Inertial measures of motion for clinical biomechanics: comparative assessment of accuracy under controlled conditions - effect of velocity.

Inertial 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.The 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.Evaluated AHRS systems demonstrated good absolute static accuracy (mean error < 0.5(o)) and clinically acceptable absolute accuracy under condition of slow motions (mean error between 0.5(o) and 3.1(o)). In slow motions, relative accuracy varied from 2(o) to 7(o) depending on the type of AHRS and the type of rotation. Absolute and relative accuracy were significantly affected (p