Your body is comprised of 3 different muscle types: cardiac (heart), visceral (smooth) and skeletal muscles. (fitnessandpower.com)
Many people don't know that muscle type influences flexibility. (huffingtonpost.com)
While I think the article is really good and gives A LOT of insight to different muscle types and training them, I have to disagree a bit on some parts here. (fitnessblackandwhite.com)