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Results for “Postural control”

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At least 289 records · Page 16Linked to original sources

PubMed2005

The magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing with vision depends on the eye-visual target distance.

The purpose of the present experiment was to investigate whether, with vision, the magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing depends on the eye-visual target distance. Twelve young university students were asked to stand upright as immobile as possible in three visual conditions (No vision, Vision 1m and Vision 4m) executed in two conditions of No fatigue and Fatigue of the calf muscles. Centre of foot pressure displacements were recorded using a force platform. Similar increased variances of the centre of foot pressure displacements were observed in the fatigue relative to the No fatigue condition for both the No vision and Vision 4m conditions. Interestingly, in the vision 1m condition, fatigue yielded: (1) a similar increased variance of the centre of foot pressure displacements to those observed in the No vision and Vision 4m conditions along the medio-lateral axis and (2) a weaker destabilising effect relative to the No vision and Vision 4m conditions along the antero-posterior axis. These results evidence that the ability to use visual information for postural control during bipedal quiet standing following calf muscles fatigue is dependent on the eye-visual target distance. More largely, in the context of the multisensory control of balance, the present findings suggest that the efficiency of the sensory reweighting of visual sensory cues as the neuro-muscular constraints acting on the subject change is critically linked with the quality of the information the visual system obtains.

Adult↗

PubMed1998

Interaction of vestibular, somatosensory and visual signals for postural control and motion perception under terrestrial and microgravity conditions--a conceptual model.

This article considers the intersensory interaction mechanisms and biomechanical aspects of human spatially oriented behavior and asks to what extent these are interrelated on earth by gravity and how they might be affected under microgravity. The interactions between vestibular, somatosensory and visual inputs for postural control are obscured by several complications (biomechanics, multi-body dynamics, multimodal feedback control, cognition etc.). However, they can be revealed in psychophysical studies on human self-motion perception. Based on such studies, we present a conceptual model, which we think is valid also for postural control. It accounts for the multi-segmental structure of the body, allowing local control of inter-segmental joints, but uses one global reference system for all segments, which is derived from the intersensory interactions. We hold that, at a sensory level, the system is tied together by linkages between vestibular, visual and somatosensory information which develop through experience of inertial and gravitational reaction forces. On earth these linkages are established even in the absence of active behavior by gravity, allowing the incorporation of one's body and its support into a notion (Gestalt) of ourselves in the environment. Under microgravity, in contrast, the linkages have to be actively established for postural and perceptual stability in the environment (e.g., by grasping a handle on the wall). From this work we recommend that future research under altered gravity conditions should be guided by models that include biomechanics, considerations of intersensory interaction and dynamic control mechanisms. Such an integrative conceptual framework will be helpful for reaching a general understanding of spatially oriented behavior.

Gravitation↗

PubMed2001

Influence of a visuo-spatial, verbal and central executive working memory task on postural control.

In this study, participants were required to perform different working memory (WM) tasks (a verbal task, a visuo-spatial task with two levels of difficulty and a central executive task) under different challenges to postural control (sitting, shoulder width stance and tandem stance). When a WM task was added, changes in postural sway were characterized by an increase in frequency and decrease in amplitude of sway indicating a tighter control. We found no changes in postural control between the different types of WM tasks, which might support a general capacity limitation hypothesis. However, no changes were found in performance of the WM when postural stance was modified and no changes were found in postural sway, when the difficulty level of the visuo-spatial task was modified. Consequently, the results seem to indicate that the addition of a WM task, regardless of task type or task difficulty, forces the central nervous system to choose a tighter control strategy.

Adult↗

PubMed1997

Reduced cognitive functions in a group of whiplash patients with demonstrated disturbances in the posture control system.

Past studies examining whether or not cognitive changes actually have occurred as a result of a whiplash (WL) accident have produced varying results. The aim of this study was to identify possible cognitive dysfunctions in a group with persistent problems after whiplash due to injuries to the posture control system and related structures. The whiplash subjects (n = 23) were selected on the basis of their reduced gain in the Smooth Pursuit Neck Torsion test (SPNT). The WL group differed significantly from a closely matched control group on tests of learning and memory, and prolonged divided attention and concentration. After attempting to rule out other ways of interpreting these differences (such as pain, depression, medication, and premorbid health problems), these data were interpreted as lending support to the notion of a causal connection between the disturbed posture control system and some cognitive malfunctions.

