Muscles used for breathing

There are three main groups of muscles necessary for respiration:

  • Diaphragm: Located below the lungs and spans across the entire body, it plays an integral role in the respiratory system. Diaphragm contractions cause an increase of space in the thoracic cavity and a decrease of pressure, a hollow area enclosed by the ribs, vertebral column, and the sternum, which enables the lungs to expand and perform inspiration. During expiration, the diaphragm relaxes, the lungs recoil back to their original volume, the size of the thoracic cavity decreases, and air flows out. Pregnant women’s diaphragm is pushed up by 4 cm due to the increasing uterus size, which prevents the lungs from expanding to their fullest capacity.

  • Intercostal muscles: The muscles in between the ribs assist in breathing. During inspiration, they contract and assist in the elevation of the ribs and sternum. This creates an expansion of the thoracic cavity due to the elevation and bending of the ribs. During expiration, intercostal muscles relax, which causes the rib cage to recoil back and the thoracic cavity to shrink in size.

  • Pectoral Muscles: There are three types, including the external intercostal muscles (the most superficial muscle of intercostal muscles), the internal intercostal muscles, and the innermost intercostal muscles. They all assist in the elevation of the rib cage during inspiration.

  • Accessory muscles: Muscles used in active expiration. Among others include the scalene, the pectoralis major, the trapezius, and the external intercostals.

This is an illustration of a human torso with an overview of all the muscles that are responsible for breathing. Surrounding the lungs there are the ribs and the intercostal muscles. A muscle in each side of the chest called pectoralis minor, located outside of the ribs, goes all the way from the center of each lung to the respective shoulder. Below the lungs, there is the diaphragm, which is protected by the low part of the ribs.

Figure 1. Overview of the main muscles responsible for breathing.