Why do we stipulation to stretch, especially after we get up up from a night sleep?

Why do we stipulation to stretch, especially after we get up up from a night sleep?
To make our muscles work again so that we will touch less tired.
I've hear it warms your muscles up by some extent because your muscles are "jerking" within your body.
Ants are the only insects that stretch when they stir up, neat huh? :P