Adult↗

PubMed1995

The Waterloo Vision and Mobility Study: postural control strategies in subjects with ARM.

Binocular vision function and standing balance control was assessed in 16 subjects with age-related maculopathy (ARM) (mean age 73.9 +/- 7.4 years) and 19 controls (mean age 69.1 +/- 5.5 years). Balance control was assessed using the center of pressure signal from force plate data. It was quantified using the root mean square (RMS) error of the amplitude, sampled over a 1 min period. This was evaluated during normal standing, and while the input from the kinesthetic and/or visual systems were disrupted. The two subject groups showed significantly different RMS values across conditions (P < 0.005). The differences in RMS between ARM and control groups were only significant when the input to the kinesthetic sensory system was disrupted. Our results suggest that in the normal standing condition, the kinesthetic and vestibular systems compensated for the lack of useful information from the visual system in ARM subjects. When kinesthetic system input was disrupted, balance control of the ARM group was significantly poorer than the control. There was a weak correlation between postural control and contrast sensitivity. Various strategies for preventing falls in elderly patients with low vision are suggested.

Aged↗

PubMed2005

Development of a quantitative assessment system for correlation analysis of footprint parameters to postural control in children.

It is known that neurological impairments impact postural stability, but few studies have observed the biomechanical influence of foot structure on balance. The aim of this study was to develop an integrated device for investigating the relationship between static balance and the foot structure, derived from a footprint image, under clinical tests of sensory interactions. Quantitative analysis of the footprint image acquired during balanced standing was developed as an indirect measure of the longitudinal arch, an important structural component of the foot. A data pool was collected from 64 children, 32 children from each of two age groups (4-5 years old versus 8-10 years old). Six common footprint parameters derived from the footprint angle or contact area were used to investigate the relationship between footprint parameters and postural stability. Postural balance ability was evaluated by analyzing sway area in posturography under visual or somatosensory confliction conditions. The footprint parameters, derived from the footprint image, inter-correlated well with each other (p < 0.01). The relationships between footprint parameters and sway area were correlated only for younger children under visually deprived (eye close) and cutaneous unreliable (standing on compliant foam) conditions. This implies that the correlations between footprint parameters and sway area are very subtle which can only be observed in unreliable visual and somatosensory conditions of younger children. In addition, younger children with a lower arch height would have a smaller sway area and better posture control which might result from more cutaneous somatosensation or a flexible biomechanical structure in low arch feet during conditioned static standing.

Child↗

PubMed2004

No acute changes in postural control after soccer heading.

BACKGROUND: Soccer heading has been proposed as a potential cause of cerebral dysfunction. OBJECTIVE: To examine the acute effects of two types of soccer heading on postural control. METHODS: Collegiate soccer players were randomly assigned to one of four groups: control, linear heading, simulated rotational heading, or rotational heading. Each subject completed a baseline postural stability assessment on day 1. On day 2 the same assessment was completed for the control subjects. The simulated rotational heading group completed a simulated heading drill before postural stability testing. The linear and rotational heading groups performed a heading drill with 20 balls at 88.71 km/h (55 mph), before postural stability testing. Separate one between (group), three within (surface, eyes, and day), mixed model, repeated measures analyses of variance were conducted on values for total sway and mean centre of pressure. RESULTS: The mixed model analysis of variance of results showed no significant differences (p>0.05) for the interactions of interest for either variable. Results suggest no acute changes in measures of postural control in soccer players completing either a linear or rotational soccer heading drill of 20 balls at a fixed speed. CONCLUSION: Non-significant interactions between surface, eyes, day, and group indicate that sensory interaction of the balance mechanism components are not be compromised by the heading drill. This research supports previous studies suggesting that there are no acute risks associated with routine soccer heading. A direct comparison between these findings and those suggesting long term chronic deficits, however, cannot be made. Other studies that report chronic cerebral deficits in soccer players may have resulted from factors other than soccer heading and warrant further examination.

Adolescent↗

PubMed1998

Postural control in sitting children with cerebral palsy.

