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Query: UMLS:C0241981 (loss of balance)
 452 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of this experiment was to examine if, with aging, the task of reintegrating sensory information perturbs balance and requires additional attentional demand. Young adults and the elderly were asked to maintain a stable upright posture while standing on a force platform. Visual and ankle proprioceptive information were removed or perturbed and suddenly reinserted. Subjects also had to respond vocally as quickly as possible to an unpredictable auditory stimulus presented before or following a sensory reintegration and in control conditions. Reaction times to the auditory stimuli were used as an index of the attentional demands necessary for calibrating the postural system. Reintegration of proprioception in absence of vision and under vision yielded a faster center of pressure velocity for both groups. This effect, however, was more important for the elderly than the young adults. An increased attentional demand was observed for both groups when proprioceptive information had to be reintegrated in absence of vision. Altogether, these results propose that, for the elderly persons, postural contexts requiring a reweighting of sensory inputs could lead to increased risk for loss of balance and falls if insufficient attentional resources are allocated to the postural task.
Gait Posture 2001 Dec
PMID:Attentional demands for postural control: the effects of aging and sensory reintegration. 1160 Mar 23

Toe-standing is observed in a number of populations who are able to stand without loss of balance and also those who have balance problems. Intuitively, individuals who stand on their toes are able to successfully regulate their whole body movement in order to keep themselves stable. Force platform data were collected for ten able-bodied subjects during three quiet standing postures, (a) heel-toe standing; (b) half-toe standing and (c) standing en demi pointe (full toe-standing). Differences in control mechanisms with each posture were compared using stabilogram diffusion analysis. During open-loop control (short-term), toe-standing is less stable than heel-toe standing (P<0.05). There is greater stochastic activity when toe-standing (P<0.05), suggesting that any short-term instability is being compensated for by an increase in muscle activity across the lower joints. During closed-loop control (long-term), there is no difference in mediolateral (ML) stochastic activity (increased activity has been linked to falls) between toe-standing and heel-toe standing. In addition, toe-standing is more stable than heel-toe standing (P< s0.05). Toe-standing, in and of itself, may not be responsible for balance problems in populations who compulsorily toe-stand.
Gait Posture 2004 Feb
PMID:Postural control: toe-standing versus heel-toe standing. 1474 Dec 99

Given that a physical definition for a loss of balance (LOB) is lacking, the hypothesis was tested that a LOB is actually a loss of effective control, as evidenced by a control error signal anomaly (CEA). A model-reference adaptive controller and failure-detection algorithm were used to represent central nervous system decision-making based on input and output signals obtained during a challenging whole-body planar balancing task. Control error was defined as the residual generated when the actual system output is compared with the predicted output of the simple first-order polynomial system model. A CEA was hypothesized to occur when the model-generated control error signal exceeded three standard deviations (3sigma) beyond the mean calculated across a 2-s trailing window. The primary hypothesis tested was that a CEA is indeed observable in 20 healthy young adults (ten women) performing the following experiment. Seated subjects were asked to balance a high-backed chair for as long as possible over its rear legs. Each subject performed ten trials. The ground reaction force under the dominant foot, which constituted the sole input to the system, was measured using a two-axis load cell. Angular acceleration of the chair represented the one degree-of-freedom system output. The results showed that the 3sigma algorithm detected a CEA in 94% of 197 trials. A secondary hypothesis was supported in that a CEA was followed in 93% of the trials by an observable compensatory response, occurring at least 100 ms later, and an average of 479 ms, later. Longer reaction times were associated with low velocities at CEA, and vice versa. It is noteworthy that this method of detecting CEA does not rely on an external positional or angular reference, or knowledge of the location of the system's center of mass.
Gait Posture 2004 Jun
PMID:Is a "loss of balance" a control error signal anomaly? Evidence for three-sigma failure detection in young adults. 1512 14

