This particular stretch helps to stretch the costal muscles and cartilage, helping to strengthen them and pull the chest into a more cosmetically appealing shape. Hence it is a great stretch for Pectus Excavatum.
Stand at end of wall or in doorway facing perpendicular to wall. Place inside of bent arm on surface of wall. Position bent elbow shoulder height.
Turn body away from positioned arm. Hold stretch. Repeat with opposite arm.
Upper chest becomes more stretched with elbow lower. Lower chest and pectoralis minor become more stretched with elbow higher.
Pectoralis Major, Sternal
Pectoralis Major, Clavicular