Lesson 10: Pectoralis Major, Latissimus Dorsi and Teres Major

by Brent Brookbush DPT, PT, MS, PES, CES, CSCS, ACSM H/FS

Lesson 10: Pectoralis Major, Latissimus Dorsi and Teres Major

Study GuideQuick Reference - Pecs Lats and Teres Major

Note: If you intend to do the activities below do not open the "Study Guide" - all the answers are already filled in.  The study guide is just a quick reference tool, similar to flash cards - great for preparing for an exam.

Introduction:

In this lecture we will be discussing the Pectoralis Major, Latissimus Dorsi & Teres Major:

Etymology:

  • Pectoral (n.) early 15c., “ornament worn on the breast,” from Middle French pectoral and directly from Latin pectorale “breastplate,” noun use of neuter of adjective pectoralis (see pectoral (adj.)). – As a shortened form of pectoral muscle, attested from 1758. Slang shortening pec for this is first recorded 1966. Related: Pectorals; pecs. (Etymology Online)
  • Latissimus - From Latin lātissimus (“widest, broadest”), superlative of lātus (“wide, broad”) (Wiktionary)
  • Dorsidorsal (adj.) early 15c., from Old French dorsal (14c.) or directly from Medieval Latin dorsalis, corresponding to Latin dorsualis "of the back," from dorsum "back," of uncertain origin. (Etymology Online)
  • Teres - of latin origin referring to "round" or "cylindrical" (Wikipedia)
  • Majormajor (adj.) c.1300, from Latin maior (earlier *magjos), irregular comparative of magnus "large, great" (see magnate). (Etymology Online)

What joint do these muscles cross?

These muscles originate on the axial skeleton (except the Teres Major which originates on the lateral border of the scapula) and insert into the bicipital groove of the anterior humeral head.  These muscles cross the shoulder (glenohumeral joint) and assist in motion of the arm.  Although they may have an indirect role on scapular motion, in this lesson we will only consider actions of the shoulder.  Before we start analyzing the function of each muscle, make a word bank for yourself. What are the joint actions of the shoulder? The muscles in this lecture must perform joint actions in this word bank... they cannot perform any other actions.  For example, there is no such thing as retraction of the shoulder joint.

  • Sagittal Plane Joint Actions:
  • Frontal Plane Joint Actions:
  • Transverse Plane Plane Joint Actions:

You did a similar exercise in a previous lesson Joints of the Shoulder Girdle and Scapular Joint Actions:

Pectoralis Major:

Pectoralis Major - http://upload.wikimedia.org/wikipedia/commons/thumb/d/de/Gray410.png/375px-Gray410.png

Attachments: 

  • Origin: Medial half of clavicle, sternum and costal cartilages or ribs 1 or 2 through ribs 6 or 7.
  • Insertion:  Bicipital groove of Humerus

Activity:

You determine the actions - 

  1. Based on the direction of fibers - in what plane do you think this muscle will play the largest role? (Highlight the joint actions in that plane)
  2. As this muscle contracts it pulls the lateral aspect of the humeral head medially.  What happens to the arm?
  3. What is the name of that joint action?
  4. Keeping in the same plane as the first 3 questions, what joint action occurs if the pectoralis major contracts with the shoulder abducted to 90°?
  5. Now consider the fibers of the sternal head only (see image above), and consider how the pectoralis major may contribute to other planes of motion.  With the arm still abducted to 90° or more, which direction will these lower fibers of the pectoralis major pull the arm? What is the name of that joint action?
  6. Now consider the fibers of the clavicular head only (see image above).  Starting from "anatomical position," if the clavicular head contracts alone which joint action will it contribute to? (Hint, the same action may be performed by the muscle just lateral and running nearly parallel to the clavicular head of the pectoralis major)
  7. Re-write your answers into one succinct table?
  8. Check your answers.

