Validation of a smartphone embedded inertial measurement unit for measuring postural stability in older adults

Abstract

Background. Identifying older adults with increased fall risk due to poor postural control on a large scale is only possible through omnipresent and low cost measuring devices such as the inertial measurement units (IMU) embedded in smartphones. However, the correlation between smartphone measures of postural stability and state-of-the-art force plate measures has never been assessed in a large sample allowing us to take into account age as a covariate.Research question. How reliably can postural stability be measured with a smartphone embedded IMU in comparison to a force plate?Methods. We assessed balance in 97 adults aged 50 to 90 years in four different conditions (eyes open, eyes closed, semi-tandem and dual-task) in the anterio-posterior and medio-lateral directions. We used six different parameters (root mean square and average absolute value of COP displacement, velocity and acceleration) for the force plate and two different parameters (root mean square and average absolute value of COM acceleration) for the smartphone.Results. Test-retest reliability was smaller for the smartphone than for the force plate (intra class correlation) but both devices could equally well detect differences between conditions (similar Cohen's d). Parameters from the smartphone and the force plate, with age regressed out, were moderately correlated (robust correlation coefficients of around 0.5).Significance. This study comprehensively documents test-retest reliability and effect sizes for stability measures obtained with a force plate and smartphone as well as correlations between force plate and smartphone measures based on a large sample of older adults. Our large sample size allowed us to reliably determine the strength of the correlations between force plate and smartphone measures. The most important practical implication of our results is that more repetitions or longer trials are required when using a smartphone instead of a force plate to assess balance.

Reliability and Validity Study of Inertial Sensor-Based Application for Static Balance Measurement

“…D. H et al [28] showed similar results to this study that both sensors have high reliability, and supports the results of this study. On the other hands, the reliability of this study was higher than the study of De Groote et al [19], which reported that the smartphone acceleration sensor has moderate-high reliability. The reason is that this study used a smartphone equipped with an LSM6DSO sensor with improved accuracy than the LSM6DS3 sensor used in De Groote's research.…”

“…On the other hand, the smartphone inertial sensor measures the value of acceleration and angular velocity through the movement of COM from the body. As the body's activity increases, these values become larger [23] Therefore, two signals differ slightly in the movement position, so the relationship cannot be expressed as completely linear [19]. However, because both variables show body sway in proportion to the numerical value and the inertial measurement technologies have the potential to be a reliable alternative compared to the balance evaluation of the force plate [25], many studies have compared simultaneous validity through analysis between the two signals [19,23,26,27].…”

“…As the body's activity increases, these values become larger [23] Therefore, two signals differ slightly in the movement position, so the relationship cannot be expressed as completely linear [19]. However, because both variables show body sway in proportion to the numerical value and the inertial measurement technologies have the potential to be a reliable alternative compared to the balance evaluation of the force plate [25], many studies have compared simultaneous validity through analysis between the two signals [19,23,26,27]. Therefore, this study tried to verify that the acceleration sensor and gyroscope sensor mounted in smartphones have reliability and validity in measuring the static balance abilities.…”

“…They were repeated twice for 35 seconds. When tests were completed, results were repeated a day later (24 hours) with the same postures and methods in order to identify the test-retest reliability [19]. A Galaxy S20 (SM-G981N, Samsung, Korea) mounted with an inertial sensor (LSM6DSO MEMS, STMicroelectronics, Switzerland) was used to measure the static balance tests.…”

“…An inertial measurement unit (IMU), which is key to various rehabilitation studies using smartphones, is a device that measures the speed, direction, gravity, and acceleration of moving objects, consisting of acceleration sensors, geomagnetic sensors, and gyroscope sensors [18]. Various studies have been conducted clinically to develop a smartphone-based balance assessment system by attaching acceleration sensors and gyroscope sensors to the body [17][18][19][20].…”