Control Of Postural Sway Research Articles

The effect of lateral and medial wedges on control of postural sway

The human body is represented as a set of independent or related rigid segments that are linked by simple mechanical connections (Roll et al., 1988) described an internal representation of the body...

Regularity of Center of Pressure Trajectories in Expert Gymnasts during Bipedal Closed-Eyes Quiet Standing.

We compared postural control of expert gymnasts (G) to that of non-gymnasts (NG) during bipedal closed-eyes quiet standing using conventional and nonlinear dynamical measures of center of foot pressure (COP) trajectories. Earlier findings based on COP classical variables showed that gymnasts exhibited a better control of postural balance but only in demanding stances. We examined whether the effect of expertise in Gymnastic can be uncovered in less demanding stances, from the analysis of the dynamic patterns of COP trajectories. Three dependent variables were computed to describe the subject’s postural behavior: the variability of COP displacements (ACoP), the variability of the COP velocities (VCoP) and the sample entropy of COP (SEnCoP) to quantify COP regularity (i.e., predictability). Conventional analysis of COP trajectories showed that NG and G exhibited similar amount and control of postural sway, as indicated by similar ACoP and VCoP values observed in NG and G, respectively. These results suggest that the specialized balance training received by G may not transfer to less challenging balance conditions such as the bipedal eyes-closed stance condition used in the present experiment. Interestingly, nonlinear dynamical analysis of COP trajectories regarding COP regularity showed that G exhibited more irregular COP fluctuations relative to NG, as indicated by the higher SEnCoP values observed for the G than for the NG. The present results showed that a finer-grained analysis of the dynamic patterns of the COP displacements is required to uncover an effect of gymnastic expertise on postural control in nondemanding postural stance. The present findings shed light on the surplus value in the nonlinear dynamical analysis of COP trajectories to gain further insight into the mechanisms involved in the control of bipedal posture.

The influence of the aquatic environment on the control of postural sway

Balance training in the aquatic environment is often used in rehabilitation practice to improve static and dynamic balance. Although aquatic therapy is widely used in clinical practice, we still lack evidence on how immersion in water actually impacts postural control. We examined how postural sway measured using centre of pressure and trunk acceleration parameters are influenced by the aquatic environment along with the effects of visual information. Our results suggest that the aquatic environment increases postural instability, measured by the centre of pressure parameters in the time-domain. The mean velocity and area were more significantly affected when individuals stood with eyes closed in the aquatic environment. In addition, a more forward posture was assumed in water with eyes closed in comparison to standing on land. In water, the low frequencies of sway were more dominant compared to standing on dry land. Trunk acceleration differed in water and dry land only for the larger upper trunk acceleration in mediolateral direction during standing in water. This finding shows that the study participants potentially resorted to using their upper trunk to compensate for postural instability in mediolateral direction. Only the lower trunk seemed to change acceleration pattern in anteroposterior and mediolateral directions when the eyes were closed, and it did so depending on the environment conditions. The increased postural instability and the change in postural control strategies that the aquatic environment offers may be a beneficial stimulus for improving balance control.

The mechanisms of the effect of light finger touch on postural control

The effect of light finger touch on reducing postural sway has been widely replicated; however, the mechanism of this effect has not been well understood. While the sensory hypothesis states that sensory stimuli available from light finger touch is used to automatically diminish postural sway, the suprapostural task hypothesis argues that posture is adjusted by the demand imposed by the precision requirements of light finger touch. The object of this study was to test the sensory and the suprapostural task hypotheses. Thirty-four adults kept quiet standing while lightly touching a stable plate using index finger with various touch forces (very light touch and light touch), and precision demands (low and high demand). Consistent with the sensory hypothesis, postural stability was significantly greater with light touch as compared to very light touch, as greater touch force results in greater amount of sensory stimuli. Also, consistent with the suprapostural task hypothesis, postural stability was significantly increased under high precision rather than low precision demand conditions. The current results indicated that both hypotheses were valid, suggesting that the sensory and the suprapostural task effects can coexist for adaptive control of postural sway, and in various scenarios, one is dominant over another.

