A Transverse Contour Model of Distributed Muscle Forces and Spinal Loads during Lifting and Twisting

This study has developed a realistic three-dimensional transverse contour model of distributed muscle forces and spinal consequences (compression, torsion, and shear) that occur during dynamic lifting, static holding, and dynamic twisting. The model utilizes multiple force vectors to represent broad flat muscles along with traditional single vector modeling of other trunk muscles. Instead of a two-dimensional transverse cutting plane, this model introduces a system analysis boundary in the form of a three-dimensional transverse cutting contour that was created by in vivo digitization of human subjects in symmetric and asymmetric postures. This transverse contour more realistically illustrates the complex nature of the human biomechanical system during the performance of industrial work in three-dimensional space. To investigate this model, surface electromyography data were collected from seven subjects. Also, to confirm the findings from surface data and to alleviate muscle signal crosstalk concerns, fine-wire electromyography data were collected from one additional subject. Both the surface and fine-wire data showed that differential muscle forces existed within each of the external obliques, internal obliques, and latissimus dorsi. Moreover, the data were used for validation which confirmed the viability of the model. This multi-vector distributed-force transverse contour model was found to be particularly useful for describing shear and compression during three-dimensional twisting.