There has been debate in the literature on how to calculate the moment of muscles that are curved and span several joint. How does AnyMomentMeasure2 calculate the moment of a muscle that is curved and spans over several joints? For example the PsoasMajor?
Also in muscles with straight lines of action, I tried to calculate the length of the muscle by taking the distance between the insertion and origin points, and compare it to Lmt. I found that the difference could be from 7 to 14% sometimes. Is this a rounding error?
It is a good question, the AnyForceMomentMeasure2 is based on the principle of virtual work. So if you are looking at a certain point it is doing virtual pertubations to this point and looking at the effect it has on the muscles etc. So using this principle it does not matter if the muscle are spanning multiple joints or is curved, it is a general method that can handle all cases. The AnyForceMomentMeasure2 calculates on all the elements which is listed in the measure so if you list all forces acting on a segment it will give zero.
It sounds strange with the lmt, are you sure the kinematics was solved in both cases before doing the caluclation?, the results should fit 100%. Another source of error could be if the kinematic tolerance is set too high in the study. You could introduce a simple formula like this to do the calculation of the length:
[SIZE=3]AnyVar[/SIZE] lengthtest = vnorm(.GlobalRef.TricepsLong.r-.Segs.ForeArm.Triceps.r,2);
[SIZE=2]Please ask again if you have further questions:
When using AnyMomentMeasure2; If I want to measure the “contact force” within the knee, while the knee is performing a bending for example, all that I need is to list the Shank (AnySeg) , the Reactions of the Knee Joint (AnyForceBase) and a node (AnyRefFrame) to respect of which the Contact Force will be calculated.
Is that the right way?
Or should I add the drivers and the muscles in the list?
I would recommend you to see the following files:
Then yon can see how you can use this AnyMomentMeasure2 object to get what you want.