Determination of subject specific whole-body centre of mass using the 3D Statically Equivalent Serial Chain

This study investigates the possibility of using the so-called Statically Equivalent Serial Chain approach to estimate the subject-specific 3D whole-body centre of mass (CoM) location. This approach is based on a compact formulation of the 3D whole-body CoM position associated with a least squares identification process. This process requires a calibration phase that uses stereophotogrammetric and dynamometric data collected in selected static postures. After this calibration phase, the instantaneous position of the identified subject-specific 3D whole-body CoM can be estimated for any motor task using kinematic data only. This approach was experimentally validated on twelve healthy young subjects. The Statically Equivalent Serial Chain solution was validated during static trials with the centre of pressure, with the double integrated ground reaction forces during dynamic tasks, and also compared with a segmental method using a stereophotogrammetric system and anthropometric tables. Considerations relative to the choice of algorithm parameters, such as the number of necessary static postures and their time duration, are discussed. The proposed method shows much smaller differences between the projection of the centre of mass and the centre of pressure (root mean square value under 3.5%) than the method using anthropometric tables (root mean square value over 9%). Same conclusion can be made during dynamic tasks with a smaller difference obtained for SESC (root mean square value under 4% at contrary the 20% obtained with anthropometric table).