Keyboard shortcut: U
This operator converts a BlockSurface into a BlockMuscle and configures the objects to behave like a muscle, repositioning the interiors when you move the insertions (end objects).
When a collection is in Muscle ON mode, Intermediate objects cannot be freely moved, rotated or scaled since they are anchored between the end objects that act like muscles. However, they can still be sculpted and edited to adjust their shape.
Steps to follow:
Select the objects from the collections that you want to convert to muscles.
Press the "U" key to convert them to muscles.
An end of the muscle will be activated for you to move and reposition.