Comparison of three methods for estimating vertical displacement of center of mass during level walking in patients

Three methods of estimating the vertical displacement of the center of mass (COM) during level walking were compared in 30 consecutive patients with gait disability. The methods were: (1) sacral marker method, (2) segmental analysis method and (3) force plate method. The force plate method produced data with a lower range and a different distribution than the other two methods. There was no significant difference between the data of the sacral marker and segmental analysis methods (Johnsonʹs modified t-test, P = 0.16). These two methods are likely more accurate and sensitive methods of estimating the changes in the vertical displacement of COM than the force plate method. The segmental analysis method is prone to errors because the model and anthropometric estimations used may not be applicable to every patient. The sacral marker method is a simple, inexpensive, effective and accurate tool to estimate the vertical displacement of the COM.