Upright Postural Control Research Articles

Special issue on Control and Automation in Cyber-Physical Systems

This special issue consists of ten previously unpublished papers selected from over 130 submissions to the 2011 International Conference on Cyber Technology in Automation, Control, and Intelligent Systems (IEEE-CYBER 2011) held on 20–23 March 2011 in Kunming, China. A cyber-physical system (CPS) is typically designed as a network of interacting elements with physical input and output. In the near future, the expected advances in science and engineering will not only enhance the links between computational and physical elements, but also significantly improve the autonomy, efficiency, functionality, reliability and safety level of CPS. These advances will expand the applicability of CPS in many technical fields including intervention (e.g. collision avoidance), precision (e.g. robotic surgery and nanoscale manufacturing), operation in dangerous or inaccessible environments (e.g. search and rescue, fire fighting and deep-sea exploration), and augmentation of human capabilities (e.g. telerobotics, haptic interface and healthcare monitoring/delivery). The selected papers illustrate a wide range of ongoing work in the areas of controller design, engineering applications and information engineering. Tan et al. present a novel hierarchical and structural 3D object model description for wireless camera networks. They describe the concrete data structure, reconstruction method and fusion method of the model with experimental results showing the feasibility, efficiency and effectiveness of the networks. Liu et al. show a new approach for adaptive torque distribution of 4-powered caster vehicle (4-PCV) on complex terrain without any additional sensor. Simulation results indicate the effectiveness of the proposed estimation approach and the performance of the torque distribution schemes. Pei et al. introduce the influence of visual feedback indicator scales on human upright postural control. They demonstrate a reduction of the visual feedback indicator scale inspires a postural power to shift to a higher frequency, and this reduction also induces a fall-after-rise pattern of postural energy distribution. Yao et al. develop a novel microfluidic based telemedicine system capable of detecting insulin and conveying the results to physicians located off-site through the Internet. They combine an integrated polydimethylsiloxane-based microfluidic device with a telemedicine strategy to offer new opportunities for diabetes care, especially for facilitating patients in the rural areas. Shi et al. present a novel translation system that can capture human gestures through micro IMUs and then translate the gestures into specific meanings. The experimental performance shows that the correct recognition rate ranges from 27.5% to 100% with an overall correction rate of 66.25%. Bi et al. propose a systematic trajectory generation method for a biped robot walking on slopes utilizing the inverted pendulum model. They also demonstrate that this robot can adapt to uneven floor conditions by employing control algorithms. Pan et al. elucidate the automatic generation of a modular reconfigurable robot, including single-open-chain robots and multi-chain robots. They also show an illustrative example and conduct experiment studies to affirm the theoretical analysis. Jing et al. investigate a radial basis function neural network modelling approach applied for compensating the noncontact inductive gap sensor in the high-speed maglev train. They experimentally show that the compensated gap signal meets the requirement of the levitation control system. Chen et al. introduce an ordinal isolated algorithm extracting outliers in terms of the order of being isolated in a recursive uniform data space partition process. The experiments show that the CPU time of ordinal isolation increases linearly with linearly growing data sets. Mu et al. present a new algorithm called the iterated square-root cubature Kalman filter. The new algorithm is applied to the state estimation of a re-entry ballistic target with unknown ballistic coefficient. Simulation results show that this novel algorithm has a superior performance and robustness over the unscented Kalman filter and the squareroot cubature Kalman filter. As a whole, the aforementioned Ten papers present a general introduction to recent progress in the areas of intelligent control, biomedical engineering, information engineering and engineering applications in which networking plays a fastgrowing role to facilitate the performance. It is hoped that this issue will serve as a catalytic agent for future research in similar areas. Finally, we would like to thank the reviewers who have helped with the review process of this special issue and the authors for their effort in revising their papers according to the reviewers’ comments.

