CMC for other activities

[Kang Li]

I am wondering if anyone have ever used CMC to simulate other activity such as stair climbing?
The RRA only work for gait and walking, is it right?

[Rebecca Routson]

I am using CMC for stair climbing. Do you have any specific questions I can answer?

[Kang Li]

Hi Rebecca,

Thanks for your response. I am working on modeling stair climbing of injured knee. I get excessive large residual forces. I am wondering if you have ever get the large force. If so, are you able to correct it using RRA?

Best,

Kang

[Rebecca Routson]

Kang,

The RRA for my data, did reduce the residuals quite a bit. My residuals were not terribly high to begin with though. I also passed my data through RRA more than once.

Becca

[Kang Li]

Hi Becca,
Thank you for the info. I am wondering which version of OpenSim you are using for your work.
I am a little bit hesitating to switch to OpenSim 2.0 or higher version because of the stability issue.

Kang

[Rebecca Routson]

Kang,

I am using 2.02, but I have too many forceplate to not use 2+.

Becca

[Kang Li]

HI Rebecaa,

My model takes off during RRA as described by Daniel(https://simtk.org/forum/message.php?msg_id=1889). I am wondering if you had such kind of problems before. If so, how did you solve the problem?

Thanks in advance.

Kang

[Rebecca Routson]

Kang,

If there are no ground reaction forces applied at your start time your model will either fall through the ground or start floating away. So the 1st thing that I would check is that you have GRF. Let me know if that doesn't help, I have a few more ideas.

Becca

[Kang Li]

Thanks, I will check the GRF,
in the IK process, it has the GRF. I have the GRF arrows shown in the animation.
But in the following output, one strange thing is that the torso mass has been significantly changed. Do you know how the torse mass adjustment works?

Loading external loads kinematics from file subject01_lsa2_ik.mot ...
Storage: file=subject01_lsa2_ik.mot (nr=59 nc=121)
Low-pass filtering external load kinematics with a cutoff frequency of 6...
Storage: file=subject01_lsa2_grf10.mot (nr=7781 nc=19)

Note: requested COM adjustment time range 0.12 - 0.7 clamped to nearest available data times 0.12 - 0.7

Computing average residuals between 0.12 and 0.7
Average residuals before adjusting torso COM:
FX=34653.4 FY=-5933.09 FZ=-15191.5
MX=3292.19 MY=-4689.98 MZ=9463.19

CMCTool.adjustCOMToReduceResiduals:
torso weight = 362.705
dx=0.1, dz=-0.1

dmass = 605.007

Recommended mass adjustments:
ground: orig mass = 0, new mass = 0
pelvis: orig mass = 12.7226, new mass = 107.517
femur_r: orig mass = 10.0483, new mass = 84.9162
tibia_r: orig mass = 4.0052, new mass = 33.8472
talus_r: orig mass = 0.10803, new mass = 0.912939
calcn_r: orig mass = 1.35037, new mass = 11.4117
toes_r: orig mass = 0.233992, new mass = 1.97743
femur_l: orig mass = 10.0483, new mass = 84.9162
tibia_l: orig mass = 4.0052, new mass = 33.8472
talus_l: orig mass = 0.10803, new mass = 0.912939
calcn_l: orig mass = 1.35037, new mass = 11.4117
toes_l: orig mass = 0.233992, new mass = 1.97743
torso: orig mass = 36.9857, new mass = 312.559

Computing average residuals between 0.12 and 0.7
Average residuals after adjusting torso COM:
FX=-559.094 FY=4235.62 FZ=-5655.68
MX=-537.208 MY=928.487 MZ=50.5848

[Rebecca Routson]

Kang,

As far as I am aware OpenSim does not automatically adjust your subjects mass. You can check this though by looking at the properties of your model.

It looks like your residuals are huge. I would suggest:
1. Only run RRA and CMC where there are actually GRF applied and not while your subject may be off of your force plates.
2. Check your COP data to make sure that you have good data and that your forces are applied where you think. Also that you don't have any huge outliers.
3. You will probably want to rescale your model based on the dmass and iterate your RRA until you get smaller residuals.
4. Also you may want to check to make sure that you have the COM of the pelvis updated for your model specifically.

Hope that helps.

Becca