Building a leg press simulation with OpenSim and Notepad pp

[Nicolas Warneking]

Hello,

My name is Nicolas and I am a beginner with OpenSim modeling and programming. I am trying to develop a model to simulate muscle and joint forces in a leg press. My first model was written in Matlab. The leg press consisted of three brick bodies and the human body was illustrated with ellipsoids. I connected both feet to the foot plate of the leg press with a weld constraint on each side. I connected the pelvis ellipsoid with another weld constraint to the back cushion of the leg press. I generated test force data and test motion data to run an static optimization which worked out.

Now I am trying to add a more detailed human model to my leg press. I chose the Catelli V4.0 model because of the high hip flexion over 90 deg. To connect the leg press created in Matlab with the Catelli model, I used notepad pp. I am able to combine both models into one. With the default values for the joints, I can place the body in the leg press.

My idea is to connect the pelvis and the feet with the leg press, making it a closed physical chain. With the force applied to the footplate of the leg press, I should be able to plot the muscle forces. This is my idea. Can you tell me if this idea should work or am I on the wrong way? Do you have any hints for me what to take into account?

Unfortunately I am struggling to generate Weld constraints in Notepad pp. I get a warning or the model does not even load in OpenSim. One main issue for me is that I can not find any sizes of the models bodies, for example for the pelvis or feet. Can you tell me how I can find out what the sizes are? I want to use those information to make the constraint at the right point.

Any support would be greatly appreciated,

Nico