The Ultimate Anatomical Guide Part 1 (Shoulders)

By Joe “Yu Yevon” King


Welcome to part one of the Ultimate Anatomical Guide series. My goal with these articles is to expand your knowledge of your skeletal muscle system.


As soldiers of the iron, we must know our bodies to know how to blast them into hypertrophy. It is common knowledge that the more we know about our inner workings, the better equipped we are to develop programs designed to take us to the next level in this sport. Take Kevin Levrone for example. He arguably has the best shoulder development of anyone in the world. Do you think someone like Kevin blindly works his shoulders without even thinking about what muscles he is actually contracting? Of course not! Throughout this article, I will cover the joint actions and in-depth shoulder anatomy!


Editors Note:  A quick tip on this article.  Mr. King reveals some incredible aspects of the shoulder complex in the following paragraphs.  You will find an elaborate array of joint actions and anatomical facts.  My suggestion to to visualize each action, as he explains them, and try and see yourself utilizing that action while in the gym.  Finally take careful notice to how he ties these concepts together in what I feel is one of the most intricate aspects of both bodybuilding, strength training, and even speed training.  By applying these principles, your mind's capacity to visualize the contractile properties in this region will more than double. 




You may not have realized it, but your shoulders perform twelve main functions. They are as follows:


Shoulder (scapular) elevation - To Move the scapula upward, or superiorly, as in closer to the skull.


Shoulder (scapular) depression - To Move the scapula downward, or inferiorly, as in closer to the plantar surface of the feet.


Shoulder (scapular) protraction - Used when spreading the lats.



 Shoulder (scapular) retraction - Performed when you squeeze the shoulder blades together


Shoulder flexion - Used when performing front raises.



Shoulder extension - To move the shoulder joint straight backwards.  Similar to a hammering motion.

Shoulder internal rotation - Rotating the shoulder joint medially or toward the midline of the body.

Shoulder external rotation -  Rotating the shoulder joint medially or toward the midline of the body.


Shoulder adduction - Adduction means to bring a body part closer to the midline or center of the body. 

Shoulder abduction - Abduction means to take a body part away from the midline or center of the body. 


Shoulder horizontal abduction - This is abduction in a horizontal or transverse plane, as in reverse dumbell flys.


Shoulder horizontal adduction -  This is abduction in a horizontal or transverse plane, as in flat dumbell flys.


How are all these movements possible? Many muscles, both large and small, make up the shoulder region and allow us to perform these movements. Before we look at the muscle structures, let us first look at the bone structure surrounding the shoulder joint.





Anterior view:







The deltoideus muscle (also called the deltoids) is made of three main sections called the anterior deltoid, medial deltoid, and posterior deltoid. These three muscle parts have insertions in many different places including the humerus, clavicula, coronoid process, spina scapulae, scapula and acromion. The deltoideus, along with the prominence of the upper end of the humerus bone, produces the rounded contour of the shoulder. It’s rounder and fuller in front than behind, where it presents a flatter form. The insertion of the deltoideus is marked by a depression on the lateral side of the middle arm. The deltoideus is supplied by the fifth and sixth cervical through the axillary nerve.


Side Note: The deltoid is a different type of muscle than some of those found throughout the rest of the body. The delts are made of three pennate muscles making the deltoid a multipennate muscle group. A pennate muscle proportionately moves heavier loads than say a fusiform muscle (such as the biceps brachii), but for shorter distances. When performing lateral raises, for example, the pennate heads of the medial deltoid – very powerful, but with a weak contraction potential – work synergistically with the anterior and posterior heads of the deltoid to bring the arm horizontal.


Now for some joint actions! Let’s discuss the anterior deltoid in more detail. The origin of the anterior deltoid is on the lateral third of the clavicle and inserts in the deltoid tuberosity of the humerus bone. Its actions are flexion, horizontal adduction, and medial rotation of the humerus. The medial deltoid has an origin on the lateral acromion. Its main action is abduction of the humorus to 90 degrees. The posterior deltoid has an origin on the spine of the scapula. Its main actions include extension, horizontal abduction, and lateral rotation of the humerus.














Now I will discuss some of the smaller muscles that work synergistically with the deltoids.


Fiber ratios: To read more on fiber ratios, check out President Wilson’s article this month!


Superficial: 53.3% type I (43-68), 46.7% II fibers. Deep: 61.0% type I (44-77), 39>0% II fibers.




Posterior view:







This muscle inserts near the latissimus dorsi and has similar actions. Together with the infraspinatus and teres minor (I’ll discuss those next), it pulls downward to help stabilize the head of the humerus during shoulder abduction. The teres major has an origin on the inferior angle of the scapula (on the dorsal surface) and the lower third axillary border of the scapula. Its insertion is the medial lip of the bicepital groove of the humerus. Its actions are extension, medial rotation and adduction of the humerus. Of all the scapular muscles, the only one which influences surface form is the teres major; it assists the latissimus dorsi in forming the thick, rounded posterior axillary fold. The teres major is a thick, but flat muscle. The fibers are directed both upward and lateral-ward, and end in a flat tendon only about five centimeters long.


Side Note: The teres major, along with the subscapularis, pectoralis, and latuissimus dorsi are all major components of throwing a ball. If you play a sport that involves a throwing motion (internal rotation of the shoulder) then it is imperative that you strengthen these muscles.




Posterior view:








The teres minor resembles a thick piece of beef jerky. This muscle reinforces the capsule of the shoulder joint and is considered to be one of the rotator cuff muscles. The Teres minor also helps to stabilize the head of the humerus. It has an origin on the upper two thirds of the axillary border of the scapula and inserts into the inferior facet of the greater tubercle of the humerus. Its main functions include lateral rotation and extension of the humerus.




