Modeling the body/chair interaction – an integrative experimental–numerical approach

Objective. To develop a systematic methodology towards a realistic model, of the body/chair interaction as a tool to analyze sitting posture and the cushioning system influence on the pelvis/lower back stress development. Background. The model concept comprises an integrative structure including both the pelvis girdle and the lower spine, as well as the surrounding soft tissues with their specific characteristic behavior during sitting. Methods. In vivo measurements were performed, in order to obtain a set of contact moduli defining the behavior of the soft tissues under tension during the sitting down process. Additionally in vivo indentation of a metal ball into the same soft tissues during sitting were performed in order to obtain the characteristic moduli. A finite element model was also developed for the specific analyses. Results. Validation of the model was achieved by comparing its results with in vivo measurements of contact stresses developed between the body and a stiff target seat area. Loading the model using two alternative cushioning materials lead to different sets of stresses within the model; as the stiffness of the seat decreased, the peak contact stresses, as well as the internal body stresses substantially decreased.