Visual contributions to postural stability in older adults

BACKGROUND: With advancing age, there is a generalized reduction in visual functioning which has been associated with impaired postural stability and increased risk of falls. However, little is known about which visual abilities are the most important in the control of postural sway when standing. OBJECTIVE: To determine whether specific visual abilities predict stability when standing on firm and compliant surfaces. METHODS: Tests of visual function, peripheral sensation, strength, reaction time and sway were administered to 156 community-dwelling men and women aged 63-90 years. The visual tests included high- and low-contrast visual acuity, contrast sensitivity, depth perception, stereopsis and lower visual field size. Postural sway was measured with eyes open on a firm and a compliant foam rubber surface. RESULTS: On the firm surface, sway was significantly associated with only one sensorimotor measure: proprioception in the lower limbs. In contrast, on the compliant surface, sway was associated with all of the visual measures, quadriceps strength and reaction time. Multiple regression analysis revealed that contrast sensitivity, stereopsis and quadriceps strength were significant independent predictors of total sway when subjects stood on the compliant surface. CONCLUSION: The study findings confirm the importance of vision, in particular contrast sensitivity and stereopsis, in the control of posture under challenging conditions, and suggest some mechanisms for the association between impaired vision and falls in older people.     

The effects of repetitive haemarthrosis on postural balance in children with haemophilia

Sensory information from visual, vestibular and proprioceptive systems is necessary to control posture and balance. Impairment in proprioception due to repetitive joints bleeding may lead to a deficit in postural balance which, in turn, leads to high joint stress and risk of bleeding recurrence. Despite the increase in attention in this field during the past few years, the data concerning to how bleeds can affect postural control in children with haemophilia (CWH) remain scarce. This study aimed to evaluate the postural balance in CWH. Twenty CWH Haemophilia Group (HG) and 20 age‐matched children Control Group (CG) were recruited to this study. A force plate was used to record centre of pressure (COP) displacement under four different postural conditions during quiet standing: eyes open on firm surface, eyes open on foam surface, eyes closed on firm surface and eyes closed on a foam surface. Variables of COP as sway area and mean velocity and in anterior–posterior (y) medio‐lateral (x) direction were processed and for each variable sensory, quotients were calculated and compared between groups. No differences were found in visual and vestibular quotients variables between groups. A higher value was found in sway area variable on proprioception quotient in the HG when compared with CG (P = 0.042). CWH with repetitive joint bleed on lower limbs showed differences in postural balance when compared with non‐haemophiliac children. The identification of early balance impairments in CWH can help us understand better the effects of bleeds inside joints on postural control and plan a more effective preventive and rehabilitative treatment.     

Trunk sway measures of postural stability during clinical balance tests: effects of age.

BACKGROUND: The major disadvantage of current clinical tests that screen for balance disorders is a reliance on an examiner's subjective assessment of equilibrium control. To overcome this disadvantage we investigated, using quantified measures of trunk sway, age-related differences of normal subjects for commonly used clinical balance tests. METHODS: Three age groups were tested: young (15-25 years; n = 48), middle-aged (45-55 years; n = 50) and elderly (65-75 years; n = 49). Each subject performed a series of fourteen tasks similar to those included in the Tinetti and Clinical Test of Sensory Interaction in Balance protocols. The test battery comprised stance and gait tasks performed under normal, altered visual (eyes closed), and altered proprioceptive (foam support surface) conditions. Quantification of trunk sway was performed using a system that measured trunk angular velocity and position in the roll (lateral) and pitch (fore-aft) planes at the level of the lower back. Ranges of sway amplitude and velocity were examined for age-differences with ANOVA techniques. RESULTS: A comparison between age groups showed several differences. Elderly subjects were distinguished from both middle-aged and young subjects by the range of trunk angular sway and angular velocity because both were greater in roll and pitch planes for stance and stance-related tasks (tandem walking). The most significant age group differences (F = 30, p <.0001) were found for standing on one leg on a normal floor or on a foam support surface with eyes open. Next in significance was walking eight tandem steps on a normal floor (F = 13, p <.0001). For gait tasks, such as walking five steps while rotating or pitching the head or with eyes closed, pitch and roll velocity ranges were influenced by age with middle-aged subjects showing the smallest ranges followed by elderly subjects and then young subjects (F = 12, p <.0001). Walking over a set of low barriers also yielded significant differences between age groups for duration and angular sway. In contrast, task duration was the only variable significantly influenced when walking up and down a set of stairs. An interesting finding for all tasks was the different spread of values for each population. Population distributions were skewed for all ages and broadened with age. CONCLUSIONS: Accurate measurement of trunk angular sway during stance and gait tasks provides a simple way of reliably measuring changes in balance stability with age and could prove useful when screening for balance disorders of those prone to fall.     

