the precise definition of the plot tool’s list

[qin geyu]

Hi:
When I use the plot tool of Opensim, There are many lists, such as moment, moment arm, fiber length ,muscle tendon length, total fiber force, tendon length, tendon force and so on. I can think of them by literal meaning，but I want to get the moment of the knee，only to Calculate the sum of the muscles’ moment？Is the moment arm corresponding to moment, Force multiplied by arm is the moment，what’s meaning of the force, Is the total fiber force? Or what? And the fiber length, muscle tendon length, total fiber force, tendon length, tendon force, Are all of them Incremental, or changed data. Where can found the precise definition of the plot tool’s list? Looking forward to replying, Thanks!

[Thomas Uchida]

See the "Curve Creation Panel" page in the documentation (http://simtk-confluence.stanford.edu:80 ... tion+Panel), specifically the "Built-in Curves" section.

[qin geyu]

For this part of the content, I have read before, but still do not know a series of vertical coordinates of the plot tool is incremental data, or the length after the change, if I want to draw the joint moment diagram, whether it can be directly selected Y moment -knee_angle, select extend and bend muscle summation, abscissa selection time, whether it is the joint moment to achieve its movement form, and how can I get the starting and ending point of the existing muscle coordinates to learning its muscle trend？looking forward to your help，thanks！

[Thomas Uchida]

if I want to draw the joint moment diagram, whether it can be directly selected Y moment -knee_angle, select extend and bend muscle summation, abscissa selection time, whether it is the joint moment to achieve its movement form

I'm not sure I fully understand your question. If you're trying to compute the joint torques responsible for a given movement, you can use the Inverse Dynamics Tool (http://simtk-confluence.stanford.edu:80 ... e+Dynamics).

how can I get the starting and ending point of the existing muscle coordinates to learning its muscle trend?

Are you trying to determine a muscle's path? You can find this information by selecting a muscle in the Navigator panel and clicking the "..." button in the Properties panel beside "GeometryPath". More information can be found on the "Muscle Editor" page on Confluence (http://simtk-confluence.stanford.edu:80 ... cle+Editor).

[qin geyu]

I have read the guidance of user, but there are still some problems：
Question 1: want to get the starting and ending coordinates of the muscles, and then get the existing model of the exact direction of muscle, x、y、z data of fixed、via,、moving point Is offset? Not the starting and ending coordinates of the muscle, how to get the starting and ending coordinates?
Question 2: sums muscles' moment of plot is the moment corresponding to the angular acceleration calculated from the joint angle? M = I * a, I want to get the inertia according to M and a, and then establish a lower limb mathematical model.
Question 3: Are all Y coordinates data in the plot incremented or after changing, and are units in the international standard?
Question 4: I use Q. Liu GIL experimental data to do ID in Opensim1.5.5, the result is a multi-column data list, but I do not know what is it? the force or torque?
Thanks for your guidance~

[Thomas Uchida]

Question 1: want to get the starting and ending coordinates of the muscles, and then get the existing model of the exact direction of muscle, x、y、z data of fixed、via,、moving point Is offset? Not the starting and ending coordinates of the muscle, how to get the starting and ending coordinates?

Sorry, but I don't understand your question. Hopefully you can find an answer on the "Muscle Editor" page (http://simtk-confluence.stanford.edu:80 ... cle+Editor), which describes how to get the endpoints and any intermediate points of the muscle path. If you're trying to get these coordinates expressed in ground, you can select the muscle in the Navigator panel, click the "..." button beside "GeometryPath", and select "ground" in the "Body" column corresponding to each point; the X, Y, Z coordinates will then be re-expressed relative to ground.

Question 2: sums muscles' moment of plot is the moment corresponding to the angular acceleration calculated from the joint angle? M = I * a, I want to get the inertia according to M and a, and then establish a lower limb mathematical model.

The moment generated by a muscle is the product of its moment arm and the force it generates.

Question 3: Are all Y coordinates data in the plot incremented or after changing, and are units in the international standard?

I don't know what you mean by "incremented" and "after changing". In a moment-vs-angle plot, the y-axis is the moment (in N·m) and the x-axis is the angle (in degrees).

Question 4: I use Q. Liu GIL experimental data to do ID in Opensim1.5.5, the result is a multi-column data list, but I do not know what is it? the force or torque?

I suggest using OpenSim version 3.3. There is lots of documentation on the Inverse Dynamics Tool (http://simtk-confluence.stanford.edu:80 ... e+Dynamics). You also might want to work through the tutorials and perhaps some of the examples as well (http://simtk-confluence.stanford.edu:80 ... +Tutorials).

[qin geyu]

There are some problems again~
1. F * moment_arm = moment, where F is the force of each muscle, and what is the relationship between this Force and plot total fiber force. when moment is the sum of muscles’moment，moment _arm is the sum of muscles’ moment_arm, and What is the force’s physical meaning?
2. What's the difference between moment summed by muscle in plot and ID moment?
3. The skeletal centroid position is available, the mass is also available, the moment can be get by m * g * L, this moment is a constant, and what is the difference between this moment and moment in question 1 ?
4. In the properties window of The skeletal centroid, inertia xx, yy, zz is relative to the bone end of the coordinate system, or relative to the pelvic coordinate system, and what is the physical meaning of the moment which is inertia xx、yy、zz multiplied by the acceleration？
Thanks for your help！

[Thomas Uchida]

F * moment_arm = moment, where F is the force of each muscle, and what is the relationship between this Force and plot total fiber force.

The joint moment generated by an OpenSim muscle is the product of the moment arm and the tendon force. The fiber force and tendon force may not be the same. Please see the literature (e.g., Zajac, 1989; Millard et al., 2013) for details.

Zajac, F.E. Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. Critical Reviews in Biomedical Engineering 17(4):359–410, 1989.

Millard, M., Uchida, T., Seth, A., Delp, S.L. Flexing computational muscle: modeling and simulation of musculotendon dynamics. ASME Journal of Biomechanical Engineering 135(2):021005, 2013. http://nmbl.stanford.edu/publications/p ... rd2013.pdf

when moment is the sum of muscles’moment，moment _arm is the sum of muscles’ moment_arm, and What is the force’s physical meaning?

The quotient [sum of the moments generated by all muscles] / [sum of all moment arms] is meaningless as far as I can tell. Imagine computing this quotient and then adding another muscle that generates no force but whose moment arm is nonzero: the numerator would remain the same but the denominator would increase, rendering a quotient whose physical significance is unclear.

What's the difference between moment summed by muscle in plot and ID moment?

It depends how the muscle moments were generated. For example, see the "Getting Started with Static Optimization" (http://simtk-confluence.stanford.edu:80 ... timization) and "How Static Optimization Works" (http://simtk-confluence.stanford.edu:80 ... tion+Works) pages on Confluence.

[qin geyu]

Hello：
M = I * a ，a is the angular acceleration generated by the joint angle calculation, I is inertia，in order to obtain the curve of I change, which moment should be used in the following three,
A) Joint moment= tendon force (each muscle) * moment arm (each muscle)
B) the sum of muscles'moment in plot
C) The moment generated by ID
Or the three are not right, how to get the M?

The following three figures are ABC's graphs, respectively。

[qin geyu]

A is obtained through Opensim3.0,, B, C is obtained through Opensim1.5.5, they were used the same data and settings files to plot, why the difference is so big, what is the reason of the phenomenon，thanks~