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PubMed1997

Automatic control of postural sway by visual motion parallax.

The purpose of this study was to establish whether visual motion parallax participates in the control of postural sway. Body sway was measured in ten normal subjects by photoelectric recordings of head movements and by force-plate posturography. Subjects viewed a visual display ("background"), which briefly moved (2 s) along the y (horizontal) axis, under three different conditions: (1) direct fixation of the background, (2) fixation of a stationary window frame in the foreground, and (3) fixation of the background in the presence of the window in the foreground ("through the window"). In response to background fixation, subjects swayed in the same direction as stimulus motion, but during foreground (window) fixation they swayed in the opposite direction. The earlier forces observed on the force platform occurred at circa 250 ms in both conditions. The results show that motion parallax generates postural responses. The direction of these parallax-evoked postural responses-opposite to other visually evoked postural responses reported so far-is appropriate for stabilizating posture in natural circumstances. The findings show that motion parallax is an important source of self-motion information and that this information participates in the process of automatic postural control. In the "fixating through the window" condition, which does not mimic visual conditions induced by body sway, no consistent postural responses were elicited. This implies that postural reactions elicited by visual motion are not rigid responses to optokinetic stimulation but responses to visual stimuli signalling self-motion.

Adult↗

PubMed1998

The postural stability control and gait pattern of idiopathic scoliosis adolescents.

OBJECTIVE: The static postural equilibrium and gait patterns between idiopathic scoliotic (IS) patients and normal subjects were studied to verify the best method to identify the functional disability in IS patients. DESIGN: The static stability in six postures and gait patterns among normal subjects and IS patients were compared. BACKGROUND: Postural stability control and gait analysis are non-invasive methods to identify many diseases. However, the dysfunction of IS patients in postural stability control and gait pattern is not clear. The results of this research may lead to further understanding of the etiology of idiopathic scoliosis in the postural equilibrium influencing aspects. METHODS: Thirty IS patients and fifteen normal subjects were recruited for postural stability control test and gait analysis using the force plate and 3-D motion analysis system. RESULTS: The IS patients generally produced higher sway area, lateral sway, sagittal sway, and sway radius than normal subjects. The cadence is smaller in the IS patients, but the stance phase and stride phase are similar to normal subjects. CONCLUSIONS: The IS patients are poor in postural stability control but their gait pattern is similar to that of normal subjects. Standing with trunk at full flexion is the most effective position to identify the postural stability control of IS patient.

Journal Article↗

PubMed2004

The visual control of stability in children and adults: postural readjustments in a ground optical flow.

The aim of this research was to analyse the development of postural reactions to approaching (AOF) and receding (ROF) ground rectilinear optical flows. Optical flows were shaped by a pattern of circular spots of light projected on the ground surface by a texture flow generator. The geometrical structure of the projected scenes corresponded to the spatial organisation of visual flows encountered in open outdoor settings. Postural readjustments of 56 children, ranging from 7 to 11 years old, and 12 adults were recorded by the changes of the centre of foot pressure (CoP) on a force platform during 44-s exposures to the moving texture. Before and after the optical flows exposure, a 24-s motionless texture served as a reference condition. Effect of ground rectilinear optical flows on postural control development was assessed by analysing sway latencies (SL), stability performances and postural orientation. The main results that emerge from this experiment show that postural responses are directionally specific to optical flow pattern and that they vary as a function of the motion onset and offset. Results showed that greater developmental changes in postural control occurred in an AOF (both at the onset and offset of the optical flow) than in an ROF. Onset of an approaching flow induced postural instability, canonical shifts in postural orientation and long latencies in children which were stronger than in the receding flow. This pattern of responses evolved with age towards an improvement in stability performances and shorter SL. The backward decreasing shift of the CoP in children evolved in adults towards forward postural tilt, i.show $132#e. in the opposite direction of the texture's motion. Offset of an AOF motion induced very short SL in children (which became longer in adult subjects), strong postural instability, but weaker shift of orientation compared to the receding one. Postural stability improved and orientation shift evolved to forward inclinations with age. SL remained almost constant across age at both onset and offset of the receding flow. Critical developmental periods seem to occur by the age of 8 and 10 years, as suggested by the transient 'neglect' of the children to optical flows. Linear vection was felt by 90% of the 7 year olds and decreased with age to reach 55% in adult subjects. The mature sensorimotor coordination subserving the postural organisation shown in adult subjects is an example aiming at reducing the postural effects induced by optical flows. The data are discussed in relation to the perceptual importance of mobile visual references on a ground support.

