It might seem that these is just one big chest muscle, but that’s not true! The little one of the 2 chest muscle brothers (see the picture) is the one causing so many problems with the shoulders. It rotates our shoulders down creating little or no space for muscles, ligaments and tendons in the shoulder.
Take a look at the picture again. Do you see it? Pectoralis minor (the little muscle) connects the ribs and the top of the scapula. Therefore, to stretch it properly, you need to put your arm up. See the Movegeen hygiene techniques (Upper Body: the V-shape stretch.