Volume 89, Issue 9 , Pages 1772-1774, September 2008
The Effects of Scale Display of Visual Feedback on Postural Control During Quiet Standing in Healthy Elderly Subjects
Article Outline
Abstract
Pinsault N, Vuillerme N. The effects of scale display of visual feedback on postural control during quiet standing in healthy elderly subjects.
Objective
To assess the effects of scale display of visual feedback (VFB) on postural control during quiet standing in healthy elderly subjects.
Design
Before and after intervention trials.
Setting
Medical university bioengineering laboratory.
Participants
Twelve healthy elderly subjects (mean age, 70.2±2.8y; mean body weight, 65.5±4.1kg; mean height, 163.4±6.5cm).
Intervention
Participants were asked to stand upright as immobile as possible in an eyes-open condition and 3 VFB conditions involving increasing scale displays: 2 to 1 (VFB2), 5 to 1 (VFB5), and 10 to 1 (VFB10). These latter conditions correspond to the ratio between the real displacements of the center of pressure (COP), as measured by the force platform, and their visualization on the monitor screen.
Main Outcome Measure
COP displacements were recorded using a force platform.
Results
VFB had different effects on the COP displacements depending on the scale display; no significant difference was observed between the VFB2 and the eyes-open conditions, whereas the VFB5 and VFB10 conditions yielded decreased COP displacements relative to the eyes-open condition.
Conclusions
The effectiveness of the VFB system in improving postural control during quiet standing in elderly subjects depends on the scale display. These findings could have implications in clinical and rehabilitative areas.
Key Words: Elderly, Feedback, Posture, Rehabilitation
List of Abbreviations: ANOVA, analysis of variance, AP, anteroposterior, COP, center of pressure, ML, mediolateral, VFB, visual feedback
FALLS REPRESENT A COMMON event in older adults. Indeed, previous studies have reported that 30% of community-dwelling elderly people over the age of 65 years experience 1 or more falls every year.1 The physical and psychologic consequences of falls, including fear of falling, loss of confidence, restriction of activity, reduced quality of life and independence, physical injuries (eg, fractures of the hip, neck, leg, radius, ulna and other bones in the arm), and even injury-related deaths, are devastating, making falls among older adults a major public health problem. Advancing age is often associated with a decline in the integrity and functionality of sensory systems2, 3 that may lead to postural control deficit in the elderly, which is recognized as a major contributing factor related to falls.4 Within this context, a technique widely used in physical therapy and rehabilitation to improve postural control consists of supplying patients with VFB information about their own COP displacements to supplement the reduced or altered natural sensory information.5, 6, 7 In such a protocol, the subject stands on a force platform, the COP position is depicted in real time on a computer screen, and he/she is required to use this additional information to regulate their postural sway. A recent study8 reported that the VFB yielded no significant postural improvement in healthy older adults. At this point, however, it is possible that the scale of the visual display of VFB presented in this study (1 to 1) was not large enough to allow subjects to efficiently use it to reduce their postural sway during quiet standing.
Our experiment was designed to address this issue by assessing the effects of the scale display of VFB on postural control during quiet standing in elderly subjects.
Methods
Participants
Twelve elderly adults (mean age, 70.2±2.8y; mean body weight, 65.5±4.1kg; mean height, 163.4±6.5cm) voluntarily participated in the study. They gave their informed consent to the experimental procedure as required by the Declaration of Helsinki (1964) and the local ethics committee. Inclusion criteria consisted of people who were 65 years of age and older, and able to stand and walk without aid. Persons with musculoskeletal problems, defects in the peripheral sensory system of the lower extremities, vascular pathology, neurologic disorders, vestibular impairment, or a history of eye disease or abnormality were excluded, as were those with a history of falls. All subjects were looked at by an ophthalmologist and had normal or corrected-to-normal vision with glasses or contact lenses.
Task and Procedures
Participants stood barefoot on a force platforma (sampling frequency, 64Hz), with feet abducted at 30°, heels separated by 3cm, and their arms hanging loosely by their sides. They were asked to remain as immobile as possible in 4 experimental conditions. In the eyes-open condition, they were required to fixate on the intersection of a black cross (20×25cm) placed on a white wall 1m in front of them at eye level. In the 3 VFB conditions, they performed the postural task using a VFB system, whose principle consisted in displaying in real time the horizontal trajectory of the COP on a 21-inch monitor screen placed against the wall 1m in front of them at eye level. Note that subjects did not receive any additional visual cues from the background or the periphery in the VFB relative to the eyes-open condition, ruling out the possibility that the differences observed between the eyes-open condition and the VFB conditions stemmed from the motion parallax. The AP and ML displacements of the COP were depicted on the screen from top to bottom and from left to right, respectively. To facilitate the tracking, the data-acquisition software was programmed in such a way that the spot (4 pixels wide) was always positioned at the center of the screen at the onset of the trial, and only the last 64 COP positions (ie, 1s) were represented. VFB was presented under 3 different scale displays: 2 to 1 (VFB2), 5 to 1 (VFB5), and 10 to 1 (VFB10). These conditions correspond to the ratio between the real displacements of the COP, as measured by the force platform, and their visualization on the monitor screen. For instance, in the VFB2 condition, a COP displacement of 1cm inferred a 2-cm displacement of the spot on the monitor. A practice trial was performed before the test to ensure that the subjects mastered the relationship between their postural sways and the spot displacements. Three 32-second trials for each condition were presented. The order of presentation of the 4 experimental conditions was counterbalanced across participants.
