Sway Speed Research Articles

Postural control during the Stroop test in dyslexic and non dyslexic teenagers.

Postural control in quiet stance although simple still requires some cognitive resources; dual cognitive tasks influence further postural control. The present study examines whether or not dyslexic teenagers experience postural instability when performing a Stroop dual task for which their performances are known to be poor. Fifteen dyslexics and twelve non-dyslexics (14 to 17 years old) were recruited from the same school. They were asked to perform three tasks: (1) fixate a target, (2) perform an interference Stroop test (naming the colour or the word rather than reading the word), (3) performing flexibility Stroop task: the subject performed the interference task as in (2) except when the word was in a box, in which case he had to read the word. Postural performances were measured with a force platform. The results showed a main task effect on the variance of speed of body sway only: such variance was higher in the flexibility task than for the other two tasks. No group effect was found for any of the parameters of posture (surface, mediolateral and anteroposterior sway, variance of speed). Further wavelet analysis in the time-frequency domain revealed an increase in the spectral power of the medium frequency range believed to be related to cerebellum control; an accompanying increase in the cancellation time of the high frequency band related to reflexive loops occurred for non-dyslexics only. These effects occurred for the flexibility task and could be due to its high cognitive difficulty. Dyslexics displayed shorter cancellation time for the medium frequency band for all tasks, suggesting less efficient cerebellar control, perhaps of eye fixation and attention influencing body sway. We conclude that there is no evidence for a primary posture deficit in 15 year old teenagers who come from the general population and who were recruited in schools.

Effects of aging on lateral stability in quiet stance.

Recent studies have demonstrated that assuming the postural corrective torque is regulated by a proportional-integralderivative (PID) controller in the anterior/posterior direction, although few studies have discussed the medial/ lateral (M/L) direction through PID control. Instability in the M/L direction has been reported to be closely related with the risk of falling in the elderly. The purpose of this study is to evaluate the mechanism of postural control in the M/L direction in the elderly. The movement of a marker on the subject's back was measured by a CMOS video camera and trunk sway speeds in the M/L direction (TSSX) were calculated as absolute values in whole time series. Using trunk sway data, we identified the gain of PID parameters (proportional gain: KP, integral gain: KI derivative gain: KD). In addition, we calculated the frequency spectrum of trunk sway using the marker locus from 0.016 to 5 Hz by fast Fourier transform. A total of 40 healthy subjects aged from 20 to 85 years old was evaluated with the PID control algorithm in a model of postural control in the M/L direction and their parameter values were estimated. KP significantly increased with age, whereas KD tended to decrease. The TSSX and power ratio of medium frequency (0.2-2.0 Hz) significantly increased with age, but the power ratio of low frequency (0.02-0.2 Hz) tended to decrease. KP and KI were significantly correlated with the power ratio of medium frequency. There was a significant negative correlation between KD and TSSX. Our results indicate that dependence on hip and ankle stiffness, which may be controlled by proportional gain, increases with age for postural control in the M/L direction. A disability in the feedback mechanism based on velocity information for postural control, which may be associated with derivative gain, tends to increase with age but shows considerable individual variation.

Effect of mild cognitive impairment on balance

Objective To investigate the effect of mild cognitive impairment (MCI) on balance. Methods 87 subjects with subjective memory impairment were enrolled, and subdivided into two groups, MCI and non-MCI, according to diagnostic criteria of amnestic subtype of MCI according to the 1999 MCI international panel (Current Concepts in Mild Cognitive Impairment). These two groups were matched for age and gender. Posturography was used to assess balance by measuring the mediolateral and anteroposterial sway speed and distance in the standing position, with both opened and closed eyes. Results The mediolateral sway speed and distance were higher in the MCI group than the non-MCI group, with both opened and closed eyes (p < 0.05). However, there was no significant difference between the MCI group and non-MCI in anteroposterior sway speed and distance. These results were confirmed in a multivariate model adjusting for gender, age, weight, height, foot size, and education. The mediolateral, and anteroposterior sway speed and distance values were higher on eye closing status than on eye opening status in both the MCI and control groups (p < 0.00). Conclusion The falling risk is assumed to be higher in MCI subjects than in non-MCI subjects, especially due to decreased mediolateral balance, as shown in our adjusted analysis. These findings underscore the importance of specific balance exercise in which mediolateral balance is measured and visual compensation training programs for MCI subjects in order to prevent fall and related fracture, as well as the importance of programs for improvement of cognitive function.