Adaptation, Physiological↗

PubMed1989

Dynamic performance of vibration induced anterior-posterior sway during upright posture in normal subjects.

Human postural control works as a dynamic feedback control system. The dynamic performance of postural control for anterior-posterior movements during upright posture are defined by three parameters. These parameters reflect the stiffness, the damping and the swiftness of a response to an induced perturbation. In the present study 23 normal subjects were investigated. Both with open and closed eyes, there was a negative correlation between swiftness and stiffness. With open eyes there was also a weak correlation between swiftness and damping. When the subjects were tested with open eyes there was a prominent and highly significant increase of stiffness and a reduction of swiftness of the responses. It was found that proprioceptive information from the calf muscles contributes in postural control of movements up to 1 Hz and visual information is important for movements up to 0.05 Hz. The present findings suggest that postural control changes dynamic strategies depending on the available sensory feedback.

Adolescent↗

PubMed1995

Balance testing in saturation diving.

UNLABELLED: The literature is sparse and equivocal concerning the possible influence of hyperbaric exposure on postural control and the vestibular system. HYPOTHESIS: Deep heliox diving may influence postural control and the vestibular system. METHOD: Multiple objective measurements of postural control were made in four divers by means of a static balance platform before, during and after an onshore experimental saturation heliox chamber dive of 32 d duration. Saturation pressure was 4.6 MPa, corresponding to a depth of 450 m of seawater (msw). Downward excursions to 470 msw were also performed. Clinical ENT and otoneurological examination, including bithermal caloric vestibular testing with electronystagmography (ENG) was performed before and after the dive. RESULTS: Reduced postural control was detected by the balance platform test in all four divers from approximately 200 msw and deeper. Body sway showed a distinct increase during compression, reaching a maximum value during the bottom phase. The Romberg index was not suitable for describing shifts in postural stability. All sway parameters returned to pre-dive values after surfacing. Immediately post-dive, most caloric responses were reduced, compared to the pre-dive results. CONCLUSION: We conclude that deep heliox diving influences postural control and the vestibular system. Computerized stabilometry is a convenient and sensitive method of monitoring postural control during saturation diving. The path length of the center of pressure (COP) seems to be suitable as a monitoring parameter.

Adult↗

PubMed2004

Characteristics of learning voluntary control of posture in lesions of the pyramidal and nigrostriatal systems.

The aim of the study reported here was to investigate impairments on the learning of voluntary control of the center of pressures using visual feedback in patients with lesions of the corticospinal and nigrostriatal systems. Participants were 33 patients with Parkinson's disease and 20 patients with hemipareses due to circulatory lesions in the basin of the middle cerebral artery. Subjects stood on a stabilometric platform and used two computer games over 10 days to learn to shift the body relative to the foot to move the centre of pressures, indicated by the position of a cursor on the screen, with the target and to move the target to a specified part of the screen. The games differed in terms of the postural tasks. In one, the direction of movement of the center of pressures was not known to the subjects, and subjects learned a general strategy for posture control; the other formed a strictly defined postural coordination. Both groups of patients were found to have impairments of voluntary control of the position of the center of pressures. There were no differences between groups of patients, in terms of the severity of the initial performance deficit in the task involving shifts of the center of pressures in different directions (the general strategy for controlling the center of pressures), while learning of this task was more difficult for patients with Parkinson's disease. The initial deficit in the fine postural coordination task was more marked in patients with Parkinsonism, though learning in these patients was significantly better than in patients with hemipareses. It is suggested that the mechanisms of involvement of the nigrostriatal and corticospinal systems in learning the voluntary control of posture have elements in common as well as unique elements.

