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PubMed2005

Postural control during quiet standing following cervical muscular fatigue: effects of changes in sensory inputs.

The purpose of the present experiment was to investigate the effects of cervical muscular fatigue on postural control during quiet standing under different conditions of reliability and/or availability of somatosensory inputs from the plantar soles and the ankles and visual information. To this aim, 14 young healthy adults were asked to sway as little as possible in three sensory conditions (No vision, No vision-Foam support and Vision) executed in two conditions of No fatigue and Fatigue of the scapula elevator muscles. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed that (1) the cervical muscular fatigue yielded increased CoP displacements in the absence of vision, (2) this effect was more accentuated when somatosensation was degraded by standing on a foam surface and (3) the availability of vision allowed the individuals to suppress this destabilising effect. On the whole, these findings not only stress the importance of intact cervical neuromuscular function on postural control during quiet standing, but also suggest a reweigthing of sensory cues in balance control following cervical muscular fatigue by increasing the reliance on the somatosensory inputs from the plantar soles and the ankles and visual information.

Adult↗

PubMed2000

The effect of age-related declines in proprioception and total knee replacement on postural control.

BACKGROUND: An experiment was designed to examine the effects of a decrease in threshold joint position sense (TJPS) at the knee and ankle and of total knee replacement (TKR) on postural control in older adults. It was hypothesized that older adults with a decrease in TJPS and those who had undergone TKR would display increased center of pressure (COP) variance during quiet stance and late onsets for muscle responses to balance threats. METHODS: Older adult subjects (> or = 70 years) were evaluated and grouped according to the status of their ankle and knee threshold joint position sensation as well as their surgical history. COP data were collected while subjects stood on a force plate with feet together under eyes-open and -closed conditions. Threats to balance were given using a platform that moved forward and backward. RESULTS: Older subjects with poor knee extension TJPS had significantly increased COP variance, although those with very poor knee flexion and extension TJPS demonstrated even greater increases. Similarly, subjects with decreased ankle TJPS demonstrated increased COP variance. However, reduced TJPS did not affect the ability of subjects to respond to threats to balance. Post-TKR subjects showed no reductions in any aspect of postural control. CONCLUSIONS: This study showed that the task of standing quietly has a direct relationship to threshold JPS, although the task of recovering from an abrupt perturbation does not. Older adult TKR results suggest that there is no negative effect on balance from elective joint replacement.

Aged↗

PubMed2000

Postural control in Parkinson's disease after unilateral posteroventral pallidotomy.

Postural control changes were studied in 27 patients with Parkinson's disease after unilateral posteroventral pallidotomy (PVP). Patients were evaluated before PVP and at 3, 6 and 12 months post-PVP, both 'off' and 'on' parkinsonian medications, with selected evaluation tools representing functional performance, functional balance and posturographic components of balance. The majority of variables in the 'off' state were significantly improved at 3 months post-PVP. Improvement was maintained at 6 months but had declined for some variables by the 12 month follow-up. Standing up from a chair (P = 0.009), the balance and gait sections of the Performance-Oriented Assessment (P < or = 0.0004), and the limits of stability (LOS) posturography variables (P < 0.0005) of the average time to reach a target, the number of targets missed and the initial excursion distance to the target (P = 0.029) retained significant improvement at the 12 month follow-up. When the patients were in the 'on' state, LOS posturography variables of average time to target, average path length deviation, and the number of targets missed were the only variables significantly improved at 3 months post-PVP (P = -0.013) and this improvement was maintained at 12 months post-PVP (P = 0.012-0.041). Unilateral PVP improves axial symptoms of Parkinson's disease involved in functional performance such as gait disturbance as well as improving postural stability in the 'off' state. Generally, the maximum improvement is seen at 3 months post-PVP with many variables remaining significantly improved at 12 months post-PVP. Axial dyskinesias in the 'on' state are also significantly reduced with the improvement maintained at 12 months post-PVP. These findings suggest that unilateral pallidotomy is not only effective in abolishing levodopa-induced dyskinesias, but that it also improves the axial signs of Parkinson's disease.

