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J Biomech. 2007;40(2):451-7. Epub 2006 Mar 10.

The equations of motion for a standing human reveal three mechanisms for balance.

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Laboratory of Human Movement Analysis, Center for Rehabilitation, University Medical Center Groningen, Center for Human Movement Sciences, University of Groningen, PO Box 196, 9700 AD Groningen, The Netherlands.


The equations of motion for a standing multi-segment human model are derived. Output quantity of these equations is the horizontal acceleration of the whole-body centre of mass (CoM). There are three input terms and they can be identified as the three mechanisms by which balance can be maintained: (1) by moving the centre of pressure with respect to the vertical projection of the CoM, (2) by counter-rotating segments around the CoM, and (3) by applying an external force, other than the ground reaction force. For the first two mechanisms the respective contributions to CoM acceleration can be obtained from force plate recordings. This is illustrated by some example data from experiments, which show that the contribution from mechanism 2 can be considerable, e.g. in one-legged standing.

[Indexed for MEDLINE]

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