4 Very Important Muscles

The rotator cuff – just what is it? The rotator cuff is not singular. It actually is a group of 4 muscles. The four muscles of the rotator cuff group are a group of muscles that work in the shoulder to keep the humerus in place. These four muscles are critical for shoulder stability, and along with their tendons allow for the wide range of motion in the shoulder. These muscles arise from the scapular and connect to the head of the humerus forming a cuff at the shoulder joint. The four muscles that make up the rotator cuff are: the Infraspinatus, the Supraspinatus, the Teres Minor and the Subscapularis.

Let’s take a look at each one of the rotator cuff muscles:


The supraspinatus originates above the spine of the scapular and inserts on the greater tuberosity of the humerus. Its main function is to stabilize the upper arm by holding the head of the humerus in position. It is important in throwing motions. Daily uses: holding shopping bags away from the body.


The infraspinatus muscle originates below the spine of the scapula and inserts on the posterior aspect of the greater tuberosity of the humerus.
This rotator cuff muscle crosses the shoulder joint and is commonly injured. It is the main external rotator of the shoulder and the most commonly injured of the four. Daily uses: brushing your hair.

Teres Minor:

The teres minor originates on the lateral scapula border and inserts on the inferior aspect of the greater tuberosity of the humerus. The teres minor surrounds the shoulder. Its main action in conjunction with the infraspinatus is to externally rotate the shoulder. Daily uses: brushing your hair.


The subscapularis muscle originates on the anterior surface of the scapula sitting directly over the ribs, and inserts on the lesser tuberosity of the humerus. It acts to depress the head of the humerus allowing it to move freely in the joint during elevation of the arm.
Daily uses: tucking the back of your shirt in your pants.

The supraspinatus and infraspinatus are the most commonly injured rotator cuff muscles. Sports that involve a lot of shoulder rotation (pitching, swimming, kayaking) often put the rotator cuff muscles under a lot of stress.

As you can see, the rotator cuff group of muscles are small muscles on an individual basis, but together they provide stability while allowing tremendous mobility to the shoulder. A strain or injury to any one of these vital muscles will have an impact on scapular position, humeral head position and overall function of the shoulder and scapular.

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About the author

Narina Prokosch, RN, CPT

Registered Nurse National Academy of Sports Medicine Certified Personal Trainer Functional Movement Screen Certified Level I Functional Movement Screen Certified Level II Owner Victoria Wellness Professionals Ltd. Growing up in the Fraser Valley, Narina spent her teenage and early adult years showing horses. Competing as a bodybuilder from Novice to National level, she has always valued and appreciated fitness, and her ability to train and enjoy an active lifestyle. As a registered nurse, Narina worked in the operating room at Royal Jubilee Hospital, and spent five years on the open heart surgical Team. With over thirty years of strength training, Narina has always been disappointed in how many people, especially women, attempted to start a fitness program only to become discouraged and quit. Her vision is to encourage men and women to pursue a healthy lifestyle through incorporating fitness into their lives. Narina has united her passion for fitness and nursing background to provide clients with professional assistance to guide them.