MATLAB and 'Normalized fiber length'

[Takuma Inai]

Hello,

I have recently been exploring how to control OpenSim (3.1) with MATLAB (API). To get 'Normalized fiber length,' I wrote a script code (please see below) in MATALAB.

Although I could get 'Normalized fiber length' of the musculoskeletal model (Rajagopal et al.; Model_Rajagopal_2015.osim), I could not get 'Normalized fiber length' of another musculoskeletal model (Arnold et al.; Model_Arnold_2010.osim).

I found the same problem in this topic (viewtopicPhpbb.php?f=91&t=5834&p=0&start=0&view=). According to the topic, I will need to change 'Muscle type' from 'Schutte1993Muscle_Deprecated' to 'Thelen2003Muscle' or 'Millard2012EquilibriumMuscle.'

Although I checked this site (https://simtk.org/api_docs/opensim/api_docs/index.html) regarding API, I did not know how to change 'Muscle type' using MATLAB. Would you please modify my script code to get 'Normalized fiber length' of the musculoskeletal model (Arnold et al.)?

Best regards,

Takuma Inai
Institute for Human Movement and Medical Sciences
Niigata University of Health and Welfare

%=================

clear;
close all;
clc;

import org.opensim.modeling.*
cd(uigetdir());

%=================
% Rajagopal et al.
%=================

ModelName1 = 'Model_Rajagopal_2015';
myModel1 = Model(strcat(ModelName1,'.osim'));
state1 = myModel1.initSystem();

myModel1.updCoordinateSet().get('hip_flexion_r').setValue(state1,deg2rad(45));

myForce1 = myModel1.getMuscles().get('psoas_r');
muscleType1 = char(myForce1.getConcreteClassName()); % 'Millard2012EquilibriumMuscle'

eval(strcat('myMuscle1=',muscleType1,'.safeDownCast(myForce1);'));

myMuscle1.setDefaultActivation(0.01);
myModel1.equilibrateMuscles(state1);

display(myMuscle1.getNormalizedFiberLength(state1));

%=================
% Arnold et al.
%=================

ModelName2 = 'Model_Arnold_2010';
myModel2 = Model(strcat(ModelName2,'.osim'));
state2 = myModel2.initSystem();

myModel2.updCoordinateSet().get('hip_flexion_r').setValue(state2,deg2rad(45));

myForce2 = myModel2.getMuscles().get('psoas_r');
muscleType2 = char(myForce2.getConcreteClassName()); % 'Schutte1993Muscle_Deprecated'

eval(strcat('myMuscle2=',muscleType2,'.safeDownCast(myForce2);'));

myMuscle2.setDefaultActivation(0.01);
myModel2.equilibrateMuscles(state2);

display(myMuscle2.getNormalizedFiberLength(state2));

[Thomas Uchida]

The Schutte1993Muscle_Deprecated model is deprecated and, as such, is no longer supported. Also note that you are using an old version of OpenSim and may want to upgrade to 3.3.

I did not know how to change 'Muscle type' using MATLAB

An easy way to change muscle type is by opening the .osim file in a text editor. Note that it may be necessary to adjust muscle properties as well.

Would you please modify my script code to get 'Normalized fiber length' of the musculoskeletal model (Arnold et al.)?

You should be able to use the getFiberLength() method from the Muscle class (https://simtk.org/api_docs/opensim/api_ ... 46468804f4) and then normalize by optimal fiber length (https://simtk.org/api_docs/opensim/api_ ... e843918a75).

[Takuma Inai]

Dear Mr Uchida,

Thank you for the quick response.
I do appreciate your help.

Best regards,

Takuma Inai
Institute for Human Movement and Medical Sciences
Niigata University of Health and Welfare