Postural sway and integration of proprioceptive signals in subjects with LBP

Patients with non-specific low back pain (LBP) may use postural control strategies that differ from healthy subjects. To study these possible differences, we measured the amount and structure of postural sway, and the response to muscle vibration in a working cohort of 215 subjects. Subjects were standing on a force plate in bipedal stance. In the first trial the eyes were open, no perturbation applied. In the following 6 trials, vision was occluded and subjects stood under various conditions of vibration/no vibration of the lumbar spine or m. Triceps Surae (TSM) on firm surface and on foam surface. We performed a factor analysis to reduce the large amount of variables that are available to quantify all effects. Subjects with LBP showed the same amount of sway as subjects without LBP, but the structure of their sway pattern was less regular with higher frequency content. Subjects with LBP also showed a smaller response to TSM vibration, and a slower balance recovery after cessation of vibration when standing on a solid surface. There was a weak but significant association between smaller responses to TSM vibration and an irregular, high frequency sway pattern, independent from LBP. A model for control of postural sway is proposed. This model suggests that subjects with LBP use more co-contraction and less cognitive control, to maintain a standing balance when compared to subjects without LBP. In addition, a reduced weighting of proprioceptive signals in subjects with LBP is suggested as an explanation for the findings in this study.

Influence of gender and physical exercise on balance of healthy young adults

Objective To verify the effects of gender and physical activity on postural sway. Method A cross-sectional study was conducted to analyze upright balance of young men and women between the ages of 20-30, both active and sedentary. Study participants were 60 individuals, who were divided into: active women (n = 15), sedentary women (n = 15), active men (n = 15) and sedentary men (n = 15). The International Physical Activity Questionnaire (IPAQ) short form, was used to evaluate each participant’s level of physical activity. According to the questionnaire, active individuals are those who carry out moderate activity, with an energy expenditure between 3.5 and 6 METs (1 MET: 3.5 ml/kg/min), or vigorous activity, with an energy expenditure above 6 METs, at least three days a week for 20 minutes. To assess control of postural sway, we measured the amplitude and velocity of anteroposterior (AP) and mediolateral (ML) sway in standing position, with their eyes open and closed, with and without foam, on a force platform. Results Comparison between genders revealed that, when compared to sedentary women, sedentary men displayed poorer performance in velocity and amplitude of AP postural control sway with their eyes closed, with and without foam. There were no differences in the amplitude and velocity of ML sway, both with open and closed eyes among groups (p < 0.05). There were no differences when comparing physically active men and women either. Conclusion Sedentary men seem to rely more on vision for maintaining postural control in quiet standing situations with respect to women.

The pattern of coupling dynamics between postural motion, isotonic hand movements and physiological tremor

This study was designed to examine differences in the coupling dynamics between upper limb motion, physiological tremor and whole body postural sway in young healthy adults. Acceleration of the hand and fingers, forearm EMG activity and postural sway data were recorded. Estimation of the degree of bilateral and limb motion–postural sway coupling was determined by cross correlation, coherence and Cross-ApEn analyses. The results revealed that, under postural tremor conditions, there was no significant coupling between limbs, muscles or sway across all metrics of coupling. In contrast, performing a rapid alternating flexion/extension movement about the wrist joint (with one or both limbs) resulted in stronger coupling between limb motion and postural sway. These results support the view that, for physiological tremor responses, the control of postural sway is maintained independent to tremor in the upper limb. However, increasing the level of movement about a distal segment of one arm (or both) leads to increased coupling throughout the body. The basis for this increased coupling would appear to be related to the enhanced neural drive to task-specific muscles within the upper limb.

