A simplified marker set to define the center of mass for stability analysis in dynamic situations.

The extrapolated center of mass (XCoM), a valuable tool to assess balance stability, involves defining the whole body center of mass (CoMWB). However, accurate three-dimensional estimation of the CoMWB is time consuming, a severe limitation in certain applications. In this study, twenty-four subjects (young and elderly, male and female) performed three different balance tasks: quiet standing, gait and balance recovery. Three different models, based on a segmental method, were used to estimate the three-dimensional CoMWB absolute position during these movements: a reference model based on 38 markers, a simplified 13-marker model and a single marker (sacral) model. CoMWB and XCoM estimations from the proposed simplified model came closer to the reference model than estimations from the sacral marker model. It remained accurate for dynamic tasks, where the sacral marker model proved inappropriate. The simplified model proposed here yields accurate three-dimensional estimation of both the CoMWB and the XCoM with a limited number of markers. Importantly, using this model would reduce the experimental and post-processing times for future balance studies assessing dynamic stability in humans.