It’s the most mobile and arguably the most vulnerable joint in the body. Here’s what you need to know about the muscles of the shoulder to find greater stability and prevent injury.
The shoulder girdle’s mobility is a study in functional architecture. It was designed to help us climb, hang from trees, and occasionally even crawl. These days, however, most of us tend to move the shoulder joint in one direction only—out in front of us. Think about it: We spend the vast majority of our time on computer keyboards, cell phones, holding the steering wheel, or pushing a shopping cart. The result? We don’t take our shoulders through their full range of motion on a regular basis, and this repetition of forward-reaching tasks overtightens certain muscles in the shoulder joint while weakening others. Over time, this creates chronic misalignments of multiple muscles in the shoulder complex and eventually leads to pain and injury—particularly when we start weight-bearing on this joint on the yoga mat.
Anatomy of the Shoulder
The shoulder is made up of more than a dozen muscles, as well as the following four joints:
Acromioclavicular (AC) Joint
Where the shoulder blade (scapula) attaches to the collarbone
Glenohumeral (GH) Joint
Where the upper arm bone (the humerus) fits into the shallow ball-and-socket joint of the shoulder blade
Scapulocostal (SCC) Joint
Connects the rib cage to the shoulder blade
Sternoclavicular (SC) Joint
Connects the collarbone to your sternum
Top Shoulder Injuries
Unfortunately, the rotator cuff (see below) has become synonymous with “injury.” Here are two of the most common shoulder injuries and why they occur, plus try 4 Poses to Prevent + Heal Shoulder Injuries
Rotator Cuff Bursitis/Impingement
This typically refers to inflammation caused by excessive irritation of the supraspinatus tendon, which passes directly underneath the AC joint. If the shoulders are out of alignment repeatedly in weight-bearing poses like Down Dog, Upward-Facing Dog, and Chaturanga, the supraspinatus tendon and its bursa (a fluid-filled sack that cushions the tendon) can become impinged in the narrow, bony tunnel underneath the AC joint. The result? Pain.
Two tendons attach to the biceps: One connects over the humeral head into the shallow GH joint on the scapula; the other attaches to the coracoid process, a bony protrusion on the scapula. When students complain of pain in the front of the shoulder, it can mean one or both of these biceps tendons are irritated. A likely culprit is poor alignment of the shoulders in Chaturanga. When lowering, the biceps tendons can easily become overstretched and even tear.
The rotator cuff, explained
Surrounding the glenohumeral joint is the rotator cuff, a group of four muscles that help negotiate the position of the humeral head within its socket. These muscles originate from different landmarks on the scapula and latch onto the head of the humerus. They are:
Subscapularis (not shown)
Located on the front side of the scapula; helps you internally rotate the arm
Located on the top side of the scapula; initiates abduction, or the lifting of your arm out to the side
The bigger muscle on the back surface of the scapula; externally rotates the arm bone and stabilizes the shoulder joint
The smaller muscle on the back surface of the scapula; externally rotates the shoulder
To keep the rotator cuff muscles injury-free, it’s crucial to stabilize the entire shoulder girdle when you place weight on your hands—like in Plank Pose, for example. In an efficient Plank, the body recruits multiple muscles to stabilize the shoulder girdle. Two key muscles that stabilize the scapulae against your rib cage at the ScC joints are the serratus anterior muscles (which protract the shoulder blades, pulling them away from the spine) and the rhomboids (which retract the shoulder blades, pulling them toward the spine). While the serratus anterior and rhomboids have opposing actions, they work together to help keep your scapulae from winging off your back and wreaking havoc on the rest of your shoulder joints and muscles.
About Our Pros
Writer Jill Miller is the co-founder of Tune Up Fitness Worldwide and creator of the corrective exercise format Yoga Tune Up® and author of The Roll Model. She has presented case studies at the Fascia Congress and the International Symposium of Yoga Therapists, and teaches at fitness and yoga conferences worldwide. Learn more at yogatuneup.com.
Model Carrie Owerko is a New York–based Senior Iyengar Yoga teacher and Laban Movement Analyst. She also leads Yoga Journal’s online course Iyengar 101: A 6-Week Master Class on Iyengar Yoga's Legendary Poses and Principles.Sign up nowfor our adventurous Iyengar class, a fun, creative journey that will profoundly deepen and transform your approach to yoga and teach you everything you need to know about BKS Iyengar’s unique method.