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At least 1,423 records · Page 79Linked to original sources
PubMed1999

Support stability influences postural responses to muscle vibration in humans.

We studied the effect of support stability on postural responses to the vibration of Achilles tendons and of neck dorsal muscles in healthy humans. For this purpose we compared postural responses on a rigid floor and on 6 cm high rocking supports (see-saws) of different curvatures (different radii: 30, 60 and 120 cm). The subject stood with eyes closed, the centre of the feet coincided with the centre of the see-saw. We recorded platform tilt, horizontal displacements of the upper body, ankle joint angle and activity of ankle joint muscles. On the rocking platform subjects maintained balance in a sagittal direction by making see-saw rotations placing the support under the body's centre of gravity. Equilibrium maintenance requires that the torque in the ankle joint increases during forward body displacements, as on the rigid floor, and be accompanied by a plantar flexion (not by a dorsiflexion) in the ankle joint. The directional dependence of vibration-induced reactions on the see-saw was the same (relative to space) as on the rigid floor: backward body displacement during Achilles tendon vibration and forward body displacement during neck muscle vibration. A decrease of support stability (with a decrease of the radius from 120 to 30 cm) diminished significantly the effect of Achilles tendon vibration and to a lesser extent the effect of neck muscle vibration. In contrast, the increase of platform stability by hand contact with a stable external object gave rise to prominent body sway in response to Achilles tendon vibration. Neck muscle vibration on the movable support provoked a quick initial forward body sway. This initial quick response was absent during vibration of the Achilles tendons. We conclude that postural responses to muscle vibration reflect the participation of different muscles in posture control and depend on the support properties. Support instability changes the role of proprioceptive information and the state of the system of equilibrium maintenance.

Achilles Tendon↗
PubMed2003

Postural sway in normal subjects aged 20-70 years.

So far, no population-based reference material of postural sway has been presented in the literature. This study evaluated postural control by measuring posturographic parameters, with the aim of establishing useful standards with regard to gender, age, body weight, cigarette smoking, alcohol consumption and articular hypermobility. This was performed in an age-stratified random sample of 195 subjects from the Copenhagen City Heart Study, of whom, 133 agreed to participate. Measurement of postural sway was performed the Balance Master Pro(R). Outcome parameters were average angular velocity, target sway area, per cent maximum stability and per cent ankle strategy. Using SAS Proc Mixed, backward stepwise elimination was performed and 95% prediction intervals were obtained. Sway increased with increasing difficulty of the test (P<0.001) and with increasing age (P<0.001). No differences were found between the sexes. Ankle-strategy did not change with age, but decreased with increasing body weight, and increased in subjects reporting a consumption of modest amounts of alcohol (P<0.001), or with the finding of increased hypermobility (P = 0.006). The present material may be used as a reference in further studies of postural control.

Adult↗
PubMed1999

Postural control of ballet dancers: a specific use of visual input for artistic purposes.

Dance is a specific expression of human motor behaviour. This artistic physical activity depends upon an effective technical training with important postural components and necessitates the codification of sensory inputs to build mental representations of the action to be produced. Proprioception and vision being two fundamental sensory modalities in classical ballet, this study attempted to determine the importance of the visual input for postural control during the practice of this activity. First, this work compared the performances of 18 professional ballet dancers and 46 non-dancers on a platform of forces during static posturographic tests in open or closed eyes situation. Then, we studied how professional dancers achieve balance in postures specific of classical ballet: on demi-pointe and on pointe. The results indicate that visual inputs are important in classical ballet since dancers only performed better than controls in eyes open conditions. The similar results obtained on pointe with eyes open or closed conversely suggest that training in classical ballet develops specific modalities of balance which are not transferable to posture control in daily life situations.

Adolescent↗
PubMedDate not supplied

[Spatial orientation and postural regulation in patients with idiopathic scoliosis].

