Passive force in shoulder model

Main Forum
1

Hi

I have taken the BergmannGH validation model as a starting point and have developed a model with just the scapula, the humerus and the rotator-cuff muscles. The scapula is fixed using AnyStdJoint and the humerus is joined to the scapula using AnySphericalJoint. I have modeled the muscles using AnyMuscleModel3E as I am interested in the passive forces in these muscles.

When I run a kinematics operation with the humerus driver position and velocity set to zero for all dof (i.e. humerus does not move relative to scapula) I get the following error messages:

  1. Kinematics (Operation: Main.MyStudy.Kinematics):
    0.0) PreOperation (Operation: Main.MyStudy.Kinematics.PreOperation):
    0.0) InitialConditions (Operation: Main.MyStudy.InitialConditions):
    0.0) …Design variables have been updated.
    0.1) …Load time positions have been re-established.
    0.2) …Kinematic analysis completed. The kinematic constraints have been resolved.
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/MuscleParameters.any : infraspinatus_3 : Muscle without strength : The muscle has been stretched too much
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/W…s/T…s/Feb4/MuscleParameters.any : infraspinatus_5 : Muscle without strength : The muscle has been stretched too much
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/MuscleParameters.any : supraspinatus_1 : Muscle without strength : The muscle has been stretched too much
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/W…s/T…s/Feb4/MuscleParameters.any : supraspinatus_2 : Muscle without strength : The muscle has been stretched too much
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/W…s/T…s/Feb4/MuscleParameters.any : supraspinatus_3 : Muscle without strength : The muscle has been stretched too much
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/W…s/T…s/Feb4/MuscleParameters.any : supraspinatus_4 : Muscle without strength : The muscle has been stretched too much
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/W…s/T…s/Feb4/MuscleParameters.any : supraspinatus_5 : Muscle without strength : The muscle has been stretched too much
    WARNING(OBJ.MCH.MUS2) : D:/An…dy/W…s/T…s/Feb4/MuscleParameters.any : supraspinatus_6 : Muscle without strength : The muscle has been stretched too much
    0.3) …Initial conditions are fully updated.
  2. Kinematic analysis…
  3. …Kinematic analysis completed

My initial thought is that I need to calibrate the muscles to get better estimates for the tendon lengths? Do I have the right idea or is there another problem? If calibration is needed how can you identify what position to calibrate the muscles in?

Thanks

2

Hi Monique,

You have the right thought. This message is because of incompatibility between the tendon lengths of the muscles and the actual origin-insertion length given by the skeletal dimensions.

Best regards,
John