Effects of age and pathology on stance modifications in response to increased postural threat
Highlights
► Potential of a physical threat to stability elevated postural anxiety. ► Trunk sway changes in response to elevated anxiety depended on age. ► Anxiety increased sway in young adults but decreased sway in older adults. ► Trunk sway did not change in response to elevated anxiety in individuals with PD. ► This lack of adaptation should be considered when training balance and gait in PD.
Introduction
An anxiety or fear related to falling is frequently reported in older adults [1] and is even more common in individuals with postural control problems [2]. This type of anxiety or fear has been linked to different behavioral outcomes including postural instability, increased risk of falls, restriction of daily activities, loss of independence, and reduced quality of life [1], [3]. Given these negative associations, there is a need to better understand the influence of emotions on postural control [4].
The introduction of a physical or social threat to posture has been used as a method to investigate the effects of state-related changes in emotions on postural control in young adults [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. The findings from this research have been mixed with an increase, decrease, or no change in postural sway reported in conditions of increased postural threat. Research has shown that, when standing at a height of up to 1.6 m above the ground, young adults adopted a stiffening strategy characterized by reduced amplitude and increased frequency of postural adjustments [5], [6], [7]. Consistent with this work, a “freezing-like posture” has been observed when young adults viewed unpleasant images such as photographs of mutilation [8], [9], [10]. However, when standing at higher heights, young adults who displayed a robust fear response demonstrated increased amplitude and frequency of postural adjustments and not the typically observed stiffening strategy [11]. Young adults also increased the amplitude as well as the frequency of postural adjustments in the time directly before the delivery of a vibratory stimulus to the calf muscle [12] or an aversive sound [13]. Other research has shown that young adults did not modify standing posture in response to the presence of an expert who evaluated their posture [14].
Research has also been conducted to determine if age or pathology are factors that alter the ability to modify postural control to changes in emotional context (i.e., introduction of a threat to posture). Similar to work on young adults, the results of this research have been varied. For example, a stiffening strategy when standing at a height has also been observed in older adults [15], [16] and patients with Parkinson disease (PD) [17]. However, older adults, but not patients with PD, modified postural control (i.e., reduced amplitude of postural adjustments) when standing at a height with a step restriction [18]. A lack of modification to a change in context has also been observed in patients with phobic postural vertigo who did not modify postural control in the same manner as healthy adults when standing and anticipating an anxiety-inducing stimulus [12]. Larger amplitude and frequency of postural adjustments have been observed when older adults were evaluated by an expert [14].
This research suggests that emotional responses may not have a general effect on postural control, but that the effects are dependent upon the context associated with the threat used to evoke the emotional response, and the population investigated. Furthermore, it appears that these modifications to postural control may benefit or interfere with stability. As there are a number of different situations encountered in daily life that can generate a threat to posture, it is important to investigate whether modifications to postural control are consistent across these situations or whether specific modifications are observed depending on the context associated with the threat.
The current study investigated trunk sway modifications in anticipation of a physical threat to trunk stability in young adults, older adults and patients with PD. It was hypothesized that young and older adults would show a decrease in trunk sway [5], [6], [7], [15], [16] and patients with PD would demonstrate a decrease [17] or no changed in trunk sway [18] when standing and anticipating a postural threat.
Section snippets
Participants
Sixteen young adults (mean ± standard deviation age, 22.0 ± 1.6 years), 16 older adults (mean ± standard deviation age, 67.3 ± 7.1 years), and 16 older adults diagnosed with idiopathic PD (mean ± standard deviation age, 64.1 ± 9.6 years; mean ± standard deviation disease duration since diagnosis, 3.8 ± 2.3 years) volunteered to participate in this study. All participants were living in the community and were ambulatory. Exclusion criteria for young and older adults included any self-reported musculoskeletal,
Postural anxiety
The results showed a significant main effect of group for postural anxiety (F(2, 45) = 7.69, p = 0.001). Post hoc comparisons were completed between groups and revealed that young adults reported lower postural anxiety scores compared to PD patients (p = 0.001). No other comparisons between groups were significant. The results also showed a significant main effect of postural threat for postural anxiety (F(1, 45) = 23.53, p < 0.0001). Young and older adults and PD patients all reported more postural
Discussion
This study investigated changes in trunk sway in response to elevated postural anxiety evoked by a potential physical threat to stability. Our manipulation was successful as all participants, independent of age or disease, reported significant increases in postural anxiety when anticipating a postural threat. The trunk sway modifications observed in response to elevated postural anxiety were dependent on age and disease.
It was hypothesized that, in conditions of elevated postural anxiety, young
Conflict of interest statement
No authors had any conflict of interest that may have biased this work.
Acknowledgement
Research supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).
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