Figure 1.

Schematic of the spatial margin of stability (MoS) in the anterior–posterior (AP; top row) and medio-lateral (ML; bottom row) directions. Adapted from Hak et al. [7]. (a) The AP MoS was defined as the distance in the AP direction between the extrapolated centre of mass (XCoM) and the posterior border of the leading foot at initial contact. Therefore, taking a shorter step increases the AP MoS (top left), while taking a longer step decreases the AP MoS (top right). (b) The ML MoS was defined as the minimum distance between the XCoM and the lateral border of the foot during foot contact. Therefore, a wider step results in a greater ML MoS (bottom left), while a narrower step results in a smaller ML MoS (bottom right). Although the definition from Hak et al. [7] differs from the definition used in the present study, the same principles apply.