Shoulder Girdle Agonist Muscles

• Agonist muscles of the shoulder girdle

Pectoralis Minor

• Originates on the anterior surfaces of the 3rd to 5th ribs.
• Insertion point is the coracoid process of the scapula.
• Actions include abduction, downward rotation, and depression of the scapula.
• Movement occurs in the transverse and frontal planes.
• Palpation is difficult as it lies under the pectoralis major muscle, inferior to the coracoid process during resisted depression.
• Enhanced by placing the hand behind the back and actively lifting it away.
• Innervated by the medial pectoral nerve (C8 and T1).

Serratus Anterior

• Arises from the surface of the upper 9 ribs at the side of the chest.
• Connects to the anterior aspect of the entire length of the medial border of the scapula.
• Responsible for abduction and upward rotation.
• Movement occurs in the transverse and frontal planes.
• Palpate the frontal and lateral side of the chest below ribs five and six, proximal to the origin during abduction.
• Best palpated with the glenohumeral joint flexed 90 degrees.
• Palpate the upper fibers between the lateral borders of the pectoralis major and latissimus dorsi in the axilla
• Innervated by the long thoracic nerve (C5-C7).

Trapezius Upper Fibers

• Originates at the base of the skull, occipital protuberance, and posterior ligaments of the neck.
• Inserts on the posterior aspect of the lateral 3rd of the clavicle.
• Responsible for elevation, extension of the head at the neck, and rotation of the head at the neck.
• Movement happens in the frontal and sagittal and transverse planes.
• Palpate between the occipital protuberance and C6, laterally to the acromion during elevating and extending the head at the neck.
• Innervated by the spinal accessory nerve and branches of C3 and C4.

Trapezius Middle Fibers

• Originates from the spinous process of the 7th cervical and upper 3 thoracic vertebrae.
• Inserts on the medial border of the acromion process and superior border of the scapular spine.
• Actions include elevation, adduction, and upward rotation.
• Motion occurs in the frontal plane.
• Palpate from C7 to T3 and laterally to the acromion process and scapular spine during adduction.
• Spinal accessory nerve and branches of C3 and C4 provide innervation.

Trapezius Lower Fibers

• Originates from the spinous process of the 4th to 12th thoracic vertebrae.
• Insertion is at the triangular space at the base of the scapular spine.
• Actions include adduction, depression, and upward rotation.
• Motion occurs in the transverse and frontal planes.
• Palpated from T4 to T12 and the medial aspect of the scapular spine during depression and adduction.
• Shares innervation with the spinal accessory nerve and branches of C3 and C4.

Rhomboids

• Originates from the spinous processes of the 7th cervical and first 5 thoracic vertebrae.
• Connects to the medial border of the scapula, inferior to the scapular spine.
• Responsible for adduction, downward rotation, and elevation.
• Movement occurs in the transverse and frontal planes.
• Palpation is difficult due to the depth of the muscle relative to the trapezius.
• Palpate through the trapezius muscle during adduction.
• Best palpated by placing the subject's ipsilateral hand behind the back to relax the trapezius and bring the rhomboid into action.
• Innervated by the dorsal scapular nerve (C5).

Levator Scapulae

• Originates from the transverse processes of the upper 4 cervical vertebrae.
• Insertion is the medial border of the scapula from the superior angle to the scapular spine.
• Responsible for elevation.
• Motion occurs in the frontal plane.
• Palpation is difficult due to the depth of the muscle.
• Best palpated at insertion just medial to the superior angle of the scapula when slightly elevated.
• Innervated by dorsal scapular nerve C5 and branches of C3 and C4.

The shoulder girdle muscles and their function. The Pectoralis Minor originates on the anterior surfaces of the 3rd to 5th ribs and inserts on the coracoid process of the scapula. The Serratus Anterior arises from the surface of the upper 9 ribs at the side of the chest.