Evaluation of the biomechanical load in three dimensional soaking posture in bathtub

Abstract

In order to design a comfortable bathtub to soak, it is important to evaluate the biomechanical load in the soaking posture. In the previous researches, joint torques as the biomechanical load were calculated. However, in these researches, biomechanical models in the sagittal plane were used and therefore only two dimensional joint torques were calculated. The objective of this study was to calculate the joint torques in three dimensional soaking posture in the bathtub. In order to calculate the joint torques, the soaking posture and reaction forces from the bathtub were obtained by an experiment. Marker coordinates were obtained in the experiment. From the marker coordinates, the directions of the body segments as well as joint angles were calculated. These data were used to calculate the joint torques in the biomechanical model with considerations of gravity, buoyancy, reaction forces from the bathtub, and passive elastic joint torques. From the results, it was confirmed that the components of the joint torques which were not calculated in the previous researches of the sagittal model had certain values.