The internal intercostals muscles are a group of small, thin muscles located between the ribs in the thoracic region of the spine. They are responsible for moving the ribs during inhalation and exhalation, and are important for activities such as breathing and singing. The internal intercostals muscles originate at the outer surface of the ribs and then insert at the inner surface of the ribs.

They are important for moving the ribs during inhalation and exhalation. This movement is important for activities such as breathing and singing, as it allows the lungs to expand and contract and allows air to flow into and out of the body. The internal intercostals muscles also play a role in providing stability to the ribcage, which is important for protecting the internal organs and maintaining a proper posture.

These muscles are active whenever we breathe, sing, or perform any other activity that involves movement of the ribs. They are also used when we laugh, cough, or sneeze, as well as when we perform movements that require stability of the ribcage, such as standing on one leg or performing single-leg exercises.