Just praacticing rendering the interior of the figure just using colors and without line art. This is pretty similar to the drawing style I use for Real Superheroines. The line art on the outside is done with the "For Effect" pen that comes with Clip Studio Paint. Think of it as a "Nike swoosh" pen that tapers strongly towards the ends. It's like drawing with strips of ribbon.
In the comic panels I only include a few lines on the interior of the figure, usually to denote costume lines and then a few to show musculature. For this one, I left out the interior lines inside the body, so the lines that I would usually draw to indicate the spine and scapulae, I instead just rendered with airbrushed shading.
I used a reference photo I found online:
And here is the time lapse video: