Musculature of the Shoulder

The muscles controlling the Shoulder Girdle are both numerous and complicated. Many serve several purposes, effecting one or more of the articulations of scapula and/or humerus as discussed previously. To make this rather dry subject a bit more applicable, I am going to divide them broadly into muscles that act upon the scapula, muscles that act upon the humerus, and muscles that act on both. Within these categories, I will name the function(s) of each muscle. The images shown are from the timeless Gray's Anatomy, available at http://www.bartleby.com/107/
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Muscles acting on the Scapula

• Trapezius: elevation (upper fibres), depression (lower fibres), retraction (middle fibres), upward rotation (upper and lower fibres synchronously)
• Rhomboids: retraction, downward rotation
• Levator scapulae: (elevation)
• Serratus anterior: protraction, upward rotation
• Pectoralis minor: depression, tilts scapula anteriorly
  

Muscles acting on the Humerus:

• Biceps brachii: flexion (with elbow fixed)
  
• Triceps brachii: extension (with elbow fixed, long head only)
  
• Deltoid: flexion (anterior fibres), abduction (middle fibres), extension (posterior fibres)
  
• Supraspinatus: abduction, stabilising head of humerus as part of rotator cuff
  
• Infraspinatus: external rotation, stabilising humerus as part of rotator cuff
  
• Subscapularis: internal rotation, stabilising humerus as part of rotator cuff
• Teres minor: external rotation, stabilising humerus as part of rotator cuff
• Teres major: internal rotation, adduction
  
• Coracobrachialis: adduction

Muscles acting on both Scapula and Humerus

• Pectoralis major: Humeral flexion (especially in abduction), extension (from fully flexed), adduction (lower fibres), internal rotation. Scapular protraction+elevation (upper fibres), protraction+depression (lower fibres)
• Latissimus Dorsi: Humeral extension, adduction, internal rotation. Scapular depression, retraction

So that is a whistlestop tour through the muscles that act upon the shoulder girdle. I've pretty much skimmed over a huge topic, so don't start picking me up on things I've missed. These are the most important bits. Clicking on the images should hopefully make them larger, so that the names can be read and muscles identified. I've pretty much skimmed over a huge topic, so don't start picking me up on things I've missed! These are the most important bits. Similarly, don't get too bogged down in this, however; it is a bit dry and not too important. In the next few posts, I will be covering more specific muscles in greater detail, as well as an analysis of various in-gym movements and the muscles necessary to bring them about. Thanks for reading!