Poor posture is not just about the back muscles. No matter how much you strengthen and stretch your back, you will not be able to improve your posture if your chest muscles (pecs) are too tight. Pecs can tighten and shorten for many reasons; in fact, any activity that involves bringing your shoulders forward and keeping your arms in front of you shortens the chest muscles. Examples are cooking over a stove, reading, and computer work. Also, sleeping on your side may cause your shoulders to be slightly forward, which shortens the chest muscles. It is important to stretch your pecs daily to improve your posture. One way to stretch your pecs is to lie on a foam roller, open your arms to the side and bend the elbows at a 90 degree angle.