FreePostureMove model

Hi

I have tried running the FreePostureMove model but hit a couple of
problems….

  1. I ran the FreePostureMove model with simple constant force muscles
    but received the following error message:

C:\research\Repository.6\Repository.6
\ARep\Aalborg\FreePostureTrial\FreePostureMove.Main.any
(80) : ‘Study’ : Muscle recruitment analysis failed, simplex
solver reports that solution does not satisfy all constraints.

I reduced the hip and shoulder articulation angles from 90 degrees to
45 degrees but this did not help.

  1. I also tried using a 3-element muscles model pre-facing with the
    following calibration step:

AnyBodyStudy Study = {
AnyFolder &Model = .Model;
RecruitmentSolver = MinMaxNRSimplex;
tEnd = 1.0;
Gravity = {0.0, -9.81, 0.0};
nStep = 150;
MuscleEliminationTol = 1e-7;
}; // End of study
AnyBodyCalibrationStudy Cal = {
//This calibration sequence will calibrate the legs and arms
AnyFolder &HumanFolderRef= Main.Model.HumanModel; //This is the
reference to
//the folder which contains the human model

#include “…\BRep\Aalborg\BodyModels\FullBodyModel\CalibrationSe
quence.any”
nStep=1;
};

}; //Main

But the model hung part way through (on step 21 to be precise).

All comments on sources of error appreciated.

Thanks

James Shippen

Hi James

I am sorry about the slow respond on this one, it must have slipped
through somehow.

Please zip the FreePosture model you have problems with and upload
it to the file section of this group, then it will be easier to
solve the problem. It will be enough to zip the FreePostrue
application folder not the BRep.

Best regards
Søren, AnyBody Support

— In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@…>
wrote:
>
> Hi
>
> I have tried running the FreePostureMove model but hit a couple of
> problems….
>
> 1) I ran the FreePostureMove model with simple constant force
muscles
> but received the following error message:
>
> C:\research\Repository.6\Repository.6
> \ARep\Aalborg\FreePostureTrial\FreePostureMove.Main.any
> (80) : ‘Study’ : Muscle recruitment analysis failed, simplex
> solver reports that solution does not satisfy all constraints.
>
> I reduced the hip and shoulder articulation angles from 90 degrees
to
> 45 degrees but this did not help.
>
> 2) I also tried using a 3-element muscles model pre-facing with
the
> following calibration step:
>
> AnyBodyStudy Study = {
> AnyFolder &Model = .Model;
> RecruitmentSolver = MinMaxNRSimplex;
> tEnd = 1.0;
> Gravity = {0.0, -9.81, 0.0};
> nStep = 150;
> MuscleEliminationTol = 1e-7;
> }; // End of study
> AnyBodyCalibrationStudy Cal = {
> //This calibration sequence will calibrate the legs and arms
> AnyFolder &HumanFolderRef= Main.Model.HumanModel; //This is
the
> reference to
> //the folder which contains the human model
>
>
#include “…\BRep\Aalborg\BodyModels\FullBodyModel\CalibrationS
e
> quence.any”
> nStep=1;
> };
>
> }; //Main
>
> But the model hung part way through (on step 21 to be precise).
>
> All comments on sources of error appreciated.
>
> Thanks
>
> James Shippen
>

Hi

I’ve up-loaded the files:
J.Shippen - FreePostureMove Simple Muscle
Main file for FreePostureMove with simple muscle model

J.Shippen - FreePostureMove Simple 3 element Muscle
Main file for FreePostureMove with 3 element muscle model and
calibration study.

When I execute either model, with or without calibration for the
latter model, I receive the error message ‘Muscle recruitment
analysis failed’.

Apologies for not zipping the files (couldn’t immediately find a free
zipper!) but the remainder of the model is as per Repository.6.

