Relative contribution of individual support in the control of undisturbed upright stance

Upright undisturbed stance constitutes a fundamental attitude involving very cunning sensori-motor strategies. Until now, few analyses on postural control have been undertaken to explain the influence of both supports in this particular task. With the aim of analysing asymmetrical postures resulting from neurological (hemiplegia) or traumatic (amputation) origins, a new analysis and a reference framework are proposed, describing the influence of each support in upright stance maintenance. Ten healthy adults (eight men and two women ranging in age from 20 to 42 years) volunteered for this study. The subjects were required to remain as still as possible in upright stance. The control mechanisms for equilibrium maintenance were estimated by separate measures of the elementary and resultant centres of pressure through two force platforms. The analysis of the relationship between the elementary and resultant centres of pressure on the one hand and the centre of gravity on the other hand emphasises that both took place similarly and at the same time in the control of upright undisturbed stance. This control is done through two strategies that come into play at the level of the ankle and/or hip in the medio-lateral and antero-posterior directions, respectively. Furthermore, the various trajectories (elementary and resultant centres of pressure, centre of gravity) and analytical methods (frequential, correlations and cross-correlations) are compared. This methodology should be very interesting in the analysis of pathologies inferring postural asymmetry in weight distribution, since one could suppose that asymetric patients could be characterised by specific control of both supports. [Copyright &y& Elsevier]