When most people think of the shoulder anatomy, they think of the deltoids. This is because the deltoids are what you would consider the major muscles of the shoulder anatomy; they’re the muscles you see when you roll up your t-shirt sleeve or wear a wife beater.
Each deltoid muscle has three “heads,” or distinct parts: the anterior, lateral and posterior deltoid heads. They are shown in the image below.
The anterior deltoid is located on the front of your shoulder. It is the part of the shoulder that borders the chest muscles. Its main function is shoulder flexion, which is characterized by raising your upper arms up to the front and overhead. This muscle is targeted during front raises and pressing exercises (e.g. barbell overhead press, push press).
The lateral deltoid is located on the outside of your shoulder. This is the deltoid head that, if highly developed, gives the effect of having very broad shoulders, as well as the “capped” shoulder look. Note that genetics play a major role with this, and there’s only so much one can do if he has naturally sloping shoulders.
The main function of the lateral deltoid is shoulder abduction. This movement is characterized by raising your upper arms upward, at your sides. This muscle is targeted in exercises such as the dumbbell lateral raise, dumbbell raise and upright row.
If you’re a beginner, you may be tempted to load up on shoulder exercises that target the outer deltoids. But please don’t fall prey to this desire. You need to develop the entire shoulder musculature (not to mention the rest of your body) before you worry about shaping this relatively minor muscle head.
The posterior deltoid is often overlooked, in comparison to the anterior deltoid. This is because trainees tend to emphasize push exercises over pull exercises. The eventual result is a muscular imbalance, which leads to inefficient movement (and by extension, poor performance of exercises). Even worse, it can cause a postural deficiency…
…The solution? Do more compound pull exercises and isolation exercises for the posterior deltoids.
Rotator Cuff Muscles
The other, lesser known shoulder muscles include four small muscles that make up the rotator cuff. These muscles aren’t as visible as the deltoids, but they are equally (if not more) important. See below to view an image of the rotator cuff structure:
The rotator cuff is a complex and delicate structure of the shoulder anatomy. Located near the shoulder’s ball-and-socket joint, it is comprised of four individual muscles and their tendons. Specifically, the four rotator cuff muscles include the following:
These muscles are much smaller and essentially unnoticeable as part of the physique. However, they play an incredibly important role in the body. That is, in addition to stabilizing the shoulder, they provide us with the ability to rotate our upper arms and shoulders through wide ranges of motion.