Thanks for your assistance

James

— In anyscript@yahoogroups.com, “AnyBody Support” <support@…>
wrote:
>
> Hi James
>
> I am sorry about the slow respond on this one, it must have slipped
> through somehow.
>
> Please zip the FreePosture model you have problems with and upload
> it to the file section of this group, then it will be easier to
> solve the problem. It will be enough to zip the FreePostrue
> application folder not the BRep.
>
> Best regards
> Søren, AnyBody Support
>
> — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> wrote:
> >
> > Hi
> >
> > I have tried running the FreePostureMove model but hit a couple
of
> > problems….
> >
> > 1) I ran the FreePostureMove model with simple constant force
> muscles
> > but received the following error message:
> >
> > C:\research\Repository.6\Repository.6
> > \ARep\Aalborg\FreePostureTrial\FreePostureMove.Main.any
> > (80) : ‘Study’ : Muscle recruitment analysis failed, simplex
> > solver reports that solution does not satisfy all constraints.
> >
> > I reduced the hip and shoulder articulation angles from 90
degrees
> to
> > 45 degrees but this did not help.
> >
> > 2) I also tried using a 3-element muscles model pre-facing with
> the
> > following calibration step:
> >
> > AnyBodyStudy Study = {
> > AnyFolder &Model = .Model;
> > RecruitmentSolver = MinMaxNRSimplex;
> > tEnd = 1.0;
> > Gravity = {0.0, -9.81, 0.0};
> > nStep = 150;
> > MuscleEliminationTol = 1e-7;
> > }; // End of study
> > AnyBodyCalibrationStudy Cal = {
> > //This calibration sequence will calibrate the legs and arms
> > AnyFolder &HumanFolderRef= Main.Model.HumanModel; //This is
> the
> > reference to
> > //the folder which contains the human model
> >
> >
>
#include “…\BRep\Aalborg\BodyModels\FullBodyModel\CalibrationS
> e
> > quence.any”
> > nStep=1;
> > };
> >
> > }; //Main
> >
> > But the model hung part way through (on step 21 to be precise).
> >
> > All comments on sources of error appreciated.
> >
> > Thanks
> >
> > James Shippen
> >
>

Hi James

I get a warning about you having to many reactions compared to the
amount of DOF in your calibration study.
This could be your problem, but I am not sure.
You can zip the directory by right click on the directory in windows
and say “Send to” Compressed(zipped) Folder.
Then we can have a look on the whole model. Or have you not changed
anything there?

Best regards
Christian, AnyBody Support

— In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@…> wrote:
>
> Hi
>
> I’ve up-loaded the files:
> J.Shippen - FreePostureMove Simple Muscle
> Main file for FreePostureMove with simple muscle model
>
> J.Shippen - FreePostureMove Simple 3 element Muscle
> Main file for FreePostureMove with 3 element muscle model and
> calibration study.
>
> When I execute either model, with or without calibration for the
> latter model, I receive the error message ‘Muscle recruitment
> analysis failed’.
>
> Apologies for not zipping the files (couldn’t immediately find a free
> zipper!) but the remainder of the model is as per Repository.6.
>
> Thanks for your assistance
>
> James
>
>
>
>
> — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> wrote:
> >
> > Hi James
> >
> > I am sorry about the slow respond on this one, it must have slipped
> > through somehow.
> >
> > Please zip the FreePosture model you have problems with and upload
> > it to the file section of this group, then it will be easier to
> > solve the problem. It will be enough to zip the FreePostrue
> > application folder not the BRep.
> >
> > Best regards
> > Søren, AnyBody Support
> >
> > — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> > wrote:
> > >
> > > Hi
> > >
> > > I have tried running the FreePostureMove model but hit a couple
> of
> > > problems….
> > >
> > > 1) I ran the FreePostureMove model with simple constant force
> > muscles
> > > but received the following error message:
> > >
> > > C:\research\Repository.6\Repository.6
> > > \ARep\Aalborg\FreePostureTrial\FreePostureMove.Main.any
> > > (80) : ‘Study’ : Muscle recruitment analysis failed, simplex
> > > solver reports that solution does not satisfy all constraints.
> > >
> > > I reduced the hip and shoulder articulation angles from 90
> degrees
> > to
> > > 45 degrees but this did not help.
> > >
> > > 2) I also tried using a 3-element muscles model pre-facing with
> > the
> > > following calibration step:
> > >
> > > AnyBodyStudy Study = {
> > > AnyFolder &Model = .Model;
> > > RecruitmentSolver = MinMaxNRSimplex;
> > > tEnd = 1.0;
> > > Gravity = {0.0, -9.81, 0.0};
> > > nStep = 150;
> > > MuscleEliminationTol = 1e-7;
> > > }; // End of study
> > > AnyBodyCalibrationStudy Cal = {
> > > //This calibration sequence will calibrate the legs and arms
> > > AnyFolder &HumanFolderRef= Main.Model.HumanModel; //This is
> > the
> > > reference to
> > > //the folder which contains the human model
> > >
> > >
> >
> #include “…\BRep\Aalborg\BodyModels\FullBodyModel\CalibrationS
> > e
> > > quence.any”
> > > nStep=1;
> > > };
> > >
> > > }; //Main
> > >
> > > But the model hung part way through (on step 21 to be precise).
> > >
> > > All comments on sources of error appreciated.
> > >
> > > Thanks
> > >
> > > James Shippen
> > >
> >
>

