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At least 973 records · Page 54Linked to original sources
PubMed2002

Treadmill exercise negatively affects visual contribution to static postural stability.

This study was undertaken to explore the nature of impaired postural stability following physical exercise. Nine healthy subjects (aged 24 +/- 3 years) were subjected to 30 min of treadmill walking or running on two separate occasions. Walking and running speeds (1.9 to 2.2 m/s) were chosen to induce equal energy expenditure. During treadmill exercise, kinematic analysis of head movement was performed. Prior to and immediately following exercise, postural sway was evaluated as mean velocity of centre of pressure (VCOP), measured on a force plate during 30 s quiet stance with eyes open or eyes closed. The results indicate that exercise increased two-dimensional postural sway by 9 - 19 % in eyes open, but not in the eyes closed condition. The deteriorating effect of exercise was both evident in the sagittal and in the frontal plane, although the effect on the former was slightly more transient. Post-exercise sway values were significantly higher after running than after walking. Kinematic analysis of head movement confirmed larger vertical displacement and acceleration pattern in running compared to walking. It is concluded that exercise of moderate intensity deteriorates visual contribution to postural stability. The effect is evident as an initial destabilisation in the sagittal direction and a less transient loss of latero-lateral stability. Running tends to disturb postural stability more than walking, possibly due to more excessive head movement and disturbance of vestibular and visual information centres.

Adult↗
PubMedDate not supplied

Postural instability induced by virtual reality exposure: development of a certification protocol.

Exposure to virtual environments often causes users to experience symptoms of motion sickness. An accessory manifestation of motion sickness symptoms is postural disequilibrium. If the postural disequilibrium that occurs persists beyond the time an individual is within the confines of the laboratory or system site, user safety could be compromised and products liability issues could be forthcoming. In this study, a portable, automated postural assessment system is developed that can be employed before and after exposure to a virtual reality (VR) system in order to certify that a user's balance on exiting the system is at least demonstrably as good as it was on entering. It is argued that if the "coming out" balance performance is sufficiently poorer than the "going in" balance, then the user should be retained until the pretest balance performance is regained. The results from a set of normative and validation experiments on postural equilibrium identified several reliable measures of stance that could serve as a basis for certification. Furthermore, a new automated video-based measure using only head movement showed that performance over sessions is stable and reliable. The head movement changes that occur with stimuli, such as alcohol and simulator exposure, are well behaved, predictable, and significant even with small samples. The implication is that the proposed objective measure of postural stability, in conjunction with procedures for obtaining self-reports of symptoms, can afford some measure of certification that exposure to a given VR system is without harm.

Accident Prevention↗
PubMed1999

Brain activation during maintenance of standing postures in humans.

The regulatory mechanism of bipedal standing in humans remains to be elucidated. We investigated neural substrates for maintaining standing postures in humans using PET with our mobile gantry PET system. Normal volunteers were instructed to adopt several postures: supine with eyes open toward a target; standing with feet together and eyes open or eyes closed; and standing on one foot or with two feet in a tandem relationship with eyes open toward the target. Compared with the supine posture, standing with feet together activated the cerebellar anterior lobe and the right visual cortex (Brodmann area 18/19), and standing on one foot increased cerebral blood flow in the cerebellar anterior vermis and the posterior lobe lateral cortex ipsilateral to the weight-bearing side. Standing in tandem was accompanied by activation within the visual association cortex, the anterior and posterior vermis as well as within the midbrain. Standing with eyes closed activated the prefrontal cortex (Brodmann area 8/9). Our findings confirmed that the cerebellar vermis efferent system plays an important role in maintenance of standing posture and suggested that the visual association cortex may subserve regulating postural equilibrium while standing.

Adult↗
PubMed1985

Effects of postural bias during support surface displacements and rapid arm movements.

