Calculating support reaction forces in physics-based seated posture prediction for pregnant women

Whether it is sitting in an office, in a car, on a couch, or in wheelchairs, people spend much of their everyday lives in a seated posture. A large area of study in ergonomics focuses on the support reaction forces (SRFs) involved with seated posture and the effects these forces can have on soft tissue. The effects of these forces are of particular interest for pregnant women, for whom the SRFs are critical due to the size, shape, and weight change of the abdomen. This paper details a simulation-based study that calculates the related SRFs needed to retain static equilibrium in physics-based seated posture prediction for pregnant women. A physics-based optimization method is employed that minimizes human performance measures to predict realistic postures. The digital pregnant woman model used in this study is a full term pregnant woman containing 56 degrees of freedom. The SRFs are predicted based on the location of a 3-D zero-moment point and Newton's third law. Multiple seated orientations based on an experimental study found in published literature are simulated. When comparing these simulation results to the literature data, a good correlation can be established, which provides an initial validation of the proposed methods.