limits of stability scores for backward (p= 0.042), left side (p= 0.05), and the total score (p= 0.04). There were significant differences in postural sway anteroposterior direction in perturbed surface with eyes closed condition (p= 0.004) and total limits of stability scores of perturbed surface with eyes closed condition (p= 0.046).

CONCLUSIONS

The study showed that balance test scores stabilized at different sessions from 1st to 3rd assessment period. Maximum normalized scores were reached at the third trial.

Normative data for static balance testing in healthy individuals using open source computerized posturography

PURPOSE

Computerized posturography is the gold standard for balance assessment. Because of the great cost and dimensions of commercial equipments, low-cost and portable devices have been developed and validated, such as RombergLab, a software in open source term which works connected with a low-cost force platform. The objective of this study was to obtain normative posturography data using this software.

METHODS

A multicentric prospective and descriptive study, with 350 healthy participants, was designed. Static postural stability (measured using the modified clinical test of sensory interaction on balance) was evaluated using the software connected to the force platform. Using the confidence ellipse area (CEA) in each condition, global equilibrium score (GES) was calculated and adjusted for significant variable factors using cluster analysis.

RESULTS

Mean (SD) GES was 0.72 (0.22). Age (p < 0.01), height (p < 0.01) and recruitment center (p < 0.05) were found as influence factors for GES. Cluster analysis obtained 16 groups stratified by age and height. GES decreases with age and height (p < 0.005). No significant interaction of age nor height was found with GES in these clusters (p > 0.05). After correction for height and age, GES was no longer influenced by the recruitment center (p > 0.05).

CONCLUSIONS

With the introduction of the global equilibrium score values of the present study into the software, we consider RombergLab v1.3 a reference posturography tool for healthy individuals. Further studies are needed for validating it as a suitable instrumented test for screening between healthy and pathologic subjects and its reliability over time for the follow-up of patients.

Task-specific and variability-driven activation of cognitive control processes during motor performance

It has long been postulated that cognitive and motor functions are functionally intertwined. While the idea received convincing support from neuroimaging studies providing evidence that motor and cognitive processes draw on common neural mechanisms and resources, findings from behavioral studies are rather inconsistent. The purpose of the present study was to identify and verify key factors that act on the link between cognitive and motor functions. Specifically we investigated whether it is possible to predict motor skills from cognitive functions. While our results support the idea that motor and cognitive functions are functionally intertwined and different motor skills entail distinct cognitive functions, our data also strongly suggest that the impact of cognitive control processes on motor skill proficiency depends on performance variability, i.e. on how challenging a motor task is. Based on these findings, we presume that motor skills activate specific cognitive control processes on two levels: basic processes that are solely related to the type of the motor task, and variability-driven processes that come into play when performance variability is high. For practitioners, these findings call for specific and challenging motor training interventions to directly tap into the to-be-improved cognitive skills and to involve a maximum of cognitive processes.

A Tailor-Made Exercise Program for Improving Balance and Mobility in Older Adults With Type 2 Diabetes

Effectiveness of an exercise program designed for improving postural control and mobility in older adults with type 2 diabetes was investigated. Ninety-three adults 65 or older diagnosed with type 2 diabetes and able to walk unaided were recruited. The intervention group received exercise training focused on ankle strengthening and mobility twice per week for 10 weeks. The control group did not participate in any exercise program. After 10 weeks, the intervention group showed significantly greater improvement in the mean Sensory Organization Test composite score (4.4 vs. 0.3; p = 0.01) as well as visual ratio (0.1 vs. 0.002; p = 0.01) and vestibular ratio (0.1 vs. 0.003; p < 0.001) than the control group after adjusting for covariates. A greater trend of improvement in the Timed Up and Go and Single-Leg Stance Test was also found in the intervention group. Exercise training focusing on the ankle is effective in enhancing the postural stability of older adults with type 2 diabetes and can potentially be effective in improving single-leg standing balance and mobility. [Journal of Gerontological Nursing, 44(2), 41-48.].