Physiological complexity and system adaptability: evidence from postural control dynamics of older adults

The degree of multiscale complexity in human behavioral regulation, such as that required for postural control, appears to decrease with advanced aging or disease. To help delineate causes and functional consequences of complexity loss, we examined the effects of visual and somatosensory impairment on the complexity of postural sway during quiet standing and its relationship to postural adaptation to cognitive dual tasking. Participants of the MOBILIZE Boston Study were classified into mutually exclusive groups: controls [intact vision and foot somatosensation, n = 299, 76 ± 5 (SD) yr old], visual impairment only (<20/40 vision, n = 81, 77 ± 4 yr old), somatosensory impairment only (inability to perceive 5.07 monofilament on plantar halluxes, n = 48, 80 ± 5 yr old), and combined impairments (n = 25, 80 ± 4 yr old). Postural sway (i.e., center-of-pressure) dynamics were assessed during quiet standing and cognitive dual tasking, and a complexity index was quantified using multiscale entropy analysis. Postural sway speed and area, which did not correlate with complexity, were also computed. During quiet standing, the complexity index (mean ± SD) was highest in controls (9.5 ± 1.2) and successively lower in the visual (9.1 ± 1.1), somatosensory (8.6 ± 1.6), and combined (7.8 ± 1.3) impairment groups (P = 0.001). Dual tasking resulted in increased sway speed and area but reduced complexity (P < 0.01). Lower complexity during quiet standing correlated with greater absolute (R = -0.34, P = 0.002) and percent (R = -0.45, P < 0.001) increases in postural sway speed from quiet standing to dual-tasking conditions. Sensory impairments contributed to decreased postural sway complexity, which reflected reduced adaptive capacity of the postural control system. Relatively low baseline complexity may, therefore, indicate control systems that are more vulnerable to cognitive and other stressors.

An approach towards the control of underwater vehicles

Abstract Underwater vehicles present difficult control-system design problems due to their nonlinear dynamics, uncertain models, and the presence of disturbances that are difficult to measure or estimate. In this paper, one approach has been carried out for controlling voltage supplied to two horizontal propellers of an underwater vehicle with the objective of controlling the following variables, the yaw angle, the yaw rate and the sway speed. The design is based on the recursive procedure of the multivariable backstepping. The designed algorithm jointly with a simple optimization procedure, that minimizes the energy consumption, is capable of handling these problems with effectiveness. This method, as opposite to the input-feedback linearization, deals directly with nonlinearities and is highly robust to imprecise models. Simulation results are reported to demonstrate the effectiveness of the proposed approaches with an improvement on the precision manoeuvring.

변속 무인 수중 잠수정을 위한 강인 경로 추적 제어

본 논문에서는 시간에 따라 종방향 속도가 변하는 무인 수중 잠수정의 경로 추적 제어기 설계 방법을 제안한다. 본 논문에서 제안한 경로 추적 제어기는 운동학적 제어기와 동역학적 제어기로 구성된다. 운동학적 제어기는 무인 수중 잠수정이 시간에 따라 속도가 변하는 기준 경로를 따라 가기 위해 종방향 속도와 yaw 각속도를 계산하고, 계산된 값이 동역학적 제어기의 기준 입력 값이 된다. 즉, 동역학적 제어기는 추진력과 회전력을 제어하여 무인 수중 잠수정의 종방향 속도와 yaw 각속도가 운동학적 제어기에서 계산한 값과 일치하도록 설계한다. 이 때 사용한 동역학적 제어기는 무인 잠수정의 옆 미끄럼 속도를 외란으로 가정하고, 종방향 속도와 yaw 각속도를 슬라이딩 모드 제어 기법을 이용하여 설계한다. 한편 설계된 제어기의 안정도 판별을 위해 Lyapunov 방법을 이용하여 제어기의 안정성을 보인다. 마지막으로, 컴퓨터 시뮬레이션을 이용하여 설계된 제어기의 성능을 검증한다. In this paper, we propose a robust path tracking control method for autonomous underwater vehicle with variable speed. The proposed path tracking controller consists of a kinematic controller and a dynamic controller. First, the kinematic controller computes the surge speed and yaw rate to follow the reference path with variable speed. Then the dynamic controller controls the thrust force and yaw torque to move the AUV actually. In the dynamic control, we assume that the sway speed is a disturbance. In addition the dynamic controller is designed based on sliding mode conrol. We also demonstrate the stability of the proposed control method by Lyapunov stability theory. Finally, simulation results illustrate the performance of the proposed control method.

