Fig. 2.

(a) The schematic for approximating the base of support (BOS, the sole) which is the right foot in this study. The BOS is represented by a decagon. Ten vertexes of the decagon, as indicated by the open circles, are the toe end (1), the heel (2), the first metatarsal joint (3), the fifth metatarsal joint (4), two ends of the heel width (5 and 6); vertexes of 7 and 8 are between 1 and 3, and between 1 and 4, respectively; vertexes of 9 and 10 are between 2 and 5, and between 2 and 6, respectively. The definitions of foot length, foot widths, and ball length were adopted from the literature¹. The reference point for calculating the relative position of the center of mass (COM) to the BOS is the most leftward point on the outline of the BOS. In all simulations, the reference point was the position of the first metatarsal joint because we assume that the foot is along the Z axis. When applying this BOS definition to experimental data, the reference point might be altered due to foot's orientation deviating from the Z asix, as shown in (b).