Data Analysis
The surface covered by the trajectory of the COP with a 90% confidence interval and the variance of positions of the COP along the AP and ML axes were used to describe the participant's postural sway.
Statistical Analysis
Statistical analyses were performed using Statisticab for Windows. Dependent variables were submitted to separate 1-way ANOVAs (4 conditions: eyes open vs VFB2 vs VFB5 vs VFB10). Post hoc analyses (LSD test) were used when a significant effect of condition was observed. The level of significance was set at .05.
Results
Analysis of the surface area covered by the trajectory of the COP showed a significant effect of condition (F1,33=6.52, P<.01). Post hoc analyses further indicated (1) no significant difference between the VFB2 and the eyes-open condition (P>.05) and (2) narrower surface areas in the VFB5 and VFB10 conditions relative to the eyes-open condition (P<.001, P<.01, respectively) (fig 1A).
Fig 1.
Mean and SD values for (A) the surface area covered by the trajectory of the foot COP and the variances of COP displacements along (B) the ML and (C) AP axes obtained in the eyes open (EO) condition and the 3 VFB conditions involving increasing scale displays (VFB2, VFB5, VFB10). These latter conditions correspond to the ratio between the real displacements of the COP, as measured by the force platform, and their visualization on the monitor screen. Legend: eyes-open condition, white bars; VFB2 condition, black bars; VFB5 condition, gray bars; VFB10 condition, hatched bars. Significant P values for comparisons with the eyes open condition (P>.05 not significant [NS]; *P<.05; †P<.01; ‡P<.001).
Similar results were observed for the variances of positions of the COP. Along the ML axis, the ANOVA showed a significant effect of condition (F1,33=3.82, P<.05), yielding (1) no difference between the VFB2 and the eyes-open condition (P>.05) and (2) decreased variances of the COP displacements in the VFB5 and VFB10 conditions relative to the eyes-open condition (all P<.05) (fig 1B). Along the AP axis, the ANOVA showed a significant effect of condition (F1,33=9.71, P<.001), yielding (1) no difference between the VFB2 and the eyes-open condition (P>.05) and (2) decreased variances of the COP displacements in the VFB5 and VFB10 conditions relative to the eyes-open condition (all P<.001) (fig 1C).
Discussion
Results showed that the effects of VFB on COP displacements differed depending on the scale display. On the one hand, no significant difference was observed between the VFB2 and the eyes-open conditions, suggesting that healthy older adults were not able to use VFB to reduce their COP displacements. This absence of postural improvement when the VFB was available relative to when it was not is in line with recent results.8 Interestingly, although Dault et al8 reported that a VFB provided with a scale display of 1 to 1 was not sufficient to allow healthy older adults to improve their postural control during quiet standing, our results extended this observation to a visual display of 2 to 1.
On the other hand, the VFB5 and VFB10 conditions yielded decreased COP displacements relative to the eyes-open condition, suggesting that older adults were able to integrate VFB to significantly reduce their COP displacements in both the sagittal and frontal planes. These results are in accordance with a previous study reporting that healthy older adults could efficiently use VFB information, when appropriately provided, to improve their postural control during quiet standing.9 Considering that increasing the scale display decreased the thresholds of visual detection of the COP displacements, these results also are consistent with those evidencing that the effectiveness of visual information in decreasing postural sway increases as the eye–visual target distance decreases (ie, as the threshold of visual detection of the COP displacements decreases).10, 11, 12 On the whole, the present findings provide evidence that the way in which the visual information is fed back (ie, the scale of the visual display) constitutes a determining factor in the effectiveness of this protocol in improving balance in healthy elderly subjects.
Conclusions
The present study evidenced that (1) supplying healthy elderly subjects with the trajectory of their COP during quiet standing did not always result in a reduction of their postural sway, and (2) the effectiveness of the VFB in improving postural control during quiet standing in healthy elderly people depends on the scale display. By determining the conditions that allow elderly adults to benefit from VFB to regulate their postural sway, these findings could have implications in clinical and rehabilitative areas. Finally, the present study focused on healthy older adults only (ie, on people without impairment on visual acuity, rheumatic diseases, or musculoskeletal disorders). Further studies assessing whether sensory and/or motor impaired older adults, representing the most common sample in rehabilitation medicine, could benefit from the VFB are thus needed to strengthen the potential relevance and significance of this technique to the clinical practice.
Suppliers
Acknowledgments
We thank the anonymous reviewers for helpful comments and suggestions; and special thanks to Alicia Bakamem, Eng, for various contributions.
References
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Supported by Ministère de l'Enseignement National et de la Recherche Technologique, France (contrat 21528-2006).
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.
Reprints are not available from the author.
PII: S0003-9993(08)00426-7
doi:10.1016/j.apmr.2008.02.024
© 2008 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.
Volume 89, Issue 9 , Pages 1772-1774, September 2008
