Symmetry comparison between sacrum and center of mass during walking

Sacrum motion is used extensively in clinical research to represent movement of the entire body by replacing the center of mass. The primary objective of this article was to investigate the effect of this replacement on symmetry determination. The secondary objective was to assess the correlation between the symmetries of trajectories of center of mass and sacrum, and that of spatiotemporal parameters. Three-dimensional trajectories obtained from 37 markers placed on anatomical landmarks of 15 healthy subjects were recorded while walking at three speeds on the treadmill. Trajectory of center of mass was determined using segmental analysis method. The results indicated that two symmetries, one determined using sacrum marker and the other using segmental analysis method, were different and this difference was more pronounced in anterior-posterior direction. In other words, harmonic analysis of sacrum and center of mass trajectories revealed different results. Furthermore, low-to-moderate correlations were observed between spatiotemporal parameters symmetry and symmetries obtained from both center of mass and sacrum. In conclusion, the results indicated that it may not be analytically acceptable to substitute sacrum for center of mass in symmetry determination.