The purpose of this study was to evaluate body-sway characteristics during anticipatory and reactive postural compensation. Mechanisms of postural control were studied during self-initiated rapid arm movements (RAMs) and unexpected support surface displacements (SSDs). Ten healthy subjects, 5 men and 5 women with a mean age of 28 years, were blindfolded and stood symmetrically on a moveable force platform or with weight shifted right (R) or left (L). Averaged electromyographs were obtained from L anterior deltoid, L ipsilateral biceps femoris (BFi), R contralateral biceps femoris (BFc), R quadriceps (Q), R medial gastrocnemius (G), and R tibialis anterior (TA) muscles. During SSD, the relative timing of distal-proximal synergists was altered during all biased postures. In L biased standing, functional pairs, TA-Q and G-BF, discharged at their shortest latencies. Anterior deltoid onset times during RAM were most preparatory during R weight shift. Sway latencies were shorter also in biased standing. Absolute sway latency, peak sway, and time-to-peak sway were significantly longer in SSD conditions in comparison with RAM. When disturbances in balance cannot be predicted, lower extremity preloading facilitates contralateral muscle-discharge patterns at shorter latencies. In some neurological conditions that result in incorrect body alignment, the mechanical effects of postural bias rather than the abnormal control mechanisms may at least contribute to alterations in the postural response. These results provide a basis for evaluating balance in patients with neurological deficit.

Adult↗
PubMed1997

Anticipatory postural adjustments before load pickup in a bi-manual whole body lifting task.

Balance regulation and movement control were examined in the context of bi-manual lifting. Subjects picked up a load (20% body mass) after several unloaded cycles using the leg-lift technique. The addition of the load to the body caused the system center of mass to shift forward and thus presented the subject with an expected perturbation of balance. To examine whether the disturbances to balance were counteracted by anticipatory postural adjustments, the last cycle, in which the barbell was grasped and lifted, was compared with the preceding unloaded cycle. Using a global mechanical analysis of the movement, we found that anticipatory postural adjustments were present before load pickup in bi-manual lifting. These anticipatory postural adjustments were characterized by a backward directed horizontal momentum, a backward directed horizontal component of the ground reaction force accompanied with a forward shift of the center of pressure, and a backward shift of the center of mass (CoM). These characteristics could all be understood from the mechanical consideration that adding a load in front of the body induces a forward shift of the CoM. However, major compensations of the position of the CoM were also observed after bar grasp. It is therefore proposed that commands giving rise to postural adjustments are closely tied to commands controlling the ongoing movement. On the basis of this insight the strict dichotomy in the control of posture and movement is being questioned.

Adult↗
PubMed2001

Postural stability assessment following concussion: one piece of the puzzle.

Clinicians regularly assess concussion according to the symptoms that an athlete manifests at the time of injury, as well as during subsequent evaluations. The subjectivity involved with symptom assessment, however, often leaves the clinician without a clear picture of the athlete's true mental status. Neuropsychologic testing has become very popular in the sports medicine community for assessing the cognitive domain of neurologic functioning, and postural stability testing is gaining credence for assessing the motor domain. The objective of this review was to determine the efficacy of postural stability testing as an adjunct to concussion assessment of athletes. Multiple studies, using both sophisticated force plate technology, as well as those using less sophisticated clinical balance tests, have identified postural stability deficits lasting several days following sport-related concussion. It appears that postural stability testing provides a useful tool for objectively assessing the motor domain of neurologic functioning, and should be considered a reliable and valid adjunct to the assessment of athletes suffering from concussion. Although symptom severity, neurocognitive function, and postural stability are often affected initially following concussion, they are not necessarily related or even affected to the same degree.

Athletic Injuries↗
PubMed2006

Postural control deficits in participants with functional ankle instability as measured by the balance error scoring system.

OBJECTIVE: To determine if postural control deficits are present in participants with functional ankle instability (FAI) as measured by the Balance Error Scoring System (BESS). DESIGN AND SETTING: We used a between-groups design to assess postural control. All testing was conducted in a university athletic training facility. PARTICIPANTS: Sixty collegiate Division I athletes were included in this study. Thirty participants had functional ankle instability and thirty participants had no history of ankle injuries. MAIN OUTCOME MEASUREMENTS: Postural control was measured using the BESS. The BESS test battery requires participants to stand unsupported on two different surfaces (firm and foam) in three different stances (double, single, and in tandem). Each condition lasted 20 seconds. The number of errors were calculated for each individual condition and then summed to produce a total BESS score. RESULTS: We found a significant group by condition interaction (F5,290 = 5.12, P < 0.001) and significant main effects for group (F1,58 = 16.01, P < 0.001) and condition (F5,290 = 228.88, P < 0.001). Post hoc analyses revealed that subjects with functional ankle instability scored more errors (poorer balance) on the single stancefirm condition (2.9 +/- 2.1 versus 1.6 +/- 1.3 errors), tandem stancefoam condition (4.3 +/- 2.4 versus 2.7 +/- 1.6 errors), single stancefoam condition (7.0+/-1.6 versus 5.6 +/- 1.8 errors), and total BESS score (15.7 +/- 6.0 versus 10.7 +/- 3.2). CONCLUSIONS: Postural control deficits were identified in participants with functional ankle instability using the BESS. These deficits could be a contributing factor to the repeated episodes of instability and giving way that often occurs following an inversion ankle sprain. These results suggest the BESS, traditionally used for monitoring recovery from mild head injury, may also be useful in screening athletes for postural deficits following lower extremity injury.