Altered postural control during the luteal phase in women with premenstrual symptoms

The purpose of this study was to investigate postural control in women with and without premenstrual symptoms (PMS) in three hormonally verified phases of the menstrual cycle. Thirty-two women were recruited to participate in the study and 25 of these women were included in the results. Menstrual cycle phases were determined by sex hormone analyses in serum and LH detection in urine. A prospective rating of PMS was used to divide the subjects into two groups: one with PMS (cyclic) and one without (non-cyclic). For measurement of postural control, subjects stood on a force platform (AMTI) in two-legged stance (eyes open and closed) and one-legged stance (eyes open and closed). There were no significant differences in the two-legged stance between the phases of the menstrual cycle or between groups. In one-legged stance with eyes open, there was a significant increase in postural displacement in the mid-luteal phase in the cyclic group, but no differences were detected between phases in the non-cyclic group. These findings may be related to the previously reported increased injury rate and psychomotor slowing in the luteal phase in women with PMS.     

Influence of the visual environment on the postural stability in healthy older women

BACKGROUND: A poor postural stability in older people is associated with an increased risk of falling. It is recognized that visual environment factors (such as poor lighting and repeating patterns on escalators) may contribute to falls, but little is known about the effects of the visual environment on postural stability in the elderly. OBJECTIVE: To determine whether the postural stability of older women (using body sway as a measure) differed under five different visual environment conditions. METHODS: Subjects were 33 healthy women aged 65-76 years. Body sway was measured using an electronic force platform which identified the location of their centre of gravity every 0.05 s. Maximal lateral sway and anteroposterior sway were determined and the sway velocity calculated over 1-min trial periods. Body sway was measured under each of the following conditions: (1) normal laboratory lighting (186 lx); (2) moderate lighting (10 lx); (3) dim lighting (1 lx); (4) eyes closed, and (5) repeating pattern projected onto a wall. RESULTS: Each measure of the postural stability was significantly poorer in condition 4 (eyes closed) than in all other conditions. Anteroposterior sway was greater in condition 3 than in conditions 1 and 2, whilst the sway velocity was greater in condition 3 than in condition 2. Lateral sway did not differ significantly between different lighting levels (conditions 1-3). A projected repeating pattern (condition 5) did not significantly influence the postural stability relative to condition 1. CONCLUSIONS: The substantially greater body sway with eyes closed than with eyes open confirms the importance of vision in maintaining the postural stability. At the lowest light level, the body sway was significantly increased as compared with the other light levels, but was still substantially smaller than on closing the eyes. A projected repeating pattern did not influence the postural stability. Dim lighting levels and removing visual input appear to be associated with a poorer postural stability in older people and hence might be associated with an increased risk of falls.     

