Movements of the Shoulder (Glenohumeral) Joint Flexion and Extension Abduction and Adduction Internal and External Rotation Horizontal Adduction and Abduction

Deltoid (Middle Fibers) O: Lateral aspect of acromion I: Deltoid tuberosity on lateral humerus A: Abduction of shoulders

Deltoid (anterior fibers) O: Anterior lateral third of clavicle I: Deltoid tuberosity on lateral humerus A: abduction, flexion, horizontal adduction, & internal rotation of shoulder

Deltoid (Posterior Fibers) O: Inferior edge of spine of scapula I: deltoid tuberosity on lateral humerus A: Abduction, extension, horizontal abduction, & external rotation of shoulder

Coracobrachialis O: Coracoid process of scapula I: Middle of medial border of humeral shaft A: Flexion, adduction, & horizontal adduction of shoulder

Rotator Cuff Muscles Supraspinatus Infraspinatus Teres minor Subscapularis

Supraspinatus O: Medial 2/3 of supraspinatus fossa I: Superiorly on the greater tubercle of humerus A: Abduction and stabilization of humeral head in glenoid fossa

Infraspinatus O: Medial aspect of infraspinatus fossa just below the spine of the scapula I: Posteriorly on the greater tubercle of humerus A: External rotation, horizontal abduction, extension of shoulder, & stabilization of humeral head in the glenoid fossa

Teres minor O: Posteriorly on the upper and middle aspect of the lateral border of scapula I: Posteriorly on the greater tubercle of humerus A: External rotation, horizontal abduction, extension of shoulder, stabilization of humeral head in glenoid fossa

Subscapularis O: Entire anterior surface of subscapular fossa I: Lesser tubercle of humerus A: Internal rotation, adduction, extension of shoulder, stabilization of humeral head in glenoid fossa

Teres major O: Posteriorly on the inferior third of lateral border of scapula and just superior to the inferior angle I: Medial lip of intertubercular groove of humerus A: Extension (from flexed position), internal rotation, & adduction (from abducted position) of shoulder

Muscular Stability of the Glenohumeral joint

Common Injuries to the Shoulder Dislocations glenoid fossa covers 1/3 of diameter of humeral head common in the anterior, posterior, and inferior directions Rotator Cuff Damage Rotator cuff impingement syndrome (swimmer’s shoulder) abnormal acromion process, inflammation of supraspinatus tendon Rotational Injuries Throwing mechanics ( > 90° abduction and external rotation) labrum tears due to fatigue of rotator cuff muscles (subscapularis)

Latissimus Dorsi O: Posterior crest of ilium, back of sacrum, & spinous processes of lumbar & lower six thoracic vertebrae (T6-T12); slips from the lower three ribs I: medial side of interturbecular groove of humerus, just anterior to the insertion of teres minor. A: Adduction, extension, internal rotation, horizontal abduction

Pectoralis Major (Upper Fibers / Clavicular Head) O: medial ½ anterior surface of clavicle I: Flat tendon 2 or 3 inches wide to the outer lip of the intertubercular groove of humerus A: Internal rotation, horizontal adduction, flexion, abduction (>90 degrees), & adduction (<90 degrees) of shoulder

Pectoralis major (Lower Fibers / Sternal Head) O: Anterior surfaces of the costal cartilages of the first six ribs and adjacent portion of sternum I: Flat tendon 2 or 3 inches wide to the outer lip of the intertubercular groove of humerus A: Internal rotation, horizontal adduction, adduction and extension of shoulder from flexed position to anatomical position.

Decline and Incline Bench Press

Agonist and Antagonist Relationship Agonist – is a muscle described as being primarily responsible for a specific joint movement while contracting Antagonist – is a muscle that counteracts or opposes the contraction of another muscle Simply, these are relative terms describing “opposites”

If an agonist muscle is considered a concentric contractor for a movement then the antagonist muscle is the eccentric contractor for the same movement. Generally, concentric and eccentric contractions do not occur at the same time for a given movement.

What determines which one is working is the purpose of movement, acceleration (speeding-up) or deceleration (slowing-down). Examples