Article

The purpose of this study was to test the hypothesis that the center of pressure
(COP) velocity reflects the center of mass (COM) acceleration due to a large
derivative gain in the neural control system during quiet standing. Twenty-seven
young (27.2+/-4.5 years) and twenty-three elderly (66.2+/-5.0 years) subjects
participated in this study. Each subject was requested to stand quietly on a
force plate for five trials, each 90 s long. The COP and COM displacements, the
COP and COM velocities, and the COM acceleration were acquired via a force plate
and a laser displacement sensor. The amount of fluctuation of each variable was
quantified using the root mean square. Following the experimental study, a
simulation study was executed to investigate the experimental findings. The
experimental results revealed that the COP velocity was correlated with the COM
velocity, but more highly correlated with the COM acceleration. The equation of
motion of the inverted pendulum model, however, accounts only for the correlation
between the COP and COM velocities. These experimental results can be
meaningfully explained by the simulation study, which indicated that the neural
motor command presumably contains a significant portion that is proportional to
body velocity. In conclusion, the COP velocity fluctuation reflects the COM
acceleration fluctuation rather than the COM velocity fluctuation, implying that
the neural motor command controlling quiet standing posture contains a
significant portion that is proportional to body velocity.
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Langue : ANGLAIS