Plot change in tendon length

[nilay Shah]

I have a motion file representing angle of ankle. I wanted to plot tendon change vs ankle angle from motion file. The normal method of plotting using tool -> plot... gives me data from ankle angle -90 to 90 degrees. My motion file contains ankle angle 0.07 to 0.45 radians. How can I plot tendon length data based on simulation of the model ?

I would like to clarify if this question is not clear.

Thank you for your time and help,
Nilay

[jimmy d]

Nilay,

If you have motion loaded; In the plotter select X-QUANTITY>>Coordinates(Deg.)

hope that helps,
-James

[nilay Shah]

Thank you for your response however there is limitation in using this feature. In the motion file, I have data that provides the ankle position during landing. This angle increases and decreases rather than strictly increasing. I think this is causing the error in the plot. I was wondering if this is the limitation of opensim. I understand that at same angle of ankle, the tendon length will be same but the forces could be different on ankle at different time and this could be causing different length changes in muscle. That's the reason for me to see values at different angle of ankle.

[jimmy d]

Hi Nilay,

The OpenSim plotter can plot almost all muscle properties (that I am aware of) against the joint angles during a motion. The crucial thing is to have the model AND motion loaded in the GUI. In the plotter you would then select "Y-Quantity: tendon-length", "Muscle:med_gas_r", "X-Quantity:Coordinate(Deg.)"

In the below (linked) tutorial, it shows you how to plot muscle properties during a crouch gait walking cycle; http://simtk-confluence.stanford.edu:80 ... l+Modeling

Let us know how it goes,
-james

[nilay Shah]

Thank you for your response and link you provided. This link you provided was extremely helpful for following the plot however even after following the rules, I am still having error. I have attached the error message to give you idea of the error message I have encountered. Currently I have installed Opensim 3.1. Motion file contains 3 columns: time, subtalar_angle_r and ankle_angle_r. The model I am using for my project is "Simulation-Based Design to Prevent Ankle Injuries". Here is the link
http://simtk-confluence.stanford.edu:80 ... e+Injuries.

Thank you for your time and help
Nilay

[jimmy d]

Error message read: "Bad call to Simbody API method GCVSPLUtil::gcvspl(): The values in x must be strictly increasing"

The error is coming from the data being passed to a spline function. This suggests that your time data isn't strictly increasing.

Let us know if that helps,
-james

[nilay Shah]

Thank you for your help. This helped me in understanding my mistake. In fact, now I realized my other techniques that I implemented for the generating .mot file.

-Nilay

[Ryan Bakker]

James,

Is the plotter able to plot ligament class properties as well?

-Ryan