Children with cerebral palsy (CP) display postural problems, largely interfering with daily life activities. Clarification of neural mechanisms controlling posture in these children could serve as a base for more successful intervention. Studies on postural adjustments following horizontal forward and backward displacements of a movable platform in ten school-age children with spastic diplegia and non-disabled controls revealed that sitting CP children, like standing CP children, show direction specific postural adjustments, indicating that the basic pattern of muscle coordination in these conditions is conserved. Dysfunctions are especially present in the modulation of the response pattern of ventral muscles during forward translations. They consist of: (1) a stereotyped and non-variable activation of all ventral muscles; (2) an abnormal top-down muscle recruitment; and (3) an excessive degree of antagonistic co-activation. The altered patterns of muscle coordination could be the result of two interacting mechanisms, the primary deficit due to the early brain damage and a compensation due to the postural instability. Especially the latter dysfunction furnishes opportunities for therapeutic help.

Cerebral Palsy↗

PubMed2005

Changes in coordination of postural control during dynamic stance in chronic low back pain patients.

The human postural system operates on the basis of integrated information from three independent sources: vestibular, visual and somatosensory. It is conceivable that a derangement of any of these systems will influence the overall output of the postural system. The peripheral proprioceptive system or the central processing of proprioceptive information may be altered in chronic low back pain (CLBP). We therefore investigated whether patients with CLBP exhibited an altered postural control during quiet standing. Dynamic posturography was performed by 12 CLBP patients and 12 age-matched controls. Subject's task was to stand quietly on a computer-controlled movable platform under six sensory conditions that altered the available visual and proprioceptive information. While the control of balance was comparable between the two groups across stabilized support surface conditions (1-3), CLBP patients oscillated much more than controls in the anterior-posterior (AP) direction in platform sway-referenced conditions (4-6). Control experiments ruled out that increased sway was due to pain interference. In CLBP patients, postural stability under challenging conditions is maintained by an increased sway in AP direction. This change in postural strategy may underlie a dysfunction of the peripheral proprioceptive system or the central integration of proprioceptive information.

Adaptation, Physiological↗

PubMed2007

Effect of attention focus on acquisition and retention of postural control following ankle sprain.

OBJECTIVE: To examine the effect of attentional focus instructions and dynamic balance training on ankle sprain recovery. DESIGN: Randomized controlled trial. SETTING: Outpatient physical therapy department. PARTICIPANTS: Forty volunteers (age range, 19-33y) referred to treatment within 4 months after sustaining a grade 1 or 2 ankle sprain with no concurrent impairments. Participants were randomly allocated to 1 of 2 groups differing in training instructions. INTERVENTION: Postural control training consisted of ten 20-second trials, performed on 3 consecutive days, at 2 stability levels of the Biodex Stability System (BSS). Training instructions directed the participants to either an internal or an external focus of attention. Assessments were conducted on the BSS pre- and post-training, and 48 hours after the last session (retention test). MAIN OUTCOME MEASURES: Overall stability as indicated by variance in platform displacement in all directions; anteroposterior (AP) variance of platform displacement; and mediolateral variance of platform displacement. RESULTS: Increases in overall and AP stability were observed immediately following training in both groups and were maintained at the retention test. Interaction effect indicates greater improvement in the external-focus group. CONCLUSIONS: Our results suggest that external focus of attention is advantageous for the learning of a postural control task following an ankle injury.

Adult↗

PubMed1983

Visual influence on postural control in the cat.

The influence of horizontal optokinetic stimulation on posture and postural readjustments, induced by horizontal rotation of a turntable, were studied in the cat. Optokinetic stimulations at constant velocities lead to modifications of posture depending on the velocity of the stimulus. However, habituation as well as interindividual variability of these postural responses make difficult a systematic and quantitative approach to the phenomenon. Optokinetic stimulations at sinusoidal velocities induced reproductible postural responses, whose phase and gain were studied at different velocities and frequencies of stimulation. At low frequencies (from 0.05 Hz to 0.2 Hz) the postural responses tend to lead the position of the optokinetic stimulus while a lag appears at higher frequencies (up to 1 Hz). In these conditions the gain increases and seems to depend on the performances of the simultaneously elicited oculomotor response. Induced postural readjustments are also modulated by the relative velocity of the visual stimulation with respect to the cat. A given visual input is more effective on an induced postural readjustment than on the posture of a static animal, especially at low frequencies (from 0.05 Hz to 0.3 Hz). These data extend to the cat the strong visual component of the postural control system previously described in other species.