Perceived pain, fear of falling and physical function in women with osteoporosis

The aim of this cross-sectional study was to evaluate pain intensity-related differences in physical performance and fear of falling in elderly women with osteoporosis. A sample of 82 osteoporotic women (73.8 ± 8.1 years) with and without vertebral fractures was included. Numeric rating scale (NRS) measures (0 = no pain, 10 = unbearable) were applied to obtain actual pain intensity and to stratify between patients with mild (0–3), moderate (4–6) and severe (7–10) pain. Activity-related fear of falling was evaluated with the Falls Efficacy Scale-International Version (FES-I). Physical performance measures included maximum voluntary quadriceps strength, postural sway and gait speed measures. Controlling for age, fractures, and history of falls ANCOVA with Scheffe's post hoc test indicated significant slower walking velocities and greater postural sway for patients with severe pain. Furthermore, significant group differences could be detected for muscle strength and fear of falling. Patients with more intense pain (NRS ≥ 5) were 6.4 times (odds ratio; 95%CI: 1.5–26.7) more likely to score below average in fall-related self-efficacy and all physical performance tests. Among women with osteoporosis, heightened back pain intensity increases fear of falling and decreases physical performance irrespective of vertebral fractures and history of falls.

Visual deprivation leads to gait adaptations that are age- and context-specific: I. Step-time parameters

In children, visual information is crucial for static postural control, although age-related differences exist in the impact of visual perturbation on postural sway. Since static postural control and locomotion are closely related, we expect age-related differences in the impact of visual deprivation on dynamic stability and gait. It is hypothesised that this is related to the important role of vision in postural control. Postural stability and gait was tested in 20 adults and 40 children (3–11 years old) under two different visual conditions: eyes open (EO) and eyes closed (EC).Significant differences were found between EO and EC for postural sway, dimensionless walking speed, dimensionless stride length and duration of double support. Thus, we can state that visual deprivation affects locomotion both in adults and children. Concerning walking speed a significant interaction effect was observed with age. The difference in walking speed between EO and EC is larger in children than in adults.Furthermore, we found significant correlations between postural sway and walking speed, step frequency and stride length. These observations support the hypothesis that gait adaptations in situations of visual deprivation are related to balance problems.

Parametric Identification of Ship Maneuvering Models by Using Support Vector Machines

System identification combined with free-running model tests or full-scale trials is one of the effective methods to determine the hydrodynamic coefficients in the mathematical models of ship maneuvering motion. By analyzing the available data, including rudder angle, surge speed, sway speed, yaw rate, and so forth, a method based on support vector machines (SVM) to estimate the hydrodynamic coefficients is proposed for conventional surface ships. The coefficients are contained in the expansion of the inner product of a linear kernel function. Predictions of maneuvering motion are conducted by using the parameters identified. The results of identification and simulation demonstrate the validity of the identification algorithm proposed. The simultaneous drift and multicollinearity are diminished by introducing an additional ramp signal to the training samples. Comparison between the simulated and predicted motion variables from different maneuvers shows good predictive ability of the trained SVM.

Postural control during prolonged standing in persons with chronic low back pain

Prolonged standing has been associated with the onset of low back pain symptoms in working populations. So far, it is unknown how individuals with chronic low back pain (CLBP) behave during prolonged unconstrained standing (PS). The aim of the present study was to analyze the control of posture by subjects with CLBP during PS in comparison to matched healthy adults. The center of pressure (COP) position of 12 CLBP subjects and 12 matched healthy controls was recorded in prolonged standing (30 min) and quiet stance tasks (60 s) on a force plate. The number and amplitude of COP patterns, the root mean square (RMS), speed, and frequency of COP sway were analyzed. Statistical analyses showed that CLBP subjects produced less postural changes in the antero-posterior direction with decreased postural sway during the prolonged standing task in comparison to the healthy group. Only CLBP subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS, COP speed and COP frequency in the quiet standing trial after the prolonged standing task in comparison to the pre-PS trial. The present study provides additional evidence that individuals with CLBP might have altered sensory-motor function. Their inability to generate responses similar to those of healthy subjects during prolonged standing may contribute to CLBP persistence or an increase risk of recurrent back pain episodes. Moreover, quantification of postural changes during prolonged standing could be useful to identify CLBP subjects prone to postural control deficits.

