Elsevier

Human Movement Science

Volume 29, Issue 6, December 2010, Pages 1011-1022
Human Movement Science

Dynamic postural stability is not impaired by moderate-intensity physical activity in healthy or balance-impaired older people

https://doi.org/10.1016/j.humov.2010.06.001Get rights and content

Abstract

Older people are increasingly being encouraged to be more physically active but this may lead to physiological fatigue, tiredness and other effects, which, at high levels, can adversely alter postural stability. However, older adults rarely perform physical activity at high intensities. This study aimed to determine whether a single bout of moderate-intensity physical activity, similar to that experienced during daily living, alters dynamic postural stability, particularly among those at risk of falling. Thirty-one healthy young, 33 healthy older and 21 balance-impaired older, adults performed a rapid, voluntary step-up task before and immediately after a 14 min, self-paced, moderate-intensity physical activity protocol. Timing of step components from vertical ground reaction forces, mediolateral displacement of center of pressure, and onset and amplitude of hip abductor muscle activity were recorded during the step task. All groups demonstrated the same changes after the activity, with slightly shorter weight-shift phase duration, smaller displacement of the center of pressure towards the stance leg during weight shifting, and earlier onset of stance leg gluteus medius activity. These changes indicate improved coordination of the step task after activity. Thus this study showed that dynamic postural stability is not adversely affected immediately following moderate-intensity physical activity, even among balance-impaired elderly.

Introduction

Physical activity can lead to a range of acute effects including sensations of tiredness and cardiovascular system responses, as well as physiological fatigue leading to decreased ability to generate muscular force (Allman and Rice, 2002, Gandevia, 2001, Hunter et al., 2004). In previous studies, older people have demonstrated compromised postural stability following high levels of physical activity (Adlerton and Moritz, 2001, Moore et al., 2005). Postural stability is a major contributor to balance and balance deficits are a primary risk factor for falling in the elderly (Lord and Clark, 1996, Maki et al., 1994, Stel et al., 2003, Tinetti et al., 1988). Thus it follows that falls risk in older adults could be increased if the ability to maintain postural stability were transiently compromised following bouts of physical activity.

Previous studies of postural stability following physical activity have concentrated on the effect of exercise involving maximal efforts or reaching task failure (Adlerton and Moritz, 2001, Moore et al., 2005). This type of exercise is dissimilar to most physical activity experienced by older people during daily living or rehabilitation, making clinical application difficult. Further, the previous studies have demonstrated altered postural stability by measuring postural sway in quiet standing, while most falls among older adults are reported to occur during movement (Shumway-Cook & Woollacott, 2001). Investigation of the effect of moderate levels of physical activity on postural stability during movement such as rapid stepping, would more directly address the issue of whether older people may be at greater risk of falling following everyday physical activity.

Rapid voluntary step tasks have been previously used to investigate dynamic postural control in older adults. Delayed responses and longer movement times when stepping, and altered associated muscle activity have been found in older adults when compared with young individuals (Brauer and Burns, 2002, Demura et al., 2005, Michel-Pellegrino et al., 2008), and when balance-impaired elders are compared with healthy older adults (Medell and Alexander, 2000, Schulz et al., 2007, St. George et al., 2007). In addition, delayed and longer movement time during a rapid forward step has also been shown to be predictive of falling (Brauer, Burns, & Galley, 2000). Mediolateral stability appears to be of particular relevance to falling both because of the relatively greater balance deterioration in this plane of motion (Maki and McIlroy, 1996, Piirtola and Era, 2006) and the more severe consequences of a sideways directed fall (Greenspan et al., 1998, Kannus et al., 2006). A forward step-up task, where the foot is stepped onto a higher surface, has been shown to challenge mediolateral stability to a greater extent than a level forward step (Sims & Brauer, 2000).

This study aimed to determine if physical activity, at moderate intensity and similar to daily living tasks, has an acute effect on dynamic postural stability when performing a rapid voluntary step-up task, and whether older adults and balance-impaired older adults have a different acute response to young people.

Section snippets

Participants

Thirty-one healthy young people, 33 healthy older adults, and 21 balance-impaired older adults participated in this study. Volunteers from any group were excluded if they had disease processes or sensory deficits directly affecting balance, such as chronic pain, hip replacement, stroke, vestibular symptoms, known peripheral sensation loss or uncorrectable loss of visual acuity. They were also excluded if they were unable to safely exercise due to pain or cardiovascular system disease. The young

Timing of step-up task components

There were no differences between the groups in their response to the activity for all timing variables (Group × Test interactions all p > .05) (Table 2). There was a significant difference in the weight shift time (p  .05) when participants from all three groups were pooled, with weight shift time being shorter by a mean of 17 ms (95%CI 1–33 ms) post-activity. However when within-subject test effects were investigated post hoc, there were no significant differences in pre- versus post-activity for

Effect of physical activity on dynamic postural stability

This study investigated the immediate effect of moderate-intensity physical activity on performance of a rapid voluntary step-up task in three groups of participants. Overall, the activity resulted in few changes in the measured characteristics of voluntary stepping. Following the activity, participants from all groups stood with their center of pressure (COP) shifted a little more towards the stance leg at baseline, moved their COP a shorter distance towards the stance leg during weight shift,

Conclusions

As a result of the findings from this study, bouts of physical activity similar to that experienced during daily living appear not to lead to detrimental changes in dynamic postural stability for healthy or balance-impaired older people. While this is good news, the study only begins to answer the question of whether older people are more unsteady or not immediately following physical activity. Further research is required before conclusions about fall risk immediately following physical

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