Comparing methods of estimating the total body centre of mass in three-dimensions in normal and pathological gait

It is common clinical practice to estimate the position of the total body centre of mass (CM)as being a ®xed point in the centre of the pelvis (CP). Previous work has shown that there are significant differences between CP and the estimate of the position of CM from the second integral of ground reaction force data (GRF). In this study the CM was determined during an entire gait cycle in 11 able-bodied subjects (6 adults and 5 children) and 5 children withlumbosacral myelomeningocoele using both methods (GRF and CP). The CM was also estimated using a full body multi-segment kinematic model (KM). In agreement with previouswork the excursion of CP showed signi®cant differences from that of GRF. CP always had a larger total excursion than GRF. KM however, showed no signi®cant differences from GRF inany of the three orthogonal directions in any group. These results show that the use of a full body kinematic model gives a better representation of the CM than does a ®xed point in the pelvis, especially in pathological gait patterns