Numerical simulation of contraction in muscle packages
Aim of this research is the development and validation of a three-dimensional finite element muscle model for dynamic muscle contraction considering changes on the geometry of the muscle. Skeletal muscles are tight packed inside the body (e.g. calf) and interact with the surrounded muscle tissue, thus a free deformation is impossible. The (intramuscular) transfer of forces in longitudinal and transversal direction influences the force development and deformation of single muscles. Maybe this fact complicates muscle coordination and a sophisticated force development. However, in daily routine muscles have to accomplish complex movements. In order to get a deeper understanding of muscle packages under the premise of force and velocity generation, analyses of muscle architecture, three-dimensional deformation and force development of muscle packages are necessary.
Several experiments are carried out aiming to the identification of the active/passive mechanical properties and structural parameters of each muscle of the muscle package. A step-by-step approach is used in order to compute the specific model parameters at each scale, where the information of the previous steps is used for the computation of more complex model parameters. In order to compare the experimental and modelling data, the geometry of the muscle is recorded during contraction. Therefore, the motion of three-dimensional muscle geometries of isolated muscles is captured with a camera system. The reconstruction of the muscle geometries is realised first by hand and finally optimised for an automatic reconstruction of the muscle geometries during the whole contraction.
Three successive steps are needed for characterising the muscle package. First, experiment and simulation at the soleus muscle is realised. The muscle architecture, fibre distribution, and the contraction behaviour of the gastrocnemius muscle are much more complex compared to the soleus muscle. Having this in mind, in the second step the modelling approach is validated on experimental data of the gastrocnemius muscle. Finally, the third step focuses on the development and validation of the first three-dimensional model muscle package (soleus, gastrocnemius, and plantaris muscle). To model the interaction between neighbouring muscles, experiments are realised to specify the force transfer. A basic requirement for the validation process is the combination between the determination of muscle force and three-dimensional muscle shape deformation (using optical measurement systems) for single muscles as well as for the whole muscle package.
