Geometric model and spinal motions of the average male in seated postures

The position of the pelvis relative to the thorax in the seated posture and the distribution of mid-sagittal bending in the lumbar spine are not well understood. In this study, a computer graphics model and a mid-sagittal bending motion program were created. Initial seated postures were formed and, through the use of a motion program which utilized different distributions of lumbar motion, several published studies were simulated to evaluate the relative positions of the pelvis and thorax. The published studies were best simulated by equally distributing the rotation in the mid-sagittal plane among the L5/S1 interspace through the T12/L1 interspace and using the initial postures.