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PubMed1991

Postural stability and associated physiological factors in a population of aged persons.

A battery of 13 visual, vestibular, sensorimotor, and balance tests was administered to 95 elderly persons (mean age 82.7 years) to examine the relationships between specific sensorimotor functions and measures of postural stability. When subjects stood on a firm surface, increased body sway was associated with poor tactile sensitivity and poor joint position sense. When subjects stood on a compliant surface (which reduced peripheral sensation) with their eyes open, increased body sway was associated with poor visual acuity and contrast sensitivity, reduced vibration sense, and decreased ankle dorsiflexion strength as well as reduced joint position sense. Increased body sway with eyes closed on the compliant surface was associated with poor tactile sensation, reduced quadriceps and ankle dorsiflexion strength, and increased reaction time. Poor performance in two clinical measures of postural stability was associated with reduced sensation in the lower limbs as measured by joint position sense, tactile sensitivity and vibration sense, reduced quadriceps and ankle dorsiflexion strength, and slow reaction times. The prevalence of vestibular impairments was high in this group, but vestibular function was not significantly associated with sway under any of the test conditions. The results suggest that reduced sensation, muscle weakness in the legs, and increased reaction time are all important factors associated with postural instability. An analysis of the percentage increases in sway under conditions where visual and peripheral sensation systems are removed or diminished, compared with sway under optimal conditions, indicated that peripheral sensation is the most important sensory system in the maintenance of static postural stability.

Aged↗
PubMed1991

Fear of falling and postural performance in the elderly.

A cross-sectional study was performed to investigate the association between fear of falling and postural performance in the elderly. One hundred ambulatory and independent volunteers (aged 62-96) were subjected to five types of balance tests: (a) spontaneous postural sway, (b) induced anterior-posterior sway, (c) induced medial-lateral sway, (d) one-leg stance, and (e) a clinical balance assessment scale. Pseudorandom platform motions were used in the induced-sway tests. The subjects were classified into both "faller"/"nonfaller" and "fear"/"no-fear" categories, to allow the influence of fear of falling and falling history to be separated in the analyses. Subjects who expressed a fear of falling were found to exhibit significantly poorer performance in blindfolded spontaneous-sway tests and in eyes-open, one-leg stance tests. The clinical scale was the only balance measure that showed a significant association with retrospective, self-reported falling history. We could not ascertain whether the fear of falling affected balance-test performance in an artifactual manner, or whether the fear and poorer performance were related to a true deterioration in postural control. Until this issue can be resolved, balance-test performance should be interpreted with caution when testing apprehensive individuals. Furthermore, studies of postural control and falling should allow for the potentially confounding influence of fear of falling.

Accidental Falls↗
PubMed1991

Postural sway characteristics of the elderly under normal and altered visual and support surface conditions.

One of the most pervasive findings in the literature on the aged is the general slowing of cognitive-motor responses with advancing age. Hence, an increased slowness in the processing of information from vestibular, visual, and somatosensory systems could contribute greatly to a decline in postural stability. To examine this question, in a cross-sectional investigation, postural sway behavior of elderly (n = 18) and young (n = 10) adults was examined under conditions that stressed the slower integrative mechanisms rather than the reflexive mechanisms of postural control. The postural sway behavior of young and elderly subjects was examined for a prolonged duration (80 s), under altered visual and/or support surface (5 cm thick foam surface) conditions, and contrasted with normal stance. Results showed that the exclusion or disruption of one of the sensory inputs, alone, was not consistently sufficient to differentiate between elderly and young adults, because of compensation by the remaining sensory sources. Both alterations together (i.e., visual and surface), however, had a substantially greater effect upon the elderly than the young.

Adult↗
PubMed1987

Clinical measurement of postural control in adults.

Postural control is the ability to maintain equilibrium and orientation in a gravitational environment. Effective approaches for clinical measurement of postural control remain to be developed. This article summarizes important neurophysiological and clinical considerations for developing measurement tools to assess postural control in adults. The postural control system is divided into three basic functional components for assessment: 1) biomechanical components, 2) motor coordination components, and 3) sensory organization components.

Biomechanical Phenomena↗
PubMed1990

Electromyographic analysis of postural adjustments in two methods of balance testing.

