What are wrap objects?

[William A]

Hi All,

I am trying to understand the OpenSim model geometries. I have some questions regarding the wrap objects:

1. What are the wrap objects?
2. What are their functions?
3. For what computations are they used? And how are they used for those computations?

Thanks,
William

[Thomas Uchida]

Wrap objects are shapes (cylinders, ellipsoids, etc.) that constrain the path of a muscle. Wrap objects ensure the muscle moment arms are appropriate over the required range of motion, prevent the muscle paths from passing through bones and deeper muscles, etc. You can see an example in Rajagopal et al., 2016, Figure 2(c) (https://nmbl.stanford.edu/wp-content/up ... al2016.pdf).