Postural sway and perception of affordances in children at risk for developmental coordination disorder

Gibson (The ecological approach to visual perception, Houghton Mifflin, Boston, 1979/1986) defined affordances as opportunities for motor behaviors, and highly emphasized the interaction between perception and action. Research on children with developmental coordination disorder commonly reports difficulties in judgments of affordances (perception) and in postural control (action). However, how perception and action are coupled has not been studied yet. The present study sought to evaluate the relationship between control of postural sway and perception of affordances in children at risk for developmental coordination disorder (RDCD) and typically developing children (TDC). We hypothesized that the relationship between perception and action would differ between groups. Participants made a series of judgments about their maximum sitting height (SHmax) while standing with and without wearing 10 cm blocks on feet. Postural sway and the judgment accuracy were recorded. Our findings showed that RDCD swayed more during judgment sessions and made less accurate judgments compared to TDC. In addition, TDC reduced postural sway from inter-judgment to judgment sessions, whereas the postural sway of RDCD remained identical between sessions. Last, while TDC reduced postural sway across judgment trials and revealed a learning effect of the judgments about SHmax in the block condition, RDCD never modulated postural sway and did not learn their SHmax in both non-block and block conditions. Overall, modulation of postural sway differed between groups during judgment sessions and between inter-judgment and judgment sessions, whereby their perceptual judgments about SHmax were differentially influenced. To summarize, this study demonstrated a difference in perception and action coupling between RDCD and TDC.

The effect of whole body vibration training on postural sway in patients with spinal cord injury: a pilot study

Objective: The aim of this study was to determine the impact of the application of whole body vibration training (WBV) on the balance ability of patients with an American Spinal Injury Association (ASIA) type C or D spinal cord injury. Design: Randomized controlled trial. Methods: Twelve patients with spinal cord injury were enrolled in this study. The participants were randomized to an experimental group (n=6) or control group (n=6). The subjects in the experimental group received WBV exercise and the control group received the sham exercise without vibration. The vibrations were adjusted vertically to the patient at a 30 Hz frequency and 3 mm amplitude. The whole body vibration lasted for 16 minutes in total including 5-minutes warm-up and cool-down at the beginning and end of the program, respectively. The static sitting balance ability was assessed by measuring the postural sway while sitting on the force plate with the eyes opened or closed. Postural sway length was measured for 30 seconds with a self-selected comfortable position. Results: In the static balance test, the anterio-posterior, medio-lateral, and total postural sway length with the eyes open and closed was improved significantly before and after the intervention in the experimental group (p<0.05). The experimental group showed significantly more improvement than the control group (p<0.05). Conclusions: Our results demonstrated that WBV training has a positive effect on improving static sitting balance and enhanced control of postural sway in patients with an ASIA-C or D type spinal cord injury.

The effect of lateral or medial wedges on control of postural sway in standing

The objective of this study was to evaluate the effects of lateral and medial wedges on postural sway. Twenty healthy volunteers (mean age range of 28.45±3.34) participated in the study. They stood barefoot with eyes open or closed on each of the three surfaces: 10° lateral wedges, 10° medial wedges, and no wedges. Force platform data were collected and the mean and root mean square (RMS) distance, range, and velocity and the mean frequency of the center of pressure (COP) were calculated in the anterior-posterior (AP) and medial-lateral (ML) directions. Standing on both lateral and medial wedges was associated with improved postural stability seen through the decreased mean and RMS distance of COP displacement in ML direction. The results of this study suggest that standing on either lateral or medial wedges might enhance postural control in standing.