Adult↗

PubMed2006

Effects of linear versus sigmoid coding of visual or audio biofeedback for the control of upright stance.

Although both visual and audio biofeedback (BF) systems for postural control can reduce sway during stance, a direct comparison between the two systems has never been done. Further, comparing different coding designs of audio and visual BF may help in elucidating how BF information is integrated in the control of posture, and may improve knowledge for the design of innovative BF systems for postural control. The purpose of this paper is to compare the effects of linear versus sigmoid coding of trunk acceleration for audio and visual BF on postural sway in a group of eight, healthy subjects while standing on a foam surface. Results showed that sigmoid-coded audio BF reduced sway acceleration more than did a linear-coded audio BF, whereas a linear-coded visual BF reduced sway acceleration more than a sigmoid-coded visual BF. In addition, audio BF had larger effects on reducing center of pressure (COP) displacement whereas visual BF had larger effects on reducing trunk sway. These results suggest that audio and visual BF for postural control benefit from different types of sensory coding and each type of BF may encourage a different type of postural sway strategy.

Auditory Perception↗

PubMed2006

[Attentional control of postural stability in institutionalised elderly people: effects of a physical exercise program].

OBJECTIVE: We aimed to examine the effect of a physical activity program on postural sway and on the attentional control of postural abilities in elderly frail adults. METHOD: Twelve older adults (age 81.4+/-9 years) institutionalised in a geriatric care institution participated in the physical activity program posture-balance-mobility (PBM) twice a week (1 hour per session) for 12 weeks. We analysed stabilometric data for surface and length of the center of pressure (COP) sway, with eyes open and eyes closed, under single-task and dual-task conditions on a firm floor before and after the training program. During the static postural evaluation and under the dual-task condition, subjects performed an attention-demanding cognitive task, the random number generation task. RESULTS: Only the length of COP sway was more important under the dual-task condition than under the single-task condition (p=0.05). At baseline, cognitive performance was significantly weaker under the dual-task condition (standing) than under the single-task condition (seated), with eyes closed but not eyes open (p<0.05). However, after the training program, the performance of the cognitive task did not significantly differ between the dual-task condition with eyes closed and the single-task condition with eyes closed. CONCLUSION: The training program allowed elderly subjects to improve their ability to perform an attention-demanding cognitive task while standing still, in particular with their eyes closed. Although balance seemed to be less stable under the dual-task condition than under the single-task condition, these results could be interpreted as an improvement of the attentional control of postural stability.

Aged, 80 and over↗

PubMed1998

EMG responses to maintain stance during multidirectional surface translations.

To characterize muscle synergy organization underlying multidirectional control of stance posture, electromyographic activity was recorded from 11 lower limb and trunk muscles of 7 healthy subjects while they were subjected to horizontal surface translations in 12 different, randomly presented directions. The latency and amplitude of muscle responses were quantified for each perturbation direction. Tuning curves for each muscle were examined to relate the amplitude of the muscle response to the direction of surface translation. The latencies of responses for the shank and thigh muscles were constant, regardless of perturbation direction. In contrast, the latencies for another thigh [tensor fascia latae (TFL)] and two trunk muscles [rectus abdominis (RAB) and erector spinae (ESP)] were either early or late, depending on the perturbation direction. These three muscles with direction-specific latencies may play different roles in postural control as prime movers or as stabilizers for different translation directions, depending on the timing of recruitment. Most muscle tuning curves were within one quadrant, having one direction of maximal activity, generally in response to diagonal surface translations. Two trunk muscles (RAB and ESP) and two lower limb muscles (semimembranosus and peroneus longus) had bipolar tuning curves, with two different directions of maximal activity, suggesting that these muscle can play different roles as part of different synergies, depending on translation direction. Muscle tuning curves tended to group into one of three regions in response to 12 different directions of perturbations. Two muscles [rectus femoris (RFM) and TFL] were maximally active in response to lateral surface translations. The remaining muscles clustered into one of two diagonal regions. The diagonal regions corresponded to the two primary directions of active horizontal force vector responses. Two muscles (RFM and adductor longus) were maximally active orthogonal to their predicted direction of maximal activity based on anatomic orientation. Some of the muscles in each of the synergic regions were not anatomic synergists, suggesting a complex central organization for recruitment of muscles. The results suggest that neither a simple reflex mechanism nor a fixed muscle synergy organization is adequate to explain the muscle activation patterns observed in this postural control task. Our results are consistent with a centrally mediated pattern of muscle latencies combined with peripheral influence on muscle magnitude. We suggest that a flexible continuum of muscle synergies that are modifiable in a task-dependent manner be used for equilibrium control in stance.

