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Results for “Postural control”

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At least 37 records · Page 2Linked to original sources
PubMed1976

[The study of control of posture by frequency analysis of surface electromyogram: an analysis of changes in muscular activity under the controlled posture (author's transl)].

In order to examine the function of muscle for control of posture a frequency analysis was performed of surface EMGs taken from the arm (M. deltoideus) held at the shoulder level. The results indicate that: (a) Power spectra first with a dominant especially with respect to 45-55 Hz component changed significantly 2 components of 5-60 Hz and 65-75 Hz when a 5 min experiment were repeated 3 times, and (b) the ratios of increased power was remarkable in both bands of 10-15 Hz and 30-35 Hz with repeating trials. The control of posture was discussed from the standpoint of behavioral psychology.

Adult↗
PubMed1976

Adapting reflexes controlling the human posture.

Doubt about the role of stretch reflexes in movement and posture control has remained in part because the questions of reflex "usefulness" and the postural "set" have not been adequately considered in the design of experimental paradigms. The intent of this study was to discover the stabilizing role of stretch reflexes acting upon the ankle musculature while human subjects performed stance tasks requiring several different postural "sets". Task specific differences of reflex function were investigated by experiments in which the role of stretch reflexes to stabilize sway doing stance could be altered to be useful, of no use, or inappropriate. Because the system has available a number of alternate inputs to posture (e.g., vestibular and visual), stretch reflex responses were in themselves not necessary to prevent a loss of balance. Nevertheless, 5 out of 12 subjects in this study used long-latency (120 msec) stretch reflexes to help reduce postural sway. Following an unexpected change in the usefulness of stretch reflexes, the 5 subjects progressively altered reflex gain during the succeeding 3-5 trials. Adaptive changes in gain were always in the sense to reduce sway, and therefore could be attenuating or facilitating the reflex response. Comparing subjects using the reflex with those not during so, stretch reflex control resulted in less swaying when the task conditions were unchanging. However, the 5 subjects using reflex controls oftentimes swayed more during the first 3-5 trials after a change, when inappropriate responses were elicited. Four patients with clinically diagnosed cerebellar deficits were studied briefly. Among the stance tasks, their performance was similar to normal in some and significantly poorer in others. Their most significant deficit appeared to be the inability to adapt long-latency reflex gain following changes in the stance task. The study concludes with a discussion of the role of stretch reflexes within a hierarchy of controls ranging from muscle stiffness up to centrally initiated responses.

Adaptation, Physiological↗
PubMedDate not supplied

A method for evaluating vestibular control of posture.

Tests that measure the patient's ability to control his posture generally have failed to yield clinically useful information about vestibular function. The primary reason for this failure is that postural control does not depend on vestibular function when visual and proprioceptive cues are available. To test vestibular function, one should use a procedure that forces the patient to rely on vestibular cues by eliminating cues from these other sensory systems. Such a procedure is described. Vision is eliminated by eye closure, and proprioceptive cues are minimized by rotating the supporting surface to null changes in ankle angle. Data are presented which show that postural responses are complex, but that they appear to conform to the pattern originally observed by Nashner. A method potentially capable of separately evaluating semicircular canal and otolith function is described.

Ankle Joint↗
PubMed1978

Visual input: its importance in the control of postural sway.

A new and measurable parameter in the study of static equilibrium is described. Using a minicomputer, the locus of postural sway was measured during 1 minute periods in 144 volunteer subjects, including 105 control subjects and 39 persons with above-knee amputations. It was hypothesized that the above-knee amputee group had lost a relatively predictable degree of proprioception and kinesthetic sense. Vestibular mechanisms were normal and, therefore, constant in both groups. Using a simple arithmetic formula, the effect of such loss of proprioception was estimated by comparing the amputee group with the nonamputee group, while the contribution of visual input was estimated by comparing both groups with their eyes open and closed. Using this parameter, no clear age dependency was demonstrated. The mean locus of sway for the amputee group was the same as the nonamputee group with the eyes open. However, a comparison of the eyes open/eyes closed ratio in both groups demonstrated a significantly greater increase for the amputee group than for control subjects (p less than 0.001). In the future, mean locus of sway might provide a useful clinical method of measurement and the eyes open/eyes closed ratio might provide a simple and useful method to communicate the dependency upon vision in individual patients.

Adolescent↗
PubMed1992

Electrostimulation effects of the vagus nerve on balance in epilepsy.

Preliminary results of selected postural measures in quiet standing indicate that stimulation of the vagus nerve appears not to be producing adverse effects. With this specific sample size, more testing is needed to determine long-term effects and future data analyses will examine correlations between electroencephalogram results, drug levels, and seizure frequency. In the present study three subjects have had old injuries to hips and ankles. Two subjects had normal values for postural control prior to stimulation, while other subjects were severely abnormal. In future, studies should include larger homogeneous sample sizes, as the current subjects show marked variability in age and premorbid health backgrounds. Future work should also control more vigorously for variables such as visual input (i.e., blindfolding subjects instead of simply closing the eyes). Evaluation of postural control mechanisms will be continued to assess stability changes in these patients as seizure frequency continues to subside.