The primary purpose of this study was to compare postural responses during two methods of balance testing: 1) a platform perturbation test (PP), with destabilizing forces of uniform magnitude given at the base of support, and 2) a postural stress test (PST), with destabilizing forces of increasing magnitude given at the waist. A secondary purpose was to examine the relationship between balance strategy scores and the patterns of muscle responses as determined by electromyographic analysis on the PST. Postural responses to backward sway of 17 healthy subjects, aged 60 to 79 years (means = 69.0, s = 5.3), were characterized bilaterally by EMG recording of the tibialis anterior, quadriceps femoris, gastrocnemius, and hamstring muscles. We examined three measures of bilateral postural responses: 1) latency to first muscle response (FR) among the four lower extremity muscle groups, 2) tibialis anterior muscle latency (TA), and 3) patterns of muscle responses. Our results demonstrated significantly shorter (p less than .001) TAs and FRs (in milliseconds) on the PST than on the PP (PST TA: = means = 80.3, s = 12.4; PP TA: = means = 142.6, s = 13.4; PST FR: means = 75.9, s = 10.4; PP FR: = means = 140.4, s = 13.6). The ankle strategy was the most frequently used pattern of muscle response during both the PP and the PST, but it occurred less frequently on the PST than on the PP (PP = 72.5%, PST = 50.9%) (p less than .05). No consistent relationship was observed between the balance strategy scores as determined by videotape analysis of the PST and the patterns of muscle responses as determined by EMG analysis.

Aged↗
PubMed1997

The effect of Tai Chi Quan and computerized balance training on postural stability in older subjects. Atlanta FICSIT Group. Frailty and Injuries: Cooperative Studies on Intervention Techniques.

BACKGROUND AND PURPOSE: This study explored whether two exercise programs would affect the ability to minimize postural sway of 72 relatively inactive, older subjects who participated in the Atlanta FICSIT trial. SUBJECTS: Subjects were randomly assigned to (1) a computerized balance training group, (2) a tai chi group, or (3) an educational group serving as a control for exercise. Each group consisted of 24 members. METHODS: All subjects were evaluated under four postural conditions before, immediately after, and 4 months following their respective interventions, each of which was given over 15 weeks. RESULTS: Platform balance measures revealed greater stability after training among subjects in the balance training group but little change in stability among subjects in the tai chi and educational group. Subjects in the tai chi group were less afraid of falling after training compared with subjects in other groups with similar covariates. CONCLUSION AND DISCUSSION: Unlike computerized balance training, tai chi does not improve measures of postural stability. Because tai chi delayed onset to first or multiple falls in older individuals, this effect does not appear to be associated with measures of enhanced postural stability. Tai chi may gain its success, in part, from promoting confidence without reducing sway rather than primarily facilitating a reduction in sway-based measures.

Accidental Falls↗
PubMed2002

The assessment of postural stability after ambulatory anesthesia: a comparison of desflurane with propofol.

UNLABELLED: We designed this study to evaluate postural stability in outpatients after either desflurane or propofol anesthesia. After IRB approval, 120 consenting women undergoing gynecological laparoscopic procedures were randomly assigned to receive either desflurane or propofol-based general anesthesia. After surgery, patients' postural stability was measured as body sway velocity by using a computerized force platform in the following conditions: 1) standing on a firm surface with eyes open versus closed and 2) standing on a foam surface with eyes open versus closed. These measurements were made before anesthesia, immediately after the patient achieved a Post-Anesthesia Discharge Score of 9, and at actual discharge home. At the time patients first achieved a Post-Anesthesia Discharge Score of 9, the body sway in the Propofol group was significantly more than in the Desflurane group when patients were asked to stand on a foam surface with eyes closed (testing the ability of using vestibular information for balance control). We concluded that the desflurane-based anesthetic was associated with better postural control than the propofol-based anesthetic in the early recovery period after outpatient gynecological laparoscopic procedures. IMPLICATIONS: The residual effects of the short-acting general anesthetics desflurane and propofol on patient's balance function during recovery after surgery were assessed with a computerized force platform. The results showed that desflurane seemed to be associated with better postural control than propofol in the early recovery period.

Adult↗
PubMed2005

Selective utilization of spatial working memory resources during stance posture.

While it has been shown that visual imagery tasks interfere with balance control, the neural mechanisms underlying the interference are unclear. Within a healthy young adult population, we employed a dual-task methodology to investigate the role of visual working memory in stance postural control. The employment of specific visual object and visual spatial working memory cognitive tasks facilitated the selective activation of cortically dissociated working memory resources. Challenging postural sets did not significantly impact object working memory performance, but clearly degraded performance on a spatial working memory task, suggesting that interactions between stance postural control and visual working memory are limited to the spatial domain. Results demonstrated no significant effect of the cognitive tasks upon postural stability.

