# External forces applied to MoCap data

Hi

Just to prove that you can’t please all the people all of the time,
my question relates to a model which is working when I don’t think it
should!!!

I am driving FreePostureMove with MoCap data. I have modelled ground
reaction forces with AnyGeneralMuscle where the AnyMuscleModelUsr1
strength is conditional on ground contact.

During phases of no foot contact there is the potential that dynamic
equilibrium could not be achieved due to MoCap measurement errors.
Therefore I attached `weak’ linear and rotational muscles between the
pelvis and ground. The strength of the weak muscles was 2 magnitude
less than ground contact muscles (ground contact muscles were not too
stiff nor the imaginary muscles too weak to cause ill-conditioning).

The model ran in an ID analysis and continued to run as I reduced the
imaginary muscles’ stiffness until they became zero (well less than
Study.StrongMuscleLimit = 0.001;). Thus implying even during no foot
contact the MoCap data collection was perfect!

Does my approach make sense? How can movement containing inevitable
measurement errors be analysed in the presence of an incomplete set
of external forces?

Thanks

James

Hi James

Your approach do make sense, if you have no foot contact you have
applied the weak muscles between the pelvis and ground which should
be able to carry the load, this should work if it is setup correctly.

I can only think of one possible explanation to that the model still
runs Inv. Dyn. Anal. when there is no strength in the weak muscles,
and it is out of balance, there must be one or more reactions between
the human model and the ground which is active, by accident.

You write that the model is driven by markes, i guess you know this
already but by default a driver adds a reactions of the driven dof,
unless it is switched off, by writing “Reaction.Type={Off}”. If your
model is driven by the markers one of those drivers could have
reactions in them by accident, this would be a direct reaction with
the ground.

by looking at the Constraint.Reaction property of the drivers.

Best regards
SÃ¸ren, AnyBody Support

— In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@…>
wrote:
>
> Hi
>
> Just to prove that you can’t please all the people all of the time,
> my question relates to a model which is working when I don’t think
it
> should!!!
>
> I am driving FreePostureMove with MoCap data. I have modelled
ground
> reaction forces with AnyGeneralMuscle where the AnyMuscleModelUsr1
> strength is conditional on ground contact.
>
> During phases of no foot contact there is the potential that
dynamic
> equilibrium could not be achieved due to MoCap measurement errors.
> Therefore I attached `weak’ linear and rotational muscles between
the
> pelvis and ground. The strength of the weak muscles was 2
magnitude
> less than ground contact muscles (ground contact muscles were not
too
> stiff nor the imaginary muscles too weak to cause ill-
conditioning).
>
> The model ran in an ID analysis and continued to run as I reduced
the
> imaginary muscles’ stiffness until they became zero (well less than
> Study.StrongMuscleLimit = 0.001;). Thus implying even during no
foot
> contact the MoCap data collection was perfect!
>
> Does my approach make sense? How can movement containing
inevitable
> measurement errors be analysed in the presence of an incomplete set
> of external forces?
>
> Thanks
>
> James
>

Hi SÃ¸ren

reactions to Off. I’ll continue to investigate.

On a related matter, when I specify tArray an unknown error is
generated during model load. Any thoughts on a work-around.