Determinants and consequences for standing balance of spontaneous weight-bearing on the paretic side among individuals with chronic stroke

Hemiparetic stroke patients commonly bear more weight on the non-paretic side which seems intuitively linked to unilateral control deficits. However, there is evidence that some post-stroke favour weighting the paretic side, which may be problematic given altered capacity of the paretic limb to contribute to the control of upright posture. This study explores the prevalence and clinical determinants of stance asymmetry, and the relationship between stance asymmetry and postural control among chronic stroke patients. Subjects (n=147; >6 months post-stroke) stood on two force plates in eyes-open and eyes-closed conditions; 59 were symmetric, 18 had paretic asymmetry (PA), and 70 had non-paretic asymmetry (NPA). Root mean square (RMS) of antero-posterior and medio-lateral centre-of-pressure under each limb and both limbs combined were compared. RMS of total medio-lateral centre-of-pressure was greater for both asymmetric groups compared with the symmetric group. PA subjects relied less on the loaded limb for control than NPA subjects and relied more on visual information for postural control than those who were symmetric. There were no differences in the characteristics of individuals between the PA and NPA groups. The loading of the paretic limb was not related to impaired postural control during stationary standing which was attributable, in part, to individuals relying on control from the non-paretic limb, in spite of lower vertical load, and a greater dependence on visual contributions. There was no evidence that greater loading on the paretic limb was related to persisting dyscontrol but may rather reflect a learned strategy.

A New Proposal on How Motor Memory Is Consolidated

A New Proposal on How Motor Memory Is Consolidated

The association between multiple sclerosis-related fatigue and balance as a function of central sensory integration

BackgroundFatigue and impaired upright postural control (balance) are the two most common complaints in persons with multiple sclerosis (MS), with limited evidence on how they are related. ObjectiveTo examine the relationship between symptomatic fatigue and balance as a function of central sensory integration in persons with multiple sclerosis. Materials and methodsSeventeen persons with relapsing-remitting MS were enrolled in this cross-sectional study. Primary measurements included fatigue (modified fatigue impact scale – MFIS); balance (dynamic posturography, sensory organization testing – SOT); and walking capacity (six-minute walk test – 6MWT). ResultsFatigue scores were significantly associated with balance: MFIS total (r=−0.78; p<0.001), physical subscale (r=−0.77; p<0.001), cognitive subscale (r=−0.75; p=0.001) and psychosocial subscale (r=−0.53; p=0.030) scores. MFIS total score was a significant predictor of balance (p≤0.001), accounting for 62% of the variability in SOT composite scores. Significant differences in fatigue (d=1.75; p=0.005) and balance (d=1.74; p=0.005) were found for participants who had cerebellar and brainstem involvement compared to those without. ConclusionsSymptomatic fatigue is significantly related to balance and is a significant predictor of balance as a function of central sensory integration in persons with MS. Fatigue and balance are associated with cerebellar and brainstem involvement. This study provides early evidence supporting the theory that for those persons with MS who struggle to maintain steady balance during tasks that stimulate the central sensory integration process, complaints of significant levels of fatigue are probable.

Influences of visual feedback indicator scales on human upright postural control

Human upright postural control is highly related to visual information. In order to explore the influence of visual feedback on static upright postural control, postural sway of eight healthy young adults was investigated under visual feedback circumstances. In the investigation, postural feedback information was visualized by an indicator composed of a movable spot and a stationary circle, and in addition to Shannon entropy analysis, time domain and frequency domain analyses were employed to inspect postural control adjustment. The experiment results indicate that even though indicator scale changes do not induce significant postural differences in time domain and random characteristics, reduction of the visual feedback indicator scale inspires a postural power shift to higher frequencies. In addition, this reduction also induces a fall-after-rise pattern of postural energy distribution in the frequency range of 0.5–1 Hz.

