An anatomical diagram of shoulder muscles

Shoulder Anatomy 102: A Beginner’s Guide to the Major Muscles of the Shoulder Girdle

Meagan McCrary
Updated: 
June 17, 2019

Now that you have the general idea of the overall bony structure of the shoulder girdle, let’s start to become familiar with the major groups of muscles involved, beginning with some anatomical terms you often hear in class.

Deltoids

Deltoids are the rounded triangle-shaped muscles located at the tops of the shoulders and upper arm bones, passing up and over the shoulder joints (what most people think of as their shoulders). Often called “delts” for short, the muscle has three divisions: front or anterior delts, rear or posterior delts, and outer or lateral delts. These muscles give the deltoids their triangular shape, delta being the Greek word for triangle.

In class, you may hear your teacher refer to your inner and outer deltoids, often asking you to place your hands as wide as your outer deltoids in a preparation for Downward Facing Dog. Your outer deltoids are the width of your outer shoulders, while your inner deltoids are essentially the width of your chest.

Pectorals

Pectorals, or more commonly called “pecs,” are two sets of muscles: pectoralis major and minor. Pectoralis major is the large, flat muscles that forms the front of the chest and is primarily responsible for movement of the shoulder joint, drawing the heads of the arm bones forward. They’re the muscles that help you push up in a push up.

Pectoralis minors are thin, triangular-shaped muscles that lie under the pec majors. They pull the shoulder blades downward and forward, and also assist in lifting the rib cage in respiration. Deep under pec majors, they’re hard to stretch and often need to be released.

Trapezius

While most of us think of our traps as that really tense band of muscles at the tops of our shoulders, the trapezius is actually a broad, diamond-shaped muscle that runs down to the mid-back and up to the base of the skull.

The muscles we are familiar with are only the upper trapezius, responsible for elevating the shoulder blades. When you relax your upper traps you allow your shoulder blades to come down. The less familiar middle trapezius help draw the shoulder blades toward the spine, while the lower trapezius pull them down the back. Engaging the middle and lower trapezius will actually help release the upper traps.

Latissimus Dorsi

Commonly referred to as “lats,” the latissimi dorsi are the large, v-shaped muscles located on the back of the body, forming two-thirds of the superficial back muscles. Broad and flat, they sweep diagonally across the back, from the spine, across the ribs and through the armpit to their insertion point on the inner upper arm bones, covering the tips of the shoulder blades.

The major role of the lats is to draw the arms down and toward the body. Try it: Find your latissimi dorsi muscles by standing with your arms out at your sides at the height of your shoulders. With your fingers spread, press your palms and arms down toward the floor, feeling your lats contract.

However, the latissimi dorsis also play a role in anchoring the outer shoulder blades down the back—drawing the bottom tips of the shoulder blades inward and broadening the tops. When the upper arm bones are in a fixed position, such as in Upward Facing Dog, contracting the lats will draw the chest forward and up through the arm bones. When a teacher asks you to engage your outer shoulder blades up the back in Downward Facing Dog, he or she is really asking you to contract your lats, pulling the outer shoulder blades down your back (which can be confusing when you’re upside down) and broadening your chest.

Rhomboids

Flat rectangular muscles attached to either side of the spine and inserting along the inner edge of the shoulder blades, the rhomboids draw the shoulder blades together on the upper back. They help stabilize the shoulder blades on the back and lift the rib cage.

Serratus Anterior

The serrati anterior work in opposition to the rhomboids. The teeth-like serratus attach to the sides of the ribs and also insert along the inside of the shoulder blades, pulling them forward off the back. Together with rhomboids, they negotiate the placement of the shoulder blades on the back.

Teachers sometimes refer to the serrati anterior as your “armpit” muscles, or they will ask you to turn your side ribs on. You can really feel this action in a cat pose as you press down through the palms and round through the upper back, pulling the shoulder blades forward.

Then move into cow pose, using the rhomboids to draw your shoulder blades toward the spine. Balance the two actions and place your shoulder blades on your back.

Rotator Cuff

The rotator cuff is a group of four muscles that literally create a continuous cuff around the shoulder joint, to help keep the head of the arm bone in the shoulder socket. They play an extremely important role in stabilizing the shoulders in all weight-bearing poses.

Read the first article in this series from YogaUOnline and Meagan McCrary - Yoga Anatomy 101: A Beginner's Guide to the Shoulder Girdle.

Study with YogaUOnline and Julie Gudmestad: Shoulder Strength and Stability: Serratus Anterior.
 

YogaUOnline contributor Meagan McCraryMeagan McCrary is an experienced yoga teacher (E-RYT 500) and writer with a passion for helping people find more comfort, clarity, compassion and joy on the mat and in their lives. She is the author of Pick Your Yoga Practice: Exploring and Understanding Different Styles of Yoga a comprehensive encyclopedia of prominent yoga styles, including each system’s teaching methodology, elements of practice, philosophical and spiritual underpinnings, class structure, physical exertion and personal attention. Currently living in Los Angeles, Meagan teaches at the various Equinox Sports Clubs, works privately with clients and leads retreats internationally. You can find her blog, teaching schedule and latest offerings at www.MeaganMcCrary.com