Fig. 1. Human model and coordinate frame. The human model has 16 segments with 32 internal degrees of freedom. Using human morphological data from the literature, mass is distributed throughout the model in a realistic manner. The coordinate frame is oriented by the right-hand rule with the z-axis directed vertically, the y-axis pointing in the direction of the walking motion (anterior–posterior direction), and the x-axis pointing to the right of the participant (medio-lateral direction).