QUESTION: Etiology of idiopathic scoliosis is unknown. In literature a primarily neurogenic disturbance of postural regulation is discussed with subsequent changes of the spine. In the present paper, individual functions of postural regulation in patients with idiopathic scoliosis were examined by neurophysiologic investigations and compared to a normal population. METHOD: The body sway of 28 patients was investigated in upright position under various testing conditions by means of a force measuring platform, allowing examination of the efferent part of postural regulation as well as the sensory systems involved. Registration of the eye movements (ENG) made it possible to investigate the function of the vestibulo-cerebellar system. Furthermore the optokinetic capability of scoliotic patients was tested by determination of the subjective visual vertical (SVV). RESULTS: It turned out that none of the neurophysiologic test procedures showed clearly pathological findings in scoliotic patients as compared to a normal population. CONCLUSION: It has not to be considered as probable that idiopathic scoliosis is caused by a disturbance of postural regulation.

Adolescent↗
PubMed1992

Maturation of set-modulation of lower extremity EMG responses to postural perturbations.

To analyse the influence of different "postural sets" on stance stabilizing EMG responses in children, EMG responses to toe-up tilt perturbations were recorded in 70 children between the age of 9 months and 10 years, as well as in a control group of 10 adults under different postural set conditions, using either bilateral destabilization with eyes opened, eyes closed, or introducing additional minute upper extremity support. Recordings were also made with the children seated in front of the platform with the ankle joint angle being identical to that in the standing condition. Also recordings were made after unilateral destabilization in bilateral lower leg muscles, to determine if there is a generalization of EMG response patterns to the mechanically not disturbed side. Across all age-groups the principal modulation of EMG response changes according to postural conditions was identical. Long latency (LL) EMG responses were down-regulated when additional upper extremity support was provided. LL-responses were abolished in the sitting condition. With unilateral destabilizations throughout all age-groups short latency responses were restricted to the perturbed side, whereas long latency responses could be obtained symmetrically. The proximal to distal gradient of recruitment of muscle groups, remained identical across all age-groups. The data indicate that the basic organizational principle of stance stabilizing EMG responses and their modification by postural sets remains invariant across development. This indicates that the involved organizational principles are present as soon as a child is able to stand upright and are not subject to further shaping by motor learning.

Child↗
PubMed2000

Postural behaviour responses to visual stimulation in patients with vestibular disorders.

Patients with different vestibular disorders exhibit changes in postural behaviour when they receive visual stimuli, reproducing environmental stimulation. Postural control was studied using an AMTI Accusway platform, measuring the confidential ellipse (CE) and sway velocity (SV). Postural responses were recorded according to the following stimulation paradigm: i) without specific stimuli; ii) smooth pursuit with pure sinusoids of 0.2 Hz (foveal stimulation); and iii) optokinetic stimulation (retinal stimuli). Patients with central vestibular disorders (CVD), cerebellar damage and unilateral peripheral vestibular lesions (UPVL) in asymptomatic periods were studied. A group of normal subjects was studied as control. Signal processing was done with a scalogram by wavelets in order to observe the relation between time and frequency in postural control. While patients with CVD and cerebellar disease showed a significant increase in CE and SV in the three conditions of the paradigm compared to the normal group, the patients with UPVL showed no change. Wavelets processing showed that the main sway occurs in the Y axis (antero-posterior) and below at 0.4 Hz in normal subjects, while the CVD and cerebellar patients showed sway frequencies in both the X and Y axes. The clinical implications of these findings are discussed.

Adult↗
PubMed1998

Postural control in benign paroxysmal positional vertigo before and after recovery.

Thirty-two patients affected by idiopathic benign paroxysmal positional vertigo (BPPV) of the posterior semicircular canal were studied before, 3 days and I month after a resolutive Semont manoeuvre by means of dynamic posturography. The overall postural control in BPPV patients was shown to be impaired, as demonstrated by the pathological equilibrium scores. Data obtained before treatment showed a specific pattern of vestibular involvement and a pathological composite score. After the liberatory manoeuvre the Sensory Organization Test indicated a significant improvement in the pathological composite and vestibular scores. However, significant differences from controls were still detected 3 days and 1 month after clinical recovery from BPPV. The results clearly show that, in BPPV patients, there is an impairment of the vestibular system, which seems unable to maintain a normal postural balance. This deficit can be particularly detected when dynamic posturography evaluates the vestibular cues. After the liberatory manoeuvre a consistent improvement in the overall postural control has been observed but the residual differences from controls seem to suggest that damage to the otoconial maculae influences postural control, even when there is significant improvement in the clinical signs.