As ever…many thanks

James

ERROR : Model load : unknown error

— In anyscript@yahoogroups.com, “AnyBody Support” <support@…>
wrote:
>
> Hi James
>
> Your approach do make sense, if you have no foot contact you have
> applied the weak muscles between the pelvis and ground which should
> be able to carry the load, this should work if it is setup
correctly.
>
> I can only think of one possible explanation to that the model
still
> runs Inv. Dyn. Anal. when there is no strength in the weak muscles,
> and it is out of balance, there must be one or more reactions
between
> the human model and the ground which is active, by accident.
>
> You write that the model is driven by markes, i guess you know this
> already but by default a driver adds a reactions of the driven dof,
> unless it is switched off, by writing “Reaction.Type={Off}”. If
your
> model is driven by the markers one of those drivers could have
> reactions in them by accident, this would be a direct reaction with
> the ground.
>
> Please try to check your drivers for unwanted reactions in general,
> by looking at the Constraint.Reaction property of the drivers.
>
> Best regards
> SÃ¸ren, AnyBody Support
>
>
> — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> wrote:
> >
> > Hi
> >
> > Just to prove that you can’t please all the people all of the
time,
> > my question relates to a model which is working when I don’t
think
> it
> > should!!!
> >
> > I am driving FreePostureMove with MoCap data. I have modelled
> ground
> > reaction forces with AnyGeneralMuscle where the
AnyMuscleModelUsr1
> > strength is conditional on ground contact.
> >
> > During phases of no foot contact there is the potential that
> dynamic
> > equilibrium could not be achieved due to MoCap measurement
errors.
> > Therefore I attached `weak’ linear and rotational muscles between
> the
> > pelvis and ground. The strength of the weak muscles was 2
> magnitude
> > less than ground contact muscles (ground contact muscles were not
> too
> > stiff nor the imaginary muscles too weak to cause ill-
> conditioning).
> >
> > The model ran in an ID analysis and continued to run as I reduced
> the
> > imaginary muscles’ stiffness until they became zero (well less
than
> > Study.StrongMuscleLimit = 0.001;). Thus implying even during no
> foot
> > contact the MoCap data collection was perfect!
> >
> > Does my approach make sense? How can movement containing
> inevitable
> > measurement errors be analysed in the presence of an incomplete
set
> > of external forces?
> >
> > Thanks
> >
> > James
> >
>

PS Perhaps I shouldn’t have used the phrase ‘work-around’ as the
obvious one is tStart/nStep/tEnd.

However I am finding that muscle activity can be very fleeting during
therefore the finer control offered by tArray would be most useful.

Thanks (again)

James

> >
> > Hi James
> >
> > Your approach do make sense, if you have no foot contact you have
> > applied the weak muscles between the pelvis and ground which
should
> > be able to carry the load, this should work if it is setup
> correctly.
> >
> > I can only think of one possible explanation to that the model
> still
> > runs Inv. Dyn. Anal. when there is no strength in the weak
muscles,
> > and it is out of balance, there must be one or more reactions
> between
> > the human model and the ground which is active, by accident.
> >
> > You write that the model is driven by markes, i guess you know
this
> > already but by default a driver adds a reactions of the driven
dof,
> > unless it is switched off, by writing “Reaction.Type={Off}”. If
> your
> > model is driven by the markers one of those drivers could have
> > reactions in them by accident, this would be a direct reaction
with
> > the ground.
> >
> > Please try to check your drivers for unwanted reactions in
general,
> > by looking at the Constraint.Reaction property of the drivers.
> >
> > Best regards
> > SÃ¸ren, AnyBody Support
> >
> >
> > — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> > wrote:
> > >
> > > Hi
> > >
> > > Just to prove that you can’t please all the people all of the
> time,
> > > my question relates to a model which is working when I don’t
> think
> > it
> > > should!!!
> > >
> > > I am driving FreePostureMove with MoCap data. I have modelled
> > ground
> > > reaction forces with AnyGeneralMuscle where the
> AnyMuscleModelUsr1
> > > strength is conditional on ground contact.
> > >
> > > During phases of no foot contact there is the potential that
> > dynamic
> > > equilibrium could not be achieved due to MoCap measurement
> errors.
> > > Therefore I attached `weak’ linear and rotational muscles
between
> > the
> > > pelvis and ground. The strength of the weak muscles was 2
> > magnitude
> > > less than ground contact muscles (ground contact muscles were
not
> > too
> > > stiff nor the imaginary muscles too weak to cause ill-
> > conditioning).
> > >
> > > The model ran in an ID analysis and continued to run as I
reduced
> > the
> > > imaginary muscles’ stiffness until they became zero (well less
> than
> > > Study.StrongMuscleLimit = 0.001;). Thus implying even during
no
> > foot
> > > contact the MoCap data collection was perfect!
> > >
> > > Does my approach make sense? How can movement containing
> > inevitable
> > > measurement errors be analysed in the presence of an incomplete
> set
> > > of external forces?
> > >
> > > Thanks
> > >
> > > James
> > >
> >
>

