Updated May 01, 2014.

Definition:

The intercostals are the layers of muscle between your ribs. In yoga, these muscles are most often felt in backbends, during which the front of the chest stretches intensely and twists. The intercostals are also very important in expanding and contracting the chest during normal breathing, as well as in pranayama practice. Three-part breath, in which you lie on your back and slowly inflate and deflate the chest with your breath, is a good way to get a feel for the action of the intercostals.