Extra Bits Sketch Dump 1 :: Upper Body/Arm Muscles
I used a couple of references to practice some upper body muscles and how they change during poses. Going with female body builders of the late 80s and early 90s feels like a good choice, as it's normally the look I prefer or requested.
It helps to practice, especially when it comes to muscles and presenting them correctly.
References
Top: Tonya Knight (Slightly morphed; via deviantART)
Bottom: Shelley Beattie (Via Listal)