Postural Control in People with Osteoarthritis of the Cervical Spine

Objective This study examines whether there is a relationship between clinical correlates of osteoarthritic changes of the cervical spine and changes in postural stability. Methods This was a control group study with repeated measures. Twenty-three patients were recruited from the chiropractic University Clinic to participate in this study. The presence and severity of osteoarthritic changes of the cervical spine were determined radiologically. Balance control was evaluated by testing subjects' postural stability on a force platform with and without vision. A general clinical assessment of the neuromusculoskeletal system was performed to screen for any physical condition that could affect postural stability. Participants' characteristics were compared between each group using a 1-way analysis of variance for independent samples, and postural stability variables were submitted to a 2-way repeated measures analysis of variance. Results Subjects with signs of osteoarthritis of the cervical spine showed an increased range of sway, a faster sway speed, and a greater excursion than control subjects. They also showed a larger degree of lower limb neuropathy than control subjects. Conclusion The postural instability shown by the osteoarthritic group may be due to the effects of the lower limb peripheral neuropathy alone or due to a combination of both cervical degenerative changes and peripheral changes. Further research is needed to clearly isolate the effects of the degeneration of the cervical spine on postural control.

Response characteristics and maneuverability of a small twin screw displacement hull vessel in seas

This paper presents the response characteristics and maneuverability of a small twin screw displacement hull vessel quantified through a series of full-scale trials conducted in different environmental conditions. The 20-m test vessel is instrumented with actuator, environmental, and motion sensors. Several different maneuvers are performed at different speeds, including steady maneuvers with constant control input and transient maneuvers with varied control input to quantify and characterize the response of small vessels to aid in automatic controller and simulation development. Straight-line runs are performed in both forward and reverse over the entire operating range of the test vessel to investigate the relationship between throttle position, RPM, and surge velocity. Turning maneuvers are conducted over the achievable rudder deflection range to quantify the vessels turning radius and the relationships with surge, sway, and rotational speed. Other maneuvers include stationary rotation with the engines operating in opposite gears, and transient tests when the vessel is rapidly accelerated and decelerated. These actuator tests not only quantify the response of the actuators, but also set guidelines for the minimum dwell times that should be observed when shifting gears. These data found using a comprehensive sensor suite provide valuable benchmarks for several maneuvers that can be used for simulation validation and the actuator response information provides valuable set points and performance characteristics/limitations that should be considered in control development. The data from these tests were repeatable from run to run and thus, with sufficient instruments, at sea maneuvers can be used to collect a comprehensive set of data that can expand on data collected in tow tests.

前庭神経炎患者のＢｏｄｙ Ｔｒａｃｋｉｎｇ Ｔｅｓｔを用いた動的体平衡機能の検討

Body Tracking Test (BTT) is a testing method of the dynamic body balance function wherein movement of the center of gravity in accordance with a moving visual target stimulus is examined to evaluate the tracking function of the body. The objects were the patients who were diagnosed as having vestibular neuronitis at the Department of Otolaryngology in Toho University medical center Sakura hospital, and were undergoing hospital treatment. Lateral BTT was performed in 31 subjects, and antero-posterior (A-P) BTT in 45 subjects. Although gaze nystagmus was noted, inspection was enforced when a standing position posture was possible. In lateral BTT, the average (cm/second) horizontal direction body sway speed was compared, however, no clear lateral difference was noted. In the antero-posterior (A-P) BTT, it inquired using the direction body sway average center displacement (cm) of X. Deviation was seen by the affected side in stabilometry. Deviation was seen by the unaffected side in the antero-posterior (A-P) BTT. This phenomenon differs from the deviation pattern until now and is considered to involve participation of the higher centers.

