Fig. 2.

Time profiles of the shear force F_X (left), the moment of force about the frontal axis M_Y (middle), and the center of pressure in anterior–posterior direction (COP_AP, right) averaged across 51 cycles for a typical subject who performed the task with the 1.8 kg load attached at the ankle level pulling backward. At 0 and 100% of the sway cycle the subject was in the most forward position (F) (dorsiflexion at the ankle joint). At 50% of the sway cycle, the subject was in the most backward position (B) (plantarflexion at the ankle joint). Note that time patterns of the COP_AP and M_Y are nearly identical. For further analysis, F_X and M_Y were defined as the two performance variables