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Human Performance

2.3.2.1 Inhalation

Two muscles are responsible for breathing:

- Intercostal muscles (between the ribs)

- The diaphragm muscle

The intercostal muscles are the muscles between the ribs.

These muscles lift the ribcage when they contract. The ribcage is lifted and pulls

the outer pleura outward. This creates negative pressure in the pleural fluid,

causing the inner pleura to also be pulled outward.

The lung wall moves with it, causing the lungs to expand, and air flows into the

lungs.

The diaphragm is a dome-shaped muscle located beneath the lungs. When it
contracts, it flattens, and the lung wall at the base of the lungs moves with it.

This makes the lungs longer, increasing the volume and drawing air in.

During intense physical work, several other muscles that attach to the ribcage

can be used to strengthen the breathing movements. For example, the neck

muscles, which originate from the skull and attach to the upper part of the

ribcage, are engaged.

2.3.2.2 Exhalation

Unlike inhalation, which requires muscle activation, exhalation occurs

"automatically" when these muscles relax.

The elastic connective tissue surrounding the alveoli causes the lungs to recoil

when tension is released, pushing air out.

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Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 136