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At least 991 records · Page 55Linked to original sources
PubMed2004

Contribution of muscle strength and integration of afferent input to postural instability in persons with stroke.

OBJECTIVE: To determine the relationship of muscle strength to postural sway in persons with stroke under standing conditions in which vision and ankle proprioception were manipulated. METHODS: Forty persons with stroke and 40 healthy older adult controls were recruited from the community and underwent balance testing consisting of 6 conditions that manipulate vision and somatosensory information while standing. Postural sway was measured during each condition. In addition, lower extremity joint torques and cutaneous sensation from the plantar surface of the foot were assessed. RESULTS: Postural sway was increased with more challenging standing conditions (i.e., when multiple sensory systems were manipulated) to a greater extent with the group with stroke compared to controls. Muscle strength was only correlated to sway during the most challenging conditions. Furthermore, a greater number of persons with stroke fell during the balance testing compared to controls. CONCLUSIONS: Impairments in re-weighting/integrating afferent information, in addition to muscle weakness, appear to contribute to postural instability and falls in persons with stroke. These findings can be used by clinicians to design effective interventions for improving postural control following stroke.

Aged↗
PubMedDate not supplied

Feasibility of functional electrical stimulation for control of seated posture after spinal cord injury: A simulation study.

We performed this study to determine the feasibility of controlling and stabilizing seated posture with functional electrical stimulation (FES) after paralysis from spinal cord injury (SCI) using computer simulations and a 3-dimensional model of the hip and trunk. We used the model to approximate the range of postures in the sagittal and transverse planes attainable by a seated subject and to estimate the maximum restorative moment that could be produced in a neutral posture in response to a disturbance. The simulations predicted that approximately 28 degrees of forward flexion in the sagittal plane (combined hip and trunk) and 9 degrees of lateral bending in the transverse plane should be possible with FES and that a maximum disturbance rejection moment of approximately 45 newton meters could be expected with the chosen muscle set. We tested a subject with a motor complete thoracic SCI and implanted electrodes in a subset of the selected muscles to compare the moments the subject required to maintain various hip and trunk positions with those predicted by the model. Although a significant range of seated postures was possible with FES, the data demonstrated that more complete activation of the paralyzed muscles would be needed for the subject to fully achieve the theoretical range of motion. With further refinements, we could apply these techniques to the design of control systems for regulation of seated posture and dynamic motion of the torso.

Computer Simulation↗
PubMed2005

A nonlinear dynamic approach for evaluating postural control: new directions for the management of sport-related cerebral concussion.

Recent research suggests that traditional biomechanical models of postural stability do not fully characterise the nonlinear properties of postural control. In sports medicine, this limitation is manifest in the postural steadiness assessment approach, which may not be sufficient for detecting the presence of subtle physiological change after injury. The limitation is especially relevant given that return-to-play decisions are being made based on assessment results. This update first reviews the theoretical foundation and limitations of the traditional postural stability paradigm. It then offers, using the clinical example of athletes recovering from cerebral concussion, an alternative theoretical proposition for measuring changes in postural control by applying a nonlinear dynamic measure known as 'approximate entropy'. Approximate entropy shows promise as a valuable means of detecting previously unrecognised, subtle physiological changes after concussion. It is recommended as an important supplemental assessment tool for determining an athlete's readiness to resume competitive activity.

Athletic Injuries↗
PubMed2005

Acute effects of a single bout of resistance exercise on postural control in elderly persons.

Many elderly persons are engaging in resistance exercise to counter muscle atrophy due to aging. Here, the acute effects of resistance exercise on postural control mechanisms were examined. Postural control was quantified by mean square center-of-pressure displacements were calculated utilizing force vectors in accordance with previously developed equations. Stabilogram-diffusion plots utilized the displacements as data points after curve-fitting techniques were applied. Two regions, representing the open-loop and closed-loop postural control mechanisms, are shown by the plots and separated at the critical point, which represents the shift in control mechanisms. 21 older adults (age M=71.2, SD=3.84, range 66-81 years) performed three sets of 10-12 repetitions for six resistance exercises for the lower extremity until fatigue. Immediately after exercise, postural stability was reduced. This was represented by a shift of the critical point to the right, indicating an increase in open-loop control. Since resistance training has an acute negative effect on postural control, it is advised to assist elderly clients carefully and immediately after resistance training.