Hi

Due to the 5Mb upload limit I have uploaded the
Arep\Aalborg\FreePosture folder and called it J_Shippen_Free Posture.

Thanks for the Windows zip-tip!

James

— In anyscript@yahoogroups.com, “AnyBody Support” <support@…>
wrote:
>
> Hi James
>
> I get a warning about you having to many reactions compared to the
> amount of DOF in your calibration study.
> This could be your problem, but I am not sure.
> You can zip the directory by right click on the directory in windows
> and say “Send to” Compressed(zipped) Folder.
> Then we can have a look on the whole model. Or have you not changed
> anything there?
>
> Best regards
> Christian, AnyBody Support
>
>
> — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
wrote:
> >
> > Hi
> >
> > I’ve up-loaded the files:
> > J.Shippen - FreePostureMove Simple Muscle
> > Main file for FreePostureMove with simple muscle model
> >
> > J.Shippen - FreePostureMove Simple 3 element Muscle
> > Main file for FreePostureMove with 3 element muscle model and
> > calibration study.
> >
> > When I execute either model, with or without calibration for the
> > latter model, I receive the error message ‘Muscle recruitment
> > analysis failed’.
> >
> > Apologies for not zipping the files (couldn’t immediately find a
free
> > zipper!) but the remainder of the model is as per Repository.6.
> >
> > Thanks for your assistance
> >
> > James
> >
> >
> >
> >
> > — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> > wrote:
> > >
> > > Hi James
> > >
> > > I am sorry about the slow respond on this one, it must have
slipped
> > > through somehow.
> > >
> > > Please zip the FreePosture model you have problems with and
upload
> > > it to the file section of this group, then it will be easier to
> > > solve the problem. It will be enough to zip the FreePostrue
> > > application folder not the BRep.
> > >
> > > Best regards
> > > Søren, AnyBody Support
> > >
> > > — In anyscript@yahoogroups.com, “jamesshippen”
<jamesshippen@>
> > > wrote:
> > > >
> > > > Hi
> > > >
> > > > I have tried running the FreePostureMove model but hit a
couple
> > of
> > > > problems….
> > > >
> > > > 1) I ran the FreePostureMove model with simple constant force
> > > muscles
> > > > but received the following error message:
> > > >
> > > > C:\research\Repository.6\Repository.6
> > > > \ARep\Aalborg\FreePostureTrial\FreePostureMove.Main.any
> > > > (80) : ‘Study’ : Muscle recruitment analysis failed,
simplex
> > > > solver reports that solution does not satisfy all constraints.
> > > >
> > > > I reduced the hip and shoulder articulation angles from 90
> > degrees
> > > to
> > > > 45 degrees but this did not help.
> > > >
> > > > 2) I also tried using a 3-element muscles model pre-facing
with
> > > the
> > > > following calibration step:
> > > >
> > > > AnyBodyStudy Study = {
> > > > AnyFolder &Model = .Model;
> > > > RecruitmentSolver = MinMaxNRSimplex;
> > > > tEnd = 1.0;
> > > > Gravity = {0.0, -9.81, 0.0};
> > > > nStep = 150;
> > > > MuscleEliminationTol = 1e-7;
> > > > }; // End of study
> > > > AnyBodyCalibrationStudy Cal = {
> > > > //This calibration sequence will calibrate the legs and
arms
> > > > AnyFolder &HumanFolderRef= Main.Model.HumanModel; //This
is
> > > the
> > > > reference to
> > > > //the folder which contains the human model
> > > >
> > > >
> > >
> >
#include “…\BRep\Aalborg\BodyModels\FullBodyModel\CalibrationS
> > > e
> > > > quence.any”
> > > > nStep=1;
> > > > };
> > > >
> > > > }; //Main
> > > >
> > > > But the model hung part way through (on step 21 to be
precise).
> > > >
> > > > All comments on sources of error appreciated.
> > > >
> > > > Thanks
> > > >
> > > > James Shippen
> > > >
> > >
> >
>

