Whole-body center of mass location in seated posture
Authors: Matthew P. Reed
The location of the body center of mass (CM) is useful for a wide range of biomechanics analyses relevant to the design of seats, chairs, restraint systems, and other products and environments intended for human use. The body CM is usually estimated by summing the contributions of individual body segments, often using on cadaver-based estimates calculated from regression equations, using standard anthropometric variables as inputs. However, torso CM location may not be well estimated by these methods for seated postures, in which the torso is in a markedly different posture than the supine in which cadavers are segmented. For the current analysis, whole-body laser scan data were analyzed to estimate the location of the center of mass in relaxed seated postures. Scan data from 447 women and 315 men were analyzed by computing the center of volume of horizontal slices through the body from the knees through the top of the head, excluding the upper extremities. Constant density was assumed. Estimates of the mass of the legs and upper extremities were applied at the knees and elbows, respectively. The fore-aft CM location was significantly related to body weight. In the measured posture, the CM is about 220 mm forward of the back of the buttocks for adult men of median body mass (about 77 kg). The average fore-aft CM location for a person with a body mass of 140 kg (308 lb) is about 273 mm forward of the back of the buttocks, a difference of 63 mm.