Aged↗
PubMed2001

Modality of postural movement in men and women with both arms flexed during standing.

We investigated postural movement associated with bilateral arm flexion in response to a light signal during standing in 179 healthy men and women to assess whether individual and sex differences arc evident in the postural movement pattern. The following results were obtained. (a) A correlation of -.87 was noted between movement angles of the foot-leg and leg-trunk. (b) Individual differences in movement angle were approximately twice as large in the hip joint as in the ankle and knee joints, and the movement angle of the leg trunk showed approximately half the number of extension as flexion movements. (c) The postural movement pattern was categorized on the basis of the movement angle of the foot leg and leg trunk into the following three patterns: hip flexion, backward leaning, and hip extension. The percentages of subjects showing these patterns were 59.2%, 33.5%, and 7.3%, respectively. (d) The inclination angle reflecting the righting response showed a gradual increase in size in the order of trunk, head, and neck. However, the righting response was not controlled precisely enough to enable subjects to maintain the inclination angle in a quiet standing posture. (e) We identified a significant sex difference in the relative frequency of subjects in the postural movement pattern.

Adolescent↗
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↗
PubMed1993

Contribution of the vestibular primary neuron and the sensory cell to posture recovery.

The right vestibular nerve of the frog was cut peripherally to the vestibular ganglion. The frog sustained a tilting posture toward the right side. This tilting disappeared and the frog returned to normal posture. Based on this finding, the following experiments were done: In experiment I, the right vestibular nerve was again cut after posture recovery. The tilting angle was smaller and the recovery period shorter than after the 1st neurectomy. In experiment II, the left nerve was cut after posture recovery. The tilting angle toward the left was greater than that of the 1st neurectomy. In experiment III, the frog underwent bilateral neurectomy. A piece of the bone was inserted into the cut ends of the right nerve to inhibit nerve regeneration. The frog slowly developed tilting toward the right side. The above results indicate that both reactivation of the endorgan and the central compensatory mechanism play essential roles, for postural recovery after vestibular neurectomy.

Animals↗
PubMed1995

Postural control in Menière's disease and acoustic neurinoma when studied on a linearly oscillating platform.

We investigated the effect of visual control on postural stability on a moving platform in 36 patients with Menière's disease (MD) in 25 patients with operated acoustic neurinoma (AN) and in 19 healthy controls. The force platform was placed on rails and oscillated linearly at frequencies from 0.2 to 5 Hz at a constant velocity of 30 mm/s. In all subjects, the support surface oscillation produced postural instability that differed significantly from the base line stability. The body sway velocity increased almost linearly with the increase of stimulation frequency. The MD patients swayed more than the AN patients at base line measurements in non-visual conditions but not during platform movement. In visual conditions the AN patients stabilized their posture significantly better than the MD patients, who showed deteriorating visual control of posture during platform movement. The controls differed from the patients in all test conditions except 5 Hz stimulation, which causes the body segment to fall into resonance. The Romberg quotients (RQ) in MD patients was significantly poorer during platform movement than in controls, except at 5 Hz stimulation. The AN patients had higher RQ values than controls, and mainly used vision to compensate their vestibular deficit. Thus, patients with MD fail to control their posture efficiently with vision during movement which may explain the visually induced dizziness in MD patients.

Adult↗
PubMed1998

Postural equilibrium: functional system and its stabilization by means of osteoreflexotherapy.

Our investigations have confirmed that the osteoreceptive sensory system participates in the polysensoric regulation of animal and human posture. Experiments with animals have demonstrated that the irritation of osteoreceptors by electric pulses leads to osteoreceptive response potentials of the same parts of the brain (Deiter's nuclei, cerebellum, caudate nucleus, cortical motor centre etc.) which participate in the regulation of animal and human posture and other motion acts. Close functional relations have been established between the skin, bone, vestibular and muscle sensory systems in the brain structures where the osteoreceptive excitation converges. The studies of osteoreceptive sensory system have served as a theoretical base for new techniques of posture stabilization. These are based on osteoreceptive irritations caused by electrical pulses or by intraosseal pressure increase at injections of the physiological solution. It has been found that each bone has its own specific role in posture regulation. In all cases of bone irritation the posture stabilization of various degrees has been confirmed. However, it has been demonstrated that the most effective results have been obtained by affecting the processus spinosus of seventh cervical vertebra and the lower extermity bones, especially those of tibiae and calcaneus.

