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Genetic and environmental contribution to postural balance of older women in single and dual task situations.

The purpose of the present study was to examine the effect of a second task on postural balance and to determine the role of genetic influences on postural balance when dual tasking among 206 monozygotic and 227 dizygotic female twins, aged 63-76 years. Balance was measured as medio-lateral and antero-posterior velocity of the centre of pressure (COP) (mm/s) and velocity moment (mm(2)/s) while standing on a force platform. Doing an arithmetic task increased movement of the COP while the hand motor task had no effect on movement of the COP. The genetic contribution to balance in the single task situation was minor (14%, 95% confidence interval, CI: 11-35%) whereas in the dual task situation it was moderate (28%, 95% CI: 0.02-42%). The finding can be explained in the light of the underlying phenotypes of dual tasking, such as cognitive processing that is found to be under considerable genetically controlled even in old age. Moreover, the present study supports previous studies suggesting that, especially among older people, when simultaneously maintaining balance and performing another cognitively demanding task, additional central processing is recruited.

Aged↗

Contribution of genetic and environmental effects to postural balance in older female twins.

The aim of the present study was to determine the relative roles of genetic and environmental influences on postural balance in older women. The participants were 97 monozygotic (MZ) and 102 dizygotic (DZ) female twins, aged 64-76 yr. Postural sway was measured during side-by-side stance with eyes open and eyes closed, and during semitandem stance with eyes open on a force platform. Sway data were condensed into four first-order and one second-order latent factors. The second-order factor, named balance, incorporates sway data from multiple tests and thus best describes the phenotype of postural balance. The contribution of genetic and environmental influences on the variability of the latent factors was assessed by using structural equation modeling. Additive genetic influences accounted for 35% and shared environmental influences accounted for 24% of the total variance in the balance factor. In the present study, postural balance in older women had a moderate genetic component. Genetic influences on postural balance may be mediated through gene variation in the systems that control posture. The finding that individual environmental influences accounted for almost one-half of the variance in postural balance points to the potential of targeted interventions to maintain and improve balance control in older persons.

Aged↗

Effects of hormonal replacement therapy on the postural balance among postmenopausal women.

OBJECTIVE: To establish whether hormone replacement therapy affects postural balance in postmenopausal women. METHODS: Nineteen healthy postmenopausal women with vasomotor symptoms were included. Median age was 54 years, median time since menopause was 3 years. They underwent dynamic posturography before and after 4 and 12 weeks of transdermal estrogen treatment (17 beta-estradiol 50 micrograms/day) as well as after 2 additional weeks of combined estrogen-progestagen treatment. The dynamic posturography method quantifies the amplitude, frequency, and pattern of body sway and tests the visual, vestibular, and somatosensory systems, which together maintain balance. The two most difficult tests either cancel visual and distort somatosensory inputs or give distorted information from both the visual and somatosensory systems. RESULTS: Hormone replacement therapy increased static balance performance assessed by dynamic posturography. A highly significant improvement was seen in the two most difficult tests between the pretreatment test and the test performed after 4 weeks of estrogen therapy (P < .01, P < .001, respectively). This improvement was sustained after 12 weeks and also during the 14th week, with the women on combined estrogen-progestagen treatment. CONCLUSION: Estrogen treatment increased balance performance measured by dynamic posturography, indicating that the beneficial effects from estrogens on postmenopausal fracture risk may include central nervous system effects on balance. Two weeks' addition of gestagen to the treatment regimen did not counteract the estrogen effects.

Estradiol↗

Disorders of posture, balance, and gait in Parkinson's disease.

Disorders of movement function related to posture, balance, and gait are common occurrences for many persons with Parkinson's disease. Numerous studies have identified a broad variety and heterogeneous distribution of postural and locomotor changes. These alterations are often associated with diminished functional ability, poor prognosis, and frequent falls. Present pharmacologic management appears to have a limited influence on postural instability and associated falls, and, despite anecdotal information, there is scant information on the therapeutic effectiveness of physical interventions aimed at enhancing these functions. Future advances would likely be facilitated by: (1) determining the nature and extent of the specific involvement of postural and locomotor control mechanisms; (2) coalescing findings on motor control processes with clinical information to develop rehabilitation approaches that target specific motor manifestations; and (3) conducting long-term clinical trials to demonstrate the efficacy of interventions.

