Joint Reaction Analysis + Moco?

[Madeline Grosklos]

New Moco user here!

I designing a study for my PhD and would love to use MocoTrack and MocoSolve to answer my questions. However, a key element of the hypotheses involves changing joint contact forces with altered muscle strengths. I cannot find any information on if I am able to compute something like the joint reaction analysis tool (in OpenSim) in Moco.

It is imperative that I am calculating and reporting the compressive forces at the joint, and not just the net torques.

Thanks in advance

[Pasha van Bijlert]

Hi Madeline,

I posted some matlab code that computes the JointReactions from a converged solution in moco a while back. That was for a previous version of moco. I just posted a new version of that script, since I'd made the required changes after updating anyway. The code is in this thread.

There was also recently a discussion on the forum about what the JointReactions actually represent.

Cheers,
Pasha

[Madeline Grosklos]

Thank you Pasha,

This is perfect. It will be a while until I am able to apply it to my data, but with this I can confidently defend my methods in my upcoming candidacy proposal.

The thread on JointReactions was also insightful. Such a tangled web of a topic and a great conversation about it!

Best,
Madeline

[Madeline Grosklos]

Hi Pasha,

I am explicitly interested in the anterior hip JointReactions, and was wondering if I am able to define parent and child bodies to ensure that I am looking at just the anterior region and not the entire joint.

I hope this is not a silly question. I am assuming it is possible but wanted to ask someone with more experience.

Best,
Maddie

[Nicholas Bianco]

Hi Madeline,

It's not possible to "split up" the joint reactions between anterior/posterior segments of a joint. There's only one set of 3D forces and moments based on the definition of a joint.

One approach would be to create a hip model with multiple compartments, similar to Zach Lerner's knee model. If there's any relationships between hip moments and compartment forces, that could be used to create a the MocoGoal that you need.

-Nick

[Madeline Grosklos]

Thanks Nick,

Your response made me realize I was thinking about it wrong. I will be able to determine when the joint force is anteriorly directed on the acetabulum and that will be good enough for my application.

Maddie