Center of pressure velocity reflects body acceleration rather than body velocity during quiet standing.
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.
Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehabilitation Institute-University Health Network, 520 Sutherland Drive, Toronto, Ontario M4G 3V9, Canada; Rehabilitation Engineering Laboratory, Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada. Electronic address: k.masani@utoronto.ca.
Kei
K
Masani
Department of Mechanical Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, Alberta T6G 2G8, Canada; Glenrose Rehabilitation Hospital, Alberta Health Services, 10230 - 111 Avenue NW, Edmonton, Alberta T5G 0B7, Canada.
Albert H
AH
Vette
Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba Meguro-ku, Tokyo 153-8904, Japan.
Masaki O
MO
Abe
Department of Life Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Kimitaka
K
Nakazawa
D000054:Acceleration; D000328:Adult; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D006801:Humans; D008297:Male; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology; D011312:Pressure; D011434:Proprioception / Q000502:physiology
Center of pressure; Human posture; Posturography; Standing