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  #1  
Old 01-23-2018, 09:35 PM
Yogesh Yogesh is offline
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Default Flexion in Standing model not containing Rectus abdominis muscle force

Hello,

My name is Yogesh and I am a student at the University of Toledo Engineering Center for Orthopedic Excellence.

We are creating a FEA model that contains the rib cage, pelvis, and femur (femur muscle forces deactivated). We have obtained the muscle forces using the standing model for flexion, but, do not have a value for the rectus abdominis?

Why is this? The rectus abdominis is a prime mover for flexion in the body. When we run our FEA model using the flexion muscle forces, it is doing hyperextension.

Please guide us in the right direction,

Yogesh.
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  #2  
Old 01-24-2018, 02:21 PM
pgalibarov's Avatar
pgalibarov pgalibarov is offline
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Hi Yogesh,

Please provide more information about your simulation so we could replicate the problem. Is it one of our standard examples or a modified model?


Kind regards,
Pavel
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  #3  
Old 01-24-2018, 08:57 PM
Yogesh Yogesh is offline
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Hi Pavel,

We are using a standard example, specifically the Standing Model.

We simulated around 10 degrees of flexion and extension after manipulating the pelvisthoracicextension value.

We noticed that during flexion, we receive a near zero value for the muscle Rectus Abdominis. This should not be the case for flexion. The kinesiology of the trunk during flexion shows that the Rectus Abdominis is a prime mover for flexion.

When running extension in the standing model, there is a large value for the Rectus Abdominis (around 85). This should be an antagonizing force.

We applied these muscle forces in our FEA model and saw that when using the flexion muscle forces, our model was doing extension. When we input the values for the muscle forces during extension, our model was doing flexion.

Please point us in the right direction.

Thank you,
Yogesh.
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  #4  
Old 01-25-2018, 12:44 AM
msan00 msan00 is offline
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Hi Yogesh

I think what you are observing in the AnyBody model is correct. From your description, it seems you have put the model into 10 degrees of flexion in a static posture. In this case, you have to expect the spine extensors (not flexors) to be active in order to counteract the effect of gravity.

I have a feeling that you may have omitted the effects of gravity in your FEA (or whatever other external loads you may have). In this case, the fea model would perform extension rather than the expected static posture.

I hope that helps.

Best regards
Michael
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The AnyBody Research Group
Aalborg University
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  #5  
Old 01-25-2018, 07:31 PM
Yogesh Yogesh is offline
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Hi Michael,

I understand what you are saying. We are trying to show flexion in our FEA using muscle forces from anybody. Since the standing model is a static model, how can we physically move our FEA model to show flexion using muscle forces found in the standing model? Will we need to add an external load since the prime movers do not have any loads to replicate flexion in our FE model?

Thank you,
Yogesh.
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  #6  
Old 01-25-2018, 09:55 PM
msan00 msan00 is offline
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Hi Yogash

I suggest two things: 1) set up an AnyBody simulation where the spine flexors are active for instance a sit up exercise. 2) Export from AnyBody not only the muscle forces but also the joint reaction forces for the last joint in your FEA model (at the end that you do not ground).

If you apply both these to your FEA model, you should obtain similar spine movements as soon in AnyBody.

Best regards
Michael
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The AnyBody Research Group
Aalborg University
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  #7  
Old 01-25-2018, 10:47 PM
Yogesh Yogesh is offline
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Hi Michael,

We are looking to simulate all motions in our FEA model (flexion, extension, bendings, and rotations). We want muscle forces for the action of the motion, not the forces for a predefined posture to counteract the force of gravity. For example, we would like to know what the value of the muscle force of the rectus abdominis is during the act of flexion since it is a prime mover. Is this possible using a different model?

Do you happen to have an example of a model like this or is there a model in the AMMR that has active spine flexors in which we can simulate flexion in our case?

Last edited by Yogesh; 01-25-2018 at 11:14 PM.
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  #8  
Old 01-30-2018, 02:54 PM
msan00 msan00 is offline
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Quote:
Originally Posted by Yogesh View Post
Hi Michael,

We are looking to simulate all motions in our FEA model (flexion, extension, bendings, and rotations). We want muscle forces for the action of the motion, not the forces for a predefined posture to counteract the force of gravity. For example, we would like to know what the value of the muscle force of the rectus abdominis is during the act of flexion since it is a prime mover. Is this possible using a different model?

Do you happen to have an example of a model like this or is there a model in the AMMR that has active spine flexors in which we can simulate flexion in our case?
Hi Yogesh,

What you need is to set up AnyBody models that actually perform the tasks you are interested in.

I think there are basically two different approaches you can take to accomplish this.

1) You can find/collect some recorded motion capture data and external forces. In such case, you should use one of the motion capture models to analyse the movements.

2) You should define body postures and movements, matching your desired tasks. These you can then use to define new drivers and external forces starting from one of the example models in the repository.

I am not aware that we have models already performing the tasks that you mentioned above.

Best regards
Michael
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Michael Skipper Andersen, Ph.D.
Associate Professor
The AnyBody Research Group
Aalborg University
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