The aim of this study was to validate the difference and effectiveness of the trunk muscle force for effect of the muscle path in the 3-dimensional trunk musculoskeletal model. The skeletal models were constructed from each thoracolumbar vertebrae, sacrum, ribs and sternum, and the muscle models were constructed short dorsal muscles, transversospinalis muscles, erector spinae muscles, abdominal muscles and psoas muscle. In order to define muscle path, we constructed 2-types muscle path models which were connecting origin point and insertion point by straight line muscle (Via-Point) using Magnetic Resonance Imaging (MRI) data (Via-Point type), and performing Wrapping (curve approximation that like along the objects) towards transversospinalis muscles and erector spinae muscles originated from Via-Point muscle (Wrapping type). Verification of constructed models compared with muscle force in 3-type orientations (static standing, flexion and left lateral bending). As a result, muscle force changed performing Wrapping in trunk muscles, and difference of muscle path demonstrated affects in vivo loading estimation.
