Figure 2.

Onset of the unintended hip descent (thin solid vertical line) after the slipping (right) limb touch-down (RTD) from 2 typical young subjects: (A) one who recovered and (B) one who fell. This instant is identified as the point when the hip height (ie, the vertical distance from the ground to the midpoint between 2 hip centers) trajectory (thick broken line) traversed below 3 standard deviations (shaded area) from its mean trajectory (thick solid line) taken from the subjects' regular (unperturbed) gait. This onset timing is nearly identical to the onset of negative vertical (downward) hip velocity (thin broken vertical line). Hip height is normalized as percentage of body height (%bh).