Tendon Length is a negative value

[Julie Iskander]

I am using the APIs to create my model and calculate muscle lengths at different positions of the model.

What does it mean when I use getTendonLength and get a -ve value?
How can a tendon be conpressed? What does that mean?
Can someone help me?

[Dimitar Stanev]

It is strange, can you post the code? Why do you care about the tendon length and not the muscle length?

[Julie Iskander]

rjointCoordinateSet[1].setValue(si, convertDegreesToRadians(-32), true);
cout << "Muscle Fiber Length at -32 Abduction" << endl;
for (int i = 0; i < 6; i++)
{
cout << muscles->getName() << " - ";
cout << muscles->getLength(si) << " - " << muscles->getFiberLength(si) << " - " << muscles->getTendonLength(si)<< endl;;
}

I was just moving the model and getting new values of the muscle.

Why don't FiberLength change to reflect compression or elongation of muscle? Only Length and TendionLength?

[Dimitar Stanev]

I think you have to realize the state to position. model.realizePosition(si)

[Julie Iskander]

realizePosition is not accessable from Model class

[Dimitar Stanev]

It is possible that this method is supported in the newest version of OpenSim that I use or you haven't included the headers. You can try this also:

Code: Select all

model.getMultibodySystem().realize(si, Stage::Position);

Best

[Julie Iskander]

Thanks a lot
It worked with the following lines together

Code: Select all

osimModel.getMultibodySystem().realize(si, Stage::Position);
osimModel.equilibrateMuscles(si);