Adult↗
PubMed2005

The influence of concurrent cognitive tasks on postural sway in children.

PURPOSE: The purpose of this study was to examine the influence of concurrent tasks on postural sway in children. METHODS: Nineteen fourth-grade students, while standing on a balance platform, were asked to stand still, count backward, and read second-grade level sentences. The AMTI Accusway System was used to calculate the length of center of pressure path (LCOP), sway range (SR), and variability (SV) in mediolateral (ML) and anteroposterior (AP) directions of sway. RESULTS: Analysis of variance revealed a main effect of cognitive task condition for SR-AP, SR-ML, SV-AP, and SV-ML. Post hoc comparisons revealed lower values of those four dependent measures for the counting backward task than for the standing still task and lower SV-AP for the counting backward task than for the reading task. In addition, there was a trend toward greater LCOP when performing a concurrent cognitive task. CONCLUSIONS: The demands of concurrent cognitive tasks while standing affect postural sway in children. The findings of this study contribute to our understanding of postural control in children and may explain why improvements in postural skills attained in clinical settings may not transfer to improved performance in other settings.

Analysis of Variance↗
PubMed2005

Application of cross time-frequency analysis to postural sway behavior: the effects of aging and visual systems.

In this paper, the effects of visual feedback and aging on postural sway systems and signals are investigated by analyzing the transient phase difference between "input" and "output" which correspond to center of pressure (COP) and center of mass (COM), respectively. In order to analyze the transient phase difference characteristics of COP and COM, a relatively new cross time-frequency analysis technique that provides time- and frequency-localized phase difference information is utilized. The feedback control process in the postural sway is interpreted in terms of a feedback compensator which is characterized in terms of a phase difference. Using the experimental results of the transient phase difference obtained from the cross time-frequency distribution, it is demonstrated that the postural control of young persons are more stable and rely more on visual sensory feedback to stabilize postural control compared to that of the elderly persons.

Adaptation, Physiological↗
PubMed1987

Maturation of postural sway in young children.

The postural sway of 76 healthy young children aged from two to 14 years was investigated to identify age-related changes in the extent of sway, the effects of eye-closure, and the spectral composition of sway. Postural sway was measured from the excursions of the centre of pressure of ground reaction forces, and was analysed for both time and frequency. Within the age-range of the children tested, postural sway decreased linearly with age. Boys tended to become more stable at a faster rate than girls, but started from an initially greater level of instability. The children's Romberg quotients, which provide an index of the influence of eye-closure on sway magnitude, were remarkably low in comparison with adult values. Power spectral analysis of the postural sway showed that the principal energy was contained below 0.7 Hz for both lateral and antero-posterior sway, but that very young children had some power in the 0.8 to 2.0 Hz range. Taken together, these results confirm and extend the previously established view that children use visual information to control balance in a manner different from that of adults, and that it is not until after the age of seven years that adult-like balance-control strategies begin to appear. Also, in contrast to adults, the appearance of sway at high frequencies in children is not necessarily associated with any pathology.

Adolescent↗
PubMed2005

Posturographic description of the regaining of postural stability following stroke.

BACKGROUND: Failing balance and increased liability to falling are common complaints among hemiplegic subjects. During rehabilitation much effort is put into regaining postural stability. PURPOSE: To describe the regaining of postural stability during rehabilitation for the first year following stroke in hemiplegic patients MATERIALS AND METHODS: Twenty-six patients were included within 5 days of suffering a stroke resulting from a CT-verified clearly defined thromboembolic lesion, localized in the vascular bed of middle cerebral artery on either side. Posturographic evaluation of sway was performed on a commercially available force plate system (Balance Master Pro). Measured parameters included per cent maximum stability (PMS), per cent ankle strategy (AST), and average angular velocity (AVE). An additional parameter was derived by calculating the slope (SLP) of the linear relationship between stability and ankle strategy. SLP reflects the predisposition of the stroke patient to keep using ankle strategy when faced with increasingly difficult balance tasks. The presence of familiarization to the measurement method was examined by including a preliminary measurement not otherwise included in the analysis of changes during the first year of follow-up. The temporal evolvement of sway was described by measuring sway parameters 1, 2, 4, 8 and 52 weeks following stroke. The proportions of the variation in sway caused by measurement error and between patients were compared. RESULTS: All parameters improved over time, as demonstrated by significant improvements from each of week 1, 2, 4 and 8 to week 52. There was evidence of familiarisation for PMS, AST and AVE, but not for SLP. Estimation of variance components showed that between patient variation accounts for between two-thirds and four-fifths of the total variation. A considerable part of this variation was caused by individual differences in the temporal improvement of sway over time. Patients considered the evaluation of postural sway demanding and time consuming resulting in a relatively large loss to follow-up: 15 patients completed the 8-week visit while seven completed the 1 year visit. CONCLUSION: Postural stability increases for the first year following stroke. There is evidence of familiarization towards the measurements process for the traditional posturographic parameters PMS, AST and AVE, but not for the derived parameter SLP, which might make the latter a candidate for a sway parameter reflecting basic mechanisms of upholding upright stance in hemiplegic patients. The estimated variance components stress the considerable between-patient variation and question the ability of the force plate method to monitor individual sway performance of such patients during the rehabilitation process.