Functional Synergies Underlying Control of Upright Posture during Changes in Head Orientation

BackgroundStudies of human upright posture typically have stressed the need to control ankle and hip joints to achieve postural stability. Recent studies, however, suggest that postural stability involves multi degree-of-freedom (DOF) coordination, especially when performing supra-postural tasks. This study investigated kinematic synergies related to control of the body’s position in space (two, four and six DOF models) and changes in the head’s orientation (six DOF model).Methodology/Principal FindingsSubjects either tracked a vertically moving target with a head-mounted laser pointer or fixated a stationary point during 4-min trials. Uncontrolled manifold (UCM) analysis was performed across tracking cycles at each point in time to determine the structure of joint configuration variance related to postural stability or tracking consistency. The effect of simulated removal of covariance among joints on that structure was investigated to further determine the role of multijoint coordination. Results indicated that cervical joint motion was poorly coordinated with other joints to stabilize the position of the body center of mass (CM). However, cervical joints were coordinated in a flexible manner with more caudal joints to achieve consistent changes in head orientation.Conclusions/SignificanceAn understanding of multijoint coordination requires reference to the stability/control of important performance variables. The nature of that coordination differs depending on the reference variable. Stability of upright posture primarily involved multijoint coordination of lower extremity and lower trunk joints. Consistent changes in the orientation of the head, however, required flexible coordination of those joints with motion of the cervical spine. A two-segment model of postural control was unable to account for the observed stability of the CM position during the tracking task, further supporting the need to consider multijoint coordination to understand postural stability.

Influence of body position on fibularis longus and soleus Hoffmann reflexes

It is widely accepted that Hoffmann (H) reflex amplitudes of the soleus decrease as complexity of body positions increases, but it is not known if this same mechanism of postural control is seen in other ankle muscles such as fibularis longus (FL). Our purpose was to assess if FL H-reflex changed in different body positions and if the adaptations were correlated to soleus H-reflex modulation. Fifteen healthy subjects had their FL and soleus H-reflexes measured in three positions (prone, bipedal, unipedal). Maximal H-reflexes (H-max) and motor responses (M-max) were collected bilaterally. The average H-max and M-max were used to calculate Hmax/Mmax ratios. To control influences of background muscle activity on H-reflex measures, the ratios were normalized to their corresponding mean EMG amplitudes over a 50-ms time epoch. H-reflex amplitudes of both muscles were significantly lower in unipedal stance than other positions. Additionally, there were strong correlations (R2>0.7) in H-reflex modulation between the two muscles when transitioning from prone to either bipedal or unipedal stance. Down-modulation of H-reflex when transitioning to unipedal stance was present in both FL and soleus suggesting that H-reflex modulation of both muscles may play a similar role in control of upright posture.

Ankle muscle activation in people with haemophilia

Since normative surface EMG (SEMG) values for muscles acting at the knee joint are available for people with haemophilia, increasing interest is noticeable for other joints affected by haemophilic arthropathy. Adequate activity of shank muscles is an important key for appropriate postural control. The aim of this study was to determine differences in muscle activation patterns of lower leg muscles between people with and without haemophilia during upright standing. SEMG of tibialis anterior (TA), fibularis longus (FL), lateral (LG) and medial (MG) heads of gastrocnemius, and soleus (SO) muscles of both sides were recorded in 25 haemophilic patients (H) and 25 non-haemophilic control subjects (C) while standing on even ground. The Gilbert-Score was used to assign sides to major (H-MA) and minor (H-MI) affected ankle joints in H. To normalize the SEMG amplitudes, amplitude ratios (percentage of cumulated activity) were calculated. Compared to controls, TA ratios showed higher and MG reduced levels in both H groups (P < 0.01). In the H-MA subgroup of H, FL also joined the TA behaviour whereas SO had similar activation direction as MG. Although possible descending influences from the knee joints cannot be excluded, this can be interpreted as a compensational mechanism due to the severity of the orthopaedic status of the ankle, which with increasing heaviness is accompanied by reduced plantar flexion capability. However, ankle joint integrity appears to be reduced in H, with TA and MG seeming to play key roles for neuromuscular control of upright posture.

