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PubMed1990

Postural control in elderly subjects.

The postural stability of 23 subjects aged 85 years or over was studied with a force platform. The sensory function of the lower limbs was disturbed with small vibrators placed on both calf muscles and/or by placing the subjects on a platform covered with foam plastic. When compared with a group (n = 100) of 50-60-year-old subjects, the elderly subjects had significantly higher sway velocities even during nonperturbed conditions. The perturbation of muscle spindles with vibration and/or pressoreceptor function with foam plastic did not increase the postural instability of the elderly subjects. Visual deprivation had a significant effect on postural stability, and the visual influx contributed about 50% of the postural stability. Postural control is reduced as a result of loss of sensory cues of pressoreceptors and also deterioration in function of stretch reflexes initiated from muscle spindles. The very elderly seem to rely on visual control of posture; this is slow, which can be one reason for susceptibility to falls.

Age Factors↗
PubMed1998

Aging and time to instability in posture.

Two experiments are reported that were set up to examine the spatial-temporal boundaries of postural instability in upright stance as a function of age (60-96 years) and postural conditions. Subjects stood on a force platform under different experimental conditions (vision/no vision and arms up/down) so that the effect of age on key dynamic properties of postural stability could be determined. The findings showed that the ratio of the area of the motion of the center of pressure to the area within the stability boundary increased with age. Also, the virtual time-to-contact with the postural stability boundary decreased with age. Collectively, the findings show that the margins to the spatial-temporal boundaries of postural stability decrease with advancing age in the elderly. These reduced margins of dynamic stability may be a factor contributing to the progressive instability of posture with aging in the elderly.

Aged↗
PubMed1998

Inefficient postural responses to unexpected slips during walking in older adults.

BACKGROUND: Slips account for a high percentage of falls and subsequent injuries in community-dwelling older adults but not in young adults. This phenomenon suggests that although active and healthy older adults preserve a mobility level comparable to that of young adults, these older adults may have difficulty generating efficient reactive postural responses when they slip. This study tested the hypothesis that active and healthy older adults use a less effective reactive balance strategy than young adults when experiencing an unexpected forward slip occurring at heel strike during walking. This less effective balance strategy would be manifested by slower and smaller postural responses, altered temporal and spatial organization of the postural responses, and greater upper trunk instability after the slip. METHODS: Thirty-three young adults (age range=19-34 yrs, mean=25+/-4 yrs) and 32 community-dwelling older adults (age range=70-87 yrs, mean=74+/-14 yrs) participated. Subjects walked across a movable forceplate which simulated a forward slip at heel strike. Surface electromyography was recorded from bilateral leg, thigh, hip, and trunk muscles. Kinematic data were collected from the right (perturbed) side of the body. RESULTS: Although the predominant postural muscles and the activation sequence of these muscles were similar between the two age groups, the postural responses of older adults were of longer onset latencies, smaller magnitudes, and longer burst durations compared to young adults. Older adults also showed a longer coactivation duration for the ankle, knee, and trunk agonist/antagonist pairs on the perturbed side and for the knee agonist/antagonist pair on the nonperturbed side. Behaviorally, older adults became less stable after the slips. This was manifested by a higher incidence of being tripped (21 trials in older vs 5 trials in young adults) and a greater trunk hyperextension with respect to young adults. Large arm elevation was frequently used by older adults to assist in maintaining trunk stability. In an attempt to quickly reestablish the base of support after the slips, older adults had an earlier contralateral foot strike and shortened stride length. CONCLUSION: The combination of slower onset and smaller magnitude of postural responses to slips in older adults resulted in an inefficient balance strategy. Older adults needed secondary compensatory adjustments, including a lengthened response duration and the use of the arms, to fully regain balance and prevent a fall. The shorter stride length and earlier contralateral foot strike following the slip indicate use of a more conservative balance strategy in older adults.

Accidental Falls↗
PubMed2001

The interacting effects of cognitive demand and recovery of postural stability in balance-impaired elderly persons.

