Kinematics modelling

Hello again,
I have been working with musculoskeletal modelling of ballet dance movements for a while now. I got kinematics to run smoothly for 4 dance movements for a dancer. Now i have a new dancer .c3d file with similar dance movements and when i try to model and run the analysis. the musculoskeletal model in anybody gets distorted and the arm movement is unnatural, I dont understand the problem here.
I have followed a similar approach as i did for the previous dancer modelling.

Things i have changed from the fullbody.main.any to model my new dancer


  • c3d file input
  • body posture

-body mass and height

-Qualisys marker protocol
-Extra drivers

Error message:

AnyBody files:

is there something you could suggest, i could really use your expertise.

Hi Bharathhs,

The shoulders looks rather strange and i suspect the kinematic problem could related to the scapula/ thoracic constraint.

I can not see any markers on the head? are you sure the model is not too high? i think it would help if the subject was shorter and the SC joint would be more straight.

I looked briefly at the files but failed to find your model among the files

Best regards

its fullbodymain, under plug in gait Mocap samples.

yes, I also realized the scapula and thorax distorted movement when i run the kinematics. due to which the hip girdle also is displaced a bit.
In this thesis i had been given the prepared c3d files, It used Qualisys marker placement set, in this there was no marker in the head.
According to my supervisor, The body hieght and mass given: 158 cm and 46 Kg.
I also feel the the scaled human body model is bigger than the input c3d file, it could be a little more smaller, I will try to confirm on this,
But if you could look into the fullbody main under mocap examples, you will find my file.

Hi Bharathhs,

I have looked at the model the C7 marker seem to be open for optimization in the vertical direction. Please try to fix the location of this marker so not having it optimized.
Secondly try to set the trunkheight optimization off in the labsspecific.any file honestly it is a bit strange that the optimization worked for trunkheight, since it is not well defined when the C7 can move and there are no skull markers.
The height variable will not be really used in a model like this since the optimization of the model will change the overall height, there is no way to optimize e.g. leg lengths while ensuring total height becomes a certain value. You can adjust the size of the subject in segment dimensions directly on the subject specific file, so simply set trunk and skull height so that it fit the markers.

Best regards

thanks for the advice.
I have my model with C7 marker locked in all direction, not allowing any kind of optimization, the trunk optimization is set to off along with head height in lab specific , the problem still persists, I am trying to look into other markers to lock optimization.
So as you said the body height in subject specific doesnt not matter as the segment lengths are getting optimized. I also confirmed the the entered data for mass and height are the right dimensions.(may be 1 cm or 1 Kg difference but not more)
Is there any thing else that i could look into at the moment. to change the body from getting disfigured.

Here is a quick answer.

Try to change the trunkheight and skullheight in the subjectspecific.any file, this will change the height of the subject and possible help

yes, it worked.
Now the parameter identification runs completely fine. and also been able to run complete analysis with inverse dynamics.
it so happened that after i run my parameter identification i have longer thigh lengths and shorter shank length. i tried to moniter the thigh length through the paramter optimization the length decreases. is there a way i could look into this problem.

After Parameter optimization


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