Accidental Falls↗

[Effects of exposure to occupational hand-arm vibration on maintenance of postural balance].

In order to determine the relationship between exposure to hand-arm vibration through the use of vibration tools and dysfunction in the maintenance of postural balance, 106 male forestry workers were examined by stabilometry for deflection in the center of gravity and in the air conduction hearing levels. A questionnaire survey was also conducted among the workers in order to obtain details regarding their age, the types of tools used by them, and the duration for which they had used a chain saw. The vibration acceleration of a chain saw has been limited to a level of 3 G or less since 1976 in accordance with the notification from the Japanese Forestry Agency and the Ministry of Labor. In fact, chain saws with significantly reduced vibration acceleration in comparison with those used before 1976 have been available. Therefore, in 2000, we conducted a test on forestry workers who were divided into two groups-workers who had used a chain saw for 25 years or more (25-yr-or-more group) and workers who had used a chain saw for 24 yr or less (24-yr-or-less group). Compared to the 24-yr-or-less group, the 25-yr-or-more group exhibited significantly higher levels of average deflection in the center of gravity, expressed as the enveloped (aENV) and rectangular (aREC) areas, and in the hearing levels at 500, 1000, 2000, 4000 and 8000 Hz. For the aENV, the correlation coefficients revealed significant relationships between the hearing levels at 4,000 Hz, the duration of use of a chain saw, and age. Since the duration of use of a chain saw exhibited a significant relationship with age, it was necessary to eliminate the effect of age on the aENV. Subsequently, we divided all the workers into age groups spanning ten years each (from 20 to 70 yr) and compared the aENV among the same age groups in both the 25-yr-or-more and the 24-yr-or-less groups. The averages of the aENV for each age group were higher in the 25-yr-or-more group than in the 24-yr-or-less group. In particular, a significant difference was observed in the group of workers in their 40s. Moreover, the average of aENV value was significantly higher in the 25-yr-pr-more group than in the 24-yr-or-less group among the workers between 46 and 68 yr, with their ages being congruent in both groups. While investigating the impact on the workers who had used chain saws, it might be difficult to examine the effect of occupational vibration independent of the noise load. Nevertheless, this study suggests the possibility that a decrease in the maintenance of postural balance has a stronger relationship with exposure to thumping vibration in the past than with the age factor.

Adult↗

A new postural balance control system for rehabilitation training based on virtual cycling.

A new rehabilitation training system was developed to improve postural balance control by combining virtual reality technology with an unfixed bicycle. Twenty healthy subjects participated in the present study by riding the virtual cycling system under two different conditions: with or without visual feedback. Data were collected on the following parameters: path deviation, cycling velocity, etc. As a result of conducting the repeated training, results showed improvement not only in the ability to control balance and weight shift but also in the overall cycling ability including the degree of path deviation and the cycling speed. It was concluded that the system was effective as a training device and, in addition, the technology might have a wider applicability to the rehabilitation field.

Adult↗

The effect of activity history and current activity on static and dynamic postural balance in older adults.

The purpose of this study was to investigate the effects of former athleticism and current activity status on static and dynamic postural balance in older adults. Fifty-six subjects participated in four study groups including former athletes, currently active (AA; n = 15; 69.1+/-4.4 years.; 77.8+/-9.8 kg), former athletes, currently inactive (AI; n = 12; 66.7 years.; 87.2+/-15.1 kg), controls currently active (CA; n = 14; 68.6 +/- 4.5 years.; 73.9+/-15 kg), and controls currently inactive (CI; n = 15; 72.8+/-4.8 years; 81.1+/-14.8). All subjects were tested for height, weight, flexibility, thigh circumference, and static (sharpened Romberg/unipedal stance), and dynamic (step length and width) balance tests. The sharpened Romberg (eyes open) test showed that AA (60.0+/-0 s) and CA (59.4+/- 0.5 s) balanced significantly longer than AI (41.5+/-7.2 s), and CI (41.8+/-6.1 s) (p<0.05). The unipedal (eyes open) test balance scores for AA, CA, AI, and CI were respectively 40.0+/-4.5, 55.1+/- 3.4, 33.0+/-7.1, and 27.5+/-6.1 s, with CA significantly better than CI (p<0.05). In dynamic balance AA and CA (746.1+/-28.0 and 724.6+/-24.3 mm) showed significantly longer step lengths (p<0.05) than CI (643.7+/-26.5 mm). The eyes closed test results for relative group comparisons were similar. Overall, two-way analysis of variance showed a significant activity main effect for all dependent variables measured (p<0.05). The results indicated that current activity status plays a key role on balance performance in older adults. Furthermore, former athletic activity history provides no protection for the age related onset of postural imbalance.