Hi

To truncate this support thread, and as I have made very few changes
to my version of FreePostureMove, could we abandon that version and
can I state the question I was trying to solve…

I wish to import MoCap data into AnyBody. As is widely acknowldeged,
the issue of DoF vs Constraints requires the careful selection of
driven measures. Therefore I was considering using joint angles (and
3 translations eg pelvis) as the generalised co-ordinates as it
appears easier to select a non-redunadant, non-overconstrain set.
And because these angles can be readily calculated within Vicon’s
BodyBuilder and dumped to C3D. The structure of FreePostureMove
appears to be very close to this approach.

Naturally I will have to use a model with muscle for the inverse
dynamics and therefore the question is…what modifications should
I make to FreePostureMove.main.any to include either a simple or 3-
element Hill type muscle?

I have tried commenting

#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyModel_No
Muscles.any”

and uncommenting

//#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyModel.
any”

or

//#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyModel_
Mus3E.any”

but this causes an error.

Thanks

James

— In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@…>
wrote:
>
> Hi
>
> Due to the 5Mb upload limit I have uploaded the
> Arep\Aalborg\FreePosture folder and called it J_Shippen_Free
Posture.
>
> Thanks for the Windows zip-tip!
>
> James
>
>
> — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> wrote:
> >
> > Hi James
> >
> > I get a warning about you having to many reactions compared to the
> > amount of DOF in your calibration study.
> > This could be your problem, but I am not sure.
> > You can zip the directory by right click on the directory in
windows
> > and say “Send to” Compressed(zipped) Folder.
> > Then we can have a look on the whole model. Or have you not
changed
> > anything there?
> >
> > Best regards
> > Christian, AnyBody Support
> >
> >
> > — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> wrote:
> > >
> > > Hi
> > >
> > > I’ve up-loaded the files:
> > > J.Shippen - FreePostureMove Simple Muscle
> > > Main file for FreePostureMove with simple muscle model
> > >
> > > J.Shippen - FreePostureMove Simple 3 element Muscle
> > > Main file for FreePostureMove with 3 element muscle model and
> > > calibration study.
> > >
> > > When I execute either model, with or without calibration for
the
> > > latter model, I receive the error message ‘Muscle recruitment
> > > analysis failed’.
> > >
> > > Apologies for not zipping the files (couldn’t immediately find
a
> free
> > > zipper!) but the remainder of the model is as per Repository.6.
> > >
> > > Thanks for your assistance
> > >
> > > James
> > >
> > >
> > >
> > >
> > > — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> > > wrote:
> > > >
> > > > Hi James
> > > >
> > > > I am sorry about the slow respond on this one, it must have
> slipped
> > > > through somehow.
> > > >
> > > > Please zip the FreePosture model you have problems with and
> upload
> > > > it to the file section of this group, then it will be easier
to
> > > > solve the problem. It will be enough to zip the FreePostrue
> > > > application folder not the BRep.
> > > >
> > > > Best regards
> > > > Søren, AnyBody Support
> > > >
> > > > — In anyscript@yahoogroups.com, “jamesshippen”
> <jamesshippen@>
> > > > wrote:
> > > > >
> > > > > Hi
> > > > >
> > > > > I have tried running the FreePostureMove model but hit a
> couple
> > > of
> > > > > problems….
> > > > >
> > > > > 1) I ran the FreePostureMove model with simple constant
force
> > > > muscles
> > > > > but received the following error message:
> > > > >
> > > > > C:\research\Repository.6\Repository.6
> > > > > \ARep\Aalborg\FreePostureTrial\FreePostureMove.Main.any
> > > > > (80) : ‘Study’ : Muscle recruitment analysis failed,
> simplex
> > > > > solver reports that solution does not satisfy all
constraints.
> > > > >
> > > > > I reduced the hip and shoulder articulation angles from 90
> > > degrees
> > > > to
> > > > > 45 degrees but this did not help.
> > > > >
> > > > > 2) I also tried using a 3-element muscles model pre-facing
> with
> > > > the
> > > > > following calibration step:
> > > > >
> > > > > AnyBodyStudy Study = {
> > > > > AnyFolder &Model = .Model;
> > > > > RecruitmentSolver = MinMaxNRSimplex;
> > > > > tEnd = 1.0;
> > > > > Gravity = {0.0, -9.81, 0.0};
> > > > > nStep = 150;
> > > > > MuscleEliminationTol = 1e-7;
> > > > > }; // End of study
> > > > > AnyBodyCalibrationStudy Cal = {
> > > > > //This calibration sequence will calibrate the legs and
> arms
> > > > > AnyFolder &HumanFolderRef=
Main.Model.HumanModel; //This
> is
> > > > the
> > > > > reference to
> > > > > //the folder which contains the human model
> > > > >
> > > > >
> > > >
> > >
>
#include “…\BRep\Aalborg\BodyModels\FullBodyModel\CalibrationS
> > > > e
> > > > > quence.any”
> > > > > nStep=1;
> > > > > };
> > > > >
> > > > > }; //Main
> > > > >
> > > > > But the model hung part way through (on step 21 to be
> precise).
> > > > >
> > > > > All comments on sources of error appreciated.
> > > > >
> > > > > Thanks
> > > > >
> > > > > James Shippen
> > > > >
> > > >
> > >
> >
>

