The 3D trajectory of the body centre of mass and other mechanical aspects of race walking

Race Walking (RW) athletes are required to have always at least one foot in contact with the ground. While coded as a variety of ‘walking’ (W), potential and kinetic energy of the body centre of mass (BCoM) are in phase as in running (R). Aims of this work were to measure the 3D BCoM trajectory, in order to check the resemblance with W or R, and its speed dependence. 16 athletes were tested on treadmill and on 5 force platforms at different speeds by using both direct and inverse dynamics techniques. On treadmill BCoM was computed from the kinematics of 11 rigid segment model, sampled by 8 Vicon MX cameras at 300Hz. The RW trajectory was found to be different both from W, with the lowest position reached at single mid-support and the highest one during double support, and from R, since left and right semi-trajectories do not meet at their top. Also, RW trajectory has a smaller vertical excursion than in R, as a result of the discipline constraint. Symmetry indices (one for each spatial axis) of BCoM kinematics on the treadmill are greater and more consistent in RW than in W or R, witnessing the high athletic level of the participants. The trajectories from inverse dynamics were found to be differently shaped and wider than from the direct dynamics (the golden standard) due to the 3D position bias of BCoM induced by RW peculiar hip movement. A methodological study will be designed to minimize that bias by optimizing the marker set used to measure the trunk movement.