FIGURE 1.

Average contributions to the vertical and horizontal acceleration of the COM from (a) ground reaction forces (GRFs), (b) muscles, and (c) the resistance to gravity by skeletal alignment across speeds within each phase of stance, including both limbs. Each ray represents the resultant vector of the vertical and horizontal accelerations averaged across subjects. The grey waveforms shown in (a) are the normalized vertical GRFs for the support limb averaged across subjects. Since the peak vertical GRF/kg during Phase 3 is lower during SS and fast speeds in comparison to that during the slow speed, this demonstrates that there is less of a need for vertical support with increasing speed during Phase 3.