Aged↗

PubMed2003

Postural control during a sit-to-stand task in individuals with mild Parkinson's disease.

Individuals with Parkinson's disease (PD) typically have difficulty rising from a chair. A major contributing factor may be altered anticipatory postural control; this hypothesis has been fueled by reports of altered function of the supplementary motor area in PD, an area linked to the preparation of movements. This study tested the hypothesis that individuals with PD would exhibit altered anticipatory postural control which would include a reduced preparatory hip flexion and decreased forward displacement of the COM prior to lift-off of the buttocks from the chair. Ten male subjects with PD and ten male age-matched controls were instructed to rise from a chair without the use of their arms at their comfortable pace on two separated days during on and off-medication states. Body movements were recorded with an optoelectronic device, in addition to forces under the buttocks and each foot to calculate lower extremity joint angles, joint movements and net body centre of mass displacement (COM). The sit-to-stand (STS) duration was the same for the PD-on and controls, but greater for the PD-off group. The PD groups (on and off) used a hip flexion strategy (greater preparatory hip flexion displacement and forward COM displacement, reduced knee extensor moments) compared to the controls. Contrary to predictions, subjects with PD exaggerated, rather than reduced, the movement preparation of the STS using a hip flexion strategy. Possible underlying causes of this flexion strategy could include compensation for poor lower extremity muscle strength and a need for greater postural stability during the lift-off phase.

Adaptation, Physiological↗

PubMed2005

Tactile directional sensitivity and postural control.

People are good at telling the direction of a moving tactile stimulus and this capacity provides a sensitive clinical test of somatosensory disturbances. Tactile directional sensitivity depends on two different kinds of somatosensory information, i.e. spatiotemporal information and information about friction-induced changes in skin stretch. The objective of this study was to compare the relative contribution to postural control of these two types of information for both glabrous and hairy skin. Postural sway amplitudes and sway paths were recorded, with or without access to tactile and/or visual stabilizing stimuli. Subjects were standing on two types of surface, either solid metal or 50 mm foam plastic. Two types of stimulus were used to generate sway-related tactile information. One was a thin air-stream that was used to assess the contribution by spatiotemporal information, and the second was a narrow steel rod that was glued to the skin to assess the contribution by skin-stretch information. The stimuli were applied to the hairy skin of the forearm and to the glabrous skin of the fingertip. In addition, we studied the ability to tell the direction of movement of an air-stream stimulus on glabrous and hairy skin. The air-stream caused significant sway reductions when applied to glabrous, but not hairy skin. The weak effect on hairy skin reflected the perceptually poor directional sensitivity for the air-stream stimulus in this cutaneous area. In contrast, the glued rod reduced sway when applied to both glabrous and hairy skin reflecting the tactile afferents' high sensitivity to skin stretch in these areas. Both types of tactile stimulus reduced sway amplitudes more than sway paths for both hairy and glabrous skin. The visual cue, on the other hand, tended to reduce sway paths more than amplitudes. The two types of tactile receptive surface seem to influence postural control in the same manner, despite anatomical and physiological differences. The results invite speculation that patients with poor directional sensitivity might have reduced postural stability compared with healthy individuals.

Adult↗

PubMed2004

Improvement of motor development and postural control following intervention in children with sensorineural hearing loss and vestibular impairment.

OBJECTIVE: The purpose of this study was to determine the effect of exercise intervention on the progressive motor development delay and postural control impairments in children with sensorineural hearing loss and concurrent vestibular impairment. METHODS: Twenty-one children with sensorineural hearing loss and vestibular impairment were randomly assigned to two groups (exercise and placebo) matched for age and gross motor development level. Exercise intervention consisted of compensatory training, emphasizing enhancement of visual and somatosensory function, and balance training. Placebo intervention focused on language development activities. Each intervention was administered three times weekly for 12 weeks. Motor development and posturography testing was completed pre- and post-intervention. To examine the mechanisms of change, somatosensory, visual and vestibular functional effectiveness ratios were calculated from posturography stability scores. Children in the placebo group later participated in exercise intervention, and a second post-test completed. Data were analyzed by group, as well as merged once all had received exercise intervention. RESULTS: Post-intervention, motor development scores significantly improved in the exercise, not the placebo group (P=0.004). Although not significant, improvement in posturography scores were evident in the exercise group. Once the post-exercise data from both groups were merged (n=21), improvements in these scores were significant (< or =0.02). The difference from the normative sample was eliminated. CONCLUSIONS: Exercise intervention focused on the enhancement of sensory integrative postural control abilities is effective for the arrest of the progressive motor development delay in children with sensorineural hearing loss and vestibular impairment.

Child↗

PubMedDate not supplied

Does practice modify the relationship between postural control and the execution of a secondary task in young and older individuals?

BACKGROUND: Numerous daily activities require performing more than one task simultaneously, such as standing while engaging in a conversation. Recent studies have shown that postural control may be degraded when individuals are asked to perform a secondary task and that this effect seems to be more pronounced in older adults. Since various types of secondary tasks have been used in postural control studies, the novelty of the tasks may partly explain why dual-task interference occurs. It is known that novel tasks require greater attentional resources and thus may interfere to a greater extent with the performance of another task. Therefore, by practicing this dual-task situation, interference could perhaps be diminished. Since the dual-tasking efficiency is reduced with aging, practice could be very beneficial to older adults. OBJECTIVES: The main goal of this study was to examine whether practice could modify the changes seen in postural sway when individuals are asked to perform a secondary task while maintaining upright stance and whether older individuals could benefit to a greater extent from practice than would young individuals. The second goal was to examine the dual-task performance in young versus older adults and to determine whether older individuals benefit equally or to a greater extent from practice as compared with young individuals. METHODS: Young and older individuals were asked to stand on a force platform while performing a secondary task or no task. The secondary task condition was repeated six times to examine the effects of practice. RESULTS: Practice did not modify the performance of postural sway, but did lead to an increase in speed of execution of the secondary task for both groups equally. In young participants, the amplitude of sway was decreased, and the frequency of sway was increased, indicating an increased stiffness when performing the cognitive task. Older participants showed increased amplitude of sway and increased frequency of sway in the mediolateral direction only. CONCLUSIONS: Since the dual-task condition was only repeated six times, it could be hypothesized that the effect of practice would be greater, if more trials were added or if more practice sessions were included. More research is needed to verify this hypothesis.

Adult↗

PubMed2005

Effect of 3,4-diaminopyridine on the postural control in patients with downbeat nystagmus.

Downbeat nystagmus (DBN) is a common, usually persistent ocular motor sign in vestibulocerebellar midline lesions. Postural imbalance in DBN may increase on lateral gaze when downbeat nystagmus increases. 3,4-Diaminopyridine (3,4-DAP) has been shown to suppress the slow-phase velocity component of downbeat nystagmus and its gravity-dependent component with concomitant improvement of oscillopsia. Because the pharmacological effect is thought to be caused by improvement of the vestibulocerebellar Purkinje cell activity, the effect of 3,4-DAP on the postural control of patients with downbeat nystagmus syndrome was examined. Eye movements were recorded with the video-based Eyelink II system. Postural sway and pathway were assessed by posturography in lateral gaze in the light and on eye closure. Two out of four patients showed an improvement of the area of postural sway by 57% of control (baseline) on eye closure. In contrast, downbeat nystagmus in gaze straight ahead and on lateral gaze did not benefit in these two patients, implying a specific influence of 3,4-DAP on the vestibulocerebellar control of posture. It was concluded that 3,4-DAP may particularly influence the postural performance in patients with downbeat nystagmus.

4-Aminopyridine↗

PubMed1999

Effect of articulatory and mental tasks on postural control.

The present study sought to determine whether the increased postural instability produced by a spoken mental task was due to competing demands for attentional resources or perturbation of posture by articulation. Postural sway was measured in 36 normal subjects under the following conditions: repeating a number aloud (articulation), counting backwards aloud in multiples of seven (articulation and attention), counting backwards silently (attention), and no mental task (neither articulation nor attention). Articulation resulted in a significant increase in sway, whereas no effect of attention was observed. We conclude that in order to accurately assess the effect of attentional demands on postural control, it is important to eliminate or control the effects of articulation.

Adolescent↗

PubMed2003

Evaluation of the lambda model for human postural control during ankle strategy.

An accurate modeling of human stance might be helpful in assessing postural deficit. The objective of this article is to validate a mathematical postural control model for quiet standing posture. The postural dynamics is modeled in the sagittal plane as an inverted pendulum with torque applied at the ankle joint. The torque control system is represented by the physiological lambda model. Two neurophysiological command variables of the central nervous system, designated lambda and micro, establish the dynamic threshold muscle at which motoneuron recruitment begins. Kinematic data and electromyographic signals were collected on four young males in order to measure small voluntary sway and quiet standing posture. Validation of the mathematical model was achieved through comparison of the experimental and simulated results. The mathematical model allows computation of the unmeasurable neurophysiological commands lambda and micro that control the equilibrium position and stability. Furthermore, with the model it is possible to conclude that low-amplitude body sway during quiet stance is commanded by the central nervous system.

Adult↗

PubMed2006

Reliability of a functional clinical test battery evaluating postural control, proprioception and trunk muscle activity.

OBJECTIVE: The purpose of this study was to examine the repeatability and reproducibility of the different tests of a clinical test battery evaluating the components of functional spinal stability: postural control (sway velocity data), proprioception (repositioning error), and muscle activation (electromyographic data). DESIGN: A total of 28 healthy volunteers participated in this study: 14 in the repeatability study and 14 in the reproducibility study. Each subject was tested three times, with an interval of 1 wk between the test sessions. The intraclass correlation coefficients and the standard error of the measurements as a percentage of the grand mean were calculated. RESULTS: The intraclass correlation coefficients for both the repeatability and the reproducibility evaluation showed good to excellent reliability for all variables (intraclass correlation coefficient, 0.60-0.98). The standard error of the measurements as a percentage of the grand mean ranged from 0.004 to 19.94. CONCLUSIONS: The functional clinical test battery investigated in this study proved to be a reliable tool in the assessment of healthy subjects. The evaluation of postural control, proprioception, and muscle activity (coordination, stabilization, maximal voluntary isometric contraction, endurance, and flexion-relaxation) showed good to excellent repeatability and reproducibility. Further analysis of the reliability of these variables in a clinical setting, particularly in patients with low back pain, seems appropriate.

Abdominal Muscles↗

PubMed2002

Analysis of short- and long-term effects of adaptation in human postural control.

The short-term (i.e., days) and long-term (i.e., months) effects of adaptation to posturography examinations were investigated in 12 normal subjects who were repeatedly examined for five consecutive days and again after 90 days. The examinations were conducted both with eyes open and closed, and the perturbations were evoked by a pseudorandomly applied vibration stimulation to the calf muscles. The evoked anteroposterior responses were analyzed with a method considering adaptation in the slow changes in posture and in the stimulus-response relationship. Repetition of examinations on a daily basis revealed a gradual improvement of postural-control performance. The body sway induced by the stimulation was significantly reduced and the dynamical properties changed. Most of the improvements remained after 90 days, but some parameters such as the complexity of the control system used were increased to the initial level. The results confirm previous observations that postural control contains several partially independent adaptive processes, observed in terms of alteration of posture and as a progressive reduction of body sway induced by stimulation. The method used for the adaptation analysis in this study could be applied to analyze biological systems with multiple individual adaptive processes with different time courses or characteristics, or where the adaptation processes are related to multiple internal or external factors.

Adaptation, Physiological↗

PubMed1980

A predictive model study of the visual contribution to canine postural control.