Posterior view:








The supraspinatus muscle pulls the head of the humerus into the glenoid fossa and thus acts as an effective stabilizer for humeral abduction. It reinforces the capsule of the shoulder joint and is one of the rotator cuff muscles. The supraspinatus has an origin on the supraspinatus fossa of the scapula and an insertion in the superior facet of the greater tubercle of the humerus. Its actions include stabilization of the head of the humerus. The muscle fibers  converge to a tendon, which then crosses the upper part of the shoulder joint, and is inserted into the highest of the three impressions on the greater tubercle of the humerus.




Posterior view:










The infraspinatus is a thick, triangular muscle, which occupies the chief part of the infraspinatus fossa. This muscle reinforces the capsule of the shoulder joint and is yet another rotator cuff muscle. The infraspinatus has an origin on the infraspinatus fossa of the scapula and inserts in the middle facet of the greater tubercle of the humerus. Its main actions are lateral rotation and extension of the humerus.




Anterior view:









The subscapularis assists in various shoulder actions depending on the position of the humerus. This is the fourth and final rotator cuff muscle. These muscles together work to guard the glenohumeral joint (shoulder joint). The subscapularis has an origin on the subscapular fossa of the scapula and inserts in the lesser tubercle of the humerus (remember the other three rotator cuff muscles insert in the greater tubercle).




Anterior view:






This muscle is named after its origin and insertion. Its main actions include flexion and adduction of the humerus. The corobrachialis has an origin on the coracoid process of the scapula and inserts in the middle third of the medial surface of the humeral shaft. When the arm is raised, the coracobrachialis reveals itself as a narrow elevation emerging from under the cover of the anterior axillary fold and running medial to the body of the humerus. In well-developed bodybuilders, the coracobrachialis can be seen adding to the freakiness of their physique! The coracobrachialis is prominent in this picture of Flex Wheeler:


















Synergy – How it all comes together


Although I have shown the muscles of the shoulder are all quite unique from one another, it is simply remarkable how these muscles can all work together fluently. This cooperation is called synergy. Lets take a look how the muscles around the glenohumeral articulation:


Under normal conditions the deltoids and supraspinatus roll the humeral head in an upward direction. To counteract this upward roll, the infraspinatus and teres minor depress the humeral head. The depression, or inferior slide, enables the humeral head to clear the subacromial structures and avoid impact with the acromion process. The infraspinatus and teres minor also provide external rotation of the humerus allowing the greater tubercle to move without impinging upon the acromion process. Normal arthrokinematic motion in the shoulder relies on specific forces of the muscles to insure proper motion.


Editors Note:  Fantastic Discussion on the subject of synergy! 


ImpingementA dangerous problem


Sometimes things don’t work as smoothly as we would like. As hardcore athletes, we are susceptible to injury, especially with the extremes we push our bodies to. A common shoulder injury is impingement.


As I outlined above, the rotator cuff consists of four muscles: the supraspinatus, infraspinatus, teres minor and subscapularis. Impingement of the glenohumeral articulation refers to compression of the rotator cuff, specifically the supraspinatus against the acromion. The anterior acromion and the coracocromial ligament are the most common sites of impingement. The supraspinatus outlet is the space between the anterior acromion, the acromioclavicular joint, and the coracoacromial ligament. The supraspinatus tendon passes beneath these structures. Any narrowing of this outlet due to the shape of the acromion, prominence of the undersurface of the acromioclavicular joint, an anterior acromial spur, or thickening of the coracocromial ligament can lead to impingement. The impingement can cause the tendon or subacromial bursa to become inflamed.


This inflammation is referred to as tendinitis or bursitis. This condition is very detrimental to any athlete. Studies have shown that impingement can also be caused by weakness in the rotator cuff muscles, this is why I stress strengthening the rotator cuff. To further prevent impingement, it is also important to strengthen the muscles about the scapula including the inferior, medial, and superior trapezius, rhomboids and serratus anterior.




As I stated above, it is essential that you know and understand the inner workings of your body before you can take your bodybuilding to the next level. With this series, you will have the resources to do just that.


In your quest to blast these muscles into a state of anabolic growth, check out this awesome training program by our outstanding moderator and training guru – Adam “Old School” Knowlden:


8 Weeks to bigger shoulders (link to


Keep on battling the iron!


Yu Yevon




1.     Sieg K. W., Adams S.P., Illustrated Essentials of Musculoskeletal Anatomy Fourth Edition. Published by MegaBooks, Gainesville, Fla. 2002.


2.     Delavier F., Strength Training Anatomy. Human Kinetics, Champaign Ill. 2001.


3.     Henry Gray, F.R.S., T. Pickering Pick, F.R.C.S., Robert Howden, M.A., M.B., S.M., Gray’s Anatomy. Running Press Book Publishers, Philadelphia, PN. 1974.


4.     Katz, Gary. 1988: EXERCISE PRESCRIPTION NOTES #1: Prescription    of external rotation exercise for the shoulder. National Strength & Conditioning Association Journal: Vol. 10, No. 3, pp. 56–57.


5.     Tyson, Alan. 1995: Prevention and Rehabilitation of Shoulder Impingement. Strength and Conditioning: Vol. 17, No. 1, pp. 31–34.


6.     Johnson, M.A., Polgar, J., Weightman, D., Appleton, D. Data on the distribution of fibre types in thirty-six human muscles. An autopsy study.


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