발목 강화 운동과 기능적 전기 자극치료가 뇌졸중 환자의 보행기능 및 균형능력에 미치는 영향

The purpose of this study is to comparatively analyze the effects of ankle strength exercise and functional electrical stimulation on ability balance control and gait of stroke patients. The results of the study will be used as basic data for help in independent life of stroke patients. Subject person of this study is 20 stroke patients, sex ratio was 10 men, 10 women. Experimental group (5 men, 5 woman) ran parallel ankle strength exercise and functional electric stimulation treatment, and control group (5 men, 5 woman) ran parallel functional electric stimulation treatment and exercise treatment. Measured balance ability and walking speed, ankle angle after 8 weeks experiment 3 inning a week. The results were as follows; 1. Weight bearing rate by Berg balance scale and BPM increased to keep in mind in experimental grooup and control group, and change that position sway by BPM, sway path, sway area, the all sway speeds displayed decrease that keep in mind, and are less relatively in control group was seen. And difference of change amount between two groups displayed statistically significant. It means that this improved two groups total balance ability but ankle strength exercise and same time of functional electric stimulation treatment are more effect. 2. Change of walking speed and ankle joint angle displayed decrease that two groups keep in mind after all experiments in TUG that display walking speed in experimental group and control group. But, ankle joint angle both was no difference that two groups keep in mind after and experiment. And difference that keep in mind in walking speed too as result that significant difference of change amount of two groups appeared. When applied running parallel ankle strength exercise and functional electric stimulation treatment in stroke patients, both experimental group and control group appeared that balance and ability to walk are increased. Also, was expose that difference that keep in mind between group as result that significant difference of change amount of two groups is. Can explain that this means that ankle strength exercise and same time of functional electric stimulation treatment were more effective in treatment of stroke patient.

Functional Mobility and Postural Control in Essential Tremor

Parisi SL, Héroux ME, Culham EG, Norman KE. Functional mobility and postural control in essential tremor. Objective To evaluate functional mobility and postural control in participants with essential tremor (ET). Design Cross-sectional cohort study. Setting Motor performance research laboratory. Participants Sixteen participants with ET including head tremor (age, 59.4±12.0y), 14 participants with ET and no head tremor (age, 57.1±15.9y), and 28 healthy controls (age, 58.4±12.4y). Interventions Not applicable. Main Outcome Measures We assessed the Timed Up & Go, time to ascend and descend stairs, Dynamic Gait Index, and Berg Balance Scale (BBS). Participants completed the Activities-specific Balance Confidence Scale and the Human Activity Profile. We assessed postural control using center-of-pressure measures from force platform recordings of quiet standing in 5 conditions. Results Participants with ET including head tremor performed worse than controls on all functional mobility performance and self-report measures ( P<.05) except the BBS and stair descent time. Mean performance of ET participants without head tremor was intermediate between the other 2 groups. Sway speed measures of postural control showed similar patterns, but no significant group differences in post hoc analysis. There were no statistically significant or clinically important correlations between measures of tremor status and functional mobility status. Conclusions Participants with ET show reduced functional mobility, especially those with head tremor.

Adaptive changes in postural strategy selection in chronic low back pain

Chronic low back pain (CLBP) patients achieve postural stability during challenging stance conditions by increasing sway speed. We investigated the mechanisms underlying this behavior, and whether postural strategy selection may be influenced by short-term experience of postural perturbation. Thirteen CLBP patients and thirteen age-matched controls underwent posturography tests. Subjects were asked to stand quietly: (a) with eyes open and eyes closed, and (b) while expecting a series of four backward translations of the support surface. Data from condition (a) was subjected to sway density analysis (SDA). This computes the number of consecutive spaces and respectively time samples during which center of pressure (COP) displacements remained inside a 2.5 mm radius. Three parameters of this analysis were considered: the mean number of peaks (MP), reflecting the time spent by COP in regions of stability, the mean time between peaks (MT) relating to the rate of production of posturographic commands, and the mean spatial distance (MD), reflecting the distance between stable regions. In condition (b) the mean COP positions were analyzed during the time (500 ms) preceding each translation. The MD was significantly increased in the CLBP group as compared to controls (P < 0.01), while the MP and MT did not present any significant difference. The expectation of backward translations initially produced a different COP positioning between the two groups (P < 0.0001) which decreased with repetition of platform translations (controls: PDelta1-4 < 0.002; patients: PDelta1-4 < 0.005). The findings show that the timing and the rate of the balance motor commands is comparable between the two groups. On the other hand, there is greater distance between regions of stability in the patient group. Such modification of motor control patterns might be the consequence of a reweighting of sensory input, possibly due to a deterioration of its reliability. Platform translation findings show that both groups aimed at optimizing their posture selection strategy based on prior testing experience. CLBP patients make use of a different postural motor strategy to maintain quiet stance. This is probably the consequence of an imprecise internal estimate of body sway, due to reduced accuracy in the sensory integration process.

