Enhanced somatosensory information decreases postural sway in older people
Highlights
► We examined the effects of textured insole surfaces on changing postural sway of young and older people during standing. ► We tested people under conditions of vision, no vision, firm and foam surfaces. ► The textured insole surface decreased postural sway in older people especially while standing on a foam surface with no vision. ► Changes in postural sway were attributed due to the enhancement of the somatosensory information received from the feet.
Introduction
Age-related declines in sensory and motor function can result in postural instability and an increased risk of falls leading to injury, hospitalization and mortality [1]. One third of community-dwelling older people over 65 years fall at least once a year [2]. Accurate detection and integration of somatosensory information from the feet is important for balance control [3]. Degeneration of peripheral sensory receptors, exemplified in diabetic peripheral neuropathy [4], can lead to a diminished capacity to detect information from the soles of the feet during interactions with the external environment [5], [6]. Diminished somatosensory function has also been identified as a significant age-related change and is believed to be a significant contributor to postural instability and falls [7]. Older participants have a lower sensitivity of the plantar surface of the foot than younger individuals [6], [8], which can increase postural sway [9].
Artificially reducing somatosensory information, by cooling [10] or local anesthetic ischemia induced by hypoxic anesthesia of the feet and ankles [11], can increase postural sway. Standing on a foam surface reduces the reliability of somatosensory information and increases postural sway. These effects are exacerbated when vision is excluded and greater reliance is placed on somatosensory information [12]. The effects of standing on a foam surface have been equated to diabetic peripheral neuropathy [4], [6] and more recently Patel et al. [13] reported that standing on a foam surface with eyes closed decreased the reliability of somatosensory information of feet. This observation was also supported by findings of Vuillerme and Pinsault [14] who recognized that somatosensory inputs from the feet were degraded by standing on a foam surface.
Previous research has provided some evidence that artificially enhancing cutaneous information can change postural sway and potentially improve postural stability [15], [16]. Kavounoudias et al. [17] showed that supra-threshold vibratory stimulation of the feet during quiet stance altered postural sway; bilateral stimulation of the forefoot resulted in backward leaning. Similarly, sub-threshold mechanical vibration applied to the soles of the feet increased the detection of plantar pressure changes, with a consequent reduction in postural sway in older people [16] and peripheral neuropathy patients [18]. However, practically, vibratory devices can be expensive and complex to adopt as effective interventions to decrease postural sway. Clearly there is a need to develop and evaluate simple and inexpensive interventions that can enhance somatosensory feedback from the feet and diminish postural sway.
Recent research has suggested that passive devices may provide an inexpensive and effective alternative to decrease postural sway. Palluel et al. [19] reported reduced postural sway during quiet stance for older people while wearing sandals with firm rubber nodules. However, sandals may not be suitable footwear for all individuals and their use can be limited by environmental, work and social constraints. Furthermore, sandals and other footwear have been suggested to introduce different confounding effects due to differences in shoe design and construction [20]. Additionally, Palluel et al. [19] only evaluated postural sway on a firm surface and did not randomize the order of testing conditions, which may have introduced a learning effect into their results. Assessing postural sway while standing on a foam surface may decrease the reliability of somatosensory information from the feet and provide a more useful way to evaluate the effect of somatosensory changes on postural sway, especially without visual input. Similarly, Corbin et al. [21] reported reduced postural sway in younger participants while wearing insoles which had a textured pattern; but their effectiveness in older people was not assessed. Recently Hatton et al. [20] noticed that mediolateral sway was decreased when standing on textured surfaces in older people. However, the performance of a younger control group was not evaluated in their study.
The aim of this study was to examine the efficacy of a newly designed textured insole surface for reducing postural sway in healthy younger and older adults during standing balance. Due to aging effects on the peripheral nervous system it was expected that insole surface attenuation effects on postural sway were likely to be greater in the older groups, compared to the younger groups, especially under conditions where peripheral somatosensory information was more important in maintaining postural stability.
Section snippets
Participants
Seven elderly adults (four males and three females; mean age 72 ± 4 years; Body Mass Index (BMI) 25.6 ± 2.2 kg/m2) and ten healthy young adults (six males and four females; mean age 27 ± 3 years; BMI 22.3 ± 2.4 kg/m2) participated in this study. Elderly participants were randomly selected from a pre-existing database of healthy older adults who had expressed an interest in being involved in this type of research. All participants were free of significant cognitive impairment (Mini Mental State
Results
Clear differences in postural sway as a function of age, insole surface and standing surface were revealed by a significant Group*Surface*Insole interaction for C90 area, PL, AP and ML sway and ML SD (p < 0.05).
Discussion
This study examined the efficacy of inexpensive textured insole surfaces in reducing postural sway under conditions that challenged the somatosensory system in younger and older participants.
Consistent with previous research [23], the current study demonstrated that, overall, older participants displayed greater postural sway than younger participants during standing with bare feet. However, the older group demonstrated a significant and progressive decrease in postural sway from the barefoot
Acknowledgements
This research was supported by research grants from Queensland University of Technology and Parkinson's Queensland Inc. Feng Qiu was supported by a China Scholarship Council (CSC) scholarship. Furthermore, the authors are grateful to those participants who gave so generously of their time and helped to make this research possible.
Conflict of interest statement
We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our
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