Calculate thickness of thin muscle

Thanks for your reply, I sort of managed to get the skeleton but I do not get a complete curve of the skeleton (I just get these dots) with these parameters in “Extract skeleton” module:
Skeleton type: 1D
Do not prune branches: yes
Number of points: 9000000

thickness_skeleton

How do I get a complete curve?
And if I achieve this curve, how do I get the thickness in your described way?
You mentioned:

Am I supposed to use the Ruler and just measure the distance, or is there a more accurate way to measure the thickness?