Multisensory interactions in the automatic control of postural sway

Visual motion signals are an important source of self-motion information that are used in postural control. Bronstein and Buckwell (Exp. Brain Res. 113, 243–248, 1997) showed that postural reactions to visual motion are not rigid responses to optokinetic stimulation but specific responses appropriate for stabilising posture in natural circumstances: body sway, for instance, was abolished when participants fixated a static object in front of a laterally moving background, which in itself induced sway. We test whether haptic and auditory as well as visual fixation points reduce body sway induced by a background that either moved left/right or forward/back on a large (3 × 7 m) 3D visual display. 10 participants were asked to respond when a fixation target, whichs was presented either on a background or foreground, changed colour. Body sway was measured using a VICON motion tracking system. We tested three conditions that replicated Bronstein and Buckwell’s original study and show that body sway, induced by lateral motion of the background is abolished when participant fixate on a (virtual) foreground object. We extended their study by showing that 3D motion (looming/receding background) has a similar effect to lateral motion and to show that body sway can be effectively reduced by providing either auditory (a loudspeaker emitting a white noise) and haptic (participants lightly touch a tripod with their index finger) cues. Our findings show that postural control draws auditory and haptic as well as visual cues. The findings are relevant to the design of virtual reality systems and provide a method for objective measures of presence in virtual environments.

EEG correlates of postural audio-biofeedback

The control of postural sway depends on the dynamic integration of multi-sensory information in the central nervous system. Augmentation of sensory information, such as during auditory biofeedback (ABF) of the trunk acceleration, has been shown to improve postural control. By means of quantitative electroencephalography (EEG), we examined the basic processes in the brain that are involved in the perception and cognition of auditory signals used for ABF. ABF and Fake ABF (FAKE) auditory stimulations were delivered to 10 healthy naive participants during quiet standing postural tasks, with eyes-open and closed. Trunk acceleration and 19-channels EEG were recorded at the same time. Advanced, state-of-the-art EEG analysis and modeling methods were employed to assess the possibly differential, functional activation, and localization of EEG spectral features (power in α, β, and γ bands) between the FAKE and the ABF conditions, for both the eyes-open and the eyes-closed tasks. Participants gained advantage by ABF in reducing their postural sway, as measured by a reduction of the root mean square of trunk acceleration during the ABF compared to the FAKE condition. Population-wise localization analysis performed on the comparison FAKE – ABF revealed: (i) a significant decrease of α power in the right inferior parietal cortex for the eyes-open task; (ii) a significant increase of γ power in left temporo-parietal areas for the eyes-closed task; (iii) a significant increase of γ power in the left temporo-occipital areas in the eyes-open task. EEG outcomes supported the idea that ABF for postural control heavily modulates (increases) the cortical activation in healthy participants. The sites showing the higher ABF-related modulation are among the known cortical areas associated with multi-sensory, perceptual integration, and sensorimotor integration, showing a differential activation between the eyes-open and eyes-closed conditions.

Altered control of postural sway following cerebral infarction

Balance impairment is common following cerebral infarction. However, the effects of lesion hemisphere on postural control are largely unknown. We examined dependence upon vision and noninfarcted regional brain tissue volumes for postural control in individuals with right and left hemisphere middle cerebral artery (MCA) infarcts. Subjects with right MCA infarct (n = 17, age = 65 +/- 8 years, 7 +/- 6 years poststroke), left MCA infarct (n = 20, age = 65 +/- 8 years, 7 +/- 6 years poststroke), and controls (n = 55, age = 65 +/- 8 years) were studied. Postural control was defined by average velocity and the range and variability of mediolateral (ML) and anteroposterior (AP) sway during eyes-open and eyes-closed standing. Regional brain volumes were quantified using anatomic MRI at 3 Tesla. Right and left hemisphere stroke groups had similar infarct volumes and outcomes. Subjects with right hemisphere infarcts demonstrated greater sway velocity, ML range, and ML variability with eyes closed compared to eyes open. In this group, smaller occipital lobe volumes were associated with greater eyes-open sway velocity (R = -0.64, p = 0.012) and ML range (R = -0.82, p = 0.001). Smaller cerebellar volumes were associated with greater eyes-closed sway velocity (R = -0.60, p = 0.015), ML range (R = -0.70, p = 0.007), and ML variability (R = -0.85, p < 0.001). These associations were not observed in left hemisphere infarct subjects or controls. AP sway was unaffected by infarct hemisphere or visual condition and did not correlate with regional brain volumes. Right hemisphere middle cerebral artery infarcts are associated with increased dependence on vision and noninfarcted brain regions (i.e., occipital lobes, cerebellum) to control postural sway. Strategies emphasizing postural tasks under reduced visual conditions may enhance functional recovery in these individuals.

