# 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
Deltoid: ~2015

If I apply AnyForce3D (equivalent to AnyMoment3D):
Brachialis: ~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?

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
> Deltoid: ~2015
>
> If I apply AnyForce3D (equivalent to AnyMoment3D):
> Brachialis: ~84