PS Perhaps I shouldn’t have used the phrase ‘work-around’ as the
obvious one is tStart/nStep/tEnd.

However I am finding that muscle activity can be very fleeting during
therefore the finer control offered by tArray would be most useful.

Thanks (again)

James

> >
> > Hi James
> >
> > Your approach do make sense, if you have no foot contact you have
> > applied the weak muscles between the pelvis and ground which
should
> > be able to carry the load, this should work if it is setup
> correctly.
> >
> > I can only think of one possible explanation to that the model
> still
> > runs Inv. Dyn. Anal. when there is no strength in the weak
muscles,
> > and it is out of balance, there must be one or more reactions
> between
> > the human model and the ground which is active, by accident.
> >
> > You write that the model is driven by markes, i guess you know
this
> > already but by default a driver adds a reactions of the driven
dof,
> > unless it is switched off, by writing “Reaction.Type={Off}”. If
> your
> > model is driven by the markers one of those drivers could have
> > reactions in them by accident, this would be a direct reaction
with
> > the ground.
> >
> > Please try to check your drivers for unwanted reactions in
general,
> > by looking at the Constraint.Reaction property of the drivers.
> >
> > Best regards
> > SÃ¸ren, AnyBody Support
> >
> >
> > — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> > wrote:
> > >
> > > Hi
> > >
> > > Just to prove that you can’t please all the people all of the
> time,
> > > my question relates to a model which is working when I don’t
> think
> > it
> > > should!!!
> > >
> > > I am driving FreePostureMove with MoCap data. I have modelled
> > ground
> > > reaction forces with AnyGeneralMuscle where the
> AnyMuscleModelUsr1
> > > strength is conditional on ground contact.
> > >
> > > During phases of no foot contact there is the potential that
> > dynamic
> > > equilibrium could not be achieved due to MoCap measurement
> errors.
> > > Therefore I attached `weak’ linear and rotational muscles
between
> > the
> > > pelvis and ground. The strength of the weak muscles was 2
> > magnitude
> > > less than ground contact muscles (ground contact muscles were
not
> > too
> > > stiff nor the imaginary muscles too weak to cause ill-
> > conditioning).
> > >
> > > The model ran in an ID analysis and continued to run as I
reduced
> > the
> > > imaginary muscles’ stiffness until they became zero (well less
> than
> > > Study.StrongMuscleLimit = 0.001;). Thus implying even during
no
> > foot
> > > contact the MoCap data collection was perfect!
> > >
> > > Does my approach make sense? How can movement containing
> > inevitable
> > > measurement errors be analysed in the presence of an incomplete
> set
> > > of external forces?
> > >
> > > Thanks
> > >
> > > James
> > >
> >
>

James,

I just tested the tArray initilization. You are quite right: It does
not work, and I also get the unknown error. I have bug-reported the
matter, which is a mechanism we use internally to get bugs tracked
and fixed. Thanks for bringing this to our attention.

In general, any occurrence of “Unknown error” is in principle a bug
regardless of how crazy the model may be. This error message is only
for handling cases that were not anticipated by the programmers, and
ideally there should not be any of those.

It is a great help that you guys report back to us when you find an
unknown error.

