DEVELOPMENT, COHERENCE AND RELIABILITY OF A WEARABLE INERTIAL MEASUREMENT UNIT FOR MEASURING POSTURAL SWAY

Ekvall Hansson E1, Tornberg Å21Lund University, Department of Health Sciences, Lund, Sweden, 2Lund University, Department of Health Sciences/Child and Family Health, Lund, SwedenBackground: Balance can be measured in many different ways and situations, depending on the task and on the objective of measurement; efforts have been made to determine adequate and clinically useful measures of balance for different populations specifically in terms of identifying people at risk of falling. However, these efforts do not seem to be sufficient to determine who actually sustains a fall-related fracture. Postural sway is one measure of balance that has been suggested as appropriate for identifying individuals who are at high risk of falling. Postural sway is often measured using a force plate, which is suitable for laboratory use but harder to apply in clinical practice. The use of a wearable device increases the usefulness of postural sway as a measure of balance and risk of fall in clinical practice. However, it is important to test the validity of such a device before using.Purpose: The aim of this study was to describe the development of a wearable inertial measurement unit (IMU) for measuring postural sway and to test the coherence of the IMU against the gold standard; also, to test the intra-trial reliability.Methods: This study has a cross-sectional design in three steps, where measurement of postural sway in the medio-lateral and anterior-posterior directions was performed simultaneously on a force plate and with a wearable device, called the Snubblometer (snubbla is stumble in Swedish). Twenty-four healthy volunteers participated in the first test, 23 in the second and 32 in the third. Paired student's t-test was used when comparing postural sway assessed with the force plate against postural sway assessed with an IMU. Pearson's correlation (rp) was used for analysis of the coherence between the force plate and the IMU. Test-retest correlations were calculated both for intra-session and inter-session relations. Intra-class correlation coefficient and coefficient of variance were used to analyse intra-session and inter-session reliability. As part of the inter-session reliability analysis, the standard error of measurement (SEM) was assessed and calculated as SEM = SD x √.Results: The coherence between the IMU and the force plate was 0.84 (strong) in the medio-lateral direction with eyes open (EO) and 0.88 (strong) with eyes closed (EC). The ICC for intra-trial reliability for the IMU varied between 0.50 to 0.67 (moderate to good) with a CV between 17.8% to 22.1% and ICC varied between 0.75 to 0.86 (good) for inter-trial reliability, with an SEM of 0.98 to 1.96 mm/s.Conclusion(s): We have demonstrated that the IMU was both reliable and highly coherent with golden standard, although the two assessment methods were not interchangeable.Implications: The ability to move the balance lab out into real life in the form of a wearable device will provide opportunities to perform research that has not been possible before.Keywords: Balance, Wearable device, FallsFunding acknowledgements: The study was funded by Vinnova (TheSwedish Innovation Agency).Topic: Human movement analysis; Disability & rehabilitation; Older peopleEthics approval required: YesInstitution: Lund UniversityEthics committee: Regional Ethical Review Board in LundEthics number: 2016/585All authors, affiliations and abstracts have been published as submitted.