The evaluation of deficits on dynamic postural sway control and its correlation with lumbar mobility in females with chronic low back pain

Introduction: Previous studies on chronic low back pain (CLBP) have addressed the biomechanical performance of trunk, including its mobility, and the static balance performance in the related population. However, the onset of low back pain is commonly linked with dynamic activities and therefore, the evaluation of the balance performance in dynamic condition would be clinically important. The objectives of this study were to assess the dynamic postural control and its relationship with trunk mobility in chronic low back pain patients. Materials and Methods: Twenty-four female patients with chronic low back pain and 24 able-bodied females, all between 25 to 45 years old, voluntarily participated in this study. Dynamic postural control, lumbar mobility and back pain were measured by a Biodex system, Schober technique and Quebec questionnaire, respectively. Multivariate analysis of variance (repeated measure) and Pearson correlation coefficient were used for data analysis (α < 0.05). Results: Chronic low back pain patients had greater dynamic postural sway (P < 0.0001). In chronic low back pain, the function of lower limbs and the trunk’s proprioception were affected. This deficit was better observed in closed eyes condition. Lumbar mobility was significantly reduced in chronic low back pain group, However there was no significant relationship between the lumbar mobility and the postural control (P < 0.001). Conclusion: Chronic low back pain is associated with greater postural sway and reduced lumbar mobility. These variables are independent and should be considered in both detection and treatment process separately. More studies are sequined to determine if these parameters are primary or secondary

Influence of dual tasks on sitting postural sway in children and adolescents with myelomeningocele

Performing dual tasks, e.g. cognitive and motor tasks simultaneously, may be especially challenging to children with motor disorders. Changes in postural sway have been used to evaluate the effect of dual tasks. Increases in postural sway frequency and concurrent decrease in sway amplitude have been interpreted as tighter control of postural sway. The purpose of this study was to analyze postural sway under single and dual task conditions, while sitting. Thirteen children and adolescents with myelomeningocele and a matched control group were included in the study. The participants performed two single and two dual tasks each. The single task was a sitting still task. The dual tasks were one visual-spatial task and one executive task while simultaneously sitting still. Amplitude, velocity and frequency of center of pressure displacement of postural sway were analyzed between tasks and between groups. The results of the cognitive tasks were analyzed as well. The results revealed different patterns in the groups. During single tasks, the MMC group displayed significantly lower frequencies and velocities of center of pressure displacement compared to the control group. Adding the visual-spatial task influenced postural sway significantly in the control group, while adding the executive task influence the postural sway significantly in the MMC group. The myelomeningocele group confirmed our clinical experience by performing the cognitive tasks slowly but accurately. Further studies are needed to evaluate whether motor function, sensory function, structural anomalies in the brain or any other causes, separately or together, may explain the observed differences in the groups.

An enhanced level of motor cortical excitability during the control of human standing

The study examined the role of the motor cortex in the control of human standing. Subjects (n = 15) stood quietly with or without body support. The supported standing condition enabled subjects to stand with a reduced amount of postural sway. Peripheral electrical stimulation, transcranial magnetic stimulation (TMS) or transcranial electrical stimulation (TES) was applied to elicit a soleus (SOL) H-reflex, or motor-evoked potentials (MEPs) in the SOL and the tibialis anterior (TA). Trials were grouped based on the standing condition (i.e. supported vs. normal) as well as sway direction (i.e. forward and backward) while subjects were standing normally. During normal when compared to supported standing, the SOL H-reflex was depressed (-11 +/- 4%), while the TMS-evoked MEPs from the SOL and TA were facilitated (35 +/- 11% for the SOL, 51 +/- 15% for the TA). TES-evoked SOL and TA MEPs were, however, not different between the normal and supported standing conditions. The data based on sway direction indicated that the SOL H-reflex, as well as the SOL TMS- and TES-evoked MEPs were all greater during forward when compared to backward sway. In contrast, the TMS- and TES-evoked MEPs from the TA were smaller when swaying forward as compared to backward. The results indicated the presence of an enhanced cortical excitability because of the need to control for postural sway during normal standing. The increased cortical excitability was, however, unlikely to be involved in an on-going control of postural sway, suggesting that postural sway is controlled at the spinal and/or subcortical levels.

