BergmannGH model

Main Forum
1

Hi there,

I am working with the BergmannGH shoulder model from the AMMRV1.0 repository.
When I run the kinematic analysis (it is an abduction up to 45degrees and back to 0degrees, humerus rel. to thorax) a flexion occurs which ranges from -9degrees up to 5 degrees and back to -9degrees. Do you have an explanation for that? Actually there should be only an abduction…

2

Hi,
please have a look at the JointsAndDrivers file. Actually the Flexion is not driven. Instead of this, the hand is kept in the frontal plan. The flexion you see is basically a result of this.
Best regards,
Sebastian

3

Thanks!
Now 2 more questions occurred.

  • When I had a look at the definitions of the segments in the model U:\Anybody\AnyBody\AMMRV1.0\AMMRV1.0\Body\AAUHuman\Arm\Seg.any
    I saw that there is an offset in the humerus segment, but no offsets in the other segments clavicle, scapula etc. what does the offset mean?

-the other question is concerning the definition of elbow flexion/elbow pronation. The two rotations occur around the x-Axis, after ISB recommendation elbow flexion is around the Zh axis, pronation/supination around the Yr axis. How come that it is here twice around the x-Axis?

Thanks already in advance for your answer.

Best regards
Daniela

Thanks for your answer in advance.
best regards,
daniela

4

Hi Daniela,

  • The offset in the humerus segment is just used to correct the location of the elbow joint. The correction could have been completly included in the sRel, the use of the offset just allows to keep track of the changes and improvements.

  • The arm model is not using exactly the same coordinate system as the ISB recommendation. The coordinate system definition comes from the reserch group that provided the anatomic data for the model. So in our model the elbow flexion/extension axis is the x axis of the humerus.
    The pronation joint is a little diferent, the axis of rotation is defined on the Ulna by the points ps2 and us, this corresponds roughly to the y axis of the ulna. So the pronation joint has nothing to do with the humerus coordinate system.

Best regards, Sylvain.

5

Hi!

Now I have just a simple question: If I have a driver-is it right that the angles are driven in the way that the refframe at the second position moves relative to the refframe at the first position? I run the model and changed the order of the refframes(for instance pelvis relative to thorax, and thorax relative to pelvis). When I looked at the model and I set the refframe in the order that pelvis was first and thorax was second refframe I could observe a movement in the pelvis(my dataset includes angles thorax to pelvis), and no movement in the thorax. That’s why it is not so clear for me anymore…

Thanks for your answer.

6

Hi,
If you define a joint with two ref frames, the system basically measures the distances and orientations between those. Usually this measurements are done in the reference frame of the first defined. You can also use the Ref= option. This can be set to either -1 (global coordinate system) 0 (first defined) or 1 (second defined). Please have also look at the definition of the joints in the Reference manual.
Best regards,
Sebastian