Figure 2

Laboratory setup for the analysis of COP displacement during APAs. a) Placement of the two force plates b) COP displacement in the medio-lateral (x) and antero-posterior (y) directions during the gait initiation process in a healthy subject. APA onset, Heel-Off, Toe-Off, and Foot Contact instants of the leading foot and the Toe-Off instant of the trailing one are reported. Imbalance (from APA onset to heel-off of the leading foot), unloading (from heel-off to toe-off of the leading foot), and swing (from toe-off to foot contact of the leading foot) phases are indicated. L1 line passing through the points representing the COP position at APA onset and at the toe-off of the trailing foot instants, and L2 line passing through the points representing the COP position at APA onset and at the toe-off of the leading foot instants are drawn. d_1MAX represents the maximal distance from L1 attained by the COP (corresponding to toe-off of the leading foot), while d_2MAX represents the maximal distance from L2 attained by the COP (corresponding to heel-off of the leading foot).