Obtaining muscle force components

OpenSim Moco is a software toolkit to solve optimal control problems with musculoskeletal models defined in OpenSim using the direct collocation method.
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Guillermo Muñoz
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Joined: Sat Nov 23, 2019 11:08 am

Obtaining muscle force components

Post by Guillermo Muñoz » Tue Oct 19, 2021 9:37 am

Hello everyone. I am working with MocoInverse, in concrete I've built a 4-bars mechanism, in which I've implemented two muscles, each of them is attached to one side of the input bar, as seen in the picture.

Image

I have coded a Muscle Driven problem, using MocoInverse tool so as to perform an Inverse Dynamics analysis. In the .sto output file resulting after the optimization, by default two magnitudes are shown: the muscle activation and the normalized tendon force. However, I've discovered that another .sto file is generated with the magnitudes I choose to see:

Image

I understand that the resulting tendon force in the 2nd .sto file, if I divide it by the maximum isometric force, is equivalent to the normalized tendon force in the 1st .sto file. My surprise comes when I plot them, and the normalized tendon force obtained in the 2nd .sto file results to be the double of the first one. Have I misunderstood this tendon force? Is the way I've shown the correct form to obtain passive and active forces? If not, what would be the correct way to obtain the force and its components (active and passive)? Thank you very much.
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Nicholas Bianco
Posts: 1044
Joined: Thu Oct 04, 2012 8:09 pm

Re: Obtaining muscle force components

Post by Nicholas Bianco » Thu Nov 18, 2021 2:13 pm

Hi Guillermo,

Thanks for you post, sorry for missing this one. Did you ever resolve this issue?

If not, would be mind posting a plot of the two tendon forces you're computing?

Best,
Nick
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