Superior short-term learning effect of visual and sensory organisation ability when sensory information is unreliable in adolescent rhythmic gymnasts

Rhythmic gymnasts specialise in dynamic balance under sensory conditions of numerous somatosensory, visual, and vestibular stimulations. This study investigated whether adolescent rhythmic gymnasts are superior to peers in Sensory Organisation test (SOT) performance, which quantifies the ability to maintain standing balance in six sensory conditions, and explored whether they plateaued faster during familiarisation with the SOT. Three and six sessions of SOTs were administered to 15 female rhythmic gymnasts (15.0 ± 1.8 years) and matched peers (15.1 ± 2.1 years), respectively. The gymnasts were superior to their peers in terms of fitness measures, and their performance was better in the SOT equilibrium score when visual information was unreliable. The SOT learning effects were shown in more challenging sensory conditions between Sessions 1 and 2 and were equivalent in both groups; however, over time, the gymnasts gained marginally significant better visual ability and relied less on visual sense when unreliable. In conclusion, adolescent rhythmic gymnasts have generally the same sensory organisation ability and learning rates as their peers. However, when visual information is unreliable, they have superior sensory organisation ability and learn faster to rely less on visual sense.

Analyses of balance and flexibility of obese patients undergoing bariatric surgery

OBJECTIVE

To assess the postural control and flexibility of obese subjects before and both six and 12 months after bariatric surgery. To verify whether postural control is related to flexibility following weight reductions resulting from bariatric surgery.

METHODS

The sample consisted of 16 subjects who had undergone bariatric surgery. All assessments were performed before and six and 12 months after bariatric surgery. Postural balance was assessed using an Accusuway® portable force platform, and flexibility was assessed using a standard chair sit and reach test (Wells' chair).

RESULTS

With the force platform, no differences were observed in the displacement area or velocity from the center of pressure in the mediolateral and anteroposterior directions. The displacement speed from the center of pressure was decreased at the six month after the surgery; however, unchanged from baseline at 12 months post-surgery. Flexibility increased over time according to the three measurements tested.

CONCLUSIONS

Static postural balance did not change. The velocity of postural adjustment responses were increased at six months after surgery. Therefore, weight loss promotes increased flexibility. Yet, improvements in flexibility are not related to improvements in balance.

The effect of aging on vertical postural control during the forward and backward shift of the center of pressure

Preventing fall-related injuries is becoming a priority as the world population ages. This study's purpose was to examine the effect of aging on vertical postural control in the community-dwelling elderly. Thirty-six elderly individuals and twenty-two healthy young adults were asked to shift their centers of pressure (COPs) as far as possible while standing. The COP position, angle of each lower leg joint, and postural muscle activities were measured using a force plate, three-dimensional motion analyzer, and electromyogram, respectively. The vertical position of the center of mass (COM) was also measured to assess the change in vertical postural control. The backward COP shift in the elderly group was significantly smaller than that in the young group, and both the forward and backward COM shifts were significantly smaller in elders relative to those in youths. The COM position in the elderly group during the backward COP shift was also significantly lower than that in the young group. Knee and ankle joint movements differed between the two groups during the backward COP shift. Factor analysis indicated that dorsal and ventral muscle groups were involved in the COP shift. Specifically, the relationship between the biceps femoris muscle and the voluntary COP shift was reinforced in the elderly group. These findings suggest that the vertical postural strategy changes in the elderly during the backward COP shift.

Elderly Use Proprioception Rather than Visual and Vestibular Cues for Postural Motor Control

Multiple factors have been proposed to contribute to the deficits of postural control in the elderly. They were summarized as sensory, motor, and higher-level adaptation deficits. Using a model-based approach, we aimed to identify which of these deficits mainly determine age-related changes in postural control. We analyzed postural control of 20 healthy elderly people with a mean age of 74 years. The findings were compared to data from 19 healthy young volunteers (mean age 28 years) and 16 healthy middle-aged volunteers (mean age 48 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by pseudorandom anterior-posterior tilts of the body support surface. We found that spontaneous sway amplitude and velocity were significantly larger, and sway frequencies were higher in elderly compared to young people. Body excursions as a function of tilt stimuli were clearly different in elderly compared to young people. Based on simple feedback model simulations, we found that elderly favor proprioceptive over visual and vestibular cues, other than younger subjects do. Moreover, we identified an increase in overall time delay challenging the feedback systems stability, and a decline in the amplitude of the motor feedback, probably representing weakness of the motor system. In general, these parameter differences between young and old may result from both deficits and compensation strategies in the elderly. Our model-based findings correlate well with deficits measured with clinical balance scores, which are widely used in clinical practice.

