I am studying OpenSIM. In plot window, there is Normalized fiber length submenu in Y-Quantity button.
I have a few questions about this.

1) What does mean the normalized? According to my research, it divides the fiber-length by the optimized length, but there is no information on how to optimize it.
2) Does the fiber mean muscle fiber? Then what is the unit?

If you have any information related to my questions, please provide to me.