Analysis of Variance↗
PubMed2004

Effect of personal protective eyewear on postural stability.

Vision is a significant factor in postural stability; this study is the first to report on the effect of OSHA regulated personal protective eyewear on physiological factors associated with postural stability. Twenty college students between the ages of 19 and 25 were randomly tested in each of three eyewear conditions (control, new, and artificially aged) using a NeuroCom Balance Master System and the mCTSIB protocol. Subjects were pre-tested with no eyewear (control) on each day followed by a 5-min assembly task with random eyewear assignment. Subjects were then post-tested following the same protocol while wearing the eyewear. Data were evaluated using a two (pre/post) x three (eyewear) repeated measures analysis of variance (ANOVA). There was a significant main effect for both the eyes open/firm flat surface, and eyes open/foam flat surface conditions (p <or=.05). These findings suggest that while personal protective eyewear may serve to protect an individual from eye injury, an individual's use of such personal protective eyewear may have deleterious effects on sensory input from the visual system and compensatory strategies to maintaining or regaining postural stability. Individuals who employ protective eyewear on a daily basis need to be aware of the effect of altered visual input resulting from eyewear on their postural stability, especially during sensory-challenging tasks, such as navigating ladders, scaffolding and elevated surfaces, typically found in construction environments.

Accidental Falls↗
PubMed2002

Postural muscle responses following changing balance threats in young, stable older, and unstable older adults.

The authors determined the postural muscle response to support surface perturbations, in relation to aging and level of stability of 16 young adults and 32 older adults who were classified into stable (SOA) and unstable (UOA) groups on the basis of their functional balance abilities. Forward and backward support surface translations of various amplitudes and velocities were used so that postural responses of the standing adults could be elicited. The thigh and leg postural muscle responses were recorded with surface electromyography (EMG). The older groups had significantly longer onset latency in the anterior postural muscles, smaller integrated EMG in the posterior muscles, and greater extent of integrated EMG attenuation over time. The UOA showed longer onset latency in the gastrocnemius following slow backward perturbation and used a greater percentage of the functional capacity of the gastrocnemius muscle than the SOA did. Those findings indicate that the SOA and UOA had limited ability to adapt to changing balance threats; the UOA were more limited than the SOA. When designing balance training programs, therefore, therapists should consider the adult's level of functional stability.

Adult↗
PubMed1998

Postural asymmetry reduction by vestibular caloric stimulation in left hemiparetic patients.

The purpose of this study was to investigate the effects of caloric vestibular stimulation on the postural sway characteristics of hemiparetic patients. Two groups of 15 hemiparetic patients each (right and left) were compared to a group of 15 control subjects. Hemiplegic patients were selected for the study if they showed ability to stand without external support for at least 30 seconds. Posturographic evaluation was performed on a statokinesimetric platform just before and after a cold contralesional ear irrigation (20 degrees C) during 60 seconds. Two quantitative parameters were analysed: the antero-posterior difference and the lateral difference, reflecting the asymmetry of standing in the antero-posterior and frontal planes, respectively. The results of the 3 groups studied were compared with a Student's t-test. Before stimulation, as previously reported, left hemiparetic patients showed a predominant lateral displacement of the centre of pressure toward the side of the lesion, as compared to right hemiparetic patients. After vestibular stimulation, the lateral displacement was reduced in both patient groups, predominantly in the left hemiparetic group. After vestibular stimulation, the lateral displacement thus was not different in both patient groups and in the control group. Antero-posterior differences were not significantly different in the patient groups and in the control group before stimulation and were not affected by vestibular stimulation. The suggestion is made that greatest postural imbalance produced by right brain damage could reflect a persistent distorsion of a "spatial postural representation". Vestibular stimulation may restore symmetrical activity in the cerebral structures involved in the generation of this "spatial postural representation".

Adult↗
PubMed2003

A clinical model for the assessment of posture and balance in people with stroke.

