Inertia compensation for perturbations on instrumented treadmills

Abstract

Instrumented treadmills and perturbations of the treadmill are commonly used for gait analysis and can provide real time biomechanical information and feedback of gait patterns and abnormalities. Force plates in the treadmill are combined with motion capture data and fed into a musculoskeletal model. High accuracy of the force plates is needed to give reliable feedback for gait analysis. The accuracy still needs to be tested under dynamic conditions, with the belt running. Also, inertial and gravitational forces are measured during perturbations as a result of the rotation and translation of the platform in which the force plates are positioned. This results in an error in the forces and moments as measured by the force plates, which is added up to the forces exerted by a subject. Inertia compensation models have been developed and showed promising results but have not been validated extensively. This study aimed to optimize and validate an inertia compensation model for perturbations on instrumented treadmills and validate the force measurements under dynamic conditions. It was shown that the treadmill can accurately measure the center of pressure (error = 1-6 mm), forces (error = 1-7 N) and moments (error = 0.5-4 Nm). A new calibration trial was found with higher sway accelerations which improved the inertia compensation model and left residuals forces and moments below 2 N(m). Moreover, it showed that using this inertia compensation model for pitch and sway trials led to a reduction of the kinetic residuals of up to 96% and values close to baseline measurements.