Validity of Valor Inertial Measurement Unit for Upper and Lower Extremity Joint Angles

Abstract

Inertial measurement units (IMU) are increasingly utilized to capture biomechanical measures such as joint kinematics outside traditional biomechanics laboratories. These wearable sensors have been proven to help clinicians and engineers monitor rehabilitation progress, improve prosthesis development, and record human performance in a variety of settings. The Valor IMU aims to offer a portable motion capture alternative to provide reliable and accurate joint kinematics when compared to industry gold standard optical motion capture cameras. However, IMUs can have disturbances in their measurements caused by magnetic fields, drift, and inappropriate calibration routines. Therefore, the purpose of this investigation is to validate the joint angles captured by the Valor IMU in comparison to an optical motion capture system across a variety of movements. Our findings showed mean absolute differences between Valor IMU and Vicon motion capture across all subjects' joint angles. The tasks ranged from 1.81 degrees to 17.46 degrees, the root mean squared errors ranged from 1.89 degrees to 16.62 degrees, and interclass correlation coefficient agreements ranged from 0.57 to 0.99. The results in the current paper further promote the usage of the IMU system outside traditional biomechanical laboratories. Future examinations of this IMU should include smaller, modular IMUs with non-slip Velcro bands and further validation regarding transverse plane joint kinematics such as joint internal/external rotations.

Keywords: biomechanics; inertial measurement unit; motion capture; validation; wearable sensors.

Figure 1

Representative illustration of Valor inertial measurement unit placement. Ten Valor Velcro straps are used to secure each Valor IMU to the subjects’ ankles, shanks, thighs, waist, trunk, and upper arms, as seen marked by the red circles.

Figure 2

Left and right ankle, knee, and hip joint angles are represented by the average curves between Vicon motion capture (V3D), shown in red, and the Valor inertial measurement unit (Valor), shown in blue. Data from a representative subject performing the vertical jump task.

Figure 3

Left and right shoulder joint abduction and flexion angles are represented by the average curves between Vicon motion capture (V3D) shown in red, and the Valor inertial measurement unit (Valor), shown in blue. Data from a representative subject performing the vertical jump task.

Figure 3

Left and right shoulder joint abduction and flexion angles are represented by the average curves between Vicon motion capture (V3D) shown in red, and the Valor inertial measurement unit (Valor), shown in blue. Data from a representative subject performing the vertical jump task.