PURPOSE: The lack of models to define and describe rehabilitation processes have often been identified as limiting research and the development of clinical practice. This study describes the development of a clinical model to address a key aspect of stroke physiotherapy--the assessment of posture and balance. METHOD: Twenty seven experienced neurological physiotherapists (PT) in six focus groups were used. Participants were shown photographs of a typical stroke patient in sitting and standing positions and were asked 'What would you note if you were assessing the posture and balance of this patient?' Answers were displayed on flip charts to allow immediate feedback about the accuracy and completeness of data. Thematic content analysis was then used. RESULTS: A complex reasoning process emerged to answer three main questions: What can the patient do? How does s/he do it? Why does s/he do it that way? To answer these questions physiotherapists established balance disability (by observing the patient's ability to perform a series of increasingly demanding balance tasks), identified postural and movement impairments (by observing alignment and movement of body segments relative to each other and to the expected norm for that patient) and assessed muscle activity (by observation and palpation). CONCLUSIONS: Focus groups have been used to elicit a clinical model for the assessment of posture and balance, the content of which will be used to inform a new outcome measure.

Evaluation Studies as Topic↗
PubMed2005

Effect of load position on muscle forces, internal loads and stability of the human spine in upright postures.

A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.

Computer Simulation↗
PubMed1991

Effect of work load and respirator wear on postural stability, heart rate, and perceived exertion.

The effects on postural stability (sway) were investigated for different work loads under conditions of wearing a full facepiece respirator and not wearing any respiratory protection device. Fifteen subjects accomplished light (40 W), moderate (85 W), and heavy (125 W) work loads under the two conditions. Measurements of postural sway were made immediately after each load by using a multicomponent, strain gage-type force platform. Changes in each subject's movement pattern of the center of pressure were quantitated and compared to their initial baseline sway tests. Each subject's heart rate and perceived exertion were also recorded during each condition. A statistically significant effect (p = 0.007) caused by work load was observed for total length of sway with or without a respirator. An interaction approaching statistical significance (p = 0.056) between work load and respirator use was found. This indicated that sway increased more quickly and in a more consistently linear fashion with increasing work load under the respirator condition (p = 0.02) compared to the nonrespirator condition. The results from the respirator condition showed linear increases in postural sway length across the entire range of work loads, but sway length in the nonrespirator condition showed an increase only at 125-W work loads. The greater increase in sway during the postural balance test could be attributable to the increasing work load-induced proprioceptive fatigue effect on the nervous system's ability to process signals from proprioception systems incongruent with body sway. The heart rate was significantly higher during respirator wear (an increase in heart rate averaging 5.62 beats/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1982

The relationship of postural sway in standing to the incidence of falls in geriatric subjects.

A double-blind study was undertaken to determine the relationship (if one exits) between the extent of postural sway in standing of individual elderly subjects and their frequency of falling. A total of 205 subjects were studied; their average age was 81.8 years. Thirty per cent of the men, and 46% of the women, had one or more falls; the proportion of all subjects with one or more falls was 42%. The average speed of sway was significantly greater (P less than 0.05) for those who fell one or more times in a year than for those who did not fall. In this group of institutionalized elderly, there was no sex-related difference in the mean speed of sway; moreover, no age-related trend was demonstrated by the regression of mean speed upon age for all subjects. The mean speed of sway even for the non-fallers was found to be greater than that measured in a sample of non-institutional elderly subjects studied in the past. Thus, mean speed of postural sway was found to be only of statistical value for determining the risk of falling among these institutionalized elderly. We found postural sway to be an indicator of a tendency to fall, but the difference was less than might have been expected. No trend of increasing postural sway correlating with the increased frequency of falls was found.

Accidents↗
PubMed1999

Perception of postural limits in elderly nursing home and day care participants.

This study explored whether, when compared to young community-dwelling individuals, elderly nursing home and day care participants have less accurate perceptions of their postural stability borders (postural limits). Subjects estimated their performance before executing maximum forward reaches while maintaining the feet stationary. Whereas young subjects tended to underestimate their reaching limits, elderly subjects displayed no significant difference between estimated and actual values. Furthermore, errors in estimated reach limits associated with reaching ability, with less-able reachers tending to more greatly overestimate their abilities. This suggests that elderly nursing home and day care participants, and especially those with impaired postural limits, lack the potential "safety factor" observed in young subjects of underestimating their stability borders. Therefore, the link between decreased postural limits and falls in older persons may in part be due to lack of awareness of such declines, and the resulting tendency to plan movements which create loss of balance.