BACKGROUND: Although postural recovery is attentionally demanding in healthy elderly persons, an inability to recover balance due to competition for attentional resources between the postural system and a second task could contribute to falls in older adults with poor balance. This study examined the attentional demands of balance recovery from a mild postural disturbance in balance-impaired elderly persons. A second purpose of this research was to determine the effect of performing a cognitive task on the recovery of balance in balance-impaired elderly persons. METHODS: Fifteen healthy older adults and 13 older adults with clinical balance impairment were exposed to balance disturbances by means of sudden movement of a platform on which they stood. A dual-task paradigm where postural recovery served as the primary task and verbal reaction time to auditory tones served as the secondary task was used to assess attentional demand. To determine the effect of the cognitive task on postural recovery, kinetic, kinematic, and neuromuscular measures of a feet-in-place response were investigated. RESULTS: Balance recovery using a feet-in-place response was attentionally demanding in both groups of older adults and was more demanding in balance-impaired than in healthy elderly persons. With the concurrent performance of a cognitive task, balance-impaired elderly persons took longer to stabilize their center of pressure and regain balance than in a single task, while healthy elderly persons showed no change between conditions. In addition, only balance-impaired elderly individuals had a greater center-of-pressure resultant velocity during recovery in a dual-task compared with a single-task situation. CONCLUSIONS: The ability to recover balance using a feet-in-place response was more attentionally demanding in balance-impaired than in healthy elderly persons. The recovery of balance was also slower and less efficient in balance-impaired elderly persons when simultaneously performing a cognitive task, whereas the ability of healthy elderly individuals to recover was not influenced by concurrent task demands. This suggests that dual-task performance may contribute to postural instability and falls in balance-impaired elderly individuals.

Accidental Falls↗
PubMed2003

Changes in postural stability in women aged 20 to 80 years.

BACKGROUND: A study of postural stability was undertaken to identify the relationship between vision and support surface across age decades. Understanding when reliance on vision for postural stability emerges and the support conditions contributing to this instability may provide the evidence required to introduce falls-prevention strategies in younger age decades. METHODS: We measured postural stability in 453 women aged 20 to 80 years using the Balance Master force-plate system while the women performed the modified Clinical Test for the Sensory Interaction and Balance (firm and foam surfaces, eyes open and closed) and the Single-Limb Stance Test (eyes open and closed). RESULTS: Women in their 60s and 70s were more unstable than younger women in bilateral stance on a firm surface with the eyes closed. This instability was evident from the 50s when a foam surface was introduced and from the 40s when single-limb stance was tested with eyes closed. A further decline in stability was demonstrated for each subsequent decade when the eyes were closed in single-limb stance. CONCLUSIONS: Age, visual condition, and support surface were significant variables influencing postural stability in women. Reliance on vision for postural stability was evident for women from the 40s when single-limb stance was tested, from the 50s when bilateral stance on foam was tested, and from the 60s when a firm surface was used. The cause(s) of this decline in stability requires further investigation, and screening for postural instability between the ages of 40 and 60 is advocated.

Adult↗
PubMed2006

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.

Accidental Falls↗
PubMed2001

Changes in postural sway during a period of sustained wakefulness in male adults.

Nocturnal variations in postural sway during a period of sustained wakefulness were studied in seven healthy male adults. Postural sways with the subject's eyes open and with them closed were measured every hour from 22:00 to 04:00 h the following day. Parameters of postural sway [rectangle area (RA), root mean square of length in the anterior-posterior direction (RMSL-y), and medium-frequency-band (0.2-1.0 Hz) power of postural sway in the lateral (MF-x) and anterior-posterior (MF-y) directions] showed significant nocturnal variations. RA, RMSL-y, MF-x and MF-y increased after midnight and reached peaks at 04:00 h. Moreover, changes in RA and MF-y depended on visual conditions. The increases in RA and MF-y were larger with the eyes closed than with them open. These postural sway parameters showed positive correlations with subjectively rated sleepiness and negative correlations with electroencephalographic alpha activity. The results suggest that changes in postural sway during the night are influenced by the increase in sleepiness.

Activity Cycles↗
PubMed1990

Coordination of posture and movement.

Movement is performed against a background of subtle postural adjustments that counteract destabilizing forces imposed by the movement. Despite the importance of these postural adjustments to the safe and efficient performance of movement, little is known about the properties of these postural accompaniments. The purpose of this article is twofold. First, it provides a review of properties of postural adjustments that accompany a variety of limb and trunk movements. Second, a schema for the coordination of posture and movement is proposed. This schema suggests that a central nervous system model of body dynamics is essential to anticipatory control of posture during movement.

