The external intercostals are located in the intercostal spaces between the ribs, forming part of the muscles associated with the thoracic cage. They are relatively thin muscles that run obliquely between adjacent ribs.

Origin:
Originating from the inferior border of the rib above, the external intercostals take their starting point from the lower margin of each rib.

Insertion:
The muscles insert into the superior border of the rib below, extending along the length of each intercostal space. This insertion site establishes a connection with the upper margin of each adjacent rib.

Function:
Functionally, the external intercostals play a crucial role in the mechanics of breathing. During inhalation, these muscles contract, causing the ribcage to expand. This expansion contributes to an increase in the thoracic volume, facilitating the intake of air into the lungs. The external intercostals are particularly active during forced inhalation or during activities that require increased respiratory effort. Their contraction elevates the ribs and assists in creating a negative pressure in the thoracic cavity, allowing air to flow into the lungs. The external intercostals are vital components of the respiratory system, contributing to the rhythmic process of breathing.

Most often the respiratory system, more specifically, the inspiratory and expiratory muscles, are not thought to be trainable except through aerobic type activities.
This, however, is only partially true. The respiratory system muscles can also be strengthened with specific strength training exercises.

Volume 12 - The Respiratory System of our Kinesiology of Exercise Ebooks is a first for a book on strength training for the respiratory system.