Adolescent↗
PubMed1996

Postural stability assessment in sewer workers.

In this study, postural stability was measured with a microcomputer-based force platform as an indirect assessment of central nervous system effect in 28 sewer workers (age range 23.4 to 64.5 years, standard deviation of 8.7 years). All workers performed four 30-second postural sway tests. The organic-solvent exposure was measured by a photo-ionization detector. The photo-ionization detector was calibrated to measure volatile organic solvents in total benzene equivalence, and concentrations were measured in various parts of the plant. The mean exposure was .32 parts per million (ppm) benzene equivalent (range of .02 to .95 ppm, standard deviation .19 ppm). Based on a covariate adjusted linear multiple-regression model, a statistically significant (p < .05) positive correlation was demonstrated between postural sway and organic-solvent exposure. These workers also had increased postural sway compared with a nonexposed population. The statistically significant correlation between postural sway determinations and organic-solvent exposure was surprising given the very low exposures measured. It is possible that the organic-solvent exposure might not be the causative agent, but rather that the solvents themselves correlate with some other causative exposure, ie, total volatile organics as implicated in the cause of sick-building syndrome.

Adult↗
PubMed1996

Measures of postural steadiness: differences between healthy young and elderly adults.

Measures of postural steadiness are used to characterize the dynamics of the postural control system associated with maintaining balance during quiet standing. The objective of this study was to evaluate the relative sensitivity of center-of-pressure (COP)-based measures to changes in postural steadiness related to age. A variety of time and frequency domain measures of postural steadiness were compared between a group of twenty healthy young adults (21-35 years) and a group of twenty healthy elderly adults (66-70 years) under both eyes-open and eyes-closed conditions. The measures that identified differences between the eyes-open and eyes-closed conditions in the young adult group were different than those that identified differences between the eye conditions in the elderly adult group. Mean velocity of the COP was the only measure that identified age-related changes in both eye conditions, and differences between eye conditions in both groups. The results of this study will be useful to researchers and clinicians using COP-based measures to evaluate postural steadiness.

Adult↗
PubMed1996

Effect of forward lean on postural ankle dynamics.

Previous studies investigating postural control using platform perturbations demonstrated that forward leaning occurs under certain experimental conditions. This study examined a potential benefit of forward leaning, investigating the hypothesis that forward lean acts to increase the effective stiffness of the postural ankle dynamics. A systems modeling approach was used to evaluate the effect of forward lean (4 degrees ankle flexion beyond normal stance) on dynamic postural responses to continuous random antero-posterior platform acceleration in four healthy young adults. Motion was limited to the ankle joint using a restraint device and responses were characterized in terms of center-of-pressure displacement. Also, EMG and kinematic data were used to partition measured ankle torque into impedance and activation (postural "reflex") components. The results failed to show a consistent effect, due to lean, on the ankle dynamics. A significant increase in phasic ankle torque due to increased muscle impedance during forward lean was counterbalanced by a comparable decrease in net "reflex" ankle torque. The change in "reflex" torque was apparently due to decreased phasic dorsiflexor activity in forward lean, since phasic plantarflexor activity did not change significantly. Functionally, the results suggest that forward lean occurs for reasons other than stiffening of the overall postural ankle dynamics.

Adult↗
PubMed1992

Postural stability, tardive dyskinesia and developmental disability.

The postural stability of four adult populations was examined through force platform methods. The four groups were classified as: (1) developmentally disabled (severely and profoundly mentally retarded) with tardive dyskinesia; (2) developmentally disabled but with no history of neuroleptic medication; (3) tardive dyskinetic but of normal intelligence; and (4) a normal and healthy control group. Postural conditions included standing still with arms at side, standing still with one arm or both arms parallel to the ground, and standing still while swinging both arms in the sagittal plane. The findings showed that both tardive dyskinetic and/or developmentally disabled groups exhibited greater sway and variability in centre of pressure motion in contrast to the control group. The developmentally disabled with tardive dyskinesia group also exhibited a strong tendency to produce a different form to the postural sway strategy in that they produced rhythmical centre of pressure motions during stance that were, to some degree, task dependent. The findings show that the combined effects of developmental disability and tardive dyskinesia produce qualitatively and quantitatively different features in postural stability patterns. The data suggest that postural stability measures may be a useful index to assess tardive dyskinesia.

