Thanks for your kind words, Danilo!
I‘ve had this problem too when I first went through the Anatomy module in Term 3+4, when I did figures there was always too much muscle on my character‘s frames.
The answer to your question is simple: I measure. A LOT.
I am also trying to keep my focus on portraying correct form, instead of drawing the muscles themselves. (On the Proko YT channel you can find a great video about „Mannequinization“, which helps a lot)
Keeping the Anatomy in mind, but having the main focus on correct proportions and bringing a 3D object onto a 2D canvas is an approach that works well for me.
Hope that helps!