James,

Please see my replies below.

> I wish to import MoCap data into AnyBody. As is widely
> acknowldeged,
> the issue of DoF vs Constraints requires the careful selection of
> driven measures. Therefore I was considering using joint
> angles (and
> 3 translations eg pelvis) as the generalised co-ordinates as it
> appears easier to select a non-redunadant, non-overconstrain set.
> And because these angles can be readily calculated within Vicon’s
> BodyBuilder and dumped to C3D. The structure of FreePostureMove
> appears to be very close to this approach.

Yes, this is true.

> Naturally I will have to use a model with muscle for the inverse
> dynamics and therefore the question is…what modifications
should
> I make to FreePostureMove.main.any to include either a simple or 3-
> element Hill type muscle?
>
> I have tried commenting
>
>
#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyModel_N
o Muscles.any”
>
> and uncommenting
>
> //#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyMod
el.
> any”
>
> or
>
> //#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyMod
el_
> Mus3E.any”
>
> but this causes an error.

You are doing it correctly.

I tried your model as well as the model directly from the
repository. In the repository model it is necessary to rename
PelvisThoraxFlexion.any to PelvisThoraxExtension.any, but you
already worked that out.

Both your model and the repository version fail in step 24 of the
analysis with a recruitment error. This error happens when there are
insufficient muscle forces or supports to balance the model, and in
spite of having more than 500 muscles on the model, this can still
happen in some postures because the mechanism is so complicated. The
problem is that the equilibrium equations become singular and hence
have no solution.

In numerical analysis, singularity is rarely an absolute property.
We use an optimization algorithm to solve the muscle recruitment
problem, and it can sometimes get “confused” by problems that are
too symetric or where the load in certain directions is very small
(thus requiring it to solve the problem 0 = 0). So this little trick
will make your model run:

Go to the study section of the main file and locate Gravity
specification. Then replace it by this:

 Gravity = {0.001, -9.81, 0.001};

As you can see, this imposes are very small and entirely
insignificant gravity in the hrizontal directions. This is enough to
give the optimizer a road to solve the problem and it proceeds to
step 84 or so before failing with a similar error.

