I have a few question regarding the modeling of the shoulder. For the simulation I am using the model FreePostureHandSR of AMMR 1.4.1.
First of all, I am interested in the studies of Vu and Mayo, as the model (muscle attachments) is based on these datasets of the Dutch Shoulder Group. Unfortunately, I can not find any information except this overview: http://www3.fbw.vu.nl/research/Lijn_A4/shoulder/overview.htm. But all of the links are broken including the ones listed in the file "ShoulderArm.root.any".
Second, in this file (“ShoulderArm.root.any”) it is written that the coordinate systems are according to the ISB proposal which I think is not completely true. The coordinate system of the humerus is rotated 90° around the y-axis compared to the ISB version.
At last, I do not quite understand the difference between GHNetMoment and GHNetMomentMuscles in the file "ArmHandMoments.any".
I changed the reference frame of the GHNetMomentMuscles from “…Seg.Scapula.gh.RotNode” to “…Seg.Humerus.gh”. If the gravity and inertia forces are included, Mlocal (=M*ref.Axes) is equal to zero and Flocal equal to the GH reaction forces. This makes sense, since the muscle forces should be in equilibrium. But what is the meaning of the GHNetMoment? As far as I understand, these two moments provide information about the size of the error in the equilibrium of forces?
In this context, I also do not understand why the RotNodes are introduced. Are they just used such that the moments of both shoulder joints point into the same direction, independent of the coordinate system?
The RotNodes are introduced to be able to handle right and left sides in the same manner so that 90 flexion is positive on both sides.
Here is the description from the model file
// ElbowPronationNetMoment
// ElbowFlexionNetMoment
// GHNetMoment
//will measure the moments and forces supplied by the muscles spanning these and on top of these
//moments and force the forces and moments from the constraints in the joints will be added.
//The resulting force and moment are equal to the to total moment and force which
//could replace both the muscles spanning the joint and the joints reactions.
//The measures named:
// ElbowPronationNetMomentMuscles
// ElbowFlexionNetMomentMuscles
// GHNetMomentMuscles
//will measure ONLY the moments and forces supplied by the muscles spanning these joint and not the moments and forces which from the constraints in the joints.
//The resulting force and moment are equal to the to total moment and force which
//are supplied by the muscles.
So these two measures is a way to measure the moments generated around the certain dof, it is not related to the error of the inverse dynamic simulation.