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Postural control during prolonged standing.

Freitas S.M.S.F.,. Wieczorek S.A., Marchetti P.H and Duarte M. (2005) Age-related changes in human postural control of prolonged standing. Gait and Posture. 22: 322-330.

Abstract: The aim of this study was to investigate postural control mechanisms in older adults during prolonged standing tasks. During a normal day we spend periods of time in prolonged standing, for example, when washing the dishes, or talking to someone over the garden fence. Little is known about the motor control characteristics of prolonged standing, particularly in older adults. Freitas et al recorded the centre of pressure (COP) position of 14 older and 14 younger adults during prolonged standing (30min) and quiet stance tasks (60s). A quiet stance task was followed by the prolonged stance task and then a second quiet stance task was performed. Characteristics of the COP movements were described. During the prolonged standing task it was usual to make adjustments to the body position and COP to maintain comfort. The older adults were able to complete the prolonged standing task but produced smaller postural adjustments and less sway than the younger adults. Following the prolonged standing task both the older and younger adults altered their sway characteristics of the second quiet stance task in comparison to the first quiet stance task, indicating that sway characteristics may be influenced by prior task performance. The authors suggested that the reduction of COP movement in older adults may be related to a loss of postural control and an increased risk of falling.

Berg, K., Wood-Dauphinee, S., Williams, J. I., & Gayton, D. (1989). Measuring balance in the elderly: preliminary development of an instrument. Physiotherapy Canada, 41(6), 304-311.

Duarte M., & Zatsiorsky V.M., (1999). Patterns of centre of pressure migration during prolonged unconstrained standing. Motor Control. 3:12-27.

McClenaghan, B.A., Williams, H.G., Dickerson, J. Doewda, M., Thombs, L., Eleazer, P., (1996). Spectral characteristics of aging postural control. Gait & Posture. 4:112-21.

Commentary

This paper provides interesting information about the control of quiet stance. In the clinic we often look at quiet stance in our patients, and consider sway characteristics, judging someone with increased sway to have poor balance. Seldom do we consider that reduced sway may be indicative of postural control problems as Freitas et al's suggest.

In normal everyday function it is usual for us to stand for reasonably prolonged periods of time in one position. During prolonged standing tasks there are continuous low amplitude swaying movements, with the occasional fast postural change as we move weight from one foot to another and change our position to avoid discomfort. In normal healthy adults there are 1-2 fast postural changes made per minute.

Seldom do we assess a patient's ability to stand for prolonged periods. The Berg Balance Scale (Berg et al 1989) includes an assessment of standing, but the instructions are to maintain the position for 2 minutes, clinical experience with this suggests that people tend to stand still, trying not to move their feet. It would be of interest to know what older adults do in a more unconstrained prolonged standing task.

In the above study the authors investigated the manner in which older adults stand for prolonged periods. Twenty-eight people were recruited into the study, 14 older and 14 younger adults. A weakness in the sample selection was that of the 14 elderly participants three had arthritis of the knee and two had labyrinthitis, these factors may influence balance and sway characteristics. However the authors indicate that there was no difference in the performance of these people compared to the rest of the sample. The older adults were on average 68 [+ or -] 4 years of age and the young adult group was 28 [+ or -] 7 years of age.

Participants stood on a force plate for 1 minute, then 30 minutes, then 1 minute again. In the prolonged stance task (30 minutes) the participants were allowed to move their feet as needed, in the short tasks they had to stand as still as possible. The amount of sway in antero-posterior and medio-lateral directions was calculated. The patterns of lateral sway were characterised according to previous work (Duarte & Zatsiorsky, 1999) and consisted of 3 patterns, shifting (like a small step), fidgeting (a fast, large movement of the COP to another position and then a slow return to about the same position) and drifting (slow continuous movement of the COP in one direction).

The results indicated that there was no difference in the average number of fast postural changes between the older and younger adults (2.4 and 2.2 per minute respectively). Fidgeting was the most common pattern. The younger adults tended to move further in both directions than the older adults. In the last 10 minutes of the prolonged stance trial movements in an AP and M-L direction were generally greater than those in the first 10 minutes of the trial. An interesting finding was that when the centre of pressure was plotted over the whole 30 minutes younger adults had a multi-centred pattern. Meaning that they displaced their centre of pressure a number of times and kept in that position (see figure 1 for clarification). Most older adults had only one centre of pressure location. It is worth noting that of the 3 older adults who had a multi-centred pattern, one had arthritis and one labyrinthitis, this may suggest that with pathologies there are further changes to the characteristics of sway patterns.

[FIGURE 1 OMITTED]

A medio-lateral shifting of weight has previously been reported as an important mechanism for postural control (McClenaghan et al, 1996). The decrease in medio-lateral weight shift shown in Freitas et al's study may indicate a deficit in this postural control mechanism in older adults. The use of a single force plate in the study meant that it was not possible to determine whether medio-mediolateral shifts were due to weight transfer from one lateral foot to the other or a stepping movement. It would be of use to know if small steps or weight shifts without steps were the predominant strategy used by individuals and how this differed between the group. This could be ascertained using 2 force plates, with one foot on each.

This paper provides us with useful food for thought. When we are assessing postural control in our patients we should think about assessing prolonged standing where appropriate. An important factor may be the ability to be mobile (transferring weight from foot to foot, perhaps taking small steps) during the task. Of course if we give the instruction to 'stand as still as possible' then we may not see this mobility of the centre of pressure. Our patients may show signs of increased sway as an indicator of poor postural control (for example a person with cerebellar ataxia) but they may also show reduced amounts of sway as an indicator of poor postural control. Perhaps we should be on the lookout for both. I am not advocating that we test prolonged standing in all our patients (certainly not for 30 minutes!), but I do think that for some patients it may be an interesting, appropriate and useful consideration.

Dr Denise Taylor, PhD, MSc (Rehabilitation), Grad Dip Phys Senior Lecturer at the School of Physiotherapy and researcher in the Physical Rehabilitation Research Centre, Auckland University of Technology.

(abstract prepared by Denise Taylor)
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Author:Taylor, Denise
Publication:New Zealand Journal of Physiotherapy
Geographic Code:8NEWZ
Date:Mar 1, 2006
Words:1222
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