Timed stance performances reflect differences in age,prevalence of comorbidities,medication use,fall history and activity level: Early screening for balance loss is indicated

Objectives: To determine if 10‐second trials of bilateral and one‐legged stance measures detected balance loss and influence of known risk factors for falls in women aged 20–80 years. Methods: 456 healthy adult women attempted 10‐second trials of bilateral stance (firm and foam surfaces) and one‐legged stance, with eyes open (EO) and eyes closed (EC). Data for age, co‐morbidities, medication use, fall history and activity level were compared for three categories of stability: (i) stable: all trials completed; (ii) unsteady: completed/failed one to two trials; and (iii) failed all trials. Results: Bilateral stance on foam (EC) and one‐legged stance (EO) yielded low failure rates for women older than 50 years (up to 15% categorised as unsteady and 6% as unstable). Compared to stable women, the unsteady and unstable women were older (P < 0.001) reported more co‐morbidities, using more medications (P < 0.001), more falls (P < 0.05) and less activity (P < 0.05). Conclusions: Women older than 50 years who fail 10‐second trials of bilateral stance (foam EC) and one‐legged stance (EO) should be referred for education and fall prevention intervention.     

Balance impairments in individuals with symptomatic knee osteoarthritis: a comparison with matched controls using clinical tests

OBJECTIVES: To compare balance in individuals with symptomatic knee osteoarthritis (OA) and in age-, gender- and body-mass-matched controls using simple clinical measures. METHODS: Thirty-three people with OA and 33 controls participated. Static postural sway [antero-posterior (AP), lateral and total] was measured using a swaymeter on two different surfaces and under two visual conditions. Dynamic standing balance was assessed using the 'step test'. RESULTS: Both groups displayed similar postural sway on most variables measured. Significantly greater sway was noted in the OA group on a firm surface in both lateral (eyes open) and AP directions (eyes closed), as well as total sway (eyes closed) (P < 0.05). Poorer dynamic standing balance was observed in the OA group as evidenced by the step test (P < 0.0001). CONCLUSIONS: Balance deficits can be identified in the osteoarthritic population using simple, inexpensive measures. However, the clinical relevance of the small deficits identified remains unknown and warrants further investigation.     

Sensory interaction on static balance: A comparison concerning the history of falls of community-dwelling elderly

Aim:   To determine whether elderly subjects with distinct histories of falls presented differences concerning the influence of sensory interaction on balance.
Methods:   Cross-sectional research. Ninety-six community-dwelling elderly subjects were divided into three groups, according to the history of falls within the past year (group 1, no falls; group 2, one fall; and group 3, recurrent falls). The Clinical Test of Sensory Interaction and Balance was used to evaluate the influence of sensory inputs on standing balance. The test required the subject to maintain stability during 30 s, under six conditions: (i) firm surface with eyes open; (ii) firm surface with eyes closed; (iii) firm surface with visual conflict; (iv) unstable surface with eyes open; (v) unstable surface with eyes closed; and (vi) unstable surface with visual conflict. The time expended on conditions and the number of abnormal cases were compared between groups. Each group was evaluated in relation to its performance in the progression of conditions.
Results:   More abnormal cases occurred in group 3 compared to group 1 for conditions (iv) and (v); and compared to group 2 for condition (iv). Group 3 remained less time than group 1 under conditions (iv), (v) and (vi). Groups 1, 2 and 3 presented relevant decrements in trial duration from conditions (iv) to (v). For group 3, a significant decay was also noted from condition (i) to (ii).
Conclusion:   Sensorial interaction in the elderly varies according to their history of falls. Thus, it is possible to correctly guide the rehabilitation process and to prevent sensorial decays according to an individual's history of falls.     

The relationship between hippocampal volume and static postural sway: results from the GAIT study