How an acute mastering of balance on a seesaw can improve the relationship between “static” and “dynamic” upright postural control

Postural control ability has been widely evaluated using undisturbed upright stance protocols. However, standing on a seesaw may offer additional insights due to changes in the available sensory information and the amplification of the motor command resulting from the translational and rotational movement of the device. These two tasks share close biomechanical and neurophysiological principles. To highlight their possible linkage, 32 young healthy adults participated in this study, which consisted of testing postural performance while standing on a firm surface or on a seesaw producing rolling or pitching movements. The results showed increased CP displacements along the seesaw's pitching or rolling axis and also along the perpendicular axis. However, comparing the two tasks can be difficult because of discrepancies in the ability to rapidly master the new constraints brought about by the seesaw. To highlight the role played by adaptation, 15 subjects of the whole sample participated in a complementary protocol consisting of a 20-min training session aimed at improving the mastery of the seesaw producing pitch motions. The relationship between the amplitudes of the CP displacements between “static” and “dynamic” tasks was investigated. Interestingly, whereas no statistically significant linear correlation was found before training, several significant correlations were found after pitch training for AP displacements. By emphasizing the key role played by short-term adaptation in standing performance, these results are likely to have potential implications regarding the conception of standardized tests aimed at evaluating postural ability in healthy or disabled subjects.

The Reproducibility of Berg Balance Scale and the Single-Leg Stance in Chronic Stroke and the Relationship Between the Two Tests

To assess the reproducibility of the Berg Balance Scale (BBS) and the Single-leg Stance (SLS), and the validity of the SLS as an independent test of upright postural control in patients with chronic stroke. An intra-rater test-retest reproducibility study. The BBS and the SLS were assessed twice, 7 days apart. A university hospital. Fifty individuals; 6-46 months after a stroke. The reproducibility of the BBS and the SLS was evaluated with intraclass correlation coefficient (ICC(2,1)), the mean difference between the 2 test sessions (d) with 95% confidence interval (95% CI), the standard error of measurement (standard error of measurement [SEM]%), the smallest real difference (SRD%), and the Bland-Altman graphs. To assess validity of SLS, the relationship between the SLS and the BBS was analyzed by the Pearson correlation coefficient. The ICC(2,1) was 0.88 for the BBS, and the ICC(2,1) values were 0.88 for the nonparetic limb and 0.92 for the paretic lower limb for the SLS. The smallest change that indicates a real improvement for a group of individuals, SEM%, was 3% for BBS, 15% for the nonparetic limb and 27% for the paretic limb for SLS. The smallest real difference for a single individual was 8% for BBS but was higher for SLS, at 42% for the nonparetic limb, and 74% for the paretic limb. There was a significant relationship between the SLS and the BBS (r = 0.65-0.79; P < .001). The BBS and the SLS are reproducible measurements in patients with chronic stroke, but only the BBS is sensitive enough to follow changes over time or after an intervention. The SLS is strongly related to the BBS and can be used as an independent test to measure upright postural control after a stroke.

Intervention of Self-Monitoring Body Movement has an Immediate Beneficial Effect to MaintYasudaain Postural Stability

Clinicians in rehabilitation sometimes encourage patients to become consciously aware of somatosensory inputs from the body. However, it is still unclear whether such intervention has any beneficial role on human postural control. The present study conducted two experiments to investigate whether an intervention involving conscious awareness of the body (i.e., self-monitoring) contributes to improved ability of postural control as measured immediately after an intervention of self-monitoring. All participants were subjected to four interventions: (a) self-monitoring actual movement (referred to as “move + monitoring” condition), (b) self-monitoring the imagined movement (“imagery”), (c) actual movement without self-monitoring (“move + arithmetic”), and (d) performing an arithmetic task without movement (“arithmetic”). The amounts of postural sway among measurements after the four interventions were compared. The results showed that, for the unipedal posture, but not for the bipedal posture, postural stability was higher after the move + monitoring intervention. This suggests that the self-monitoring activity is beneficial to postural control when maintaining upright posture is more challenging. Postural stability was also higher after the imagery condition, ensuring that the beneficial effects would have resulted from the activity of self-monitoring itself but not simply from accurate movement. These results were replicated in the two experiments, showing the reliability of the data. Interestingly, such beneficial effects were evident not only when participants self-monitored the movement of the ankle joint, i.e., the joint which is directly involved in upright postural control, but also when they self-monitored movement of the wrist (Experiment 1) or shoulder (Experiment 2).Therefore, the beneficial effects of self-monitoring are likely to be independent of the body parts used for self-monitoring.

