Lisähenityslihaksia

Lisähenityslihaksia, or accessory breathing muscles, are muscles that can assist the primary muscles of respiration, primarily the diaphragm and intercostal muscles, when increased ventilatory demands are placed on the body. These muscles are typically recruited during strenuous physical activity, in individuals with respiratory diseases, or during forceful exhalation.

The primary accessory muscles of inspiration include the sternocleidomastoid, scalene muscles (anterior, middle, and posterior), pectoralis major and minor, serratus anterior, and the trapezius. These muscles work by elevating the rib cage and sternum, thereby increasing the volume of the thoracic cavity. The sternocleidomastoid attaches to the sternum and clavicle, pulling them upwards. The scalenes lift the first two ribs. The pectoralis major and minor muscles can help lift the ribs when the arms are stabilized. The serratus anterior can also contribute to rib elevation.

Accessory muscles of expiration are less commonly discussed as the diaphragm and internal intercostals are usually sufficient. However, during forceful exhalations, such as coughing or during severe respiratory distress, muscles like the abdominal muscles (rectus abdominis, external and internal obliques, transversus abdominis) and the internal intercostals can contract to decrease the volume of the thoracic cavity, forcing air out of the lungs more rapidly and completely.

The use of accessory breathing muscles is often an indicator of increased work of breathing. While beneficial for meeting higher oxygen demands, chronic reliance on these muscles can lead to fatigue and discomfort, and is a characteristic sign in conditions like chronic obstructive pulmonary disease (COPD) or asthma.