Stand with one arm against the corner of a wall or the edge of a doorframe. Using the edge push the head of the humerus bone backwards (this minimises the stress on the anterior capsule) and turn your head in the opposite direction to intensify the stretch.
Retract (bring shoulder blades together) and depress (lower towards the ground) the scapula (shoulder blade).
Another way to stretch the pectoralis major and the minor, is to move your arms up the door frame and push through, retracting and depressing with each push through.
This is another quick and easy pec stretch you can do anywhere, no wall or doorway required!
The Sternocleidomastoid muscle is a double-headed muscle that runs from the temporal bone (behind your ear) and the occipital bone (the base of the skull at the back of your head) into the top of the sternum (manubrium sterni) and into the middle of the collarbone (clavicle).
It is responsible for bending the neck to the same side and turning the head to the opposite side.
The first diagram demonstrates stretching the head that is attached to the collar bone and the second diagram demonstrates stretching the head that is attached to the sternum.