Min/Max Criteria

Referencing your paper, “Muscle recruitment by the min/max criterion -
a comparative numberical study,” I have created (previously) a simple
arm model in AnyBody similar to the arm model you reference from
Siemienski (1992). Within Matlab I created a program that takes
muscle strength, moment arm, and external load values and inputs them
into the equation:

fi(M) = ((M)/(N1r1+N2r2+N3r3+…Niri))*Ni

Within Matlab, when my muscles have constant strength, my resulting
muscle forces always end up being the same, which makes sense based on
the above equation.

For example, if I have the following information:
Brachialis: F0 = 300 N, r = 0.070711 m
Brachioradialis: F0 = 300 N, r = 0.12 m
Biceps Long: F0 = 300 N, r = 0.012403

I get muscle force outputs from Matlab saying that the muscle force
for all muscles is: 984.67 N.

(It should be noted that the moment arm values have been calculated
from a previously designed arm model, which is why they aren’t “easy”
numbers like the example in your paper.)

However, when I try to replicate the same thing within AnyBody, I get
the following muscle-force values:
If I apply AnyMoment3D:
Brachialis: ~524
Brachioradialis: ~524
Deltoid: ~2015

If I apply AnyForce3D (equivalent to AnyMoment3D):
Brachialis: ~84
Brachioradialis: ~84
Biceps Long: ~322

Within the model I changed the upper and lower arm to be mass-less.

How come I can’t get my Matlab simple model to give me the outputs
that my AnyBody simple model gives me?

Thanks for your help,
Sarah

Hi Sarah

The equation you write applies only for a one dof model where the
moment direction is known.

The results that you lists looks like they could be from a two dof
model since there are two levels of force, and bicpes long would
normally span two joints, but i am not sure?

The difference in the results using AnyMoment3d abd AnyForce3D could
be a moment arm issue, since the ratios 84/322= 524/2015. Maybee you
have a different moment arm than you think when you apply the
AnyForce3d.

If you continue to have problems with the results please upload the
model and we will have a look at at it.

Best regards
Soeren AnyBody Support

— In anyscript@yahoogroups.com, “Sarah R. Sullivan”
<sarsulli@e…> wrote:
>
> Referencing your paper, “Muscle recruitment by the min/max
criterion -
> a comparative numberical study,” I have created (previously) a
simple
> arm model in AnyBody similar to the arm model you reference from
> Siemienski (1992). Within Matlab I created a program that takes
> muscle strength, moment arm, and external load values and inputs
them
> into the equation:
>
> fi(M) = ((M)/(N1r1+N2r2+N3r3+…Niri))*Ni
>
> Within Matlab, when my muscles have constant strength, my resulting
> muscle forces always end up being the same, which makes sense
based on
> the above equation.
>
> For example, if I have the following information:
> Brachialis: F0 = 300 N, r = 0.070711 m
> Brachioradialis: F0 = 300 N, r = 0.12 m
> Biceps Long: F0 = 300 N, r = 0.012403
>
> I get muscle force outputs from Matlab saying that the muscle force
> for all muscles is: 984.67 N.
>
> (It should be noted that the moment arm values have been calculated
> from a previously designed arm model, which is why they
aren’t “easy”
> numbers like the example in your paper.)
>
> However, when I try to replicate the same thing within AnyBody, I
get
> the following muscle-force values:
> If I apply AnyMoment3D:
> Brachialis: ~524
> Brachioradialis: ~524
> Deltoid: ~2015
>
> If I apply AnyForce3D (equivalent to AnyMoment3D):
> Brachialis: ~84
> Brachioradialis: ~84
> Biceps Long: ~322
>
> Within the model I changed the upper and lower arm to be mass-
less.
>
> How come I can’t get my Matlab simple model to give me the outputs
> that my AnyBody simple model gives me?
>
> Thanks for your help,
> Sarah
>