[A forward leaning posture affects more the amplitudes of the centre of pressure displacements than those of the centre of gravity].
OBJECTIVE
An ordinary and practical method to assess the postural control mechanisms is to measure, through a force platform, the point of application of the resultant reaction forces. The recorded signal, the centre of pressure CP, is used to compute the motions of the vertical projection of the centre of gravity (CG(v)) and those of the difference CP-CG(v). The former is considered in this postural task as the controlled variable whereas the latter is thought to express the ankle resultant stiffness. Interestingly, the CG(v) motions can be extracted from the CP trajectory through a simple mathematical model.


METHODS
The relationship between CP and the elementary motions CP-CG(v) and CG(v) has been tested in the present study by comparing the postural effects induced by a leaning forward position to a normal one consisting to stand still.


RESULTS
A large increase is noticed for the amplitudes of the CP-CG(v) motions for both medio-lateral ML and antero-posterior AP directions. On the other hand, a similar effect appears for the CG(v) motions but only on the ML direction. Nevertheless, the frequency analysis indicates that the constancy of the CG(v) motions on the AP direction is accompanied by a change in the frequency distribution, as assessed by the MPF parameters.


CONCLUSIONS
These features highlight the necessity, to interpret rigorously the postural performance, to take into account in separate ways each of the elementary CP-CG(v) and CG(v) motions which, combined, constitute the CP displacements.
Rougier
P
P
Laboratoire de modélisation des activités sportives, université de Savoie, Domaine universitaire de Savoie-Technolac, 73376 cedex, Le Bourget du Lac, France. patrice.rougier@univ-savoie.fr
D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D004856:Postural Balance / Q000502:physiology; D011187:Posture; D013997:Time Factors
Le maintien d'une posture d'inclinaison vers l'avant modifie davantage les amplitudes des déplacements du centre des pressions que celles du centre de gravité.