Adult↗
PubMed2026

High-altitude hypoxia alters the visual control of standing balance in lowlanders and Tibetan highlanders.

High-altitude hypoxia affects both visual function and postural control, yet the influence of optic-flow perturbations on standing balance under hypoxic stress remains unclear. Tibetan highlanders (TH) exhibit adaptations to chronic hypoxia, but whether their visually driven postural responses differ from those of lowlanders (LL) has not been investigated. We examined how high-altitude exposure and acclimatization influence static and dynamic visual contributions to balance by delivering sinusoidal optic-flow perturbations in virtual reality at low altitude (1,400 m) and after incremental ascent to high altitude (4,300 m) in acclimatizing LL (n = 15) and TH (n = 14). Anteroposterior center of pressure (AP CoP) velocity and mean power frequency (MPF) were measured during three visual-field conditions (full-, central-, and peripheral-vision) and two optic-flow velocities (peak 1 m/s and 8 m/s at 0.25 Hz). At high altitude, both groups showed attenuated responses to optic flow compared with 1,400 m, reflected by reduced AP CoP velocity and lower MPF across visual-field conditions, consistent with reduced responsiveness to dynamic visual-motion cues under high altitude hypoxia. In contrast, during eyes-open quiet stance [no virtual reality (VR)], TH but not LL exhibited increased AP CoP velocity and MPF at 4,300 m, and no altitude effect was observed with eyes-closed in either group. This finding indicates that TH adopt a visually dependent postural strategy at altitude, whereas LL show minimal changes in static visual balance control but reduced responsiveness to fast dynamic motion. Together, these findings demonstrate that high-altitude hypoxia disrupts dynamic visual processing for balance control in both groups, while revealing group differences in the use of static visual cues during quiet stance.NEW & NOTEWORTHY This is the first study to investigate how high-altitude hypoxia alters visually driven postural control using virtual reality (VR) optic-flow perturbations. We show that hypoxia attenuates sway responses to optic-flow in both lowlanders and Tibetan highlanders, and that visual weighting differs between these groups. These findings reveal altitude- and population-related changes in sensory weighting during standing balance, advancing sensorimotor understanding of postural control in hypoxia.

Humans↗
PubMed1979

Dynamic role of vision in the control of posture in man.

The influence of moving visual surround on the manitenance of upright posture has been studied in man during combined motion of a platform (cart) on which subjects were standing. The normal visual surround was either moving together with the cart, or with a velocity equal to cart velocity either in the same or in the opposite direction of car motion (cart acceleration was either 0.2 m/s2 or 0.05 m/s2). The changes in body pitch observed under these three conditions of visual surround motion were in the same direction as those observed when visual surround motion was given in isolation. However, their amplitude was greater, particularly when visual surround motion was in conflict with body motion.

Acceleration↗
PubMed1976

A biofeedback study of postural sway.

An experiment was performed to control postural sway under auditory and visual feedback signals using a new apparatus. The subjects of 52 healthy high school girls were divided into 13 small groups. Each small group had four subjects who were assigned to one of the following four groups; 1) visual feedback group, 2) auditory feedback group, 3) auditory and visual feedback group, and 4) control group. Comparisons were made as to the duration of the green lamp being on, which indicated sway stayed around the initial central gravity. The results showed that auditory and visual feedback groups had a significant increase in the duration as compared to other three groups. With regard to the changes in the areas of postural sway, the largest increase was seen in the auditory and visual group. While the three feedback groups showed downward curves, the control group showed an upward one. Thus it is suggested that postural sway can be voluntarily controlled by a combination of an auditury feedback procedure and a visual feedback procedure, but not be either of them independently.

Adolescent↗
PubMed1976

A biofeedback study of postural sway.

An experiment was performed to control postural sway under auditory and visual feedback signals using a new apparatus. The subjects of 52 healthy high school girls were divided into 13 small groups. Each small group had four subjects who were assigned to one of the following four groups; 1) visual feedback group, 2) auditory feedback group, 3) auditory and visual feedback group, and 4) control group. Comparisons were made as to the duration of the green lamp being on, which indicated sway stayed around the initial central gravity. The results showed that auditory and visual feedback groups had a significant increase in the duration as compared to other three groups. With regard to the changes in the areas of postural sway, the largest increase was seen in the auditory and visual group. While the three feedback groups showed downward curves, the control group showed an upward one. Thus it is suggested that postural sway can be voluntarily controlled by a combination of an auditory feedback procedure and a visual feedback procedure, but not by either of them independently.

Adolescent↗