The role of the hippocampus in postural control, in particular in maintaining upright stance, has not been fully examined in normal aging. This study aims to examine the association of postural sway with hippocampal volume while maintaining upright stance in healthy older individuals. Seventy healthy individuals (mean age 69.7 ± 3.4 years; 41.4 % women) were recruited in this study based on cross-sectional design. Hippocampal volume (quantified from a three-dimensional T₁-weighted MRI using semi-automated software), three center of pressure (COP) motion parameters (sway area, path length of anterior-posterior (AP) and medial-lateral (ML) displacement) while maintaining upright stance (eyes open and closed), and the relative difference between open and closed eye conditions were used as outcome measures. Age, sex, body mass index, lower limb proprioception, distance vision, 15-item geriatric depression scale score, total cranial volume, and white matter abnormalities were used as covariates. The sway area decreased from open to closed eye condition but this variation was non-significant (P = 0.244), whereas path length of AP and ML displacement increased significantly (P < 0.003). Increase in sway area from open to closed eyes was associated with greater hippocampal volume (β ?18.21; P = 0.044), and a trend for an association of increase in path length of AP displacement (P = 0.075 for open eyes and P = 0.071 for closed eyes) with greater hippocampal volume was reported. The hippocampus is involved in upright postural control in normal aging, such that an increase in sway area of COP motion from open to closed eyes is associated with greater hippocampal volume in healthy older adults.     

Effects of a physical activity program on postural stability in older people

BACKGROUND AND AIMS: The objective of this non-randomized study was to determine the influence of a specific physical activity program on the postural stability of older people. METHODS: Seventy-four subjects (72.4 +/- 0.7 yrs) participated in an individualized three-month physical activity program designed to improve posture, balance and mobility--the PBM program. Sessions were held twice weekly. Postural stability was assessed using a force platform, subjects being in static and dynamic conditions, and with open and closed eyes. Changes in stabilometric parameters (Sway area, ML mean, AP mean, Total length, ML length and AP length) of the intervention group were compared to those of 14 control subjects (71.8 +/- 1.5 years). RESULTS: A two-way analysis of variance with repeated measures did not show any significant post-program change in postural stability in the hard floor condition. In contrast, Sway area (p < 0.0005), Total length (p < 0.001) and AP length (p < 0.01) were significantly reduced after the training program in the foam floor condition, with open and closed eyes. In addition, in the medio-lateral axis condition and with closed eyes, AP length in the intervention group was significantly reduced (p < 0.01), and in the antero-posterior axis condition with both open and closed eyes, Sway area (p < 0.0005), Total length (p < 0.0005) and AP length (p < 0.05) decreased significantly. CONCLUSIONS: As shown by the results in the foam floor and dynamic conditions, our individualized physical activity program improved the postural stability of older people when the standing position was challenged. However, the lack of significant results for the hard floor condition suggests that three months is not sufficient to improve static balance. The PBM physical activity program can be used for balance training in older people, but further studies are required to determine the time needed to effect improvements in static balance in this population.     

Posturographic analysis of balance control in patients with haemophilic arthropathy

Summary.  Musculoskeletal disorders in haemophiliacs represent the highest percentage of lesions, giving rise to haemophilic arthropathy (HA) which predominantly affects lower limbs, influencing postural control, standing and walking. Leading a sedentary lifestyle seems to influence strength and muscular resistance in haemophiliacs which, in turn, are related to articular stability and the prevention of articular degenerative processes. The objective of this work was to study alterations in balance to subsequently evaluate the appropriate therapeutics and how this influences the development of arthropathy. Twenty-five haemophiliacs with HA, 25 haemophiliacs without HA (NHA) and 25 healthy control subjects (CTL) took part in this study. Tests were performed on a force platform and the subjects remained as still as possible for 30 s under different conditions: (i) bilateral stance with eyes open; (ii) bilateral stance with eyes closed; (iii) right unilateral stance; and (iv) left unilateral stance. The results of these tests indicated significant differences ( P  < 0.05) between the groups HA, NHA and CTL. The HA group presented worse results for both unilateral and bilateral stance when compared with the other two cohorts. Surprisingly, the NHA group displayed a worse balance than the controls. A single calculated parameter (mean frequency) did not show significant differences. This apparently indicates the absence of pathology in the nervous system in relation to postural control. The results suggest that our patients should participate in physical exercise programmes, rehabilitation and physiotherapy to improve their postural control.     

Lateral stability, sensorimotor function and falls in older people.