Animals↗

PubMed2006

Differential integration of kinaesthetic signals to postural control.

The purpose of the present experiment was to identify whether non-visual sensory cues involved in the maintenance of balance control could be weighted differently from one subject to another in condition during which kinaesthetic signals, stemming from the ankle proprioceptors and plantar pressure somatosensory sensors, were altered. A large population of blindfolded healthy young university students (n = 140) were asked to sway as little as possible on: (1) a firm support (Firm condition) and (2) an unstable support used to impair the exploitation of the kinematic ankle proprioceptive and plantar pressure somatosensation (Foam condition). Centre of foot pressure (CoP) displacements were recorded using a force platform. Analyses of the surface area, range, and mean velocity of the CoP displacements showed significant negative correlations between the postural sway observed in the Firm condition and the increase in postural sway observed in the Foam condition. In other words, the alteration of ankle proprioception had a greater destabilising effect in subjects exhibiting the smallest CoP displacements when standing in a normal proprioception condition. The present findings suggest that the exploitation of the kinaesthetic relationships to postural control varied from one subject to another, hence evidencing the need to introduce differential approach to assess the general impact of preferential modes of spatial referencing in postural control.

Adult↗

PubMed2004

Underdevelopment of the postural control system in autism.

OBJECTIVE: To determine if abnormalities exist in postural control in autism and if they are related to age. METHODS: Dynamic posturography was performed in 79 autistic individuals without mental retardation and 61 healthy volunteers between ages 5 and 52 years. Both the sensory organization and the movement coordination portions of the test were performed. RESULTS: The autistic subjects had reduced postural stability (p = 0.002). Examination of age effects revealed that the development of postural stability was delayed in the autistic subjects (p < 0.001) and failed to achieve adult levels (p = 0.004). Postural stability was reduced under all conditions but was clinically significant only when somatosensory input was disrupted alone or in combination with other sensory challenges (mean reduction in stability of 2.6 +/- 1.0 for the first three conditions without somatosensory disruption vs 6.7 +/- 2.7 for the last three conditions with somatosensory disruption), indicating problems with multimodality sensory integration. CONCLUSIONS: The evidence from this and studies of the motor system suggests more general involvement of neural circuitry beyond the neural systems for social behavior, communication, and reasoning, all of which share a high demand on neural integration of information.

Adolescent↗

PubMed1993

Intrasubject variability of selected force-platform parameters in the quantification of postural control.

Platform stabilometry is increasingly applied to monitor or re-educate standing balance in clinical rehabilitation. Consequently, insight is needed into the validity, reliability, and sensitivity of different force-platform parameters. This study focuses on the intrasubject variability as the major source of variance (unreliability) in the study of human motor skills. The intrasubject variability of several, commonly applied force-platform parameters was determined across ten repeated tests of quiet two-legged standing in healthy subjects to identify the most consistent and stable parameters in the quantification of postural control. The variability of the root mean square (RMS) amplitude, peak-to-peak amplitude, mean frequency, and RMS velocity of the fore-aft and lateral components of the center-of-pressure fluctuations was investigated under varying (visual and cognitive) task conditions. The results indicate that all selected parameters show considerable intrasubject variability irrespective of the task context. Nonetheless, both the RMS amplitude and RMS velocity in either direction of sway do not demonstrate a significant trend across repeated tests. Among the selected parameters, the RMS velocity in the fore-aft direction shows the greatest intrasubject consistency, as well as a high sensitivity to, for example, visual deprivation. These findings support the reliability and validity of this parameter in the clinical quantification of postural control.

Adult↗

PubMed2005

Basic elements of arm postural control analyzed by unloading.