Adolescent↗
PubMed1999

Further evidence for age-related deficits in human postural function.

The aim of the present study was to investigate the effects of aging on postural function in human subjects. Subjects aged 18-39 years (n = 24), 40-59 years (n = 24) and 60 years or older (n = 27) were tested for postural stability using an electronic balance platform. There was a significant increase in postural instability with increasing age (P < 0.0001), and as the conditions of testing became more difficult (P < 0.0001) (e.g., with eyes closed). Elderly males were found to have significantly poorer postural control than elderly females in the visual-vestibular conflict conditions (P < 0.05). These results further demonstrate a decline in postural function with increasing age, which may be related to deterioration in the peripheral or central vestibular systems and may be partly responsible for the high incidence of falls in the elderly.

Accidental Falls↗
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↗
PubMed2001

Human postural responses to different frequency vibrations of lower leg muscles.

We analyzed human postural responses to muscle vibration applied at four different frequencies to lower leg muscles, the lateral gastrocnemius (GA) or tibialis anterior (TA) muscles. The muscle vibrations induced changes in postural orientation characterized by the center of pressure (CoP) on the force platform surface on which the subjects were standing. Unilateral vibratory stimulation of TA induced body leaning forward and in the direction of the stimulated leg. Unilateral vibration of GA muscles induced body tilting backwards and in the opposite direction of the stimulated leg. The time course of postural responses was similar and started within 1 s after the onset of vibration by a gradual body tilt. When a new slope of the body position was reached, oscillations of body alignment occurred. When the vibrations were discontinued, this was followed by rapid recovery of the initial body position. The relationship between the magnitude of the postural response and frequency of vibration differed between TA and GA. While the magnitude of postural responses to TA vibration increased approximately linearly in the 60-100 Hz range of vibration frequency, the magnitude of response to GA vibration increased linearly only at lower frequencies of 40-60 Hz. The direction of body tilt induced by muscle vibration did not depend on the vibration frequency.

Adult↗
PubMed2001

Postural sway of subjects wearing the U.S. Army chemical protective ensemble after functional activity.

BACKGROUND: This study assessed the effects of wearing the chemical protective clothing ensemble (CPE) vs. the battle dress uniform (BDU) on postural sway after 18 min of simulated field activity. Postural sway is a measure of static balance where a person maintains his/her center of gravity over his/her base of support by swaying fore to aft usually around the ankle joint axis. HYPOTHESES: Subjects' postural sway would increase more post-exercise while wearing the CPE vs. the BDU. The increase in postural sway while wearing the CPE would be due to decreased visual and somatosensory inputs. METHODS: Static balance was measured on 25 subjects pre- and post-exercise on the NeuroCom SMART Balance Master using the Sensory Organization Test protocol. Following a test-retest, repeated measures design, each subject completed the protocol twice, once while wearing only the BDU and once while wearing the CPE. RESULTS: A 2 x 2 repeated measures, multivariate analysis of variance revealed no significant difference between the static balance of subjects wearing the CPE vs. wearing the BDU pre- or post-exercise. CONCLUSIONS: The authors suggest that the wearing of the CPE does not affect static balance, even after completing 18 min of functional tasks. Future research should objectively quantify the amount of fatigue postexercise and employ a protocol that has been previously shown to increase postural sway.

Adult↗
PubMed2002

The effect of predictable and unpredictable motor tasks on postural control after traumatic brain injury.

This study examined the effects of environmental predictability on postural control during functional reaching while seated in healthy individuals and patients with traumatic brain injury (TBI). The postural perturbation used required reaching to the left versus reaching to the right, while seated, under predictable versus unpredictable conditions. Indexes of postural control--trajectory stability and response reach times--were measured using an electromechanical system in ten patients with TBI and ten healthy subjects. In the TBI group, greater trajectory stability and shorter response reach time were recorded under unpredictable conditions when reaching to both the right and left (d-index 0.57-2.3). In the control group, greater trajectory stability and shorter response time were recorded under predictable and unpredictable environments compared with the TBI group (d-index 0.46-0.95). This study refutes the hierarchical, predictable-to-unpredictable-environment model of postural control evaluation and treatment. The relationship between information processing demands and postural skill appears more complex than a simple linear association. Predictable and unpredictable conditions may be used concurrently, not sequentially, in TBI rehabilitation.

