No...(thank God)...I get into position for whatever the character situation calls for, and they snap a pic to use as reference, add the costume, color, and viola!!
I will say this...getting the correct angle for "superhero" fighting positions can be quite challenging as it doesnt exactly fit the mold for "normal" fighting/ real life....much like shooting a bodypart article...the angles used for the camera arent even close to what real training would dictate...
But...the pay is good and it's cool to see yourself as a superhero in a Marvel comic...especially when you grew up reading/ collecting them...!