Age-related changes in human postural control of prolonged standing

doi:10.1016/j.gaitpost.2004.11.001

Gait & Posture

Volume 22, Issue 4, December 2005, Pages 322-330

https://doi.org/10.1016/j.gaitpost.2004.11.001 Get rights and content

Abstract

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 (60 s) 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.

Introduction

In our everyday life, we frequently stand for a prolonged period (more than a few minutes) while chatting to somebody, waiting in a line, or standing in a work environment, i.e., we stand in order to perform another task — which in this context may be referred as a supra-postural task [1]. In such natural standing, continuous low-amplitude and slow swaying of the body is commonly interrupted by postural changes characterized by fast and gross body movements [2], [3], [4]. These postural changes are thought to be performed in order to diminish the discomfort caused by psychological factors (increase of tension, mental stress, and reduction of motivation and concentration) and physiological factors (increase of venous pooling in the lower extremities, occlusion of blood flow, vertigo, muscular fatigue and increased joint pressure) [3], [4], [5], [6], [7], [8].

Analyses of healthy adults standing for a prolonged period have quantified the average number of these postural changes, which are between 1 and 2 min⁻¹ [3], [6], [9]. Such analyses have shown that, superimposed on these deterministic local events, humans present similar patterns of oscillation over different space and time scales, constituting a fractal stochastic process [10], [11]. In this way, postural changes and an increase in body sway during prolonged standing are viewed as effective responses of the postural control system to complete the task with minimal effort. Nevertheless, standing for a prolonged period, i.e., for hours, causes fatigue [12], [13], [9]. Discomfort and fatigue related to prolonged standing have been estimated by scales of rated perceived exertion and discomfort, measurements of performance, electromyographic activity of leg muscles, venous pressure, skin temperature, changes in foot and leg dimensions and frequency of postural changes, among other variables [6], [8], [12], [13], [14], [9]. The rationale for using frequency of postural changes as an indicator of fatigue during prolonged standing is that postural changes are viewed as a response to avoid discomfort and fatigue. Hence, it is expected that postural changes be performed more often across time due to the increase in discomfort and fatigue during prolonged standing.

All studies to date examining prolonged standing have evaluated healthy adult individuals, mainly because prolonged standing is common in working environments and frequently causes impairments in the workforce [12], [4], [9]. Despite the greater impact that prolonged standing may have upon individuals with balance problems, the effects of standing for a prolonged period on individuals other than healthy adults is unknown. An anecdotal recommendation suggests that elderly individuals should not stand for prolonged periods, although no study has focused on this issue. The basis for this recommendation lies with the fact that ageing is associated with decreases in many physiological functions related to postural control [15], [16]. That elderly individual may be affected by balance problems and a lack of mobility is shown by the fact that 30% of individuals older than 65 years old experience falls. Falls are the leading cause of unintentional injury deaths for these individuals in the United States [17], [18], [19]. While falling is a multifactorial problem, it is possible that individuals with postural deficits, particularly elderly individuals, may be incapable of generating adequate postural responses during prolonged standing. This might lead to fatigue and ultimately contribute to the risk of falling.

Due to the decrease in the physiological functions related to ageing, elderly individuals may be more affected during standing tasks. Considering postural changes as responses to avoid discomfort and fatigue, it is possible that elderly individuals present a higher frequency of postural changes during prolonged standing. Conversely, elderly individuals are also affected by a decrease in mobility [20], [21]. A lack of mobility may mean that elderly individuals present fewer postural changes or postural changes with decreased amplitude. A decrease in the number and amplitude of postural changes in elderly individuals could also reflect a strategy to voluntarily perturb the body to sway as little as possible due to fear of falling. The effect of fatigue on the postural sway during quiet standing of healthy adults has also received attention [22], [23], [24]. In these studies, fatigue has been induced by voluntary contractions of leg muscles in different motor activities. Increased postural sway during quiet stance after fatiguing exercise demonstrated that fatigue can cause deterioration of postural control in quiet standing. However, it is unknown how fatigue due to prolonged standing might affect the postural sway of elderly individuals during quiet standing.

In the present study, we address the manner in which elderly individuals stand for a prolonged period and how demanding this task is for them in comparison to healthy adults. We therefore carried out posturographic analyses of prolonged standing and quiet standing tasks performed by both groups of individuals. We hypothesize that elderly individuals will present a different behavior than adults during prolonged standing, and that their control of equilibrium will be more affected by this task.

Section snippets

Subjects

Fourteen elderly individuals with the following characteristics were included in the current study: mean age (±S.D.) of 68 ± 4 years, range 61–76 years, height of 1.58 ± 0.08 m, and mass of 64 ± 12 kg. Fourteen healthy adults (28 ± 7 years, range 19–40 years, 1.65 ± 0.11 m, and weighing 63 ± 10 kg) also participated in this study. None of the subjects in the adult group had any known history of postural or skeletal disorders, but in the elderly group there were three subjects with arthritis of the knee and two

Results

All the adults as well as all the elderly subjects were able to stand for 30 min and performed postural changes while standing. The median and inter-quartile range values of the amplitude and number of COP patterns in the AP and ML directions for the adult and elderly groups during the prolonged standing trial are shown in Fig. 2. The total number of COP patterns in the stabilograms was not different between adults (median, 25th–75th percentiles: 65, 57–76; 2.2 postural changes per minute) and

Discussion

The purpose of the present study was to characterize prolonged standing and its effect on postural control in elderly subjects in comparison to adults. We hypothesized that elderly individuals would present a different behavior to that in adults during prolonged standing. We also expected that postural control would be more affected by prolonged standing for the elderly subjects, in comparison to adults. Our main findings suggest that elderly individuals exhibit postural changes of smaller

Acknowledgements

This work was supported by a FAPESP/Brazil grant (#00/03624-5) to M. Duarte. S. Freitas and S. Wieczorek are thankful to FAPESP for their scholarships (#01/03429-0 and #00/11363-7).

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Age-related changes in human postural control of prolonged standing

Abstract

Introduction

Section snippets

Subjects

Results

Discussion

Acknowledgements

Human Movement Sci

Int J Ind Ergonomics

Neurosci Lett

Phys Lett A

Neurobiol Aging

Electroencephalogr Clin Neurophysiol

Gait Posture

Stabilographic analysis of unconstrained standing

Ergonomics

Postural adaptations to workbench modifications in standing workers

Ergonomics

Pressure distribution under symptom-free feet during barefoot standing

Foot Ankle

Patterns of center of pressure migration during prolonged unconstrained standing

Motor Control

Hypotheses of peripheral and central mechanisms underlying occupational muscle pain and injury

Eur J Appl Physiol Occup Physiol

Influence of compression hosiery on physiological responses to standing fatigue in women

Med Sci Sports Exerc

Constrained standing: evaluating the foot/floor interface

Ergonomics