Identification Method for Seated Balance Control Based on Horizontal Support-Surface Sway and Dual Force-Platform Measurements

Identifying seated balance control may contribute to estimation of time delay and evaluation of vestibular weighting. However, few practical methods exist for measuring seated body motion or identifying seated balance control. This study aimed to estimate upper-body center of mass (COM) displacement during sitting under horizontal sway of the support surface using a practical measurement method and to identify a seated balance control system for each individual. Two force platforms under the buttocks and feet were synchronized with a support surface accelerometer. Under unpredictable horizontal perturbations composed of a multi-cosine waveform below 1.50 Hz, balance control was identified in an eyes-closed condition using a parametric model incorporating delayed COM state feedback and horizontal head acceleration feedback, the latter representing otolith-mediated detection of horizontal head acceleration. When validated against an optical motion capture system (five participants), the identified parameters exhibited an average relative error of less than 5%. A two-day reproducibility test (25 participants) yielded intraclass correlation coefficients (ICC(1,1)) of the four identified parameters ranging from 0.57 to 0.73, indicating moderate reliability. The identified head acceleration feedback gain may indicate head acceleration sensitivity, even among healthy adults.