Postural sway at ground and bevel levels in subjects with spina bifida occulta

To assess whether the postural function is impaired by comparing the performances in upright standing at ground and bevel levels in adult subjects with spina bifida occulta (SBO). Eighty subjects with SBO (38 with minor type and 42 with major type) and 35 healthy control subjects participated in the study. All participants performed ten tests while standing upright on a platform at ground level (0 degrees, baseline) and on a beveled surface (with their feet in dorsiflexion and plantarflexion at 10 degrees and 20 degrees). Tests were done with their eyes open and closed. The postural sway was examined using a force platform (CATSYS, Danish) that records sway intensity and velocity. Sway intensity and sway velocity were universally associated with group, degree of bevel, open- or closed-eyes condition, and dorsiflexion or plantarflexion after adjusting for age and gender. With respect to sway intensity, the differences of minor or major SBO group were significantly decreased at different bevel degrees when compared with control groups, whereas the differences between minor and major SBO were significant differences at 10 degrees and 20 degrees. With respect to sway velocity, the differences of major SBO group were significantly decreased at different bevel degrees when compared with minor SBO and control groups, whereas the difference in minor SBO was only significant at 0 degrees when compared with control. Group differences (minor SBO vs. control, major SBO vs. control) showed a significant decrease in sway velocity when comparing at 10 degrees than at 0 degrees and at 20 degrees than at 0 degrees. In all subjects with SBO, the sway intensity/velocity values obtained with open eyes and with plantarflexion had lower values, when compared with values obtained with closed eyes and with dorsiflexion. This study supports the hypothesis that SBO impairs control of postural sway in both the resting upright and stressful postures. Our results imply that the larger the bone defect at the lumbosacral midline, the more the group differences in different stressful conditions. Both velocity and intensity were able to reflect the function of the postural sway from our results. This is the first report to add the bevel degree and foot position, as well as visual input as being the part of the study in investigating the postural sway.

The Effects of Fitness and Fatness on Balance and Gait in Elderly Men.

0355 Reductions in physical activity have been linked to declines in cardiovascular (CV) fitness and increases in obesity across the lifespan. The effects of CV fitness and body fatness on function, as estimated by balance and gait outcomes, have been understudied in the elderly. Rising rates of obesity and physical inactivity in the aged may contribute to declines in static and dynamic balance, as well as ambulatory function. PURPOSE: To determine if fitness and body fatness impact balance and gait measures in a group of healthy, community-dwelling, elderly males. METHODS: Sixteen males (M ± SD: 72.1 ± 4.7 y), upon enrollment in a randomized clinical trial investigating the effects of exercise on immune function, volunteered for this study. CV fitness was determined from a maximal oxygen uptake test, expressed relative to body weight (VO2max). Body composition (%Fat) was determined by DXA. Gait performance was assessed using timed stair descent (STdown) and ascent (STup), timed 8-Foot Up and Go (UP-GO), and self-paced 7-meter walk with obstacle (WLK). Balance performance was assessed using: 1) the Berg balance scale (BERG), a quantitative method of assessing balance function that simulates conditions encountered in daily life; 2) the composite score on the EquiTest computerized dynamic posturography system (EQU); and 3) standing postural sway and limits of stability using a force platform (SWAY). RESULTS: Average VO2max was 21.9 ± 4.6 m1/kg/min and body fatness was 26.8 ± 6.1 %Fat, reflecting typical values for healthy elderly males. Positive relations existed between %Fat and WLK (r = 0.55, p < 0.05), UP-GO (r = 0.68, p < 0.01), STdown (r = 0.58, p < 0.05), STup (r = 0.63, p < 0.05). Additionally, strong negative relations existed between VO2max and UP-GO (r = −0.62, p < 0.05), STdown (r = −0.70, p < 0.01), ST up (r = −0.72, p < 0.01). Due to the strong relation between %Fat and VO2max (r = −0.62, p < 0.05), partial correlations were also examined for the above dependent measures. When controlling for VO2max, only the relation between %Fat and WLK remained significant (r = 0.58, p < 0.05); however, when controlling for %Fat, the relation between VO2max and UP-GO, STdown and STup dissolved suggesting that body fatness is more important than cardiovascular fitness for gait performance. No relation existed between %Fat or VO2max and BERG, EQU, and SWAY. CONCLUSION: As expected, neither fitness nor fatness affect static balance nor postural sway control measures. Independent of fitness, fatness negatively impacts gait performance. Further study is needed regarding the relation between physical activity, obesity and balance and gait performance in the elderly. Supported by NIH AG18861 to Woods

