Validity and repeatability of inertial measurement units for measuring gait parameters

Abstract

Inertial measurement units (IMUs) are small wearable sensors that have tremendous potential to be applied to clinical gait analysis. They allow objective evaluation of gait and movement disorders outside the clinic and research laboratory, and permit evaluation on large numbers of steps. However, repeatability and validity data of these systems are sparse for gait metrics. The purpose of this study was to determine the validity and between-day repeatability of spatiotemporal metrics (gait speed, stance percent, swing percent, gait cycle time, stride length, cadence, and step duration) as measured with the APDM Opal IMUs and Mobility Lab system. We collected data on 39 healthy subjects. Subjects were tested over two days while walking on a standard treadmill, split-belt treadmill, or overground, with IMUs placed in two locations: both feet and both ankles. The spatiotemporal measurements taken with the IMU system were validated against data from an instrumented treadmill, or using standard clinical procedures. Repeatability and minimally detectable change (MDC) of the system was calculated between days. IMUs displayed high to moderate validity when measuring most of the gait metrics tested. Additionally, these measurements appear to be repeatable when used on the treadmill and overground. The foot configuration of the IMUs appeared to better measure gait parameters; however, both the foot and ankle configurations demonstrated good repeatability. In conclusion, the IMU system in this study appears to be both accurate and repeatable for measuring spatiotemporal gait parameters in healthy young adults.

Keywords: Accuracy; Biomechanics; Gait detection; Inertial sensors; Wearable; Wearable devices.

Figure 1

Schematic of the human gait cycle and the spatiotemporal parameters validated in this study. Specifically, we validated the IMU system’s ability to measure the stance percent, swing percent, stride duration (gait cycle time), stride length, and step duration in addition to the speed and cadence of the cycle.

Figure 2

Bland-Altman plots for validity of both foot and ankle configurations during treadmill, split-belt, and overground walking conditions. The plots show the validity of gait speed as measured with the IMUs against the speed measured with the treadmills and ten meter walk test for each subject and speed. The Y-axis of the plot corresponds to the difference between the two measurement systems, while the X-axis is the average of the two measurements. Solid lines mark the average difference for the whole sample, while the dashed lines correspond to the 95% limits of agreement. Sample size: Treadmill (n = 25); Split-belt (n = 11); Overground (n = 14).