Characteristics of temporal fluctuation of the vertical ground reaction force during quiet stance in Parkinson's disease

Stance instability is seen in late stage Parkinson's disease (PD). Stabilometer-based center-of-pressure (COP) evaluation is an easy, routine method for measuring postural control ability. Most of the stabilometer- and force plate-based studies on upright postural control have discussed horizontal COP component control. Previous studies on vertical component control have been few, and no fractal analysis-based study on the component has been reported. We aimed to show the influence of neurological changes and aging on the vertical component and the difference in fluctuation pattern behavior in healthy young and elderly subjects as well as Parkinsonian patients. Detrended fluctuation analysis was used to study characteristics of fluctuation of vertical ground reaction force. In the three groups, all scaling exponents (α, α1, α2), which are time-correlated data of vertical ground reaction force, had a value >0 and <0.5 (0<α<0.5). Additionally, α and α2 were significantly different between PD and the other groups. Significant differences were observed between PD and the other groups regarding RMS, maximum peak value, and coefficient of variance.We demonstrated statistically significant differences in vertical ground reaction force between Parkinsonian patients and the other groups, suggesting that a neurological influence with PD may be markedly reflected in the vertical ground reaction force.

Effects of Vestibular Rehabilitation on Multiple Sclerosis–Related Fatigue and Upright Postural Control: A Randomized Controlled Trial

Fatigue and impaired upright postural control (balance) are the 2 most common findings in people with multiple sclerosis (MS), with treatment approaches varying greatly in effectiveness. The aim of this study was to investigate the benefits of implementing a vestibular rehabilitation program for the purpose of decreasing fatigue and improving balance in patients with MS. The study was a 14-week, single-blinded, stratified blocked randomized controlled trial. Measurements were conducted in an outpatient clinical setting, and interventions were performed in a human performance laboratory. Thirty-eight patients with MS were randomly assigned to an experimental group, an exercise control group, or a wait-listed control group. The experimental group underwent vestibular rehabilitation, the exercise control group underwent bicycle endurance and stretching exercises, and the wait-listed control group received usual medical care. Primary measures were a measure of fatigue (Modified Fatigue Impact Scale), a measure of balance (posturography), and a measure of walking (Six-Minute Walk Test). Secondary measures were a measure of disability due to dizziness or disequilibrium (Dizziness Handicap Inventory) and a measure of depression (Beck Depression Inventory-II). Following intervention, the experimental group had greater improvements in fatigue, balance, and disability due to dizziness or disequilibrium compared with the exercise control group and the wait-listed control group. These results changed minimally at the 4-week follow-up. Limitations The study was limited by the small sample size. Further investigations are needed to determine the underlying mechanisms associated with the changes in the outcome measures due to the vestibular rehabilitation program. A 6-week vestibular rehabilitation program demonstrated both statistically significant and clinically relevant change in fatigue, impaired balance, and disability due to dizziness or disequilibrium in patients with MS.

Control of bipedal posture following localised muscle fatigue of the plantar-flexors and finger-flexors

The present experiment investigated the control of bipedal posture following localised muscle fatigue of the plantar-flexors and finger-flexors. Twelve young healthy adults voluntarily participated in this study. They were asked to stand upright as still as possible with their eyes closed in two randomly ordered experimental sessions. Each session consisted of pre- and post-fatigue bipedal static postural control measurements immediately before and after a designated fatiguing protocol for plantar-flexor and finger-flexor muscles. Centre of foot pressure (CoP) displacements were recorded using a force platform. The results showed that the postural effects of localised muscle fatigue differed between the muscles targeted by the fatiguing procedures. Indeed, localised muscle fatigue of the plantar-flexors yielded increased CoP displacements, whereas localised muscle fatigue of the finger-flexors had no significant effect on the CoP displacements. In other words, fatigue localised to muscles which are involved in the performance of the postural task (plantar-flexors) degraded postural control, whereas fatigue localised to muscles which are not involved in the performance of the postural task did not. Taken together, the present findings support the recent conclusions that the effects of localised muscle fatigue on upright postural control is joint- and/or muscle-specific, and suggest that localised muscles fatigue of the plantar-flexors could mainly affect bipedal postural control via sensorimotor rather than cognitive processes.