Antipsychotic Agents↗
PubMed2006

Effects of anterior cruciate ligament (ACL) injury on postural control and muscle activity of head, neck and trunk muscles.

The aim of the study was to evaluate the effects that an anterior cruciate ligament injury of the knee has on postural control and activity of neck, head and trunk muscles to investigate the existence of connections between the masticatory system and body posture. Surface electromyographic activity of the muscles at mandibular rest position, and during maximal voluntary clenching and posturometric and stabilometric measurements of 25 adult patients having pathology on the left knee were compared with a control non-pathological group. At rest, the patients showed a higher muscular activity of anterior temporalis, masseter, sternocleidomastoid and lower trapezius, compared with the control subjects (P < 0.05). At maximal voluntary clenching, the patients showed a lower muscular activity of the right anterior temporalis and masseter and a higher muscular activity of the lower trapezius, compared with the control subjects. For the stabilometric measurements, all the subjects showed a significant reduction in the postural centre of pressure path length during the test with eyes open and cotton rolls, compared with the test with eyes closed and mandibular rest position (P < 0.05). In addition, the patients showed a significant displacement of the postural centre of pressure in a forward direction (P < 0.05) and into the right side (P < 0.05), compared with the control subjects. Anterior cruciate ligament injury appears to be associated to a change in the activity of head, neck and trunk muscles and to a change in the position of the postural centre of pressure. Cotton rolls seem to improve the stability of the subject.

Adult↗
PubMed2005

Postural stability in primary open angle glaucoma.

BACKGROUND: This study evaluated the visual contribution to postural steadiness in primary open angle glaucoma (POAG), in correlation with the mean deviation (MD) measured through conventional perimetry, and with the Advanced Glaucoma Intervention Study (AGIS) score, which quantifies the extent of losses in the visual field. METHODS: In 35 POAG patients and 21 age-matched normal subjects, the sway of the centre of pressure of the feet, on a firm or foam support, was recorded. The subjects stood on a force-plate with eyes closed, or with one or two eyes open. RESULTS: For all subjects, the sway velocity was lower with vision than without vision, indicating the existence of a visual contribution to posture at all stages of glaucoma. This contribution was significantly lower for POAG patients than for normals in monocular and binocular vision, and decreased with the MD, or as the AGIS score increased. Among the maximum, minimum and average values of the two monocular MD, the MD of the worse eye presented the most significant negative correlation with the visual contribution to posture. The somatosensory contribution to postural steadiness was larger in POAG patients, as compared to normals, in monocular or binocular vision. CONCLUSION: Primary open angle glaucoma induces a deficit in the visual contribution to postural steadiness, which should be taken into account for the prevention of falls.

Adult↗
PubMed2005

Reversals of anticipatory postural adjustments during voluntary sway in humans.

We describe reversals of anticipatory postural adjustments (APAs) with the phase of a voluntary cyclic whole-body sway movement. Subjects (n=9) held a standard load in extended arms and released it by a bilateral shoulder abduction motion in a self-paced manner at different phases of the sway. The load release task was also performed during quiet stance in three positions: in the middle of the sway range and close to its extreme forward and backward positions. Larger APAs were seen during the sway task as compared to quiet stance. Although the direction of postural perturbation associated with the load release was always the same, the direction of the APAs in the leg muscles reversed when the subjects were close to the extreme forward position as compared to the APAs in other phases and during quiet stance. The trunk muscles showed smaller APA modulation at the extreme positions but larger modulation when passing through the middle position, depending on the direction of sway, forward or backward. The phenomenon of APA reversals emphasizes the important role of safety in the generation of postural adjustments associated with voluntary movements. Based on these findings, APAs could be defined as changes in the activity of postural muscles associated with a predictable perturbation that act to provide maximal safety of the postural task component.

Adult↗
PubMed2006

Time-to-boundary measures of postural control during single leg quiet standing.