Influence of vision and static stretch of the calf muscles on postural sway during quiet standing

The purpose of this experimental study was to evaluate the effects of vision and stretching of the calf muscles on postural sway during quiet standing. Under pre-stretch conditions, participants stood on a force plate for 30 s and the sway of the ground reaction force center of pressure was recorded. The following postural sway variables were calculated off-line: sweep speed, sway speed, standard deviation, maximal mediolateral range, maximal anteroposterior range, mean mediolateral position and mean anteroposterior position. For post-stretch conditions, participants stood quietly on a device that was utilized to impose a static 3 min ankle joint dorsiflexion stretch. Immediately thereafter, participants moved onto the force platform where postural sway parameters were again recorded. Randomized eyes-open and eyes-closed conditions were tested in both cases. Results showed that postural sway significantly increased due to stretch (sweep speed, sway speed, standard deviation, maximal anteroposterior range, mean anteroposterior position), as well as eye closure (sweep speed, sway speed, standard deviation, maximal mediolateral range, maximal anteroposterior range). The interaction between stretch and eye closure was also significant (sweep speed, sway speed, standard deviation, maximal mediolateral range), suggesting that there were only minor increases in postural sway after stretch under the eyes-open condition. It was suggested that stretching of the calf muscles has the effect of increasing postural sway, although this effect can be greatly compensated for when vision is included.

Postural stability and unilateral posterior crossbite: Is there a relationship?

The aim of this study was to test the hypothesis that unilateral posterior crossbite influences postural stability of the whole body. Twenty-six subjects (14 males and 12 females) affected with unilateral posterior crossbite were selected and compared with 52 controls matched for age and gender. Postural stability was assessed using a stabilometric platform. The following stabilometric measurements were assessed: weight distribution on foot area and speed of body sway. Tests were performed under two occlusal conditions: teeth in intercuspal position (ICP) and while keeping two cotton rolls between teeth without clenching. The weight distribution on foot area and the speed of body sway were not significantly influenced from crossbite (with and without lateral mandibular slide), occlusal conditions (ICP, cotton rolls), and gender. Therefore, the treatment of this malocclusion in order to prevent or to treat postural disorders is not justified.

Análisis postural de la prueba "Timed-up-and-go" en pacientes con vértigo

Introduction and Objectives:To characterize and analyze the "Timed-up-and-go" test in non-fallers patients with peripheral vertigo. To assess if turning to the side of the lesion induces a more intense instability. Material and Methods:The test was performed after carefully explanation to the patient who was allowed to do some attempts. Postural measurements were the angle and angular speed of trunk sway in roll and pitch. It was done with a special device adapted to the trunk with two sensors specially built for that purpose. Conclusions:Dizzy, non-fallers patients perform this test in a period of time considered as normal. Canal paresis influences in roll trunk sway when the patient performs the TUG only when turning to the normal side.

Age-related changes in human postural control of prolonged standing

The aim of this study was to characterize prolonged standing and its effect on postural control in elderly individuals in comparison to adults. It is unknown how elderly individuals behave during prolonged standing and how demanding such a task is for them. We recorded the center of pressure (COP) position of 14 elderly subjects and 14 adults while they performed prolonged standing (30 min) and quiet stance tasks (60s) on a force plate. The number and amplitude of the COP patterns, the root mean square (RMS), speed, and frequency of the COP sway were analyzed. The elderly subjects were able to stand for prolonged periods but they produced postural changes of lesser amplitude and a decreased sway during the prolonged standing task. Both the adults and the elderly subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS and COP speed in the quiet standing trial after the prolonged standing task, in comparison to the trial before. We suggest that the lack of mobility in elderly subjects may be responsible for the observed sub-optimal postural changes in this group. The inability of elderly individuals to generate similar responses to adults during prolonged standing may contribute to the increased risk of falls in the older population.