AIMS: To design simple tests of lateral stability for assessing balance in older people and to determine whether poor performances in these tests are associated with impaired vision, lower limb sensation, quadriceps strength, simple reaction time, and falling in this group. DESIGN: A cross-sectional and retrospective study. SETTING: Falls and Balance Laboratory, Prince of Wales Medical Research Institute. PARTICIPANTS: One hundred fifty-six community-dwelling men and women aged 63-90 years (mean age 76.5, SD = 5.1). OUTCOME MEASURES: The maximal lateral sway in a near-tandem stability test with eyes open and closed and the necessity of taking a protective step in the near-tandem stability test with eyes closed. RESULTS: All 156 subjects could complete the near-tandem stability test with eyes open, but only 99 subjects (63.5%) could undertake the test with eyes closed without taking a protective step. Subjects with a history of falls had increased lateral sway both with eyes open and eyes closed as well as poorer visual acuity, proprioception, and quadriceps strength. Fallers were also significantly more likely to take a protective step when undertaking the near-tandem stability test with eyes closed. Multiple regression analysis revealed that impaired lower limb proprioception, quadriceps strength, and reaction time were the best predictors of increased maximal sway in the near-tandem stability test with eyes open. Reduced proprioception and quadriceps strength, in addition to age, were also found to be the best determinants of the necessity of taking a protective step in the near-tandem stability test with eyes closed. CONCLUSIONS: The study findings identify simple new tests that are associated with falling in older people and elucidate the relative importance of specific physiological systems in the maintenance of lateral stability.     

Mechanisms of Postural Control in Alcoholic Men and Women: Biomechanical Analysis of Musculoskeletal Coordination During Quiet Standing

Background: Excessive sway during quiet standing is a common sequela of chronic alcoholism even with prolonged sobriety. Whether alcoholic men and women who have remained abstinent from alcohol for weeks to months differ from each other in the degree of residual postural instability and biomechanical control mechanisms has not been directly tested. Method: We used a force platform to characterize center‐of‐pressure biomechanical features of postural sway, with and without stabilizing conditions from touch, vision, and stance, in 34 alcoholic men, 15 alcoholic women, 22 control men, and 29 control women. Groups were matched in age (49.4 years), general intelligence, socioeconomic status, and handedness. Each alcoholic group was sober for an average of 75 days. Results: Analysis of postural sway when using all 3 stabilizing conditions versus none revealed diagnosis and sex differences in ability to balance. Alcoholics had significantly longer sway paths, especially in the anterior–posterior direction, than controls when maintaining erect posture without balance aids. With stabilizing conditions the sway paths of all groups shortened significantly, especially those of alcoholic men, who demonstrated a 3.1‐fold improvement in sway path difference between the easiest and most challenging conditions; the remaining 3 groups, each showed a ～2.4‐fold improvement. Application of a mechanical model to partition sway paths into open‐loop and closed‐loop postural control systems revealed that the sway paths of the alcoholic men but not alcoholic women were characterized by greater short‐term (open‐loop) diffusion coefficients without aids, often associated with muscle stiffening response. With stabilizing factors, all 4 groups showed similar long‐term (closed loop) postural control. Correlations between cognitive abilities and closed‐loop sway indices were more robust in alcoholic men than alcoholic women. Conclusions: Reduction in sway and closed‐loop activity during quiet standing with stabilizing factors shows some differential expression in men and women with histories of alcohol dependence. Nonetheless, enduring deficits in postural instability of both alcoholic men and alcoholic women suggest persisting liability for falling.     

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.     

