  Kinematic measurements of two simultaneous coordinates from postural sway
during quiet standing were performed employing multiple ultrasonic transducers.
The use of accurate acoustic devices was required for the detection of the
small random noise displacements. The trajectory in the anteroposterior -
mediolateral plane of human chest was measured and compared with the trajectory
in anteroposterior direction from the upper and lower body. The latter was
statistically analyzed and appeared to be strongly anti-correlated. The
anti-correlations represent strong evidence for the dominance of hip strategy
during an unperturbed one minute stance. That the hip strategy, normally
observed for large amplitude motions, also appears in the small amplitude of a
quite stance, indicates the utility of such noise measurements for exploring
the biomechanics of human balance.
