Hi Thomas
You are right, my argumentation is not entirely correct there could be more
reasons for the missing abductor activity; I will try to explain in more
detail.
I have looked at your figure; I think your assumption looks ok. There is a
difference with respect to the model though because the pelvis is carried by
the environment through the AnyReacForce.
There nothing wrong in using the AnyReacForce though in this model, because
the GRF has been measured. I guess one argument could be that having the
left leg in the air and the right on the plate the G force on your drawing
will not be present directly because this is carried by the AnyReacForce on
the pelvis. However the measured GRF on the right leg reflects also the load
from the left leg (and the rest of the body), so this takes care of this.
- I guess there can be more reasons to the abduction muscles being
inactive. The center of pressure is very important, if this is too much to
the lateral side, it may reduce the need of activity in the abductor
muscles. We actually had problems with the location of the center of
pressure wrt. the foot in the medial/lateral direction. So we ended up
adding a sideway offset to the center of pressure location. The amount of
this offset can be seen in the environment.any file, you should be able to
find if you search for “offset”. We think that the reason for the need of
this offset can be the inadequate synchronisation between the mocap system
and the forceplate system, or it can be the location of the markers on the
foot which is not correct.
- The missing abductor activity could also be the horizontal forces I
mentioned in the last posting.
- Finally it could be that updating the model would change the role of
abductor muscles.
I hope this made things clearer, otherwise please write again.
Best regards
Søren, AnyBody Support
From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of knox40
Sent: 09 November 2007 09:12
To: anyscript@yahoogroups.com
Subject: [AnyScript] Re: Muscle Forces and Hip Reaction Force
Hi Søren,
you might be right that I’ve used an older version of the Gait 3D
model, thanks. I will download now the newest model.
Regarding the abductor forces I do not fully understand your
argument. Therefore I’ve added a picture to the files
(Muscle_Abductor) to explain my position better.
If a person standing only on the right leg, the weight of the rest
of the body (~5/6 BW) must be hold by the right hip joint. The
resultant hip joint force R is holding horizontal balance with the
abductor muscle force F, so that there is only a vertikal ground
reaction force.
I know this is very simplified but in general it should be right, or
not? So you don’t need a horizontal gound reaction force to produce
a abductor muscle force.
Only if the upper body is right above the hip joint, the abductor
should be zero…
Please tell me if I’m wrong so that I can consider this in my model.
Thank you in advance.
Best regards
Thomas
— In anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com,
“AnyBody Support” <support@…>
wrote:
>
> Hi Thomas
>
>
>
> I think you might not be running the latest version of the Gait3D
model?.
>
>
>
> In order to double check this, I just downloaded the latest model
from:
> http://www.anybody.
<http://www.anybody.aau.dk/repository/Repository6.1/index.htm>
aau.dk/repository/Repository6.1/index.htm
>
>
>
> I then tried to run the Gait3D model it gave right hip reactions
with peak
> values of approximately 2600 N, so I think you might be running an
old
> version of the model. Most certain you have done this, but please
also
> remember to calibrate the muscles.
>
>
>
> About the abductor muscles I hope changing the model will solve
this also.
> In general these muscles will be active if there is an abduction
moment to
> balance, if this is the case they will be active. So if they are
absent it
> may be because the horizontal component of the measured ground
reaction
> force is small. I have not checked this, but if you have other
data sources
> you could try comparing the measured ground reaction forces with
other
> datasets.
>
>
>
> Please ask again if you have further questions.
>
>
>
> Best regards
>
> Søren, AnyBody Support
>
>
>
> _____
>
> From: anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com
[mailto:anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com]
On Behalf
> Of knox40
> Sent: 08 November 2007 11:11
> To: anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com
> Subject: [AnyScript] Muscle Forces and Hip Reaction Force
>
>
>
> Hallo,
>
> I’ve done a simple model for a person going upstairs. I’ve used
the
> measured hip reaction force from Bergmann to validate that model
> (thanks Søren). Now the model looks OK and I had a look at the
> appropriate muscle forces. Here I was surprised at the relative
low
> forces in the abductor and adductor muscles.
>
> Then I had a look to the gait 3d model. Here is the same thing.
The
> adductor and abductor muscles are relative low during gait.
> How can that be as they are responsible to keep the pelvis in
> balance?
> Already Pauwels found out, that the lever arm ratios and hence the
> abductors are responsible for the hip reaction force of multiple
> body weight. By looking into the literature the muscle forces do
not
> fit very well to released data (e.g. Musculotendon Parameters for
> Lower Limb muscles summarized by Scott Delp etc.)
> How can that be? If it is so complex to calculate muscle forces,
how
> can I trust the results then?
>
> By looking to the joint reaction force of the gait 3d model, I was
> also astonished about the high peak forces into the hip joint (ca.
> 5000N). They do not fit well to the Bergmann measurements with
about
> (2000 to 2500N depending on walking speed).
>
> I hope somebody can explain these varying values to me.
>
> Thank you in advance.
>
> Best regards
>
> Thomas
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
[Non-text portions of this message have been removed]