Shoulder Injuries & The Rotator Cuff | Part 1 – Anatomy & Common Injuries

When it comes to athletic performance, the shoulder is pretty much the most utilized part of the upper body. Practically, every exercise that targets a specific upper body muscle group, requires some kind of movement in the shoulder joint. Now, here is something important right away – The shoulder joint has the biggest range of motion out of all joints in the body. However, that big range of motion comes at the price of joint stability, making the shoulder one of the most vulnerable joints in the body.

Shoulder injuries are common and without a doubt the worst type of injuries. This is due to the fact that they basically force you to completely stop upper body training for some time. In this series of articles, we are going to look into the shoulder, its anatomy, functions, and exercises to help you strengthen it and prevent injuries. Of course, the superficial deltoid muscles are just one part of the shoulder, beneath which we can find the more important, stabilizing muscle groups.

Without further ado, let’s have a look at the shoulder, in-depth.

Shoulder Muscles Anatomy

Shoulder Muscles Anatomy


The shoulder joint is a ball & socket joint, located between the humerus (upper arm bone) and the scapula. The main muscles of the shoulder joint are:

  • The deltoids (Front, side & rear)
  • Supraspinatus
  • Infraspinatus
  • Teres Minor
  • Subscapularis

Now, though most of us focus mainly on the deltoids with overhead pressing movements & lateral raises, the last 4 muscles on the list above are often neglected. These 4 little muscles make up what we refer to as the “Rotator cuff”. (

The rotator cuff is what actually stabilizes the shoulder joint and if well-developed makes it far less likely for a shoulder injury to occur. Besides serving as a good injury prevention tool, a healthy rotator cuff will also make you stronger on every other upper body movement. This is especially valid for pushing movements, where the arms are unstable under bigger loads.

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Functions of the shoulder

Functions of the shoulder

Each of the shoulder joint muscles is responsible for certain movements, so let us briefly explain those.

The Deltoids

The superficial muscles of the shoulder are the deltoids, which surround the shoulder joint from all sides. This is why the deltoids are further separated into 3 zones:

  1. Anterior (front) deltoids
  2. Medial (side) deltoids
  3. Posterior (rear) deltoids

The front deltoid head gives a rounder look from the front and is mainly engaged when you lift your arm up from the front. Next to it is the side deltoid, which can give the shoulder line a wider look and is primarily engaged when you lift your arm laterally (to the side).

Lastly, the rear deltoid gives the shoulders a complete, round look, and is primarily engaged when you do movements that pull the shoulder back. Now, though these are the main functions of the deltoid muscles, none of the 3 are ever completely isolated from one another.

These muscles always work in synergy but depending on the exercise, one of the 3 is emphasized.

The Rotator Cuff

Beneath the deltoids are the deep shoulder muscles, which as we mentioned, serve as stabilizers of the shoulder joint. The supraspinatus goes from the upper portion of the shoulder blade and attaches to the head of the humerus. Functionally, the supraspinatus absorbs some of the tension that falls on the shoulder joint and more importantly, keeps the head of the humerus firmly pressed in the shoulder socket.

The infraspinatus is one of the bigger rotator cuff muscles, as it covers most of the shoulder blade and again, attaches at the humerus head. In terms of functionality, this is the muscle that is primarily responsible for the external rotation of the shoulder but also stabilizes the shoulder joint at its socket.

Teres Minor is a relatively small muscle of the rotator cuff, which goes from the lower lateral portion of the shoulder blade, to the head of the humerus. The main functions of the teres minor are external rotation and arm adduction (the movement of the arm towards the midline of the body).

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Subscapularis is the last of the 4 rotator cuff muscles and its main role is to stabilize the head of the humerus in the shoulder socket. Upon contraction, this muscle can also internally and medially rotate the humerus. Lastly, the subscapularis has adduction & extension functions at some angles.

Common Shoulder Injuries

Now that you know some basic anatomy of the shoulder joint, let’s talk about the most common sports-related shoulder injuries. The most common injuries of the shoulder are caused by inflammation, strain, or in the worst case, a complete rupture of one or more tendons of the shoulder musculature.

Now, there are a number of reasons why these injuries occur, but it is important to acknowledge this – The shoulder tendons (and tendons in general) have a weak blood supply as opposed to the muscles. This, therefore, leads to a lesser amount of oxygen and nutrients going to those tissues, making them far more susceptible to degeneration as we age.

The second most common reason for shoulder injuries is systematic overexertion with exercises that engage the shoulder, as well as a poor exercise form.

Common shoulder injuries include:

  • Shoulder dislocation

This is a displacement of the shoulder from its normal position in the socket. A dislocation is usually the result of an impact/fall or overexertion at an awkward angle.

  • Frozen shoulder

The frozen shoulder is another common injury, which is usually the result of inflammation of the shoulder socket. A frozen shoulder is usually accompanied by stiffness, pain, and limited range of motion in the shoulder joint.

  • Rotator cuff tears

This type of injury is common in athletes who mainly use the upper body at high levels of exertion and awkward angles (think rock climbing). With resistance training, this type of injury often occurs during high exertion on heavy pressing movements like the bench press and the overhead shoulder press.

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It is mainly expressed in shoulder pain, instability, and limited range of motion. Most tears are partial, but in severe cases, a tendon may completely come off the bone.

  • Bursitis

Bursae are small, lubricating sacs located in joints across the body. In the shoulders, the bursae are located between the rotator cuff & the bone above the shoulder (acromion).

Bursitis is essentially a condition that occurs when that lubricating sac gets inflamed and usually results in pain, tenderness, and a decreased range of motion.


In the second part of this article series, we are going to tell you more about the means of preventing shoulder injuries, as well as exercises to make the shoulders bigger and stronger.

Here are some important takeaways from this article:

  • The shoulder joint is the most mobile joint in the body, but also one of the less stabilized, which makes it susceptible to injury.
  • This joint is involved in all upper body movements, which is why training intensity & programming should be carefully managed
  • Besides the superficial deltoids, the shoulder has stabilizer deep muscles known as the “rotator cuff”

If you have not yet experienced a shoulder injury, there are preventative measures you can (and should) consider, even if your shoulders are completely healthy. In the second article of this series, we are going to discuss shoulder stabilizing & strengthening exercises, as well as workout tips. All of these will ultimately help you maintain shoulder health and avoid any type of injuries.

See you in the next article!