Joint Reaction Force during Arm Abduction

[Marc Grepper]

Hey there,

For my Project I need to estimate reaction forces on the glenoid surface during arm movements for example abduction. There are a few questions I cannot answer:

1. Is the Static Optimization the right method to find out muscle forces? If not, what is the workflow(tools) to get correct results?

2. What is the maths behind the Static Optimization and the Inverse Dynamics?

3. Are there any inertia effects inculded in the simulation? Because I get the same muscle forces from Static Optimization for lifting the arm in 2seconds as in 5seconds?

4. When I let the model lift its arm in 1 second the results get messed up through noise, which I can't find the source, is there a numerical problem?

Thanks for your help,
Marc

[jimmy d]

Hi Marc,

1. Is the Static Optimization the right method to find out muscle forces? If not, what is the workflow(tools) to get correct results?

Static Optimization and CMC OpenSim methods for calculating muscle activations/forces. They are used in differing contexts and the choices are really down to the researcher.

2. What is the maths behind the Static Optimization and the Inverse Dynamics?

http://simtk-confluence.stanford.edu:80 ... tion+Works
http://simtk-confluence.stanford.edu:80 ... mics+Works

3. Are there any inertia effects included in the simulation? Because I get the same muscle forces from Static Optimization for lifting the arm in 2seconds as in 5seconds?

SO calculates the muscle forces required to generate the required joint torques. You time course of muscle forces will be different.

4. When I let the model lift its arm in 1 second the results get messed up through noise, which I can't find the source, is there a numerical problem?

How high are the accelerations and torques? sounds like if the movement has high/rapidly changing accelerations you are going to have issues.

Cheers,
-james