Aged↗

A new rehabilitation training system for postural balance control using virtual reality technology.

A new rehabilitation training system, designated as a virtual cycling system, was developed to improve postural balance control by combining virtual reality (VR) technology with a bicycle. Several parameters including path deviation, path deviation velocity, cycling time, and head movement were extracted and evaluated to quantify the extent of control. The system was effective as a training device and, in addition, the technology might have a wider applicability to the rehabilitation field.

Adult↗

Calf muscle-tendon properties and postural balance in old age.

We tested the hypothesis that compromised postural balance in older subjects is associated with changes in calf muscle-tendon physiological and mechanical properties. Trial duration and center of pressure (COP) displacements were measured in 24 younger (aged 24+/-1 yr), 10 middle-aged (aged 46+/-1 yr), and 36 older (aged 68+/-1 yr) healthy subjects under varying levels of postural difficulty. Muscle-tendon characteristics were assessed by dynamometry, twitch superimposition, and ultrasonography. In tandem and single-leg stances, trial duration decreased (<or=65% lower, P<0.001) and COP displacements increased (<or=90% higher, P<0.05) with age. Muscle strength, size, activation capacity, and tendon mechanical properties decreased with age by 55, 13, 13, and 36-48%, respectively (P<0.05). Regressions with these parameters and balance indexes were significant (P<0.05) for single-leg and tandem (0.69<r2<0.90) postures only, indicating that the age-related changes in muscle-tendon characteristics may explain the majority of the variance in balance performance during tasks more difficult than habitual bipedal stance.

Accidental Falls↗

Prenatal exposure to alcohol affects the ability to maintain postural balance.

Prenatal exposure to alcohol is known to affect gross motor functioning. Animal studies have shown that balance is particularly affected, and there is some evidence that similar deficits exist in alcohol-exposed children. In the current study, postural balance, or the ability to maintain equilibrium, was assessed in a group of alcohol-exposed children (ALC group; n = 11) and controls (NC group; n = 11) individually matched for age and sex. Balance was measured across six conditions designed to systematically manipulate or eliminate visual or somatosensory information. Equilibrium and strategy scores for each condition and a derived composite balance score were analyzed. Although the ALC group had a lower mean composite balance score, their performance was similar to that of the NC group on all conditions where somatosensory input was reliable. However, when somatosensory input was manipulated, and when both somatosensory and visual input were inaccurate, the ALC group performed more poorly than controls. Interestingly, there were no differences between the ALC group and NC group in the type of control strategy used to maintain balance. These results suggest that alcohol-exposed children are overly reliant on somatosensory input. When this input is atypical, alcohol-exposed children display significantly greater anterior-posterior body sway and are unable to compensate using available visual or vestibular information. These deficits may be related to cerebellar anomalies previously reported in fetal alcohol syndrome children.

Adolescent↗

Objective assessment of postural balance through use of the variable resistance balance board.

The purpose of this study was to evaluate postural balance with a practical clinical assessment tool. I evaluated eight men and eight women in their 20s, using a variable resistance balance board, to determine the deviation of their average center of pressure in the anterior-posterior plane during stance. The resulting data were compared with the average center of pressure deviation of eight men in their 20s as measured by Murray et al with a force platform. The difference between the two men's groups was not statistically significant (p less than .05). These findings suggest that physical therapists may determine average center of pressure data and may assign progressive balance tasks that match any patient's level of center of pressure control.