Adult↗
PubMed1992

[The effect of head position and functional status of the cervical spine on body sway in the upright posture].

In 30 subjects (16 men and 14 women) stabilometry was used to investigate the stability of posture with closed eyes and different positions of the head (backward, forward, right and left turn). Cervical spine mobility of the subjects studied was determined by vertebrogenic examination. The maximum backward extension of the head was found to reduce most markedly posture stability. Correlation analysis revealed a relationship between the functional state of the cervical spine and the degree of posture stability impairment induced by backward extension of the head, with the impairment being more pronounced in the forward-backward direction. The obtained results show that changes in the quality of proprioceptive information from the cervical spine region are also involved in determining the stability level of upright posture. The findings imply that posture with backward extension of the head can be used as a loading test for detecting ataxia of cervical origin.

Adult↗
PubMedDate not supplied

Evaluation of abnormalities of orthostatic postural control in systemic sclerosis.

OBJECTIVE: Systemic sclerosis (SSc) is a multi-systemic disease of unknown etiology characterized by damage to the small arteries, arterioles and capillaries. The documented occurrence of various neuropathies in SSs patients led us to hypothesize that there is a potential for postural control impairments in such disease. This study was aimed at evaluating the orthostatic postural control of SSc patients who do not manifest balance or hearing symptoms. METHODS: Postural stability was assessed in 36 female SSc patients by means of a static computerized posturography technique. Their immunological and microvascular condition were evaluated by means of blood tests and microcapillaroscopy of the digital vessels. Posturography and microcapillaroscopy were performed before and after treating the patients with Iloprost. In order to compare results, posturography was also carried out on a control group composed of 10 healthy women of similar age. Both groups were studied in two different sensory conditions, i.e. with eyes opened and with eyes closed. RESULTS: Posturography results showed relevant differences in body sway between patients and control subjects. Fourier spectral analysis of body sway showed that, independently from visual control, SSc patients exhibit a higher level of low/middle frequency oscillations (both on the lateral and the anteroposterior axis). No relationship was established between disease stage and postural performance. CONCLUSION: This study seems to indicate a subtle neurophysiological dysfunction in the orthostatic postural control of female SSc patients. Further tests on the somatosensory neurological function of SSc patients may help support the above mentioned findings.

Dizziness↗
PubMedDate not supplied

Effect of head orientation on human postural stability following unilateral vestibular ablation.

Effective interpretation of vestibular inputs to postural control requires that orientation of head on body is known. Postural stability might deteriorate when vestibular information and neck information are not properly coupled, as might occur with vestibular pathology. Postural sway was assessed in unilateral vestibulopathic patients before and acutely, 1, 4, and 18+ months after unilateral vestibular ablation (UVA) as well as in normal subjects. Postural equilibrium with eyes closed was quantified as scaled pk-pk sway during 20 s trials in which the support surface was modulated proportionally with sway. Subjects were tested with the head upright and facing forward, turned 45 degrees right, and 45 degrees left. Equilibrium was uninfluenced by head orientation in normal subjects. In contrast, patients after UVA showed both a general reduction in stability and a right/left head orientation-dependent asymmetry. These abnormalities adaptively recovered with time. It is concluded that vestibular inputs to postural control are interpreted within a sensory-motor context of head-on-body orientation.

Adolescent↗
PubMedDate not supplied

Recovery of postural control after an acute unilateral vestibular lesion in humans.

Postural control during stance was investigated using the EQUITEST system in 10 patients during recovery after an acute unilateral vestibular lesion and was compared to the time course of recovery of the static and dynamic vestibulo-ocular imbalance. During the acute phase the patients showed a characteristic pattern with normal upright stance as long as at least one accurate sensory input (visual or somatosensory) was provided and severe postural disturbances when they had to rely primarily on vestibular afferences. Both static vestibulo-ocular and vestibulo-spinal balance recovered very fast, showing basically normal results on postural testing within about 2 weeks after the lesion. Thereafter, no pathological pattern was detectable during postural testing even in patients with persistent complete unilateral vestibular lesions. Reflexive postural responses to unexpected rapid displacements of the support surface seemed not to be influenced by vestibular imbalance even in the acute phase of the lesion.

Acute Disease↗