Minimization of Pressure and Shear Load in Sitting and Lying, Based on Biomechanical Modeling

Abstract

Human body-product interaction is, next to clothes, most intensive and prolonged in beds and seats. In ergonomics this is a classical antropometric issue which emphasizes on standards for sizes which accommodate different body measures. However, biomechanics of lying and seating got less attention. As an introduction to the papers in this symposium three basic biomechanical models will be described. The first model describes how pressure and shear on the ischial tuberosities is related to the position of seat and backrest. The choice of foam, fluid or gas for body support is another basic issue for minimization of pressure and shear. The next biomechanical topic is load on internal body structures in (quasi-)static postures. This issue is of great interest because of related neck, low back and other complaints. The model on transfer of lumbosacral load to iliac bones and legs explains that in sitting, even with the use of backrest and armrests, muscles in the abdominal wall must be continuous active to form a deep muscle corset for stability of joints in the lumbopelvic region. One conclusion is, that leg crossing is functional and should be implemented in ergonomics. With the help of biomechanics and related verification measurements a list of design criteria is formulated. Often body support contravenes with basic biomechanical design criteria. Examples are office chairs, cockpit chairs and wheel chairs but also (hospital) beds.