Specifications

90
Subject to
• Equilibrium equations fulfilled
• Muscles are not allowed to push
In the standard setup of InverseDynamicAnalysis operations in the AnyBody Modeling System, e1 and e2
are both zero. This means that the system is minimizing the maximum muscle activity in each time step. Let
us have a look at the consequences of that. Have you loaded demo.diffmusarm2D.any
into the system yet?
If not, please do it now, and run the InverseDynamicAnalysis. Open a ChartFX View, and browse your way
through the output tree to the muscles. Expand any muscle, click "Activity", and replace the muscle's name
in the specification line with an asterisk like this:
ArmModelStudy.Output.Model.Muscles.*.Activity
You should get the picture shown below:
Although we have eight muscles in the model you see only a few curves. The explanation is that, in the
absence of e1 and e2 in the problem formulation above, the system minimizes the maximum activity of any
muscle and this causes the muscle activity curves to fall on top of each other. So each curve you see is
really several curves covering each other. However, since the muscles have different strengths, the common
activities lead to different muscle forces. If we similarly plot the muscle forces by means of the Specification
line:
ArmModelStudy.Output.Model.Muscles.*.Fm
we will get this result: