The rib cage also contains muscles with an expiratory action. These are the internal intercostal muscles, which slope backward; contraction causes the ribs to move downward and inward, similar to the lowering of a bucket handle.Both internal and external intercostal muscles are also involved in flexing and twisting the trunk.Read more about Breathe Strong, Perform Better.ntercostal muscle contraction also brings about stiffening of the rib cage during lifting, pushing, and pulling movements, which makes the intercostal muscles an important contributor to these movements.