Adult↗

[Postural balance following stroke: towards a disadvantage of the right brain-damaged hemisphere].

In the light of studies published in the last ten years, we have suspected a differential influence of the sides of hemispheric cerebral lesions on posture and balance. A study was aimed at verifying this hypothesis, the method of which being original because many possible confounding factors such as age, sex as well as topography and size of the brain lesion have been taken into account in the statistical analysis. Inclusion criteria were: right-handed patients, first stroke, no previous disease which might have affected balance. Their postural abilities (ranging from 0 to 36) were assessed 90 +/- 3 days after stroke onset on a clinical scale. This clinical assessment was used here because it could be easily performed in all patients, irrespective of the severity of their impairment. Lesion locations were determined using the Atlas by Talairach and Tournoux and the number of cerebral areas altered gave an estimation of the lesion size. The first fifty patients consecutively admitted to rehabilitation and responding to the inclusion criteria were thus examined (25 with a right and 25 with a left hemispheric lesion; 14 women and 36 men; mean age 57.2 = yrs). The main result was lower postural performances in right brain-damaged patients than in left brain damaged patients (21.5 vs 29.4; p = 0.01). Postural abilities were also inversely related to age (r = -0.28; p = 0.04), lesion size (r = -0.41; p = 0.003) and were lower in women than in men (22.1 vs 28.8; p = 0.02). This study therefore confirms the existence of a right hemispheric dominance for postural control. The existence of inverse correlation between postural abilities and the number of omitted targets in cancellation task on one hand (r = -0.63, p < 0.001), the ipsilesional bias in line bissection on the other hand (r = -0.36; p = 0.01), argued for a relationship between the main result of this study and the well known cerebral organization of spatial information processing, based on a right hemisphere dominance for spatial attention and/or representation. The 'postural neglect' concept is discussed.

Aged↗

Effect of chronic low-level exposure to jet fuel on postural balance of US Air Force personnel.

This study used the postural stability technique to investigate the neurological effects of cumulative low-level exposure to raw JP-8 jet fuel vapor on aircraft maintenance personnel. All subjects performed two sets of four 30-second postural sway tests. The results of mean cumulative exposure levels (in parts per million +/- standard error of mean) were the following: naphthas, 1308 +/- 292; benzene, 21.2 +/- 5.7; toluene, 23.8 +/- 6.1; and m-,o-, p-xylene, 22.7 +/- 5.4. Covariate adjusted regression analysis of the exposed group data showed a statistically significant association (P < 0.05) between the solvents (benzene, toluene, and xylene) and increased postural sway response. For all solvent exposures, the "eyes closed, on foam" test provided the strongest association between sway length and JP-8 benzene (r2 range, 0.45 to 0.52), implying subtle influence on vestibular/proprioception functionalities.

Adult↗

Subthalamic nucleus lesions are neuroprotective against terminal 6-OHDA-induced striatal lesions and restore postural balancing reactions.

Inactivation of the subthalamic nucleus (STN) by deep brain stimulation or lesioning can ameliorate symptoms in Parkinson' disease (PD) and may alter the underlying progressive degenerative process. We evaluated the effects of STN lesions in a terminal lesion model of PD in rats. Multiple intrastriatal 6-OHDA injections (4 x 7 microg) resulted in a partial loss of striatal TH-positive innervation (-30 to -40%) and nigral dopaminergic neurons (-60%), which was associated with behavioral deficits as observed in drug-induced rotational asymmetry, side-stepping, and postural balancing reactions. Unilateral ibotenic acid lesions of the STN did produce a 50-60% loss of STN neurons based on stereological analysis, which did not induce a functional impairment in rotational asymmetry or spontaneous sensorimotor behaviors. When STN lesions were performed 1 week prior to the 6-OHDA terminal striatal lesions, a significant rescue effect (+23%) on nigral dopaminergic neurons against terminal 6-OHDA neurotoxicity could be demonstrated, whereas striatal TH-positive fiber loss was not attenuated in these animals. In addition, animals with combined STN and striatal lesions exhibited a significant recovery in postural balancing reactions induced by 6-OHDA terminal lesions and did not show a significant impairment in any of the other behavioral parameters examined. Taken together, STN lesions can exert neuroprotective effects on nigral dopamine neurons in a partial lesion model of PD which result in recovery of spontaneous sensorimotor behavior. These findings may therefore provide new insights into the functional interaction between the glutamatergic and the dopaminergic neurotransmitter systems and foster novel therapeutic concepts for the early and middle phases of Parkinson's disease.