Adult↗

PubMed1994

Control of posture in patients with neurologically asymptomatic HIV infection and patients with beginning HIV-1-related encephalopathy.

OBJECTIVE: Stance control measurements (sway velocity, sway area, and postural reflexes) were performed in 36 patients with neurologically asymptomatic human immunodeficiency virus infection (HIV) and in 10 patients with beginning HIV type 1 (HIV-1)-related encephalopathy. All recordings were performed using a movable platform system. OBSERVATIONS: Static posturography and postural reflexes revealed pathologic results in patients with beginning HIV-1-related encephalopathy and in about 25% of patients with nonsymptomatic HIV infection in comparison with age- and sex-matched control subjects. CONCLUSIONS: Postural control is well preserved in early HIV infection; thus, it is not an appropriate measure for detecting subclinical deficits, but disturbances of postural control seem to be one of the first neurological abnormalities in patients with beginning HIV-1-related encephalopathy.

AIDS Dementia Complex↗

PubMedDate not supplied

[Residual postural changes after cranial trauma].

A group of 29 clinically stable post-traumatic brain injury patients were studied for postural disturbances utilizing both a balance force platform and the Tinetti equilibrium test. The stabilometric exam included 6 different aspects of balance, with the goal of evaluating the importance of the sensory afferents on postural control. Posturographic data revealed a global reduction of postural control. TBI patients tended to rely more on visual feedback in postural control than did age-matched controls, and exhibited problems with sensory integration as the complexity of the balance tasks was increased. The site of lesion correlated positively with postural control problems, with brainstem and subcortical gray matter lesions most frequently being involved.

Adolescent↗

PubMed1991

Origins of the proprioceptive function of vision: visual control of posture in one day old domestic chicks.

Recently hatched domestic chicks control their upright bipedal posture, at least in part, with respect to the flow of visual information at the retina, as do human infants when they first acquire control of the head, of sitting, and of standing. Some implications of the similarity of the proprioceptive function of vision in chicks and in humans for the origins and development of postural control are discussed.

Aging↗

PubMed1987

Neuromuscular control of posture in the infant and child: is vision dominant?

This study explored the effects of vision and maturation on the characteristics of neuromuscular responses underlying balance control in both seated and standing children of five age groups (3 1/2-5 months, 8-14 months, 2-3 years, 4-6 years, and 7-10 years). A platform was used to unexpectedly disturb the child's balance in the anterior or posterior direction. Responses of the leg, trunk, and neck muscles were recorded using surface electromyograms. Vision was not required for the activation of these responses in any of the age groups tested. However, comparison of the muscle response latencies of standing children to posterior platform translation in the two visual conditions showed a significant reduction in latency for neck flexors in the 2- to 3-year-olds with vision removed and ann increase in the total number of monosynaptic reflexes. No reduction in latency was found in the older age groups. The hypothesis of a shift from an early long latency visual dominance to a shorter latency proprioceptive one during childhood is discussed. Postural control showed a cephalo-caudal developmental gradient with postural responses appearing first in the neck, then trunk, and finally, legs, as children developed from 3 to 14 months of age. A wide variety of response patterns was seen in the 3- to 5-month-olds, indicating that postural responses are not functional prior to experience with stabilizing the center of mass.