John

— In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@…>
wrote:
>
> Hi SÃ¸ren
>
> reactions to Off. I’ll continue to investigate.
>
> On a related matter, when I specify tArray an unknown error is
> generated during model load. Any thoughts on a work-around.
>
> As ever…many thanks
>
> James
>
>
>
> ERROR : Model load : unknown error
>
> — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> wrote:
> >
> > Hi James
> >
> > Your approach do make sense, if you have no foot contact you have
> > applied the weak muscles between the pelvis and ground which
should
> > be able to carry the load, this should work if it is setup
> correctly.
> >
> > I can only think of one possible explanation to that the model
> still
> > runs Inv. Dyn. Anal. when there is no strength in the weak
muscles,
> > and it is out of balance, there must be one or more reactions
> between
> > the human model and the ground which is active, by accident.
> >
> > You write that the model is driven by markes, i guess you know
this
> > already but by default a driver adds a reactions of the driven
dof,
> > unless it is switched off, by writing “Reaction.Type={Off}”. If
> your
> > model is driven by the markers one of those drivers could have
> > reactions in them by accident, this would be a direct reaction
with
> > the ground.
> >
> > Please try to check your drivers for unwanted reactions in
general,
> > by looking at the Constraint.Reaction property of the drivers.
> >
> > Best regards
> > SÃ¸ren, AnyBody Support
> >
> >
> > — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> > wrote:
> > >
> > > Hi
> > >
> > > Just to prove that you can’t please all the people all of the
> time,
> > > my question relates to a model which is working when I don’t
> think
> > it
> > > should!!!
> > >
> > > I am driving FreePostureMove with MoCap data. I have modelled
> > ground
> > > reaction forces with AnyGeneralMuscle where the
> AnyMuscleModelUsr1
> > > strength is conditional on ground contact.
> > >
> > > During phases of no foot contact there is the potential that
> > dynamic
> > > equilibrium could not be achieved due to MoCap measurement
> errors.
> > > Therefore I attached `weak’ linear and rotational muscles
between
> > the
> > > pelvis and ground. The strength of the weak muscles was 2
> > magnitude
> > > less than ground contact muscles (ground contact muscles were
not
> > too
> > > stiff nor the imaginary muscles too weak to cause ill-
> > conditioning).
> > >
> > > The model ran in an ID analysis and continued to run as I
reduced
> > the
> > > imaginary muscles’ stiffness until they became zero (well less
> than
> > > Study.StrongMuscleLimit = 0.001;). Thus implying even during
no
> > foot
> > > contact the MoCap data collection was perfect!
> > >
> > > Does my approach make sense? How can movement containing
> > inevitable
> > > measurement errors be analysed in the presence of an incomplete
> set
> > > of external forces?
> > >
> > > Thanks
> > >
> > > James
> > >
> >
>

Hi

…any chance of the tArray bug fix making the next software
update? I appreciate all of the functionality could (eventually) be
derived from tStart/nStep/tEnd but the convenience of tArray would be
most useful for my work.

As a supplementary question, I am finding that the activity of
various muscles changes radically between time steps as shown in the
uploaded file shippen_gait_muscle.avi. Is this typical or indicative
of an error by me?

Ta!

James

— In anyscript@yahoogroups.com, “AnyBody Support” <support@…>
wrote:
>
> James,
>
> I just tested the tArray initilization. You are quite right: It
does
> not work, and I also get the unknown error. I have bug-reported the
> matter, which is a mechanism we use internally to get bugs tracked
> and fixed. Thanks for bringing this to our attention.
>
> In general, any occurrence of “Unknown error” is in principle a bug
> regardless of how crazy the model may be. This error message is
only
> for handling cases that were not anticipated by the programmers,
and
> ideally there should not be any of those.
>
> It is a great help that you guys report back to us when you find an
> unknown error.
>
> John
>
> — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> wrote:
> >
> > Hi SÃ¸ren
> >
> > reactions to Off. I’ll continue to investigate.
> >
> > On a related matter, when I specify tArray an unknown error is
> > generated during model load. Any thoughts on a work-around.
> >
> > As ever…many thanks
> >
> > James
> >
> >
> >
> > ERROR : Model load : unknown error
> >
> > — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> > wrote:
> > >
> > > Hi James
> > >
> > > Your approach do make sense, if you have no foot contact you
have
> > > applied the weak muscles between the pelvis and ground which
> should
> > > be able to carry the load, this should work if it is setup
> > correctly.
> > >
> > > I can only think of one possible explanation to that the model
> > still
> > > runs Inv. Dyn. Anal. when there is no strength in the weak
> muscles,
> > > and it is out of balance, there must be one or more reactions
> > between
> > > the human model and the ground which is active, by accident.
> > >
> > > You write that the model is driven by markes, i guess you know
> this
> > > already but by default a driver adds a reactions of the driven
> dof,
> > > unless it is switched off, by writing “Reaction.Type={Off}”. If
> > your
> > > model is driven by the markers one of those drivers could have
> > > reactions in them by accident, this would be a direct reaction
> with
> > > the ground.
> > >
> > > Please try to check your drivers for unwanted reactions in
> general,
> > > by looking at the Constraint.Reaction property of the drivers.
> > >
> > > Best regards
> > > SÃ¸ren, AnyBody Support
> > >
> > >
> > > — In anyscript@yahoogroups.com, “jamesshippen”
<jamesshippen@>
> > > wrote:
> > > >
> > > > Hi
> > > >
> > > > Just to prove that you can’t please all the people all of the
> > time,
> > > > my question relates to a model which is working when I don’t
> > think
> > > it
> > > > should!!!
> > > >
> > > > I am driving FreePostureMove with MoCap data. I have
modelled
> > > ground
> > > > reaction forces with AnyGeneralMuscle where the
> > AnyMuscleModelUsr1
> > > > strength is conditional on ground contact.
> > > >
> > > > During phases of no foot contact there is the potential that
> > > dynamic
> > > > equilibrium could not be achieved due to MoCap measurement
> > errors.
> > > > Therefore I attached `weak’ linear and rotational muscles
> between
> > > the
> > > > pelvis and ground. The strength of the weak muscles was 2
> > > magnitude
> > > > less than ground contact muscles (ground contact muscles were
> not
> > > too
> > > > stiff nor the imaginary muscles too weak to cause ill-
> > > conditioning).
> > > >
> > > > The model ran in an ID analysis and continued to run as I
> reduced
> > > the
> > > > imaginary muscles’ stiffness until they became zero (well
less
> > than
> > > > Study.StrongMuscleLimit = 0.001;). Thus implying even during
> no
> > > foot
> > > > contact the MoCap data collection was perfect!
> > > >
> > > > Does my approach make sense? How can movement containing
> > > inevitable
> > > > measurement errors be analysed in the presence of an
incomplete
> > set
> > > > of external forces?
> > > >
> > > > Thanks
> > > >
> > > > James
> > > >
> > >
> >
>

Yes, our chief developer has just located the bug, and it will be
fixed in the next mnor release.

