Estimation of centre of gravity movements in sitting posture: application to trunk backward tilt

The aim of this study was to highlight, in sitting posture, the value of distinguishing between the movements of the vertical projection of the centre of gravity (CGv) and its difference from the centre of pressure (CP−CGv). A protocol for healthy, young, trained adults, consisting in tilting their trunk backward or keeping it vertical was used. A frequency analysis shows that statistically significant effects were only seen on CP−CGv movements: the RMS increased by 37% (p=0.004), while the MPF decreased by 5% (p=0.016), suggesting an increased muscular activity in these tilting postures. In contrast, no statistically significant effects on CP and CGv were reported. These data highlight the advantage, in sitting posture, of splitting overall CP displacements into basic components (i.e. CGv and CP−CGv), each of them having a biomechanical significance.