Although assistive devices, such as walkers and canes are often prescribed to aid in balance control, recent studies have suggested that such devices may actually increase risk of falling. In this study, we investigated one possible mechanism: the potential for walkers or canes to interfere with, or constrain, lateral movement of the feet and thereby impede execution of compensatory stepping reactions during lateral loss of balance. Lateral stepping reactions were evoked, in 10 healthy young adults (ages 22-27 years), by means of sudden unpredictable medio-lateral support surface translation. Subjects were tested while holding and loading a standard pickup walker or single-tip cane or while using no assistive device (hands free or holding an object). Results supported the hypothesis that using a walker or cane can interfere with compensatory stepping. Collisions between the swing-foot and mobility aid were remarkably frequent when using the walker (60% of stepping reactions) and also occurred in cane trials (11% of stepping reactions). Furthermore, such collisions were associated with a significant reduction (26-37%) in lateral step length. It appeared that subjects were sometimes able to avoid collision by increasing the forward or backward displacement of the swing-foot or by moving the cane; however, attempts to lift the walker out of the way occurred rarely and were usually impeded due to collision between the contralateral walker post and stance foot. The fact that compensatory stepping behavior was altered significantly in such a healthy cohort clearly demonstrates some of the safety limitations inherent to these assistive devices, as currently designed.
Gait Posture 2004 Aug
PMID:Can use of walkers or canes impede lateral compensatory stepping movements? 1519 24

Dizziness and or unsteadiness, associated with episodes of loss of balance, are frequent complaints in those suffering from persistent problems following a whiplash injury. Research has been inconclusive with respect to possible aetiology, discriminative tests and analyses used. The aim of this pilot research was to identify the test conditions and the most appropriate method for the analysis of sway that may differentiate subjects with persistent whiplash associated disorders (WAD) from healthy controls. The six conditions of the Clinical Test for Sensory Interaction in Balance was performed in both comfortable and tandem stance in 20 subjects with persistent WAD compared to 20 control subjects. The analyses were carried out using a traditional method of measurement, total sway distance, to results obtained from the use of wavelet analysis. Subjects with WAD were significantly less able to complete the tandem stance tests on a firm surface than controls. In comfortable stance, using wavelet analysis, significant differences between subjects with WAD and the control group were evident in total energy of the trace for all test conditions apart from eyes open on the firm surface. In contrast, the results of the analysis using total sway distance revealed no significant differences between groups across all six conditions. Wavelet analysis may be more appropriate for detecting disturbances in balance in whiplash subjects because the technique allows separation of the noise from the underlying systematic effect of sway. These findings will be used to direct future studies on the aeitiology of balance disturbances in WAD.
Gait Posture 2005 Jun
PMID:Is the method of signal analysis and test selection important for measuring standing balance in subjects with persistent whiplash? 1588 29

The head, containing the gravity sensors (vestibular system) and the visual system, must be stabilized in space to provide a steady reference. During walking, the head also needs to be free to move to allow scanning of surrounding objects and steering of locomotion. With aging, deteriorations in motor and sensory systems and their integration are commonly observed. Nevertheless, the strategies used by elderly subjects to complete challenging tasks that require precise sensorimotor integration, such as turning the head rapidly during gait, is not known. The objective of this study was to determine the effects of aging on the movement coordination of the head, trunk and pelvis when executing a rapid head motion in response to a visual signal. Elderly and young subjects turned their head rapidly (up, down, left, right or none) in response to a visual signal, during standing and walking. The 3-D positions of head, trunk and pelvis were recorded and analyzed. All subjects, young and old, successfully performed the task during both standing and walking without any loss of balance. Postural stability was maintained as large head motions were accompanied by relatively small trunk and pelvis movements. Horizontal plane movements associated with right and left head turns were significantly larger than sagittal plane movements associated with head up and down motions. Head motions were significantly slower and smaller in elderly subjects, and resulted in disrupted horizontal plane trunk-pelvis coordination during walking. We conclude that head, trunk and pelvis movements are coordinated in a task-dependent manner such that their movement amplitudes induced by rapid voluntary head motions are larger in walking than in standing. This task-dependent movement coordination is affected by aging.
Gait Posture 2006 Aug
PMID:Aging affects coordination of rapid head motions with trunk and pelvis movements during standing and walking. 1609 45

