Anatomy For Athletes – Part 9 – Shoulder Muscles

Anatomy For Athletes - Shoulders

In Parts 1 through 5 of the Anatomy For Athletes Mini-Series I described the primary functions, training considerations and exercises for each of the lower body muscle groups.  In Parts 6, 7 and 8 I discussed the abdominal, intrinsic back muscles, and upper back muscles.

In this post I’ll cover the functional anatomy of the deltoid and rotator cuff muscles.

How To Design Your Own Training Programs

Functional Anatomy of the Deltoids

If you read Part 8 of the Anatomy For Athletes Mini-Series, you might notice some parallels between the delts and the traps….

Like the traps, the delts have three distinct subsections:  the anterior, middle, and posterior heads.

The anterior (front) head internally rotates and flexes the arm.  In other words, it flexes the arm forward and rotates it toward midline.  The anterior portion of the deltoids are worked during horizontal pressing exercises, so there’s no need to train them directly, especially since they’re often overactive and/or overtrained.

The middle portion of the deltoid — like the middle trap — is indirectly involved in a number of different movements.  It’s most active with overhead pressing and lateral raises, so if you include these exercises in your programs, then you’re likely getting more than enough mid-delt work.

The posterior (rear) deltoid extends and externally rotates the arm.  In other words, it pulls the arm back and rotates it away from mid-line.  Like the lower portion of the traps, it’s often under-trained.  It is, however, pretty important to include some posterior delt work in your programs because of it’s function as an external rotator.

Examples of deltoid exercises:

  • Anterior:  horizontal pressing variations (e.g. bench press), front raises
  • Middle: overhead pressing variations, lateral raises
  • Posterior: reverse fly variations, band pull-apart, prone "T", row variations

(I've included video exercise examples at the end of the post.)

Considerations For Training

It isn't really necessary to isolate the anterior or middle portions of the deltoid because they get worked enough with vertical and horizontal pressing exercises.  But it’s pretty important to include exercises for the posterior deltoid, especially if you have internally rotated shoulders or you do a lot of horizontal pressing.

Functional Anatomy of the Rotator Cuff

Originally, I was going to leave this section out because this mini-series was really only about covering the "major muscle groups".  But, a lot of my clients are athletes and rotator cuff tears are pretty common among the athletic population.  So… I decided to do my due diligence and include it.

The rotator cuff is made up of 4 muscles — supraspinatus, infraspinatus, teres minor and subscapularis.  The easiest way to remember their names is to use the acronym SITS.

Here's a quick description and a few exercise examples for each of the rotator cuff muscles...


In a normal, healthy shoulder, the supraspinatus is the first muscle to abduct the arm (i.e. pull the arm away from midline, like in a lateral dumbbell raise).  Once you get past the first 15-20 degrees of abduction, the mid-deltoid takes over.

The supraspinatus commonly causes pain due to impingement in people with poor posture and shoulder alignment.

Examples of supraspinatus exercises:

  • Side-lying dumbbell abduction
  • Full can
  • Empty can
  • 0-degree external rotation

Infraspinatus and Teres Minor

Infrapsinatus and teres minor are the primary external rotators of the shoulder.  In other words, they rotate the arm away from the body’s midline.  The posterior deltoid also contributes to external rotation, but not to the same degree as these two muscles.

Infrapsinatus and teres minor are often overpowered by the internal rotators of the shoulder — pec major, lats, anterior deltoid, and subscapularis — because they are often undertrained in comparison.

Examples of Infrapspinatus and Teres Minor Exercises:

  • External rotation variations (NOTE: it's important to include external rotation exercises at various angles of abduction)
  • L-lateral Raises
  • Cuban Presses


The subscapularis is the only rotator cuff muscle that internally rotates the shoulder.  It’s usually tight and overactive.  Most people, especially those with shoulder issues can benefit from active release therapy and flexibility work for this muscle.

Examples of subscapularis exercises:

  • Internal rotation variations

Considerations for Training

For strong, healthy shoulders include external rotation exercises and rhythmic stabilization exercises for the rotator cuff muscles (see the section below for examples).

Unless you have a specific injury or chronic instability in your shoulder, it’s not necessary to include exercises that specifically target the supraspinatus or subscapularis.  (If you suspect that you have issues with these muscles, consult with a physiotherapist.)

Shoulder Exercise Videos

Next Up:  Anatomy For Athletes — Part 10 — Pecs and Upper Arms, check back in a few days for that.

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How To Design Your Own Training Programs