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2016-06-03 17:13
Submitted by:
Michele Baldoni (baldoni9)
Assigned to:
Nobody (None)
Joint Reaction Analysis not considering all forces

Detailed description
I am working on the lumbar spine model by Christophy and collaborators, including 4 muscles.
I run the Static Optimization on the model with ligaments that I added. The results include ligaments forces, and their value is coherent with what I expected based on the ligament properties I have defined. The problem is that when I input the force file resulting from Static Optimization to the Joint reaction analysis, I get this warning:

"WARNING: The forces file contains actuators that are not in the model's actuator set."

And then the results from Joint Reaction are not consistent with what expected; it looks to me as though the analysis ignores the muscle forces.
In fact, I made some tests: if I set a PCSA force for all ligaments equal to 0, they produce 0 force in Static Optimization, so I expected the results of Joint reaction to be equal to the case in which I completely disable the ligaments. Instead, with ligaments disabled, I get reasonable Joint reaction forces, and no warning during the analysis, while when I enable the ligaments setting a PCSA force of 0, I get inconsistent joint forces (for example, for the same joint I get 1040 N without ligaments and 200 N with ligaments having PCSA=0).

Also, I manually modified the force file output by Static Optimization: the original one included one column for each muscle and ligament, with ligaments listed first. If I edit the column putting the muscles first, and then input the modified file into Joint Reaction analysis, I get completely different results (close to the 1040 N caused by muscle forces). My conclusion is that the analysis recognizes that the model includes only 4 actuators (4 muscles), while the force file includes 4 muscles + 5 ligaments = 9 actuators. Therefore it prints the warning and then only considers the first 4 columns of the force file.

I attach the force files and plots.

Could you please fix this? Is there a workaround in the meantime?

Thank you.

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Size Name Date By Download
2 KiBLumbar_C_4_StaticOptimization_force.sto2016-06-03 17:13baldoni9Lumbar_C_4_StaticOptimization_force.sto
2 KiBLumbar_C_4_StaticOptimization_force_InverseOrder.sto2016-06-03 17:13baldoni9Lumbar_C_4_StaticOptimization_force_InverseOrder.sto
38 KiBOriginalForceFilePlot.PNG2016-06-03 17:13baldoni9OriginalForceFilePlot.PNG
29 KiBInverseOrderPlot.PNG2016-06-03 17:13baldoni9InverseOrderPlot.PNG
Field Old Value Date By
File Added579: Lumbar_C_4_StaticOptimization_force.sto2016-06-03 17:13baldoni9
File Added580: Lumbar_C_4_StaticOptimization_force_InverseOrder.sto2016-06-03 17:13baldoni9
File Added581: OriginalForceFilePlot.PNG2016-06-03 17:13baldoni9
File Added582: InverseOrderPlot.PNG2016-06-03 17:13baldoni9