But this is very problem and movement dependent, so instead of
spending a lot of time making this version of the model run I
propose you go ahead and impose the movement you like on the model,
and if there is a problem with it after you have imposed the correct
movement and load, then we take it from there.

Also, I replaced the specification of the solver by this:

 RecruitmentSolver = MinMaxSimplex;

It makes the analysis run a bit faster.

Finally, your version of the model seems to have too many reaction
forces compared to the number of degrees of freedom. This should not
make the solution fail, but it can cause instability in the muscle
forces the system computes. I have not analyzed where the additional
reaction forces come from, but they do not seem to be present in the
original version of the model.

Best regards,
John

Many thanks - I’ll give it a go.

James

— In anyscript@yahoogroups.com, “AnyBody Support” <support@…>
wrote:
>
> James,
>
> Please see my replies below.
>
> > I wish to import MoCap data into AnyBody. As is widely
> > acknowldeged,
> > the issue of DoF vs Constraints requires the careful selection of
> > driven measures. Therefore I was considering using joint
> > angles (and
> > 3 translations eg pelvis) as the generalised co-ordinates as it
> > appears easier to select a non-redunadant, non-overconstrain
set.
> > And because these angles can be readily calculated within Vicon’s
> > BodyBuilder and dumped to C3D. The structure of FreePostureMove
> > appears to be very close to this approach.
>
> Yes, this is true.
>
> > Naturally I will have to use a model with muscle for the inverse
> > dynamics and therefore the question is…what modifications
> should
> > I make to FreePostureMove.main.any to include either a simple or
3-
> > element Hill type muscle?
> >
> > I have tried commenting
> >
> >
>
#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyModel_N
> o Muscles.any”
> >
> > and uncommenting
> >
>
> //#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyMod
> el.
> > any”
> >
> > or
> >
>
> //#include “…\BRep\Aalborg\BodyModels\FullBodyModel\BodyMod
> el_
> > Mus3E.any”
> >
> > but this causes an error.
>
> You are doing it correctly.
>
> I tried your model as well as the model directly from the
> repository. In the repository model it is necessary to rename
> PelvisThoraxFlexion.any to PelvisThoraxExtension.any, but you
> already worked that out.
>
> Both your model and the repository version fail in step 24 of the
> analysis with a recruitment error. This error happens when there
are
> insufficient muscle forces or supports to balance the model, and in
> spite of having more than 500 muscles on the model, this can still
> happen in some postures because the mechanism is so complicated.
The
> problem is that the equilibrium equations become singular and hence
> have no solution.
>
> In numerical analysis, singularity is rarely an absolute property.
> We use an optimization algorithm to solve the muscle recruitment
> problem, and it can sometimes get “confused” by problems that are
> too symetric or where the load in certain directions is very small
> (thus requiring it to solve the problem 0 = 0). So this little
trick
> will make your model run:
>
> Go to the study section of the main file and locate Gravity
> specification. Then replace it by this:
>
> Gravity = {0.001, -9.81, 0.001};
>
> As you can see, this imposes are very small and entirely
> insignificant gravity in the hrizontal directions. This is enough
to
> give the optimizer a road to solve the problem and it proceeds to
> step 84 or so before failing with a similar error.
>
> But this is very problem and movement dependent, so instead of
> spending a lot of time making this version of the model run I
> propose you go ahead and impose the movement you like on the model,
> and if there is a problem with it after you have imposed the
correct
> movement and load, then we take it from there.
>
> Also, I replaced the specification of the solver by this:
>
> RecruitmentSolver = MinMaxSimplex;
>
> It makes the analysis run a bit faster.
>
> Finally, your version of the model seems to have too many reaction
> forces compared to the number of degrees of freedom. This should
not
> make the solution fail, but it can cause instability in the muscle
> forces the system computes. I have not analyzed where the
additional
> reaction forces come from, but they do not seem to be present in
the
> original version of the model.
>
> Best regards,
> John
>