Computerized Dynamic Posturography in Patients with Diabetic Peripheral Neuropathy and Visual Feedback-Based Balance Training Effects

BACKGROUND: Diabetic peripheral neuropathy (DPN) often has reduced stability during standing conditions.AIM: To compare balance control in diabetic patients and normal subjects using computerized dynamic posturography and to assess effect of visual feedback-based balance training in DPN.MATERIALS AND METHODS: A total of 57 patients of type 2 diabetes mellitus and 30 age-matched normal control subjects were recruited. The sensory organization test was done before and after the training program.RESULTS: There was a significant decrease of mean (± SD) of composite equilibrium score and somatosensory ratio score between subgroups of DPN and control healthy group (p < 0.05).  There was a significant increase of mean (± SD) of composite equilibrium score and the somatosensory ratio score after treatment as compared to results before training (p < 0.05) in mild DPN.  Moreover, there were a significant correlation between composite equilibrium score and disease duration before training in the severe DPN (r = 0.368, p < 0.05). CONCLUSIONS: Computerized dynamic posturography is an important quantitative tool in the assessment of posture instability and allows for early disclosure of the failure of the postural control system. Visual feedback-based balance training was shown to be a promising method for fall prevention among early diabetes mellitus with peripheral neuropathy.

Control of static balance among women after mastectomy. Vision impact on the quality of the equilibrium response

Wstęp: Stabilność strukturalna ocenia wpływ wybranego zmysłu na reakcje równoważne. Celem przeprowadzonych badań było określenie znaczenia kontroli wzrokowej w utrzymaniu równowagi statycznej kobiet po amputacji piersi.

Materiał i metoda: W badaniu wzięło udział 150 kobiet, w grupie badanej znajdowało się 75 kobiet w wieku średnio 60 (±7,6), BMI 26 (±3,6) po zabiegu amputacji piersi oraz po leczeniu chemioterapeutycznym lub radioterapii. Żadna z kobiet w trakcie badania nie była w trakcie leczenia. Leczenie zakończono 2-5 lat (sd 3,6±0,5) przed wykonaniem testów. Do grupy kontrolnej zakwalifikowano 75 kobiet w wieku 59 (±6,5), BMI 26 (±7,9). Badanie przeprowadzono przy użyciu dwupłytowej platformy tensometrycznej. Kwantyfikacja składała się z dwóch 30 sekundowych prób, pierwsza próba z oczami otwartymi oraz druga po 5-10 sekundowej przerwie z oczami zamkniętymi.

Wyniki: Różnice istotne statystycznie występowały w obrębie znacznej części parametrów mierzonych dla oczu zamkniętych oraz w przypadku wszystkich parametrów współczynnika Romberga. Były to: długości ścieżki COP (centre of pressure) (p=0,0411), długość ścieżki COP mierzonej w kierunku przednio-tylnym (p=0,0251), średniego wychylenia COP (p=0,0025), maksymalnego wychylenia w osi OX (odnoszącego się do zakresu stabilności bocznej) (p=0,0447). Ponadto istotne statystycznie różnice wystąpiły pomiędzy parametrami: średniej prędkości poruszającego się COP w 2D (p=0,0432) oraz w osi OY (p=0,0240).

Wnioski: Równowaga po amputacji piersi było zależna od narządu wzroku w mniejszym stopniu niż w grupie kontrolnej. W programie usprawniania kobiet po mastektomii należy uwzględnić trening proprioceptywny z wyłączeniem narządu wzroku, dla poprawy jakości reakcji równoważnej i zwiększenia stabilności postawy.

Postural responses during volitional and perturbed dynamic balance tasks in new lower limb amputees: a longitudinal study

This study examined the adaptation of postural responses in transtibial amputees during both perturbed and volitional dynamic balance tasks during a five-month period following discharge from inpatient rehabilitation. Seven unilateral transtibial amputees performed the sensory organisation test (SOT) and the limits of stability (LOS) test protocols on the NeuroCom Equitest(®) at one, three and six months post-discharge from in-patient rehabilitation. Overall balance ability improved significantly (p=0.01) following discharge as did utilisation of somatosensory input (p=0.01), with hip strategy use decreasing. Reaction time and movement velocity did not change significantly in the majority of target directions for the LOS test. However, endpoint COG excursion and directional control were significantly increased in a number of directions (p≤0.05). Although balance ability improved following discharge from rehabilitation, participants were heavily reliant upon vision in order to maintain balance. Following discharge from rehabilitation, amputees were seemingly able to increase the spatial and accuracy aspects of volitional exploration of their LOS. However, temporal aspects did not display any adaptation, suggesting a trade-off between these aspects of postural control. Further practice of performing volitional postural movements under increasing time pressure, for example using low-cost gaming tools, may improve balance ability and postural control.