Journal Article↗

PubMed2002

Is There a Link Between Chronic Ankle Instability and Postural Instability?

OBJECTIVE: To provide clinicians and researchers with an expanded perspective on the association between functional ankle instability and postural control. DATA SOURCES: I searched MEDLINE and SPORT Discus for the years 1966-2001 using the key words ankle, instability, and balance. Additional information was obtained from cross-referencing pertinent articles. DATA SYNTHESIS: Conflicting reports have been published about whether postural control is disrupted in people with chronic ankle instability. The variety of testing methods and operational definitions used by various investigators make drawing a consensus difficult. In contrast, the results of investigations considering postural-control strategy disruptions in persons with chronic ankle instability have been compatible. Depending upon the effectiveness of an altered strategy, postural-control deficiencies may fail to be revealed in the absence of challenging tasks and environmental conditions. CONCLUSIONS/RECOMMENDATIONS: If we accept the idea that postural control is disrupted after orthopaedic injury, the next step becomes identifying the causative factors within the postural-control system. Experimental evidence surrounding the role of lateral ankle-ligament mechanoreceptors in posture suggests that they cannot be the sole source of the alterations revealed. Consideration should be directed to other potential areas within the postural-control system, as outlined in the text, during ankle evaluations and rehabilitation.

Journal Article↗

PubMed2002

Diabetic neuropathy and surface sway-referencing disrupt somatosensory information for postural stability in stance.

In order to determine the type of somatosensory information for postural control that is most affected by neuropathy, we compared the relative effects of three methods of sway-referencing the surface in a group of subjects with profound loss of somatosensory function associated with sensory polyneuropathy from diabetes with age-matched control subjects. Sway-referencing disrupted somatosensory feedback for postural control by servo-controlling the dorsi- and plantar-flexion rotation of the support surface in proportion to anterior-posterior excursion of (1) ankle angle, (2) center of body mass (CoM) angle or (3) filtered center of pressure (CoP). Postural sway in subjects with somatosensory loss was significantly larger than normal on a firm surface but not on the sway-referenced surfaces, suggesting that sway-referencing disrupts somatosensory information for postural control already disrupted by neuropathy. Control subjects standing on any sway-referenced surface swayed significantly more than neuropathy subjects who stood on a firm surface, suggesting that sway-referencing disrupts more somatosensory information than disrupted by severe neuropathy. CoP sway-referencing was less sensitive than ankle or CoM sway-referencing for distinguishing postural sway in subjects with somatosensory loss from age-matched control subjects. Given that filtered CoP sway-referencing disrupts the ability to utilize somatosensory information related to surface reactive force to a greater extent than the other two methods of sway-referencing, then these results support the hypothesis that subjects with diabetic peripheral neuropathy have lost more CoP information, than ankle or CoM angle information, for controlling postural sway in stance.

Adult↗

PubMed1999

Effects of physical and sporting activities on balance control in elderly people.

OBJECTIVE: Balance disorders increase with aging and raise the risk of accidental falls in the elderly. It has been suggested that the practice of physical and sporting activities (PSA) efficiently counteracts these age related disorders, reducing the risk of falling significantly. METHODS: This study, principally based on a period during which the subjects were engaged in PSA, included 65 healthy subjects, aged over 60, who were living at home. Three series of posturographic tests (static, dynamic with a single and fast upward tilt, and dynamic with slow sinusoidal oscillations) analysing the centre of foot pressure displacements or electromyographic responses were conducted to determine the effects of PSA practice on balance control. RESULTS: The major variables of postural control were best in subjects who had always practised PSA (AA group). Those who did not take part in PSA at all (II group) had the worst postural performances, whatever the test. Subjects having lately begun PSA practice (IA group) had good postural performances, close to those of the AA group, whereas the subjects who had stopped the practice of PSA at an early age (AI group) did not perform as well. Overall, the postural control in the group studied decreased in the order AA > IA > AI > II. CONCLUSIONS: The period during which PSA are practised seems to be of major importance, having a positive bearing on postural control. It seems that recent periods of practice have greater beneficial effects on the subject's postural stability than PSA practice only at an early age. These data are compatible with the fact that PSA are extremely useful for elderly people even if it has not been a lifelong habit.

