Specifications

150
};
If you run the model again and plot the same graphs, you will see this:
The wall is obviously useful in the initial stages of the movement where the torque generated by the
reaction force is in the beneficial direction for both the joints. In the later stages of the movement the
presence of the wall decreases the envelope of the muscle forces slightly, but it has increased the torque in
the elbow. The explanation is that the elbow can increase its action beyond what is necessary to carry the
load and generate and additional pressure against the wall, which then decreases the torque in the shoulder.
This example shows how complicated the mechanics of the body is: Even this very simplified case would
have different solutions if the parameters of the model were different. For instance if the shoulder were
much stronger compared to the elbow, then the elbow would not have been able to help the shoulder in the
latter case because the elbow would have the higher load compared to its strength. On the contrary, the
shoulder would have been able to help the elbow in the former case by generating an additional force
pushing against the wall.
This completes the part of this tutorial dealing with muscles. But we are not completely finished yet. The
next lesson
deals with the important topic of ligament modeling.
Lesson 7: Ligaments
Ligaments are passive structures that connect articulating bones and keep joints assembled. Mechanically
they are much like muscles but with no active contractile element. Ligaments only provide forces when they
are stretched by the relative movement of the bones they connect.
This tutorial demonstrates how to define, control, and calibrate ligaments. We need a model to work on.
Please download and save the model Demo.Ligament.any
. Once you have stored it on your hard disk, load it
into the AnyBody Modeling System and run the SetInitialConditions operation.