Expansion
Sternocleidomastoid, scalenes and pectorals for inspiration; abdominal wall for expiration
Expansion
Accessory inspiratory muscles - they elevate the ribs and sternum:
- Sternocleidomastoid
- Scalenus anterior, medius and posterior
- Pectoralis major and minor
- Serratus anterior
- Latissimus dorsi
Expiratory muscles - quiet expiration is passive, but forced expiration uses:
- Rectus abdominis, external and internal oblique, transversus abdominis
- Internal intercostals
The pectoral and latissimus muscles only help if their usual insertion is fixed, which is exactly why a breathless patient braces their arms on a table or on their knees. That tripod position converts the limb muscles into rib elevators.