A 3D Foot-Ground Model Using Disk Contacts

A foot contact model is an important component of any forward-dynamic human gait simulation. This work presents a preliminary experimental validation of a three-dimensional (3D) foot contact model that represents the heel and forefoot using a pair of contact disks. The disk elements are well-suited to modeling the foot because they are computationally efficient and are mechanically stable when flat on the ground. We evaluated the foot model by comparing its ankle position to the subject’s ankle position (measured using skin-mounted reflective markers and infrared cameras) when both feet developed the same ground reaction force (GRF) and center-of-pressure (COP) profiles (measured using a force plate). We used this novel approach because the experimental GRF and COP measurements are accurate, but the kinematic data is usually corrupted with 1 cm of skin-movement error at the foot. The results indicate that the disk-based foot model is an accurate representation of the subject’s barefoot except during toe-off, and when the COP is on the extreme medial boundaries of the foot. The experimental data and foot model presented in this work is provided as supplementary material online.