Dogs were trained to stand on a movable table and their quiet stance was perturbed by osccillation of the table during normal sighted condition and during blindfolded condition. The data formed the frequency response characteristic (describing function) for postural control with and without visual input. A feedback model was tested to assess the effect of visual input during the perturbation of quiet stance. The results of the tests of the model indicate that the effect of a visual input depends on the context of the multiple sensory factors influencing postural control. The effectiveness of the visual input increases if there is a conflict between the visually derived body position cues and the other cues that indicate the orientation of the body.

Animals↗

PubMed2001

Impaired postural control of the lumbar spine is associated with delayed muscle response times in patients with chronic idiopathic low back pain.

STUDY DESIGN: Balance performance in unstable sitting and trunk muscle response to quick force release were measured in 16 patients with chronic low back pain and 14 matched healthy control subjects. OBJECTIVES: To determine whether patients with low back pain will exhibit poorer postural control, which will be associated with longer average muscle response times. SUMMARY OF BACKGROUND DATA: Larger postural sway during standing and delayed trunk muscle response times for patients with low back pain have been reported in several independent studies. METHODS: Unstable sitting test was accomplished by attaching different sized hemispheres to the bottom of a seat. Subjects performed trials with eyes open and closed while the displacements of the center of pressure were measured with a force plate underneath the seat. Response to a quick force release was recorded from 12 major trunk muscles with surface electromyography. Subjects performed isometric trunk exertions in a semi-seated position when the resisted force was suddenly released with an electromagnet. Average muscle response times and balance performance were correlated using a linear regression analysis. RESULTS: Patients with low back pain demonstrated poorer balance performance than healthy control volunteers, especially at the most difficult levels. Patients also had delayed muscle response times to quick force release. Average muscle onset times together with age and weight correlated significantly with balance performance with closed eyes (R(2) = 0.46), but not with eyes opened (R(2) = 0.18). CONCLUSIONS: Patients with chronic low back pain demonstrated poorer postural control of the lumbar spine and longer trunk muscle response times than healthy control volunteers. Correlation between these two phenomena suggests a common underlying pathology in the lumbar spine.

Adult↗

PubMed2005

From egocentric to exocentric spatial orientation: development of posture control in bimanual and trunk inclination tasks.

The authors investigated the emergence of independent control of body segments in bimanual tasks involving either voluntary or involuntary trunk motion by tracking the transition from an ego- to an exocentric mode of postural control during childhood (i.e., from body-referenced orientation to externally referenced action). A paradigm combining a seated manual task and various trunk manipulations described the coordination strategies used by 24 children at different ages (2 to 9 years) and by adults. The following questions were asked: (a) When do children begin to dissociate upper limb movements from those of the trunk? (b) What segmental strategies are exhibited by each age group (2-3, 4-6, and 7-9 years, and adults)? Kinematic analyses revealed that younger children (2-6 years) used either the trunk or the support surface as reference to orient the limbs. Older children (7-9 years) began to use a gravitational reference frame similar to that of adults; they uncoupled upper limb motion from the trunk in either voluntary or imposed conditions. Young children patterned the forearm trajectory after the initiating segment (support surface or the trunk), thus reducing the degrees of freedom during the dual task. Echoing previous reports, 7-9 years of age appears to be a critical period in which children master postural control and develop an internal representation of body scheme.

Adult↗

PubMed2000

The effects of visual input on postural control mechanisms: an analysis of center-of-pressure trajectories using the auto-regressive model.

New measures to characterize center-of-pressure (COP) trajectories during quiet standing were proposed and then utilized to investigate changes in postural control with respect to visual input. Eleven healthy male subjects (aged 20-27 years) were included in this study. An instrumented force platform was used to measure the time-varying displacements of the COP under each subject's feet during quiet standing. The subjects were tested under eyes-open and eyes-closed conditions. The COP time series were separately analyzed for the medio-lateral and antero-posterior directions. The proposed measures were obtained from the parameter estimation of auto-regressive (AR) models. The percentage contributions and geometrical moment of AR coefficients showed statistically significant differences between vision conditions. The present COP displacements under the eyes-open condition showed higher correlation with the past COP displacements at longer lag times, when compared to the eyes-closed condition. In contrast, no significant differences between vision conditions were found for conventional summary statistics, e.g., the total length of the COP path. These results suggest that the AR parameters are useful for the evaluation of postural stability and balance function, even for healthy young individuals. The role of visual input in the postural control system and implications of the findings were discussed.