Animals↗

Changes in postural balance in frail elderly women during a 4-week visual feedback training: a randomized controlled trial.

BACKGROUND: Balance training programs have not shown consistent results among older adults, and it remains unclear how different training methods can be adapted to frail elderly people. OBJECTIVE: The purpose of this study was to investigate the effects of a 4-week visual feedback-based balance training on the postural control of frail elderly women living in residential care homes. METHODS: Elderly women of two residential care facilities were randomized to an exercise group (EG, n = 20) and to a control group (CG, n = 7). The EG participated in training sessions three times/week for 4 weeks. The exercises were carried out with a computerized force platform with visual feedback screen. The dimensions of balance function studied were standing body sway, dynamic weight shifting, and Berg Balance Scale performance. RESULTS: The EG showed significant improvement in balance functions. The performance time in dynamic balance tests improved on average by 35.9% compared with a 0.6% increase in the CG (p = 0.025-0.193). The performance distance in these tests decreased on average by 28.2% in the EG as compared with a 9.8% decrease seen in the CG. The Berg Balance Scale performance improved by 6.9% compared with a 0.7% increase in the CG (p = 0.003). The standing balance tests in the more demanding standing positions showed improvements in the EG, whereas similar changes in the CG were not found. CONCLUSIONS: Our findings suggest that balance training based on visual feedback improves the balance control in frail elderly women living in residential care, also enhancing the performance of functional balancing tasks relevant to daily living. The subjects were motivated to participate in the training, as indicated by the high compliance (97.5%) with the program.

Aged↗

Influence of visual blur on object-motion detection, self-motion detection and postural balance.

We have compared the influence of visual blurring (either by use of plastic foils or by plus lenses) on detection of object-motion and self-motion, and on visual control of postural balance. Three experiments were performed--in all of which object-motion and self-motion detection latencies (response times) and postural sway (sway path) increased with increasing visual blurring. We conclude that visual blurring either by foils or by glasses affects object- and self-motion perception and postural sway in a similar way.

Attention↗

A prospective study of postural balance and risk of falling in an ambulatory and independent elderly population.

BACKGROUND: An ability to predict risk of future falling is needed in order to target high-risk individuals for preventive intervention. The purpose of this study was to compare the ability of different measures of postural balance to predict risk of falling prospectively in an ambulatory and independent elderly population. METHODS: Balance tests were performed on 100 volunteers (aged 62-96), and falling was then monitored prospectively over a one-year period. The balance testing comprised measurements of: (a) spontaneous postural sway, (b) induced anterior-posterior sway, (c) induced medial-lateral sway, (d) anticipatory adjustments preceding volitional arm movements, (e) timed one-leg stance, and (f) performance on a clinical balance assessment scale. Small pseudorandom platform motions were used to perturb balance in the induced-sway tests. Using force plates, the spontaneous- and induced-sway responses were quantified in terms of the amplitude, speed, and mean frequency of the center-of-pressure displacement; input-output models were also used to parameterize the induced-sway performance. RESULTS: Although a number of measures showed evidence of significant differences between fallers and nonfallers, the differences were most pronounced for measures related to the control of lateral stability. Lateral spontaneous-sway amplitude (blindfolded conditions) was found to be the single best predictor of future falling risk, particularly for the large group of falls that were precipitated by a biomechanical perturbation. This measure was able to predict future falling risk with moderate accuracy, even in those individuals with no recent history of falling. CONCLUSIONS: The results suggest that control of lateral stability may be an important area for fall-preventative intervention. The ability of a simple and safe force-plate measure of spontaneous postural sway to predict future falling risk suggests a possible clinical application as a preliminary screening tool for risk of falling.

Accidental Falls↗