Suppression of eye movements improves balance.

The aim of this study was to investigate the possible interaction of vestibulo-ocular and vestibulo-spinal functions. Spontaneous eye movements and anterior-posterior and lateral body sway were recorded simultaneously in 10 patients with vestibular neuritis (Experiment 1) and in 11 healthy subjects (Experiment 2) while all subjects wore a mask that allowed fixation of a head-fixed target. For the healthy subjects, there was no significant difference in postural sway for the conditions of eyes open in darkness and fixation of the head-fixed target. For the patients, the question was whether transient suppression of the spontaneous nystagmus by fixating the target affected excessive body sway or whether modulation of nystagmus and postural sway were largely independent. The mean peak slow-phase velocity of the spontaneous nystagmus decreased from 13.5 +/- 5.6 to 4.3 +/- 2.4 degrees /s during fixation. The suppression of nystagmus also reduced postural sway while standing on foam rubber. Mean value decreased from 25.2 +/- 7.6 to 16.2 +/- 7.7 mm (right-left root mean square values; ANOVA, P = 0.003). Since a head-fixed target was used to suppress spontaneous eye movements, the data cannot be explained by any stabilizing effect of afferent visual cues. Instead, ocular motor efference copy signals or reafferences may have contributed to the postural instability of patients with vestibular neuritis, which would explain the reduction of postural sway during fixation suppression of the nystagmus. Thus, ocular motor signals rather than afferent visual cues about retinal slip are used for visual control of postural sway, at least in this experimental paradigm.

Force measurements of postural sway and rapid arm lift in seated children with and without MMC

Objective. The aim was to investigate the horizontal ground reaction forces of seated postural sway and rapid arm lift in children with and without myelomeningocele. Background. It is unclear whether children with myelomeningocele have limited control of body posture entirely caused by the impairment in the legs or also by other dysfunction. Methods. 11 children with myelomeningocele, 10–13 years, and 20 children without physical impairment were investigated. Data were collected by force plate measurements during quiet sitting and during rapid arm lift. The forces were expressed as the corresponding acceleration of the centre of mass. The amplitude and the frequency of the centre of mass acceleration quantified the sway. Movement time, onset and anteroposterior peak acceleration were analysed during arm lift. Results. The children with myelomeningocele had a low sway frequency under both conditions: eyes open and eyes closed. The movement time was longer for these children compared to the controls. The onset of initial anteroposterior centre of mass acceleration preceded the arm lift and was directed forward in both groups. The peak centre of mass acceleration was usually directed backward. Conclusions. The control of postural sway was different in children with myelomeningocele compared to children without disabilities and this could not be explained by the cele level. The children with myelomeningocele had a slow motor performance of the seated sway and during arm lift. Relevance Slow motor performance involves functional limitations in the individual child and is important for the therapy program.