Biomechanical Phenomena↗
PubMed1997

Evaluation of postural stability in children: current theories and assessment tools.

Children with many types of motor dysfunction have problems maintaining postural stability. Because maintenance of postural stability is an integral part of all movements, therapists evaluate and treat to improve postural stability in these children. This article reviews current pediatric assessment tools for postural stability and issues affecting testing this construct in children. The tests and measurements are classified according to their testing purpose and the National Center for Medical Rehabilitation Research disablement framework, focusing on the impairment and functional limitation dimensions. Postural stability is defined from a systems perspective with tests related to the sensory, motor, and biomechanical systems described. Reliability and validity information on the measurements is discussed. Relatively few measurements of postural stability in children are available that have acceptable reliability and validity documentation. Suggestions for research on test development in this area are discussed.

Activities of Daily Living↗
PubMed1997

Postural and gait disturbance correlated with decreased frontal cerebral blood flow in Alzheimer disease.

In a group of 45 patients with Alzheimer disease (AD) and 15 control subjects, we studied the relationship between parameters showing postural and gait disturbance and regional cerebral blood flow (rCBF) measured with N-isopropyl-p-[123I]iodoam-phetamine single photon emission computed tomography at different clinical stages. Patients with AD with mild dementia exhibited only increased postural sway associated with a reduced mean value of rCBF in the cortex. At a moderate stage, the reduced mean values of rCBF in the cortex and in the frontal lobe were associated with increased postural sway and stride length variability and with decreased stride length. At a severe stage, reduced rCBF in the basal ganglia and in the frontal lobe additionally were associated with increased postural sway, double support time, and stride length variability, and with decreased walking speed and stride length. In multiple regression analysis, there was a high contribution by rCBF in the frontal lobe to account for postural and gait disturbance in AD. We propose that impaired frontal lobe circulation is an important factor causing postural and gait disturbance as AD progresses.

Aged↗
PubMed1997

Anticipatory postural adjustments in the back and leg lift.

This study examined anticipatory postural adjustments in a dynamic multi-joint action in which a relatively fast voluntary movement is being executed while balance is maintained in the field of gravity. In a bi-manual whole body lifting task, the pickup of the load induces a forward shift in the position of the center of mass, challenging the dynamic balance regulation while simultaneously impeding the ongoing extension movement. We investigated whether anticipatory postural adjustments are an addition to a voluntary motor command or an inherent component of this command. Using a global mechanical analysis of the movement, we found that anticipatory postural adjustments are present in bimanual lifting, both in back lifting and leg lifting, and that lifting technique had a significant influence on the pattern of the adjustments. If the mass of the object was reduced unexpectedly, balance was disturbed in 92% of the mass-reduced trials. These findings suggest that the anticipatory postural adjustments to be performed are specified in advance such that the expected changes in the mechanical interaction with the environment are taken into account. The observations lend support to the hypothesis that the control of the observed anticipatory postural adjustments is an integral part of the control of the lifting movement itself. Consequently, the strict dichotomy in the control of posture and movement is being questioned.

Adult↗
PubMed2000

Effects of back extensor strength training versus balance training on postural control.

PURPOSE: Aim of this study was to investigate effects of 1) regular back extensor strength training as opposed to balance training, and 2) the influence of the sequence of both training types on postural control, force, and muscle efficiency. METHODS: Twenty-six young, healthy subjects were investigated at baseline, 1 month and 2 months later. At each examination, subjects completed a posturographic, balance skill, and isometric maximum voluntary (MVC) back extension testing, including surface electromyographic (SEMG) recordings. After baseline evaluation, subjects were assigned to either daily strength training or balance training. After 1 month, the type of training was exchanged between groups. RESULTS: After 1 month, back extensor strengthening led to decreased postural stability on hard surface, whereas there were no change after balance skill training. Analysis of the low- and high-frequency components of the sway signal revealed that strength training increased control efforts as indicated by an increased high-frequency component in order to maintain postural stability and unchanged low-frequency component. Balance skill training, however, increased postural stability as indicated by a decreased low-frequency component. The control effort remained unchanged. After completing either sequence of training, all postural parameters remained unchanged in both groups. Muscular efficiency as measured by SEMG root mean square during a standardized motor skill task revealed improved muscle economy regardless of the type of training. Back extension torque improved in both groups. CONCLUSION: To avoid reduction of postural stability in rehabilitation processes, we recommend to include antagonist muscles in a comprehensive strength training regime or balance skill training.

