# stiffness of lumbar segments

Dear all,

the lumbar segments of the standing model are connected by ball joints. I
wonder if there is a stiffness modelled between the segments?
How can something like a rotational spring been added?

Greetings, Thomas

Hi Thomas

This can be done using an AnyForce force object and an interpolation
function for writing the force functionâ€¦

//some stiffness function dependent on angle values

AnyInterpolFun Stiffness1={

T={-20,10,0,10,20}*pi/180; //Angle values

Data={{10,5,0,-5,-10}}; //some moment values

Type=Bspline;

};

//adding this stiffness to the joints

AnyForce spring={

AnySphericalJoint &ref1=â€¦…L1L2Jnt;

F={Stiffness1(L1L2Jnt.Pos[0]), Stiffness1(L1L2Jnt.Pos[1]),
Stiffness1(L1L2Jnt.Pos[2]) };

};

These lines will add a moment to the joints depending on the joint position;
this will work as a rotational spring with a variable stiffness.

Best regards

SÃ¸ren

From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of Thomas Zander
Sent: 14 March 2008 12:57
To: anyscript@yahoogroups.com
Subject: [AnyScript] stiffness of lumbar segments

Dear all,

the lumbar segments of the standing model are connected by ball joints. I
wonder if there is a stiffness modelled between the segments?
How can something like a rotational spring been added?

Greetings, Thomas

[Non-text portions of this message have been removed]

Thank you SÃƒÂ¸ren,

does your answer imply, that the standing model has no stiffness between the
lumbar segments? Do you also think that the ligaments’ and discs’ stiffnesses
have a considerable impact on the calculated muscle forces?
(I am a bit astonished, but maybe due to some reason the stiffnesses are of
minor influence?)

Greetings, Thomas

>
> This can be done using an AnyForce force object and an interpolation
> function for writing the force functionÃ‚â€¦
>

>>
>> the lumbar segments of the standing model are connected by ball joints. I
>> wonder if there is a stiffness modelled between the segments?
>>
>>

Hi again.

I would like to repeat my question.
(I didn’t want to criticize the standing model.)
If it is true that the standing model has no lumbar stiffness: What
would you think, are the calculated forces higher or smaller than they
would be with lumbar stiffness?

Bye, Thomas

>
> >
> > This can be done using an AnyForce force object and an interpolation
> > function for writing the force functionÃ‚â€¦
> >
>
> >>
> >> the lumbar segments of the standing model are connected by ball
joints. I
> >> wonder if there is a stiffness modelled between the segments?
> >>
> >>
>

Hi Thomas

You are right there is no stiffness modelled into the lumbar spine as the
model is today. It is not, that this is difficult to do in terms of adding
the needed objects; it is more a question on getting the right parameters
for doing so. We could add rotational springs into the model but if these
are too strong they will add unrealistic loads to the model. Ligaments could
also bee added, but again it is a problem to get the right parameters, this
is one of the reasons for omitting this in the model, but if you have the
data available it is relatively easy to implement.

I am not sure how much impact adding the stiffness on the model will have,
it may also depend a lot on the working condition. As I have understood it,
when the spine model was developed originally it was considered to include
this, but at that point there seemed to be no consensus in the literature on
how important the stiffness would be. Some sources said it was important,
others said the opposite, so it was not included.

Best regards

SÃ¸ren, AnyBody Support

From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of Thomas Zander
Sent: 17 March 2008 10:56
To: anyscript@yahoogroups.com
Subject: Re: [AnyScript] stiffness of lumbar segments

Thank you SÃ¸ren,

does your answer imply, that the standing model has no stiffness between the

lumbar segments? Do you also think that the ligaments’ and discs’
stiffnesses
have a considerable impact on the calculated muscle forces?
(I am a bit astonished, but maybe due to some reason the stiffnesses are of
minor influence?)

Greetings, Thomas

>
> This can be done using an AnyForce force object and an interpolation
> function for writing the force functionâ€¦
>

>>
>> the lumbar segments of the standing model are connected by ball joints. I
>> wonder if there is a stiffness modelled between the segments?
>>
>>

[Non-text portions of this message have been removed]

Hi Thomas

It is a very relevant question to post;

I did not see this posting when I answered the previous one.

the activities higher or lower, there will be no general rule. For a
standing model leaning forward or backward it will most likely lower the
activity because the stiffness will take away load from the muscles, but in
other conditions it could have the opposite effect.

Best regards

SÃ¸ren, AnyBody Support

From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of zandfub1
Sent: 18 March 2008 13:49
To: anyscript@yahoogroups.com
Subject: [AnyScript] Re: stiffness of lumbar segments

Hi again.

I would like to repeat my question.
(I didn’t want to criticize the standing model.)
If it is true that the standing model has no lumbar stiffness: What
would you think, are the calculated forces higher or smaller than they
would be with lumbar stiffness?

Bye, Thomas

>
> >
> > This can be done using an AnyForce force object and an interpolation
> > function for writing the force functionÃ‚â€¦
> >
>
> >>
> >> the lumbar segments of the standing model are connected by ball
joints. I
> >> wonder if there is a stiffness modelled between the segments?
> >>
> >>
>

[Non-text portions of this message have been removed]