Regulation of the distance between the center of mass and the minimum moment axis for stabilized locomotion in humans
Résumé
This study aims at showing that, to ensure stability, humans tend to minimize the distance between their center of mass and the minimal moment axis of contact forces. This work is based on a theoretical reasoning in mechanics and on experiments in human walking movement. A destabilizing setup was built on which five different experiments were carried out by 15 volunteers. We computed the distance between the minimal moment axis of the contact forces and the center of mass of the participants. This distance significantly increased (p < 0.001, ranging from 55.1 mm to 150.9 mm) as subjects balance was perturbed through the five different conditions (walking on a destabilizing setup, increasing walking speed, grasping or not a fixed element). Furthermore, the analysis of each segment's position with regard to the studied axis shows that heaviest segments are kept close to it, while lightest segments are less constrained around it (p < 0.001, from 145.7 mm to 493.1 mm). This might reveal a strategy used to obtain a fine control of the center of mass distance from the axis and thus a good regulation of the variation of whole body angular momentum. Tracking this distance could be used for different purposes, such as fall detection, prosthesis studies and trajectory generation in humanoid robotics.
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