This study was aimed at assessing the possible relationship between upright and sitting postures in healthy adults. The center of pressure trajectories from the force platform on which the subjects stood or sat were analyzed through a frequency analysis and modeled through the fractional Brownian motion framework. The same type of control process was involved during sitting and upright posture maintenance. Both upright and sitting posture would be controlled by the same mechanical law and/or by the same type of central process. Conversely, these two postures presented different characteristics and a relative independence. Both postures displayed specific biomechanical constraints and involved specific effectors, in particular along the anterior-posterior axis. Thus, performances in these two postures are completely independent in the anterior-posterior axis, whereas they are slightly linked in the medio-lateral axis. Improved trunk functions to improve postural stability have an interest solely to improve lateral stabilization.
The authors are with the Laboratoire de modélisation des Activités Sportives, Université de Savoie, Domaine Scientifi que de Savoie-Technolac, 73 376 Le Bourget du Lac cedex, France.