Keyboard shortcut: CTRL + SHIFT + ALT + U
This operator converts a BlockMuscle surface into a BlockSurface and configures the objects in the collections where you select some objects so they stop behaving like a muscle. After applying the changes, you will be able to reposition the interior objects by moving them as well as the ends.
Steps to follow:
Press the keyboard shortcut "CTRL + SHIFT + ALT + U" to stop behaving like a muscle.