mechanics of breathing

Inspiration at rest

External intercostals contract, lifting rib cage and sternum up and out

Diaphragm contracts and flattens

Volume of thoracic cavity increases

Pressure decreases, air goes into lungs

Inspiration during exercise

External intercostals, diaphragm, sternocleidomastoid, pectoralis major all contract

Greater up and out movement of rib cage and sternum

Volume of thoracic cavity increases more than at rest

Pressure of thoracic cavity decreases more than at rest, increases volume of air inspired/depth of breathing

Expiration at rest

External intercostals relax, lowering rib cage and sternum down and in

Diaphragm relaxes and returns to dome shape

Volume of thoracic cavity decreases

Pressure increases, air pushed out of lungs

Expiration during exercise

External intercostals, diaphragm, rectus abdominis, internal intercostals

Greater down and in movement of rib cage and sternum

Decreased volume of thoracic cavity more than at rest

Increased pressure of thoracic cavity more than at rest, increased volume of air inspired/rate of breathing per minute