A novel approach to quantifying postural stability in single leg stance is assessment of time-to-boundary (TTB) of center of pressure (COP) excursions. TTB measures estimate the time required for the COP to reach the boundary of the base of support if it were to continue on its instantaneous trajectory and velocity, thus quantifying the spatiotemporal characteristics of postural control. Our purposes were to examine: (a) the intrasession reliability of TTB and traditional COP-based measures of postural control, and (b) the correlations between these measures. Twenty-four young women completed three 10-second trials of single-limb quiet standing on each limb. Traditional measures included mean velocity, standard deviation, and range of mediolateral (ML) and anterior-posterior (AP) COP excursions. TTB variables were the absolute minimum, mean of minimum samples, and standard deviation of minimum samples in the ML and AP directions. The intrasession reliability of TTB measures was comparable to traditional COP based measures. Correlations between TTB and traditional COP based measures were weaker than those within each category of measures, indicating that TTB measures capture different aspects of postural control than traditional measures. TTB measures provide a unique method of assessing spatiotemporal characteristics of postural control during single limb stance.

Adult↗
PubMed1993

Influence of sensory manipulation on postural control in Parkinson's disease.

Postural control was assessed on a tilting platform system in 20 patients with idiopathic Parkinson's disease and 20 age-matched controls. The amount of information provided by vision and lower limb proprioception was varied during the experiment to investigate the influence of changes in sensory cues on postural control. The patient group with clinical evidence of impaired postural control (Hoehn and Yahr III) had significantly higher sway scores over all sensory conditions than either the Hoehn and Yahr II group or controls. The pattern of sway scores indicated that no obvious deficit in the quality, or processing, of sensory information was responsible for the postural instability observed in this group. The patients in both Hoehn and Yahr groups were also able to respond appropriately to potentially destabilising sensory conflict situations and significantly improved their sway scores when provided with visual feedback of body sway. The results indicate that in Parkinson's disease, the main site of dysfunction in postural control is likely to be at a central motor level.

Adult↗
PubMed2005

The effect of cataract surgery on postural control.

PURPOSE: Falls are a significant cause of morbidity in the elderly. Because decreased vision is known to be a significant risk factor for falling in this age group, we sought to examine the effect of the removal of cataract, a major cause of visual handicap, on postural stability. METHODS: Postural stability was measured in 23 patients who underwent cataract surgery, before and 1 to 4 months after surgery. Stability indices included Stability Effect, Fourier Spectrum of Postural Sway, and Synchronizations, and, based on these measurements, Falling Index, which had been shown in earlier studies to predict the risk of falling. RESULTS: Visual acuity in the surgical eye significantly improved in all patients after surgery (P < 0.01) and did not change in the fellow eye. Stability improved in most patients (19/23) and Fourier Spectrum of Postural Sway improved in the high-frequency bands (above 0.5 Hz), when viewing with the surgical eye, but not when viewing with the nonsurgical eye (P < 0.05). By Falling Index, before surgery, 12 of 23 patients were at high risk of falling, and only six were at low risk. After surgery, 16 of 23 were at low risk and only three remained at high risk (chi(2) test, P < 0.008). CONCLUSIONS: Cataract surgery significantly improves postural stability. Considering the high cost of treating fall-related injuries in the elderly, the findings may imply that cataract surgery is cost effective in this regard.

Accidental Falls↗
PubMed1989

Effects of unilateral loss of vestibular function on the vestibulo-ocular reflex and postural control.

Long-term recovery from surgically induced unilateral loss of vestibular function was studied in 14 patients. Seven patients underwent surgical extirpation or section of the vestibular nerve, and seven patients underwent labyrinthectomy without vestibular nerve section. The vestibulo-ocular reflex (VOR) and postural control were evaluated preoperatively and monitored for up to 4 years postoperatively with use of pseudorandom rotation (combined sinusoidal frequencies from 0.009 to 1.5 Hz) and moving platform posturography. Immediately following surgery all patients showed minimal reductions in the VOR gain constant, but marked reduction in the time constant, and marked increase in slow eye velocity bias. Bias returned to normal values within about 10 days, but time constants never returned to normal values. Results of standard Romberg tests in these patients were normal throughout the preoperative and postoperative periods. However, all patients showed marked postural control abnormalities in tests of the ability to maintain balance in unusual sensory environments in the immediate postoperative period. Seventy-five percent of the patients eventually recovered normal postural control. Postural control returned to near baseline performance with a time course similar to that of the VOR bias. However, postural control also continued to improve after the recovery of VOR bias was complete.

Adolescent↗