To address the question of how arm posture is controlled, we analyzed shoulder-elbow unloading responses in the horizontal plane for different directions of the initial load. The initial load, produced by a double-joint manipulandum, was suddenly diminished to 1of 12 randomly presented levels (60 to -10% of the initial load; in 6 out of 12 cases the final load direction varied by +/-20 degrees ). Subjects were instructed "not to intervene" in response to unloading. Neither the unloading onset nor the final load level was predictable and we assumed that the responses to rapid unloading were involuntary. Unloading elicited a smooth hand movement characterized by a bell-shaped velocity profile. The changes in hand position, joint angles, and joint torques generally increased with greater amounts of unloading. For each direction of the initial load, tonic electromyographic activity of the shoulder and elbow muscles also changed, depending on the amount of unloading. The shoulder and elbow joint torques before and after unloading were a function of the difference between the actual configuration of the arm and its referent configuration (R) described by the angles at which each joint torque was zero. The R configuration changed depending on the direction of the initial load. Our electromyographic data imply that these changes result from a central modification of muscle activation thresholds. The nervous system may thus control the R configuration in a task-specific way by leaving it unchanged to generate involuntary responses to unloading or modifying it to accommodate a new load direction at the same initial position. It is concluded that the R configuration is a major variable in both intentional and involuntary control of posture.

Adult↗

PubMed1998

Development of new muscle synergies in postural control in spinal cord injured subjects.

The development of new patterns of postural control in patients with a complete thoracic spinal cord injury (SCI) during their active clinical rehabilitation was studied. Especially the role of non-postural muscles, like the latissimus dorsi (LD) and the trapezius pars ascendens (TPA), in maintaining and restoring sitting balance during standardized bimanual task performance was investigated. Twelve patients, diagnosed with an acute complete thoracic SCI between spinal cord level T2 and T12, participated in a longitudinal experimental study. Changes in the centre of pressure (CP) and electromyographic activity of the erector spinae (ES) at level L3, T9 and T3, the LD, the TPA, the pectoralis major (PM), the serratus anterior and the oblique abdominal muscles were investigated at several moments in the rehabilitation process. Results show a gradual development of specific muscle activation patterns for both high and low thoracic SCI patients. These patterns seem to be related to a combination of restoration of function of the ES-L3 and ES-T9 in the low thoracic SCI subjects and increased compensatory muscle use of the LD, TPA and PM in high SCI patients. The range in which low thoracic SCI patients can actively vary their CP increased slightly during rehabilitation.

Adolescent↗

PubMed1996

Haptic cues for orientation and postural control in sighted and blind individuals.

Haptic cues from fingertip contact with a stable surface attenuate body sway in subjects even when the contact forces are too small to provide physical support of the body. We investigated how haptic cues derived from contact of a cane with a stationary surface at low force levels aids postural control in sighted and congenitally blind individuals. Five sighted (eyes closed) and five congenitally blind subjects maintained a tandem Romberg stance in five conditions: (1) no cane; (2,3) touch contact (< 2 N of applied force) while holding the cane in a vertical or slanted orientation; and (4,5) force contact (as much force as desired) in the vertical and slanted orientations. Touch contact of a cane at force levels below those necessary to provide significant physical stabilization was as effective as force contact in reducing postural sway in all subjects, compared to the no-cane condition. A slanted cane was far more effective in reducing postural sway than was a perpendicular cane. Cane use also decreased head displacement of sighted subjects far more than that of blind subjects. These results suggest that head movement control is linked to postural control through gaze stabilization reflexes in sighted subjects; such reflexes are absent in congenitally blind individuals and may account for their higher levels of head displacement.

Adult↗

PubMed2002

Attentional focus on supra-postural tasks affects postural control.

We examined whether the attentional focus adopted on a supra-postural task has an influence on postural control. Similar to Riley, Stoffregen, Grocki, and Turvey (Human Movement Science 18 (1999) 795), participants were instructed to stand still while lightly touching a loosely hanging sheet with their fingertips. However, instructions varied slightly under two conditions: Participants were either asked to minimize movements of the finger (internal focus) or to minimize movements of the sheet (external focus). In contrast to Riley et al.'s findings, both touch conditions resulted in increased postural sway, compared to a baseline condition (no touch). However, in line with previous findings (e.g., Wulf, McNevin, & Shea, Quarterly Journal of Experimental Psychology 54A (2001) 1143), frequency of responding (fast Fourier transformation) was greater under the external focus condition, compared to both internal focus and baseline conditions. The findings indicate improved static balance responses under external focus conditions and compromised static balance response under internal focus conditions.

Adult↗