Accidental Falls↗

PubMed2005

Postural sway during single and repeated cold exposures.

INTRODUCTION: Tissue cooling changes sensory and neuromuscular functions that are also involved in postural control. The purpose of the study was to determine how acute and repeated exposures to cold affect whole body postural control. METHODS: Postural sway was measured from 10 subjects during standing with eyes open (EO) and closed (EC) using an inclinometer-based method. Sway was assessed at at 10 degrees C on 10 consecutive days and at 25 degrees C on days 1, 5, and 10. Sway path length, area, velocity, side-to-side and forward-backward movement were assessed. At the same time, rectal and skin temperatures, muscle tonus/ shivering, thermal sensations, and comfort were recorded. RESULTS: Acute exposure to 10 degrees C caused thermal discomfort, significantly lowered (26.1-26.5 degrees C) mean skin temperatures, slightly lowered rectal temperature (36.7 degrees C) and increased (140-260%) muscle tone, increased sway path length (67-87%, p < 0.05), velocity (63-71%, p < 0.05), total sway area (42-67%, p < 0.05), and forward-backward movement (35-57%, p < 0.05) compared with 25 degrees C. Side-to-side movements were not altered in the cold. Postural sway increased with EC, and further when exposed to cold, but the effect of cold was smaller compared with EO. Repeated exposures over the 10-d period decreased sway 10-40% both at 25 degrees C and at 10 degrees C (p < 0.05-0.01), suggesting motor learning. The difference in sway between 25 degrees C and 10 micro C remained the same throughout the 10-d period, suggesting that the observed cold habituation responses do not affect sway. CONCLUSIONS: The results demonstrate that postural control is impaired in cold, which may affect physical performance in cold environmental conditions.

Adult↗

PubMed2000

The role of ocular oscillations upon visually dependent postural stabilization in patients affected by congenital nystagmus.

Visually dependent postural stabilization decreases as a consequence of a long-standing reduction of visual cues in patients affected by congenital nystagmus. The aim of the present study was to verify whether the changes in postural control in this group of patients are due to ocular oscillations or to reduced visual acuity. Therefore, postural control was evaluated when the nystagmus was blocked by the blocking position or by prisms and compared with the postural score observed in a group of normal controls whose visual acuity had been artificially reduced to the same level as that of the patients using Bangerter's filters. The results show a statistically significant improvement of visually dependent postural stabilization when ocular oscillations are inhibited either by the gaze blocking position or by prisms. They also show that postural control in normal subjects with Bangerter's filters is reduced, but is still significantly better than that observed when ocular oscillations are inhibited in patients affected by congenital nystagmus. Our data strongly support the role of ocular oscillations in visually dependent postural control, since postural impairment recovered under any condition in which ocular oscillations were abolished, despite differences in visual acuity. Our data also show that reduced visual acuity decreases visually dependent postural control to a lesser degree than ocular oscillations. This could be due to the fact that ocular oscillations are a disturbing input, usually inhibited centrally, in order to avoid oscillopsia. This mechanism is probably responsible for the reduced role of visual cues in the postural control in this group of patients. The reduction of visual acuity, by comparison, merely causes a decrease in visual cues, depending on the degree of visual loss. It can be concluded that the impaired postural control in patients affected by congenital nystagmus is mainly due to ocular oscillations, with reduced visual acuity creating a secondary effect.

Adult↗