Accidental Falls↗
PubMed1999

Attentional demands and postural recovery: the effects of aging.

BACKGROUND: Cognitive demands associated with balance and locomotion may contribute to the incidence of falling among older adults. This study addressed issues related to the effects of aging on the attentional demands of recovering from an external disturbance to balance. This research also investigated whether performing a secondary cognitive task differentially affects postural recovery in young versus older adults. METHOD: Fifteen young and 10 healthy older adults were exposed to a series of balance disturbances. Attentional demands were assessed using a dual task paradigm where postural recovery served as the primary task, and counting backwards served as a concurrent secondary cognitive task. The effect of the counting task was assessed by comparing kinematic variables related to feet-in-place and stepping recovery strategies. RESULTS: Recovering upright stance was found to be attentionally demanding in both age groups. The type of recovery strategy did not influence attentional demands in young adults; however, a hierarchy of increasing attentional demands between the ankle strategy and compensatory stepping was apparent among older adults. In addition, stepping appears to be more attentionally demanding for older adults than for younger adults. Counting backwards did not affect the type of strategy used; however, it did affect the kinematics of stepping. For both age groups, steps occurred when the center of mass was located in a more central location within the base of support when the secondary task was added. CONCLUSIONS: The ability to recover a stable posture following an external perturbation is more attentionally demanding for older adults than for younger adults. This would suggest that for some older adults, an increased risk for loss of balance and falls may result if sufficient attentional resources are not allocated to the task of postural recovery.

Accidental Falls↗
PubMed2000

Cognitive influence on postural stability: a neuromuscular analysis in young and older adults.

BACKGROUND: Previous literature indicates that attentional resources are required for recovery of postural stability. Previous studies have also examined the effect of aging on the performance of a static postural task while a secondary cognitive task is being conducted. This study describes the effect of a cognitive task on the neuromuscular response characteristics underlying reactive balance control in young versus older adults. METHODS: The attentional demand on the neuromuscular system was examined in 14 young and 12 healthy older adults by analysis of the integrated electromyography activity while the adults were performing a dual-task paradigm. The primary task involved standing platform perturbations and the secondary task was a math task that involved subtraction by threes. Integrated electromyography activity was compared between the cognitive (math and balance) task versus control (balance only) task. RESULTS: For both groups of subjects, onset latency of postural muscle responses did not change under dual-task conditions. In contrast, the amplitude of postural muscle activity was significantly affected by performance of a secondary task. When electromyography data were combined for both young and older adults, there was a decrease in muscle response amplitude in both agonist (gastrocnemius) and antagonist (tibialis anterior) muscles when the cognitive math task was performed. This was apparent at 350-500 milliseconds from plate onset for the gastrocnemius and between 150 and 500 for the tibialis anterior. When young and older adults were compared, an age by task interaction effect was seen in muscle response amplitude for the agonist (gastrocnemius) muscle between 350 to 500 milliseconds, with older adults showing a significantly greater reduction than young adults. CONCLUSION: The decline of muscle activity when the secondary task was performed suggests that less attentional processing capacity was available for balance control during the dual-task paradigm. The results also indicate that the dual-task activity has a greater impact on balance control in the older adults than in the young adults.

Adult↗
PubMed1989

Age, functional postural reflexes, and voluntary sway.

This experiment considered age-related changes in functional relationships between postural reflexes and voluntary movement. Young and older adults received horizontal perturbations during normal stance and when engaged in voluntary sway. Electromyographic activity showed that (a) older adults had poorer coordination between postural reflexes and voluntary movement, and (b) their stabilizing responses to postural disturbances during voluntary sway were slower. In addition, the onsets of activity of functionally important muscles were less tightly bilaterally coupled, and patterns of muscle onsets were less stereotypically organized in older adults. The results suggest that older adults experience some breakdown in the timing and sequencing of muscle activity and in the functional coordination of their postural reflexes with voluntary sway.

Adolescent↗