Sharif Digital Repository

The recruitment pattern of trunk muscles is determined using a three-dimensional model of the spine with two joints and six symmetric pairs of muscles in which both equilibrium and stability requirements are satisfied. Model predictions are verified using Anybody Modeling System (AMS) and Abaqus. The model is used to test the hypothesis that antagonistic muscle activities are necessary for the spinal stability. The model with stability constraints predicts muscle activities greater than those predicted without stability consideration. In agreement with experimental data, the stability-based model predicts antagonistic muscle activities. It is shown that spinal stability increases with trunk... 

Two artificial neural networks (ANNs) are constructed, trained, and tested to map inputs of a complex trunk finite element (FE) model to its outputs for spinal loads and muscle forces. Five input variables (thorax flexion angle, load magnitude, its anterior and lateral positions, load handling technique, i.e., one- or two-handed static lifting) and four model outputs (L4-L5 and L5-S1 disc compression and anterior-posterior shear forces) for spinal loads and 76 model outputs (forces in individual trunk muscles) are considered. Moreover, full quadratic regression equations mapping input-outputs of the model developed here for muscle forces and previously for spine loads are used to compare the...