Adult↗
PubMed1990

Aging and postural control. A comparison of spontaneous- and induced-sway balance tests.

Two different balance testing methods were compared: (1) measurement of spontaneous postural sway during quiet standing, and (2) measurement of induced postural sway in response to an applied postural perturbation. Eyes-open tests were performed in 64 healthy young and elderly adults and in five elderly subjects with a history of falling. In both balance tests, the sway was defined in terms of the displacement of the center of pressure on the feet. Spontaneous sway was quantified using a number of different amplitude- and frequency-based parameters. Induced sway was measured in response to anterior-posterior acceleration of a platform on which the subject stood. The induced-sway test was specially designed to be safe and nonthreatening for elderly subjects; thus, the platform perturbation was confined to small accelerations and a gentle pseudorandom motion was used. To derive a measure of postural stability, the data from this test were fitted with a model that was then used to predict the response to sudden (transient) perturbations, thereby simulating the response in actual falls. Although both induced- and spontaneous-sway measures demonstrated significant aging-related decreases in stability, the differences were more pronounced for the induced-sway data. Conversely, some of the spontaneous-sway measures were much more successful in distinguishing the fallers from the nonfallers. There was a significant correlation between induced-sway and certain spontaneous-sway measures in the normal young adults; however, in the elderly normals and fallers, the data from the two types of balance tests either showed no correlation or, for certain spontaneous-sway measures, tended to show an inverse relationship.

Acceleration↗
PubMed1991

Postural responses and effector factors in persons with unexplained falls: results and methodologic issues.

Automatic postural responses and effector factors were examined in 10 persons with unexplained falls after clinical examination and 24 older controls. Fallers were more unstable than controls on clinical tests of balance (20% of fallers vs 79.2% of controls were able to stand on one foot (P less than .005), 40% of fallers and 100% of controls were stable while turning in place (P less than .001), postural stress test median score was 12 for fallers and 20 for controls (P less than 0.001). We found prolonged tibialis anterior latency (fallers 158.8 +/- 23.7, controls 143.2 +/- 15.7 milliseconds, P = 0.03), marked losses in ankle strength (dorsiflexion: faller 3.2 +/- 2.9, controls 8.9 +/- 4.2 foot-pounds, P less than 0.001; plantarflexion: fallers 7.9 +/- 5.3, controls 21.4 +/- 11.1 foot-pounds, P less than 0.001), and decreases in range of motion (ankle plantarflexion: fallers 29.2 +/- 7.0, controls 37.8 +/- 12.4 degrees, P = 0.02). Gastrocnemius latency and electromyographic (EMG) measures of sequence showed no differences between fallers and controls. Sequence measures were not symmetric between the lower extremities in either fallers or controls. In this population of persons with unexplained falls who demonstrated substantial impairments in functional balance, effector factors appear more impaired than automatic postural responses. Alternatively, contemporary analysis of automatic postural responses may require further development before it can be useful to study balance problems in older persons.

Accidental Falls↗
PubMed2005

Exercise leads to faster postural reflexes, improved balance and mobility, and fewer falls in older persons with chronic stroke.