To achieve a unified assessment of postural instability in Parkinson's disease (PD) over a range of clinical stance and gait tasks, which may provide an insight into a tendency to fall, we measured trunk sway in the anterior-posterior and medial-lateral directions in freely moving PD patients and age-matched controls. We also measured task duration as time to complete the task or time to loss of balance. Patients had larger amplitudes of trunk sway velocities for stance tasks (e.g. mean pitch velocity when standing on two-legs eyes closed equalled 19.1 +/- 6.4 for PD patients on medication versus 4.8 +/- 0.3 degrees/s for controls, p = 0.0003) and for an expected (following prior warning) retropulsion test (mean roll angle equalled 4.3 +/- 0.5 degrees for PD patients versus 2.2 +/- 0.6 degrees for controls, p = 0.0003) than controls. Patients were more likely to fall earlier for stance tasks, and took longer to complete gait tasks (e.g. walking 3 m eyes closed, mean time 6.8 +/- 0.6 sees versus 4.9 +/- 0.1 sees, p = 0.0001). These differences between patients and controls were, in most cases, independent of medication. Based on these results we defined a simple test battery of stance and gait tasks that could discriminate between PD patients who had recent falls and controls. These results indicate that trunk sway measures recorded during stance and gait tasks provide useful information on balance deficits leading to falls in PD patients.
Gait Posture 2005 Nov
PMID:Trunk sway measurements during stance and gait tasks in Parkinson's disease. 1627 66

The aims of this study were to investigate which arm movements are made during trip recovery, to determine the contributions of arm movements in trip recovery and to identify differences in these contributions between younger and older adults and different recovery strategies. A group of seven older adults (65-75 years) and a group of eight younger adults (20-35 years) were examined. Participants completed a trip recovery protocol in which 3-D kinematic and kinetic data were collected for recovery movements following unexpected trips during locomotion. In younger adults, arm movements were associated with an elevated body centre of mass (CM) position during recovery. Arm movements also served to reduce the angular momentum in the direction of the trip by 13% between trip stimulus and recovery foot contact in 'elevating' recovery strategies. Arm movements in older adults contributed an additional 3% to the destabilising angular momentum during 'elevating' recoveries. It was concluded that older adults exhibit a more 'protective' recovery strategy (to limit injury resulting from fall impacts following loss of balance) and younger adults exhibit a more 'preventive' strategy (to prevent loss of balance).
Gait Posture 2008 Feb
PMID:The role of arm movement in early trip recovery in younger and older adults. 1756 98

The purpose of this study was to identify the effects of external loads on balance control during upright stance, and to examine the ability of a new balance control model to predict these effects. External loads were applied to 12 young, healthy participants, and effects on balance control were characterized by center-of-pressure (COP) based measures. Several loading conditions were studied, involving combinations of load mass (10% and 20% of individual body mass) and height (at or 15% of stature above the whole-body COM). A balance control model based on an optimal control strategy was used to predict COP time series. It was assumed that a given individual would adopt the same neural optimal control mechanisms, identified in a no-load condition, under diverse external loading conditions. With the application of external loads, COP mean velocity in the anterior-posterior direction and RMS distance in the medial-lateral direction increased 8.1% and 10.4%, respectively. Predicted COP mean velocity and RMS distance in the anterior-posterior direction also increased with external loading, by 11.1% and 2.9%, respectively. Both experimental COP data and model-based predictions provided the same general conclusion, that application of larger external loads and loads more superior to the whole body center of mass lead to less effective postural control and perhaps a greater risk of loss of balance or falls. Thus, it can be concluded that the assumption about consistency in control mechanisms was partially supported, and it is the mechanical changes induced by external loads that primarily affect balance control.
Gait Posture 2009 Jan
PMID:Effects of external loads on balance control during upright stance: experimental results and model-based predictions. 1863 73

The objective of this study was to examine the combined electromyographic (EMG) and mechanical response to a rearward perturbation and to separate the response into three categories: preset properties of the muscle, reflex changes to the muscle, and active changes to the muscle. We hypothesized that an active response is required to maintain balance on a moving platform. Eleven healthy adult subjects stood on a platform oscillating at three frequencies (0.75, 1.0, and 1.25 Hz). Ankle extensor EMG activity and ankle moment were analyzed and compared for initial movement cycles. Timing of events in EMG and moment data were examined to separate observed changes into the three categories. Results showed an initial rise in ankle moment as the platform started to move backwards, followed by a more rapid reflex increase. After a slight drop, ankle moment again rose due to active response. By the third cycle of platform movement, the EMG and moment were synchronized with the platform movement, maintaining the body in a desired posture. Initial preset properties of the ankle extensor muscles combined with reflex activity were not sufficient to maintain balance. Following an initial reflex reaction, further active control was required to match the timing of the ankle moment and the platform motion and avoid a loss of balance. This study provides new insight for the rehabilitation of postural deficits.
Gait Posture 2009 Jun
PMID:Initial electro-mechanical response to rearward perturbation. 1925 Aug 27


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