Evaluation of amplitude- and frequency-based techniques for attenuating inertia-based movement artifact during surface translation perturbations.

Background: Surface translations are a method of perturbing an individual's balance to evoke balance control responses. However, the force plates used to measure kinetic responses often contain artifacts due to inertial properties coupled with the dynamics of surface translation perturbations. Techniques to attenuate these movement artifacts are not well established within the literature.

Research Question: Are amplitude- or frequency-based subtraction processing techniques effective at attenuating inertia-based movement artifacts in kinetic signals during surface translations?

Methods: One-hundred and two backward surface translations were analyzed from five participants. Perturbation-matched unloaded pre-trials were collected to characterize force plate movement artifacts. For each trial, baseline data was processed to account for inertial artifacts using both amplitude- and frequency-based subtraction methods producing 3 datasets. Root mean square error (RMSE) between the datasets and expected tracings of an unloaded force plate were calculated. The effects of these processes on calculated knee flexion/extension (FE) moment were characterized using an inverse dynamics model which incorporated ground reaction forces and participant kinematics.

Results: Both amplitude- and frequency-based processing methods resulted in near identical changes and substantially reduced RMSE values compared to original data. An RMSE reduction of 91.4 % was observed for the unloaded force channel which aligned with the direction of translation. Peak stance knee FE moments decreased by an average of 3.7 Nm and the average largest difference between the original data and both processing techniques across all trials was 30.4 Nm.

Significance: The results provide quantitative evidence that both data processing methods can successfully attenuate the presence of movement artifact found within force plate signals during surface translations. This study provides recommendations to researchers on effective methods for improving data processing techniques to attenuate force plate movement artifacts introduced by surface translations, towards more accurate estimates of joint kinetics during balance reactions.