Breathing Mechanics (AQA GCSE Physical Education (PE))

Inhaling & Exhaling

• The process of breathing in and out is known as ventilation

  • Breathing in = inhalation or inspiration

  • Breathing out = exhalation or expiration

• Ventilation involves the movement of several structures within the chest cavity:

  • The intercostal muscles

    • These muscles are attached to the inside and outside of the rib cage

  • The ribs

    • These bones form the rib cage that protects the heart and lungs

  • The diaphragm

    • This muscular membrane separates the chest cavity from the abdominal organs

    • The relaxed diaphragm forms a dome which flattens when the muscle contracts

The process of inhalation

• The following events enable inhalation:

  • The diaphragm contracts and flattens

  • Intercostal muscles contract to pull the ribs up and out

  • The volume of the chest cavity increases, leading to a decrease in air pressure inside the lungs relative to the external environment

  • Air moves inwards from an area of high pressure to an area of low pressure

Inhalation diagram

During inhalation the diaphragm moves down and the ribs move up and out, increasing the volume of the chest cavity

The process of exhalation

• The following events enable exhalation

  • The diaphragm relaxes and moves upwards back into a dome shape

  • Intercostal muscles relax allowing the ribs to drop down and in

  • The volume of the chest cavity decreases, leading to an increase in air pressure inside the lungs relative to the external environment

  • Air moves outwards from an area of higher pressure to an area of lower pressure

Exhalation diagram

During exhalation the diaphragm moves up and the ribs move down and in, reducing the volume of the chest cavity

Exercise and breathing

• During exercise the supply of oxygen to the body needs to increase; this is aided by changes to the ventilation process:

  • During inhalation

    • The volume of the chest cavity is increased further by the action of pectoral and sternocleidomastoid muscles; this allows more air to be drawn into the lungs

      • Pectoral muscles are located in the front of the chest

      • Sternocleidomastoid muscles attach the neck to the top of the rib cage

  • During exhalation

    • The rib cage is pulled down and in more rapidly by the contraction of abdominal muscles; this forces more air out of the lungs

      • This differs from exhalation at rest, which is an entirely passive process

Additional breathing muscles diagram

The pectoral and sternocleidomastoid muscles aid inhalation and the abdominal muscles aid exhalation during exercise