OBJECTIVES: To determine the effect of two different community-based group exercise programs on functional balance, mobility, postural reflexes, and falls in older adults with chronic stroke. DESIGN: A randomized, clinical trial. SETTING: Community center. PARTICIPANTS: Sixty-one community-dwelling older adults with chronic stroke. INTERVENTION: Participants were randomly assigned to an agility (n=30) or stretching/weight-shifting (n=31) exercise group. Both groups exercised three times a week for 10 weeks. MEASUREMENTS: Participants were assessed before, immediately after, and 1 month after the intervention for Berg Balance, Timed Up and Go, step reaction time, Activities-specific Balance Confidence, and Nottingham Health Profile. Testing of standing postural reflexes and induced falls evoked by a translating platform was also performed. In addition, falls in the community were tracked for 1 year from the start of the interventions. RESULTS: Although exercise led to improvements in all clinical outcome measures for both groups, the agility group demonstrated greater improvement in step reaction time and paretic rectus femoris postural reflex onset latency than the stretching/weight-shifting group. In addition, the agility group experienced fewer induced falls on the platform. CONCLUSION: Group exercise programs that include agility or stretching/weight shifting exercises improve postural reflexes, functional balance, and mobility and may lead to a reduction of falls in older adults with stroke.

Accidental Falls↗
PubMed1999

The effect of supervised rehabilitation on strength, postural sway, position sense and re-injury risk after acute ankle ligament sprain.

The effect of an early rehabilitation program, including postural training, on ankle joint function after an ankle ligament sprain was investigated prospectively. Ninety-two subjects, matched for age, sex, and level of sports activity, were randomized to a control or training group. All subject received the same standard information regarding early ankle mobilization. In addition, the training group participated in supervised physical therapy rehabilitation (1 h, twice weekly) with emphasis on balance training. Postural sway, position sense and isometric ankle strength were measured 6 weeks and 4 months after the injury, and at 12 months re-injury data were obtained. In the training group, there was a significant difference between the injured and uninjured side for plantar flexion (P < 0.01), eversion (P < 0.01) and inversion (P < 0.05), but not for dorsiflexion at 6 weeks. In the control group, there was a significant difference between the injured and uninjured side for plantar flexion (P < 0.01), eversion (P < 0.01), inversion (P < 0.01), and dorsiflexion (P < 0.05) at 6 weeks. Postural sway, but not position sense, differed between the injured and uninjured side in both groups (P < 0.01) at 6 weeks. The side-to-side percent differences were similar in both groups for all variables (P > 0.05) at 6 weeks, and there were no side-to-side differences at 4 months in either group. In the control group, 11/38 (29%) suffered a re-injury, while this number was only 2/29 (7%) in the training group (P < 0.05). These data showed that an ankle injury resulted in reduced ankle strength and postural control at 6 weeks, but that these variables had normalized at 4 months, independent of the supervised rehabilitation. However, the findings also demonstrated that supervised rehabilitation may reduce the number of re-injuries, and therefore may play a role in injury prevention.

Adult↗
PubMed1996

Training affects the development of postural adjustments in sitting infants.

1. The present study addressed the question of whether daily balance training can affect the development of postural adjustments in sitting infants. 2. Postural responses during sitting on a moveable platform were assessed in twenty healthy infants at 5-6, 7-8 and 9-10 months of age. Multiple surface EMGs and kinematics were recorded while the infants were exposed to slow and fast horizontal forward (Fw) and backward (Bw) displacements of the platform. After the first session the parents of nine infants trained their child's sitting balance daily. 3. At the youngest age, when none of the infants could sit independently, the muscle activation patterns were direction specific and showed a large variation. This variation decreased with increasing age, resulting in selection of the most complete responses. Training facilitated response selection both during Fw and Bw translations. This suggests a training effect on the first level of the central pattern generator (CPG) model of postural control. 4. Training also affected the development of response modulation during Fw translations. It accelerated the development of: (1) the ability to modulate EMG amplitude with respect to platform velocity and initial sitting position, (2) antagonist activity and (3) a distal onset of the response. These findings point to a training effect on the second level of the CPG model of postural adjustments.

Age Factors↗
PubMed1999

A procedure to determine equilibrium postural configurations for arbitrary locations of the feet.

This research was directed toward predicting postural equilibrium configurations in normal humans for asymmetric locations of the feet. The objective of the study was to identify trends in the variation of the location of ground center of pressure (COP) with increasing levels of asymmetry in the foot placement. The procedure developed here minimized the muscular effort (active torques) in the lower extremities while maximizing postural stability margins for given foot locations. Minimizing muscular effort led to fully extended knees, and maximal stability margin led to the COP moving toward the rear foot in asymmetric stance. A combined analytical-numerical optimization scheme was used to avoid singularities that can arise due to the fact that at equilibrium postural configurations, the torso lies at or near the workspace boundary of the lower extremities. Experiments were conducted and the results obtained were in keeping with the model predictions. This basic understanding of asymmetric stance is important for studying asymmetric postural mechanics in the presence of external disturbances, and for extending the results from normal subjects to humans at both ends of the life span.

Algorithms↗