Accessory Muscle Actions

Elevates the sternum, increases AP diameter of the chest

• Scalenes

• SCM

• Upper trap

• Latissimus dori

Extends the thoracic spine and raises the rib cage

• Serratus anterior

• Pectoralis minor

• Pectoralis major

• Erector spinae

Posterior fibers assist in inspiration by pulling the trunk into extension

• SCM

• Serratus anterior

• Pectoralis minor

• Latissimus dorsi

Elevates and fixes the first and second ribs

• SCM

• Scalene

• Upper trap

• Erector spinae

Helps to elevate the thoracic cage

• Latissimus dorsi

• SCM

• Erector spinae

• Upper trap

Uses its insertion as its origin to lift the ribs and sternum when the arms and shoulders are fixed.

• Pectoralis major

• Erector spinae

• Serratus anterior

• SCM