Inertial Measures of Motion for Clinical Biomechanics: Comparative Assessment of Accuracy under Controlled Conditions - Effect of Velocity

Mathieu Hamel,Karina Lebel,Christian Duval,David Carrier,Patrick Boissy

doi:10.1371/journal.pone.0079945

Abstract

BackgroundInertial measurement of motion with Attitude and Heading Reference Systems (AHRS) is emerging as an alternative to 3D motion capture systems in biomechanics. The objectives of this study are: 1) to describe the absolute and relative accuracy of multiple units of commercially available AHRS under various types of motion; and 2) to evaluate the effect of motion velocity on the accuracy of these measurements.MethodsThe criterion validity of accuracy was established under controlled conditions using an instrumented Gimbal table. AHRS modules were carefully attached to the center plate of the Gimbal table and put through experimental static and dynamic conditions. Static and absolute accuracy was assessed by comparing the AHRS orientation measurement to those obtained using an optical gold standard. Relative accuracy was assessed by measuring the variation in relative orientation between modules during trials.FindingsEvaluated AHRS systems demonstrated good absolute static accuracy (mean error < 0.5o) and clinically acceptable absolute accuracy under condition of slow motions (mean error between 0.5o and 3.1o). In slow motions, relative accuracy varied from 2o to 7o depending on the type of AHRS and the type of rotation. Absolute and relative accuracy were significantly affected (p<0.05) by velocity during sustained motions. The extent of that effect varied across AHRS.InterpretationAbsolute and relative accuracy of AHRS are affected by environmental magnetic perturbations and conditions of motions. Relative accuracy of AHRS is mostly affected by the ability of all modules to locate the same global reference coordinate system at all time.ConclusionsExisting AHRS systems can be considered for use in clinical biomechanics under constrained conditions of use. While their individual capacity to track absolute motion is relatively consistent, the use of multiple AHRS modules to compute relative motion between rigid bodies needs to be optimized according to the conditions of operation.

Highlights

Mobility is a fundamental part of self-care activities and instrumental activities of daily living within an individual’s place of residence or the community
Existing AHRS systems can be considered for use in clinical biomechanics under constrained conditions of use
Accurate tracking is limited to a specific motion capture volume with either a clear line of sight between multiples cameras and the markers used for the optical systems, or without any ferrous elements to minimize magnetic tracker distortion for the magnetic tracking systems

Summary

Introduction

Mobility is a fundamental part of self-care activities and instrumental activities of daily living within an individual’s place of residence or the community. It is achieved through coordinated physiological and mechanical interactions between bones, muscles, ligaments and joints under the control of the central and peripheral nervous systems. Mobility impairments are measured using self-report questionnaires, performance based clinical tests or with instrumented techniques such as 3D capture of joint motion with optical or magnetic tracking systems. 3D capture of joint motion with optical or magnetic tracking systems is expensive, complex to configure and operate for clinicians but offer highly accurate tracking within a given volume [1]. The objectives of this study are: 1) to describe the absolute and relative accuracy of multiple units of commercially available AHRS under various types of motion; and 2) to evaluate the effect of motion velocity on the accuracy of these measurements

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Conclusion