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In Depth: Muscles

The muscles in the shoulder help give it wide range of movement and help maintain the main shoulder joint, the glenohumeral.

The largest muscle of the shoulder is the deltoid. This large triangular muscle covers the glenohumeral joint and gives the shoulder its round shape. It stretches across the top of the shoulder from the clavicle in the front to the scapula in the back. It then stretches downward to near the center of the humerus bone. Different fibers of the muscle are responsible for different actions, including raising the arm and assisting the pectoralis muscle. One important function of the deltoid is preventing joint dislocation when a person carries heavy objects.

Other muscles that aid in shoulder movement include:

  • Infraspinatus: This rotator cuff muscle helps raise and lower the arm.
  • Tricep brachii: This large muscle in the back of the upper arm helps straighten the arm.
  • Pectoralis major: This large fan-shaped muscle stretches from the armpit up to the collarbone and down across the lower chest region. It connects to the sternum (breastbone).
  • Pectoralis minor: The smaller of the pectoralis muscles, this muscle fans out from the upper ribs up to the shoulder area.
  • Teres major: This muscle helps rotate the upper arm.
  • Bicep brachii: Commonly known as the bicep muscle, this muscle rests on top of the humerus bone. It rotates the forearm as well as flexes the elbow.
  • Latissimus dorsi: This flat rectangular muscle of the back helps the arms rotate as well as move away and closer to the body.
  • Subscapularis: This is a large triangular muscle near the humerus and collarbone. It helps rotate the humerus.
  • Supraspinatus: This small muscle at the top of the shoulder. It helps raise the arm away from the body.

Four muscles—the supraspinatus, infraspinatus, teres minor, and subscapularis—make up the rotator cuff. It stabilizes the shoulder and holds the head of the humerus into the glenoid cavity to maintain the principal shoulder joint.

As these muscles are used in a wide range of motion and are responsible for bearing heavy loads, shoulder muscle pain is a common ailment. The most common cause of shoulder pain is overexertion of a muscle or injury to it. Twisting, pulling, or falling are common ways muscles in the shoulders become painful. Although repetitive use injuries affect the deep muscles more, pulled muscles from lifting something too heavy or overexerting can create pain and soreness that usually subsides in a few days.

Shoulder muscle pain can usually be easily treated with resting the affected muscle and icing, elevating, and compressing the area. 

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