Adult↗

PubMed2000

Postural control in the lamprey: A study with a neuro-mechanical model.

The swimming lamprey normally maintains the dorsal-side-up orientation due to activity of the postural control system driven by vestibular organs. Commands for postural corrections are transmitted from the brain stem to the spinal cord mainly by the reticulospinal (RS) pathways. As shown in previous studies, RS neurons are activated by contralateral roll tilt, they exhibit a strong dynamic response, but much weaker static response. Here we test a hypothesis that decoding of these commands in the spinal cord is based on the subtraction of signals in the left and right RS pathways. In this study, we used a neuro-mechanical model. An intact lamprey was mounted on a platform that restrained its postural activity but allowed lateral locomotor undulations to occur. The activity in the left and right RS pathways was recorded by implanted electrodes. These natural biological signals were then used to control an electrical motor rotating the animal around its longitudinal axis toward the stronger signal. It was found that this "hybrid" system automatically stabilized a normal orientation of the lamprey in the gravitational field. The system compensated for large postural disturbances (lateral tilt up to +/-180 degrees ) due to wide angular zones of the gravitational sensitivity of RS neurons. In the nonswimming lamprey, activity of RS neurons and their vestibular responses were considerably reduced, and the system was not able to stabilize the normal orientation. However, the balance could be restored by imposing small oscillations on the lamprey, which elicited additional activation of the vestibular organs. This finding indicates that head oscillations caused by locomotor movements may contribute to postural stabilization. In addition to postural stabilization, the neuro-mechanical model reproduced a number of postural effects characteristic of the lamprey: 1) unilateral eye illumination elicited a lateral tilt ("dorsal light response") due to a shift of the equilibrium point in the vestibular-driven postural network; 2) removal of one labyrinth resulted in a loss of postural control due to an induced left-right asymmetry in the vestibulo-reticulospinal reflexes, which 3) could be compensated for by asymmetrical visual input. The main conclusion of the present study is that natural supraspinal commands for postural corrections in the roll plane can be effectively decoded on the basis of subtraction of the effects of signals delivered by the left and right RS pathways. Possible mechanisms for this transformation are discussed.

Animals↗

PubMed2006

Postural control in persons with late effects of polio.

BACKGROUND: Persons who have suffered from acute poliomyelitis may decades later experience reduction of balance and gait capacity due to muscle weakness, fatigue and/or pain. This may affect the activity level in daily life of these persons. AIMS OF THE STUDY: The aim of this study was to describe observer assessed and subjectively perceived postural control in persons with late effects of polio and to evaluate the correlation between postural control and gait velocity for this population. METHOD: 50 persons (mean age 59.8 yrs) with diagnosed polio disease and without other causes of mobility disorders were included. Balance was tested with the Timed Up and Go test (TUG), the Functional Reach test (FR) and the Falls Efficacy Scale (FES) (Swedish Version). Gait velocity over 30 m was measured for convenient and maximal velocity. RESULTS: The subjects had reduced balance (TUG mean 9.0 sec, FR mean 23.5 cm) and perceived balance problems in ADL items (FES(S) median 119.5, normal value 130). They also showed reduced gait velocity compared to healthy persons of the same age (mean 1.01 m/s compared to 1.30 m/s, convenient speed). Correlations were demonstrated between the reduced balance and decreased convenient and maximal gait velocity (TUG/gait velocity: r = -0.7 (convenient), r = -0.8 (maximal), p <or= 0.01). CONCLUSIONS: The knowledge of reduced balance and gait velocity in persons with late effects of polio may have an impact on how to provide service to this group to ensure safety in activities in daily life, including gait.

Activities of Daily Living↗