Effects of visual feedback of center-of-pressure displacements on undisturbed upright postural control of hemiparetic stroke patients

To assess whether insights from postural control without additional visual feedback (VFB) could be gained to explain the possible VFB effects (or non-effects) on upright stance performance. The center-of-pressure (CP) displacements of 39 patients with a recent hemispheric stroke (93 days ± 56; mean ± s.d.) were analyzed in two conditions (eyes open and VFB) through various classical parameters and fractional Brownian motion (fBm) modeling. Correlations between their ability to use the VFB technique appropriately and parameters assessing the eyes open condition were also computed. The fBm modeling showed that the VFB technique improves the control of the CP trajectories over the longer time intervals. In both conditions, the patients with right hemiparesis, compared to those with left hemiparesis, demonstrated improved control of their CP displacement along the AP axis over the shortest time intervals. Overall, 28% of the patients did not use the VFB technique. The correlation analysis indicated that the larger the spontaneous CP movements in the eyes open condition, the greater the effect of the VFB technique. By emphasizing its particular effects and the profile of the patients who used the technique, these data specify the conditions allowing hemiparetic patients to use the VFB technique appropriately and immediately.

The role of eye movement in upright postural control

Vision contributes to upright postural control by providing afferent feedback to the cerebellum. Vision is generally classified into central and peripheral vision. In measurements of postural sway, in which participants are required to maintain a stable upright posture while fixating on a visual target, non-retinal eye positional information due to the fixation is used as well as the retinal information from both visual fields. However, little is known about the role of non-visual eye positional information in postural control. This study examined the role of non-visual eye position information in upright postural control by comparing participants’ centre of pressure (COP) sway between two experimental conditions: (1) a space-fixed visual target condition (control), in which eye movement was not controlled, and (2) a head-fixed visual target condition (treatment), in which eye movement was inhibited. Using 12 university students, COP sway and electrooculograms (EOG) were measured under both conditions. In the space-fixed condition, participants maintain an upright posture while fixating on a visual target fixed on a screen 1 m in front of them. In the head-fixed condition, participants maintained an upright posture while gazing at a target moving in sync with their head sway on the screen. The COP was evaluated by path length, area, root mean square, velocity and position. Eye movements were evaluated by the mean eye movement angle. The mean eye movement angle was significantly larger in the vertical direction then in the horizontal direction in both experimental conditions and was also found to be larger in the space-fixed condition than in the head-fixed condition. No significant different was found in any COP parameter between both conditions. It was suggested that non-visual eye position information from the external eye muscles to the sensory perception system contributes little to postural stabilisation under the measurement conditions used in this study.

Human upright posture control in a virtual visual environment

The sagittal and frontal components of the stabilogram were monitored in 14 healthy subjects standing on a rigid or pliant support under three different conditions of visual control: with the eyes opened (EO), with the eyes closed (EC), or in a virtual visual environment (VVE). Under the VVE conditions, the subjects looked at a three-dimensional image of elements of a room (a 3-D artificial room) that was generated by a computer and locked to the fluctuations of the body center of gravity (CG) so that the visual connection between body sway and shifts of the visual environment typical of normal visual conditions was reproduced. Frequency filtration of the fluctuations of the foot’s center of pressure (FCP) was used to isolate the movements of the vertical projection of the CG and determine the difference between these two variables. The changes in the variables (CG and FCP-CG) were estimated using spectral analysis followed by the calculation of the root mean square (RMS) amplitudes of their spectral fluctuations. In subjects standing on a rigid support, the RMS amplitudes of the spectra of both variables were the highest under the VVE and EC conditions and the lowest under the EO conditions. In subjects standing on a pliant support, body sway was considerably enhanced, which was accompanied by a different pattern of visual influences. The RMS values were the highest under the EC conditions and were lower by a factor of 2–2.5 under the EO and VVE conditions. Thus, it has been demonstrated that the cerebral structures controlling posture ignore the afferent input from the eyes under VVE conditions, if the subject is standing on a rigid support and the CG fluctuations are relatively small; however, this afferentation is efficiently used for maintaining the posture on a pliable support, when the body sway is substantially enhanced.

