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The rotator cuff compresses the glenohumeral joint during abduction of the arm, an action known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle.
The supraspinatus forms part of the rotator cuff and is one of its most frequently damaged components, whether from acute injury or gradual degeneration. [7] Bad posture and age are leading risk factors, with a high prevalence of unsymptomatic partial and full tears, as well as symptomatic syndromes with chronic pain.
The rotator cuff is a group of four muscles that surround the shoulder joint and contribute to the shoulder's stability. The muscles of the rotator cuff are supraspinatus, subscapularis, infraspinatus, and teres minor. The cuff adheres to the glenohumeral capsule and attaches to the humeral head.
The infraspinatus is the main external rotator of the shoulder. When the arm is fixed, it adducts the inferior angle of the scapula. Its synergists are teres minor and the deltoid. [4] The infraspinatus and teres minor rotate the head of the humerus outward (external, or lateral, rotation); they also assist in carrying the arm backward. [1]
The external rotator muscles include: Muscles. of arm/humerus at shoulder [1] Deltoid muscle; Supraspinatus; Infraspinatus; Teres minor; of thigh/femur at hip [2]
The teres minor (Latin teres meaning 'rounded') is a narrow, elongated muscle of the rotator cuff.The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the greater tubercle of the humerus and the posterior surface of the joint capsule.
"The rotator cuff could be injured by this movement." Physical therapist Brett Russell agrees. "There are better ways to attempt a pull-up, such as an assisted pull-up machine," he says.
The greater tubercle of the humerus is the outward part the upper end of that bone, adjacent to the large rounded prominence of the humerus head. It provides attachment points for the supraspinatus, infraspinatus, and teres minor muscles, three of the four muscles of the rotator cuff, a muscle group that stabilizes the shoulder joint.