Date Published: January 23, 2019
Publisher: Public Library of Science
Author(s): Fabienne Reynard, David Christe, Philippe Terrier, Juliane Müller.
Many diseases and conditions decrease the ability to control balance. In clinical settings, there is therefore a major interest in the assessment of postural control. Trunk accelerometry is an easy, low-cost method used for balance testing and constitutes an alternative method to the posturography using force platforms. The objective was to assess the responsiveness of accelerometry in a battery of 12 quiet standing tasks. We evaluated the balance of 100 healthy adults with an accelerometer fixed onto the sternum. We used the average amplitude of acceleration as an indirect measure of postural sways. The tasks of increased difficulty were realized with or without vision. The battery of tasks was repeated four times on two different days to assess reliability. We analyzed the extent to which the task difficulty and the absence of vision affected the trunk sway. The influence of individual characteristics (age, height, mass, sex, and physical activity level) was also assessed. The reliability analysis revealed that four repetitions of the battery of tasks are needed to reach a high accuracy level (mean ICC = 0.85). The results showed that task difficulty had a very large effect on trunk sways and that the removal of vision further increased sways. Concerning the effects of individual characteristics, we observed that women tended to oscillate more than men did in tasks of low difficulty. Age and physical activity level also had significant effects, whereas height and mass did not. In conclusion, age, sex, and physical fitness are confounders that should be considered when assessing patients’ balance. A battery of simple postural tasks measured by upper-trunk accelerometry can be a useful method for simple balance evaluation in clinical settings.
Postural control is the act of maintaining, achieving or restoring a state of balance during any posture or activity . Many diseases and conditions can alter postural control and, hence, increase the risk of falls [2–5]. Consequently, there is a major interest in postural control assessment for diagnostic purposes and for evaluation of the efficacy of therapies [2,3,5,6].
We planned to measure 4800 standing tasks, that is, 12 tasks within two intrasession repetitions and two intersession repetitions measured in 100 subjects. Although there were 149 missing tasks (3%) due to organizational and technical issues, we obtained at least two measures per participant for each standing task. No participants experienced very large imbalance and touched the safety bar longer than a couple of seconds. No participants reported fatigue and lack of attention during the experiment.
We measured 100 healthy adults performing 12 quiet standing tasks with an accelerometer fixed onto the sternum. We used the average amplitude of the acceleration signal (RMS) as an indirect measure of the thorax sway, and, hence, as an index of postural response. We aimed at highlighting typical traits of postural control. We noticed low repeatability of a single sway measure (S1 File), which emphasizes the need for averaging several trials together. We confirmed three well-known observations: 1) sways increase with task difficulty; 2) vision is important to attenuate postural sways; and 3) sways increase with age. In addition, we highlighted more subtle facts: 1) postural control acts differently along the AP and ML directions; 2) leg dominance has no effect on sway amplitude; 3) women oscillate laterally slightly more than men when performing bipedal standing tasks; 4) body mass and height do not have a relevant effect on sway amplitude; and 5) being more active may protect against age effects.
The current study shows that a battery of standing tasks measured with a wearable accelerometer fixed to the upper trunk can evaluate postural control thoroughly. Whereas most other studies have focused on specific aspects of balance, our study covers a large spectrum of explanatory variables. The method seems responsive enough to distinguish among those diverse effectors and offers comparable reliability as other methods.