Biarticular muscle moment arm

[Pouya Amiri]

Hi all,

I am trying to find the moment arm of muscles around the knee joint. For a biarticular muscle like Rectus Femoris the moment arm depends on both knee and hip angle. How can I find the muscle moment arms in an experimental walking trial (marker data and GRF), where both hip and knee angles are changing at the same time?

I do not know if this is possible or not. I know that OpenSim gives this for different knee or hip angles at the same time. but I don't know how can it be done for specific trial?

Thanks.

[Brian Umberger]

Hi Pouya,

Once you have a motion loaded in OpenSim, such as an inverse kinematics result, you may plot muscle-related variables (such as moment arms) against the motion, rather than against a specific joint angle. In the Plotter, for the X-Quantity, select your motion (it will be near the bottom of the list). Following your example, it will plot the rectus femoris knee joint moment arm for the particular hip and knee angles that occurred during the motion you use for plotting.

Hope this helps.
Brian

[Pouya Amiri]

Thanks Brian.

I did it. Actually it was under the name of "Coordinates". But showed moment arms in time.