The impact of obesity on balance control in community-dwelling older women

Older individuals have impaired balance control, particularly those that are frail and/or have sensory deprivations. Obese individuals show faster body sway during upright stance than normal weight individuals, suggesting that they also have difficulty controlling balance even if they do not have the same sensory issues as the older people. Therefore, the objective of this study was to examine if obesity is associated to a decreased balance control in older women. Postural sway of normal weight (n?=?15, age?=?70.8?±?5.5 years; BMI?=?22.2?±?1.9 kg/m²), overweight (n?=?15, age?=?71.7?±?4.3 years; BMI?=?27.3?±?1.3 kg/m²), and obese (n?=?15, age?=?71.1?±?4.3 years; BMI?=?33.1?±?3.4 kg/m²) women was measured with a force platform for normal quiet stance lasting for 30 s in opened and closed eyes conditions. The obese group oscillated at a faster speed than the normal weight group (vision 0.99?±?0.29 cm/s vs. 0.70?±?0.16 cm/s, p?<?0.01; no vision 1.43?±?0.50 cm/s vs. 0.87?±?0.23 cm/s, p?<?0.01). The obese group exhibited greater range in both axes without vision compared to the normal weight group (p?<?0.05). When observing sway density parameters, the obese group also spent less time in stability zones (2 mm radius area in which the center of pressure is relatively stable), and the distance between these stability zones are greater than the normal weight group in both visual conditions (p?<?0.01 and p?<?0.05, respectively). Obesity clearly affects postural control in older women. Our results suggest that obesity has a negative impact on the capacity of older woman to adequately use proprioceptive information for posture control. As postural instability or balance control deficits are identified as a risk factor for falling, our results also suggest that obesity in older women could be considered as another potential contributing factor for falling.     

Postural stability in school-age children with mild bronchial asthma disease (a pilot study)

Objective: This study assessed the postural stability in children with asthma using balance tests under conditions of a comfortable foot placement and with a foot placement provoking instability. Methods: A group of 10 school children from 8 to 10 years old with mild intermittent asthma and 10 healthy children of the same age range performed four balance tests in a randomized order: preferred stance, adjusted stance, and tandem stance each under both conditions of eyes opened (EO) and eyes closed (EC), as well as a one-legged stance with eyes-opened conditions. To determine postural stability, the center of pressure (CoP) movement was recorded. Basic stabilographic parameters were calculated: CoP velocity in the anterior–posterior direction, CoP velocity in the medial–lateral direction, and the total CoP velocity. Results: Statistically significant differences between the groups were found only for the one-legged stance. Significantly greater anterior–posterior CoP velocity (p?=?0.05) and total CoP velocity (p?=?0.03) were found in children with asthma when standing on the preferred foot. A significantly greater medial–lateral velocity (p?=?0.02) was also found in the non-preferred foot of children with asthma. Conclusions: We can conclude that standing on one leg might be an appropriate test with which to identify balance differences between young children with mild intermittent asthma and healthy children.     

Long-term exercise and its effect on balance in older, osteoarthritic adults: results from the Fitness, Arthritis, and Seniors Trial (FAST)

OBJECTIVES: To examine the effects of 18-month aerobic walking and strength training programs on static postural stability among older adults with knee osteoarthritis. DESIGN: Randomized, single-blind, clinical trial of therapeutic exercise. SETTING: Both center-based (university) and home-based. PARTICIPANTS: A cohort of 103 older adults (age = 60 years) with knee osteoarthritis who were participants in a large (n = 439) clinical trial and who were randomly assigned to undergo biomechanical testing. INTERVENTION: An 18-month center- (3 months) and home-based (15 months) therapeutic exercise program. The subjects were randomized to one of three treatment arms: (1) aerobic walking; (2) health education control; or (3) weight training. MEASUREMENTS: Force platform static balance measures of average length (Rm) of the center of pressure (COP), average velocity (Vel) of the COP, elliptical area (Ae) of the COP, and balance time (T). Measures were made under four conditions: eyes open, double- and single-leg stances and eyes closed, double- and single-leg stances. RESULTS: In the eyes closed, double-leg stance condition, both the aerobic and weight training groups demonstrated significantly better sway measures relative to the health education group. The aerobic group also demonstrated better balance in the eyes open, single-leg stance condition. CONCLUSIONS: Our results suggest that long-term weight training and aerobic walking programs significantly improve postural sway in older, osteoarthritic adults, thereby decreasing the likelihood of larger postural sway disturbances relative to a control group.     