Postural Effects of the Scaled Display of Visual Foot Center of Pressure Feedback Under Different Somatosensory Conditions at the Foot and the Ankle

Vuillerme N, Bertrand R, Pinsault N. Postural effects of the scaled display of visual foot center of pressure feedback under different somatosensory conditions at the foot and the ankle. Objectives To assess the effects of the scaled display of visual foot center of pressure (COP) feedback on upright postural control under different somatosensory conditions at the foot and the ankle. Design Before and after intervention trials. Setting University medical bioengineering laboratory. Participants Young healthy adults (N=8; mean age, 23±2.5y; mean body weight, 76.8±11.2kg; mean height, 179.8±6.8cm). Interventions Participants were asked to stand upright, as immobile as possible, in 3 visual conditions: a stationary cross feedback (SC-FB) condition and 2 different foot COP feedback (COP-FB) conditions involving increasing scale displays of 2:1 (COP-FB2) and of 10:1 (COP-FB10). These latter conditions correspond to the ratio between the COP displacement on the screen and the actual COP displacement measured by the force platform. This postural task was executed on 2 (firm, foam) support surface conditions. In the foam condition, a 2-cm thick foam support surface was placed under the participants' feet to alter the quality and/or quantity of somatosensory information at the foot and the ankle. Main Outcome Measure COP displacements were recorded using a force platform. Results In the firm support surface condition, no significant difference was observed between the COP-FB2 and the SC-FB conditions, whereas the COP-FB10 condition yielded decreased COP displacements relative to the SC-FB condition. In the foam support surface condition, both the COP-FB2 and the COP-FB10 conditions yielded decreased COP displacements relative to the SC-FB condition, with a greater stabilizing effect in the COP-FB10 than COP-FB2 condition. Conclusions The postural effects of the scale display of visual COP feedback differed depending on the somatosensory conditions at the foot and the ankle. These findings suggest that increased reliance on augmented sensory information for controlling upright posture in conditions of altered somatosensory input from the foot and ankle could have implications in clinical and rehabilitative areas.

Contribution of the Multifidus Muscle for Control of Upright Posture in Subjects with Spina Bifida Occulta

The multifidus muscle plays a role in controlling lumbosacral position and postural sway. One of its attachment sites is the exact site of spina bifida occulta (SBO). To investigate the role of the muscle for postural control in SBO. Cross-sectional cohort. Eighty subjects with SBO (38 in minor; 42 in major) and controls. N/A. Subjects stood upright on a platform at 0 degrees and on an inclined surface (10 degrees and 20 degrees) with feet in plantarflexion/dorsiflexion, together with eyes open and closed. The platform system measured posture to obtain sway area and sway mean for statistics. Upon sway area/mean, the group differences of major/minor SBO vs. control were all significant. Sway means of minor SBO were lower than those of major SBO at corresponding inclined degrees. Subjects with SBO demonstrated increased sway as compared to controls.

Effectiveness of an electro-tactile vestibular substitution system in improving upright postural control in unilateral vestibular-defective patients

We investigated the effects of an electro-tactile vestibular substitution system (EVSS) on upright postural control in 12 unilateral vestibular-defective patients. The underlying principle of this system consists in supplying the user with additional information about his/her head orientation /motion with respect to gravitational vertical, normally provided by the vestibular system, through electro-tactile stimulation of his/her tongue. Subjects were asked to stand as immobile as possible with their eyes closed in two No-EVSS and EVSS conditions. Reduced centre-of-foot pressure displacements were observed in the EVSS relative to the No-EVSS condition. These results, demonstrating the effectiveness of the EVSS system in improving upright postural control in unilateral vestibular-defective patients, could have implications in clinical and rehabilitative areas.