Best regards,
John

— In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@…>
wrote:
>
> Hi
>
> …any chance of the tArray bug fix making the next software
> update? I appreciate all of the functionality could (eventually)
be
> derived from tStart/nStep/tEnd but the convenience of tArray would
be
> most useful for my work.
>
> As a supplementary question, I am finding that the activity of
> various muscles changes radically between time steps as shown in
the
> uploaded file shippen_gait_muscle.avi. Is this typical or
indicative
> of an error by me?
>
> Ta!
>
> James
>
> — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> wrote:
> >
> > James,
> >
> > I just tested the tArray initilization. You are quite right: It
> does
> > not work, and I also get the unknown error. I have bug-reported
the
> > matter, which is a mechanism we use internally to get bugs
tracked
> > and fixed. Thanks for bringing this to our attention.
> >
> > In general, any occurrence of “Unknown error” is in principle a
bug
> > regardless of how crazy the model may be. This error message is
> only
> > for handling cases that were not anticipated by the programmers,
> and
> > ideally there should not be any of those.
> >
> > It is a great help that you guys report back to us when you find
an
> > unknown error.
> >
> > John
> >
> > — In anyscript@yahoogroups.com, “jamesshippen” <jamesshippen@>
> > wrote:
> > >
> > > Hi SÃ¸ren
> > >
> > > reactions to Off. I’ll continue to investigate.
> > >
> > > On a related matter, when I specify tArray an unknown error is
> > > generated during model load. Any thoughts on a work-around.
> > >
> > > As ever…many thanks
> > >
> > > James
> > >
> > >
> > >
> > > ERROR : Model load : unknown error
> > >
> > > — In anyscript@yahoogroups.com, “AnyBody Support” <support@>
> > > wrote:
> > > >
> > > > Hi James
> > > >
> > > > Your approach do make sense, if you have no foot contact you
> have
> > > > applied the weak muscles between the pelvis and ground which
> > should
> > > > be able to carry the load, this should work if it is setup
> > > correctly.
> > > >
> > > > I can only think of one possible explanation to that the
model
> > > still
> > > > runs Inv. Dyn. Anal. when there is no strength in the weak
> > muscles,
> > > > and it is out of balance, there must be one or more reactions
> > > between
> > > > the human model and the ground which is active, by accident.
> > > >
> > > > You write that the model is driven by markes, i guess you
know
> > this
> > > > already but by default a driver adds a reactions of the
driven
> > dof,
> > > > unless it is switched off, by writing “Reaction.Type={Off}”.
If
> > > your
> > > > model is driven by the markers one of those drivers could
have
> > > > reactions in them by accident, this would be a direct
reaction
> > with
> > > > the ground.
> > > >
> > > > Please try to check your drivers for unwanted reactions in
> > general,
> > > > by looking at the Constraint.Reaction property of the drivers.
> > > >
> > > > Best regards
> > > > SÃ¸ren, AnyBody Support
> > > >
> > > >
> > > > — In anyscript@yahoogroups.com, “jamesshippen”
> <jamesshippen@>
> > > > wrote:
> > > > >
> > > > > Hi
> > > > >
> > > > > Just to prove that you can’t please all the people all of
the
> > > time,
> > > > > my question relates to a model which is working when I
don’t
> > > think
> > > > it
> > > > > should!!!
> > > > >
> > > > > I am driving FreePostureMove with MoCap data. I have
> modelled
> > > > ground
> > > > > reaction forces with AnyGeneralMuscle where the
> > > AnyMuscleModelUsr1
> > > > > strength is conditional on ground contact.
> > > > >
> > > > > During phases of no foot contact there is the potential
that
> > > > dynamic
> > > > > equilibrium could not be achieved due to MoCap measurement
> > > errors.
> > > > > Therefore I attached `weak’ linear and rotational muscles
> > between
> > > > the
> > > > > pelvis and ground. The strength of the weak muscles was 2
> > > > magnitude
> > > > > less than ground contact muscles (ground contact muscles
were
> > not
> > > > too
> > > > > stiff nor the imaginary muscles too weak to cause ill-
> > > > conditioning).
> > > > >
> > > > > The model ran in an ID analysis and continued to run as I
> > reduced
> > > > the
> > > > > imaginary muscles’ stiffness until they became zero (well
> less
> > > than
> > > > > Study.StrongMuscleLimit = 0.001;). Thus implying even
during
> > no
> > > > foot
> > > > > contact the MoCap data collection was perfect!
> > > > >
> > > > > Does my approach make sense? How can movement containing
> > > > inevitable
> > > > > measurement errors be analysed in the presence of an
> incomplete
> > > set
> > > > > of external forces?
> > > > >
> > > > > Thanks
> > > > >
> > > > > James
> > > > >
> > > >
> > >
> >
>