Age-related differences in the effect of a perceived threat to stability on postural control

BACKGROUND: Studies indicate that the strategy for postural control may be affected by psychological factors, and that young adults respond to perceived threat to stability by increasing their ankle stiffness. The objective of this study was to compare the postural control strategy adopted by young and old adults when faced with postural threat induced by manipulating surface height. METHODS: Sixty elderly (mean age 77.5+/-4.4 years) and 20 young volunteers (mean age 21.5+/-3.7 years) participated in the study. Movement of the center of pressure (COP) was recorded for 60 seconds with a portable force-plate, as participants stood with eyes open and closed, both at ground level and 85 cm above ground level. Analysis of variance and Tukey-Kramer tests were conducted to determine the effects of age, postural threat, and vision on mean power frequency (MPF), on amplitude variability both in the anterior-posterior (AP) and medio-lateral (ML) directions, and on mean COP sway velocity, with the significance level set at p=.05. RESULTS: Postural threat did not affect COP measures for the young adults, whereas it induced greater changes in MPF in the AP and ML directions in the elderly participants. A similar trend was observed in the elderly group for amplitude variability in the ML direction and for mean COP sway velocity. CONCLUSIONS: In comparison with young adults, elderly adults tend to have an exaggerated postural response to conditions that are perceived as threatening to stability. This response involves primarily increases in MPF, with limited compensatory decreases in amplitude variability observed only in the ML direction.     

Visual acuity and contrast sensitivity in relation to falls in an elderly population.

Visual acuity and contrast sensitivity were measured in 95 residents of a hostel for the aged (mean age = 83 years) using a dual-contrast letter chart and the Melbourne Edge Test (MET). Vision (as measured by visual acuity, the MET, low-contrast visual acuity, and difference between high- and low-contrast acuity) decreased significantly with age and all four measures were significantly correlated. Subjects with a clinical eye disorder had poorer vision than those without a disorder although the differences were not significant. Visual acuity and contrast sensitivity were not associated with body sway when subjects were standing on a firm base. However, when the subjects were placed in a situation which provided reduced support (standing on a compliant surface), body sway was associated with poor visual acuity and contrast sensitivity. There was also a difference in contrast sensitivity between those who fell one or more times in a year of follow-up and those who did not fall. It appears that reduced vision may be a predisposing factor to postural imbalance and falls in elderly persons.     

Interaction between attention demanding motor and cognitive tasks and static postural stability

BACKGROUND: Due to the often-reported decrease in postural stability in the elderly, it is important to understand factors that may contribute to reduced postural stability. It is possible that attention-demanding focal tasks performed concurrent with postural regulation influence postural stability. OBJECTIVE: This study utilized dual-task methodology to determine if motor or cognitive focal tasks interact with center of pressure (COP) excursion during static bipedal stance in healthy young and healthy elderly subjects (n = 18). METHODS: The cognitive task involved silently solving an orally-presented multi-step arithmetic problem over a 30-second period. The motor task was a 30-second bilateral static finger-thumb pinch task performed at 10% of maximal voluntary contraction with a pair of pinch-force transducers. Each focal task was performed separately, and in a condition in which both tasks were performed simultaneously. COP excursion was compared in quiet standing (no focal task) and during performance of the focal tasks with full vision and with vision occluded. RESULTS: Performance on the focal tasks was unaffected by increased postural demands during stance as compared to a seated baseline condition. This was the case for both age groups, and for the full vision and occluded vision conditions. Medio-lateral COP excursion was reduced over the quiet standing pretest condition when attentional focus was on the cognitive task, suggesting that COP was influenced centrally during cognition. In contrast, COP excursion increased over the quiet standing pretest condition when performing the motor focal task, suggesting a reduced ability to suppress sway when the motor system was concurrently occupied with a voluntary task that shared the same input-output resources. CONCLUSION: The ability to share attentional resources among focal and postural tasks was similar in healthy young and elderly subjects.