Adult↗
PubMed1994

Visual stabilization of posture in the elderly: fallers vs. nonfallers.

BACKGROUND: Postural instability is one of the important contributors to falling in observers aged 65 years and older. In this study we examine the role of vision in the relation between postural stability and falling, as well as in the relation between postural stability and the fear of falling. METHODS: Community-dwelling adults 65 years and older were administered a questionnaire about their history of falls and fear of falling (N = 185). Postural sway was measured in the same subjects with eyes open and eyes closed. Visual function was assessed by measures of visual acuity and contrast sensitivity. RESULTS: The 29 subjects who reported falling in the last year showed less of a visual contribution to posture stabilization than those who reported no falls. Controlling for age and gender, there is a 2.13-fold increase in the likelihood of reporting falling for a 0.1 decrement in the visual stabilization index when it is measured within the context of reliable somatosensory feedback. Those who reported a fear of falling and those who reported no fear showed similar visual stabilization. Contrast sensitivity was significantly associated with visual stabilization when it was measured within the context of reliable somatosensory feedback. CONCLUSIONS: The visual contribution to postural stabilization is significantly greater in nonfallers compared to fallers, and it is significantly associated with contrast sensitivity.

Accidental Falls↗
PubMed2006

Adaptive task prioritization in aging: selective resource allocation to postural control is preserved in Alzheimer disease.

OBJECTIVE: With age, the performance of multiple tasks decreases, a pattern exaggerated in Alzheimer disease (AD). At the same time, recent research, based on adaptive theories of healthy aging, indicates a preference of older adults to allocate resources toward tasks of higher immediate value (e.g., postural control). This study investigated whether such models also hold for pathologic cognitive aging. METHOD: Using a dual-task paradigm, the authors combined a working memory with a postural control task under easy and difficult conditions in patients with AD, older adults, older adults low on performance on a cognitive marker test, and young adults (N = 40). Participants repeatedly performed a cognitive and a postural control task both simultaneously and in isolation over the course of eight sessions. RESULTS: Consistent with earlier studies on divided attention in age and AD, the authors found large dual-task performance decrements with age and more so in AD. When not challenged, patients with AD showed large performance decrements under dual-task conditions in both postural control and working memory. With increasing difficulty in the postural control task, however, older adults, and more so patients with AD, maintained a high level of functioning in postural control, as compared with working memory. CONCLUSION: The findings indicate that the theory of selective optimization with compensation extends to pathologic aging and have broad implications for models of dual-task performance and executive control in aging and AD.

Adult↗
PubMed1998

Postural control--a comparison between patients with chronic anterior cruciate ligament insufficiency and healthy individuals.

Postural control in the sagittal plane was evaluated in 22 patients with chronic anterior cruciate ligament (ACL) deficiency and the result was compared to that of a control group of 20 uninjured subjects. Measurement of the body sway was done on a fixed and sway-referenced force plate in both single-limb and two-limb stance, with the eyes open and closed, respectively. Further, an analysis of the postural reactions to perturbations backwards and forwards, respectively, was made in single-limb stance. The results demonstrated statistically significant deficits of the postural control in the patient group compared to the control group, but also within the patient group. There was a significantly higher body sway within the patient group when standing on a stable support surface on the injured limb than standing on the uninjured limb with the eyes open, but no difference with the eyes closed. When standing on a stable support surface, there was a significantly higher body sway in the patient group standing on the injured leg than in the control group, both with eyes open and closed. The patient group also showed a significantly impaired postural control compared to the control group when standing on the uninjured leg with the eyes closed. There was no difference between the groups in the two-limb stance. When standing on the sway-referenced support surface, the patient group had a significantly larger body sway than the control group when the eyes were open, but there was no significant difference between the groups with the eyes closed. The measurement of the postural corrective responses to perturbations backwards and forwards showed that the reaction time measured from the initiation of the force plate translation, and the amplitude of the body sway was significantly greater in the patient group than in the control group. We conclude that patients with a continuing chronic ACL insufficiency several years after injury have an impaired postural control in the antero-posterior direction in single-limb stance on their injured leg. They also show a greater body sway and a prolonged reaction time when subjected to antero-posterior perturbations when standing on their injured leg.

