Testing the assumption of normality in body sway area calculations during unipedal stance tests with an inertial sensor

Abstract

The quantification of postural sway during the unipedal stance test is one of the essentials of posturography. A shift of center of pressure (CoP) is an indirect measure of postural sway and also a measure of a person's ability to maintain balance. A widely used method in laboratory settings to calculate the sway of body center of mass (CoM) is through an ellipse that encloses 95% of CoP trajectory. The 95% ellipse can be computed under the assumption that the spatial distribution of the CoP points recorded from force platforms is normal. However, to date, this assumption of normality has not been demonstrated for sway measurements recorded from a sacral inertial measurement unit (IMU). This work provides evidence for non-normality of sway trajectories calculated at a sacral IMU with injured subjects as well as healthy subjects.

Using Inertial Sensors to Quantify Postural Sway and Gait Performance during the Tandem Walking Test

“…Thus, we utilized jerkiness, a measure of the rate of change in acceleration and deceleration, which reflects the amount of upper body control [32,33,34]. Sway Jerkiness was obtained using a modification of the objective function suggested by Flash and Hogan [28] and calculated as follows: Sway Jerkiness=12∫0t((dxdt)2+(dydt)2)dt where x and y are the acceleration data measured in the ML and AP directions, respectively. We measured the amount of jerky sway at the head, trunk, and pelvis during TW.…”

“…To compensate sensor tilt, we implemented a routine that aligned the frame of the sensor. Specifically, by using data recorded from a short standing period before the TW test, we virtually tilted the sensor’s frame of reference in alignment with the participant’s body such that gravity aligned with the x-axis corresponding to the body’s superior–inferior axis, y-axis with the ML axis, and z-axis with the anterior–posterior (AP) axis [ 28 , 29 ].…”

The development and concurrent validity of a real-time algorithm for temporal gait analysis using inertial measurement units

“…MAPRs were attached to thighs and shanks as described by Kim et al (2016a) with an additional sacral sensor, as described by Kim et al (2016b). A hand-held button that was synchronized with the MAPR system was used to flag interval times.…”

“…Vertical ground reaction force (GRF) was captured on a custom-built Matscan System (2.57m long, sensel resolution 0.8382 cm 2 , Type 3150L sensors; Tekscan) (Kim et al, 2016b) positioned in the center of a 12.25 m walkway with a sampling rate of 50 Hz. The MatScan was chosen as the criterion measure because of its high accuracy (Giacomozzi, 2010), and moderate to good reliability (ICC .44-.95) for measuring plantar pressures during gait (Zammit et al, 2010;Hafer et al, 2013), and ability to capture multiple steps per pass.…”