Fractal properties of postural sway during quiet stance with changed visual and proprioceptive inputs

We studied the fractal dynamics of postural sway during quiet stance with changed visual and/or proprioceptive information. Radius-vector length and angle of rotation of center of foot pressure (COP) displacements were used as parameters of postural sway. The experiments were performed on 24 healthy volunteers of both sexes aged 20-30 years. Using a battery of nonlinearity tests, differences in the degree of fractality of both parameters during stance were found. We found that the behavior of radius-vector was similar to fractional Brownian motion, while that of angle of rotation was similar to flicker noise. Quantitative parameters that can be used to characterize the changes in radius-vector length and angle of rotation include self-similarity intervals and fractal dimension. In healthy subjects, the process of postural control maintains its fractal structure independently of altered sensory information. We believe that this analysis provides information about new methods for evaluating postural sway behavior during quiet stance.

Balance performance in head-shake computerized dynamic posturography: aging effects and test-retest reliability

BACKGROUND

The ability of the Sensory Organization Test (SOT) to detect subtle balance problems has been challenged. The Head-Shake Sensory Organization Test (HS-SOT) has been developed to improve the delineation of balance performance.

OBJECTIVE

The purposes of this study were: (1) to examine age-related differences in balance measured with the HS-SOT and (2) to establish the test-retest reliability of the HS-SOT in younger adults who were healthy and older adults who were healthy.

DESIGN

A test-retest design was used in this observational measurement study.

METHODS

Ninety-two younger adults who were healthy (mean age=28.3 years) and 73 older adults who were healthy (mean age=60.3 years) underwent the SOT and the HS-SOT. Seventy-seven of them (56 younger adults, 21 older adults) underwent the same assessments 1 to 2 weeks later.

RESULTS

The equilibrium scores in HS-SOT conditions 2 (head movements with eyes closed while standing on a firm surface) and 5 (head movements with eyes closed while standing on a sway-referenced surface) were significantly lower than those in tests without dynamic head movements added (SOT conditions 2 and 5). Older adults attained significantly lower scores in both HS-SOT conditions than their younger peers. The test-retest reliability values, reported as intraclass correlation coefficients (ICC [3,2]), of the HS-SOT scores in conditions 2 and 5 for the younger adults were .85 and .78, respectively; those for the older adults were .64 and .55, respectively. The corresponding minimal detectable change values for the former were 2.7 and 16.2, and those for the latter were 3.6 and 22.7.

LIMITATIONS

Only head rotation movements on the horizontal plane were tested.

CONCLUSIONS

Adding head movements to the SOT increased the separation of younger adults who were healthy and older adults who were healthy. The HS-SOT has good reliability, and the reported minimal detectable change values may facilitate the interpretation of clinical studies in which the HS-SOT is used to assess changes in balance performance in younger and older adults.

A comparison of balance performance: computerized dynamic posturography and a random motion platform

OBJECTIVE

To establish the clinical utility of the PROPRIO 5000 as a balance assessment device by establishing convergent validity with the NeuroCom sensory organization test (SOT).

DESIGN

Cross-sectional.

SETTING

Balance research laboratory.

PARTICIPANTS

Young adults (N=40; 21.1+/-1.4y).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Performance on each of the 6 NeuroCom SOT testing conditions and PROPRIO 5000 dynamic motion analysis score.

RESULTS

Correlational analyses between output variables yielded significant relationships between the dynamic motion analysis score from the 0 to 10 second (r=-.38), 10 to 20 second (r=-.34), and 20 to 30 second (r=-.35) intervals and the SOT composite balance score.

CONCLUSIONS

The initial stages of the PROPRIO 5000 and the NeuroCom SOT battery may evaluate similar aspects of postural control. However, as the magnitude of PROPRIO perturbations increased, the relationship between the devices diverged and the complete PROPRIO assessment is not thought to pair with the SOT assessment. Differences between the 2 devices may be associated with varying degrees of test difficulty and the necessary postural control strategies involved in responding to continual balance perturbations (PROPRIO 5000) or to different sensory inputs (SOT).