Exercise Graph (Chest Flye):

Chest Flye using dumbbells Chest Flye using dumbbells. - By No machine-readable author provided. GeorgeStepanek assumed (based on copyright claims). - No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=42914

Directions:

  1. Look at the exercise depicted in the illustration above and determine the plane of motion.
  2. List the moving joints in the far left column (there may be more rows than moving joints)?
  3. List the joint action occurring at each joint.
  4. List the muscles that contribute to those joint actions.

Exercise: Chest Fly
Plane:
Joints (Moving)Joint ActionMuscles:
 1.Hint: 2 muscles for each joint action
 2.Hint: 2 muscles for each joint action

Latissimus Dorsi:

Latissimus Dorsi - http://upload.wikimedia.org/wikipedia/commons/2/2c/Latissimus_dorsi_muscle_animation.gif

Attachments: 

  • Origin: Lower 4 ribs, crest of ilium, thoracolumbar fascia, spinous processes of T7-L5, thoracolumbar fascia, and inferior angle of scapula
  • Insertion:  Bicipital groove of Humerus

Activity:

You determine the actions - 

This muscle contributes to actions in all 3 planes:

  1. Starting with the frontal plane - if the arms are raised overhead, which direction will this muscle pull the arm?
  2. What is that joint action called?
  3. Now the sagittal plane - if the arms are stretched out in front of the body, which direction will this muscle pull the arm?
  4. What is that joint action called?
  5. Now the tricky one, transverse plane - given that the muscle travels around the medial side of the humerus to attach to the anterior side of the humeral head, which type of rotation will this muscle contribute too?
  6. Re-write your answers into one succinct table?
  7. Check your answers.

Teres Major:

Note how the Teres Major follows a similar path from scapula to Humerus as the Latissimus Dorsi Note how teres major follows a similar path from scapula to humerus as the latissimus dorsi. - http://dragongatefitness.files.wordpress.com/2012/11/backanat.jpg

Attachments: 

  • Origin: Inferior angle of scapula (below Teres Minor)
  • Insertion:  Bicipital groove of Humerus

Activity:

  1. Despite a different origin, this muscle nearly blends with the muscle we just discussed, including an insertion at the same bony landmark.  The teres major is very similar to which muscle?
  2. As this muscle follows a similar course from the scapula and around the medial side of the humerus to the anterior humeral head, which joint actions do you expect it to contribute to?
  3. Re-write your answers into one succinct table?

  • Study Note: Make a special note of the major in teres major.  This muscle has a "little brother" who does not share the same joint actions.  As “major” is latin for "greater or larger", I try to remember that the teres major muscle assists the large latissimus dorsi. 

Activity:

Internal and External Rotators of the Shoulder

  1. Name all of the muscles that will contribute to internal rotation and external rotation of the shoulder

Internal Rotators

External Rotators

 1.

 2.

 3. 1.

 4. 2.

 5. 3.

Critical Thinking:

  • Do you notice an imbalance between the number and size of the muscles listed on each side of the graph?  Do you think this could be a contributing factor to the internally rotated shoulders we see in those individuals with poor upper body posture?

Activity:

Are the Pectoralis Major and Latissimus Dorsi really Opposites?

"Push/Pull" routines, also known as "Chest & Back" routines are common used resistance/weight training routines.  They are thought to promote balance, but do they really?

1. In the graph below, fill in all of the joint actions for each muscle and compare.

Pectoralis Major, Pectoralis Minor, and Latissimus Dorsi - http://ittcs.files.wordpress.com/2010/11/img_0350.jpg?w=500&h=675

Pectoralis MajorLatissimus Dorsi
 1. 1.
 2. 2.
 3. 3.
 4.

Critical Thinking:

  • Obviously the Pecs and Lats have far more in common than we previously thought.  Can you think of any functional activities where these two muscles work together to perform an action concentrically? Do these "Push/Pull" routines truly promote balance, or add to the propensity of the shoulder to adopt an internally rotated position in those with poor upper body posture?

Lesson 11 - Arm Muscles

© 2014 Brent Brookbush

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