Adolescent↗
PubMed2004

Manipulabilities of the index finger and thumb in three tip-pinch postures.

Tip-pinch, in which the tips of the index finger and thumb pick up and hold a very fine object, plays an important role in the function of the hand. The objective of this study was to investigate how human subjects affect manipulabilities of the tips of the index finger and thumb within the flexion/extension plane of the finger in three different tip-pinch postures. The index finger and thumb of twenty male subjects, were modeled as linkages, based on measurement results obtained using two three-dimensional position measurement devices. The manipulabilities of the index finger and thumb were investigated in three tip-pinch postures, using three criteria indicating the form and posture of the manipulability ellipse of the linkage model. There were no significant differences (p > 0.05, ANOVA) in each criterion of each digit across the subjects, except for two criteria of the thumb. The manipulabilities of the index finger and thumb were separately similar across all subjects in tip-pinch postures. It was found that the manipulability for the cooperation of the index finger and thumb of all the subjects in tip-pinch depended on the posture of the index finger, but not on the posture of the thumb. In two-dimensional tip-pinch, it was possible that the index finger worked actively while the thumb worked passively to support the manipulation of the index finger.

Adult↗
PubMed2006

Postural muscle tone in the body axis of healthy humans.

Across the entire human body, postural tone might play its most critical role in the body's axis because the axis joins the four limbs and head into a single functioning unit during complex motor tasks as well as in static postures. Although postural tone is commonly viewed as low-level, tonic motor activity, we hypothesized that postural tone is both tonically and dynamically regulated in the human axis even during quiet stance. Our results describe the vertical distribution of postural muscle tone in the neck, trunk, and hips of standing human adults. Each subject stood blindfolded on a platform that axially rotated the neck, trunk, or pelvis at 1 degrees /s and +/-10 degrees relative to the neutral position (i.e., facing forward). The measured resistance to axial rotation was highest in the trunk and lowest in the neck and was characterized by several nonlinear features including short-range stiffness and hysteresis. In half of the subjects, axial muscle activity was relatively constant during axial rotation, and in the other half, muscle activity was modulated by lengthening and shortening reactions, i.e., decreasing activity in lengthening muscles and increasing activity in shortening muscles, respectively. Axial resistance to rotation was reduced in subjects whose muscle activity was modulated. The results indicate that axial tone is modulated sensitively and dynamically, this control originates, at least in part, from tonic lengthening and shortening reactions, and a similar type of control appears to exist for postural tone in the proximal muscles of the arm.

Adult↗
PubMed1999

Emergence of postural patterns as a function of vision and translation frequency.

Emergence of postural patterns as a function of vision and translation frequency. We examined the frequency characteristics of human postural coordination and the role of visual information in this coordination. Eight healthy adults maintained balance in stance during sinusoidal support surface translations (12 cm peak to peak) in the anterior-posterior direction at six different frequencies. Changes in kinematic and dynamic measures revealed that both sensory and biomechanical constraints limit postural coordination patterns as a function of translation frequency. At slow frequencies (0.1 and 0.25 Hz), subjects ride the platform (with the eyes open or closed). For fast frequencies (1.0 and 1.25 Hz) with the eyes open, subjects fix their head and upper trunk in space. With the eyes closed, large-amplitude, slow-sway motion of the head and trunk occurred for fast frequencies above 0.5 Hz. Visual information stabilized posture by reducing the variability of the head's position in space and the position of the center of mass (CoM) within the support surface defined by the feet for all but the slowest translation frequencies. When subjects rode the platform, there was little oscillatory joint motion, with muscle activity limited mostly to the ankles. To support the head fixed in space and slow-sway postural patterns, subjects produced stable interjoint hip and ankle joint coordination patterns. This increase in joint motion of the lower body dissipated the energy input by fast translation frequencies and facilitated the control of upper body motion. CoM amplitude decreased with increasing translation frequency, whereas the center of pressure amplitude increased with increasing translation frequency. Our results suggest that visual information was important to maintaining a fixed position of the head and trunk in space, whereas proprioceptive information was sufficient to produce stable coordinative patterns between the support surface and legs. The CNS organizes postural patterns in this balance task as a function of available sensory information, biomechanical constraints, and translation frequency.

Adult↗