First, let’s go over the muscles and their actions. Then, I will give you suggestions for exercises and stretches. The easiest way to do this is in a table format. First, I am going to list the origin (O:) of each muscle. The origin is generally, not always, but generally the non-moving attachment of a muscle. Then I will list the insertion (I:), which is generally, not always, the moving attachment of a muscle. Muscles attach to bones, sometimes through tendons and sometimes not, and muscles always cross at least one joint because muscles move bones at joints. Lastly, I will list the actions (A:) of each muscle. Beginning with the deeper muscles and moving out toward the skin and the superficial muscles.
O: Infraspinous Fossa O: Supraspinous Fossa
I: Greater Tubercle of the Humerus I: Greater Tubercle of the Humerus
A: Lateral rotation of the shoulder, A: Abduction of the arm to the first 15 degrees,
adduction of the arm, mild extension of the stabilization of the glenohumeral joint
shoulder, stabilization of the glenohumeral joint
Adduction happens when the arm moves toward the midline of the body, while abduction happens when the arm moves away from the midline. Extension of the shoulder happens when the arm moves posterior at the shoulder, while flexion of the shoulder happens when the arm moves anterior at the shoulder. Lateral rotation happens when the arm rotates toward the back of the body, and medial rotation happens when the arm rotates toward the front of the body.
Teres Minor Subscapularis
O: Upper 2/3 of the lateral border of the Scapula O: Subscapular Fossa
I: Greater Tubercle of the Humerus I: Lesser Tubercle of the Humerus
A: Lateral rotation of the shoulder, stabilization A: Medial rotation of the shoulder,
of the glenohumeral joint stabilization of the glenohumeral joint
Latissimus Dorsi Teres Major
O: Medial 1/2 of the iliac crest, Spinous Processes O: Lower 2/3 of lateral border of Scapula
of T7 – S5, posterior aspect of Ribs 9 – 12, inferior I: Medial lip of the Intertubercular or Bicepital
angle of the Scapula groove
I: Medial lip of the Intertubercular or A: Medial rotation of shoulder, adduction of
Bicepital groove shoulder, extension of shoulder
A: Medial rotation of the shoulder, extension of
the shoulder, adduction of the shoulder
A few things, one, notice that latissimus is a huge back muscle. Attachments on the iliac crest, which is the top of the hip bone, and the spinous processes – which are the bony prominences we feel in the middle of our back on the posterior aspect of our vertebrae – of T7 – S5 mean lattissimus attaches from the mid-back (T7) all the way down to the bottom of the sacrum (S5). But latissimus’ actions are all at the shoulder. This muscle links your shoulder to your lower back and hip. The next thing to take note of is that both latissimus and teres major run through the axilla. The axilla is the underarm. Both of these muscles come from the back, go through the axilla, and insert on the front of the humerus.
Finally, notice that there is a teres minor and a teres major. If a muscle name has a term like minor in it, there will always be a major, or vice versa. If a muscle name has an anterior in it, there will always be a posterior, or if the name has a superior in it, there will always be an inferior. In this case, teres minor is in the rotator cuff and helps infraspinatus, and teres major helps latissimus.