Dental occlusion and postural control in adults

We studied the influence of a dental occlusion perturbation on postural control. The tests were performed in three dental occlusion conditions: (Rest Position: no dental contact, Maximal Intercuspal Occlusion: maximal dental contact, and Thwarted Laterality Occlusion: simulation of a dental malocclusion) and four postural conditions: static (stable platform) and dynamic (unstable platform), with eyes open and eyes closed. A decay of postural control was noted between the Rest Position and Thwarted Laterality Occlusion conditions with regard to average speed and power indexes in dynamic conditions and with eyes closed. However, the head position and stabilization were not different from those in the other experimental conditions, which means that the same functional goal was reached with an increase in the total energetic cost. This work shows that dental occlusion differently affects postural control, depending on the static or dynamic conditions. Indeed, dental occlusion impaired postural control only in dynamic postural conditions and in absence of visual cues. The sensory information linked to the dental occlusion comes into effect only during difficult postural tasks and its importance grows as the other sensory cues become scarce.

The effect of foam surface properties on postural stability assessment while standing

A common assessment of postural control often involves subjects standing on a compliant surface, such as a foam block, to make balance tests more challenging. However, the physical properties of the foam block used by different researchers can vary considerably. The objective of this study was to provide an initial approach for investigating whether two of the foam properties, i.e. density and elastic modulus, influenced recorded anteroposterior and lateral torque variance with eyes open and eyes closed. Thirty healthy adults (mean age 22.5 years) were assessed with posturography using three different types of foam block placed on a force platform. These blocks were categorised: firm foam, medium foam and soft foam by their elastic modulus. To investigate the spectral characteristics of recorded body movements, variance values were calculated for total movements, movements <0.1Hz and movements >0.1Hz. Results showed that anteroposterior and lateral torque variances >0.1Hz were larger when standing on the firm foam compared with medium and soft foam and in turn were larger on the medium foam compared with the soft foam with eyes closed. Moreover, GLM and correlation analysis demonstrated that the properties of the foam blocks affected anteroposterior torque variance >0.1Hz and lateral torque variance in all frequency ranges. In addition, the stabilising effect of vision in the anteroposterior direction had a greater influence when the subjects' stability was increasingly challenged by the support surface, as illustrated by the higher torque variance values. In conclusion, caution should be taken when analysing balance deficits with foam test setups, because the foam properties may influence the recorded body movements.

Learning Effects of Repetitive Administrations of the Sensory Organization Test in Healthy Young Adults

OBJECTIVES

To evaluate the learning effect of multiple administrations of the Sensory Organization Test (SOT) on performance and to begin to establish clinical meaningful change scores for the SOT.

DESIGN

Descriptive case series.

SETTING

University-affiliated clinic.

PARTICIPANTS

Healthy young adults (6 men, 7 women; mean age, 24+/-4y).

INTERVENTION

All subjects performed the standardized SOT using the SMART EquiTest 5 times over a 2-week period, and 1 month later.

MAIN OUTCOME MEASURE

Composite and individual SOT test condition standardized equilibrium scores.

RESULTS

Test-retest reliability (intraclass correlation coefficient model 2,3) of the composite (.67) and equilibrium score (range, .35-.79) were fair to good. Repeated-measures analysis of variance revealed a significant (P<.05) increase in the composite and equilibrium scores for conditions 4, 5, and 6 over the 5 sessions that plateaued after the third session, and were retained at 1 month. The 95% confidence interval for the composite score change from session 1 to session 4, the plateau of the learning effect, was 3.9 to 8.1.

CONCLUSIONS

Although the findings of this study would indicate that multiple baseline measures are desirable for the more challenging conditions, a composite change of greater than 8 points would indicate change due to rehabilitation.

Changes in multi-segmented body movements and EMG activity while standing on firm and foam support surfaces

Postural control ensures stability during both static posture and locomotion by initiating corrective adjustments in body movement. This is particularly important when the conditions of the support surface change. We investigated the effects of standing on a compliant foam surface using 12 normal subjects (mean age 26 years) in terms of: linear movements at the head, shoulder, hip and knee; EMG activity of the tibialis anterior and gastrocnemius muscles and torques towards the support surface. As subjects repeated the trials with eyes open or closed, we were also able to determine the effects of vision on multi-segmented body movements during standing upon different support surface conditions. As expected, EMG activity, torque variance values and body movements at all measured positions increased significantly when standing on foam compared with the firm surface. Linear knee and hip movements increased more, relative to shoulder and head movements while standing on foam. Vision stabilized the head and shoulder movements more than hip and knee movements while standing on foam support surface. Moreover, vision significantly reduced the tibialis anterior EMG activity and torque variance during the trials involving foam. In conclusion, the foam support surface increased corrective muscle and torque activity, and changed the firm-surface multi-segmented body movement pattern. Vision improved the ability of postural control to handle compliant surface conditions. Several essential features of postural control have been found from recording movements from multiple points on the body, synchronized with recording torque and EMG.